Inverse finite element analysis for an axisymmetric model of vertical tooth extraction.

BACKGROUND AND OBJECTIVE: Tooth extraction is a common clinical procedure with biomechanical factors that can directly influence patient outcomes. Recent development in atraumatic extraction techniques have endeavoured to improve treatment outcomes, but the characterization of extraction biomechanics is sparse. An axisymmetric inverse finite element (FE) approach is presented to represent the biomechanics of vertical atraumatic tooth extraction in an ex-vivo swine model. METHODS: Geometry and boundary conditions from the model are determined to match the extraction of swine incisors in a self-aligning ex vivo extraction experiment. Material parameters for the periodontal ligament (PDL) model are determined by solving an inverse FE problem using clusters of data obtained from 10 highly-controlled mechanical experiments. A seven-parameter visco-hyperelastic damage model, based on an Arruda-Boyce framework, is used for curve fitting. Three loading schemes were fit to obtain a common set of material parameters. RESULTS: The inverse FE results demonstrate good predictions for overall force-time curve shape, peak force, and time to peak force. The fit model parameters are sufficiently consistent across all three cases that a coefficient-averaged model was taken that compares well to all three cases. Notably, the initial modulus ,u, converged across trials to an average value of 0.472 MPa with an average viscoelastic constant g of 0.561. CONCLUSIONS: The presented model is found to have consistent parameters across loading cases. The capability of this model to represent the fundamental mechanical characteristics of the dental complex during vertical extraction loading is a significant advancement in the modelling of extraction procedures. Future work will focus on verifying the model as a predictive design tool for assessing new loading schemes in addition to investigating its applications to subject-specific problems.

In vivo measurement of strain in the periodontal space of pig (Sus scrofa) incisors using in-fiber Bragg sensors.

The incisor teeth in pigs, Sus scrofa, function in association with a disc-shaped snout to explore the environment for potential food. Understanding how mechanical loading applied to the tooth deforms the periodontal ligament (PDL) is important to determining the role of periodontal mechanoreceptors during food exploration and feeding. The objective of this study was to use fiber Bragg (FBG) sensors to measure strain in vivo within the PDL space of pig incisors. The central mandibular incisors of pigs underwent spring loaded lingual tipping during FBG strain recording within the labial periodontal space. FBG sensors were placed within the periodontal space of the central mandibular incisors of ~2-3-month-old farm pigs. The magnitude and orientation of spring loads are expected to mimic incisor contact with food. During incisor tipping with load calibrated springs, FBG strains in vitro (N = 6) and in vivo (N = 6) recorded at comparable load levels overlapped in range (-10-20 µÎµ). Linear regressions between peak FBG strains, that is, the highest recorded strain value, and baseline strains, that is, strain without applied spring load, were significant across all in vivo experiments (peak strain at 200 g vs. baseline, p = .04; peak strain at 2000 g vs. baseline p = .03; peak strain at 2000 g vs. 200 g, p = .004). These linear relationships indicate that on a per experiment basis, the maximum measured strain at different spring loads showed predictable differences. A Friedman test of the absolute value of peak strain confirmed the significant increase in strain between baseline, 200 g, and 2000 g spring activation (p = .02). Mainly compressive strains were recorded in the labial PDL space and increases in spring load applied in vivo generated increases in FBG strain measurements. These results demonstrate the capacity for FBG sensors to be used in vivo to assess transmission of occlusal loads through the periodontium. PDL strain is associated with mechanoreceptor stimulation and is expected to affect the functional morphology of the incisors. The overall low levels of strain observed may correspond with the robust functional morphology of pig incisors and the tendency for pigs to encounter diverse foods and substrates during food exploration.

In vitro biomechanics of divot use, and their placement, in orthodontic aligner therapy.

