The finishing and early marginal fracture of clinical amalgam restorations

J. Dent.

1989; 17: 11 l-l

111

16

The finishing and early marginal fracture of clinical amalgam restorations* R.W.

Bryant

Department

of Operative Dentist/y,

University of Sydney, Australia

Catherine J. Collins Westmead

Dental Clinical School, Westmead,

NSW, Australia

KEY WORDS: Amalgam, Operative techniques, Clinical performance

J. Dent

1989;

17: 11 l-l

16 (Received 28 July 1988;

reviewed 15 September

1988;

accepted 28 February 1989)

ABSTRACT One operator placed 249 Tytin amalgam restorations in Class I and II preparations in the permanent teeth of 60 patients each of whom received a minimum of three restorations. At least one of these restorations was carved-only, at least one was immediately finished (at 8 or 10 min after trituration), and at least one restoration was polished (more than 24 h after placement). Restorations were principally assessed for marginal fracture at baseline and 1 year using the 1 l-unit scale for the evaluation of photographs developed by Mahler. Five factors were also assessed clinically at 1 year. Amalgam restorations, polished using finishing burs and rubber points at least 24 h after placement, exhibited more initial marginal fracture than carved-only or immediately finished restorations. At 1 year, the three techniques were comparable except for the superior surface texture of the polished restorations. The technique of immediate finishing of amalgam restorations has nothing to commend it in preference to existing techniques.

INTRODUCTION Following the introduction of high-copper amalgams and clinical studies on the performance of amalgam restorations, many dentists are seeking to polish restorations which, in previous years, would have remained unfinished. A number of clinical studies have compared alternative finishing techniques, by assessing the performance of amalgam restorations, using a variety of clinical evaluation criteria and indirect methods. The clinical studies have compared different combinations of carved restorations, polished restorations, or immediately finished (at approximately 8 min) restorations (Carron et aZ., 1983; Fenton and Smales, 1984; Letzel and Vrijhoef, 1984; Straffon ef aZ.. 1984; Mayhew et aZ., 1986). Straffon et al. (1984) described clinical evaluation criteria that were modifications of those developed by Cvar and Ryge ( 1973), in order to provide greater insight *Based on findings presented August 1987.

at the IADR

0 1989 Butterworth & Co. Publishers 0300-5712/89/03011 l-06 $03.00

Ltd.

(ANZ

Div.) Meeting in

into the early changes taking place in restorations. Fenton and Smales (1984) used an alternative set of clinical criteria. To evaluate indirectly the marginal integrity of the amalgam restorations using black and white photographs, two studies used six-point category scales to compare carved-only and 24-h polished restorations (Letzel et al., 1978; Letzel and Vrijhoef, 1984; Mayhew et al.. 1986). Another study used a scale that was similar to that used in their clinical evaluation of marginal adaptation to compare immediate and 24-h finished restorations (Stratfon et al., 1984). Fenton and Smales (1984) used relatively coarse criteria to evaluate marginal fracture of carved and immediately finished restorations, in comparison with the criteria used by Straffon et al. (1984) which were aimed at identifying smaller changes in the restorations. Mahler et al. (1970, 1973) described a technique of determining marginal fracture by comparing photographs of the occlusal surfaces of amalgam restorations to a reference set of five photographs on an 1 l-unit scale and

112

J. Dent. 1989;

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have used the technique extensively to evaluate the performance of many types of dental amalgams (Mahler and Marantz, 1979; Mahler.et al., 1980). To improve their evaluation of early changes, an expanded, eightphotograph reference set for the 1 l-unit scale was used in a recent study (Bryant et al., 1985). The aims of this study were to examine the influence at baseline on the marginal integrity of restorations finished by three different techniques and to compare changes at 1 year using, as the principal method of assessment, the photographic technique developed by Mahler. MATERIALS

