Stress shielding and amplification in alveolar cortical-cancellous bone fractures: An analysis of implant-bone stress interactions

The effectiveness of dental implants greatly relies on the attainment of osseointegration and the sustained stability of the implant in the long run.  An essential factor in achieving this success lies in comprehending the shift from primary to secondary stability and the consequences of microcracks that occur during the drilling of alveolar bone before implantation.  The objective of this study is to examine the stress interactions occurring in double-edge parallel cracks within heterogeneous (cortical-cancellous) bone under different loading conditions, particularly mode I, mode II, and mixed-mode.  Two-dimensional bone fracture models were developed using numerical modeling techniques to simulate homogeneous and heterogeneous fracture types in alveolar cancellous and cortical-cancellous bone.  An elastic stress interaction algorithm was employed in the finite element (FE) analysis.  The stress intensity factors (SIF) were estimated using the contour integral method.  It should, however, be noted that overall fracture toughness is usually higher when the material is subjected to single mode loading either mode I or mode II as compared to mixed mode loading.  In view of noteworthy variation in flexibility in the composite constitution of the bone, the distribution of stress in alveolar cortical-cancellous bone in fractured condition varies considerably.  Stress shielding and its occurrence in several areas of the implant also receive consideration in the study; the interaction of stress shielding, stress amplification, and the unification process that takes place due to the presence of bone heterogeneity.  However, it is necessary to mention that for mode I load, only augmentation was observed.  On the other hand, mode II increased from shielding to amplification with the unification point in the range of 0.275 mm to 0.325 mm.  The transitions from shielding to amplification were noted in mixed-mode loading, and these loading types had a common point in the graph with $a/W$ values between 0.175 mm and 0.225 mm.  Therefore, it is valuable to reflect various stress interactions that are related to alveolar cortical-cancellous bone fractures, which we described in this paper.  These ideas are of great importance in increasing the stability of dental implant.