Comparative stress analysis of mid-pontic and full-pontic CAD/CAM implant prosthesis using different restoration materials

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Abstract
OBJECTIVE:To evaluate the magnitude and distribution of stress on peri-implant bone influenced by the elastic properties of indirect restorative materials (Cerasmart, Enamic, E-max, 4Y-ZrO2, and 3Y-ZrO2), dental implant materials (Alumina Toughened Zirconia ATZ Implant vs. Ti-6Al-4V), design of the implant fixed prosthesis (full-pontic cantilevered vs. mid-pontic cantilevered) and loading conditions. Validate finite element models in dental implants by means of photoelasticity studies by analyzing fringe contours in the implant area and by means of strain gauge studies by analyzing the microstrain of the peri-implant bone area. MATERIALS AND METHODS: Cerasmart, Enamic, E-max, and ZrO2 YZ CAD/CAM screw-retrievable, cement-retained implant bridges #24, 25, total as n=16 IFDP, were divided and prepared for 4.2×10 mm Nobel Pearl Tapered ATZ Zirconia prosthesis (n = 8) and for 3.75×10 mm Nobel Parallel Conical Connection Ti-6AL-4V (n = 8). Mid-pontic and full-pontic cantilevered designs were created using Dentsply-Sirona Inlab software (SW 20.0). The prosthesis was milled with a Dentsply-Sirona inLab MC X5. The restoration models used were STL-designed files IFDP of the 360 scans of the implant and esthetic abutments imported from the Dentsply-Sirona inlab CAD software SW 20 and a section of mandibular bone with a single implant containing a cemented retained implant bridge IFDP #24,25 for both implant ATZ and Ti-6AL-4V. All the implants were embedded into photoelastic PL-2 resin (Vishay Micro-Measurements Group) For the photoelastic measurement, each specimen was subjected to an axial static load related to the 3rd fringe order at the connector area using a universal testing machine (Instron 5566A). The fringe color changes were recorded using a Nikon D5600 camera. Strain gauges provide a non-destructive method used to measure microstrain in the peri-implant area, allowing for the reuse of implants. For this study sawbones blocks (21x15x15mm) were prepared and ATZ and Ti alloy implants positioned within, strain gauges were aligned and attached, and a 150 N load was applied in the connector area. Connected to a Wheatstone bridge circuit, the gauges measured microstrain around implants #24 and 25 IFDP. In the Finite Element Analysis FEA, a three-dimensional (3D) finite element analysis was performed to obtain the maximum stress on crown, bone, and implant. Different crown materials (Cerasmart, Enamic, E-max, 4Y-ZrO2, and -ZrO2 YZ were considered for each of the two implant materials: 3.75x10mm Ti Nobel parallel and 4.2x10mm ATZ. A 150-N static load was applied on the incisal edges to the axial axis of the implant with different loading scenarios: central, distal cantilevered, mid cantilevered, and multiple loading positions. The data was analyzed using a multi-way ANOVA regression model using JMP Pro. Validation tests (Load Displacement, Load to failure test) were performed on an Instron 5566A and used as a reference for experimental methods (photoelastic and strain gauges) and numerical ones (FEA). RESULTS: In general, the ATZ implant group showed a higher magnitude of stress than the Ti group, as seen as in microstrain values of peri-implant bone were 216 µε in ATZ and 185 µε in Ti groups. In the ATZ implant group, there was a higher magnitude of stress on the full-pontic design compared to the mid-pontic design. Compared to the full-pontic design, the Ti implant group showed a higher stress in the crown region for mid-pontic, while lower stress in the implant region and no significant difference in supporting bone; however, in the mid-pontic design, the stress is well distributed on both sides of the implants. No significant difference in stress magnitude was observed with different crown materials. However, in the Ti alloy and ATZ groups, e.max exhibited the highest von Mises stress among all IFDP restoration materials. CONCLUSION: The implant material with lower elastic modulus, mid-pontic cantilevered design, and central or multiple contact distributed loading showed lower stress magnitude. The mid-pontic IFDP design offers a practical option when adequate mesiodistal distance for a full-pontic design is unavailable. When using Alumina Toughened Zirconia (ATZ) implants compared to Titanium (Ti) alloy implants, there is a significant increase in stress on the peri-implant bone, no significant differences in Young’s modulus among various restorative materials, indicating similar elasticity characteristic, significant differences were observed in the cantilevered load applications across different IFDP designs, impacting their biomechanical performance. The study employed load-displacement and load-to-failure tests for the validation of photoelastic analysis and strain gauge experiments. All of these results demonstrate a strong correlation to FEA results, underscoring their reliability and accuracy in assessing IFDP designs.
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2024
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