PREPARATION OF MOUTH FOR REMOVABLE PARTIAL DENTURES

INTRODUCTIONMouth preparation contributes to

the philosophy 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 includes procedures in four categories:

1. oral surgical preparation 2. conditioning of abused and irritated tissue 3. periodontal preparation 4. preparation of abutment teeth.

A)PRE-PROSTHETIC MOUTH PREPARATION

B)PROSTHETIC MOUTH PREPARATION

The objectives of the procedures involved in all four areas are to return the mouth to optimum health and to eliminate any condition that would affect the success of the removable partial denture.

Mouth preparation must be accomplished before the impression procedures that will produce the master cast on which the removable partial denture will be fabricated.

  Oral surgical and periodontal procedures should

precede abutment tooth preparation and should be completed far enough in advance to allow the necessary healing period. If at all possible, at least 6 weeks, but preferably 3 to 6 months, should be provided between surgical and restorative dentistry procedures.

ORAL SURGICAL PREPARATION All preprosthetic surgical treatment for

the removable partial denture patient should be completed as early as possible.

Longer the interval between surgery & impression procedure, more complete the healing & more stable the denture bearing areas.

1. EXTRACTIONo Planned extractions should occur early in the

treatment regimen but not before completion of a careful and thorough evaluation of each remaining tooth in the dental arch.

o Each tooth must be evaluated concerning its strategic importance and its potential contribution to the success of the removable partial denture.

2. REMOVAL OF RESIDUAL ROOTS All retained roots or root fragments should be

removed if they are in close proximity to the tissue surface or if there is evidence of associated pathological findings.

Residual roots adjacent to abutment teeth may contribute to the progression of periodontal pockets and compromise the results from subsequent periodontal therapy.

3. IMPACTED TEETH All impacted teeth in edentulous areas

and those adjacent to abutment teeth is considered for removal.

Asymptomatic impacted teeth in the elderly that are covered with bone, with no evidence of a pathological condition, should be left to preserve the arch morphology.

Early removal of impactions prevents infections.

4. MALPOSED TEETH The loss of individual tooth or groups of

teeth may lead to extrusion, drifting, or combinations of mal-positioning of the remaining teeth.

Alveolar bone supporting extruded teeth will be carried occlusally as the teeth continue to erupt.

Such teeth and their supporting alveolar bone can be surgically repositioned.

5. CYSTS AND ODONTOGENIC TUMORS

A periapical roentgenogram should be taken to confirm or deny the presence of a lesion.

All radiolucencies or radiopacities observed in the jaws should be investigated for any pathologies.

6. EXOSTOSES AND TORI The existence of abnormal bony enlargements

should not be allowed to compromise the design of the removable partial denture

Mucosa covering the bony protuberance is extremely thin and friable.

Removable partial denture components in proximity to this type of tissue may cause irritation and chronic ulceration.

Exostoses approximating gingival margins may complicate the maintenance of periodontal health & lead to eventual loss of strategic abutment teeth.

7. HYPERPLASTIC TISSUE Hyperplastic tissue is seen in the form of fibrous

tuberosities, soft flabby ridges, folds of tissue in the vestibule or floor of the mouth, and palatal papillomatosis.

All these forms of excess tissue should be removed to provide a firm base for the denture.

Removal will produce more stable denture, reduce stress & strain on the supporting teeth & tissue.

Surgical approaches should not reduce vestibular depth.

Palatal papillomatosis

8. MUSCLE ATTACHMENTS AND FRENA As a result of the loss of bone height, muscle

attachments may insert on or near the residual ridge crest.

The mylohyoid, buccinator, mentalis, and genioglossus muscles are those most likely to introduce problems.

Appropriate ridge extension procedures can reposition attachments & remove bony spines which will enhance the comfort & function of removable partial denture.

The maxillary labial and mandibular lingual frena are the most common sources of frenum interference with denture design.

9. BONY SPINES AND KNIFE-EDGE RIDGES Sharp bony spicules should be

removed and knifelike crests gently rounded.

These procedures should be carried out with minimum bone loss.

10. POLYPS,PAPILLOMAS AND HEMANGIOMAS All abnormal soft tissue lesions should be

excised & submitted for pathological examination before the fabrication of removable partial denture.

11. HYPERKERATOSES, ERYTROPLASIA AND ULCERATION

All abnormal, white, red, or ulcerative lesions should be investigated.

Biopsy of areas greater than 5mm should be completed & if lesions are large multiple biopsies should be taken.

12. DENTOFACIAL DEFORMITY Patients with a dentofacial deformity often have

multiple missing teeth as part of their problem. Correction of the jaw deformity can simplify the dental rehabilitation.

Before specific problems with the dentition can be corrected,patients overall problem must be evaluated thoroughly.

