- Email: [email protected]
Is the wear of dental composites still a clinical concern?
d e n t a l m a t e r i a l s 2 2 ( 2 0 0 6 ) 689–692
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/dema
Is the wear of dental composites still a clinical concern? Is there still a need for in vitro wear simulating devices? Jack L. Ferracane ∗ Division of Biomaterials and Biomechanics, Department of Restorative Dentistry, Oregon Health & Science University, 611 S.W. Campus Drive, Portland, OR 97239, USA
a r t i c l e
i n f o
a b s t r a c t
Keywords:
While once considered a major concern for posterior restorations, wear of dental composites
Wear
has been substantially reduced by changes in formulation and is considered today by many
Dental composite
to be a solved problem. However, minimal evidence exists in the literature to support this
Clinical studies
conclusion for large restorations, especially those involving the replacement of functional
Wear testing devices
cusps, despite the fact that these restorations are routinely performed. Evidence shows that wear may be of minimal importance for restorations of small to moderate size. However, the literature does suggest that failure rates are higher for larger restorations, and that wear may still be a significant mode of failure for patients with bruxing and clenching habits. In this light, the wear of composites continues to be studied by many researchers, and it is justifiable to seek well-defined and reproducible in vitro methods for predicting this multifactorial phenomenon. © 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
¨ Nearly 10 years ago, Soderholm and Richards [1] published an article that asked whether the wear resistance of dental composites was a solved problem. They concluded the following, “Based on some clinical data, we can conclude that under some conditions, occlusal wear of posterior composites remains a clinical problem, although not as bad as it was 10 years ago.” A PubMed literature search for “dental compos¨ ite” shows that since 1995, when the Soderholm and Richards article was written, 5970 articles have been published. This number represents nearly 45% of all of the articles in the database identified by the term “dental composite” since 1970 (Fig. 1). There are only a few articles in the literature on this material pre-1970. If the same search is conducted over the period 1995–2004 using the search terms “dental composite (wear OR abrasion)”, one finds 551 articles, or more than 9% of the total articles
∗
on dental composite in that time period, and nearly 53% of all of the dental composite wear articles written since 1970. Since, 1970, nearly 8% of all of the articles written on dental composite have included “wear” or “abrasion” in their title or abstracts. Over the last 10 years this percentage has actually increased to 9%. In fact, the number of articles published on “dental composite (wear OR abrasion)” in the past 5 years has remained relatively stable at about 60 per year (Fig. 1 inset). If wear of dental composite is no longer of any concern, one must question why so many researchers continue to devote so much time to studying it. Therefore, it is perhaps useful to raise the question again, “Is the wear of dental composite still a clinical concern?” The purpose of this article is to re-evaluate the issue of the wear resistance of posterior dental composites in light of the extant knowledge. This article will serve as an introduction and foundation for the following series of three articles that resulted from presentations made during a 2005 IADR symposium entitled “Intra-oral Restora-
Tel.: +1 503 494 4327; fax: +1 503 494 8260. E-mail address: [email protected]. 0109-5641/$ – see front matter © 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2006.02.005
690
d e n t a l m a t e r i a l s 2 2 ( 2 0 0 6 ) 689–692
al. [4] reported on the clinical wear of nine composites for up to 3 years, and showed a reduction in alfa scores of 35–51% from baseline to 3 years. Quantitative wear analysis using casts (Leinfelder scale) showed typical annualized wear rates of 30–50 m. While this study also showed that the wear rate for the composites declined with time, the authors suggested that wear at 3 years could be predicted from wear data at 6 months. Despite this claim, clinical wear studies continued to be conducted over the course of years rather than months. As later studies showed, the wear rate for some materials, such as the microfill composites, was nearly linear with time, in contrast to the declining wear rate observed for the conventional composites.
Fig. 1 – PubMed search results for the term ‘dental composite’ showing percent of total articles since 1970 that were published in 5-year periods, and the percent of articles on dental composite that can be identified with the search term ‘dental composite (wear OR abrasion)’ during those periods. Inset: annual number of articles found from 2000 to 2004 using the latter search term.
tive Materials Wear: Rethinking the Current Approaches.” The symposium provided an overview of the existing methods for simulating wear, a discussion of the best ways to measure wear, and an in depth look at how to quantify and validate wear simulation devices.
