journal of dentistry 42 (2014) 503–516

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Review

The teaching of posterior resin composites: Planning for the future based on 25 years of research Nairn H.F. Wilson a, Christopher D. Lynch b,* a b

King’s College London Dental Institute, London, United Kingdom School of Dentistry, Cardiff, United Kingdom

article info

abstract

Article history:

Objectives: The restoration of posterior teeth affected by caries, trauma or wear remains one

Received 5 February 2014

of the commonest procedures in the practice of dentistry. Over the past 20 years the first

Accepted 20 February 2014

author and latterly the second author have led a series of surveys around the world to capture information on the teaching of posterior resin composites. The aim of this paper is to identify trends, reflect on the findings and make recommendations for the further

Keywords:

development of this important aspect of the curriculum for primary dental qualifications.

Resin composites

Methods: Surveys on the teaching of posterior resin composites were completed in 1986,

Posterior composites

1997–99, 2004–05 and 2007–2009. The findings from these surveys were reviewed and drawn

Dental education

together to allow historical and contemporary international trends to be identified. Recom-

Operative dentistry

mendations for further developments in the teaching of posterior resin composites were

Dentine bonding

formulated from the cumulated data and trends identified. Results: Information was available from a total of 679 survey returns. Increased teaching of posterior resin composites has been observed over the period of the surveys: while 90% of dental school curricula did not include any didactic teaching of posterior resin composites in the mid-1980s, this dropped to 4% or less in the late 1990s, and to 0% in the early 2000s. In the late 2000s, however, 21% of dental schools still did not teach the placement of resin composites in three-surface cavities in permanent molar teeth. Areas of confusion were reported in the teaching of certain aspects of cavity design, notably the use of bevels, and in the protection of operatively exposed dentine. Conclusions: While there has been steady growth in, and trends towards evidence-based teaching of posterior resin composites in dental schools around the world over the last 20–25 years, there is a need for further developments and harmonisation in this important aspect of curricula for primary dental qualifications. This need is now pressing, subsequent to the signing of the Minamata Convention. It is recommended that all new graduates, from no later than 2020, should have the knowledge, skills, competences and confidence to effectively restore damaged and diseased posterior teeth with state-of-the-art resin composite systems. # 2014 Elsevier Ltd. All rights reserved.

* Corresponding author at: School of Dentistry, Cardiff University, Heath Park, Cardiff CF14 4XY, United Kingdom. E-mail address: [email protected] (C.D. Lynch). http://dx.doi.org/10.1016/j.jdent.2014.02.014 0300-5712/# 2014 Elsevier Ltd. All rights reserved.

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1.

journal of dentistry 42 (2014) 503–516

Introduction

Recent developments in the restoration of teeth have focussed on advances and the application of minimal intervention approaches to treatment.1 The main advantage of such approaches to treatments is the avoidance of the unnecessary sacrifice of healthy and salvageable tooth tissue as part of the treatment, leaving restored teeth more able to withstand loading in function and with an enhanced prognosis. Critical to these developments has been advances in resin composites and associated adhesive technologies, and numerous improvements in relevant operative techniques, instrumentation and devices.2,3 While evidence-based, minimal intervention, resin composite approaches to the restoration of posterior teeth are of increasing popularity, they remain to be viewed favourably, let alone suitably applied, by practitioners wedded to the traditional use of dental amalgam.4,5 Many of these practitioners, including some dental educators, are sceptical about the evidence that posterior resin composites, notwithstanding their advantages in terms of offering minimal intervention approaches to treatment, more aesthetic clinical outcomes and enhanced patient satisfaction, may be found to perform as well as restoration of dental amalgam in clinical service. Others, regrettably, would appear to be largely, if not solely limited to the use of dental amalgam in the restoration of posterior teeth given local, outdated funding arrangements, circumstances and thinking.6 Contrary to residual negative thinking and stoic reluctance to accept the growing body of supportive evidence, posterior resin composite restorations are now widely accepted to be a viable, successful and predictable alternative to more traditional approaches to the direct restoration of posterior teeth, notably the placement of restorations of dental amalgam.7–17 When placed appropriately, the advantages offered by posterior resin composites have been shown to include:  a modern minimal intervention approach to tooth restoration: following access, sufficient to instrument the lesion and complete the desired preparation, the judicious removal of at least all infected carious dentine, and careful finishing to optimise bonding and marginal seal, the resulting cavity can be readily restored with resin composite, typically without the use of a liner or base, subject to using appropriate instrumentation and state of the art techniques. The need to remove caries-affected dentine, let alone intact tooth substance to create retentive features such as undercuts, locks, grooves and dovetails, as is necessary prior to the placement of a restoration of dental amalgam, can be avoided;  the ability to bond the resin composite restoration to the remaining tooth tissues. This greatly enhances the marginal integrity of a resin composite restoration and the extent to which the biomechanical properties of the tooth are restored in the process;  the ability to incorporate preventive measures in the restorative procedure; for example, the sealing of adjacent pits and fissures;

