Masking of High-Translucency Zirconia for Various Cores.

CLINICAL RELEVANCE: Various core materials with different shades affect the final color of high-translucency monolithic zirconia restorations. The blue core shows the greatest color difference in final zirconia restorations followed by metal, A3 dentin-shade resin core, and white core. SUMMARY: The purpose of this study was to evaluate the masking ability of high-translucency monolithic zirconia for various core materials. A computer-aided design-computer-aided manufacturing system was used to design a zirconia disc with a diameter of 10 mm and a thickness of 1.0 mm. Four groups of cores (n=15 each) were fabricated with blue-colored dual-cure resin, white-colored dual-cure resin, A3 dentin-shade composite resin, and titanium block with 10-mm diameter and 5-mm thickness.Dual-cure, self-adhesive resin cement discs with a thickness of 25.0 ± 0.02 µm were fabricated. The color was measured using a handheld spectrophotometer. Color measurements of all specimens were performed on a white background. To assess the masking ability of zirconia, the difference between the values measured with zirconia on a white background and the values measured with zirconia on each of the four types of core material as a background with the cement specimens interposed (zirconia + cement + core) was determined. To enhance the optical connection between the specimens, distilled water was applied between each layer during each measurement.The results showed that the value of ΔE was highest for the blue core followed by metal, A3 dentin-shade resin core, and white-resin core. No significant differences were observed between the metal core and the A3 dentin-shade resin core or between the A3 dentin-shade resin core and the white core. The blue core had the significantly highest ΔE value based on Tukey's honest significant difference test.Different core materials affect the final color of high-translucency monolithic zirconia restorations. Thus, our study showed that the final color of high-translucency monolithic zirconia restorations could be affected by the type of core material used.

Effect of Insufficient Light Exposure on Polymerization Kinetics of Conventional and Self-adhesive Dual-cure Resin Cements.

OBJECTIVES: The purpose of this study was to investigate the influence of insufficient light exposure on the polymerization of conventional and self-adhesive dual-cure resin cements under ceramic restorations. METHODS: Two conventional dual-cure resin cements (Rely-X ARC, Duolink) and two self-adhesive resin cements (Rely-X U200, Maxcem Elite) were polymerized under different curing modes (dual-cure or self-cure), curing times (20 and 120 seconds), and thickness of a ceramic overlay (2 and 4 mm). Polymerization kinetics was measured by Fourier transform infrared spectroscopy for the initial 10 minutes and after 24 hours. Data were analyzed using mixed model analysis of variance (ANOVA), one-way ANOVA/Student-Newman-Keuls post hoc test, and paired t-test (α=0.05). RESULTS: When light-curing time was set to 20 seconds, the presence of the ceramic block significantly affected the degree of conversion (DC) of all resin cements. Especially, the DC of the groups with 20 seconds of light-curing time under 4 mm of ceramic thickness was even lower than that of the self-cured groups at 24 hours after polymerization (p<0.05). However, when light-curing time was set to 120 seconds, a similar DC compared with the group with direct light exposure (p>0.05) was achieved in all dual-cure groups except Maxcem Elite, at 24 hours after polymerization. CONCLUSIONS: For both conventional and self-adhesive dual-cure resin cements, insufficient light exposure (20 seconds of light-curing time) through thick ceramic restoration (4 mm thick) resulted in a DC even lower than that of self-curing alone.

Buccal bone plate thickness of the Asian people.

Distances from the apex to the buccal bone plate were measured on the computed tomography (CT) images of 1806 teeth from 66 patients, using an image analyzer program (Image-Pro Plus, Ver. 4.0, Media Cybernetics). In the mandible, the mean distance from the distal apex of the mandibular second molar to the buccal bone plate was the largest distance measured, at 8.51 mm, followed by distance from the mesial root to the buccal bone (7.34 mm). In the mandibular first molar, the mean distal and mesial bone thicknesses were 5.18 mm and 4.09 mm, respectively. However, when there were two distal roots, the distance of the disto-lingual root to the buccal plate was found to be 9.52 mm, which constitutes the greatest measured thickness. In the maxillary buccal roots, the distances from the mesio-buccal and disto-buccal root of the second molar to the buccal bone plate were the largest, at 4.63 mm and 3.61 mm, respectively. The average distances from the palatal apex of the maxillary first and second molars to the buccal bone plate were 10.69 mm and 10.17 mm, respectively, while, from the palatal bone plate, average distances of 3.15 mm and 3.08 mm were measured. Special considerations, such as bony lid approach, lingual approach, or intentional replantation may be required, especially when a patient has a surgical need in the second molars and the disto-lingual root of the mandibular first molar, or in the palatal root of the maxillary molars.

Molecular epidemiology and association of putative pathogens in root canal infection.

The purpose of this study was to investigate the epidemiology of putative pathogens in root canals with apical periodontitis and to determine the associations among the putative pathogens. Eighteen symptomatic and 20 asymptomatic teeth from 36 subjects were studied. This research was performed with polymerase chain reaction and hybridization using rRNA-based oligonucleotide probes. The most frequently found species was Fusobacterium sp. (68.4%), followed by Peptostreptococcus micros (44.7%) and Porphyromonas gingivalis (26.3%). Sixteen teeth (42.1%) contained one or more species of the selected black-pigmented bacteria. Bacteroides forsythus and Treponema sp. were detected in 8 teeth and 6 teeth, respectively. Among the analyzed bacteria, significant relationships were shown in the combination of B. forsythus/P. gingivalis and Treponema sp./P. gingivalis. There was no significant association between any bacteria and any symptoms.