|Section 23 - Treatment Planning - RPD's
001. Steffel, V. L. Planning removable partial dentures. J Prosthet Dent 12:524-535, 1962.
002. Applegate, O. C. The rationale of partial denture choice. J Prosthet Dent 10:891-907, 1960.
003. McCracken, W. L. Differential diagnosis: Fixed or removable partial dentures. JADA 63:767-775, 1961.
004. Beumont, A.J. A clinical view of mandibular premolars in removable partial denture design. Quint Int 21:21-26, 1990.
005. Rissin, L., House, J. E., Conway, C., Loftus, E. R. and Chauncey, H. H. Effect of age and removable partial dentures on gingivitis and periodontal disease. J Prosthet Dent 42:217-223, 1979.
006. Bergman, B., Hugoson, A. and Olsson, C. Caries, periodontal and prosthetic findings in patients with removable partial dentures: A ten-year longitudinal study. J Prosthet Dent 48:506-514, 1982.
007. Reed, H.V. Stress-equalizing removable partial denture. Quint Int 21:283-287, 1990.
008. Dail, R. A. Removable partial dentures and oral health: A literature review. J Western Soc Periodontol, Periodontal Abstracts 25:122-129, 1977.
009. Chandler, J. A. Clinical evaluation of patients eight to nine years after placement of removable partial dentures. J Prosthet Dent 51:736-743, 1984.
010. Leupold, R. J. and Faraone, K. L. Etched castings as an adjunct to mouth preparation for removable partial dentures. J Prosthet Dent 53:655-658, 1985.
011. Graser, G.N., and Rogoff, G.S. Removable partial overdentures for special patients. DCNA 43:4:741-757, 1990.
012. Kratochvil, F. J., Davidson, P. N. and Guijt, J. Five-year survey of treatment with removable partial dentures. Part I. J Prosthet Dent 48:237-244, 1982.
013. Franzetti, J. J. Periodontal considerations and guidelines for therapy. DCNA 29:17-38, 1985.
014. Firtell, D., et al. Reaction of the anterior abutment of a Kennedy CLII removable partial denture to various clasp arm designs: An in vitro study. J Prosthet Dent 53:77-82, 1985.
015. Zarb, G.A. and MacKay, H. F. Cosmetics and removable partial dentures - The class IV partially edentulous patient. J Prosthet Dent46:360-368, 1981.
016. Firtell, D. and Jacobson, T. Removable partial dentures with rotational paths of insertion. J Prosthet Dent 50:8-15, 1983.
017. Mariello, C. The sublingual bar: Planning and realization. Compend Contin Educ Dent 8:559-571, 1985.
018. Myers, R. E., Pfeifer, D. L., Mitchell, D. L. and Pelleu, G. B., Jr. A photoelastic study of rests on solitary abutments for distal-extension removable partial dentures. J Prosthet Dent 56:702-707, 1986.
019. Hebel, K. S., Graser, G. N. and Featherstone, J. D. B. Abrasion of enamel and composite resin by removable partial denture clasps. J Prosthet Dent 52:389-397, 1984.
Section 23: Treatment Planning – Removable Partial Dentures
Handout not available at this time
- Abstracts -
23-001. Steffel, V.L. Planning Removable Partial Dentures. J Prosthet Dent. 12:524-535, 1962.
Purpose: To provide information relating to diagnosis, prognosis and definitions for restoration by removable partial dentures.
Summary: Clasp retained removable partial dentures should not be designed solely for efficiency in mastication. The preservation of these supporting teeth should be our ultimate aim in design. Only the dentist, who manipulates the mounted diagnostic casts, studies the roentgenograms, and examines and questions the patient as to his oral and general health, has adequate knowledge to dictate denture design. He alone can predict the long range response of the patient's tissues to oral rehabilitation.
1. The biologic response of tissue to stress depends upon the tolerance of the tissue.
2. Partial dentures should be designed for bilateral distribution of stresses.
3. The type of retainer which will function best in all respects is the one which should be employed in any specific location.
