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onlays
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A retrospective clinical study on the longevity of posterior Class II cast gold inlays/onlays ⁎
A. Mulica, , G. Svendsenb, S.E. Kopperuda a b
Nordic Institute of Dental Materials (NIOM), Oslo, Norway Department of Cariology, Faculty of dentistry, University of Oslo, Oslo, Norway
A R T I C L E I N F O
A B S T R A C T
Keywords: Clinical study Gold inlays Longevity Operative dentistry
Objective: To investigate the longevity and reasons for failure of posterior cast Class II gold inlays and onlays among a group of Norwegian adults. The term inlay was used for both inlays and onlays. Methods: A cohort of 138 patients regularly attending a general practice for check-up were examined in 2016. The patients had a total of 391 posterior gold inlays placed in the period 1970–2015. The inlays were categorized as successful, repaired or failed. Reasons for failure were classified as either “secondary caries”, “fractures”, “lost inlay” or “other”. Participation was voluntary and no compensation was given. Results: The mean age of the patients at placement was 50.8 years (SD: 12.7 yr). Most gold inlays were placed in molars (85.9%) and 14.1% in premolars; 49.4% of the inlays were in the maxilla and the 50.6% in the mandibula. Average length of follow-up was 11.6 years (range: 1–46 years, SD: 7.9); 82.9% were classified as successful, 10.7% as repaired and 6.4% as failed. Reasons for failure were secondary caries (41.3%), lost inlay (25.4%), fractures (23.8%) and other (9.5%). Mean annual failure rate (AFR) was 1.69% for repaired and failed inlays combined. However, if repaired inlays were considered as success, the AFR decreased to 0.57%. Multilevel Cox regression analyses identified low age of the patient and high number of restored surfaces as risk factors for failure. Conclusion: The present retrospective clinical study demonstrated an acceptable annual failure rate for Class II cast gold inlays.
Clinical significance All dental restorations have a limited lifespan and will eventually need to be repaired or replaced. It is important to have in mind that the longevity of gold restorations have not been shown to be superior to that of resin composite, which should still be the first material of choice. However, gold inlays could be considered when the right indications are present. 1. Introduction Changes in restorative treatment and ideology have forced dentists and patients to be faced with an overwhelming number of dental material options for posterior restorations. However, failure of restorations continues to be a problem in dental practice, and it is estimated that about 60% of a dentist’s working day still is attributed to placement and replacement of restorations [1]. Use of amalgam as a dental restorative material has been banned in Norway since 2008, and resin composites have become the almost exclusively used restorative material [2,3]. In ⁎
many parts of the world, the use of amalgam is also decreasing [4–8]. However, for some patients an alternative to resin composites could be desirable [3]. Indirectly placed gold cast restorations have for many years been considered as a durable restorative material with longevity superior to other restorative materials. This assumption may not be sufficiently supported by scientific evidence. First of all, there are few - if any recent papers on longevity of gold inlays. Second, the longevity of gold inlays presented in earlier studies may not be as advantageous compared with what can be achieved with today’s restorative materials and cementation procedures. A review by Hickel and Manhart [9] found annual failure rates (AFR) for cast gold inlays to range from 0% to 5.9%, with a median AFR of 1.2%. In the same study, the median AFR for amalgam, composite and glass-ionomer restorations was 3.3%, 2.2% and 7.7%, respectively. In another review, Manhart et al. [10] found a mean AFR for posterior stress-bearing restorations to be: 3.0% for amalgam, 2.2% for composite, 2.9% for composite inlays, 1.7% for CAD/CAM ceramic restorations and 1.4% for cast gold inlays and onlays. These AFR values may have been impressive at that time, but
Corresponding author. E-mail address: [email protected] (A. Mulic).
https://doi.org/10.1016/j.jdent.2017.12.010 Received 3 July 2017; Received in revised form 8 December 2017; Accepted 16 December 2017 0300-5712/ © 2017 Elsevier Ltd. All rights reserved.
Please cite this article as: MULIC, A., Journal of Dentistry (2017), https://doi.org/10.1016/j.jdent.2017.12.010
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shade in the light of recent studies presenting AFR’s of resin composites around 1–3% [11–14]. Mjör and Medina [15] found that the longevity of cast gold restorations exceeded that of other dental materials present at that time by a factor of two to four. However, that study is based on data on ‘age of failed restorations’; an analysis which has been shown to overestimate the longevity of older materials (e.g. gold inlays) compared to newer materials (e.g. resin composites) [16]. Survival analyses in which the life time of both restorations that have failed and those that remain in service is taken into account, such as Kaplan-Meier statistics, is hitherto the best method for calculating longevity of dental restorations [16,17]. Thus, if gold cast inlays should continue to be a part of dentists’ arsenal of restorative materials, newer studies performed by Kaplan-Meier analyses should be performed. The use of cast gold restorations have been low lately [1,3]. Advances in adhesive technique and escalation in aesthetic demands have increased indications for tooth-coloured restorations. In a recent questionnaire study presenting a patient case with a fractured amalgam restoration in a premolar, only 3.1% of the Norwegian dentists considered to restore the tooth with a gold inlay. Other, more aesthetic, prosthetic options were chosen by 10.9% of the dentists [3]. The manufacturers are steadily offering new tooth-coloured materials with improving properties, both for direct and indirect techniques, as well as materials for CAD/CAM techniques. To ad knowledge to the quality of this old technique, in order to compare and be aware of what to expect from the new materials, the aim of the present study was to investigate the longevity and reasons for failure of posterior Class II gold cast restorations among a group of Norwegian adults in a private practice.
