Development of a standardized testing system for orthodontic sliding mechanics.

BACKGROUND: The primary objective of this study was to develop a computer-controlled three-dimensional friction measuring system, the orthodontic friction simulator (OFS). A clinically-based in vitro experiment considering wet and dry friction for conventionally and self-ligated brackets is presented to elucidate debate surrounding sliding mechanics and illustrate capabilities of the OFS. METHODS: The OFS was designed and manufactured using sound engineering principles and with the primary concern of being able to measure all forces and moments generated during sliding mechanics. This required the implementation of a six-axis load cell. A variety of translation and rotation stages were also incorporated to allow for precise positioning of the bracket relative to the archwire. Once designed and built, the OFS was then used to compare conventional and self-ligation methods in both the wet and dry state. Damon Q brackets and 0.018″ × 0.025″ stainless steel wires were used for all tests with a sample size of n = 65 for each ligation method. Archwires were pulled at a speed of 0.1 mm/s in 11 increments of 0.1 mm. At each increment, the bracket would be rotated 0.5° resulting in a total archwire travel of 1.1 mm and a second-order bracket angle range of 0°-5°. A repeated measures ANOVA was conducted to determine if ligation method and/or addition of moisture effected resulting orthodontic loads. RESULTS: The developed equipment for studying orthodontic sliding mechanics was able to measure forces and moments in all three directions; a capability not previously realized in the literature. Additionally, it was found that passive ligation significantly reduced resistance to sliding, P ≤ 0.05, while the dry/wet state did not. CONCLUSIONS: The OFS certainly proved to be an adequate instrument for the scientific evaluation of orthodontic sliding mechanics. It is capable of measuring loads generated in all directions and is a fully automated apparatus allowing for simple and repeatable friction tests to be conducted. Furthermore, the addition of saliva was not found to significantly influence the loads generated during sliding mechanics regardless of ligation method.

The effect of perturbations on resistance to sliding in second-order moments comparing two different bracket types.

Orthodontic literature has shown all ligation methods to behave similarly in the clinical situation; however, the reasoning behind this still requires further investigation. A novel frictional device able to measure forces at the level of the bracket along with a custom perturbation device was used to investigate the effect of perturbations on resistance to sliding (RS) using conventional and passive ligated brackets. 150 3M Victory Series twins (0.022 slot) and 150 Damon Q brackets (0.022 slot) were tested using an 0.018 x 0.025 stainless steel wire for RS. There were 5 test groups consisting of equal numbers (n=30) representing combinations of high and low amplitude and frequency of perturbations along with a control. Second order angulation tested ranged from 0 to 6 degrees. Results for conventional brackets in the presence of perturbations at 0 degrees showed there was a statistically significant reduction (P<0.001) in RS when compared to controls. At 6 degrees, this difference (P<0.001) was seen in both high perturbation groups and one of the low perturbation groups. For passive ligated brackets, no statistically significant difference between groups was seen at 0 degrees. However, at 6 degrees high perturbation groups both resulted in statistically significant (P<0.001) reductions in RS when compared to controls. From this study it was concluded that passive ligated brackets have a lower RS when compared to conventional ligated brackets under all test conditions and angulations. Also, amplitude of perturbations has a larger role than frequency in reduction of RS values.

Effect of ligation method on maxillary arch force/moment systems for a simulated lingual incisor malalignment.

INTRODUCTION: The objectives of this study were to determine whether there is a difference in the magnitude of forces and moments produced by elastic ligation when compared to passive ligation, and whether these forces and moments propagate differently along the arch for the two ligation types. A lingual incisor malalignment was used in this study. METHODS: The Orthodontic Simulator (OSIM) was used to quantify the three-dimensional forces and moments applied on the teeth given a lingually displaced incisor. A repeated measures MANOVA was performed to statistically analyze the data. RESULTS: The interaction factor illustrated convincing evidence that there is a difference in maximum force and moment values for all outcome variables between ligation types considering all tooth positions along the arch. The mean differences for FX and FY between ligation types were found to be clinically significant, with values for elastic ligation consistently higher than passive ligation. CONCLUSION: It was found that the maximum forces and moments produced by elastic ligation are greater than those produced by passive ligation and that the magnitude of this difference for the mesiodistal and buccolingual forces is clinically relevant. Additionally, it was determined that elastic ligation causes forces and moments to propagate further along the arch than passive ligation for all outcome variables.

