A Comparative In Vivo Analysis of Microhardness in Three Provisional Restorative Materials

Provisional restorations are vital in fixed prosthodontics, offering interim esthetics, function, and support until the final restorations are placed. This in vivo study compared the microhardness of three provisional restorative materials, namely, computer-aided design/computer-aided manufacturing (CAD/CAM)-milled polymethyl methacrylate (PMMA), bisacrylic (Protemp 4), and heat-cured PMMA, after 14 days of intraoral exposure.

Thirty patients aged 18-50 years, requiring metal-ceramic crowns on the mandibular first or second molars, were selected from the Department of Prosthodontics, Ganni Subba Lakshmi Dental College and Hospital, Rajahmundry, India. After tooth preparation, impressions were made using irreversible hydrocolloids, and the casts were poured with die stones. Two temporary crowns per material were fabricated for each patient using the indirect impression technique: CAD/CAM-milled PMMA via intraoral scanning and milling, bisacrylic via putty index, and heat-cured PMMA via compression molding. One crown per pair (Group A, control) was tested immediately, whereas the other (Group B, case) was cemented intraorally with zinc oxide-eugenol for 14 days. All crowns were embedded in standardized wax blocks and subjected to Vickers microhardness testing (1 kg load, 15 s).

Independent t-tests revealed a highly significant reduction in microhardness (p < 0.001) in the case groups compared with the control groups for all materials. Mean microhardness in the control group was 22.4 ± 1.2 kg/mm² for CAD/CAM-milled PMMA, 20.8 ± 1.0 kg/mm² for Protemp 4, and 25.6 ± 1.4 kg/mm² for heat-cured PMMA; in case groups, values dropped to 18.1 ± 0.9 kg/mm², 16.5 ± 0.8 kg/mm², and 22.3 ± 1.1 kg/mm², respectively. Heat-cured PMMA exhibited a significantly higher microhardness in both groups (p < 0.001), with CAD/CAM-milled PMMA and Protemp 4 showing comparable values.

The findings indicated that heat-cured PMMA offered superior resistance to intraoral degradation, guiding clinicians toward optimal material selection for durable provisional restorations. Further studies should assess their long-term performance and additional properties.