Investigation of the effect of implant crown ratio and material type on the force transmitted to the implant in implant-supported restorations: a finite element analysis study

Aims: The crown implant ratio may pose a problem, especially when short implants are used. This condition is associated with marginal bone loss. Therefore, in this study, it was aimed to evaluate the stresses arising from the bone, implant and its parts and the restoration by finite element analysis (FEA), as a result of comparing a situation with ideal bone support and a similar situation with vertical bone loss. The null hypothesis is that the type of material and crown length chosen for implant-supported restorations will not make a difference in terms of stress on implants of different sizes. Methods: For this study, 8 mm implants were placed in the 44-46 region and a group with a 3-unit 12 mm length fixed prosthesis and a group with 12 mm implants and a 3-unit 8 mm length fixed restoration were designed. The data of the implant parts were obtained from a implant company (Bilimplant, İstanbul, Turkiye) and placed in the appropriate position within a bone data drawn in the Solidworks 2013 software (Solidworks Corp., USA). Appropriate multi-unit parts were then added and 3-unit restorations were designed with exocad. Necessary arrangements were made in the Geomagic Design X 2020 (3D systems, Morrisville, NC, USA) program, the restorations were given the characteristics of 2 different materials (lithium disilicate and zirconia). Applying a force of 200 N on the occlusal direction, the maximum principal stress values ​​​​occurring in the bone, implant, multi-unit, restoration and occlusal screw were recorded. Results: Principal stress (Pmax) values recorded on the implant for the 1st premolar were higher on the 12 mm implant (B1 and B2 groups) and lower on the 8 mm implant. For the implant applied to the 1st molar region, higher stress values were observed in the groups with 8 mm implants (A1 and A2 groups), while lower values were observed with 12 mm implants (B1 and B2 groups). Conclusion: As the crown/implant ratio increases in favour of the implant, the survival of the unit decreases. In addition, it is more appropriate to prefer rigid materials in implant restorations.