- Email: [email protected]
Double-crown–retained removable dental prostheses: A retrospective study of survival and complications
Double-crowneretained removable dental prostheses: A retrospective study of survival and complications Franz Sebastian Schwindling, DDS, DrMedDent,a Britta Dittmann, DDS, DrMedDent,b and Peter Rammelsberg, DDS, DrMedDent, PhDc Heidelberg University Hospital, Heidelberg, Germany Statement of problem. Research data are scarce on double-crowneretained removable dental prostheses. In doublecrowneretained removable dental prostheses, crown-like copings are definitively cemented to the abutment teeth and serve as prosthesis attachments. Purpose. The purpose of this study was to evaluate the survival of double-crowneretained removable dental prostheses in use for 7 years and to determine their most common complications. Material and methods. A retrospective analysis was conducted to investigate the clinical outcome of 117 prostheses in 86 patients with 385 abutment teeth. Thirty-two telescopic-crowneretained removable dental prostheses, 51 conicalcrowneretained removable dental prostheses, and 34 resilient telescopic-crowneretained overdentures were clinically reexamined by 1 investigator. Prosthesis success was defined as survival without severe complications (abutment tooth extraction). Statistical analyses were performed with Kaplan-Meier modeling and Cox regression (a¼.05). Results. Minor complications, for example, the decementation of primary crowns (34.2%), failure of the veneer of secondary crowns (11.1%), fracture of the denture base (17.1%), and the need for relining (12%), were common. Cumulative prosthesis survival for all types of prostheses was 93.8% after 7 years. After the same period, prosthesis success was 90% for telescopiccrowneretained removable dental prostheses and 78.5% for conical-crowneretained removable dental prostheses and resilient telescopic-crowneretained overdentures. Conclusions. The medium-term double-crowneretained removable dental prosthesis survival found in this retrospective investigation appears acceptable. When bearing in mind the limits of this study, this kind of prosthesis might be a viable treatment option for patients with a reduced dentition. However, more laboratory and clinical research is necessary to reduce the incidence of minor complications and confirm the present in vivo results in larger patient groups. (J Prosthet Dent 2014;-:---)
Clinical Implications In double-crowneretained removable dental prostheses, the loss of a single abutment tooth can often be compensated for by minor prosthesis modification and does not result in failure of the prosthesis, which explains the promising survival rates. Decementations, veneer failure, relining, and denture-base fractures were the most frequent complications that led to the need for aftercare.
Approximately half of adults in Western societies have had some type of prosthetic dental restoration, and between 13% and 29% of adults have a
removable dental prostheses (RDP).1 This substantial number of patients is indicative of the relevance of clinical research into RDP maintenance and survival.
Assistant Professor, Department of Prosthodontics. Private practice, Mering, Germany. c Professor and Chair, Department of Prosthodontics. b
Schwindling et al
The adequate retention of dentures is regarded as one of the most important factors that affects their success.2 The different attachment systems used
2
Volume for RDP retention include clasps,3-5 magnets,6 intracoronal and extracoronal attachments,7 and double crowns. Double-crown attachments are characterized by inner copings (primary crowns), which are definitively cemented to the abutment teeth and secondary crowns, which are integrated within the removable prosthesis.8 These secondary crowns are veneered with a composite resin. Apart from providing adequate retention,9 double crowns have the advantage of transferring occlusal forces along the axis of the abutment teeth because of the circumferential relationship of the secondary crown to its abutment tooth.8 Moreover, oral hygiene is facilitated because of the good access to the abutment teeth when removing the prosthesis. The disadvantages of this attachment type are the need for an extensive tooth preparation to prevent excessive contouring of the abutment teeth and also the challenging fabrication process. Three types of double crowns have been described10: the parallel-walled telescopic crown,8 the conical crown with tapered design,11 and the resilient telescopic crown with clearance fit. Clearance fit refers to a free space between primary and secondary crowns. Double-crowneretained RDPs (D-RDP) fabricated in this manner provide guidance and stability against horizontal dislodging motion without directing occlusal forces onto the abutment teeth.12,13 Resilient telescopic crowns are used for overdentures in patients with few remaining teeth. Double crowns are well established in prosthetic dentistry,14 with some reports on the incidence of technical These investigations failure.3,15-22 revealed that the most frequent complications of D-RDPs are loss of primary crowns,3 failure of the veneer of secondary crowns,3 and partial prosthesis fracture.17 Information on the survival of D-RDPs is scarce: a systematic literature review found only 2 studies on this topic.14 This investigation, therefore, was designed to study D-RDPs that had been in use for up to
10 years to determine prosthesis survival and the most common complications. Moreover, prosthesis survival without major complications was to be addressed, together with covariates that affect “prosthesis success.”
MATERIAL AND METHODS Study design Four hundred ninety-four patients received 604 D-RDPs at the Department of Prosthodontics, Ludwig-Maximilians University Munich, between 1992 and 1998 (Fig. 1). All prostheses were provided during predoctoral courses, with supervision by resident dentists, in accordance with a standardized protocol, or were provided by the residents themselves. To obtain information about the maintenance and survival of the prostheses after several years, an attempt was made to invite all 494 patients via telephone or postal letter to recall examinations. In the meantime, 21 patients had died, 7 were seriously ill, 5 had moved to foreign countries, and 10 more expressed their unwillingness to participate in a clinical study. Some patients did not respond to telephone calls (3 calls at different times of day on
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different days of the week) or postal letters. Two hundred twenty-five patients were polled by telephone (a response rate of 43.4%) and invited to the department. Eighty-six participants attended 1 recall session. The state of the abutment teeth and their corresponding veneers, as well as the integrity of the denture base, were determined by means of a clinical investigation during the recall sessions. The numbers of primary crown recementations, relinings, and abutment tooth losses were determined from the patient records. The participants also were asked whether recementations, relinings, repairs, or extractions had been conducted elsewhere.
