The objective of this study was to analyze the in vitro and in vivo corrosion products of low and high copper amalgams. The four different types of amalgam alloy used in this study were Fine cut, Caulk spherical, Dispersalloy, and Tytin. After each amalgam alloy and Hg were triturated according to the directions of the manufacturer by means of the mechanical amalgamator(Amalgam mixer. Shinhung Co. Korea), the triturated mass was inserted into a cylindrical metal mold which was 12mm in diameter and 10mm in height. The mass was condensed by 150Kg/cm compressive force. The specimen was removed from the mold and aged at room temperature for about seven days. The standard surface preparation was routinely carried out by emery paper polishing under running water. In vitro amalgam specimens were potentiostatically polarized ten times in a normal saline solution at $37^{\circ}C$(potentiostat : HA-301. Hukuto Denko Corp. Japan). Each specimen was subjected to anodic polarization scan within the potential range -1700mV to+400mV(SCE). After corrosion tests, anodic polarization curves and corrosion potentials were obtained. The amount of component elements dissolved from amalgams into solution was measured three times by ICP AES(Inductive Coupled Plasma Atomic Emission Spectrometry: Plasma 40. Perkim Elmer Co. U.S.A.). The four different types of amalgam were filled in occlusal and buccal class I cavities of four human 3rd molars. After about five years the restorations were carefully removed after tooth extraction to preserve the structural details including the deteriorated margins. The occlusal surface, amalgam-tooth interface and the fractured surface of in vivo amalgam corrosion products were analyzed. In vivo and in vitro amalgam specimens were examined and analyzed metallographically by SEM(Scanning Electron Microscope: JSM 840. Jeol Co. Japan) and EDAX(Energy Dispersive Micro X-ray Analyser: JSM 840. Jeol Co. Japan). 1. The following results are obtained from in vitro corrosion tests. 1) Corrosion potentials of all amalgams became more noble after ten times passing through the in vitro corrosion test compared to first time. 2) After times through the test, released Cu concentration in saline solution was almost equal but highest in Fine cut. Ag and Hg ion concentration was highest in Caulk spherical and Sn was highest in Dispersalloy. 3) Analyses of surface corrosion products in vitro reveal the following results. a)The corroded surface of Caulk spherical has Na-Sn-Cl containing clusters of $5{\mu}m$ needle-like crystals and oval shapes of Sn-Cl phase, polyhedral Sn oxide phase. b)In Fine cut, there appeared to be a large Sn containing phase, surrounded by many Cu-Sn phases of $1{\mu}m$ granular shapes. c)Dispersalloy was covered by a thick reticular layer which contained Zn-Cl phase. d)In Tytin, a very thin, corroded layer had formed with irregularly growing Sn-Cl phases that looked like a stack of plates. 2. The following results are obtained by an analysis of in vivo amalgam corrosion products. 1) Occlusal surfaces of all amalgams were covered by thick amorphous layers containing Ca-P elements which were abraded by occlusal force. 2) In tooth-amalgam interface, Ca-P containing products were examined in all amalgams but were most clearly seen in low copper amalgams. 3) Sn oxide appeared as a polyhedral shape in internal space in Caulk spherical and Fine cut. 4) Apical pyramidal shaped Sn oxide and curved plate-like Sn-Cl phases resulted in Dispersalloy. 5) In Tytin, Sn oxide and Sn hydroxide were not seen but polyhedral Ag-Hg phase crystal appeared in internal space which assumed a ${\beta}_l$ phase.

Physical properties of composite resins such as strength, resistance to wear, discoloration, etc, depend on the degree of conversion of the resin components. The clinical behavior of restorative resins varies brand to brand. Part of this variation is associated with the filler and differences in the polymer matrix. The polymer matrix of resins may differ because the involved monomers are dissimilar and because of variation in the catalyst system. The purpose of this study was to evaluate the degree of conversion of the composite resins according to the depth of cure and light curing time. 7mm diameter cylindrical aluminum molds were filled with each of five different hybrid light curing composite resins(Z-100, Charisma, Herculite XRV, Prisma TPH, Veridonfil) on the thin resin films. The molds were 1mm, 2mm, 3mm, 4mm, and 5mm in depth to produce resin films of various heights. Each sample was given 20sec, 40sec, and 60sec illumination with a light source. The degree of conversion of carbon double bonds to single bonds in the resin films was examined by means of Fourier Transform Infrared Spectrometer. The results were obtained as follows; 1. There was difference in the degree of conversion among five light curing composite resins according to the depth of cure for 20sec, 40sec, and 60sec illumination with light source with statistical significance(P<0.05). 2. Five light curing composite resins show lower degree of conversion at surface of the resin than depth of 1mm. 3. The degree of conversion of five light curing composite resins was siginificantly reduced from the maximum for the resin film when the light passed through as little as 1mm of each composite. 4. The degree of conversion of five light curing composite resins decrease significantly at the depth of 4mm, and polymerization was not occured at the depth of 5mm except for Prisma TPH. 5. The degree of conversion of five light curing composite resins was increased with increased light curing time, and there was no significant differences in the degree of conversion above 4mm in Z-100, 3mm in Charisma, and at depth of 5mm in Herculite XRV and Veridonfil(P>0.05).

The bond strengths of composite resin to tooth dentin vary with the methods of cavity preparation and surface treatment. Recent developments in techniques of dentinal surface treatment have renewed interest in microabrasive as a means of tooth preparation, The purpose of this study was to determine the effects of a new method of cavity preparation on the bond of composite resin to dentin. Freshly extracted 144 healthy human third molars were used in this study. The dentin surfaces prepared with #600 SiC abrasive paper were divided into control and air abrasion groups according to the method of dentin surface preparation using different combinations of delivery pressure, time, and acid etching. The shear bond strengths were measured after the composite resin (Clearfil Photo Bright) was bonded to prepared dentin surfaces by light-curing using a dentin bonding system (All-bond 2), In addition, the average surface roughness was measured to investigate the effect of differently prepared dentin surfaces on the shear bond strengths. The surface changes of prepared dentin and the debonded dentin surfaces were observed with SEM (S-2300, Hitachi Co., Japan). The following results from this-study were obtained ; 1. There was no significant difference of shear bond strengths according to the changes of delivery pressure and time. 2. The shear bond strengths were lower than the control in the air abraded-only groups, but those of the additional acid-etched groups were higher than the control. 3. The shear bond strengths to all air-abraded surfaces were increased by acid etching. 4. The correlation between shear bond strengths and surface roughness was not certain, although the mean surface roughness of all air-abraded surfaces has increased evidently while it has slightly decreased for additional acid etching. 5. On SEM examination, the dentinal tubules were almost occluded in the air abraded-only groups, but those were opened in the additional acid-etched groups. 6. The debonded surfaces were showed adhesive failure mode in the air abraded- only groups, while those were showed mainly the mixed and cohesive failure mode in the additional acid-etched groups. These results suggest that the layer produced during cavity preparation or surface treatment with air abrasion must be removed for maximum bond strength of composite resin to dentin.

