Abstract
Resin composites have become the first choice for direct posterior restorations and are increasingly popular among clinicians and patients. Meanwhile, a number of clinical reports in the literature have discussed the durability of these restorations over long periods. In this review, we have searched the dental literature looking for clinical trials investigating posterior composite restorations over periods of at least 5 years of follow-up published between 1996 and 2011. The search resulted in 34 selected studies. 90% of the clinical studies indicated that annual failure rates between 1% and 3% can be achieved with Class I and II posterior composite restorations depending on several factors such as tooth type and location, operator, and socioeconomic, demographic, and behavioral elements. The material properties showed a minor effect on longevity. The main reasons for failure in the long term are secondary caries, related to the individual caries risk, and fracture, related to the presence of a lining or the strength of the material used as well as patient factors such as bruxism. Repair is a viable alternative to replacement, and it can increase significantly the lifetime of restorations. As observed in the literature reviewed, a long survival rate for posterior composite restorations can be expected provided that patient, operator and materials factors are taken into account when the restorations are performed.
1
Introduction
Direct restorations have been largely employed to restore posterior teeth due to their low cost and less need for the removal of sound tooth substance when compared to indirect restorations, as well as to their acceptable clinical performance . Despite the fact that both amalgam and composite resin are considered suitable materials for restoring Class I and Class II cavities, some advantages can be related to composite restorations such as better esthetics; their adhesive properties, resulting in reduced preparation size ; and reinforcement of the remaining dental structure . A clinical study has shown that painful vital teeth with incomplete fractures can be treated successfully by replacing the amalgam fillings with bonded composite restorations . On the other hand, posterior composite restorations have been shown to produce higher failure rates due to secondary caries . However, although used in many practices around the world, amalgam is facing its demise, leaving resin composite as the most likely material for posterior restorations for widespread use in the near future.
Even though acceptable survival rates are achieved with Class I and II restorations in dental health care, the replacement of failing restorations is still a relevant issue. Dentists still spend a significant amount of time replacing restorations, contributing to the repetitive restorative cycle described by Elderton . Factors related to the patient, operator, tooth, cavity size, and materials have been reported in the literature as potentially relevant for restoration failures , although evidence of this is still limited.
Despite the considerable differences in properties among commercial composites as found in laboratory analysis , in vitro tests are limited in predicting the clinical survival of composite restorations. Due to the constant influx of new posterior restorative materials on the market and the need for manufacturers to prove the clinical safety of their new materials, there has been an emphasis on relatively short-term clinical studies with a limited number of restorations, mostly placed in low-risk patients. In those studies, differences in performance are seldom found, as most materials perform well on a short-term basis, with a few exceptions .
To estimate how long posterior composite restorations last, long-term studies are needed to identify modes of failure and possible reasons for these failures. In a comparative amalgam–composite study after 5 years, no differences in performance were found; after 12 years, however, the composite showed significantly better performance . Given the considerable differences between (non-bonded) amalgam and composite and the fact that, after 5 years, no differences in performance were observed, it is not likely that the majority of composite restorations will show different longevity when investigated before at least 5 years of clinical service. Because of limited observation times of most clinical studies , limited information is available on the performance determinants and reasons for the failure of posterior composite restorations in the long term. Although the rapid evolution of composites makes it difficult for long-term evaluations to be conducted using materials still available in the market, the good results shown with previous and presently available materials in clinical studies foster the question of whether new materials are actually improvements, and the authors tend to conclude that this is not likely. This means that, based on the available long-term studies, especially studies with observation times exceeding 5 years, an expectation regarding the long-term behavior of posterior composite restorations can be made. In the present article, we aim to review and discuss, with an emphasis on the available long-term literature, the longevity of posterior composite restorations, and the main factors associated with restoration failures.
2
Methods and results
2.1
Selection of papers
To investigate the longevity of composite restorations as reported in clinical studies in the dental literature, a PubMed search for articles that evaluated longitudinal data for posterior resin composite restorations published between 1996 and 2011 was performed. The terms used in the search were ‘posterior composite restorations’ and ‘survival’ or ‘longevity’ or ‘failure’. After selecting only papers reporting clinical longevity studies of composite restorations with evaluation periods of at least 5 years, a total of 34 papers reporting on varied materials, techniques, and methods of evaluation was found. The selected papers included prospective and retrospective clinical studies, as well as longevity studies based on secondary data. Excluded for longevity assessment were cross-sectional studies as these are considered to deliver unreliable data with respect to longevity . The selected papers were searched for the reported longevity outcome, expressed in annual failure rates (AFRs) or median survival, and factors associated with composite failure as mentioned by the respective authors.
