Richard W Billington | Search PubMed

PubMed2006

Interoperator variability during polishing.

OBJECTIVE: The object of this study was to establish the 3 variables used in polishing by measuring the range of loads, speeds, and times used by practitioners when finishing and polishing samples of amalgam, resin composite, and glass-ionomer cement. These parameters could then be used to establish clinically relevant values that might optimize clinical finishing techniques. METHODS AND MATERIALS: Samples of the 3 materials were attached to the load cell of a universal testing machine that was attached to an X-Y plotter. Practitioners were asked to finish the samples using 4 grades of a polishing disk system. Prior to using each grade of disk, the practitioner selected a speed. The sample was finished using one grade of disk until the practitioner was satisfied with the finish achieved. The process was then repeated with the next grade of disk. From the tracings for each disk the load and time were calculated. RESULTS: There was a wide variation in the loads, speeds, and times used by the practitioners to finish the 3 materials, and it was not possible to find any relationship among the 3 variables. It appeared that practitioners finished the materials in an arbitrary manner. CONCLUSION: No clear evidence was obtained to determine optimal combinations of load, speed, and time for finishing of amalgam, resin composite, or glass-ionomer cement. However, the results of this study indicate a range of values commonly used for each parameter in clinical practice, which could be useful for manufacturers in providing finishing instructions for their products.

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PubMed2002

The effect of the disc support system on biaxial tensile strength of a glass ionomer cement.

OBJECTIVE: This was to examine how varying the type of support, from a complete ring to a series of point supports, affected the biaxial tensile strength of one glass ionomer cement. METHOD: Three support diameters from 11.5 to 28.6 mm were achieved using 3 mm ball bearings as point supports equidistantly spaced around the diameter. From 3-30 point supports were used depending on diameter. At the maximum number of point supports for each diameter the support points were 3 mm apart. After 24h storage in water at 37 degrees C the biaxial tensile strength of 1 mm thick glass ionomer restorative cement discs was measured using a loading rate of 1 mm min(-1). The load at break was converted to biaxial tensile strength using the Timoschenko and Woinowsky-Kreiger equation using a Poisson's ratio value of 0.30. The mean strength of six specimens tested per support regime was calculated. RESULTS: Comparison with the mean result obtained from using a continuous knife-edge support showed there to be no significant difference (unpaired t-test) between the different support systems except in two cases, both being when a four-point support was used. Neither the support diameter nor the number of point supports was crucial. SIGNIFICANCE: Results from studies where different systems have been used to support brittle cement discs may be compared.

Dental Bonding↗