 the subsequent ability to readily and predictably refurbish and repair restorations in clinical service, offering opportunity to greatly delay the trajectory down the ‘‘restorative death spiral’’;  a tooth-coloured and aesthetic appearance, with good patient acceptance. An important aspect of posterior resin composites, which are techniques sensitive, is the training of the future dental workforce in their use. For posterior resin composites to be successfully applied and realise their potential, it is critically important that the dental team is competent in this approach to the restoration of posterior teeth, with dental practitioners shouldering the responsibility of leading the dental team in its safe, effective management of patient. Herein lies a concern, given that dental school programmes are often criticised by, amongst others, practitioners who practice state-of-the-art dentistry for ‘‘lagging behind’’ developments in dental practice18 and producing graduates who are ‘‘not as good as they used to be’’ in terms of being both competent and confident to provide contemporary primary dental care.19 To address such concerns, dental schools around the world have to decide when, and to what extent to introduce the teaching of a new approach, in the knowledge that new teaching will, to a greater or lesser extent, be at the expense of traditional teaching, in a typically overcrowded and pressurised curriculum. The introduction of the teaching of posterior resin composites and associated minimal intervention techniques into dental school teaching provides a good case study of the issues and difficulties, and variations in and between countries in adapting, if not changing teaching to reflect the modern and anticipated future aspects of the clinical practice of dentistry. Substantial evidence now exists from primary and secondary/specialist sectors of dentistry to support the routine use of posterior resin composite restorations.7–17 This has not always been the case: as recently as the late 1990s, a review paper recommended that ‘‘the placement of composite in posterior teeth be restricted to small occlusal and occlusoproximal restorations’’ and preferably teeth with ‘‘limited occlusal function’’.20 There have, however, been huge developments and a considerable amount of research in the area over the last 10–15 years, posing the question: How many dental school curricula have been developed to reflect these changes, let alone the now substantial evidence-base? Furthermore, subsequent to the signing of Minamata Convention which, amongst a wide range of measures, seeks an international reduction (phase-down) in the placement of dental amalgam, it is considered important to know the extent to which dental schools have shifted to the teaching of alternative materials to dental amalgam, notably resin composite systems.21,22 Over the past twenty five years the first author and latterly the second author have led a series of surveys in different countries to capture information on the teaching of posterior resin composites.23–37 The aim of this paper is to draw together the results of these surveys, identify current and historical trends, and make recommendations for further developments in the teaching of posterior resin composites, in particular, subsequent to the signing of the Minamata Convention.

Table 1 – Previous publications which have detailed the teaching of posterior composites. Year

Country

2009

Spain

2

2009

US & Canada

3

2009

UK & Ireland

4

2008

Iran

5

2007

Japan

6

2005

US

7

2005

Canada

8

2004

UK & Ireland

9

1999

Brazil

10

1997

Japan

11

1997

Europe

12

1997

US & Canada

13

1986

World-wide

Title

Authors

Journal

Citation

Castillo-de Oyagu¨e R, Lynch C, McConnell R, Wilson N

Med Oral Patol Oral Cir Bucal

2011; 16: e1005–13

Lynch CD, Frazier KB, McConnell RJ, Blum IR, Wilson NH

J Am Dent Assoc

2011; 142: 612–20

Lynch CD, Frazier KB, McConnell RJ, Blum IR, Wilson NH

Br Dent J

2010; 209: 129–36

Sadeghi M, Lynch CD, Wilson NH

Eur J Prosthodont Restor Dent

2009; 17(4): 182–7

Hayashi M, Seow LL, Lynch CD, Wilson NH Lynch CD, McConnell RJ, Wilson NH

J Oral Rehabil

2009; 36: 292–8

J Am Dent Assoc

2006; 137: 619–25

Lynch CD, McConnell RJ, Hannigan A, Wilson NH

J Can Dent Assoc

2006; 72: 321

Lynch CD, McConnell RJ, Wilson NH

Eur J Dent Educ

2006; 10: 38–43

Gordan VV, Mjo¨r IA, Veiga Filho LC, Ritter AV

Quintessence Int

2000; 31: 735–40

Fukushima M, Iwaku M, Setcos JC, Wilson NH, Mjo¨r IA

Int Dent J

2000; 50: 407–11

Wilson NH, Mjo¨r IA

J Dent

2000; 28: 15–21

Mjo¨r IA, Wilson NH

J Am Dent Assoc.

1998; 129: 1415–21.

Wilson NH, Setcos JC

J Dent

1989; 17 Suppl. 1: S29–33

505

Teaching the placement of posterior resin-based composite restorations in Spanish dental schools. Minimally invasive management of dental caries: contemporary teaching of posterior resin-based composite placement in U.S. and Canadian dental schools. State-of-the-art techniques in operative dentistry: contemporary teaching of posterior composites in UK and Irish dental schools. Trends in dental education in the Persian Gulf—an example from Iran: contemporary placement of posterior composites. Teaching of posterior composites in dental schools in Japan. Teaching the placement of posterior resin-based composite restorations in U.S. dental schools. Teaching the use of resin composites in Canadian dental schools: how do current educational practices compare with North American trends? Teaching of posterior composite resin restorations in undergraduate dental schools in Ireland and the United Kingdom. Teaching of posterior resin-based composite restorations in Brazilian dental schools. Teaching of posterior composite restorations in Japanese dental schools. The teaching of Class I and Class II direct composite restorations in European dental schools. Teaching Class I and Class II direct composite restorations: results of a survey of dental schools. The teaching of posterior composites: a worldwide survey.

journal of dentistry 42 (2014) 503–516

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Table 2 – Distribution of schools surveyed. Era

Country

Year

Number of schools contacted

Number of respondent schools

Response rate (%)

Late-00s

Spain US & Canada UK & Ireland Iran Japan

2009 2009 2009 2008 2007

15 67 17 18 27

15 49 17 18 23

100 73 100 100 79

Mid-00s

US Canada UK & Ireland

2005 2005 2004

52 10 15

47 10 15

90 100 100

Late 1990s

Brazil Japan Northern & Central Europe US & Canada

1999 1997 1997 1997

92 29 185 65

63 27 104 54

68 93 56 83

1980s

World-wide

1986

536

237

44

1128

679

2.

Materials and methods

Surveys on the teaching of posterior resin composites were completed in 1986, 1997–99, 2004–05 and 2007–2009. The key findings from these studies (Table 1) were drawn together and summarised in tabular form. Historical and contemporary trends were identified. The key findings included:  inclusion of the teaching of posterior resin composites within the dental school curriculum  preclinical and clinical teaching  clinical placement of posterior restorations  differences in cavity design taught  contraindications taught to the placement of posterior resin composites  management of operatively exposed dentine  restoration of proximal contours  light curing technologies taught Given differences in methodology between different surveys, statistical analyses were not undertaken. Instead, descriptive analyses are reported.