Complications and survival Minor complications, for example, decementation, veneer failure, a need of relining, or fractures of the denturebase acrylic resin or framework, were recorded, along with their frequency. These complications were reversible and could be solved within a few hours of laboratory work or within the dental office by recementation. Prosthesis survival and success were evaluated, with prosthesis survival being defined as
Treated patients N = 494
Interviewed patients n = 225
T-RDPs n = 37
T-RDPs or C-RDPs n = 55
C-RDPs n = 87
R-RDPs n = 103
Reexamination session N = 86
T-RDPs n = 32
C-RDPs n = 51
R-RDPs n = 34
1 Study flow.
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the prosthesis still being in use. The reasons for prosthesis loss were loss of all remaining abutment teeth and the impossibility of adjusting the prosthesis after abutment tooth loss (as after multiple extractions). Prosthesis success meant that the prosthesis was still in use and that no severe complication had occurred. Severe complications were defined as loss of any abutment tooth along with a subsequent need for denture-base extension. However, these RDPs remained in use without modification of the remaining double crowns or the metal framework.
Statistical analysis Statistical analyses were performed with IBM SPSS Statistics version 19 (IBM Corp). The observation period started with the day of prosthesis insertion and ended with the day of clinical reevaluation. Kaplan-Meier modeling was used to calculate prosthesis survival and success. The log-rank test was used to show the possible effects of the type of double crown on these values. The statistical unit was the prosthesis. Cox regression was used to test 4 predictors and their possible effect on success: sex, patient age, double-crown type, and location
Table I.
(maxilla and/or mandible). P.05 was regarded as indicative of exploratory significant difference. Dropout analysis (Pearson c2 test) was performed to test whether the reexamined cohort was significantly different from the initially contacted cohort in its sex structure, type of double crown, and/or prosthesis location.
and 34 resilient telescopic-crowne retained overdentures (R-RDP). The mean number of abutment teeth was 2.97 in the mandible and 3.65 in the maxilla. The patients who received R-RDPs had significantly fewer abutment teeth than patients with the other types of double crowns.
RESULTS
Minor complications
Reexamined study population
Recementation of primary crowns was necessary for 40 of the 117 reexamined prostheses (34.2%). Thirty-five percent of these prostheses required repeated recementations (minimum, 2; maximum, 7). With reference to the number of abutment teeth, 47 of the reexamined 385 primary crowns (12.2%) were affected. Of these, 27.7% were repeatedly recemented. Reveneering was necessary for 11.1% of the prostheses that were reevaluated, with 92.3% in need of multiple reveneering (up to 7 times in 1 case). Relining was necessary in 12% of the prostheses that were reexamined in the recall session. Cracks or fractures in the framework or denture base were observed in 17.1% of the reassessed prostheses. Repeated damage of the framework and base was not encountered for any prosthesis (Table I).
Eighty-six patients with 117 prostheses and 385 abutment teeth attended clinical reevaluation sessions. The mean (standard deviation) time in situ before reexamination was 6.26 2.2 years (minimum, 1.9; maximum, 8.9). 51 participants were women, and 35 were men. No significant difference was found between the number of abutment teeth for male and female patients. The prostheses were inserted in a senior population; mean (standard deviation) patient age was 69 9.2 years (minimum, 47; maximum, 87). Forty-seven percent of prostheses were placed in the maxilla and 53% in the mandible. Thirty-two prostheses were telescopiccrowneretained RDPs (T-RDP); 51 conical-crowneretained RDPs (C-RDP),
Minor complications of D-RDPs
Frequency of Intervention
Recementation: Prostheses Affected
Cracks and Fractures in Prosthesis Framework or Base: Prostheses Reveneering: Relining: Affected Prostheses Affected Prostheses Affected
0
77
104
103
97
1
26
1
14
20
2
6
6
3
3
1
4
1
2
5
0
0
6
1
2
3
1
7 Total
40/117 (34.2%) prostheses 13/117 (11.1%) prostheses in need of reveneering in need of at least 1 at least once; 12/13 recementation; 14/40 (35%) (92.3%) in need of in need of repeated multiple reveneering recementation
Schwindling et al
14/117 (12%) prostheses in need of relining
20/117 (17.1%) prostheses with cracks and fractures
4
Volume
100%
Survival
95%
90%
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DISCUSSION
85% Survival Censored 80% 0
1
2
3
4
5
6
7
Time in use (years) 2 Kaplan-Meier modeling of prosthesis survival after 7 years. Number of extracted abut-
ment teeth
Abutment Teeth in Need of Intervention
Abutment Tooth Extraction: Prostheses Affected
0
92
1
22
2
2
3
1
4 5 6 7 Total
Issue
showed that the double-crown type had a significant effect on prosthesis success (P¼.017). A severe complication was 2.2 times more likely when R-RDPs were used. Patient age, sex, and prosthesis location (jaw) had no significant effect. Dropout analysis, after the application of the Pearson c2 test revealed no significant difference between the structure of the initially recruited cohort and the reexamined group (sex, P¼.153; doublecrown type; P¼.33; location, P¼.267).
Survival
Table II.