4. The location of the teeth remaining and available for support and the way they are used are much more important than the number of teeth remaining.
5. Splinting of teeth by clasping in sequence is effective for adding stability to a restoration and avoiding the overworking of abutment teeth.
6. Modern periodontal procedures which are saving teeth are making partial denture service increasingly necessary.
7. Removable partial dentures can effectively stabilize loose teeth (especially by the use of continuous clasps) so that they will grow firm again.
8. Elastic clasps are more efficient for retention and less traumatizing to abutment teeth than clasps which lack resiliency.
9. Removable partial dentures move slightly under functional loads.
10. Teeth splinted together by fixed restorations provide strong abutments.
23-002. Applegate, O. C. The rationale of partial denture choice. J Prosthet Dent 10: 891-907, 1960.
Purpose: Evaluate the factors affecting the choice of prosthodontic treatment.
1. Bone maintenance potential- a physical examination is necessary to assess systemic conditions that might affect the patient’s capability to replace bone.
2. Previous cervical bone loss- the prosthetic load is affected, since occlusal stresses are magnified because the extra-alveolar segment of the abutment tooth has been lengthened.
3. Abutment root form, length, and stability- the length of the root determines the intra-alveolar support which can counteract the extra-alveolar stress or the work portion of the lever arm. The amount of remaining alveolar wall which supports the abutment load is reduced rapidly when the root is steeply tapered. The splinting of two or more adjacent teeth is the most dependable solution to this problem.
4. Extent of periodontal involvement- the degree of lateral mobility of an abutment is of lesser significance . Firmness recovery depends upon removal of predisposing factors which produce excess mobility.
5. Caries susceptibility- is a factor that determines the choice in between making a complete or partial denture.
6. Size and form of the residual ridge-if ridge form is poor, adequate stress control will be a problem. Example, if it is low and flat, it will reduce the support surface.
7. Location of the remaining teeth- location of the remaining teeth is more important in construction than the number of teeth that are left.
B. Clinical classification of partially edentulous situations
1. Class I- situation where all the remaining teeth are anterior to the bilateral edentulous ridges.
2. Class II- situation in which remaining teeth of either the right or left side are anterior to the unilateral edentulous ridge.
3. Class III- situations are those in which an edentulous space is bounded by teeth both anteriorly and posteriorly. In this situation, one or more boundary teeth are unable to assume the total abutment support of the prosthesis.
4. Class IV- situation in which the edentulous space lies anterior to the remaining teeth which bound it both to the right and left of the median line. This class is frequently exemplified by two or more incisors missing. The loss of one or both cuspids in addition to the incisors is encountered less often.
5. Class V- situation in which a space is bounded by remaining teeth at its posterior and anterior terminals. Example, a space extending from a weak lateral incisor to the mandibular second molar.
6. Class VI- another situation that has boundaries of teeth remaining anteriorly, thus three out of six groups have the same anatomic landmarks. However class VI conditions are such that the complete occlusal load can be tooth borne and, therefore, a fixed or removable unilateral prosthesis is possible.
Conclusion: The Kennedy classification has many excellent features , but it needs to be modified.
23-003. McCracken, W. L. Differential diagnosis: Fixed or removable partial dentures. JADA 63: 767-775, 1961.
Purpose: To review indications for fixed and removable partial dentures
Materials & Methods: None
Discussion: The article states three main criteria to help in the choice between a fixed or removable partial denture.
- By which method of treatment will the patient be best served?
- Is the prosthetic service recommended the best that dentistry has to offer?
If compromises are necessary, are the alternative methods of treatment acceptable by today’s standards?