2.
Historical perspective
One of the first multi-year clinical studies published on posterior composites showed the percent of restorations with excellent scores (alfa) for anatomical form to decrease from 100% at baseline to only 15% at 3 years due to excessive wear [2]. Dr. Phillips concluded “. . . the routine use of composite resins in Class II restorations would seem to be contraindicated . . .” The results from other studies during the same time period concurred. In an attempt to develop composites with improved polishability and abrasion resistance, manufacturers began to develop composites with smaller reinforcing fillers. In the 1980s as the materials improved and clinicians became more accustomed to them, the use of composite as a posterior restorative increased rapidly. During this time, many clinical studies were designed specifically to quantitate the extent of wear occurring intraorally, and differences between materials became apparent. Heymann et al. [3] reported on the 2-year clinical performance of class I and II restorations involving five composites, including two microfill and three conventional materials. The anatomic form, as rated with the USPHS criteria, declined from 100% alfa at baseline to 70–86% alfa at 2 years. Simultaneously, stone cast replicas poured from impressions of the restorations showed wear (estimated according to the Leinfelder method) of the microfill composites to be lower than that of the conventional composites (111–113 m as compared with 150–199 m, respectively). At the same time, Leinfelder et
3. Recent clinical evidence of composite wear Numerous studies continued to be conducted to assess the wear and overall performance of dental composites, many commissioned by the manufacturers in order to gain acceptance for the particular material from the American Dental Association. One early material that gained full acceptance from the ADA for restricted use in posterior teeth was FulFil (Caulk Dentsply), which showed annualized wear values (Leinfelder method) of 25–45 m in several studies [4–8]. Full acceptance from the ADA at the time meant a wear rate of no more than 250 m over 4 years, and Ful-Fil experienced approximately half that amount. In 2001, the ADA acceptance program guidelines for resin based composites for posterior restorations (unrestricted use) was modified to include only an 18 months evaluation, with mean maximum wear not to exceed 50 m when measured over the 1-year period from 6 to 18 months (wear measured from casts with suitable method for which accuracy and precision must be documented). This relatively high wear rate represents a fairly easy target for nearly all commercial composites on the market today. In 1996, CRA (Clinical Research Associates) published a report of a 2-year evaluation of the clinical performance of 13 posterior composites and one amalgam [9]. Their data showed that the most wear resistant composite had more than twice the amount of wear as an amalgam over the 2 years (i.e. 60 m versus 28 m) (measuring method not specified). The least wear resistant composites showed nearly 135 m of wear when measured from baseline to 2 years. However, because nearly half of the wear at 2 years has been shown to occur over the time period from baseline to 6 months [4], most of the composites tested would have likely passed the ADA criteria. This left one to conclude that wear was becoming less of a concern for posterior composites placed in small to moderate-sized preparations. Further proof for this assertion has been generated in numerous long-term studies, spanning 6–17 years in duration, which have shown that posterior composites perform adequately to very good in small to moderate-sized cavities when the margins are within enamel [10–15]. Other studies conducted during the 1980s revealed another phenomenon of posterior composites relating to the loading patterns on the teeth. Using a three coordinate measuring table and a contact free optical sensor for the z-dimension, Braem et al. [16] showed that wear of composites in the areas of
dental materials
occlusal contacts was significantly higher (typically 2–3×) than the wear measured in the areas that were free of contacts over a period of 1 year. Mair et al. [17] later reported similar findings over the longer time period of 3 years. Some of the earlier studies were not as discriminating for this type of localized degradation because they measured wear on casts by evaluating the material at the margins only. Further evidence for heightened wear of composite that might be dependent upon cavity geometry was revealed in a multi-center trial of a single composite, Occlusin, which was produced by ICI at the time [18]. This study, conducted over 5 years, showed that the wear of the composite increased with the size of the restoration, and that this was especially true for composites in molar teeth versus those in premolars. The difference in wear between molars and premolars and between first and second molars has also been reported by Wilder et al. [19]. While it is likely that much of the wear resistance of a given material is determined by its formulation, specifically the quantity and size of the reinforcing fillers, the degree of cure of the polymer matrix also has been shown to significantly affect