ABSTRACT
The optimal conditions for opaquing techniques during porcelain application have not been confirmed. In this study the metal-ceramic bond strength was measured among one porcelain and three dental alloys, namely a gold-platinum-palladium alloy, a silver-free gold-palladium alloy, and a base metal alloy, with two opaquing techniques (a single masking layer versus a thin overfired layer followed by a second masking layer). In addition, the opaque porcelain was fired over an oxidized and nonoxidized alloy surface for the silver-free gold-palladium alloy. No significant differences in bond strength were recorded between the two opaquing techniques with the gold-platinum-palladium and base metal alloys. There was no substantial differences between the two opaquing techniques when opaque was applied over an oxidized gold-palladium alloy surface and bond strengths were substantially greater over an oxidized surface. However, when the opaque was applied to a nonoxidized gold-palladium surface the two-layer technique created a significantly greater bond strength.
Subject(s)
Dental Bonding , Dental Porcelain/chemistry , Dental Prosthesis Design , Metal Ceramic Alloys/chemistry , Chromium Alloys/chemistry , Dental Casting Investment/chemistry , Gold Alloys/chemistry , Materials Testing , Microscopy, Electron, Scanning , Oxidation-Reduction , Palladium/chemistry , Platinum/chemistry , Stress, Mechanical , Surface PropertiesABSTRACT
Prosthodontists surveyed preferred inverted V-shaped canine cingulum ledge rest seats located at the junction of the middle and cervical thirds of the lingual surface. Most respondents indicated that they preferred a ledge depth of at least 1.0 mm and indicated that their preparations usually did not extend into dentin. When the respondents evaluated various ledge depths, the mean depth of those judged adequate was 0.74 mm, which was less than the respondent and textbook recommendations. Premolar occlusal rest seats judged adequate generally met textbook size guidelines. The mean clinical incidence of dentin exposure with cingulum ledges and occlusal rest seats was 61%, close to the 55% exposure rate found on extracted teeth. Dentin Detector Gel effectively identified clinical dentin exposure but tooth sensitivity was not a good indicator of dentin exposure. Seventy-one of the 107 rest seats studied for incidence of caries and decalcification had exposed dentin but only two of the 71 had lesions. Ten of the 107 had small enamel fractures, primarily occurring on cingulum ledges.