Porpilyromonas endodontalis is specifically involved in endodontic infections. The bacterium can be isolated almost exclusively only from infected rool canals. P. gingivalis also has been implicated in endodontic infection. Pathogemcity of P. gingival is is attributed to a variety of virulence factors, especially proteases, produced by the bacterium. Importance of P. endodontalis in endodontic infection has been revealed. However, the pathogenic property of P. endodontalis has not been extensively studied. The present study was undertaken to characterize the proteolytic activity of P. endodontalis and compare the activity with that of P. gingivalis which has the most potent and diverse proteases among oral bacteria. For this purpose, culture supematants(SUP) and cell extracts(CE) were obtained from these two bacteria and were subjected to zymography using 15% polyacrylamide gel copolymerized with gelatin, type I, IV collagens or albumin. Hydrolysis of the collagens was further investigated by the cleavage assay using native type I and IV collagens in solution-phase. The results were as follows: 1. P. endodontalis apparently has a proteolytic activity that is comparable with that of P. gingivalis. 2. SUP and CE obtained from P. endodontalis and P. gingival is showed the strongest activity for gelatin, followed by type I and IV collagens, and albumin. 3. In the zymography, no noticeable difference in proteolytic activity for gelatin and albumin between the SUP and CE was observed, but in the cleavage assay using native collagens, the SUP showed a stronger collagenolytic activity than the CE. 4. The gelatinolytic activity of both the SUP and CE from these two bacteria was diminished in the presence of $CaCl_2$ or reducing agents such as ${\beta}$-mercaptoethanol and dithiothreitol(DTT). 5. Type I(calf skin and human placenta) collagenolytic activity of P. endodontalis and P. gingivalis was reduced by DTT but not affected by $CaCl_2$. The inhibitory effect of DTT, however, was reduced to some extent by $CaCl_2$. 6. Type IV collagenolytic activity of these two bacteria was not affected by $CaCl_2$ but increased to some extent in association with the reducing agents. 7. Hydrolysis of albumin by P. endodontalis and P. gingivalis was demonstrated only in the presence of the reducing agents. The overall results indicate that with respect to proteolytic activity, P. endodontalis appears to be as potent as P. gingivalis, or maybe more, and its proteolytic characteristic is similar to that of P. gingivalis. This suggests that P. endodontalis has so potent proteolytic activity that can participate by itself in endodontic infections and apical periodontitis, causing tissue destruction.

Finding a right repair material for furcation perforation is one of the major issues in clinical endodontics. In this experiment, three materials, calcium sulfate, amalgam, and calcium hydroxide were tested for perforated furcation repair. Sixty premolars and molars of five dogs were used. A #4 round bur was used to create the perforation. All experimental teeth were divided into two repair-time groups. One was immediate-repair group, where the perforation was repaired immediately, the other was delayed-repair group, where the perforation was left open for four weeks and then repaired with the same manner as in the immediate-repiar group. All chamber openings were sealed with amalgam and then radiographed. The animals were sacrificed at eighth week following the repair procedure. Radiographic evaluation for furcal bone destruction was done. Histologic evaluation was ranked as 0,1,2,3 according to the inflammation degrees. New bone formation was also recorded. The following conclusions were drawn within the limits of the experimental results: 1. In immediate-repair group, no significant differences existed between the materials. 2. In delayed-repair group, calcium sulfate showed significantly less furcal bone destruction and lower inflammation degree than amalgam.(p<0.05) 3. Overextruded specimens showed more severe inflammation than unextruded specimens. 4. Most of the specimens showed certain degrees of inflammatory reaction and incomplete hard tissue healing. 5. In delayed-repair group, treated group showed less inflammation than untreated control group.

Eighty two of extracted bovine mandibular incisors were sectioned transversely through the cementoenamel junction(CEJ) and instrumented to a size minimum-# 110 file at the working length by 5.25 % NaOCl irrigation. The roots in group 1 were received a final irrigation with 10ml of 17% EDTA followed by 10ml of 5.25% NaOCl, group 2, 10ml of 40% citric acid followed by 10ml of 5.25% NaOCl, group 3, 20ml of 5.25% NaOCl, and control group, 20ml distilled water. Canal walls of four roots in each group and control group were examined by SEM(x3000). Calcium hydroxide was placed into all experimental roots except control group. Each root was placed in nalgen bottle containing unbuffered distilled water. The pH level of the medium surrounding tooth was recorded at 0, one hour, and daily for 1week, then 14days, 21days, and 28days using pH electrode. At 1, 3, 7, 14, 21days, and 28days, four roots from each group were split longitudinally and the ratio change was recorded using spectroiluorometer. The results were followings : 1. The smear layer was totally removed from canal walls in group 1 and 2, but was observed in group 3 and control group. 2. The hydroxyl ion diffused more rapidly through radicular dentin when smear layer was removed from canal walls. 3. The hydroxyl ion derived from calcium hydroxide began to diffuse from the root canal to the exterior surface of the root at 1day, and continued to 1-2weeks. 4. The pH level of dentin near the CEJ was not different in all experimental group regardless of presence of smear layer. It is clinically advisable to place calcium hydroxide into root canal for 1-2weeks for the purpose of expectation of diffusion of hydroxyl ion. But, after the placement of calcium hydroxide into root canal, the consequent pH level of external root surface will be futher studied with respect to it's effect on the root and periodontium.

Recently composite resin luting cement have been widely used according as esthetic requirement was increased. The purpose of this study was to evaluate of shear bond strength of four resin cements to bovine dentin. The materials used in this study were All-Bond 2(dentin bonding agent), Duolink cement, Bistite resin cement, Twinlook cement, Clearfil CR inlay cement. A total 40 acrylic cylinders with bovine dentin were divided into four groups. Four experimental groups were as follows; Group l(AB) : Specimens bonded with All-Bond 2 and Duolink Cement Group 2(BT) : Specimens bonded with Bistite Resin Cement Group 3(TL) : Specimens bonded with Twinlook Cement Group 4(CR) : Specimens bonded with Clearfil CR Inlay Cement Mter 1 hour of bonding, all specimens were stored for 24 hours in water at $37^{\circ}C$ and tested with Instron universal testing machine between bovine dentin and resin cements. The data were evaluated statistically at the 95% confidence level with a one-way analysis of variance and Tukey's range statistics. The following results obtained; 1. The group l(AB) was highest shear bond strength and the group 3(TL) was 10west(p>0.05). 2. Group 2(BT), 4(CR) were similar shear bond strength and there was no significant difference(p<0.05). 3. Group 1(AB), 4(CR) with acid etching were showed resin tags on the opened dentinal tubules, but Group 2(BT), 3(TL) without acid etching were not showed resin tags. 4. Group l(AB) was showed intimate adaptation than other groups.