3.

Results

3.1.

Details of respondent schools

The distribution of schools surveyed is shown in Table 2. Over the period of investigation, data has been collected from 679 survey responses from dental schools across the world. For convenience, each of these surveys have been categorised chronologically into relevant ‘eras’, namely: 1980s, late 1990s, mid-2000s and late-2000s.

3.2.

1980s survey

The data from the 1980s survey is available in a different manner to that of the later surveys. As such, it is difficult to make direct comparisons between the data from the initial

studies and the subsequent investigations. The key points noted in the 1980s surveys included:  Less than 10% of respondent schools reported that they included the preclinical, let alone any other teaching of posterior resin composites in their curriculum;  One-in-12 schools would allow or possibly encouraged (but did not require) students to place posterior resin composites clinically;  The reasons reported by schools for not teaching posterior resin composites, at that time, included: a lack of long term data on the performance of resin composite restorations, limitations of resin composite materials, including difficulties in placement, and that resin composite materials and associated instruments and devices were undergoing rapid development, much of which had not been tried and tested and had an uncertain future.

3.3.

Teaching of posterior resin composites

Looking across the survey reports, it is possible to identify trends to increase the teaching of different types (one-, twoand three-surface restorations) and sizes of posterior resin composites. It is possibly more interesting, however, to consider the numbers of respondent schools which indicated that they did not teach posterior resin composites restorations (Table 3). While as many as 44% of schools did not include any (didactic) teaching of posterior resin composites in the 1980s, this dropped to 4% or less in the late 1990s and to 0% in the early-2000s. Within the various surveys, specific questions were asked about the types of restorations taught – molar and/or premolar, occlusal single surface, two-surface occlusoproximal, and three-surface occlusoproximal restorations. Data on historical trends in this area, reported according to number of schools not teaching different types of restorations, are included in Table 4. By the time of the late 2000s, 26 (21%) of the schools included in the surveys did not teach threesurface occlusoproximal resin composite restorations in permanent molars (15 schools in Japan, eight schools in the US and Canada, two schools in the UK and Ireland and one

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journal of dentistry 42 (2014) 503–516

Table 3 – Information on schools who reported not including teaching of posterior resin composites in their dental school curricula. Era

Country

Year

Number of respondent schools

Percentage of schools not including teaching of posterior resin composites

Late-2000s

Spain US & Canada UK & Ireland Iran Japan

2009 2009 2009 2008 2007

15 49 17 18 23

0 0 0 0 0

Mid-2000s

US Canada UK & Ireland

2005 2005 2004

57 10 15

0 0 0

Late 1990s

Brazil Japan Northern & Central Europe US & Canada

1999 1997 1997 1997

92 29 49 54

0 7 2 2

1980s

Japan US & Canada Europe Other

1986 1986 1986 1986

14 63 83 78

36 33 29 33

school in Spain). Similarly 21 (17%) of the schools included in the surveys did not include teaching of three surface occlusoproximal resin composite restorations in premolar teeth (14 schools in Japan, four schools in the US and Canada, two schools in the UK and Ireland and one school in Spain).

3.4.

66% of schools in the UK and Ireland, 70% in Canada, and 81% in the US), there has subsequently been an increase in the percentage of schools teaching the use of resin composite before teaching the use of dental amalgam, in particular, in UK and Irish dental schools (UK and Irish dental schools, 63%; US and Canadian schools, 26%).

Preclinical teaching 3.5.

Information as to whether the use of resin composite or dental amalgam was taught first in preclinical teaching on the restoration of posterior teeth is presented in Fig. 1. (No information was collected on this topic in the 1980s or late 1990s round of surveys.) While it was found that dental amalgam was taught first in most schools in the early 2000s:

Clinical placement of posterior restorations

Information on the proportions of restorations of resin composite and dental amalgam placed by dental students is reported in Fig. 2. (No information on this aspect of the relevant teaching was collected in the 1980s or late 1990s round of surveys.) Overall, there has been a steady shift

Table 4 – Information on types of posterior composite restorations taught.a Era

Country

Year

Number of respondent schools

Schools not teaching various types of posterior composite restoration (%, n) Occlusal premolar

(0) (0) (0) (0) (0)

0% 0% 0% 0% 4%

(0) (0) (0) (0) (1)

2-Surface occlusoproximal molar 0% 2% 0% 0% 26%

(0) (1) (0) (0) (6)

3-Surface occlusoproximal premolar 7% 8% 12% 0% 61%

(1) (4) (2) (0) (14)

3-Surface occlusoproximal molar

Spain US & Canada UK & Ireland Iran Japan

2009 2009 2009 2008 2007

15 49 17 18 23

0% 0% 0% 0% 0%

Mid-00s

US Canada UK & Ireland

2005 2005 2004

47 10 15

0% (0) 0% (0) 0% (0)

0% (0) 0% (0) 0% (0)

2% (1) 0% (0) 7% (1)

2% (1) 0% (0) 7% (1)

11% (5) 10% (1) 33% (5)

32% (15) 10% (1) 33% (5)

Late 1990s

Brazil Japan Northern & Central Europe US & Canada

1999 1997 1997

63 27 49

0% (0) 7% (2) 2% (1)

10% (6) 7% (2) 2% (1)

3% (2) 33% (9) 8% (4)

49% (31) 33% (9) 8% (4)

13% (8) 77% (21) 16% (8)

67% (42) 77% (21) 16% (8)

1997

54

2% (1)

2% (1)

6% (3)

6% (3)

26% (14)

26% (14)

No information collected on this question in the 1986 survey.

