THE EFFECT OF LACTIC ACID CONCENTRATION AND pH OF LACTIC ACID BUFFER SOLUTIONS ON ENAMEL REMINERALIZATION

There are considerable in vitro and in vivo evidences for remineralization and demineralization occurring simultaneously in incipient enamel caries. In order to "heal" the incipient dental caries, many experiments have been carried out to determine the optimal conditions for remineralization. It was shown that remineralization is affected by different pH, lactic acid concentrations, chemical composition of the enamel, fluoride concentrations, etc. Eighty specimens from sound permanent teeth without demineralization or cracks, 0.15 mm in thickness, were immersed in lactic acid buffered demineralization solutions for 3 days. Dental caries with a surface zone and subsurface lesion were artificially produced. Groups of 10 specimens were immersed for 10 or 12 days in lactic acid buffered remineralization solutions consisting of pH 4.3 or pH 6.0, and 100, 50, 25, or 10 mM lactic acid. After demineralization and remineralization, images were taken by polarizing microscopy (x100) and micro-computed tomography. The results were obtained by observing images of the specimens and the density of the caries lesions was determined. 1.As the lactic acid concentration of the remineralization solutions with pH 4.3 was higher, the surface zone of the carious enamel increased and an isotropic zone of the subsurface lesion was found. However, the total decalcification depth increased at the same time. 2.In the remineralization solutions with pH 6.0, only the surface zone increased slightly but there was no significant change in the total decalcification depth and subsurface zone. In the lactic acid buffer solutions with the lower pH and higher lactic acid concentration, there were dynamic changes at the deep area of the dental carious lesion.ope

The influence of cavity configuration on the microtensile bond strength between composite resin and dentin

This study was conducted to evaluate the influence of the C-factor on the bond strength of a 6th generation self-etching system by measuring the microtensile bond strength of four types of restorations classified by different C-factors with an identical depth of dentin. Eighty human molars were divided into four experimental groups, each of which had a C-factor of 0.25, 2, 3 or 4. Each group was then further divided into four subgroups based on the adhesive and composite resin used. The adhesives used for this study were AQ Bond Plus (Sun Medical, Japan) and Xeno III (DENTSPLY, Germany). And composite resins used were Fantasista (Sun Medical, Japan) and Ceram-X mono (DENTSPLY, Germany). The results were then analyzed using one-way ANOVA, a Tukey's test, and a Pearson's correlation test and were as follows. 1. There was no significant difference among C-factor groups with the exception of groups of Xeno III and Ceram-X mono (p < 0.05). 2. There was no significant difference between any of the adhesives and composite resins in groups with C-factor 0.25, 2 and 4. 3. There was no correlation between the change in C-factor and microtensile bond strength in the Fantasista groups. It was concluded that the C-factor of cavities does not have a significant effect on the microtensile bond strength of the restorations when cavities of the same depth of dentin are restored using composite resin in conjunction with the 6th generation self-etching system.ope

Effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resin

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.ope

Selective detection of viable Enterococcus faecalis using propidium monoazide in combination with real-time PCR

Polymerase chain reaction (PCR) can detect bacteria more rapidly than conventional plate counting. However DNA-based assays cannot distinguish between viable and dead cells due to persistence of DNA after cells have lost their vitality. Recently, propidium monoazide (PMA) treatment has been introduced. The purpose of this study is to evaluate the applicability of the PMA treatment and real-time PCR method for cell counting in comparison with plate counting and to evaluate the antibacterial efficacy of 2% CHX on E. faecalis using PMA treatment in combination with real-time PCR. Firstly, to elucidate the relationship between the proportion of viable cells and the real-time PCR signals after PMA treatment, mixtures with different ratios of viable and dead cells were used. Secondly, relative difference of viable cells using PMA treatment in combination with real-time PCR was compared with CFU by plate counting. Lastly, antibacterial efficacy of 2% CHX on E. faecalis was measured using PMA treatment in combination with real-time PCR. The results were as follows : 1. Ct value increased with decreasing proportion of viable E. faecalis. 2. There was correlation between viable cells measured by real-time PCR after PMA treatment and CFU by plate counting until Optical density (OD) value remains under 1.0. However, viable cells measured by real-time PCR after PMA treatment have decreased at 1.5 of OD value while CFU kept increasing. 3. Relative difference of viable E. faecalis decreased more after longer application of 2% CHX.ope

