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PREPARATION OF MOUTH FOR REMOVABLEPARTIAL DENTURES

231Oral surgical preparation,231Extractions,232Removal of residual roots,232Impacted teeth,233Malposed teeth,233Cysts and odontogenic tumors,233Exostoses and tori,233Hyperplastic tissue,234Muscle attachments and frena,234Bony spines and knife-edge ridges,235Polyps, papillomas, and traumatic hemangiomas,235Hyperkeratoses, erythroplasia, and ulcerations,235Dentofacial deformity,235Osseointegrated devices,236Augmentation of alveolar bone,237Conditioning of abused and irritated tissue,238Use of tissue conditioning materials,239Periodontal preparation,241Objectives of periodontal therapy,241Periodontal diagnosis and treatmentplanning,241Initial disease control therapy (phase 1),243Definitive periodontal surgery (phase 2),246Recall maintenance (phase 3),248Advantages of periodontal therapy,248Abutment teeth preparation,249Abutment restorations,249Contouring wax patterns,250Rest seats,250Self-assessment aids

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Mouth Preparations

Mouth Preparations Include Procedures in Three Categories-

1. Oral surgical preparations

2. Periodontal preparations

3. Reshaping of teeth

OBJECTIVE

To Return the Mouth to Optimal Health and To Eliminate Any

Condition That Would Be Detrimental To the Success of Partial

Denture

GENERAL GUIDELINES

It must be accomplished before impression procedures for master

cast on which denture is to be constructed.

Oral surgical & periodontal procedures should precede abutment

preparations to allow healing period.

There should be atleast 6 weeks, preferably 3 months between

surgical and restorative procedures.

ORAL SURGICAL PROCEDURES

Longer is the time interval between the surgery & impression

procedure, more complete is the healing - more stable will be the

denture bearing area.

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Various Conditions Requiring Oro-surgical Intervention

Badly decayed non-strategic teeth.

Residual roots.

Impacted teeth

Malposed teeth

Cysts & odontogenic tumors

exostoses & tori

Hyperplastic tissue

Interfering muscle attachments & freni

Bony spicules & knife edge ridges.

Polyps, papillomas, & traumatic hemangiomas.

Hyperkeratosis, erythroplasia & ulcerations

Extractions

Regardless of its condition each tooth must be evaluated for

its strategic importance. No heroic attempts should be made to salvage

a seriously involved tooth, which would contribute little to success of

RPD. Extraction of non-strategic teeth that are detrimental to the

design of RPD is a necessary part of the over all treatment plan.

Residual Roots

Generally retained roots or fragments should be removed

(esp. if there is evidence of pathology). Residual roots adjacent to

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abutment teeth can cause progression of periodontal pockets. Removal

is accomplished from facial or palatal surfaces to preserve ridge height.

Impacted Teeth

All impacted teeth are considered for removal. Periodontal

implications of the impacted teeth are similar to that of retained roots.

Skeletal structure of body changes frequently. Alterations that affect

bony structure of jaws can minute exposure of impacted teeth to oral

cavity via sinus tracts. This can cause serious infections & bone

destruction.

Malposed Teeth

Loss of teeth may lead to extrusion, mesial drifting of

remaining teeth. Alveolar bone supporting extruded teeth is also carried

occlusally. Orthodontics may be helpful in realigning these teeth.

Otherwise surgical correction can be done for teeth & the supporting

alveolar bone.

Cysts & Odontogenic Tumors

Panoramic radiographs must be taken to detect any unsuspected

pathology. IOPA should be taken for any suspicious area seen in OPG.

The diagnosis must be confirmed through consultation & if necessary

biopsy specimen should be submitted to the pathologist.

Exostoses & Tori

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Exostoses or tori should not be allowed to compromise the

design of the RPD. Modifications may accommodate exostoses but

result in additional stress to the supporting elements & a compromised

function. Mucosa covering these is usually thin & liable to ulcerate.

Exostoses’ approximating gingival margins complicate maintenance of

periodontal health and strategic abutment may be lost eventually.

Removal of exostoses & tori not a complicated procedure and

advantages from their removal are numerous in contrast to the

deleterious effect their presence can create.

