Partial denture design comparisons between inexperienced and experienced undergraduate students and the teaching staff of a UK dental school.

This study aimed to assess the ability of inexperienced and experienced BDS students and teachers of removable partial denture (RPD) design, to prescribe/design RPDs for an identical partial denture case. Second and fourth/fifth year BDS students and experienced teachers of RPD design were selected to provide a treatment plan for a patient requiring RPDs using identical models. The designs produced were compared against a design produced by the authors before the study began. Not one design for the 100 participants matched the author's design. Under 30% of second year students surveyed the models before designing. Only a small percentage of the participants indicated the path of insertion and removal they had chosen and less than half the student groups and only 60% of the staff group provided clear, correct instructions to the technician. Large disagreements existed between the individuals within groups and between individual groups regarding the selection of component parts. There were wide differences in opinion among the undergraduate student groups as to which are the best design options for particular cases. Teachers of RPD design were found to be far from confident and have no consensus of opinion when designing RPDs.

A digital image analysis system for the assessment of tooth whiteness compared to visual shade matching.

OBJECTIVE: To assess tooth whiteness clinically using an image analysis system and a whiteness algorithm to compare with visual shade matching. METHODOLOGY: Images of the maxillary anterior teeth of 20 subjects were obtained using an image analysis system adapted for tooth whiteness measurement. Red, green, and blue values from each image, and Commision Internationale de l'Eclairage whiteness index (CIE WI) values were calculated. A visual shade match was also carried out using a Vitapan 3D Master 26-tab shade guide. RESULTS: The range of CIE WI values for image analysis and visual shade matching was 32.86-85.91 and 32.68-79.84, respectively. Limits of agreement between methods were +17.71 and -14.60 CIE WI units. The 95% confidence interval of the difference was calculated as -0.176 to +3.083. A two-tailed Student t-test with a 95% confidence level showed significant differences (p = 0.028) between the paired CIE WI values of each tooth for the two measurement techniques. As the accuracy and reliability of the image analysis system was found to be high in previous in vitro studies, the differences between the two methods were probably related to the inherent subjectivity of visual shade matching. CONCLUSION: The adapted digital image analysis system could be used as an alternative to, or in conjunction with visual shade matching.

Colour effects on extracted teeth after a tooth whitening regime: assessment in an artificial oral cavity.

The purpose of this study was to assess the reliability of a digital image analysis system and to assess its suitability for quantifying the colour (including whiteness) of extracted teeth in a purpose built artificial oral cavity after a whitening regime. Extracted teeth were treated with a scale and polish and a bleaching solution. The Image analysis system showed excellent intra operator repeatability. Significant tooth colour and whiteness changes occurred after the bleaching treatment. The digital image system has been shown to be a reliable and valid method for assessing colour and whiteness changes on extracted teeth after whitening treatments.

Visual whiteness ranking of a Vitapan 3D Master shade guide by untrained assessors.

OBJECTIVE: This study was conducted to obtain the ranking order of a 29-tab (including three "bleaching tabs") Vita Shade Guide for perceived "whiteness" by untrained assessors, and to compare this ranking with both the shade guide manufacturer's rank order and a colorimetrically derived rank order. METHODOLOGY: A total of 85 people, not trained in color assessment by shade guides, were asked to rank order the tabs of a Vitapan 3D Master shade guide for perceived "whiteness" under standardized lighting conditions. A whiteness ranking was also obtained colorimetrically using a Minolta CM-2600d spectrophotometer calibrated to give CIE whiteness values. The data were analysed using means, standard deviations, and standard errors. RESULTS: The assessors varied more in their rankings for darker shades than the lighter ones. The order derived by the assessors and the colorimetry order did not match well with the manufacturer's order, especially toward the darker shades. CONCLUSION: For use in studies of whitening products, a new order of the Vitapan 3D Master shade guide tabs has been developed in relation to whiteness.

The determination of freeway space using two different methods.

The aim of this study was to determine the average freeway space of dentate subjects and relate this to recommended ranges for edentulous patients, also to see if any differences were observed between two different methods of measuring freeway space. The freeway space of 72 dentate subjects was measured, first using a Willis gauge, and secondly using a pair of sprung dividers. The intra- and interoperator variability was evaluated as was the reproducibility of the accuracy of both techniques. The mean freeway space using the Willis gauge was 3.3 mm, for both intra and inter operator variability, and with the sprung dividers 3.1 and 2.9 mm, respectively, with no significant difference being seen between any combination of results (P > 0.05). Individual measurements within the two measuring methods being assessed showed significant differences (P < 0.05). The mean measurements of freeway space in dentate subjects found in this study were within the recommended 2-4 mm range, however, 15% of the subjects in the study had freeway space measurements outside this range. This study would suggest that the range for freeway space measurement could more realistically be 2-7 mm.

Dimensional change of refractory materials used for ceramic veneers.

The current literature considers a number of clinical factors which affect the fit of all-ceramic laminate veneers. However, little consideration has been given to the refractory die materials, and the laboratory techniques used during the construction of these restorations. This study found a wide range of dimensional change occurred during setting and through six firing cycles, for seven refractories recommended for the construction of laminate veneers. It is therefore important that where patient treatment involves the use of veneers the clinician considers the suitability of the materials offered by the laboratory, in order to obtain the optimum marginal integrity.

The effect of surface treatments on the bond strength of a nonprecious alloy-ceramic interface.

PURPOSE: The purpose of this study was to compare the effect of seven different alloy surface treatments on the bond strength of the porcelain-metal interface. MATERIALS AND METHODS: Three layers of opaque porcelain and a measured thickness of dentin porcelain were applied to nickel-chromium alloy. A tensile bond strength test was used. RESULTS: The alloy surface treatment that exhibited the highest bond strength was sandblast + surface grinding + sandblast + de-gas, whereas the alloy surface treatment that exhibited the lowest bond strength was sandblast + surface grinding + sandblast + steam cleaning + de-gas. There was a significant difference between the two methods (P < 0.05). CONCLUSION: It was concluded that de-gassing the alloy prior to porcelain application increased the bond strength and excess surface grinding of the alloy reduced bond strength; steam cleaning the alloy surface prior to de-gassing and porcelain application also significantly reduced the bond strength.

The laboratory construction and teaching of ceramic veneers: a survey.

OBJECTIVE: The aim of this study was to identify current trends in the methods and materials used during teaching and construction of ceramic laminate veneers within the laboratory. METHOD: A questionnaire was designed to determine the most popular laboratory techniques and materials used during the teaching and construction of ceramic veneers at a number of university dental schools and teaching hospitals in the United Kingdom, Ireland and Hong Kong, and to identify the role of technical staff. RESULTS: The responses showed that approximately 63% of teaching hospitals and 53% of dental schools were involved with either the construction or teaching of laboratory techniques for ceramic veneers. Of two substrate materials identified, it was clear that the use of phosphate refractory models was preferred to the platinum foil technique. A wide range of refractory and ceramic materials was reported, some of which were supplied as combined system products. However, a larger number were ceramics and refractory materials acquired from independent manufacturers and therefore not necessarily matched. CONCLUSION: Although clear information was provided by the manufacturers to identify the thermal expansion coefficient of their dental ceramic, this is not the case for most of the phosphate refractory materials. As a result, intermixing of individual ceramic and refractory products was commonplace with some combinations having different thermal expansion coefficients. To avoid this thermal mismatch, clear information relating to both products needs to be provided by the manufacturers.