2010

MOSTAFA FAYAD

Assistant Lecture of

Removable Prosthodontic

PARTIAL DENTURE THEORYAND PRACTICE

OBJECTIVES AND CLASSIFICATION

Mostafa Fayad 1

OBJECTIVES AND CLASSIFICATION OF PARTIAL DENTURES

TERMINOLOGY

Prosthesis: Is an artificial replacement of an absent part of the human body.

Prosthetics: The art and science of supplying an artificial replacement for

missing parts of the human body.

Appliance used only for device worn by patient in course of treatment. e.g.

orthodontic appliance and splint

Prosthodontics: The branch of dentistry pertaining to the restoration and

maintenance of oral functions, comfort, appearance, and health of the patient

by the restoration of natural teeth and/or the replacement of missing teeth

and contiguous oral and maxillofacial tissue with an artificial substitute.

Dentulous Patients: Patients having a complete set of natural teeth.

Edentulous Patients: Patients having all their teeth missing.

Partially Edentulous Patient: Patients having one or more but not their entire

natural teeth missing.

Removable Partial Denture (RPD): An appliance that restores one or more but

not all of the missing natural teeth and associated oral structures for partially

edentulous patients.

Abutment: A tooth, a portion of a tooth, or that portion of a dental

implant that serves to support and/or retain prosthesis.

Free End Edentulous Area (Distal extension edentulous area): An edentulous

area, which has an abutment tooth on one side only.

Bounded Edentulous Area: An edentulous area, which has an abutment tooth on each end.

Dental cast: a positive life size reproduction of a part or parts of the oral

cavity.

The word cast is preferable than word model which used only for

demonstration

OBJECTIVES AND CLASSIFICATION

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Andrews Bridge

The combination of a fixed dental prosthesis incorporating a bar with a

removable dental prosthesis that replaces teeth with the bar area, usually

used for edentulous anterior spaces. The vertical walls of the bar may

provide retention for the removable component. By James Andrews.

Gillett Bridge

Eponym for a partial removable dental prosthesis utilizing a Gillett clasp

system, which was composed of an occlusal rest notched deeply into the

occlusal axial surface with a gingivally placed groove and a circumferential

clasp for retention. The occlusal rest was custom made in a cast restoration.

MORA Device

Acronym for mandibular orthopedic repositioning appliance, a type

of removable dental prosthesis with a modification to the occlusal surfaces

used with the goal of repositioning.

Angle of Gingival Convergence

According to Schneider, the angle of gingival convergence is located

apical to the height of contour on the abutment tooth. It can be identified by

viewing the angle formed by the tooth surfaces gingival to the survey line

and the analyzing rod or undercut gauge in a surveyor as it contacts the

height of contour.

Continuous Gum Denture

An artificial denture consisting of porcelain teeth and tinted porcelain

denture base material fused to a platinum base.

Fulcrum Line

It is an imaginary line, connecting occlusal rests, around which a partial

removable dental prosthesis tend to rotate under masticatory forces. The

determinants for the fulcrum line are usually the cross arch occlusal rests

located adjacent to the tissue borne components.

Semi precision Rest

A rigid metallic extension of a fixed or removable dental prosthesis that

fits into an intracoronal preparation in a cast restoration.

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Nesbit Prosthesis

Eponym for a unilateral partial removable dental prosthesis design, that

De. Nesbit introduced in 1918.

Resilient Attachments

An attachment designed to give a tooth borne/soft tissue borne

removable dental prosthesis sufficient mechanical flexion, to withstand the

variations in seating of the prosthesis due to deformation of the mucosa and

underlying tissues without placing excessive stress on the abutments.

CONSEQUENCES OF TOOTH LOSS

1- A loss of ridge volumeboth height and widthcan be expected

Bone loss is greater in the mandible than the maxilla, more pronounced

posteriorly than anteriorly, and it produces a broader mandibular arch while

constricting the maxillary arch.

2- Alteration in the oral mucosa

The attached gingiva of the alveolar bone can be replaced with less

keratinized oral mucosa, which is more readily traumatized.

3- Aesthetic impact

Facial features can change Secondary to altered lip support and/or

reduced facial height as a result of a reduction in occlusal vertical dimension.

4- Reduction in masticatory efficiency

It is the ability to reduce food to a certain size in a given time frame. It

has been shown that there is a strong correlation between masticatory

efficiency and the number of occluding teeth in dentate individuals.

5.T.M.J.dysfunction

6. Tipping, migration, rotation and superimposition of remaining teeth.

7.Altered speech

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Partial Dentures:

Partial dentures are appliances restoring one or more but not the whole

set of natural teeth . These Appliances maybe in form of:

I- Fixed partial prosthesis ( bridge ):

An appliance which restores one or more missing teeth it is permanently

cemented to the neighboring natural teeth and cannot be removed by the

patient.

II- Removable partial prosthesis:

An appliance which restores missing teeth and the associated oral

structures for a partially edentulous patient " it can be removed by the patient .

Removable partial dentures may restore :

(a) Bounded edentulous area : which has an abutment tooth on each end.

(b) Free end edentulous area : which has an abutment tooth on one side

only . Partial dentures restoring free end cases are called distal- extension

partial dentures.

III- Partial over dentures : Partial over dentures are removable partial

dentures that are constructed to overly and gain additional support

from either :

Natural teeth that are reduced in height and contour or : Implants inserted in the edentulous areas .

IV- Removable partial Dentures for Maxillo facial Defects :

These are removable prostheses restoring tissue defects which are

either developmentally or traumatically acquired. They are usually

retained by clasps on the remaining natural teeth.

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Types of removable partial dentures :

( 1 ) Unilateral partial dentures : Partial dentures which restore teeth on one

side of the arch without being extended to the opposite side

( 2 ) Bilateral partial dentures : partial dentures restoring missing teeth and

extended on both sides of dental arch .

According to retention to natural teeth

a- Extra coronal retention

b- Intracranial retention

According to material

-Metallic - acrylic -flexible

OBJECTIVES OF REMOVABLE PARTIAL DENTURES

1- Preservation of the Remaining Tissues:

The primary purpose of RPD is the preservation of the health of the remaining

tissues.

A- Preservation of the health of the remaining teeth.

The loss of teeth leads to migration, tilting or drifting of the

remaining natural teeth into the edentulous spaces (Fig.1-3), such

movements leads to unequal distribution of load on the remaining

teeth. In addition to food impaction in the interstitial spaces leading to

caries and /or gingivitis.

B- Prevention of muscles and TMJ Dysfunction.

Absence or movements of posterior teeth may cause:

A- Changes in the pattern of mandibular closure (Fig.1-4).

B- Change in the vertical and horizontal relations of the

mandible and maxilla. Consequently muscles and TMJ Dysfunction

may arise.

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C-Preservation of the residual ridge.

By preventing rapid bone resorption which may happen due to

lack of function.

D-Preservation of the tongue contour and space.

2 Restore the Continuity of the Dental Arch to Improve Masticatory

Function:

A reduction of the number of teeth leads to a decrease in the chewing

efficiency and greater effort on the digestive organs leading to digestive

disorders, accordingly replacing lost teeth will greatly improve the chewing

capability of the patients, distribute the load over the entire arch and improve

the balance over the whole masticatory system.

3- Improvement of Esthetics, and Providing Support to the Paraoral

Muscles, Lips and Cheeks:

Teeth and the alveolar ridge give support to the musculature of the lips

and cheeks. Non-replacement of the missing teeth gives the patient a senile

appearance characterized by nose-chin approximation and wrinkles around

the lips. Missing teeth can be replaced with predictable results using partial

denture.

4- Restoration of Impaired speech:

Anterior teeth play an essential role in phonetics, particularly in the

production of labio and linguo-dental sound. Loss or wrong position of

anterior teeth and subsequent alveolar ridge resorption can result in phonetic

impairment.

Proper replacement of artificial teeth in relation to the lip tongue and alveolar ridge also the proper contouring of dentures help in restoration of speech defects.

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5- Enhance psychological comfort:

Partial dentures should restore and correct the appearance for the

psychological benefits of the patient, by providing socially acceptable

esthetics. A comfortable prosthesis will encourage and help in patient

rehabilitation .

INDICATIONS FOR REMOVABLE PARTIAL DENTURES

1. No abutment tooth posterior to edentulous space (Free end edentulous

area)).

2. After recent extraction, usually done only to improve esthetics, or for

patient satisfaction.