INTRODUCTION: To evaluate biomechanics of an aligner utilizing divots and the effect of their vertical placement on the right maxillary central incisor. METHODS: An in vitro Orthodontic SIMulator (OSIM) was used to test forces and moments generated by aligners incorporating divots. The OSIM arch was scanned to generate a. STL version that was modified to create four models by placing divots on different positions of the right central maxillary incisor: GI - divots on gingival-third of lingual surface and incisal-third of labial surface; GM - divots on gingival-third of lingual surface and middle-third of labial surface; MI - divots on middle-third of lingual surface and incisal-third of labial surface; MM - divots on middle-third of lingual surface and middle-third of labial surface. Aligners (n = 30/model) were fabricated using a 0.75 mm thick polyethylene terephthalate material and Biostar® machine following the manufacturer's recommendations. A one-way MANOVA followed by one-way ANOVA (α = 0.05) was utilized to test effect of models on buccolingual force (Fy) and mesiodistal moment (Mx) at 0.20 mm of lingual displacement of the right maxillary central incisor. RESULTS: Mean Mx for GI (-5.68 ± 7.38 Nmm), GM (3.75 ± 5.54 Nmm), MI (-4.27 ± 1.48 Nmm) and MM (1.96 ± 0.99 Nmm) models showed statistical differences between GI and GM, GI and MM, GM and MI and MI and MM. GI exerted the largest Fy (1.87 ± 0.75 N) followed by GM (1.10 ± 0.47 N), MI (0.70 ± 0.23 N) and MM (0.28 ± 0.08 N) with significant differences between GI and GM, GI and MI, GI and MM and GM and MM models. CONCLUSIONS: Vertical divot placement on a right central incisor had a significant effect on aligner biomechanics. Buccolingual forces exerted by models GI, GM and MI were within the range suggested by literature for bodily tooth movement without major root tipping for GM and MI models.

A novel method for simulating ex vivo tooth extractions under varying applied loads.

BACKGROUND: Tooth extraction is a common surgical procedure where the invasiveness of the surgery can affect the nature of the dentoalveolar remodelling which follows. However, there is very little biomechanical data relating the loading applied during tooth extraction to the outcomes of the procedure. The purpose of this pilot study is to present a novel ex vivo experimental method for measuring tooth extraction mechanics and to explore preliminary metrics for predicting extraction success. METHODS: A custom experimental apparatus was developed in-house to extract central incisors from ex vivo swine mandible samples. Twenty-five (n = 25) incisors were extracted at different rates in displacement- and force-control, along with an intermittent ramp-hold scheme for a total of five schemes. Peak forces and extraction success were recorded for each test. Video analysis assisted in determining the instantaneous stiffnesses of the dental complex during continuous extractions, which were compared using the K-means clustering algorithm. FINDINGS: Tooth extraction forces ranged from 102 N to 309 N, with higher-rate tests tending towards higher peak forces (141 N - 308 N) than the lower-rate tests (102 N-204 N) for displacement- and force-controlled schemes. The K-means algorithm clearly identified load rates among tests, indicating that higher-rate loading increased system stiffness relative to the lower-rate tests. INTERPRETATION: The developed experimental method demonstrated a desirable degree of control. The preliminary results suggest the influence of load rate on the mechanical response of the dental complex and extraction outcome. Future work will further investigate the biomechanics of tooth extraction and relate them to tissue damage to improve future tooth extraction procedures.

Three-dimensional morphometric analysis of cranial sutures - A novel approach to quantitative analysis.