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25/117 (21.4%) of prostheses affected; 3/25 (12%) repeated tooth loss
Major complications The survival rate of the prostheses that were clinically reassessed was calculated by Kaplan-Meier analysis
and amounted to 93.8% after 7 years in use (Fig. 2). Six prostheses had to be replaced because of loss of all abutment teeth or because of the impossibility of adjusting the prosthesis after loss of abutment teeth; 3 had been inserted in the mandible and 3 in the maxilla. After 5 years, the survival rate was 96.5%. For 21.4% (n¼25) of the prostheses, any of the abutment teeth had to be extracted. For 12% (n¼3) of these, more than 1 tooth was lost during the observation period (Table II). Success, defined as survival without severe complications, was modeled by using Kaplan-Meier analysis (Fig. 3). After 5 years, the success rate was 100% for T-RDPs, 91.9% for C-RDPs, and 90.4% for R-RDPs. After 7 years, 90% of the T-RDPs were successful. After the same time, only 78.5% of the C-RDPs and the R-RDPs were successful. The log-rank test revealed a trend (P¼.085): R-RDPs were prone to more major complications after use for up to 10 years. Cox regression confirmed this result and
The Journal of Prosthetic Dentistry
In this investigation, recementation procedures were necessary for 34.2% of the prostheses (12.2% with reference to the number of abutment teeth). Of the prostheses evaluated, 17.1% had cracks and fractures in the denture base or framework, 12% needed relining, and the veneer failed for 11.1%. After 7 years, prosthesis survival was 93.8%, and prosthesis success was 90% for T-RDPs and 78.5% for C-RDPs and R-RDPs. Because of the retrospective nature of this analysis, the results might be affected by the failure of the patient’s memory or inadequate documentation. Furthermore, the response rate of 43.4% is lower than that reported for similar studies.15,16 The lack of a consistent recall system might be responsible for this, because patient dropout is lower for studies with stricter recall regimes.23 The mean age of this cohort was 69 years, and, because this was a senior group, more participants probably had serious diseases or died than the younger participants of other studies. The dropout analysis revealed no significant differences between the composition of the initially responding group that was contacted via telephone and the 86 patients who attended recall sessions. The results for survival and success in this trial were based on a period of observation limited to 7 years, even though some prostheses had been in use for more than 10 years. The number of prostheses that had been in situ for this period, however, was too small to allow conclusions to be drawn.
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5 Success
100%
Success
80%
Type of double crown
60%
T-RDPs C-RDPs R-RDPs T-RDPs-censored C-RDPs-censored
40%
R-RDPs-censored
0
1
2
3
4
5
6
7
Time in use (years) 3 Kaplan-Meier modeling of prosthesis success after 7 years.
Minor complications The results of this study were in agreement with literature reports that show the loss of cementation of primary crowns is the most common problem for D-RDPs. Hofmann et al17 found decementation occurred for 32.5% of telescopic double crowns and 20% of conical double crowns after a mean observation period of 4.2 years. Eisenburger et al19 reported a slightly lower incidence of 17% for telescopic crowns after 8 years. Decementation might be a result of mistakes in tooth preparation, poor fit of the primary crowns, excessive retention forces of the secondary crowns,13,22 or errors in the cementation process. Furthermore, the large number of dentists involved in the fabrication of prostheses in dental clinics might be important because of their differing knowledge of a particular patient situation.22 The relining rate of 12% of the reexamined prostheses was lower than has been previously reported:
Schwindling et al
Igarashi and Goto16 found one-third of conical-crowneretained prostheses to be in need of relining to improve denture-base fit. The highest incidence was recorded with configurations other than Kennedy class III. However, the observation period of 10 years was longer than that of the present study. Among the minor complications, cracks and fractures in the framework or denture base were present in 17.1% of the prostheses. Behr et al3 reported metal framework fracture in 7% of C-RDPs and 2.7% of T-RDPs after a mean observation period of 4.6 years. Moreover, fractures of the acrylic resin denture base occurred in 4.7% of C-RDPs.3 Wagner and Kern18 reported fractures in 16.7% of denture acrylic resin and 11.1% of frameworks of reexamined D-RDPs after a mean observation time of 10 years. The values in the present study might be higher than previously reported values because some of the laboratory steps were undertaken by inexperienced students. Most fractures of the metal framework appear to be a
result of faults during the casting process, fatigue as a result of the inadequate fit of the prostheses, or damage to the prostheses caused by careless handling by the patients.17 Moreover, functional loads deform the denture base, with subsequent damage to denture-base structures.24 Veneer failure was another complication investigated in this study. A similar frequency of this complication has been reported after many investigations.3,17,18,20 The elastic deformation of the secondary crown and the veneering technique used are responsible for the frequent fractures found in composite resin veneer.16,22 Failure of the veneer appears to occur even more often with C-RDPs than with T-RDPs because of the greater elastic deformation of the outer crowns in this system.21 The minor complications addressed in this study are not unusual for D-RDPs. Particularly with regard to veneer failure, additional laboratory and clinical research is needed to improve layering techniques. Despite these problems, costs for repairs are estimated to be lower for double crowns than for claspretained prostheses.17
Survival and success The literature does not provide sufficient information about the long-term outcome for D-RDPs. In a literature review on prosthesis survival, only 2 prospective and 5 retrospective studies of this type of prosthesis were found with observation periods between 4 and 10 years.14 Of these 7 studies, only 2 retrospective investigations provided information about the survival of the prostheses, whereas the others focused on the survival of abutment teeth. Wöstmann et al22 reported a survival rate of 95.1% for T-RDPs after a mean observation period of 5.3 years. In comparison with conventional claspretained RDPs, the survival of D-RDPs appears better, although evidence is minimal.14 When considering replacement and not wearing the RDP as failure criteria, the survival of clasp-retained
6
Volume prostheses was significantly lower, 75% after 5 years.5 The definition of prosthesis success in this study was survival without severe complications. Abutment tooth loss was regarded as a severe complication because prostheses partially lose support, which alters the force transfer to the remaining dentition and the mucosa. In addition, the base of the prosthesis has to be adjusted or the prosthesis has to be relined in the dental laboratory. To our knowledge, this investigation is the first to report the success of D-RDPs. For implant-supported D-RDPs, survival without major complications has already been reported after a similar approach.25 The results for factors that contributed to prosthesis survival without complications are in agreement with results from other investigations. Only a minimum, insignificant effect of prosthesis location on survival has been reported in the literature.22 Sex had no significant effect on prosthesis survival, neither in this study nor in the literature.19,22 Wöstmann et al22 also reported that age had no effect on the probability of survival, which is in agreement with this investigation. Wenz et al13 found no significant increase in the risk of abutment loss when the restoration was placed on 3 or fewer remaining teeth and the concept of resilient support was applied. This result is in contrast with this study, in which R-RDPs had significantly more major complications. R-RDPs were used when only a few teeth remained, even though the long-term prognosis for the teeth was somewhat questionable. Therefore, the presented results are in agreement with several studies that reported that a small number of abutment teeth negatively affects RDP survival.22
CONCLUSION Minor complications, for example, decementations, veneer failure, and denture-base fractures, are the most frequent complications that lead to the
need for aftercare of D-RDPs. Nevertheless, the prosthesis survival rate was acceptable after midterm periods of observation.