Effect of wire size on maxillary arch force/couple systems for a simulated high canine malocclusion.

AIMS: To better understand the effects of copper nickel titanium (CuNiTi) archwire size on bracket-archwire mechanics through the analysis of force/couple distributions along the maxillary arch. The hypothesis is that wire size is linearly related to the forces and moments produced along the arch. MATERIALS AND METHODS: An Orthodontic Simulator was utilized to study a simplified high canine malocclusion. Force/couple distributions produced by passive and elastic ligation using two wire sizes (Damon 0.014 and 0.018 inch) measured with a sample size of 144. RESULTS: The distribution and variation in force/couple loading around the arch is a complicated function of wire size. The use of a thicker wire increases the force/couple magnitudes regardless of ligation method. Owing to the non-linear material behaviour of CuNiTi, this increase is less than would occur based on linear theory as would apply for stainless steel wires. CONCLUSIONS: The results demonstrate that an increase in wire size does not result in a proportional increase of applied force/moment. This discrepancy is explained in terms of the non-linear properties of CuNiTi wires. This non-proportional force response in relation to increased wire size warrants careful consideration when selecting wires in a clinical setting.

Role of the midpalatal suture in FEA simulations of maxillary expansion treatment for adolescents: a review.

The overall goal of this review was to observe how the material properties of the unfused midpalatal suture have been considered by researchers in finite element analyses of maxillary expansion. Literature from Scopus, PubMed, and Biosis were all considered. Upon completion of the review, it was found that researchers assumed the suture to be vacant, have the same elastic properties as bone, or have elastic properties indicative of soft tissues. By performing a simplified analysis of the maxilla complex during expansion, it is shown that the suture may have a significant influence on treatment outcome. As a result, despite valuable contributions from previous studies, it would be ideal to incorporate a more representative model of the midpalatal suture into finite element simulations.

Analytically determined mechanical properties of, and models for the periodontal ligament: critical review of literature.

OBJECTIVE: This review is intended to highlight and discuss discrepancies in the literature of the periodontal ligament's (PDL) mechanical properties and the various analytical models, approaches and assumptions used in simulating its behaviour. The present study then offers to propose a model development that allows for a better phenomenological description of PDL behaviour under static, near clinical, orthodontic loading conditions. METHODOLOGY: Searches were performed on biomechanical and orthodontic publications (in databases: Compendex, EMBASE, MEDLINE, PubMed, ScienceDirect and Scopus). RESULTS: The review revealed that significant variations exist, some on the order of six orders of magnitude, in the PDL's elastic constants and mechanical properties. Possible explanations may be attributable to different modelling approaches and behavioural assumptions. SIGNIFICANCE: The discrepancies highlight the need for further research into determining what the key factors that contribute to tooth movement are, their correlations and their degree of impact. Despite the PDL's definitive role in orthodontic tooth movement, proposed models of the PDL's mechanical behaviour thus far have been unsatisfactorily inadequate. Hence, there is a need to develop a robust PDL model that more accurately simulates the PDL's biomechanical response to orthodontic loads. Better understanding of the PDL's biomechanical behaviour under physiologic and traumatic loading conditions might enhance the understanding of the PDL's biologic reaction in health and disease. Providing a greater insight into the response of the PDL would be instrumental to orthodontists and engineers for designing more predictable, and therefore more efficacious, orthodontic appliances.

Experimentally determined mechanical properties of, and models for, the periodontal ligament: critical review of current literature.

Introduction. This review is intended to highlight and discuss discrepancies in the literature of the periodontal ligament's (PDL) mechanical properties and the various experimental approaches used to measure them. Methods. Searches were performed on biomechanical and orthodontic publications (in databases: Compendex, EMBASE, MEDLINE, PubMed, ScienceDirect, and Scopus). Results. The review revealed that significant variations exist, some on the order of six orders of magnitude, in the PDL's elastic constants and mechanical properties. Possible explanations may be attributable to different experimental approaches and assumptions. Conclusions. The discrepancies highlight the need for further research into PDL properties under various clinical and experimental loading conditions. Better understanding of the PDL's biomechanical behavior under physiologic and traumatic loading conditions might enhance the understanding of the PDL's biologic reaction in health and disease. Providing a greater insight into the response of the PDL would be instrumental to orthodontists and engineers for designing more predictable, and therefore more efficacious, orthodontic appliances.

