| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
J Am Dent Assoc, Vol 137, No 6, 783-788.
© 2006 American Dental Association |
RESEARCH |
 |
ABSTRACT |
|---|
 TOP ABSTRACT SUBJECTS, MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Methods. The authors recalled patients who had received two-unit cantilevered RBFPDs at least 24 months before the recall examination. The authors recorded the following data: patient’s sex and age, operator’s experience, prosthesis cementation date, endodontic treatment if performed, bone support, tooth mobility, the presence of shim-stock contacts on the abutment or pontic in intercuspal position, and the presence of aproximal axial contacts adjacent to the prosthesis. They also recorded the date of any debonding with subsequent treatment. They asked the patients qualitative questions about their prostheses.
Results. A total of 269 prostheses were placed in 214 patients and had a mean service life of 51.7 months ± 19.5 months standard deviation, with a range of 13.2 to 141.6 months. Of 14 failed prostheses, 12 debonded, resulting in a success rate of 94.8 percent and clinical retention rate of 95.5 percent. No discernable rotation or drifting of the abutments was apparent in any of the prostheses. Overall patient satisfaction with RBFPDs was good, with an average assessment score of 8.5.
Conclusions. The authors observed a 95.5 percent clinical retention rate of 269 two-unit RBFPDs, with no apparent drifting of the abutments. Longer-term follow-up studies are required.
Clinical Implications. Two-unit RBFPDs are conservative and clinically retentive prostheses in the short to medium term.
Key Words: Resin-bonded fixed partial denture; retrospective study; longevity
The clinical success of resin-bonded fixed partial dentures (RBFPDs) has been attributed to many variables, and evidence-based information has been accumulated relative to two of them: tooth preparation and prosthesis design. Various aspects of tooth preparation have been proposed for the successful use of fixed RBFPDs (pontic bound by retainers), and the use of grooves1–5 and rest seats with resistance form2–4 appear to be important factors for clinical retention. Tooth preparation, however, has not always been considered a necessary feature for the clinical success of RBFPDs.6 The extension of the metal framework associated with prosthesis design is considered an important feature for clinical longevity. Furthermore, inadequate axial "wraparound" of posterior abutments and the lack of occlusal coverage where tooth-to-tooth occlusal contacts occur have been cited as factors that may contribute to clinical debonding of fixed RBFPDs.1,7–9 The main aim of tooth preparation and framework extension is to reduce stresses on the bonding interface and to increase retention.3
Another important factor of pros-thesis design and success relates to the number of units in the framework. Studies have shown that RBFPDs and splints with more than two abutments have a greater incidence of debonding.6,10–12 This has been attributed to complex interabutment stresses that occur with multiple abutments; these stresses challenge the retainer framework and adhesive interface leading to premature debonding.13,14 Extrapolation from this would suggest that single-abutment, single-pontic prostheses have no interabutment stresses. This should make these prostheses more successful clinically than their three-unit fixed-fixed counterparts.
Prosthodontic textbooks, however, do not advocate the use of two-unit cantilevered fixed partial dentures (FPDs), and the only instance in which it is indicated appears to be for the replacement of missing lateral incisors using the canine as the abutment.15–17 In addition, clinical studies have reported that conventional cantilevered two-unit FPDs are both more successful10,12,13,18–20 and less successful12–24 than fixed FPDs, though these differences were not always significant. While a number of articles have discussed the biomechanical problems associated with cantilever FPDs, they usually refer to three-unit prostheses that are subject to complex interabutment stresses.15–17
We conducted this retrospective study to assess the clinical retention of two-unit cantilevered RBFPDs inserted in patients at The Prince Philip Dental Hospital, University of Hong Kong, and to observe any adverse tooth movement of the abutment.