Table 1 Empirical failure rates and 95% confidence interval (95%CI) calculated using KaplanMeier statistics. Time
Failure rate
95% CI
3 years 5 years 7 years 10 years 18 years
0.99 0.98 0.97 0.95 0.88
0.98–1.00 0.96–1.00 0.95–0.99 0.92–0.98 0.80–0.96
2. Material and methods The patient‘s electronic dental records (EDR) and radiological records of a general practice in Norway were used for collecting the data for this study. All Class II gold inlays in premolars and molars of patients attending the dental practice for check-up and follow-up treatment in 2015–2016 were included in the study. The inlays were placed in the time period 1970–2015. In addition, data on 23 patients that were no longer attending the dental practice were extracted from the patient records and included in the study. In these cases the last registered examination at the dental clinic was used as the censoring date. In the present study, the term inlay is used for both inlays and restorations including cusps (onlays). Full golden crowns were excluded. The same practitioner (GS) evaluated the inlays included in the present study as part of the patients’ regular dental and radiological examination. The gold inlays were evaluated based on clinical and radiological examination, and categorized as successful, repaired or failed. Inlays that had previously been repaired or failed were assessed retrospectively based on listings in the dental records, and the dates of replacement and reason for failure were extracted. Reasons for failure were classified as either “secondary caries”, “fractures”, “lost inlay” or “other” (extracted tooth or endodontically treated tooth). Patient-related information, such as gender and age at the time of placement of the restoration, was extracted from the electronic dental records (EDR). The patients’ general risk of failure (due to caries, fractures and other incidences) was estimated by their accumulated DMFT-score over a 20years period (1996–2016), which covered most of the observation period. The reason for this time interval was that the dental clinic started using EDR’s in 1996, providing access to DMFT data. The mean annual failure rate of the investigated restorations was calculated according to the formula (1-y)z = (1-x), in which “y” is the mean annual failure rate and “x” is the total failure rate at z years [18]. Empirical failure rates at 3, 5, 7, 10 and 18 years with 95% CI were calculated using Kaplan-Meier statistics (Table 1). Kaplan-Meier analyses were also used to create survival curves (Fig. 1). The possible dependence of multiple inlays placed in the same patients was taken into account by use of a multi-level approach. The multi-level Cox regression models were fitted with gamma-distributed heterogeneity
Fig. 1. Survival curves for the gold inlays performed by Kaplan Meier statistics. In the statistical material for the green curve, only total replacements were considered as failures, while in the red curve both total replacements and repaired gold inlays were considered as failures. The difference shows the benefit of repair on the longevity of gold inlays. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
using the coxph-function in the software R, presenting a frailty model with time effects on the patient level given by: h(t, X) = h0 (t) exp(βiXij + αj) Here, h0(t) is the baseline hazard that describes the shape of the hazard rate as a function of time, exp(βiXij) is the hazard ratio that describes how the size of the hazard rate depends on the covariates, while αj represents the patient frailty term. The multi-level Cox regression analyses were performed with failure of gold inlay as the dependent variable and the following independent variables: patient’s age, gender, patient‘s risk (total accumulated DMFT-score during 20 years), jaw (mandible vs. maxilla), tooth type (molar vs. premolar), number of surfaces of the inlay and cuspal coverage (no/yes). Collinearity was checked using the criterion VIF < 5 and no independent variables were found to invalidate the analysis. A significance level of 5% was used throughout. IBM SPSS 24.0.0.2 (Statistical Package for the Social Sciences) and R version 3.4.1 (The R Foundation for Statistical Computing) were used to analyse the data. STATA 14.2 (Statistics/Data Analysis) was used to create hazard plots. Participation was voluntary and no compensation was given to the respondents. The implementation of the study was approved by the Regional Committee for Medical Research Ethics in Norway (ID: 2015/ 1324). 2
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3. Results From 1970–2015 a total of 391 Class II posterior gold inlays were placed in 138 patients (81 males and 57 females). The number of inlays in each patient ranged from one to thirteen. About one-third of the patients (n = 44) received only one inlay, 27 (19.6%) patients received two inlays, 26 (18.8%) patients received three and 41 (29.7%) patients received four or more inlays. The distribution of the 391 gold inlays according to gender was 67.8% placed in male (n = 265) and 32.2% placed in female patients (n = 126). The mean age of the patients at placement of the inlays was 50.8 years (SD: 12.7 yr). Most gold inlays were placed in molars (85.9%, n = 334) and 14.1% were placed in premolars. The distribution of inlays was quite similar in the maxilla (49.4%, n = 192) and the mandible (50.6%, n = 197). Almost twothirds of the inlays had cuspal coverage (69.8%). The number of restored surfaces varied from two to five. Average length of follow-up of the inlays was 11.6 years (range: 1–46 years, SD: 7.9). After the individual follow-up period, 82.9% (n = 324) were classified as successful, 10.7% (n = 42) had been repaired and 6.4% (n = 25) were deemed to have failed. Reasons for failure were secondary caries (41.3%), lost inlay (25.4%), fractures (23.8%) and other (9.5%), e.g. endodontic complications. The main reasons for repair (n = 42) were secondary caries and fractures. Mean annual failure rate (AFR) was calculated to be 1.69% for repaired and failed inlays combined. However, if repaired inlays were considered as success, the AFR decreased to 0.57%. This difference is shown in Fig. 1, presenting separate survival curves for these two approaches. Empirical failure rates at different time points are given in Table 1. Multi-level Cox-regression analyses were performed to identify factors related to failure of the gold restorations (Table 2). In the adjusted analyses, increasing age of the patient and increasing number of restored surfaces remained statistically significant. Thus, the patients’ gender, patient‘s risk, the inlay’s location in the jaw and tooth type, and whether there was cuspal coverage or not were not found to be significantly related to the survival of the gold restorations. Hazard plots show that the hazard (risk of failure of gold inlays) for patients older than 50 years was lower than for patient aged below 50 years. Thus, lower risk of failure is expected as the patient gets older (Fig. 2). There was also a clear indication that if the number of surfaces was five, then the hazard (risk of failure) was higher than in inlays with < 5 surfaces. Thus, as the number of surfaces increases, so does the risk of failure and the risk is more prominent if the number of surfaces is above four (Fig. 3).
Fig. 2. Hazard plots based on the Multi-level Cox regression analyses, showing a significantly lower hazard (risk of failure of gold inlays) for patients older than 50 years compared with patient below 50 years.
Fig. 3. Hazard plots based on the Multi-level Cox regression analyses, showing a clear indication that if the number of surfaces was five, then the hazard (risk of failure) was higher than in inlays with less than five surfaces.