- Is the dentist willing to assume the professional liability for the accomplishment of the treatment being recommended
Indications for fixed restorations
- Tooth-bounded Edentulous Regions - NOTE : Not to be used when the edentulous span is too long and the abutment teeth cannot withstand the occlusal forces, and also when the abutment teeth are periodontally involved and need cross arch stabilization
- Modification Spaces - Used especially when a lone standing abutment tooth is present (pier abutment situation)
- Anterior Modification Spaces - Exceptions are in areas of excessive ridge resorption
- Nonreplacement of Missing Molars - may be possible to do a cantilever bridge from two bicuspid abutments
Indications for removable partial dentures
- Free-end situations (Kennedy Class I and II)
- After Recent Extractions - interim until site heals
- Long span - too long to support the edentulous space with fixed restorations
- Need for Effect of Bilateral Bracing - the RPD may act as a periodontal splint by providing cross arch bracing
- Esthetics in Anterior Region
- Excessive Loss of Residual Bone - occurs from the labial in the anterior region
- Unusually Sound Abutment Teeth - in selected instances
- Economic Considerations
Conclusion: The author feels that in replacement of missing teeth, a fixed prosthesis should be the preference unless a specific rationale for removable is noted.
23-004. Beumont, A. J. A clinical view of mandibular premolars in removable partial denture design. Quint Int 21: 21-26, 1990.
Purpose: Discuss several factors that must be considered when using premolars in partial denture design.
1. Tooth anatomy-coronal form of the tooth-height of contour needs to be surveyed since it can provide surfaces for reciprocation and retention.
2. Tooth anatomy-root- crown-root ratio must exceed 1:1 with minimal tooth mobility, for the tooth to be suitable for an abutment for the RPD. A marginal ratio is not necessarily a reason to abandon a potential abutment as long as the tooth has minimal mobility.
3. Relationship of the tooth to those in the same arch- tipping of teeth due to extraction, leaves the height of contour on the facial surface of the premolars at the level of the free gingival margin (ideal for reciprocation), but places the height of contour near the lingual cusp tip, making retention difficult. Forces that are not directed along the axis of the tooth, can be destructive periodontally.
4. Relationship of the tooth to those in the opposite arch- cusps in hyperocclusion should be eliminated, they might occlude on rest seats and the partial framework might be thin and fracture.
5. Complications provided by an existing restoration- placement of a rest seat, partially in enamel and partially in a restoration, should be avoided. Weakened cusps must be protected, and the restoration of choice is the gold onlay. The placement of a rest seat in porcelain is not advised. If the restoration needs to be replaced great care must be taken to avoid weakening the lingual or the buccal cusps.
6. Restorative material considerations- gold is the best contact and support surface for the cast assembly. Amalgam is good for rest seats, but poor for abrasion resistance: guiding planes, as well as surfaces in contact with clasp arms. For porcelain-fused to metal restorations care must be taken to place rest seat and guide plane all in metal.
7. Esthetics- they can be enhanced by lowering the survey line on the facial aspect as possible, or by using an I-bar. This is because as the patient ages the mandibular teeth tend to show more as the orbicularis oris muscle looses its tone.
8. Major connector- the amount of free gingival margin determines the type of major connector. The choice and design of the major connector decide the choice and design of minor connectors ( rest seats, retentive surfaces, etc.)
Conclusion: The patient’s preexisting RPD provides clues on how to design, the new partial. This is done more for patient acceptance than for tissue preservation.
23-005. Rissin, L., House, J.E., Conway, C., Loftus, E.R., and Chauncey, H.H. Effect of Age and Removable Partial Dentures on Gingivitis and Periodontal Disease. J Prosthet Dent 42:217-223, 1979
Purpose: A cross sectional study to evaluate statistically the effect of age and removable partial dentures in various factors associated with gingivitis and periodontal disease.
Methods: The population used were 694 subjects from the former 1963 VA Normative Aging Study who did not smoke to eliminate the smoking factor. Subjects were scored by examination for six "periodontal disease variables"- plaque deposition, calculus deposition, gingivitis, pocket depth, bone loss, and tooth mobility. This data was collected and compared as RPD wearers to non RPD wearers via a one way analysis of variance (ANOVA).
