No abstract available.

The possibility of applying a bi-axial flexure strength test on composite resin was examined using three point and bi-axial flexure strength tests to measure the strength of the light-cured resin and to compare the relative reliability using the Weibull modulus. The materials used in this study were light-curing restorative materials, MICRONEW(TM), RENEW(R) (Bisco, Schaumburg, USA). The bi-axial flexure strength measurements used the piston-on-3-ball test according to the regulations of the International Organization for Standardization (ISO) 6872 and were divided into 6 groups, where the radius of the specimens were 12 mm (radius connecting the 3-balls: 3.75 mm), 16 mm (radius connecting the 3-balls: 5 mm), and the thickness were 0.5 mm, 1 mm, 2 mm for each radius. The bi-axial flexure strength of the MICRONEW(TM) and RENEW(R) were higher than the three point flexure strength and the Weibull modulus value were also higher in all of the bi-axial flexure strength groups, indicating that the bi-axial strength test is relatively less affected by experimental error. In addition, the 2 mm thick specimens had the highest Weibull modulus values in the bi-axial flexure strength test, and the MICRONEW(TM) group showed no significant statistical difference (p > 0.05). Besides the 2 mm MICRONEW(TM) group, each group showed significant statistical differences (p < 0.05) according to the thickness of the specimen and the radius connecting the 3-balls. The results indicate that for the 2 mm group, the bi-axial flexure strength test is a more reliable testing method than the three point flexure strength test.
Radius ; Social Control, Formal

The purpose of this study was to evaluate the effect of instrument compliance on the polymerization shrinkage stress measurements of dental composites. The contraction strain and stress of composites during light curing were measured by a custom made stress-strain analyzer, which consisted of a displacement sensor, a cantilever load cell and a negative feedback mechanism. The instrument can measure the polymerization stress by two modes: with compliance mode in which the instrument compliance is allowed, or without compliance mode in which the instrument compliance is not allowed. A flowable (Filtek Flow: FF) and two universal hybrid (Z100: Z1 and Z250: Z2) composites were studied. A silane treated metal rod with a diameter of 3.0 mm was fixed at free end of the load cell, and other metal rod was fixed on the base plate. Composite of 1.0 mm thickness was placed between the two rods and light cured. The axial shrinkage strain and stress of the composite were recorded for 10 minutes during polymerization, and the tensile modulus of the materials was also determined with the instrument. The statistical analysis was conducted by ANOVA, paired t-test and Tukey's test (alpha<0.05). There were significant differences between the two measurement modes and among materials. With compliance mode, the contraction stress of FF was the highest: 3.11 (0.13), followed by Z1: 2.91 (0.10) and Z2: 1.94 (0.09) MPa. When the instrument compliance is not allowed, the contraction stress of Z1 was the highest: 17.08 (0.89), followed by FF: 10.11 (0.29) and Z2: 9.46 (1.63) MPa. The tensile modulus for Z1, Z2 and FF was 2.31 (0.18), 2.05 (0.20), 1.41 (0.11) GPa, respectively. With compliance mode, the measured stress correlated with the axial shrinkage strain of composite; while without compliance the elastic modulus of materials played a significant role in the stress measurement.
Chimera ; Collodion ; Compliance ; Contracts ; Displacement (Psychology) ; Elastic Modulus ; Light ; Polymerization ; Polymers ; Resins, Synthetic ; Sprains and Strains

