journal of dentistry 42 (2014) 671–676
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/jden
Comparison of incidence of complications and aesthetic performance for posterior metal-free polymer crowns and metal–ceramic crowns: Results from a randomized clinical trial Brigitte Ohlmann a,*, Justo Lorenzo Bermejo b, Peter Rammelsberg a, Marc Schmitter a, Andreas Zentho¨fer a, Thomas Stober a a
Department of Prosthodontics, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany Institute of Medical Biometry and Informatics, University of Heidelberg, Im Neuenheimer Feld 305, 69120 Heidelberg, Germany b
article info
abstract
Article history:
Objectives: The purpose of this randomized clinical study was to evaluate the clinical
Received 7 November 2013
performance of posterior, metal-free polymer crowns after follow-up for up to six years,
Received in revised form
and to compare it with the performance of metal–ceramic crowns.
17 February 2014
Methods: Eighty single crowns, manufactured from a polymer composite resin, were set on
Accepted 1 March 2014
posterior teeth. Half of these received a glass–fibre framework (group 1) whereas half were prepared without framework stabilization (group 2). As the control group, 40 conventional metal–ceramic crowns were inserted. Primary endpoints were incidence of complications,
Keywords:
investigated on a time-to-event basis, plaque status, and aesthetic performance.
Posterior
Results: Thirty clinically relevant complications occurred after a median time of 2.3 years.
Polymer
Median follow-up time was four years. The most frequent complications were delamination
Crowns
(n = 24) and root-canal treatment (n = 4) of the crowns; the incidence of complications was
Clinical
not significantly different among crown materials ( p = 0.60). Twenty crowns had to be
Randomized
replaced (six polymer crowns in group 1, nine polymer crowns in group 2, four crowns in the control group, and one tooth (in group 1) had to be extracted). Mean plaque and gingival indexes for the test groups did not differ from those for the control group. Conclusions: Within a median follow-up period of four years, the clinical performance of posterior polymer crowns with and without a glass–fibre framework was not significantly different from that of metal–ceramic crowns, although the number of catastrophic failures of composite crowns was higher than that of the metal–ceramic crowns. Clinical significance: On the basis of the study results, posterior polymer crowns may be an alternative to metal–ceramic crowns, although additional research is needed before they can be recommended, without reservation, as permanent restorations. # 2014 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +49 6221 568799; fax: +49 6221 561775. E-mail address: [email protected] (B. Ohlmann). http://dx.doi.org/10.1016/j.jdent.2014.03.002 0300-5712/# 2014 Elsevier Ltd. All rights reserved.
672
1.
journal of dentistry 42 (2014) 671–676
Introduction
Although favourable clinical results have been obtained for metal and metal–ceramic crowns,1,2 the desire for aesthetic metal-free crowns has led to increased research into toothcoloured materials. Because the incidence of failure was high for early allceramic restorations,3 especially chipping of zirconia restorations,4,5 composite resin materials were used as alternatives. Although promising results were obtained for class I or class II restorations, on which most clinical studies are based,6–8 composite resin complete crowns had a bad reputation and were not recommended for permanent restorations,9,10 primarily because of their unstable aesthetics11 and high wear,11–13 compared with all-ceramic crowns, and the tendency of plaque to accumulate.13,14 Recent advances in composite resin materials have improved their properties, however, and it seemed possible that polymer composites resin could be an interesting alternative for permanent restorations, with such advantages as simple laboratory procedure and the possibility of repair. Although initial, promising, results from clinical studies of metal-free polymer crowns have been reported,15 other results still suggest limited use in permanent restorations because of the high incidence of complications13 with the most common mode of failure being fracture of the crowns. Because in vitro results suggest fracture resistance is greater for glass–fibre reinforced posterior single molar crowns,16 it may be possible to reduce the incidence of fractures of composite resin crowns. Lack of randomized control groups prevents unbiased comparison with conventional metal–ceramic crowns, however. Thus, the objective of this prospective clinical study was assessment of the clinical performance of a microfilled polymeric material (Trend HP1), with or without fibre network stabilization, for manufacture of posterior crowns, compared with a metal–ceramic crown control group, after up to six years of follow-up. The tested null hypothesis was equal incidence of complications in the three groups.
2.