Analysis of maxillary arch force/couple systems for a simulated high canine malocclusion: Part 1. Passive ligation.

OBJECTIVE: To better understand the mechanics of bracket/archwire interaction through analysis of force and couple distribution along the maxillary arch. MATERIALS AND METHODS: An orthodontic simulator was utilized to study high canine malocclusion. Force/couple distributions, referenced to the center of resistance (CR) of each tooth, produced by passive ligation brackets and round wire were measured. Tests were repeated for 12 bracket sets with 12 wires per set. RESULTS: Propagation of the force/couple systems around the arch was minimal. Binding was observed only on the teeth adjacent to the displaced canine. For most of the teeth, reduced resistance to sliding of the passive ligation bracket yielded minimal tangential and normal forces at the bracket and contributed to lower moments at CR. CONCLUSIONS: Some potential mechanical advantages of passive ligation systems are suggested for the case studied. In particular, limited propagation around the arch reduces the occurrence of unwanted force/couple systems.

Analysis of maxillary arch force/couple systems for a simulated high canine malocclusion: Part 2. Elastic ligation.

OBJECTIVE: To better understand the mechanics of bracket/archwire interaction through analysis of force and couple distribution along the maxillary arch using elastic ligation and to compare these results with passive ligation. MATERIALS AND METHODS: An orthodontic simulator was used to study a high canine malocclusion. Force and couple distributions produced by elastic ligation and round wire were measured. Forces and couples were referenced to the center of resistance of each tooth. Tests were repeated for 12 bracket sets with 12 wires per set. Data were compared with those derived from similar tests for passive ligation. RESULTS: Propagation of the force/couple systems around the arch using elastic ligation was extensive. Elastic ligation produced significantly more resistance to sliding, contributing to higher forces and couples at the center of resistance than were observed for passive ligation. CONCLUSIONS: The results of this study suggest some potential mechanical advantages of passive over elastic ligation. In particular, limited propagation around the arch in passive ligation reduces the occurrence of unwanted force/couple systems compared with elastic ligation. These advantages may not transfer to a clinical setting because of the conditions of the tests; additional testing would be required to determine whether these advantages can be generalized.

Transverse, vertical, and anteroposterior changes from bone-anchored maxillary expansion vs traditional rapid maxillary expansion: a randomized clinical trial.

INTRODUCTION: The purpose of this study was to compare the transverse, vertical, and anteroposterior skeletal and dental changes in adolescents receiving expansion treatment with tooth-borne and bone-anchored expanders. Immediate and long-term changes were measured on cone-beam computed tomography (CBCT) images. METHODS: Sixty-two patients needing maxillary expansion were randomly allocated to 1 of 3 groups: traditional hyrax tooth-borne expander, bone-anchored expander, and control. CBCT images were taken at baseline, immediately after expansion, after removal of the appliance (6 months), and just before fixed bonding (12 months). Repeated measures multivariate analysis of variance (MANOVA) was applied to the distances and angles measured to determine the statistical significance in the immediate and long time periods. Bonferroni post-hoc tests were used to identify significant differences between the treatment groups. RESULTS: Immediately after expansion, the subjects in the tooth-borne expander group had significantly more expansion at the crown level of the maxillary first premolars (P = 0.003). Dental crown expansion was greater than apical expansion and skeletal expansion with both appliances. The control group showed little change (growth) over the 6-month interval. At 12 months, no group had a statistically significant difference in angle changes, suggesting symmetric expansion. Both treatment groups had significant long-term expansion at the level of the maxillary first molar crown and root apex, first premolar crown and root, alveolus in the first molar and premolar regions, and central incisor root. Tooth-borne expansion resulted in significantly more long-term expansion at the maxillary premolar crown and root than did bone-borne expansion. CONCLUSIONS: Both expanders showed similar results. The greatest changes were seen in the transverse dimension; changes in the vertical and anteroposterior dimensions were negligible. Dental expansion was also greater than skeletal expansion.

