Novel multi-axial alveolar distractor - Part I: Design, manufacture, and mechanical/functional tests.

PURPOSE: This study developed a novel multi-axial alveolar distractor and evaluated its safety and effectiveness by performing various mechanical tests and finite element (FE) analysis. MATERIALS AND METHODS: A ball-and-socket joint with a high degree of freedom was proposed as the design concept to make the distractor produce a cone trajectory motion range of up to 60° with respect to the transport screw (central axis). This device was manufactured with Ti6Al4V alloy. Mechanical functional tests included four-point bending resistance testing of the base bone plate, pull-out testing of the multi-axial alveolar distractor, welding strength testing between the base bone plate and ball-and-socket joint mechanism, and torque strength testing of the ball-and-socket joint. These tests were performed to ensure the effectiveness and safety of the multi-axial alveolar distractor. The base bone plate FE analysis of four-point bending resistance and pull-out testing of the multi-axial alveolar distractor were performed to confirm the results obtained from the experimental testing. RESULTS: The bending strength for the four-point bending test and the maximum force for pull-out testing were 530.88 N mm and 716.33 N, respectively. Substantial equivalence FE simulations also found that large deformations for four-point bending and pull-out testing were smaller than those for the commercial alveolar distractor, indicating that our new distractor is as safe and effective as the commercially available device. The maximum debonding torque resistance for ball-and-socket joint mechanism welding strength was 3481.1 N mm, meaning it is unable to fall off during a surgical operation. No damage was found at the welding edge. The maximum average resistance force in the ball-and-socket joint was 30.26 N without rotation, allowing it to resist distraction forces during bone regeneration - an important safety consideration. CONCLUSION: The alveolar distractor designed using a ball-and-socket joint concept can achieve multi-axial distraction with various angle adjustments in 3D space. Thorough mechanical/functional tests confirm the effectiveness and safety of our new multi-axial alveolar distractor.

Biomechanical evaluation of a novel hybrid reconstruction plate for mandible segmental defects: A finite element analysis and fatigue testing.

PURPOSE: This study develops a novel hybrid (NH) reconstruction plate that can provide load-bearing strength, secure the bone transplant at the prosthesis favored position, and also maintain the facial contour in a mandibular segmental defect. A new patient-match bending technique which uses a three-dimensional printing (3DP) stamping process is developed to increase the interfacial fit between the reconstruction plate and mandibular bone. MATERIALS AND METHODS: The NH reconstruction plate was designed to produce a continuous profile with non-uniform thickness and triangular cross-screw patterns with a locking-screw feature at the plate base. Two mandible segmental defect finite element models including the NH reconstruction plate to secure a bone flap for occlusal requirement and the commercial straight (CS) reconstruction plate to secure a bone flap along the lower mandible border were generated for biomechanical fatigue testing. RESULTS: The simulated results showed that the maximum von Mises stresses of the reconstruction plate for CS secured model are about 4.5 times more than the NH secured model. The bone strains around the fixation screws showed that the CS secured model was meaningfully higher than that of the NH secured model and exceeded the bone limit value. No fracture of any component was found in any sample in the fatigue testing. CONCLUSION: In conclusion, the newly developed NH reconstruction plate can secure the transplant position in accordance to the individual occlusal requirements without sacrificing the maintenance of facial contour. Finite element-based biomechanical evaluation demonstrates superior mechanical strength compared to commercial standard plates.

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.

Do dual-thread orthodontic mini-implants improve bone/tissue mechanical retention?

PURPOSE: The aim of this study was to understand whether the pitch relationship between micro and macro thread designs with a parametrical relationship in a dual-thread mini-implant can improve primary stability. MATERIALS AND METHODS: Three types of mini-implants consisting of single-thread (ST) (0.75 mm pitch in whole length), dual-thread A (DTA) with double-start 0.375 mm pitch, and dual-thread B (DTB) with single-start 0.2 mm pitch in upper 2-mm micro thread region for performing insertion and pull-out testing. Histomorphometric analysis was performed in these specimens in evaluating peri-implant bone defects using a non-contact vision measuring system. RESULTS: The maximum inserted torque (Tmax) in type DTA was found to be the smallest significantly, but corresponding values found no significant difference between ST and DTB. The largest pull-out strength (Fmax) in the DTA mini-implant was found significantly greater than that for the ST mini-implant regardless of implant insertion orientation. Mini-implant engaged the cortical bone well as observed in ST and DTA types. CONCLUSION: Dual-thread mini-implant with correct micro thread pitch (parametrical relationship with macro thread pitch) in the cortical bone region can improve primary stability and enhanced mechanical retention.

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.

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

PURPOSE: To evaluate the biomechanical interactions of a miniimplant using a temporary anchorage device (TAD) for orthodontic traction. MATERIALS AND METHODS: A miniimplant was designed with dual thread (DT) with a TAD that can be connected optionally onto the miniimplant with 60-degree switching unit and an extended arm for tying orthodontic wire. Finite element analysis was used to calculate the relative miniimplant displacement and bone strain under immediate load (500 gW) on behalf of the maximum lateral force during orthodontic treatment. The TAD removal forces were measured by pullout testing. RESULTS: Simulated results showed that the maximum von Mises bone strain concentrated at the cervical regions around the miniimplant. The corresponding strain value in DT miniimplant assembled with TAD was greater than those for DT and single-thread implants with 2.24 and 1.73 times, respectively. Small relative miniimplant displacement (<20 µm) was found in all cases. The TAD removal force remained larger than 2 times the finger-pulling force (9.3 N) after 5 repeated removal tests. CONCLUSION: The DT miniimplant connected with TAD can provide translation and rotation features to change the angles and directions of orthodontic tractions for most effective anchorage preparation.

