Replicas of a dentate human mandible were prepared in photoelastic resin material. They were positioned in a supporting frame by means of struts, representing the principal muscles of mastication. Occlusal loading was simulated, and the stresses generated within the models were examined by three-dimensional photoelastic stress analysis.

Dental Stress Analysis↗

PubMedDate not supplied

A comparison of athletic mouthguard materials.

The development of protective mouthguards resulted from extensive injuries during participation in contact sports. This has produced a dramatic decrease in the incidence of injuries to the orofacial complex. Numerous materials and techniques have been used for mouthguard fabrication. The purpose of this investigation was to make an in vivo comparison of various thermoplastic mouthguard materials. Mouthguards were fabricated upon maxillary models of 40 members of the UCLA football team. The mouthguards were made of the following materials: poly (vinyl acetate-ethylene) copolymer clear thermoplastic; polyurethane; and laminated thermoplastic. Eleven measurements were taken for each mouthguard to demonstrate dimensional changes that occurred with wear. Statistical analyses determined differences between the types of mouthguards. The clear thermoplastic revealed less dimensional change than the polyurethane material. The laminated thermoplastic showed significantly less dimensional change than the other materials tested.

Football↗

PubMedDate not supplied

Accuracy of an electric torque-limiting device for implants.

The torque output of the Nobelpharma electric torque controller was determined using a special setup on an Instron test machine. The devices were held in a vice and oriented so that activation of the drivers caused a pure torsion effect. Measured torque levels generally varied significantly between individual devices. Further, significant differences generally existed between the nominal torque levels and the corresponding measured values. Torque application errors varied from target values by 1% to 165%. For the clinician to deliver appropriate torque levels, these data indicate that a simple means for chairside calibration and adjustment should be available.

Analysis of Variance↗

PubMedDate not supplied

In vitro bracket bond strength to acid-etched or air-abraded enamel.

PURPOSE: This study evaluated, in vitro, the capacity of a dentin bonding agent to improve the bond strength of orthodontic brackets using air abrasion enamel preparation. METHODS: Each of the enamel surfaces received a different treatment prior to bonding procedures. Group 1 received acid-etched with 38% phosphoric acid for 30 seconds. Group 2 received acid-etched with 38% phosphoric acid for 30 seconds, dentin bonding agent (Scotchbond MultiPurpose) applied after rinse completed. Group 3 received abrasion-etched (particle size 50 microns, 120 psi). Group 4 received abrasion-etched, dentin bonding agent applied after etching completed. Unfilled adhesive resin (Ormco light cured sealant) was applied followed by a premolar bracket (Ormco meshed mini-twin) with adhesive (Ormco light cured adhesive) placed on the back. Shear bond strengths were measured using an INSTRON machine and the site of bond failure was determined under 3X magnification. RESULTS: The shear bond strength obtained with a traditional acid-etch, in vitro, was not improved significantly by the use of a dentin bonding agent. Air abraded surfaces showed very low bond strengths with all treatments. CONCLUSIONS: Tested in vitro, air-abraded surfaces provide clinically unacceptable bond strength when compared to acid-etched enamel surfaces.

Acid Etching, Dental↗

PubMedDate not supplied

Effects of cement type and thickness on retention of serrated pins.

The retentive capacity of cemented pins was determined. Zinc phosphate, polycarboxylate, and cyanoacrylate were used to cement threaded pins (0.024 inch) into precise channels of 0.025, 0.026, and 0.027 inch. Highest retentive values were realized when zinc phosphate and polycarboxylate cements were used with the smallest pin-channel mismatch. Ethyl cyanoacrylate was least retentive and demonstrated no mismatch dependency.

Cyanoacrylates↗

PubMedDate not supplied

Mechanical properties of a nonprecious type III alloy.

Explore the source record for details and available documents.

Chromium↗

PubMedDate not supplied

Passivity of fit and marginal opening in screw- or cement-retained implant fixed partial denture designs.

The relationship of stress generation upon placement of cement-retained or screw-retained implant restorations has not been thoroughly investigated. Passivity of fit and marginal discrepancies of screw- and cement-retained implant fixed partial denture (FPD) designs were determined using a photoelastic model of a partially edentulous posterior mandibular arch with 3 screw-type implants. Buccal and lingual marginal openings, measured with a traveling microscope before cementation or screw tightening, revealed no statistical difference in adaptation between designs. Screw tightening caused a reduction in marginal opening (changes significant, P < .05). The opening with the cemented FPDs was similar before and after cementation. Photoelastic evaluation of the FPDs showed that cement-retained FPDs exhibited a more equitable stress distribution than did their screw-retained counterparts.

Cementation↗

PubMedDate not supplied

Shrinkage stresses associated with incremental composite filling techniques in conservative Class II restorations.

Conservative Class II preparations are widely utilized, however the stresses produced by incremental composite placement/curing has not been demonstrated. The purpose of this investigation was to visualize the stresses generated by composite resin placed into photoelastic models of conservative Class II preparations using different incremental techniques. Conservative Class II preparations on three different primary molar replicas were cast life-sized in a photoelastic material. Incremental placement/curing techniques used were oblique, gingival-occlusal, and facial-lingual and were compared with bulk placement/curing. The photoelastic stresses produced with conservative Class II restorations were of lower intensity than conventional Class II and larger composite restorations previously reported. Few differences in shrinkage-induced stresses were observed between the incremental placement/curing techniques tested. Lowest shrinkage stresses were generated by the bulk placement/curing technique.

Birefringence↗

PubMedDate not supplied

Effect of application technique and dentin bonding agent interaction on shear bond strength.

This study evaluated the interaction of five clinical application techniques and the shear bond strength of four DBAs (OptiBond FL, Clearfil SE Bond, PQ1 and Prime & Bond NT). A hybrid resin composite (Herculite XRV restorative resin) was attached to human dentin surfaces using five application techniques: Group A--adhesive spread with a 3M brush for 30 seconds, followed by compressed air 0.5 cm from the surface for one second to remove the excess adhesive. Group B--adhesive spread with a 3M brush for 30 seconds, followed by compressed air 0.5 cm from the surface for three seconds to remove the excess adhesive. Group C--adhesive spread with 3M brush for 30 seconds, excess adhesive removed with a clean brush, two strokes side by side, no compressed air. Group D--adhesive spread with a Micro-applicator brush for 30 seconds followed by compressed air 0.5 cm from the surface for one second to remove the excess adhesive. Group E--adhesive spread with a Micro-applicator brush for 30 seconds, the excess adhesive removed with a clean brush, two strokes side by side and no compressed air. The specimens were stored in distilled water at 37 degrees C for 24 hours, followed by thermocycling between 5 degrees C and 55 degrees C for 1,000 cycles. The shear bond strengths were determined on a universal testing machine operating with a crosshead speed of 5 mm/minute. The fracture sites were examined by 20x stereo microscope to determine the type of failure that occurred during the debonding procedure. Bond strength data were compared with analysis of variance at a significance level of p<0.05. Post hoc comparisons of means were performed with t-tests with p-values adjusted for multiple comparisons. This in vitro study concluded that there was an interaction between the application technique and bonding agent tested. All DBAs utilized the one-second compressed air technique, which yielded the highest bond strengths.

Air↗