Hyperplastic Tissue

Hyperplastic tissue is seen in the form of fibrous tuberosities,

soft flabby ridges, folds of redundant tissues in vestibule or floor of

mouth. All these should be removed to provide a firm base for denture.

Stable denture reduces stress & strain on supporting teeth & tissues.

Hyperplastic tissue can be removed with scalpel, curette,

electrosurgery, laser or a combination of these procedures. Care should

be taken so that surgical approaches do not reduce vestibular depth.

Surgical stents often helpful during the healing phase in such patients.

An old denture properly modified can be used as surgical stent. Excised

tissue should be sent to oral pathologist for microscopic study.

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Muscle Attachments & Freni

As a loss of alveolar bone height, muscle attachments may

come to lie near the alveolar crest. Mylohyoid, buccinator, mentalis &

genioglossus are common in this regard. In addition to that mentalis &

genioglossus produce bony protuberances at their attachment

occasionally. Appropriate ridge extension procedures can reposition

attachments Genioglossus is difficult to reposition but careful surgery

reduces the prominence of genial tubercles & it also increases sulcus

depth in anterior lingual area. Skin & mucosal grafts are now common

rather than secondary epithelialization for facial aspect of mandible.

Palate is often the donor site for mucosal grafts, although skin can be

used for larger areas.

Maxillary labial & mandibular lingual freni most commonly

interfere with denture design. They can be easily modified using

surgical procedures. Freni should never compromise the design &

comfort of RPD.

Bony Spines & Knife Edge Ridges

Bony spicules should be removed & knife edge ridges gently

rounded. Procedures are to be carried out with minimum bone loss. If

insufficient ridge support results with correction of knife-edge ridges,

vestibuloplasty should be resorted to.

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Polyps, Papillomas

All abnormal soft tissue lesions should be excised & submitted

for pathological examination. Even if patient presents a history for an

indefinite period, its removal is indicated. Additional stimulation to

area by prosthesis may produce discomfort or malignant changes.

Hyperkeratosis, Erythroplasia & Ulcerations

All abnormal white, red, or ulcerative lesions are to be

investigated regardless of their relationship to proposed denture.

Incisional biopsies of areas larger than 5mm and multiple biopsies for

regions over 2cm should be taken. Biopsy report determines whether

wide or narrow margins are to be excised. Occasionally partial denture

design has to be radically modified to avoid areas of possible

sensitivity, such as after irradiation for malignancy.

PERIODONTAL PREPARATION

The periodontal preparation of the mouth usually follows, or is

performed simultaneously with, the oral surgical procedure. Periodontal

therapy should be completed before restorative dentistry procedures are

begun for any dental patient. The periodontal health of the remaining

teeth then, especially those to be used as abutment teeth, must be

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evaluated carefully by the dentist and corrective measures instituted

before partial denture fabrication.

Objectives of Periodontal Therapy

The objective of periodontal therapy is the return to health of the

supporting structures of the teeth, creating an environment in which the

periodontium may be maintained.

The specific criteria for satisfying these objectives are as follows: -

Removal of all etiologic factors contributing to periodontal

disease.

Elimination or reductions of all pockets with the establishment

of gingival sulci free of gingival inflammation.

Establishment of functional occlusal relationships.

Development of a personalized plaque control program and

definitive maintenance schedule.

Periodontal diagnosis and treatment planning diagnosis

The diagnosis of periodontal diseases is based on a systematic

and carefully accomplished examination of the periodontium. It follows

the procurement of the health history.

In the examination procedure, nothing is as important as the

careful exploration of the gingival sulcus and recording of the probing

pocket depth with a suitably designed instrument. The probe is inserted

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gently but firmly between the gingival margin and the tooth surface,

and the depth of the sulcus is determined circumferentially around each

tooth. Usually depths are recorded for the distobuccal mesial,

mesiobuccal, distolingual, lingual and mesiolingual aspects of each

tooth. A critical assessment of sulcular health, by judging the amount

of bleeding produced on probing, is considered an important indication

of sulcus condition and, along with pocket depth, is an excellent

indicator of health and disease.

