The effect of different pretreatment methods of PMMA-based crowns on the long-term tensile bond strength to dentin abutments

The objective of the study was to test the effect of different pretreatments on tensile bond strength (TBS) of adhesively bonded CAD/CAM-generated polymethyl methacrylate (PMMA) crowns to dentin. Two hundred human molars were prepared and divided into 20 groups (n = 10/group). PMMA crowns were pretreated thusly: Monobond Plus/Heliobond (MH), Visio.link (VL), Ambarino P60 (AM), VP connect (VP), and nontreated as control groups (CG). Two resin cements were used for cementation of crowns: Clearfil SA Cement (CSA) and Variolink II (VAR). TBS was measured initially (24 h water storage, 37 A degrees C) and after aging (5,000 thermal cycles, 5/55 A degrees C). TBS was analyzed using one-way ANOVA with Scheff, post hoc, unpaired Student t, Mann-Whitney U, Kruskal-Wallis H, and chi-squared tests. Within CSA, pretreatment with MH and VL showed higher initial TBS compared with AM-treated groups. All other groups showed no statistical differences. For MH, VL, AM, and VP in combination with CSA, a negative impact of aging was observed (p < 0.001), whereas in all VAR groups, no impact was measured. Pretreatment with MH (p = 0.001) and VP (p = 0.008) presented higher initial TBS for CSA than for VAR. After aging, MH (p = 0.025) and VL (p = 0.034) cemented with VAR showed higher results than CSA. All tested groups showed very low TBS values. Pretreatments with MH, VL, and VP have minimally improved the tensile strength after aging. Although the tensile strength results were low, crowns adhesively cemented with pretreatments with MH, VL, and VP showed, after aging, a higher tensile strength than nontreated groups.