R e s i n - b o n d e d fixed partial dentures: A recall study H u a n - K o n g C h a n g , B.D.S., M.S.,* O m a r Z i d a n , B.D.S., H . D . D . , M.S., Ph.D.,** I g n a t i u s K. L e e , D . D . S . , M.S., *°* a n d O r l a n d o G o m e z - M a r i n , M.Sc., P h . D . °*°*
National Defense Medical Center, Taipei, Taiwan, and University of Minnesota, School of Dentistry, Minneapolis, Minn. A clinical recall program w a s initiated at the U n i v e r s i t y of Minnesota to e v a l u a t e the l o n g e v i t y and factors affecting l o n g e v i t y of resin-bonded fixed partial dentures (FPDs). Of the 49 resin-bonded FPDs e v a l u a t e d in the clinic, 43 w e r e acid-etched metal, resin-bonded FPDs, four w e r e combinations of resin-bonded and conventional FPDs, and two w e r e composite resin pontics. None of the combination FPDs and one of the two composite resin pontics w e r e judged as failed at the e x a m i n a tion. Of the 43 acid-etched metal resin-bonded FPDs, 15 w e r e found to be debonded (failure rate = 34.9%). The a v e r a g e l e n g t h of s e r v i c e for the 43 FPDs w a s 47.3 months. The a v e r a g e time of p l a c e m e n t to debondment w a s 33 months for the 15 debonded FPDs. The failure rate for m a x i l l a r y FPDs and FPDs with two retainers w e r e significantly l o w e r than the failure rate for mandibular FPDs and FPDs with more than two retainers (p > 0.05). The clinical significance of the present study w a s discussed. (J PROSTHET DENT 1991;65:778-81.)
T
h
e
introduction of the acid etching technique by Buonocore1 and the development of a resin system based on the monomer BIS-GMA by Bowen 2 resulted in the extensive use of composite resins in the field of operative dentistry. The use of composite resin technology in the field of prosthodontics began in the early 1970s when Rochette 3 introduced a fixed partial denture (FPD) using composite resin for attachment of perforated cast-gold retainers to the lingual surfaces of the abutment teeth. Retention of the FPD relied primarily on undercuts present on the perforated retainer and in acid-etched enamel. Livaditis and Thompson 4 in 1982 introduced an etching technique for a nickle-chromium alloy (Biobond C&B) and suggested the use of this technique for improved resin-bonded retainers. Wood5 described the fabrication of an FPD using acidetched metal retainers and porcelain pontic. The FPD was bonded directly to etched enamel using a composite resin. This so-called "Maryland bridge" has the advantage of having a true mechanical bond between the metal/resin interface and the absence of exposed resin cement in the oral cavity. Beginning in 1982, the Graduate Operative Dentistry Program at the University of Minnesota offered resinbonded FPDs on an experimental basis to patients who otherwise would have required conventional FPD treat*Lecturer, Department of Dentistry, National Defense Medical Center. **Associate Professor, Department of Restorative Dentistry, University of Minnesota, School of Dentistry. ***Assistant Professor, Department of Restorative Dentistry, University of Minnesota, School of Dentistry. .... Associate Professor, Department of Epidemiology and Public Health, University of Miami, School of Medicine, Miami, Fla. 10/1/25876
778
ment. This study (1) initiated a clinical recall program to evaluate the longevity of all resin-bonded FPDs placed in the Graduate Operative Dentistry Program Clinic and (2) investigated the variables that might affect the longevity of the resin-bonded FPD. MATERIAL
AND
METHODS
Subjects
All patients who had resin-bonded FPDs made between May 1982 and August 1986 were selected. Recall letters with a return postcard were sent to these patients, inviting them to visit the clinic for a free follow-up evaluation of their FPDs. The letters were followed up, whenever possible, by direct telephone contact. A total of 63 patients, 30 men and 33 women, ranging between 18 and 84 years of age, with a total of 82 units of resin-bonded FPDs were evaluated. Pertinent information was abstracted from patients' dental charts regarding age and gender, date of placement of the FPD, type of FPD (acid-etched metal resin-bonded, resin-bonded/conventional, resin pontic), tooth numbers involved in pontics and abutments, type of alloy used, operator responsible for placement, type of resin used for cementation, and use of rubber dam or not during cementation. Clinical