Three-dimensional orthodontic force measurements.

INTRODUCTION: Until recently, much of the orthodontic biomechanics literature was restricted to 2-dimensional experimental studies and, more recently, to assumption-based 3-dimensional computer modeling. There is little evidence in the literature regarding 3-dimensional experimental measurements and analysis of orthodontic force systems. METHODS: The purpose of this study was the design, construction, and validation of a laboratory-based human mouth model capable of accurately measuring forces and moments applied by orthodontic fixed appliances on all teeth in 1 arch. A high canine malocclusion was simulated, and forces and moments acting on the canine, lateral incisor, and premolar were measured with passive and conventional ligation. RESULTS: We were successful in building this human mouth model. The error in force measurements of the 14 transducers was 1.54%. The force system resulting from passive ligation brackets was considerably different from that of conventional ligation. CONCLUSIONS: This method will allow us, for the first time in the history of our specialty, to determine with great accuracy the forces acting on orthodontically treated teeth. Future research will focus on simulating many types of orthodontic clinical applications of full-fixed or partial-fixed appliances.

Three-dimensional accuracy of measurements made with software on cone-beam computed tomography images.

INTRODUCTION: The purpose of this article was to evaluate the accuracy of measurements made on 9- and 12-in cone-beam computed tomography (CBCT) images compared with measurements made on a coordinate measuring machine (CMM), which is the gold standard. METHODS: Ten markers were placed on a synthetic mandible, and landmark coordinates and linear and angular measurements were determined with the CMM. Three-dimensional CBCT images, measuring 9 and 12 in, were taken of the mandible with a CBCT machine (NewTom 3G, Aperio Services, Verona, Italy), and landmark coordinates and linear and angular measurements were obtained with AMIRA (Mercury Computer Systems, Berlin, Germany) software. RESULTS: The coordinate intrareliability correlation coefficient was almost perfect between the 3-dimensional CBCT images and the CMM measurements. With the Student t test, we found no significant statistical difference between linear and angular measurements from the CMM and the NewTom 3G images, which differed less than 1 mm and 1 degrees , respectively. CONCLUSIONS: The NewTom 3G produces a 1-to-1 image-to-reality ratio.

Torque expression of self-ligating brackets.

INTRODUCTION: The labiolingual inclination of maxillary and mandibular incisors is considered by many orthodontists to be an important determinant of pleasing dental esthetics and ideal stable occlusion. In contemporary fixed appliances, attaching a rectangular orthodontic archwire to a bracket with a rectangular slot makes third-order control possible. The purpose of this study was to measure the difference in third-order moments that can be delivered by engaging 0.019 x 0.025-in stainless steel archwires to 2 active self-ligating brackets (In-Ovation, GAC, Bohemia, NY; Speed, Strite Industries, Cambridge, Ontario, Canada) and 2 passive self-ligating brackets (Damon2, Ormco, Orange, Calif; Smart Clip, 3M Unitek, Monrovia, Calif). METHODS: A bracket/wire assembly torsion device was developed. This novel apparatus can apply torsion to the wire while maintaining perfect vertical and horizontal alignment between the wire and the bracket. A multi-axis force/torque transducer was used to measure the moment of the couple (torque), and a digital inclinometer was used to measure the torsion angle. Fifty maxillary right central incisor brackets from each of the 4 manufacturers were tested. RESULTS: There was a significant difference in the engagement angle between the 2 types of brackets; on average, torque started to be expressed at 7.5 degrees of torsion for the active self-ligating brackets and at 15 degrees of torsion for the passive self-ligating brackets. The torque expression was higher for the active self-ligating brackets up to 35 degrees of torsion. Torsion of the wire past this point resulted in a linear increase of the measured torque for the Damon2, the Smart Clip, and the In-Ovation brackets. The torque was relatively constant past 35 degrees of torsion for the Speed bracket. CONCLUSIONS: We conclude that active self-ligating brackets are more effective in torque expression than passive self-ligating brackets.