mouth prep vikas

7/29/2019 Mouth Prep Vikas

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DEPTT OF PROSTHODONTICS CROWN AND BRIDGE

Mouth preparation for removable

partial denture

Seminar

Dr. Vikas Aggarwal


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CONTENTS

1. Introduction2. Pre prosthetic mouth preparation

Surgical preparation

Conditioning of abused and irritated tissues

Periodontal preparation

Treatment of muscular symptoms

Correction of occlusal plane

Conservative/endodontical preparation

Correction of malalignment

3. Prosthetic mouth preparation Developing guiding planes Changing height of contour Modifying retentive undercut. Rest seat preparation

4. Conclusion5. References


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INTRODUCTION

The preparation of the mouth is fundamental to a successful removable partial

denture service. Mouth preparation, perhaps more than any other single factor,

contributes to the philosophy by Devans that the prescribed prosthesis must

not only replace what is missing but also preserve the remaining tissue and

structures that will enhance the removable partial denture

"Mouth preparation" is a term intended to cover all types of changes

effected in the teeth, foundation ridges or oral structures which may be deemed

necessary to accomplish a better partial denture result. (Applegate 3rd ed)

Mouth preparation follows the preliminary diagnosis and the

development of a tentative treatment plan. Final treatment plan can be deferred

until the response to the preparatory procedures can be ascertained.

Mouth preparation can be generally classified as pre-prosthetic mouth

preparation that involves removal of any hindrances to prosthetic treatment and

prosthetic mouth preparation that involves mouth preparation done to facilitateprosthetic treatment.

1. Pre prosthetic mouth preparation Surgical preparation Conditioning of abused and irritated tissues Periodontal preparation Treatment of muscular symptoms Correction of occlusal plane Conservative/endodontic preparation Correction of malalignment


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2. Prosthetic mouth preparation Developing guiding planes Changing height of contour Modifying retentive undercut. Rest seat preparation

1) SURGICAL PREPARATION

They should be planned and completed well in advance. The longer the

interval between the surgery and the impression procedure, the more complete

the healing and consequently the more stable the denturebearing mucosa. The

important consideration is that the patient not be deprived of any treatment that

would enhance the success of the partial denture.

a) Extractionsb) Removal of residual rootsc) Removal of impacted teethd) Malposed teethe) Cysts and odontogenic tumorsf) Exostosis and torig) Hyperplastic tissuesh) Muscle attachment and frenii) Bony spines and knife edge ridges

j) Polyps, papilloma and traumatic haemangiomask) Hyperkeratosis,erythoplakia,and ulcerationl) Dentofacial deformitym)Ridge augmentationn) Osseointegrated devices


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a) Extractions

Planned extraction should be carried out after thorough evaluation of the

remaining teeth in the dental arch. The non-strategic teeth that present

complications or those whose presence may determine the design of the partial

denture should be extracted. Teeth with doubtful prognosis of which retention

would contribute little if anything, even if successfully treated and maintained,

are contraindicated.

b) Removal of residual roots

All retained roots or root fragments should be removed particularly if

they are in close proximity to the tissue surfaces or when they contribute to the

progression of periodontal pockets.

The removal of root tips can be carried out from the facial and palatal

surfaces without compromising the alveolar bone height or harming the adjacent

teeth.

c) Removal of impacted teeth

All impacted teeth are indicated for extraction because they can becomesource of spread of infection to the adjacent healthy teeth.

The skeletal structure of the body changes with age. Asymptomatic

impacted teeth covered with bone in elderly individuals with no evidence of

pathology should be left to preserve the arch morphology. This should be

documented in patients records. Age alterations that affect the jaws can result

in minute exposures of impacted teeth to the oral cavity through the sinus. Earlyelective removal of impactions can prevent later serious acute and chronic

infection with extensive bone loss.

d) Malposed teeth

The loss of individual or groups of teeth may lead to extrusion, mesial drifting,

or combinations of malpositioning of remaining teeth. In some cases the

alveolar bone will be carried occlusally along with the extruded teeth.


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Orthodontics can be used to correct such occlusal discrepancies. Otherwise

surgical repositioning of the malposed teeth and the supporting bone can be

done.

e) Cysts and odontogenic tumors

All radiolucencies or radiopacities observed in the jaws should be

investigated. Panoramic radiographs are recommended to survey the jaws for

unusual pathologies.

