Biomechanical evaluation of an orthodontic miniimplant used with revolving (translation and rotation) temporary anchorage device by finite element analysis and experimental testing

Peri-implant bone resorption risk of anterior maxilla narrow single implants: a finite-element analysis

Statement of the problem: Narrow implants have been recommended in high esthetic demand regions to ensure greater buccal bone thickness (BBT) and minimize soft-tissue recession due to insufficient bone support. However, a limited area of bone-implant interface can increase the risk of peri-implant bone resorption due to occlusal forces. Purpose: This article encourages the use of evidence-based finite element analysis to optimize the aesthetic outcomes in maxillary lateral incisor single-supported implant crown by accurate biomechanical planning. This study aimed to analyze the best implant dimensions that would preserve the maximum BBT and avoid peri-implant bone resorption due to occlusal forces. Materials and methods: A maxilla segment was constructed based on anthropological measurements. Four implant diameters (Ø = 3.25; 3.50; 3.75 or 4.00 mm) and two lengths (L = 10 or 13 mm) were simulated. The occlusal force parameters were defined to simulate clinical conditions. The bone resorption risk analysis was based on Frost's mechanostat theory altering the strain output to strain energy density (SED). The peri-implant bone resorption risk indexes (PIBR_ri) were calculated by dividing the average of the top ten SED elements of the cortical and trabecular buccal wall by the pathologic resorption limit for each bone. Results: For trabecular bone, only the model Ø4.00_L13 exhibited a low PIBR_ri. For cortical bone, all models presented a low PIBR_ri, except for models Ø3.25. Conclusion: The selection of a 3.25 mm dental implant to preserve a 2 mm BBT should be avoided since it generates a high peri-implant bone resorption risk induced by occlusal overload.

Customized surgical template fabrication under biomechanical consideration by integrating CBCT image, CAD system and finite element analysis

This study developed a customized surgical template under mechanical consideration for molar intrusion. Two finite element (FE) models were analyzed for the primary stability under 100 gf traction forces with one mini-screw inserted at the buccal side in horizontal and another in palatal side with two optional positions at 60° (P60) or 15° (P15) angles with inclination toward the molar occlusal surface. The surgical template was generated using rapid prototyping (RP) printing for the clinical application based on improved primarily stability model. The surrounding bone strains for models P15 and P60 were far lower than the bone remodeling critical value. Model P60 presented much lower micro-motion in the screw/bone interface and the screw head displacement than those values in model P15. Using FE analysis for biomechanical evaluation and combining with CT image, image superimposed method and CAD technique can fabricate accuracy/security customized surgical template for mini-screws with better primary stability.

Biomechanical Effects of Various Bone-Implant Interfaces on the Stability of Orthodontic Miniscrews: A Finite Element Study

INTRODUCTION

Osseointegration is required for prosthetic implant, but the various bone-implant interfaces of orthodontic miniscrews would be a great interest for the orthodontist. There is no clear consensus regarding the minimum amount of bone-implant osseointegration required for a stable miniscrew. The objective of this study was to investigate the influence of different bone-implant interfaces on the miniscrew and its surrounding tissue.

METHODS

Using finite element analysis, an advanced approach representing the bone-implant interface is adopted herein, and different degrees of bone-implant osseointegration were implemented in the FE models. A total of 26 different FE analyses were performed. The stress/strain patterns were calculated and compared, and the displacement of miniscrews was also evaluated.

RESULTS

The stress/strain distributions are changing with the various bone-implant interfaces. In the scenario of 0% osseointegration, a rather homogeneous distribution was predicted. After 15% osseointegration, the stress/strains were gradually concentrated on the cortical bone region. The miniscrew experienced the largest displacement under the no osseointegra condition. The maximum displacement decreases sharply from 0% to 3% and tends to become stable.

CONCLUSION

From a biomechanical perspective, it can be suggested that orthodontic loading could be applied on miniscrews after about 15% osseointegration without any loss of stability.

Finite Element Analysis of Bone Stress for Miniscrew Implant Proximal to Root Under Occlusal Force and Implant Loading

Because of the narrow interradicular spaces and varying oral anatomies of individual patients, there is a very high risk of root proximity during the mini implants inserting. The authors hypothesized that normal occlusal loading and implant loading affected the stability of miniscrew implants placed in proximity or contact with the adjacent root. The authors implemented finite element analysis (FEA) to examine the effectiveness of root proximity and root contact. Stress distribution in the bone was assessed at different degrees of root proximity by generating 4 finite element models: the implant touches the root surface, the implant was embedded in the periodontal membrane, the implant touches the periodontal surface, and the implant touches nothing. Finite element analysis was then carried out with simulations of 2 loading conditions for each model: condition A, involving only tooth loading and condition B, involving both tooth and implant loading. Under loading condition A, the maximum stress on the bone for the implant touching the root was the distinctly higher than that for the other models. For loading condition B, peak stress areas for the implant touching the root were the area around the neck of the mini implant and the point of the mini implant touches the root. The results of this study suggest that normal occlusal loading and implant loading contribute to the instability of the mini implant when the mini implant touches the root.

A Revolving Temporary Anchorage Cap Connecting to an Orthodontic Miniscrew Using In Vitro Experimental Testing: Safety and Biomechanical Evaluations

PURPOSE

This study is to develop a plastic revolving (translation and rotation) temporary anchorage cap (TAC) as the orthodontic anchor and evaluate its biomechanical safety and clinical used feasibility.

MATERIALS AND METHODS

The TAC was designed to connect onto a mini-implant head with 45-degree switching unit and extended arm for tying an orthodontic elastic chain/coil spring. The removal force between the TAC and mini-implant head and torque resistance on the mini-implant/bone interface were performed to evaluate the biomechanical safety. Clinical molar uprighting and mesial drive application were performed to reveal the TAC feasibility/capacity.

RESULTS

The removal force was 43.95 N (>>finger-pulling force 9.3 N) to prevent the TAC from detaching, and the torque resistance was 159.25 N·mm to maintain micromotion smaller than 30.4 μm between the screw and bone. The strain value in using TAC treatment was found to be about 2 times that of traditional tracing (without using TAC) in molar uprighting/mesial drive application.

CONCLUSIONS

The plastic revolving TAC can provide optional use with translation/rotation features to change the angles and directions in orthodontic tractions and increase treatment efficiency under biomechanical safety considerations.

Biomechanical evaluation of an orthodontic mini-implant with plastic removal cap: an in-vitro experimental testing

This study evaluates the biomechanical interactions of a mini-implant using a plastic revolving cap (PRC) with translation/rotation features for optional orthodontic traction. An orthodontic mini-implant and the PRC consisting of a hexagon connection onto mini-implant with 60 degree switching unit and an extended arm to provide orthodontic wire tied at different positions. The PRC removal force was measured by pull-out testing. The PRC removal force remained larger than three times the finger pulling force (9.3N) after 5 repeated removal tests. The results for the PRC resistant testing showed that the PRC rotational resistant force (20.31±0.83N) is larger than the maximum traction force (about 4.9N) for orthodontic treatment. The mini-implant used with PRC can provide translation and rotation features to change the angles and directions of orthodontic tractions for most effective anchorage preparation under safety consideration.