0% 0% 0% 0% 0%

2-Surface occlusoproximal premolar

Late-00s

a

(0) (0) (0) (0) (0)

Occlusal molar

7% 16% 12% 0% 65%

(1) (8) (2) (0) (15)

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journal of dentistry 42 (2014) 503–516

100%

80%

60%

Posterior composite Amalgam

40%

Metal inlays (Japan only) 20%

0% UK & Ireland

USA

Canada

Japan

Iran

UK & Ireland

USA & Canada

Spain

2004

2005

2005

2007

2008

2009

2009

2009

Fig. 1 – Technique taught first in preclinical course.

towards the placement of posterior resin composites, rather than restorations of dental amalgam by dental students from the mid 2000s. Thirty percent of posterior restorations placed by students were of resin composite in the mid 2000s, rising to around 50% in the late 2000s in US and Canadian schools, with as much as 55% in UK and Irish dental schools.

3.6.

Differences in cavity design taught

Data on differences in cavity design taught for posterior resin composite and amalgam restorations is summarised in Table 5. (No information was collected on this in the 1980s or late 1990s round of surveys.) The most common differences – noted in the mid 2000s and the late 2000s, included no need for ‘extension for prevention’ (late 2000s: 80% of schools) and the use of ‘slot-type’ cavities for occlusoproximal restorations, with no occlusal component (late 2000s: 59% of schools). Bevelling, of either occlusal or proximal cavosurface margins,

remains common (late 2000s: 22% and 43% of schools, respectively).

3.7.

Contraindications to posterior resin composites

The five most common contraindications taught for the placement of posterior resin composites in the late 2000s round of surveys are shown in Table 6. A history of adverse reaction to resin composite materials remains the most commonly taught contraindication (Japanese dental schools, 95%; US and Canadian schools, 94%; UK and Irish schools, 88%; Iranian schools, 89%; Spanish schools, 87%). With the exception of one region (Japan), none of the other regions in late 2000s surveys included cavity size as a contraindication to posterior resin composite placement in the five most common contraindications. Cavity size data is presented in detail in Table 7. This reveals how cavity size has influenced the teaching of posterior resin composite

Percentage of restorations

80

60

Posterior composite

40

Other materials

20

0 UK & Ireland

USA

Canada

Japan

Iran

UK & Ireland

USA & Canada

Spain

2004

2005

2005

2007

2008

2009

2009

2009

Fig. 2 – Proportions of direct posterior restorations placed by undergraduate students.

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journal of dentistry 42 (2014) 503–516

Table 5 – Principles of cavity design taught: differences with ‘traditional’ amalgam cavities.a Era

Country

Year

Number of respondent schools

Principles of cavity design taught: differences with ‘traditional’ amalgam cavities (%, n) No ‘extension for prevention’

Late-00s

Spain US & Canada UK & Ireland Iran Japan

2009 2009 2009 2008 2007

15 49 17 18 23

Mid-00s

US Canada UK & Ireland

2005 2005 2004

47 10 15

a

67% 78% 59% 89% 100%

‘Slot type’ cavity (i.e. no occlusal component

(10) (38) (10) (16) (23)

73% 67 47% 56% 43%

70% (33) 80% (8) 87% (13)

(11) (33) (8) (10) (10)

55% (26) 80% (8) 87% (13)

Rounded internal line angles 87% 3% 47% 78% 96%

(13) (31) (8) (14) (22)

81% (38) 70% (7) 87% (13)

Bevelled occlusal margins 60% 8% 18% 0% 48%

(9) (4) (3) (0) (11)

28% (13) 0% (0) 27% (4)

Bevelled box margins

73% 47% 18% 62% 17%

(11) (23) (3) (11) (4)

49% (23) 60% (6) 20% (3)

No information collected on this question in the 1986 survey, or those in the late 1990s.

placement. While the restoration of small cavities with resin composites has never seemed to be a concern, the data recorded reveals ongoing concerns in relation to placement of resin composites in larger cavities (i.e., where the buccolingual width of the cavity exceeds one-half of the intercuspal width of the tooth), albeit to a lesser extent in recent years, compared to earlier surveys.

posterior resin composite, with this trend being more obvious in European data than North American school data (‘‘deep’’ – inner third of dentine- no liner or base placed: Spain, 47% of schools; UK and Ireland, 41% of schools; Japan, 35% of schools; US and Canada, 12% of schools; Iran, 11% of schools).

3.9. 3.8.

Restoration of proximal contours

Management of operatively exposed dentine

Trends in the teaching of the management of operatively exposed dentine are apparent from the data presented in Table 8. The data suggests that in recent years there has been an increased trend towards ‘‘bonding’’ only (i.e., no liner or base placed) rather than ‘‘basing’’ prior to the placement of a

Information on techniques taught for the restoration of proximal contours is presented in Fig. 3. (No information was collected on this in the 1980s or late 1990s round of surveys.) While the use of some form of circumferential metal matrix system remains the most popular technique taught, there has been an increase in the teaching of sectional matrix

Table 6 – The five most common contraindications taught to the placement of posterior resin composites in dental schools surveyed in the late-00s round of surveys (percentages refer to percentages of respondent schools who agreed this was a contraindication).