Materials and methods
Study participants were included on the basis of a clinical need for replacement of single teeth with complete-coverage restorations. All patients in the study group gave informed consent and the university’s review board approved the study (L-317/2002). Criteria for excluding patients from the study were: being under the age of 18, being incapable of taking out a contract, pregnancy or lactation, clenching or grinding of teeth, or known allergic reaction to the materials used, all evaluated from answers to specific questions by the examiner. Constant unacceptable oral hygiene status (plaque index = 3) was also defined as an exclusion criterion. Root-filled teeth were included in the study. The study group consisted of 66 patients (37 females and 29 males) aged between 22 and 73 years (mean age 46 years). The 66 patients received a total of 120 posterior single crowns, divided into three groups: 40 polymer crowns with
framework stabilisation (group 1), 40 polymer crowns without framework stabilisation (group 2), and 40 metal–ceramic crowns (control group). Patients received a maximum of three crowns. If three crowns were inserted in one patient, one crown from each of the two test groups and from the control group was randomly assigned to the abutment teeth. For patients receiving two posterior crowns, crowns from different groups were randomly assigned to the abutment teeth. The groups were not age or sex-balanced. Clinical treatment and laboratory procedures were standardized and all commercial products were used in accordance with the manufacturers’ recommendations. Damaged teeth were restored with the core-build up material Rebilda SC1 (Voco GmbH, Cuxhaven, Germany). Reduction of the occlusal surface was a minimum of 1.5 mm, and axial reduction (chamfer design) was set at 0.8 mm. Impressions of the prepared teeth were taken with polyether material (Impregum1; 3MEspe, Seefeld, Germany). The polymer crowns were made of a polymeric material (Trend HP1; Ivoclar Vivadent, Ellwangen, Germany). Polymer crowns of group 1 received a glass–fibre framework (Vectris1; Ivoclar Vivadent), whereas polymer crowns of group 2 were made without additional stabilization. As control group, metal–ceramic crowns (IPS d.Sign961; IPS d.Sign1; Ivoclar Vivadent) were made. Manufacturing procedures and clinical steps are described in detail in the previous publication reporting one-year results.17 The polymer crowns were cemented with resin cement (Variolink1 II; Ivoclar Vivadent) and the metal–ceramic crowns were cemented by use of a hybrid cement (Protec cem1; Ivoclar Vivadent). After cementation, all patients received brief instruction on oral hygiene. Recalls were scheduled after two weeks (recorded as ‘‘baseline’’) and then yearly up to six years. Clinical evaluation was performed by a dentist who was not involved in original treatment of the patient. Documentation included sensitivity and percussion tests, gingival index (GI) and plaque index (PI),18 wear of remaining teeth, static and dynamic contacts, antagonistic material, antagonistic support, and dentists’ subjective evaluation of surface gloss. Complications, for example caries, endodontic treatment, fractures of the facing or core material, debonding, and discolouration, were recorded on the basis of USPHS criteria.19 The aesthetic performance of the crowns was subjectively evaluated by use of visual rating scales (VAS), from 0 (completely inadequate) to 10 (perfect). Patients and examiners were unaware of the previous results.
2.1.
Statistical analysis
The effect of crown material on PI, GI, and aesthetic performance was investigated by use of Wilcoxon two-sample tests. These three outcome variables were investigated at baseline and after 48 months. Survival time was calculated from the insertion date to the date of any or repairable complications. For patients without complications, survival time was censored at last contact. Multivariate Cox regression analysis was used to identify risk factors for any complications
journal of dentistry 42 (2014) 671–676
673
and for repairable complications. Within-patient clustering of crowns was taken into account by incorporating a random patient effect in the Cox model. Exploratory investigation of plaque differences was also conducted. The level of significance was set at 5%. Probability values were not corrected for multiplicity. Assuming an average incidence of complications of 0.25, this study, with 40 samples per group, has statistical power of approximately 0.8 to identify a 0.30 difference in the incidence of complications (type I error 0.05, uncorrected chisquared test). Statistical analysis was performed by use of SAS Version 9.2 (SAS Institute Inc., NC, USA).
3.
Results
3.1.
Incidence of complications
Nine crowns had to be excluded because patients failed to keep appointments. Thus, a total of 111 crowns (36 crowns in group 1, 38 crowns in group 2, and 37 crowns in the control group) were included in statistical analysis of the incidence of complications. Median follow-up time was four years. After a median time of 2.3 years, a total of 30 clinically relevant complications had occurred: (A) Twenty-one complete failures: The twenty-one complete failures comprised nineteen expanded delaminations or fractures (six polymer crowns in group 1, nine polymer crowns in group 2, and four crowns in the control group) (Fig. 1), one loosened crown in the control group which could not be recemented, and one tooth in group 1 which had to be extracted because of unsuccessful rootcanal treatment. (B) Nine minor failures: Five crowns with minor delaminations (one in group 1, two in group 2, and two in the control group) could be repaired with composite resin (Fig. 2).
Fig. 2 – Repairable delamination of a polymer crown.
In the first year, endodontic problems occurred in each group (two in group 1, one in group 2, and one in the control group) and were successfully handled by root-canal treatment. Four crowns became loose in the first year (three in group 2, one in the control group), and were successfully recemented. All of these successfully recemented crowns later suffered from minor or major delaminations and were included as complete or minor failures in the statistics. Results from statistical analysis on a time-to-event basis are summarized in Table 1. The incidence of complications was highest for crowns inserted in patients aged 51–60 years (n = 27 with 11 complications and eight repairable complications), but age differences did not reach statistical significance. The incidence of any complications was lower for female patients than for males. Neither the rate of wear of the remaining teeth ( p 0.76), the antagonistic support ( p 0.36), the antagonistic material ( p 0.26), nor the presence of dynamic ( p 0.58) or static ( p = 0.33) contacts demonstrated a significant influence of the complication rate. Overall incidence of complications was 26% lower for metal–ceramic crowns (HR = 0.74) and 16% higher for polymer crowns without Vectris than for polymer crowns with Vectris (reference), but differences were not statistically significant ( p = 0.60 for any complication and p = 0.33 for repairable complications). The random patient effect included in the Cox regression was not statistically significant.