3. Long edentulous bounded span, too extensive for fixed restoration.

4. Periodontally weak teeth not sufficiently sound to support fixed- partial

denture.

5. With excessive loss of residual bone, the use of labial flange or need to

restore lost tissues.

6. Need of bilateral bracing (cross arch stabilization).after periodontal

diseases treatment ,fixed prosthesis provide only antero-posterior

stabilization only not mediolateral .

7. Enhancing esthetics in anterior region, by the use of translucent

artificial teeth instead of dull fixed partial denture pontic.

8. Young age (less than 17 years).

9. Geriatric patients

10. Immediate replacement.

11. Economic considerations, attitude and desire of the patient.

12. Physical problems.

13. Unfavorable maxillo-mandibular relation.

Contraindication

1- Large tongue.

2- Mentally retarded.

3- Poor oral hygiene.

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ADVANTAGES OF REMOVABLE PARTIAL DENTURE OVER FIXED

PARTIAL DENTURE:

1- They can be constructed for any case whilst fixed P.D. are confined to

short spans bounded by healthy teeth and with a normal occlusion.

2- Cheaper than fixed partial denture.

3- They are more easily cleaned.

4- They are more easily repaired.

5- No tooth reduction is required.

Disadvantages of a Removable Partial Denture:

1- It can cause caries: by harboring food debris in close contact with the

natural teeth a partial denture may promote caries. This will depend on

several factors, chief of which are:

a) The age of the patient, up to the age of 25 years caries susceptibility is

greatest, there after it tends to decrease.

b) The oral hygiene of the patient.

c) The design of the denture: this is all important because well designed

dentures will cause for less damage to the mouth than those of through

less design.

2- It can damage the supporting tissues of the teeth: removable partial

dentures may cause damage to the gum margins by:

a) Fitting too closely into the gingival tissues: through and causing

mechanical injury to it.

b) Allowing food to pack down between the denture and the teeth.

3- It may loosen the natural teeth by leverage: clasps which grip the teeth

too tightly or indirect retainers which are badly placed may cause excessive

stresses to be induced in the natural teeth .

4- It can cause traumatic damage to the palate.

5. Clasps can be unesthetic, particularly when they are placed on visible tooth

surfaces.

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HAZARDS OF IMPROPERLY DESIGNED PARTIAL DENTURES

An improperly designed and constructed partial denture may adversely

affect the tissues in the following manner:

1- Stagnation of food around component parts of partial denture in contact

with tooth surfaces that are not readily cleaned causes tooth decay .

2- Induce stresses on abutment teeth and tissues. If these stresses exceed the

physiologic limits of tissue tolerance, pathologic and destructive changes may

occur:

a) Excessive stresses on abutment teeth cause periodontal membrane

destruction, pocket formation, mobility, and even loss of these teeth.

b) Inflammation, ulceration and gingival recession may occur due to

excessive stresses and undue coverage of tissues with the restoration.

Inadequate denture support due to inadequate stoppers, this causes

displacement of the restoration towards the tissues causing gum stripping.

c) Stresses may also cause bone resorption and loss of the bony foundation

necessary to support the prosthesis.

3- Improper occlusion of teeth or the presence of premature contact may cause

T.M.J. disorders.

PHASES OF PARTIAL DENTURE SERVICE

1- Education of patient: the process of informing a patient about a health matter

to secure informed consent, patient cooperation, and a high level of patient

compliance. Patient education should begin at the initial contact with the

patient and continue throughout treatment.

2- Diagnosis, treatment planning, design, treatment sequencing, and mouth

preparation.

3- Support for Distal Extension Denture Bases.

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4- Establishment and Verification of Occlusal Relations and Tooth

Arrangements.

5- Initial Placement Procedures.

6- Periodic Recall.

REASONS FOR FAILURE OF CLASP-RETAINED P.D.

Diagnosis and treatment planning1. Inadequate diagnosis2. Failure to use a surveyor or to use a surveyor properly during treatment

planningMouth preparation procedures1. Failure to properly sequence mouth preparation procedures2. Inadequate mouth preparations, usually resulting from insufficient planning of

the design of the partial denture or failure to determine that mouth preparations have been properly accomplished

3. Failure to return supporting tissue to optimum health before impression procedures

4. Inadequate impressions of hard and soft tissueDesign of the framework1. Failure to use properly located and sized rests2. Flexible or incorrectly located major and minor connectors3. Incorrect use of clasp designs4. Use of cast clasps that have too little flexibility, are too broad in tooth

coverage, and have too little consideration for estheticsLaboratory procedures1. Problems in master cast preparationa. Inaccurate impressionb. Poor cast-forming procedures

OBJECTIVES AND CLASSIFICATION

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c. Incompatible impression materials and gypsum products2. Failure to provide the technician with a specific design and necessary

information to enable the technician to execute the design3. Failure of the technician to follow the design and written instructionsSupport for denture bases1. Inadequate coverage of basal seat tissue2. Failure to record basal seat tissue in a supporting formOcclusion1. Failure to develop a harmonious occlusion2. Failure to use compatible materials for opposing occlusal surfacesPatient-dentist relationship1. Failure of the dentist to provide adequate dental health care information,

including care and use of prosthesis2. Failure of the dentist to provide recall opportunities on a periodic basis3. Failure of the patient to exercise a dental health care regimen and respond to

recall

CLASSIFICATION OF PARTIALLYEDENTULOUS ARCHES

Need for classification:

1- To differentiate between different partial denture.

2- It facilities writing or speaking about partial denture designs and referral or

prescription writing to the laboratory thus facilitating communication.

3- To formulate good treatment plane.

4- To anticipate difficulties commonly to occur for each class.

Requirements of an Acceptable Classification:

Classifications are important to facilitate communication between the dentist

and the laboratory technician. Acceptable classification should satisfy the

following requirements:

1.Permit immediate visualization of the type of partially edentulous arch.

2.Permit immediate differentiation between bounded and free extension

partial dentures.

3. It should be universally accepted.

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4. Serve as guide to design used.

Classifications

Several methods of classification based on various factors have

been proposed.

A- Classification According to the Extent of the Removable

Partial Denture:

1- Unilateral RPD (Removable Bridge): which restore missing teeth on one

side of the arch without being extended to the other side. This unilateral

design provides least amount of tooth preparation and least amount of tooth

and soft tissue contact.

For unilateral removable partial denture to be successful:

1. clinical crown of abutment tooth must be long enough to

resist rotational forces.

2. The buccal and lingual surfaces of the abutment tooth

must be parallel to resist tipping forces.

3. Retentive undercuts should be available on both the

buccal and lingual surfaces of each abutment.

* Unilateral removable partial denture should be used with caution. as

the chance of the denture becoming dislodged and aspirated is too great.

Bilateral RPD: which restore missing teeth and extended on both sides

of the dental arch.

B- Cummer's classification : This classification mainly based upon various the position of

the direct patner of the finished restoration . The direct retainer

may be diagonally, diametric, unilaterally or multilaterally placed.

This classification describes the restored rather than the unrestored

arch, so it is of line value because it follows denture design .

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C - Bailyn classification : Bailyn,s classification is based on the support afforded to the

denture by the tissues . the restorations may be :

o Tissue born prosthesis : the denture is enterily supported by

the mucosa and the underlying bone .

o Tooth born prosthesis : the denture is entirely supported by

abutment teeth .

o Tooth tissue supported prosthesis : the denture is supported

bu both abutment teeth and moucosa.

D- Fridman's classification : Fridman classified partial dentures in to :

Group A for anterior restoration

Group B- For bounded posterior restoration

Group C- For posterior free end restoration (c= cantilever) .

E - Osborne and Lammie (1974)

Class I: Denture supported by mucosa and underlying bone

Class II: Denture supported by teeth

Class III: Denture supported by a combination of mucosa and tooth-

borne means.

Class IV: Denture supported by implants.

F.Beckett and Wilson

Class I: Bounded saddle and the abutment cant support the saddle

Class II: Free end saddle

A. Tooth and tissue support

B. Tissue support

Class III: Bounded saddle and the abutment can support the saddle

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Skinner's Classification

He introduced the classification in 1959. He said that about 1,31,072

combinations of partially edentulous arches are possible.

His classification is based on the relation of the edentulous arches to the

abutment teeth.

Class I: Abutment teeth are present anterior and posterior to the edentulous

space. It may be unilateral or bilateral.

