In this study, the changes in the degree of conversion (DC) and the microtensile bond strength (MTBS) of self-etching adhesives to dentin was investigated according to the time after curing. The MTBS of Single Bond (SB, 3M ESPE, USA), Clearfil SE Bond (SE, Kuraray, Japan), Xeno-III (XIII, Dentsply, Germany), and Adper Prompt (AP, 3M ESPE, USA) were measured at 48h, at 1 week and after thermocycling for 5,000 cycles between 5℃ and 55℃. The DC of the adhesives were measured immediately, at 48h and at 7 days after curing using a Fourier Transform Infra-red Spectrometer. The fractured surfaces were also evaluated with scanning electron microscope. The MTBS and DC were significantly increased with time and there was an interaction between the variables of time and material (MTBS, 2-way ANOVA, p = 0.018; DC, Repeated Measures ANOVA, p < 0.001). The low DC was suggested as a cause of the low MTBS of self-etching adhesives, XIII and AP, but the increase in the MTBS of SE and AP after 48h could not be related with the changes in the DC. The microscopic maturation of the adhesive layer might be considered as the cause of increasing bond strength.

The objective of this study was to investigate the effects of various occlusal loads on the stress distribution of the buccal cervical region of a normal maxillary second premolar, using a three dimensional finite element analysis (3D FEA).

After 3D FE modeling of maxillary second premolar, a static load of 500N of three load cases was applied. Stress analysis was performed using ANSYS (Swanson Analysis Systems, Inc., Houston, USA). The maximum principal stresses and minimum principal stresses were sampled at thirteen nodal points in the buccal cervical enamel for each four horizontal planes, 1.0 mm above CEJ, 0.5 mm above CEJ, CEJ, 0.5 mm under CEJ.

The results were as follows

1. The peak stress was seen at the cervical enamel surface of the mesiobuccal line angle area, asymmetrically.

2. The values of compressive stresses were within the range of the failure stress of enamel. But the values of tensile stresses exceeded the range of the failure stress of enamel.

3. The tensile stresses from the perpendicular load at the buccal incline of palatal cusp may be shown to be the primary etiological factors of the NCCLs.

This study was aimed to elucidate the biological function of OD314 (Apin protein), which is related toameloblast differentiation and amelogenesis. Apin protein, calcifying epithelial odontogenic (pindborg) tumors (CEOTs)-associated amyloid, were isolated from CEOTs, and has similar nucleotide sequences to OD314. We examined expression of the OD314 mRNA using in-situ hybridization during tooth development in mice. Expression of OD314 and several enamel matrix proteins were examined in the cultured ameloblast cell line up to 28 days by reverse transcription-polymerase chain reaction (RT-PCR) amplification. After inactivation and over-expression of the OD314 gene in ameloblast cell lines using U6 vector-driven RNA interference and CMV-OD314 construct, RT-PCR were performed to evaluate the effect of the OD314 during amelogenesis.

The results were as follows:

1. In in-situ hybridization, OD314 mRNAs were more strongly expressed in ameloblast than odontoblast.

2. When ameloblast cells were cultured in the differentiation and mineralization medium for 28 days, the tuftelin mRNA expression was maintained from the beginning to day 14, and then gradually decreased to day 28. The expressions of amelogenin and enamelin were gradually decreased according to the ameloblast differentiation.

3. Inactivation of OD314 by U6-OD314 siRNA construct down-regulated the expression of OD314, MMP-20, and tuftelin, whereas over-expression of OD314 by CMV-OD314 construct up-regulated the expression of OD314 and MMP-20 without change in tuftelin.

These results suggest that OD314 is considered as an ameloblast-enriched gene and may play the important roles in ameloblast differentiation and mineralization.

The purposes of this study were to compare the effects of one or two applications of all-in-one adhesives on microtensile bond strengths (µTBS) to unground enamel and to investigate the morphological changes in enamel surfaces treated with these adhesives using a scanning electron microscopy (SEM).

Twenty-five noncarious, unrestored human mandibular molars were used. The unground enamel surfaces were cleansed with pumice. The following adhesives were applied to lingual, mid-coronal surfaces according to manufacture's directions; Clearfil SE bond in SE group, Adper Prompt L-Pop™1 coat in LP1 group, 2 coats in LP2 group, Xeno® III 1 coat in XN1 group, and 2 coats in XN2 group. After application of the adhesives, a hybrid light-activated resin composite was built up on the unground enamel. Each tooth was sectioned to make a cross-sectional area of approximately 1.0 mm² for each stick. The microtensile bond strength was determined. Each specimen was observed under SEM to examine the morphological changes. Data were analyzed with one-way ANOVA.

The results of this study were as follows;

1. The microtensile bond strength values were; SE (19.77±2.44 MPa), LP1 (13.88±3.67 MPa), LP2 (14.50±2.52 MPa), XN1 (14.42±2.51 MPa) and XN2 (15.28±2.79 MPa). SE was significantly higher than the other groups in bond strength (p < 0.05). All groups except SE were not significantly different in bond strength (p < 0.05).

2. All groups were characterized as shallow and irregular etching patterns.

Competition will usually develop between the opposing walls as the restorative resin shrinks during polymerization. Magnitude of this phenomenon may be depended upon cavity configuration and volume.

