Objectives: The machinability of a material can be measured with the calculation of its brittleness index (BI). It is possible that different materials with different BI could produce restorations with varied marginal integrity. The degree of marginal chipping of a milled restoration can be estimated by the calculation of the marginal chipping factor (CF). The aim of this study is to investigate any possible correlation between the BI of machinable dental materials and the CF of the final restorations. Methods: The CEREC TM system was used to mill a wide range of materials used with that system; namely the Paradigm MZ100 TM (3M/ESPE), Vita Mark II (VITA), ProCAD (Ivoclar-Vivadent) and IPS e.max CAD (Ivoclar-Vivadent). A Vickers hardness Tester was used for the calculation of BI, while for the calculation of CF the percentage of marginal chipping of crowns prepared with bevelled marginal angulations was estimated. Results:The results of this study showed that Paradigm MZ100 had the lowest BI and CF, while IPS e.max CAD demonstrated the highest BI and CF. Vita Mark II and ProCAD had similar BI and CF and were lying between the above materials. Statistical analysis of the results showed that there is a perfect positive correlation between BI and CF for all the materials. Conclusions: The BI and CF could be both regarded as indicators of a material's machinability. Within the limitations of this study it was shown that as the BI increases so does the potential for marginal chipping, indicating that the BI of a material can be used as a predictor of the CF.

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The quality of construction of fixed bridge prostheses directly affects their long-term survival. The cost, alloy composition and marginal fit of bridges made by 30 commercial dental laboratories is assessed. Duplicate models of a three unit bridge preparation were sent to 30 different laboratories, as if required for a patient receiving treatment under the General Dental Service. Material was sent via general dental practitioners, requesting metal-ceramic bridges made from 45% Au alloy, precious metal or non-precious metal. Proximal contacts were overbuilt at 65% of sites and pontic tissue contacts were excessive in all but one bridge. Eight laboratories did not use alloys corresponding to the request made. The mean marginal gaps of non-precious metal bridges (145 microns) were significantly greater than those for 45% gold alloy (106 microns). Marginal fit was poor and a number of factors have been observed, with other postulated, which may have contributed to this problem.

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Summary. An in vitro study was performed to assess the depth of penetration of a fissure sealant after cleaning the occlusal surfaces with an air‐polishing unit, and to compare the results with those obtained after cleaning with pumice and water and after no cleaning. Forty‐six clinically non‐carious premolars and permanent molars were randomly distributed into three groups. Following cleaning, etching and fissure sealing, the teeth were sectioned. Each section was examined under a light reflecting microscope and the depth of resin penetration was determined. Fissure cleaning with an air‐polishing unit produced a statistically significant increase in depth of penetration of sealant resin, and its use as a standard cleaning method before fissure sealing is recommended. Résumé. Le but de cette étude in vitro a été de mesurer la profondeur de pénétration d'un sealant pour fissures après nettoyage des surfaces occlusals par un systéme de polissage par air, après nettoyage avec de l'eau et de la poudre de pierre ponce et sans nettoyage 46 prémolaires et molaires permanentes non cariées cliniquement ont été distribuées au hasard en trois groupes. Aprés nettoyage etching et scellement des sillons, les dents ont été sectionées. Ohque coupe a été examinée au microscope et la profondeur de pénétration de la résine a été notée. Le nettoyage par un systéme de polissage par air a augmenté de façon significative la profondeur de pénétration de la résine de scellement. Son utilisation est donc recommandée avant les scellements de sillons. Zusammenfassung. Eine in Vitro‐Studie wurde angesetzt zur Beurteilung der Penetrationstiefe eines Fissurenversieglers nach der Reinigung der Okklussionsflächen mit einer Luftpolier‐Einrichtung. Die gefundenen Resultate wurden verglichen mit denjenigen welche erreicht wurden nach einer Reinigung mit Birnstein und Wasser und denjenigen ohne Reinigung. 46 klinisch kariesfreie Molaren und Prämolaren wurden in 3 Gruppen verteilt. Nach der Reinigung, dem Aetzen und dem Versiegeln wurden Schliffe angefertigt. Jeder Schliff wurde mit einem lichtreflektierenden Mikroskop untersucht und die Tiefe des eingedrungenen Kunststoffes gemessen. Die Fissurenreinigung mit dem Luftpolierer ergab eine statistisch signifikant grössere Tiefe des Versieglers. Deshalb ist diese Reinigungsmethode zu befürworten. Resumen. Se realizó un estudio in vitro para determinar la profundidad de la penetración de un sellante de fisuras despues de limpiar las superficies con una unidad de aire abrasivo y comparar los resultados con los obtenidos despues de la limpieza con piedra pómez y despues de no realizar ninguna limpieza. Un total de 46 premolares y molares clínicamente no cariados fueron distribuídos en tres grupos. Despues de la limpieza, se realizó el grabado ácido, se colocó el sellante y los dientes fueron seccionados. Cada sección fue examinada con un microscopio de luz y la profundidad de la penetración de la resina determinada. La limpieza de las fisuras con aire abrasivo permitió una mayor penetración de la resina e...