Nasser Barghi

Influence of ceramic thickness on the polymerization of light-cured resin cement.

The curing of two light-activated resin cements under two ceramic materials was examined to assess the influence of ceramic thickness on polymerization. The degree of resin cure was determined by microhardness measurements (Knoop) on resin cement samples cured under five ceramic thicknesses with light exposures of 30 to 120 seconds. These cements cured under thin ceramic specimens with recommended exposures. With thick ceramics, both cements cured better under the glass-ceramic, but neither reached a level of maximum cure under the porcelain.

SEM evaluation of etch patterns by three etchants on three porcelains

Three etchants (Super Etch, Stripit, and Acidulated Phosphate Fluoride Gel) were evaluated for their ability to create micromechanical retentive areas in three commercial porcelains (Ceramco II, Mirage, and Vita).

Dimensional changes in casting titanium removable partial denture frameworks

The difficulties encountered in casting titanium and its alloys have until recently hindered any widespread use of titanium in restorative dentistry. Now both equipment and materials are available for the routine use of titanium in the dental laboratory. This study used one of the casting systems and examined dimensional changes that occur during the construction of a removable partial denture framework. Nineteen castings were measured for horizontal and vertical plane changes. Results show these castings to have cross arch contraction, vertical plane expansion, and near neutral anterio-posterior change. It seems that pure titanium is within the range of dimension changes generally accepted for base metal removable partial denture alloys of the nickel-chromium variety.

Marginal accuracy and geometry of cast titanium copings

The biocompatibility of titanium with human tissue is well established; its potential as an alternate metal for crown restorations has yet to be fully investigated. This study measured the geometry and accuracy of coping margins cast in Ti, 99.5% chemically pure. Twenty castings with 45-degree facial and 90-degree palatal margins were made by indirect technique with a commercial system using recommended procedures. They were then cemented with ZnPO4 cement. The coping and die assemblies were embedded in resin, sectioned longitudinally, and measured with a microscope at x50 power. Casting shrinkage was characteristic, particularly along the horizontal axis in the plane of the shoulder. Although horizontal linear shrinkage of 45-degree margins was greater than that for the 90-degree form, the surface of marginal discrepancy was greatest with the 90-degree configuration.

Occlusion and chewing side preference

C hewing side preference as it relates to occlusion has not been thoroughly studied. Hildebrand’ observed that, “The teeth appear, as a rule, to exercise an influence on the choice of the masticatory side in such that the side is chosen where most teeth are in contact during lateral gliding (i.e., where there is the best articulation). In cases where the articulation is equally good or equally bad on both sides, mastication usually takes place on the right and left sides alternately.” Other studies have investigated correlations between occlusion and chewing patterns. Lord2 introduced the concept that the central nervous system synthesizes a physiologic chewing pattern unique to each individual.2 In studying the chewing patterns of school children, Ahlgren’ also reported that the chewing pattern is characteristic of an individual. Goldaracena et aL4 correlated the preferred side for chewing with the presence or absence of dental caries in the Maya Indian. They concluded that the presence of extensive dental caries may affect the chewing side preference. This article relates the findings of a study that examined the relationship of actual occlusal conditions, including masticatory dysfunction, to chewing side preference.

Porcelain shade stability after repeated firing

There were no color changes detected in the first five firings for both air- and vacuum-fired porcelain. Slight changes were noticed in subsequent firings. These color changes were more noticeable in the air-fired samples than in the vacuum-fired samples. However, changes in the porcelain color after repeated firing were not sufficiently significant to cause rejection of the samples. The porcelain shade remains stable with repeated firing if the firing procedure is carefully carried out.

The marginal integrity of the temporary acrylic resin crown

A primary objective of the temporary crown is to maintain good gingival health prior to placement of the final restoration. Unless the temporary crown has a well adapted and well contoured margin, it may be difficult to achieve this goal. In addition to good gingival health, several other desirable ends are achieved by assuring well adapted margins on temporary crowns. One of these is decreased sensitivity, which is demonstrated when freshly prepared dentin is left exposed to the oral environment. Also, better esthetic values are obtained when margins of temporary crowns extend to the finishing lines of anterior preparations. It is desirable to construct temporary crowns which have well adapted margins at the finishing lines of the preparations to protect the prepared tooth.* This report describes a method which will predictably facilitate the construction of such well adapted margins. This technique was first performed on a Typodont and later applied to patients.

Efects of batch variation on shade of dental porcelain

Three different batches of three commercially available porcelains were applied to 36 specimens of two noble alloys. The shades were visually compared by nine observers. Results indicated the following. No color differences were found among specimens of individual batches. Discerning color changes were observed among three batches of one brand of porcelain. The porcelain fired in the laboratory may not match the manufacturers standard shade guide. Batch to batch variation of porcelain may necessitate the fabrication of customized shade tabs with fresh batches of porcelain.

Evaluation of the bonding of three porcelain repair systems.

1. Fractured porcelain bars repaired with Fusion/Concise displayed significantly greater repair strength (p less than .05) than bars repaired with Den-Mat and Cervident. 2. Comparing mean strengths of all samples before and after repair with Fusion/Concise indicated that only 18% of the original strength was regained following repair. 3. The low repair strengths of the tested materials indicate that their use is a temporary clinical procedure.

A study of various factors influencing shade of bonded porcelain.

Seventy-two specimens of four commercially used precious metals were constructed. The porcelain applied to these specimens was glazed up to nine times for shade comparison. Specimens were also studied with a scanning electron microscope prior to and after application of the porcelain. The important observations from this study were: 1. The four types of precious metals looked alike after casting and surface treatment and prior to application of porcelain. 2. Porcelain-bonded-to-metal shades were not influenced by the types of precious metals used. 3. Porcelain-bonded-to-metal shades remained stable after six glazings and changed only slightly after nine firings.