Table 2 Multi-level Cox regression analyses of factors related to failure of gold restorations. UNADJUSTED
Age Continous variable Gender Male Female Patient risk (accumulated DMFT) Continous variable Jaw Maxilla Mandible Tooth type Premolar Molar Surfaces Continous variable (2–5) Cuspal coverage No Yes
ADJUSTED
% (n)
HR
95% CI
P-value
HR
95% CI
100 (391)
0.96
0.91
–
67.8 (265) 32.2 (126)
1.18
0.40
100 (391)
1.04
49.4 (192) 50.4 (197)
1.00
0.07
0.91
0.85
–
0.96
< .01
–
3.46
0.76
2.01
0.66
–
6.14
.22
0.94
–
1.16
0.46
1.11
0.98
–
1.25
.10
0.78
0.34
–
1.79
0.56
0.62
0.25
–
1.53
.30
14.1 (55) 85.4 (334)
0.63
0.20
–
1.93
0.42
0.40
0.12
–
1.41
.15
89.0 (348)
1.47
0.93
–
2.33
0.10
2.55
1.19
–
5.43
.02
30.2 (105) 69.8 (243)
1.35
0.54
–
3.39
0.52
0.38
0.08
–
1.91
.24
3
P-value
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fillings. Unfortunately, data on the patients’ bite forces was not possible to extract from the dental records. It may, however, be assumed that gold inlays are a preferable treating option in challenging patients, and therefore, the risk for fracture is higher compared with when placed in patients with e.g. normal occlusion. Fractures were the most frequent cause of failure in a recent systematic review [28] that estimated the survival rates for glass-ceramic and feldspathic porcelain (inlays, onlays and overlays) to be between 92% and 95% after 5 years, and 91% after 10 years. Cuspal coverage was found not to affect the longevity of inlays in our study, but there was a significant impact from the number of restored surfaces. That shows that patients in our study did not benefit from cusp-capping the teeth, but that massively restored teeth were weakened compared to less restored teeth. This is in line with results from several other studies on restoration longevity [29–32]. A recent study investigated the longevity of direct restorations placed by a group of general dental practitioners (n = 24), and concluded that even though the wide variation in annual failure rate exists between the clinicians, the restorations are placed with a satisfactory longevity [33]. The main weakness of our study is that all of the restorations were placed and evaluated retrospectively by one dentist, and therefore the results may not be reassigned to a broad variety of general dentists [17]. The results may depend on the dentist’s skill of the preparations and placing the gold inlays; it may be argued that these restorations may have been placed by operators who might have special interest or skills in this field of operative dentistry. In addition, the thresholds for repairing or replacing a restoration vary widely between operators [1,2,34]. The decision between repairing or replacing may be a reflection of the practitioner‘s attitude towards possibilities for repair e.g. “expensive” gold restorations are rather repaired then replaced. This will again influence the differences in AFR between survival and success. An interesting assumption by Laske el al. [33] and Burke & Lucarotti [35] is that changing dentists leads to a higher replacement rate of fillings. Most of the patients included in the present study have been treated by one dentist for many years, and this may contribute to a higher restorations survival than could be expected for larger team practice with more clinicians treating the same patient. Nevertheless, according to new directions for clinical studies presented by Opdam et al., “the reliability of patient records used for retrospective studies is highly dependent upon the number of individuals who remain patients and receive all their dental treatment in the practice(s) over extended periods of time” [17]. A reasonable approach to strengthen evidence-based information on the longevity of the restorations in dental practice is to design and perform prospective, practice-based studies. However, with the general low use of gold inlays today, such a study would be difficult to perform, and thus by practical reasons today’s conclusions need to be based on retrospective studies. In a recent questionnaire based study investigating the treatment decisions in 2009 among Norwegian dentists [3], more that 50% of the clinicians would never restore a MOD (mesial-occlusal-distal)-cavity on premolars and molars in adult patients with gold inlays. Almost all dentists (99%) included in the questionnaire stated to restore this cavity with composite “Often” or “Always”, which demonstrates that composite has become the dominating material of choice in Norway. Even though aesthetic demands and need for tooth-coloured restorations are increasing, gold inlays are considered as an effective treatment option in posterior teeth. The abovementioned questionnaire [3] revealed that gold inlays were preferred more often than ceramic (CAD/CAM) and composite inlays when restoring the MOD-cavity in a premolar or molar. The clinical assumption is that for patients with severe attrition and high biting forces, as well as replacement of a large amalgam restoration, gold inlay is a preferable treatment. However, the teaching of gold inlays is fading out of the undergraduate program in many dental schools as indirect restorations are preferably tooth-coloured, minimally invasive and adhesive. Therefore, it is likely that in time gold will phase out in dentistry. In general, all restorative treatment weakens the tooth and increases the risk of fractures [32]. Thus, when replacing
4. Discussion In the present retrospective, clinical study, the Class II posterior gold inlays showed high longevity and an acceptable failure rate after up to 20 years. The most common reason for failure was secondary caries. The longevity of dental restorations is dependent upon many different factors, related to the restorative material, the patient and to the dentist [9,11]. Even though limited data are available on the longevity of gold restorations, they are by many dentists considered to be longlasting. This is confirmed by the acceptable mean annual failure rate (AFR) in the present study (0.57% for failed inlays only). Similarly, other studies have shown promising results for gold restorations. Donovan et al. [19] found the survival rate to be 95.4% in a retrospective, clinical study of 1314 gold restorations; where inlays had a failure rate of 4.7% after more than 20 years. These findings have also been confirmed in several other studies where the AFR range from 0% and up to 5.9% [9]. However, the gold restorations are considered to be costly. Compared with amalgam restorations, the cost factor for gold have been calculated to be 3.8 to 6.3 times higher [20]. Consequently, other restorations could be preferred in posterior teeth. In two separate questionnaire studies among Norwegian dentists, gold was suggested for replacing a MOD restoration in an upper premolar by only 3.2% and 0.3% of the dentists respectively, compared with 86% and 94% choosing resin composite, respectively [1,3].The overall use of materials other than amalgam and resin composite in a practice-based network have been shown to be only 5% for both US and Scandinavian dentists when placing restorations in premolars and molars [21]. Resin composite has in many parts of the world replaced amalgam as the dominating material of choice for direct restorations [22,23]. The longevity of posterior composite restorations today is by many researchers considered to be similar to that of amalgams, presenting AFRs of 1–3% [11–14,24]. Beck et al. [14] found in a meta-analysis of prospective studies a mean AFR to be 1.64% after 1–4 years of observation, and 1.97% after 5–19 years. Similar results were reported in a systematic review by Opdam and co-workers: the mean AFR was 1.8% after 5 years, and 2.4% after 10 years [12]. Consequently, the present study showed good longevity of gold inlays. However, the scientific support to claim that gold is superior to composite resin as an alternative for amalgam is still weak. The main reasons for failure of the gold restorations have been tooth fractures, marginal defects, insufficient retention and secondary caries [25]. In the present study, the reasons for failure of the gold inlays were secondary caries, lost inlay, fractures and other (e.g. endodontic complications). This is similar to the resin composites, where the most common biological reason for failure has been reported to be secondary caries and fracture of the restorations [12–14,26]. Secondary caries and fractures predominate as dentists' perceived reasons for replacement of restorations [3]. It may be argued that people who want to pay the high costs for gold restorations are likely more motivated and having a low caries risk. However, a recent population-based cross-sectional study from Norway concluded that behavioural variables (e.g. toothbrushing, sugar soft drink consumption etc.) seem to have greater influence compared with socio-economic variables (household income) [27]. An individual may be at high caries risk, regardless of his/hers financial status. In the present study the patients’ general risk of failure (due to caries, fractures and other incidences) was estimated by their accumulated DMFT-score over a 20-years period (1996–2016). DMFT might not be an optimal parameter for measuring caries risk among adult patients, and this may explain why that factor had no significant influence on the results. One of the main reasons for failures (23.8%) was fractures. The gold inlays are often considered as an effective treatment option in more challenging patients, e.g. in posterior teeth for patients with high masticating forces and for replacement of large, posterior amalgam 4
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large restorations in patients with high biting forces, dentists should prefer durable materials. According to modern dental philosophy and concept of minimal intervention dentistry, repair of any defective restoration, should always be considered as an option. In the present study, 10.7% of the inlays were repaired during the observation period and still in function. The repair process may therefore be considered successful. Other studies have also showed that the longevity of restorations could benefit from being repaired, rather than replaced. A clinical study of composite restorations with 22 years follow-up showed an AFR of 1.9%. If, however, repaired restorations were considered not to be failures, the AFR improved to 0.7% [36]. Opdam et al. [37] have demonstrated a similar reduction of AFR from 1.83% to 0.72% when repair was considered successful in the statistical material. In the present study the AFR decreased from 1.69% to 0.57% when repaired inlays were considered as success.