This study evaluated shear bond strength between porcelain and resin cement according to various surface treatments of porcelain, and surface condition of debonded porcelain. 50 porcelain specimens(Celay block A2M7) and composite resin specimens(Clearfil Photo-Bright) were prepared, and divided into 5 experimental groups according to the treatment method of porcelain surface. 5 experimental groups by surface treatments were as follows; CONTROL Group : No surface treatment was done on the surface of porcelains. SAND Group : The surface of porcelains were sandblasted with $50{\mu}m$ aluminum oxide for 5 seconds. HF Group: The surface of porcelains were etched with 8% Hydrofluoric acid for 4 minutes. SIL Group: The surface of porcelains were coated with silane coupling agent and heated at $100^{\circ}C$ for 5 minutes. SAND+HF+SIL Group : The surface of porcelains were sandblasted with $50{\mu}m$ aluminum oxide for 5 seconds and etched with 8% Hydrofluoric acid for 4 minutes, and coated with silane coupling agent and heated at $100^{\circ}C$ for 5 minutes. After surface treatments on the prepared porcelain surface two pastes of Panavia 21$^{(R)}$ were mixed, they were applied between composite resin block and porcelain surface, and then excessive resin cements were removed, and its margin was surrounded with Oxyguard II. All specimens were stored for 24 hours in water at $37^{\circ}C$ and tested with Instron testing machine between porcelains and resin cements, and debonded porcelain surfaces were observed under Scanning Electon Microscope(Hitachi S-2300) at 20kvp. The values from each group were compared statistically by Student's t-test. The obtained results were as follows; 1. The shear bond strength without surface treatment of porcelain was the lowest among all experimental groups(p<0.05). 2. The detached porcelain surface with sandblasting alone had more remarkable cracks than with only Hydrofluoric Acid or Silane coupling 2gent, but showed the lowest value of shear bond strength among surface treated groups(p<0.05), 3. When porcelain surface was treated by hydrofluoric acid, it affected shear bond strength more than silane coupling agent, but there were no significant statistical differences(p>0.05). 4. When three methods were combined to increase shear bond strength between porcelains and resin cements, its value was the highest than the others(p<0.05). 5. In Scannig Electron Micrograph of detached porcelain surface with no treatment, the sample revealed adhesive failure between the porcelain and resin cement whereas detached porcelain surface with combination of three method cohesive failure on the porcelain.

This study was designed to evaluate the influences of evaporation of liquid of dental cements by drying during long term using. Zinc phosphate cement, polycarboxylate cement, and glass ionomer cement were used, and evaluated the properties as follows; consistency, setting time, film thickness, solubility, and compressive strength according to the ADA specification. The specimens of control group were made by mixing the newly opened liquid using the powder-liquid ratio recommended by the manufacturer, and the specimens of ES groups were made by mixing the 10% evaporated liquid by drying with the powder-liquid ratio recommeded by the manufacturer, and the specimens of EM group were made by mixing the 10% evaporated liquid with the powder-liquid ratio modified for standard consistency. The following conclusions were drawn ; 1. The viscosity of mixture of all kinds of cements were increased by the evaporation of liquid, especially the viscosity of glass ionomer cement were influenced significantly. 2. The amount of liquid should be increased to get a standard consistency at the using of evaporated liquid of cement, the most significant increase of liquid amount was required on Ketac-Cem. 3. The setting times were increased at both cases of mixing of evaporated liquid with powder - liquid ratio recommended by manufacturer or modifided through consistency test. 4. At an experimental group of mixing of the evaporated liquid with powder-liquid ratio recommended by manufacturer, solubility was decreased and film thickness was increased. 5. By the result of evaporation of cement liquid, the compressive strength of polycarboxylate cement was increased slightly and it of glass ionomer cement was increased, however, by the increase of amount of liquid to be possible to manipulate the compressive strength were decreased.

Cariogenicity of the bacteria is attributed to their binding capacity to the teeth. Bacterial attachment to oral surfaces is an essential step for colonization and subsequently infection. Therefore, it is conceivable that caries prevention can be achieved fundamentally by inhibition of bacterial attachment. The rationale for caries prevention through the use of sugar substitutes or limited use of sugar has been revealed. Among many sugar substitutes, xylitol has been shown to exhibit the most profound cariostatic effect, inhibiting glucose metabolism and possibly binding of mutans streptococci. The purpose of this study was to examine the effect of xylitol on binding of different species of oral bacteria. The effect of xylitol on binding of [$^3H$]-labeled oral bacteria to hydroxyapatite coated with human saliva(SHA) as a model for the pellicle-coated tooth surfaces was investigated. The strains of oral bacteria used in this study were A. viscosus T14V, A. viscosus WVU627, P. gingivaiis 2561, P. gingivalis A7Al-28, S. gordonii G9B, S. gordonii Challis, S. sobrinus 6715, S. mutans UA101, S. mutans KPSK -2, S. mutans T8, and S. mutans UA130. The obtained results were as follows: 1. P. gingivalis A7 Al-28, S. mutans UA130, S. mutans T8 grown with xylitol showed greater binding to SHA than the organism grown without xylitol. Among these, S. mutans T8 showed the greatest rate of increase in its binding to SHA ; 8-fold increase in its binding with xylitol. 2. S. mutans KPSK -2 grown with xylitol showed 2 times lesser binding to SHA than the organism grown without xylitol. 3. Binding ability of the remaining strains grown with xylitol to SHA was almost same as that of the organisms grown without xylitol. The overall results suggest that use of xylitol in the oral cavity may affect the complex oral bacterial ecosystem.

The difficulty of endodontic retreatment depends on various factors and it is affected by retention of post. In this experiment, root canal therapy was done in extracted human teeth and cut into 10mm length from the root apex, and then cemented by zinc phosphate cement, Vitremer$^{(R)}$(glass ionomer) luting cement and Panavia 21$^{(R)}$(resin cement). Post preparation was done by #4 Parapost drill at 6mm length and cement was inserted by lentulo spiral. After 24 hours, tensile bond strength, post removal time was measured after the ultrasonic application and the separation site was measured. The following results were obtained. 1. In measuring tensile bond strength, there is no statistical difference between zinc phosphate cement and Panavia 21$^{(R)}$, but Vitremer$^{(R)}$ showed lower value compared with those two cements. (p<0.001) 2. When the post removal time was measured after ultrasonic application, significant different value in order of Panavia 21$^{(R)}$, zinc phosphate cement and Vitremer$^{(R)}$ was shown. (p<0.001) 3. As a result of examining the separating site of each cement, all 16 of zinc phosphate cement group showed the fracture site between cement and post, Vitremer$^{(R)}$ was 13/16, and Panavia 2$^{(R)}$ was 8/16. In case of tooth restoration using Parapost, the use of Panavia 21 showed good retention property than Vitremer$^{(R)}$, but when retreatment is needed the difficulty of post removal will be increased.

Much evidence now exists from both in vivo and in vitro studies to support the claim that small caries lesions can 'heal'. But, there are still different views on the mechanism of remineralization. So in order to find the best condition for the remineralization of incipient dental caries in maximum efficient way, the author conducted the experiment which reveals the effect of pH on remineralization. 40 specimens of sound permanent teeth without demineralization or crack, $100{\mu}m$ in thickness, were immersed in lactic acid buffered demineralization solution for 4 days. Dental caries with surface zone and subsurface lesion were artificially produced. All specimens were immersed in lactic acid buffered remineralization solution of pH 4.0, 4.5, 5.0, 5.5 containg fluoride ion for 10 days. The results were obtaind by observing the specimens for every 10 days under polarized microscopy at x25. 1. Remineralization did not occur in entire depth of body of lesion at given degree of saturation and concentration of fluoride ion. 2. The pattern of remineralization has increased according to increase of pH. So it can be concluded that supersaturated solution with fluoride ion can be affected by pH in remineralization of enamel, and pH 5.5 seems to be very effective in remineralization of deep and surface zone of dental caries. However, more complex factors exist in achieving complete remineralization and further continuous researches are needed to clarify the factors.