>50% of schools agreed

two-thirds of the intercuspal width (61%)

History of allergy to composite materials (89%) Poor patient cooperation (83%)

Poor patient cooperation (53%)

Subgingival margins (82%) High caries risk (70%) Replacement of a large amalgam restoration (67%)

Subgingival margins (60%)

Inability to place rubber dam (47%) Poor oral hygiene (41%)

Replacement of a large amalgam restoration (33%) High caries risk (33%)

Subgingival margins (72%) Poor oral hygiene (72%) Pathological wear (56%)

Replacement of a large amalgam restoration (39%) Poor patient cooperation (39%) Poor oral hygiene (35%)

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journal of dentistry 42 (2014) 503–516

Table 7 – Number of schools which considered the following cavity dimensions to be contraindications to the placement of occlusoproximal composites in premolars or molars.a Era

Country

Year Number of respondent schools

Buccolingual width of occlusal portion is 2/3 of intercuspal width

Buccolingual width of proximal box is >1/2 of intercuspal width

Premolars Molars Premolars Molars Premolars Molars Premolars Late-00s

Spain US & Canada UK & Ireland Iran Japan

2009 2009 2009 2008 2007

15 49 17 18 23

0% (0) 2%(1) 0% (0) 6% (1) 4% (1)

0% 2% 0% 6% 4%

Mid-00s

US Canada UK & Ireland

2005 2005 2004

47 10 15

4% (2) 0% (0) 0% (0)

4% (2) 0% (0) 0% (0)

Late 1990s Brazil Japan Europe US & Canada

1999 1997 1997 1997

63 27 104 54

3% 11% 12% 6%

(2) (3) (12) (3)

5% 7% 10% 6%

(0) (1) (0) (1) (1)

0% 18% 0% 6% 4%

(3) (2) (10) (3)

(0) (9) (0) (1) (1)

0% 24% 0% 6% 9%

(0) (12) (0) (1) (2)

33% 55% 18% 17% 22%

(5) (27) (3) (3) (11)

27% 57% 24% 17% 61%

(4) (28) (4) (3) (14)

20% 24% 0% 6% 13%

(3) (12) (0) (1) (3)

Molars 20% 33% 0% 6% 22%

(3) (16) (0) (1) (5)

23% (11) 30% (3) 7% (1)

34% (16) 30% (3) 13% (2)

57% (27) 70% (7) 60% (9)

66% (31) 70% (7) 67% (10)

32% (15) 20% (2) 20% (3)

22% 41% 20% 35%

60% 59% 42% 67%

76% 81% 62% 86%

86% 88% 78% 89%

Not reported 41% (11) 41% (11) 35% (36) 59% (61) 50% (27)b 50% (27)b

(14) (11) (21) (19)

(38) (16) (44) (36)

(48) (22) (64) (46)

(54) (24) (81) (48)

49% (23) 20% (2) 27% (4)

a

This question was asked in relation to ‘‘indications’’ in the late 1990s surveys, but contraindications in the later surveys. The results from the late 1990s surveys have been adjusted to take this into account. No information collected on this question in the 1986 survey. b The report from the US & Canadian 1997 study states ‘‘about half of the schools reported having faciolingual limitations on the width of the interproximal box’’. An exact figure is not stated. Therefore for the purposes of this work, it is assumed to be 50%.

systems in recent years (late 2000s: US and Canadian schools, 93%; UK and Irish schools, 47%; Spanish schools, 46%; Iranian schools, 33%; Japanese schools, 17%). The continued teaching of transparent matrix systems has been noted.

3.10.

conducted in the late 2000s indicate that this situation has been reversing.

4.

Discussion

Light curing technologies

The data collected on the teaching of different light curing technologies is summarised in Fig. 4. (No information was collected on this in the 1980s or late 1990s round of surveys.) While the surveys from the mid 2000s indicated that the use of quartz halogen light curing units was more common than the use of light emitting diode units, data from the surveys

This review provides valuable insight into the significant changes that have taken place in the teaching of operative dentistry techniques, in particular in relation to the restoration of posterior teeth, over the past 20 years. Of particular note is timing and rate of changes in the teaching within and between countries relative to developments in the relevant evidence-base. It is suggested that developments

Table 8 – Teaching of management of operatively exposed dentine (moderate/middle-third and deep/inner-third cavities; Ca(OH)2 = calcium hydroxide; GIC = glass ionomer cement).a Era

Country

Year Number of respondent schools

Techniques taught for management of operatively exposed dentine (%, n) Deep (inner third of dentine)

Moderately deep (middle third of dentine)

No liner/base Ca(OH)2 & GIC GIC only No liner/base Ca(OH)2 & GIC GIC only Late-00s

Spain US & Canada UK & Ireland Iran Japan

2009 2009 2009 2008 2007

15 49 17 18 23

87% 49% 76% 22% 91%

Mid-00s

US Canada UK & Ireland

2005 2005 2004

47 10 15

70% (33) 70% (7) 40% (6)

Late 1990s Brazil Japan Europe US & Canada

1999 1997 1997 1997

63 27 104 54

a

52% 63% 27% 58%

(13) (24) (13) (4) (21)

(33) (17) (28) (31)

No information collected on this question in the 1986 survey.

0% 2% 0% 0% 0%

(0) (1) (0) (0) (0)

0% (0) 0% (0) 0% (0) 3% 11% 65% 32%

(2) (3) (68) (17)

0% 49% 18% 78% 13%

(0) (24) (3) (14) (3)

47% 12% 41% 11% 35%

(7) (6) (7) (2) (8)

13% 49% 41% 94% 48%

(2) (24) (7) (17) (11)

40% 61% 24% 28% 48%

(6) (30) (4) (5) (11)

36% (17) 40% (4) 67% (9)

10% (4) 30% (3) 20% (3)

64% (30) 30% (3) 73% (11)

45% (21) 60% (6) 73% (11)

48% 22% 10% 3%

6% 26% 10% 11%

70% 44% 69% 72%

80% 67% 77% 47%

(30) (6) (10) (2)

(4) (7) (10) (6)

(44) (12) (72) (39)

(50) (18) (80) (25)

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journal of dentistry 42 (2014) 503–516

100

Percentage of schools

80

60 Circumferenal metal Circumferenal transparent Seconal Metal

40

20

0 UK & Ireland

USA

Canada

Japan

Iran

2004

2005

2005

2007

2008

UK & Ireland USA & Canada

2009

2009

Spain 2009

Fig. 3 – Matrix systems taught for occlusoproximal restorations.

in techniques taught to dental students may be found to be relatively rapid and widespread, and ahead of the development of robust evidence base, if an innovation offers a faster, simpler and less expensive alternative to a traditional technique. In contrast, when the innovation, as is the case with posterior resin composites, is more demanding, time consuming and costly, it would appear that adoption can be a long drawn out affair, despite acceptance of advantages and relevant evidence of sufficient quality. In the case of shifting to the teaching of posterior resin composites, rather than the traditional use of dental amalgam, the situation may have been confounded by a number of factors, including, for example, clinical teachers lacking the knowledge, skills and confidence to teach the relevant techniques, qualifying examinations assessing students in traditional rather than contemporary approaches to the restoration of posterior teeth, or simply a reluctance by schools or amongst teachers to set aside traditional, mechanistic concepts in favour of adopting a modern, preventatively orientated approach to the restoration of posterior teeth.

