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					Journal of Dental Research
http://jdr.sagepub.com Relationship of Restoration Width, Tooth Position, and Alloy to Fracture at the Margins of 13- to 14-year-old Amalgams
J.W. Osborne and E.N. Gale J DENT RES 1990; 69; 1599 DOI: 10.1177/00220345900690091201 The online version of this article can be found at: http://jdr.sagepub.com/cgi/content/abstract/69/9/1599

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Relationship of Restoration Width, Tooth Position, and Alloy to Fracture at the Margins of 13- to 14-year-old Amalgams
J.W. OSBORNE and E.N. GALE'
Department of Restorative Dentistry, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Box C284, Deliver, Colorado 80262; and 'Department of Behavioral Sciences, SUNY at Buffalo, Buffalo, New York 14214

The effect of width of the restoration, tooth position, and amalgam type on the fracture of the margins of 13- to 14-year-old, high-copper, amalgam restorations was evaluated. The evaluation assessed 193 photographs of restorations by use of ridit analysis and a rank-ordering test. The results indicated that the width of the restoration was the predominant factor and that tooth position and the different high-copper alloys were less significant. Interactions between tooth position and width indicated that lower premolars with conservative restorations exhibited the least fracture at the margins, and upper premolars with a wide preparation exhibited the most. It is postulated that tooth deflection under mastication may play a role in longterm fracture at the margins of amalgams. J Dent Res 69(9):1599-1601, September, 1990

of tooth position, restoration width, and alloy brand on fracture at the margins of 13- and 14-year-old amalgam restorations.

Materials and methods.
Recently, two amalgam studies assessed the clinical performance of 13- and 14-year-old amalgams (Osborne et al., 1989a, b). These studies were initiated at Indiana University in 1974 and 1975. Originally, over 1200 restorations of 12 different alloys in one study and 600 restorations of ten alloys in the other were placed by one operator. Each patient received at least five amalgams. Alloy type and location were selected on a random basis so that the patients could serve as their own control. Each alloy was manipulated according to manufacturer's instructions. After hand condensation, sharp instruments were used for carving the restorations, and they were polished 24 h or later post-operatively. Two evaluation procedures were used for determination of fracture at the margins. The first was a ridit analysis, described by Mahler et al. (1970), in which the photographs of restorations were categorized into six groups of increasing amounts of fracture at the margins. The second analysis was a rankordering test (Osborne et al., 1976). The ridit means were computed to give a relative position of the rate of fracture at the margins, and the method has been discussed in other papers (Fleiss et al., 1979; Osborne et al., 1976). The more powerful rank-ordering test was used for indication of significant differences. Detailed methodology as to patient selection, restorative procedure, manipulations of materials, and photographic evaluation has been described previously (Osborne et al., 1978a; Osborne and Gale, 1979). The 4 x 4 x 3 factorial design for this evaluation was: (1) restoration width - conservative, medium, and wide; (2) tooth position - upper molar, lower molar, upper premolar, and lower premolar; and (3) alloy - Dispersalloy, Indiloy, Sybraloy, and Tytin. The first factor was defined on the basis of fraction of isthmus inter-cuspal distance (isthmus width), as follows: conservative - 1/4 of isthmus width or less; medium - between 1/4 and 1/3 of isthmus width; and wide - 1/3 or more of isthmus width. The alloys, their manufacturer, and number of restorations evaluated are presented in Table 1. The 193 restorations of the four alloys evaluated in this study represent 31% of the original restorations placed in 1974 and 1975. Results. Since the restorations came from two different studies, the ridit analysis and rank-ordering test were applied for determination of whether there was any difference in alloy performance from one study to another. The difference was not statistically significant. Table 2 summarizes the ridit means and rank-ordering test on the three main effects. Nonparametric statistics were used
1599

Introduction.
Clinical studies have demonstrated that a number of factors influence in vivo performance of a restoration. For the amalgam restoration, these include: the brand of alloy used (Mahler et aL., 1970; Osborne et al., 1980; Letzel et aL., 1989), operator variables (Letzel et al., 1989; Mahler and Marantz, 1979), and patient oral habits (Goldberg et al., 1980). The criterion most often used for assessment of the present and future clinical performance of the amalgam is fracture at the margins. Although this defect may not be a reason for replacement of an amalgam restoration, it is the problem most observed with this most widely used restorative material. Tooth position and restoration width have also been shown, in various degrees, to have an effect on the clinical performance of amalgam. Goldberg et at. (1980) found that fracture at the margins was affected by tooth position, but not by the class of restoration. Mahler and Marantz (1980) reported that lower premolars had less fracture at the margins than other teeth, but the effect was small. They also found that there was no difference with either restoration class or restoration size. Berry et al. (1981) found that restoration size had a profound effect on fracture at the margins. The narrow or conservative restorations exhibited less fracture at the margins than did wider restorations. Osborne and Gale (1981) examined 429 two-yearold amalgams and reported that narrow restorations and those in lower premolars had less fracture at the margins than wider restorations and those in other teeth. The greatest effect was the narrow restoration with the least fracture at the margin. Although wider restorations had a greater amount of fracture at the margins, there was no significant difference between medium and wide restorations. The above clinical studies have relied on shorter-term results, and the effects of longer clinical time have not been determined. The purpose of this study was to evaluate effects
Received for publication November 14, 1989 Accepted for publication February 16, 1990