Class II: All the teeth are present posterior to the denture base which

functions as a partial denture unit. It may be unilateral or bilateral.

Class III: All abutment teeth are anterior to the denture base which

functions as a partial denture unit. It may be unilateral or bilateral.

Class IV: Denture bases are located anterior and posterior to the remaining

teeth, and these may be unilateral or bilateral.

Class V: Abutment teeth are unilateral in relation to the denture base, and

these may be unilateral or bilateral.

H- Kennedy's Classification:

Dr. Edward Kennedy proposed this classification in 1923. This is the

most popular classification. It is based on locations and number of

edentulous areas.

Class I: Bilateral edentulous areas (free-end saddles) located posterior to the

remaining natural teeth.72%

Class II: A unilateral edentulous area (free-end saddle) located posterior to

the remaining natural teeth.14%

Class III: A unilateral edentulous area with natural teeth remaining both

anterior and posterior to it.8,5%

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Class IV: A single, but bilateral (crossing the midline ), edentulous area

located anterior to the remaining natural teeth.3%

Applegate later added two classes

Class V: A unilateral edentulous area with natural teeth remaining both

anterior and posterior to it but the anterior abutment is not suitable for

support.

Class VI: A unilateral edentulous area with natural teeth remaining both

anterior and posterior to it with abutments capable for total support.

FISET'S ADDITIONS

Class VII A partially edentulous situation in which all remaining natural

teeth are located on one side of the arch, or of the median line

Class VIII A partially edentulous situation in which all remaining natural

teeth are located in one anterior corner of the arch

Class IX A partially edentulous situation in which functional and cosmetic

requirements or the magnitude of the interocclusal distance require the use

of a telescoped prosthesis (partial or complete).The remaining teeth are

capable of total or partial support for the prosthesis.

Class X A partially edentulous situation in which the remaining teeth are

incapable of providing any support. If the teeth are kept to maintain

alveolus integrity, the arch must be restored with an OVERDENTURE

which is a complete denture supported primarily by the denture foundation

area

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The numeric sequence of the classification system is based on the

frequency of occurrence of each class. Class I being the most common While

class IV is the least common. This classification was then modified by

Applegate .

Why a unilateral edentulous area is considered as class II?

Because it include features of both class I and class III especially if

modification is present.

Advantages

1- It is the most widely used method of classification of the partially

edentulous arches.

2- It is simple and can be easily applied to nearly all partially

edentulous bases.

3- It permits immediate visualization of the partially edentulous arch

and permits a logical approach to the problems of design.

Applegate has provided the following eight rules governing the

application of the Kennedy system.

Applegate's Rules for Applying the Kennedy Classification:

Rule (1) : Classification should follow rather than precede any

extraction of teeth that might alter the original classification.

Rule (2) : If the third molar is missing and not to be replaced, it is not

considered in the classification.

Rule (3) : If a third molar is present and is to be used as an abutment, it

is considered in the classification.

Rule (4) : If a second molar is missing and is not to be replaced (that is,

the opposing second molar is also missing and is not to be replaced ), it is not

considered in the classification.

Rule (5) : The most posterior edentulous area or areas always determine

the classification.

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Rule (6) : Edentulous areas other than those determining the classification

are referred to as modification spaces and are designated by their number.

Rule (7) : The extent of the modification is not considered, only the

number of additional edentulous areas.

Rule (8) : There can be no modification areas in Class IV arches. Any

edentulous area lying posterior to the "single bilateral area crossing the

midline" would instead determine the classification.

Class IV Partial dentures especially those having long edentulous areas

are considered mesial extension bases. They require the same denture design

principles as class I partial dentures.

ACP classification system for partial edentulism J Prosthodont 2002;11:181-193.

Prosthodontic Diagnostic Index ( PDI )

The American College of Prosthodontists (ACP) has developed a classification

system for partial edentulism based on diagnostic findings. This classification

system is based on diagnostic findings. Four categories of partial edentulism

are defined, Class I to Class IV, with Class I representing an uncomplicated

clinical situation and class IV representing a complex clinical situation. Each

class is differentiated by specific diagnostic criteria.

Diagnostic Criteria

1. Location and extent of the edentulous area(s)

2. Condition of abutments

3. Occlusion

4. Residual ridge characteristics.

Class I

This class is characterized by ideal or minimal compromise in the

location and extent of edentulous area (which is confined to a single arch),

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abutment conditions, occlusal characteristics, and residual ridge conditions.

All 4 of the diagnostic criteria are favorable.

1. The location and extent of the edentulous area are ideal or minimally

compromised:

The edentulous area is confined to a single arch. The edentulous area does not compromise the physiologic support of the abutments.

The edentulous area may include any anterior maxillary span that does not exceed 2 incisors, any anterior mandibular span that does not exceed

4 missing incisors, or any posterior span that does not exceed 2 premolars

or 1 premolar and 1 molar.

2. The abutment condition is ideal or minimally compromised, with no

need for preprosthetic therapy.

3. The occlusion is ideal or minimally compromised, with no need for

preprosthetic therapy; maxillomandibular relationship: Class I molar and

jaw relationships.

4. Residual ridge morphology conforms to the Class I complete

edentulism description.

Class II

This class is characterized by moderately compromised location and

extent of edentulous areas in both arches, abutment conditions requiring

localized adjunctive therapy, occlusal characteristics requiring localized

adjunctive therapy, and residual ridge conditions.

1. The location and extent of the edentulous area are moderately

compromised:

Edentulous areas may exist in 1 or both arches The edentulous areas do not compromise the physiologic support of the abutments.

Edentulous areas may include any anterior maxillary span that does not exceed 2 incisors, any anterior mandibular span that does not exceed 4

incisors, any posterior span (maxillary or mandibular) that does not exceed

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2 premolars, or 1 premolar and 1 molar or any missing canine (maxillary or

mandibular).

2. Condition of the abutments is moderately compromised:

Abutments in 1 or 2 sextants have insufficient tooth structure to retain or support intracoronal or extracoronal restorations.

Abutments in 1 or 2 sextants require localized adjunctive therapy.3. Occlusion is moderately compromised:

Occlusal correction requires localized adjunctive therapy. Maxillomandibular relationship: Class I molar and jaw relationships.4. Residual ridge morphology conforms to the Class II complete

edentulism description.

Class III

This class is characterized by substantially compromised location and

extent of edentulous areas in both arches, abutment condition requiring

substantial localized adjunctive therapy, occlusal characteristics requiring

reestablishment of the entire occlusion without a change in the occlusal

vertical dimension, and residual ridge condition.

1. The location and extent of the edentulous areas are substantially

compromised:

Edentulous areas may be present in 1 or both arches. Edentulous areas compromise the physiologic support of the abutments. Edentulous areas may include any posterior maxillary or mandibular edentulous area greater than 3 teeth or 2 molars, or anterior and posterior

edentulous areas of 3 or more teeth.

2. The condition of the abutments is moderately compromised:

Abutments in 3 sextants have insufficient tooth structure to retain or support intracoronal or extracoronal restorations.

Abutments in 3 sextants require more substantial localized adjunctive therapy (ie, periodontal, endodontic or orthodontic procedures).

Abutments have a fair prognosis.

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3. Occlusion is substantially compromised:

Requires reestablishment of the entire occlusal scheme without an accompanying change in the occlusal vertical dimension.

Maxillomandibular relationship: Class II molar and jaw relationships.4. Residual ridge morphology conforms to the Class III complete

edentulism description.

Class IV

This class is characterized by severely compromised location and

extent of edentulous areas with guarded prognosis, abutments requiring

extensive therapy, occlusion characteristics requiring reestablishment of

the occlusion with a change in the occlusal vertical dimension, and residual

ridge conditions.

1. The location and extent of the edentulous areas results in severe occlusal

compromise:

Edentulous areas may be extensive and may occur in both arches. Edentulous areas compromise the physiologic support of the abutment teeth to create a guarded prognosis.

Edentulous areas include acquired or congenital maxillofacial defects. At least 1 edentulous area has a guarded prognosis.2. Abutments are severely compromised:

Abutments in 4 or more sextants have insufficient tooth structure to retain or support intracoronal or extracoronal restorations.

Abutments in 4 or more sextants require extensive localized adjunctive therapy.

Abutments have a guarded prognosis.3. Occlusion is severely compromised:

Reestablishment of the entire occlusal scheme, including changes in the occlusal vertical dimension, is necessary.

