Abstract
Purpose The purpose of this study was to evaluate and compare the effect of three mandibular full-arch superstructures on the peri-implant bone stress distribution during mandibular flexure caused by mid-opening (27 mm) and protrusion mandibular movements. Materials and Methods Three-dimensional finite element models were created simulating six osseointegrated implants in the jawbone. One model simulated a 1-piece framework and the other simulated 2-piece and 3-piece frameworks. Muscle forces with definite direction and magnitude were exerted over areas of attachment to simulate multiple force vectors of masticatory muscles during mandibular protrusion and opening. Results During the movement of 27.5 mm jaw opening, the 1-piece and 3-piece superstructures showed the lowest values of bone stress around the mesial implants, gradually increasing towards the distal position. During the protrusion movement, bone stress increased compared to opening for any implant situation and for a divided or undivided framework. The 3-piece framework showed the highest values of peri-implant bone stress, regardless of the implant situation. Conclusions The undivided framework provides the best biomechanical environment during mandibular protrusion and opening. Protrusion movement increases the peri-implant bone stress. The most mesial implants have the lowest biomechanical risk.
Highlights
Mandibular flexure is a complex mandible deformation process that changes the shape and decreases the width of the mandible arch during opening and protrusion mandibular movements due to contraction of the lateral pterygoid muscles and other masticatory muscles
While the use of sectional prosthesis designs in 2- or 3-piece superstructures through the symphysis region has been suggested to minimize the effect of mandibular flexure and peri-implant bone stress [10, 12,13,14], other studies have found smaller stress values for 1-piece superstructures compared to sectioned ones [15]
The smallest bone stress occurred around mesial implants at both sides, progressively increasing towards more distal positions, except for the 3-piece framework prosthesis, where the highest peri-implant bone stress was recorded in implants in the first premolar location
Summary
Mandibular flexure is a complex mandible deformation process that changes the shape and decreases the width of the mandible arch during opening and protrusion mandibular movements due to contraction of the lateral pterygoid muscles and other masticatory muscles. Four widely recognized deformation patterns [1] have been proposed: symphyseal bending associated with medial convergence, dorsoventral shear, corporal rotation, and anteroposterior shear Any of these deformation patterns can cause compressive, tensile, or shear stresses on the mandibular bone tissue, the range and distribution of these stresses depending on the nature and amount of force exerted by masticatory muscles, mandibular geometry, and bone quantity and quality [2]. Is splinted teeth mobility reduced and the protective effect of the periodontal ligament cancelled, and the BioMed Research International direction of movement of the teeth changes after the splint is performed This causes a leverage effect and different flexion forces that increase or modify bone stress/strain distribution around teeth or implants [2] in mandibular flexure during mandibular movements with or without occlusal load [2, 5,6,7]. While the use of sectional prosthesis designs in 2- or 3-piece superstructures through the symphysis region has been suggested to minimize the effect of mandibular flexure and peri-implant bone stress [10, 12,13,14], other studies have found smaller stress values for 1-piece superstructures compared to sectioned ones [15]
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