The extent and pattern of bone loss can be estimated from

radiographs, and this information serves to substantiate the impression

gained from the clinical examination. Each tooth should be evaluated

carefully for mobility. If the etiologic factor can be removed, many

mobile teeth will become stable and can be used successfully to help

support and retain the partial denture. Mobility is an indication of the

condition of the supporting structures and is caused by inflammatory

changes in the periodontal ligament, traumatic occlusion, or loss of

attachment. Most often it is a result of a combination of the three. A

mobile tooth can be useful if the causes of mobility can be corrected.

Treatment Planning

Depending on the extent and severity of the periodontal changes

present, a variety of therapeutic procedures ranging from simple to

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relatively complex may be indicated. The first phase is considered

disease control or initial therapy because the objective is to essentially

eliminate or reduce local etiologic factors before any periodontal

surgical procedures are accomplished. Procedures that are

accomplished as part of the initial preparation phase include oral

hygiene instruction, scaling, and root planning and polishing, as well as

endodontics, occlusal adjustment, and temporary splinting, if indicated.

During the second, or periodontal surgical phase any needed

periodontal surgery, for example, free gingival grafts, osseous grafts,

or pocket reduction, is accomplished. The maintenance of periodontal

health is accomplished in phase 3 and is ongoing. A definitive recall

schedule at 3 to 4 months is essential.

Initial Disease Control Therapy (Phase I)

The patient should be instructed in the use of disclosing wafers,

soft nylon toothbrush, and unwaxed dental floss. At subsequent

appointments oral hygiene can be evaluated carefully, & other oral

hygiene aids added, such as a rubber tip stimulator. Without good oral

hygiene any dental procedure, regardless of how well it is performed, is

ultimately doomed to failure.

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Scaling and Root Planning

Scaling and root planning are fundamental to performing surgical

periodontal procedure. The use of ultrasonic instrumentation for gross

calculus removal followed by root planning with sharp periodontal

curettes is recommended. The curette is designed specifically for root

planning and, when used correctly in combination with ultrasonic

instrumentation, will result in calculus removal and root surface

decontamination.

Elimination of local irritating factors other than calculus

Overhanging margins of amalgam alloy and inlay restorations,

overhanging crown margins, and open contacts leading to food

impaction should be corrected before definitive prosthetic treatment is

started. Although periodontal health predisposes to a much better

environment for restorative procedures, it is not always possible or

prudent to delay all restorative procedures until complete periodontal

therapy and healing have occurred. This is especially true for patients

with deep-seated carious lesions, for whom pulpal exposures are a

possibility. Excavation of these areas and placement of adequate

restorations must be incorporated early in treatment. The placement of

temporary fillings must not, in itself become a local etiologic factor.

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Elimination of Gross Occlusal Interferences

Bacterial plaque accumulations and calculus deposits are the

primary factors involved in the initiation and progression of

inflammatory periodontal disease. However, poor restorative dentistry

can contribute to damage to the periodontium, and poor occlusal

relationship may act as another factor that contributes to more rapid

loss of periodontal attachment. Selective grinding procedure is

generally applied at this stage. Traumatic cuspal interferences are

removed by judicious grinding procedures. Deflective contacts in the

centric path of closure are removed, eliminating mandibular

displacement from the closing pattern. The indication for occlusal

adjustment is based on the presence of pathology rather than on a

preconceived articulation pattern. Occlusion on natural teeth needs to

be perfected only to a point at which cuspal interference within the

patient’s functional range of contact is eliminated and normal

physiologic function can occur.

Guide to Occlusal Adjustment

Accurately mounted diagnostic casts are extremely helpful in

determining static cusp to fossa contacts of opposing teeth and as guide

in the correction of occlusion anomalies.

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a) A static coordinated occlusal contact of the maximum number of

teeth when the mandible is in centric relation to the maxillae

should be the first objective. The procedure is as follows:-

b) A prematurely contacting cusp should be reduced only if the cusp

point is in premature contact in both centric and eccentric

relations. If a cusp point is in premature contact in centric relation

only, the opposing sulcus should be deepened.

c) When anterior teeth are in premature contact in centric relations, or

in both centric and eccentric relations, corrections should be made

by grinding the incisal edge of the lower teeth.

d) Usually, premature contacts in centric relation are relieved by

grinding the buccal cusps of the lower teeth, the lingual cusp of

upper teeth, and the incisal edges of the lower anterior teeth.