Dental schools need to be forward-thinking in the continuous process of curriculum development, mindful that existing students may well continue to practice dentistry for >50 years into the future. At present that means well into the second half of the present, twenty first century, when oral healthcare provision will be very different from that currently practiced. At the time of graduation dental students should be safe beginners fit for future purpose, not just safe beginners. Dental schools which continue to struggle with decisions about which materials, and in what order, to teach in instruction in the restoration of posterior teeth, should look at the experiences of dental schools which have been forwardthinking, notably a dental school such as the school in Nijmegen, which discontinued the teaching of dental amalgam in 2001.38 It is acknowledged that being ‘‘ahead of the curve’’ poses certain risks in the teaching of dental students, but being ‘‘behind the curve’’ can be equally problematical. It is suggested that waiting for the publication of more long term data on the clinical performance of posterior resin composites, or to see how general dental practitioners deal with the issue is

100

Percentage of schools

80

60 Quartz tungsten halogen Light eming diode

40

20

0 UK & Ireland

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Canada

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Iran

UK & Ireland

USA & Canada

Spain

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2005

2005

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2008

2009

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2009

Fig. 4 – Light-curing technologies taught.

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not in the best interests of students, in particular, when there is international agreement to phase down the use of dental amalgam subsequent to the signing of the Minamata Convention.21,22 As the authors have suggested in a recent paper,21 dental schools which remain undecided, or in two minds about what to do about the teaching of posterior resin composites, should give serious consideration to discontinuing the teaching of dental amalgam to new cohorts of students, with the possible short- to medium-term exception of some instruction in amalgam replacement therapy and repair, if many patients attending the school belong to the ‘‘heavy metal generation’’.39 Studying the patterns of teaching revealed by the surveys included in this review illustrates some of the wider issues and challenges faced by dental schools over the last 20 years.23–37 It is clear that up to the late 1990s, the clinical/practical teaching of posterior resin composite techniques was limited (‘‘. . . not included in any form in more than 90% of respondent dental schools’’)34 and did not seem to match the increased placement of posterior resin composites in clinical practice. In other words, most dental schools were lagging behind developments in clinical practice and, as a consequence, could be accused of failing to produce graduates fit for immediate purpose, let alone future purpose. With a few notable examples, the teaching of posterior resin composites in the remaining dental schools was usually limited to preclinical curriculum, with some limited examples of clinical instruction, resulting in, as noted from a North American study, graduating students having ‘‘limited clinical experience in the placement of Class I and Class II composites’’.35 In such situations dental schools could be accused of causing confusion in the minds of students: Why teach it preclinically, if at best clinical application is exceptional? Furthermore, given ‘‘considerable variation in the principles taught and in the clinical experience gained by undergraduate students’’,35 there was confusion amongst those working with or employing the emerging dental workforce, with some calling for the introduction of national qualifying examinations in countries where such arrangements do not exist. Why do the dental schools of a country, if not a region not all teach the same approach to something as fundamental as the restoration of posterior teeth? Such questions should be considered in the context of the times when there were, and continue to be many, different, fast moving developments across the spectrum of dental biomaterials science, with lots of conflicting information and recommendations in the dental literature. For example, a key opinion leader paper, published in 1997, recommended, possibly conservatively in hindsight, that posterior resin composites had a place in the clinical practice of dentistry, but ‘‘limited to the occlusal surfaces of premolars, and preferably those with limited occlusal function’’.20 Guidance from the American Dental Association published in 1998 made similar recommendations.40 While advising caution in relation to the placement of posterior resin composites, such restorations were accepted to have certain indications. So, dental schools could be ‘‘damned’’ if they taught posterior resin composites and ‘‘damned’’ if they did not. On balance, it is suggested that dental schools should lead from the front and spearhead innovations in clinical practice, and in ways which do not confuse students as to what best to do in specific