Objective: Differences in complexity of cranial suture forms on the endocranial (i.e., deep) and ectocranial (i.e., superficial) skull surfaces have been noted in the literature, indicating through thickness three-dimensional (3D) suture variability depending on the chosen section and necessity for considering the complete 3D structure in many cases. This study aims to evaluate the variability of suture morphology through the skull thickness using a rat model, and to provide more robust metrics and methodologies to analyze suture morphology. Design: X-ray micro-computed tomographic (µCT) imaging methods were utilized in order to provide internal structure information. Methods were developed to isolate and analyze sutures widths and linear interdigitation index (LII) values on each adjacent offset transverse plane of the µCT datasets. LII was defined as the curved path length of the suture divided by the linear length between the ends of the region of interest. Scans were obtained on 15 female rats at ages of 16, 20, and 24 weeks (n = 5/age). Samples were imaged at 18 µm resolutions with 90 kV source voltage, 278 µA source amperage, and 0.7° increments. Suture widths and LII values were compared using a Kruskal-Wallis test. Results: 3D variability in local suture widths within individuals, as well as through thickness variabilities in planar widths and LII was observed. Kruskal-Wallis tests for bulk through thickness averaged suture widths and LII were found to be statistically insignificant, despite clear geometric differences through suture thicknesses. Conclusion: Although the bulk morphometric variability between age groups was found to be statistically insignificant, the 3D variability within individuals point to the importance of analyzing suture form using 3D metrics when studying suture development, response to functional activity, or morphometry in general.

A Preliminary Step Towards a Physical Surrogate of the Human Calvarium to Model Fracture.

A surrogate model of the human calvarium can be used to assess skull-fracture-related head injuries without continuously requiring post-mortem human skulls. Skull simulants developed in the literature often require sophisticated manufacturing procedures and/or materials not always practical when factoring in time or expense considerations. This study's objective was to fabricate three exploratory surrogate models (1. pure epoxy prototype, 2. epoxy-chalk mix prototype, and 3. epoxy-chalk three-layered prototype) of the calvarium to mimic the calvarium's mechanical response at fracture using readily available and cost-effective materials, specifically epoxy and chalk. The surrogates and calvaria were subject to quasi-static and dynamic impact 4-point bending and their mechanical responses were compared statistically. Under quasi-static loading, all three surrogates showed a considerable number of differences in mechanical response variables to calvaria that was deemed significant (p < 0.05). Under dynamic impact loading, there was no sufficient evidence to reject that the average mechanical response variables were equal between the epoxy-chalk three-layered prototype and calvaria (p > 0.05). This included force and bending moment at fracture, tensile strain at fracture, tensile and compressive stress at fracture, tensile modulus, and tensile strain rate. Overall, our study illustrates two main remarks: (1) the three exploratory surrogate models are potential candidates for mimicking the mechanical response of the calvarium at fracture during impact loading and (2) employing epoxy and chalk, which are readily available and cost-effective has the potential to mimic the mechanical response of calvaria in impact loading.

The effect of morphometric and geometric indices of the human calvarium on mechanical response.

BACKGROUND: When developing a surrogate model of the human skull, there is a multitude of morphometric and geometric properties to consider when constructing the model. To simplify this approach, it is important to identify only the properties that have a significant influence on the mechanical response of the skull. The objective of this study was to identify which morphometric and geometric properties of the calvarium were significant predictors of mechanical response. METHODS: Calvarium specimens (N = 24) were micro-computed tomography scanned to determine morphometric and geometric properties. The specimens were assumed to be Euler-Bernoulli beams and were subject to 4-point quasi-static bending to determine mechanical response. Univariate linear regressions were performed whereby the morphometric and geometric properties were independent or predictor variables and the mechanical responses were dependent or outcome variables. FINDINGS: Nine significant linear regression models were established (p < 0.05). In the diploë, trabecular bone pattern factor was a significant predictor of force and bending moment at fracture. The inner cortical table had more significant predictors (thickness, tissue mineral density, and porosity) of mechanical response compared to the outer cortical table and diploë. INTERPRETATION: Morphometric and geometric properties had a key influence on the calvarium's biomechanics. Trabecular bone pattern factor and the morphometry and geometry of the cortical tables must be considered when evaluating the mechanical response of the calvarium. These properties can aid the design of surrogate models of the skull that seek to mimic its mechanical response for head impact simulation.

Size-specific filtration efficiency and pressure drop of school-aged children's woven and nonwoven masks at varying face velocities.