2.2
Longevity of posterior composite restorations
From Table 1 , the following conclusions regarding the longevity of posterior composite restorations can be made: on average, the AFRs of Class I and II posterior composite restorations placed in vital teeth vary between 1% and 3%. This is in accordance with the results reported in the most recent review published by Manhart et al. . For endodontically treated teeth, the AFRs vary from 2% to 12.4%.
| Author, year | Evaluation period/study design a | Materials tested | Evaluated restorations | AFR b /outcome/survival rate of composite | Factors associated with composite failure |
|---|---|---|---|---|---|
| Da Rosa Rodolpho et al., 2011 | 22 years, RL | Composite | Class I and II | AFR: between 1.5% and 2.2% | Tooth type, cavity size, material |
| Opdam et al., 2010 | 12 years, RL | Composite vs. amalgam | Large Class II | AFR: 1.68% | Caries risk |
| Fokkinga et al., 2008 | 17 years, PL | Composite | Endodontically treated teeth with or without a prefabricated metal post | AFR: 2.8% (restoration level) and 1.2% (tooth level) | No factors associated |
| Bernardo et al., 2007 | 7 years, PL | Composite vs. amalgam | Class I and II | AFR: 2.1% | Secondary caries |
| Opdam et al., 2007 | 9 years, RL | Composite | Class II with a total-etch technique or with glass-ionomer lining | AFR: 1.3% (total-etch) and 3.3% (glass-ionomer lining) | Presence of a lining, caries risk |
| Opdam et al., 2007 | 5 and 10 years, RL | Composite vs. amalgam | Class I and II | AFR: 1.7% (5 years) and 1.8% (10 years) | Amount of restored surfaces |
| Soncini et al., 2007 | 5 years, PL | Amalgam vs. composite/compomer | Children aged 6–10 with more than one posterior restoration | AFR: 2.98% | Number of restorations, cavity size |
| Lindberg et al., 2007 | 9 years, PL | Composite/composite–compomer open sandwich | Class II | AFR: 1.1% | No factors associated |
| Gordan et al., 2007 | 8 years, PL | Composite | Class I and II | AFR: 0% | Not investigated |
| Da Rosa Rodolpho et al., 2006 | 17 years, RL | Composite | Class I and II | AFR: 2.4% | Tooth, cavity type, cavity size |
| Burke et al. and Lucarotti et al., 2005 | Up to 10 years, RS | Amalgam, composite and glass-ionomer | Class I and II | AFR: 8.4% (5 years) and 5.7% (10 years) | Operator: age, country of qualification, employment status; Clinical: cavity size, root filling; Patient: age, charge-paying status, practice assiduity |
| Nagasiri et al., 2005 | 5 years, RL | Composite, amalgam and OZE | Endodontically treated molars | AFR: 12.4% | Remaining coronal tooth structure |
| Mannocci et al., 2005 | 5 years, PL | Amalgam/composite with post, endodontically treated tooth | Class II | AFR: 2% | More root fracture with amalgam, more secondary caries with composite |
| Opdam et al., 2004 | 5 years, RL | Composite | Class I and II placed by dental students | AFR: 2.6% | Operator: year of graduation; Clinical: proximal contact status |
| Andersson-Wenckert et al. 2004 | 9 years, PL | Composite and glass-ionomer, open sandwich | Class II | AFR 3.2% | Not investigated |
| Coppola et al., 2003 | 5 years, RS | Composite vs. amalgam | Posterior restorations with 2 surfaces at least | Average longevity: 42 months | Dentist experience |
| Hayashi and Wilson, 2003 | 5 years, PL | Composite | Class I and II | AFR: 3.76% | Marginal deterioration, cavomarginal discoloration |
