Mandibular Arch Configuration and Immediate Protocol. A Finite Element Assessment

Objectives: The aim of this study was to evaluate the influence of different mandibular arch configurations on the stress distribution in lower protocol using 3-D finite element analysis (FEA).

Material and methods: 3 FEA models of a mandibular segment were built varying the mandibular arch (A) configuration in transversal plane: small (SA) - mandibular arch with the interforaminal distance (IFD)=45mm; regular (RA) - IFD=55mm; and large (LA) - IFD=65mm. Following that configuration, the two most posterior implants were placed closer to lingual side for the ML, and closer to the buccal side for the MS. A prefabricated lower bar was attached to 4 implants (4.00 x 13.00mm (NEOPRONTO®)) and placed in the same position for all models. The loading (L) conditions were: L1 - anterior loading on the top surface of the bar, between the two anterior implants; L2 - posterior loading, unilaterally, at the end of the bar. An appropriate boundary condition was applied and the ANSYS (10.0) was used to obtain the stress fields (maximum principal stress - σmax) for the cortical bone.

Results: For L2 condition, the anterior implants showed the highest σmax in the bone for SA and LA. The bone around the posterior implants showed the highest compressive stress (-4.39 to -4.48MPa) in comparison with the RA (-0.32MPa) for L2. For L1 condition, the LA showed the highest σmax in the cortical bone around the posterior implants (4.80MPa). The influence of arch configuration was small for SA and RA in L1.

Conclusions: The SA and LA showed the largest differences of σmax, with a non adequate bone wall configuration around the anterior and posterior implants, respectively. As SA and LA configurations can represent extreme clinical conditions for prefabricated immediate bar, the guided surgery can be a better option to establish an adequate bone formation around implants.