• Restorative Dentistry and Endodontics
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• v.34 no.2
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• pp.87-94
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• 2009

The purpose of this study was to assess the current materials, methods and difficulties according to the year of licence and educational background of Korean dentists in Class II direct composite resin restorations. Total 17 questions were included in the questionnaire. Questions were broadly divided into two parts: first. operator's information. and second. the materials and methods used in Class II posterior composite restoration. The questionnaire was sent to dentists enrolled in Korean Dental Association via e-mail. Total 12,193 e-mails were distributed to dentists. 2,612 e-mails were opened, and 840 mails (32.2%) were received from respondents. The data was statically analyzed by chi-square test using SPSS(v. 12.0.1, SPSS Inc. Chicago, IL, USA). Male dentists among respondents was 79%. 60.3% of the respondents acquired their licences recently (1998-2007), and 77% practiced in private offices. 83.4% have acquired their knowledge through school lectures, conferences and seminars. For the Class II restorations, gold inlays were preferred by 65.7% of respondents, while direct composite resin restorations were used by 12.1 % amalgam users were only 4.4% of respondents. For the restorative technique, 74.4% of respondents didn't use rubber dam as needed. For the matrix. mylar strip (53.4%), metal matrix (33.8%) and Palodent system (6.5%) were used. 99.6% of respondents restored the Class II cavity by incremental layering. Obtaining of the tight interproximal contact was considered as the most difficult procedure (57.2%) followed by field isolation (21 %). Among various bonding systems, 22.6% of respondents preferred SE Bond and 20.2% used Single Bond. Z-250 was used most frequently among a variety of composite resins.

• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.4
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• pp.297-305
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• 2018

Purpose: This study aimed to analyze stress distribution and maximum von Mises stress generated in intracoronal restorations and in tooth structures of mandibular molars with various types of cavity designs and materials. Materials and Methods: Three-dimensional solid models of mandible molar such as O inlay cavity with composite and gold (OR-C, OG-C), MO inlay cavity with composite and gold (MR-C, MG-C), and minimal invasive cavity on occlusal and proximal surfaces (OR-M, MR-M) were designed. To simulate masticatory force, static axial load with total force of 200 N was applied on the tooth at 10 occlusal contact points. A finite element analysis was performed to predict stress distribution generated by occlusal loading. Results: Restorations with minimal cavity design generated significantly lower values of von Mises stress (OR-M model: 26.8 MPa; MR-M model: 72.7 MPa) compared to those with conventional cavity design (341.9 MPa to 397.2 MPa). In tooth structure, magnitudes of maximum von Mises stresses were similar among models with conventional design (372.8 - 412.9 MPa) and models with minimal cavity design (361.1 - 384.4 MPa). Conclusion: Minimal invasive models generated smaller maximum von Mises stresses within restorations. Within the enamel, similar maximum von Mises stresses were observed for models with minimal cavity design and those with conventional design.

• The korean journal of orthodontics
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• v.31 no.2 s.85
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• pp.225-236
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• 2001

It is widely accepted that the shape and structure of bone are closely related to the activity of attached muscle. Numerous clinical and animal experimental studies indicated the significant effects of masticatory muscle function on maxillofacial morphology. Recently, the development of ultrasonography has spread throughout different fields of medicine. In the clinical examinations, ultrasonography is a convenient, inexpensive technique to apply with accurate and reliable results. The aim of this study is to assess the thickness of the masseter muscle and its correlation to maxillofacial skeleton by examining 35 male and 15 female dental students at Kangnung National University. The masseter muscle thickness of the subjects were measured by ultrasonographic scanning with a 7.5MHz linear probe, and their maxillofacial morphology were investigated by lateral cephalometric radiographs. The relationship between the masseter muscle thickness and maxillofacial morphology of normal adult was statistically analyzed, and the following results were obtained. 1. The average thickness of male masseter muscle was 13.8${\pm}$1.71mm in the relaxed state and 14.8${\pm}$1.77mm at maximal clenching state, while that of female was 11.6${\pm}$1.58mm and 12.4${\pm}$1.47mm, respectively. Ethnic difference in thickness of the masseter muscle and maxillofacial skeleton was found when the results of many researchers were compared with those of this study. 2. The thickness of the masseter muscle in both sexes increased significantly at maximal clenching state than in relaxed state(P<0.05). 3. The masseter muscle thickness of male was greater than that of female both in the relaxed state and maximal clenching states(P<0.05). 4. In males, the thickness of the masseter muscle was negatively correlated with the mandibular plane angle and positively correlated with the mandibular ramus height and anterior cranial base length(P<0.05). It may suggest that the male with thicker masseter muscle has smaller facial divergence. 5. No significant correlation was found between the masseter muscle thickness and maxillofacial morphology in females(P<0.05). Therefore, these data suggest that ultrasonography can add valuable information to the conventional examinations of masseter muscle function.

