Document Type

Thesis

Date of Degree

Spring 2017

Degree Name

MS (Master of Science)

Degree In

Oral Science

First Advisor

Rodrigo Rocha Maia

Abstract

The purpose of this study was to determine which type of bevel in a class IV dental composite restoration is the most esthetic and has the best blend to natural tooth structure via clinical and spectrophotometric evaluations. The null hypotheses were as follows: (1) there is no difference in visual evaluation rank scores among five groups of evaluators for each type of bevel; (2) there is no agreement in the visual evaluation rank scores of the seven groups of bevels among all evaluators or within each group of evaluators; (3) there is no difference in the lightness values among seven types of bevels at each of eight measurement points or for the whole tooth as measured by a spectrophotometer; and (4) there is no correlation between the visual evaluation and the spectrophotometric evaluation.

The class IV samples were made via CAD/CAM milling for standardization. There were seven groups: negative control (no bevel); short (1mm) and straight bevel; short (1mm) and scalloped bevel; long (2mm) and straight bevel; long (2mm) and scalloped bevel; infinite (3+mm) and straight bevel; and infinite (3+mm) and scalloped bevel. The fractures were restored with the same type of dental composite via a digitally designed mold fabricated with a 3D printer. Once completed, the samples were randomized and evaluated visually by 91 people in five groups (faculty, graduate residents, pre-doctoral dental students, assistants/hygienists, and auxiliary staff). Evaluators placed the samples in the order they deemed least to most esthetic within a lightbox set to CIE Standard Illumination D65. After the visual evaluation, the lightness (L*) values were measured optically with a reflectance spectrophotometer at eight points on each of the seven bevel groups, as well as on an un-prepared typodont tooth used for reference.

One-way ANOVA on ranked data with the post-hoc Bonferroni test was conducted to detect a significant difference in median rating score among five groups of evaluators, and Kendall’s W was used to evaluate an agreement among multiple raters. One-way ANOVA with the post-hoc Tukey’s HSD was used to find a significant difference in mean lightness values among seven types of bevels. Dunnett’s test was used to compare the reference group with each of the seven bevel groups when evaluating the lightness values. Pearson Correlation test along with the simple linear regression analysis were used to determine whether a significant relationship existed between visual evaluation scores and lightness values.

The groups were ranked from least to most esthetic as follows: no bevel, short and straight bevel, short and scalloped bevel, long and straight bevel, long and scalloped bevel, infinite and straight bevel, and infinite and scalloped bevel by the 91 evaluators and Kendall’s W was 0.80 (strong agreement). Moreover, no significant difference in rating scores was found among the five groups of evaluators regarding each type of bevel (p>0.05). The overall mean lightness values observed in groups 1-3 were significantly higher than those in groups 6 and 7 (P< 0.05), but no significant difference was noted among groups 1-5 or among groups 4-7. As the lightness values measured by the spectrophotometer decreased, the overall visual evaluation score increased. The Pearson Correlation Coefficient of -0.89 indicated there was a strong negative correlation between the two variables (p=0.0066). Linear regression analysis revealed that the predictor of lightness was significant (strong negative correlation, R-square 0.99, p< 0.0001).

The first null hypothesis was accepted and the second, third, and fourth were rejected. There was no difference in median visual evaluation rank scores among five groups of evaluators for each type of bevel, however, there was agreement in the ranked order as the findings of this study indicated that infinite and scalloped bevel was the most preferred and no bevel was the least preferred via a strong agreement the evaluators. There was a significant difference in lightness values among the seven bevel groups; the shorter bevels had higher L* values that were closer to the L* values of the reference tooth while the longer bevels had lower L* values. The correlation data showed that placing a longer bevel (3+mm) allowed for a more gradual transition and better blending capabilities between the tooth structure and dental composite. The overall conclusion from this study was the longer the bevel, the more gradual the change in Lightness (L*), which correlated to the more esthetic restoration, as determined by the evaluators.

Keywords

build-ups, conservative, dentistry, fracture, operative, resin

Pages

xv, 142 pages

Bibliography

Includes bibliographical references (pages 140-142).

Comments

This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: http://www.lib.uiowa.edu/sc/contact/

Copyright

Copyright © 2017 Tracy A. D'Antonio

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