Ji Hwan Kim

Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains.

PURPOSE This study examined the wear resistance of human enamel and feldspathic porcelain after simulated mastication against 3 zirconia ceramics, heat-pressed ceramic and conventional feldspathic porcelain. MATERIALS AND METHODS Human teeth and feldspathic porcelain cusp were tested against ceramic discs. 5 brands were tested - 3 monolithic zirconia, Prettau, Lava, and Rainbow, one lithium disilicate, IPS e.max Press, and one feldspathic porcelain, Vita-Omega 900. The surface was polished using a 600 grit and 1200 grit SiC paper. Each group was loaded for 300,000 cycles in a chewing simulator. The wear resistance was analyzed by measuring the volume of substance lost. The wear surfaces were observed by scanning electron microscopy to determine the wear characteristics. RESULTS Vita-Omega 900 led to the greatest amount of enamel wears followed by IPS e.max Press, Prettau, Lava and Rainbow. There was a significant difference between Vita-Omega 900 and IPS e.max Press (p<0.05). The wear values for human enamel were significantly greater than those for feldspathic porcelain, regardless of the surface roughness of the ceramic specimens (p<0.05). CONCLUSION The wear behaviour of human enamel and feldspathic porcelain varies according to the type of substrate materials. On the other hand, 3 zirconia ceramics caused less wear in the abrader than the conventional ceramic. CLINICAL SIGNIFICANCE Dental professionals should be aware of the wear effect of dental restorations on the opposing teeth or restorations. The amount of enamel wear was highest in feldspathic porcelains whereas zirconia ceramics caused less wear on the opposing teeth.

An evaluation of marginal fit of three-unit fixed dental prostheses fabricated by direct metal laser sintering system.

OBJECTIVES This in vitro study aimed to evaluate and compare marginal fit of three-unit fixed dental prostheses (FDPs) fabricated using a newly developed direct metal laser sintering (DMLS) system with that of three-unit FDPs by a conventional lost wax technique (LW) method. METHODS Ten cobalt-chromium alloy three-unit FDPs using DMLS system and another ten nickel-chromium alloy FDPs using LW method were fabricated. Marginal fit was examined using a light-body silicone. After setting, the silicon film was cut into four parts and the thickness of silicon layer was measured at 160× magnification using a digital microscope to measure absolute marginal discrepancy (AMD), marginal gap (MG) and internal gap (IG). A repeated measure ANOVA for statistical analysis was performed using the SPSS statistical package version 12.0 (α=0.05). RESULTS The mean values of AMD, MG, and IG were significantly larger in the DMLS group than in the LW group (p<0.001). Means of AMD, MG and IG in the first molars were 83.3, 80.0, and 82.0μm in the LW group; and 128.0, 112.0, and 159.5μm in the DMLS group, respectively. No significant difference between measurements for premolars and molars was found (p>0.05). SIGNIFICANCE The marginal fit of the DMLS system appeared significantly inferior compared to that of the conventional LW method and slightly larger than the acceptable range. For clinical application further improvement of DMLS system may be required.

Effects of the sintering conditions of dental zirconia ceramics on the grain size and translucency

PURPOSE This study aimed to identify the effects of the sintering conditions of dental zirconia on the grain size and translucency. MATERIALS AND METHODS Ten specimens of each of two commercial brands of zirconia (Lava and KaVo) were made and sintered under five different conditions. Microwave sintering (MS) and conventional sintering (CS) methods were used to fabricate zirconia specimens. The dwelling time was 20 minutes for MS and 20 minutes, 2, 10, and 40 hours for CS. The density and the grain size of the sintered zirconia blocks were measured. Total transmission measurements were taken using a spectrophotometer. Two-way analysis of variance model was used for the analysis and performed at a type-one error rate of 0.05. RESULTS There was no significant difference in density between brands and sintering conditions. The mean grain size increased according to sintering conditions as follows: MS-20 min, CS-20 min, CS-2 hr, CS-10 hr, and CS-40 hr for both brands. The mean grain size ranged from 347-1,512 nm for Lava and 373-1,481 nm for KaVo. The mean light transmittance values of Lava and KaVo were 28.39-34.48% and 28.09-30.50%, respectively. CONCLUSION Different sintering conditions resulted in differences in grain size and light transmittance. To obtain more translucent dental zirconia restorations, shorter sintering times should be considered.