The research of the dentin bonding system was mainly on the chemistry and bonding strength. And in vitro assessement of biocompatibility of dentin bonding system was not completely developed. The purpose of this study was to evaluate the cytotoxic effect of several dentin primers. Scotchbond Multi-Purpose (3M Dental Products. USA). Gluma (BayerDental. Germany). All-Bond (Bisco. USA). ProBond (CaulkDensply, USA) and VeridonFil (Dongyang Nylon. Korea) were included. Cytotoxicity was tested using MTT cell viability test. 0.5 ul. 1 ul. 2 ul and 10 ul of each primer were added to the 96 well plate of incubated L929 cell lines. After 30-minute. 1. 4. 24 and 72-hour exposures. absorbance of L929 cells was observed with ELISA reader. All data were analyzed using t-test. All primers showed cytotoxicity on L929 cells under every conditions used in this study. Absorbance of L929 cells was decreased by time. Scotch bond group exhibited the lowest absorbance value in all exposure time and value.

The purpose of our study is to evaluate the ability of nickel-titanium(NiTi) files in maintaining the original curvature of a curved root canal during canal preparation. Curved canals on translucent resin blocks were prepared with NiTi and stainless steel files, and they were placed at the platform which can reproduce the same position. The unprepared and prepared canal forms were accurately compared by double exposure technique of photography. By finite element methods we also analyzed stress distributions of NiTi and stainless steel files in a curved canal. The results were as follows : 1. NiTi files were excellent in maintaining the original curvature of a curved canal than stainless steel files after canal preparation. 2. The results of canal preparation with these files were well verified by the analysis of stress distributions using finite element methods.

The changes of microstructures, morphology of sclerotic dentin and bonding aspects generated by an adhesive resin was investigated. Incisors and premolars showing natural cervical abrasions were collected and conditioned with 10 % phosphoric acid or 10 % maleic acid. The sclerotic dentin specimens were then rinsed and blot-dried and applied with dentin adhesive (All Bond 2) to the conditioned dentin surface. To examine the morphologic change of the sclerotic dentin specimen after etching and bonding procedure, the treated specimens were examined by SEM. To analyze the chemical composition of sclerotic dentin and crystals occluding dentinal tubules, the sclerotic dentin specimen was powdered and examined with X-ray Diffractometer. To investigate the Ca/P weight percent ratio within the dentinal tubules, the sclerotic dentin specimen was fractured perpendicularly to the long axis of the tooth from the center of cervical abrasion lesion and then examined with EDX(Energy Dispersive X-ray) microanalyzer. The results were as follows : 1. The increased width of peritubular dentin and the depositions of the irregular amorphous materials within the dentinal tubules were showed in the sclerotic dentin specimens. 2. After the treatment of sclerotic dentin specimen with 10 % phosphoric acid or 10 % maleic acid, the lateral side of tubules rather than cross-sectional tubule openings was showed exclusively at the incisal and gingival incline of the specimens. 3. After the treatment of sclerotic dentin specimen with 10 % phosphoric acid or 10 % maleic acid, the hybrid layer was not formed evidently and the resin tag was not formed or shortly penetrated into the tubules with the thinner diameter. 4. According to the results of XRD analysis of the sclerotic dentin specimen, Hydroxyapatite and Octacalcium phosphate were predominent, however, Whitlockite crystals were rare. 5. The mean Ca/P weight percent ratio analysed from 5 fractured sclerotic dentin specimens was $2.322{\pm}0.170$ at the intertubular dentin, $1.826{\pm}0.051$ within the dentinal tubule.

During preparation of narrow curved canals, procedural accidents such as, ledge, zipping, and transportation are frequently encountered and may lead to failure of endodontic therapy. To reduce these procedural errors and efficiently manage curved canals, various modifications in instrumentation technique and the design and flexibility of instruments have been advocated. This study compared the maintenance of the original canal curvature, cross sectional canal shape, and preparation time during instrumentation with stainless steel hand (K-Flexo) file, and nickel-titanium rotary files (Profile and Lightspeed). Thirty resin blocks with simulated curved canals of 20~25 degrees were used and divided into three groups of 10 each. In group 1, canals were instrumented using a quarter turn/pull technique with K-Flexofiles. Group 2 canals were prepared with rotary NiTi Profiles. Group 3 was prepared with rotary NiTi Lightspeed instrument. Before and after instrumentation, all canals were scanned using stereo microcope, FlexCam camera, and Photoshop 3.0 computer program. The results were as follows : 1. All groups showed some loss of canal curvature after instrumentation. Average loss of canal curvature was 8.6 degrees for K-Flexofile, 7.7 degrees for Profile, and 5.8 degrees for Lightspeed. Lightspeed exhibited significantly less curvature loss than K-Flexofile (p<0.05). 2. At the apical 1-mm level, Profile produced significantly rounder canals than Lightspeed (p<0.05). At the 3-mm level, Profile and Lightspeed exhibited significantly rounder canals than K-Flexofile (p<0.05). 3. Preparation with Lightspeed was significantly faster than Profile and K-Flexofile, and Profile was faster than K-Flexofile (p<0.05). 4. There was no significant difference in incidence of zipping between the hand K-Flexofile and rotary NiTi (Profile and Lightspeed) instruments. Most of apical canals were slightly widened near the apical foramen. As a results of this study, rotary NiTi instruments are superior to the K-Flexofile in regard to the maintenance of original canal curvature, cross-sectional shape and preparation time. But more investigations and studies should be needed to evaluate the ideal canal instrumentation.