Maxillomandibular relationship: class II division 2 or Class III molar and jaw relationships.

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4. Residual ridge morphology conforms to the class IV complete

edentulism description.

Other characteristics include severe manifestations of local or systemic

disease, including sequelae from oncologic treatment, maxillomandibular

dyskinesia and/or ataxia, and refractory patient (a patient who presents with

chronic complaints following appropriate therapy).

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Implant-Corrected Kennedy (ICK) Classification System for Partially Edentulous Arches Journal of Prosthodontics 17 (2008) 5025

Guidelines for the new classification system

The new classification system will follow the Kennedy method with

the following guidelines:

(1) No edentulous space will be included in the classification if it will be

restored with an implant-supported fixed prosthesis.

(2) To avoid confusion, the maxillary arch is drawn as half circle facing up

and the mandibular arch as half circle facing down. The drawing will appear as

if looking directly at the patient; the right and left quadrants are reversed.

(3) The classification will always begin with the phrase "Implant-Corrected

Kennedy (class)," followed by the description of the classification. It can be

abbreviated as follows:

(i) ICK I, for Kennedy class I situations,

(ii) ICK II, for Kennedy class II situations,

(iii) ICK III, for Kennedy class III situations, and

(iv) ICK IV, for Kennedy class IV situations.

(4) The abbreviation max for maxillary and man for mandibular can

precede the classification. The word modification can be abbreviated as mod.

(5) Roman numerals will be used for the classification, and Arabic numerals

will be used for the number of modification spaces and implants.

(6) The tooth number using the American Dental Association (ADA) system is

used to give the number and exact position of the implant in the arch. (Note:

other tooth numbering systems such as Federation Dentaire Internationale

[FDI] can be used, as can the tooth name. The ADA system was used by the

authors because of familiarity).

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Universal numbering system table

Permanent Teeth

upper left upper right

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

lower left lower right

(7) The classification of any situation will be according to the following

order: main classification first,

then the number of modification spaces,

followed by the number of implants in parentheses according to their

position in the arch preceded by the number sign (#).

(8) The classification can be used either after implant placement to describe

any situation of RPD with implants, or before implant placement to indicate the

number and position of future implants with an RPD.

(9) A different name, ICK Classification System, is given to this classification

system to be differentiated from other partially edentulous arch classification

systems.

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ICK I (#2, 15).

ICK I (#2).

ICK I mod 3 (#18, 22, 28, 31).

ICK II (#2).

ICK II mod 1 (#21, 26, 30).

ICK III mod 3 (#23, 26).

ICK IV (#6, 11)

OBJECTIVES AND CLASSIFICATION

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Component Parts of removable partial dentures

Denture bases. Artificial teeth . Supporting rests. Connectors: Major connectors

Minor connectors

Retainers : Direct retainers Indirect retainers

These components may provide one or more of the following functions:

1-Support:

a. The resistance of a denture to tissue ward movement.

b. Adequate and wide distribution of the load to the teeth and mucosa.

2- Retention: The resistance of a denture to vertical displacement force (to

move away from its tissue foundation)).

3- Indirect retention: The resistance of denture rotation away from the

tissues about an axis.

4- Bracing: The resistance of a denture to lateral forces.

5- Reciprocation: The resistance of lateral forces on the abutment during

insertion and removal of the removable partial denture .

Reciprocation is required as the denture is being displaced occlusally

whilst the bracing function, comes into play when the denture is fully seated.

6- Stability: The resistance of a denture to tipping movement.

Tipping movement: Vertical rotation around a line parallel to ridge crest

(twisting of the denture base)

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COMPONENT PARTS OF RPD

Components of metallic removable partial dentures are all rigid, with

the exception of the flexible retentive clasp arm located in an undercut area for

retaining the restoration against dislodging forces.

The components of removable partial denture are:

1. One or More Denture Bases.

2. Artificial teeth.

3. Supporting rests.

4. Major connectors.

5. Minor connectors.

6. Direct retainers.

7. Indirect retainers.

These Components May Provide One or More of the Following Functions:

1-Support: The resistance of a denture to tissue ward movement.

2- Retention: The resistance of a denture to vertical displacement force (to move

away from its tissue foundation).

3- Indirect retention: The resistance of denture rotation away from the tissues

about an axis.

4- Bracing: The resistance of a denture to lateral forces.

5- Reciprocation: The resistance of lateral forces on the abutment during insertion

and removal of the removable partial denture.

Reciprocation is required as the denture is being displaced occlusally whilst the

bracing function, comes into play when the denture is fully seated.

6- Stability: The resistance of a denture to tipping movement.

Tipping movement: Vertical rotation around a line parallel to ridge crest

(twisting of the denture base)

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Denture Base

The denture base is the part of the denture, which rests on the foundation

tissues and to which artificial teeth are attached. The denture base helps in

transferring occlusal stresses to the supporting oral structures.

Types of Denture Bases

1- Bounded partial denture bases

The bounded partial denture base covers an edentulous span between two

abutment teeth.

2- Free-end partial denture bases (distal-extension base)

The base bounded by a natural tooth only on one side, while the other side is

free. This type is sometimes called distal extension base.

3- Bar type saddle

In case of posterior bounded saddle, where esthetic is not important, a bar of

metal is attached directly to the connector to form occlusal surface and no mucosal

contact .

Functions of the Denture Base

1. Carries the artificial teeth.

2. Transfers occlusal stresses to the supporting oral structures.

3. Provides support in distal-extension and long span bounded dentures.

The snowshoe principle, which suggests that broad coverage furnishes the best

support with the least load per unit area, is the principle of choice for providing

maximum support. Therefore support should be the primary consideration in

selecting, designing, and fabricating a distal extension partial denture base.

4. Provides denture retention for distal-extension dentures by physical means.

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Mostafa Fayad 3

5. Provides denture bracing against horizontal movement when extended to cover

lateral borders of the ridge for distal-extension dentures.

6. Provides stabilization against tipping of the distal-extension dentures (On the

contra-lateral side).

7. The denture base and the artificial teeth serve to prevent migration and over

eruption of the remaining teeth.

8. Provide stimulation by massage of the underlying tissues of the residual ridge.

Oral tissues placed under functional stress within their physiological tolerance

maintain their form and tone better than similar tissues suffering from disuse.

9. A the tooth-supported partial denture base that replaces anterior teeth must

perform the following functions:

(1) Provide desirable esthetics;

(2) Support and retain the artificial teeth in such a way that they provide

masticatory efficiency and assist in transferring occlusal forces directly to

abutment teeth through rests;

(3) prevent vertical and horizontal migration of remaining natural teeth;

(4) Eliminate undesirable food traps (oral cleanliness);

(5) Stimulate the underlying tissue.

Requirements of an Ideal Denture Base Material

1- Accuracy of adaptation to the tissues with minimal dimensional changes.

2- Sufficient strength in order to resist fracture and distortion.

3- Low specific gravity, i.e. light in weight in the mouth.

4- Biological acceptability, non-allergic and non-irritating surface capable of receiving

and maintaining a good finish

5- Allow thermal conductivity necessary for tissue stimulation.

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Mostafa Fayad 4

6- Can easily be kept clean.

7- Esthetic acceptability.

8- Potential for future relining.

9- Low initial cost.

CRITERIA FOR SELECTION

A. NEED TO RELINE.

1. Tooth-mucosa borne partial dentures direct functional forces as

pressure to the mucoosseous tissues. When resorptive changes occur, the

base requires relining to maintain optimum support. Resin bases are

easily relined.

1. In tooth borne partial dentures with long span bases, the base

may require periodic relining to compensate for idiopathic or pressure

induced resorptive changes

B. NEED TO RESTORE MISSING TISSUES. A resin base may be shaped

and shaded to restore anatomic contour and esthetics.

C. LIMITED VERTICAL SPACE. When vertical space is limited, the

minimal space may require a stronger metal base.

D. MAGNITUDE OF APPLIED FORCES. The anticipated occlusal forces

may influence the choice of materials.

E. EASE OF ADJUSTMENT. Resin bases are more easily adjusted than

metal bases.

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Denture Base Material

I- Metallic denture bases

Metallic denture bases are generally used in thinner sections than resin bases.

They are made in the form of metal plates having metal posts that allow for

mechanical attachment with the acrylic resin layer holding the artificial teeth.

