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RESEARCH REPORT |
1 Department of Restorative Dentistry and Endodontology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan;
2 Guy’s, King’s and St Thomas’ Dental Institute, UK; and
3 University Dental Hospital of Manchester, UK;
*corresponding author, mikarin{at}dent.osaka-u.ac.jp
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: marginal adaptation • clinical evaluation • posterior composite
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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The USPHS criteria (Cvar and Ryge, 1971; Appendix, Fig. A1, www.dentalresearch.org) have been widely used for the clinical evaluation of restorations. These criteria involve visual inspection and the use of a dental explorer for the evaluation of the marginal quality of restorations, which are graded into one of four ratings: A (Alfa), replacement unnecessary; B (Bravo), replacement questionable; C (Charlie), replacement for preventive reasons; and D (Delta), immediate replacement. However, the methods of evaluation seem to be open to question, since the detection of marginal steps relies on the individual examiner’s visual acuity, manual sensitivity, and technique and experience, let alone the sharpness of the dental explorer, which remains to be standardized for the purpose of clinical trial methodologies.
The purpose of the ongoing series of studies, an element of which is reported in this paper, was to establish an objective and reliable method to evaluate the marginal adaptation of restorations. The initial investigation, as reported in this paper, was to undertake retrospective analyses to clarify the prognosis of posterior composites with marginal deterioration and to evaluate the quality of marginal evaluations by analyzing the distribution of marginal step height rated by clinical criteria. The hypothesis tested was that the marginal adaptation evaluation of posterior composites in clinical trials may be precise and distinguishable between the steps with different clinical ratings.
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MATERIALS & METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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Failure Rate
Five-year failure rates were calculated by means of the following equation:
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All dropped restorations were excluded from the equation. The overall failure rate and the failure rates for the restorations observed to have had some or no marginal deterioration at one, two, three, four, and five years were calculated. The failure rates for the restorations with marginal deterioration were then compared with those with ideal margin. The overall failure rates were also compared with the failure rates for the restorations found to have had less than ideal marginal qualities. Differences in the failure rates for restorations with and without observed deterioration in the qualities of their margins were investigated by means of the chi-square test at a 95% level of confidence.
Marginal Step Measurement
A total of 435 epoxy replicas was investigated. These were comprised of 200 restorations, selected at random, which at one- to five-year recalls had been given A (Alfa) ratings for marginal adaptation, 200 randomly selected restorations with records of B (Bravo) ratings for marginal adaptation, and the 35 restorations in the program found to have had C (Charlie) ratings for marginal adaptation.
Step height in the most deteriorated area of each of the 435 restorations was measured under standardized conditions by means of a digital step-height instrument (University of Manchester Dental School, UK) with a stylus of less than 100 µm at the measuring tip and a calibrated vertical sensitivity of 1 µm.
For the determination of step height, the stylus was placed at the highest point of a step along the marginal edge. The tip of the stylus was then placed at the lowest point of the step. The difference in height between the points was recorded in microns as the step height for that margin (Appendix, Fig. A2, www.dentalresearch.org). Ten measurements were made for each step. The maximum and minimum values were excluded. The mean of the remaining eight values was taken to be the step height of the restoration.
Step heights for the restorations with different clinical ratings, obtained at different centers, were compared by means of Kruskal-Wallis and Scheffé’s F tests with a 95% level of confidence (StatView Macintosh v4.5, SAS Institute Inc., Cary, NC, USA).
The distributions of step heights overall and in relation to the restorations with individual clinical ratings were analyzed mathematically by use of curve analysis software (Table CurveTM 2D Windows v4.07, SPSS Inc., Chicago, IL, USA). This incorporated a non-linear regression routine that ranked curve-fit equations according to goodness-of-fit.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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. The restorations with B ratings for marginal adaptation at three-year review were 5.0 times more likely to have failed five years after placement than restorations with A ratings for marginal adaptation. The restorations with deterioration in marginal adaptation were between 2.0 and 5.0 times more likely to have failed by five years than the restorations with ideal margin. There were significant differences in the failure rates for the restorations with and without deterioration in marginal adaptation at the two-, three-, and four-year reviews (chi-square test, p < 0.01). When the failure rates for the restorations with deterioration in marginal adaptation were compared with the failure rates for all the restorations placed, the restorations with deterioration in marginal adaptation were found to be between 0.7 and 2.0 times more likely to have failed, with the differences at the two-year review being statistically significant (chi-square test, p = 0.015).
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Marginal step heights overall were distributed over a range from 23 µm to 988 µm (Appendix, Table A2, www.dentalresearch.org). The distributions of step heights overall and in relation to the restorations with A and B ratings were represented by curves obtained by log-normal regression (Fig. 1). The regression equation was as follows:
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where a, b, c, and d are adjustable parameters. Log-normal regression showed a high, typically greater than 0.98, coefficient of determinations (r2) for the steps in the restorations overall and in the restorations with A and B ratings. The distribution of the steps in the restorations with C ratings did not show a good fit to curves representing any non-linear regression equation with a high correlation coefficient.
