The purpose of this study was to evaluate the effect of film thickness of various resin cements on bonding efficiency in indirect composite restoration by measurement of microtensile bond strength, polymerization shrinkage, flexural strength and modulus, fractographic FE-SEM analysis. Experimental groups were divided according to film thickness (< 50 µm-control, 50 µm-T50, 100 µm-T100, 150 µm-T150) using composite-based resin cements (Variolink II, Duo-Link) and adhesive-based resin cements (Panavia F, Rely X Unicem). The data was analyzed using ANOVA and Duncan's multiple comparison test (p < 0.05).

The results were as follows;

Variolink II showed higher microtensile bond strength than that of adhesive-based resin cements in all film thickness (p < 0.05) but Duo-Link did not show significant difference except control group (p < 0.05).

This study was performed to assess the radiopacity of a variety of root canal sealers according to the specification concerning root canal sealers.

Ten materials including Tubli-Seal™, Kerr Pulp Canal Sealer™, AH 26®, AH plus®, AH plus jet™, Ad sea l™, Sealapex™, NOGENOL™, ZOB seal™, Epiphany™ and dentin were evaluated in this study. In the first part, densitometric reading of an each step of aluminum step wedge on occlusal film was performed at different voltage and exposure time. In the second part, ten specimens were radiographed simultaneously with an aluminum step wedges on the occlusal films under decided condition. The mean radiographic den sity values of the materials were transformed into radiopacity expressed equivalent thickness of aluminum (mm Al).

The following results were obtained.

1. Among the various conditions, the appropriate voltage and exposure time that meet the requirement density was 60 kVp at 0.2 s

2. All of the materials had greater radiopacity than 3 mm Al requirement of ANSI/ADA specification No. 57 (2000) and ISO No. 6876 (2001) standards.

3. The radiopacity of materials increased as thickness of materials increased.

4. The mm Al value of each specimen at 1mm in thickness has a significant difference in the statistics.

It suggests that root canal sealers have a sufficient radiopacity that meet the requirement.

This study was aimed to investigate whether an oxygen inhibition layer (OIL) is essential for the interfacial bonding between resin composite layers or not.

A composite (Z-250, 3M ESPE) was filled in two layers using two aluminum plate molds with a hole of 3.7 mm diameter. The surface of first layer of cured composite was prepared by one of five methods as followings, thereafter second layer of composite was filled and cured: Group 1 - OIL is allowed to remain on the surface of cured composite; Group 2 - OIL was removed by rubbing with acetone-soaked cotton; Group 3 - formation of the OIL was inhibited using a Mylar strip; Group 4 - OIL was covered with glycerin and light-cured; Group 5 (control) - composite was bulk-filled in a layer. The interfacial shear bond strength between two layers was tested and the fracture modes were observed. To investigate the propagation of polymerization reaction from active area having a photo-initiator to inactive area without the initiator, a flowable composite (Aelite Flow) or an adhesive resin (Adhesive of ScotchBond Multipurpose) was placed over an experimental composite (Exp_Com) which does not include a photoinitiator and light-cured. After sectioning the specimen, the cured thickness of the Exp_Com was measured.

The bond strength of group 2, 3 and 4 did not show statistically significant difference with group 1. Groups 3 and 4 were not statistically significant different with control group 5. The cured thicknesses of Exp_Com under the flowable resin and adhesive resin were 20.95 (0.90) um and 42.13 (2.09), respectively.

It was reported that esthetic composite resin restoration reinforces the strength of remaining tooth structure with preserving the natural tooth structure. However, it is unknown how much the strength would be recovered. The purpose of this study was to compare the fracture resistance of three types of undermined cavity filled with composite resin with that of non-cavitated natural tooth.