BACKGROUND: Differences in physiology and breathing patterns between children and adults lead to disparate responses to aerosols of varying sizes. No standardized method exists for measuring the filtration efficiency (FE) of children's masks to reflect such differences. METHODS: Using an adult N95 mask as a control and two different face velocities (vf) (9.3 cm/s representing adults and 4.0 cm/s representing school-aged children), we tested the pressure drop (ΔP) through children's nonwoven masks (surgical and KN95) and children's woven masks (100% cotton and partially-cotton-based masks), as well as their size-specific FE between aerodynamic particle diameters of 0.02 and 2.01 µm. RESULTS: All three types of mask showed a 1 to 9% absolute increase in minimum FE at the lower vf and a significant decrease in ΔP. For children's surgical masks the increase in FE was significant for most of the examined particle sizes, but for children's woven masks the increase was limited to particles smaller than 0.04 µm. CONCLUSIONS: Lower vf for children is likely to lead to a higher FE, lower ΔP, and consequently higher filter qualities in children's masks. For woven masks, the FE for particles larger than 0.04 µm was low (typically <50%) for both vf's studied.

The in vitro biomechanics of anterior arch expansion using fixed lingual appliances with coil springs or archwire stops.

INTRODUCTION: The presented study investigates differences in the biomechanics of straight and mushroom fixed lingual appliances when implementing coil springs and stops for anterior arch expansion. MATERIALS AND METHODS: An in vitro orthodontic simulator was used to measure three-dimensional forces and moments on each tooth of a simulated maxillary arch. Mushroom and straight archwire forms of 0.016″ NiTi round archwire were considered, using 0.010″ × 0.030″ NiTi open coils and 0.016″-0.018″ archwire stops (n = 44 per group). Teeth in the anterior dental arch were moved from a neutral to crowded position to replicate anterior crowding of central and lateral incisors. Forces and moments of interest for lateral incisors and first premolars were compared using repeated measures mixed multivariate analysis of variance (α = 0.05). RESULTS: Three comparisons between straight versus mushroom archwires and two comparisons of coil springs vs. stops were not statistically significant. Overall, it was found that the use of a straight lingual archwire produced larger differences in forces and moments between using stops and coil springs than when using a mushroom archwire. Using stops produced larger forces and moments for both types of archwires as compared to using coil springs. The largest expansion forces were produced using straight archwires with stops, exceeding 3.0 N of force. Straight archwires with coil springs produced the lowest expansion forces on lateral incisors, just exceeding 1.5 N. CONCLUSIONS: The findings of this study have elucidated significant differences in the biomechanics of transverse arch expansion using straight or mushroom fixed lingual appliances with coil springs or stops.

The Mechanical Characterization and Comparions of Male and Female Calvaria Under Four-Point Bending Impacts.

The circumstances in which we mechanically test and critically assess human calvarium tissue would find relevance under conditions encompassing real-world head impacts. These conditions include, among other variables, impact velocities, and strain rates. Compared to quasi-static loading on calvaria, there is less reporting on the impact loading of the calvaria and consequently, there are relatively fewer mechanical properties on calvaria at relevant impact loading rates available in the literature. The purpose of this work was to report on the mechanical response of 23 human calvarium specimens subjected to dynamic four-point bending impacts. Impacts were performed using a custom-built four-point impact apparatus at impact velocities of 0.86-0.89 m/s resulting in surface strain rates of 2-3/s-representative of strain rates observed in vehicle collisions and blunt impacts. The study revealed comparable effective bending moduli (11-15 GPa) to the limited work reported on the impact mechanics of calvaria in the literature, however, fracture bending stress (10-47 MPa) was relatively less. As expected, surface strains at fracture (0.21-0.25%) were less compared to studies that performed quasi-static bending. Moreover, the study revealed no significant differences in mechanical response between male and female calvaria. The findings presented in this work are relevant to many areas including validating surrogate skull fracture models in silico or laboratory during impact and optimizing protective devices used by civilians to reduce the risk of a serious head injury.