| Pallesen and Qvist, 2003 | 11 years, PL | Composite, direct vs. indirect | Medium to large Class II | AFR: 1.45% | Tooth type |
| Turkun et al., 2003 | 7 years, PL | Composite | Class I and II | AFR: 0.82% | No factors associated |
| van Nieuwenhuysen et al., 2003 | 5–22 years, RL | Amalgam, composite and crowns | Posterior extensive restorations | Average survival time: 7.8 years | Clinical: tooth type, extension of restoration, pulpal vitality, use of base material; Patient: age, 3-year period of treatment |
| Busato et al., 2001 | 6 years, PL | Composite | Class I and II | AFR: 2.5% | Not investigated |
| Gaengler et al., 2001 | 10 years, PL | Composite with glass ionomer cement | Class I and II | AFR: 2.6% | Not investigated |
| Kohler et al., 2000 | 5 years, PL | Composite | Class II | AFR: 5.5% | Caries risk |
| van Dijken, 2000 | 11 years, PL | Composite, direct inlays/onlays and restorations | Class II | AFR: 1.6% (inlays/onlays) and 2.5% (direct restorations) | Tooth type |
| Wassel et al., 2000 | 5 years, PL | Composite, direct vs. inlay | Class I and II | AFR: 1.5% | Not investigated |
| Lundin and Koch, 1999 | 5 and 10 years, PL | Composite | Class I and II | AFR: 2% (5 years) and 2.1% (10 years) | Not investigated |
| Raskin et al., 1999 | 10 years, PL | Composite | Class I and II | AFR: 8.6% | Not investigated |
| Wilder et al., 1999 | 17 years, PL | Composite | Class I and II | AFR: 1.4% | Not investigated |
| Collins et al., 1998 | 8 years, PL | Composite | Class I and II | AFR: 1.71% | Not investigated |
| Mair, 1998 | 10 years, PL | Composite vs. amalgam | Class II | 100% of success | Not investigated |
| Nordbo et al., 1998 | 10 years, PL | Composite | Saucer-shaped Class II | AFR: 3.0% | Not investigated |
a R: retrospective; P: prospective; L: longitudinal; S: secondary data acquisition.
2
Methods and results
2.1
Selection of papers
To investigate the longevity of composite restorations as reported in clinical studies in the dental literature, a PubMed search for articles that evaluated longitudinal data for posterior resin composite restorations published between 1996 and 2011 was performed. The terms used in the search were ‘posterior composite restorations’ and ‘survival’ or ‘longevity’ or ‘failure’. After selecting only papers reporting clinical longevity studies of composite restorations with evaluation periods of at least 5 years, a total of 34 papers reporting on varied materials, techniques, and methods of evaluation was found. The selected papers included prospective and retrospective clinical studies, as well as longevity studies based on secondary data. Excluded for longevity assessment were cross-sectional studies as these are considered to deliver unreliable data with respect to longevity . The selected papers were searched for the reported longevity outcome, expressed in annual failure rates (AFRs) or median survival, and factors associated with composite failure as mentioned by the respective authors.
2.2
Longevity of posterior composite restorations
From Table 1 , the following conclusions regarding the longevity of posterior composite restorations can be made: on average, the AFRs of Class I and II posterior composite restorations placed in vital teeth vary between 1% and 3%. This is in accordance with the results reported in the most recent review published by Manhart et al. . For endodontically treated teeth, the AFRs vary from 2% to 12.4%.