This study was to know the usefulness of argon laser for composite resin, to prove the polymerized effect of heat treatment of composite resin inlay and to get the curing method for optimal physical properties of composite resin inlay. In this study we used four light curing units and one heat curing unit: Visilux $II^{TM}$, a visible light gun: $SPECTRUM^{TM}$, an argon laser: Unilux AC$^{(R)}$ and Astorn XL$^{(R)}$, visible light curing unit: CRC-$100^{TM}$ for heat treatment. Compared to a control group, we divided the experemental groups into five as follows: Control group: Light curing(Visilux $II^{TM}$) Experimental group 1 : Light curing(Visilux $II^{TM}$) + Light curing(Unilux AC$^{(R)}$) Experimental group 2: Light curing(Visilux $II^{TM}$) + Light curing(Astron XL$^{(R)}$) + Heat treatment(CRC-$100^{TM}$) Experimental group 3 : Laser curing($SPECTRUM^{TM}$) Experimental group 4 : Laser curing($SPECTRUM^{TM}$) + Light curing(Unilux AC$^{(R)}$) Experimental group 5 : Laser curing($SPECTRUM^{TM}$) + Light curing(Astron XL$^{(R)}$) + Heat treatment (CRC-$100^{TM}$) According to the above classification, we made samples through the curing of Clearfil CR Inlay$^{(R)}$, which is a composite resin for inlay, in a separable cylindrical metal mold and polycarbonate plate. And then, we measured and compared the value of compressive strength, diametral tensile strength and the surface micro hardness of each sample. The results were as follows : 1. Among the experimental groups, group 5 showed the highest value of compressive strength, $157.50{\pm}10.24$ kgf and control group showed the lowest value of compressive strength, $103.93{\pm}21.93$ kgf. Control group showed significant difference with the experimental groups(p<0.001). Group 2 which was treated by the heat showed higher compressive strength than that of group 1 which was not, and there was significant difference between group 1 and group 2(p<0.001). Group 5 which was treated by heat showed higher compressive strength than group 4 which was not, and there was significant difference group 4 and group 5(p<0.001). 2. Among the experimental groups, group 5 showed the highest value of diametral tensile strength, $95.84{\pm}1.97$ kgf and control group showed the lowest value of diametral tensile strength, $81.80{\pm}2.17$ kgf. Control group which was cured by visible light showed higher diametral tensile strength than group 3 which was cured Argon Laser. Group 2 which was treated by heat showed higher compressive strength than that of group 1 which was not, and there was significant difference between group 1 and group 2(p<0.001). Group 5 which was treated by heat showed higher compressive strength than group 4 which was not, and there was a significant difference group 4 and group 5(p<0.001). 3. Among the experimental groups, group 5 showed the highest value of microhardness of top surface, $148.42{\pm}9.57$ kgf and control group showed the lowest value of microhardness, $111.43{\pm}7.63$ kgf. In the case of bottom surface, group 5 showed the highest value of $146.19{\pm}7.62$ kgf, and control group showed the lowest, $104.03{\pm}11.05$ kgf. Group 3 which was cured by Argon Laser showed higher diametral tensile strength than control group which was cured only with a visible light gun. Group 2 which was treated by heat showed higher compressive strength than that of group 1 which was not, and there was a significant difference between group 1 and group 2(p<0.001). Group 5 which was treated by heat showed higher compressive strength than group 4 which was not, and there was a significant difference group 4 and group 5(p<0.001). 4. According to the above results, we took a conclusion that argon laser can be used as a useful unit for curing the composite resin and heat treatment can improve the physical properties of the composite resin inlay.

The purpose of this study was to evaluate the shear bond strength of light-cured glass ionomer cements to dentin surface according to curing time induced by argon laser. In this study, 160 extracted human molars with sound crown were used. The dentin surface of these teeth were exposed with high speed diamond bur under water spray and polished with 120, 320, 400, 800, 1200 grits sand paper. 160 extracted human molars were randomly assigned into four groups (control, experimental 1, 2 & 3) with 40 teeth each. Control group used a visible light curing unit, XL 1000(3M Co., U.S.A) and experimental groups used argon laser($SPECTRUM^{TM}$). And then each group subdivided into two groups (A, B) according to filling materials. Subdivided A group used Fuji II LC(GC Co., Japan), B group used Vitremer(3M Co., U.S.A). The curing units and curing time of each group were as follows : Control group : visible light, 40 seconds Experimental group 1 Experimental group 2 Experimental group 3 : argon laser, 10 seconds : argon laser, 20 seconds : argon laser, 30 seconds The glass ionomer cements were bonded to dentin surface of each specimen. The specimens were stored in 100% relative humidity at 37"c for 7days. And then, the shear bond strength were measured by universal testing machine(Shimatzu Co. Japan) at crosshead speed of 5mm/min and 100kg in full scale and analyzed statistically. The following results were obtained : 1. Experimental group 2-A showed the highest shear bond strength with $9.87{\pm}1.24$ kgf and control group B showed the lowest shear bond strength with $4.08{\pm}0.78$ kgf(P<0.01). 2. The Fuji II LC showed higher shear bond strength with $9.49{\pm}1.24$ kgf than that of the Vitremer with $4.23{\pm}1.24$ kgf. There was significant difference between Fuji II LC and Vitremer(p<0.01). 3. There was no significant differences among experimental groups according to curing time induced by argon laser. 4. There was no significant differences between control group and experimental groups according to curing units.

The purposes of this study were to evaluate and compare the pulpal anesthesia induced by an inferior alveolar nerve block and that by Gow-Gates technique, and to investigate the relationship between pulpal anesthesia and intraoral soft tissue responses. After one side of mandibule was anesthetized with inferior alveolar nerve block or Gow-Gates technique using 2 % lidocaine with 1 : 100,000 epinephrine in 19 volunteers of ages between 24 and 29 (16 males and 3 females, average age 25.9 yrs.), electric pulp tests were done on the canine teeth of the anesthetized side and contralateral one before, at 1 min, continued at every 5 minutes until 60 min, and every 10 minutes until 100 min after completion of local anesthetic injection. Degree of pulpal anesthesia was classified as anesthetic failure, possible anesthesia and complete anesthesia by the criteria based on the thresholds to electric pulp test of contralateral canine and the currents of the electric pulp tester. Subjective signs on the lower lip and tongue were checked and prick-pin tests were done on the buccal gingiva of the first molar, buccal and lingual gingiva of the canine tooth at 5, 10 and 20 min after the completion of anesthetic injection. Thresholds to electric pulp test, degree of pulpal anesthesia and relationship between the pulpal anesthesia and soft tissue responses were analyzed with SPSS, paired t-test, Wilcoxon matched-pairs signed-ranks test and correlation analysis. The results were as follows : No significant differences were found in the peak thresholds to electric pulp test, in the induction time to it and in the depth of pulpal anesthesia between inferior alveolar nerve block and Gow-Gates technique (p>0.05). There was no significant relationship between pulpal anesthesia and soft tissue responses in both inferior nerve block and Gow-Gates technique.

The purposes of this study were to evaluate the changes in root canal configuration with canal instrumentation using different file types and techniques and to investigate most appropriate instrumentation technique in maintaining the original canal configuration with different file types. Fifty curved mesiobuccal or distobuccal canals of extracted human maxillary molar teeth were instrumented using a step-back technique with stainless steel K-files or nickel-titanium K-files, a crown-down pressureless technique with stainless steel K-files or nickel-titanium K-files and nickel-titanium engine-driven files. Radiographs were taken before and after instrumentation using a specially designed device that allowed for the pre-and postinstrumentation canals to be taken with the same X-ray angulation. Magnified X-ray images on a magnifier screen were traced and post instrumentation canal images were compared with the preinstrumentation ones. Changes in canal curvature and the incidence of procedural accidents were analyzed. The results were as follows : Crown-down pressureless technique with nickel-titanium K-files and nickel-titanium engine-driven filing produced no significant changes in canal curvature (p>0.05), while the step-back technique with stainless steel K-files or nickel-titanium K-files (p<0.01) and the crown-down pressureless technique with stainless steel K-files (p<0.05) produced significant changes. With nickel-titanium K-file, crown-down pressureless technique produced significantly less changes in canal curvature than step-back technique (p<0.05), while there was no significant difference between techniques with stainless steel K-files (p>0.05). File types exerted no significant influences in the changes of canal curvature both in the step-back technique and crown-down pressureless technique (0>0.05). Regardless of the file types used, step-back technique produced more procedural accidents such as ledge or elbow formation, apical zipping and apical transportation than the crowndown pressureless technique and nickel-titanium engine-driven filing. Both with stainless steel K-files and with nickel-titanium K-files, the incidence of apical extrusion of canal debris was higher in step-back technique than in crown-down pressureless technique.