Cysts, odontogenic tumors, should be removed because their presence

may compromise the design of the removal partial dentures.

f) Exostoses and tori

The presence of abnormal bony enlargements should not be allowed to

compromise the design of the partial denture. Although modification in design

to accommodate for exostoses can be done, this will place additional stresses to

supporting elements and compromise the function.

The mucosa covering these enlargements is thin and friable. Partial

denture components in proximity to this type of tissue can cause irritation andchronic ulceration. Also exostoses close to gingival margin lay complicate

maintenance of periodontal health and lead to eventual loss of strategic

abutment teeth.

g) Hyperplastic tissue

They are seen in form of fibrous tuberosities, soft flabby ridges, folds of

redundant tissue in the vestibule or floor of the mouth and palatal papillomatosisAll these forms of excess tissue should be removed to form a firm base for the

partial dentures.

Hyperplastic tissue can be removed with any preferred combination such

as scalpel, curette, electrosurgery, or by laser. Some form of surgical stent

should be considered for such patients for a comfortable and enhanced healing.

All such excised tissues should be sent to oral pathologist for microscopic

study.


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h) Muscle attachments and frena

Loss of alveolar bone height renders the muscle attachments near the

alveolar crest making the designing of the partial dentures difficult. Mylohyoid,

buccinator, mentalis and genioglossus muscles are those which can cause

problems. Sometimes some muscles (mentalis, genioglossus) produce bony

protuberances at their attachments which interfere with design of partial

denture.

Repositioning of these supra-placed muscles by ridge extension is

necessary in such condition to enhance comfort and function. Mylohyoid can be

easily repositioned but genioglossus is much more difficult to reposition.

The maxillary labial and mandibular lingual freni may interfere in partial

denture design. These should be modified with surgical interventions.

i) Bony spines and knife- edge ridges

Sharp bony spicules should be removed and knife-edge ridges rounded to

facilitate easy designing of the partial dentures. These procedures should becarried out with minimal bone loss. Vestibular deepening or ridge augmentation

procedures can be considered.

j) Polyps, papilloma and traumatic haemangiomas

All abnormal soft tissue lesions should be excised and submitted for pathologic

examination. New or additional stimulation to the tissue may producediscomfort or even malignant changes.

k) Hyperkeratosis, erythoplakia, and ulceration

All abnormal red, white and ulcerative patches should be investigated and

treated accordingly. A biopsy of areas larger than 5 mm should be completed,

and if the lesions are large (more than 2 cm in diameter), multiple biopsies

should be taken. The biopsy report will determine whether the margins of the


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These conditions are usually associated with ill-fitting or poorly occluding

removable partial dentures. However, nutritional deficiencies, endocrine

imbalances, severe health problems (diabetes or blood dyscrasias), and bruxism

must be considered in a differential diagnosis.

If a new removable partial denture or the relining of a present denture is

attempted without first correcting these conditions, the chances for successful

treatment will be compromised because the same old problems will be

perpetuated. The patient must be made to realize that fabrication of a new

prosthesis should be delayed until the oral tissues can be returned to a healthy

state.

The first treatment procedure should be an immediate institution of a

good home care program. A suggested home care program includes rinsing the

mouth three times a day with a prescribed saline solution; massaging the

residual ridge areas, palate, and tongue with a soft toothbrush; removing the

prosthesis at night; and using a prescribed therapeutic multiple vitamin along

with a prescribed high- protein, low-carbohydrate diet. Some inflammatory oralconditions caused by ill-fitting dentures can be resolved by removing the

dentures for extended periods.

Use of tissue conditioning materials

The tissue conditioning materials are elastopolymers that continue to flow

for an extended period, permitting distorted tissues to rebound and assume theirnormal form. These soft materials apparently have a soothing effect on irritated

mucosa, and because they are soft, occlusal forces are probably more evenly

distributed.


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Maximum benefit from using tissue-conditioning materials may be obtained by:

Eliminating deflective or interfering occlusal contacts of old dentures (byremounting on an articulator if necessary)

Extending denture bases to proper form to enhance support, retention, andstability

Relieving the tissue side of denture bases sufficiently (2 mm) to providespace

Applying the material in amounts sufficient to provide support and acushioning effect

Following the manufacturer's directions.The conditioning procedure should be repeated until the supporting tissues

display an undistorted and healthy appearance. Usually intervals of 3 to 4 days

between changes of the conditioning material are clinically acceptable. An

improvement in irritated and distorted tissues is usually noted within a few

visits, and in some patients a dramatic improvement will be seen. Usually three

or four changes of the conditioning material are adequate, but in some instances

more changes are required. If positive results are not seen within 3 to 4 weeks,

one should suspect more serious health problems and request consultation from

a physician.

