The influence of examiner type on dental students' OSCE scores.

The purpose of this study was to evaluate the difference in grading of objective structured clinical examinations (OSCEs) at Harvard School of Dental Medicine (HSDM) by full-time faculty examiners, part-time faculty examiners, and postgraduate resident examiners. The OSCE is an evaluation of clinical competence and is used as a multidisciplinary examination at HSDM. Two examiners are selected for each of ten disciplines. Evaluators meet to review the case before the OSCE is given, and faculty examiners are given the opportunity to write exam questions based on the students' expected level of knowledge and ability. All examiners also meet on the day of the OSCE to review the case and discuss relevant issues. Students are randomly assigned to examiners and meet with one examiner at a time in each discipline during the examination. Analysis of OSCE scores on four exams given to HSDM students between 2012 and 2013 suggests that part-time faculty members tended to score students significantly higher than full-time faculty members or postgraduate residents. This may be a result of reduced contact time between students and the part-time faculty although it may also point to a need for more efforts in calibration of the part-time faculty members who take part in the OSCE.

Assessment of a prototype computer colour matching system to reproduce natural tooth colour on ceramic restorations.

OBJECTIVES: The aim of this study was to assess the accuracy of a prototype computer colour matching (CCM) system for dental ceramics targeting the colour of natural maxillary central incisors employing a dental spectrophotometer and the Kubelka-Munk theory. METHODS: Seventeen human volunteers with natural intact maxillary central incisors were selected to participate in this study. One central incisor from each subject was measured in the body region by a spectrophotometer and the reflectance values were used by the CCM system in order to generate a prescription for a ceramic mixture to reproduce the target tooth's colour. Ceramic discs were fabricated based on these prescriptions and layered on a zirconia ceramic core material of a specified colour. The colour match of each two-layered specimen to the target natural tooth was assessed by CIELAB colour coordinates (ΔE(*), ΔL(*), Δa(*) and Δb(*)). RESULTS: The average colour difference ΔE(*) value was 2.58±84 for the ceramic specimen-natural tooth (CS-NT) pairs. ΔL(*) values ranged from 0.17 to 2.71, Δa(*) values ranged from -1.70 to 0.61, and Δb(*) values ranged from -1.48 to 3.81. There was a moderate inverse correlation (R=-0.44, p-value=0.0721) between L(*) values for natural target teeth and ΔE(*) values; no such correlation was found for a(*) and b(*) values. CONCLUSION: The newly developed prototype CCM system has the potential to be used as an efficient tool in the reproduction of natural tooth colour.

The optical effect of composite luting cement on all ceramic crowns.

PURPOSE: To investigate the optical properties of resin-based composite cements and assess their effects on the color of all ceramic crowns. MATERIAL AND METHODS: Optical properties of three cements (Variolink II, Esthetic, Nexus II) were analyzed using disk samples (100 microm and 1.0 mm diameter) based on CIELAB color coordinates L*a*b*C* and opacity index. Empress (Ivoclar) and Katana (Noritake) crowns were filled with four different shades of die material (IPS die material ST3, ST5, ST9 and Tetric Evo Ceram Bleach XL). The shade of the crowns was measured with each of three shades of composite cement (Chroma, Bleach and Opaque, Esthetic cement). ST3 and glycerin served as the control. Color differences were calculated in incisal, body and cervical regions. RESULTS: In the cervical and body regions, the color change caused by the bleach abutment could not be altered by using different colored cements for the Empress and Katana crowns. In the cervical region, the color changes effected by the dark brown abutment could be reversed with the bleach luting cement; in the body region this was true only for the Empress crown. Neither different abutment colors nor different luting cement shades resulted in perceptible color changes in the incisal regions. Mean DeltaE* values in the three areas (incisal, body, cervical) were significantly different (p-value<0.01); in the cervical and body regions Empress mean DeltaE* was significantly larger (p<0.01). CONCLUSION: The composite cements evaluated in this study created perceptible color differences with particular combinations of die material, cement and ceramic crown.

Clinical evaluation of perceptibility of color differences between natural teeth and all-ceramic crowns.

OBJECTIVES: Color matching still remains as one of the most challenging tasks in clinical dentistry. With the advancement of intraoral color matching instruments the importance of the development of color thresholds becomes increasingly important. The objective of this study was to set a gold standard for the color difference (DeltaE) at which all-ceramic crowns cannot be distinguished from natural teeth. METHOD: All-ceramic crowns with a zirconia coping (LAVA, 3M ESPE, St. Paul, MN, USA) and layered porcelain (Cerabien CZR, Noritake, Nagoya, Japan) fabricated to match contralateral maxillary central incisors were assessed by experienced observers. Eleven all-ceramic crowns (AC) were assessed as "excellent/perfect matches;" these crowns were then measured using a spectrophotometer and compared to their natural counterparts. Unrestored natural maxillary teeth (NT) were compared to unrestored contralateral teeth in 22 subjects. Six areas were measured in both groups to determine color differences (DeltaE*). RESULTS: Mean DeltaE* value between the restorations and natural teeth was 1.6. Mean DeltaE* between contralateral natural teeth was 0.9. Incisal areas of natural teeth exhibited greater differences in color than other compared areas. CONCLUSION: A DeltaE*=1.6 represented the color difference that could not be detected by the human eye.