AND METHOD

One operator placed 249 amalgam restorations (Tytin, BN 6828509, S.S.White, Philadelphia, PA, USA) in 60 patients, each of whom required at least three Class I or II restorations in permanent teeth. Deeper cavities received, according to depth, amount required and previous history of the tooth, a quick-setting base of either the zinc oxideeugenol type (Kalsogen; De Trey, Weybridge, Surrey, UK) or the calcium hydroxide type (Dycal; Caulk/ Dentsply, Milford, DE, USA). Each patient received at least three restorations. At least one of these was carved-only (code C), at least one was immediately finished (code I), and at least one restoration was polished (code P). Finishing techniques were systematically allocated (not by the operator) to specific restorations in a way that minimized the influence of tooth type and position, and restoration class and size. Before carving, the restorations were burnished to maximize adaptation. After the occlusion had been adjusted and carving completed, the operator was advised (by reference to the allocation form) which one of the three finishing techniques had been allocated for that restoration. Until this stage the operator, who had not been involved in allocating the techniques, was unaware which finishing technique was to be used. It was observed that, on average, proximo-occlusal restorations required at least one more capsule of amalgam and more time to place the amalgam than occlusal restorations. For this reason, immediate finishing (I) commenced 8 min after trituration of the amalgam for Class I restorations and 10 min after trituration for Class II restorations. Fluoridecontaining zirconium silicate paste (Floran, Creighton Pharmaceuticals, Sydney, Australia) was used in unwebbed rubber cups in a low-speed handpiece for a maximum of 90 s. At a subsequent appointment, restorations allocated for polishing (P) were completed using tungsten carbide finishing burs and rubber polishing points (Shofu, Dental Corp., Menlo Park, CA, USA). For the photographic evaluation, black and white prints were obtained of the occlusal surfaces of the restorations at a magnification of 4.1 X, with standardization of contrast and brightness. Baseline photographs were obtained within 4 weeks of finishing and photographs for the l-year recall were obtained at an average of 13.1 months (s.d. 1.3 months) after placement. Three

trained evaluators independently assessed the extent of marginal fracture of the restorations using the method developed by Mahler. For each evaluator, the marginal fracture values for restorations finished by the same technique in each patient were averaged to provide a within-patient mean for that technique. Because each patient received at least one restoration finished by each of the three techniques, this procedure served to remove the influence of the patient effect. For each evaluator, paired comparisons were carried out between the within-patient means for these techniques to compare techniques C and P, C and I, and P and I, using the ‘Student’s’ t distribution to test the null hypothesis pr, = 0 (Snedecor and Co&ran, 1980). Finally, the indexes for the three evaluators were averaged to produce a marginal fracture index for each technique at each assessment time. At recall, the restorations were assessed clinically, using modified criteria based principally on those developed at the University of Michigan (Straffon et al. 1984), for marginal adaptation, surface texture, surface discoloration and caries (Table I) and patients were asked to report any unacceptable sensitivity to thermal stimuli. Each clinical evaluation was carried out by any two of three clinicians. The two evaluators assessed independently. In the event of disagreement, a decision was reached by immediate re-examination and discussion. Differences among techniques were compared using the Chi square test (Phillips, 1978). Written patient consent was obtained at the start of the project and the protocol was approved by the Human Ethical Research Committee of Westmead Hospital (Westmead, NSW, Australia). RESULTS The statistical analyses of paired comparisons of the three finishing techniques for the evaluation of marginal fracture at baseline are shown in Table II. Averaged marginal fracture indexes for each evaluator’s assessment of each technique are shown in Table III. The polished (finished after at least 24 h) restorations (P) were assessed by each evaluator as showing a greater extent of marginal fracture than either technique C or I. These differences were statistically highly significant but may not necessarily have been clinically detectable. Differences between C and I restorations were small. At 1 year, for each evaluator, the average marginal fracture values for the three techniques differed by less than 0.15 marginal fracture category units (Mahler scale). No differences between paired comparisons were statistically significant at the 5 per cent probability level. Within-evaluator paired comparisons for each technique between assessments at baseline and l-year recall were all highly significant. These differences ranged from approximately 1.0 to 1.8 marginal fracture category units in extent, an amount likely to be clinically detectable.

Bryant and Collins: Finishing and marginal fracture of clinical amalgams

113

Tab/e L Criteria for clinical evaluation* Clinical criteria

Rating

A Marainal adaptation Amalgam is continuous with adjacent tooth structure 0 Margin not detectable with a sharp probe passing in either direction 1 Margin detectable by probe only-along less than 50% of exposed margin (No visible evidence of crevice-no exposure of cavity wall) Margin detectable by probe only-along more than 50% of exposed 2 margin Visible evidence of a crevice (with cavity wall exposed) into which the 3 probe will penetrate-along less than 50% of exposed margin 4 Visible evidence of a crevice into which the probe will penetrate-along more than 50% of exposed margin Crevice formation with exposure of underlying dentine or base 5 B. Surface 0 1 2 3

texture No roughnessglossy Slight roughness-fine granules-‘satiny’ Obvious roughness and/or scratches and/or Very rough and/or pitted

coarse granules (granular)

C. Surface discoloration Still reflective; no colour change 0 1 Light grey (slight discoloration); non-reflective Dull grey-dark (localized or generalized) 2 Black-dark grey 3 D. Recurrent marginal caries There is no evidence of caries contiguous with the margin of the 0 restoration 1 There is evidence of caries contiguous with the margin of the restoration *Modified -criteria based on Straffon er a/. (1984). Smales (1984).