REFERENCES 1. Zitzmann NU, Hagmann E, Weiger R. What is the prevalence of various types of prosthetic dental restorations in Europe? Clin Oral Implants Res 2007;18(suppl 3): 20-33. 2. Helal MA, Baraka OA, Sanad ME, Ludwig K, Kern M. Effects of long-term simulated RDP clasp attachment/detachment on retention loss and wear for two clasp types and three abutment material surfaces. J Prosthodont 2012;21:370-7. 3. Behr M, Hofmann E, Rosentritt M, Lang R, Handel G. Technical failure rates of double crown-retained removable partial dentures. Clin Oral Investig 2000;4:87-90. 4. Rehmann P, Orbach K, Ferger P, Wöstmann B. Treatment outcomes with removable partial dentures: a retrospective analysis. Int J Prosthodont 2013;26:147-50. 5. Vermeulen AH, Keltjens HM, van’t Hof MA, Kayser AF. Ten-year evaluation of removable partial dentures: survival rates based on retreatment, not wearing and replacement. J Prosthet Dent 1996;76:267-72. 6. Gonda T, Yang TC, Maeda Y. Five-year multicenter study of magnetic attachments used for natural overdenture abutments. J Oral Rehabil 2013;40:258-62. 7. Zitzmann NU, Rohner U, Weiger R, Krastl G. When to choose which retention element to use for removable dental prostheses. Int J Prosthodont 2009;22:161-7. 8. Isaacson GO. Telescope crown retainers for removable partial dentures. J Prosthet Dent 1969;22:436-48. 9. Özyemis¸ci-Cebeci N, Yavuzyilmaz H. Comparison of the effects of friction varnish and electroforming on the retention of telescopic crowns. J Prosthet Dent 2013;109:392-6. 10. Frisch E, Ziebolz D, Rinke S. Long-term results of implant-supported over-dentures retained by double crowns: a practice-based retrospective study after minimally 10 years follow-up. Clin Oral Implants Res 2012;24: 1281-7. 11. Hultén J, Tillström B, Nilner K. Long term clinical evaluation of conical crown retained dentures. Swed Dent J 1993;17:225-34. 12. Wenz HJ, Lehmann KM. A telescopic crown concept for the restoration of the partially edentulous arch: the Marburg double crown system. Int J Prosthodont 1998; 11:541-50. 13. Wenz HJ, Hertrampf K, Lehmann KM. Clinical longevity of removable partial dentures retained by telescopic crowns: outcome of the double crown with clearance fit. Int J Prosthodont 2001;14:207-13.
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14. Koller B, Att W, Strub JR. Survival rates of teeth, implants, and double crown-retained removable dental prostheses: a systematic literature review. Int J Prosthodont 2011;24: 109-17. 15. Bergman B, Ericson A, Molin M. Long-term clinical results after treatment with conical crown-retained dentures. Int J Prosthodont 1996;9:533-8. 16. Igarashi Y, Goto T. Ten-year follow-up study of conical crown-retained dentures. Int J Prosthodont 1997;10:149-55. 17. Hofmann E, Behr M, Handel G. Frequency and costs of technical failures of clasp- and double crown-retained removable partial dentures. Clin Oral Investig 2002;6:104-8. 18. Wagner B, Kern M. Clinical evaluation of removable partial dentures 10 years after insertion: success rates, hygienic problems, and technical failures. Clin Oral Investig 2000;4:74-80. 19. Eisenburger M, Gray G, Tschernitschek H. Long-term results of telescopic crown retained denturesea retrospective study. Eur J Prosthodont Restor Dent 2000;8:87-91. 20. Ericson A, Nilsson B, Bergman B. Clinical results in patients provided with conical crown retained dentures. Int J Prosthodont 1990;3:513-21. 21. Hahnel S, Bürgers R, Rosentritt M, Handel G, Behr M. Analysis of veneer failure of removable prosthodontics. Gerodontology 2012;29:e1125-8. 22. Wöstmann B, Balkenhol M, Weber A, Ferger P, Rehmann P. Long-term analysis of telescopic crown retained removable partial dentures: survival and need for maintenance. J Dent 2007;35:939-45. 23. Bergman B, Hugoson A, Olsson CO. Caries, periodontal and prosthetic findings in patients with removable partial dentures: a ten-year longitudinal study. J Prosthet Dent 1982;48:506-14. 24. Kapur KK, Deupree R, Dent RJ, Hasse AL. A randomized clinical trial of two basic removable partial denture designs. Part I: comparisons of five-year success rates and periodontal health. J Prosthet Dent 1994; 72:268-82. 25. Schwarz S, Bernhart G, Hassel AJ, Rammelsberg P. Survival of double-crownretained dentures either tooth-implant or solely implant-supported: an 8-year retrospective study. Clin Implant Dent Relat Res 2012. Dec 6. http://dx.doi.org/10.1111/cid.12023. [Epub]. Corresponding author: Dr Franz Sebastian Schwindling Department of Prosthodontics Heidelberg University Hospital Im Neuenheimer Feld 400 69120 Heidelberg GERMANY E-mail: [email protected] Copyright ª 2014 by the Editorial Council for The Journal of Prosthetic Dentistry.
