The purpose of this study was to evaluate the influence of sodium ascorbate on microtensile bond strengths of total-etching adhesive system to pulp chamber dentin treated with NaOCl.

Pulp chambers of extracted human non-caries permanent molars were treated as follows: group 1, with 0.9% NaCl; group 2, with 5.25% NaOCl; group 3, with 5.25% NaOCl and 10% sodium ascorbate for 1min; group 4, with 5.25% NaOCl and 10% sodium ascorbate for 1 min and 10ml of water; group 5, with 5.25% NaOCl and 10% sodium ascorbate for 5 min; group 6, with 5.25% NaOCl and 10% sodium ascorbate for 5 min and 10ml of water; group 7, with 5.25% NaOCl and 10% sodium ascorbate for 10 min; group 8, with 5.25% NaOCl and 10% sodium ascorbate for 10 min and 10ml of water. Treated specimens were dried, bonded with a total-etching adhesive system (Single bond), restored with a composite resin(Z250) and kept for 24h at 100% humidity to measure the microtensile bond strength.

NaOCl-treated group (group 2) demonstrated significantly lower strength than the other groups. No significant difference in microtensile bond strengths was found between NaCl-treated group (group 1) and sodium ascorbate-treated groups (group 3-8). The results of this study indicated that dentin treated with NaOCl reduced the microtensile bond strength of Single bond. Application of 10% sodium ascorbate restored the bond strength of Single bond on NaOCl-treated dentin. Application time of sodium ascorbate did not have a significant effect.

Present tooth bonding system can be categorized into total etching bonding system (TE) and self-etching boding system (SE) based on their way of smear layer treatment. The purposes of this study were to compare the effectiveness between these two systems and to evaluate the effect of number of themocycling on microleakage of class V composite resin restorations.

Total forty class V cavities were prepared on the single-rooted bovine teeth and were randomly divided into four experimental groups: two kinds of bonding system and another two kinds of thermocycling groups. Half of the cavities were filled with Z250 follwing the use of TE system, Single Bond and another twenty cavities were filled with Metafil and AQ Bond, SE system. All composite restoratives were cured using light curing unit (XL2500, 3M ESPE, St. Paul, MN, USA) for 40 seconds with a light intensity of 600 mW/cm².

Teeth were stored in distilled water for one day at room temperature and were finished and polished with Sof-Lex system. Half of teeth were thermocycled 500 times and the other half were thermocycled 5,000 times between 5℃ and 55℃ for 30 second at each temperature.

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

From this study, following results were obtained: There was no interaction between variables of bonding system and number of thermocycling (p = 0.485). Microleakage was not affected by the number of thermocycling either (p = 0.814). However, Composite restoration of Metafil and AQ Bond, SE bond system showed less microleakage than composite restoration of Z250 and Single Bond, TE bond system (p = 0.005).

The purpose of this study was to evaluate the etching effects and bond strength of total etching and self-etching adhesive system on unground enamel using scanning electron microscopy and microtensile bond strength test.

The buccal coronal unground enamel from human extracted molars were prepared using low-speed diamond saw. Scotchbond Multi-Purpose (group SM), Clearfil SE Bond (group SE), or Adper Prompt L-Pop (group LP) were applied to the prepared teeth, and the blocks of resin composite (Filtek Z250) were built up incrementally. Resin tag formation was evaluated by scanning electron microscopy, after removal of enamel surface by acid dissolution and dehydration. For microtensile bond strength test, resin-bonded teeth were sectioned to give a bonded surface area of 1mm². Microtensile bond strength test was perfomed.

The results of this study were as follows.

1. A definite etching pattern was observed in Scotchbond Multi-Purpose group.

2. Self-etching groups were characterized as shallow and irregular etching patterns.

3. The results (mean) of microtensile bond strength were SM; 26.55 MPa, SE; 18.15 MPa, LP; 15.57 MPa. SM had significantly higher microtensile bond strength than SE and PL (p < 0.05), but there was no significant differance between SE and PL.