Compressive strength comparison and crystal morphology of dental cements.
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Dental Cements↗
Biomedical subjects
R G Randolph
Publications and source records attributed to R G Randolph.
Rotary instrument finishing of microfilled and small-particle hybrid composite resins.
Tungsten carbide burs operated at high speeds for trimming and finishing microfilled composite resins are contraindicated as they disrupt the composite resin surface. Diamond burs operated at low speeds do not disrupt the surface on microfilled and small-particle hybrid composite resins. High-speed finishing with carbide burs on small-particle (hybrid) composite resins produces not only a nondisrupted surface but leaves the surface flat and smooth--free from the characteristic striations and grooves left by diamond burs. These results suggest that the rotary instruments used to finish a composite resin must be selected in accordance with the type of composite resins used.
Composite Resins↗
Comparison study of elastic impression material.
The study of four elastic impression materials indicated that master castings could be more accurately seated on casts made from MOD impressions than from full crown impressions. A discrepancy between clinical acceptance and statistical identity was also demonstrated. The study indicated that by altering just one variable, the pour time, a wide range of results is obtained, some clinically acceptable and others clinically unacceptable.
Crowns↗
Clinical measurement of distally directed headgear loading.
A method was developed to measure the distally directed load that is delivered to molar teeth by orthodontic headgear. Measurements on a three-dimensional model and on four patients showed that the intraoral load at the maxillary molar teeth was generally the same as or greater than the measured extraoral force. Higher loadings on the molar teeth were thought to be caused by lever arms present in the headgear assemblies. Both the power arm face-bow and the symmetrical face-bow were effective in delivering an unbalanced load when one arm was bent well outward. The unilateral effect was decreased as the extraoral force was increased. Bending of the face-bow by the stronger extraoral forces probably was responsible for the decreased unilateral effect. The effect of lever arms in the headgear assembly on the load delivered to the teeth warrants further study.
Adolescent↗
Shear testing of the porcelain-metal bond.
A simple shear test was employed to determine the bonding strength of porcelain to a gold metal substrate and to a non-precious metal substrate after they had been aged in double-distilled water at 37 degrees C for four and 12 months. A 7.4% and 18.1% decrease in bond strength after four months and 12 months, respectively, was observed for the porcelain-gold system, and a decrease of 21.2% and 21.4% after four and 12 months, respectively, for the non-precious-porcelain system. A significant difference was observed between the bond strengths of the porcelain-metal composites: 51.17 +/- 11.29 MPa for the porcelain-gold system and 31.83 +/- 3.65 MPa for the porcelain-non-precious system.
Dental Alloys↗