Schwindling et al
Clinical Implications In double-crowneretained removable dental prostheses, the loss of a single abutment tooth can often be compensated for by minor prosthesis modification and does not result in failure of the prosthesis, which explains the promising survival rates. Decementations, veneer failure, relining, and denture-base fractures were the most frequent complications that led to the need for aftercare.
Approximately half of adults in Western societies have had some type of prosthetic dental restoration, and between 13% and 29% of adults have a
removable dental prostheses (RDP).1 This substantial number of patients is indicative of the relevance of clinical research into RDP maintenance and survival.
Assistant Professor, Department of Prosthodontics. Private practice, Mering, Germany. c Professor and Chair, Department of Prosthodontics. b
Schwindling et al
The adequate retention of dentures is regarded as one of the most important factors that affects their success.2 The different attachment systems used
2
Volume for RDP retention include clasps,3-5 magnets,6 intracoronal and extracoronal attachments,7 and double crowns. Double-crown attachments are characterized by inner copings (primary crowns), which are definitively cemented to the abutment teeth and secondary crowns, which are integrated within the removable prosthesis.8 These secondary crowns are veneered with a composite resin. Apart from providing adequate retention,9 double crowns have the advantage of transferring occlusal forces along the axis of the abutment teeth because of the circumferential relationship of the secondary crown to its abutment tooth.8 Moreover, oral hygiene is facilitated because of the good access to the abutment teeth when removing the prosthesis. The disadvantages of this attachment type are the need for an extensive tooth preparation to prevent excessive contouring of the abutment teeth and also the challenging fabrication process. Three types of double crowns have been described10: the parallel-walled telescopic crown,8 the conical crown with tapered design,11 and the resilient telescopic crown with clearance fit. Clearance fit refers to a free space between primary and secondary crowns. Double-crowneretained RDPs (D-RDP) fabricated in this manner provide guidance and stability against horizontal dislodging motion without directing occlusal forces onto the abutment teeth.12,13 Resilient telescopic crowns are used for overdentures in patients with few remaining teeth. Double crowns are well established in prosthetic dentistry,14 with some reports on the incidence of technical These investigations failure.3,15-22 revealed that the most frequent complications of D-RDPs are loss of primary crowns,3 failure of the veneer of secondary crowns,3 and partial prosthesis fracture.17 Information on the survival of D-RDPs is scarce: a systematic literature review found only 2 studies on this topic.14 This investigation, therefore, was designed to study D-RDPs that had been in use for up to
10 years to determine prosthesis survival and the most common complications. Moreover, prosthesis survival without major complications was to be addressed, together with covariates that affect “prosthesis success.”
MATERIAL AND METHODS Study design Four hundred ninety-four patients received 604 D-RDPs at the Department of Prosthodontics, Ludwig-Maximilians University Munich, between 1992 and 1998 (Fig. 1). All prostheses were provided during predoctoral courses, with supervision by resident dentists, in accordance with a standardized protocol, or were provided by the residents themselves. To obtain information about the maintenance and survival of the prostheses after several years, an attempt was made to invite all 494 patients via telephone or postal letter to recall examinations. In the meantime, 21 patients had died, 7 were seriously ill, 5 had moved to foreign countries, and 10 more expressed their unwillingness to participate in a clinical study. Some patients did not respond to telephone calls (3 calls at different times of day on
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Issue
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different days of the week) or postal letters. Two hundred twenty-five patients were polled by telephone (a response rate of 43.4%) and invited to the department. Eighty-six participants attended 1 recall session. The state of the abutment teeth and their corresponding veneers, as well as the integrity of the denture base, were determined by means of a clinical investigation during the recall sessions. The numbers of primary crown recementations, relinings, and abutment tooth losses were determined from the patient records. The participants also were asked whether recementations, relinings, repairs, or extractions had been conducted elsewhere.
Complications and survival Minor complications, for example, decementation, veneer failure, a need of relining, or fractures of the denturebase acrylic resin or framework, were recorded, along with their frequency. These complications were reversible and could be solved within a few hours of laboratory work or within the dental office by recementation. Prosthesis survival and success were evaluated, with prosthesis survival being defined as
Treated patients N = 494
Interviewed patients n = 225
T-RDPs n = 37
T-RDPs or C-RDPs n = 55
C-RDPs n = 87
R-RDPs n = 103
Reexamination session N = 86
T-RDPs n = 32
C-RDPs n = 51
R-RDPs n = 34
1 Study flow.
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the prosthesis still being in use. The reasons for prosthesis loss were loss of all remaining abutment teeth and the impossibility of adjusting the prosthesis after abutment tooth loss (as after multiple extractions). Prosthesis success meant that the prosthesis was still in use and that no severe complication had occurred. Severe complications were defined as loss of any abutment tooth along with a subsequent need for denture-base extension. However, these RDPs remained in use without modification of the remaining double crowns or the metal framework.