Mandible and maxillae may be positioned anteriorly or posteriorly, and their relationship to the facial planes may be surgically altered to achieve improved apperance

13. OSSEOINTEGRATED DEVICES Implant devices offer significant stabilizing

effect on dental prosthesis through a rigid connection to living bone.

The system that pioneered clinical prosthodontic applications with the use of commercially pure (CP) titanium endosseous implants is that of Branemark. This titanium implant was designed to provide a direct titanium-to-bone interface (osseointegrated)

14. AUGMENTATION OF ALVEOLAR BONE Ridge augmentation is done with the use of

autogenous and alloplastic materials. Larger ridge volume gains necessitate

consideration of autogenous grafts. Clinical results depends on careful evaluation

of need for augmentation,projected volume of required material & site & method of placement.

CONDITIONING OF ABUSED & IRRITATED TISSUEPatients who require conditioning treatment often

demonstrate the following symptoms: 1. Inflammation and irritation of the mucosa

covering the denture bearing areas. 2. Distortion of normal anatomic structures, such

as incisive papillae, the rugae, and the retro molar pads

3. A burning sensation in residual ridge areas, the tongue, and the cheeks and lips.

These conditions associated with ill fitting or poorly occluding removable partial dentures.

The tissue conditioning materials are elastopolymers that continue to flow for an extended period, permitting distorted tissue to rebound and assume its normal form.

These soft materials apparently have a massaging effect on irritated mucosa, and because they are soft, occlusal forces are probably more evenly distributed.

Maximum benefit from using tissue conditioning materials may be obtained by

(1) eliminating deflective or interfering occlusal contacts of old dentures

(2) extending denture bases to proper form to enhance support, retention, and stability

(3) relieving the tissue side of denture bases sufficiently (2 mm) to provide space for even thickness and distribution of conditioning material

(4) applying the material in amounts sufficient to provide support and a cushioning effect and

(5) following the manufacturer's directions for manipulation and placement of the conditioning material.

The conditioning procedure should be repeated until the supporting tissues display an undistorted and healthy appearance.

PERIODONTAL PREPARATION

The periodontal preparation of the mouth usually follows any oral surgical procedure and is performed simultaneously with tissue conditioning procedures.

The elimination of exostoses, tori, hyperplastic tissue, muscle attachments, and frena can be incorporated with periodontal surgical techniques.

Periodontal therapy should be completed before restorative dentistry procedures are begun for any dental patient. The periodontal health of the remaining teeth, especially those to be used as abutments, must be evaluated and corrective measures instituted before removable partial denture fabrication.

OBJECTIVES OF PERIODONTAL THERAPY 1. Removal and control of all etiological factors

contributing to periodontal disease, along with a reduction or elimination of bleeding on probing

2. Elimination of, or reduction in, pocket depths, with the establishment of healthy gingival sulci whenever possible

3. Establishment of functional atraumatic occlusal relationships and tooth stability

4. Development of a personal plaque control program and definitive maintenance schedule

PERIODONTAL DIAGNOSIS AND TREATMENT PLANNINGDIAGNOSIS Diagnosis is done using direct vision, palpation,

periodontal probe, mouth mirror, and other auxiliary aids, such as curved explorers, furcation probes, diagnostic casts, and appropriate radiographs.

Most important evaluation procedure-exploration of gongival sulcus,recording periodontal pocket & sites that bleed on probing.

A critical evaluation of the following fac tors should be made: (1) type, location, and severity of bone loss; (2) location, severity, and distribution of furcation

involvements; (3) alterations of the peri odontal ligament space; (4) alterations of the lamina dura; (5) presence of calcified deposits; (6) location and conformity of restorative margins (7) evaluation of crown and root morphologies; (8) root proxim ity; (9) caries; and (10) evaluation of other associated anatomic features, such

as the mandibular canal or sinus proximity. Each tooth should be evaluated carefully for mobility. Tooth

mobility is an indication of the condition of the supporting structures and is usually caused by inflammatory changes in the periodontal ligament, traumatic occlusion, loss of attachment, or a combination of the three. 

TREATMENT PLANNING Periodontal treatment planning can usually be divided into

three phases. Initial Disease Control Therapy (Phase 1) Disease control or initial therapy

phase.Objective is to eliminate & reduce local etiological factors before periodontal surgical procedures are accomplished.

Oral Hygiene Instruction Scaling and Root Planing Elimination of Local Irritating Factors ; Other

Than Calculus Elimination of Gross Occlusal Interferences 

Definitive Periodontal Surgery (Phase 2) Periodontal Surgery Periodontal flaps. Guided tissue regeneration. Periodontal plastic surgery

(mucogingival surgery)  Recall Maintenance (Phase 3) 3- to 4-month recall to maintain results

achieved by nonsurgical and surgical therapy.

