The effect of tooth preparation form on the fit of Procera copings.

PURPOSE: This study evaluated the marginal and internal adaptation of Procera copings using different tooth preparations. The variations comprised 4 finish line forms, 3 occlusal forms, 3 occlusocervical undulation forms to the proximal finish line, and 3 proximal auxiliary retention forms. MATERIALS AND METHODS: One hundred twenty preparations were made and copings were fabricated, cemented, embedded in an epoxy resin, sectioned, and measured at 14 sites. RESULTS: The feather-edge finish line had the highest mean external marginal opening (135 +/- 79 microns), compared with the chamfer finish line (64 +/- 38 microns), the 0.8-mm rounded shoulder (51 +/- 34 microns), and the 0.5-mm rounded shoulder (68 +/- 56 microns). All 3 forms of occlusal reduction produced comparable internal adaptation at the axial wall. Specimens with normal occlusal reduction had the best occlusal adaptation at the cusp tip but not to a statistically different degree from the exaggerated form. Variations in the vertical height of interproximal finish lines did not significantly affect marginal opening. However, proximal retentive features less than 2.5 mm wide and more than 0.5 mm deep cannot be accurately reproduced with the present Procera scanner tip. CONCLUSION: Feather-edge finish-line forms, deep retentive grooves, and deep occlusal morphology are not well reproduced using this system, but all other finish-line forms and design variations are accurately and clinically acceptably reproduced using this system.

The effect of using custom or stock trays on the accuracy of gypsum casts.

This study examined the linear dimensional stability of nonaqueous elastomeric impressions made from stock and custom trays by measuring casts derived from those impressions at 1 hour, 1 day, and 1 week. There was a small statistical difference among casts produced from stock versus custom trays compared to the master model. However, there was no significant difference in casts produced from impressions poured at 1 hour, 1 day, and 1 week. A custom tray with a 2.0 to 2.5 mm tray spacing had the least amount of variation, yet the differences between custom and stock trays may not be clinically significant.

Marginal accuracy of metal ceramic restorations with porcelain facial margins.

This study compared porcelain facial margins made with the direct-lift technique using high-fusing shoulder porcelains and the platinum foil technique with conventional body porcelain. Marginal accuracy was measured directly and the marginal sharpness computed by the software program MacDraft. Both Vita high-fusing shoulder porcelain and Vita SM 90 porcelain produced restorations that had significantly smaller mean facial marginal openings than crowns created with platinum foil. However, the SM 90 porcelain recorded significantly greater cross sectional or internal marginal discrepancies than the other two techniques (p < 0.05). Externally, the shoulder porcelains followed the facial rounding of the stone die; thus porcelain marginal roundings can be manifested as either negative roundings or underextensions and positive roundings or overextensions. The lack of marginal sharpness of porcelain facial margins may be influenced more by the die material rather than by the marginal porcelain or the technique.

Infection control in fixed prosthodontics.

The breadth and depth of our knowledge of infection control continues to increase in dramatic proportions. The literature is already massive and there is nothing to suggest an abatement of this situation. In truth, we can expect the very opposite; an escalation in attention at every level of concern, from the effectiveness of the chemical agents as actually used in the dental environment, to our methods of delivery, as well as the effects on the materials, equipment, and even the personnel in the dental setting. This trend undoubtedly will continue as our understanding of disease processes and the mechanisms of disease transmission increases. This will, in part, directly impact the scope and direction of future study of infection control practices in dentistry.

Materials and techniques in fixed prosthodontics.

If we have learned anything from our experiences with all-ceramic systems such as Cerestore, Cerapearl, and even Dicor, it is that it takes years to uncover the strengths, weaknesses, and limitations of new materials and technologies. Manufacturers' initial claims for fit, strength, esthetics, biocompatibility, wear characteristics, and clinical performance should be viewed as preliminary until supported by independent laboratory and clinical studies. Laboratory testing alone may not provide sufficient insight into the relative strengths and weaknesses of products or assure comparable performance in the commercial dental laboratory or the ultimate testing arena, the oral environment. Moreover, the diversity of the new materials and techniques discussed demonstrates the breadth and depth of the technologic changes in dental biomaterials. The rate at which these dental products enter the marketplace and their sheer number alone are indeed staggering. Furthermore, these advances are not emerging from any single nation but from manufacturers all around the world (Japan, Germany, as well as the United States), indicating our international reliance on one another. Clearly, the decade of the 1990s is emerging as an exciting period in the development of biomaterials in comprehensive fixed prosthodontics and dentistry in general.