THE EFFECT OF LACTIC ACID CONCENTRATION AND pH OF LACTIC ACID BUFFER SOLUTIONS ON ENAMEL REMINERALIZATION

본 연구의 목적은 유산 완충 용액의 pH 및 유산 농도 변화가 법랑질에서 인공 우식 병소의 재광화 양상에 미치는 영향을 평가하기 위함이다. 유산 완충 용액을 이용하여 법랑질을 탈회시키고, 유산의 농도가 100, 50, 25, 10 mM이고 pH가 4.3인 네 가지 재광화 용액 (Group 1, 2, 3, 4)에 10일, pH 6.0인 네 가지 재광화 용액 (Group 5, 6, 7, 8)에 12일간 처리한 후 무기질의 양적 변화를 편광 현미경에서 얻은 상에서의 탈회 깊이의 변화, 우식 표면층 깊이의 변화로 측정하였다. 또한 micro-computed tomography (micro-CT) 를 이용하여 탈회 후와 재광화 후를 촬영하여 얻은 상으로부터 lesion 부위의 density를 비교하였다. 1. pH 4.3에서 유산 농도가 증가할수록 우식 표면층의 증가와 표층하 탈회부 중 심층부의 isotropic zone 등의 재광화 현상을 보이나, 전체 탈회 깊이 역시 증가하였다. 2. pH 6.0에서 우식 표면층에 국한된 재광화 현상을 보이고, 전체 탈회 깊이는 변화가 없었다. 이상의 실험 결과로 미루어 포화도가 일정한 유산 완충 용액으로 재광화 유도시 pH가 낮고 유산의 농도가 높을수록 표면으로부터 심층부 동역학적 변화에 더 영향을 주었으며, micro-CT를 이용한 우식 병소 부위의 density 확인을 통해 무기질의 침착과 방출 현상을 객관적으로 평가할 수 있었다. There are considerable in vitro and in vivo evidences for remineralization and demineralization occurring simultaneously in incipient enamel caries. In order to "heal" the incipient dental caries, many experiments have been carried out to determine the optimal conditions for remineralization. It was shown that remineralization is affected by different pH, lactic acid concentrations, chemical composition of the enamel, fluoride concentrations, etc. Eighty specimens from sound permanent teeth without demineralization or cracks, 0.15 mm in thickness, were immersed in lactic acid buffered demineralization solutions for 3 days. Dental caries with a surface zone and subsurface lesion were artificially produced. Groups of 10 specimens were immersed for 10 or 12 days in lactic acid buffered remineralization solutions consisting of pH 4.3 or pH 6.0, and 100, 50, 25, or 10 mM lactic acid. After demineralization and remineralization, images were taken by polarizing microscopy () and micro-computed tomography. The results were obtained by observing images of the specimens and the density of the caries lesions was determined. 1.As the lactic acid concentration of the remineralization solutions with pH 4.3 was higher, the surface zone of the carious enamel increased and an isotropic zone of the subsurface lesion was found. However, the total decalcification depth increased at the same time. 2.In the remineralization solutions with pH 6.0, only the surface zone increased slightly but there was no significant change in the total decalcification depth and subsurface zone. In the lactic acid buffer solutions with the lower pH and higher lactic acid concentration, there were dynamic changes at the deep area of the dental carious lesion

(The) comparison of relative reliability on biaxial and three point flexural strength testing methods of light cu