intraoral wear [20]. Thus, the clinician is encouraged to ensure that the composite is adequately cured by providing sufficient light exposure during the placement of the material. Recent long-term studies of the performance of dental composites as posterior restoratives in two to three surface preparations suggest that these materials perform adequately, with wear only being a significant concern when the patient has abnormal occlusal habits, such as clenching and bruxing [21,22]. However, other long-term studies of extensive composite restorations reveal that the performance of these materials is still poorer than that of amalgam or gold castings [23]. There are a few studies in which composites have been used as crown or crown veneer materials. Ekfeldt and Oilo [24] showed in a limited study of three patients, that the wear of a microfill composite crown material against a porcelain–metal antagonist was 3–4× greater than the wear observed for porcelain or metal crowns. The microfill composite wore in a fatigue mode, but with evidence of a tribochemical effect. Depew and Sorensen [25] presented a study of the wear of a composite veneering material (Artglass) for gold crowns using the MTS Tooth Profiling System, and showed a mean maximum wear depth of 113 m at 2 years, with a range of 56–480 m. Interestingly, the high wear of the Artglass composite had been confirmed in an in vitro study using an oral wear simulator and showed wear of this material in both low load abrasion (18–20 N) and higher load attrition (80–90 N) to be essentially twice that of the direct composite Charisma from the same manufacturer [26]. Clinical Research Associates (1998) showed results of a 1–2 year study of three prosthodontic composites (belleGlass, Artglass, Targis) placed as crowns [27]. The materials showed evidence of occlusal pitting after 1 year and average wear levels of 62–106 m (measuring method not specified). The average wear of one of the composites (Artglass) was followed for 2 years and showed wear of 125 m, in agreement with the results of Depew and Sorensen [25]. These composite crowns were followed for a total of 4 years, and showed wear levels of 125–243 m [28]. The overall conclusion was that the composite crowns performed fairly well. However, it is obvious from this work that the wear of one material may be doubled that of another. Thus, it may be difficult to make gen-
22
( 2 0 0 6 ) 689–692
691
eral statements about the wear of these materials in extensive restorations without actually assessing this parameter.
4.
Is wear still a concern?
In light of the collective evidence, one might be guided to ¨ the same conclusion made by Soderholm and Richards [1]. While the wear resistance of dental composite restoratives is no longer considered to be a major concern for most restorations, the relatively limited information available suggests that it may still be a concern for very large restorations in direct occlusal contact, or for those patients with bruxing and clenching behavior. Thus, the assessment of wear in clinical studies, the prediction of wear for new materials based on in vitro test methods, and the refinement of methods for quantitating wear remain as important concerns for dental researchers. There are many questions to address when performing in vitro wear evaluations, and to date, little has actually been accomplished to standardize test methods or data reporting. Critical questions include the following: • What type(s) of wear should or needs to be simulated in a wear simulating device (i.e. abrasive, attritive, erosive, adhesive), and what quantity should be reported (i.e. depth, area, volume)? • What level of discriminating ability should the simulation/measuring device have to be considered useful (i.e. does the device distinguish most materials or simply show that they fall within some range of an acceptable standard, such as enamel or some other material)? • What assurances should the user be required to provide in order to give the audience confidence in the results produced by the simulation/measuring device (i.e. accuracy, precision, performance of standards, etc.)? The critical evaluation of the current state-of-the-art in this area presented in the following three manuscripts provides guidance for answering these important questions.
references
¨ [1] Soderholm KJ, Richards ND. Wear resistance of composites: a solved problem? Gen Dent 1998;46:256– 63. [2] Phillips RW, Avery DR, Mehra R, Swartz ML, McCune RJ. Observations on a composite resin for Class II restorations: three-year report. J Prosthet Dent 1973;30:891–7. [3] Heymann HO, Wilder Jr AD, May Jr KN, Leinfelder KF. Two-year clinical study of composite resins in posterior teeth. Dent Mater 1986;2:37–41. [4] Leinfelder KF, Wilder Jr AD, Teixeira LC. Wear rates of posterior composite resins. J Am Dent Assoc 1986;112:829–33. [5] Wendell JJ, Vann Jr WF. Wear of composite resin restorations in primary versus permanent molar teeth. J Dent Res 1988;67:71–4. [6] Lundin SA. Studies on posterior composite resins with special reference to class II restorations. Swed Dent J Suppl 1990;73:1–41. [7] Barnes DM, Blank LW, Thompson VP, Holston AM, Gingell JC. A 5- and 8-year clinical evaluation of a posterior composite resin. Quintessence Int 1991;22:143–51.
