The International Journal of Prosthodontics, 05/1997

The amount of heat produced by dental implant osteotomy (receptor site) preparation at different speeds and the effects of heat production on the prognosis of implant treatment are controversial. In Part I of this two-part study, heat production was measured in vivo during osteotomy preparation at low (maximum 2,000 rpm), intermediate (maximum 30,000 rpm), and high (maximum 400,000 rpm) speeds in the rabbit tibia, and an inverse relationship was observed between drill speed and heat production. For the measurement of heat production (Part I), a thermocouple probe was inserted into a prepared receptor site in the anteromedial aspect of the tibial metaphysis. Temperature was recorded while an osteotomy was drilled 1 mm from the thermocouple receptor site. Distilled water was used as coolant in conjunction with all drilling, and all osteotomies were prepared by a single researcher to eliminate the variable of interoperator difference in technique. An inverse relationship was observed between drill speed and heat production. An analysis of variance indicated significant differences in heat production among the three drilling speeds (P 0.05). The results of Part 1 of this study indicate that for the configuration and material of bur used, the high-speed range minimizes heat production.

This study investigated the effect of marginal gap width, luting cement, and restorative material on the wear resistance of the luting cement in areas where no occlusal contact is present. Three types of resin luting cement and one resin-modified glass-ionomer cement were used with two inlay systems, a resin composite, and an all-ceramic system. Bovine enamel represented tooth structure. Toothbrush abrasion was the wear modality. Three predetermined gap widths were selected: 240 ± 30 um, 150 ± 30 um, and 60 ± 30 um. All specimens were thermocycled. Re gardless of the luting cement or the restorative material, there was a significant difference (P 0.05) in wear resistance of the cement among the three gap distances at both the enamel and restoration interface. Vertical wear of the luting cement at the enamel interface increased linearly with marginal gap distance when all four cements were considered together (r to the second power > 0.51), regardless of type of restorative material used. The resin-modifed glass-ionomer cement showed the least amount of wear for all variables considered. Significant differences in wear were found between the four luting cements at wide gap distances (240 um) at the enamel interface, regardless of type of restorative material used. No significant differences were found between the two restorative materials at the enamel interface at the three gap distances.

A pressure chamber was used to compare microleakage associated with complete metal crowns cemented to extracted teeth using three different luting agents. Complete crowns were cemented on 60 extracted premolar teeth: 20 were cemented using a zinc phosphate cement, 20 usin g a glass-ionomer cement, and 20 using a resin cement. Following 7 days of storage in normal saline, each of the teeth in the experimental groups was pressure cycled 15 times, during which time the occurrence of microleakage was monitored. Microleakage was found to occur in crowns cemented with the zinc phosphate and glass-ionomer cements; no microleakage was detected with the resin-cemented crowns. Microleakage was also found to occur sooner and to a greater extent with zinc phosphate than with glass-ionomer cement.

Fifteen laser-welded Olympia alloy samples were divided into three gorups of five samples each, with different gap distances between the welded halves. The first group was welded with a 0.0-mm gap distance. The second and third groups had Olympia shims placed in 0.3- and 1.0-mm gaps, respectively, prior to laser welding. Each of the samples was tested to failure in load fatigue at 30 Hz in a fatigue testing device using an applied stress of 35,000 psi (241.4 MPa). The means and standard deviations for the number of cyles required to produce fatigue failure for each group was 494,618 ± 118,311 cycles for the group welded with 0.0-mm gap diatance, and 242,741 ± 44,623 and 232,021 ± 55,877 cycles for the 0.3- and 1.0-mm specimens, respectively. A one-way analysis of variance shoed that the 0.0-mm gap specimens had the greatest number of cycles to failure (P - 0.05). There was no significant difference between the other two groups. With the exception of two specimens that failed at the weld center, all failures occurred at the edge of the weld.