Metal such as chrome cobalt alloy, gold, or stainless steel is used. Chrome cobalt

alloy is the most commonly used alloy the material is used in cast form only. It

provides the needed rigidity for removable partial dentures even in thin section. It

has low specific gravity which is nearly half that of gold and provides high

resistance to corrosion.

Advantages of Metal bases as compared to resin bases:

1- Accuracy and Permanence of Form

Denture bases fit more accurately to the underlying tissues. Accurate

metal castings are not subject to distortion by the release of internal

strains as are acrylic denture resins.

The metal base provides an intimacy of contact that contributes

considerably to the retention of denture prosthesis. (called interfacial

surface tension).

Additional posterior palatal seal may be eliminated entirely when a

cast palate is used for a complete denture, as compared with the need for

a definite post-dam when the palate is made of acrylic resin.

Permanence of form of the cast base is also ensured because of its

resistance to abrasion from denture cleaning agents.

2- Comparative Tissue Response

Cast metal base contributes to the health of oral tissue when

compared with an acrylic resin base. Perhaps some of the reasons for this

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Mostafa Fayad 6

are the greater density and the bacteriostatic activity contributed by

ionization and oxidation of the metal base.

Acrylic resin bases tend to accumulate mucinous deposits

containing food particles and calcareous deposits.

3- Thermal Conductivity

Cast metal base has Greater thermal conductivity, while

denture acrylic resins have insulating properties.

4- Weight and Bulk

Metal alloy may be cast much thinner than acrylic resin and

still have adequate strength and rigidity. Cast gold must be given

slightly more bulk to provide the same amount of rigidity but may still

be made with less thickness than acrylic. less weight and bulk are

possible when the denture bases are made of chrome or titanium

alloys.

an acrylic resin base may be preferable to the thinner metal

base in (1) extreme loss of residual alveolar bone may make it

necessary to add fullness to the denture base to restore normal facial

contours and (2) to fill out the buccal vestibule to prevent food from

being trapped in the vestibule beneath the denture.(3) Denture base

contours for functional tongue and cheek contact can best be

accomplished with acrylic resin.(4) acrylic resin bases may be

contoured to provide ideal polished surfaces that contribute to the

retention of the denture, restoration of facial contours, and prevention

of the accumulation of food at denture borders.

5- More hygienic as the fitting surface is polished and non-porous with

less tendency for food accumulation.

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Mostafa Fayad 7

6- Stimulation to the underlying tissue so prevents some alveolaratrophy that would otherwise occur under a resin base and thereby would prolong the health of the tissue that it contacts.

7- Disadvantages of Metal Bases

1. Metal bases are difficult to rebase or reline when ridge resorption

occurs.

2. They are difficult to repair.

3. The color of metal bases does not simulate the natural appearance or

oral tissues.

Retentive post used with metal base.

Indication: 1- short span posterior tooth born 2- when maximum strength is required

3- vertical height limited 4- significance anterior overlap

The choice of alloy is based on several factors:

(1) weighed advantages or disadvantages of the physical properties of the alloy;

(2) The dimensional accuracy with which the alloy can be cast and finished;

(3) The availability of the alloy;

(4) The versatility of the alloy; and

(5) The individual clinical observation and experiences with alloys in respect to

quality control and service to the patient.

A-Chrome cobalt alloy:

It is used in cast form only, needs special investments and special casting

and polishing machine and high casting temperature (2400 f).

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Mostafa Fayad 8

Advantages:

Accurate and rigid even in thin sections.

Low specific gravity 7-9 gram/cm3 nearly 1/2 of that of gold.

Highly polished surface.

High resistance to corrosion and abrasion.

Low density (weight), high modulus of elasticity (stiffness),

Cheaper than gold..

A low-fusing, chrome-cobalt alloy or gold alloy can be cast to wrought wire, and wrought-wire components may be soldered to

either gold or chrome-cobalt alloys

B-Gold (type 4)

Disadvantages in relation to chrome cobalt:

1-Heavier than chrome cobalt (specific gravity 15 gm/ cm3).

2- More rigid than acrylic resin but less than chrome cobalt. Modiolus of

rigidity 14106 P.S.I

3- More expensive.

Some times used for lower partial denture to help in retention due to more

specific gravity (weight).

The modulus of elasticity refers to stiffness of an alloy. Gold alloys have a

modulus of elasticity approximately one half of that for chromium-cobalt

alloys for similar uses.

The greater stiffness of chromium-cobalt alloy is advantageous but

at the same time offers disadvantages. The hardness of chromium-cobalt

alloys presents advantages when Greater rigidity can be obtained with the

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Mostafa Fayad 9

chromium-cobalt alloy in reduced sections in which cross-arch stabilization

is required, thereby eliminating an appreciable bulk of the framework. Its

greater rigidity is also an advantage when the greatest undercut that can be

found on an abutment tooth is in the nature of 0. 05 inch. A gold retentive

element would not be as efficient in retaining the restoration under such

conditions as would the chromium-cobalt clasp arm. The hardness of

chromium-cobalt alloys presents a disadvantage when a component of the

framework, such as a rest, is opposed by a natural tooth or by one that has

been restored. We have observed more wear of natural teeth opposed by

some of the various chromium-cobalt alloys as contrasted to the Type IV

gold alloys.

A high yield strength and a low modulus of elasticity produce higher

flexibility. The gold alloys are approximately twice as flexible as the

chromium cobalt alloys, which is a distinct advantage in the optimum

location of retentive elements of the framework in many instances. The

greater flexibility of the gold alloys usually permits location of the tips of

retainer arms in the gingival third of the abutment tooth.

The stiffness of the chromium-cobalt alloys can be overcome by

1- Including wrought-wire retentive elements in the framework.

2- The bulk of a retentive clasp arm for a removable partial denture is often

reduced for greater flexibility when chromium-cobalt alloys are used as

opposed to gold alloys. This, however, is inadvisable because the grain size

of the chromium-cobalt alloys is usually larger and is associated with a lower

proportional limit, and so a decrease in the bulk of chromium-cobalt cast

clasps increases the likelihood of fracture or permanent deformation.

The retentive clasp arms for both alloys should be approximately the

same size, but the depth of undercut used for retention must be reduced by

one half when chromium-cobalt is the choice of alloys.

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It has been observed that gold frameworks for removable partial dentures are

more prone to produce uncomfortable galvanic shocks to abutment teeth

restored with silver amalgam than frameworks made of chromium-cobalt

alloy.

c- Stainless steel:

It is used mainly in swaged form.

The disadvantages of this type are;

1- Less accurate than chrome cobalt or gold

2- Less commonly used.

d- TI/AL/vanadiaum / e- Commercial pure titanium

Commercially pure (CP) titanium and titanium in alloys containing

aluminum and vanadium, or palladium (Ti-0 Pd), should be considered potential

future materials for removable partial denture frameworks.

Currently, when CP titanium is cast under dental conditions, the material

properties change dramatically. During the casting procedure, the high affinity of

the liquid metal for elements such as oxygen, nitrogen, and hydrogen results in their

incorporation from the atmosphere.

The typical Young's modulus of elasticity of titanium alloy is half that of

chromium-cobalt and just slightly higher than type IV gold alloys. This would

require a different approach to clasp design than with chromium-cobalt alloys and

present some advantages. Wrought titanium alloy

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II- Non-metallic, acrylic resin denture bases

Acrylic removable partial dentures are considered as temporary partial dentures. It

is made of acrylic denture base, artificial teeth and wrought wire clasps.

Advantages:

1. Esthetically acrylic resin is satisfactory and looks better in the mouth due to

its pink colour.

2- Acrylic bases are light in weight.

3- The material is easy to reline, rebase or repair.

4- Needs simple processing procedures.

Disadvantages of resin base:

1. Resin bases are weak, brittle and are liable to fracture.

2. In order to attain enough strength, resin bases are made bulky

3. Acrylic bases have low thermal conductivity.

4. The fitting surface is porous and not polished which may lead to

retention of soft food particles and plaque causing bad oral hygiene, bad

odour and inflammation of the tissues.

Indications of Acrylic removable partial dentures:

1- When age and time factors may prohibit the construction of the definitive

prosthesis.

2- During the healing process after extraction until the permanent restoration is

made.

3- Cases with extreme bone loss. The presence of acrylic resin is necessary to

restore the original contour of the ridge, giving more satisfactory results than

metal bases.

