Effect of microthreads on removal torque and bone-to-implant contact: an experimental study in miniature pigs

PURPOSE: The objective of this study was to evaluate the effect of microthreads on removal torque and bone-to-implant contact (BIC). METHODS: Twelve miniature pigs for each experiment, a total of 24 animals, were used. In the removal torque analysis, each animal received 2 types of implants in each tibia, which were treated with sandblasting and acid etching but with or without microthreads at the marginal portion. The animals were sacrificed after 4, 8, or 12 weeks of healing. Each subgroup consisted of 4 animals, and the tibias were extracted and removal torque was measured. In the BIC analysis, each animal received 3 types of implants. Two types of implants were used for the removal torque test and another type of implant served as the control. The BIC experiment was conducted in the mandible of the animals. The P1-M1 teeth were extracted, and after a 4-month healing period, 3 each of the 2 types of implants were placed, with one type on each side of the mandible, for a total of 6 implants per animal. The animals were sacrificed after a 2-, 4-, or 8-week healing period. Each subgroup consisted of 4 animals. The mandibles were extracted, specimens were processed, and BIC was analyzed. RESULTS: No significant difference in removal torque value or BIC was found between implants with and without microthreads. The removal torque value increased between 4 and 8 weeks of healing for both types of implants, but there was no significant difference between 8 and 12 weeks. The percentage of BIC increased between 2 and 4 weeks for all types of implants, but there was no significant difference between 4 and 8 weeks. CONCLUSIONS: The existence of microthreads was not a significant factor in mechanical and histological stability.

Three-dimensional finite element analysis for influence of marginal bone resorption on stress distribution in internal conical joint type implant fixture / 대한치과보철학회지

PURPOSE: The change of the marginal bone around dental implants have significance not only for the functional maintenance but also for the esthetic success of the implant. The purpose of this study was to investigate the load transfer of internal conical joint type implant according to marginal bone resorption by using the three-dimensional finite element analysis model. MATERIALS AND METHODS: The internal conical joint type system was selected as an experimental model. Finite element models of bone/implant/prosthesis complex were constructed. A load of 300 N was applied vertically beside 3 mm of implant axis. RESULTS: The pattern of stress distribution according to marginal bone resorption was similar. The maximum equivalent stress of implant was increase according to marginal bone resorption and the largest maximum equivalent stress was shown at model of 1 mm marginal bone resorption. Although marginal bone loss more than 1mm was occurred increasing of stress, the width of the stress increase was decreasing. CONCLUSION: According to these results, the exposure of thin neck portion of internal conical joint type implant is most important factor in stress increasing.

Effect of implant surface microtopography by hydroxyapatite grit-blasting on adhesion, proliferation, and differentiation of osteoblast-like cell line, MG-63

OBJECTIVE: This study examined the potential of the in vitro osteogenesis of microtopographically modified surfaces, RBM (resorbable blasting media) surfaces, which generate hydroxyapatite grit-blasting. METHODS: RBM surfaces were modified hydroxyapatite grit-blasting to produce microtopographically modified surfaces and the surface morphology, roughness or elements were examined. To investigate the potential of the in vitro osteogenesis, the osteoblastic cell adhesion, proliferation, and differentiation were examined using the human osteoblast-like cell line, MG-63 cells. Osteoblastic cell proliferation was examined as a function of time. In addition, osteoblastic cell differentiation was verified using four different methods of an ALP activity assay, a mineralization assay using alizarin red-s staining, and gene expression of osteoblastic differentiation marker using RT-PCR or ELISA. RESULTS: Osteoblastic cell adhesion, proliferation and ALP activity was elevated on the RBM surfaces compared to the machined group. The cells exhibited a high level of gene expression of the osteoblastic differentiation makers (osteonectin, type I collagen, Runx-2, osterix). imilar data was represented in the ELISA produced similar results in that the RBM surface increased the level of osteocalcin, osteopontin, TGF-beta1 and PGE2 secretion, which was known to stimulate the osteogenesis. Moreover, alizarin red-s staining revealed significantly more mineralized nodules on the RBM surfaces than the machined discs. CONCLUSION: RBM surfaces modified with hydroxyapatite grit-blasting stimulate the in vitro osteogenesis of MG-63 cells and may accelerate bone formation and increase bone-implant contact.