examination
The following information was recorded by a dentist during the examination. 1. Debonding. Evidence of debonding was confirmed using visual and tactile methods. 2. Caries. All abutment teeth were examined to detect presence of dental caries. Debonded metal retainers were removed to allow for the assessment of dental caries. 3. Occlusion. Articulating paper was used to check for
JUNE 1991
VOLUME 65
NUMBER 6
RESIN-BONDED FPD: RECALL, LONGEVITY
T a b l e I. S u m m a r y of acid-etched metal resin-bonded
T a b l e II. S u m m a r y of factors evaluated and failure
FPDs evaluated
rates
Total number of FPDs evaluated Average length of service (range)
43 47.3 mo (2-67 too)
Total number of FPDs debonded Average length of service (range)
15 33 mo (2-67 mo)
Failure rate
34,9%
Percent of debonded retainers with caries 40% Percent of other retainers with caries 0%
presence of contact on the pontic in centric occlusion and during lateral movements. P e r i o d o n t a l health. The presence of gingival inflammation, plaque, calculus accumulation, and probing depths were recorded for each of the a b u t m e n t teeth. Probing depth was measured at four sites: mesiobuccal, mesiolingual, distobuccal, and distolingual. Statistical
analysis
The relationship of failure to gender, length of service, F P D location (arch and quadrant), F P D length (number of retainers and pontics), pontic occlusion (centric occlusion and lateral movements), use of rubber dam during cementation, use of bonding agent for cementation, type of alloy used, type of cementing resin used, operator, and periodontal health (gingival inflammation, plaque) were analyzed using the chi-square test. Comparison on the average periodontal probing depth between the debonded F P D group and the successful F P D group was made using the t test. Results were considered statistically significant if the p value was less than 0.05. The statistical tests were applied using the FPD, not the patient, as a unit of analysis. Since there was a total of 37 patients and 43 Maryland FPDs involved in the analysis, it is recognized that this type of analysis violates the basic assumption of independence of measurement required by the chi square and the t tests. RESULTS
Eighty-two resin-bonded FPDs were inserted in 63 patients by 8 operators between May 1982 and August 1986. Of the 63 patients contacted for this recall study, 37 patients with 49 FPDs were evaluated clinically. The response rate was 58.7% by patient and 59.8% by FPD. Of the 49 resin-bonded FPDs evaluated in this recall study, 43 were acid-etched metal resin-bonded FPDs, four were combinations of resin-bonded and conventional full crown FPDs, and two were composite resin pontics bonded directly onto a b u t m e n t teeth. The range of time from initial placement to follow-up examination was 2 to 67 months, with an average of 47.3 months for acid-etched
THE JOURNAL OF PROSTHETIC DENTISTRY
Factors
Failure rate
Patient gender Male Female Length of service 53 months and over under 53 months FPD Location (arch) Maxilla Mandible FPD Location (quadrant) Anterior Posterior Ant/Post FPD length (No. of retainers) 2 Over 2 FPD Length (No. of pontics) 1 Over 1 Pontic occlusion (centric occlusion) No contact Contact Pontic occlusion (lateral movement) No contact Contact Use of rubber dam Yes No/Don't know Use of bonding agent Yes No/Don't know Type of alloy used Rex III Litecast Biocast Type of resin used Comspan Others Operator A B Others Periodontal health (gingivitis) Present Absent Periodontal health (plaque/calculus) Present Absent Periodontal health (pocket depth) Success FPDs (average pocket depth, 4 sites) = 2.17 mm Failed FPDs (average pocket depth, 4 sites) = 2.16 mm
Statistical significance
p = 0.08* 47.6% 22.7 % p = 0.28* 27.3% 42.9% p = 0.005* 14.3 % 54.5 % p = 0.60* 28.6 % 33.3 % 46.2 % p = 0.02* 22.2% 56.2% p = 0.25* 30.3 ~ 50.0% p = 0.78* 33.3 % 37.5 % p = 0.41" 40.0 % 27.8 % p = 0.7" 31.3 % 37.0 % p = 0.29* 26.3 % 41.7 % p = 0.17" 10.0% 45.0 % 37.5 % p = 0.78* 33.3 % 37.5 % p = 0.51" 28.6 % 30.8 % 50.0 % p = 0.39* 45.5% 31.3% p = 0.07* 2.5% 28.6% p = 0.9t
*Chi square test. Ct test.