PURPOSE: To evaluate the effect of light-curing on the immediate and delayed micro-shear bond strength (microSBS) between yttria-tetragonal zirconia polycrystal (Y-TZP) ceramics and RelyX Ultimate when using Single Bond Universal (SBU). MATERIALS AND METHODS: Y-TZP ceramic specimens were ground with #600-grit SiC paper. SBU was applied and RelyX Ultimate was mixed and placed on the Y-TZP surface. The specimens were divided into three groups depending on whether light curing was done after adhesive (SBU) and resin cement application: uncured after adhesive and uncured after resin cement application (UU); uncured after adhesive, but light cured after resin cement (UC); and light cured after adhesive and light cured resin cement (CC). The three groups were further divided depending on the timing of microSBS testing: immediate at 24 hours (UUI, UCI, CCI) and delayed at 4 weeks (UUD, UCD, CCD). microSBS was statistically analyzed using one-way ANOVA and Student-Newman-Keuls multiple comparison test (P<0.05). The surface of the fractured Y-TZP specimens was analyzed under a scanning electron microscope (SEM). RESULT: At 24 hours, microSBS of UUI group (8.60+/-2.06 MPa) was significantly lower than UCI group (25.71+/-4.48 MPa) and CCI group (29.54+/-3.62 MPa) (P<0.05). There was not any significant difference between UCI and CCI group (P>0.05). At 4 weeks, microSBS of UUD group (24.43+/-2.88 MPa) had significantly increased over time compared to UUI group (P<0.05). The SEM results showed mixed failure in UCI and CCI group, while UUI group showed adhesive failure. CONCLUSION: Light-curing of universal adhesive before or after application of RelyX Ultimate resin cement significantly improved the immediate microSBS of resin cement to air-abrasion treated Y-TZP surface. After 4 weeks, the delayed microSBS of the non-light curing group significantly improved to the level of light-cured groups.
Adhesives* ; Ceramics* ; Resin Cements

PURPOSE: This study was conducted to evaluate the association between serum 25-hydroxyvitamin D (25(OH)D) levels and dental caries experience in Korean adolescents based on the 2010 ~ 2014 Korean National Health and Nutrition Examination Surveys. METHODS: The study subjects were 2,655 Korean adolescents aged 10 to 18 years. Subjects were classified into four groups according to their serum 25(OH)D levels. We used logistic regression to evaluate the relationship between vitamin D and for dental caries experience after adjusting for age, household income level, recipient of basic livelihood, tooth brushing and visiting dental clinics. RESULT: Multiple logistic regression analysis showed that serum 25(OH)D insufficiency (20 ng/mL≤25(OH)D<30 ng/mL) was associated with increased odd ratios (ORs) for dental caries experience in boys (OR = 2.577, 95% CI = 1.013–6.557), compared with serum 25(OH)D sufficiency (25(OH)D≥30.0 ng/mL). CONCLUSION: The serum 25(OH)D levels were found to be related to risk of dental caries experience in Korean adolescent boys.
Adolescent* ; Dental Caries* ; Dental Clinics ; Family Characteristics ; Humans ; Logistic Models ; Tooth ; Vitamin D

Since the introduction of restorative dental composites, their physical properties have been significantly improved. However, polymerization shrinkage is still a major drawback. Many efforts have been made to develop a low shrinking composite, and silorane-based composites have recently been introduced into the market. In addition, many different methods have been developed to measure the polymerization shrinkage. In this study, we developed a new method to measure the linear polymerization shrinkage of composites without direct contact to a specimen using a particle tracking method with computer vision. The shrinkage kinetics of a commercial silorane-based composite (P90) and two conventional methacrylate-based composites (Z250 and Z350) were investigated and compared. The results were as follows: 1. The linear shrinkage of composites was 0.33-1.41%. Shrinkage was lowest for the silorane-based (P90) composite, and highest for the flowable Z350 composite. 2. The new instrument was able to measure the true linear shrinkage of composites in real time without sensitivity to the specimen preparation and geometry.
Kinetics ; Polymerization ; Polymers ; Silorane Resins ; Track and Field ; Vision, Ocular

PURPOSE: The study aimed to determine the personality types of the graduate students in Seoul National University School of Dentistry (SNU SD) and analyze the specific personal types that were linked to their performance in problem-based learning (PBL). METHODS: A total of 263 graduate students in SNU SD from 2011 to 2013, participated in PBL and completed the Myers-Briggs Type Indicator (MBTI) GS form, which was analyzed statistically to determine whether their MBTI personality types were independent of their PBL performance. In particular, MBTI types were regressed on evaluation subcategories, including tutor evaluation and oral test. RESULTS: ESTJ (20.9%) and ISTJ (18.6%) were the most common MBTI personality types in dental graduate students. Compared with males, female students performed significantly better on the PBL. Judging was the most notable type in PBL performance, with its J-P index being statistically significant. CONCLUSION: PBL is implemented, based on the perspective of student-centered education. Accordingly, the types of personality that usually matriculate in dental school should be monitored, and a student-centered approach to dental education should be adopted.
Dentistry ; Education ; Education, Dental ; Female ; Humans ; Male ; Personality Inventory ; Problem-Based Learning* ; Schools, Dental ; Seoul