3) PERIODONTAL PREPARATIONS

The periodontal procedures follows surgical procedures and done

simultaneously along with tissue conditioning procedures. The periodontal

procedures are necessary to restore the mouth to the state of health required for

definite treatment. The periodontal health of the remaining teeth especially the

abutment teeth is evaluated carefully and corrective measures are instituted

before fabricating the removable partial denture.


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Objectivesof periodontaltherapy:

Removal of all etiologic factors contributing to periodontaldiseases.

Elimination or reduction of all pockets with the establishment ofgingival sulci free of inflammation.

Establishment of functional atraumatic occlusal relationships andtooth stability

Development of a personalized plaque control programme anddefinite maintenance schedule.

Periodontal diagnosis and treatment planing

Diagnosis

The diagnosis of periodontium is based on systematic and careful

observation of the periodontium. It follows the procurement of health history of

patient. It is performed using direct vision, palpation, periodontal probe, mouth

mirror, and other auxiliary aids such as curved explorers, furcations probes,

diagnostic casts and roentgenograms.

Most important is careful exploration of the gingival sulcus and recording

the probing pocket depth. The probe is inserted gently but firmly between the

gingival margin and the tooth surface, and the depth of gingival sulcus is

determined circumferentially around each tooth. A critical assessment of the

sulcular health can be done by judging the amount of bleeding on probing. This

along with the pocket depth is an excellent indicator of health and disease.


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Dental roentgenograms

They are used to supplement clinical examination but cannot substitute it.

The extent and pattern of bone loss can be estimated. They also provide

information regarding the following:

Type location and severity of bone loss Location, severity and distribution of furcation involvement. Alteration of periodontal ligament space. Alterations of the lamina dura Calcified deposits Location and conformity of restoration margins Evaluation of crown and root morphologies. Root proximity Caries Evaluation of other associated anatomic structures, such as mandibular

canal or sinus proximity.

Mobility

Each tooth should be evaluated for mobility. It is graded according to ease and

extent of tooth movement. Normal mobility is in order of 0.05 to 0.10 mm.

Grade Imobility slightly more than normal.

Grade IImoderately more than normal.

Grade IIIsevere mobility with vertical displacement.

Mobility is assessed with ends of two instruments. If fingers are used the

movement of soft tissue may mask accurate determination of mobility

If etiologic factors are removed most Grade I and II mobile teeth will become

stable and can be used to support the partial denture. Mobility in itself is not an


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indication for extraction. Grade III cannot be reversed and thus cannot be used

for support of the partial denture.

Treatment planning

Depending on the severity of periodontal changes a series of simple to complex

procedures may be indicated. The treatment planning can be divided into the

following phases.

Phases in Treatment

Disease control therapy phase-phase 1

Definitive periodontal surgery phase-phase 2

Maintenance phase- phase 3

Disease Control Therapy Phase-Phase 1

This phase consists of:Oral hygiene instructions

The patient should be instructed in the use of disclosingwafers, soft nylon toothbrush, and unwaxed dental floss.

At subsequent appointments oral hygiene can beevaluated 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 & root planing

Ultra sonic instruments are used for gross calculus removal.

This is followed by root planning with sharp curettes.

Elimination of other local irritating factors

Overhanging margins of amalgam & inlay restoration. Overhanging crown margins. Open contacts leading to food impactions. Deep carious lesions should be eliminated before the start of

definitive prosthetic treatment .

Elimination of occlusal interferences

Poor occlusal relationship may act as a factor thatcontributes to more rapid loss of periodontal attachment.

Selective grinding procedure is generally applied at thisstage. 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 thepresence of pathology rather than on a preconceived

articulation pattern.

Occlusion on natural teeth needs to be perfected only to apoint at which cuspal interference within the patients

functional range of contact is eliminated and normal

physiologic function can occur.

Guide to Occlusal Adjustment (Schuyler)

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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1) 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:-

a) 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.

b) 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.

c) 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.

2) 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 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


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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.

5) Any sharp edges left by grinding should be rounded off

Splinting

In many partially edentulous mouths some of all the remaining teeth lose

their periodontal and bone support rendering them mobile and not suitable to

provide support to the partial dentures. In order to use such teeth as abutments

additional support for these teeth by splinting them together is necessary.