ADVANTAGES OF PERIODONTAL THERAPY First, the elimination of periodontal disease

removes a pri mary etiological factor in tooth loss. Second, a periodontium free of disease presents a

much better environment for restorative correction.

Third, the response of strategic but questionable teeth to periodontal therapy provides an important opportunity for reevaluating their prognosis before the final decision is made to include (or exclude) them in the removable partial denture design.

And last, the overall reaction of the patient to periodontal procedures provides the dentist with an excellent indication of the degree of cooperation to be expected in the future.

ABUTMENT TEETH PREPARATION

ABUTMENT RESTORATIONS Esthetic veneer type of crowns should be

used when a canine or premolar abutment is to be restored or protected. Less frequently does the molar have to be treated in such a manner, and except for maxillary first molars the full cast crown is usually acceptable.

When there is proximal caries on abutment teeth with sound buccal and lingual enamel surfaces, in a mouth exhibiting average oral hygiene and low caries activity, a gold inlay may be indicated.

CONTOURING WAX PATTERNS Indirect techniques permit the contouring

of wax patterns on the master cast with the aid of the surveyor blade. All abutment teeth to be restored with castings can be prepared at one time and an impression made that will provide an accurate stone replica of the prepared arch. Wax patterns may then be refined on separated individual dies or removable dies. All abutment surfaces facing edentulous areas should be made parallel to the path of placement by the use of the surveyor blade.

ENAMELOPLASTY It is the intentional alteration of the occlusal

surface of the teeth to change their form. It is done when the abutment tooth does not

provide any surface undercut. It is prepared close to and parallel to the

gingival margin. The surface should be highly polished and

should measure 2mm occluso-gingivally and 4mm mesio-distally.

A small round ended tapered diamond stone is used to make a depression that is very gradual and smooth.

REST SEATS After the proximal surfaces of the wax patterns have

been made parallel, and buccal and lingual contours have been established to satisfy the requirements of stability and retention with the best possible esthetic placement of clasp arms, the occlusal rest seats should be prepared in the wax pattern rather than in the finished restoration. The placement of occlusal rests should be considered at the time the teeth are prepared to receive cast restorations so that there will be sufficient clearance beneath the floor of the occlusal rest seat. Occlusal rest are placed so that any occlusal force will be directed axially and that there will be the least possible inter ference to occlusion with the opposing teeth.

Perhaps the most important function of a rest is the division of stress loads from the removable partial denture to provide the greatest efficiency with the least damaging effect to the supporting abutment teeth. For a distal extension removable partial den ture, the rest must be able to transmit occlusal forces to the abutment teeth in a vertical direction only, thereby permitting the least possible lateral stress to be transmitted to the abutment teeth.

To permit occlusal stresses to be directed toward the center of the abutment tooth, the angle formed by the floor of the occlusal rest with the minor connector should be less than 90°. In other words, the floor of the occlusal rest should incline slightly from the marginal ridge toward the center of the tooth.

This proper form can be readily accomplished in the wax pattern if care is taken during crown or inlay preparation to provide the location of the rest. If direct restorations are used, sufficient bulk must be present in this area to allow proper occlusal rest seat form without weakening the restoration. When the rest seat is placed in sound enamel, it is best accom plished by the use of round carbide burs (No. 4, 6, and 8 sizes) that leave a smooth enamel surface.

Rest seat preparations in sound enamel (or in existing restorations that are not to be replaced) should always follow the recontouring of proximal tooth surfaces. The preparation of proximal tooth surfaces should be done first because if the occlusal portion of the rest seat is placed first and the proxi mal tooth surface is altered later, the outline form of the rest seat is sometimes irreparably altered.

Following proximal surface recontouring (guide plane preparation), the larger round bur is used to lower the marginal ridge 1.5 to 2.0 mm while creating the relative outline form of the rest seat. The result is a rest seat preparation with the marginal ridge low ered and the gross outline form established, but with out sufficient deepening of the rest seat preparation toward the center of the tooth. A smaller round bur (a No. 4 or 6) may then be used to deepen the floor of the rest seat to a gradual incline toward the center of the tooth. Enamel rods are then smoothed by the planing action of a round bur revolving with little pressure. Abrasive rubber points are sufficient to complete the polishing of the rest seat preparation.

SUMMARY Mouth preparation is fundamental to a successful

removable partial denture. Mouth preparation includes procedures in four

categories-oral surgical preparation, conditioning of abused & irritated tissue, periodontal preparation & preparation of abutment tooth.

These procedures return mouth to optimum health & eliminate any condition that would affect success of removable partial denture.

CONCLUSION The success or failure of a removable partial

denture depends on how well the mouth preparations are accomplished. It is only through intelligent planning and competent execution of mouth prepara tions that the denture can satisfactorily restore lost dental functions and contribute to the health of the remaining oral tissue.