Statistical analysis Statistical analyses were performed with IBM SPSS Statistics version 19 (IBM Corp). The observation period started with the day of prosthesis insertion and ended with the day of clinical reevaluation. Kaplan-Meier modeling was used to calculate prosthesis survival and success. The log-rank test was used to show the possible effects of the type of double crown on these values. The statistical unit was the prosthesis. Cox regression was used to test 4 predictors and their possible effect on success: sex, patient age, double-crown type, and location
Table I.
(maxilla and/or mandible). P.05 was regarded as indicative of exploratory significant difference. Dropout analysis (Pearson c2 test) was performed to test whether the reexamined cohort was significantly different from the initially contacted cohort in its sex structure, type of double crown, and/or prosthesis location.
and 34 resilient telescopic-crowne retained overdentures (R-RDP). The mean number of abutment teeth was 2.97 in the mandible and 3.65 in the maxilla. The patients who received R-RDPs had significantly fewer abutment teeth than patients with the other types of double crowns.
RESULTS
Minor complications
Reexamined study population
Recementation of primary crowns was necessary for 40 of the 117 reexamined prostheses (34.2%). Thirty-five percent of these prostheses required repeated recementations (minimum, 2; maximum, 7). With reference to the number of abutment teeth, 47 of the reexamined 385 primary crowns (12.2%) were affected. Of these, 27.7% were repeatedly recemented. Reveneering was necessary for 11.1% of the prostheses that were reevaluated, with 92.3% in need of multiple reveneering (up to 7 times in 1 case). Relining was necessary in 12% of the prostheses that were reexamined in the recall session. Cracks or fractures in the framework or denture base were observed in 17.1% of the reassessed prostheses. Repeated damage of the framework and base was not encountered for any prosthesis (Table I).
Eighty-six patients with 117 prostheses and 385 abutment teeth attended clinical reevaluation sessions. The mean (standard deviation) time in situ before reexamination was 6.26 2.2 years (minimum, 1.9; maximum, 8.9). 51 participants were women, and 35 were men. No significant difference was found between the number of abutment teeth for male and female patients. The prostheses were inserted in a senior population; mean (standard deviation) patient age was 69 9.2 years (minimum, 47; maximum, 87). Forty-seven percent of prostheses were placed in the maxilla and 53% in the mandible. Thirty-two prostheses were telescopiccrowneretained RDPs (T-RDP); 51 conical-crowneretained RDPs (C-RDP),
Minor complications of D-RDPs
Frequency of Intervention
Recementation: Prostheses Affected
Cracks and Fractures in Prosthesis Framework or Base: Prostheses Reveneering: Relining: Affected Prostheses Affected Prostheses Affected
0
77
104
103
97
1
26
1
14
20
2
6
6
3
3
1
4
1
2
5
0
0
6
1
2
3
1
7 Total
40/117 (34.2%) prostheses 13/117 (11.1%) prostheses in need of reveneering in need of at least 1 at least once; 12/13 recementation; 14/40 (35%) (92.3%) in need of in need of repeated multiple reveneering recementation
Schwindling et al
14/117 (12%) prostheses in need of relining
20/117 (17.1%) prostheses with cracks and fractures
4
Volume
100%
Survival
95%
90%
-
DISCUSSION
85% Survival Censored 80% 0
1
2
3
4
5
6
7
Time in use (years) 2 Kaplan-Meier modeling of prosthesis survival after 7 years. Number of extracted abut-
ment teeth
Abutment Teeth in Need of Intervention
Abutment Tooth Extraction: Prostheses Affected
0
92
1
22
2
2
3
1
4 5 6 7 Total
Issue
showed that the double-crown type had a significant effect on prosthesis success (P¼.017). A severe complication was 2.2 times more likely when R-RDPs were used. Patient age, sex, and prosthesis location (jaw) had no significant effect. Dropout analysis, after the application of the Pearson c2 test revealed no significant difference between the structure of the initially recruited cohort and the reexamined group (sex, P¼.153; doublecrown type; P¼.33; location, P¼.267).
Survival
Table II.
-
25/117 (21.4%) of prostheses affected; 3/25 (12%) repeated tooth loss
Major complications The survival rate of the prostheses that were clinically reassessed was calculated by Kaplan-Meier analysis
and amounted to 93.8% after 7 years in use (Fig. 2). Six prostheses had to be replaced because of loss of all abutment teeth or because of the impossibility of adjusting the prosthesis after loss of abutment teeth; 3 had been inserted in the mandible and 3 in the maxilla. After 5 years, the survival rate was 96.5%. For 21.4% (n¼25) of the prostheses, any of the abutment teeth had to be extracted. For 12% (n¼3) of these, more than 1 tooth was lost during the observation period (Table II). Success, defined as survival without severe complications, was modeled by using Kaplan-Meier analysis (Fig. 3). After 5 years, the success rate was 100% for T-RDPs, 91.9% for C-RDPs, and 90.4% for R-RDPs. After 7 years, 90% of the T-RDPs were successful. After the same time, only 78.5% of the C-RDPs and the R-RDPs were successful. The log-rank test revealed a trend (P¼.085): R-RDPs were prone to more major complications after use for up to 10 years. Cox regression confirmed this result and
The Journal of Prosthetic Dentistry
In this investigation, recementation procedures were necessary for 34.2% of the prostheses (12.2% with reference to the number of abutment teeth). Of the prostheses evaluated, 17.1% had cracks and fractures in the denture base or framework, 12% needed relining, and the veneer failed for 11.1%. After 7 years, prosthesis survival was 93.8%, and prosthesis success was 90% for T-RDPs and 78.5% for C-RDPs and R-RDPs. Because of the retrospective nature of this analysis, the results might be affected by the failure of the patient’s memory or inadequate documentation. Furthermore, the response rate of 43.4% is lower than that reported for similar studies.15,16 The lack of a consistent recall system might be responsible for this, because patient dropout is lower for studies with stricter recall regimes.23 The mean age of this cohort was 69 years, and, because this was a senior group, more participants probably had serious diseases or died than the younger participants of other studies. The dropout analysis revealed no significant differences between the composition of the initially responding group that was contacted via telephone and the 86 patients who attended recall sessions. The results for survival and success in this trial were based on a period of observation limited to 7 years, even though some prostheses had been in use for more than 10 years. The number of prostheses that had been in situ for this period, however, was too small to allow conclusions to be drawn.