Forty sound upper molars were allocated randomly into four groups of 10 teeth. After flattening occlusal enamel, undermined cavities were prepared in thirty teeth to make three types of specimens with various thickness of occlusal structure (Group 1 ~ 3). All the cavity have the 5 mm width mesiodistally and 7 mm depth bucco-lingually. Another natural 10 teeth (Group 4) were used as a control group. Teeth in group 1 have remaining occlusal structure about 1 mm thickness, which was composed of mainly enamel and small amount of dentin. In Group 2, remained thickness was about 1.5 mm, including 0.5 mm thickness dentin. In Group 3, thickness was about 2.0 mm, including 1 mm thickness dentin. Every effort was made to keep the remaining dentin thickness about 0.5 mm from the pulp space in cavitated groups. All the thickness was evaluated with radiographic Length Analyzer program.

After acid etching with 37% phosphoric acid, one-bottle adhesive (Single Bond™, 3M/ESPE, USA) was applied following the manufacturer's recommendation and cavities were incrementally filled with hybrid composite resin (Filtek Z-250™, 3M/ESPE, USA). Teeth were stored in distilled water for one day at room temperature, after then, they were finished and polished with Sof-Lex system.

All specimens were embedded in acrylic resin and static load was applied to the specimens with a 3 mm diameter stainless steel rod in an Universal testing machine and cross-head speed was 1 mm/min. Maximum load in case of fracture was recorded for each specimen.

The data were statistically analyzed using one-way analysis of variance (ANOVA) and a Tukey test at the 95% confidence level.

The results were as follows:

Fracture resistance of the undermined cavity filled with composite resin was about 75% of the natural tooth.

Within the limits of this study, it can be concluded the fracture resistance of the undermined cavity filled with composite resin was lower than that of natural teeth, however remaining tooth structure may be supported and saved by the reinforcement with adhesive restoration, even if that portion consists of mainly enamel and a little dentin structure.

The purpose of this study was to evaluate the effect of thickness, filling methods and curing methods on the polymerization of dual cured core materials by means of microhardness test.

Two dual cured core materials, MultiCore Flow (Ivoclar Vivadent AG, Schaan, Liechtenstein) and Bis-Core (Bisco Inc., Schaumburg, IL, USA) were used in this study. 2 mm (bulky filled), 4 mm (bulky filled), 6 mm (bulky and incrementally filled) and 8 mm (bulky and incrementally filled)-thickness specimens were prepared with light cure or self cure mode. After storage at 37℃ for 24 hours, the Knoop hardness values (KHN) of top and bottom surfaces were measured and the microhardness ratio of top and bottom surfaces was calculated. The data were analyzed using one-way ANOVA and Scheffe multiple comparison test, with α = 0.05.

The effect of thickness on the polymerization of dual cured composites showed material specific results. In 2, 4 and 6 mm groups, the KHN of two materials were not affected by thickness. However, in 8 mm group of MultiCore Flow, the KHN of the bottom surface was lower than those of other groups (p < 0.05). The effect of filling methods on the polymerization of dual cured composites was different by their thickness or materials. In 6 mm thickness, there was no significant difference between bulk and incremental filling groups. In 8 mm thickness, Bis-Core showed no significant difference between groups. However, in MultiCore Flow, the microhardness ratio of bulk filling group was lower than that of incremental filling group (p < 0.05). The effect of curing methods on the polymerization of dual cured composites showed material specific results. In Bis-Core, the KHN of dual cured group were higher than those of self cured group at both surfaces (p < 0.05). However, in MultiCore Flow, the results were not similar at both surfaces. At the top surface, dual cured group showed higher KHN than that of self cured group (p < 0.05). However, in the bottom surface, dual cured group showed lower value than that of self cured group (p < 0.05).

The purposes of this study were to examine the variability of adhesive thickness on the different site of the cavity wall when used total-etch system without filler and simplified self-etch system with filler and to evaluate the relationship between variable adhesive thickness and microtensile bond strength to the cavity wall.

A class I cavity in six human molars was prepared to expose all dentinal walls. Three teeth were bonded with a filled adhesive, Clearfil™ SE bond and the other three teeth were bonded with unfilled adhesives, Scotchbond™ Multi Purpose. Morphology and thickness of adhesive layer were examined using fluorescence microscope. Bonding agent thickness was measured at three points along the axial cavity wall, edge of cavity margin (rim), halfway down each cavity wall (hlf), internal angle of the cavity (ang). After reproducing the adhesive thickness at rim, hlf and ang, micro-tensile bond strength were evaluated.

