Cheol-We Kim

Effect of surface topography on the color of dental porcelain

The objectives of this study were to evaluate the color difference depending on the surface topography of roughness and glazing, and to determine the effects of color measuring geometry and the standard illuminant on the color of a dental porcelain. Disk specimens of A3 shade were fired with commercial dental porcelain for PFM. Specimens were divided into non-polished (ST 1), polished with 200, 400, 1000, 1500-grit SiC papers (ST 2, 3, 4, 5) and glazed (ST 6) groups. After measuring the average surface roughness (Ra), color was determined under the illuminant A and D65 on a spectrophotometer with the specular component excluded (SCE) and included (SCI) geometry. Ra values were significantly influenced by the surface topography. With the SCE, the CIE L* value after glazing was significantly lower than that after polishing. Color differences (ΔE*) measured with the SCE were higher than those with the SCI (2.61–4.66 vs. 0.93–1.57). Therefore the SCE geometry seemed to more accurate protocol for the color measurement of dental porcelain.

Influence of illuminating and viewing aperture size on the color of dental resin composites

OBJECTIVES The objective was to evaluate the difference in the color of dental resin composites by the illuminating and viewing aperture sizes. The influences of the color measuring geometry, standard illumination and surface roughness on the color were also determined. METHODS Color of five brands of resin composites of A2 shade was measured after-polymerization and after-polishing. Color was measured according to the CIE L(*)a(*)b(*) color scale with the SCE and SCI geometry under the CIE standard illumination of A and D65. The illuminating/viewing aperture sizes were 11 mm/8 mm (8 mm) and 3 mm/3 mm (3 mm). RESULTS Regardless of the measuring geometry, CIE L(*), a(*) and b(*) values measured at 3 mm were lower than those at 8 mm. Changes in L(*), a(*) and b(*) values by the difference in the aperture size were 17.22-21.32, 3.43-6.64 and 13.82-16.81, respectively, and the color difference (DeltaE(*)) was 16.23-27.87 with the SCE geometry. Regardless of the aperture size, DeltaE(*) values caused by polishing measured with the SCE were significantly higher than those with the SCI. SIGNIFICANCE Aperture size, measuring geometry and surface conditions of specimen should be considered when comparing the result of color measurement.

Frictional Forces Between Lingual Brackets and Archwires Measured by a Friction Tester

Frictional resistance tends to rapidly increase as the angle between a bracket and an archwire increases beyond a critical angle. The purpose of this study was to determine a new measuring method with a pin on disk friction tester for the measurement of the frictional force between lingual brackets and archwires. A lingual bracket is different from a labial bracket in dimensions and in some clinical aspects. The influence of artificial saliva was also surveyed. Two brands of lingual brackets and one brand of labial standard bracket with an 0.018-inch slot size were used. Archwires of three alloys (stainless steel [SS], Ormco; beta-Titanium [TM], Ormco; cobalt-chrome, [EL], RMO) with 0.016 x 0.022- and 0.017 x 0.025-inch dimensions were used. Measurements were conducted with an angular velocity of 0.6 degrees/s for 90 seconds and a normal force of 100 g at 25 degrees C in a dry and 34 degrees C in an artificial saliva environment. For SS and EL archwires, the frictional force with the FJT bracket was greater than that with ORM bracket (P < .01). Compared with SS and TM archwires, 0.016 x 0.022-inch EL archwire showed a higher frictional force with two lingual brackets (P < .01). Significant differences in frictional force existed between dry and artificial saliva environments (P < .05), and the effects varied by the bracket-archwire couples. The estimated critical contact angles were greater than the theoretical values. This new method can be a useful protocol for measurement of frictional force because it can measure the frictional force under the conditions of continuous angular change between bracket and archwire.

Effect of fluoride addition on the properties of dental alginate impression materials

Fluoride-containing dental alginate impression materials can exert a considerable reduction in enamel solubility. The objective was to evaluate the effects of fluoride addition in the alginate impression materials on the properties and subsequent release of fluoride. Four experimental alginate impression materials were studied. Materials were mixed with distilled water (control) or 100-ppm fluoride solution. One or two percent NaF, or 1% SnF2 was added to the materials, which were mixed with distilled water. Fluoride release, flexibility, recovery from deformation, setting time, compressive strength and elastic modulus were determined in accordance with the ISO 1563 and ANSI/ADA Spec. 18. Fluoride release increased after addition of fluoride, and the released amount was 0.762–14.761 ppm. Addition of NaF or SnF2 resulted in higher fluoride release than the control group (p<0.05). After fluoride addition, flexibility was 15.45–20.27%, and the recovery from deformation did not change except one material. Compressive strength after fluoride addition was 0.36–1.12 MPa. Addition of NaF or SnF2 in an alginate impression material may result in effective release of fluoride without deteriorating the properties of material itself.