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Bailit, Economic impact of regulating the use of amalgam restorations, Public Health Rep. 122 (5) (2007) 657–663. [24] S.D. Heintze, V. Rousson, Clinical effectiveness of direct class II restorations − a meta-analysis, J. Adhes. Dent. 14 (5) (2012) 407–431. [25] M. Stoll, K. Sieweke, V. Pieper, A. Stachniss, Longevity of cast gold inlays and partial crowns–a retrospective study at a dental school clinic, Clin. Oral Investig. 3 (2) (1999) 100–104. [26] U. Palotie, M.M. Vehkalahti, Reasons for replacement of restorations: dentists' perceptions, Acta Odontol. Scand. 70 (6) (2012) 485–490. [27] N. Oscarson, I. Espelid, B. Jonsson, Is caries equally distributed in adults? A population-based cross-sectional study in Norway – the TOHNN-study, Acta Odontol. Scand. 75 (8) (2017) 557–563. [28] F.B. Morimoto, M.M. Rebello de Sampaio, N. Braga, M. Sesma, Survival rate of resin and ceramic inlays, onlays, and overlays: a systematic review and meta-analysis, J. Dent. Res. 95 (9) (2016) 985–994. [29] J.P. Van Nieuwenhuysen, W. D'Hoore, J. Carvalho, V. Qvist, Long-term evaluation of extensive restorations in permanent teeth, J. Dent. 31 (6) (2003) 395–405. [30] M. Bernardo, H. Luis, M.D. Martin, B.G. Leroux, T. Rue, J. Leitao, T.A. DeRouen, Survival and reasons for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial, J. Am. Dent. Assoc. 138 (6) (2007) 775–783. [31] J.A. Soncini, N.N. Maserejian, F. Trachtenberg, M. Tavares, C. Hayes, The longevity of amalgam versus compomer/composite restorations in posterior primary and permanent teeth: findings From the New England Children's Amalgam Trial, J. Am. Dent. Assoc. 138 (6) (2007) 763–772. [32] T. Miyamoto, S.M. Morgano, T. Kumagai, J.A. Jones, M.E. Nunn, Treatment history of teeth in relation to the longevity of the teeth and their restorations: outcomes of teeth treated and maintained for 15 years, J. Prosthet. Dent. 97 (3) (2007) 150–156. [33] M. Laske, N.J. Opdam, E.M. Bronkhorst, J.C. Braspenning, M.C. Huysmans, Longevity of direct restorations in Dutch dental practices. Descriptive study out of a practice based research networks, J. Dent. 46 (2016) 12–27. [34] L. Casagrande, M. Laske, E.M. Bronkhorst, M. Huysmans, N.J.M. Opdam, Repair may increase survival of direct posterior restorations – A practice based study, J. Dent. 64 (2017) 30–36. [35] F.J. Burke, P.S. Lucarotti, How long do direct restorations placed within the general dental services in England and Wales survive? Br. Dent. J. 206 (1) (2009) 26–37 (E2; discussion). [36] T.A. Da Rosa Rodolpho, M.S. Donassollo, A.D. Cenci, R.R. Loguercio, E.M. Moraes, N.J. Bronkhorst, F.F. Opdam, 22 Year clinical evaluation of the performance of two posterior composites with different filler characteristics, Dent. Mater. Off. Publ. Acad. Dent. Mater. 27 (10) (2011) 955–963. [37] N.J. Opdam, E.M. Bronkhorst, B.A. Loomans, M.C. Huysmans, Longevity of repaired restorations: a practice based study, J. Dent. 40 (10) (2012) 829–835. [38] C.F. Brantley, J.D. Bader, D.A. Shugars, S.P. Nesbit, Does the cycle of rerestoration lead to larger restorations? J. Am. Dent. Assoc. 126 (10) (1995) 1407–1413.
