Apparent cytotoxicity of base metal casting alloys.

The cytotoxic potentials of three Ni-Cr based alloys and an Fe-Cr based alloy were assessed. In tissue culture, casting of all four test materials and powders of the Fe-Cr based material did not elicit adverse cellular changes. However, cultures containing Ni-Cr powders showed prominent zones of lysis and cell alteration. The cytotoxic potential of products obtained from the surfaces of casting alloys may offer an expedient means for estimation of long-term clinical toxicity.

Marginal discrepancy of screw-retained and cemented metal-ceramic crowns on implants abutments.

This in vitro study quantified the marginal discrepancy of the implant-to-prosthetic-crown interface on nonsubmerged dental implants restored with either a cemented or a screw-retained approach. Metal-ceramic crowns were fabricated for 20 ITI 4.1 x 10 mm solid-screw titanium implants. Ten implants received octa abutments and screw-retained crowns fabricated on premachined gold cylinders. The remaining 10 implants were restored with 5.5-mm solid abutments and metal-ceramic crowns cemented alternately with a glass-ionomer or a zinc phosphate luting agent. Inspection of the implant-crown interface was conducted using light microscopy under x 50 magnification at selected stages in the process of crown fabrication. Statistical analysis revealed a significant difference (P < .001) in the mean marginal fit between screw-retained (8.5 +/- 5.7 microns) and luted implant-supported crowns. This difference was observed both before (54.4 +/- 18.1 microns) and after cementation with glass-ionomer (57.4 +/- 20.2 microns) or zinc phosphate (67.4 +/- 15.9 microns).

Implant materials, designs, and surface topographies: their effect on osseointegration. A literature review.

The aim of this article was to review the literature on materials, designs, and surface topographies of endosseous dental implants. The different categories of dental implants and the parameters of their design were analyzed in relation to their effect and significance in the process of osseointegration. The events that immediately follow implantation were described, emphasizing the factors that play a role in the development of the bone-implant interface. In addition, the methods and techniques that allow qualitative and quantitative evaluation of the interfacial zone were reviewed and their clinical correlation was assessed.

Scanning microscopy of cervical erosion.

The dentitions of 900 dentists were examined for the presence of cervical erosion. Of these, 48 individuals of 5.3% had obserable erosion. Silicone impressions were made of the eroded labial surfaces in a typical quadrant, and epoxy resin models were constructed. These were examined in the scanning electron microscope. Cross sections of the replicas were examined in the light microscopy. Of the 48 replicas (24 of the maxilla and 24 of the mandible), the most severe erosion was found on the first premolars in 62% of the individuals, on second premolars in 19% on cuspids in 12%, and on first molars in 6%. The margin of the defect toward the gingiva was level with or just below and parallel to the gingival crest. The erosion pattern was distinguished by two shapes--an angular lesion with a flattened floor associated with deep lesions (68%), and a rounded, smaller defect with no sharp interior angles and less tooth damage (32%). It is postulated that cervical erosion may result from two different mechanisms--a more common, destructive process, angular and deep; and a less severe, shallow process with rounded form.

Characterization of airborne particles from irreversible hydrocolloids.

Airborne particles of irreversible hydrocolloid powders were monitored and characterized. Ten to fifteen percent of the particles were siliceous fibers with dimensions of less than 3mum in diameter and more than 20mum in length. These dimensions conform closely to the dimensions of the fibrogenic and carcinogenic fibres of asbestos, glass, and aluminum oxide. With almost daily utilization of irreversible hydrocolloid materials in the dental office, the improper handling of the materials could be hazardous to the health of dental personnel. It is recommended that inhalation of aerosols arising from irreversible hydrocolloid powders be avoided.

Abrasive particles in tobacco products: a possible factor in dental attrition.

Tobacco products are known to cause oral soft-tissue lesions, but they may also directly affect the teeth. Abrasive particles contained in tobacco products may contribute to dental attrition. We studied tobacco samples from 16 brands of cigars, eight brands of snuff, four brands of chewing tobacco and several unprocessed tobacco leaves used as cigar wrappers. Insoluble particulate matter made up about 0.5 percent of the weight of an average tobacco sample.

A soft tissue simulated cast for implant prosthesis.

A master cast that simulates the mucosa around implant fixtures and abutments facilitates implant prosthesis fabrication. It is helpful if this simulation is not altered during laboratory procedures. A technique is described for a master cast that includes a removable mucosal component. This technique can be applied when either implant or abutment analogs are positioned in the cast.

Conversion of an implant radiographic template into a surgical template.

A method is presented for converting a radiographic template into a surgical template using the information acquired from the analysis of tomograms. Necessary changes of the implant position and angulation are transferred to the indexed and sectioned cast. Realignment of the initial template with the correct position allows its modification into a surgical template.

Review of the pH of hemostatic agents used in tissue displacement.

Newer hemostatic agents such as the tetrahydrozolines and oxymetazolines have a more acceptable pH and should be kinder to tooth structure and soft tissue than the conventional solutions. Although additional study is needed, it would seem prudent to be cautious in using low pH hemostatic agents and avoid the exposure to sensitive intraoral tissues-particularly delicate tissues--or tooth preparation close to the dental pulp.

In vitro investigation of the wear of human enamel by dental porcelain.

