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12 Pipop Saikaew先生【Mahidol University】:Smear layer, TEM, surface prepatation

 12 Pipop Saikaew先生【Mahidol University】:Smear layer, TEM, surface prepatation

■ 経歴等

Doctor of Dental Surgery, Mahidol University, Bangkok, Thailand(08年卒)
Higher Grad in Operative Dentistry, Mahidol University, Bangkok, Thailand(11年卒)
Master degree in Dental Science (Operative Dentistry), Mahidol University, Bangkok, Thailand(13年卒)

Ph.D. in Dental science (Operative Dentistry), Hokkaido University, Hokkaido, Japan

■ 現在の肩書:

Lecturer at Faculty of Dentistry, Mahidol University, Bangkok, Thailand

■ 研究キーワード

Smear layer, self-etching adhesive, universal adhesive, transmission electron microscope, surface preparation

■ Research outline(研究概要)

Adhesive system can be divided into 2 strategies: smear layer removal (etch-and-rinse) and smear layer modification (self-etch). Smear layer is completely removed by phosphoric acid in etch-and-rinse system. On the other hand, due to the weak acidity of the self-etching system, smear layer is partially dissolved by acidic monomer. The residual smear layer is subsequently incorporated into the hybrid layer. There was a concern that smear layer might affect the penetration of self-etching adhesive to underlying dentin, especially mild self-etching adhesives.



However, previous studies demonstrated the controversial results about this issue. In addition, characteristics of smear layer may vary according to the instrument used for surface preparation and lead to the different outcome when bonded to self-etching system.


My research topics are focused mainly on the effect of smear layer created from different instruments on the bonding performance of self-etching adhesives and how to improve the bonding effectiveness when using self-etching adhesives.


■ Research results(研究成果)

According to the results of my previous studies, the bonding outcome of self-etching adhesives were affected by the instruments for smear layer preparation. The thickness of smear layer is also important but the density of smear layer has more impact on the resultant bond strength. Silicon carbide papers are routinely used in laboratory research to standardize the dentin surface. However, the diamond burs are more clinically relevant. It was the diamond bur-cut smear layer that demonstrated negative effect on the bond strength of self-etching adhesive. The plausible explanation might be due to the different characteristic of smear layer from different surface preparations. The higher heat and pressure created during high-speed cutting with diamond bur might lead to the more compact smear layer and therefore, more difficult for mild acidic monomer of self-etching adhesive to demineralize. The remnant of smear layer that incorporated into the hybrid layer might be the reason for the lower bond strength.
Therefore, it is important to understand the effect of different smear layer preparation when self-etching adhesive is used.


The second research topic is about how to improve the bond strength using self-etching adhesive. Due to mild acidity of self-etching adhesive, many bonding modifications can be done to improve the bonding performance. The mechanical application e.g. active application or double application demonstrated the beneficial effect regarding smear layer removal, resin penetration and more integrated adhesive layer. Some adhesive might be suggested by the manufacturer to apply and leave without disturb but we found that actively applied the adhesive can improve the bond strength.


The recent materials were claiming that the bond strength is still high even the adhesive is applied with the reduced application time (quick bonding technique). However, we are the first group that demonstrated the drawback of such application technique. Bonding with reduced application time led to the lower bond strength and more porosity in the adhesive layer. The porosity might be the solvent entrapped in the adhesive layer that failed to evaporate due to the limited application time. By applying the adhesive according to the manufacturer’s instruction allowed more time for adhesive to demineralize smear layer and more solvent evaporation.


Another way to improve solvent evaporation is to extended air-blowing time. We found that extension of the air-blowing time from 5 s (as suggested by the manufacturer) to 15 s or 30 s can improve the immediate and long-term bond strength of the ethanol-based adhesive. However, the effect is material dependent. For the acetone-based adhesive, the bond strength was similar but the solvent entrapped in the adhesive layer were reduced, as observed the lower incidence of porosity in the adhesive layer from SEM observation.


■ Future research(展望)

As I mentioned before that the instrument for smear layer preparation is important when using self-etching adhesive, my research topic is now focusing on the effect of the current bur-cut smear layer. We regularly use coarse diamond bur for tooth preparation. However, it was reported that carbide bur also gives the good outcome. In addition, the superfine diamond bur with the smaller abrasive particle size might lead to the thinner smear layer and higher bond strength. These bur-cut smear layers combined with the simulate pulpal pressure would be interesting to see whether there is any difference.


■ For Clinicians(臨床家の先生方にお伝えしたいこと)

For clinicians, I think that it is important to understand that what kind of smear layer that we are dealing with. Most publications tested the bonding performance of the adhesive on the SiC-ground dentin. Therefore, the outcome might be different when compared to the bur-cut dentin. One more thing is to apply the adhesive according to the manufacturers’ instruction. Most of the shortcuts lead to the wrong way or inferior outcome. It is better to do more than the instruction rather than finding shortcuts.


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