Results: Individuals that wore an RPD showed increased mean values for the following:
- pocket depth
- bone loss
- tooth mobility
Conclusion: The primary effect of the RPD is on tooth mobility and may accelerate bone loss when the appropriate etiological factors are present.
23-006. Bergman, A. and Olsson, C. Caries, Periodontal and Prosthetic Findings in Patients with Removable partial dentures: A Ten-Year Longitudinal Study. J Prosthet Dent 48:506-514, 1982.
Purpose: To study the effect of the removable partial denture when the patient is highly motivated and given proper periodontal care and maintenance as needed.
Methods & Materials: 10 year longitudinal study of 27 patients, most with lower bilateral distal-extension dentures. Patients were given an aggressive oral hygiene protocol, restorative dentistry, and surveyed crowns as indicated for RPD construction. The patient oral hygiene was monitored at each step and addressed as indicated. They were recalled 2 weeks after delivery, then yearly for 10 years. At each recall oral hygiene was reinstructed, and maintenance dentistry preformed.
- Plaque index, gingival index, pocket depth, and tooth mobility: no difference of change from original readings
- Alveolar bone level: small changes noted, but not statistically significant
- Caries and restorations: average of about one new surface per patient
- Prosthetics and other factors: 12 RPD had to be replaced (mean service time was 8 years)
Conclusion: Study suggests that the RPD does not cause periodontal and carious lesions.
Note: As with most of these studies, it is mentioned that most patients were evaluated yearly, but some were seen more often. In this case this may skew the results in their favor due to control of non-compliant individuals.
23-007. Reed, H.V. Stress-equalizing removable partial denture. Quint Int 21: 283-287, 1990.
Purpose: Discuss the advantages and disadvantages of free-end removable partial dentures.
Discussion: The mandibular free-end distal extension removable partial denture rests on soft tissue. When stress, such as mastication, is applied to the occlusal surface, the free end or ends move down on the underlying tissue.
Mesiodistal stresses are not as harmful as lateral stresses. To lessen the stresses on the abutment teeth of the RPD patient, a hinge has been incorporated into the appliance. The hinge is placed on the distal area of the abutment. When stress is placed on the free-end of the base, the base moves gingivally and there is less stress on the abutment teeth. There are two serious flaws with this hinge system. First, in time the tissue loses resiliency, and the appliance base is not pushed off the tissue. The next stress pushes the appliance further gingivally, and resorption of tissue results. As resorption continues, the base of the RPD no longer is adapted to the underlying tissue and the space continues to get bigger, hence more movement and more resorption of the underlying tissue. Second, the hinge is next to the abutment tooth in the base of the RPD, there is no movement at this area, but the longer (distally) the base, the more movement (gingivally) as the base rotates around the axis of the hinge. The area adjacent to the abutment tooth experiences no movement, while the distal end of the base experiences too much movement (traumatic) and the result is resorption of the tissues. The longer the base area the more movement, hence more resorption.
Precision-retained RPD’s are excellent appliances. The stimulation is within physiologic limits and in the proper direction. Resorption and rebasing are not major factors. There is one flaw to this appliance, the "guideplane effect" is present and if the bases are not properly adapted to the underlying tissues, distogingival stress may be placed on the abutment teeth.
Levitch designed a free-end RPD that overcomes these problems. The RPD uses a broken stress-type connector between the clasp and the base area. The connector is placed on the distolingual area of the abutment tooth. A double lingual bar or a split linguoplate is incorporated on the appliance. The appliance develops a back action movement rather than a direct action movement. Stresses such as chewing, placed on the base area of the partial in a Type I lever will cause the abutment tooth to rotate around the axis of the hinge. This will result in resorption of the hard tissues and eventual loss of the tooth.
23-008. Dail, R.A. Removable Partial Dentures and Oral Health: A Literature Review. J Western Soc Periodontol, Periodontal Abstracts 25:122-129,1977.
Purpose: To review pertinent literature in an attempt to identify indications for the removable prosthesis and the effect it may have on oral health.