Numerous materials such as amalgam, IRM, SuperEBA, dessicated ZOE, and Ketac-Silver have been used as a root-end filling material or to repair furcation perforations. But so far no material has been found to satisfy all of the requirements of an ideal restorative material. Recently, mineral trioxide aggregate (MTA) has been suggested for use as a root end filling material and for the repair of furcation perforations. The purpose of this study was to compare the effect of MTA on the proliferation of MC3T3/E1 osteoblastic cell, formation of bone nodule, alkaline phosphatase activity, and finally the tissue reaction of bone with those of amalgam, IRM, SuperEBA, dessicated ZOE, and Ketac-Silver. The following conclusions were drawn within the limits of the experimental results : 1. MTA showed a excellent proliferation of osteoblastic cell and Ketac-Silver showed moderate proliferation of osteoblastic cell. The rest of test materials showed no proliferation of osteoblastic cell. 2. Many of definite bone nodules were found in the MTA group. In contrast, Ketac-Silver group showed no definite bone formation but only showed mild sign of bone formation. 3. Alkaline phosphatase activity of Ketac-Silver and MTA showed similar results. But both of them showed higher activity than that of other materials (p<0.005). 4. The tissue reaction to implanted MTA in the calbarium of mouse was milder than that observed with other materials. The tissue reaction of dessicated ZOE showed the worst results among the test materials.

In addition to their function, there is growing interest in esthetics of restorations for teeth from fracture and loss. Because the perception of color depends on a lot of factors such as light source, object, observer and so on. It is difficult to make an objective expression. Therefore the using of mechanical equipment is recommended to exclude these variables and observer's vias. This study was carried out to evaluate the teeth color with a newly developed digital camera and to suggest a way to solve its flaws. After photo-taking and storaging the images of normal teeth into a computer, color spaces were examined with an image analysis system, Adobe Photoshop 3.04 and a statistical significance was determined between groups in term of teeth positions and ages. Results were as follow ; 1. Central incisor looked darker than lateral incisor(p<0.05), but lateral incisor and canine showed a similar lightness. 2. Central incisor showed more greenish color than lateral incisor and canine(p<0.05). 3. Canine showed higher yellowish value than central and lateral incisors(p<0.05). 4. Central incisor and canine showed no difference with aging. But in lateral incisor, teeth in fifth decade were lighter than those of third(p<0.05) and teeth in third decade were more reddish and yellowish than those of fourth decade(p<0.05).

Incidence of using esthetic composite resin in the posterior area is increasing but there were lots of inconsistent reports about their microleakage and marginal adaptation. The purpose of this study was to evaluate the differences of microleakage and marginal adaptation according to restorative techniques. 30 cavities with enamel gingival margin were prepared and restored with 3 types of composite resin [Z-100($Scotchbond^{TM}$ MP), AELITEFIL ($Onestep^{TM}$), Her culite XRV(Fuji BOND LC)] in direct technique and another 30 cavities were restored with preformed CR inlays and 3 different modern resin and resin-modified GI cements (Superbond C&B, Choice, Fuji Duet). Samples were chemically stressed in 75% ethanol for 24 hours and were thermocycled (5-$55^{\circ}C$(500 times. The degree of microleakage through proximal and gingival margins was examined by 1 % MB dye and the degree of marginal adaptation by examining the margins via SEM. The following results were obtained ; 1. In direct groups, Herculite XRV [Fuji BOND LC, 35.13 (15.50) %] group showed statistically different, less microleakage than Z-100 [$Scotchbond^{TM}$ MP, 72.91 (16.91 %] group and AELITEFIL [One-step, 93.73 (13.66) %] group (p<0.05). 2. In indirect groups, the degree of microleakage in Mean(S.D.) were: Super bond C & B [39.00 (24.35) %], Choice [57.19 (33.80) %], Fuji Duet [58.22 (40.36) %]. But there was no significant difference. 3. There was no significant difference between resin cement and resin-modified GI cement. 4. There were gaps at the interface with the tooth structure, but no gap was seen at the interface with restoration in all specimens. 5. In direct groups, Herculite XRV(Fuji BOND LC) group made little gap compared with other groups, but 40-$50{\mu}m$ thickness of bonding agent, Fuji BOND LC, looked like a cement used in indirect technique. 6. All indirect groups showed a variety of cement thickness, from less than $20{\mu}m$ to over $100{\mu}m$ and that dimension of buccal/lingual margin was less than that of gingival margin.

An accurate working length is an essential factor in the success of endodontic treatment. There are several methods for determining working length; electronic apex locator, tactile sense by clinician, and radiography. Among these methods, the most commonly used method is radiography. But this method requires excessive radiation, long developing time, and many equipments. In additon, it could give an image distortion and two dimensional image. To improve these disadvantages, an intraoral digital radiographic system (Digora$^{(R)}$) which use an imaging plate instead of a film, was developed. The purpose of this investigation was to compare Digora imaging with conventional radiography in determining the working length. Maxillary first or second molars of human dried skull were used. Files were inserted into canals at randomly selected lengths, from 2mm short of the radiographic apex to 2rnm beyond. Radiographs and Digora images(Digora positive and Digora negative) were evaluated to determine the adjustment needed to place the file 0.5mm from the radiographic apex. The results were as follows ; 1. There was no significant difference in accuracy between those evaluated in ${\pm}0.5mm$ and those accurately evaluated in the 3 images. 2. When comparing the accuracy of each image without distinguishing the 3 images, in the group accurately determined within ${\pm}0.5mm$, the mesiobuccal group showed significantly higher accuracy compared to the palatal group(p<0.05).

Resin modified glass ionomers were introduced in 1988 to overcome the problems of moisture sensitivity and low early mechanical strength of conventional glass ionomers and to maintain their clinical advantages. The purpose of this study was to evaluate the color stability of four resin modified glass ionomers(Fuji II LC, Vitremer, Dyract and VariGlass), one resin composite material(Z-100), and one conventional glass ionomer(GC Fuji II) under several conditions. These conditions were as follows: 1) before curing, 2) after curing, 3) after polishing, 4) after 500 thermocycling, 5) after 1,000 thermocycling, 6) after 1,500 thermocycling and 7) after 2,000 thermocycling. Three specimens of each material/shade combination were made. Materials were condensed into metal mold with a diameter of 10 mm and a thickness of 2.0 mm, and were pressed between glass plates. The material was polymerized using a light polymerizing unit(Visilux II, 3M, USA). After removal of excess, the surface was polished sequentially on wet sandpapers. A reflection spectrophotometer(Model TC-6FX, Tokyo Denshoku Co., Japan) was used to determine CIELAB coordinates($L^*,a^*$ and $b^*$) of each specimen. CIE standard illumination C was used as the light source. The results were as follows : 1. In comparing different shades of same material, CIELAB color difference(${\Delta}E^*$) value was not significantly different from each other(p>0.05). 2. CIELAB color difference(${\Delta}E^*$) values between after-curing and after-polishing were ranged from 5.53 to 27.08. These values were higher than those of other condition combinations. 3. CIELAB color difference(${\Delta}E^*$) values between before-thermocycling and after-thermocycling were ranged from 1.40 to 7.81. Despite the number of thermocycling increased, CIELAB color difference(${\Delta}E^*$) value was low. 4. The color stability of resin modified glass ionomers was more stable than that of conventional glass ionomers but less stable than that of Z100.