779
CHANG ETAL
Table III. Relationship between failure rate and FPD
Table IV. Relationship between failure rate and FPD
location
length
Arch location
No. of FPDs
No. of failures
Failure rate
No. of FPDs
No. o f failed FPDs
Failure rate
Maxilla
21
3
14.3 %
2
27
6
22.2%
Mandible
22
12
54.5%
Over 2
16
9
56.3 %
metal resin-bonded FPDs, 48 to 63 months with an average of 53.8 months for resin-bonded/conventional FPD, and 62 and 69 months, respectively, for the two resin pontic FPDs. None of the resin-bonded/conventional FPDs were judged to have failed. One of the two resin pontic FPDs examined was found to be debonded. Overall results of the 43 acid-etched metal resin-bonded FPDs evaluated are recorded in Table I. Fifteen FPDs were found to be debonded at the recall examination. The overall failure rate was 34.9 % and the average time from initial placement to debonding was 33 months. Caries activity was detected in 40 % of the abutment teeth that had debonded retainers. Table II summarizes the effects of all the factors evaluated in this study on the failure rate of the 43 acid-etched metal resin-bonded FPDs. Factors showing statistically significant effects toward the failure rate were (1) FPD location by arch and (2) FPD length by number of retainers. The failure rate was 54.5% for mandibular FPDs and 14.3 % for maxillary FPDs. Failure rate of FPDs with more than two retainers was 56.2 % and 22.2 % for FPDs with two retainers. Statistical analysis on the results of failure rate and other evaluated factors provided no significant difference. Factors evaluated included: patient gender, length of service, location of FPD by quadrant, FPD length by number of pontic, pontic occlusion, use of rubber dam, use of bonding agent, type of alloy used, type of resin used, operator placing the FPD, and the periodontal health of the abutment teeth. Table III summarizes the results of the effect of FPD location by arch on failure rate. Twenty-one maxillary FPDs were evaluated in this study and three were found to be debonded during the examination (failure rate = 14.3%). Twelve of the 22 mandibular FPDs examined were found to be debonded, which resulted in a failure rate of 54.4 %. Table IV summarizes the results of the effect of FPD length by the number of retainers on failure rate. Twentyseven FPDs with two retainers each were evaluated in this study and six were found to be debonded during the examination (failure rate --- 22.2 % ). Of the 16 FPDs with more than two retainers, nine were found to be debonded, with a failure rate of 56.3 %. DISCUSSION Studies on the longevity of acid-etched metal resinbonded FPDs reported failure rates ranging from 10.5% to 17.5%. 6-9 Results of the present recall study reported a
780
No. of r e t a i n e r s
substantially higher failure rate of 34.9 %. The high failure rate could be attributed to one or more of the following factors: (1) Lack of knowledge of the optimal retainer framework design and enamel modification when FPDs were placed in the earlier phase. Meiers and Meetz 1° suggested a facial wrap and proximal groove design to prevent lingual displacement; to prevent gingival displacement an occlusal/cingulum rest or inlay preparation design was recommended. (2) In the earlier phase the accuracy of how the metal was etched was unknown. Hill et al. 11 reported that errors in estimating the surface area of metal retainers could adversely affect the bond strength. (3) Poor selection of abutment teeth in questionable periodontal health. The significantly higher failure rate observed with FPDs placed in the mandibular arch compared with the maxillary arch may be attributable to one or more of the following reasons: (1) Moisture control during cementation may be more difficult to obtain in the mandibular arch than in the maxillary arch if a rubber dam was not used. (2) During normal masticatory function, retainers on the mandibular arch are subjected to a dislodging force, while retainers on the maxillary arch will experience a more favorable seating force. FPDs with more than two retainers have a significantly higher failure rate than FPDs with two retainers. The results suggest that, contrary to the conventional FPD design where an increase in the number of abutment teeth will usually result in increased retention, this may not be true for resin-bonded FPDs. Increasing the number of abutment teeth may actually lower the longevity of resinbonded FPDs. This result may not be surprising if one considers the mechanics of tooth movement and the basic differences between conventional and resin-bonded FPDs. Most of the occlusal or incisal aspects of the abutment teeth of a resin-bonded FPD are not covered by the retainer. Consequently, any force applied to an uncovered surface on the abutment teeth can result in a physiologic movement of the abutment teeth independent of the FPD and of the other abutment teeth. This type of movement could, eventually result in dislodging of the retainer. The same situation will not occur with a conventional FPD because of more fully covered abutment teeth and secondary retentive factors, such as grooves. Clinically, the ability to effectively make use of grooves is sometimes limited by the thickness of the enamel available on the abutment teeth, especially on the mandibular anterior teeth.