Investigating the role of aligner material and tooth position on orthodontic aligner biomechanics.

The primary objective of this work was to investigate the effect of material selection and tooth position on orthodontic aligner biomechanics. Additionally, material property changes with thermoforming were studied to elucidate its role in material performance in-vitro. An orthodontic simulator (OSIM) was used to evaluate forces and moments at 0.20 mm of lingual displacement for central incisor, canine and second premolar using Polyethylene terephthalate (PET), Polyurethane (PU) and Glycol-modified polyethylene terephthalate (PET-G) materials. The OSIM was scanned to generate a model used to fabricate aligners using manufacturer-specified thermoforming procedures. Repeated measures of MANOVA was used to analyze the effect of teeth and material on forces/moments. The role of thermoforming was evaluated by flexural modulus estimated by 3-point bend tests. Pre-thermoformed and post-thermoformed samples were prepared using as-received sheets and those thermoformed over a simplified arch using rectangular geometry, respectively. Groups were compared using Two-way ANOVA. The PET, PU, and PET-G materials exerted maximum buccal force and corresponding moments on the canine. PU exerted more buccal force than PET-G on the canine and second premolar, and more than PET on the second premolar. The impact of thermoforming varied according to the specific polymer: PET-G remained stable, there was a slight change for PET, and a significant increase was noted for PU from pre-thermoformed to post-thermoforming. The results of this study elucidate the influence of material and arch position on the exerted forces and moments. Further, the mechanical properties of thermoplastic materials should be evaluated after thermoforming to characterize their properties for clinical application.

Cranial suture morphometry and mechanical response to loading: 2D vs. 3D assumptions and characterization.

Cranial sutures are complex soft tissue structures whose mechanics are often studied due to their link with bone growth in the skull. Researchers will often use a cross-sectional two-dimensional slice to define suture geometry when studying morphometry and/or mechanical response to loading. However, using a single cross section neglects the full suture complexity and may introduce significant errors when defining their form. This study aims to determine trends in suture path variability through skull thickness in a swine model and the implications of using a 'representative' cross section on mechanical modeling. To explore these questions, a mixture of quantitative analysis of computed tomography images and finite element models was used. The linear interdigitation and width of coronal and sagittal sutures were analyzed on offset transverse planes through the skull thickness. It was found that sagittal suture width and interdigitation were largely consistent through the skull thickness, whereas the coronal suture showed significant variation in both. The finite element study found that average values of displacement and strain were similar between the two-dimensionally variable and three-dimensionally variable models. Larger ranges and more complex distributions of strain were found in the three-dimensionally variable model. Outcomes of this study indicate that the appropriateness of using a representative cross section to describe suture morphometry and predict mechanical response should depend on specific research questions and goals. Two-dimensional approximations can be sufficient for less-interdigitated sutures and when bulk site mechanics are of interest, while taking the true three-dimensional geometry into account is necessary when considering spatial variability and local mechanical response.

Modelling and evaluating periodontal ligament mechanical behaviour and properties: A scoping review of current approaches and limitations.

This scoping review is intended to synthesize the techniques proposed to model the tooth-periodontal ligament-bone complex (TPBC), while also evaluating the suggested periodontal ligament (PDL) material properties. It is concentrated on the recent advancements on the PDL and TPBC models, while identifying the advantages and limitations of the proposed approaches. Systematic searches were conducted up to December 2020 for articles that proposed PDL models to assess orthodontic tooth movement in Compendex, Web of Science, EMBASE, MEDLINE, PubMed, ScienceDirect, Google Scholar and Scopus databases. Although there have been many studies focused on the evaluation of PDL material properties through numerous modelling approaches, only a handful of approaches have been identified to investigate the interface properties of the PDL as a complete dynamical system (TPBC models). Past reviews on the analytical and experimental determination of the PDL properties already show a concerning range in reported output values-some nearly six orders of magnitude in difference-that strongly suggested the need for further investigation. Surprisingly, it has not yet been possible to determine a narrower range of values for the PDL material properties. Moreover, very few scientific approaches address the TPBC as an integrated complex system model. In consequence, current methods for capturing the PDL material behaviour in a clinical setting are limited and inconclusive. This synthesis encourages more systematic, pragmatic and phenomenological research in this area.