The purpose of this study was to examine the distribution of lymphocyte populations in normal, reversibly inflamed and irreversibly inflamed human dental pulp tissues using flow cytometry. Flow cytometry, with specific antibody and fluorochrome reagent allows us to know cellular properties of hematolymphoid cells by measuring fluorescence of stained cells. Before extirpation of pulps in routine endodontic treatment, the clinical diagnosis were performed by symptom. The extirpated pulp tissues were divided into normal pulp group (N=5), reversible pulpit is group(N=10) and irreversible pulpitis group(N=7). The specimen was placed into RPMI 1640 medium, minced into small pieces, and then digested in medium with collagenase. The cell suspension was resuspended in PBS for monoclonal antibody staining of T lymhocytes(CD3+), B lymphocytes (CD19+), T helper cell (CD4+) and T supressor cell (CD8+). The percentages of cells were counted by FACStar(BD) flow cytometer. Following results were obtained; 1. In the most normal and inflamed pulps, the percentages of T lymphocyte, B lymphocytes, T helper cell and T suppressor/cytotoxic cell were less than 1 % in total counted pulpal cells. 2. The higher percentages of T, B, T helper and T suppressor cells were observed in irreversible pulpitis group as compared with the normal pulp and reversible pulpitis group but the differences between groups were not statistically significant (p>0.05). 3. The percentages of T helper cells (CD4 + cells) were greater than that of T suppressor/cytotoxic cells (CD8 + cells) in the inflamed pulps.

Maintaining the original canal path during instrumentation is a challenge in narrow curved canals. This study compared the maintenance of the original canal path of curved root canals during instrumentation with two kinds of stainless steel K-files(Brassler USA & Mani Japan), K-flexofiles(Maillefer Swiss) and Ni-Ti files(Brassler USA, Savannah, GA) using circumferential filing technique to # 40 MAF on 60 extracted human molars. Buccal and mesial canals with minimal initial curvature of 20 degrees were used. The maximal initial curvature was 41.5 degrees. Sixty curved canals divided into four groups according to file type(Group 1 : Ni-Ti file, Group 2 : K-flexofile, Group 3: K-file(Brassler), Group 4 : K-file(Mani)). Radiographs of canals were obtained before and after canal shaping. And postoperative radiographs were compared with preoperative radiographs using superimposition method. Data analysis was performed using Covariance analysis and paired-comparison test. The results observed were as follow ; 1. The angle of curvature was better maintained with Ni-Ti file than with stainless steel files. (p<0.01) 2. There was no significant difference in maintaining canal curvature between K-flexofile, Brassler$^{(R)}$ K-file and Mani$^{(R)}$ K-file, although there was some differences in mean values of postoperative canal curvature. 3. Paired-comparison t test revealed significant differences within each of the three stainless steel file types when comparing the mean differences before and after instrumentation, but no significant differences were observed within Ni-Ti file group.

The purpose of this study is to observe the corrosion characteristics of five dental amalgams(CAULK FINE CUT, OPTALLOY II, DISPERSALLOY, TYTIN, and VALIANT) in the solutions with fluoride compound through the anodic polarization curve obtained by using a potentiostat. After each amalgam alloy and Hg being triturated, the triturated mass was inserted into the cylindrical metal mold, and condensed by hydraulic pressure(160 kg/$cm^2$). Each specimen was removed from the metal mold. Specimens were polished with the silicone carbide grinding paper 24 hours after condensation and stored at room temperature for 1 week. The anodic polarization curves were employed to compare the corrosion behaviours of the amalgams in 0.9 % saline solution and in the saline solutions with 2.2 ppm, 0.05 %, 2 % NaF, and 8 % $SnF_2$ at $37^{\circ}C$ with 3-electrode potentiostat. After the immersion of specimen in electrolyte for 30 minutes, the potential scan was begun. The potential scan range was -1500m V to + 800m V(vs. S.C.E.) in the working electrode and the scan rate was 50 mV/sec. The results were as follows, 1. The corrosion potential, the potential of anodic current peak, and transpassive potential in the saline solutions with NaF shifted to lower direction than those in normal saline solution, and the current density in the saline solutions with NaF was higher than that in normal saline solution. The differences were increased as the concentrations of NaF became higher. 2. The corrosion potential and transpassive potential in the saline solution with $SnF_2$ shifted to higher direction than those in normal saline solution, and the current density in the saline solution with $SnF_2$ was higher than that in normal saline solution after the corrosion potential. The anodic polarization curves in the saline solution with $SnF_2$ had no outstanding anodic current peak. 3. The corrosion potentials for high-copper amalgams were much higher than those for CAULK FINE CUT and OPTALLOY II in normal saline solution, but, as the concentrations of fluoride compound became higher, the differences in corrosion potentials between them were decreased. The corrosion potentials had the similarity in the saline solution with 2% NaF or 8% $SnF_2$. 4. The current density for TYTIN was the lowest among the others in normal saline solution and in the saline solution with 2.2 ppm or 0.05 % NaF. 5. There was no significant difference in current density between Pd-enriched VALIANT and other high-copper amalgams.

Porphyromonas endodontalis and Prevotella intermedia are black-pigmented anaerobic gram negative rods which have been isolated from infected root canals and submucous abscesses of endodontic origin. And they are associated with clinical symptoms such as pain, percussion, and foul odor. It has been reported that there are 3 serotypes according to capsule membrane in P. endodontalis and 2 DNA homology groups and 3 serotypes in P. intermedia, but there is no data available regarding genetic diversity for the species P. endodontalis and P. intermedia. The purpose of this study is to investigate genetic diversities between individual strains of P. endodontalis and P. intermedia which are indistinguishable by serotyping and biotyping using bacterial DNA restriction endonuclease analysis. 45 teeth with at least one clinical symptoms, with single canal, and with pulp necrosis were sampled. For sampling bacteria, access cavity was prepared after disinfecting tooth and its surroundings. Then the paper point was inserted to the apex of the canal, leave there for 15 seconds, and finally it was placed into PRAS Ringer's solution and PBS solution. P. endodontalis and P. intermedia were identified by biochemical test and IIF after subculturing black and brown colonies which were produced after 7 days of incubation on BAP in anaerobic chamber. P. endodontalis and P. intermedia strains were grown in BHI broth and whole genomic DNA was extracted by phenol-chloroform extraction technique and digested by restriction endonuclease, Eco RI and Pst I. The resulting DNA fragments were separated by agarose gel electrophoresis, stained with EtBr and photographed under UV light. The results were as follows : 1. In both P. endodontalis and P. intermedia, different serotypes could be found within a root canal of same patient. 2. There were obvious genetic heterogeneity within a patient and within a serotype in both P. endodontalis and P. intermedia. 3. P. endodontalis serotype c, isolated from different patients, exhibited limited genotypic diversity.