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Mostafa Fayad 12

4- When cost is a prime requisite.

5- Acrylic bases of temporary acrylic removable partial dentures.

6- Immediate denture

7- Transitional and interim denture

8- Only few isolated teeth remaining.

Contraindications:

1. Single tooth edentulous spaces.

2. Where protrusive or lateral occlusal guidance will be on the prosthetic teeth.

Types of resin.

a.Polymethylmethacrylatc. (PMMA) (Most commonly used.)

b.Grafted polymethylmethacrylate.

c. 4-meta (4-methacryloxyethyl trimellitate anhydride) containing PMMA.

Potential to chemically bond to alloys capable of oxidation so it

reduce microleakage at metal-resin interface.

d. Polyvinyl.

e. Composite resin.

III- Combined Metallic and Acrylic Resin Bases:

Acrylic resin bases attached to metallic denture framework through

metallic minor connectors.

Metal resin interface exhibits a potential space which may enlarge during

thermo cycling and permit the entrance of microorganisms and fluids. This may

lead to discoloration, plaque accumulation and resin deterioration at the interface.

They are used in the following conditions:

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1. Free-end saddle cases as in Kennedy class I, II and IV and in class III cases

having long edentulous spans to facilitate future relining. Relining is required

to compensate for bone resorption and loss of support, which frequently

occur in these cases.

2. Patients vulnerable to an increased rate of bone loss as diabetic patients or

patients on steroid therapy.

3. Cases with extreme bone loss. The presence of acrylic resin is necessary to

restore the original contour of the ridge giving more satisfactory results than

metal bases.

4. Long span cases.

5. Recent extraction cases which will need early relining.

6. Cases with bone resorption prognosis as diabetic patients.

7. Class IV for appearance.

Methods of Attaching Denture Bases

Denture Base Retention (Grid-work) minor Connector

Acrylic resin bases are attached to metallic denture framework by

means of a minor connector designed so that a space exists between it

and the underlying tissues of the residual ridge. (Relief of at least a 20-gauge

thickness over the basal seat areas of the master cast is used to create a raised

platform on the investment cast on which the pattern for the retentive frame

is formed)

The minor connectors are either made in the form of

a) Lattice work construction.

b) Mesh construction.

c) Bead, wire, or nail-head minor connectors (used with a metal base).

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Retentive mesh and retentive lattice are used when a plastic denture base will

contact the edentulous ridge.

Loops, beads, and posts are used with a metal base to which prosthetic teeth are attached with processed plastic.

This type of minor connector must be

strong enough to anchor the denture base securely;

rigid enough to resist breakage or flexing,

Must not interfere as possible with arrangement of the artificial teeth.

Extension:

In the maxillary arch if the denture base is a distal extension base (no tooth posterior to the edentulous space), the minor connector must extend

the entire length of the residual ridge to cover the tuberosities.

When a distal extension ridge in the mandibular arch is being treated, the minor connector should extend two-thirds the length of the edentulous

ridge.

1- An open latticework (ladder-like pattern).

The latticework consists of two struts of metal, pieces of

12- or 14-gauge half-round wax and 18-gauge round wax are

used to form a ladder like framework., extending longitudinally

along the edentulous ridge.

A longitudinal strut should not be positioned along the ridge crest as it may

act as a wedge in the resin and may cause resin fracture.

In the mandibular arch one strut should be positioned buccal to the crest of

the ridge and the other lingual to the ridge crest.

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In the maxillary arch one strut is positioned buccal to the ridge crest, and the

border of the major connector acts as the second strut.

Smaller struts, usually 16 gauge thick, connect the two struts and form the

latticework. These connecting struts run over the crest of the ridge and should be

positioned to interfere as little as possible with arrangement of the artificial teeth.

Generally, one cross strut between each of the teeth to be replaced should be

satisfactory.

The latticework minor connector can be used whenever multiple teeth are to

be replaced. It provides the strongest attachment of the acrylic resin denture base to

the removable partial denture. It is also the easiest of the denture base retainers to

reline if this becomes necessary because of ridge resorption.

In construction, wax forms of the struts are positioned on the refractory

(investment) cast, which is duplicated from the master cast.

It is necessary to provide a relief space over the dentulous ridges for both the

latticework and the mesh minor connector so that there will be a space between

the struts or mesh and the underlying ridge.

It is in this space and around the struts or mesh that the acrylic resin denture

base will be formed. The locking of the acrylic resin around and through the

latticework provides the retention of the denture base.

Relief under the grid-work should not be started immediately adjacent to the abutment tooth but should begin 1.5 - 2 mm from the abutment tooth.

The junction of grid works to the major connector should be in the form of a butt joint with a slight undercut in the metal.

The grid work on a mandibular distal extension should extend about 2/3 of the way from abutment tooth to retromolar pad but not on the ascending portion of the ridge mesial to the pad. It should has a tissue stop at their posterior limit to provide direct contact with the ridge.

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Maxillary distal extension grid-works should extend at least 2/3 of the length of the ridge to the hamular notch. However, the junction or finishing line of the maxillary major connector should extend fully to point to the hamular notch area so that the acrylic resin base can be extended into this area and provide a smooth transition from the connector to the base.

2- in a closed meshwork configuration (plastic mesh pattern).

The mesh type of minor connector consists of a thin sheet of metal with multiple small holes that extendsover the crest of the residual ridge to the same buccal, lingual, and posterior limits as does the latticework minor connector.

It can be used whenever multiple teeth are to be replaced.

The mesh pattern is less satisfactory as the space available for incorporating acrylic resin between metallic strips is narrow so it makes it more difficult to pack the acrylic resin dough because more pressure is needed against the resin to force it through the small holes and not allow for enough bulk of resin which become weak and may detached from the metal base. It also does not provide as strong an attachment for the denture base.

The major difference between retentive mesh and retentive lattice is the size of the openings. Retentive mesh has small openings while retentive lattice has much larger openings.

The mesh type tends to be flatter, with more potential rigidity, but may provide less retention for the acrylic if the openings are insufficiently large.

The lattice type has superior retentive potential, but can interfere with the setting of teeth, if the struts are made too thick or poorly positioned.

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Mostafa Fayad 17

Both types are acceptable if correctly designed.

3- Metal denture bases

Posts, loops, beads , nail head, wire loop retention or metal stop may be used to for retention of the resin. with metal denture base, which is cast so that it fits directly against the edentulous ridge; no relief is provided beneath the minor connector.

The retention is gained by the projection of metal on this surface. These projections may be

beads (made by placing beads of acrylic resin polymer in the waxed denture base and investing, burning out, and casting these beads);

wires that project from the metal base,

In the form of nail-head.

This form of denture base is hygienic because of better soft tissue response to metal than acrylic resin. But it can not be relined adequately in the event that ridge resorption takes place.

This type should be used on tooth-supported, well-healed ridges and when

inter arch space is limited and the available vertical space is so limited that an

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Mostafa Fayad 18

acrylic resin base would be thin and weak. Because relining is not possible metal

bases are generally not indicated for extension RPDs.

Minor connectors forming mandibular distal extension bases extend

posteriorly about two-thirds the length of the edentulous ridge. They should be

slightly extended onto the buccal and lingual surfaces of the ridge. This design adds

strength to the acrylic denture base and helps to minimize-distortion of cured resin

bases, which occurs due to the release of strains after processing. However, minor

connectors for maxillary distal extension bases may sometimes be extended to

cover the entire length of the residual ridge.

Minor connectors forming denture bases should include tissue stops and

finishing line:

Tissue stops:(tissue foot)

It is a foot included in the fitting surface of minor connector designed for retaining acrylic base.

Tissue stops are integral parts of minor connectors.

They provide stability to the framework during the stages of transfer and processing. They are particularly useful in preventing distortion of the

framework during acrylic resin processing procedures.

Altered cast impression procedures often necessitate that tissue stops be augmented subsequent to the development of the altered cast. This can be

readily accomplished with the addition of autopolymerizing acrylic resin.

Tissue stops are essential parts in the fitting surface of minor connectors. They are usually two or three in number that contact the cast.

Tissue stops stabilize the framework on the master cast during processing as acrylic resin is packed in the retention spaces.

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Mostafa Fayad 19

Tissue stops elevate the minor connectors, forming the denture base, from the ridge, by a space equal to the thickness of acrylic bases.