5. Conclusions Unfortunately, all dental restorations have a limited lifespan and will eventually be replaced or repaired. During a lifetime this may lead to a destruction of the tooth - a death spiral [38], and therefore dentists are obligated to offer patients a restoration that can serve them well. Even though aesthetics and high cost have unquestionably become a major consideration for the patients and the dentists, treatment with gold inlays may still be considered as a treatment of choice when specific indications are present. However, it is important to have in mind that the longevity of gold restorations has not shown to be superior to what can be achieved by resin composite, which should be the first material of choice. Conflict of interest None. Funding This work did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit-sectors. Acknowledgements Dr. Ibrahimu Mdala from the University of Oslo, is acknowledged for statistical guidance in the Multilevel Cox-regression analyses. References [1] F. Staxrud, A.B. Tveit, H.V. Rukke, S.E. Kopperud, Repair of defective composite restorations. A questionnaire study among dentists in the Public Dental Service in Norway, J. Dent. 52 (2016) 50–54. [2] S. Vidnes-Kopperud, A.B. Tveit, I. Espelid, Changes in the treatment concept for approximal caries from 1983 to 2009 in Norway, Caries Res. 45 (2) (2011) 113–120. [3] S.E. Kopperud, F. Staxrud, I. Espelid, A.B. Tveit, The post-Amalgam era: norwegian dentists' experiences with composite resins and repair of defective amalgam restorations, Int. J. Environ. Res. Public Health 13 (4) (2016) 441. [4] C.D. Lynch, R.J. McConnell, N.H. Wilson, Trends in the placement of posterior composites in dental schools, J. Dent. Educ. 71 (3) (2007) 430–434. [5] N.J. Opdam, E.M. Bronkhorst, J.M. Roeters, B.A. Loomans, A retrospective clinical study on longevity of posterior composite and amalgam restorations, Dent. Mater. Off. Publ. Acad. Dent. Mater. 23 (1) (2007) 2–8. [6] K. Sunnegardh-Gronberg, J.W. van Dijken, U. Funegard, A. Lindberg, M. Nilsson, Selection of dental materials and longevity of replaced restorations in Public Dental Health clinics in northern Sweden, J. Dent. 37 (9) (2009) 673–678. [7] A. Baraba, S. Domejean-Orliaguet, I. Espelid, A.B. Tveit, I. Miletic, Survey of Croatian dentists' restorative treatment decisions on approximal caries lesions, Croat. Med. J. 51 (6) (2010) 509–514. [8] S.A. Eklund, Trends in dental treatment, 1992 to 2007, J. Am. Dent. Assoc. 141 (4) (2010) 391–399. [9] R. Hickel, J. Manhart, Longevity of restorations in posterior teeth and reasons for failure, J. Adhes. Dent. 3 (1) (2001) 45–64.
5
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A retrospective clinical study on the longevity of posterior Class II cast gold inlays/onlays ⁎
A. Mulica, , G. Svendsenb, S.E. Kopperuda a b
Nordic Institute of Dental Materials (NIOM), Oslo, Norway Department of Cariology, Faculty of dentistry, University of Oslo, Oslo, Norway
A R T I C L E I N F O
A B S T R A C T
Keywords: Clinical study Gold inlays Longevity Operative dentistry
Objective: To investigate the longevity and reasons for failure of posterior cast Class II gold inlays and onlays among a group of Norwegian adults. The term inlay was used for both inlays and onlays. Methods: A cohort of 138 patients regularly attending a general practice for check-up were examined in 2016. The patients had a total of 391 posterior gold inlays placed in the period 1970–2015. The inlays were categorized as successful, repaired or failed. Reasons for failure were classified as either “secondary caries”, “fractures”, “lost inlay” or “other”. Participation was voluntary and no compensation was given. Results: The mean age of the patients at placement was 50.8 years (SD: 12.7 yr). Most gold inlays were placed in molars (85.9%) and 14.1% in premolars; 49.4% of the inlays were in the maxilla and the 50.6% in the mandibula. Average length of follow-up was 11.6 years (range: 1–46 years, SD: 7.9); 82.9% were classified as successful, 10.7% as repaired and 6.4% as failed. Reasons for failure were secondary caries (41.3%), lost inlay (25.4%), fractures (23.8%) and other (9.5%). Mean annual failure rate (AFR) was 1.69% for repaired and failed inlays combined. However, if repaired inlays were considered as success, the AFR decreased to 0.57%. Multilevel Cox regression analyses identified low age of the patient and high number of restored surfaces as risk factors for failure. Conclusion: The present retrospective clinical study demonstrated an acceptable annual failure rate for Class II cast gold inlays.
Clinical significance All dental restorations have a limited lifespan and will eventually need to be repaired or replaced. It is important to have in mind that the longevity of gold restorations have not been shown to be superior to that of resin composite, which should still be the first material of choice. However, gold inlays could be considered when the right indications are present. 1. Introduction Changes in restorative treatment and ideology have forced dentists and patients to be faced with an overwhelming number of dental material options for posterior restorations. However, failure of restorations continues to be a problem in dental practice, and it is estimated that about 60% of a dentist’s working day still is attributed to placement and replacement of restorations [1]. Use of amalgam as a dental restorative material has been banned in Norway since 2008, and resin composites have become the almost exclusively used restorative material [2,3]. In ⁎
many parts of the world, the use of amalgam is also decreasing [4–8]. However, for some patients an alternative to resin composites could be desirable [3]. Indirectly placed gold cast restorations have for many years been considered as a durable restorative material with longevity superior to other restorative materials. This assumption may not be sufficiently supported by scientific evidence. First of all, there are few - if any recent papers on longevity of gold inlays. Second, the longevity of gold inlays presented in earlier studies may not be as advantageous compared with what can be achieved with today’s restorative materials and cementation procedures. A review by Hickel and Manhart [9] found annual failure rates (AFR) for cast gold inlays to range from 0% to 5.9%, with a median AFR of 1.2%. In the same study, the median AFR for amalgam, composite and glass-ionomer restorations was 3.3%, 2.2% and 7.7%, respectively. In another review, Manhart et al. [10] found a mean AFR for posterior stress-bearing restorations to be: 3.0% for amalgam, 2.2% for composite, 2.9% for composite inlays, 1.7% for CAD/CAM ceramic restorations and 1.4% for cast gold inlays and onlays. These AFR values may have been impressive at that time, but
Corresponding author. E-mail address: [email protected] (A. Mulic).
https://doi.org/10.1016/j.jdent.2017.12.010 Received 3 July 2017; Received in revised form 8 December 2017; Accepted 16 December 2017 0300-5712/ © 2017 Elsevier Ltd. All rights reserved.