circumstances. When supporting evidence is limited or unsubstantiated, dental schools should seek to address the research need. A step change in the teaching of posterior resin composites occurred in the mid-2000s, as evidenced by the findings from the mid 2000s and late 2000s surveys. Far from the application of posterior resin composite being restricted to occlusal cavities in first premolars with ‘‘limited occlusal function’’, there is evidence that – from 2004 onwards – the teaching of posterior resin composites advocated a much wider range of applications for such restorations. In addition, many more posterior resin composites were being placed by dental students – 30% of posterior restorations placed by dental students in US, UK and Irish dental schools and 37% in Canadian dental schools.23–26 A number of important developments may have lead to the step change, either individually or collectively. The most important of these developments was a substantial strengthening of the evidence base demonstrating that the performance of posterior resin composite was at least comparable to that of amalgam restoration in different clinical settings, including primary dental care.8,9,12 Other pertinent developments included growing interest in minimal intervention approaches in operative dentistry and the publication of educational guidelines on the restoration of posterior teeth.41 A review of failure rates of restorations, published in 2004, revealed the annual failure rate of posterior resin composites to be 2.2%, compared to 3.0% for restorations of dental amalgam.8 In addition, evidence from a large study conducted in a primary dental care setting revealed the 10-year success of posterior resin composites to have exceeded that of restorations of dental amalgam.9 Notwithstanding arguments over the comparability of cavities into which resin composites and amalgams had been placed in the various studies, the message was clear: when placed appropriately in posterior teeth, resin composites offer the most successful treatment option for minimal intervention restorations in posterior teeth. In 2007 the British Association of Teachers of Conservative Dentistry, including representation from UK and Irish dental schools, published consensus guidelines on the teaching of the restoration of posterior teeth to undergraduate dental students.41 These guidelines recommended that resin composites should be regarded as the ‘‘material of choice’’ when restoring primary (initial) lesions of caries in posterior teeth.41 These developments set the background to the most recent round of surveys in the late 2000s.27–31 These surveys revealed, amongst other developments, that 55% and 49% of direct posterior restorations placed by dental students in UK and Irish and Canadian and US dental schools respectively were of resin composites.29,30 How the trends observed over the last 20 years will continue to develop is unclear. A further round of surveys are planned for 2014 to provide up to date data on this important aspect of teaching in primary dental degree programmes. It could be considered that developments in the teaching of posterior resin composites may have been influenced by persistent scepticism over the merits and value of posterior resin composites amongst established practitioners, some of whom may well support dental schools as part time teachers. Recent surveys of restorative materials use in UK dental practices,4,5 indicate that, contrary to teaching in most UK

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dental schools,29 dental amalgam remains the preferred material for direct, load baring restorations in posterior teeth, and American Dental Association surveys reveal that US dentists,42 contrary to teaching in most US dental schools,30 place more posterior resin composites than restorations of dental amalgam. It is anticipated that the apparent disconnects between best educational approaches, expert opinion and current practice in the application of posterior resin composites will be resolved with the passage of time, possibly sooner rather than later subsequent to the signing of the Minamata Convention. This, of course, assumes that it will be some time before a new class of direct restorative material, with clinically demonstrable advantages over resin composites, is introduced, successfully translated into clinical practice and triggers a start to a whole new cycle of changes in the instruction of dental students. From the results of the surveys, it may be concluded that, overall, trends in the teaching of posterior resin composites in North American schools have lagged behind the trends in UK and Ireland schools (Fig. 2).29,30 The greater reluctance to move away from the preferred use of dental amalgam in North American schools could possibly be explained, at least in part, by the requirements of the State and National Board examinations which, it is understood, remain focussed on the use of dental amalgam for the restoration of posterior teeth. In addition, it is noted from Fig. 1 that, in contrast to what happens now in the majority of UK and Irish dental schools, the first (preclinical), and possibly lasting experience most North American dental students have of restoring posterior teeth continues to be the use of dental amalgam. This is believed to be but one example of teaching in North American dental schools being more ‘traditional’ than the approaches adopted in at least UK and Irish dental schools. First educational exposures tend to influence the way dental students ‘‘think’’. If a student ‘‘thinking’’ is set off down the track of interventive, mechanistic approaches to the restoration of posterior teeth, such thinking, at least in the experience of the authors, can be difficult to change when students are introduced to the use of alternative materials. Despite the size of intracoronal cavities no longer being seen to be contraindications to the placement of posterior resin composites, some dental schools still do not provide clinical teaching of posterior resin composites for the restoration of certain multi-surface cavities in permanent molar teeth (Tables 6 and 7). This is out-of-step with some recent long term evidence which counters concerns over the success of multi-surface posterior resin composite restorations in permanent molar teeth, acknowledging that careful case selection in favour of an indirect rather than direct approach is required, and meticulous attention to, for example, measures to limit the effects of polymerisation shrinkage is a prerequisite to the successful application of resin composites in large multi-surface cavities.7,43 Within the other 20-year trends observed in the teaching of posterior resin composites, some items of special note include:  Continued teaching of cavosurface margin bevels as a feature of cavity designs, despite widely acknowledged concerns regarding their suitability (Table 5);

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 Continued uncertainty and variation in the management of operatively exposed dentine (Table 8);  Increased teaching of the use of sectional matrix systems for the restoration of proximal contours, in accordance with best available evidence, but continued teaching of the use of transparent matrix systems and outdated light-transmitting wedges (Fig. 3).

Bevels The inclusion of cavosurface margin bevels in cavity designs for posterior composites remains an issue to be resolved. In the most recent round of surveys (late 2000s), bevelling of either the occlusal (22% of respondent schools) or proximal cavosurface margin (43% of respondent schools) was found to remain widespread (Table 5).27–31 At one time, the addition of an occlusal cavosurface margin, in addition to the intraenamel bevel typically formed in the finishing of occlusal cavosurface margins, was considered to enhance marginal bonding and seal, let alone blend the restoration into the remaining tooth tissues. This, however, is no longer the case.44,45 The addition of a bevel to the occlusal cavosurface margin of a preparation for a posterior resin composite, which adds little, if anything to the qualities and in-service performance of a newly place posterior resin composite, may subsequently give the impression that a much larger restoration is present than is actually the case. When restorations with additional occlusal bevels come to be repaired or replaced, confusion over the extent of the restoration tends to result in unnecessary extension of the cavity, with otherwise avoidable loss of sound tooth tissue. In addition, posterior resin composites with additional occlusal bevels are more prone to marginal chipping and related marginal staining than posterior resin composites with no additional cavosurface margin bevelling, in particular when bevelled margins are placed in occlusal contact areas. While there is some evidence to support the application of a bevel to, in particular, the non-undercut sections of the cavosurface margin of a proximal box to be restored with resin composite,46,47 the value of such bevelling must be weighed against the risk of iatrogenic damage to the adjacent tooth, as well as the loss of already-thin enamel in the cervical regions of the tooth,48,49 and the difficulty of restoring the bevel once a properly adapted sectional matrix has been placed.