3.2. Plaque accumulation, gingival health, and aesthetic performance after four years
Fig. 1 – Irreparable fracture of a polymer crown.
Forty crowns had to be excluded from statistical analysis of plaque accumulation, gingival health, and aesthetic performance because the patients were not examined. Thus, a total of 80 crowns (25 crowns in group 1, 29 crowns in group 2, and 26 crowns in the control group) were included in the statistical analysis. After four years in service, mean values of the PI were 0.56 (SD: 0.73) for group 1 and 0.63 (SD: 0.76) for group 2; these were not significantly different ( p 0.25) from that for the control
674
Table 1 – Estimated hazard ratios for any complications and repairable complications, on the basis of a Cox regression model. Characteristic
Age
Rate of wear of remaining teeth
Antagonistic support Antagonistic material
Presence of dynamic occlusal contacts
Presence of static occlusal contacts
Crown material
Vitality of the teeth
Degree of tooth mobility
Crowns
Any complication Events
p value
Hazard ratio
95% confidence interval
Reference 2.60 4.52 1.76
24–40 41–50 51–60 61–77
26 41 27 26
2 10 11 7
0.11
Male Female
50 69
16 14
0.05
No clinical Minor anterior Minor anterior and posterior Major wear/dentine exposure
13 35 42 30
5 8 9 8
0.76
113 7 32 50 38
28 2 8 11 11
0.36
No Yes
66 54
17 13
0.58
No Yes
16 104
2 28
0.33
Polymer crowns with Vectris Polymer crowns without Vectris Metal–ceramic crowns
40 40 40
10 12 8
0.60
Vital teeth Root filled teeth
76 44
17 13
0.53
0 1 2
77 42 1
19 10 1
0.48
Periodontal Combined/gingival Natural tooth/metal Ceramic Composite/combination
Repairable complication
0.26
Events
p value
Hazard ratio
95% confidence interval
1 5 8 5
0.17
0.57–11.9 1.00–20.4 0.35–8.75
Reference 2.47 6.34 2.96
0.29–21.2 0.79–50.8 0.35–25.4
Reference 0.48
10 9
0.18
0.23–1.00
Reference 0.54
0.22–1.83
Reference 0.71 0.62 0.55
3 4 7 5
0.94
0.23–2.27 0.21–1.85 0.18–1.70
Reference 0.77 0.85 0.65
0.17–3.45 0.22–3.29 0.16–2.74
0.90
Reference 1.96 Reference 0.55 1.09
0.22–1.40 0.44–2.71
18 1 7 5 7
Reference 0.81
10 9
0.85
0.39–1.70
Reference 2.06
0.48–8.69
0 19
– –
– –
Reference 1.16 0.74
6 9 4
0.33
0.50–2.70 0.29–1.87
Reference 1.55 0.65
0.55–4.36 0.18–2.31
Reference 1.26
10 9
0.31
0.61–2.61
Reference 1.59
0.65–3.92
Reference 0.97 3.39
12 6 1
0.27
0.44–2.10 0.45–25.6
Reference 0.85 4.76
0.32–2.26 0.61–37.0
0.46–8.29
0.15
Reference 1.13 Reference 0.32 0.74
0.10–1.03 0.26–2.12
Reference 1.09
0.44–2.68
0.15–8.52
– –
journal of dentistry 42 (2014) 671–676
Gender
Level
journal of dentistry 42 (2014) 671–676
Fig. 3 – Plaque index (PI) after 4 years.
Fig. 4 – Aesthetic performance after 4 years.
group (0.40; SD: 0.75) (Fig. 3). Mean GI were 0.56 (SD: 0.81) for group 1 and 0.53 (SD: 0.77) for group 2, also not significantly different from that for the control group (0.35; SD: 0.59) ( p 0.51). Patients’ and dentists’ subjective ratings of aesthetic performance are given in Fig. 4; there were no statistically significant differences between groups ( p 0.16).
4.