Discussion: The objective of treatment with an RPD is the perpetual preservation of what remains rather than the meticulous restoration of what is missing. RPD effects are briefly discussed including overall longevity, periodontal and mobility considerations, caries, edentulous ridge, occlusion and direction of forces. RPD design considerations to eliminate or reduce any hazardous effects are presented, including clasps, major and minor connectors, and distal extension cases. An incorrectly designed RPD may be considered a potentially destructive appliance. But, by having sound design and a motivated patient, the RPD can be a useful, necessary treatment modality.
23-009. Chandler, J. A. Clinical Evaluation of Patients Eight to Nine Years After Placement of Removable Partial Dentures. J Prosthet Dent 51:736-743, 1984.
Purpose: To report the results of an 8-9 year evaluation of patients studied by Schwalm. The study evaluated RPD’s constructed with principles commonly used: altered cast impression, guide planes, rigid major connectors, rest seats along the long axis, lingual plates and lingual bars relative to the space, wrought circumferential wire, CrCo framework, and relief of major connector over tissues.
Methods & Materials: 38 of the original 92 patients were examined. Evaluation included periodontal probing, mobility of teeth, plaque levels, caries, bone level, and the RPD’s condition.
- 34 of the original 44 RPD’s were still being worn. 21 were worn only during the day, 10 were worn 24hrs. a day, and 3 were always worn except when eating.
- 9 of the 10 RPD’s not worn were mandibular. 12 of the original 44 had relines. Generally, patients were satisfied with the fit.
- Tooth loss: 8 of 291 teeth at risk were lost during the 9 years.
- Caries: 52% of lesion were located in surfaces covered by the RPD.
- Surface depth: Increases in surface depth.
- Tooth mobility: No changes in RPD abutment teeth.
- Plaque levels: No significant changes.
- Gingival inflammation: Increases were noted in areas with RPD coverage.
- Alveolar bone loss: No statistical changes noted.
Conclusion: RPD’s provided a reasonable service for those wearing them. Increased levels of gingival inflammation were noted, but few teeth were lost.
23-010. Etched castings as an adjunct to mouth preparations for removable partial dentures. J Prosthet Dent 53:655-658, 1985.
Purpose: To investigate clinically the feasibility of using electrochemically etched castings bonded to etched enamel as an adjunct to mouth preparation for placement of removable partial dentures.
Materials and methods: Thirty one etched metal castings were placed to (1) provide vertical stops, (2) to form cingulum rest, (3) to form occlusal rest, (4) to splint teeth, (5) to build up occlusal surfaces, (6) to develop more ideal guiding planes, (7) to alter tooth contour.
Results: All the etched casting remained in place for the time period of the study (30-46 months).
Discussion: The etched castings can be bonded to etched enamel for use in mouth preparation procedures.
23-011. Graser, G.N. and Rogoff, G.S. Removable Partial Overdentures for Special Patients. DCNA 34:4:741-757, 1990.
Purpose: The purpose of this paper to describe a treatment modality which offers the benefits of superior esthetics and function without jeopardizing the already compromised dentitions of patients with acquired or congenital anomalies.
Rationale and Indications:
1. Reversible procedure
2. Cost effective
3. Minimal or no tooth preparation
4. Ability to restore a significant loss of VDO
5. Decreased clinical chair time
Advantages: (over the complete overdenture):
1. Covers only the teeth which reduces the bulkiness of the prosthesis and allows for a more rapid adaptation
2. Improved phonetics
3. Supported by a metal framework which minimizes fracture potential
1. The need for palatal coverage - cleft palate with significant hard and soft tissue defects
2. The need for denture base support - absence of a significant number of teeth, especially posterior teeth
Discussion: General Treatment Planning Considerations-
a) 2-3 mm of interocclusal space is required in the anterior region beyond the patient's VDO
b) Dual or rotary path of insertion
c) (Complications) - facing fractures and dental caries
Summary: The removable partial overdenture is a viable treatment modality for special patients with specific needs.