Evaluation of the marginal and internal gap of metal-ceramic crown fabricated with a selective laser sintering technology: two- and three-dimensional replica techniques

PURPOSE One of the most important factors in evaluating the quality of fixed dental prostheses (FDPs) is their gap. The purpose of this study was to compare the marginal and internal gap of two different metal-ceramic crowns, casting and selective laser sintering (SLS), before and after porcelain firing. Furthermore, this study evaluated whether metal-ceramic crowns made using the SLS have the same clinical acceptability as crowns made by the traditional casting. MATERIALS AND METHODS The 10 study models were produced using stone. The 20 specimens were produced using the casting and the SLS methods; 10 samples were made in each group. After the core gap measurements, 10 metal-ceramic crowns in each group were finished using the conventional technique of firing porcelain. The gap of the metal-ceramic crowns was measured. The marginal and internal gaps were measured by two-dimensional and three-dimensional replica techniques, respectively. The Wilcoxon signed-rank test, the Wilcoxon rank-sum test and nonparametric ANCOVA were used for statistical analysis (α=.05). RESULTS In both groups, the gap increased after completion of the metal-ceramic crown compared to the core. In all measured areas, the gap of the metal cores and metal-ceramic crowns produced by the SLS was greater than that of the metal cores and metal-ceramic crowns produced using the casting. Statistically significant differences were found between cast and SLS (metal cores and metal-ceramic crown). CONCLUSION Although the gap of the FDPs produced by the SLS was greater than that of the FDPs produced by the conventional casting in all measured areas, none exceeded the clinically acceptable range.

Accuracy and precision of polyurethane dental arch models fabricated using a three-dimensional subtractive rapid prototyping method with an intraoral scanning technique

Objective This study aimed to evaluate the accuracy and precision of polyurethane (PUT) dental arch models fabricated using a three-dimensional (3D) subtractive rapid prototyping (RP) method with an intraoral scanning technique by comparing linear measurements obtained from PUT models and conventional plaster models. Methods Ten plaster models were duplicated using a selected standard master model and conventional impression, and 10 PUT models were duplicated using the 3D subtractive RP technique with an oral scanner. Six linear measurements were evaluated in terms of x, y, and z-axes using a non-contact white light scanner. Accuracy was assessed using mean differences between two measurements, and precision was examined using four quantitative methods and the Bland-Altman graphical method. Repeatability was evaluated in terms of intra-examiner variability, and reproducibility was assessed in terms of inter-examiner and inter-method variability. Results The mean difference between plaster models and PUT models ranged from 0.07 mm to 0.33 mm. Relative measurement errors ranged from 2.2% to 7.6% and intraclass correlation coefficients ranged from 0.93 to 0.96, when comparing plaster models and PUT models. The Bland-Altman plot showed good agreement. Conclusions The accuracy and precision of PUT dental models for evaluating the performance of oral scanner and subtractive RP technology was acceptable. Because of the recent improvements in block material and computerized numeric control milling machines, the subtractive RP method may be a good choice for dental arch models.

White light scanner-based repeatability of 3-dimensional digitizing of silicon rubber abutment teeth impressions.

PURPOSE The aim of this study was to evaluate the repeatability of the digitizing of silicon rubber impressions of abutment teeth by using a white light scanner and compare differences in repeatability between different abutment teeth types. MATERIALS AND METHODS Silicon rubber impressions of a canine, premolar, and molar tooth were each digitized 8 times using a white light scanner, and 3D surface models were created using the point clouds. The size of any discrepancy between each model and the corresponding reference tooth were measured, and the distribution of these values was analyzed by an inspection software (PowerInspect 2012, Delcamplc., Birmingham, UK). Absolute values of discrepancies were analyzed by the Kruskal-Wallis test and multiple comparisons (α=.05). RESULTS The discrepancy between the impressions for the canine, premolar, and molar teeth were 6.3 µm (95% confidence interval [CI], 5.4-7.2), 6.4 µm (95% CI, 5.3-7.6), and 8.9 µm (95% CI, 8.2-9.5), respectively. The discrepancy of the molar tooth impression was significantly higher than that of other tooth types. The largest variation (as mean [SD]) in discrepancies was seen in the premolar tooth impression scans: 26.7 µm (95% CI, 19.7-33.8); followed by canine and molar teeth impressions, 16.3 µm (95% CI, 15.3-17.3), and 14.0 µm (95% CI, 12.3-15.7), respectively. CONCLUSION The repeatability of the digitizing abutment teeths silicon rubber impressions by using a white light scanner was improved compared to that with a laser scanner, showing only a low mean discrepancy between 6.3 µm and 8.9 µm, which was in an clinically acceptable range. Premolar impression with a long and narrow shape showed a significantly larger discrepancy than canine and molar impressions. Further work is needed to increase the digitizing performance of the white light scanner for deep and slender impressions.

Validation of a Korean version of the Child Oral Health Impact Profile (COHIP) among 8- to 15-year-old school children

OBJECTIVES The purpose of this study was to assess reliability, discriminant validity, and convergent validity of the Oral Health Impact Profile (COHIP) Korean version in a representative community sample of 8- to 15-year-old Korean children. METHODS A Korean version of COHIP was developed according to the standard procedure of cross-cultural adaptation of self-reported instruments. A representative community sample of 2236 schoolchildren was selected by cluster sampling method. RESULTS Mean age of the participants was 11.8 years. Mean and median of the overall COHIP score were 103.3 (SD 13.3) and 106, respectively. Internal reliability and retest reliability were excellent with Chronbachs alpha 0.88 and intraclass correlation coefficient 0.88. Face validity was confirmed with 98% of participants reporting the COHIP questionnaire was easy to answer. Nonclinical factors such as self-rated oral health or satisfaction with oral health were significantly related with overall COHIP score and five subscale scores (P < 0.001) in a consistent manner. Children with carious permanent teeth and with orthodontic treatment need had highly significantly lower overall COHIP score (P < 0.01). CONCLUSION The Korean version of the COHIP was successfully developed. The internal reliability, retest reliability, face validity, discriminant validity, and convergent validity of the COHIP Korean version were confirmed.

