George B. Pelleu

The influence of selected light intensities on color perception within the color range of natural teeth

A study was undertaken to evaluate the influence of light intensity on the ability to discriminate color differences within the color range of natural teeth. The results show that shade selection is not significantly affected within the range of 75 to 300 fc. Neither the specialty of the dentist nor the amount of time in practice appeared to be a factor in making color discriminations. However, 7 of the 50 dentists serving as subjects were found to be color defective, and a difference was found between their color discrimination abilities and those of normal persons. This suggests that color-defective dentists should obtain assistance when matching tooth shades.

The tensile strength of a composite resin reinforced with carbon fibers

A study was undertaken to compare the flexure strength of unmodified and carbon fiber-reinforced composite resins. If the addition of carbon fibers to a dental composite resin increases the resins resistance to fracture, some of the shortcomings associated with acid-etched bonded fixed partial dentures can be overcome. The findings of the study, however, showed that the addition of carbon fibers to a dental composite resin actually decreased the flexure strength.

The effect of various clasping systems on the mobility of abutment teeth for distal-extension removable partial dentures

Three clasping systems were placed in five patients, and measurements of abutment tooth mobility were made. These data were compared to previously established baselines and statistically analyzed. The findings of the study are: 1. There was no difference in abutment tooth mobility during the 4-week test period with each of the three clasping systems. The important factor may have been the fit of the distal-extension denture base over the residual ridge, which provides the stability to prevent increases in abutment mobility. 2. Any mobility increases were in a buccal direction only, or toward the flexible retentive clasp arm. There was never any change in lingual mobility. 3. All five patients chose the I-bar retainer as the design of choice due to its increased resistance to dislodgment. Periodic recall of distal-extension removable partial denture patients is mandatory to ensure proper stress distribution and prevent increases in abutment tooth mobility.

Physical properties of a repeatedly used nonprecious metal alloy

Some physical properties of nonprecious alloys were compared after repeated casting without the addition of any new alloy. The tensile strength, percentage of elongation, and hardness properties were determined and compared. There were no significant differences observed in the physical properties tested among any of the four generations of casting. This finding indicates that the metal can be reused for at least four generations.

An evaluation of four variables affecting the bond strength of porcelain to nonprecious alloy

Four variables that could possibly affect the bond strength of the porcelain to nonprecious alloy were investigated. The variables were directional variations of metal preparation using the Paasché Air Eraser with aluminum oxide fast-cut abrasive, atmosphere variations in the furnace from low to high temperature limits of the degassing cycle, time variations at normal atmosphere of 1,850 degrees F. (degassing upper-limit timing), and firing of the opaque layer of porcelain at different temperatures. A total of 162 Ticon alloy interfaces were prepared, from which 81 paired test samples were constructed. Porcelain was fused to the samples and tested under specified conditions of preparation utilizing an Instron Universal testing machine. It was determined that firing the opaque layer at 1,840 degrees F. at a rate of 75 degrees F. per minute more than doubled the mean bond strength of all samples. The time at the upper limit of the degassing cycle also had a significant effect on the bond. As the time increased, the bond strength decreased. Complete bonds between porcelain and nonprecious metals were demonstrated when the fracture occurred in the porcelain and not at the interface. It is recommended that the opaque firing and degassing be done in accordance with the foregoing findings.

Dimensional stability of autopolymerizing acrylic resin impression trays

A study was undertaken to determine the optimal interval between fabrication of an autopolymerizing acrylic resin custom impression tray and making a final impression. Twenty mandibular arch-shaped trays, 10 each of Fastray and Formatray resin, were evaluated for dimensional change. Both materials behaved similarly. Cross-arch contraction of the borders of buccal flanges and unilateral expansion of the borders of buccal-to-lingual flanges were observed. These changes indicate distortion. Linear dimensional changes occurred throughout 6 hours, which suggests that any impression made in a methyl methacrylate acrylic resin custom impression tray should be poured as soon as is conveniently possible. Significant linear dimensional changes were observed for only 40 minutes from the initiation of tray fabrication. This study concludes that while an aged tray is preferred, it is acceptable to make an impression in an autopolymerizing resin custom impression tray after 40 minutes.

Arbitrary mandibular hinge axis locations

This study compared selected arbitrary hinge axis locations with the kinematic axis location. Fifty subjects were studied, and the data were statistically analyzed. Results showed significant differences between the location of experimental arbitrary axis point and those of Beyron, Gysi, and Bergstrom in relation to the kinematic axis. The arbitrary points of Beyron, Gysi, and Bergstrom showed directional tendencies, whereas the experimental arbitrary points were evenly distributed around the kinematic axis. This study indicates that the experimental arbitrary axis point more closely and consistently approximated the kinematic axis than the arbitrary points of Beyron, Gysi, and Bergstrom. The finding suggests that the clinical use of a point on Campers line, 10 mm from the superior border of the tragus, results in a more accurate transfer of the maxillary cast to the articulator.

An evaluation of commercial pastes for finishing composite resin surfaces.

A study was conducted to determine the effectiveness of several commercial pastes in polishing the surfaces of composite resin material. Five samples of Concise composite resin contained within Plexiglas block holders were prepared using Mylar matrices. One block was disked only; three blocks were disked and polished, each with a different paste. The remaining block was the control. The surface roughness of all samples was measured with a stylus profile instrument. Five extracted teeth were prepared in the same manner with Concise composite resin and Mylar strip matrix. In each tooth, the surface was finished by disking only or by disking followed by polishing with one of three pastes. The fifth tooth was the control. The samples were examined by use of a scanning electron microscope. Quantitative evaluation of over-all computer data indicated that the smoothest surface was found immediately ater removal of the Mylar matrix and that pastes leave a rougher surface than is left with a disc.

Marginal opening of single and twin platinum foil-bonded aluminous porcelain crowns

The marginal openings of single and twin foil-bonded aluminous porcelain crowns were compared in crowns fabricated indirectly for extracted teeth and directly on typodont teeth. The crowns were cemented with zinc phosphate, embedded in plastic, and sectioned. Marginal opening was measured directly with a traveling microscope. There was no significant difference between the marginal openings of twin- and single-foil crowns fabricated indirectly for extracted teeth. When the crowns were constructed directly on typodont teeth to eliminate the variables of impression-making and die fabrication, the single-foil crowns possessed a significantly smaller marginal opening than the twin-foil crowns. Both the twin- and single-foil complete porcelain crowns resulted in clinically acceptable margins. The single-foil crowns were easier to make.

A comparative study of the centrifugal and vacuum-pressure techniques of casting removable partial denture frameworks

A study was undertaken to evaluate two techniques for casting accuracy on removable partial denture frameworks: centrifugal casting and vacuum-pressure casting. A standard metal die with predetermined reference points in a horizontal plane was duplicated in refractory investment. The casts were waxed, and castings of nickel-chrome alloy were fabricated by the two techniques. Both the casts and the castings were measured between the reference points with a measuring microscope. With both casting methods, the differences between the casts and the castings were significant, but no significant differences were found between castings produced by the two techniques. Vertical measurements at three designated points also showed no significant differences between the castings. Our findings indicate that dental laboratories should be able to use the vacuum-pressure method of casting removable partial denture frameworks and achieve accuracy similar to that obtained by the centrifugal method of casting.