Comparison of Epoxy Resin and Rigid Polyurethane Foam as a Bone Substitute to Study Implant Biomechanics

Introduction  The study of biomechanical factors is crucial for discerning the solutions relating to implant failures. These factors are analyzed using in vitro models. These models help us to understand the relation of these variables with implant biomechanics. Multiple materials are available for use as bone substitutes for in vitro studies. Each material has its own pros and cons, and there is no single material that can ideally replicate bone behavior under intra-oral conditions.  Objectives The objective of this study was to synthesize and compare the two synthetic bone substitute materials as a biomechanical bone model to evaluate the stress distribution in the peri-implant region using strain gauge analysis.  Materials and methods The two bone substitutes used were polyurethane (PU) foam (Sawbones, Vashon, Washington, United States) and epoxy resin (Polycraft ClearTop 35 Epoxy Water Clear Resin System, MB Fibreglass, Newtownabbey, Northern Ireland). The PU models were designed in two densities to mimic bone type 2 as per the Misch classification. A mold was used for the epoxy resin models. Dental implants of two different thread designs were used for biomechanical load transfer. The implants were placed in both types of models using the manufacturer's instructions. A strain gauge was bonded over each model adjacent to the upper third (coronal) region of each implant. The strain gauge was connected to the strain meter. A combined (axial and non-axial) loading ranging from 50 N to 300 N magnitude was applied using a universal testing machine (UTM). The load was applied using a porcelain fused to a metal prosthesis bonded over a bolt head which was fixed in the crosshead of the UTM. The strain rate was 0.95 mm/min, and the strain values were recorded using a strain meter. The collected data was organized and analyzed using IBM SPSS Statistics for Windows, Version 22.0 (Released 2013; IBM Corp., Armonk, New York, United States). Results All strain values recorded were less than 3000 µε and within the physiological loading zone per the Frost theory. The difference between the strains produced in both models was statistically significant (p≤0.05). The strain values recorded were higher in the PU model as compared to epoxy resin. Conclusions PU foam can be preferred as a bone substitute in biomechanical studies as it provides a more accurate estimation of strain in the peri-implant region. Its wide range of available densities can allow researchers to mimic various types of bones, facilitating the analysis of stress and strain distribution produced by the implants under study.