The cause of mobility must be assessed and the causative factors should be

eliminated. Secondary mobility resulting from presence of inflammatory lesion

may be reversible.

Teeth may be immobilized during periodontal treatment by acid etching

teeth with composite resin, with fiber reinforced resin, with cast removable

splint, or with intracoronal attachments.

Splinting can be achieved by a removable restoration or by fixed restoration

which becomes a permanent splint.

Splinting of weakened teeth in partially edentulous arch located in a position

where the partial denture will not require an unusual amount of support, is

achieved by using fixed splinting, this maintains the continuity of the arch,

avoids additional modification spaces, thus simplifying the construction and


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fitting of partial dentures and improving prognosis. Fixed splinting must be

accomplished with full or partial coverage crowns soldered together; this gives

additional resistance to antero-posterior stresses. To offer resistant to lateral

forces, the splint must be extended anteriorly to include canine teeth and also

include the lateral plane of the posterior teeth.

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, 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 deformi ties 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.


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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 patients requirements. In moderate to severe

periodontitis, 3-4 months recall system is followed.

4) TREATMENT OF MUSCULAR SYMPTOMS

Prior to adjustment of the occlusion of the teeth the muscular symptoms

should be analyzed. Patients with partially edentulous arches often show

symptoms of muscle spasm. Therefore the first objective of the operator is to

eliminate this muscle spasm. This can be achieved by giving the patient an

acrylic overlay splint with a flat occlusal surface which will eliminate premature

tooth contacts causing deviation of the mandible leading to spasm. Adjunct

therapies like short-wave therapy, infra-red radiation, and light massage are

designed to increase the volume of the blood flowing through the muscles and

thereby removing the offending metabolites. The use of muscle relaxant drugs

like Diazepam 5-10 mg B.D is effective in relaxing the symptoms.

5) CORRECTION OF OCCLUSAL PLANE

The occlusal plane in most partially edentulous mouths will be uneven.

The severity of this irregularity will determine the treatment necessary to

correct the condition. Teeth that have been unopposed for a long time tend to

overerupt, e.g. the maxillary molars if unopposed will migrate downwards

carrying the maxillary tuberosity with them creating a problem to reestablish the

occlusal plane. This is because surgery to reduce the bone height may encroach

upon the maxillary sinus.


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Normally the occlusal plane is corrected by reduction of the height of

overerupted teeth.

Methods undertaken are:

Orthodontic tooth movement Enameloplasty Onlay Crowns Endodontics with crown or coping Extraction Surgery

Orthodontics is the ideal treatment to upright the tilted teeth and reestablish

the occlusal plane. If this is not possible other methods are employed.

Enameloplasty word used to describe the removal of a portion of enamel

surface of tooth to accomplish specified purpose. It consists of reduction of cusp

height in order to level the curve of spee. Penetration of enamel layer should be

avoided, However in older individuals with wear and subsequent secondary

dentine formation slightly more tooth structure can be removed. Care to be

taken not to mutilate the anatomic contours such as accessory grooves, and

sluiceways must be restored. Reduction is done with tapered diamond cylinder

or stones in high speed hand piece. The cut enamel surface is smoothened

with carborundum containing rubber wheels and fluoride gels.

Onlays were common previously but now rarely used. The occlusal surface can

be covered with onlay rest free of pits and fissures. The use of chrome- cobalt

can cause extreme wear of natural teeth. Tooth colored resin may be processed

over the metal, however this will wear rapidly. The simplest method is the use

of cast gold onlays. One of main advantages of onlay is maintain the natural


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contours of enamel surfaces of tooth. However full crowns,are replacing onlays

presently because of esthetic and retentive concerns.

Crowns are indicated when the facial and lingual surfaces need to be altered, to

produce desirable height of contour, a guiding plane, or a retentive undercut. If

tooth reduction is too great then endodontic treatment should be considered.

If the strategically positioned teeth need to be retained as abutment teeth for

partial denture and required to be corrected extensively then intentional

endodontics with crowns are considered.

Extraction-It should be the goal of a designer of removable partial dentures to

retain as many of the remaining teeth as possible. However, at times retaining

certain teeth can greatly complicate or even compromise the success of the

treatment. For example, if orthodontic treatment cannot be accomplished to

realign severely malposed molars or premolars, extraction must be considered.

