Effect of QAM-based Primers on the adhesive interface

Objectives:  Quaternary ammonium methacrylates (QAMs) inhibit dentin metalloproteinases involved in hybrid layer degradation. Thus, the incorporation of QAMs in dentin-primers has been proposed. The aim of this study was to measure microtensile bond-strength (mTBS) and interfacial nanoleakage expression (NE) of a commercial adhesive system after dentin pre-treatment with three different QAMs used as therapeutic primers. The tested hypothesis was that the use of QAMs as dentin primers would not reduce immediate mTBS or increase NE.

Methods:  Twenty human molars were selected and sectioned to expose middle-deep dentin. Dentin specimens were acid-etched with 35% phosphoric acid for 15s and divided in four groups depending on the primer used: (1) 70% METMAC+29% ethanol+1% TPO; (2) 70% MCMS+29% ethanol+1% TPO; (3) 70% ATA+29% ethanol+1% TPO; (4) no primer (control). Each QAM-based primer was applied twice for 30s and gently air-dried. All specimens were then bonded with Scotchbond 1XT (SB1XT; 3M ESPE) polymerized for 20s and composite build-ups were prepared. Specimens were sectioned in sticks (0.9x0.9mm) in accordance with the non-trimming microtensile technique. Sticks were stored for 24h at 37°C in artificial saliva before being pulled to failure (1 mm/min). Bond-strength data were statistically analyzed with one-way Anova and Tukey's post-hoc test. Additional specimens were immersed in silver nitrate for NE analysis under light-microscopy and statistically analyzed (χ2 test).

Results:  Means and standard deviations (expressed as MPa) of mTBS are summarized in Table 1. No difference was found in the NE of QAMs-treated specimens compared to control (p>0.05).

Conclusions:  The tested hypothesis was partially accepted because only MCMS gave mTBS results comparable to control. Further studies are needed to evaluate if QAMs can be suitable primers for clinical applications. Supported, in part, by grant R01 DE01530-6 from the NIDCR to DP (PI).