STATEMENT OF PROBLEM: Metal ceramic systems are advocated when both esthetics and strength are required. A major drawback to many porcelains is their wear and destruction of opposing natural dentition. PURPOSE: This study evaluated the wear of enamel opposing 1 traditional and 2 recently introduced low-fusing feldspathic dental porcelains. MATERIAL AND METHODS: Six blocks of Ceramco II, Finesse, and Omega 900 feldspathic porcelain materials were fabricated and fired according to manufacturer recommendations. Porcelain blocks were polished through 0.25 microm diamond polishing paste. Thirty-six enamel specimens were obtained and milled to a 2 mm (+0.5 mm) diameter. Enamel specimens were attached to an offset cam motor operating at 60 Hz. Enamel specimens were in constant contact with the stationary porcelain blocks under a load of 600 g and traversed a distance of 8 mm. Diameter and height of enamel specimens were measured at times of 0, 6, 12, 24, and 48 hours and subsequent determination of enamel volume loss recorded. Profilometric surface roughness of the ceramic blocks was also measured for the corresponding times. RESULTS: Statistical analysis revealed that both Finesse and Omega 900 feldspathic porcelains caused significantly less enamel volume loss when compared with Ceramco II porcelain at all time intervals. Surface roughness revealed no consistent significant differences among porcelains. CONCLUSION: Both Finesse and Omega 900 porcelains were not as destructive to human tooth structure as Ceramco II porcelain. These results suggest an advantage of the new, lower-fusing porcelains in conditions where natural dentition wear is a concern.

Implant abutment screw rotations and preloads for four different screw materials and surfaces.

STATEMENT OF PROBLEM: Chronic implant screw loosening remains a problem in restorative practices. Some implant manufacturers have introduced abutment screws with treated surfaces in an effort to increase preload and reduce potential loosening. Purpose. This study evaluated the materials and surfaces of 4 commercially available abutment screws on preload generation. MATERIAL AND METHODS: Twenty of each of the following abutment screws-Gold-Tite (Gt), TorqTite (Tt), gold alloy (Ga), and titanium alloy (Ta)-were divided into 2 groups. Measurements were recorded for each abutment screw on a mounted 3.75 x 18 mm external hex implant with a titanium abutment. Rotational angle measurements were conducted on the 4 abutment screws at 20 and 32 Ncm. Removal torque values were recorded and used to indirectly generate preload values. Random implant block specimens were sectioned and qualitatively evaluated with an SEM. RESULTS: At 20 and 32 Ncm, the largest rotational angles were recorded for the Tt groups: 21.2 +/- 3.1 degrees and 38.1 +/- 8.7 degrees, respectively. The greatest preload values at 20 and 32 Ncm were calculated for the Gt groups: 596.8 +/- 101.2 N and 1015.3 +/- 191.2 N, respectively. SEM analysis of the 4 implant block specimens revealed mating thread contacts located in the middle portion of the superior surface of the abutment screw thread. The greatest number of mating thread contacts were seen in the Gt implant block specimen (14 of 20 possible thread contacts). CONCLUSION: The Gt and Tt abutment screws with enhanced surfaces that help reduce the coefficient of friction produced greater rotational angles and preload values than the conventional gold alloy and titanium alloy screws.

Marginal fit and surface roughness of crowns made with an accelerated casting technique.

STATEMENT OF PROBLEM: Conventional investing and casting techniques following the manufactures' recommendations are time-consuming. Accelerated casting techniques have been reported, but their accuracy has not been adequately studied for complete crown castings. PURPOSE: This study evaluated the marginal fit and surface roughness of complete crowns made with a conventional and an accelerated casting technique. MATERIALS AND METHODS: Part I of the study determined the mean time interval required for each investment to reach its maximum exothermic setting reaction temperature. Part II determined the marginal discrepancy of standardized complete crowns cast in a high noble metal ceramic alloy, with the use of four phosphate-bonded investments. A conventional technique (as recommended by the manufacturer) was compared with an accelerated technique that used 13- to 17-minute bench set time (as determined in part 1 for each investment)_ and 15-minute wax elimination cycle in a 815 degrees C (1500 degrees F) preheated furnace. Part III evaluated the surface roughness of castings made with the same techniques as in part II. RESULTS: For the marginal discrepancy and surface roughness, crowns fabricated with the accelerated casting technique were not significantly (P > 0.05) different from those fabricated with the conventional technique. CONCLUSION: The accelerated casting technique described in this study could be a vital alternative to the time-consuming conventional techniques.

Marginal gap of crowns made with a phosphate-bonded investment and accelerated casting method.

STATEMENT OF PROBLEM: Numerous materials and methods have been used for complete crown fabrication. Conventional investing and casting procedures for phosphate-bonded investments require a 2- to 4-hour process before completion. Accelerated laboratory techniques have been used, but may not result in castings with equal marginal accuracy. PURPOSE: This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods. MATERIAL AND METHODS: Forty-four individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed in the fabrication of 44 single-unit castings. Twenty-two casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. Perpendicular and 25-degree tilted measurements of marginal gap were documented for each. Evidence of marginal gap was then evaluated by t test. RESULTS: Measurements recorded on the perpendicular and on a 25-degree tilt showed no statistically significant difference between conventional and accelerated groups. All gap measurements except one were within the range of clinical acceptability. The measurements revealed that conventional and accelerated perpendicular gap means were 13.2 and 13.6 microm, respectively, and the average tilted gap means were 31.6 and 32.2 microm, respectively. CONCLUSIONS: A phosphate-bonded investment (Ceramigold) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.