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.2
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• pp.377-398
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• 1999

Calcium fluoride, created by topical fluoride application, is the reservoir for fluoride ion regulated by pH in the oral environment. Therefore, the amount and the maintenance of calcium fluoride have an important role in preventing dental caries. The aim of this study is to evaluate the effect of Nd:YAG laser irradiation on the generation of calcium fluoride and the acid resistance of tooth enamel. The bovine anterior permanent teeth were prepared (n=276), and divided into following groups : no treatment (control) fluoride application alone, laser irradiation alone, laser irradiation after fluoride application, and fluoride application after laser irradiation. And each group was subdivided based on the application time of 1.23% acidulated phosphate fluoride (APF) (5 min and 30 min) and the irradiation energy of Nd:YAG laser ($20J/cm^2\;and\;40J/cm^2$). In case of fluoride application, each group was divided according to KOH treatment. Twenty three treatment conditions were made for this experiment and twelve specimens were assigned to each treatment condition. In each treatment condition, ten specimens were used for chemical analysis and two specimens were observed under SEM. In groups without treating KOH, fluoride content and the depth of enamel dissolved were measured using enamel biopsy technique. In groups with treating KOH, the amount of calcium fluoride was measured by the treatment with 1 M KOH for 24 hours and enamel biopsy was performed after KOH treatment. The results were analyzed by the fluoride content and the depth of enamel dissolved by enamel biopsy, amount and thickness of calcium fluoride, and the surface structures of enamel. The results are as follows: 1. In groups without treating KOH, the fluoride content of removed enamel showed a positive relationship with the energy density of laser when the laser irradiated before fluoride application 2. In groups without treating KOH, the depth of enamel dissolved decreased more with the combined laser and fluoride treatment than with laser or fluoride treatment, except for the case of $20J/cm^2$ laser irradiation after 5 minute fluoride application (p<0.05). 3. The amount of calcium fluoride did not increased by laser treatment with no statistical significance(p>0.05). 4. The particle size of calcium fluoride increased in case of fluoride treatment after laser irradiation, compared with fluoride application alone. In case of laser treatment after fluoride application, the particle size of calcium fluoride increased and some of the particles fused as well. 5. There were no significant differences in the fluoride content of dissolved enamel between groups without treating KOH and control group, except for the case of laser irradiation after treatment of APF for 30 minutes (p>0.05). 6. In groups with treating KOH, depth of removed enamel in the groups of combined treatment with laser and fluoride was shallower than that in fluoride application groups (p<0.05). 7. In groups without treating KOH, the relationship between fluoride content and the depth of enamel dissolved showed more negative (Spearman correlation coefficient: -0.6281) than in groups with treating KOH (Spearman correlation coefficient: -0.3792). The greater amount of calcium fluoride could be found in case where there was a significant differences of the depth of enamel dissolved between groups with and without treating KOH. From these results, it can be concluded that laser seems to be a little effects on the amount of calcium fluoride formation, but has some effect on the lowering the solubility of calcium fluoride. As the combined treatment of laser and fluoride application showed more effective acid-resistant property, more extended recall period for fluoride application can be achieved with this combined treatment in the clinic.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.2
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• pp.108-118
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• 2009