JUNE 1991 VOLUME 65 NUMBER 6
RESIN-BONDED FPD: RECALL, LONGEVITY
Statistically, this recall study failed to detect any other factors that may significantly affect the longevity of resinbonded FPDs. However, the importance of the other factors may be clinically significant. The use of a rubber dam during cementation is highly recommended. Acid-etching of different base metal alloys used for retainers resulted in different relief patterns and bond strengths. 12 Thus the choice of alloy used could also be important in determining the longevity of the FPD. Periodontal health of the patient should be considered. Poor periodontal health is a major contraindication for a resin-bonded FPD. CLINICAL
IMPLICATION
Based on the present clinical recall study and on other published reports on acid-etched metal resin bonded FPDs, the following clinical recommendations are made: (1) Indications for using resin-bonded FPDs should be restricted to patients in whom replacement of one missing tooth and the use of one abutment on either side is involved. (2) The abutment teeth should be in excellent periodontal condition. (3) The use of an anticipated longterm FPD for splinting of periodontally involved teeth is contraindicated. (4) The design of the retainer must include elements that will prevent lingual and gingival displacement. (5) The choice of an alloy and a method for acid-etching should be consistent with findings in published reports. 12 (6) Moisture control during cementation must be emphasized. (7) The decision to place resinbonded FPDs in the mandibular arch must be made with the limitations in mind (unfavorable forces, moisture control, and limited enamel thickness for placement of proximal groove). (8) An aggressive and ongoing follow-up program must be initiated to detect debonding and the presence of dental caries.
SUMMARY The results of this recall study on acid-etched metal resin bonded FPDs showed that: (1) Average length of service is
47.3 months for the 43 FPDs examined. (2) Overall failure rate is 34.9 %. (3) Maxillary FPDs have a significantly lower failure rate than mandibular FPDs (14.3% and 54.5%, respectively). (4) FPDs with two retainers have a significantly lower failure rate than FPDs with more than two retainers (22.2% and 56.3%, respectively). REFERENCES 1. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34:849-53. 2. Bowen RL. Properties of a silica-reinforced polymer for dental restorations. J Am Dent Assoc 1963;66:57-64. 3. Rochette AL. Attachment of a splint to enamel of lower anterior teeth. J PROSTHET DENT 1973;30:418-23. 4. Livaditis GL, Thompson VP. Etched casting: an improved retentive mechanism for resin-bonded retainers. J PROSTHET DENT 1982;47:52-8. 5. Wood M. Etched casting resin bonded retainers: an improved technique for periodontal splinting. Int J Periodontics Restorative Dent 1982;2:925. 6. Hamada T, Shigeto N, Yanagihara T. A decade of progress for the adhesive fixed partial denture. J PROSTHET DENT 1985;54:24-9. 7. Mohl G, Mehra R. Clinical evaluation of etched metal resin bonded bridges [Abstract]. J Dent Res 1986;65:311. 8. Thompson VP, Wood M. Etched casting bonded retainer recalls: results at 3-5 years [Abstract]. J Dent Res 1986:65:311. 9. Clyde JS, Boyd T. The etched cast metal resin-bonded {Maryland) bridge: a clinical review. J Dent 1988;16:22-6. 10. Meiers JC, Meetz HK. Design modifications for etched-metal, resinbonded retainers. Gen Dent 1985;33:41-4. 11. Hill GL, Zidan O, Gomez-Marin O. Bond strengths of etched base metals: effects of errors in surface area estimation. J PROSTHET DENT 1986;56:41-6. 12. Zidan O. Etched base-metal alloys: comparison of relief patterns, bond strengths and fracture modes. Dent Mater 1985;1:209-13. Reprint requests to: DR. IGNATIUSK. LEE 4-215 MOOS TOWER SCHOOL OF DENTISTRY UNIVERSITY OF MINNESOTA 515 DELAWAREST. SE MINNEAPOLIS, MN 55455
Contributing author Elaine M. E. Hill, Dental Assistant, University of Minnesota, School of Dentistry, Minneapolis, Minn.
Guides for authors available The Guide to Preparing Articles for THE JOURNAL OFPROSTHETICDENTISTRY,revised by Professor Paul Barton, Editorial Consultant to the JOURNAL,and the editors, is available to prospective authors. The guide provides the format for developing different types of scientific manuscripts, a checklist for effective writing, and detailed instructions for preparing manuscripts in the style acceptable by the JOURNAL. Also available are the Guidelines for Reporting Statistical Results and an Author's Guide to Controlling the Photograph. Guides can he obtained from the office of the Editor (Dr. Judson C. Hickey, The Journal of Prosthetic Dentistry, Medical College of Georgia, School of Dentistry, Augusta, GA 30912).