692
dental materials
[8] Tyas MJ, Wassenaar P. Clinical evaluation of four composite resins in posterior teeth five-year results. Aust Dent J 1991;36:369–73. [9] CRA Report, 20(4), 1996. [10] Mair LH. Ten-year clinical assessment of three posterior resin composites and two amalgams. Quintessence Int 1998;29:483–90. [11] Nordbo H, Leirskar J, von der Fehr FR. Saucer-shaped cavity preparations for posterior approximal resin composite restorations: observations up to 10 years. Quintessence Int 1998;29:5–11. [12] Wilder Jr AD, May Jr KN, Bayne SC, Taylor DF, Leinfelder KF. Seventeen-year clinical study of ultraviolet-cured posterior composite Class I and II restorations. J Esthet Dent 1999;11:135–42. [13] Busato AL, Loguercio AD, Reis A, de Oliveira Carrilho MR. Clinical evaluation of posterior composite restorations: 6-year results. Am J Dent 2001;14:304–8. [14] Gaengler P, Hoyer I, Montag R. Clinical evaluation of posterior composite restorations: the 10-year report. J Adhes Dent 2001;3:185–94. [15] DeMarco FF, Rodolpho PAR, Cenci MS, Donassollo TA. Clinical evaluation of posterior composite restorations: 16 years follow-up. J Dent Res 2005;84A:167. [16] Braem M, Lambrechts P, Van Doren V, Vanherle G. In vivo evaluation of four posterior composites: quantitative wear measurements and clinical behavior. Dent Mater 1986;2:106–13.
22
( 2 0 0 6 ) 689–692
[17] Mair LH, Vowles RW, Cunningham J, Williams DF. The clinical wear of three posterior composites. Br Dent J 1990;169:355–60. [18] Wilson NH, Norman RD. Five-year findings of a multiclinical trial for a posterior composite. J Dent 1991;19:153–9. [19] Wilder AD, Bayne SC, Heymann HO. Long-term clinical performance of direct posterior composites. Trans Acad Dent Mater 1996;9:151–69. [20] Ferracane JL, Mitchem JC, Condon JR, Todd R. Wear and marginal breakdown of composites with various degrees of cure. J Dent Res 1997;76:1508–16. [21] van Dijken JW. Direct resin composite inlays/onlays: an 11 year follow-up. J Dent 2000;28:299–306. [22] Pallesen U, Qvist V. Composite resin fillings and inlays An 11-year evaluation. Clin Oral Invest 2003;7:71–9. [23] Van Nieuwenhuysen JP, D’Hoore W, Carvalho J, Qvist V. Long-term evaluation of extensive restorations in permanent teeth. J Dent 2003;31:395–405. [24] Ekfeldt A, Oilo G. Wear of prosthodontic materials—an in vivo study. J Oral Rehab 1990;17:117–29. [25] Depew T, Sorensen J. A pilot clinical study on the Artglass system. J Dent Res 1998;77:900 [Abstract #2150]. [26] Freiberg S, Ferracane J. Evaluation of cure, properties and wear resistance of Artglass dental composite. Am J Dent 1998;11:214–8. [27] CRA Report, 22(10), 1998. [28] CRA Report, 25(7), 2001.