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2014
5 Success
100%
Success
80%
Type of double crown
60%
T-RDPs C-RDPs R-RDPs T-RDPs-censored C-RDPs-censored
40%
R-RDPs-censored
0
1
2
3
4
5
6
7
Time in use (years) 3 Kaplan-Meier modeling of prosthesis success after 7 years.
Minor complications The results of this study were in agreement with literature reports that show the loss of cementation of primary crowns is the most common problem for D-RDPs. Hofmann et al17 found decementation occurred for 32.5% of telescopic double crowns and 20% of conical double crowns after a mean observation period of 4.2 years. Eisenburger et al19 reported a slightly lower incidence of 17% for telescopic crowns after 8 years. Decementation might be a result of mistakes in tooth preparation, poor fit of the primary crowns, excessive retention forces of the secondary crowns,13,22 or errors in the cementation process. Furthermore, the large number of dentists involved in the fabrication of prostheses in dental clinics might be important because of their differing knowledge of a particular patient situation.22 The relining rate of 12% of the reexamined prostheses was lower than has been previously reported:
Schwindling et al
Igarashi and Goto16 found one-third of conical-crowneretained prostheses to be in need of relining to improve denture-base fit. The highest incidence was recorded with configurations other than Kennedy class III. However, the observation period of 10 years was longer than that of the present study. Among the minor complications, cracks and fractures in the framework or denture base were present in 17.1% of the prostheses. Behr et al3 reported metal framework fracture in 7% of C-RDPs and 2.7% of T-RDPs after a mean observation period of 4.6 years. Moreover, fractures of the acrylic resin denture base occurred in 4.7% of C-RDPs.3 Wagner and Kern18 reported fractures in 16.7% of denture acrylic resin and 11.1% of frameworks of reexamined D-RDPs after a mean observation time of 10 years. The values in the present study might be higher than previously reported values because some of the laboratory steps were undertaken by inexperienced students. Most fractures of the metal framework appear to be a
result of faults during the casting process, fatigue as a result of the inadequate fit of the prostheses, or damage to the prostheses caused by careless handling by the patients.17 Moreover, functional loads deform the denture base, with subsequent damage to denture-base structures.24 Veneer failure was another complication investigated in this study. A similar frequency of this complication has been reported after many investigations.3,17,18,20 The elastic deformation of the secondary crown and the veneering technique used are responsible for the frequent fractures found in composite resin veneer.16,22 Failure of the veneer appears to occur even more often with C-RDPs than with T-RDPs because of the greater elastic deformation of the outer crowns in this system.21 The minor complications addressed in this study are not unusual for D-RDPs. Particularly with regard to veneer failure, additional laboratory and clinical research is needed to improve layering techniques. Despite these problems, costs for repairs are estimated to be lower for double crowns than for claspretained prostheses.17
Survival and success The literature does not provide sufficient information about the long-term outcome for D-RDPs. In a literature review on prosthesis survival, only 2 prospective and 5 retrospective studies of this type of prosthesis were found with observation periods between 4 and 10 years.14 Of these 7 studies, only 2 retrospective investigations provided information about the survival of the prostheses, whereas the others focused on the survival of abutment teeth. Wöstmann et al22 reported a survival rate of 95.1% for T-RDPs after a mean observation period of 5.3 years. In comparison with conventional claspretained RDPs, the survival of D-RDPs appears better, although evidence is minimal.14 When considering replacement and not wearing the RDP as failure criteria, the survival of clasp-retained
6
Volume prostheses was significantly lower, 75% after 5 years.5 The definition of prosthesis success in this study was survival without severe complications. Abutment tooth loss was regarded as a severe complication because prostheses partially lose support, which alters the force transfer to the remaining dentition and the mucosa. In addition, the base of the prosthesis has to be adjusted or the prosthesis has to be relined in the dental laboratory. To our knowledge, this investigation is the first to report the success of D-RDPs. For implant-supported D-RDPs, survival without major complications has already been reported after a similar approach.25 The results for factors that contributed to prosthesis survival without complications are in agreement with results from other investigations. Only a minimum, insignificant effect of prosthesis location on survival has been reported in the literature.22 Sex had no significant effect on prosthesis survival, neither in this study nor in the literature.19,22 Wöstmann et al22 also reported that age had no effect on the probability of survival, which is in agreement with this investigation. Wenz et al13 found no significant increase in the risk of abutment loss when the restoration was placed on 3 or fewer remaining teeth and the concept of resilient support was applied. This result is in contrast with this study, in which R-RDPs had significantly more major complications. R-RDPs were used when only a few teeth remained, even though the long-term prognosis for the teeth was somewhat questionable. Therefore, the presented results are in agreement with several studies that reported that a small number of abutment teeth negatively affects RDP survival.22
CONCLUSION Minor complications, for example, decementations, veneer failure, and denture-base fractures, are the most frequent complications that lead to the
need for aftercare of D-RDPs. Nevertheless, the prosthesis survival rate was acceptable after midterm periods of observation.