치의학과/석사[한글] 이번 실험의 목적은 이축 굴곡 강도 시험의 복합레진에서의 적용가능성을 위해 기존의 3점 굴곡 강도 시험과 이축 굴곡 강도 시험을 이용하여 치과용 광중합형 레진의 강도를 측정하고, 이를 Weibull modulus를 이용하여 상대적 신뢰도를 비교하는 것이다. 이번 실험에 사용된 재료는 MICRONEWTM, RENEW?(Bisco, Schaumburg, USA)의 두 가지 광중합형 수복 재료이다. 3점 굴곡 강도 측정은 International Organization for Standardization(ISO) 4049, American National Standards Institute (ANSI)/ American Dental Association(ADA) Specification No.27 에서 규정하고 있는 방법을 사용하였으며 25mm×2mm×2mm규격의 시편을 20개 제작하였다. 이축 굴곡 강도 측정에는 International Organization for Standardization(ISO) 6872 규정에 따라 piston-on-3-ball test를 사용하였으며 검사 시편은 직경이 각각 12mm(지지원의 반지름 3.75mm), 16mm(지지원의 반지름 5mm), 두께가 각각 0.5mm, 1mm, 2mm인 여섯 개의 군으로 나누어 제작하였으며 각 군당 시편을 20개씩 제작하였다. 모든 시편은 23시간 동안 (37±1)°C distilled water bath에 23시간 담가 놓은 후 너비와 두께를 측정하였다. 만능시험기(Intron6022?, Instron Co., U.K.)을 사용하고 loading rate는 0.75mm/min로 유지하였으며 포아송 비는 0.24를 적용하였다. MICRONEWTM 와 RENEW?의 실험 결과, 이축 굴곡 강도가 3점 굴곡 강도보다 높은 평균값을 나타내었고 이축 굴곡 강도의 모든 군이 3점 굴곡 강도보다 높은 Weibull modulus 값을 보여, 이축 굴곡 강도 시험이 상대적으로 실험적 오차의 영향을 적게 받는 방법으로 신뢰할 수 있었다. 또한 이축 굴곡 강도 시험에서 시편의 두께가 2mm일 때 가장 높은 Weibull modulus를 나타내었으며 이축 굴곡 강도 시험군중, MICRONEWTM의 두께 2mm군에서는 지지원의 반지름에 따른 굴곡 강도의 통계학적 유의차이가 없었고(p>0.05), 이를 제외한 모든 군에서 시편의 두께와 지지원의 반지름에 따른 굴곡 강도의 통계학적 유의차이가 있었다(p<0.05). 위의 결과로 미루어 볼 때 두께 2mm군에서 이축 굴곡 강도는 기존의 3점 굴곡 강도 시험보다 우수한 것으로 추천할 수 있는 방법이다. [영문]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, MICRONEWTM, RENEW(r)(Bisco, Schaumburg, USA). The three point flexure strength measurements were used according to the regulations of the International Organization for Standardization(ISO) 4049, American National Standards Institute (ANSI)/ American Dental Association(ADA) Specification No.27 and 20 specimens (25mm x 2mm x 2mm) were fabricated. 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 12mm (radius connecting the 3-balls: 3.75mm), 16mm (radius connecting the 3-balls: 5mm), and the thickness were 0.5mm, 1mm, 2mm for each radius. Each group included 20 specimens which were immersed in (37±1)°C distilled water bath for 23 hours prior to the width and thickness measurements. A universal test machine (Intron6022(r), Instron Co., U.K.) was used by maintaining the loading rate at 0.75mm/min and the applying Poisson rate of 0.24. The bi-axial flexure strength of the MICRONEWTM 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 2mm thick specimens had the highest Weibull modulus values in the bi-axial flexure strength test, and the MICRONEWTM group showed no significant statistical difference (p>0.05). Besides the 2mm MICRONEWTM 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 2mm group, the bi-axial flexure strength test is a more reliable testing method than the three point flexure strength test.ope

Cerec3의 partial ceramic crowns에서 변연 및 내면 간극에 대한 치아 삭제 디자인의 효과

Dept. of Dentistry/박사[한글] [영문]The purpose of this study was to evaluate the marginal and internal gaps in Cerec3 partial ceramic crowns (PCCs) of three different preparation designs in vitro using microcomputed tomography (CT). Cerec3 PCCs of three different preparation designs (n = 20) were fabricated according to the following: Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After fixation of PCCs, the CT scanning was performed. For obtaining the average internal gap (AIG), the CT sections were reconstructed 3-dimensionally, and then the total volume of the internal gap was divided by the contact surface area. The 2-dimensional (2D) CT views were used to investigate the gaps at predetermined key positions in seven bucco-lingual sections and three mesio-distal cross sections. The gaps were measured using the CT at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey′s test.For the 3D reconstruction technique, the AIGs were as followed: Group I 197.3 ± 48.2μm, Group II 171.2 ± 45.1μm, and Group III 152.7 ± 27.1μm. For the 2D μCT views, the gaps of each group were the smallest on the margins ranging from 35.4 ± 32.2 to 128.4 ± 69.5μm, and the largest on the horizontal or angle walls ranging from 184.5 ± 41.2 to 406.5 ± 176.1 μm. According to the results, group I showed larger marginal and internal gaps compared with the other groups.For the PCCs, the simplified designs (groups II and III) demonstrated superior results compared to the traditional cusp capping design (group I). The marginal gaps were smaller than the internal gaps in all groups.ope