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/dema
Is the wear of dental composites still a clinical concern? Is there still a need for in vitro wear simulating devices? Jack L. Ferracane ∗ Division of Biomaterials and Biomechanics, Department of Restorative Dentistry, Oregon Health & Science University, 611 S.W. Campus Drive, Portland, OR 97239, USA
a r t i c l e
i n f o
a b s t r a c t
Keywords:
While once considered a major concern for posterior restorations, wear of dental composites
Wear
has been substantially reduced by changes in formulation and is considered today by many
Dental composite
to be a solved problem. However, minimal evidence exists in the literature to support this
Clinical studies
conclusion for large restorations, especially those involving the replacement of functional
Wear testing devices
cusps, despite the fact that these restorations are routinely performed. Evidence shows that wear may be of minimal importance for restorations of small to moderate size. However, the literature does suggest that failure rates are higher for larger restorations, and that wear may still be a significant mode of failure for patients with bruxing and clenching habits. In this light, the wear of composites continues to be studied by many researchers, and it is justifiable to seek well-defined and reproducible in vitro methods for predicting this multifactorial phenomenon. © 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
¨ Nearly 10 years ago, Soderholm and Richards [1] published an article that asked whether the wear resistance of dental composites was a solved problem. They concluded the following, “Based on some clinical data, we can conclude that under some conditions, occlusal wear of posterior composites remains a clinical problem, although not as bad as it was 10 years ago.” A PubMed literature search for “dental compos¨ ite” shows that since 1995, when the Soderholm and Richards article was written, 5970 articles have been published. This number represents nearly 45% of all of the articles in the database identified by the term “dental composite” since 1970 (Fig. 1). There are only a few articles in the literature on this material pre-1970. If the same search is conducted over the period 1995–2004 using the search terms “dental composite (wear OR abrasion)”, one finds 551 articles, or more than 9% of the total articles
∗
on dental composite in that time period, and nearly 53% of all of the dental composite wear articles written since 1970. Since, 1970, nearly 8% of all of the articles written on dental composite have included “wear” or “abrasion” in their title or abstracts. Over the last 10 years this percentage has actually increased to 9%. In fact, the number of articles published on “dental composite (wear OR abrasion)” in the past 5 years has remained relatively stable at about 60 per year (Fig. 1 inset). If wear of dental composite is no longer of any concern, one must question why so many researchers continue to devote so much time to studying it. Therefore, it is perhaps useful to raise the question again, “Is the wear of dental composite still a clinical concern?” The purpose of this article is to re-evaluate the issue of the wear resistance of posterior dental composites in light of the extant knowledge. This article will serve as an introduction and foundation for the following series of three articles that resulted from presentations made during a 2005 IADR symposium entitled “Intra-oral Restora-
Tel.: +1 503 494 4327; fax: +1 503 494 8260. E-mail address: [email protected]. 0109-5641/$ – see front matter © 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2006.02.005
690
d e n t a l m a t e r i a l s 2 2 ( 2 0 0 6 ) 689–692
al. [4] reported on the clinical wear of nine composites for up to 3 years, and showed a reduction in alfa scores of 35–51% from baseline to 3 years. Quantitative wear analysis using casts (Leinfelder scale) showed typical annualized wear rates of 30–50 m. While this study also showed that the wear rate for the composites declined with time, the authors suggested that wear at 3 years could be predicted from wear data at 6 months. Despite this claim, clinical wear studies continued to be conducted over the course of years rather than months. As later studies showed, the wear rate for some materials, such as the microfill composites, was nearly linear with time, in contrast to the declining wear rate observed for the conventional composites.
Fig. 1 – PubMed search results for the term ‘dental composite’ showing percent of total articles since 1970 that were published in 5-year periods, and the percent of articles on dental composite that can be identified with the search term ‘dental composite (wear OR abrasion)’ during those periods. Inset: annual number of articles found from 2000 to 2004 using the latter search term.
tive Materials Wear: Rethinking the Current Approaches.” The symposium provided an overview of the existing methods for simulating wear, a discussion of the best ways to measure wear, and an in depth look at how to quantify and validate wear simulation devices.
2.
