The International Journal of Prosthodontics, 03/1997

This study investigated the relationship between tooth preparation height and diameter and the resistance of cemented crowns to dynamic loading. Crown and abutment analogs were cemented using zinc oxide-eugenol, zinc phosphate, glass-ionomer, and resin composite luting agents. Abutment height varied from 1 to 7 mm in increments of 1 mm. Diameters of 3, 4, 5, 6, 7, and 8 mm were tested. A testing apparatus designed to apply dynamic stresses was used. The cemented crowns were loaded until the cement bond failed or the components reached 1 million stress cycles. The staircase technique was applied for data analysis. The results showed that: (1) the relationship between abutment height (or diameter) and resistance to dynamic lateral loading is approximately linear; and (2) crowns luted using resin composite cement we more resistant than those placed using glass-ionomer cement, w hich in turn were more resistant than crowns cemented with zinc phosphate or zinc oxide-eugenos cements.

The introduction of the original Swedish implant system (Branemark) was followed by several alternative implant systems with implants and components that closely resembled the original design and treatment protocol. Some of these alternative systems may be interchangeable. Manufacturing variations can result in as much as 0.1 mm of space between the component parts. The implant/abutment int erface fit was evaluated by scanning electron micrography for each of four implant systems, as well as interchanged components between the various systems. Results showed that certain implant system abutments are interchangeable, and that the accuracy of fit meets with or exceeds the criteria set by the original Swedish system.

To relate the characteristics of rotary instruments to the sur face they produce, crylic resin, Molloplast B, and Novus were investigated with energy dispersive analysis and scanning electron micjroscopy (secondary and backscatter images) before and after machining. The chemical composition of cutting instruments, material surfaces, and residues was identified. Machined debris embedded in Molloplast B after machining with the Molloplast stone was found to contain a mean lead content of 45%. High concentrations of barium sulphate were discovered on the arbor band-machined surface of Novus. These differences were related to clinically appropriate instrumentation, and, therefore biocompatability studies that intimately relate to the in vivo situation should be considered for new materials.

Tongue position for four selected consonants, /s/, /k/, /l/, and /t/, was observed and photographed through an opening in the cheek of a patient. The cheek had been resected to remove a tumor. On comparison of the tongue positions with those described in the literature, it was found that the variations in tongue position were negligible. Although the patient had a large facial defect, speech alrity was also not affected. As reconstructive surgery was not immediately feasible, a cheek prosthesis was fabricated for the facial aspect.

In the presence of an atrophic endentulous mandible, the stability of the mandibular denture is related to the quality of the osteomucosal support and the muscles surrounding it. A new procedure for vestibuloplasty is described that combines a periosteal flap and a gingival graft. Titanium impacted posts are used for fixation and the stabilization of the flap and graft. This clinical report presents the results for 12 patients. Clinical appraisal indicates that the technique appears to improve the anteroposterior stability of the mandibular denture, increasing the attached mucosa and offering better long-term results. The management of the gingival and muscular environment can improve the peri-implant area.

The IPS Empress pressed glass-ceramic system was used in this investigation to restore anterior and posterior single teeth. One hundred forty-four crowns were evaluated over a period of 6 to 68 months (mean period of 37 months). According to the Kaplan-Meier analysis, the estimated success rate after this period was 95.35%. Crowns were also investigated using the modified US Public Health Service criteria. Most of the crowns rated as Alpha for color match, contour, marginal integrity, recurrent caries, and marginal discoloration. The results of this study indicate that this material can be successfully used, especially in the anterior area, when the procedures outlined are carefully followed.

The authors investigated the length of time medicated displacement cord should remain in the gingival crevice prior to impression making. A silk cord (Deknatel) was placed into the sulcus and was not removed during the study. Medicated cords (Hemodent on Ultrapak #1) were minutes. Following cord removal, closure of the sulcus was recorded at intervals using a miniature video camera. Crevicular widths were measured at the midbuccal and transitional line angle areas. At both the midbuccal and transitional line angle areas, gingival crevices displaced for 2 minutes were significantly smaller at 20 seconds (P .05) than crevices following displacement for 4, 6, and 8 minutes. No significant difference in crevicular width was f ound at any time period after cord removal for crevices displaced for 4, 6, and 8 minutes. At the transitional line angle, crevicular widths were significantly smaller than at the midbuccal at 20 seconds for all times and remained so up to 180 seconds. To achieve a crevicular width of 0.2 mm, cord should remain in the gingival crevice for an optimum time of 4 minutes prior to imperssion making when using the materials evaluated in this study.