23-012. Kratochvil, F. J., Davidson, P. N., and Guijt, J. Five-Year Survey of Treatment with Removable Partial Dentures - Part 1. J Prosthet Dent 48:237-244, 1982.
Purpose: To develop a practical clinical and radiologic method to evaluate RPD treatment and establish baseline values for investigators.
Methods & Materials: Patient sampling and information obtained from dental schools in London, Amsterdam, and California. Evaluation intervals were 1 and 5 years. Patients were randomly selected in groups of 25. Data evaluated: number of patients, age, sex, type of RPD, number of abutment teeth, mobility of teeth, percentage of tooth in bone, percentage of decay, plaque index, and extracted abutment teeth.
- Pocket depth: Decreased 0.59 mm in mandible and decreased 0.32 mm in maxilla for average of 0. 47mm.
- Tooth mobility: Increased 0.13 maxilla and 0.22 mandible for average of 0.15 based on a 1-4 scale. The control teeth increased mobility 0.82.
- Bone support: Maxilla 0.68% loss of bone, mandible 0.26% loss of bone. Average of 0.47% loss compared to control of 0. 81% increase.
- Abutment teeth: Compared to control teeth over twice as prone to decay at pre and post evaluation levels.
- Plaque index: 61% of tooth surfaces had plaque accumulation.
Conclusion: Gingival pocket depth around abutment teeth was reduced. Mandibular teeth had a greater increase than maxillary teeth but overall less than control teeth. Slight amount of bone loss noted. Plaque index showed 62.4% of surfaces had plaque accumulation. 11 of 616 abutments (1.78%) were extracted.
23-013. Franzetti, J.J. Periodontal considerations and guidelines for therapy. DCNA 29: 17-38, 1985.
Purpose: Integrate treatment planning and specialized techniques directed towards restoring and maintaining the periodontium.
A. Pretreatment record
B. Treatment planning
1. Abutment selection
2. Trauma from occlusion- decide the effect , frequency, duration, magnitude of the occlusal forces. Determine if damages are reversible.
3. Mobility and splinting- increased tooth mobility is the single most important clinical sign of trauma from occlusion. Radiographically, it can be seen as a widened PDL. Nonprogressive mobility or stabilizing mobility does not affect prognosis, and the teeth that have decreased mobility are generally not indicated for splinting. Splinting is a recommendation for the RPD’s using intracoronal attachments. When all the remaining abutments are mobile more than one degree, bilateral splinting is indicated to resist stress in all directions. The major objective of splinting is to protect and preserve the periodontium.
C. Sequence of treatment
1. Informed consent
2. Preparatory management-emergency pain relief, oral hygiene instructions, correction of defective restorations, restoration of deep caries, extractions, endodontic therapy, and replacement of teeth with provisional restorations.
3. Management of occlusal disorders- selective teeth grinding, orthodontic treatment, provisional stabilization, and insertion of acrylic bite plane.
5. Surgical intervention for periodontal defects-eliminate disease processes and stabilize the periodontium.
6. Surgical techniques for hard and soft tissue defects- (1)soft tissues: gingivectomy and flaps, (2) hard tissues: osteotomy, osteoplasty, (3) dental tissues: root resection and odontoplasty. Pedicle and gingival grafts are also used.
7. Management of compromised marginal tissue.
8. Pocket reduction by inducing new attachment.
9. New connective tissue attachment.
2. Recall: controlling periodontal disease.
3. Maintenance therapy- update medical records, evaluate oral hygiene, periodontal probings, root planing and gingival curettage , review habit control, polish restorations and crowns, occlusal adjustments and full mouth radiographs.
23-014. Firtell, D., et al. Reaction of the Anterior Abutment of a Kennedy CLII Removable Partial Denture to Various Clasp Arm Designs: An In Vitro Study. J Prosthet Dent 53:77-82, 1985.