When teeth interfere with the placement of the major connector and no other

solution (such as crowning the tooth) feasible, extraction must be planned.

Surgical repositioning- Surgical repositioning of one or both jaws or ofsegments of one or both jaws can be performed to correct malrelationship of

teeth. Various forms of mandibulectomies, usually to correct gross prognathic

jaw relationships, have been performed. Maxillary segmental osteotomy is done

to superiorly repositioning posterior segments of maxillae. This is one of the

most effective methods of regaining interarch space lost due to downward

migration of the teeth and tuberosity


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6) CONSERVATIVE/ENDODONTIC PREPARATION

Fillings

Onlays

Endodontic treatment with crown/coping

Fillings: When fillings are required in abutment or other teeth, only gold or

amalgam are suitable materials lo come into contact with partial dentures as

these materials have the necessary strengths to form a foundation for occlusal

rests. Amalgam fillings or gold inlays are used to restore lost contours of the

teeth.

Onlays: The occlusal surfaces of worn teeth can be restored by onlays. The

occlusal surface of a tooth to be covered by an onlay should be free of pits and

fissures and if present, should be removed by an enameloplasty. If onlay rests

are placed than they should be constructed short of occlusal contact with

retentive beads present on the metal surface, for tooth-colored acrylic resin to be

processed over it. This is done to prevent the metal coming in contact with

natural teeth which if otherwise would cause rapid wear of the opposing enamelsurface.

Endodontic with crown/coping: Some of the strategic important teeth present

in the arch, like an anterior tooth present in a long anterior edentulous span,

should be retained and used as abutment for the partial denture. But most of the

time these strategic important tooth/teeth are over erupted are have lost some of

their periodontal support which is needed to serve as an abutment. In such casesendodontic therapy followed by cementation crown will allow such tooth/teeth

to serve as normal abutments. Porcelain jacket crowns should generally be

avoided in partially edentulous mouths as they make very poor abutments


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7) CORRECTION OF MALALIGNMENT

Teeth that are malposed, facially or lingually are more difficult to correct

There are definite, limitation to the repositioning of these malposed teeth.

Orthodontic correction of these malposed teeth is the first line of treatment.

Enameloplasty and crowns are also treatment choices. Surgical intervention is

planned only if all other measures fail to reposition these malposed teeth.

II) Prosthetic Mouth Preparation

It is done to modify the existing structures to further enhance the placement of

prosthesis.

It mainly involves reshaping of teeth

The steps involved are:

Developing guiding planes Changing height of contour Modifying retentive undercut. Abutment preparation using cast crowns Rest seat preparation

Tooth surfaces often need to be reshaped to accomplish specific purposes.

This changing of tooth contour may be accomplished in the enamel, on the

surface of an existing restoration, or by placing a new restoration.

Enameloplasty

Conservatism must be the rule when tooth preparation is to be accomplished on

enamel surfaces for a removable partial denture. Sufficient tooth reduction must

be accomplished to ensure adequate space or proper contour, but never at the

expense of overcutting the tooth


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Enameloplasty to Develop Guiding Planes

Guiding planes are those surfaces on the teeth, of sufficient area and parallel

relationship to each other, so that they may serve to determine positively the

direction of appliance movement (Applegate 1954)

Two or more vertical parallel surfaces of abutment teeth, so shaped to direct

prosthesis during placement and removal.(McCracken 12th

edn)

Two or more vertically parallel surfaces of abutment teeth, so orientated as to

direct the path of placement of removable partial dentures.( GPT 8th )

Functions of guiding planes

1. To provide one path of placement and removal2. To ensure planned and intended action of the retentive and bracing

components of the partial denture

3. To eliminate detrimental strain to the abutment teeth and the componentsof the framework in placing and removing the prosthesis

4. To eliminate gross food traps between the abutment teeth and the denturebase

5. To provide retentive characteristics against dislodgement of the denturewhen the dislodging force is other than parallel to the path of removal

6. To provide bracing characteristics against horizontal rotation of thedenture


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Guiding Planes On Abutment Teeth Adjacent to Tooth Supported

Segments

A cylindrical diamond point is generally the instrument to make the preparation.

