Adhesive bond strength of provisional screw-retained CAD-CAM crowns to titanium bases: An in vitro evaluation

To assess the adhesive bond strength of two provisional screw-retained computer-aided design and computer-aided manufacturing (CAD-CAM) crowns bonded to titanium bases (TiB) following artificial aging, tensile testing, and failure mode analysis.

Ninety CAD-CAM hybrid abutment crowns (HAC) were evaluated: poly(methyl)-methacrylate ([PMMA], n = 40), polymer-infiltrated ceramic network ([PICN], n = 40), and lithium disilicate ceramic ([LS₂], n = 10, control). HACs were cemented to TiB (internal hex, 4.3 mm diameter, 4 mm height, n = 90) using two permanent resin-based cements. Artificial aging was performed via thermocycling (5000 cycles, 5°C-55°C). Tensile bond strength (TBS) was assessed, and failure mode distribution was analyzed using loupes magnification and scanning electron microscopy. Non-parametric tests were used due to non-normal data. Mann-Whitney and Kruskal-Wallis tests compared cement and crown type impact on TBS. Chi-square tests analyzed differences in failure mode and dominant cement location.

All specimens withstood artificial aging. One LS₂ sample was excluded after exceeding the testing limit (>1118 N). PICN demonstrated the highest median TBS (749.8 N), significantly outperforming PMMA (p < 0.001) and LS₂ (p = 0.029, unadjusted pairwise Mann-Whitney U). Cement type was not a statistically significant factor within material groups. Mixed failure modes (79.8%) were predominant, and adhesive failures accounted for 20.2%. Cement remnants were primarily localized on the TiB surface (49.4%).

PICN exhibited superior bonding performance, indicating its suitability for immediate loading in implant-supported restorations. In contrast, PMMA may require modified cementation protocols to achieve optimal retention. These findings provide critical insights for material selection in prosthetic rehabilitation.