Restorative procedures can lead to weakening tooth due to reduction and alteration of tooth structure. It is essential to prevent fractures to conserve tooth. The resistance to fracture of the restored tooth may be influenced by many factors, among these are the cavity dimension and the physical properties of the restorative material. The placement of direct composite resin restorations has generally been found to have a strengthening effect on the prepared teeth. It is the purpose of this investigation to study the relationship between the cavity isthmus and the fracture resistance of a tooth in composite resin restorations. In this study, MO cavity was prepared on maxillary first premolar. Three dimensional finite element models were made by serial photographic method and isthmus(1/4, 1/3, 1/2 of intercuspal distance) were varied. Two types of model(B and R model) were developed. B model was assumed perfect bonding between the restoration and cavity wall and R model was left unfilled. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as follows : 1. Displacement of buccal cusp in R model occurred and increased as widening of the cavity, and displacement in B model was little and not influenced by cavity width. 2. There was a significant decrease of stress resulting in increase of fracture resistance in B model when compared with R model. 3. With the increase of the isthmus width, B model showed no change in the stress and strain. In R model, the stress and strain increased both in the area of buccal-pulpal line angle and the buccal side of marginal ridge, therefore the possibility of crack increased. 4. The stress and strain were distributed evenly on the tooth in B model, but in R model, were concentrated on the buccal side of the distal marginal ridge and buccal-pulpal line angle, therefore the possibility of fracture increased.

The purpose of this study was to evaluate the effectiveness of copal varnish and five bonding agents(Scotchbond Multi-Purpose Plus Dental Adhesive System, Panavia 21, All Bond 2, Superbond D-Liner II plus, Fuji Duet) in reducing microleakage under amalgam restorations. Class V cavity were prepared on both buccal and lingual surface of sixty extracted human molars with cementum margin and were filled with different kinds of liners and amalgam. All teeth were stored at $37^{\circ}C$ in physiologic saline solution. After 1 week they were thermally stressed for 500 cycles between 5 and $55^{\circ}C$ in baths containing 0.5 % basic fuchsin dye. The dye penetrations were observed with a stereomicroscope. Scanning electron micrographs were taken of representative tooth sections from each group to assess the nature of the tooth/liner/amalgam interface. The statistical test were applied to the results using a one way analysis variance (ANOVA) and Duncan's multiple range test. The results were as follows ; 1. In all groups, the enamel margin showed significantly lower leakage value than the cementum margin (p<0.05). 2. At the dentin and enamel margins, the leakage value of Copalite-lined group showed significantly higher than that of no liner group (p<0.05), but showed significantly lower than that of bonding agent lined-groups (p<0.05). 3. There was no significant difference between the bonding agent lined-groups (p>0.05). 4. On the backscattered scanning electron microscopy observation, discontinuous gaps were observed between amalgam and dentin in the bonding agent-lined amalgam restorations and the bonding agents appeared to fill the gap space and were mixed with amalgam particles. At the amalgam/tooth interface, unsealed dentin and continuous gaps were found in both unlined and Copalite-lined restorations.

The radiopacity of glass ionomer cements is quite variable. The use of a poorly radiopaque material as a base under other restorative materials can mislead the dentist to a diagnosis of recurrent decay. This study investigates the radiopacity of these materials and proposes a minimal radiopacity under which a material should not be used as a base or liner. It is important to determine the radiopacity of glass ionomer dental materials so that the clinician can appreciate the type of restorative materials used when radiographically evaluation the possibility of recurrent dental caries. In this study, radiopacity of Vitrement and Chemfil was compared with that of Cavalite, Miracle mix and polycarboxylate cement. Tooth model of artificial cavity preparation for diagnosis of recurrent caries was omitted. Radiopacity of each material was measured using relatives between thickness and radiopacity of Aluminium step wedge. The results were as follows : 1. Radiopacity of Vitrement was some higher than enamel. 2. Chemfil, restorative glass ionomer, was less radiopaque than enamel. 3. In order of higher radiopacity than enamel, Miracle mix was highest and was followed by polycarboxylate cement, Cavalite and Vitremer. 4. Vitremer, the Glass Ionomer Cement, is useful to detection of recurrent caries, because it is slightly higher radiopaque than enamel. So, it is suitable for restorative material and luting cement.

The purpose of this study was to investigate the effects of moistening mechods of dentin on the morphologic states of hybrid layers and on the interfacial bond strength between dentin and composite. Specimens were divided into 6 groups based on the surface moistening methods and materials used. After the dentin surface was conditioned with 10 % phoporic acid and irrigated: 1. The dentin surface was dried. Then bonding agent and composite were applied. 2. The dentin surface was blot-dryed. Then primer, bonding atent and composite were applied. 3. The dentin surface was dryed first. Within 20 seconds, the surface was rewetted, then primer, bonding agent and composite were applied. 4. The dentin surface was dryed. Then primer, bonding agnent and composite were applied. 5. The dentin surface was dryed first. Atter 24hrs, the surface was rewetted, and then primer, bonding agent and composite were applied. 6. The surface was conditioned with NaOCl for 5min. Then primer, bonding agent and composite were applied. To reveal the hybrid layer, scanning electron microscopy was used after the samples were ion beam etched. The shear bond strength of each group was tom pared by ANOVA. In groups 2, 3 and 4, the hybrid layer was clearly visible, but the width was more limited in group 4. In group 1 and 5, the hybrid layer was not found, and a gap was formed between dentin and composite. In group 6, the hybrid layer was not found, but the interface between the dentin and composite was intimate. The shear bond strength of each group was as follows: Group 1 : 4MPa, Group 2 : 14MPa, Group 3 : 12MPa, Group 4 : 14MPa, Group 5 : 5MPa, Group 6 : 9MPa.

The purpose of this study was to evaluate the effect of the Nd : YAG laser on the tooth hypersensitivity by the observation of the morphological changes of the dentinal surface irradiated with Nd : YAG laser by use of SEM. In 40 mandibular and maxillary molars without any carious lesion or restoration, severe attrition and abrasion, Enamel was removed with fine grit diamond bur and exposed dentinal surfaces were polished with Soflex discs. In control group (10 teeth), exposed dentinal surfaces were acid-etched with 10 % Maleic acid for 15 seconds. In the experimental group 1 (10 teeth), acid-etched dentinal surfaces with 10% Maleic acid were prepared by Nd : YAG laser (6 watts power, 1 psi water, 18 psi air) for 2 minutes. In the experimental group 2 (10 teeth), exposed dentinal surfaces were irradiated with Nd: YAG laser (10 watts power, 3 psi water, 10 psi air) until the painted black stains on the dentinal surfaces were completely removed. In the experimental group 3 (10 teeth). dentinal surfaces were prepared with Nd : YAG laser (6 watts power, 1 psi water, 18 psi air) until the painted black stanins on them were completely removed and then the irradiated dentinal surfaces were acid-etched with 10 % Maleic acid for 15 seconds. The specimens were routinely processed and observed with scanning electron microscope. The results were as follows : 1. In the irradiated dentinal surfaces, the characteristics of the melting and recrystalization on the dentinal surfaces were observed. Compared with the results in the control group, we could observe that in the irradiated dentinal surfaces, the aperture of the dentinal tubules were reduced and there were more debris obstructing the dentinal tubules. 2. In the irradiated dentinal surfaces, crater structures were commonly present and in the crater bottoms, there were a lot of bead like melted dentin structures, which had the ruptured opening in the center of them. 3. The melted dentins and cracks in the smear layer were less frequently observed in the irradiated dentinal surfaces using copious cooling water than in the irradiated dentinal surfaces using scare cooling water.