Evaluation of different approaches for using a laser scanner in digitization of dental impressions

PURPOSE This study aimed to investigate the potential clinical application of digitized silicone rubber impressions by comparing the accuracy of zirconia 3-unit fixed partial dentures (FPDs) fabricated from 2 types of data (working model and impression) obtained from a laser scanner. MATERIALS AND METHODS Ten working models and impressions were prepared with epoxy resin and vinyl polysiloxane, respectively. Based on the data obtained from the laser scanner (D-700; 3Shape A/S, Copenhagen, Denmark), a total of 20 zirconia frameworks were prepared using a dental CAD/CAM system (DentalDesigner; 3shape A/S, Copenhagen, Denmark / Ener-mill, Dentaim, Seoul, Korea). The silicone replicas were sectioned into four pieces to evaluate the framework fit. The replicas were imaged using a digital microscope, and the fit of the reference points (P1, P2, P3, P4, P5, P6, and P7) were measured using the program in the device. Measured discrepancies were divided into 5 categories of gaps (MG, CG, AWG, AOTG, OG). Data were analyzed with Students t-test (α=0.05), repeated measures ANOVA and two-way ANOVA (α=0.05). RESULTS The mean gap of the zirconia framework prepared from the working models presented a narrower discrepancy than the frameworks fabricated from the impression bodies. The mean of the total gap in premolars (P=.003) and molars (P=.002) exhibited a statistical difference between two groups. CONCLUSION The mean gap dimensions of each category showed statistically significant difference. Nonetheless, the digitized impression bodies obtained with a laser scanner were applicable to clinical settings, considering the clinically acceptable marginal fit (120 µm).

Research about Tooth Whitening and Bacteria Sticking Capability with Using Dentifrice Including Nano-Hydroxyapatite, Sodium Metaphosphate

Hydroxyapatite has high affinity rate with organic substance in an oral cavity, therefore lately nano-sized hydroxyapatite is extensively researched to increase affinity to tooth and remineralization. The objective of this research is indirectly to investigate the effect of nanohydroxyapatite on remineralization using valuation about whiteness and bacterial contamination of the bovine tooth. We have designed in vitro test for this purpose. The bovine teeth are sliced into human teeth size then the baseline whiteness of total 60 teeth is measured and assigned into 3 groups by cross-matching according to the whiteness. These samples were embedded into resin mold and underwent mechanical brushing during fixed schedule. The whiteness and bacterial contamination of teeth are measured and compared among 3 groups. Each dentifrice used in the experiment is composed of B.S.I group (30% Calcium Carbonate, precipitated-CaCo3) with abrasion rate of 100, Test Ⅰgroup (15% Sodium Metaphosphate, insoluble-NaPo3), Test Ⅱ group (15% Nano-hydroxyapate-Ca10(PO4)6(OH)2. After 20,000 strokes of mechanical brushing with each group sample teeth whiteness is measured for 2nd time and then the sample teeth were submerged into the same solution with oral bacteria for 10 days. The teeth whiteness is measured again for 3rd time and the bacteria from the surface of teeth are cultivated on agar badge for 3 days. We have compared with average of whiteness before and after test in group and each other 3 group. The whiteness of teeth was maintained in test group II, however in other group the whiteness achieved through brushing was lost. Also, Group II had the smallest area of bacterial colony on agar badge (p<0.01). It is concluded that the dentifrice including the nano-hydroxyapatite is replaced with the organic substance in enamel resulting the increase in whiteness and the resistance to bacterial colonization, which leads to the increase the enamel remineralization in teeth and result to decrease in caries susceptibility.

ANALYSIS AND INVESTIGATION OF CHEMICAL STABILITY ON PHENOLIC COMPOUNDS IN ZANTHOXYLUM SCHINIFOLIUM-CONTAINING DENTIFRICES

Chromatographic properties and chemical stability of 12 kinds of phenolic compounds Z. schinifolium were investigated and analyzed to use as an antioxidant substance in dentifrices. Twelve compounds were completely separated under 0.01% phosphoric acid-acetonitrile gradient condition at 20°C and detected by photodiode array detector. Each compound showed good linearity at optimized wavelength, and showed good precision and accuracy in dentifrices. Using this analytical method, phenolic compounds in Z. schinifolium fraction and dentifrices were successfully determined. Caffeic acid, quercetin, and xanthoxylin decomposed in aqueous solution, and other compounds were preserved over 94%. It was better to store phenolic compounds under weak acidic conditions (<pH 6) to prevent the decomposition of phenolic compounds. Mixed in dentifrices, about half of the total compounds remained for 45 d, but the preservation rate (%) showed big differences between each compound. Each fraction of Z. schinifolium -containing dentifrice was manufactured and analyzed. In Z. schinifolium dentifrices, 44% of phenolic compounds remained after 2 mo.