Discussion
If polymer crowns are to be used as permanent restorations, they must meet the standards of conventional metal or metal– ceramic crowns. The results of this study reveal clinical performance of polymer crowns was not significantly different from that of metal–ceramic crowns, irrespective of the use of an additional framework, although the number of crowns which had to be replaced in the test groups was higher. This,
675
also, was in accordance with results for polymer crowns in other studies13,15 and with results for metal–ceramic crowns.20 Some critical aspects have to be considered in order to allow clinically relevant conclusions. First, some important clinical parameters such as the amount of residual tooth structure21,22 (e.g. the percentage of intact dentine) or the clinical examination of parafunctional habits or the presence of occlusal nightguards,23 were not investigated in the present study. Furthermore, root-filled teeth as well as teeth after sufficient periodontic treatment were included in this study. All these factors may have an influence on the survival and complication rate and this has to be kept in mind when interpreting the results of this study. With regard to the effect of the endodontic status of the restored teeth Jongsma et al.24 demonstrated in their study that survival of restorations on vital teeth was higher than that of restorations on endodontically treated teeth, although these differences were not statistically significant. The results of our study also demonstrated there were no significant differences between survival on endodontically treated and vital teeth, although the risk was slightly increased, in agreement with the results of Jongsma et al.24 Accumulation of plaque by polymer crowns after four years was not significantly different from that by metal–ceramic crowns. This contrasts with results obtained after 12 months, when plaque accumulation by polymer crowns with a fibre framework was significantly greater3 than for metal–ceramic crowns. This might be because of better oral hygiene or because evaluation of plaque index is subjective. Some critical aspects must be considered when discussing the plaque accumulation and gingival health results of this study, however. First, although the number of drop-outs during the six-year observation period was comparable with that for other clinical studies,25 the number of drop-outs up to the four-year appointment was relatively high, and this suggests caution in interpreting the results of plaque accumulation or gingival health. The results for incidence of complications include the time factor, and thus the number of drop-outs was acceptable. Moreover, the study enables comparison of polymer crowns and metal–ceramic crowns, the treatment of choice, and thus, the data become important for interpretation of the clinical success of polymer crowns. Apart from complete failures, the important criterion for clinical success of crowns is the absence of complications. The most frequent complication of polymer crowns seems to be delamination and fracture of non-reinforced crowns. For metal–ceramic crowns of the control group also, however, the number of delaminations was comparable with other data for chipping or facing of metal–ceramic restorations.26 Regarding the effect of fibre reinforcement, this study revealed no clinically relevant effect of fibre reinforcement on the survival of posterior single crowns. Thus, the results of this study are in accordance with the conclusion of Behr et al.14 that single molar composite crowns do not benefit from fibre reinforcement. Because the number of failures or complications, may increase over time, however, the crowns must be evaluated over a longer period to enable valid prediction of the long-term clinical performance of these restorations. Moreover, additional research is needed to clarify the rate of wear of polymer
676
journal of dentistry 42 (2014) 671–676
crowns before they can recommended, without reservation, as permanent restorations, especially as another important aspect of reliable clinical trials, single or double blinding – which was not used in this study – should be considered in further research to increase internal validity and reduce the risk of examiner or patient biases.27
5.
Conclusions
Within a 48–72-month observation period, the results of this study reveal that the clinical performance of polymer crowns with or without fibre reinforcement were not significantly different from that of metal–ceramic crowns, although the number of catastrophic failures of composite crowns were higher compared with that of metal–ceramic crowns. Additional research is needed before they can be recommended, without reservation, as permanent restorations.
Acknowledgement We are grateful to Ivoclar Vivadent, Ellwangen, Germany for supplying the study materials and for supporting this study.
references
1. Donovan T, Simonsen RJ, Guertin G, Tucker RV. Retrospective clinical evaluation of 1,314 cast gold restorations in service from 1 to 52 years. Journal of Esthetic and Restorative Dentistry 2004;16:194–204. 2. Leempoel PJ, Eschen S, De Haan AF, Van’t Hof MA. An evaluation of crowns and bridges in a general dental practice. Journal of Oral Rehabilitation 1985;12:515–28. 3. El-Mowafy O, Brochu JF. Longevity and clinical performance of IPS-Empress ceramic restorations—a literature review. Journal of the Canadian Dental Association 2002;68:233–7. 4. Schwarz S, Schroder C, Hassel A, Bomicke W, Rammelsberg P. Survival and chipping of zirconia-based and metal– ceramic implant-supported single crowns. Clinical Implant Dentistry and Related Research 2011. 5. Sailer I, Gottnerb J, Kanelb S, Hammerle CH. Randomized controlled clinical trial of zirconia–ceramic and metal– ceramic posterior fixed dental prostheses: a 3-year followup. International Journal of Prosthodontics 2009;22:553–60. 6. Pallesen U, van Dijken JW, Halken J, Hallonsten AL, Hoigaard R. Longevity of posterior resin composite restorations in permanent teeth in Public Dental Health Service: a prospective 8 years follow up. Journal of Dentistry 2013;41:297–306. 7. da Rosa Rodolpho PA, Cenci MS, Donassollo TA, Loguercio AD, Demarco FF. A clinical evaluation of posterior composite restorations: 17-year findings. Journal of Dentistry 2006;34:427–35. 8. Bernardo M, Luis H, Martin MD, Leroux BG, Rue T, Leitao J, et al. Survival and reasons for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial. Journal of the American Dental Association 2007;138:775–83.