Deepening the sulcus of the posterior tooth or the lingual contact

area in centric relation of an upper anterior tooth changes and

increases the steepness of the eccentric guiding inclines of the

tooth; although this relieves trauma in centric relation, it may

predispose the tooth to trauma in eccentric relations.

After establishing a static, even distribution of stress over the

maximum number of teeth in centric relation, evaluate opposing tooth

contact or lack of contact in eccentric functional relations. First

balancing side contacts are seen. Subluxation, pain, lack of normal

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functional movement of the joint, or loss of alveolar support of the

teeth involved may be evidence of excessive balancing contacts.

Balancing side contacts receive less frictional wear than working side

contacts, and premature contacts may develop progressively with wear.

A reduction in the steepness of the guiding tooth inclines on the

working side will increase the proximity of the teeth on the balancing

side and may contribute to destructive prematurities. In all corrective

grinding to relieve premature or excessive contacts in eccentric

relations, care must be exercised to avoid the loss of a static

supporting contact in centric relation. This static support in centric

relation may exist between the lower buccal cusp fitting into the

central fossae of the upper tooth or between the upper lingual cusp

fitting into the central fossae of the lower tooth or may exist in both

cases. Often only one of these cusps has this static contact. In such

instances the contacting cusp must be left untouched to maintain this

essential support in the planned intercuspal position, and all corrective

grinding to relieve premature contacts in eccentric positions would be

done on the opposing tooth inclines. The lower buccal cusp is in a

static central contact in the upper sulcus more often than the upper

lingual cusp is in a static contact in its opposing lower sulcus.

1. To obtain maximum function and the distribution of functional

stress in eccentric positions on the working side, necessary

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grinding must be done on the lingual surfaces of the upper

anterior teeth. Corrective grinding on the posterior teeth at this

time should always be done on the buccal cusp of the upper

premolars and molars and on the lingual cusp of the lower

premolars and molars. The grinding of lower buccal cusps or

upper lingual cusps at this time would rob these cusps of their

static contact in the opposing central sulci in centric relation.

2. Corrective grinding to relieve premature protrusive contacts of

one or more anterior teeth should be accomplished by grinding

the lingual surface of the upper anterior teeth. Anterior teeth

should never be ground to bring the posterior teeth into contact

in either protrusive position or on the balancing side. In the

elimination of premature protrusive contacts of posterior teeth,

neither the upper lingual cusps nor the lower buccal cusps should

be ground. Corrective grinding should be done on the surface of

the opposing teeth on which these cusps function in the eccentric

position, leaving the centric contact undisturbed.

3. Any sharp edges left by grinding should be rounded off.

Periodontal Surgery Phase 2

It is a definitive periodontal surgery phase. If oral hygiene is

optimal, yet pockets with inflammation and osseous defect are present,

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various surgical techniques like gingivectomy, periodontal flap should

be considered to improve periodontal health.

Gingivectomy

Gingivectomy is indicated when there are supra bony pockets

of fibrotic tissue, absence of deformities in the underlying bony tissue

& pocket depth confined to attached gingiva. If osseous deformities are

present or if pocket depth traverses mucogingival junction

gingivectomy is not the treatment of choice.

Periodontal Flap

The flap is widely employed for the treatment of periodontal

diseases. It may be used to gain access for root planing, osseous

recontouring for pocket elimination or crown lengthening and also for

osseous grafts.

Maintenance Phase

This is phase 3 of the periodontal procedures. It includes

reinforcement of plaque control measures, thorough debridement of

root surfaces of subgingival & supra gingival plaque. Frequency of

recall is according to patient’s requirements. In moderate to severe

periodontitis, 3-4 months recall system is followed.

RESHAPING THE TEETH

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Reshaping the teeth includes

Enameloplasty

Inlays, Onlays & Crowns

Preparation of rest seats.

Enameloplasty

In enameloplasty conservatism is the rule. But sufficient

reduction must be done to ensure adequate space. Preparations can first

be made on diagnostic cast to reveal the need for crowns or inlays.

After reshaping polishing with carborundum impregnated rubber wheel

is essential. It is used to develop guiding planes, change the height of

contour & modify retentive undercuts.

