Abstract
ABSTRACTObjectives: Assess the stability of three different mini-implants, based on thread shape factor (TSF), and evaluate stresses at the mini-implant site and surrounding cortical bone on application of retraction force, at two different insertion angles. Methods: Mini-implants of three different diameters (M1 - Orthoimplant, 1.8mm), (M2 - Tomas, 1.6mm) and (M3 - Vector TAS, 1.4mm) and length of 8mm were used. Using scanning electronic microscopy, the mean thread depth, pitch and relationship between the two (TSF) were calculated. The mini-implants were loaded into a synthetic bone block and the pull-out strength was tested. One way ANOVA and Tukey post-hoc tests were used to compare the pull-out strength of mini-implants. P values < 0.05 were considered statistically significant. Finite element models (FEM) were constructed with insertion angulation at 90° and 60°, with retraction force of 150 g. The results were analyzed using ANSYS software.Results: Statistically significant difference was found among all the three mini-implants for thread depth and pitch (< 0.001). Statistically significant higher pull-out force value was seen for Orthoimplant. The stress distribution level in mini-implant and surrounding bone was observed to be smaller for Orthoimplant. Conclusion: Orthoimplant mini-implants have more favorable geometric characteristics among the three types, and less stress with 90°angulation.
Highlights
The need for orthodontic treatment modalities that maximize anchorage control and minimize patient compliance has led to the development of miniimplant-assisted orthodontics.[1]
Primary stability of mini-implant is due to the mechanical interlock between the bone and miniimplant, and it depends on many factors, including bone quality, mini-implant site and insertion angle, and design of mini-implants, such as diameter, thread form, pitch, thread size, mini-implant material,[3,4,5] and the recently introduced thread shape factor (TSF)[2]
TSF is calculated as the geometrical relationship between the mean thread depth and the pitch (D/P) and is expressed as a percentage.[2]
Summary
The need for orthodontic treatment modalities that maximize anchorage control and minimize patient compliance has led to the development of miniimplant-assisted orthodontics.[1] Temporary anchorage devices (TADs) in the form of mini-implants are used as a skeletal anchorage and their utilization has become a reliable and acceptable method.[2]. Primary stability of mini-implant is due to the mechanical interlock between the bone and miniimplant, and it depends on many factors, including bone quality, mini-implant site and insertion angle, and design of mini-implants, such as diameter, thread form, pitch, thread size, mini-implant material,[3,4,5] and the recently introduced thread shape factor (TSF)[2]. Bone remodeling processes at the bone/screw interface are correlated with the structural response of the bony tissue to the TADs and to the stress/strain field, developing within themselves and the surrounding bone.[6] Studies of stress allow optimization of the shape and geometric parameters. A key to the success or failure of mini-implant is the manner in which stresses are transferred to the surrounding bone.[7]
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