INTRODUCTION

For more than 150 years, amalgam was the primary material used for dental restorations.¹ Today, composite resin materials, due to their esthetic and adhesive properties, are overtaking amalgam. The significant improvements in their physical properties in recent years have increased their prevalence, making them the material of choice in various clinical applications.²

Composite resin restorations were first used as anterior restorations. By the late 1990s, it was recommended that the principal use of direct composite resin restorations also include posterior restorations but be limited to permanent teeth with conservative small class 1 and class 2 restorations. This recommendation included preferably premolar teeth with little, if any, occlusal function, and mainly in patients maintaining a high standard of oral hygiene.³

Similar trends were observed in dental education. In the course of 25 years, there has been a steady increase in the use of composite resin materials for posterior tooth restoration. Whereas in the mid-1980s 90% of the dental school curricula did not include any consistent teaching of posterior composite resins, the percentage dropped to 4% in the late 1990s and to 0% by the early 2000s. Moreover, today some universities teach composite restoration before introducing amalgam.^4,5

A comprehensive study compared three schools in three countries (Sweden, Wales, and Ireland) differing in their health care systems, financial remuneration schemes, and regulatory bodies. It found a direct relationship between the number of hours allocated to teaching the placement of posterior resin composites and the students' own perception of the adequacy of their learning combined with confidence in using these materials in clinical procedures. It is conceivable that students who are not confident in performing certain procedures may steer away from using these techniques in the future and may even remain incompetent in these specific procedures for some time.⁴

Guidelines of the Association for Dental Education in Europe maintained that new dentists must be competent “to restore the tooth appropriately to form, function and esthetics with different appropriate materials.” Similarly, the UK General Dental Council recommends that new graduates should be qualified in “completing a wide range of procedures in restorative dentistry, including the use of amalgam alloy restorations and tooth-colored restorations.”⁶

The present study aimed to evaluate current teaching trends, including the methods and materials used for direct restoration of posterior teeth and to evaluate whether the types of restoration performed by undergraduate students could serve as a predictive tool, with emphasis on the preference for composite materials over amalgam.

METHODS

All direct restorations performed by graduate students at the Hebrew University of Jerusalem's Hadassah School of Dental Medicine between 2004 and 2016 were registered and evaluated. The Faculty of Dental Medicine runs a six-year program in which students treat patients from the fourth year. Treatments were performed in the student clinic by students in their fourth, fifth, and sixth year of studies and supervised by experienced instructors. The duration of the clinic differs between clinical years. Fourth-year students have a six-hour clinic per week, while fifth- and sixth-year students have a 10- and 11- hour clinic, respectively.

Clinical decisions, including material choice, were supervised by instructors from the Department of Prosthodontics. The instructors' experience varied, ranging from one to 40 years.

Each treatment was documented in a computerized file. The medical records were signed by the instructors for every procedure for medical, legal, and monitoring purposes.

Data relating to tooth type, number of surfaces restored, and restoration material (amalgam/composite) were included.

For comparison, the types of restorative materials used were divided into three groups, according to the number of surfaces restored (one, two, and three), type of tooth (molars vs premolars), and jaw (maxilla vs mandible).

The data were arranged and displayed according to frequency tables and scatter charts.

RESULTS

A total of 26,925 restorations were performed in posterior teeth by undergraduate students at the Hadassah School of Dental Medicine from 2004 to 2016. During this 13-year period, the restorative material distribution was almost equal; that is, 49.54% (n=13,338) of the restorations performed were amalgam, and 50.46% (n=13,587) were composite resin. The shift in material choice may be seen in Figure 1. From 2004 to 2008, the material of choice was amalgam. From 2008 to 2012, a similar number of amalgam and composite restorations were performed. The year 2012 marked a turning point, composite resin becoming the dominant material, its use steadily rising.

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The results were analyzed further on the basis of surface number (Figure 2). The predominance of one-surface composite restorations was clear, increasing from 54.7% (n=330) in 2004 to 81.9% (n=873) in 2016, whereas amalgam restorations dropped to 18.11% (n=193). The situation was slightly different regarding two-surface restorations. The number of amalgam restorations exceeded the number of composite restorations until 2013. After that, composite restorations were preferred over amalgam. The trend during the study period was clear: from one-third, 33.3% (n=254), of the two-surface restorations in 2004 to almost two-thirds, 64.3% (n=721), in 2016. Three-surface restorations showed a similar trend. Whereas in 2004 amalgam restorations were of significantly higher proportion than composite restorations, 72.08% vs 27.92% (n=253 vs n=98), in 2016 the percentage of amalgam restorations dropped to 51.34% (n=173).

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The percentage of restorations in the premolar and molar groups is depicted in Figure 3. As can be seen, since 2010, at the expense of amalgam restorations, there has been a steady and constant increase in the percentage of composite restorations in premolars, which by 2016 reached 80.87% (Figure 3A). In molars, as shown in Figure 3B, the percentage of amalgam restorations in 2004 was 66.70% (n=775) and that of composite restorations 33.30% (n=387). The shift toward composite restorations was gradual, the balance tilting to 63.5% (n = 1035) by 2016.

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Restorations in relation to tooth location (first premolar, second premolar, first molar, second molar, and third molar) in both jaws showed a decreasing percentage of composite resin restorations with distal advance (Figure 4.)