Historical perspective
One of the first multi-year clinical studies published on posterior composites showed the percent of restorations with excellent scores (alfa) for anatomical form to decrease from 100% at baseline to only 15% at 3 years due to excessive wear [2]. Dr. Phillips concluded “. . . the routine use of composite resins in Class II restorations would seem to be contraindicated . . .” The results from other studies during the same time period concurred. In an attempt to develop composites with improved polishability and abrasion resistance, manufacturers began to develop composites with smaller reinforcing fillers. In the 1980s as the materials improved and clinicians became more accustomed to them, the use of composite as a posterior restorative increased rapidly. During this time, many clinical studies were designed specifically to quantitate the extent of wear occurring intraorally, and differences between materials became apparent. Heymann et al. [3] reported on the 2-year clinical performance of class I and II restorations involving five composites, including two microfill and three conventional materials. The anatomic form, as rated with the USPHS criteria, declined from 100% alfa at baseline to 70–86% alfa at 2 years. Simultaneously, stone cast replicas poured from impressions of the restorations showed wear (estimated according to the Leinfelder method) of the microfill composites to be lower than that of the conventional composites (111–113 m as compared with 150–199 m, respectively). At the same time, Leinfelder et
3. Recent clinical evidence of composite wear Numerous studies continued to be conducted to assess the wear and overall performance of dental composites, many commissioned by the manufacturers in order to gain acceptance for the particular material from the American Dental Association. One early material that gained full acceptance from the ADA for restricted use in posterior teeth was FulFil (Caulk Dentsply), which showed annualized wear values (Leinfelder method) of 25–45 m in several studies [4–8]. Full acceptance from the ADA at the time meant a wear rate of no more than 250 m over 4 years, and Ful-Fil experienced approximately half that amount. In 2001, the ADA acceptance program guidelines for resin based composites for posterior restorations (unrestricted use) was modified to include only an 18 months evaluation, with mean maximum wear not to exceed 50 m when measured over the 1-year period from 6 to 18 months (wear measured from casts with suitable method for which accuracy and precision must be documented). This relatively high wear rate represents a fairly easy target for nearly all commercial composites on the market today. In 1996, CRA (Clinical Research Associates) published a report of a 2-year evaluation of the clinical performance of 13 posterior composites and one amalgam [9]. Their data showed that the most wear resistant composite had more than twice the amount of wear as an amalgam over the 2 years (i.e. 60 m versus 28 m) (measuring method not specified). The least wear resistant composites showed nearly 135 m of wear when measured from baseline to 2 years. However, because nearly half of the wear at 2 years has been shown to occur over the time period from baseline to 6 months [4], most of the composites tested would have likely passed the ADA criteria. This left one to conclude that wear was becoming less of a concern for posterior composites placed in small to moderate-sized preparations. Further proof for this assertion has been generated in numerous long-term studies, spanning 6–17 years in duration, which have shown that posterior composites perform adequately to very good in small to moderate-sized cavities when the margins are within enamel [10–15]. Other studies conducted during the 1980s revealed another phenomenon of posterior composites relating to the loading patterns on the teeth. Using a three coordinate measuring table and a contact free optical sensor for the z-dimension, Braem et al. [16] showed that wear of composites in the areas of
dental materials
occlusal contacts was significantly higher (typically 2–3×) than the wear measured in the areas that were free of contacts over a period of 1 year. Mair et al. [17] later reported similar findings over the longer time period of 3 years. Some of the earlier studies were not as discriminating for this type of localized degradation because they measured wear on casts by evaluating the material at the margins only. Further evidence for heightened wear of composite that might be dependent upon cavity geometry was revealed in a multi-center trial of a single composite, Occlusin, which was produced by ICI at the time [18]. This study, conducted over 5 years, showed that the wear of the composite increased with the size of the restoration, and that this was especially true for composites in molar teeth versus those in premolars. The difference in wear between molars and premolars and between first and second molars has also been reported by Wilder et al. [19]. While it is likely that much of the wear resistance of a given material is determined by its formulation, specifically the quantity and size of the reinforcing fillers, the degree of cure of the polymer matrix also has been shown to significantly affect intraoral wear [20]. Thus, the clinician is encouraged to