THE JOURNAL OF PROSTHETIC DENTISTRY
781
National Defense Medical Center, Taipei, Taiwan, and University of Minnesota, School of Dentistry, Minneapolis, Minn. A clinical recall program w a s initiated at the U n i v e r s i t y of Minnesota to e v a l u a t e the l o n g e v i t y and factors affecting l o n g e v i t y of resin-bonded fixed partial dentures (FPDs). Of the 49 resin-bonded FPDs e v a l u a t e d in the clinic, 43 w e r e acid-etched metal, resin-bonded FPDs, four w e r e combinations of resin-bonded and conventional FPDs, and two w e r e composite resin pontics. None of the combination FPDs and one of the two composite resin pontics w e r e judged as failed at the e x a m i n a tion. Of the 43 acid-etched metal resin-bonded FPDs, 15 w e r e found to be debonded (failure rate = 34.9%). The a v e r a g e l e n g t h of s e r v i c e for the 43 FPDs w a s 47.3 months. The a v e r a g e time of p l a c e m e n t to debondment w a s 33 months for the 15 debonded FPDs. The failure rate for m a x i l l a r y FPDs and FPDs with two retainers w e r e significantly l o w e r than the failure rate for mandibular FPDs and FPDs with more than two retainers (p > 0.05). The clinical significance of the present study w a s discussed. (J PROSTHET DENT 1991;65:778-81.)
T
h
e
introduction of the acid etching technique by Buonocore1 and the development of a resin system based on the monomer BIS-GMA by Bowen 2 resulted in the extensive use of composite resins in the field of operative dentistry. The use of composite resin technology in the field of prosthodontics began in the early 1970s when Rochette 3 introduced a fixed partial denture (FPD) using composite resin for attachment of perforated cast-gold retainers to the lingual surfaces of the abutment teeth. Retention of the FPD relied primarily on undercuts present on the perforated retainer and in acid-etched enamel. Livaditis and Thompson 4 in 1982 introduced an etching technique for a nickle-chromium alloy (Biobond C&B) and suggested the use of this technique for improved resin-bonded retainers. Wood5 described the fabrication of an FPD using acidetched metal retainers and porcelain pontic. The FPD was bonded directly to etched enamel using a composite resin. This so-called "Maryland bridge" has the advantage of having a true mechanical bond between the metal/resin interface and the absence of exposed resin cement in the oral cavity. Beginning in 1982, the Graduate Operative Dentistry Program at the University of Minnesota offered resinbonded FPDs on an experimental basis to patients who otherwise would have required conventional FPD treat*Lecturer, Department of Dentistry, National Defense Medical Center. **Associate Professor, Department of Restorative Dentistry, University of Minnesota, School of Dentistry. ***Assistant Professor, Department of Restorative Dentistry, University of Minnesota, School of Dentistry. .... Associate Professor, Department of Epidemiology and Public Health, University of Miami, School of Medicine, Miami, Fla. 10/1/25876
778
ment. This study (1) initiated a clinical recall program to evaluate the longevity of all resin-bonded FPDs placed in the Graduate Operative Dentistry Program Clinic and (2) investigated the variables that might affect the longevity of the resin-bonded FPD. MATERIAL
AND
METHODS
Subjects
All patients who had resin-bonded FPDs made between May 1982 and August 1986 were selected. Recall letters with a return postcard were sent to these patients, inviting them to visit the clinic for a free follow-up evaluation of their FPDs. The letters were followed up, whenever possible, by direct telephone contact. A total of 63 patients, 30 men and 33 women, ranging between 18 and 84 years of age, with a total of 82 units of resin-bonded FPDs were evaluated. Pertinent information was abstracted from patients' dental charts regarding age and gender, date of placement of the FPD, type of FPD (acid-etched metal resin-bonded, resin-bonded/conventional, resin pontic), tooth numbers involved in pontics and abutments, type of alloy used, operator responsible for placement, type of resin used for cementation, and use of rubber dam or not during cementation. Clinical