Please cite this article as: MULIC, A., Journal of Dentistry (2017), https://doi.org/10.1016/j.jdent.2017.12.010
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shade in the light of recent studies presenting AFR’s of resin composites around 1–3% [11–14]. Mjör and Medina [15] found that the longevity of cast gold restorations exceeded that of other dental materials present at that time by a factor of two to four. However, that study is based on data on ‘age of failed restorations’; an analysis which has been shown to overestimate the longevity of older materials (e.g. gold inlays) compared to newer materials (e.g. resin composites) [16]. Survival analyses in which the life time of both restorations that have failed and those that remain in service is taken into account, such as Kaplan-Meier statistics, is hitherto the best method for calculating longevity of dental restorations [16,17]. Thus, if gold cast inlays should continue to be a part of dentists’ arsenal of restorative materials, newer studies performed by Kaplan-Meier analyses should be performed. The use of cast gold restorations have been low lately [1,3]. Advances in adhesive technique and escalation in aesthetic demands have increased indications for tooth-coloured restorations. In a recent questionnaire study presenting a patient case with a fractured amalgam restoration in a premolar, only 3.1% of the Norwegian dentists considered to restore the tooth with a gold inlay. Other, more aesthetic, prosthetic options were chosen by 10.9% of the dentists [3]. The manufacturers are steadily offering new tooth-coloured materials with improving properties, both for direct and indirect techniques, as well as materials for CAD/CAM techniques. To ad knowledge to the quality of this old technique, in order to compare and be aware of what to expect from the new materials, the aim of the present study was to investigate the longevity and reasons for failure of posterior Class II gold cast restorations among a group of Norwegian adults in a private practice.
Table 1 Empirical failure rates and 95% confidence interval (95%CI) calculated using KaplanMeier statistics. Time
Failure rate
95% CI
3 years 5 years 7 years 10 years 18 years
0.99 0.98 0.97 0.95 0.88
0.98–1.00 0.96–1.00 0.95–0.99 0.92–0.98 0.80–0.96
2. Material and methods The patient‘s electronic dental records (EDR) and radiological records of a general practice in Norway were used for collecting the data for this study. All Class II gold inlays in premolars and molars of patients attending the dental practice for check-up and follow-up treatment in 2015–2016 were included in the study. The inlays were placed in the time period 1970–2015. In addition, data on 23 patients that were no longer attending the dental practice were extracted from the patient records and included in the study. In these cases the last registered examination at the dental clinic was used as the censoring date. In the present study, the term inlay is used for both inlays and restorations including cusps (onlays). Full golden crowns were excluded. The same practitioner (GS) evaluated the inlays included in the present study as part of the patients’ regular dental and radiological examination. The gold inlays were evaluated based on clinical and radiological examination, and categorized as successful, repaired or failed. Inlays that had previously been repaired or failed were assessed retrospectively based on listings in the dental records, and the dates of replacement and reason for failure were extracted. Reasons for failure were classified as either “secondary caries”, “fractures”, “lost inlay” or “other” (extracted tooth or endodontically treated tooth). Patient-related information, such as gender and age at the time of placement of the restoration, was extracted from the electronic dental records (EDR). The patients’ general risk of failure (due to caries, fractures and other incidences) was estimated by their accumulated DMFT-score over a 20years period (1996–2016), which covered most of the observation period. The reason for this time interval was that the dental clinic started using EDR’s in 1996, providing access to DMFT data. The mean annual failure rate of the investigated restorations was calculated according to the formula (1-y)z = (1-x), in which “y” is the mean annual failure rate and “x” is the total failure rate at z years [18]. Empirical failure rates at 3, 5, 7, 10 and 18 years with 95% CI were calculated using Kaplan-Meier statistics (Table 1). Kaplan-Meier analyses were also used to create survival curves (Fig. 1). The possible dependence of multiple inlays placed in the same patients was taken into account by use of a multi-level approach. The multi-level Cox regression models were fitted with gamma-distributed heterogeneity
Fig. 1. Survival curves for the gold inlays performed by Kaplan Meier statistics. In the statistical material for the green curve, only total replacements were considered as failures, while in the red curve both total replacements and repaired gold inlays were considered as failures. The difference shows the benefit of repair on the longevity of gold inlays. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
using the coxph-function in the software R, presenting a frailty model with time effects on the patient level given by: h(t, X) = h0 (t) exp(βiXij + αj) Here, h0(t) is the baseline hazard that describes the shape of the hazard rate as a function of time, exp(βiXij) is the hazard ratio that describes how the size of the hazard rate depends on the covariates, while αj represents the patient frailty term. The multi-level Cox regression analyses were performed with failure of gold inlay as the dependent variable and the following independent variables: patient’s age, gender, patient‘s risk (total accumulated DMFT-score during 20 years), jaw (mandible vs. maxilla), tooth type (molar vs. premolar), number of surfaces of the inlay and cuspal coverage (no/yes). Collinearity was checked using the criterion VIF < 5 and no independent variables were found to invalidate the analysis. A significance level of 5% was used throughout. IBM SPSS 24.0.0.2 (Statistical Package for the Social Sciences) and R version 3.4.1 (The R Foundation for Statistical Computing) were used to analyse the data. STATA 14.2 (Statistics/Data Analysis) was used to create hazard plots. Participation was voluntary and no compensation was given to the respondents. The implementation of the study was approved by the Regional Committee for Medical Research Ethics in Norway (ID: 2015/ 1324). 2
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3. Results From 1970–2015 a total of 391 Class II posterior gold inlays were placed in 138 patients (81 males and 57 females). The number of inlays in each patient ranged from one to thirteen. About one-third of the patients (n = 44) received only one inlay, 27 (19.6%) patients received two inlays, 26 (18.8%) patients received three and 41 (29.7%) patients received four or more inlays. The distribution of the 391 gold inlays according to gender was 67.8% placed in male (n = 265) and 32.2% placed in female patients (n = 126). The mean age of the patients at placement of the inlays was 50.8 years (SD: 12.7 yr). Most gold inlays were placed in molars (85.9%, n = 334) and 14.1% were placed in premolars. The distribution of inlays was quite similar in the maxilla (49.4%, n = 192) and the mandible (50.6%, n = 197). Almost twothirds of the inlays had cuspal coverage (69.8%). The number of restored surfaces varied from two to five. Average length of follow-up of the inlays was 11.6 years (range: 1–46 years, SD: 7.9). After the individual follow-up period, 82.9% (n = 324) were classified as successful, 10.7% (n = 42) had been repaired and 6.4% (n = 25) were deemed to have failed. Reasons for failure were secondary caries (41.3%), lost inlay (25.4%), fractures (23.8%) and other (9.5%), e.g. endodontic complications. The main reasons for repair (n = 42) were secondary caries and fractures. Mean annual failure rate (AFR) was calculated to be 1.69% for repaired and failed inlays combined. However, if repaired inlays were considered as success, the AFR decreased to 0.57%. This difference is shown in Fig. 1, presenting separate survival curves for these two approaches. Empirical failure rates at different time points are given in Table 1. Multi-level Cox-regression analyses were performed to identify factors related to failure of the gold restorations (Table 2). In the adjusted analyses, increasing age of the patient and increasing number of restored surfaces remained statistically significant. Thus, the patients’ gender, patient‘s risk, the inlay’s location in the jaw and tooth type, and whether there was cuspal coverage or not were not found to be significantly related to the survival of the gold restorations. Hazard plots show that the hazard (risk of failure of gold inlays) for patients older than 50 years was lower than for patient aged below 50 years. Thus, lower risk of failure is expected as the patient gets older (Fig. 2). There was also a clear indication that if the number of surfaces was five, then the hazard (risk of failure) was higher than in inlays with < 5 surfaces. Thus, as the number of surfaces increases, so does the risk of failure and the risk is more prominent if the number of surfaces is above four (Fig. 3).