They are formed by making holes 22 mm in the relief wax placed over the ridge during preparation of the master cast before duplication.

a b

Tissue stops prevent settling of the framework downwards, and elevate the minor connectors by a

space equal to the thickness of acrylic base.

Finishing index tissue stop:

It is located distal to the terminal abutment and is a continuation of the minor connector contacting the

guiding plane. Its purpose is to facilitate finishing

of the denture base resin at the region of the

terminal abutment after processing.

Finishing Lines:

Finishing lines are butt joints created at the junction of major connectors

with the denture bases.

Finish lines must be provided on all partial denture frameworks wherever

denture base resin and the metal join.

A finish line allows the resin to terminate in a butt joint to produce a

smooth surface.

In distal extension bases, these butt joint finishing lines, are made on both

the external and internal surfaces of the major connector where acrylic resin is

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Mostafa Fayad 20

processed, while in short bounded metallic bases, the butt joint is required only on

the external surface where acrylic resin is packed, for the attachment of teeth.

External finish lines-:

An external finish line is located on the polished surface of a partial denture

and is formed in the wax pattern.

a. External finish lines are formed during the formation of the wax

pattern by carving a sharp definite angle in the wax pattern at the junction between

the major connector and the minor connectors forming the denture base.

b. This angle should be less than 90 degrees to lock the acrylic resin

securely to the minor connectors and for the acrylic base to blend smoothly and

evenly with the major connector.

c. External finish line is positioned just far enough lingual to the ridge

crest to position the artificial teeth.

d. External finish line fades into minor connectors or proximal plates as

it approaches the occlusal surfaces of the contacting teeth.

e. The external finish line should never be placed directly over the

internal finish line. It should be placed superiorly to the internal finish line so that a

minimum amount of denture base resin is used on the lingual aspect of the teeth.

For maxillary RPDs. the palatal finish line should be located so that it allows

for proper positioning of the artificial teeth while still maintaining normal tissue

contours and a smooth transition from metal to plastic. It should be located 2 mm

medial from an imaginary line that would contacts lingual surfaces of missing

posterior teeth.

For a mandibular distal extension RPD, the external finish line begins at the

distolingual aspect of the terminal tooth and angles posteriorly as it progresses

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toward the floor of the mouth. The lingual finish line for a mandibular tooth-

supported RPD should be located just far enough lingually to allow for setting of

the artificial teeth. If it is placed too far lingually (and thus inferiorly), the major

connector will be weakened.

Internal finish lines:

An internal finish line is located on the internal or tissue surface and is

formed while blocking out the master cast.

If the resin ends in a thin edge, saliva and debris will accumulate between

the denture base resin and the metal. The resin will also fracture if left too thin in

this area.

a. Internal finish lines are formed by carving the relief wax used to create

space for packing acrylic resin under mesh minor connector. This relief wax is

applied on the master cast before duplication.

b. In tooth-mucosa borne RPD the internal finishing line (IFL), it is placed

approximately at the junction of the vertical and horizontal planes of the palate to

permit proper relining since resorption of bone occurs all the way up to this level.

While in case of maxillary tooth borne PD, the IFL is slightly palatal to the EFL.

c. The internal finish line is located on the tissue surface side of the

framework. It is formed by the 24- to 26-gauge relief wax placed on the master cast

prior to duplication.

d. The internal finish line is normally placed farther from the abutment

tooth or residual ridge than the external finish line.

e. Internal finish line should be located to allow resin to cover mueo-

osseous areas where resorptive changes are anticipated. This permits the base to be

relined to reestablish mueo-osseous support.

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Mostafa Fayad 22

f. Internal finish line should be located 3-4 mm from the natural teeth.

This allows a highly polished metal surface to be placed adjacent to the free

gingival margins.

g. Internal finish line should form a well defined butt joint with the

denture base resin.

h. Internal line angle of the internal and external finish lines should be

less than 90 degrees to provide mechanical retention for the denture base resin.

i. Internal and external finish lines should not be superimposed. A

staggered (offset) relationship maintains framework strength.

j. The palatal extension of the internal finish line is determined primarily

by the need to reline the partial denture to compensate for anticipated bone

resorption.

For tooth borne partial dentures, the internal finish lines should be placed slightly palatal to the external finish lines. This staggered

relationship contributes to increased framework strength and an

adequate thickness of resin between the finish lines. Placement of

the internal finish line more palatally is usually not indicated,

since only minimal resorptive changes occur.

For tooth-mucosa borne partial dentures, the internal finish lines in the edentulous regions should be placed close to where the

vertical and horizontal planes of the palate meet. This position is

approximately 10 mm lingual to the previous position of the

lingual gingival margins of the missing teeth. This permits proper

relining, since bone resorption may occur up to this level. The

horizontal portion of the hard palate is relatively resistant to

pressure-induced resorptive changes.

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1 2 3

1: black arrow indicates the external finishing line(EFL) in tooth-mucosa borne RPD.

2:. a case of maxillary tooth-mucosa borne RPD. arrow (A) indicates The internal finishing

line(IFL), it is placed approximately at the junction of the vertical and horizontal planes of

the palate to permit relining. Arrow (B) indicates the EFL

3: in case of maxillary tooth borne PD, the IFL is slightly palatal to the EFL

External finish lines: junction of major

connector and minor connectors at palatal

finishing line should be located 2 mm

medial from an imaginary line that would

contacts lingual surfaces of missing

posterior teeth.

Denture base extension

Maximum coverage of the edentulous ridge is always desirable to allow

greatest area of bone to share in resisting the occlusal stresses exerted during

mastication. This helps in decreasing the force per unit area and keeping the forces

within the physiologic tissue tolerance.

a) Antero-posterior extension

- In bounded spaces: It is determined by the abutment teeth.

- In free-end spaces: The base extends to cover the retromolar pad in the lower arch and hamular notches and tuberosity in the upper`.

b) Buccally: The flange should extend to the mucosal reflection. The labial flange is sometimes omitted for esthetic reasons.

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c) Lingually: The flange of the lower denture base should extend to the full depth of the lingual sulcus as permitted by muscle function.

Lingual surfaces usually are made concave except in the distal palatal area.

Buccal surfaces are made convex at gingival margins, over root prominences, and at

the border to fill the area recorded in the impression. Between the border and the

gingival contours, the base can be made convex to aid in retention and to facilitate

the return of the food bolus to the occlusal table during mastication. Such contours

prevent food from being entrapped in the cheek and from working under the

denture.

Occasionally, the path of insertion can cause the denture flanges to impinge

on the mucosa above undercut portions of the residual ridge, when the partial

denture is being seated. In these instances, it is usually preferable to shorten the

flange, rather than relieving the internal surface. If the internal surface is

relieved significantly, a space will exist between the denture base and the tissues

when the denture is fully seated. Food may become trapped in the space and work

its way under the partial denture.

Relationship of denture base to abutment

The ideal relationship between the denture base carrying the artificial teeth and the

adjacent abutment should either be:

1- Close contact between the denture and the proximal surface of the abutment. In

this condition relieving the gingival margin is necessary to avoid its traumatization.

2- Open Contact between artificial teeth carried by the denture base and the

abutment above the contact point allowing enough space between them to create a

cleansable area.

On the other hand improper contact between the denture and the abutment tooth

leaving only a small space between the neck of the abutment tooth and the artificial

tooth is undesirable. This small space is difficult to clean predisposing to caries,

gingivitis and pocket formation.

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Ideal base/abutment tooth relationship

1-Close contact between the denture and the proximal surface of the abutment

2- Open Contact. Enough spaces are self-cleansing.

AESTHETICS OF RPD IN RELATION TO THE LABIAL FLANGE:

LONG ANTERIOR SADDLE

The natural appearance presented by the labial and buccal flange of a long

saddle is dependent upon:

The shaping of the gingival papillae,

The shaping of the gingival margins,

The overall contouring of the flange as a whole, and

coloring and shading.

In shaping the gingival papillae, the space between the teeth should be

filled. The resin representing the papilla may then be lightly polished to give a

surface, which is readily self-cleansing.

The shape of the entire gingival margin is usually more sharply curved if the

neck of the tooth is not prominent, but is higher and straighter if the neck is

prominent. A more vigorous expression may be obtained by emphasizing the

convexity of the gingival margin. The whole area of the gingival margin should be

polished highly to avoid food debris accumulating round the necks of the teeth.

