Abstract
ObjectiveTo assess the biomechanical effects of different prosthetic/implant configurations and load directions on 3-unit fixed prostheses supported by short dental implants in the posterior mandible using validated 3-D finite element (FE) models.MethodsModels represented an atrophic mandible, missing the 2nd premolar, 1st and 2nd molars, and rehabilitated with either two short implants (implant length-IL = 8 mm and 4 mm) supporting a 3-unit dental bridge or three short implants (IL = 8 mm, 6 mm and 4 mm) supporting zirconia prosthesis in splinted or single crowns design. Load simulations were performed in ABAQUS (Dassault Systèmes, France) under axial and oblique (30°) force of 100 N to assess the global stiffness and forces within the implant prosthesis. Local stresses within implant/prosthesis system and strain energy density (SED) within surrounding bone were determined and compared between configurations.ResultsThe global stiffness was around 1.5 times higher in splinted configurations vs. single crowns, whereby off-axis loading lead to a decrease of 39%. Splinted prostheses exhibited a better stress distribution than single crowns. Local stresses were larger and distributed over a larger area under oblique loads compared to axial load direction. The forces on each implant in the 2-implant-splinted configurations increased by 25% compared to splinted crowns on 3 implants. Loading of un-splinted configurations resulted in increased local SED magnitude.ConclusionSplinting of adjacent short implants in posterior mandible by the prosthetic restoration has a profound effect on the magnitude and distribution of the local stress peaks in peri-implant regions. Replacing each missing tooth with an implant is recommended, whenever bone supply and costs permit.
Highlights
The biomechanical conditions of dental implants differ from those of natural teeth during functional loading
Experimental validation Validation of the finite element analysis (FEA) was reported in detail in a previous study [24]
Both evaluation procedures showed the same trend in the difference of the stiffness between the different load cases for each investigated configuration, confirming a similitude of tendencies and proving a qualitative equivalence
Summary
The biomechanical conditions of dental implants differ from those of natural teeth during functional loading. From a biomechanical point of view, literature indicates that short implants offer a reduced overall contact area between bone and implants and increase the crown-to-implant ratio [12], which might cause biomechanical complications due to stress accumulation, especially under oblique loads [9, 13]. A recent meta-analysis concluded that splinted short implants do not exhibit superior performance in survival rate, marginal bone maintenance and prevention of mechanical complications compared with single-unit prosthesis [16]. The influence of overloading factors on short implant longevity is still inconclusive in the literature. In this sense, we seek to reveal which biomechanics are more favourable for a typical clinical setting in the posterior jaw with implantsupported 3-unit fixed partial dentures (FPD) with short (≤ 8 mm) and extra-short (< 6 mm) implants
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