An in vitro evaluation of orthodontic aligner biomechanics around the maxillary arch.

INTRODUCTION: The objective of this study was to evaluate the forces and moments exerted by orthodontic aligners on 3 different displaced maxillary teeth and their adjacent supporting teeth. METHODS: An in vitro orthodontic simulator was used to measure the forces and moments of a 0.75-mm thick glycol-modified polyethylene terephthalate material for 3 maxillary teeth: central incisor, canine, and second premolar. Forces and moments were recorded for tested teeth displaced lingually one by one for 0.20 mm. Repeated measures of multivariate analysis of variance was used to assess the outcome. RESULTS: The mean buccolingual force applied on a displaced canine (2.25 ± 0.38 N) was significantly (P <0.001) more than the central incisor (1.49 ± 0.18 N) and second premolar (1.50 ± 0.16 N). The mean moment (that tends to tip the teeth buccally) exerted on a canine (-20.11 ± 5.27 Nmm) was significantly more (P <0.001) than the central incisor (-8.42 ± 1.67 Nmm) and second premolar (-11.45 ± 1.29 Nmm). The forces and moments acting on teeth adjacent to the displaced tooth were clinically significant and acted in opposing directions to those on the displaced tooth. CONCLUSIONS: The results of this study highlighted that for the same amount of displacement on a given tooth, the forces and moments imposed by the orthodontic aligner depend on location around the arch. These findings highlight the need to further study aligner mechanics around the dental arch and optimize aligner design to impose desired mechanical loads to avoid detrimental effects during orthodontic tooth movement.

Experimental repeatability, sensitivity, and reproducibility of force and strain measurements from within the periodontal ligament space during ex vivo swine tooth loading.

The Periodontal Ligament (PDL) is a complex connective tissue that anchors a tooth to the surrounding alveolar bone. The small size and complex geometry of the PDL space within an intact tooth-PDL-bone complex (TPBC) limits strain measurements. An in-fiber Bragg grating (FBG) sensor offers potential for such measurements due to its small size. This work defines an experimental procedure where strain and force were measured during quasi-static, apically directed, displacement-controlled tests on swine premolar crowns. Specifically, the: inter-TPBC, intra-TPBC, and long-term repeatability after a preconditioned state was objectively identified; sensitivity to preload magnitude, TPBC alignment, and sensor depth; and reproducibility within a TPBC was determined. Data clustering was used to determine the appropriate number of preconditioning trials, ranging from one to seven. Strain and force measurements showed intra-TPBC repeatability with average adjusted root mean square from the median of 28.9% of the peak strain and 4.5% of the peak force measurement. A Mann-Whitney U test generally found statistically significant differences in peak strain and force measurements between the left and right sides, suggesting a lack of inter-TPBC repeatability. Using a Friedman test, it was shown that peak strain measures were sensitive to the TPBC alignment and sensor depth, while peak force measures were sensitive to the preload and TPBC alignment. A Friedman test suggested reproducible strain and force measurements when the FBG was replaced within the same TPBC and the preload, alignment, and sensor depth were controlled.

Cortical and trabecular morphometric properties of the human calvarium.