9. Behr M, Rosentritt M, Handel G. Fiber-reinforced composite crowns and FPDs: a clinical report. International Journal of Prosthodontics 2003;16:239–43. 10. Bohlsen F, Kern M. Clinical outcome of glass–fiberreinforced crowns and fixed partial dentures: a three-year retrospective study. Quintessence International 2003;34:493–6. 11. Vanoorbeek S, Vandamme K, Lijnen I, Naert I. Computeraided designed/computer-assisted manufactured composite resin versus ceramic single-tooth restorations: a 3-year clinical study. International Journal of Prosthodontics 2010;23:223–30. 12. Kern M, Strub JR, Lu XY. Wear of composite resin veneering materials in a dual-axis chewing simulator. Journal of Oral Rehabilitation 1999;26:372–8. 13. Lehmann F, Spiegl K, Eickemeyer G, Rammelsberg P. Adhesively luted, metal-free composite crowns after five years. Journal of Adhesive Dentistry 2009;11:493–8. 14. Behr M, Rosentritt M, Latzel D, Handel G. Fracture resistance of fiber-reinforced vs. non-fiber-reinforced composite molar crowns. Clinical Oral Investigation 2003;7:135–9. 15. Rammelsberg P, Spiegl K, Eickemeyer G, Schmitter M. Clinical performance of metal-free polymer crowns after 3 years in service. Journal of Dentistry 2005;33:517–23. 16. Lehmann F, Eickemeyer G, Rammelsberg P. Fracture resistance of metal-free composite crowns-effects of fiber reinforcement, thermal cycling, and cementation technique. Journal of Prosthetic Dentistry 2004;92:258–64. 17. Ohlmann B, Dreyhaupt J, Schmitter M, Gabbert O, Hassel A, Rammelsberg P. Clinical performance of posterior metalfree polymer crowns with and without fiber reinforcement: one-year results of a randomised clinical trial. Journal of Dentistry 2006;34:757–62. 18. Lo¨e H. The gingival index, the plaque index and the retention index system. Journal of Periodontology 1967;38:610–6. 19. Ryge G. Clinical criteria. International Dental Journal 1980;30:347–58. 20. Bader JD, Shugars DA. Summary review of the survival of single crowns. General Dentistry 2009;57:74–81. 21. Nam SH, Chang HS, Min KS, Lee Y, Cho HW, Bae JM. Effect of the number of residual walls on fracture resistances, failure patterns, and photoelasticity of simulated premolars restored with or without fiber-reinforced composite posts. Journal of Endodontics 2010;36:297–301. 22. Schmitter M, Mussotter K, Ohlmann B, Gilde H, Rammelsberg P. Dependence of in vitro fracture strength of adhesive core buildup and crown complexes on preparation design and cementation technique. Journal of Adhesive Dentistry 2008;10:145–50. 23. Koenig V, Vanheusden AJ, Le Goff SO, Mainjot AK. Clinical risk factors related to failures with zirconia-based restorations: an up to 9-year retrospective study. Journal of Dentistry 2013;41:1164–74. 24. Jongsma LA, Kleverlaan CJ, Feilzer AJ. Clinical success and survival of indirect resin composite crowns: results of a 3year prospective study. Dental Materials 2012;28:952–60. 25. Vallittu PK. Survival rates of resin-bonded, glass fiberreinforced composite fixed partial dentures with a mean follow-up of 42 months: a pilot study. Journal of Prosthetic Dentistry 2004;91:241–6. 26. Behr M, Winklhofer C, Schreier M, Zeman F, Kobeck C, Brauer I, et al. Risk of chipping or facings failure of metal ceramic fixed partial prostheses—a retrospective data record analysis. Clinical Oral Investigation 2012;16:401–5. 27. Cioffi I, Farella M. Quality of randomised controlled trials in dentistry. International Dental Journal 2011;61:37–42.
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/jden
Comparison of incidence of complications and aesthetic performance for posterior metal-free polymer crowns and metal–ceramic crowns: Results from a randomized clinical trial Brigitte Ohlmann a,*, Justo Lorenzo Bermejo b, Peter Rammelsberg a, Marc Schmitter a, Andreas Zentho¨fer a, Thomas Stober a a
Department of Prosthodontics, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany Institute of Medical Biometry and Informatics, University of Heidelberg, Im Neuenheimer Feld 305, 69120 Heidelberg, Germany b
article info
abstract
Article history:
Objectives: The purpose of this randomized clinical study was to evaluate the clinical
Received 7 November 2013
performance of posterior, metal-free polymer crowns after follow-up for up to six years,
Received in revised form
and to compare it with the performance of metal–ceramic crowns.
17 February 2014
Methods: Eighty single crowns, manufactured from a polymer composite resin, were set on
Accepted 1 March 2014
posterior teeth. Half of these received a glass–fibre framework (group 1) whereas half were prepared without framework stabilization (group 2). As the control group, 40 conventional metal–ceramic crowns were inserted. Primary endpoints were incidence of complications,
Keywords:
investigated on a time-to-event basis, plaque status, and aesthetic performance.
Posterior
Results: Thirty clinically relevant complications occurred after a median time of 2.3 years.
Polymer
Median follow-up time was four years. The most frequent complications were delamination
Crowns
(n = 24) and root-canal treatment (n = 4) of the crowns; the incidence of complications was
Clinical
not significantly different among crown materials ( p = 0.60). Twenty crowns had to be
Randomized
replaced (six polymer crowns in group 1, nine polymer crowns in group 2, four crowns in the control group, and one tooth (in group 1) had to be extracted). Mean plaque and gingival indexes for the test groups did not differ from those for the control group. Conclusions: Within a median follow-up period of four years, the clinical performance of posterior polymer crowns with and without a glass–fibre framework was not significantly different from that of metal–ceramic crowns, although the number of catastrophic failures of composite crowns was higher than that of the metal–ceramic crowns. Clinical significance: On the basis of the study results, posterior polymer crowns may be an alternative to metal–ceramic crowns, although additional research is needed before they can be recommended, without reservation, as permanent restorations. # 2014 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +49 6221 568799; fax: +49 6221 561775. E-mail address: [email protected] (B. Ohlmann). http://dx.doi.org/10.1016/j.jdent.2014.03.002 0300-5712/# 2014 Elsevier Ltd. All rights reserved.