Purpose: To isolate and study one variable: clasp design for the Kennedy Class II RPD - anterior abutment on the tooth-supported side.
Methods & Materials: An acrylic resin model of mandibular arch for Kennedy Class II. The socket of #21 (Anterior abutment on the tooth-supported side) was enlarged, and a 1.5 mm elastomeric material was placed around the root to simulate the PDL. The remaining teeth were secured in the model. A 3 mm square of Ni-Cr implanted in the edentulous ridge.
Clasp arm design evaluated cast circumferential with no undercut; 0.01 inch undercut; wrought wire (19 gauge) in 0.01 inch undercut; I-Bar 0.01 inch undercut (infrabulge); ½ T on distofacial undercut 0.01 inch (infrabulge). A wire was attached to a polygraph machine on the abutment test tooth.
Results: Circumferential clasp with a retentive arm at the survey line would deflect the least. The suprabulge clasp deflected more than the infrabulge clasp in a vertical rise. The infrabulge clasps were more deflective at a 90 direction. The wrought wire had less deflection than the cast arm in the vertical rise.
Conclusion: The cast circumferential clasp placed at the survey line showed the least movement, and a cast clasp in the undercut showed the greatest deflection.
23-015. Zarb, G.A. AND Mackay, H.F. Cosmetics and Removable Partial Dentures – The Class IV Partially Edentulous Patient. J Prosthet Dent 46:360-368, 1981.
The Class IV partially edentulous arch presents a biomechanical and cosmetic challenge. Treatment may include specific indications for fixed or removable partial dentures. Indications for removable:
1. long span edentulous areas
2. significant bone loss
3. unfavorable labial morphology
4. cleft palate or other maxillofacial defect
5. young patients, lg. pulps
Potential problems inherent in fixed:
1. cement failure
2. mechanical breakdown
3. gingival recession
4. periodontal breakdown
6. pulpal necrosis
23-016. Firtell, D. and Jacobson, T. Removable Partial Dentures With Rotational Paths of Insertion. J Prosthet Dent 50:8-15, 1983.
Purpose: To reemphasize the problems of using a rotational path of insertion.
Principles: Krol described the rotational path prosthesis seats its first segments, rotational centers, then the framework is rotated positioning to the final seat of the prosthesis. Three basic types: anterior-posterior, posterior-anterior, and lateral.
The posterior-anterior (PA) is used to replace bilateral missing posterior teeth using mesial undercuts of the distal abutments. The anterior-posterior (AP) is used to replace anterior teeth and uses mesial undercuts of the anterior abutments. The lateral rotational path uses mesial and distal undercuts of abutments on either side of unilateral edentulous space.
Whichever segment is seated first, use a rigid retainer in the proximal undercut. The second segment uses conventional clasp retention. The PA has a long occlusal rest with the AP using a long cingulum rest. Category Type I: all PA’s and AP’s replacing posterior teeth. Category Type II: rigid retainer seated first then rotated to seat the second segment.
Problems: The fit of the seated RPD framework’s rigid retainer is critical where it contacts the proximal surface of the abutment.
Contour and location of rest seats: Long rests (> ½ the mesial distal width of the abutment) with nearly parallel walls. For AP rests, they must be parallel to allow initial straight path of insertion. The posterior abutment rest seats should be bilaterally parallel to the vertical path of insertion and 1.5 mm thick.
Analyzing undercuts: Undercuts are analyzed by means of a divider. Place the tip of the divider on the cast at the rotational point and the second tip place in the proximal undercuts. The rotational undercut can be changed by altering the length of the rest. If the tip does not freely move, recontouring will need to be done.
Restoration of abutments: Cast restorations are preferred, but amalgam is acceptable.
Centers of rotation should be in the same horizontal plane. The length of the posterior edentulous ridge will affect the arcs of the radii and will change the amount of blockout required.
Anterior-posterior vertical relation of the undercut is affected by the steepness of the curve of Spee. As the curve steepness increases, the effective undercut is decreased.