| Author, year | Evaluation period/study design a | Materials tested | Evaluated restorations | AFR b /outcome/survival rate of composite | Factors associated with composite failure |
|---|---|---|---|---|---|
| Da Rosa Rodolpho et al., 2011 | 22 years, RL | Composite | Class I and II | AFR: between 1.5% and 2.2% | Tooth type, cavity size, material |
| Opdam et al., 2010 | 12 years, RL | Composite vs. amalgam | Large Class II | AFR: 1.68% | Caries risk |
| Fokkinga et al., 2008 | 17 years, PL | Composite | Endodontically treated teeth with or without a prefabricated metal post | AFR: 2.8% (restoration level) and 1.2% (tooth level) | No factors associated |
| Bernardo et al., 2007 | 7 years, PL | Composite vs. amalgam | Class I and II | AFR: 2.1% | Secondary caries |
| Opdam et al., 2007 | 9 years, RL | Composite | Class II with a total-etch technique or with glass-ionomer lining | AFR: 1.3% (total-etch) and 3.3% (glass-ionomer lining) | Presence of a lining, caries risk |
| Opdam et al., 2007 | 5 and 10 years, RL | Composite vs. amalgam | Class I and II | AFR: 1.7% (5 years) and 1.8% (10 years) | Amount of restored surfaces |
| Soncini et al., 2007 | 5 years, PL | Amalgam vs. composite/compomer | Children aged 6–10 with more than one posterior restoration | AFR: 2.98% | Number of restorations, cavity size |
| Lindberg et al., 2007 | 9 years, PL | Composite/composite–compomer open sandwich | Class II | AFR: 1.1% | No factors associated |
| Gordan et al., 2007 | 8 years, PL | Composite | Class I and II | AFR: 0% | Not investigated |
| Da Rosa Rodolpho et al., 2006 | 17 years, RL | Composite | Class I and II | AFR: 2.4% | Tooth, cavity type, cavity size |
| Burke et al. and Lucarotti et al., 2005 | Up to 10 years, RS | Amalgam, composite and glass-ionomer | Class I and II | AFR: 8.4% (5 years) and 5.7% (10 years) | Operator: age, country of qualification, employment status; Clinical: cavity size, root filling; Patient: age, charge-paying status, practice assiduity |
| Nagasiri et al., 2005 | 5 years, RL | Composite, amalgam and OZE | Endodontically treated molars | AFR: 12.4% | Remaining coronal tooth structure |
| Mannocci et al., 2005 | 5 years, PL | Amalgam/composite with post, endodontically treated tooth | Class II | AFR: 2% | More root fracture with amalgam, more secondary caries with composite |
| Opdam et al., 2004 | 5 years, RL | Composite | Class I and II placed by dental students | AFR: 2.6% | Operator: year of graduation; Clinical: proximal contact status |
| Andersson-Wenckert et al. 2004 | 9 years, PL | Composite and glass-ionomer, open sandwich | Class II | AFR 3.2% | Not investigated |
| Coppola et al., 2003 | 5 years, RS | Composite vs. amalgam | Posterior restorations with 2 surfaces at least | Average longevity: 42 months | Dentist experience |
| Hayashi and Wilson, 2003 | 5 years, PL | Composite | Class I and II | AFR: 3.76% | Marginal deterioration, cavomarginal discoloration |
| Pallesen and Qvist, 2003 | 11 years, PL | Composite, direct vs. indirect | Medium to large Class II | AFR: 1.45% | Tooth type |
| Turkun et al., 2003 | 7 years, PL | Composite | Class I and II | AFR: 0.82% | No factors associated |
| van Nieuwenhuysen et al., 2003 | 5–22 years, RL | Amalgam, composite and crowns | Posterior extensive restorations | Average survival time: 7.8 years | Clinical: tooth type, extension of restoration, pulpal vitality, use of base material; Patient: age, 3-year period of treatment |
| Busato et al., 2001 | 6 years, PL | Composite | Class I and II | AFR: 2.5% | Not investigated |
| Gaengler et al., 2001 | 10 years, PL | Composite with glass ionomer cement | Class I and II | AFR: 2.6% | Not investigated |
| Kohler et al., 2000 | 5 years, PL | Composite | Class II | AFR: 5.5% | Caries risk |
| van Dijken, 2000 | 11 years, PL | Composite, direct inlays/onlays and restorations | Class II | AFR: 1.6% (inlays/onlays) and 2.5% (direct restorations) | Tooth type |
| Wassel et al., 2000 | 5 years, PL | Composite, direct vs. inlay | Class I and II | AFR: 1.5% | Not investigated |
| Lundin and Koch, 1999 | 5 and 10 years, PL | Composite | Class I and II | AFR: 2% (5 years) and 2.1% (10 years) | Not investigated |
| Raskin et al., 1999 | 10 years, PL | Composite | Class I and II | AFR: 8.6% | Not investigated |
| Wilder et al., 1999 | 17 years, PL | Composite | Class I and II | AFR: 1.4% | Not investigated |
| Collins et al., 1998 | 8 years, PL | Composite | Class I and II | AFR: 1.71% | Not investigated |
| Mair, 1998 | 10 years, PL | Composite vs. amalgam | Class II | 100% of success | Not investigated |
| Nordbo et al., 1998 | 10 years, PL | Composite | Saucer-shaped Class II | AFR: 3.0% | Not investigated |
a R: retrospective; P: prospective; L: longitudinal; S: secondary data acquisition.