Biomechanical comparison of a single short and wide implant with monocortical or bicortical engagement in the atrophic posterior maxilla and a long implant in the augmented sinus.

PURPOSE: The present study investigated the biomechanical interactions of a monocortically or bicortically engaged short and wide implant in the atrophic posterior maxilla and compared them to those of a long implant in the augmented sinus under different loading conditions via a nonlinear finite element (FE) approach. MATERIALS AND METHODS: Nonlinear FE models of a single implant in the posterior maxilla were constructed for the following conditions: (1) A monocortically engaged 5-mm-long, 7-mm-wide implant with an internal tripodgrip abutment connection (SIT-1), (2) a bicortically engaged 6-mm-long, 7-mm-wide implant with internal tripod-grip abutment connection (SIT-2), and (3) a 13-mm-long, 4.5-mm-wide implant with an internal-hexagon abutment connection in an augmented sinus. Simulated loads of 150 N were applied axially at the central fossa, off-axis at the buccal and palatal cusps, and toward the axis at the buccal and palatal cusps. RESULTS: The simulated results showed that loading condition was the main factor influencing the mechanical responses. Oblique occlusal forces increased implant stress and stress/strain values for the surrounding bone. The use of a long implant decreased the implant stress but increased the bone stress/strain values relative to a short and wide implant. The SIT-1 and SIT-2 implants increased the implant stress on average by 2.94 and 2.67 fold, respectively. However, the SIT-2 implant reduced the average stress and strain in bone by 37%, and the SIT-1 implant reduced average stress by 33% and average strain by 32%. CONCLUSIONS: Placement of a short and wide implant in the atrophic posterior maxilla may be a possible alternative for reducing the strain/stress on the surrounding bone. Detrimental off-axis loads should always be minimized to prevent extraordinarily high bone strain and stress.

Biomechanical analysis of the effects of implant diameter and bone quality in short implants placed in the atrophic posterior maxilla.

Short dental implant (SDI) placement has been proposed as an alternative to reduce the surgical risks related to the advanced grafting procedures. The aim of this study was to simulate the biomechanical behaviors and influences of SDI diameters under various conditions of bone quality by using a validated finite element (FE) model for simulation. The CT image and CAD system were combined to construct the FE models with 6 mm length SDIs for 6, 7 and 8 mm diameters under three types of bone qualities, from normal to osteoporotic. The simulated results showed that implant diameter did not influence the von Mises strains of bone under the vertical load. The bone strains increased about 58.58% in the bone of least density under lateral load. Lateral loads induced high bone strain and implant stress than vertical loads. The bone strains of 7 mm- and 8 mm-diameter short implants were not different, and both were about 52% and 66% compared to those of 6 mm-wide short implant under lateral loads. The von Mises stress of the SDIs and their compartments were all less than the yield stress of the material under vertical and lateral loads. SDIs with diameter of 7 mm or above may have better mechanical transmission in the same length at feasible condition. Attaining a proper occlusal scheme design or selective occlusal adjustments to reduce the lateral occlusal force upon the SDIs is recommended.

Evaluation of contributions of orthodontic mini-screw design factors based on FE analysis and the Taguchi method.

This study determines the relative effects of changes in bone/mini-screw osseointegration and mini-screw design factors (length, diameter, thread shape, thread depth, material, head diameter and head exposure length) on the biomechanical response of a single mini-screw insertion. Eighteen CAD and finite element (FE) models corresponding to a Taguchi L(18) array were constructed to perform numerical simulations to simulate mechanical responses of a mini-screw placed in a cylindrical bone. The Taguchi method was employed to determine the significance of each design factor in controlling strain. Simulation results indicated that mini-screw material, screw exposure length and screw diameter were the major factors affecting bone strain, with percentage contributions of 63%, 24% and 7%, respectively. Bone strain decreased obviously when screw material had the high elastic modulus of stainless/titanium alloys, a small exposure length and a large diameter. Other factors had no significant on bone strain. The FE analysis combined with the Taguchi method efficiently identified the relative contributions of several mini-screw design factors, indicating that using a strong stainless/titanium alloys as screw material is advantageous, and increase in mechanical stability can be achieved by reducing the screw exposure length. Simulation results also revealed that mini-screw and bone surface contact can provide sufficient mechanical retention to perform immediately load in clinical treatment.

Evaluation of the relative contributions of multi-factors in an adhesive MOD restoration using FEA and the Taguchi method.

OBJECTIVES: This study determines the relative contribution of changes (design factors) in cavity dimension, restorative material, adhesive layer modulus and thickness and loading condition on the biomechanical response of a premolar adhesive Class II MOD restoration. METHODS: A validated finite element (FE) model was used to simulate the mechanical responses. The Taguchi method was employed to identify the significance of each design factor in controlling the stress. RESULTS: The results indicated that the loading condition was the major factor affecting the stress values (49% in tooth and 46% in cement). Cavity depth was found as the second contributor affecting the stress values (31 % in tooth and 30% in cement), followed by resin cement modulus (12% in tooth and 13% in cement). Other factors were found to have no significant effect on the tooth and cement stress values. Increased stress values were found with lateral force, deeper cavity and higher luting cement modulus. SIGNIFICANT: The combined use of FE analysis and the Taguchi method efficiently identified the relative contributions of several restorative factors and indicated that cavity depth was the most critical factor on the cavity dimensions in attaining a proper occlusal adjustment. Reduced lateral occlusal force and lower modulus luting material application are recommended to obtain a better force-transmission mechanism.