CHAPTER 13 Preparation of the Mouth for Removable Partial Dentures
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 that the prescribed prosthesis not only must replace what is missing but also must preserve the remaining tissues and structures that will enhance the removable partial denture.
Mouth preparation follows the preliminary diagnosis and the development of a tentative treatment plan. Final treatment planning may be deferred until the response to the preparatory procedures can be ascertained. In general, mouth preparation includes procedures in four categories: oral surgical preparation, conditioning of abused and irritated tissues, periodontal preparation, and preparation of abutment teeth. 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 be detrimental to the success of the removable partial denture.
Naturally, mouth preparation must be accomplished before the impression procedures are performed 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, and preferably 3 to 6 months, should be provided between surgical and restorative dentistry procedures. This depends on the extent of the surgery and its impact on the overall support, stability, and retention of the proposed prosthesis.
As a rule, all pre-prosthetic surgical treatment for the removable partial denture patient should be completed as early as possible. When possible, necessary endodontic surgery, periodontal surgery, and oral surgery should be planned, so that they can be completed during the same time frame. The longer the interval between the surgery and the impression procedure, the more complete the healing and consequently the more stable the denture-bearing areas.
A variety of oral surgical techniques can prove beneficial to the clinician in preparing the patient for prosthetic replacements. However, it is not the purpose of this section to present the details of surgical correction. Rather, attention is called to some of the more common oral conditions or changes in which surgical intervention is indicated as an aid to removable partial denture design and fabrication, and as an aid to the successful function of the restoration. Additional information regarding the techniques used is available in oral surgery texts and journal publications. It is important to emphasize, however, that the dentist who is providing the removable partial denture treatment bears the responsibility for ensuring that the necessary surgical procedures are accomplished in accordance with the treatment plan. Measures to control apprehension, including the use of intravenous and inhalation agents, have made the most extensive surgery acceptable to patients. Whether the dentist chooses to perform these procedures or elects to refer the patient to someone more qualified is immaterial. The important consideration is that the patient should not be deprived of any treatment that would enhance the success of the removable partial denture.
Planned extractions should occur early in the treatment regimen but not before a careful and thorough evaluation of each remaining tooth in the dental arch is completed (Figure 13-1). Regardless of its condition, each tooth must be evaluated in terms of its strategic importance and its potential contribution to the success of the removable partial denture. With the knowledge and technical capability available in dentistry today, almost any tooth may be salvaged if its retention is sufficiently important to warrant the procedures necessary. On the other hand, heroic attempts to salvage seriously involved teeth or those of doubtful prognosis for which retention would contribute little if anything, even if successfully treated and maintained, are contraindicated. Extraction of nonstrategic teeth that would present complications or those that may be detrimental to the design of the removable partial denture is a necessary part of the overall treatment plan.
Figure 13-1 Diagnostic mounting allows confirmation of the need for extraction after clinical examination. A, Anterior tooth position and chronic periodontal disease status require extraction to address the patient’s concern of malpositioned and painful teeth. B, Root tips require immediate extraction to allow ridge healing to begin. The status of the molar (#15) requires additional workup to determine pulpal involvement of the carious lesion and the extent of occlusal reduction required to optimize the occlusal plane. The decision to maintain this tooth, although potentially costly, must consider the stabilizing effect it will have on the posterior left functional occlusion.
Generally, all retained roots or root fragments should be removed. This is particularly true if they are in close proximity to the tissue surface, or if associated pathologic findings are evident. Residual roots adjacent to the abutment teeth may contribute to the progression of periodontal pockets and compromise the results of subsequent periodontal therapy. Removal of root tips can be accomplished from the facial or palatal surfaces without resulting in a reduction of alveolar ridge height or endangering adjacent teeth (Figure 13-2).
All impacted teeth, including those in edentulous areas, as well as those adjacent to abutment teeth, should be considered for removal. The periodontal implications of impacted teeth adjacent to abutments are similar to those for retained roots. These teeth are often neglected until serious periodontal implications arise.
The skeletal structure of the body changes with age. Asymptomatic impacted teeth in the elderly that are covered with bone, with no evidence of a pathologic condition, should be left to preserve the arch morphology. If an impacted tooth is left, this should be recorded in the patient’s record, and the patient should be informed of its presence. Roentgenograms should be taken at reasonable intervals to ensure that no adverse changes occur.
Alterations that affect the jaws can result in minute exposures of impacted teeth to the oral cavity via sinus tracts. Resultant infections can cause considerable bone destruction and serious illness for persons who are elderly and not physically able to tolerate the debilitation. Early elective removal of impactions prevents later serious acute and chronic infection with extensive bone loss. Any impacted teeth that can be reached with a periodontal probe must be removed to treat the periodontal pocket and prevent more extensive damage (Figure 13-3).
Figure 13-3 Lateral oblique roentgenogram showing unerupted maxillary third molar and impacted mandibular second and third molars. Maxillary third molar and mandibular second molar could be contacted by periodontal probe.
