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Biomedical subjects

R A Wicks

Publications and source records attributed to R A Wicks.

6 recordsLinked to original sources
PubMed2000

Direct tissue stops for distal extension removable partial dentures.

Supplemental impression++ strategies may be used to capture optimal registration of residual ridge tissues in distal extension-base RPDs. A procedure is described to adapt tissue stops in vivo and positively position the framework to the master cast when clinically using corrected impressions. This method is simple and cost-effective, and it promotes accurate prosthetic-tissue relationships during clinical and laboratory phase of RPD fabrication.

Dental Abutments↗
PubMed2000

Periodic evaluation of the occlusal vertical dimension of maxillary dentures from the wax trial denture through 48 hours after polymerization.

PURPOSE: This study measured the effects of commercial resin type on maxillary complete dentures with monoplane teeth by periodically comparing the occlusal vertical dimension of the polymerized dentures with the baseline, wax trial denture fiducial measurements. MATERIALS AND METHODS: Commercially available compression-molded, injection-molded, and fluid poly(methyl methacrylate) resins, as well as one compression-molded methyl acrylate ester copolymer, were evaluated. Ten dentures were fabricated from each resin using monoplane teeth. The occlusal vertical dimension at the articulator pin was measured at the wax denture stage for each specimen, and changes in occlusal vertical dimension for each denture were evaluated at a simulated laboratory remount, and at 0, 3, 6, 24, and 48 hours after a simulated clinical remount. Repeated measures analysis of variance (alpha = 0.05) and post hoc one-way factorial analysis of variance and Scheffe's F-Tests for each resin group were performed using ranks of raw data. RESULTS: Changes in the maxillary denture mean occlusal vertical dimensions were recognized throughout the evaluation periods compared with the wax-denture baseline, and time was a significant influence on displacement (p = .0001). Only the compression-molded poly(methyl methacrylate) dentures exhibited a mean laboratory remount occlusal vertical dimension that was significantly greater than the mean wax denture measurement, and all resin systems exhibited occlusal error that was significantly less than the laboratory remount measurements at 48 hours. At 48 hours, all resin groups exhibited mean occlusal vertical dimension changes that were less than 1 mm compared with the wax denture. Only compression-molded poly(methyl methacrylate) dentures exhibited a mean 48-hour clinical remount measurement that was statistically similar to the mean wax denture occlusal vertical dimension. CONCLUSIONS: Individual maxillary dentures from all resin types and at all intervals exhibited dimensional change. At the last evaluation period, the compression-molded poly(methyl methacrylate) showed no change in mean occlusal vertical dimension from baseline, whereas remaining groups exhibited occlusal vertical dimensions significantly less than baseline.

Acrylates↗
PubMed1997

Wear of visible light-cured restorative materials and removable partial denture direct retainers.

PURPOSE: This study measured the in vitro wear of visible light-cured restorative materials and removable partial denture direct retainers. MATERIALS AND METHODS: An aluminum test die was produced by replicating the facial contours of an extracted human molar (model). The replica's cervical contour was modified by placement of a restorable Class V cavity preparation. The test die became a fixed component of a testing apparatus. The restorative materials tested were Z100 (fine particle filled resin composite), Silux Plus (microfilled resin composite), and Photac-Fil (hybrid glass ionomer). Cast round, half round, I bar, and wrought-wire retainers were designed to engage a 0.254-mm undercut. Caliper measurements of the wear of restorative materials were made at intervals during testing, and after 7,500 retainer placements and removals. The measurements of material- and retainer-wear were subjected to ANOVA and Tukey tests. RESULTS: Generally, retainers with round profiles caused less wear of the restorative materials than those featuring flat contact surfaces. Wear of the materials ranged from 14 +/- 5.5 microns (Silux Plus by cast round) to 70 +/- 10.0 microns (Photac-Fil by cast half round). Mean wear of retainers, however, ranged only from 2 +/- 4.5 microns for six of 12 possible retainer-material pairings up to 12 +/- 4.5 microns (cast half round by Z100). CONCLUSIONS: Regardless of their design features, the direct retainers of this study exhibited little wear when paired with any of the restorative materials. Overall, material wear appeared to be greater than retainer wear by a factor of five. When paired with practically any retainer type, the hybrid glass ionomer (Photac-Fil) exhibited more wear than either of the two resin composites (Z100 or Silux Plus). Although not established clearly, retainers with round profiles (wrought-wire and cast round) appeared to produce less wear of restorative materials than their I bar and cast half round counterparts.