Mean marginal step heights were 122 µm for the restorations with A ratings, 253 µm for those with B, and 513 µm for those with C ratings. Significant differences were found to exist between steps with different clinical ratings (Scheffé’s F test, p < 0.0001) (Fig. 2).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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In the present study, it was originally planned to measure up to 200 restorations with A ratings and 200 restorations with B ratings. We also hoped to obtain the same number of restorations from all the eight centers. However, only a limited number of restorations with B ratings were available from four centers, even though the replicas obtained at the one- to five-year reviews were available for selection. Therefore, the maximum number of restorations with B ratings available were obtained from those centers, and then a larger number of restorations from the other four centers were measured to attain the total number planned. This was the cause of unevenness in numbers of the restorations measured from the different centers.
The step heights measured in the overall set of restorations and in the several subsets of restorations with individual clinical ratings did not show normal distributions. Even after a logarithmic transformation had been performed, the distributions were far from normal. Hence, a non-linear regression analysis was performed by means of the Table CurveTM software. The distributions of step heights overall and in the restorations with A and B ratings were successfully represented by the curve obtained from log-normal regression with very high correlation coefficients (Fig. 1
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Only 35 restorations with C ratings were available for measurement and did not provide a sample sufficient for detailed analysis. Moreover, the distribution of the step heights in the restorations with C ratings did not show a good fit to curves represented by the non-linear regression. Therefore, the analysis of the data focused on the restorations with A and B ratings, which were the ratings given to most of the restorations examined.
The results in the present study show that the overlap for step height in the restorations with A and B ratings is substantial, with 62% of the restorations with A ratings and 79.5% of those with B being included in this range. It may be considered that the distinction between A and B ratings is insufficient when current evaluation methods are used. One of the reasons for this wide range of overlap may be an unacceptable lack of certainty in the evaluation methods. The USPHS criteria specify the use of visual inspection and a dental explorer for the evaluation of margins of restorations. However, the ability to detect marginal steps relies on the individual examiner’s visual acuity, manual sensitivity, technique and experience, and the sharpness of the dental explorer, which remains to be standardized for the purpose of clinical trial methodologies.
For many decades, dental explorers have been widely used for tactile examination in the diagnosis of pit and fissure caries (Chan, 1993). However, the use of explorers in such situations is no longer recommended, due to inaccuracies in the diagnosis of caries (Penning et al., 1992) and as a consequence of harmful effects to pits and enamel surfaces (Ekstrand et al., 1987). Although the use of an explorer has been replaced in the diagnosis of caries by a detailed visual examination (Dodds, 1993), an explorer is still considered to be useful in the assessment of marginal deterioration in restorations.
A significant correlation between the detection of steps and the sharpness of the tip of the dental explorer has been reported (Rappold et al., 1992). The results indicate that an explorer with a sharp tip could detect a small step with significant accuracy; however, the appropriate sharpness of the explorer remains to be established.
The current evaluation methods for marginal adaptation according to the USPHS criteria are clinically important and meaningful, even though it includes a wide overlap between ratings. This is because a restoration with a marginal step is more likely to fail than a restoration with an ideal margin, as confirmed in the present study. Standardization of the sharpness of the explorer to be used in assessments of marginal adaptation may be effective in minimizing the overlap between A and B ratings detected in the present study. This proposal was partly anticipated by Rappold et al. (1992).
For standardization of the sharpness of an explorer, a rational guideline for defining the delineation between steps with different clinical ratings is indispensable. The present study is an attempt to establish the step height which distinguishes A from B ratings. When the steps with a height greater or less than one standard deviation of the mean were excluded, the overlap was effectively reduced to 5 µm, in which only one restoration with A ratings and four with B ratings were included. This suggests that the range between 168 µm and 173 µm may be considered the borderline between marginal steps with A and B ratings.
Further investigation is needed to test the detection ability of standardized explorers by use of the models with steps rated as A and B. This could lead to the establishment of the reliable evaluation method for the marginal adaptation of restorations.
The importance of calibration of examiners is emphasized in the USPHS criteria (Char and Ryge, 1971). The evaluation of the restorations in the OcclusinTM multi-center clinical trial program was conducted according to the same protocol. The program’s principal investigator made three- to six-month visits to each of the centers throughout the program to ensure commonality of approach by the investigators. This effort was largely successful. The use of a standardized explorer, it is suggested, would have enhanced the inter- and intra-examiner agreement even further.
Based on the present analyses of the distribution of marginal step heights, it is concluded that a wide overlap was found to exist in the distribution of step heights in restorations with different clinical ratings. An Alfa/Bravo boundary of 170 ± 3 µm was apparent. The current evaluation method of the marginal quality of restorations should be improved to make a clear distinction between clinical ratings.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Received March 7, 2002; Last revision October 7, 2002; Accepted October 18, 2002
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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Cvar JF, Ryge G (1971). Criteria for the clinical evaluation of dental restorative materials. San Francisco: US Public Health Service Publ. No.790-244, USGPO.
Dodds MW (1993). Dilemmas in caries diagnosis—applications to current practice and need for research. J Dent Educ 57:433–438.[Medline]
Ekstrand K, Qvist V, Thylstrup A (1987). Light microscope study of the effect of probing in occlusal surface. Caries Res 21:368–374.[ISI][Medline]
Penning C, van Amerongen JP, Seef RE, ten Cate JM (1992). Validity of probing for fissure caries diagnosis. Caries Res 26:445–449.[Medline]
Rappold AP, Ripps AH, Ireland EJ (1992). Explorer sharpness as related to margin evaluations. Oper Dent 17:2–6.[Medline]
Wilson NH, Norman RD (1991). Five-year findings of a multiclinical trial for a posterior composite. J Dent 19:153–159.[Medline]
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