The shape of the arch can affect the seating. A square arch has bilateral centers of rotation with radii that are parallel bilaterally and pass through all the abutments perpendicularly from an axis of rotation uniting the right and left centers. In a tapered arch, the radii are no longer parallel to each other. Care is needed when the placing the blockout for the relocated centers of rotation. Lingually tilted teeth, projections of soft tissue, and bone may prevent proper path of rotation.
23-017. The Sublingual Bar: Planing and Realization. Compend Contin Educ Dent 8:559-571, 1985.
Purpose: To discuss planning and realization of the sublingual bar.
Materials and methods: None
Discussion: The five clinical and technical steps are (1) impression "making", (2) determination of the floor mouth depth, (3) preparation of the master cast, (4) laboratory steps, (5) try-in in the mouth.
The main difference in this compared to other lingual bar techniques is the use of the wax index to determine the depth at which to construct the bar. The inferior border of the wax index defines the superior border of the bar. The sublingual bar can be maintained at an adequate distance from the gingival crevice in consideration of biomechanics, even in cases with a narrow band of attached gingiva.
23-018. Myers, R. E., Pfeifer, D.L., Mitchell, D.L. and Pelleu, G.B. Jr. A Photoelastic Study of Rests on Solitary Abutments for Distal-Extension Removable Partial Dentures. J Prosthet Dent 56:702-707, 1986.
Purpose: 2-D photoelastic analysis of stress transmission to the solitary abutment that occurs when the rest placement is altered in conjunction with guide plate modifications.
Materials & Methods: Laboratory study on a Class I mod. 1 /RPD plexiglass model. A lone standing mandibular 2nd premolar with a missing 1st premolar. 4 different rest seat configurations: 1) M; 2) D; 3) M & D; 4) continuous occlusal. A straining frame applied force load to each framework in the 1st molar area. Guide plates were tested prior to and after physiologic relief.
Results: The apical portion of the 2nd premolar demonstrated the greatest stress. The distal surface demonstrated greater stress than the mesial. The continuous rest demonstrated the most favorable distribution of stress. All of the other rests introduced lateral forces. Relieved guide plates demonstrated significantly less(58%) shear stress values when compares to unrelieved guide plates.
Discussion: Physiologic relief allows distal extension portions of the framework to move towards the edentulous mucosa and share in the support of the RPD without torquing the tooth.
Summary: In a distal extension RPD, maximum use of oral structures can aid in the total support of the prosthesis and release stresses on the solitary abutment. The preferred occlusal rest design for an RPD with a solitary abutment is a continuous rest with relieved guide plates.
23-019. Hebel, K.S., Graser, G.N. and Featherstone, J.D.B. Abrasion of Enamel of Composite resin by Removable Partial Denture Clasps. J Prosthet Dent 52:389-397, 1984.
Purpose: Evaluation of in vitro wear between RPD clasps and 1) sound enamel, 2) demineralized enamel and 3) composite resin bonded to enamel without tooth preparation.
Literature review: 1956 Phillips and Leonard- RPD clasps produces no abrasion to enamel detectable to 20 mm.
Materials & Methods: Extracted molars; RPD framework/Vitallium; circumferential clasps .01 inch buccal retentive undercut. Reciprocating device provided insertion, removal and functional movements in an artificial saliva medium. Testing was performed simulating a 3 year time period. Wear was evaluated by a micro-photographer and an SEM.
Results: Natural enamel was harder than demineralized enamel and both were harder than resin at p < .05. No significance difference was reported between natural and demineralized teeth.
Discussion: In this model, RPD clasps do wear tooth structure and this generally occurs under 20 um. The resin contoured teeth showed more abrasion than enamel, however, none of the resins were lost.
Conclusion: A .01 inch undercut is approximately 250 um. RPD denture clasps abraded natural and demineralized enamel (20 um), and composite resin (50 um). Resin contouring appears to be a practical method to create retention for partial clasps while minimizing enamel destruction.