examination
The following information was recorded by a dentist during the examination. 1. Debonding. Evidence of debonding was confirmed using visual and tactile methods. 2. Caries. All abutment teeth were examined to detect presence of dental caries. Debonded metal retainers were removed to allow for the assessment of dental caries. 3. Occlusion. Articulating paper was used to check for
JUNE 1991
VOLUME 65
NUMBER 6
RESIN-BONDED FPD: RECALL, LONGEVITY
T a b l e I. S u m m a r y of acid-etched metal resin-bonded
T a b l e II. S u m m a r y of factors evaluated and failure
FPDs evaluated
rates
Total number of FPDs evaluated Average length of service (range)
43 47.3 mo (2-67 too)
Total number of FPDs debonded Average length of service (range)
15 33 mo (2-67 mo)
Failure rate
34,9%
Percent of debonded retainers with caries 40% Percent of other retainers with caries 0%
presence of contact on the pontic in centric occlusion and during lateral movements. P e r i o d o n t a l health. The presence of gingival inflammation, plaque, calculus accumulation, and probing depths were recorded for each of the a b u t m e n t teeth. Probing depth was measured at four sites: mesiobuccal, mesiolingual, distobuccal, and distolingual. Statistical
analysis
The relationship of failure to gender, length of service, F P D location (arch and quadrant), F P D length (number of retainers and pontics), pontic occlusion (centric occlusion and lateral movements), use of rubber dam during cementation, use of bonding agent for cementation, type of alloy used, type of cementing resin used, operator, and periodontal health (gingival inflammation, plaque) were analyzed using the chi-square test. Comparison on the average periodontal probing depth between the debonded F P D group and the successful F P D group was made using the t test. Results were considered statistically significant if the p value was less than 0.05. The statistical tests were applied using the FPD, not the patient, as a unit of analysis. Since there was a total of 37 patients and 43 Maryland FPDs involved in the analysis, it is recognized that this type of analysis violates the basic assumption of independence of measurement required by the chi square and the t tests. RESULTS
Eighty-two resin-bonded FPDs were inserted in 63 patients by 8 operators between May 1982 and August 1986. Of the 63 patients contacted for this recall study, 37 patients with 49 FPDs were evaluated clinically. The response rate was 58.7% by patient and 59.8% by FPD. Of the 49 resin-bonded FPDs evaluated in this recall study, 43 were acid-etched metal resin-bonded FPDs, four were combinations of resin-bonded and conventional full crown FPDs, and two were composite resin pontics bonded directly onto a b u t m e n t teeth. The range of time from initial placement to follow-up examination was 2 to 67 months, with an average of 47.3 months for acid-etched
THE JOURNAL OF PROSTHETIC DENTISTRY
Factors
Failure rate
Patient gender Male Female Length of service 53 months and over under 53 months FPD Location (arch) Maxilla Mandible FPD Location (quadrant) Anterior Posterior Ant/Post FPD length (No. of retainers) 2 Over 2 FPD Length (No. of pontics) 1 Over 1 Pontic occlusion (centric occlusion) No contact Contact Pontic occlusion (lateral movement) No contact Contact Use of rubber dam Yes No/Don't know Use of bonding agent Yes No/Don't know Type of alloy used Rex III Litecast Biocast Type of resin used Comspan Others Operator A B Others Periodontal health (gingivitis) Present Absent Periodontal health (plaque/calculus) Present Absent Periodontal health (pocket depth) Success FPDs (average pocket depth, 4 sites) = 2.17 mm Failed FPDs (average pocket depth, 4 sites) = 2.16 mm
Statistical significance
p = 0.08* 47.6% 22.7 % p = 0.28* 27.3% 42.9% p = 0.005* 14.3 % 54.5 % p = 0.60* 28.6 % 33.3 % 46.2 % p = 0.02* 22.2% 56.2% p = 0.25* 30.3 ~ 50.0% p = 0.78* 33.3 % 37.5 % p = 0.41" 40.0 % 27.8 % p = 0.7" 31.3 % 37.0 % p = 0.29* 26.3 % 41.7 % p = 0.17" 10.0% 45.0 % 37.5 % p = 0.78* 33.3 % 37.5 % p = 0.51" 28.6 % 30.8 % 50.0 % p = 0.39* 45.5% 31.3% p = 0.07* 2.5% 28.6% p = 0.9t
*Chi square test. Ct test.
