Evaluation of the bond strength and stress distribution of space maintainers fabricated from different materials using conventional and digital methods by three-dimensional finite element analysis

Primary teeth play an important role both functionally and aesthetically, while also maintaining the arch space for permanent teeth. Premature loss of primary teeth may lead to problems such as eruption and positional anomalies in permanent dentition, as well as arch asymmetry. To prevent such complications, space maintainers are used to preserve the arch length. The present thesis study was conducted in collaboration between the Faculty of Dentistry, Karadeniz Technical University (KTÜ), and the KTÜ Medical Device Design and Manufacturing Application and Research Center (METAM). The aim of this study was to evaluate the stress distribution on ten experimental groups, created from four different materials and cemented with three types of dental cements, using finite element analysis (FEA). Three-dimensional models were generated from the data obtained by scanning the study model. Space maintainers fabricated from polyetheretherketone (PEEK), composite resin, titanium, and stainless steel were cemented with glass ionomer, resin-modified glass ionomer, and resin cements, and the stress accumulation resulting from masticatory forces was analyzed using FEA. During the process of generating the anatomical geometry for finite element analysis, Materialise Mimics and Materialise 3-matic (Materialise, Leuven, Belgium) software were utilized. The completed designs were exported from Materialise 3-Matic as ".stl" surface model files. To ensure mesh quality and uniformity, initial refinement and adjustments were performed using Nomad Sculpture software. The files were then transferred to Hypermesh for detailed mesh optimization. The maximum element aspect ratio was kept below 2.5, triangular angles were arranged between 30° and 120°, the Jacobian value was maintained above 0.8, and the skew value below 40. After the mesh structure was generated in Hypermesh, it was exported to LS-DYNA in ".k" key file format for analysis. Since the study focused only on the linear elastic behavior region, material properties were defined using the MAT_001-ELASTIC card in LS-DYNA. This card allowed for the definition of essential mechanical properties for each material, such as Young's modulus and Poisson's ratio. As a boundary condition in the analysis, both the occlusal contact area with the opposing dentition and the basal surface of the model were fixed. For the force application, in order to achieve a more realistic simulation, instead of an idealized single-point load, loading was performed by considering multiple contact areas that occur during mastication. This approach aimed to obtain a stress distribution closer to actual clinical conditions. The total applied load was 150 N (Newtons), and this load was distributed to the contact points on both the tooth and the space maintainer. In all material and cement combinations, the stresses generated in the cortical and cancellous bone remained nearly constant; approximately 20 MPa in the cortical bone and around 3 MPa in the cancellous bone. When evaluating the stresses occurring in the abutment tooth, stainless steel space maintainers exhibited the lowest stress values at 41 MPa, suggesting that metallic space maintainers producing lower stresses would be more appropriate to minimize potential damage to tooth structure. When comparing adhesive cement types, resin-modified glass ionomer cement exhibited the lowest stress values with all space maintainer materials, while glass ionomer cement produced the highest stress values. Based on the findings of the present study, to achieve the lowest stress on the abutment tooth and the most homogeneous stress distribution in the supporting tooth, stainless steel space maintainers should be preferred. Furthermore, the lowest stress within the adhesive layer was observed when resin-modified glass ionomer cements were used.