3
Aspects that influence longevity
3.1
Clinical
Clinical related factors play an important role in restoration longevity and causes of failure. Several studies have indicated that the position of the tooth in the mouth or the tooth type directly affects restoration longevity, with restorations in premolars showing better performance than those in molars . One paper reported a risk of restoration failure twice as high for molars compared to premolars . One study with a 22-year observation time found the risk of failure of restorations placed in lower molars to be 3 times higher than the risk of failure in upper premolars . However, a study on large restorations of 3 or more surfaces did not find differences between the longevity in molars and premolars .
The findings mentioned above are explained by the knowledge that restorations placed in molar teeth are subjected to higher masticatory stresses than restorations placed in premolars. Similarly, cavity size, cavity type, and the number of restored surfaces are related to the failure risk. In this context, multi-surface restorations, extensive cavities, and Class II restorations, are more likely to fail than single-surface and Class I restorations . One study showed that Class II restorations have a relative risk of failure of 2.8 compared to Class I restorations, and that restorations with 3 or more surfaces have a relative risk of failure of 3.3 in relation to single-surface restorations . Another study calculated that every surface more resulted in an increased risk of failure of 40% .
Two papers reported an increased risk of failure with a higher number of restored teeth per patient . These patients may be considered to have a higher risk of caries, which would explain the higher rates of restoration failures observed in these patients.
The type of the substrate on which the composite is placed could also affect the restoration longevity. The use of a glass-ionomer base under an adhesive restoration was shown to decrease restoration survival compared with total-etch restorations , with fracture as the main reason for failure. It is not yet clear, however, whether thickness and type of glass-ionomer cements play a role in the failure behavior. Other clinical studies in which a base of glass-ionomer was used also showed increased failure by fracture over time , but the absence of a restorative control group placed using total-etch bonding procedure in those studies or a lack of specifications for the applied liner makes it impossible to draw more definitive conclusions. It is also possible that extensive layers of calcium hydroxide linings and the amount of soft carious tissue left behind might affect the strength and longevity of composite restorations. Although there is clinical evidence that the removal of soft decayed tissue is not necessary to stop a caries process once a well-sealed restoration is placed , it remains questionable whether this will reduce the strength of the restorative complex and increase the amount of failure in the long term .
From Table 1 , it can also be concluded that posterior composite restorations placed in endodontically treated teeth have a reduced survival rate, which is explained by the extensive loss of tooth substance that these teeth suffer.
3.2
Operator
It is generally acknowledged that the operator is probably the most important factor in the longevity of a dental restoration. However, evidence from clinical studies does not support this assumption. Clinical studies on posterior restorations and clinical procedures in which more than one operator was involved, do not reveal differences in study outcome among the operators . It is likely that every dentist who is aware that his work is involved in a clinical trial will work as accurately as possible, resulting in fewer operator failures that could influence the study outcome.
However, secondary data studies suggest that the operator significantly influences the longevity of a restoration and mention relevant factors such as age, country of qualification and employment status . Moreover, it is the dentist who decides whether a restoration needs to be replaced. From those secondary data studies, it is known that patients changing dentist have an increased chance that their restorations will be replaced . Reduced lifetime for composite and amalgam restorations has been reported for patients changing dentists , being this effect accounted to the high level of variability in diagnostic decisions among clinicians. A more conservative approach toward restoration replacement would, therefore, lead to increased restoration longevity.
Technique-related aspects of a posterior restoration rely on the knowledge and sufficient skills of the operator. A study conducted by Coppola et al. revealed that efficient working dentists produce restorations with a higher survival rate than inefficient working providers. In that study , a decision-making approach was used to measure relative efficiencies of operators by considering multiple inputs and outputs regarding clinical decisions in order to identify the most efficient providers. Other study has shown that inexperienced undergraduate students were more closely associated with certain types of restoration failures than more experienced students .
