Quintessence International, 12/1999

The conservative, nonretentive cavity design of partial-coverage ceramic restorations provides a number of distinct advantages over traditional cast-metal options. However, unique challenges are associated with precise delivery of the restoration and the cleanup of excess luting resin. Restorative success and long-term gingival health are dependent on interproximal integrity at the restoration-tooth interface. This article examines the variables that affect this integrity and introduces a number of innovative techniques that assure meticulous delivery of posterior partial-coverage ceramic restorations.

Objective: Most one-bottle adhesives contain organic solvents (acetone or ethanol) that displace the water entrapped within the network of collagen fibers in etched dentin. Acetone and ethanol are volatile substances that could easily evaporate from bottles during use. The objective of this in vitro study was to assess the effects of repeated opening of bottles on dentin shear bond strengths of 4 adhesives. Method and materials: Eighty freshly extracted bovine incisors were mounted, polished to 600 grit, and randomly assigned to 8 groups (n = 10). After the application of the materials to 40 specimens at baseline, adhesive use was simulated by opening bottles for 1 minute, 2 times a day, for 3 weeks, except during weekends, when the bottles were kept refrigerated. After 3 weeks of simulated use, the same adhesives were applied to 40 additional specimens. Resin composite was applied to dentin in a No. 5 gelatin capsule and was light-cured. After 500 thermal cycles (5°C to 55°C), shear bond strength testing was performed with a universal testing machine at 0.5 cm/min. Results: Adhesives containing ethanol or water had similar mean bond strengths at baseline and at 3 weeks. The acetone-based material had a significantly lower mean bond strength at 3 weeks than at baseline. Conclusion: Acetone-based adhesives may have a shorter useful life than ethanol- and water-based adhesives.

Objective: The aim of this study, conducted in 132 randomly selected children, was to evaluate the retention of a fluoride-containing sealant on primary and permanent teeth. Method and materials: In autumn 1995, a total of 195 primary molars in 36 children aged 4.5 years on average and 391 permanent premolars and molars in 96 children aged 10.5 years on average were sealed with Helioseal-F. The manufacturer's instructions were followed closely. The teeth were cleaned with a slurry of pumice and a rotating brush, isolated with cotton rolls, dried with air, etched for 60 seconds with an etching gel (37% phosphoric acid), rinsed with an air-water combination spray, and dried. Sealant was applied with a cannula and polymerized for 60 seconds. A saliva ejector was used throughout the procedure. Sealant retention was checked 3 years after placement. Results: In the primary molars, full retention was found in 95.04%, partial retention in 3.12%, and loss of the sealant in 1.84% of the treated teeth. In the permanent molars, the corresponding rates were 95.81%, 2.83%, and 1.36%, respectively. Conclusion: Very good sealant retention was found 3 years after placement. The observed difference in retention between primary and permanent molars was not statistically significant.

Objective: The aim of this study was to evaluate the clinical performance of ceramic inlays made from machinable ceramic blocks. Method and materials: The 2 inlay systems involved computer-aided design and computer-aided machining (Cerec Cos 2.1) or copy-milling technique (Celay). The study comprised 15 Celay inlays and 15 Cerec inlays placed in 17 patients. The inlays were evaluated clinically at baseline (1 week) as well as 1 and 3 years later (modified California Dental Association quality evaluation system). Results: One Celay inlay fractured after 1 year of service, and 2 Cerec inlays were replaced, 1 after 6 months and 1 after 1 year, because of pulpal pain and persisting hypersensitivity. One Celay inlay lost retention after 2 years. At the 3-year evaluation, chipping and hairline cracks were seen in 2 Celay inlays. Progressive disintegration of the marginal luting cement was seen for both Celay and Cerec inlays. The remaining 25 inlays performed satisfactorily throughout the 3-year period. Conclusion: Because of their relatively high failure rate, these inlays should be reserved for esthetic indications.

Objective: This study evaluated amounts of debris, smear layer, and recrystallized dentin on root canal walls treated with an Nd:YAG laser. The presence of carbonized material was also assessed. Method and materials: The root canals of 36 extracted incisors were prepared by stepdown and stepback techniques and divided into 4 groups. One group was not treated further, while 3 others were exposed to the laser beam at an energy density of 159, 239, or 318 J/cm2. The roots were split longitudinally, photographed, and examined using a scanning electron microscope. The amounts of debris, smear layer, and recrystallized dentin were recorded from horizontal bands around the root, 2, 6, and 10 mm from the apices. Results: Mean smear layer scores were similar for all groups at the 3 levels examined, ranging from 2.157 to 2.851 on a scale of 0.0 to 3.0. Mean debris scores were similar for all groups at the 3 levels examined, ranging from 0.774 to 1.408 on a scale of 0.0 to 3.0. Recrystallized dentin was recorded in all 3 irradiated groups at the 2-mm level, but only in the group irradiated with 318 J/cm2 at the 6- and 10-mm levels. Severe carbonization was recorded at the 2-mm level. Conclusion: Use of the Nd:YAG laser did not reduce the mean amounts of debris and smear layer compared to a nonirradiated group. Carbonization was recorded in the apical part of the canal, but this is not obvious when only scanning electron photomicrographs are examined.