(From Costich ER, White RP Jr: Fundamentals of oral surgery, Philadelphia, 1971, Saunders.)
The loss of individual teeth or groups of teeth may lead to extrusion, drifting, or combinations of malpositioning of remaining teeth (Figure 13-4). In most instances, the alveolar bone supporting extruded teeth will be carried occlusally as the teeth continue to erupt. Orthodontics may be useful in correcting many occlusal discrepancies, but for some patients, such treatment may not be practical because of lack of teeth for anchorage of the orthodontic appliances or for other reasons. In such situations, individual teeth or groups of teeth and their supporting alveolar bone can be surgically repositioned. This type of surgery can be accomplished in an outpatient setting and should be given serious consideration before additional teeth are condemned or the design of removable partial dentures is compromised.
Figure 13-4 A, Malpositioned maxillary dentition due to loss of posterior occlusion and excessive wear of opposing mandibular anterior teeth. B, Restored dentition made possible by a combination of endodontics, periodontics, and fixed and removable partial prosthodontics.
(Courtesy Dr. M. Alfaro, Columbus, OH.)
Panoramic roentgenograms of the jaws are recommended to survey the jaws for unsuspected pathologic conditions. When a suspicious area appears on the survey film, 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. Although the diagnosis may appear obvious from clinical and roentgenographic examinations, the dentist should confirm the diagnosis through appropriate consultation and, if necessary, perform a biopsy of the area and submit the specimens to a pathologist for microscopic study. The patient should be informed of the diagnosis and provided with various options for resolution of the abnormality as confirmed by the pathologist’s report.
The existence of abnormal bony enlargements should not be allowed to compromise the design of the removable partial denture (Figure 13-5). Although modification of denture design can, at times, accommodate for exostoses, more frequently this results in additional stress to the supporting elements and compromised function. The removal of exostoses and tori is not a complex procedure, and the advantages to be realized from such removal are great in contrast to the deleterious effects that their continued presence can create. Ordinarily the mucosa covering bony protuberances is extremely thin and friable. Removable partial denture components in proximity to this type of tissue may cause irritation and chronic ulceration. Also, exostoses approximating gingival margins may complicate the maintenance of periodontal health and lead to the eventual loss of strategic abutment teeth.
Hyperplastic tissues are seen in the form of fibrous tuberosities, soft flabby ridges, folds of redundant tissue in the vestibule or floor of the mouth, and palatal papillomatosis (Figure 13-6). All these forms of excess tissue should be removed to provide a firm base for the denture. This removal will produce a more stable denture, will reduce stress and strain on the supporting teeth and tissues, and in many instances will provide a more favorable orientation of the occlusal plane and arch form for the arrangement of the artificial teeth. Appropriate surgical approaches should not reduce vestibular depth. Hyperplastic tissue can be removed with any preferred combination of scalpel, curette, electrosurgery, or laser. Some form of surgical stent should always be considered for these patients, so that the period of healing is more comfortable. An old removable partial denture properly modified can serve as a surgical stent. Although hyperplastic tissue has no great malignant propensity, all such excised tissue should be sent to an oral pathologist for microscopic study.
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 most likely to introduce problems of this nature. In addition to the problem of the attachments of the muscles themselves, the mentalis and genioglossus muscles occasionally produce bony protuberances at their attachments that may also interfere with removable partial denture design. Appropriate ridge extension procedures can reposition attachments and remove bony spines, which will enhance the comfort and function of the removable partial denture.
Repositioning of the mylohyoid muscle is successfully achieved by several methods. The genioglossus muscle is more difficult to reposition, but careful surgery can reduce the prominence of the genial tubercles, as well as provide some sulcus depth in the anterior lingual area.
Surgical procedures that use skin or mucosal grafts have largely replaced secondary epithelialization procedures for the facial aspect of the mandible. Mucosal grafts that use the palate as a donor site offer the best possibility for success; transplanted skin can be used when large areas must be grafted.
The maxillary labial and mandibular lingual frena are the most common sources of frenum interference with denture design. These can be modified easily through any of several surgical procedures. Under no circumstances should a frenum be allowed to compromise the design or comfort of a removable partial denture.
Sharp bony spicules should be removed and knifelike crests gently rounded. These procedures should be carried out with minimum bone loss. If, however, correction of a knife-edge residual crest results in insufficient ridge support for the denture base, the dentist should resort to vestibular deepening for correction of the deficiency or insertion of the various bone grafting materials that have demonstrated successful clinical trials.
All abnormal soft tissue lesions should be excised and submitted for pathologic examination before a removable partial denture is fabricated. Even though the patient may relate a history of the condition’s having been present for an indefinite period, its removal is indicated. New or additional stimulation to the area introduced by the prosthesis may produce discomfort or even malignant changes in the tumor.
