Research Update: Adhesion

Bond strength and biocompatibility are both highly significant properties of dentin adhesives. These properties of four generations of adhesive systems (Multi-Purpose/Single Bond/SE Plus/Easy Bond) were evaluated. Eighty bovine teeth had their dentin exposed (500- and 200-μm thickness). Adhesive was applied on the dentin layer of each specimen, then the microshearing test was performed for all samples. A dentin barrier test was used for the cytotoxicity evaluation. Cell cultures (SV3NeoB) were collected from testing materials by means of 200- or 500-μm-thick dentin slices and placed in a cell culture perfusion chamber. Cell viability was measured 24 h post-exposition by means of a photometrical test (MTT test). The best bonding performance was shown by the single-step adhesive Easy Bond, followed by Single Bond, SE Plus, and Multi-Purpose. The one-step system showed the best bond strength performance and was the least toxic to pulp cells. In multiple-step systems, a correct bonding technique must be done, and a pulp capping strategy is necessary for achieving good performance in both properties. The study showed a promising system (one-step self-etching), referring to it as a good alternative for specific cases, mainly due to its technical simplicity and good biological responses.

Liu Y, Dusevich V, Wang Y. J Dent Res. 2013 May 30. [Epub ahead of print]

While proanthocyanidins (PA) are effective in im­proving collagen’s resistance to collagenolytic degradation, the direct incorporation of PA into an adhesive system is detrimental to the light-curing thereof. Conversely, the use of PA as a primer could circumvent this issue, but little is known about the efficacy of PA in stabilizing collagen when applied in a clinically relevant manner. This study investigated the pre- and post-digestion morphology of an acid-etched dentin collagen layer that underwent PA treatment for time periods on a scale of seconds. The null hypothesis, that there is no difference between the PA-treated and untreated control group, had to be rejected, since it was revealed that the untreated control could not survive 1 h of exogenous collagenase digestion, while the PA-treated collagen could sustain at least 16 h of digestion with no perceptible changes in collagen structure. In addition, the stabilizing effect of the gold-standard cross-linker glutaraldehyde at comparable experimental conditions was found to be almost non-existent within the 5, 15, or 30 sec of cross-linking permitted. Therefore, PA have been proven to be extraordinarily efficient in stabilizing demineralized dentin collagen against enzymatic challenges in a clinically relevant setting, likely due to the non-covalent nature of their interaction with collagen molecules.

Lim BS, Cheng Y, Lee SP, Ahn SJ. Eur J Oral Sci. 2013;121(3 Pt 1):211-217.

This study was designed to investigate the ability of orthodontic adhesives to adsorb and release chlorhexidine (CHX) after periodic treatment with 1% CHX solution. Composite and resin-modified glass-ionomer cement (RM-GIC) adhesive disks were incubated with whole saliva or distilled water for 2 h. Release of CHX was measured using high-performance liquid chromatography after 1, 2, and 5 d of incubation, 1 min after exposure to 1% CHX solution. The CHX measurements were performed in a 5-d cycle, which was repeated four consecutive times (n = 7). The amount of CHX adsorbed and the cumulative amounts of CHX released, with respect to type of adhesive and saliva-coating, were analyzed using repeated-measures ANOVA. Chlorhexidine-adsorbed orthodontic adhesives demonstrated a short-term release of CHX, which rapidly returned to near-baseline levels within 3 d. Saliva-coating did not significantly influence CHX release from RM-GIC, but increased the amount of CHX released from the composite. This study suggests that composite adhesives may be a significantly more effective CHX reservoir than RM-GICs in the oral cavity filled with saliva.