Anthony G. Gegauff

Reassessment of die-spacer with dynamic loading during cementation.

The authors previously reported a reduction in crown seating discrepancies of approximately 200 microns resulting from the application of dynamic forces during cementation. Previous in vitro die-spacer studies used static loads with large seating discrepancies unrepresentative of clinical practice. This investigation reassessed paint-on die-spacer for its effect on completeness of seating and retention when dynamic seating was used. A series of seven complete crowns was made for each of three extracted human teeth by using 0 to 6 coats of spacer. Index marks were used to measure crown position before and after cementation. Mean seating discrepancies indicated complete seating for all groups of crowns irrespective of the number of coats of die-spacer. An analysis of variance demonstrated no significant differences in the degree of seating. However, crowns made from dies without spacer were significantly more retentive (p less than 0.05) than those made from spaced dies.

A comparative study of post preparation diameters and deviations using Para-Post and Gates Glidden drills.

Para-post and Gates Glidden drills are commonly used to create post space in endodontically treated teeth. The purpose of this study was to compare post preparation diameters and deviations for the Para-post and Gates Glidden drills. Thirty extracted mandibular canine teeth were endodontically treated and embedded in resin blocks. Buccolingual and mesiodistal long-cone radiographs were made using a jig to assure repeatability. Three operators randomly prepared post space in five teeth using Para-post drills and in five teeth using Gates Glidden drills. The post spaces were filled with a contrast medium and the blocks were reradiographed. Drill deviation and post space diameter were measured from the radiographs with a traveling stage microscope. The mean Para-post space diameter was 1.32 mm and deviation from the center of the canal was 0.34 mm. The Gates Glidden was 1.38 and 0.17 mm, respectively. The differences in drill deviation were statistically significant (p

Magnetic resonance image degradation from prosthetic magnet keepers

Eight types of prosthetic magnet keepers were imaged in a water phantom and a living human subject by a 1.5 T magnetic resonance device. Image artifacts were present for all eight samples and ranged from 160 mm to greater than 280 mm in diameter. These artifacts obliterate vital craniocervical areas making their examination by magnetic resonance impossible. Patients with magnetic keepers requiring comprehensive magnetic resonance imaging of the head and neck region must have them removed.

Thermoplastic composites for veneering posterior teeth—a feasibility study

OBJECTIVES This pilot study was conducted to explore selected commercially-available thermoplastic composites that potentially had physical properties superior to currently available dental systems for restoring esthetic posterior crowns. METHODS Polyurethane, polycarbonate, and poly(ethylene/tetrafluoroethylene) (ETFE) composites and unfilled polyurethane specimens were injection molded to produce shapes adaptive to five standardized mechanical tests. The mechanical testing included abrasive wear rate, yield strength, apparent fracture toughness (strength ratio), flexural strength, and compressive strength. RESULTS Compared to commercially available dental composites, abrasion wear rates were lower for all materials tested, yield strength was greater for the filled polycarbonates and filled polyurethane resins, fracture toughness testing was invalid (strength ratios were calculated for comparison of the pilot test materials), flexural strength was roughly similar except for the filled ETFE which was significantly greater, and compressive strength was lower. SIGNIFICANCE Commercially available thermoplastic resin composites, such as polyurethane, demonstrate the potential for development of an artificial crown material which exceeds the mechanical properties of currently available esthetic systems, if compressive strength can be improved.