This study investigated the thickness of a swollen layer between heat-activated and autopolymerized denture base polymer based on poly(methyl methacrylate) and autopolymerized repair acrylic resin. The repair surfaces of polymerized poly(methyl methacrylate) resin specimens (n = 5) were wet with methyl methacrylate liquid for 0, 0.5, 3, 30 or 60 minutes before the mixed repair resin was app lied and polymerized to the surface of the specimen. The specimens were wet ground to a thickness of 0.15 mm, and the repair joint was examined using a light microscope. The thickness of the layer of swollen poly(methyl methacrylate) at the repair joint was measured from the micrographs. Both the type of polymer, ie, heat-activated or autopolymerized, and the wetting time of the repair surface with methyl methacrylate had a significant effect on the thickness of the swollen layer (P .001). Prolonged wetting time of the repair surface of the autopolymerized poly(methyl methacrylate) increased the thickness of the swellen layer (r = .944, P = .000), but had less effect on the thickness of the swollen layer of h eat-activated poly(methyl methacrylate) (r = .391, P = .005). This study suggests that methyl methacrylate diffuses more easily into an autopolymerized poly(methyl metha crylate) than into heat-activated poly(methyl methacrylate) during the repair of denture base polymer.

The clinical performance of 325 resin-bonded fixed partial dentures (RBFPD) placed between 1984 and 1995 was reviwed. The primary indications of the 264 patients treated were trauma and aplasia. Two hundred eighty-three of the resin-bonded fixed partial dentures were primary restorations, and 42 of the restorations were secondary and tertiary after the loss of the primary resin-bonded fixed partial denture. Including the rebonded restorations, the survival rate calculated using the Kaplan-Meier method was 76% after 5 years and 60% after 10 years. Analysis of the data showed that casting alloy, pretreatment of the bonding surfaces, luting agent, and mobility of the abutment teeth were decisive prognostic factors for success. Base metal alloys, silicoating, mesh retention, and immobile abutments were positive factors. In contrast to other reports in the literature, retentive abutment preparation did not result in a higher survival rate than unprepared abutments. Small restorations in the bonding area did not affect the survival. No differences in su rvival rate were found for resin-bonded fixed partial dentures in the maxillae or mandible, or in the anterior and posterior regions. Multiunit resin-bonded fixed partial dentures had a smaller probability of survival than three-unit resin-bonded fixed partial dentures. Carious lesions were found on 4% of the abutment teeth.

The abrasive effect of variuos porcelain surfaces on human enamel was studied in vitro. Sixty pairs of tooth-porcelain specimens were tested under a standard load and rate in distilled water and with and without intermitten exposure to a carbonated beverage. The amount of wear of enamel and porcelain specimens was determined after 5,000, 15,000, and 25,000 cycles. After 25,000 cycles there was no significant difference in the enamel wear betwen glazed and polished groups, but wear produced by the unglazed groups was significantly higher (P .05). Overall, exposure to a carbonated beverage significantly increased the amount of enamel wear produced by all porcelain surfaces (P .001). The finish of the porcelain surface did not influence its wear.

This research sought to compare the microbiological status of pumice slurry in clinical and nonclinical dental laboratories. Samples were inoculated onto selective and nonse lective media. Resultant colonies were counted and identified to genus or species level. In the nonclinical laboratory, counts were constant at approximately 10 to the seventh power to 10 to the eighth power cfu/g. Pseudomonad s, staphylococci and Bacillus spp comprised the major pumice contaminants in both laboratories. It was concluded that nonclinical laboratories are not immune from the presence of potentially pathogenic microorganisms in pumice slurry. Disinfectant reduces contamination by oral microorganisms.

Eight partially irradiated oral cancer patients were treated using either mandibular implant and mucosa-supported telescopic coping prostheses or a restoration that was completely implant-supported with telescopic copings. Both types of restorations provided sufficient positional stability and peri-implant hygiene, and functional and esthetic improvement. However, only the completely implant-supported telescopic prostheses avoided soft tissue ulcers that had the potential for the development of osteoradionecrosis. This type of restoration can especially by recommended for irradiated patients.