The adhesive technology - cornerstone of modern, Minimal Invasive
Increased technique sensitivity of the total-etch system led to development of the self-etching technique. Although these systems produce good results when used correctly, total-etch multi-step adhesives were regarded as highly technique-sensitive due to the precision required for the working steps: excessive etching removed more minerals from the dentin than desired and exposed the collagen fibers to a depth which was greater than the following adhesive could penetrate. Excessive drying caused the exposed collagen fiber network to collapse and blocked the access of the adhesive to the dentin areas below. This led to lower adhesive strength and simultaneously sensitivities and biting down pain.
The selection of the volatile solvent in the bonding systems also influenced the moisture of the dentin surface required for ideal results:
Since alcohol is lighter than water, alcohol-based systems require an extremely dry surface, which means that there is a high risk of overdrying. Acetone-based adhesives, on the other hand, work best on a slightly moist surface because acetone is drawn into the tubuli through a moist surface. But since the definition of “slightly moist” is difficult to realize during actual work, the bonding results are worsened if the surface is either too dry or too moist.
Direct desensitization and conditioning with water-based self-etching
adhesives of the CLEARFIL series.
“CLEARFILTM LINER BOND 2” was introduced by Kuraray at the beginning of the 1990s as the first self-etching adhesive in the world. The objective was to eliminate the technique sensitivities caused by the total-etch technique. A water-based, self-etching primer was developed to avoid problems related to a separate etching technique or a defined surface moisture. This primer conditioned enamel and dentine in much the same way as phosphoric acid, but was not as aggressive and could be buffered in its effect by released calcium.
The slightly acidic pH value was thus reduced further and dropped to a neutral level, which allowed the primer to stay in the cavity. This made it possible to avoid complicated work steps such as rinsing, drying, changing cotton rolls as well as the risks of excessive etching and overdrying. The following adhesive without any volatile solvent could now penetrate all of the dentin layers, closing the dentin tubuli and contributing after the polymerization to prevention of post-operative sensitivities.
The development of the MDP adhesive monomer has improved further the chemical bond properties of the self-etching Kuraray adhesive. The collagen fibrils in the thin hybrid layers are not completely lost the hydroxylapatite, in contrast to the total-etch technique. The remaining hydroxylapatite can directly bond chemically with phosphate groups of Kuraray's own MDP monomer.
A similar effect can also be observed in the enamel. Although the enamel structure is only slightly affected, no fissure formation is determined between the adhesive, composite, and enamel. Although the adhesive strength without prior enamel etching was questioned when this technique was first introduced, various studies worldwide have since proven the equality of the MDP-based self-etching systems.
Due to Kuraray's lead in research in the field of adhesive and resin technology, Kuraray Dental Products achieve outstanding rankings in clinical in-vivo and in-vitro examinations. “REALITY”, an independent American test institute, certified that CLEARFILTM SE BOND caused absolutely no post-operative complaints (Issue 118, February 2000), while CRA praised the all-in-one adhesive CLEARFILTM S3 BOND as the best in its class from a total of 4 all-in-one systems which were tested. (Reports available on request)