INFLUENCE OF THREE DIFFERENT PREPARATION DESIGNS ON THE MARGINAL AND INTERNAL GAPS OF CEREC3 CAD/CAM INLAYS

The aim of this study was to evaluate the marginal and internal gaps in CEREC3 CAD/CAM inlays of three different preparation designs. CEREC3 Inlays of three different preparation designs (n=10) were fabricated according to Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After cementation of inlays. the bucco-lingual cross section was performed through the center of tooth. Cross section images of 20 magnifications were obtained through the stereomicroscope. The gaps were measured using the Leica application suite software at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey's test (${\alpha}<0.05$). The marginal gaps ranged from 80.0 to $97.8{\mu}m$ for Group I, 42.0 to $194.8{\mu}m$ for Group II, 51.0 to $80.2{\mu}m$ for Group III. The internal gaps ranged from 90.5 to $304.1{\mu}m$ for Group I, 80.0 to $274.8{\mu}m$ for Group II, 79.7 to $296.7{\mu}m$ for Group III. The gaps of each group were the smallest on the margin and the largest on the horizontal wall. For the CEREC3 CAD/CAM inlays, the simplified designs (groups II and III) did not demonstrate superior results compared to the traditional cusp capping design (group I).ope

The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns

OBJECTIVES: The purpose of this study was to evaluate the marginal and internal gaps in Cerec3 partial ceramic crowns (PCCs) of three different preparation designs in vitro using microcomputed tomography (microCT). METHODS: Cerec3 PCCs of three different preparation designs (n=20) were fabricated according to the following: Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After fixation of PCCs, the microCT scanning was performed. For obtaining the average internal gap (AIG), the microCT sections were reconstructed 3-dimensionally, and then the total volume of the internal gap was divided by the contact surface area. The 2-dimensional (2D) microCT views were used to investigate the gaps at predetermined key positions in seven bucco-lingual sections and three mesio-distal cross sections. The gaps were measured using the microCT at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey's test. RESULTS: For the 3D reconstruction technique, the AIGs were as followed: Group I 197.3+/-48.2microm, Group II 171.2+/-45.1microm, and Group III 152.7+/-27.1microm. For the 2D microCT views, the gaps of each group were the smallest on the margins ranging from 35.4+/-32.2 to 128.4+/-69.5microm, and the largest on the horizontal or angle walls ranging from 184.5+/-41.2 to 406.5+/-176.1microm. According to the results, Group I showed larger marginal and internal gaps compared with the other groups. CONCLUSIONS: For the PCCs, the simplified designs (Groups II and III) demonstrated superior results compared to the traditional cusp capping design (Group I). The marginal gaps were smaller than the internal gaps in all groups.ope

EFFECTS OF ANTICURVATURE FILING ON DANGER ZONE WIDTH IN CURVED ROOT CANALS

본 실험은 발거 된 하악 대구치의 근심 근관을 스테인레스 강 K 파일과 니켈 티타늄 전동식 파일로 근관 성형했을 때 anticurvature filing 방법의 효용성을 평가하고자 했다. 30개의 발거된 하악 대구치 60개의 근심근관을 성형 방법과 기구에 따라 3개의 군으로 나누고 근단부 근관을 30번 크기로 일정하게 확대하였다. 1군은 스테인레스 강 K 파일을 사용해 circumferential filing technique을, 2군은 스테인레스 강 K 파일을 사용해 anticurvature filing technique을 3군은 니켈 티타늄 ProFile 06 series를 사용해 anticurvature filing technique으로 근관을 성형하였다. MCT를 이용해 얻은 술전, 술후 절단면 상을 중첩해 치근단 공에서 1mm 떨어진 지점에서부터 0.5mm 간격으로 위험부위 (danger zone)의 삭제량을 비교하였다. micro-computed tomography system (skyscan-1076, SKYSCAN, Antwerpen, Belgium)을 이용해 얻은 술전 술후 절단면 상을 중첩해 치근단 공에서 1mm떨어진 지점에서부터 0.5mm 간격으로 위험부위 (danger zone)의 삭제량을 비교하였다. danger Bone 폭경의 변화량은 one-way ANOVA를 이용하여 유의성 검정을 하였고 Tukey test를 이용하여 사후검정 하였다. 그 결과, 스테인레스 강 파일을 사용한 경우 circumferential filing으로 근관 성형한 것보다, anticurvature filing으로 근관 성형한 경우가 치관부 1/3부위()의 danger zone의 삭제량이 유의성 있게 적었고 (P<0.05), 니켈 티타늄을 사용하여 anticurvature filing으로 근관 성형한 경우는 danger zone의 중간 1/3부위 ()의 삭제량이 유의성 있게 적었다 (P<0.05). 니켈티타늄을 사용하여 anticurvature filing으로 근관 성형한 경우, 스테인레스 강 파일을 사용하여 anticurvature filing으로 근관 성형한 경우보다 의 삭제량이 유의성 있게 적었다 (P<0.05). The aim of this study was to compare the effects of anti curvature 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 C06 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 level between group 1 and 2, level between group 1 and 3 and level between group 2 and 3(n=20, P<0.05).연세대학교 치과대학 교내 연구