Management of operatively exposed dentine The management of operatively exposed dentine in preparations intended for restoration by means of a posterior resin composite remains a vexed issue, resulting in much debate and confusion. While there is now widespread agreement on the management of operatively exposed dentine in ‘‘shallow cavities’’ – the resin composite restoration is simply ‘‘bonded’’ in place, rather than ‘‘based’’ (use of neither a liner nor base), the situation in relation to deeper cavities is far from clear. Consideration of the findings of the studies reported in this paper suggests that in recent years there has been a trend towards ‘‘bonding’’ rather than ‘‘basing’’ both in moderately deep and deep preparations to be restored with a posterior resin composite.23–37 This trend has been more apparent in

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European rather than North American dental schools in relation to, in particular deep preparations (‘‘deep’’ – inner third of dentine, late 2000s, no liner/base: Spain, 47%; UK and Ireland, 41%; Japan,35%; US and Canada, 12%; Iran,11%; Table 8).27–31 Previous studies have considered the merits of ‘‘bonding’’ versus ‘‘basing’’, with no real consensus emerging in relation to the most appropriate option.50–53 In the absence of clear evidence in favour of ‘‘basing’’, other than as a possible precautionary measure when managing deep caries in a posterior tooth considered to have little secondary (reparative) dentine, it is suggested that ‘‘basing’’ should increasingly be viewed as a remnant of dental amalgam placement techniques, in which the placement of a cement base in a preparation of other than minimum depth – just into dentine, provided insulation to heat conducted through the amalgam restoration. Resin composites are insulators rather than conductors of heat, and the avoidance of a base increases the surface area of dentine available for bonding within a cavity. In addition, there is some biological evidence to support the positive effects of bonding, rather than basing, in promoting the repair of affected dentine and stimulating further dentine formation.54,55 There is a need for a long-term (>3 year) clinical trial to compare the effects of ‘‘bonding’’ versus ‘‘basing’’ for posterior resin composite restorations placed in deep cavities.

Restoration of proximal contours The restoration of proximal contours and contact areas during the placement of multi-surface posterior resin composites continues to be investigated. It is not sufficient to merely restore a proximal contact area during the placement of an occlusal–proximal posterior resin composite. It is important to re-create an anatomically correct, contoured proximal surface within which there is a contact area suitably positioned, typically where the tooth had its maximum curvature. A variety of matrix systems can be considered for this purpose, including:  a circumferential metal matrix band and retainer, together with one or more adaptable, adsorbent (typically wooden) wedges  a circumferential transparent matrix band and retainer, together with a light-transmitting wedge  a sectional matrix band and tooth separating retainer, together with one of a variety of modern, or traditional (wood) wedging systems, with or without the initial use of a ‘separating’ ring. Circumferential transparent systems were introduced at a time when it was thought that polymerisation contraction of resin composites occurred in the direction of the incident curing light. Significant challenges were experienced when attempting to use ‘‘shrink towards the light’’ polymerisation techniques to optimise gingival margin adaptation. To overcome these challenges, transparent bands and lighttransmitting wedge systems were introduced. It is now known that polymerisation contraction does not occur in the direction of the incident activation light.56 Furthermore, transparent matrix and associated wedging systems have

been shown to increase the incidence of proximal overhang formation, coronally positioned, if not open proximal contact areas, and typically flat proximal contours.57 The thickness and inability to contour transparent matrix bands, and the rigidity of light transmitting wedges are believed to give rise to the problems experienced clinically. As such, there is no longer any justification for use of such systems. Indeed their use should be discouraged. Despite evidence having been available to support such thinking since the early 2000s, it was disappointing to note that such systems continued to be widely taught in the late 2000s (Japan, 61%; UK and Ireland, 59%; Spain, 53%; US and Canada, 18%; Iran, 11%).27–31 Such teaching, apart from the detrimental risks to patients, is not in the best interest of students. The application of best evidence in teaching should be consistent not selective. In contrast to the above, the use of a sectional, preformed metal matrix system offers a simpler and more effective means of restoring the proximal surface and contact area of a posterior tooth with resin composite.58–62 Anxious to see students exposed to the most effective and user friendly techniques in their clinical instruction, it was heartening to observe in the most recent round of surveys27–31 that student exposure to state of the art sectional matrix systems had increased, in particular in US and Canadian dental schools (late 2000s: US and Canada, 93%; UK and Ireland, 47%; Spain, 46%; Iran, 33%; Japan, 17%) (Fig. 3). Clearly, however, there is still a long way to go before the teaching of traditional and outdated matrix systems has been discontinued.

5.

Conclusion and recommendations

This review has considered developments and trends in the teaching of posterior resin composites since the time of the first survey of this teaching in 1986. During this time, information has been collected from 679 completed dental school questionnaires. The results provide insight into the complexity and time taken to develop and translate a widely researched and debated innovation in the restoration of teeth into dental school curricula around the world. While there has been steady growth in, and trends towards evidence-based teaching of posterior resin composites in dental schools around the world over the last 20–25 years, there is a need for further developments and harmonisation in this important aspect of curricula for primary dental qualifications. This need is now pressing, subsequent to the signing of the Minamata Convention which includes provision to phase down the use of dental amalgam. It is recommended that all new graduates, from no later than 2020, should have the knowledge, skills, competences and confidence to effectively restore damaged and diseased posterior teeth with state of the art resin composite systems.

Acknowledgement The authors would like to express their gratitude to all the individuals who have taken time to complete the questionnaires reported in this work. Without their involvement, this

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work would not have been possible. The authors would also like to acknowledge and thank their co-workers who have worked on the surveys and publications completed in different parts of the world and reported in this paper. It is hoped that colleagues around the world will assist the authors and their various co-workers around the world in completing a further round of surveys of the teaching of posterior resin composites planned for 2014.

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