Analysis of Variance↗
PubMed1994

An evaluation of fit in osseointegrated implant components using torque/turn analysis.

PURPOSE: The accurate and passive fit of dental prostheses supported by endosseous implants is of primary importance in securing long-term restorative success. In the clinical setting, adequate visual and radiographic assessment of joined implant components can be limited. Mechanical engineering principles show a linear relationship between tightening and the degree of rotation of a precision bolted assembly. At a constant torque, with certain variables controlled, a threaded fastener should return to the same rotational end position on repeated tightenings. This study evaluated the terminal screw positions of joined implant components as a potential aid to the clinician in confirming the fit of a fixed and removable prosthesis. There were three areas of experimental inquiry: (1) How reproducible are the various clinical means by which torque is applied to the fastening screws, both in absolute and relative value? (2) How reproducible are the rotational end positions of the gold (attachment) and titanium (center) screws when a controlled torque is applied? (3) Do changes in screw position occur as a function of the magnitude of artificially introduced discrepancies? MATERIALS AND METHODS: Three different torque delivery devices were evaluated: a hand-held screwdriver (DIB 048; NobelpharmaUSA, Chicago, IL), a manual torque wrench (DIA 250; NobelpharmaUSA), and an electronic Torque Controller (DEA 020; NobelpharmaUSA), using a calibrated torque measuring dynamometer (Magtrol, Inc, Buffalo, NY). The reproducibility of turning limits were determined for both the titanium and gold screws contained in five Brånemark implant assemblies. Each assembly was subjected to six trials, tightening to recommended torque. The position of each screw head was recorded with a special scribe on acetate sheets and transferred to graph paper. Five implant assemblies were invested in dental stone within a die form mold. A casting was made supported by three implant analogues. Stainless steel shims of 12.7-microns, 25.4-microns, 38.1-microns, and 50.8-microns thickness were used to create impingement and space discrepancies. Controlled trials were conducted, and changes in rotational limits for each screw were recorded. RESULTS: The following values were measured, intending to achieve a torque of 10 Ncm, based on 10 trials for each implement: hand driver, 6.48 (+/- 0.85) Ncm; torque wrench, 7.77 (+/- 0.56) Ncm; and the Torque Controller, 8.54 (+/- 0.19) Ncm. The electronic Torque Controller proved to be the most reproducible instrument and was selected as the delivery vehicle for the remainder of the study. The titanium center screws had a rotational limit that was reproducible to within 0.6 degrees (+/- 0.2 degrees). For the gold screws, it was found that at least two trials had to be conducted for each assembly before the rotational limits conformed to a reproducible position within 1.85 degrees (+/- 1.87 degrees). A linear relationship of approximately 0.9 degrees/micron was observed between the changes in rotational limit and each subsequent shim thickness. CONCLUSIONS: This study suggests that screw position can be an indicator of fit in dental implant prostheses if the end point of screw rotation is adequately indexed, specific to each assembly and screw.

Analysis of Variance↗
PubMed1994

A systematic approach to definitive planning for osseointegrated implant prostheses.

Thoughtful design selection is crucial for the perpetual success of any dental implant restoration. This article reviews treatment considerations specific to the postsurgical presentation of the implant patient. Deviations from the originally planned design may be necessary at this time. Indications for the selection of specific prosthetic modalities are offered in a sequence of paradigms to support the cognitive skills of the inexperienced clinician.

Decision Support Techniques↗