Experimental study about the bony healing of hydroxyapatite coating implants

INTRODUCTION: Hydroxyapatite(HA) coating implant can accelerate osseointegration, however, there are many controversies. MATERIALS AND METHODS: This study examined the early osseointegration of two types of hydroxyapatite coated implants. Twelve adult male miniature pigs (Medi Kinetics Micropigs, Medi Kinetics Co., Ltd., Busan, Korea) were used in this study. In the implants placed in the mandible, a histomorphometric evaluation was performed to evaluate the bone-implant contact (BIC) ratio. RESULTS: The BIC ratio increased with time. TS III HA and Zimmer HA were not significantly different (P>0.05). At 8 weeks, the BIC of Zimmer HA was higher than TS III HA, but there was no significant difference (P>0.05). CONCLUSION: HA coated implants will accelerate early osseointegration.

Effect of Tightening Torque on Abutment-Fixture Joint Stability using 3-Dimensional Finite Element Analysis / 대한치과보철학회지

STATEMENT OF PROBLEM: Loosening or fracture of the abutment screw is one of the common problems related to the dental implant. Generally, in order to make the screw joint stable, the preload generated by tightening torque needs to be increased within the elastic limit of the screw. However, additional tensile forces can produce the plastic deformation of abutment screw when functional loads are superimposed on preload stresses, and they can elicit loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum tightening torque that maximizes a fatigue life and simultaneously offer a reasonable degree of protection against loosening. PURPOSE: The purpose of this study was to present the influence of tightening torque on the implant-abutment screw joint stability with the 3 dimensional finite element analysis. MATERIAL AND METHODS: In this study, the finite element model of the implant system with external butt joint connection was designed and verified by comparison with additional theoretical and experimental results. Four different amount of tightening torques (10, 20, 30 and 40 Ncm) and the external loading (250 N, 30degrees C) were applied to the model, and the equivalent stress distributions and the gap distances were calculated according to each tightening torque and the result was analyzed. RESULTS: Within the limitation of this study, the following results were drawn; 1) There was the proportional relation between the tightening torque and the preload. 2) In case of applying only the tightening torque, the maximum stress was found at the screw neck. 3) The maximum stress was also shown at the screw neck under the external loading condition. However in case of applying 10 Ncm tightening torque, it was found at the undersurface of the screw head. 4) The joint opening was observed under the external loading in case of applying 10 Ncm and 20 Ncm of tightening torque. 5) When the tightening torque was applied at 40 Ncm, under the external loading the maximum stress exceeded the allowable stress value of the titanium alloy. CONCLUSION: Implant abutment screw must have a proper tightening torque that will be able to maintain joint stability of fixture and abutment.

Influence of tungsten carbide/carbon coating on the preload of implant abutment screws / 대한치과보철학회지

STATEMENT OF PROBLEM: In order to increase preload with reducing the friction coefficient, abutment screws coated with pure gold and Teflon as dry lubricant coatings have been introduced. But the reported data indicate that if screw repeated tightening and loosening cycle, an efficiency of increasing preload was decreased by screw surface wearing off. PURPOSE: This study was to evaluate the influence of tungsten carbide/carbon coating, which has superior hardness and frictional wear resistance, on the preload of abutment screws and the stability of coating surface after repeated closures. MATERIAL AND METHOD: The rotational values of abutment screws and the compressive forces between abutment and fixture were measured in implant systems with three different joint connections, one external butt joint and two internal cones. Moreover, the stability and the alteration of coating surface were examined by comparison of the compressive force and the removable torque values during 10 consecutive trials, observation with scanning electron microscope and analyzed the elemental composition with energy dispersive x-ray spectroscopy. RESULTS AND CONCLUSION: 1. Application of coating resulted in significant increase of compressive force in all implant systems(P.05). 3. Removable torque values were greater with non-coated screw than that with coated screw (P.05). 5. After repeated trials, the surface layer of coated screw was maintained relatively well. However, surface wearing and irregular titanium fragments were found in non-coated screw.