Tensile strength of three resin cements following two alloy surface treatments.

Retainers for composite retained prostheses ("Maryland bridges") have traditionally relied upon an etched base metal alloy for micromechanical retention. This study compared the tensile bond strength of three resin cements using two alloy surface treatments. Rexillium III and Olympia disks were cast, oxidized, and given simulated porcelain firings. Paired specimens were cemented with Comspan, Panavia EX, or C & B Metabond after air abrasion with aluminum oxide or silicoating. Air-abraded Olympia disks were tin plated prior to luting with Panavia EX. Electrolytically etched Rexillium III specimens luted with Comspan served as controls. Specimens were thermocycled and tested in tension. Highest tensile bond strengths were achieved with: (1) Olympia specimens, where the bonding surface was air abraded but tin plated before cementation with Panavia EX, and (2) Rexillium III specimens, where the bonding surface was air abraded or silicoated and the disks were cemented with C & B Metabond.

The effect of surface treatment on the Knoop hardness of Dicor.

One advantage cited for the use of Dicor over other ceramic materials is a reported Knoop hardness comparable to human enamel. However, when fabricating dental restorations, a Dicor glass-ceramic casting generally is subjected to several different surface treatments because of processing, esthetic, and functional requirements. Therefore, this study compared the Knoop hardness of Dicor specimens under three conditions: (1) cerammed, (2) cerammed and shaded, and (3) sectioned to reveal internal material. Knoop hardness differences between groups were significant (P less than or equal to .05). The cerammed surface was the hardest; it was harder than human enamel. Shaded specimens had a surface hardness comparable to dental porcelain. However, the internal glass-ceramic material, located beneath the shading porcelain and cerammed surface, had a Knoop hardness slightly higher than that of human enamel.

Comparison of two tests to determine the castability of dental alloys.

This study compared castability values in the Whitlock test with those obtained from a new castability monitor based on a dental restoration. Five metal ceramic casting alloys were induction cast with both a carbon-containing and a noncarbon phosphate-bonded casting investment to assess the reliability of the Whitlock mesh test in predicting alloy castability. Alloy performance in the Whitlock test did not parallel that of the replica coping test for all alloy-investment pairs, as would be anticipated for a reliable monitor of castability. In addition, the variability of the Whitlock castability values for some alloys was sufficient to question the test's usefulness in refining the casting process with a specific alloy.

The nonsurgical treatment of microstomia in scleroderma: a pilot study.

A 6-month clinical trial with nine scleroderma patients compared two exercise programs for the nonsurgical treatment of the decreased oral opening ( microstomia ). The experimental group employed three mouth-stretching exercises and a new oral augmentation exercise, using tongue depressors , to obtain a 5.6 mm mean increased vertical oral opening. The controls used six currently recommended "facial grimacing " exercises for a 3.0 mm mean increase. When the controls used the experimental treatment, their mean improvement increased to 5.7 mm. Although surgical correction of microstomia may be warranted, some reversal of this condition may be achieved with the aid of this new nonsurgical exercise program.

Fabrication of a flexible prosthesis for the edentulous scleroderma patient with microstomia.

The exercise prosthesis serves as an interim device to achieve an increased opening of the jaws. Once the patient is able to insert the existing denture or when an impression tray can be placed in the patient's mouth without extreme discomfort, its purpose will have been achieved; the dentures should be relined or remade. Some patients need only achieve slight increases in the maximal vertical oral opening to make prosthetic treatment possible (Fig. 6). While this technique is useful for the edentulous scleroderma patient, it may have application for individuals with limited mouth opening secondary to facial burns or other scarring. It is suggested as an alternative to surgical correction through bilateral commissurotomies.

A transitional anterior fixed prosthesis using composite resin.

A method has been described to temporarily restore an anterior edentulous space in a single appointment. The technique uses a composite resin to retain a resin denture tooth (pontic) supported by edgewise orthodontic wire. This approach is suggested as a transitional treatment for patients who are not amenable to either a definitive fixed or removable prosthesis.