In the past, dentists complained about difficulties in achieving adequate proximal contact when placing a posterior composite, and this was also found in a clinical study . Nowadays, techniques have evolved in that respect, and the operator can now use several types of matrices and separation rings that result in even tighter contact than before the treatment .
The often-mentioned problems of post-operative sensitivity related to posterior composite restorations may be related to adhesive procedures having not been done properly due to the inappropriate selection of adhesive materials and techniques or the application of materials not in accordance with the manufacturers’ instructions. It has been found in several studies that self-etch adhesives lead to less sensitivity , though, in recent literature, the sensitivity problem seems to be less prominent, which might be related to greater experience among dentists with increased knowledge concerning the proper application of state-of-art adhesive agents and increased use of self-etch materials. A relatively recent study on post-operative sensitivity found that this was mainly related to the cavity size and concluded that most sensitivity had disappeared over time .
Some clinicians tend to make restorations of very high quality when it comes to the color and anatomy of the restoration . However, these restorations are never subjected to longevity evaluation, and it is unlikely that these esthetic quality aspects have any influence on posterior restoration survival in general. Moreover, these types of composite restorations, as inspiring they can be for the colleague dentist, are not feasible to place in everyday practice.
3.3
Patients
Although evidence is limited, it is likely that the type of patient and the oral environment play an important role in the survival of dental restorations. The caries risk of patients has been shown to significantly influence the longevity of restorations. Among the selected studies, several investigated the caries risk and found increased risk of failure of restorations placed in patients with caries risk . Restorations in a high-caries risk group had a failure rate more than twice as high compared to low-risk patients . In that study, the caries risk was established by the treating dentist based on the dental history and the expected risk of new lesion . Another study that used a caries risk assessment also showed that high-caries risk patients have increased risk of failure of posterior composite restorations . In a study on direct posterior restorations in children, those with a high DMFT index had an increased risk of restoration failure .
In investigating the prevalence of satisfactory posterior composite restorations in a birth cohort, a higher prevalence of unsatisfactory restorations at the age of 24 was observed in patients exhibiting a higher level of dental caries at the age of 15 . Clinical prospective studies performed in university clinics that evaluate the longevity of restorations of new materials are likely to include only motivated patients with good oral health and, consequently, low caries risk. This would explain why, in some prospective clinical trials, a high survival rate is found in the absence of secondary caries, or with very few restorations failing due to secondary caries , while cross-sectional studies have shown that caries are the most important reason for the replacement of composite and amalgam restorations . Also, when restorations are performed in patients with a higher economic status in a private clinic, secondary caries do not seem to be a main reason for the failure of posterior composite restorations .
Tooth and restoration fracture also are important reasons for restoration failure. It is, therefore, likely that bruxing habits such as grinding and clenching play an important role in fatigue development in the tooth-restoration complex, resulting in fracture in the long term. The diagnosis of bruxism is not easy, and diagnostic tools for this are not always reliable . Sometimes, it is mentioned in the inclusion criteria for a clinical study that “bruxing patients were excluded from the sample”, with no mention of the criteria used for such a diagnosis. A clinical 3-year study on the longevity of composite restorations placed in patients with severe tooth wear showed unfavorable results compared to ‘normal patients’, indicating that the destructive mouth habits of these patients (probably with bruxism) resulted in more failures . In a study on cracked teeth , it was speculated that clenching habits might play a role in the etiology of cracked and fractured teeth, an important reason for the failure of amalgam restorations in particular . Currently, no validated criteria are available to assess bruxing habits, either for grinding nor clenching; thus, conclusions regarding a direct relationship between bruxism and restoration failure, although such a relationship is very likely, are still not possible.
Post-operative sensitivity is a patient-related factor, such as pain experience and amount of discomfort, that can vary between patients. In the past, post-operative sensitivity was acknowledged as an important problem for dentists working with composite restorations. However, as mentioned previously, post-operative sensitivity is more closely related to the adhesive system or restorative technique approach and is a less prominent problem in recent literature.