672
1.
journal of dentistry 42 (2014) 671–676
Introduction
Although favourable clinical results have been obtained for metal and metal–ceramic crowns,1,2 the desire for aesthetic metal-free crowns has led to increased research into toothcoloured materials. Because the incidence of failure was high for early allceramic restorations,3 especially chipping of zirconia restorations,4,5 composite resin materials were used as alternatives. Although promising results were obtained for class I or class II restorations, on which most clinical studies are based,6–8 composite resin complete crowns had a bad reputation and were not recommended for permanent restorations,9,10 primarily because of their unstable aesthetics11 and high wear,11–13 compared with all-ceramic crowns, and the tendency of plaque to accumulate.13,14 Recent advances in composite resin materials have improved their properties, however, and it seemed possible that polymer composites resin could be an interesting alternative for permanent restorations, with such advantages as simple laboratory procedure and the possibility of repair. Although initial, promising, results from clinical studies of metal-free polymer crowns have been reported,15 other results still suggest limited use in permanent restorations because of the high incidence of complications13 with the most common mode of failure being fracture of the crowns. Because in vitro results suggest fracture resistance is greater for glass–fibre reinforced posterior single molar crowns,16 it may be possible to reduce the incidence of fractures of composite resin crowns. Lack of randomized control groups prevents unbiased comparison with conventional metal–ceramic crowns, however. Thus, the objective of this prospective clinical study was assessment of the clinical performance of a microfilled polymeric material (Trend HP1), with or without fibre network stabilization, for manufacture of posterior crowns, compared with a metal–ceramic crown control group, after up to six years of follow-up. The tested null hypothesis was equal incidence of complications in the three groups.
2.
Materials and methods
Study participants were included on the basis of a clinical need for replacement of single teeth with complete-coverage restorations. All patients in the study group gave informed consent and the university’s review board approved the study (L-317/2002). Criteria for excluding patients from the study were: being under the age of 18, being incapable of taking out a contract, pregnancy or lactation, clenching or grinding of teeth, or known allergic reaction to the materials used, all evaluated from answers to specific questions by the examiner. Constant unacceptable oral hygiene status (plaque index = 3) was also defined as an exclusion criterion. Root-filled teeth were included in the study. The study group consisted of 66 patients (37 females and 29 males) aged between 22 and 73 years (mean age 46 years). The 66 patients received a total of 120 posterior single crowns, divided into three groups: 40 polymer crowns with
framework stabilisation (group 1), 40 polymer crowns without framework stabilisation (group 2), and 40 metal–ceramic crowns (control group). Patients received a maximum of three crowns. If three crowns were inserted in one patient, one crown from each of the two test groups and from the control group was randomly assigned to the abutment teeth. For patients receiving two posterior crowns, crowns from different groups were randomly assigned to the abutment teeth. The groups were not age or sex-balanced. Clinical treatment and laboratory procedures were standardized and all commercial products were used in accordance with the manufacturers’ recommendations. Damaged teeth were restored with the core-build up material Rebilda SC1 (Voco GmbH, Cuxhaven, Germany). Reduction of the occlusal surface was a minimum of 1.5 mm, and axial reduction (chamfer design) was set at 0.8 mm. Impressions of the prepared teeth were taken with polyether material (Impregum1; 3MEspe, Seefeld, Germany). The polymer crowns were made of a polymeric material (Trend HP1; Ivoclar Vivadent, Ellwangen, Germany). Polymer crowns of group 1 received a glass–fibre framework (Vectris1; Ivoclar Vivadent), whereas polymer crowns of group 2 were made without additional stabilization. As control group, metal–ceramic crowns (IPS d.Sign961; IPS d.Sign1; Ivoclar Vivadent) were made. Manufacturing procedures and clinical steps are described in detail in the previous publication reporting one-year results.17 The polymer crowns were cemented with resin cement (Variolink1 II; Ivoclar Vivadent) and the metal–ceramic crowns were cemented by use of a hybrid cement (Protec cem1; Ivoclar Vivadent). After cementation, all patients received brief instruction on oral hygiene. Recalls were scheduled after two weeks (recorded as ‘‘baseline’’) and then yearly up to six years. Clinical evaluation was performed by a dentist who was not involved in original treatment of the patient. Documentation included sensitivity and percussion tests, gingival index (GI) and plaque index (PI),18 wear of remaining teeth, static and dynamic contacts, antagonistic material, antagonistic support, and dentists’ subjective evaluation of surface gloss. Complications, for example caries, endodontic treatment, fractures of the facing or core material, debonding, and discolouration, were recorded on the basis of USPHS criteria.19 The aesthetic performance of the crowns was subjectively evaluated by use of visual rating scales (VAS), from 0 (completely inadequate) to 10 (perfect). Patients and examiners were unaware of the previous results.
2.1.