Enameloplasty to Develop Guiding Planes

Guiding planes are the surfaces on the proximal or lingual

surfaces of the teeth parallel to each other & more importantly to the

path of insertion of RPD. Guiding planes are made on abutment teeth-

1. Adjacent to tooth supported segments

2. Adjacent to distal extension edentulous space

3. on lingual surface

4. In anterior segment

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Adjacent To Tooth Supported Segments

Diagnostic cast, mounted on the surveying table, at the

determined tilt , is placed on the bracket table on the patient’s chair. It

is used to determine the relationship of hand piece to the tooth in

patient’s mouth. Guiding plane is always parallel to the path of

insertion. Cylindrical diamond is commonly used for creating the

guiding plane. Gentle, light, sweeping strokes from buccal to lingual

line angles are to be used. Normally 5-6 strokes are sufficient. It is a

flat surface 2-4 mm occlusogingivally. Reduction should follow the

curvature of the tooth. All prepared surfaces be polished with

carborundum impregnated rubber wheel.

Adjacent To Distal Extension Spaces

It is similar to that done for abutment teeth adjacent to tooth

supported segments. But the occluso-gingival plane of reduction is kept

1.5 to 2mm. This is done to allow slight rotation around the distal

occlusal rest, which avoids torquing forces on distal abutment tooth.

On Lingual Surfaces

The purpose of developing the guiding planes on the lingual

surface of teeth is to provide maximum resistance to lateral stresses.

More are the number of teeth used; less is the stress on an individual

tooth. The occluso gingival height 2- 4 mm. The plane should be

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located in the middle third of the crown. Gingival 3rd contour of the

tooth shouldn’t be changed as it can cause damage to the marginal

gingiva.

On Anterior Abutment Teeth

Purpose-

1. Provide parallelism for stabilization.

2. Minimize wedging action between teeth.

3. Minimize undesirable space between denture & abutment teeth.

4. Increase retention through frictional resistance.

5. Restore normal width of edentulous space

Enameloplasty to Change Height of Contour

Maxillary molars & premolars, if unsupported, tip buccally

causing height of contour to be located near the occlusal surfaces. As a

result the retentive arm position becomes esthetically compromised. It

also causes more leverage on the abutment tooth. Whereas mandibular

molars & premolars if unsupported tip lingually. This causes difficulty

in placement of reciprocal arm and/ or lingual plate. If tipping is

severe then major connector placement may be hindered. Usually this

can be accomplished by using a tapered diamond stone.

Enameloplasty to Modify Retentive Undercuts

108

It is used to increase a less than adequate retentive undercut

only if the oral hygiene of the patient is good & caries index is low.

But this should not be substituted for adequate design procedures.

For the procedure to be successful, the buccal and lingual

surfaces should be nearly vertical. If surface to receive undercut is

sloped, indentation has to be excessively deep. If opposing surface is

sloped, the reciprocal clasp arm cannot prevent retentive clasp tip from

dislodging. Retentive undercut -in the form of a gentle depression.

Create slight concavity (0.010 inch deep, 4mm MD, 2mm OG), parallel

to gingival margin without encroaching it . A round end tapered

diamond held parallel to gingival margin is used to create a gentle

depression.

Inlays Onlays and Crowns

If the remaining teeth do not possess usable natural contours

and enamel surfaces cannot be corrected to produce them, cast

restorations must be planned. Guiding planes, height of contour and

retentive undercuts can be placed in the wax patterns for the cast

restorations. Also many abutment teeth will require restorations for

more routine reasons such as caries, endodontic therapy etc.

Shaping the Wax Pattern

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The die of the tooth preparation in the cast of the remainder

arch is analyzed on the surveyor. Working cast is mounted at the same

tilt as the diagnostic cast. Once correct tilt is established substitute

analyzing rod with wax knife and carve guiding plane by shaving the

wax. Pattern must be hand carved to place height of contour at the

junction of gingival and middle third for retentive clasp. Refining can

be done in cast restoration.

Occlusion Rest Seat Preparation

Functions-

Direct forces of mastication parallel to long axis.

Prevent gingival displacement of denture.

Maintain the clasp in proper position.

Function as indirect retainer in distal extension partial denture.

Occlusal Rest Seat in Enamel

Form

Triangular in outline with base at marginal ridge and apex

pointing towards the centre of the tooth.

