The International Journal of Prosthodontics, 03/1991

This in vitro study measured the microleakage of current dentin bonding agents and glass-ionomer bases. Freshly extracted human molars were prepared to a flat surface, and dentin adhesives and composite resins were applied in a plastic matrix. Samples were stored in water at 37 degrees C, thermocycled, stained with AgNO3, embedded in epoxy resin, and sectioned for evaluation of stain penetration at the composite resin/tooth interface. The reliability index of the dentin adhesives varied significantly between materials. The enamel control had essentially no microleakage, and the aluminum oxalate dentin adhesive on dentin had significantly less microleakage than other dentin adhesives tested. Present dentin adhesives were unable to prevent, but may reduce, microleakage.

Sequential crown reductions of extracted human teeth were made to evaluate both regional differences in dentin permeability and the effects of tooth reduction. Two different methods of tooth reduction were used. In group 1, tooth reduction was nonuniform but was done in a manner similar to conventional crown preparations. Maximum, total crown permeability was measured using a pressurized fluid filtration technique after removing the smear layer. Regional reductions in permeability were accomplished by creating smear layers on mesial, distal, buccal, lingual, and occlusal surfaces sequentially. Between each step, changes in dentin permeability were measured. In group 2, tooth reductions were uniform and regional permeability was reduced by localized application of potassium oxalate. Both methods demonstrated increased permeability of dentin as the prepared surfaces approached the pulp chamber. Generally, the mesial surfaces were more permeable than the distal surfaces. The occlusal and lingual surfaces were the least permeable regions.

The effect of controlled oral hygiene was studied in 35 overdenture patients involving 80 abutments over a period of 3 years. Intensive instruction and motivation

Principles of the design and fabrication of implant-supported maxillary prostheses are described. The significance of the maxillomandibular relationships, maxillary arch size to the location of the implants, and the positioning of the restored dental arch are discussed. Angulated abutments may overcome conflicts between the position of the artificial teeth and the implants. Solutions to design features that may impair achievement of a pleasing appearance, good gingival health, and well-articulated speech are considered.

Three hydrophilic poly(vinyl siloxane) impression materials, containing an intrinsic surfactant, were compared with a hydrophobic poly(vinyl siloxane) and a polyether impression material. The hydrophobic poly(vinyl siloxane) material was dimensionally more accurate than the hydrophilic poly(vinyl siloxane) in two of three measured dimensions, but the difference was small. The polyether material was the most wettable, and the hydrophilic poly(vinyl siloxane) were more wettable than the hydrophobic poly(vinyl siloxane). However, when a topical surfactant was used, no difference in wettability was noted between the hydrophilic and hydrophobic poly(vinyl siloxane), and their wettability was comparable to the polyether material, indicating that the topical surfactant was more effective than the intrinsic surfactants. Stone dies made from the hydrophobic poly(vinyl siloxane) material were harder than those obtained from the other materials.

Patients provided with 53 distal extension-base removable partial dentures retained using rigid intracoronal slide attachments were followed up to 25 years. The initial treatment consisted of fixed partial dentures involving all remaining teeth in the treated arches and removable partial dentures having a cast cobalt-chromium framework. The removable dentures showed few complications and little need for relining. The failures primarily involved the fixed partial dentures. Seven arches required complete dentures as a result of technical complications in five patients. Cement failures, root fractures, and fractures of the fixed prostheses were most problematic. The survival rate was about 65% up to 15 years, and a survival time of 50% was extrapolated to 20 years.

Interchangeability of a semiadjustable articulator could be of significant convenience and economic benefit to the restorative dentist. The manufacturer of the Whip-Mix Model 2240 articulator claims such interchangeability. This study evaluated the accuracy of the cross-mounting capability of eight such articulators, then compared the measured results with those obtained from eight semiadjustable instruments for which the manufacturer makes no such promise of interchangeability. It was determined that the Model 2240 articular did possess accuracy when a measuring device was transferred between the eight materials tested.

High-palladium alloys for metal ceramic restorations, based on the Pd-Cu-Ga and Pd-Ga systems, were introduced to the dental profession during the past decade. These alloys have become increasingly popular because they are much less expensive than the gold-based alloys, and recently marketed high-palladium alloy compositions have excellent mechanical properties. A summary of the important melting and casting considerations for these somewhat technique-sensitive alloys is presented together with an overview of important dental materials science aspects and the results of a dental laboratory survey. A maxillary central incisor coping was chosen as the clinically appropriate specimen shape, and the gas-oxygen torch melting technique was found to produce castings with clinically acceptable levels of marginal sharpness and little evidence of microporosity. The etched as-cast high-palladium alloys exhibited fine-scale multiphase microstructures, and a noteworthy finding was that relative proportions of the microstructural constituents frequently varied for thin versus thick sections of the cast specimens.

The tensile bond strengths of a resin cement, Panavia Ex, to a spherical and an admixed amalgam were measured after surface treatment with different aluminum oxide abrasive spray procedures. The type of amalgam and the brand of aluminum oxide affected the bond strength of the resin to amalgam alloy. When the spherical alloy was air abraded using 60-microns aluminum oxide prior to cementation of a Rexillium rod using Panavia, the bond strength was not significantly different from the previously reported bond strengths of Panavia to etched enamel. Significantly lower bond strengths were obtained between Panavia and the admixed amalgam alloy. These results suggest that it may be possible to place a resin-bonded prosthesis on an abutment tooth that has been restored using a spherical amalgam alloy.

The damping effect of five restorative materials used to veneer test crowns rigidly connected to a Brånemark implant and subjected to an impact force was measured. These materials included a gold alloy; a noble metal ceramic alloy; porcelain; a laboratory-processed, light-activated microfilled resin; and a heat- and pressure-polymerized poly(methyl methacrylate) resin. The two resins were found to reduce the impact force by about 50% when compared to porcelain or the alloys. The clinical significance of the results is discussed.

This clinical trial assessed the ability of Gluma Dentin Bond to inhibit dentinal sensitivity in teeth prepared to receive complete cast restorations. Twenty patients provided 76 teeth for the study. Following tooth preparation, dentinal surfaces were coated with either sterile water (control) or two 30-second applications of Gluma Dentin Bond (test) on either intact or removed smear layers. Patients were recalled after 14 days for a test of sensitivity of the prepared dentin to compressed air, osmotic stimulus (saturated CaCl2 solution), and tactile stimulation via a scratch test under controlled loads. A significantly lower number of teeth responded to the test stimuli for both Gluma groups when compared to the controls (P less than .01). No difference was noted between teeth with smear layers intact or removed prior to treatment with Gluma.