Esthetic demand from the patient is a further factor determining restoration longevity. High demand for esthetic perfectionism is likely to result in more restorations being replaced for esthetic reasons. However, in a retrospective clinical study less than 1% of large amalgam restorations were replaced due to esthetic reasons , and no posterior composite restorations were replaced due to esthetic reasons. Therefore, with respect to the longevity of posterior composite restorations, failure due to esthetic reasons seems to be very rare.
3.4
Socioeconomic
In addition to clinical variables, patient demographic, socioeconomic and behavioral variables may also affect the longevity of posterior restorations. Very few studies have investigated the association between these variables, but the findings suggest that such factors can play an important role in the longevity of restorations. Burke et al. analyzed data from General Dental Services in England and Wales between 1991 and 2002, involving a total of 503,965 restorations. While survival analysis showed no difference between genders, the age of the patients was significant, with older patients having a shorter interval before re-intervention.
As dental caries are strongly associated with social determinants experienced during the life course , it is possible that social determinants can also influence the longevity of restorations by the same pathway. However, this remains to be established, because most investigations on restoration longevity have focused on materials and techniques or cavity preparation features . In addition, most of the clinical trials reporting the longevity of posterior restorations are carried out in university clinical settings and population-based studies are very rare . However, several retrospective studies have been conducted in general practices including at least some at-risk patients . Moreover, many of the studies that analyzed patient factors used a statistical approach considering the tooth restoration as the unique unit of analysis. To analyze the influence of socioeconomic factors on restoration longevity, one should consider the fact that variation between subjects is great, and it is also important to consider the existing variation between the teeth of the same patient. A recent study in 24-year-old subjects from a birth cohort used a multilevel statistical approach to consider variables at both the patient and tooth levels. This study showed that the socioeconomic trajectory from birth to age 15 was associated with posterior restoration failure, even after adjustment by tooth-level variables. People who had always lived in the poorest stratus of the population had more restoration failures than those who lived in the richest layer (odds ratio: 3.14; CI 95% 1.6–3.84) .
Other findings shown by a series of studies have corroborated the idea that socioeconomic and behavioral variables act directly on the longevity of posterior restorations. The charge-paying status of the patient had an association with survival for charge-payers being slightly higher over 11 years than for non-payers. Also, a strong relationship between attendance frequency and survival time was observed, with restorations of more frequent attenders performing less well than those of less frequent attenders.
3.5
Material
In vitro studies on the properties of resin composites for the restoration of posterior teeth have shown considerable differences among commercially available materials. Differences in flexural and compressive strength , elastic modulus , fracture strength and toughness , hardness , and wear resistance , among others, have been shown to be significantly different among materials when laboratory techniques were used to compare the restoratives. Despite these considerable differences, which were usually considered to be a result of differences in organic matrix components, filler loading, or particle morphology/size, only minor differences in the clinical behavior of composite restorations placed with different composite materials are often described in clinical studies .
A restriction in clinical trials is that long observation times are hardly feasible. As a result, most prospective clinical studies comparing different composites report short follow-up periods, showing no differences among the materials under investigation. A recent retrospective study, however, has shown that, after 22 years, differences in filler characteristics between composites affected their clinical performance , as superior longevity was observed for a higher filler-loaded composite (midfilled) compared with a minifilled material when restorations were evaluated in the long term. This study was the first to indicate that the physical properties of the composite may have some impact on restoration longevity. Fracture being the main reason for failure indicates that the midfilled composite, which has higher elastic modulus and hardness than the minifilled material, was less sensitive to long-term fatigue.
However, when the same population group was assessed after a 17-year follow-up , no significant differences among the materials could be observed, indicating that differences in clinical performance between composite materials with different properties may be significant only when the late failing behavior of composite restorations is taken into consideration. At the same time, it remains to be discussed whether these significant differences found after 22 years are relevant from the perspective of dental health care. Given the finding that, in most clinical studies, AFRs between 1% and 3% have been found for the composites used, one can speculate as to whether any relevant improvement in material properties can be made that would have a clinical impact. In other words, the resin composite materials for use in posterior teeth marketed in the last two decades may have a quality standard that is sufficient to fulfill the clinical requirements in most cases.
