Finite Element Analysis and In Vitro Assessment of Multirooted Custom Implants Manufactured by Additive and Subtractive Technologies

Objective: The aim of this study was to evaluate the accuracy of milled and 3D printed titanium and zirconia multi-rooted root analogue implants (RAIs) and compare their biomechanical behaviour to conventional threaded implants (TIs) experimentally and numerically through the creation of a validated finite element model. Materials and methods: A multi-rooted RAI was modelled based on tooth 47 segmented from cone-beam computed tomography (CBCT). Four RAI subgroups, 3D-printed titanium (PT), 3D-printed zirconia (PZ), milled titanium (MT), and milled zirconia (MZ), were fabricated, along with two TI subgroups (4.5 x 11 mm and 5.5 x 11 mm) as controls. Specimens were evaluated for precision and trueness using high-resolution scanning and 3D measurement software, with root mean square (RMS) deviations statistically analysed. Samples were embedded in artificial bone blocks and subjected to biomechanical testing using a specialised biomechanical test system to quantify micromotion. Additionally, a validated finite element model incorporating RAIs and TIs was developed, reproducing experimental boundary conditions. The model was assessed under immediate placement (touching contact) and osseointegrated conditions (glued contact). A 300 N load was applied axially and at 30° to evaluate equivalent stress, maximum principal stress, microstrain, and displacement. Results: PZ demonstrated the highest precision (RMS: 21±6 μm), while MZ had the highest trueness (RMS: 66±3 μm). MT exhibited the lowest trueness and the greatest deviation in the furcation area (612±64 μm). In vitro micromotion analysis showed no significant differences in the loading direction (Z-axis) between RAIs and TIs, whereas RAIs had higher total displacement compared to TIs (96.5 μm vs. 55.8 μm). Finite element analysis (FEA) showed that RAIs outperformed TIs, exhibiting lower stress, reduced microstrain (4,000 με vs. 13,000 με), and enhanced primary and secondary stability with lower micromotion. Conclusion: The manufacturing method significantly affected RAI accuracy, with PZ showing the highest precision and MZ the highest trueness. RAIs demonstrated promising biomechanical behaviour, though anatomical variations influenced predictability. FEA confirmed RAIs’ superior stress distribution and stability over TIs, highlighting their potential as a viable alternative for immediate implant placement.