For both bonding agents, adhesive thickness of ang was significantly thicker than that of rim and hlf (P < 0.05). As reproduced the adhesive thickness, microtensile bond strength was increased as adhesive thickness was increased in two bonding agents.

Adhesive thickness of internal angle of the cavity was significantly thicker than that of the cavity margin and the halfway cavity wall for both bonding agents. Microtensile bond strength of the thick adhesive layer at the internal angle of the cavity was higher than that of the thin adhesive layer at the cavity margin and the halfway cavity in the two bonding systems.

This study investigated the effect of thickness of flowable resin lining on marginal leakage in class II composite restorations. 80 experimental teeth were prepared with class II preparations with enamel margin or dentin margin. Each group was devided into four groups according to flowable resin lining thickness ; Control group - no flowable resin lining, Group 1 - 0.5 mm flowable resin lining, Group 2 - 1 mm flowable resin lining, Group 3 - 2 mm flowable resin lining. The cavities were restored using Scotchbond Multi-Purpose adhesive system, Filtek Flow and Filtek Z 250 composite resin.

Following one day storage in distilled water, the restored teeth were thermocycled for 500 cycles and immersed in 2% methylene blue for 24 hours.

The results of this study were as follows:

1. Ranking of mean microleakage scores at the enamel margins was Group 1 < Control = Group 2 < Group 3. The microleakage of Group 3 was significantly higher than that of Control, Group 1 and Group 2 (p < 0.05).

2. Ranking of mean microleakage scores at the dentin margins was Group 1 < Group 2 < Control < Group 3. The microleakage of Group 3 was significantly higher than that of Control, Group 1 (p < 0.05).

3. Compared with microleakage between the enamel and dentin margins, enamel margin group were significantly lower than dentin margin group.

In this study we measured the amount of light energy that was projected through the tooth material and analyzed the degree of polymerization by measuring the surface hardness of composites. For polymerization, Optilux 501 (Demetron, USA) with two types of light guide was used: a 12 mm diameter light guide with 840 mW/cm² light intensity and a 7 mm diameter turbo light guide with 1100 mW/cm².

Specimens were divided into three groups according to thickness of penetrating tooth (1 mm, 2 mm, 0 mm). Each group was further divided into four subgroups according to type of light guide and curing time (20 seconds, 40 seconds). Vickers'hardness was measured by using a microhardness tester. In 0 mm and 1 mm penetrating tooth group, which were polymerized by a turbo light guide for 40 seconds, showed the highest hardness values. The specimens from 2 mm penetrating tooth group, which were polymerized for 20 seconds, demonstrated the lowest hardness regardless of the types of light guides (p < 0.05).

The results of this study suggest that, when projecting tooth material over a specified thickness, the increase of polymerization will be limited even if light intensity or curing time is increased.

The purpose of this study was to evaluate the correlation between hybrid layer thickness and bond strength using confocal laser scanning microscope and microtensile bond strength test of two adhesive systems.

The dentin surface of human molars, sectioned to remove the enamel from the occlusal surface. Either Scotchbond Multi-Purpose(3M Dental Product, St. Paul, MN, U.S.A) or Clearfil SE Bond(Kuraray, Osaka, Japan) was bonded to the surface, and covered with resin-composite. The resin-bonded teeth were serially sliced perpendicular to the adhesive interface to measure the hybrid layer thickness by confocal laser scanning microscope. The specimen were trimmed to give a bonded cross-sectional surface area of 1mm², then the micro-tensile bone test was performed at a crosshead speed of 1.0 mm/min. All fractured surfaces were also observed by stereomicroscope.

There was no significant differences in bond strengths the materials(p>0.05). However, the hybrid layers of three-step dentin adhesive system, SM, had significantly thicker than self-etching adhesive system, CS(p<0.05). Pearson's correlation coefficient showed no correlation between hybrid layer thickness and bond strengths(p>0.05). Bond strengths of dentin adhesive systems were not dependent on the thickness of hybrid layer.