Background: Fixed dental prostheses typically require significant reduction of tooth. In contrast, partial coverage retainers, such as inlays and on lays, offer a more conservative approach, preserving healthy tooth structure to a maximum extent. However, conventional inlay designs as retainers for fixed dental prostheses are prone to debonding under lateral loading. This study aims to incorporate new design features to improve the retention of inlay-retained zirconia fixed dental prostheses (IRZFDP) and to compare the retention between conventional design and the modified design.
Materials And Methods: Clinical situation mimicking a missing maxillary first molar was simulated in vitro by mounting freshly extracted maxillary first premolar and maxillary second molar in auto polymerizing poly methyl methacrylate acrylic resin base, with a pontic space of 10 mm in between. Twenty-two models were subjected to test and were divided into two groups - Group A and Group B. In group A, conventional cavity preparation was done with a mesiodistal length of 4mm and 6mm for premolar and molar respectively. The occlusal inlay preparation was 2.5 mm deep and the proximal margin was 1 mm deep shoulder with no bevels. Cavity width was 4mm for both premolar and molar with approximately 6° divergence of the walls. The proximal box was prepared with 1 mm width and 2 mm extension apical to the floor of the isthmus with approximately 6° divergence. The buccolingual extension was standardized as 2/3rd of intercuspal width (ICW) in molar. The modified design in the molars involved the conventional occlusal preparation and a T- shaped buccal and lingual extension having a width of 4mm and depth of 2.5mm. IRZFDPs were cemented with dual cure resin cement and was tested for retention using universal testing machine under applied load.
Results: The retention values were summarized as mean. The comparison of mean retention values between the groups was done using independent t test. The average retention values in group A was 114.9 N and in group B was 159.4 N. Group B demonstrated a statistically significant increase in retention when compared to Group A, with a p value <0.05.
Conclusion: The modified tooth preparation design for IRZFDP exhibited a statistically significant increase in retention against tensile loads when compared to conventional tooth preparation design.