779
CHANG ETAL
Table III. Relationship between failure rate and FPD
Table IV. Relationship between failure rate and FPD
location
length
Arch location
No. of FPDs
No. of failures
Failure rate
No. of FPDs
No. o f failed FPDs
Failure rate
Maxilla
21
3
14.3 %
2
27
6
22.2%
Mandible
22
12
54.5%
Over 2
16
9
56.3 %
metal resin-bonded FPDs, 48 to 63 months with an average of 53.8 months for resin-bonded/conventional FPD, and 62 and 69 months, respectively, for the two resin pontic FPDs. None of the resin-bonded/conventional FPDs were judged to have failed. One of the two resin pontic FPDs examined was found to be debonded. Overall results of the 43 acid-etched metal resin-bonded FPDs evaluated are recorded in Table I. Fifteen FPDs were found to be debonded at the recall examination. The overall failure rate was 34.9 % and the average time from initial placement to debonding was 33 months. Caries activity was detected in 40 % of the abutment teeth that had debonded retainers. Table II summarizes the effects of all the factors evaluated in this study on the failure rate of the 43 acid-etched metal resin-bonded FPDs. Factors showing statistically significant effects toward the failure rate were (1) FPD location by arch and (2) FPD length by number of retainers. The failure rate was 54.5% for mandibular FPDs and 14.3 % for maxillary FPDs. Failure rate of FPDs with more than two retainers was 56.2 % and 22.2 % for FPDs with two retainers. Statistical analysis on the results of failure rate and other evaluated factors provided no significant difference. Factors evaluated included: patient gender, length of service, location of FPD by quadrant, FPD length by number of pontic, pontic occlusion, use of rubber dam, use of bonding agent, type of alloy used, type of resin used, operator placing the FPD, and the periodontal health of the abutment teeth. Table III summarizes the results of the effect of FPD location by arch on failure rate. Twenty-one maxillary FPDs were evaluated in this study and three were found to be debonded during the examination (failure rate = 14.3%). Twelve of the 22 mandibular FPDs examined were found to be debonded, which resulted in a failure rate of 54.4 %. Table IV summarizes the results of the effect of FPD length by the number of retainers on failure rate. Twentyseven FPDs with two retainers each were evaluated in this study and six were found to be debonded during the examination (failure rate --- 22.2 % ). Of the 16 FPDs with more than two retainers, nine were found to be debonded, with a failure rate of 56.3 %. DISCUSSION Studies on the longevity of acid-etched metal resinbonded FPDs reported failure rates ranging from 10.5% to 17.5%. 6-9 Results of the present recall study reported a
780
No. of r e t a i n e r s
substantially higher failure rate of 34.9 %. The high failure rate could be attributed to one or more of the following factors: (1) Lack of knowledge of the optimal retainer framework design and enamel modification when FPDs were placed in the earlier phase. Meiers and Meetz 1° suggested a facial wrap and proximal groove design to prevent lingual displacement; to prevent gingival displacement an occlusal/cingulum rest or inlay preparation design was recommended. (2) In the earlier phase the accuracy of how the metal was etched was unknown. Hill et al. 11 reported that errors in estimating the surface area of metal retainers could adversely affect the bond strength. (3) Poor selection of abutment teeth in questionable periodontal health. The significantly higher failure rate observed with FPDs placed in the mandibular arch compared with the maxillary arch may be attributable to one or more of the following reasons: (1) Moisture control during cementation may be more difficult to obtain in the mandibular arch than in the maxillary arch if a rubber dam was not used. (2) During normal masticatory function, retainers on the mandibular arch are subjected to a dislodging force, while retainers on the maxillary arch will experience a more favorable seating force. FPDs with more than two retainers have a significantly higher failure rate than FPDs with two retainers. The results suggest that, contrary to the conventional FPD design where an increase in the number of abutment teeth will usually result in increased retention, this may not be true for resin-bonded FPDs. Increasing the number of abutment teeth may actually lower the longevity of resinbonded FPDs. This result may not be surprising if one considers the mechanics of tooth movement and the basic differences between conventional and resin-bonded FPDs. Most of the occlusal or incisal aspects of the abutment teeth of a resin-bonded FPD are not covered by the retainer. Consequently, any force applied to an uncovered surface on the abutment teeth can result in a physiologic movement of the abutment teeth independent of the FPD and of the other abutment teeth. This type of movement could, eventually result in dislodging of the retainer. The same situation will not occur with a conventional FPD because of more fully covered abutment teeth and secondary retentive factors, such as grooves. Clinically, the ability to effectively make use of grooves is sometimes limited by the thickness of the enamel available on the abutment teeth, especially on the mandibular anterior teeth.
