Victoria A. Marker

Relationship between shade and depth of cure for light-activated dental composite resins

Abstract Depth of cure of 3 light-activated composite resins was evaluated by hardness and infrared analysis and related to the shade and translucency of the material. For one of the 3 brands, the depth of cure for the darkest shade was equivalent to that of the lightest shade, suggesting that depth of cure of light-activated composite resins may be less dependent upon shade than upon translucency.

Comparison of titanium and cobalt-chromium removable partial denture clasps

STATEMENT OF PROBLEM The use of titanium alloys for removable partial dentures is an increasingly popular application. While the flexibility of titanium would allow for cast clasps to be placed in deeper undercuts than advisable with cobalt-chromium, it is possible that the retentive forces of the titanium clasp might not maintain sufficient retention after repeated flexing of the clasp arm during insertion and removal of the partial denture. PURPOSE This study assessed the characteristics of cast clasps made of titanium and titanium alloys to determine whether these materials are suitable alternatives for removable partial denture applications. MATERIAL AND METHODS Removable partial denture clasps at two undercut depths were fabricated from commercially pure titanium, titanium alloy (Ti-6A1-4V), and cobalt-chromium. Loss of retention force was measured as the clasps underwent 3 years of simulated clinical use. The data were subjected to ANOVA and Scheffés tests to determine differences. Evidence of casting defects and porosity was evaluated by radiographic examination and nonparametric statistics. SEM microscopy was used to observe surface characteristics that were described qualitatively. RESULTS For the 0.75 mm undercut specimens, there was less loss of retention for clasps made from pure titanium and titanium alloy than for cobalt-chromium clasps. Porosity was more apparent in the pure titanium and titanium alloy clasps than in those made from cobalt-chromium, but the amount of porosity did not correspond to evidence of fractures or permanent deformation. CONCLUSIONS The long-term retentive resiliency of the pure titanium and titanium alloy clasps suggests that these materials are suitable for removable partial dentures.

Factors affecting the retention and fit of gold castings

A study was designed to simulate clinical conditions. Several factors were evaluated for effect on retention and fit (margin adaptation) of gold castings. Twenty-six castings (13 pairs) were made by different investigators using a standard preparation but with varying fabrication techniques. One of each pair of castings was made on a spaced die and one on an unspaced die. A significant difference in the postcementation retention was observed in the varying techniques of each investigator. Retentive values varied from 29 to 129 lbs. Complete seating of the castings during cementation was improved by the use of die spacer. Castings made on the spaced dies had more retention than corresponding unspaced castings. Die spacing has positive benefit when properly used. Moderate roughness of axial surfaces improves retention when zinc phosphate cement is used. Physical properties of restorative materials are important, but the individual technique and care of each investigator has a major effect on the ultimate fit and retention of the cast restoration.

Protein interactions with particulate teflon: Implications for the foreign body response

PURPOSE This study examined the nature of protein interactions with particulate polytetrafluoroethylene (PTFE, Teflon) to elucidate possible mechanisms involved in the foreign body response directed against failed Proplast/Teflon implants. MATERIALS AND METHODS Fifty milligrams PTFE prepared to particle sizes ranging from < 32 microns to > 300 microns was incubated with newborn bovine serum. The total amount of protein adsorbed to the PTFE particles was determined using a standard colorimetric assay. The structural and functional integrity of the proteins adsorbed to PTFE was also examined. For these studies, xanthine oxidase was substituted for serum, and the enzymatic activity of xanthine oxidase adsorbed to PTFE was determined. Finally, primary interactions between protein and PTFE particles were assessed in experiments using water, 2 or 8 mol/L urea, 1 mol/L Nacl, or 1% sodium dodecyl sulfate in an attempt to dissociate bound protein from the surfaces of PTFE particles. RESULTS Serum proteins bind almost instantly to the surface of PTFE particles. The effective surface area of PTFE increases dramatically with reduction of the material to small particles, as does the total amount of protein adsorbed by the particulate PTFE. Proteins bind to PTFE principally by hydrophobic interactions, and their three-dimensional structure is significantly perturbed by this interaction. In the case of xanthine oxidase, adsorption to PTFE distorts protein structure to the extent that biologic activity is eliminated. CONCLUSIONS The amount of serum protein adsorbed to PTFE particles varies inversely with particle size for a constant mass of material. It is believed that the foreign body response directed against this material is related to the amount and relative distortion of proteins adsorbed to its surface. If so, it appears that reduction of an implant to small particles (typically 50 micron or less) will dramatically increase the biologic signal to local cell populations. Thus, the severity of the biologic response to PTFE debris may be dependent largely on the size of the debris particles.