The purpose of this sturdy was to evaluate the effect of cavity configuration and volume on microleakage of composite resin restoration that has margins on the enamel site only.

The labial enamel of forty bovine teeth was ground using a model trimmer to expose a flat enamel surface. Four groups with cylindrical cavities were defined, according to volume and configuration factor (Depth × Diameter / C-factor) - Group I: 1.5 mm × 2.0 mm / 4.0, Group II: 1.5 mm × 6.0 mm / 2.0, Group III: 2.0 mm × 1.72 mm / 5.62, Group IV: 2.0 mm × 5.23 mm / 2.54.

After treating with fifth-generation one-bottle adhesive - BC Plus™ (Vericom, AnYang, Korea), cavities were bulk filled with microhybrid composite resin - Denfill™ (Vericom). Teeth were stored in distilled water for one day at room temperature and were finished and polished with Sof-Lex system. Specimens were thermocycled 500 times between 5℃ and 55℃ for 30 second at each temperature.

Teeth were isolated with two layers of nail varnish except the restoration surface and 1 mm surrounding margins. Electrical conductivity (µA) was recorded in distilled water by electrochemical method. Microleakage scores were compared and analyzed using two-way ANOVA at 95% level.

The results were as follows:

1. Small cavity volume showed lower microleakage score than large one, however, there was no statistically significant difference.

2. There was no relationship between cavity configuration and microleakage.

Factors of cavity configuration and volume did not affect on microleakage of resin restorations with enamel margins only.

This article complies a survey on the replacement of the posterior restorations and accesses possible factors that influence the replacement of posterior restorations.

The data was collected from patients that visited department of conservative dentistry from Dec 1st 2003, to Sep 3rd 2004. Teeth was restricted to posterior permanent teeth. 9 dentists recorded age, gender of patients, tooth location, cavity form and restorative material. They rated marginal adaptation, anatomic form, secondary caries of old restoration by modified Ryge criteria system. The statistical analysis was performed with Chi square test (p < 0.05) for replacement ratio according to patients, tooth factor and One-way ANOVA was performed for comparison of old restoration according to restorative material.

The results were as follows;

1. The female (62%) was statistically higher ratio than the male (38%).

2. The distribution of replacement case according to age, the rate of replacement was in descending order, 20's (38.3%), 40's (16.8%), 30's (15.9%), 10's (11.1%), 50's (9.2%), 60's (8.7%).

3. The rate of replacement was 88% for molar and 12% for premolar (p < 0.05).

4. The rate of replacement was 39% for maxillar and 61% for mandible (p < 0.05).

5. The material of restorations was amalgam (69%), gold inlay (17%), composite resin (13%).

6. In rating system by modified Ryge criteria system on margin adaptation, there was statistically significant difference between amalgam and gold inlay. But on anatomic form and caries, there was no statistically significant difference among the material of restorations.

The objective of this in situ study was to evaluate the effects of whitening strip (Claren, LG Household & Health Care Ltd, 2.6% hydrogen peroxide) and gel (Opalescence, Ultradent, 10% carbamide peroxide) on microhardness of enamel in comparison with untreated control. Extracted twenty human upper incisors were disinfected, cleaned, and labial side of each incisor sectioned into 3 fragments by 2 × 2 mm size. After sectioning, labial sides of fragments were flattened and fixed to orthodontic bracket using flowable composite resin. Specimens prepared from each tooth were attached to the labial side of upper incisors of twenty volunteers one by one and treated by three different methods: (1) untreated control (2) treated with whitening strip for 14 days (3) treated with whitening gel for 14 days.

Microhardness (Microhardness tester, Zwick) of each specimen was measured at the baseline of pre-treatment, immediate after bleaching treatment, 14 days after bleaching treatment and Knoop Hardness Number was determined. Microhardness changes of experimental groups were compared.

The results show that tooth whitening strip and gel used in this study does not effect the micro-hardness of enamel during bleaching procedure.

The purposes of this study were to compare the apical terminus width of simulated curved root canal prepared with three NiTi file systems used by undergraduates for evaluation the effects of flute angle and pitch or radial land on reducing screw-in effect and to determine more safe NiTi file system for inexperienced operators.

Fifty inexperienced undergraduate students prepared 150 simulated curved root canals in resin blocks with three NiTi file systems ; ProFile®, Hero Shaper®, K3™. The electric motor set at a speed of 300 rpm and torque of 30 in a 16 : 1 reduction handpiece was used. The simulated root canal was prepared to ISO #25 sizes with each file system. The scanned images of pre- and post-instrumented canal of resin block were superimposed. To evaluate the screw-in effect of three NiTi file systems, apical terminus width of root canal was measured from superimposed images and statistical analysis was performed.

There were significant differences in three NiTi file systems. ProFile® had significantly smaller width than Hero Shaper® and K3™ (P < 0.05), but no significant difference was observed between K3™ and Hero Shaper®.

Under the condition of this study, active file system (Hero Shaper®, K3™) with variable pitch and helical angle had more screw-in effect than passive file system (ProFile®) with constant pitch and helical angle. It seems that the radial lands play more important role in reducing screw-in effect.