REFERENCES 1. Zitzmann NU, Hagmann E, Weiger R. What is the prevalence of various types of prosthetic dental restorations in Europe? Clin Oral Implants Res 2007;18(suppl 3): 20-33. 2. Helal MA, Baraka OA, Sanad ME, Ludwig K, Kern M. Effects of long-term simulated RDP clasp attachment/detachment on retention loss and wear for two clasp types and three abutment material surfaces. J Prosthodont 2012;21:370-7. 3. Behr M, Hofmann E, Rosentritt M, Lang R, Handel G. Technical failure rates of double crown-retained removable partial dentures. Clin Oral Investig 2000;4:87-90. 4. Rehmann P, Orbach K, Ferger P, Wöstmann B. Treatment outcomes with removable partial dentures: a retrospective analysis. Int J Prosthodont 2013;26:147-50. 5. Vermeulen AH, Keltjens HM, van’t Hof MA, Kayser AF. Ten-year evaluation of removable partial dentures: survival rates based on retreatment, not wearing and replacement. J Prosthet Dent 1996;76:267-72. 6. Gonda T, Yang TC, Maeda Y. Five-year multicenter study of magnetic attachments used for natural overdenture abutments. J Oral Rehabil 2013;40:258-62. 7. Zitzmann NU, Rohner U, Weiger R, Krastl G. When to choose which retention element to use for removable dental prostheses. Int J Prosthodont 2009;22:161-7. 8. Isaacson GO. Telescope crown retainers for removable partial dentures. J Prosthet Dent 1969;22:436-48. 9. Özyemis¸ci-Cebeci N, Yavuzyilmaz H. Comparison of the effects of friction varnish and electroforming on the retention of telescopic crowns. J Prosthet Dent 2013;109:392-6. 10. Frisch E, Ziebolz D, Rinke S. Long-term results of implant-supported over-dentures retained by double crowns: a practice-based retrospective study after minimally 10 years follow-up. Clin Oral Implants Res 2012;24: 1281-7. 11. Hultén J, Tillström B, Nilner K. Long term clinical evaluation of conical crown retained dentures. Swed Dent J 1993;17:225-34. 12. Wenz HJ, Lehmann KM. A telescopic crown concept for the restoration of the partially edentulous arch: the Marburg double crown system. Int J Prosthodont 1998; 11:541-50. 13. Wenz HJ, Hertrampf K, Lehmann KM. Clinical longevity of removable partial dentures retained by telescopic crowns: outcome of the double crown with clearance fit. Int J Prosthodont 2001;14:207-13.
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14. Koller B, Att W, Strub JR. Survival rates of teeth, implants, and double crown-retained removable dental prostheses: a systematic literature review. Int J Prosthodont 2011;24: 109-17. 15. Bergman B, Ericson A, Molin M. Long-term clinical results after treatment with conical crown-retained dentures. Int J Prosthodont 1996;9:533-8. 16. Igarashi Y, Goto T. Ten-year follow-up study of conical crown-retained dentures. Int J Prosthodont 1997;10:149-55. 17. Hofmann E, Behr M, Handel G. Frequency and costs of technical failures of clasp- and double crown-retained removable partial dentures. Clin Oral Investig 2002;6:104-8. 18. Wagner B, Kern M. Clinical evaluation of removable partial dentures 10 years after insertion: success rates, hygienic problems, and technical failures. Clin Oral Investig 2000;4:74-80. 19. Eisenburger M, Gray G, Tschernitschek H. Long-term results of telescopic crown retained denturesea retrospective study. Eur J Prosthodont Restor Dent 2000;8:87-91. 20. Ericson A, Nilsson B, Bergman B. Clinical results in patients provided with conical crown retained dentures. Int J Prosthodont 1990;3:513-21. 21. Hahnel S, Bürgers R, Rosentritt M, Handel G, Behr M. Analysis of veneer failure of removable prosthodontics. Gerodontology 2012;29:e1125-8. 22. Wöstmann B, Balkenhol M, Weber A, Ferger P, Rehmann P. Long-term analysis of telescopic crown retained removable partial dentures: survival and need for maintenance. J Dent 2007;35:939-45. 23. Bergman B, Hugoson A, Olsson CO. Caries, periodontal and prosthetic findings in patients with removable partial dentures: a ten-year longitudinal study. J Prosthet Dent 1982;48:506-14. 24. Kapur KK, Deupree R, Dent RJ, Hasse AL. A randomized clinical trial of two basic removable partial denture designs. Part I: comparisons of five-year success rates and periodontal health. J Prosthet Dent 1994; 72:268-82. 25. Schwarz S, Bernhart G, Hassel AJ, Rammelsberg P. Survival of double-crownretained dentures either tooth-implant or solely implant-supported: an 8-year retrospective study. Clin Implant Dent Relat Res 2012. Dec 6. http://dx.doi.org/10.1111/cid.12023. [Epub]. Corresponding author: Dr Franz Sebastian Schwindling Department of Prosthodontics Heidelberg University Hospital Im Neuenheimer Feld 400 69120 Heidelberg GERMANY E-mail: [email protected] Copyright ª 2014 by the Editorial Council for The Journal of Prosthetic Dentistry.
Schwindling et al