Statistical analysis
The effect of crown material on PI, GI, and aesthetic performance was investigated by use of Wilcoxon two-sample tests. These three outcome variables were investigated at baseline and after 48 months. Survival time was calculated from the insertion date to the date of any or repairable complications. For patients without complications, survival time was censored at last contact. Multivariate Cox regression analysis was used to identify risk factors for any complications
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and for repairable complications. Within-patient clustering of crowns was taken into account by incorporating a random patient effect in the Cox model. Exploratory investigation of plaque differences was also conducted. The level of significance was set at 5%. Probability values were not corrected for multiplicity. Assuming an average incidence of complications of 0.25, this study, with 40 samples per group, has statistical power of approximately 0.8 to identify a 0.30 difference in the incidence of complications (type I error 0.05, uncorrected chisquared test). Statistical analysis was performed by use of SAS Version 9.2 (SAS Institute Inc., NC, USA).
3.
Results
3.1.
Incidence of complications
Nine crowns had to be excluded because patients failed to keep appointments. Thus, a total of 111 crowns (36 crowns in group 1, 38 crowns in group 2, and 37 crowns in the control group) were included in statistical analysis of the incidence of complications. Median follow-up time was four years. After a median time of 2.3 years, a total of 30 clinically relevant complications had occurred: (A) Twenty-one complete failures: The twenty-one complete failures comprised nineteen expanded delaminations or fractures (six polymer crowns in group 1, nine polymer crowns in group 2, and four crowns in the control group) (Fig. 1), one loosened crown in the control group which could not be recemented, and one tooth in group 1 which had to be extracted because of unsuccessful rootcanal treatment. (B) Nine minor failures: Five crowns with minor delaminations (one in group 1, two in group 2, and two in the control group) could be repaired with composite resin (Fig. 2).
Fig. 2 – Repairable delamination of a polymer crown.
In the first year, endodontic problems occurred in each group (two in group 1, one in group 2, and one in the control group) and were successfully handled by root-canal treatment. Four crowns became loose in the first year (three in group 2, one in the control group), and were successfully recemented. All of these successfully recemented crowns later suffered from minor or major delaminations and were included as complete or minor failures in the statistics. Results from statistical analysis on a time-to-event basis are summarized in Table 1. The incidence of complications was highest for crowns inserted in patients aged 51–60 years (n = 27 with 11 complications and eight repairable complications), but age differences did not reach statistical significance. The incidence of any complications was lower for female patients than for males. Neither the rate of wear of the remaining teeth ( p 0.76), the antagonistic support ( p 0.36), the antagonistic material ( p 0.26), nor the presence of dynamic ( p 0.58) or static ( p = 0.33) contacts demonstrated a significant influence of the complication rate. Overall incidence of complications was 26% lower for metal–ceramic crowns (HR = 0.74) and 16% higher for polymer crowns without Vectris than for polymer crowns with Vectris (reference), but differences were not statistically significant ( p = 0.60 for any complication and p = 0.33 for repairable complications). The random patient effect included in the Cox regression was not statistically significant.
3.2. Plaque accumulation, gingival health, and aesthetic performance after four years
Fig. 1 – Irreparable fracture of a polymer crown.
Forty crowns had to be excluded from statistical analysis of plaque accumulation, gingival health, and aesthetic performance because the patients were not examined. Thus, a total of 80 crowns (25 crowns in group 1, 29 crowns in group 2, and 26 crowns in the control group) were included in the statistical analysis. After four years in service, mean values of the PI were 0.56 (SD: 0.73) for group 1 and 0.63 (SD: 0.76) for group 2; these were not significantly different ( p 0.25) from that for the control
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Table 1 – Estimated hazard ratios for any complications and repairable complications, on the basis of a Cox regression model. Characteristic
Age
Rate of wear of remaining teeth
Antagonistic support Antagonistic material
Presence of dynamic occlusal contacts
Presence of static occlusal contacts
Crown material
Vitality of the teeth
Degree of tooth mobility
Crowns
Any complication Events
p value
Hazard ratio
95% confidence interval
Reference 2.60 4.52 1.76
24–40 41–50 51–60 61–77
26 41 27 26
2 10 11 7
0.11
Male Female
50 69
16 14
0.05
No clinical Minor anterior Minor anterior and posterior Major wear/dentine exposure
13 35 42 30
5 8 9 8
0.76
113 7 32 50 38
28 2 8 11 11
0.36
No Yes
66 54
17 13
0.58
No Yes
16 104
2 28
0.33
Polymer crowns with Vectris Polymer crowns without Vectris Metal–ceramic crowns
40 40 40
10 12 8
0.60
Vital teeth Root filled teeth
76 44
17 13
0.53
0 1 2
77 42 1
19 10 1
0.48
Periodontal Combined/gingival Natural tooth/metal Ceramic Composite/combination
Repairable complication
0.26
Events
p value
Hazard ratio
95% confidence interval
1 5 8 5
0.17
0.57–11.9 1.00–20.4 0.35–8.75
Reference 2.47 6.34 2.96
0.29–21.2 0.79–50.8 0.35–25.4
Reference 0.48
10 9
0.18
0.23–1.00
Reference 0.54
0.22–1.83
Reference 0.71 0.62 0.55
3 4 7 5
0.94
0.23–2.27 0.21–1.85 0.18–1.70
Reference 0.77 0.85 0.65
0.17–3.45 0.22–3.29 0.16–2.74
0.90
Reference 1.96 Reference 0.55 1.09
0.22–1.40 0.44–2.71
18 1 7 5 7
Reference 0.81
10 9
0.85
0.39–1.70
Reference 2.06
0.48–8.69
0 19
– –
– –
Reference 1.16 0.74
6 9 4
0.33
0.50–2.70 0.29–1.87
Reference 1.55 0.65
0.55–4.36 0.18–2.31
Reference 1.26
10 9
0.31
0.61–2.61
Reference 1.59
0.65–3.92
Reference 0.97 3.39
12 6 1
0.27
0.44–2.10 0.45–25.6
Reference 0.85 4.76
0.32–2.26 0.61–37.0
0.46–8.29
0.15
Reference 1.13 Reference 0.32 0.74
0.10–1.03 0.26–2.12
Reference 1.09
0.44–2.68
0.15–8.52
– –
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Gender
Level
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Fig. 3 – Plaque index (PI) after 4 years.