A gentle, light sweeping stroke from the buccal line angle to the lingual line

angle should be used. The flat surface created should ideally be 2 to 4mm in

occluso-gingival height The reduction must not be a straight slice across the

tooth surface; rather it should follow the curvature of the surface so that nearly

uniform amounts of enamel are removed

Guiding Planes on Abutment Teeth Adjacent to Distal Extension

Edentulous Spaces

The tooth preparation on the proximal surface ofabutment teeth adjacent to

distal extension edentulous spaces is accomplished in thesame manner with a

cylindrical diamond stone held parallel to the path of insertion.

A guiding plane prepared adjacent to a distal extension space should be slightly

shorter than a guiding plane prepared adjacent to a tooth supported segment.Typically, a guiding plane adjacent to a distal extension space is 1.5 to 2.0 mm

in height. The reduced height results in decreased contact with the associated

minor connector (ie, proximal plate) and permits greater freedom of movement

for the associated removable partial denture as a result; potentially destructive

torquing forces are minimized

Guiding Planes On Lingual Surfaces Of Abutment TeethMandibular posterior teeth are usually inclined lingually with a resultant high

lingual survey line. Minor recontouring can frequently improve the position of

the survey line to allow placement of the reciprocal clasp arm in its proper

position

The purpose of providing guiding planes on lingual surfaces of teeth is to

provide maximum resistances to lateral stresses. The more teeth involved in


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guiding plane preparation, the less will be the stress transmitted to each

individual tooth.

The occluso-gingival height of the preparation is 2 to 4 mm. The plane ideally

should be located in the middle third of the clinical crown of the tooth. Special

care must be shown to avoid changing the contour of the gingival third of the

tooth because damage to the marginal gingiva through the improper shunting of

food may occur if the normal morphology of the gingival third of the crown is

lost

Guiding Planes on Anterior Abutment Teeth

Guiding planes on anterior teeth adjacent to edentulous spaces provide the

parallelism needed to ensure stabilization, minimize wedging action between

the teeth, decrease undesirable space between the denture and the abutment

tooth, and increase retention through frictional resistance.

Another important purpose of these guiding planes is to reestablish the normal

width of an edentulous space. If one or more anterior teeth are lost,adjacentteeth tend to drift or tip into these spaces.Both actions result in reduced space

and make esthetic replacement of the missing teeth much more difficult.

Tipping is relatively common and often results in a large undercut apical to the

height of contour

If the tooth is not recontoured, this undercut will appear as an unsightly space

between the tipped tooth and the removable partial denture.Such a space detracts from the esthetic value of the removable partial denture

and acts as a food trap.

Recontouring should be performed to minimize the effects of tipping and to

improve the esthetic and functional results of the removable partial denture

service. This recontouring should be performed with the proposed path of

insertion in mind, and the resultant guiding planes should be parallel to the

planned path of insertion.


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Enameloplasty to Change Height of Contour

The height of contour is changed most frequently to provide better positions for

clasp arms or for lingual plating.

Ideally the retentive clasp arm should be located no higher than the junction of

the gingival and the middle thirds. This position not only enhances the esthetic

quality of the clasp, but also places clasp nearer the tooths centre of rotation

The amount of correction that can be accomplished by recontouring the enamel

surface is limited by the thickness of the enamel. Care has to be taken not to

penetrate the enamel and expose dentin

The height of contour is best lowered by using tapered diamond stones.

Enameloplasty to Modify Retentive Undercuts

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 should be 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 endtapered diamond held parallel to gingival margin is used to create a gentle

depression.


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Abutment preparation using 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

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

Rest -rigid extension of a partial removable dental prosthesis that contacts the

occlusal surface of a tooth or restoration, the occlusal surface of which may

have been prepared to receive it

Rest seat-the prepared recess in a tooth or restoration created to receive the

occlusal, incisal, cingulum, or lingual restFunctions-

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.


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Occlusal Rest Seat in Enamel

Form

Triangular in outline with base at marginal ridge and apex pointing

towards the centre of the tooth. Apex of the triangle should be rounded as

should all external margins of preparation

Should follow outline of mesial or distal fossa.

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

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 90.

Preparation

Round diamond stone is used approximating no.4 round carbide bur for

preparation. Create an outline using small round diamond stone. The island of

enamel within the outline can then be removed with the same bur. Deepest

portion of the rest seat is towards the center of the tooth. Verify preparation byred beading wax. Polishing of preparation is done using carborundum

impregnated rubber point in low speed hand piece


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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.

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.