This study investigated the effect of temporary cement remnants on freshly prepared dentin in the adhesion of resin cements. The tensile bond strength of three types of resin cements to dentin were measured in a control group and after the application of two types of temporary cement. Scanning electron microscopy and energy dispersive x-ray spectoscopy were used to confirm the presence of temporary cement remnants. Overall results suggest that temporary cement application significantly decreased the tensile bond strength in all adhesive systems (P = 0.0001, analysis of variance). Scanning electron micrographs presented granula elements on the dentin surfaces treated with temporary cement even after preconditioning. Energy dispe rsive x-ray spectroscopy results shoed the presence of zinc peaks in the specimens that was not present in the control.

This study examined the adjustments, repakirs, time, and costs required to maintain 69 implant prostheses in private prosthodontic practice for an average of 22 months, after placement. For the removable prosthesis design, the most common adjustment was contouring the prosthesis and the most common repair was retentive component replacement. Screw tightening or fracture repair wer e the most frequently needed modifications for fixed implant prostheses. Each removable implant prosthesis averaged four times as many postplacement adjustments and almost twice as many repairs as did each fixed implant prosthesis, and the mean length of each maintenance appointment was also longer for removable prostheses. Mean repair costs were approximately 60% higher for the removable design.

The original In-Ceram material (In-Ceram Alumina), composed of sintered aluminum oxide subsequently infused with a glass, features interesting mechanical properties. In-Ceram Spinell was marketed more recently to improve the esthetic potential. This study compared the flexural strength of various combinations of sintered alumina and spinel infiltrated with the associated glasses. In addition, the influence of vacuum during the infusion process was investigated using density measurements. The characteristic strength (load at which 63% of the specimens had failed) was 530 MPa for the original material, 5 23.7 MPa when the same material was infiltrated under vacuum, 481.4 MPa when sintered alumina was infused under vacuum with the glass originally marketed for the spinel, and 283.1 MPa for the sintered spinel infiltrated under vacuum with the associated glass. A significant increase in density was observed when the infiltration firing of sintered alumina was peformed under vacuum. Furthermore, the in vivo evaluation of specific esthetic parameters inherent to differenty types of cores was made and revealed the realtive opacity of alumina; spinel was found to have the ability to blend in with the underlying substrate. Both materials demonstrated a general lack of fluorescence.

A computer-aided designing and manufacturing (CAD/CAM) technique for clinical fabrication of facial prostheses was developed. Laser surface scanning was applied to acquire three-dimensional imaging data of the patient's facial defect. The three-dimensional imaging data was then transferred to a CAD/CAM interactive program for image processing, which then mathematically designed and produced a model for fabrication of the facial prosthesis. This CAD/CAM technique has the potential to simplify the procedure and decrease the laboratory work required compared to that required for the conventional plaster-cast method. This new technique also provides a novel approach to the fabrication of prostheses for the recons truction of facial defects. Two alternative three-dimen sional modeling processes, laser lithographic modeling and numerically controlled milling modeling, were integrated in this study. The possibilities and current limitations of the techniques are also discussed.

The good wetting of the acrylic resin by saliva substitutes is of clinical importance in xerostomic patients. This study evaluated the wetting properties of different artificial saliva forumulations that were mucin-based, carboxymethylcellulose-based, and concentrated ion-based on poly(methyl methacrylate) denture base resin, and compared these properties with natural saliva. The wetting properties of the test materials were examined by contact angle measurements. Ninety-six samples that measured 30 x 30 x 3 mm were examined. The wetting properties of mucin-containing and carboxymethylcellulose-containing substitutes on poly(methyl methacrylate) were significantly better than those of human saliva. Mucin-containing artificial salivas had the best weeting properties on the acrylic resin for the materials tested.

The in vitro marginal fit of three all-ceramic crown systems (In-Ceram, Procera, and IPS Empress) was compared. All crown systems were significantly different from each other at P = 0.05. In-Ceram exhibited the greatest marginal discrepancy (161 um), followed by Procera (83 um), and IPS Empress (63 um). There were no significant differences among the various stages of the crown fabrication: core fabrication, porcelain veneering, and glazing. The facial and lingual margins exhibited significantly larger marginal discrepancies than the mesial and distal margins.