Cvar and Ryge (1973)

and Fenton and

Tab/e Il. Marginal fracture assessed by photographic evaluation: statistical analysis of comparisons between pairs of finished restorations at baseline

Evaluator

Finishing techniques compared

Relative extent of marginal fracture

Value for t (df = 59)

Statistical significance of difference *** *** *

C

z:;

I

C and P I and P C and I

II II

C and P I and P C and I

C

4.7 4.1 1 .o

III III III

C and P I and P C and I

C

;I;

n.s. c** ***

0.4

n.s.

I

2.6

*** ***

C, carved-only; I, immediately finished; P, polished. Significant difference: *** at 0.1 per cent probability level, or less; * at 5 per cent probability level. ns., Difference not significant at 5 per cent probability level.

Average marginal fracture indexes for each technique at baseline and l-year recall were averaged across evaluators and these data are illustrated in Fig. 1. Averaged indexes (of the three evaluators) were, at baseline: C, 1.39; I, 1.46; P, 1a86 units; and at l-year recall: C, 3.07; I, 3.04; P, 3.00 units on the expanded Mahler photographic category scale. Five factors were assessed clinically at 1 year. Results

for marginal adaptation, surface texture and surface discoloration are shown in Table IV. At 1 year, restorations finished with technique P (polished after at least 24 h) were significantly superior in surface texture to those finished with techniques C or I (x2 = 170.6, P < 0.001, d.f. = 4). Differences among techniques for marginal adaptation and surface discoloration were not significant (P > O-05). Caries was not detected at the

114

J. Dent.

1989; 17: No. 3

Tab/e Ill. Marginal fracture assessed by photographic evaluation: average marginal fracture indexes for the three evaluators at baseline and 1 -year recall for the three finishing techniques Finishing technique code

Evaluator

Restorations (no.)

Marginal fracture index Mean s.d *

I Baseline

C

I.27 1.40 1.73 3.07 3.02 2.92

O-37 0.38 0.52 O-98 0.91 0.83

85 81 83

1.46 I.51 1.79 3.07 3.07 3.00

0.39 0.34 0.49 0.88 0.91 0.87

85

1.44

0.48

E

:: 85

2.07 1.47 3.07

0.39 o-49 0.61

Pf

81 83

3.03 3.09

0.76 060

I

K

: I P

88;

Baseline

C I

85 ::

1 -year recall

E I P

Baseline

C I

1 -year recall

1 -year recall

!z;

II

III

C, carved-only;I, immediately finished; P, polished. *Value for 1 standard deviation.

Tab/e IV: Clinical assessment of restorations at 1 year Technique and number of restorations C I P

85 81 83

Restorations exhibiting rating (no.)

0 : 0

Marginal adaptation 1 2 3 4 16 16 22

52 44 46

5

:: 15

0

Surface texture 1 2

3

Surface discoloration 0 1 2 3 65 z

19 27 17

1 1 1

C, carved-only;I, immediatelyfinished; P. polished.

margins of any restorations (by clinical and radiographic examination). No patient reported unacceptable sensitivity of restorations to thermal stimuli at 1 year. DISCUSSION At baseline, the restorations that had been polished after at least 24 h exhibited significantly more evidence of marginal fracture (chipping), as assessed using the widely respected Mahler photographic scale, than restorations that had only been carved or had been finished at 8 or 10 min after trituration. The difference, amounting to 0.4 to 0.5 units, was statistically significant but not necessarily clinically detectable. Dentists may be concerned about this finding because it would appear that, by polishing, restorations are rapidly ‘aged’; that is, the amount of marginal fracture evident is greater. However, two advantages of this polishing procedure were that it appeared to have removed some

excess (flash) amalgam beyond the margin and that these polished amalgams had superior surface texture at 1 year. The effect of polishing in removing excess was probably evident in a comparison, among the three techniques, of the average extent of additional marginal fracture exhibited at 1 year. The extent around carved and immediately finished restorations increased 40-50 per cent more in this period compared with those restorations that had been polished at baseline. Bryant (1979), in a review of the many factors associated with the marginal fracture of amalgam restorations, emphasized the role of the operator (dentist) in the amount of early marginal fracture and noted the particular importance of cavity design and carving. Smales and Fenton (1985), having investigated restorations that had been carved or immediately finished, stressed the need for care to ensure that minimal excess amalgam was left beyond the cavity margin.