The prescription of two-unit cantilevered RBFPDs became standard clinical teaching practice in 1998 at The Prince Philip Dental Hospital and was founded on previous evidence-based information.6,12,13,20,26–28 The design principles include maximizing the surface area for bonding by lowering the survey line when necessary and increasing resistance form. In this practice, the clinician strengthens the posterior C-shaped retainers by uniting the ends over the occlusal surface to form a D-shaped retainer with an occlusal bar (Figure 1
SUBJECTS, MATERIALS AND METHODS
TOP
ABSTRACT
SUBJECTS, MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
REFERENCES
We obtained our sample population from a pool of patients who had received one or more RBFPDs two years previous to the review date. We identified these patients using the hospital’s computer record system. We based patient selection for hospital care on the suitability of their treatment being performed by clinicians (graduate students, postdoctoral students or staff members) after being admitted to the hospital’s Reception and Primary Care Unit. We selected patients using the following inclusion criteria: the abutment tooth was free of periodontal disease, sufficient crown height was available for bonding and coronal tooth tissue was sound or minimally restored. There were no other recommended exclusion criteria. The clinicians carried out the treatment after controlling plaque-related disease processes and finishing simple restorative treatment. They also limited the replacement of missing molars to a premolar-sized pontic, as molar-sized pontics normally are not cantilevered from molar abutments. The clinician or supervising clinician made the final decision to place a RBFPD and determined its design based on the teaching philosophy for such prostheses.25 
). When possible, the clinician judiciously places opposing grooves anteriorly to increase resistance form (Figure 2). The clinician confines the preparation in enamel. It is possible, however, that dentin may be exposed, particularly if grooves are placed. Because of this, it is recommended that the clinician use a dentin-bonding agent with the adhesive cement. The clinician designs the pontic to receive light or no occlusal contacts in both intercuspal contact position and, when possible, lateral excursion. The clinician performs occlusal reduction when necessary by preparing either the abutment tooth, opposing dentition or both to make clearance for the retainer framework.
|
|
We identified 268 patient file numbers after conducting a search using the hospital’s computer record system. Of these, we clinically examined 214 patients, since we could not contact 54 patients who had emigrated, had a change of contact information, had time conflicts, were ill or had died. To identify possible risk factors for failure, we asked the patients a series of questions about their prostheses, using a clinical report form to collect the following data: patient’s sex, patient’s age, operator’s experience, pros-thesis cementation date, endodontic treatment if performed, bone support, tooth mobility, the presence of shim-stock contacts on the abutment or pontic in intercuspal position, and the presence of aproximal axial contacts adjacent to the prosthesis. We also asked the patients how long they thought the prosthesis would last, if the appearance of the metalwork concerned them, and if they avoided chewing on the prosthesis to protect it. We recorded the date of any debonding with subsequent treatment and the patient’s overall satisfaction with the prosthesis using a 10-point scale.
We made bone support assessments from chairside evaluations of recent radiographs by estimating the level of bone support on the abutment tooth. We categorized the levels of bone support as less than 20 percent loss, 20 to 50 percent loss and greater than 50 percent loss. We clinically assessed abutment mobility on a three-point scale (grade 1: less than 1 mm mobility, grade 2: 1 to 2 mm mobility, grade 3: greater than 2 mm mobility). We used 10-µm-thin shim-stock foil held in artery forceps to determine the presence of tooth contacts on the abutment tooth and pontic in intercuspal contact position. We used dental floss to determine the presence of interproximal tooth contacts adjacent to the pontic and retainer. This allowed us to record the presence of aproximal tooth contacts adjacent to the retainers and pontics as a means of detecting any early signs of tooth movement. However, as we did not record these and other occlusal contacts at the time of cementation, we could not ascertain whether the findings represented a static or dynamic situation.
|
RESULTS |
|---|
|
TOPABSTRACTSUBJECTS, MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Eighty-eight (41.1 percent) patients were men, and 126 (58.9 percent) patients were women. The age range was 14 to 82 years old, with a mean age of 50.2 years. Clinicians inserted the prostheses between June 1993 and October 2000. Dental students placed 149 of the 269 RBFPDs, and qualified clinicians, including hospital dentists with less than one year of experience, master’s students and teaching staff members placed the remaining 120. A total of 166 RBFPDs were placed in the maxillary arch, and 103 were placed in the mandibular arch. A total of 130 RBFPDs replaced missing incisors, 29 replaced missing canines, 91 replaced missing premolars, and 19 replaced molars (Table). Endodontically treated abutments supported seven of the prostheses, but no posts were inserted in these teeth. We considered 125 (46.5 percent) abutments to have less than 20 percent bone loss, 113 (42.0 percent) abutments to have between 20 to 50 percent bone loss, and 20 (7.4 percent) abutments to have greater than 50 percent bone loss; we could not assess 11 (4.1 percent) cases. We found that 224 abutments (83.3 percent) had grade 1 mobility, 21 abutments (7.8 percent) had grade 2 mobility, and seven (2.6) had grade 3 mobility. The data for the remaining 14 abutments were either not recorded or the abutment was extracted. A total of 196 abutments (72.9 percent) and 152 pontics (56.5 percent) had an occlusal contact in intercuspal position. We found resistance to the passing of dental floss on the tooth surfaces adjacent to the prosthesis in 217 (80.7 percent) of the cases adjacent to the pontic and in 197 (73.2 percent) of the cases adjacent to the retainer. Visual clinical examination of the prostheses and aproximal tooth contacts showed no discernable tooth movement by way of rotation, tipping or drifting.
