# Evaluation of the Effectiveness of Semolina in Improving the Bond Strength of Metal Alloys and Acrylic Resins for the Fabrication of Hybrid Prostheses for Implant Restoration: An In Vitro Study

## TL;DR

This study shows that using semolina can improve the bond strength between metal and acrylic in hybrid dental prostheses, offering a cost-effective solution.

## Contribution

The study introduces semolina as a novel, economical material to enhance the bond strength between metal alloys and acrylic resins in hybrid prostheses.

## Key findings

- Semolina significantly increased shear bond strength compared to other methods.
- Semolina outperformed DMLS Ti and DMLS CoCr in bond strength.
- Semolina burned out cleanly during dewaxing, improving mechanical bonding.

## Abstract

Introduction

Fixed prosthodontic solutions for restorations of multiple implants are often done using acrylic-metal hybrid prosthesis. These restorations have a high failure rate due to poor bond strength between metal and acrylic, despite using digital attachments and primers. This study has been done to demonstrate an economical yet effective method of increasing shear bond strength between acrylic and metal.

Materials and methods

Disc specimens of 10 mm diameter and 2 mm thickness were designed using the Meshmixer version 3.5 software (Autodesk Inc., San Rafael, USA). The standard tessellation (STL) file was imported and sent for direct metal laser sintering (DMLS) in cobalt-chromium (CoCr), titanium (Ti), and wax milling. The groups were defined. Ten samples were included in each group. Group 1: Conventional Casting in CoCr; Group 2: Conventional Casting with Opaquer (CoCr); Group 3: DMLS CoCr; Group 4: DMLS CoCr with Opaquer; Group 5: DMLS Ti; Group 6: DMLS Ti with Opaquer; Group 7: Casting with Semolina (CoCr); and Group 8: Casting with Semolina and Opaquer (CoCr). Wax-up was performed using double wax sheet thickness of modeling wax. Flasking and acrylization were done using the injection moulding technique. A universal testing machine was used for shear bond strength. Results were tabulated and statistical analysis was done using IBM SPSS Statistics for Windows (IBM Corp., Armonk, USA). The Shapiro-Wilk test was done to confirm the normality of the data, followed by the one-way analysis of variance (ANOVA) test to compare the shear bond strength between metal alloys and heat cure acrylic resin.

Results

The one-way ANOVA results reveal significant differences in bond strengths among the various groups. Conventional Casting with Opaquer showed no significant difference (p=0.335), but there were notable improvements in bond strength when compared to DMLS CoCr, DMLS CoCr with Opaquer, DMLS Ti, DMLS Ti with Opaquer, Semolina, and Semolina with Opaquer, with DMLS Ti having the largest mean difference (3.368). Conventional Casting with Opaquer significantly outperformed all groups, especially Semolina, which showed the highest mean difference (7.558). Similar trends were seen with DMLS CoCr and DMLS Ti, where Semolina consistently demonstrated superior bond strength. Overall, Semolina produced the highest bond strengths across all conditions. These results underscore the importance of material selection and treatment in enhancing bond strength.

Conclusion

Semolina can be used as an economical and reliable method to increase the shear bond strength between acrylic and metal bonding. Its ability to burn out during dewaxing without any remains or remnants in mould deems it a useful material for increasing mechanical bonding.