All abnormal white, red, or ulcerative lesions should be investigated, regardless of their relationship to the proposed denture base or framework. A biopsy of areas larger than 5 mm should be completed, and if the lesions are large (over 2 cm in diameter), multiple biopsies should be taken. The biopsy report will determine whether the margins of the tissue to be excised can be wide or narrow. The lesions should be removed and healing accomplished before the removable partial denture is fabricated. On occasion, such as after irradiation treatment or the excoriation of erosive lichen planus, the removable partial denture design will have to be radically modified to avoid areas of possible sensitivity.
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, the patient’s overall problem must be evaluated thoroughly. Several dental professionals (prosthodontist, oral surgeon, periodontist, orthodontist, general dentist) may play a role in the patient’s treatment. These individuals must be involved in producing the diagnostic database and in planning treatment for the patient. Information obtained from a general patient evaluation done to determine the patient’s health status, a clinical evaluation directed toward facial esthetics and the status of the teeth and oral soft tissues, and analysis of appropriate diagnostic records can be used to produce a database. From this database, the patient’s problems can be enumerated, with the most severe problem being placed at the top of the list. Other identified problems would follow in order of their severity. It is only after this step that input from several dentists can provide a correctly sequenced final treatment plan for the patient.
Surgical correction of a jaw deformity can be made in horizontal, sagittal, or frontal planes. The mandible and maxillae may be positioned anteriorly or posteriorly, and their relationship to the facial planes may be surgically altered to achieve improved appearance. Replacement of missing teeth and development of a harmonious occlusion are almost always major problems in treating these patients.
A number of implant devices to support the replacement of teeth have been introduced to the dental profession. These devices offer a significant stabilizing effect on dental prostheses 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 Brånemark and coworkers (Figure 13-7). This titanium implant was designed to provide a direct titanium-to-bone interface (osseointegrated), with basic laboratory and clinical results supporting the value of this procedure.
Figure 13-7 A, Brånemark system components. From lower to upper: implant, cover screws, abutment, abutment screw, gold cylinder, and gold screw. B, Basic procedures in second-stage surgery: (1) exploration to locate cover screw; (2) removal of soft tissue; (3) removal of bony tissue; (4) removal of cover screw; (5) use of depth gauge to measure the amount of soft tissue; (6) abutment connection; and (7) placement of healing cap. C, Diagram of freestanding three-unit fixed partial denture supported by two osseointegrated implants that restore the extension base area, which would have been restored with a Class II removable partial denture if implants had not been used.
(A and C redrawn from Hobo S, Ichida E, Garcia LT: Osseointegration and occlusal rehabilitation, Tokyo, Japan Quintessence, 1989.)
Implants are carefully placed using controlled surgical procedures and, in general, bone healing to the device is allowed to occur before a dental prosthesis is fabricated. Long-term clinical research has demonstrated good results for the treatment of complete and partially edentulous dental patients using dental implants. Although research on implant applications with removable partial dentures has been very limited, the inclusion of strategically placed implants can significantly control prosthesis movement (See Chapter 25, Figures 13-8 through 13-10).
Figure 13-8 A, Implant bar and natural tooth copings used to support and retain this maxillary prosthesis. B, Tissue side of prosthesis showing the implant bar space, which when fitted will derive both support and stability from the implants while retention is gained through resilient O-rings on the natural tooth copings. C, Maxillary prosthesis seated and in occlusion.
(Courtesy Dr. N. Van Roekel, Monterey, CA.)
Figure 13-9 A, An anterior implant-supported bar demonstrating excellent access for hygiene and a parallel relationship to opposing occlusion. B, Prosthesis with implant bar space (housing three retentive male components for retention and a flat surface for bar contact and support) and bilateral posterior embrasure clasps. C, Prosthesis seated and in occlusion.
(Courtesy Dr. N. Van Roekel, Monterey, CA.)
Figure 13-10 A, A Class II, modification 1 maxillary arch with a posterior implant at the distal location of the extension base. B, Maxillary gold framework with broad palatal coverage, maximum stabilization through palatal contacts of multiple maxillary teeth, and implant position at the distal extension base. A single implant should be protected from excessive occlusal forces; consequently the broad palatal coverage and maximum bracing are important features of the overall design. The ball attachment abutment was used for retentive purposes. C, Occlusal view of the prosthesis with implant (see A), which provides improved retention to the distal extension base.
(Courtesy Dr. James Taylor, Ottawa, Ontario.)
Considerable attention has been devoted to ridge augmentation with the use of autogenous and alloplastic materials, especially in preparation for implant placement. Larger ridge volume gains necessitate consideration of autogenous grafts; however, these procedures are accompanied by concerns for surgical morbidity. Alloplastic materials have displayed short-term success; however, no randomized controlled trials have been conducted to provide evidence of long-term increases in ridge width and height for removable prostheses.
Clinical results depend on careful evaluation of the need for augmentation, the projected volume of required material, and the site and method of placement. Considerable emphasis must be placed on a sound clinical understanding that some of the alloplastic materials can migrate or be displaced under occlusal loads if not appropriately supported by underlying bone and contained by buttressing soft tissues. Careful clinical judgment with sound surgical and prosthetic principles must be exercised.