Bryant and Collins: Finishing

and marginal

fracture

of clinical amalgams

115

would appear to prolong, without any real advantage, the operating time at which the restoration is placed.

CONCLUSIONS

i!

‘FI

.c

2.0

% 6

1.5

E f <

1.0

0.5

0.0

1

1 year

Baseline Evaluation

1. Amalgam restorations polished after at least 24 h using finishing burs and rubber points exhibit a greater extent of initial marginal fracture than restorations that have only been carved. 2. The three techniques assessed are comparable at 1 year except for surface texture for which restorations that are polished, at least 24 h after placement, are vastly superior. 3. The technique of immediate finishing of amalgam restorations has nothing to commend it as an alternative to delayed (traditional) polishing or carved-only. The technique prolongs the initial appointment to no advantage either initially or at 1 year.

time

Fig. 1. Marginal fracture (MF) of the restorations. Values (for the Mahler scale) represent the average for three evaluators for each technique at baseline and 1 -year recall. H, Carvedonly: E9, immediately finished; 0, polished.

At 1 year, there was no difference, on average, in the extent of marginal fracture among the techniques. All restorations exhibited a clinically detectable margin and 20 per cent had a visible crevice. Using different criteria for their photographic evaluation Straffon et al. (1984) found no significant difference at 1 year between 8-min and 24-h finished restorations in primary teeth, although the early finishing technique demonstrated superior adaptation at baseline and 6 months. Smales and Fenton (1985), using relatively coarse clinical and replica evaluation criteria, found no difference at 2 years between carved-only and immediately finished restorations. In this study, the time at which immediate finishing was carried out differed a little from other studies. For example, Fenton and Smales (1984) finished their Class II restorations after 8 min. Straffon et al. ( 1984) finished their Class II restorations in primary teeth after 8 min then checked, but did not adjust, the occlusion. Using extracted teeth, Murrey and Watkins (1985) finished restorations after 30 min and, compared with delayedpolish restorations, assessed 60 per cent of their earlyfinish Tytin restorations as unacceptable. There appears to be nothing to commend the technique of immediate finishing of amalgam restorations. It is statistically similar to the carved-only restorations at baseline, in the extent of marginal fracture, and at 1 year offers no advantage in this regard over carved-only or traditionally polished restorations. In addition, immediately finished restorations were clearly inferior in surface texture to polished restorations at 1 year and

Acknowledgements The authors wish to thank Dr D. B. Mahler, Oregon Health Sciences University, USA, for his guidance, and Dr I. Martin for assisting in the clinical and photographic evaluation. This research was partly supported by the Australian Dental Research Fund Inc.

References Bryant

R. W. (1979) Marginal fracture of amalgam

review. Part I. Amt. Dent. J. 26, 162-166; Part II. Amt. Dent. J. 26, 222-224. Bryant R. W., Mahler D. B. and Engle J. H. (1985) A comparison of methods for evaluating the marginal fracture of amalgam restorations. Dent. Mater. 1, restorations-a

235-237. Carron S., Corpron R., Straffon L. et al. (1983) Clinical

comparison of carved only and immediate polishing of class I amalgams. J. Dent. Res. 62, (AADR Abstr No. 27), 172. Cvar J. F. and Ryge G. (1973) Clinical evaluation of dental restorative materials. In: Monograph GPO 790-244. US Department of Health, Education and Welfare. Fenton R. A. and Smales R J. (1984) Immediate-polished and as-carved Tytin restorations after 12 months. J. Dent. 12,165-l 74. Letzel H. and Vrijhoef M. M. A. (1984) The influence of

polishing on the marginal integrity of amalgam restorations. J. Oral Rehabil. 11, 89-94. Letzel H., Aardening C. J. M. W., Fick J. M. et al. (1978) Tarnish, corrosion, marginal fracture and creep of amalgam restorations: a two-year clinical study. Oper. Dent. 3,82-92. Mahler D. B. and Marantz R. L. (1979) The effect of time on the marginal fracture behaviour of amalgam. J. Oral Rehabil. 6, 391-398. Mahler D. B., Terkla L. G., Van Eysden J. et al. (1970) Marginal fracture vs mechanical properties of amalgam. J. Dent. Res. 49, 1452-1457.

