Influence of QAMs on conversion and E-modulus of adhesive resins

Quaternary ammonium methacrylates (QAMs) are able to inhibit dentin matrix metalloproteinases (MMPs), which contribute to progressive degradation of collagen fibrils in hybrid layers. Thus, the addition of QAMs to adhesive resins has been proposed.

Objectives : The aim of this study was to measure the degree of conversion (DC) and elastic modulus (E) of experimental adhesive blends containing QAMs. The hypothesis tested was that DC and E of resin blends is not affected by QAMs content.

Methods: Light-curing experimental adhesive blends containing 70wt% resin (R2: 70wt% bisGMA, 28.75wt% TEGDMA; R3: 70wt% BisGMA, 28.75wt% HEMA; R4: 40wt% BisGMA, 30wt% TCDM, 28.75wt% TEGDMA; R5: 40wt% BisGMA, 30wt% BisMP, 28.75wt% HEMA), 20wt% ethanol (ETOH) and 10wt% QAMs in their anhydrous form (ATA or MCMS or METMAC) were prepared. All blends included 1wt% EDMAB+0.25wt% CQ. Resins with no QAMS were used as a control (80wt% R2-R5+20wt% ETOH). Resins were photo-polymerized with a halogen curing light for 40s. DC of resin blends was measured by FTIR, while E was measured using a biaxal flexure test. Data were analyzed with a two-way ANOVA and Tukey's post hoc test.

Results: DC was not affected by QAMs' addition (Table 1). A correlation between DC and E could not be found because E varied depending on the type of resin or QAM contained in the blends.

Table 1. Means and standard deviations of DC and E of the tested resin blends.

Resin blend	DC	E
80wt%R2+20wt%ETOH	59±5a	359±51def
80wt%R3+20wt%ETOH	63±5abc	447±40fg
80wt%R5+20wt%ETOH	60±7ab	326±24cde
70wt%R2+20wt%ETOH+10wt%ATA	71±3abc	369±38ef
70wt%R3+20wt%ETOH+10wt%ATA	75±7c	399±27ef
70wt%R5+20wt%ETOH+10wt%ATA	66±2abc	151±21a
70wt%R2+20wt%ETOH+10wt%MCMS	67±5abc	183±29ab
70wt%R3+20wt%ETOH+10wt%MCMS	70±2abc	531±34g
70wt%R5+20wt%ETOH+10wt%MCMS	75±2bc	237±37abc
70wt%R2+20wt%ETOH+10wt%METMAC	64±3abc	392±32ef
70wt%R3+20wt%ETOH+10wt%METMAC	69±7abc	833±61h
70wt%R5+20wt%ETOH+10wt%METMAC	69±6abc	260±25bcd

Same superscript letters indicate no statistical difference (p>0.05).

Conclusions: The tested hypothesis was partially accepted since QAMs addition did not affect DC when QAMs were added, while E varied in relation to resin and QAM type.

Supported, in part, by grants: FIRB RBAP1095CR and PRIN 2009SAN9K5 and 2009FXT3WL from MIUR, Italy, R01DE015306 to DHP (PI), and #8126472 from the Academy of Finland to AT-M (PI).