There is currently a gap in the literature that quantitatively describes the complex bone microarchitecture within the diploë (trabecular bone) and cortical layers of the human calvarium. The purpose of this study was to determine the morphometric properties of the diploë and cortical tables of the human calvarium in which key interacting factors of sex, location on the calvarium, and layers of the sandwich structure were considered. Micro-computed tomography (micro-CT) was utilized to capture images at 18 µm resolution of male (n = 26) and female (n = 24) embalmed calvarium specimens in the frontal and parietal regions (N = 50). All images were post-processed and analyzed using vendor bundled CT-Analyzer software to determine the morphometric properties of the diploë and cortical layers. A two-way mixed (repeated measures) analysis of variance (ANOVA) was used to determine diploë morphometric properties accounting for factors of sex and location. A three-way mixed ANOVA was performed to determine cortical morphometric properties accounting for factors of cortical layer (inner and outer table), sex, and location. The study revealed no two-way interaction effects between sex and location on the diploë morphometry except for fractal dimension. Trabecular thickness and separation in the diploë were significantly greater in the male specimens; however, females showed a greater number of trabeculae and fractal dimension on average. Parietal specimens revealed a greater porosity, trabecular separation, and deviation from an ideal plate structure, but a lesser number of trabeculae and connectivity compared to the frontal location. Additionally, the study observed a lower density and greater porosity in the inner cortical layer than the outer which may be due to clear distinctions between each layer's physiological environment. The study provides valuable insight into the quantitative morphometry of the calvarium in which finite element modelers of the skull can refer to when designing detailed heterogenous or subject-specific skull models to effectively predict injury. Furthermore, this study contributes towards the recent developments on physical surrogate models of the skull which require approximate measures of calvarium bone architecture in order to effectively fabricate a model and then accurately simulate a traumatic head impact event.

On the ability of experimental impact measures to predict tooth injuries in an ex vivo swine model.

BACKGROUND/AIM: Impact to the orofacial region, in particular teeth, is a frequent incident leading to injury in many sports and can result in health and economic costs for the injured individual. The majority of previous work has applied synthetic models such as plaster or stone, to form analogs of relevant structures to study the potential for impact-induced injury. Biomechanical studies that have applied tissue models (animal or human) for the purpose of determining the biomechanical measures associated with dental injury are rare. The aim of this study was to apply a simple ex vivo model based on swine dentition to ascertain which of a select list of measurable quantities associated with impact mechanics could predict luxation and fracture of teeth due to impact. METHODS: Mandibular central incisors of ex vivo swine dentitions were impacted using a linear drop tower with heights ranging from 1.20 m to 2.42 m. Seven mechanical predictors were assessed at impact and were then subjected to binary logistic regression techniques to determine which was the best predictor of luxations or fractures of the teeth. RESULTS: Of the seven mechanical predictors, (1) the velocity of the impacting body (R2  = 0.477), (2) a proxy measure for the change in kinetic energy of the impacting body (R2  = 0.586), and (3) the approximate energy absorbed by the tissue (R2  = 0.722) were found to be statistically significantly different (p < .05), offering the greatest specificity as indicated by receiver operator characteristics. Other measures that are frequently used in impact mechanics, including peak linear acceleration and velocity change, were not statistically significant predictors of tooth injury. CONCLUSION: Identifying mechanical predictors for dental injury of unprotected teeth provides a first step in understanding which aspects of an impact event attribute to dental injury and can lay the foundation for future studies that examine alteration in injury mechanics associated with protection devices.

Reliability and accuracy of a method for measuring temporomandibular joint condylar volume.

OBJECTIVE: The aim of this study was to develop and validate a technique for mandibular condyle segmentation and volume determination by using cone beam computed tomography (CBCT). STUDY DESIGN: A dry skull was used to generate 3 dimensional (3-D)-printed mandible models that were then imaged by using CBCT. Semiautomatic segmentation of condyles was completed. The Frankfurt plane was established and translated to the most inferior point of the sigmoid notch, and the condylar volume superior to the plane was determined. This procedure was repeated on 3-D-printed mandibles by using physical landmarks and the water displacement method to obtain the physical volume. This was repeated 3 times to evaluate reliability. Sensitivity analysis was performed to demonstrate the effect of discrepancies in locating landmarks in the Frankfurt plane. Condylar volume measurements obtained from CBCT were compared with physical measurements through repeated-measures analysis of variance (ANOVA) to determine accuracy. RESULTS: Condylar volume obtained from CBCT and physical measurements resulted in an intraclass correlation coefficient of 0.988 (0.918, 0.998) (P < .01) with both modalities, demonstrating excellent intrarater reliability. The mean difference of volume measurements between the modalities was not statistically significant (P = .365). Potential discrepancies in porion coordinates had minimal impact on condylar volume change. CONCLUSIONS: The condylar segmentation technique proved to be a reliable and accurate method for evaluating condylar volume.