Occlusal Rest Seat Preparation In Amalgam Restorations

An occlusal rest preparation in a multi surface amalgam restoration is less

desirable than that in either sound enamel or a gold restoration. Amalgam alloy

tends to flow when placed under constant pressure. Care must be taken not toweaken the proximal portion of the amalgam restoration at the isthmus during

the preparation. This may result in fracture during function.

Rest Seat Preparation For Embrasure Clasp

This preparation extends over the occlusal embrasure of two approximating

posterior teeth, from the mesial fossa of one tooth to the distal fossa of other.Insufficient tooth removal will generally lead to occlusal interferences between

the metal of the clasp and the opposing cusps. Relieving the metal to gain

occlusal freedom ultimately leads to breakage of the clasp during function.

Repair of the embrasure clasp is usually difficult.


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As the preparation passes over the buccal and lingual embrasures it should be

approximately 3.0 to 3.5 mm wide and 1.5t o 2.5 mm deep. All contours of the

preparation must be rounded after the preparation is complete

Rest Seat Preparation on Anterior Teeth

An occlusal rest on a molar or a premolar is preferred over a lingual or an

incisal rest on anterior teeth to provide support for a partial denture. Forces are

better directed down the long axis of the abutment tooth by an occlusal rest than

by a lingual or incisal rest. A canine is preferred over an incisor for support of a

denture. When a canine is not present, multiple rests on incisor teeth are needed

in place of a single rest on a single incisor tooth. A lingual rest is preferred to an

incisal rest.

Lingual Rest Seat preparation In Enamel

A lingual rest seat may be prepared in the enamel surface of an anterior tooth if

the tooth is sound, the patient practices good oral hygiene, and the caries indexis low. The cingulum should also be prominent to present a gradual slope to the

lingual surface rather than a steep vertical slope. This is the principal reason

why mandibular canines are poor candidates for a lingual rest. The lingual

surface of the tooth normally has too great a vertical slope to permit the rest seat

to be prepared without penetrating into dentin. In some instances a lingual rest

can be placed on maxillary central incisors that have prominent cingulum, butmost, often this is a compromise effort unless it is placed in a cast restoration.

The lingual rest can be prepared nearer the center of the tooth, preventing the

tipping action that an incisal rest may produce. Lingual rests are also more

acceptable esthetically and less subject to breakage and distortion. The most

satisfactory lingual rest from the standpoint of support is one that is placed on a

prepared rest seat in a cast restoration. This should be used wherever possible.

A lingual rest on a cast restoration may be used on any anterior tooth, either


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maxillary or mandibular. A lingual rest prepared in a enamel surface should be

used primarily on maxillary canines and on a limited number of maxillary

incisor teeth.

Outline Form -

Half moon shaped forming smooth curve from one marginalridge 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.

Preparation

Preparation of a cingulum rest seat is accomplished using a No. 38 carbide bur

in a high-speed handpiece. The No. 38 bur is an inverted cone with side- and

end cutting surfaces. During the preparation process, the bur is oriented at a

slight angle to the lingual surface of the tooth. The bur is then used to create acrescent-shaped rest seat that begins on one marginal ridge, passes over the

cingulum, and terminates on the opposite marginal ridge .The walls of the rest

seat are relatively smooth and that they do not present any mechanical

undercuts.

The preparation is finished using a green stone in a low-speed handpiece.

Polishing is accomplished using a carborundum impregnated rubber wheel orpoint in a low-speed handpiece

Lingual rest seat preparation in cast restorations

If a cast restoration is to be placed on abutment tooth, the rest seat should be

carved in the wax pattern and not cut in the cast restoration. A definite rest seat

thus developed will direct the forces of occlusion through the long axis of the

abutment tooth.


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Conclusion

The preparation of mouth is fundamental to a successful removal partial

denture. The prime objective of all the mouth preparation procedures is to return

the mouth to optimum health and to eliminate any condition that compromises

the success of the partial denture.

REFERENCES

1. McCrackens removable partial prosthodontics 12th edition 20112. Stewarts: Clinical removable partial prosthodontics,3rd edition 20033. Applegate OC. Essentials of Removable Partial Denture Prosthesis, 3RD .

Philadelphia: Saunders, 1965

4. Osborne & Lammies Partial prosthodontics 5th edition 19865. McCracken .L.W.Mouth preparation for partial dentures , J. Prosthet.

Dent 1956;6,(1) :39-52

6. Glan G.W., Appleby R.C. Mouth preparation for removable partialdentures. J. Prosthet. Dent. 1960;10:124-134.

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