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1600

OSBORNE & GALE

J Dent Res

September 1990

Alloy-Tooth
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Alloy - Width
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DISPERSALLOY

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0.3

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Fig. 1-Alloy-tooth interaction and its relationship to fracture at the margins (ridit means).
on the ordinal rank-ordering test, and a Kruskal-Wallis oneway analysis of variance followed by Mann-Whitney U tests was performed on each of the three dimensions. For all three dimensions, the Kruskal-Wallis one-way analysis of variance by ranks was significant. When the four alloys were compared with the Mann-Whitney U tests, the only significant difference was between Dis-

T H

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Fig. 2-Alloy-restoration width interaction and its relationship to fracture at the margins. to both original studies (Osborne et al., 1989a, b). An early report (Osborne and Gale, 1981) included the traditional low-

persalloy and Sybraloy (p <0.05), although the difference between Indiloy and Sybraloy approached significance (p < 0.06). The data for tooth position indicated that the lower premolar had the least amount of marginal breakdown. The only significant difference, however, was between the lower premolar and the upper molar (p<0.02), although the difference between the lower premolar and upper premolar also approached a significant level (p<0.06). The most prominent finding was the effect of restoration width. There were significant differences among all three widths, with the conservative restoration being significantly superior to both the medium restoration (p<0.001) and the wide restoration (p<0.001). The medium width restoration was also significantly superior (p<0.001) to the wide restoration. Figs. 1, 2, and 3 represent the interactions of the three dimensions, i.e., alloy-width, alloy-tooth, and tooth-width. Because some cells had only two restorations, analysis could not determine statistical differences.

Discussion.
The four alloys selected for this study were all high-copper amalgams available on the US market today and were common
TABLE 1

alloy Velvalloy, but this alloy is no longer commercially available. Of the three main effects, neither alloy nor tooth position exerted a strong influence on fracture at the margins. Compared with earlier studies, the use of only high-copper alloys in this study minimized the effect. Interactions of tooth-width indicate that the combination of a premolar and conservative restoration resulted in the least fracture at the margins, and the greatest fracture at the margins was in wide restorations in the upper premolar (Fig. 3). A significant difference was found when two- and threeyear data (Berry et al., 1981; Osborne and Gale, 1981) were compared with those for the 13- to 14-year-old restorations. The narrow or conservative restorations exhibited significantly less fracture at the margins, when compared with wider restorations, but the shorter-term two- and three-year results indicated little or no difference in fracture at the margins due to larger restoration sizes. There was, however, a significant difference between medium and wide restorations in the longterm data. Several theories have been proposed to explain fracture at the margins (Phillips, 1982; Derand, 1977; Jorgensen, 1965; Osborne et al., 1978b; Williams and Cahoon, 1989). Interestingly, that by Derand (1977, 1983) fits the pattern observed here. His proposal was that elastic deflection of the
copper

ALLOYS, MANUFACTURERS, AND NUMBERS OF
RESTORATIONS EVALUATED Alloy Manufacturer Number Evaluated 51 Dispersalloy Johnson & Johnson Dental Products Company East Windsor, NJ 08520 Shofu Dental Corporation Indiloy 47 Menlo Park, CA 94025 Tytin S.S. White Dental Manufacturing 50 Company Philadelphia, PA 19102 (Now Sybron/Kerr) 45 Sybraloy Sybron/Kerr Manufacturing Company Romulus, MI 48174

TABLE 2 MAIN EFFECTS, RIDIT ANALYSIS, AND RANK ORDERING Ridit Means Rank Order* Alloys 0.4608 Dispersalloy 0.4529 Indiloy 0.5104 Tytin 0.5821 Sybraloy Tooth Position Ridit Means Rank Order* Lower Premolar 0.3899 Lower Molar 0.4880 0.5269 Upper Premolar 0.5580 Upper Molar Restoration Width Ridit Means Rank Order Conservative 0.3001 All significantly different at p<0.001 Medium 0.5549 Wide 0.7436 p <0.05. I= no statistical difference.

