Spectrophotometric evaluation of the optical influence of different metal alloys and porcelains in the metal-ceramic complex

Statement of the problem. Color matching between natural teeth, shade guides, and metal-ceramic restorations is a common clinical problem. Difficulties related to color matching arise from structural differences that exist between metal-ceramic crowns and natural teeth, the limited range of available ceramic shades, inadequate shade guides, different types of metal alloys, and varying compositions of ceramic materials. Purpose. The aim of this Study was to investigate the influence of various metal alloys and 2 porcelains on the final color of metal-ceramic complex. Material and methods. Four commercial alloys for metal-ceramic restorations, a Ni-Cr (Thermobond), a Co-Cr (Wirobond), a Pd-rich noble (Cerapal-2), and a high noble Au-alloy (V-Delta) were combined with 2 porcelains (Vita Omega and Ceramco Silver) in metal-ceramic specimens with a standardized thickness of layers. Five disc-shaped (10 x 1 mm) specimens were prepared for each alloy/porcelain combination. Only opaque and dentin layers were applied (shade A3). The specimens were analyzed with a spectrophotometer, and data were obtained in the CIE Lab color system. The recorded data were analyzed with a 2-way multiple analysis of variance, a pair-wise comparison of group means (Student’s t test), and finally, a categorical regression analysis of variance (CATREG) (alpha = .01). Results. The types of alloy substrate and overlying porcelain significantly affected the color (P < .01). Au and Co-Cr alloys were found to be brighter (higher L* values) than the Ni-Cr and the Pd alloys (P < .01, SE 0.239). Cerainco porcelain was found to be most red (higher a* values) of all tested alloys (P < .01). Gold and Pd alloys caused a yellow shift to the metal-ceramic color compared to the Ni-Cr and the Co-Cr alloys with both porcelains (P < .01, SE 0.165). The detected color differences were visually perceptible for some alloy-porcclain combinations. Conclusions. The final color of metal ceramic specimens was influenced both from the type of alloy substructure and from the type of overlying porcelain

Evaluation of Dimensional Stability, Accuracy and Surface Hardness of Interocclusal Recording Materials at Various Time Intervals: An In Vitro Study

To evaluate and compare the dimensional stability, accuracy and surface hardness of three interocclusal recording materials at various time intervals. Polyvinylsiloxane, Zinc oxide eugenol, Aluwax were taken for this study. A stainless steel die of ADA specification no 19. was prepared. A total of ten samples were made with each group. The samples were measured using a travelling microscope of 10× magnification at 1, 24, 48 and 72 h time intervals. Five readings were taken for each sample, the mean was considered to measure the dimensional change, accuracy and surface hardness. The values obtained were statistically analysed by ANOVA and Tukey HSD-Honestly significant difference. Polyvinylsiloxane was the most dimensionally stable, accurate and had the highest surface hardness among the three inter-occlusal materials

Centric relation registration: intra- and interexaminer agreement after a calibration program Avaliação da reprodutibilidade intra e interexaminador no registro da relação cêntrica, após um programa de calibração

Centric relation (CR) has been considered a maxillomandibular position of choice for some dental and prosthetic procedures. Although regarded as a fully reproducible relation, there is great controversy about its clinical use and recording technique, especially in patients with signs and symptoms of temporomandibular disorders (TMD). This study aimed at evaluating the effectiveness of a training program on intra- and interexaminer agreement when determining the clinical record of the CR position. Forty individuals constituted the sample, divided into symptomatic (TMD) and asymptomatic groups. Three previously calibrated examiners performed the initial assessment and the second evaluation after 30 days in a blind design, using Dawson’s bilateral manipulation technique with and without an anterior stop. The amount of frontal and sagittal deviations in relation to intercuspal position, the presence of pain and discomfort during manipulation, and the first occlusal contact in CR were analyzed. Kendall and Kappa tests with a 5% level of significance were used to determine agreement. Values for both intra- and interexaminer agreement were deemed good. The best results were obtained for frontal deviations and assessment of pain (or absence of it) during manipulation. Sagittal deviations showed the lowest agreement in both examinations. The authors concluded that a calibration program could be effective for intra- and interexaminer agreement when recording centric relation. However, caution is recommended when analyzing some isolated items.<br>Na tentativa de estabelecer uma posição maxilomandibular reprodutível em pacientes sem dentes suportes posteriores ou portadores de oclusão instável, o conceito de relação cêntrica (RC) foi introduzido. Apesar de ser utilizada como uma posição de referência, existe uma considerável divergência de opiniões sobre a sua reprodutibilidade. Este estudo procurou avaliar se os métodos de treinamento profissional são efetivos na análise e obtenção de RC. Para isso utilizou-se uma amostra de 40 indivíduos, divididos em 20 assintomáticos e 20 portadores de disfunções da ATM. Os indivíduos foram avaliados por 3 examinadores, previamente calibrados. Foram realizados 2 exames: inicial e final (30 dias após o inicial), possibilitando dessa forma, análise da concordância interexaminadores, assim como intra- examinadores. Posteriormente, os resultados foram submetidos à análise estatística, utilizando-se os testes de concordância de Kendall e de Kappa. Os resultados foram considerados bons, sendo os melhores obtidos para a análise do desvio frontal e relato de dor (ou ausência) durante a manipulação. Os autores concluíram que os programas de calibração podem ser efetivos para análise da RC. No entanto, cautela é recomendada quando da análise de alguns itens isolados