Fig. 2. Hazard plots based on the Multi-level Cox regression analyses, showing a significantly lower hazard (risk of failure of gold inlays) for patients older than 50 years compared with patient below 50 years.
Fig. 3. Hazard plots based on the Multi-level Cox regression analyses, showing a clear indication that if the number of surfaces was five, then the hazard (risk of failure) was higher than in inlays with less than five surfaces.
Table 2 Multi-level Cox regression analyses of factors related to failure of gold restorations. UNADJUSTED
Age Continous variable Gender Male Female Patient risk (accumulated DMFT) Continous variable Jaw Maxilla Mandible Tooth type Premolar Molar Surfaces Continous variable (2–5) Cuspal coverage No Yes
ADJUSTED
% (n)
HR
95% CI
P-value
HR
95% CI
100 (391)
0.96
0.91
–
67.8 (265) 32.2 (126)
1.18
0.40
100 (391)
1.04
49.4 (192) 50.4 (197)
1.00
0.07
0.91
0.85
–
0.96
< .01
–
3.46
0.76
2.01
0.66
–
6.14
.22
0.94
–
1.16
0.46
1.11
0.98
–
1.25
.10
0.78
0.34
–
1.79
0.56
0.62
0.25
–
1.53
.30
14.1 (55) 85.4 (334)
0.63
0.20
–
1.93
0.42
0.40
0.12
–
1.41
.15
89.0 (348)
1.47
0.93
–
2.33
0.10
2.55
1.19
–
5.43
.02
30.2 (105) 69.8 (243)
1.35
0.54
–
3.39
0.52
0.38
0.08
–
1.91
.24
3
P-value
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fillings. Unfortunately, data on the patients’ bite forces was not possible to extract from the dental records. It may, however, be assumed that gold inlays are a preferable treating option in challenging patients, and therefore, the risk for fracture is higher compared with when placed in patients with e.g. normal occlusion. Fractures were the most frequent cause of failure in a recent systematic review [28] that estimated the survival rates for glass-ceramic and feldspathic porcelain (inlays, onlays and overlays) to be between 92% and 95% after 5 years, and 91% after 10 years. Cuspal coverage was found not to affect the longevity of inlays in our study, but there was a significant impact from the number of restored surfaces. That shows that patients in our study did not benefit from cusp-capping the teeth, but that massively restored teeth were weakened compared to less restored teeth. This is in line with results from several other studies on restoration longevity [29–32]. A recent study investigated the longevity of direct restorations placed by a group of general dental practitioners (n = 24), and concluded that even though the wide variation in annual failure rate exists between the clinicians, the restorations are placed with a satisfactory longevity [33]. The main weakness of our study is that all of the restorations were placed and evaluated retrospectively by one dentist, and therefore the results may not be reassigned to a broad variety of general dentists [17]. The results may depend on the dentist’s skill of the preparations and placing the gold inlays; it may be argued that these restorations may have been placed by operators who might have special interest or skills in this field of operative dentistry. In addition, the thresholds for repairing or replacing a restoration vary widely between operators [1,2,34]. The decision between repairing or replacing may be a reflection of the practitioner‘s attitude towards possibilities for repair e.g. “expensive” gold restorations are rather repaired then replaced. This will again influence the differences in AFR between survival and success. An interesting assumption by Laske el al. [33] and Burke & Lucarotti [35] is that changing dentists leads to a higher replacement rate of fillings. Most of the patients included in the present study have been treated by one dentist for many years, and this may contribute to a higher restorations survival than could be expected for larger team practice with more clinicians treating the same patient. Nevertheless, according to new directions for clinical studies presented by Opdam et al., “the reliability of patient records used for retrospective studies is highly dependent upon the number of individuals who remain patients and receive all their dental treatment in the practice(s) over extended periods of time” [17]. A reasonable approach to strengthen evidence-based information on the longevity of the restorations in dental practice is to design and perform prospective, practice-based studies. However, with the general low use of gold inlays today, such a study would be difficult to perform, and thus by practical reasons today’s conclusions need to be based on retrospective studies. In a recent questionnaire based study investigating the treatment decisions in 2009 among Norwegian dentists [3], more that 50% of the clinicians would never restore a MOD (mesial-occlusal-distal)-cavity on premolars and molars in adult patients with gold inlays. Almost all dentists (99%) included in the questionnaire stated to restore this cavity with composite “Often” or “Always”, which demonstrates that composite has become the dominating material of choice in Norway. Even though aesthetic demands and need for tooth-coloured restorations are increasing, gold inlays are considered as an effective treatment option in posterior teeth. The abovementioned questionnaire [3] revealed that gold inlays were preferred more often than ceramic (CAD/CAM) and composite inlays when restoring the MOD-cavity in a premolar or molar. The clinical assumption is that for patients with severe attrition and high biting forces, as well as replacement of a large amalgam restoration, gold inlay is a preferable treatment. However, the teaching of gold inlays is fading out of the undergraduate program in many dental schools as indirect restorations are preferably tooth-coloured, minimally invasive and adhesive. Therefore, it is likely that in time gold will phase out in dentistry. In general, all restorative treatment weakens the tooth and increases the risk of fractures [32]. Thus, when replacing
4. Discussion In the present retrospective, clinical study, the Class II posterior gold inlays showed high longevity and an acceptable failure rate after up to 20 years. The most common reason for failure was secondary caries. The longevity of dental restorations is dependent upon many different factors, related to the restorative material, the patient and to the dentist [9,11]. Even though limited data are available on the longevity of gold restorations, they are by many dentists considered to be longlasting. This is confirmed by the acceptable mean annual failure rate (AFR) in the present study (0.57% for failed inlays only). Similarly, other studies have shown promising results for gold restorations. Donovan et al. [19] found the survival rate to be 95.4% in a retrospective, clinical study of 1314 gold restorations; where inlays had a failure rate of 4.7% after more than 20 years. These findings have also been confirmed in several other studies where the AFR range from 0% and up to 5.9% [9]. However, the gold restorations are considered to be costly. Compared