Nevertheless, numerous resin-based materials to restore posterior teeth are introduced into the market each year, claiming improved properties and presenting innovations in organic and inorganic components. A significant concern regarding clinical trials to compare different restoratives is that while a given composite is being assessed after a few years of clinical service, the material might not be available in the market anymore. The major change in the inorganic formulation of composites for posterior restorations in the past decade was the introduction of nanofilled composites, created in an endeavor to provide a material with superior polish and gloss retention for the anterior and posterior areas. Clinical evaluations of nanocomposites compared with traditional hybrids are increasingly available in the literature , but the evaluation periods are still short (up to 5 years) to draw any significant conclusions. To date, no major clinical differences have been reported between nanofilled and hybrid materials, except for perceived better surface appearance/polish for nanofills . It is not likely that these nanofilled materials would show superior performance compared to hybrids when used in everyday situations including patients at all levels of risk. The main question will be whether these innovative materials will meet the standards that are, in the meantime, set by the available, mainly hybrid composites, showing that an AFR of 1–3% is feasible for the average Class II posterior composite restoration.
Microfilled composites, in contrast to hybrids, are generally not recommended for use in posterior restorations due to their lower fracture strength. Microfilled resin composites use an ‘organic filler’ approach, whereby inorganic particles and resin are cured, crushed and added to resin to produce the final composite material. The overall amount of filler that can be incorporated into these composites is limited, resulting in higher coefficients of thermal expansion and lower elastic moduli compared with conventional hybrids . Even though a clinical study investigating posterior restorations limited in size showed favorable results for a microfilled composite , the same material showed poor clinical performance when used in large restorations and patients with tooth wear .
One of the most comprehensive studies on the impact of the formulation of restorative composites on their clinical performance was published in 2001 . The effect of organic matrix components, filler composition and filler silanization were all addressed by clinically using experimental composites. The authors found that the resin formulation was a significant factor affecting wear, with a UDMA/TEGDMA-based formulation showing significantly higher wear resistance, while the silane and filler were not significant factors. However, the paper concentrated only on the wear of the restoratives, and the wear of current posterior composite restorations is not a clinical problem (see the following section of the paper). Nowadays, wear may be a problem mainly for patients with bruxing and clenching habits . These patients may be served best with a wear-resistant composite when their lost tooth substances are to be replaced. However, results indicating the clinical performance of composite restorations placed in patients with severe tooth wear are limited.
Current changes in the organic phase of dental composites focus on reducing the polymerization shrinkage and stress associated with methacrylate-based materials . A low-shrinkage, silorane-based resin composite was recently introduced, but clinical trials with this material are too recent and scarce to indicate any improvement in restoration longevity . Likewise, as with the nanofilled composites, it can hardly be imagined that these materials will show superior performance compared to the current hybrid composites in terms of survival considering the main reasons for failure reported in the following section of the paper. Recent developments in cariology indicate that marginal leakage, often considered an important phenomenon negatively influencing restoration performance, is not relevant for secondary caries development . However, there is always room for innovation , and novel materials might lead to clinical benefits even if they do not extend the survival of restorations, especially if new materials are designed to make the placement of resin-based composite restorations a less stressful and less technique-sensitive experience .
The material properties of the restorative composite for the posterior area, therefore, seem to have a minor effect on the longevity of restorations, provided that hybrid materials are used, as these materials have been shown to perform well to excellently when used in posterior composite restorations. Negative exceptions include some novel materials that turned out to be unacceptable shortly after being marketed , which is a reason that short-term clinical trials of a minimum of 3 years are still needed before a dentist can use a material in a posterior restoration in a responsible way. Meanwhile, clinicians are advised to stick with hybrid materials, which can be considered the ‘gold standard’ for posterior composite restorations.
Other factors related to the restorative complex might influence the clinical behavior of composite fillings. The use of a lining material, as previously mentioned, has been shown to significantly affect the longevity of restorations . Due to the possible increased risk of fatigue in the long term, a base or lining of glass-ionomer cement should not be applied when possible. The selection of an appropriate bonding agent, although significantly affecting the survival of Class V restorations , is usually described as having marginal to no or a relatively low impact on the clinical performance of posterior restorations. However, a well-performing dental adhesive may aid in reducing post-operative sensitivity. It is, therefore, advised that, when placing a posterior composite restoration, clinicians should use a ‘gold standard’ adhesive such as three-step, etch-and-rinse, or two-step, self-etch bonding agents.
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