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Vol. 69 No. 9

EFFECT OF TOOTH POSITION AND WIDTH ON OLDER AMALGAMS

1601

Tooth -Width
E WIDE S T 0 R A 10 T MEDIUM
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0 N

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Do

GREATER FRACTURE AT THE MARGINS

T CONSERVATIVE H
.2 .3

.4

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Fig. 3-Tooth position - restoration width and its relationship to fracture at the margins.

tooth structure under loads contributes to fracture at the margins. Retrospectively, the two- and three-year data (Berry et al., 1981; Osborne and Gale, 1981) may not allow for fracture at the margins to occur through this mechanism, but after several years, the continued elastic flexure could contribute to greater fracture at the margins. This is particularly pertinent for the upper premolar since, as Derand (1977) points out, this premolar (because of its size and shape) is most susceptible to elastic deflection and resultant gap formation at the margins. These data may have implications in the placement of onlay or cusp protection restorations when upper premolars requiring a wide restoration are originally restored or when a replacement is necessary. Fracture at the margins of amalgams is a very complex mechanism of failure, and the number and variety of theories attest to this. The Derand theory is most likely not a complete explanation of fracture at the margins, but it does appear to account for a contributing factor.
REFERENCES

BERRY, T.G.; LASWELL, H.R.; OSBORNE, J.W.; and GALE, E.N. (1981): Width of Isthmus and Marginal Failure of Restorations of Amalgam, Oper Dent 6:55-58. DERAND, T. (1977): Marginal Failure of Amalgam Class II Restorations, J Dent Res 56:481-485. DERAND, T. (1983): Marginal Failure of Amalgam: Effect of Alloy Selection and Biting Forces, Swed Dent J 7:65-68.

FLEISS, J.L.; CHILTON, N.W.; and WALLENSTEIN, S. (1979): Ridit Analysis in Dental Clinical Studies, J Dent Res 58:20802084. GOLDBERG, J.; TANZER, J.; MUNSTER, E.; AMARA, J.; THAL, F.; and BIRKHED, D. (1980): Cross-sectional Clinical Evaluation of Recurrent Enamel Caries, Restoration of Marginal Integrity, and Oral Hygiene Status, JAm Dent Assoc 102:635-641. JORGENSEN, K.D. (1965): The Mechanism of Marginal Fracture of Amalgam Fillings, Acta Odontol Scand 23:347-389. LETZEL, H.; VRIJHOEF, M.M.A.; VAN'T HOF, M.A.; MARSHALL, G.W.; and MARSHALL, S.J. (1989): A Controlled Clinical Study of Amalgam Restorations: Survival, Failures and Causes of Failure, Dent Mater 5:112-115. MAHLER, D.B. and MARANTZ, R.L. (1979): The Effect of the Operator on the Clinical Performance of Amalgam, J Am Dent Assoc 99:38-41. MAHLER, D.B. and MARANTZ, R.L. (1980): Marginal Fracture of Amalgam: Effect of Type of Tooth and Restoration Class and Size, J Dent Res 59:1497-1500. MAHLER, D.B.; TERKLA, L.G.; VAN EYSDEN, J.; and REISBICK, M.H. (1970): Marginal Fracture vs. Mechanical Properties of Amalgam, J Dent Res 49:1452-1457. OSBORNE, J.W. and GALE, E.N. (1979): Failure Rate of Margins of Amalgam with a High Content of Copper, Oper Dent 4:2-8. OSBORNE, J.W. and GALE, E.N. (1981): Failure at the Margin of Amalgams as Affected by Cavity Width, Tooth Position, and Alloy Selection, J Dent Res 60:681-685. OSBORNE, J.W.; GALE, E.N.; CHEW, C.L.; RHODES, B.F.; and PHILLIPS, R.W. (1978a): Clinical Performance and Physical Properties of Twelve Amalgam Alloys, J Dent Res 57:983-988. OSBORNE, J.W.; LEINFELDER, K.F.; GALE, E.N.; and SLUDER, T.B. (1980): Two Independent Evaluations of Ten Amalgam Alloys, J Prosthet Dent 43:622-626. OSBORNE, J.W.; NORMAN, R.D.; CHEW, C.L.; OSBORNE, P.K.; and SETCOS, J. (1989a): Clinical Evaluation of Nine High Copper Amalgams: A 13-year Assessment, J Dent Res 68:997, Abst. No. 1045. OSBORNE, J.W.; NORMAN, R.D.; CHEW, C.L.; SETCOS, J.; and WILLIAMS, K. (1989b): Long-term Clinical Assessment of Amalgam Restorations, J Dent Res 68:189, Abst. No. 57. OSBORNE, J.W.; PHILLIPS, R.W.; GALE, E.N.; and BINON, P.P. (1976): Three-year Clinical Comparison of Three Amalgam Alloy Types Emphasizing an Appraisal of the Evaluation Methods Used, J Am Dent Assoc 93:784-789. OSBORNE, J.W.; WINCHELL, P.G.; and PHILLIPS, R.W. (1978b): A Hypothetical Mechanism by which Creep causes Marginal Failure of Amalgam Restorations, J Indiana Dent Assoc 57:16-17. PHILLIPS, R.W. (1982): Skinner's Science of Dental Materials, Philadelphia: W.B. Saunders, pp. 350-351. WILLIAMS, P.T. and CAHOON, J.R. (1989): Amalgam Marginal Breakdown Caused by Creep Fatigue Rupture, J Dent Res 68:11881193.

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