with amalgam restorations, the cost factor for gold have been calculated to be 3.8 to 6.3 times higher [20]. Consequently, other restorations could be preferred in posterior teeth. In two separate questionnaire studies among Norwegian dentists, gold was suggested for replacing a MOD restoration in an upper premolar by only 3.2% and 0.3% of the dentists respectively, compared with 86% and 94% choosing resin composite, respectively [1,3].The overall use of materials other than amalgam and resin composite in a practice-based network have been shown to be only 5% for both US and Scandinavian dentists when placing restorations in premolars and molars [21]. Resin composite has in many parts of the world replaced amalgam as the dominating material of choice for direct restorations [22,23]. The longevity of posterior composite restorations today is by many researchers considered to be similar to that of amalgams, presenting AFRs of 1–3% [11–14,24]. Beck et al. [14] found in a meta-analysis of prospective studies a mean AFR to be 1.64% after 1–4 years of observation, and 1.97% after 5–19 years. Similar results were reported in a systematic review by Opdam and co-workers: the mean AFR was 1.8% after 5 years, and 2.4% after 10 years [12]. Consequently, the present study showed good longevity of gold inlays. However, the scientific support to claim that gold is superior to composite resin as an alternative for amalgam is still weak. The main reasons for failure of the gold restorations have been tooth fractures, marginal defects, insufficient retention and secondary caries [25]. In the present study, the reasons for failure of the gold inlays were secondary caries, lost inlay, fractures and other (e.g. endodontic complications). This is similar to the resin composites, where the most common biological reason for failure has been reported to be secondary caries and fracture of the restorations [12–14,26]. Secondary caries and fractures predominate as dentists' perceived reasons for replacement of restorations [3]. It may be argued that people who want to pay the high costs for gold restorations are likely more motivated and having a low caries risk. However, a recent population-based cross-sectional study from Norway concluded that behavioural variables (e.g. toothbrushing, sugar soft drink consumption etc.) seem to have greater influence compared with socio-economic variables (household income) [27]. An individual may be at high caries risk, regardless of his/hers financial status. In the present study the patients’ general risk of failure (due to caries, fractures and other incidences) was estimated by their accumulated DMFT-score over a 20-years period (1996–2016). DMFT might not be an optimal parameter for measuring caries risk among adult patients, and this may explain why that factor had no significant influence on the results. One of the main reasons for failures (23.8%) was fractures. The gold inlays are often considered as an effective treatment option in more challenging patients, e.g. in posterior teeth for patients with high masticating forces and for replacement of large, posterior amalgam 4
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large restorations in patients with high biting forces, dentists should prefer durable materials. According to modern dental philosophy and concept of minimal intervention dentistry, repair of any defective restoration, should always be considered as an option. In the present study, 10.7% of the inlays were repaired during the observation period and still in function. The repair process may therefore be considered successful. Other studies have also showed that the longevity of restorations could benefit from being repaired, rather than replaced. A clinical study of composite restorations with 22 years follow-up showed an AFR of 1.9%. If, however, repaired restorations were considered not to be failures, the AFR improved to 0.7% [36]. Opdam et al. [37] have demonstrated a similar reduction of AFR from 1.83% to 0.72% when repair was considered successful in the statistical material. In the present study the AFR decreased from 1.69% to 0.57% when repaired inlays were considered as success.
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5. Conclusions Unfortunately, all dental restorations have a limited lifespan and will eventually be replaced or repaired. During a lifetime this may lead to a destruction of the tooth - a death spiral [38], and therefore dentists are obligated to offer patients a restoration that can serve them well. Even though aesthetics and high cost have unquestionably become a major consideration for the patients and the dentists, treatment with gold inlays may still be considered as a treatment of choice when specific indications are present. However, it is important to have in mind that the longevity of gold restorations has not shown to be superior to what can be achieved by resin composite, which should be the first material of choice. Conflict of interest None. Funding This work did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit-sectors. Acknowledgements Dr. Ibrahimu Mdala from the University of Oslo, is acknowledged for statistical guidance in the Multilevel Cox-regression analyses. References [1] F. Staxrud, A.B. Tveit, H.V. Rukke, S.E. Kopperud, Repair of defective composite restorations. A questionnaire study among dentists in the Public Dental Service in Norway, J. Dent. 52 (2016) 50–54. [2] S. Vidnes-Kopperud, A.B. Tveit, I. Espelid, Changes in the treatment concept for approximal caries from 1983 to 2009 in Norway, Caries Res. 45 (2) (2011) 113–120. [3] S.E. Kopperud, F. Staxrud, I. Espelid, A.B. Tveit, The post-Amalgam era: norwegian dentists' experiences with composite resins and repair of defective amalgam restorations, Int. J. Environ. Res. Public Health 13 (4) (2016) 441. [4] C.D. Lynch, R.J. McConnell, N.H. Wilson, Trends in the placement of posterior composites in dental schools, J. Dent. Educ. 71 (3) (2007) 430–434. [5] N.J. Opdam, E.M. Bronkhorst, J.M. Roeters, B.A. Loomans, A retrospective clinical study on longevity of posterior composite and amalgam restorations, Dent. Mater. Off. Publ. Acad. Dent. Mater. 23 (1) (2007) 2–8. [6] K. Sunnegardh-Gronberg, J.W. van Dijken, U. Funegard, A. Lindberg, M. Nilsson, Selection of dental materials and longevity of replaced restorations in Public Dental Health clinics in northern Sweden, J. Dent. 37 (9) (2009) 673–678. [7] A. Baraba, S. Domejean-Orliaguet, I. Espelid, A.B. Tveit, I. Miletic, Survey of Croatian dentists' restorative treatment decisions on approximal caries lesions, Croat. Med. J. 51 (6) (2010) 509–514. [8] S.A. Eklund, Trends in dental treatment, 1992 to 2007, J. Am. Dent. Assoc. 141 (4) (2010) 391–399. [9] R. Hickel, J. Manhart, Longevity of restorations in posterior teeth and reasons for failure, J. Adhes. Dent. 3 (1) (2001) 45–64.
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