Should follow outline of mesial or distal fossa.

Minimum 0.5mm at thinnest point, 1-1.5mm at marginal ridge.

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Extension

1/3rd to 1/2 of mesiodistal diameter.

1/2 of the distance between buccal and lingual cusp tips.

Floor

Inclined towards the centre.

Spoon shaped.

Enclosed angle with the proximal surface less than 90º.

Preparation

Round diamond stone approximating no.4 round carbide bur to

be used for preparation. Create an outline using small round diamond

stone. The island of enamel within the outline can than be removed

with the same bur. Deepest portion of the rest seat is towards the

centre of the tooth. Verify preparation by red beading wax. Polish the

preparation using no.4 round steel bur revolving in reverse at moderate

speed.

Occlusal Rest Seat in New Gold Restoration

It should always be placed in wax patterns. Sufficient

occlusal clearance must be given to permit proper dimensions of rest

seat. A depression can be added to the preparation to accommodate rest

seat. Rest seat in wax pattern is prepared by using no.4 round steel bur.

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In Existing Gold Restoration

Patient must be warned of the possibility of the need to replace

the restoration. If restoration has marginal integrity and occlusal

harmony, attempt can be made to contour a rest seat in it .

Rest Seat Preparation on Anterior Teeth

Lingual / Cingulum Rest

Canine is preferred over incisor.

If canineis missing multiple rest on incisor teeth are used.

Lingual rest seat is preferred over incisal rest.

Usually it is prepared in a cast restoration.

Outline Form -

Half moon shaped forming smooth curve from one marginal ridge

to other.

Should cross the centre of tooth incisally to cingulum.

The rest seat itself is ‘V’ shaped.

The labial incline of lingual surface makes one wall.

Other wall starts of cingulum and inclines labio-gingivally

towards the centre of tooth.

If a cast restoration is to be given, the rest seat should be carved in the

wax pattern and not cut in cast restoration

Lingual Rest Seat in Enamel

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Lingual rest seat may be prepared in the tooth if tooth is sound,

good oral hygiene is present & caries index is low. Prominent cingulum

is another essential requirement. This is usually not present in

mandibular canines.

Preparation -

A. Sufficient Space Available-

Safe side ¼th inch diamond disk can be used. It must be held

parallel to path of insertion. Start low on one marginal ridge, pass over

the cingulum, and then pass gingivally to contact the other marginal

ridge.

B. Sufficient Space Not Available -

Often the presence of the lateral incisor or first pre molar will

preclude use of safe sided disk. In these cases use flat end large

diamond cylinder inclined slightly gingivally from horizontal for the

preparation. Flat end does the cutting. The rest seat must be gingival to

the contact level of opposing tooth. Polish the preparation with

carborundum impregnated rubber wheel.

Incisal Rest Seat Preparation

Should only be used on enamel surfaces.

Least desirable for anterior teeth.

Can be used successfully if abutment tooth is sound.

Usually placed near one of the incisal angles of the canine.

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If used in conjunction with circumferential clasp distal incisal

angle should be used.

If vertical projection / bar clasp, employing distal buccal

undercut for retention is used, mesial incisal rest be used for

reciprocation.

Preparation

Small safe side diamond disk or knife-edge stone is used.

Disk / stone is kept parallel to path of insertion.

First cut made vertically 1.5-2mm deep in the form of notch and

2-3mm inside of the proximal angle of the tooth.

Small flame shaped diamond point is used to rounden the notch.

Enamel proximal to notch is slightly reduced.

The groove must be carried slightly over to labial surface to

prevent facial tipping.

Groove should be continued part way down the lingual surface

as indentation to accommodate minor connector.

All sharp angles be rounded and preparation polished with

carborundum impregnated rubber wheel.

REFERENCES

Stewart KL, Rudd KD and Kuebker WA: Clinical removable partial

prosthodontics , ed. 2, St Louis, 1997, Ishiyaku EuroAmerica, Inc.

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McGivney GP and Castleberry DJ: McCraken removable partial

prosthodontics, ed. 9, St Louis, 1995, Mosby.

Davenport JC, Basker RM, Heath JR, Ralph JP: A colour atlas of

removable partial dentures, 1989, London, Wolfe Medical Publications

Ltd.