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A comparison between the maxilla and the mandible shows no noticeable differences between the trends (Figure 5.)

DISCUSSION

During the 13-year period of the study, composite resin became the dominant restorative material, the turning point evident in 2008. A growing transition toward composite resin restorations and a continuous reduction in amalgam shifted the ratio in favor of composite resin restorations in 2012 with a steady linear increase in one-, two-, and three-surface restorations, both in molars and in premolars, regardless of jaw. The shift in trend of the premolar group preceded that of the molar group. This is most likely related to esthetic considerations. Nonetheless, in three-surface restorations, slightly larger amounts of amalgam restorations were observed. It is likely that the overall trend, as in other worldwide dental faculties,^4,7 is adapting itself to the global trend toward an amalgam-free era.

The shift in treatment can be accounted for by numerous reasons. Composite materials have the ability to bond mechanically to the remaining tooth tissues, thereby strengthening the tooth's structure, restoring its original physical integrity and biomechanical properties.⁹ Yet the main reason is most likely the increased awareness of the advantage of a minimally invasive approach in treating caries.^2,8 Recent developments in restorative dentistry show that the “extension for prevention” traditional guideline should be avoided and “minimally invasive dentistry” techniques promoted instead. This would avoid unnecessary excessive removal of healthy dental tissue as part of the treatment, leaving the restored teeth with a better overall prognosis and a greater ability to withstand loading in function.^1,8

Another reason for the increase in composite use may be the sectional matrix systems that were introduced in 2008.⁹ These include not only advanced anatomic wave-like wedges but also redesigned bands and grooved, V-shaped tine rings covered with silicone, allowing proper anatomy and tight proximal contact areas,¹⁰ formerly considered problematic, in composite restorations.

Furthermore, the unceasing development of new materials and instruments, as well as improved composite resin material properties and performance, advocated more frequent use of such materials in the posterior area. For one, the new bulk-fill materials (like SDR from Dentsply and Filtek Bulk-Fill from 3M ESPE) probably contributed to favoring composite materials by reducing technique sensitivity¹¹ and procedure duration.¹² Other contributing factors may be newer, advanced adhesive systems, self-etch, and 10-methacryloyloxydecyl dihydrogenphosphate–containing materials.¹³ In addition, practitioners have had several years of experience with these materials, mastering the techniques required to handle them and perfect their use.⁴ This probably also plays a major role in relying on composite materials and abandoning amalgam.

Another contributing factor is the accumulating evidence that the overall performance of the posterior composite resin restorations is high¹⁴ and at least comparable to that of amalgam restorations in many clinical settings.^15,16 Although the annual failure rate of composite restorations is still slightly higher than that of amalgam restorations, it is likely that in future studies the annual failure rate of posterior composite resins will be lower than those found in the present reviews.^14,17,18

Patients also play an important role in these changes. The awareness and demand for an esthetic outcome, as well as the controversy over amalgam safety, have increased patient preference for composite resin restorations.

The amalgam debate is a driving force in the shift. Environmental pollution caused by medical waste containing mercury is a political issue in some countries. In Norway, for example, the use of amalgam has been banned from 2008,¹⁹ and it appears that similar bills, based mostly on this environmental background, are being promoted in other European countries.²⁰ In 2013, the Minamata Convention (a World Health Organization committee dealing with the effects of mercury on the environment) committed itself to reducing and limiting the use and production of a range of mercury-containing products, including dental amalgam.²

In March 2017, the European Parliament agreed to prohibit by July 2018 the general use of amalgam in children under 15 years of age and pregnant or breast-feeding women and required member states to draft national plans for phasing down the use of dental amalgam by July 2019, aiming to phase it out by 2022.²¹

These decisions, especially that of the Minamata Convention, have encouraged the production of alternatives to amalgam, causing an irrevocable change of what is customary in restorative dentistry,¹ as reflected also in the present study.

The present findings express the confidence and trust of clinical instructors in using composite resin materials to restore posterior teeth. Moreover, the young generation of instructors who has joined the more experienced ones may also have contributed to the increasing use of composite restorations due to their clear preference for esthetic materials.²²

It is apparent that the change in trend observed over the past 13 years is on the rise. This change seems consistent with what is happening in other schools of dentistry worldwide.

Although few studies addressed the changes, data from 2011 in the United States showed that posterior composite restorations (for both one and two surfaces) exceeded amalgam restorations in number. In three- and four-surface restorations, similar to our study, amalgam was still the material of choice.⁵ In Ireland and the United Kingdom, in the period between 2005 and 2010, a 33% drop in the number of amalgam restorations performed by students was recorded, whereas the number of posterior composite resin restorations increased by 180%.⁷

It is reasonable to assume that the change in trend observed within the faculty will be further reflected in the choices the young graduates will make. It should be emphasized that clinical instructors pass on their own practice methods to their students and that the educational experiences students accumulate throughout their studies contribute to their competency and determine the techniques they will use in their postgraduate practices as independent dentists. Students who graduated in 2008 and thereafter will be practicing dentistry for many decades in the future, making them the leading dentists of the global trend of the shift toward composite resin materials.

CONCLUSIONS

In conclusion, a clear trend in favor of composite resin restorations is evident in this 13-year survey. These results may suggest that the next generation of dentists will favor resin composite restoration, thus moving toward an amalgam-free era.