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Mostafa FayadTable of contentsSubjects1 OBJECTIVES AND CLASSIFICATION2 BIOMICHANICS OF RPD3 PARTIAL DENTURE DESIGN4 DENTAL SURVEYOR5 Denture base6 RESTS AND REST SEATS7 CONNECTORS8 attachment9 Direct retainers10 INDIRECT RETAINERS11 Stress breaker12 ARTIFICIAL TEETH13 LABORATORY PROCEDURES14 Diagnosis of pd patients15 PREPARATION OF MOUTH16 IMPRESSIONS FOR REMOVABLEPD17 ESTABLISHING OCCLUSAL RELATIONSHIPS18 trial denture stage of treatment19 Delivery of the RPD fayad20 POST INSERTION COMPLAINTS RPD21 MAINTENANCE AND REPAIRE OF RPD22 Damaging effect23 PERIODONTAL CONSIDERATIONS24 Esthetic solutions in RPD25 Phonitecs in RPD26 Other Forms of the RPD27 Swing lock28 Removable Partial Overdenture29 Rotational path30 Temporary RPD31 RPD in maxillofacial prosthesis32 C.D opposing P.D33 MS.ACTIVETY &P D
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Removable PARTIAL
DENTURE THEORY AND
PRACTICE
Mostafa FayadLecturer of Removable Prosthodontic
Faculty Of Dental Medicine
Al-Azhar University
Cairo- Egypt
2011
2nd ed
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Table of contents
Subjects
1 OBJECTIVES AND CLASSIFICATION
2 BIOMICHANICS OF RPD
3 PARTIAL DENTURE DESIGN
4 DENTAL SURVEYOR
5 Denture base
6 RESTS AND REST SEATS
7 CONNECTORS
8 attachment
9 Direct retainers
10 INDIRECT RETAINERS
11 Stress breaker
12 ARTIFICIAL TEETH
13 LABORATORY PROCEDURES
14 Diagnosis of pd patients
15 PREPARATION OF MOUTH
16 IMPRESSIONS FOR REMOVABLEPD
17 ESTABLISHING OCCLUSAL RELATIONSHIPS
18 trial denture stage of treatment
19 Delivery of the RPD fayad
20 POST INSERTION COMPLAINTS RPD
21 MAINTENANCE AND REPAIRE OF RPD
22 Damaging effect
23 PERIODONTAL CONSIDERATIONS
24 Esthetic solutions in RPD
25 Phonitecs in RPD
26 Other Forms of the RPD
27 Swing lock
28 Removable Partial Overdenture
29 Rotational path
30 Temporary RPD
31 RPD in maxillofacial prosthesis
32 C.D opposing P.D
33 MS.ACTIVETY &P D
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OBJECTIVES AND CLASSIFICATION 1RPD THEORY AND PRACTICE
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
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.
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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.
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.
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OBJECTIVES AND CLASSIFICATION 1RPD THEORY AND PRACTICE
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 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 . They 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 :
i. Natural teeth that are reduced in height and contour or :
ii. 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.
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
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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
OBJECTIVES OF REMOVABLE PARTIAL DENTURES
1- Preservation 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, such movements leads to
unequal distribution of load on the remaining teeth.
B- Prevention of muscles and TMJ Dysfunction. Absence or movements of
posterior teeth may cause:
Changes in the pattern of mandibular closure. Change in maxillomandibular relations of the mandible and maxilla.
Consequently muscles and TMJ Dysfunction may arise.
Preservation of the residual ridge. By preventing rapid bone
resorption which may happen due to lack of function.
Preservation of the tongue contour and space.
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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 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.
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 .
There is no perfect removable appliance, so "best possible" is defined as meeting, as
closely as we can, the following criteria:
It restores the lost occlusal function caused by the patient's missing teeth,
it minimizes the stress placed on abutment teeth to ensure their longevity,
it minimizes the trauma to the supporting and surrounding tissue and bone,
it's self-cleaning and does not produce food entrapment areas,
it's comfortable for the patient to use and wear, and
it meets the particular esthetic needs of your patient.
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Indications for removable partial dentures
1. No abutment tooth posterior to edentulous space (Free end edentulous area)).
2.After recent extraction, 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, using of labial flange to restore lost tissues.
6. Need of bilateral bracing (cross arch stabilization).after periodontal diseases
treatment, fixed prosthesis provide only antero-posterior stabilization(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.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:
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.
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c) The design of the denture: 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 and 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 if placed on visible tooth surfaces.
HAZARDS OF IMPROPERLY DESIGNED PARTIAL DENTURE See damaging effect
1- Stagnation of food around component parts of partial denture in contact with
tooth surfaces that are not readily cleanedcauses tooth decay .
2- Induce stresses . 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 support
causes displacement of denture 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 or presence of premature contact may cause T.M.J. disorders.
Phases of partial denture service1- 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.
4- Establishment and Verification of Occlusal Relations and Tooth Arrangements.
5- Initial Placement Procedures.
6- Periodic Recall.
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REASONS FOR FAILURE OF CLASP-RETAINED P.D.