ensure that the composite is adequately cured by providing sufficient light exposure during the placement of the material. Recent long-term studies of the performance of dental composites as posterior restoratives in two to three surface preparations suggest that these materials perform adequately, with wear only being a significant concern when the patient has abnormal occlusal habits, such as clenching and bruxing [21,22]. However, other long-term studies of extensive composite restorations reveal that the performance of these materials is still poorer than that of amalgam or gold castings [23]. There are a few studies in which composites have been used as crown or crown veneer materials. Ekfeldt and Oilo [24] showed in a limited study of three patients, that the wear of a microfill composite crown material against a porcelain–metal antagonist was 3–4× greater than the wear observed for porcelain or metal crowns. The microfill composite wore in a fatigue mode, but with evidence of a tribochemical effect. Depew and Sorensen [25] presented a study of the wear of a composite veneering material (Artglass) for gold crowns using the MTS Tooth Profiling System, and showed a mean maximum wear depth of 113 m at 2 years, with a range of 56–480 m. Interestingly, the high wear of the Artglass composite had been confirmed in an in vitro study using an oral wear simulator and showed wear of this material in both low load abrasion (18–20 N) and higher load attrition (80–90 N) to be essentially twice that of the direct composite Charisma from the same manufacturer [26]. Clinical Research Associates (1998) showed results of a 1–2 year study of three prosthodontic composites (belleGlass, Artglass, Targis) placed as crowns [27]. The materials showed evidence of occlusal pitting after 1 year and average wear levels of 62–106 m (measuring method not specified). The average wear of one of the composites (Artglass) was followed for 2 years and showed wear of 125 m, in agreement with the results of Depew and Sorensen [25]. These composite crowns were followed for a total of 4 years, and showed wear levels of 125–243 m [28]. The overall conclusion was that the composite crowns performed fairly well. However, it is obvious from this work that the wear of one material may be doubled that of another. Thus, it may be difficult to make gen-
22
( 2 0 0 6 ) 689–692
691
eral statements about the wear of these materials in extensive restorations without actually assessing this parameter.
4.
Is wear still a concern?
In light of the collective evidence, one might be guided to ¨ the same conclusion made by Soderholm and Richards [1]. While the wear resistance of dental composite restoratives is no longer considered to be a major concern for most restorations, the relatively limited information available suggests that it may still be a concern for very large restorations in direct occlusal contact, or for those patients with bruxing and clenching behavior. Thus, the assessment of wear in clinical studies, the prediction of wear for new materials based on in vitro test methods, and the refinement of methods for quantitating wear remain as important concerns for dental researchers. There are many questions to address when performing in vitro wear evaluations, and to date, little has actually been accomplished to standardize test methods or data reporting. Critical questions include the following: • What type(s) of wear should or needs to be simulated in a wear simulating device (i.e. abrasive, attritive, erosive, adhesive), and what quantity should be reported (i.e. depth, area, volume)? • What level of discriminating ability should the simulation/measuring device have to be considered useful (i.e. does the device distinguish most materials or simply show that they fall within some range of an acceptable standard, such as enamel or some other material)? • What assurances should the user be required to provide in order to give the audience confidence in the results produced by the simulation/measuring device (i.e. accuracy, precision, performance of standards, etc.)? The critical evaluation of the current state-of-the-art in this area presented in the following three manuscripts provides guidance for answering these important questions.
references
¨ [1] Soderholm KJ, Richards ND. Wear resistance of composites: a solved problem? Gen Dent 1998;46:256– 63. [2] Phillips RW, Avery DR, Mehra R, Swartz ML, McCune RJ. Observations on a composite resin for Class II restorations: three-year report. J Prosthet Dent 1973;30:891–7. [3] Heymann HO, Wilder Jr AD, May Jr KN, Leinfelder KF. Two-year clinical study of composite resins in posterior teeth. Dent Mater 1986;2:37–41. [4] Leinfelder KF, Wilder Jr AD, Teixeira LC. Wear rates of posterior composite resins. J Am Dent Assoc 1986;112:829–33. [5] Wendell JJ, Vann Jr WF. Wear of composite resin restorations in primary versus permanent molar teeth. J Dent Res 1988;67:71–4. [6] Lundin SA. Studies on posterior composite resins with special reference to class II restorations. Swed Dent J Suppl 1990;73:1–41. [7] Barnes DM, Blank LW, Thompson VP, Holston AM, Gingell JC. A 5- and 8-year clinical evaluation of a posterior composite resin. Quintessence Int 1991;22:143–51.
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dental materials
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