Background: The reduction of dental and alveolar undercuts on plaster models is an important issue in the process of planning partial and complete prostheses. In recent years, new materials such as methacrylate resins that can be used to reduce undercuts have emerged. Their great advantage is high temperature insensitivity and relatively high ease of use.
Objectives: The study aimed at determining the factors that affect the shear bond strength, and which material can be better used at the laboratory stage of preparing the plaster model to facilitate the denture bearing area and reduce the traumatizing impact of the prosthesis.
Material and methods: In the study, 2 composite materials Block-Out Gel LC (VOCO GmbH, Cuxhaven, Germany) and LC Block-Out Resin (Ultradent Products Inc., South Jordan, USA) were used for tests on the Tewerock and Stodent plaster. Specimens consisted of 20 mm × 10 mm × 10 mm plaster blocks as a base, and composite cylinders of 3 mm diameter and 5 mm height, attached to the blocks. The base of the sample was combined with a composite cylinder in the Individo Light Box halogen lamp (VOCO GmbH, Cuxhaven, Germany). A total of 120 samples were studied. The shear bond strength (SBS) test was performed using the Hounsfield H5KS model HTE S/N D83281 fitted with a 5.000-N head using a cutting knife speed of 5 mm/ min.
Results: LC Block-Out Resin and Block-Out Gel LC materials deposited on class III plaster and polymerized at temperatures of up to 100°C had the best SBS (5.59 MPa and 4.0 MPa, respectively). Samples made of LC Block-Out Resin and class IV plaster showed no statistically significant differences between all the groups. Additional polymerization under 2.4 bar was the most effective in improving SBS among Block-Out Gel LC and class IV plaster samples.
Conclusions: The results of the studies show that both the plaster type and the polymerization process have a significant effect on the SBS of light-cured methacrylate material to plaster.
Keywords: composite materials; dental and alveolar undercuts; methacrylate resins; shear bond strength; undercuts reduction.