Statement of problem: Volume stability, microstructure reproducibility and fluidity along with compatibility with dental stone must be in consideration in order to use tissue conditioner as a material for functional impression. There are few studies concerning the influence of time factor in oral condition on surface roughness of the stone and optimal retention period in the oral cavity considering such changes in surface roughness. Purpose: The purpose of this study was to find out the influence of various kinds of tissue conditioner, its powder/liquid ratio and immersion time on surface roughness of the stone. Material and methods: Materials used in this study were the three kinds of tissue conditioners(Coe-Comfort, Visco-Gel, Soft-Liner) and were grouped into three: group R-mixed with standard powder/liquid ratio that was recommended by the manufacturers, group M-mixed with 20% more powder, group L-mixed with 20% less powder. Specimens were made with the size of 20 mm diameter and 2 mm width. Each tissue conditioner specimens were subdivided into 5 groups according to the immersion time(0 hour, 1 day, 3 days, 5 days, 7 days), completely immersed into artificial saliva and were stored under $37^{\circ}C$. Specimens of which the given immersion time elapsed were taken out and were poured with improved stone, making the stone specimens. Surface roughness of the stone specimens was measured by a profilometer. Results: Within the limitation of this study, the following results were drawn. 1. Major influencing factor on surface roughness of the stone model made from tissue conditioner was the retention period(contribution ratio($\rho$)=62.86%, P<.05) of the tissue conditioner in oral cavity to make functional impression. 2. In case of Coe-Comfort, higher mean surface roughness value of the stone model with statistical significance was observed compared to that of Soft-Liner and Visco-Gel as immersion time changes(P<.05). 3. In case of group L(less), higher mean surface roughness value of the stone model with statistical significance was observed compared to that of R(recommended) and M(more) group as immersion time changes(P<.05). Conclusion: We may conclude that as the retention period of time in oral cavity influences surface roughness of the stone model the most and as the kind of tissue conditioner and its P/L ratio may influence also, clinician should well understand the optimal retention period in oral cavity and choose the right tissue conditioner for the functional impression, thus making the functional impression with tissue conditioner usefully.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.2
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• pp.148-156
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• 2008

Statement of problems: Self-etch adhesives exhibit some clinical benefits such as ease of manipulation and reduced technique-sensitivity. Nevertheless, some concern remains regarding the bonding effectiveness of self-etch adhesives to enamel, in particular when so-called 'mild' self-etch adhesives are employed. This study compared the microtensile bond strengths to ground enamel of the two-step self-etch adhesive Clearfil SE Bond (Kuraray) to the three-step etch-and- rinse adhesive Scotchbond Multi-Purpose (3M ESPE) and the one-step self-etch adhesive iBond (Heraeus Kulzer). Purpose: The purpose of this study was to determine the effect of a preceding phosphoric acid conditioning step on the bonding effectiveness of a two-step self-etch adhesive to ground enamel. Material and methods: The two-step self-etch adhesive Clearfil SE Bond non-etch group, Clearfil SE Bond etch group with prior 35% phosphoric acid etching, and the one-step self-etch adhesive iBond group were used as experimental groups. The three-step etch-and-rinse adhesive Scotchbond Multi-Purpose was used as a control group. The facial surfaces of bovine incisors were divided in four equal parts cruciformly, and randomly distributed into each group. The facial surface of each incisor was ground with 800-grit silicon carbide paper. Each adhesive group was applied according to the manufacturer's instructions to ground enamel, after which the surface was built up using Light-Core (Bisco). After storage in distilled water at $37^{\circ}C$ for 1 week, the restored teeth were sectioned into enamel beams approximately 0.8*0.8mm in cross section using a low speed precision diamond saw (TOPMET Metsaw-LS). After storage in distilled water at $37^{\circ}C$ for 1 month, 3 months, microtensile bond strength evaluations were performed using microspecimens. The microtensile bond strength (MPa) was derived by dividing the imposed force (N) at time of fracture by the bond area ($mm^2$). The mode of failure at the interface was determined with a microscope (Microscope-B nocular, Nikon). The data of microtensile bond strength were statistically analyzed using a one-way ANOVA, followed by Least Significant Difference Post Hoc Test at a significance level of 5%. Results: The mean microtensile bond strength after 1 month of storage showed no statistically significant difference between all adhesive groups (P>0.05). After 3 months of storage, adhesion to ground enamel of iBond was not significantly different from Clearfil SE Bond etch (P>>0.05), while Clearfil SE Bond non-etch and Scotchbond Multi-Purpose demonstrated significantly lower bond strengths (P<0.05), with no significant differences between the two adhesives. Conclusion: In this study the microtensile bond strength to ground enamel of two-step self-etch adhesive Clearfil SE Bond was not significantly different from three-step etch-and-rinse adhesive Scotchbond Multi-Purpose, and prior etching with 35% phosphoric acid significantly increased the bonding effectiveness of Clearfil SE Bond to enamel at 3 months.