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Abstract
Purpose
The purpose of this study was to investigate the effect of different thread designs on the marginal bone stresses around dental implant.
Materials and methods
Standard ITI implant(ITI Dental Implant System; Straumann AG, Waldenburg, Switzerland), 4.1 mm in diameter and 10 mm in length, was selected as control. Test implants of four different thread patterns were created based on control implant, i.e. maintaining all geometrical design of control implant except thread pattern. Four thread designs used in test implants include (1) small V-shape screw (model A), (2) large V-shape screw (model B), (3) buttress screw (model C), and (4) trapezoid screw (model D). Surface area for unit length of implant was 14.4 mm2 (control), 21.7 (small V-shape screw), 20.6 (large V-shape screw), 17.0 (buttress screw) and 28.7 mm2 (trapezoid screw). Finite element models of implant/bone complex were created using an axisymmetric scheme with the use of NISA II/DISPLAY III (Engineering Mechanics Research Corporation, Troy, MI, USA). A load of 100 N applied to the central node on the crown top either in parallel direction or at 30 degree to the implant axis (in order to apply non-axial load to the implant NKTP type 34 element was employed). Quantification and comparison of the peak stress in the marginal bone of each implant model was made using a series of regression analyses based on the stress data calculated at the 5 reference points which were set at 0.2, 0.4, 0.6, 0.8 and 1.0 mm from implant wall on the marginal bone surface.
Results
Results showed that although severe stress concentration on the marginal bone cannot be avoided a substantial reduction in the peak stress is achievable using different thread design. The peak marginal bone stresses under vertical loading condition were 7.84, 6.45, 5.96, 6.85, 5.39 MPa for control and model A, B, C and D, respectively. And 29.18, 26.45, 25.12, 27.37, 23.58 MPa when subject to inclined loading.
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Fig. 1.
Basic geometry model (control model: ITI implant system) showing important dimensions of the implant/bone complex used in this study. The view within the right hand side circle shows a thread design of the ITI implant system (unit: mm).
Fig. 2.
The 4 test implants with different screw designs. (A) small V-shape screw, (B) large V-shape screw, (C) buttress screw, and (D) trapezoid screw (unit: mm).
Fig. 3.
Typical finite element mesh used for control model. A view within circle presented in the right hand side shows the five stress monitoring points on the surface of marginal bone 0.2 mm apart each others.
Fig. 4.
Stress distributions (maximum compressive stress) in the marginal bone around the 5 implant models subject to a vertical load of 100 N. (A) control model (ITI implant), (B) stress band, and implants with (C) small V-shape, (D) large V-shape, (E) buttress, and (F) trapezoid screws.
Fig. 5.
Stress distributions (maximum compressive stress) in the marginal bone around the 5 implant models subject to an oblique load of 100 N. (A) control model (ITI implant), (B) stress band, and implants with (C) small V-shape, (D) large V-shape, (E) buttress, and (F) trapezoid screws.
Fig. 6.
Stress distribution on the external surface of marginal bone around the 5 implant models subject to a vertical load of 100 N.
Fig. 7.
Stress distribution on the external surface of marginal bone around the 5 implant models subject to an oblique load of 100 N.
Table 1.
Mechanical properties (bone and implant materials)
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