Diagnosis and treatment planning
1. Inadequate diagnosis
2. Failure to use a surveyor or to use a surveyor properly during treatment planning
Mouth preparation procedures
1. Failure to properly sequence mouth preparation procedures
2. Inadequate mouth preparations,
3. Failure to return supporting tissue to optimum health before impression procedures
4. Inadequate impressions of hard and soft tissue
Design of the framework
1. Failure to use properly located and sized rests
2. Flexible or incorrectly located major and minor connectors
3. Incorrect use of clasp designs
4. Use of cast clasps that have too little flexibility, are too broad in tooth coverage, and
have too little consideration for esthetics
Laboratory procedures
1. Problems in master cast preparation
a. Inaccurate impression
b. Poor cast-forming procedures
c. Incompatible impression materials and gypsum products
2. Failure to provide the technician with a specific design and necessary information .
3. Failure of the technician to follow the design and written instructions
Support for denture bases
1. Inadequate coverage of basal seat tissue
2. Failure to record basal seat tissue in a supporting form
Occlusion
1. Failure to develop a harmonious occlusion
2. Failure to use compatible materials for opposing occlusal surfaces
Patient-dentist relationship
1. Failure of the dentist to provide adequate dental health care information, including
care and use of prosthesis
2. Failure of the dentist to provide recall opportunities on a periodic basis
3. Failure of the patient to exercise a dental health care regimen and respond to recall
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CLASSIFICATION OF PARTIALLY EDENTULOUS ARCHES
Need for classification:
1- To differentiate between different partial denture.
2- It facilities writing or speaking about partial denture designs and referral orprescription 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 importantto facilitate communicationbetween 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 differentiationbetween bounded and free extension PD.
3. It should be universally accepted.
4. Serve as guide to design used.
Classifications
a- Classification according to the extent of the RPD:
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.
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B- Cummer's classification :
This classification mainly based upon various the position of the
direct retainer of the finished restoration .
The direct retainer may be diagonally, diametric, unilaterally or
multilaterally placed.
It describes the restored rather than the unrestored arch, so it
is of line value because it follows denture design .
C - Bailyn classification :
It is based on the support afforded to the denture :
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.
Class IV: Denture supported by implants.
F.Beckett and WilsonClass 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%
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.
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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
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.
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Applegate's Rules for Applying the Kennedy Classification:
Applegate has provided the following eight rules governing the application of
the Kennedy system.
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.
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.
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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. Four categories of partial
edentulism are defined, Class I to Class IV, with Class I representing anuncomplicated 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
It is characterized by ideal or minimal compromise in the location and
extent of edentulous area (which is confined to a single arch), 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.
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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 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.
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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.
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.
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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.
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 right upper left
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
lower right lower left
(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 mod 1 (#21, 26, 30).
ICK III mod 3 (#23, 26).
ICK IV (#6, 11)
ICK II (#2).
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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 rotationaway 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
thebracingfunction, 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
It 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. Providessupport 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 dentureretention for distal-extension dentures by physical means.
5. Provides denture bracing against horizontal movement when extended to cover lateral
borders of the ridge for distal-extension dentures.
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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 denturebase 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.
6- Can easily be kept clean.
7- Esthetic acceptability.
8- Potential for future relining.
9- Low initial cost.
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FACTORS DETERMINING THE SELECTION OF DENTURE BASES
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.
In tooth mucosa born PD:
The rotational movements of the RPD during function may excessively load
underlying mucosal tissues. Resin bases are easily adjusted to eliminate the
impingement.
F. LENGTH OF SPAN.
1.Long span bases. Denture base resin on metal framework.
a.Facilitates esthetic restoration of lost tissue contours.
b.Allows periodic relining to compensate for idiopathic or pressure induced
resorptive changes.
c.Facilitates adjustment if required.
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2.Short span bases. Metal base.
a.Provides maximum strength with mmimum bulk.
b.Esthetics may limit use in anterior regions.
c.Adjustment more difficult jf required,
G. INTERARCH DISTANCE. Limited interarch distance may indicate the use of
a metal base.
H. ANTICIPATED LOSS OF AN ABUTMENT TOOTH. A resin-metal base
facilitates the addition of an artificial tooth to the denture base.
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 metalcastings 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).
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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
o Cast metal base contributes to the health of oral tissue when compared with
an acrylic resin base. Perhaps some of the reasons for this are the greater
density and the bacteriostatic activity contributed by ionization and
oxidation of the metal base.
o 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
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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.
6- Stimulation to the underlying tissue so prevents some alveolar atrophy that
would otherwise occur under a resin base and thereby would prolong the health
of the tissue that it contacts.
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.
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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).
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)
properties:
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.
4- more specific gravity : Some times used for lower partial denture to help in
retention due to more specific gravity (weight).
5- Gold alloys have a modulus of elasticity approximately one half of that for
chromium-cobalt alloys for similar uses. The modulus of elasticity refers to
stiffness of an alloy.
6- 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.
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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 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 due to 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 distinctadvantage 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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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.
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.
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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:
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, 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.
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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).
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.
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1- An open latticework (ladder-like pattern).
The latticework consists oftwo 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.
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.
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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.
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 ofa thin sheet of
metal with multiple small holes that extends over 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 incorporatingacrylic 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.
Both types are acceptable if correctly designed.
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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 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.
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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. Tissue stops prevent settling of
the framework downwards, and elevate the minor connectors by a space equal to the
thickness of acrylic base.
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 theretention spaces.
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.
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.
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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
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.
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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 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 formedwhile 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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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 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.
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
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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.
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 inthe 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
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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.
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.
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AESTHETICS OF RPD IN RELATION TO THE LABIAL FLANGE:
A. LONG ANTERIOR SADDLE
The natural appearance presented by the labial and buccal flange is depend 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.
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 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.
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B. 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 onlyblend inconspicuously with the natural tissues, but also allow their colour to 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.
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RESTS AND REST SEATS 3RPD THEORY AND PRACTICE
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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
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.
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A SEMIPRECISION REST is a box-type rest seat, keyway or
matrix which is fabricated in the dental laboratory by incorporating 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 sur