JUNE 1991 VOLUME 65 NUMBER 6
RESIN-BONDED FPD: RECALL, LONGEVITY
Statistically, this recall study failed to detect any other factors that may significantly affect the longevity of resinbonded FPDs. However, the importance of the other factors may be clinically significant. The use of a rubber dam during cementation is highly recommended. Acid-etching of different base metal alloys used for retainers resulted in different relief patterns and bond strengths. 12 Thus the choice of alloy used could also be important in determining the longevity of the FPD. Periodontal health of the patient should be considered. Poor periodontal health is a major contraindication for a resin-bonded FPD. CLINICAL
IMPLICATION
Based on the present clinical recall study and on other published reports on acid-etched metal resin bonded FPDs, the following clinical recommendations are made: (1) Indications for using resin-bonded FPDs should be restricted to patients in whom replacement of one missing tooth and the use of one abutment on either side is involved. (2) The abutment teeth should be in excellent periodontal condition. (3) The use of an anticipated longterm FPD for splinting of periodontally involved teeth is contraindicated. (4) The design of the retainer must include elements that will prevent lingual and gingival displacement. (5) The choice of an alloy and a method for acid-etching should be consistent with findings in published reports. 12 (6) Moisture control during cementation must be emphasized. (7) The decision to place resinbonded FPDs in the mandibular arch must be made with the limitations in mind (unfavorable forces, moisture control, and limited enamel thickness for placement of proximal groove). (8) An aggressive and ongoing follow-up program must be initiated to detect debonding and the presence of dental caries.
SUMMARY The results of this recall study on acid-etched metal resin bonded FPDs showed that: (1) Average length of service is
47.3 months for the 43 FPDs examined. (2) Overall failure rate is 34.9 %. (3) Maxillary FPDs have a significantly lower failure rate than mandibular FPDs (14.3% and 54.5%, respectively). (4) FPDs with two retainers have a significantly lower failure rate than FPDs with more than two retainers (22.2% and 56.3%, respectively). REFERENCES 1. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34:849-53. 2. Bowen RL. Properties of a silica-reinforced polymer for dental restorations. J Am Dent Assoc 1963;66:57-64. 3. Rochette AL. Attachment of a splint to enamel of lower anterior teeth. J PROSTHET DENT 1973;30:418-23. 4. Livaditis GL, Thompson VP. Etched casting: an improved retentive mechanism for resin-bonded retainers. J PROSTHET DENT 1982;47:52-8. 5. Wood M. Etched casting resin bonded retainers: an improved technique for periodontal splinting. Int J Periodontics Restorative Dent 1982;2:925. 6. Hamada T, Shigeto N, Yanagihara T. A decade of progress for the adhesive fixed partial denture. J PROSTHET DENT 1985;54:24-9. 7. Mohl G, Mehra R. Clinical evaluation of etched metal resin bonded bridges [Abstract]. J Dent Res 1986;65:311. 8. Thompson VP, Wood M. Etched casting bonded retainer recalls: results at 3-5 years [Abstract]. J Dent Res 1986:65:311. 9. Clyde JS, Boyd T. The etched cast metal resin-bonded {Maryland) bridge: a clinical review. J Dent 1988;16:22-6. 10. Meiers JC, Meetz HK. Design modifications for etched-metal, resinbonded retainers. Gen Dent 1985;33:41-4. 11. Hill GL, Zidan O, Gomez-Marin O. Bond strengths of etched base metals: effects of errors in surface area estimation. J PROSTHET DENT 1986;56:41-6. 12. Zidan O. Etched base-metal alloys: comparison of relief patterns, bond strengths and fracture modes. Dent Mater 1985;1:209-13. Reprint requests to: DR. IGNATIUSK. LEE 4-215 MOOS TOWER SCHOOL OF DENTISTRY UNIVERSITY OF MINNESOTA 515 DELAWAREST. SE MINNEAPOLIS, MN 55455
Contributing author Elaine M. E. Hill, Dental Assistant, University of Minnesota, School of Dentistry, Minneapolis, Minn.
Guides for authors available The Guide to Preparing Articles for THE JOURNAL OFPROSTHETICDENTISTRY,revised by Professor Paul Barton, Editorial Consultant to the JOURNAL,and the editors, is available to prospective authors. The guide provides the format for developing different types of scientific manuscripts, a checklist for effective writing, and detailed instructions for preparing manuscripts in the style acceptable by the JOURNAL. Also available are the Guidelines for Reporting Statistical Results and an Author's Guide to Controlling the Photograph. Guides can he obtained from the office of the Editor (Dr. Judson C. Hickey, The Journal of Prosthetic Dentistry, Medical College of Georgia, School of Dentistry, Augusta, GA 30912).
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