This study investigated the effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resins. The linear polymerization shrinkage of each composite was measured using the custom-made linometer along with the light shutter specially devised to block the light at the previously determined interval. Samples were divided into 4 groups by light curing method; Group 1) continuous light (60s with light on); Group 2) intermittent light (cycles of 3s with 2s light on & 1s with light off for 90s); Group 3) intermittent light (cycles of 2s with 1s light on & 1s with light off for 120s); Group 4) intermittent light (cycles of 3s with 1s light on & 2s with light off for 180s). The amount of linear polymerization shrinkage was measured and its maximum rate (Rmax) and peak time (PT) in the first 15 seconds were calculated. For the measurement of cuspal deflection of teeth, MOD cavities were prepared in 10 extracted maxillary premolars. Reduction in the intercuspal distance was measured by the custom-made cuspal deflection measuring machine. ANOVA analysis was used for the comparison of the light curing groups and t-test was used to determine significant difference between the composite resins. Pyramid showed the greater amount of polymerization shrinkage than Heliomolar (p < 0.05). There was no significant difference in the linear polymerization shrinkage among the groups. The Rmax was group 4 < 3, 2 < 1 in Heliomolar and group 3 < 4 < 2, 1 in Pyramid (p < 0.05). Pyramid demonstrated greater cuspal deflection than Heliomolar. The cuspal deflection in Heliomolar was group 4 < 3 < 2, 1 and group 4, 3 < 2, 1 in Pyramid (p < 0.05). It was concluded that the reduced rate of polymerization shrinkage by intermittent polymerization can help to decrease the cuspal deflection.
Acrylic Resins ; Bicuspid ; Composite Resins ; Light ; Polymerization ; Polymers ; Polyurethanes ; Tooth

PURPOSE: The current study was designed to investigate the relationship of dietary calcium and riboflavin and their main dietary source (milk and dairy products) with the risk of periodontitis using data from 2007 to 2010 Korea National Health and Nutrition Examination Surveys. METHODS: A total of 1,690 adults aged > or = 40 years were included. We used results of dental examination regarding all sextant information on probing depth of at least two index teeth, nutritional assessment by a single 24-hour dietary recall, and demographic and medical information. The periodontitis group was defined as those who had 3-4 points, and the normal group was defined as those who had 0 points of Community Periodontal Index at all locations of six examination sites using a probe. RESULTS: Using multiple logistic regression analysis, after adjustment for age, body mass index, energy intake, income, smoking, and alcohol drinking, we found an inverse relationship between consumption of dairy products and risk for periodontitis (OR: 0.465, 95% CI: 0.224-0.964) and between dietary riboflavin intake more than the estimated average requirements and risk for periodontitis (OR: 0.535, 95% CI: 0.300-0.954) in males. CONCLUSION: Adequate intake of milk dairy products and riboflavin may be recommended for prevention of periodontitis in the Korean male population.
Adult* ; Alcohol Drinking ; Body Mass Index ; Calcium* ; Calcium, Dietary ; Dairy Products* ; Energy Intake ; Humans ; Korea ; Logistic Models ; Male ; Milk* ; Nutrition Assessment ; Periodontal Index ; Periodontitis* ; Riboflavin* ; Smoke ; Smoking ; Tooth

The aim of this study was to compare the effects of anticurvature filing with stainless steel k-file versus nickel-titanium ProFile in the shaping of mesial root canals of extracted mandibular molars. A total of 60 canals from 30 mesial roots of mandibular molar teeth were randomly assigned to three groups with n=20 each. They were prepared with different instruments and methods: The first group with stainless steel k-file and circumferential filing, the second with precurved stainless steel k-file and anticurvature filing and the third with ProFile (.06 taper) and anticurvature filing. Using a micro-computed tomography system (skyscan-1076, SKYSCAN, Antwerpen, Belgium), pre-and post-operative specimens were scanned. Subsequently, canal images were superimposed and changes in root dentin thickness were measured at distal side (danger zone) of the canal. The data was analyzed using a one-way ANOVA and the comparison of means was conducted using a post hoc multiple comparison Tukey test. There were significant differences in the change of root dentin thickness at the 7.5~8.5mm level between group 1 and 2, 3.5~6mm level between group 1 and 3 and 3.5~6mm level between group 2 and 3(n=20, P<0.05).
Dental Pulp Cavity ; Dentin ; Molar ; Stainless Steel ; Tooth