Research paper: The three-dimensional mechanical response of orthodontic archwires and brackets in vitro during simulated orthodontic torque.

Orthodontic archwire rotation around its long axis, known as third-order torque, is utilised to correct tooth rotational misalignments moving the tooth root closer to or away from the cheek through engagement with an orthodontic bracket. Studying the behaviour of archwire and brackets during an applied rotation can aid in better understanding and appreciating the mechanics of third-order torque, potentially allowing for more effective orthodontic treatment protocols. Mechanically characterising archwire behaviour during third-order torque application is a complex task due to their physical scale and geometries. An advanced measurement technique was needed to address these constraints. A three-dimensional (3D) non-contact optical method using a digital image correlation (DIC) system was developed. An orthodontic torque simulator (OTS) was used to apply and measure third-order torque with 0.483 × 0.635 mm (0.019″ x 0.025″) rectangular archwires in tandem with a 3D DIC system, whereby surface deformations and strains could be computed using correlation algorithms. The 3D DIC system was implemented to enable third-order torque experimentation with the OTS while imaging the archwire and bracket surfaces. The 3D DIC system's ability to measure 3D archwire deformations and strains was verified using a finite element model, where comparisons between 3D DIC measurements and calculated results from the model were made to ensure the measurement capabilities of 3D DIC in the context of third-order torque. The 3D DIC system was then used to compare archwire behaviour between stainless steel (SS) and titanium molybdenum alloy (TMA) archwires to study potential clinical differences in archwire behaviour, in which the archwires were rotated with a custom SS rigid dowel (RD) as well as commercial Damon Q orthodontic brackets. The quantification of third-order torque and archwire deformations and strains led to the conclusion that SS archwires led to larger torque magnitudes compared to TMA archwires. The RD resulted in larger archwire strains compared to Damon Q brackets. The 3D DIC system provides a non-contact measurement technique that can further be used with third-order torque experimentation with the OTS.

The biomechanics of posterior maxillary arch expansion using fixed labial and lingual appliances.

OBJECTIVE: To compare the biomechanics of straight labial, straight lingual, and mushroom lingual archwire systems when used in posterior arch expansion. MATERIALS AND METHODS: An electro-mechanical orthodontic simulator allowing for buccal-lingual and vertical displacements of individual teeth and three-dimensional force/moment measurements was instrumented with anatomically shaped teeth for the maxillary arch. In-Ovation L brackets were bonded to lingual surfaces, and Carriere SLX brackets were bonded to labial surfaces to ensure consistency of slot dimensions. Titanium molybdenum archwires were bent to an ideal arch form, and the teeth on the orthodontic simulator were set to a passive position. Posterior teeth from the canine to second molar were moved lingually to replicate a constricted arch. From the constricted position, the posterior teeth were simultaneously moved until the expansive force decreased below 0.2 N. Initial force/moment systems and the amount of predicted expansion were compared for posterior teeth at a significance level of α = 0.05. RESULTS: Archwire type affected both the expected expansion and initial force/moment systems produced in the constricted position. In general, the lingual systems produced the most expansion. The archwire systems were not able to return the teeth to their ideal position, with the closest system reaching 41% of the intended expansion. CONCLUSIONS: In general, lingual systems were able to produce greater expansion in the posterior regions when compared with labial systems. However, less than half of the intended arch expansion was achieved with all systems tested.