Mechanical and clinical evaluation of the effect of microscrew on root proximity and cortical bone thickness.

BACKGROUND/OBJECTIVES: Primary stability is required for successful use of microscrew. This study investigated correlations among biomechanical, morphological, and clinical values in relationship to root contact and different placement locations. MATERIALS/METHODS: Thirty-three microscrews were placed between the molars (n = 18) or in the body of the mandible (n = 15) in three pigs. Insertion torque, Periotest, resonance frequency analysis (RFA), and static and dynamic stiffness were measured. Cone beam computed tomography was performed before and after the insertion of microscrews. Interproximal microscrews were divided into root contacted microscrews (n = 9) and non-root contact microscrews (n = 9). Factorial analysis of variance was conducted, with significance set at P < 0.05. RESULTS: A significant difference was observed between bodily and root contacted microscrews in Periotest, RFA, static and dynamic stiffness, Tanδ, and bone density (RFA, P = 0.045; all others, P < 0.001). A significant difference was observed between bodily and non-root contact microscrews in Periotest, RFA, and bone density (RFA, P = 0.025; all others, P < 0.001). A significant difference was observed in static (P = 0.01) and dynamic (P = 0.038) stiffness between microscrews with and without contact. Dynamic stiffness (P = 0.02) and Tanδ (P = 0.03) showed significant correlations with Periotest results only in bodily microscrews. LIMITATIONS: Since a pig bone was used, some differences in the quality and quantity of the bone might be observed between humans. CONCLUSIONS/IMPLICATIONS: Stiffness values distinguished between microscrews with and without contact. Periotest and RFA results indicated that bodily microscrews were more stable than interproximal microscrews. Periotest and RFA may be useful with large, microscrews and/or in thick cortical bone, but further investigation is required to determine the stability of interproximal microscrews.

Evaluations of miniscrew type-dependent mechanical stability.

BACKGROUND: Miniscrew has been widely used as an absolute anchorage in orthodontic treatment. Types of miniscrew with different diameter, length, shape, and thread dimensions may have a substantial effect on mechanical stability of the miniscrew system. Thus, the objective of this study was to evaluate miniscrew type-dependent mechanical stability to assess mechanical properties of miniscrew systems in various thickness of artificial bone block using different measurement tools. METHODS: Two types of miniscrews (15 Tomas and 15 AbsoAnchor) were placed in artificial bone block with different thickness of 1.5, 2.0, 3.0 mm. Values of maximum insertion torque, removal torque, Periotest, implant stability quotient, static stiffness, dynamic stiffness, and energy dissipation ability were assessed for each miniscrew system. FINDINGS: The maximum insertion torque, removal torque, implant stability quotient, static and dynamic stiffness values significantly increased when the miniscrews were placed in thicker bone block while Periotest values decreased. The static stiffness, Periotest and implant stability quotient values were significantly correlated each other and also with other mechanical properties (p < 0.001) except tan δ (p > 0.35). However, the slopes of some correlations and absolute values of measurement were significantly different dependent on the miniscrew types (p < 0.025). INTERPRETATION: The current findings suggest that miniscrew type-dependent calibrations are required to estimate mechanical stability of the miniscrew systems despite the utilization of same measurement tool.