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Mahler D. B., Terkla L. G. and Van Eysden J. (1973) Marginal fracture of amalgam restorations. J. Dent. Res. 52,823-827. Mahler D. B., Marantz R. L. and Engle J. H. (1980) A predictive model for the clinical marginal fracture of amalgam. J. Dent. Res. 59,1420-1427. Mayhew R B., Schmeltzer L. D. and Pierson W. P. (1986) Effect of polishing on the marginal integrity of high-copper amalgams. Oper. Dent. 11, 8-13. Murrey A. J. and Watkins T. R (1985) Polishing of amalgams at 30 minutes compared to 24 hours. J. Dent. Res. 64, (IADRAADR Abstr. No. 49), 180.

Phillips D. S. (1978) In: Basic Statistics for Health Science Students. San Francisco, Freeman, pp. 123-124. Smales R. J. and Fenton R. A. (1985) Immediate-polished and as-carved Tytin restorations after 3 years. J. Dent. 13,79-83. Snedecor G. W. and Cochran W. G. (1980) In: Statistical Methods. Iowa State University Press, Iowa, USA, pp. 83-85. Straffon L. H., Corpron R E. and Dermison J. (1984) Clinical study of early polishing of class II amalgam restorations in primary teeth. J. Dent. Res. 63, (IADR/ AADR Abstr. No. 1486), 336.

Correspondence should be addressed to: Dr R. W. Bryant, c/o Department of Clinical Dentistry, Westmead Hospital Dental Clinical School, Westmead, NSW 2145, Australia.

Book Reviews

Teeth

Revisited: Proceedings of the Vllth International Symposium on Dental Morphology. Edited by D. E. Russell, J.-P. Santoro and D. SigogneauRussell. (Memoires du Museum National d’tlistoire Naturelle, Serie C, Sciences de la Terre, Tome 53.) Pp. 462. 1988. Paris, Editions du Museum National d’Histoire Naturelle. Softback, 650FFr.

This attractively produced if weighty volume contains papers presented at the International Symposium on Dental Morphology held in Paris on 20-24 May 1986, the most recent in a series of seven symposia held every 3-5 years since 1965. The varied contributions stretch beyond morphology on the descriptive level and fall into four sections: embryology and genetics, evolution of dental tissues, dental morphology and evolution, and diet and tooth wear. Of the 34 papers, 29 are in English and five in French. All have both English and French abstracts. The genetic control of tooth size is considered in two papers, one through an analysis of sex chromosomal aneuploidies and the other through a novel study of twins reared in two different environments. Ontogeny features in two further contributions. In the first, variation in number and position of future functional teeth between five reptilian species is shown to be related to differences in jaw growth, suggesting that the embryonic dental system has great evolutionary plasticity. The second is a useful quantitative comparison of cell proliferation between in vivo and in vitro mouse tooth germ development. The bulk of the book is concerned with histological or morphological features in fossil, skeletal or extant populations that contribute to charting the progress of

dental evolution. Topics covered by the eight histological studies include the enameloid tissues of lower vertebrates, enamel tubules, the evolutionary transition from preprismatic to prismatic enamel, the taxonomic value of differences in structural organization of enamel, the functional implications of enamel structure and the physicochemical changes that take place with enamel fossilization. The largest section, comprising 13 papers, is concerned with dental morphology in the stricter sense, with reports ranging from phylogenetic studies of Palaeozoic lung fishes and holocephalians, through Cretaceous, Tertiary, more recent and living mammals, to a comparison of dental and skeletal characteristics in the taxonomy of recent Cheiroptera. There are also studies of microdifferentiation in neolithic and living human populations. The final section, containing nine contributions, deals with the evolutionary response of tooth morphology to changes in diet and habitat, and with patterns of tooth wear as indicators of dietary preference. Examples are taken from early mammals to modern man. Evolutionary change therefore features in the majority of contributions, whereas the genetic control of dental morphology is barely considered. This is a disappointing imbalance since a knowledge of the genetics of tooth shape and structure is fundamental in fully understanding the basis of dental evolution. Nevertheless, the imbalance, which presumably reflects the distribution of research effort in these areas, does not diminish the usefulness of the book and these Proceedings will constitute a welcome addition to the shelves of all those who appreciate the value of dental morphology as a reflection of environmental and genetic change over evolutionary time. J. A. Sofaer