|
Of the 12 RBFPDs that debonded, only four still were functioning clinically. From the available clinical information, we could not make comments regarding aspects of tooth contacts of these lost prostheses. Given the small failure rate in the study, we considered it inappropriate to do statistical analysis, as we could draw inaccurate conclusions given the small number of failures.
|
DISCUSSION |
|---|
|
TOPABSTRACTSUBJECTS, MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
The findings of our study represent the largest review of two-unit cantilevered RBFPDs to date and lend support to the clinical success of two-unit cantilevered RBFPDs.6,10,12,13,20,26–28,31 Of the studies reporting exclusively on cantilever RBFPDs, Briggs and colleagues13 reported an 80 percent retention rate of 54 prostheses, with a mean service life of 27 months. In a more extensive study, Hussey and Linden20 observed an 88 percent retention rate of 142 cantilevered RBFPDs, with a mean service life of 36 months and with 96 percent of the prostheses remaining "functional." In a subsequent article from the same research center, Rashid and colleagues31 reviewed periodontal factors of cantilevered RBFPDs and observed a 92.8 percent retention rate from 84 prostheses, with a mean longevity of 43.6 months. Finally, in a clinical review of patients at The Prince Philip Dental Hospital, 69 patients received 82 two-unit cantilevered RBFPDs that had a mean service life of 30 months, and only three RBFPDs debonded, resulting in a retention rate of 96 percent.28
In three large clinical studies performed in dental schools that examined 1,593 RBFPDs of different designs, 288 RBFPDs were cantilevered.6,10,12 Two of these studies reported retention rates for cantilevered RBFPDs of 79 percent10 and 83 percent,12 and the third study reported a median service life for cantilevered RBFPDs of 9.8 years.6 In all three studies, fewer cantilevered RBFPDs debonded than did fixed FPDs.
We found no reports in the literature regarding adverse tooth movement of single-abutment, single-pontic design FPDs as we described in our study. Even if we found no apparent difference in longevity between conventional two-unit and three-unit single-pontic FPDs, we still would consider the two-unit prostheses to be more appropriate for restoring single-unit, short-span edentulous spaces, as they have reduced biological and financial costs.
Given the relatively small number of failures in our study, we found it difficult to identify risk factors from the information we collected. Four of the 12 prostheses that debonded (one to three times) and were recemented were functioning between 30 and 57 months. This lends support to Briggs and colleagues’13 observation and Hussey and Linden’s20 findings that cantilevered RBFPDs can be successfully functioning prostheses despite debonding.
As our study was retrospective, we could not describe or control the biomechanical variables of the prostheses inserted (for example, retainer thickness, tooth preparation features, dentin involvement and bonding surface area). Therefore, we cannot comment on the effect of these variables. However, when we clinically observed some of the debonded cases, we found that insufficient bonding surface area and a lack of abutment and framework resistance form were likely causes of the debonding.
The clinical retention rate in our study (95.5 percent) appears to be higher than those found in other studies.10,12,13,20 This higher retention rate might be attributable to the additional resistance features incorporated in the tooth preparation and framework design features such as minimum retainer thickness (> 0.8 mm) and fabrication of the pattern on an investment model.25 In other studies, the authors did not comment on such design features and fabrication procedures. Our study’s retention rate is in close agreement with those of our two previous clinical audit reports of two-unit RBFPDs inserted in 2000 (97 percent)26 and 2002 (95.1 percent).28
The fact that we could not contact 54 of the 269 patients who we had identified from the hospital’s computer records may have had an adverse effect on the study’s clinical retention rates. Five patients identified by the hospital computer records search did not have two-unit RBFPDs, which we attributed to incorrect data entry. We found it encouraging that the prosthesis insertion did not appear to be operator-sensitive, given the relatively even distribution of prostheses placed by students and staff members that were successful and unsuccessful.
|
CONCLUSIONS |
|---|
|
TOPABSTRACTSUBJECTS, MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
FOOTNOTES |
|---|
|
REFERENCES |
|---|
|
TOPABSTRACTSUBJECTS, MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