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In ageing, both the interdental papilla and the gingival margin require

modification. The papilla is positioned higher on the neck of the tooth, and the

gingival margin regresses up the root of the tooth and a pointed rather than a curved

form should be used, especially at the neck of a prominent tooth such as the canine.

Contouring of the labial flange should be carried out to simulate the

development of bony prominences over the roots of teeth and Interdental

depressions. Stippling of the attached gingiva, as well as giving a pleasing natural

appearance, has been found to restrict lip movement in some cases. The lateral

margins of labial flanges must be reduced to wafer thinness and be extended over

the root eminences of the abutment teeth.

The thin edge allows the colour of the flange to blend more naturally with

the mucosa. Coloring and shading of labial flanges must be considered to blend

harmoniously with the natural tissues of the patient. Many manufacturers supply

acrylic materials containing colored fibers, to which may be added additional stain

and shaded polymers.

SHORT ANTERIOR SADDLE

The general principles discussed in relation to long anterior saddles apply equally to shorter ones:

The artificial papilla must be shaped to match the natural closest papilla.

The shape and contour of the gingival margin must be similar to that of the natural teeth.

The junction between artificial and natural gum tissue as mixed together as possible.

The margins of the flanges must be reduced to water thinness, and whenever

possible, extended over the eminences of the abutment teeth. Such thin edges not

only blend inconspicuously with the natural tissues, but also allow their colour to

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Mostafa Fayad 27

show through. It will be necessary to employ a path of insertion that will allow the

thin acrylic to pass over the eminence.

2. A gum-fit can be done by using a longer tooth than is really indicated which is

unsightly when the necks of the teeth are revealed by the patient. Usually it is better

to use a small flange if possible since this can be very thin and discreet and nearly

undetectable at normal distances. The use of a flange also increases the saddle area

which is desirable whenever possible. Fitting to the gum is recommended in some

cases where the first premolar has to be replaced and the canine is still standing.

The ridge just posterior to the canine is often quite prominent and the tooth

angulations will be better if no flange is used. In addition, a flange in this area is

often noticeable when the patient smiles.

RESTS AND REST SEATS

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RESTS AND REST SEATS

Definitions

Rests:

Are rigid extensions of a partial denture, fitted into rest seats, which are prepared on either the occlusal, lingual surfaces or incisal edges of the teeth, providing support to the partial denture.

Support:

The quality of the prosthesis to resist displacement towards denture supporting structures.

Rest seat:

The prepared recess in a tooth or restoration created to receive occlusal, incisal, or lingual rest.

Types of Rests:

A- EXTRACRONAL (EXTERNAL) REST: which used with an extracronal clasp assembly-type direct retainer although it is primarily within the contours of the abutment tooth.

According to their shape and location on the tooth surface they may be classified as:

1- Occlusal rest.

(1) Proximal occlusal (conventional),

(2)Interproximal

(3) Transocclusal (embrasure).

(4) Extended

2- Incisal rest.

3- Lingual rest.

4- Embrasure Hooks

5- Rest Recess

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B- INTRACRONAL (INTRENAL) RESTS fit into rest preparations within the contours of an abutment tooth crown. It is used with many precision and semiprecision attachments.

PRECISION RESTS consists of two metal components manufactured to fit together precisely. One component is a box type rest seat, keyway or matrix which is incorporated into the crown of an abutment tooth. The other component is a rigid metal extension (patrix) which fits the matrix precisely and is incorporated into the RPD.

A SEMIPRECISION REST is a box-type rest seat, keyway or matrix which is fabricated in the dental laboratory byincorporating a preformed plastic pattern into the wax pattern for the crown of the abutment tooth, or by waxing the crown pattern around a special mandrel in the dental surveyor thus forming the contour of the rest preparation. After the crown is cast, the matrix is machined (milled) with a bur held in a surveyor. The patternfor the patrix of the semi precision rest is formed by a performed plastic pattern or by waxing directly to the matrix (rest preparation) in a crown or a cast of the crown. The patrix is cast as part of the RPD framework.

Rests may be classified into

A- according to relation to direct retainer

1- Primary rest: it is a component of direct retainer

2- Secondary rest: it is an additional rest used on other than abutment teeth for gaining extra support or act as indirect retainer.

B- According to shape:

1- Saucer shape. 2- Box shape

3- Dove tailed 4- Triangle

5- V- shape. 6- Saddle shape

7- Boomerang shape 8- Circular (conservative).

C- According to the abutment tooth

1- Posterior rests

2- Anterior rests

RESTS AND REST SEATS

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I- Occlusal Rest:

A rigid extension of a removable partial denture located on the occlusal surface of a posterior tooth, on a rest seat specially prepared to receive it.

Requirements of the Occlusal Rest:

1. The occlusal rest must fit the tooth accurately to minimize the food collection beneath it and preserve its location in relation to the tooth.

2. The angle formed by the occlusal rest and the vertical minor connectorshould be less than 90 o so that the transmitted occlusal forces are directed toward the long axis of the tooth.

3. It should have sufficient thickness of metal to withstand the loads without deformation or breakage.

4. It must not raise the vertical dimension of occlusion.

5. In bounded partial denture: occlusal rests are placed in the near zone of the occlusal surface of the two abutments bounding the edentulous span.

6. In free end partial dentures: the occlusal rest is placed on the far zone of the occlusal surface of the abutment, in order to decrease the torque action on the abutment tooth.

Functions of the Occlusal Rest

1. Support: it transmits forces from the prosthetic teeth to the abutment teeth so the main function of occlusal rest is to provide support to the partial dentureagainst vertical forces, this prevent settling of the denture towards the underlying tissues, which will:

a- Prevent a spreading of the clasp arms, and maintains the components of the dentures in their planned positions.

b- Prevents impingement of the gingival tissues adjacent to the abutment teeth.

N.B. partial denture without occlusal rests is called gum stripper.

2. Assist in distributing the occlusal load among two teeth or more so that each can bear a proportionate share of the masticatory load in concert with the residual ridges.

RESTS AND REST SEATS

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3. Help maintain the plane of occlusion in the region of the abutment teeth.The occlusal rest can be shaped to improve the existing occlusion by building out the occlusal surface of the tooth to allow contact with the opposing teeth.

4. It may act as indirect retention along with its minor connector if they are placed beyond the fulcrum.

5. Maintain the clasp in the correct position on the abutment tooth thus helping

to maintain the effectiveness of the retentive and reciprocal components of the

clasp.

4. Serve as a reference point for evaluating the fit of the framework to the teeth.

5. Help prevent extrusion, tipping, or migration of the abutment teeth.

8. In addition to these functions, an internal rest may provide some bracing and

retention for the RPD.

Effect of occlusal rest location on the tooth :

- An extended occlusal rest covering the whole occlusal surface of the

tooth "Onlay rest" allows for the transmission of the vertical load over the whole

occlusal surface and directs the forces along the long axis of the tooth.

- An improperly extended occlusal rest placed on one side of the

occlusal surface causes torque on the tooth when vertical forces are applied. - To

prevent this torque either:

a) Extend the occlusal rest across the mesio-distal center of the tooth,

b) Use two short oppositely placed occlusal rests one on the mesial and the other

on the distal surface of the tooth,

Forms and Requirements of Rest Seat Preparation:

1- Preparations for the occlusal rest must precede making master cast and follow proximal preparation (guiding planes and elimination of undesirable undercuts).

2- Rest seats are prepared in sound enamel, cast restoration or rarely amalgam alloy. The use of amalgam restoration as support for an occlusal rest is the least desirable because of its tendency to flow under pressure and also because of the comparative weakness of a marginal ridge made of this alloy. Occlusal rests can be prepared in an old amalgam restoration.

3- When a metal restoration (inlay, onlay or crown) is planned for an abutment tooth, the rest seat must be carved in the wax pattern of the

RESTS AND REST SEATS

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restoration and refined in the cast metal before the restoration is seated in the mouth.

4- The out line form of an occlusal rest seat should follow the outline form of the fossa present on the occlusal surface and should be rounded triangular in shape, the base of the triangle located at the marginal ridge- is about one third to one half the mesiodistal width of the tooth, it is about 2.5 mm in width, and its rounded apex is directed towards the center of the tooth .

5- it should be one half the buccolingual width of the tooth from cusp tip to cusp tip which correspond to one third of the whole buccolingual diameter of the tooth

6- The marginal ridge is lowered approximately one to 1.5 mm to permit sufficient bulk of me