Surface treatment of indirect resin composite surfaces before cementation

STATEMENT OF PROBLEM Controversy surrounds the use of hydrofluoric acid to prepare precementation surfaces of indirect composites. PURPOSE This study was conducted to compare effects of combining hydrofluoric or orthophosphoric acid with microetching as precementation treatments. MATERIAL AND METHODS Nine specimens of three composite materials were prepared to simulate heat-cured indirect restorations. The specimen surfaces were prepared with one of three treatments. Adhesive Bond II and Twinlook cements were used to bond a phosphoric acid-etched disk of P50 to the treated surface. Analysis of variance and Scheffé tests were used to assess the bond strength data. Scanning electron microscopy and microscopic analysis of the fractured and treated surfaces were also performed. RESULTS Bond strengths for all surface treatments did not significantly differ. Hybrids had a higher bond strength with etching than microfills, and mechanical roughening produced the greatest bond strengths with microfills. Microetching with orthophosphoric acid produced higher bond strengths than microetching with hydrofluoric acid on hybrids. CONCLUSIONS Acid etching alone is not sufficient to produce effective bond strengths, and hydrofluoric acid treatments are detrimental to the resin composite.

Bond strengths of high-palladium content alloys

Palladium-based alloys have had a significant import on the fabrication of ceramometal restorations. This article compares the bond strengths of four palladium-based alloys with that of a high-noble alloy. Tests were designed to closely represent clinical situations. Bond strengths of the palladium alloys compared favorably with the high-noble metals; palladium alloys containing up to 2% gold were the best.

Effects of sputtered metal oxide films on the ceramic-to-metal bond

The application of a thin oxide film is seen as a method of improving the ceramic-to-metal bond. Using sputter coating to form oxide films allows control of its thickness. The thickness of the oxide layer can also be controlled by sputter coating. Films produced by sputtering, in themselves, have superior bond strengths in that the high-energy levels that are used in the technique drive the coating material into the atomic lattice of the substrate material (dental gold). Remaining to be determined are optimum film thickness and the oxide to be used. However, the present study opens a field of study showing promise of improving porcelain-to-metal bonding in dental restoration.

Strength properties of soldered joints for a gold-palladium alloy and a palladium alloy

Strength of a soldered palladium alloy, PGC (Engelhard Corp.), and a soldered medium gold alloy, PGX (Engelhard Corp.), was examined. The results obtained were as follows: Highest strength was observed with postsoldered specimens of PGC alloy. Microstructural examination of postsoldered specimens revealed nearly pore-free solder joints with PGC and PGX alloys, and fracture appeared at the solder-alloy interface with PGC and PGX alloys. Microstructural examination of presoldered and presoldered/thermocycled specimens revealed that presoldered specimens of PGC and PGX alloys exhibited intrasolder fracture; PGX solder joints had considerably less porosity, which may explain the equivalent bond strengths of all the soldered specimens and the yield point of the controls; PGC solder joints exhibited large quantities of pores, which may explain the lower strength; pores observed in PGC alloy may be the result of the high fusing temperature of the solder; and these results indicate a need to develop a new presolder for PGC. The best result was obtained with postsoldered specimens of the PGC alloy. However, for PGX alloy, either postsolder or presolder techniques can be used.

Review of the 1994 dental materials literature

OBJECTIVES Electronic databases provide strong support for research and education literature searches. However, there is still some lag in time between publication and updates of the database. The objective of this summary was to identify and categorize the 1994 dental materials scientific literature that dealt with restorative dentistry. METHODS Seventeen primary journals were manually searched via the Tables of Contents and 88 secondary journals were manually or electronically searched. Dental materials citations were categorized into 15 major sections and several subsections, excluding case reports and literature primarily related to dental implants or biomedical materials outside of dentistry. RESULTS Nearly twelve hundred citations were identified, the largest number being associated with composites and glass ionomers. SIGNIFICANCE This list provides a comprehensive source for review by academicians and researchers to bridge the gap between initial publication and electronic citation.

A study design for an in vivo investigation of marginal fracture in amalgam restorations.

Abstract A design for studying the modes of marginal fracture in amalgam restorations is presented. Amalgam restorations were placed in denture teeth mounted in tooth-supported partial dentures. Patients were recalled at selected intervals and the condition of the restorations was recorded with intraoral photographs and high-resolution impressions. Epoxy replicas were made from the impressions. At each recall, a percentage of the restorations were retrieved for analysis of the microstructure by SEM. The study design has two advantages over most clinical studies: the development of fractured areas was recorded in the series of replicas made prior to fracture; and changes in the subsurface microstructure that may lead to fracture can be followed in the series of restorations retrieved prior to fracture. Preliminary results of the study showed amalgam restorations in denture teeth to exhibit increasing marginal fracture with time in service. The morphology of the fractures appeared similar to that observed in restorations in natural human teeth.