Fig. 4 – Aesthetic performance after 4 years.
group (0.40; SD: 0.75) (Fig. 3). Mean GI were 0.56 (SD: 0.81) for group 1 and 0.53 (SD: 0.77) for group 2, also not significantly different from that for the control group (0.35; SD: 0.59) ( p 0.51). Patients’ and dentists’ subjective ratings of aesthetic performance are given in Fig. 4; there were no statistically significant differences between groups ( p 0.16).
4.
Discussion
If polymer crowns are to be used as permanent restorations, they must meet the standards of conventional metal or metal– ceramic crowns. The results of this study reveal clinical performance of polymer crowns was not significantly different from that of metal–ceramic crowns, irrespective of the use of an additional framework, although the number of crowns which had to be replaced in the test groups was higher. This,
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also, was in accordance with results for polymer crowns in other studies13,15 and with results for metal–ceramic crowns.20 Some critical aspects have to be considered in order to allow clinically relevant conclusions. First, some important clinical parameters such as the amount of residual tooth structure21,22 (e.g. the percentage of intact dentine) or the clinical examination of parafunctional habits or the presence of occlusal nightguards,23 were not investigated in the present study. Furthermore, root-filled teeth as well as teeth after sufficient periodontic treatment were included in this study. All these factors may have an influence on the survival and complication rate and this has to be kept in mind when interpreting the results of this study. With regard to the effect of the endodontic status of the restored teeth Jongsma et al.24 demonstrated in their study that survival of restorations on vital teeth was higher than that of restorations on endodontically treated teeth, although these differences were not statistically significant. The results of our study also demonstrated there were no significant differences between survival on endodontically treated and vital teeth, although the risk was slightly increased, in agreement with the results of Jongsma et al.24 Accumulation of plaque by polymer crowns after four years was not significantly different from that by metal–ceramic crowns. This contrasts with results obtained after 12 months, when plaque accumulation by polymer crowns with a fibre framework was significantly greater3 than for metal–ceramic crowns. This might be because of better oral hygiene or because evaluation of plaque index is subjective. Some critical aspects must be considered when discussing the plaque accumulation and gingival health results of this study, however. First, although the number of drop-outs during the six-year observation period was comparable with that for other clinical studies,25 the number of drop-outs up to the four-year appointment was relatively high, and this suggests caution in interpreting the results of plaque accumulation or gingival health. The results for incidence of complications include the time factor, and thus the number of drop-outs was acceptable. Moreover, the study enables comparison of polymer crowns and metal–ceramic crowns, the treatment of choice, and thus, the data become important for interpretation of the clinical success of polymer crowns. Apart from complete failures, the important criterion for clinical success of crowns is the absence of complications. The most frequent complication of polymer crowns seems to be delamination and fracture of non-reinforced crowns. For metal–ceramic crowns of the control group also, however, the number of delaminations was comparable with other data for chipping or facing of metal–ceramic restorations.26 Regarding the effect of fibre reinforcement, this study revealed no clinically relevant effect of fibre reinforcement on the survival of posterior single crowns. Thus, the results of this study are in accordance with the conclusion of Behr et al.14 that single molar composite crowns do not benefit from fibre reinforcement. Because the number of failures or complications, may increase over time, however, the crowns must be evaluated over a longer period to enable valid prediction of the long-term clinical performance of these restorations. Moreover, additional research is needed to clarify the rate of wear of polymer
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crowns before they can recommended, without reservation, as permanent restorations, especially as another important aspect of reliable clinical trials, single or double blinding – which was not used in this study – should be considered in further research to increase internal validity and reduce the risk of examiner or patient biases.27
5.
Conclusions
Within a 48–72-month observation period, the results of this study reveal that the clinical performance of polymer crowns with or without fibre reinforcement were not significantly different from that of metal–ceramic crowns, although the number of catastrophic failures of composite crowns were higher compared with that of metal–ceramic crowns. Additional research is needed before they can be recommended, without reservation, as permanent restorations.
Acknowledgement We are grateful to Ivoclar Vivadent, Ellwangen, Germany for supplying the study materials and for supporting this study.
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