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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 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.

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.

A better understanding of the effect of density, microstructure, and strain rate on the mechanical response of polymeric foam materials is needed to improve their performance. The objective of this paper is to study the combined influence of density, microstructure, and strain-rate on the compressive stress-strain response of polymeric foams. Microstructural morphological parameters (e.g., pores sizes and wall thicknesses) have been quantified using Micro X-ray tomography and MATLAB-based techniques. Polymeric foam samples were examined under uniaxial compression loading at quasistatic (0.001 to $$0.1 s^{-1}$$ ), intermediate (1 to $$250 s^{-1}$$ ), and dynamic strain rates (3200 to $$5700 s^{-1}$$ ). All experiments were coupled with high speed cameras to measure strain using 2D digital image correlation, and to visualize deformation. The variation of the mechanical properties across alldensities (e.g., elastic modulus and collapse stress) are found to behave in a power law fashion with respect to strain rate. A comprehensive data set across a varied range of densities and strain rates, especially intermediate strain rates, is lacking in previous research, and generalized phenomenological relationships developed in this paper to predict combined influences of density, microstructure, and strain-rate over varied range of materials are important contributions of this work. The results showed that the power-law relationships act as a good predictor for the prediction of mechanical properties and elastic response, and as an indicator for damage mechanisms in these polymeric foams.

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.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.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.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.

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.

Cleft lip and palate is a congenital defect that affects the oral cavity. Depending on its severity, alveolar graft surgery and maxillary orthopedic therapies must be carried out as a part of the treatment. It is widely accepted that the therapies should be performed before grafting. Nevertheless, some authors have suggested that mechanical stimuli such as those from the maxillary therapies could improve the success rate of the graft. The aim of this study is to computationally determine the effect of maxillary therapies loads on the biomechanical response of an alveolar graft with different degrees of ossification. We also explore how the transverse width of the cleft affects the graft behavior and compare results with a non-cleft skull. Results suggest that stresses increase within the graft as it ossifies and are greater if maxillary expansion therapy is applied. This has consequences in the bone remodeling processes that are necessary for the graft osseointegration. Maxillary orthopedic therapies after graft surgery could be considered as a part of the treatment since they seem to act as a positive extra stimulus that can benefit the graft.

Objective To analyse through a systematic review the effectiveness of clear aligners by assessing: (a) predictability of clear aligners and (b) treatment outcome comparison of clear aligner therapy with fixed appliance therapy. Methods An electronic search was made from January 2014 to April 2019 using MEDLINE, Embase, Web of Science and LILACS databases without any limitations on language. Three reviewers independently assessed the articles. Quality assessment of observational studies and randomized control trial was done by using the ROBINS tool and Cochrane risk of bias tool, respectively. GRADE instrument was used to assess certainty level for each identified outcome. Results Seven eligible articles (one randomized controlled trial and six retrospective cohort) were included in our systematic review. Most of the studies (six out of seven) had a moderate risk of bias and one had a high risk of bias. Conclusions 'Low to moderate level' of certainty in regard to specific clear aligner therapy tooth movements' efficiency was identified. Clear aligners may produce clinically acceptable outcomes that could be comparable to fixed appliance therapy for buccolingual inclination of upper and lower incisors in mild to moderate malocclusions. However, not all potential clinical scenarios have been assessed in the included studies. Most of the tooth movements may not be predictable enough to be accomplished with only one set of trays with clear aligners despite the recent advances in technology.

Resin-based composites (RBCs) are commonly used in dental restorations. It is known that RBCs undergo volumetric shrinkage during photo-polymerization leading to a detrimental increased stress state at the RBC-tooth interface and potentially early restoration failure. The objectives of this in vitro study were: (1) to ascertain whether shrinkage strain could be measured using in-fibre Bragg grating (FBG) technology, without confounding effects of temperature; and (2) to ascertain whether FBGs can detect alteration in shrinkage strain with introduction of a surface condition change at the RBC-cavity analog interface.Aluminum cavity analogs with simulated cavity dimensions 3.5 mm height x 2 mm width x 8 mm length and 2 mm wall thickness were secured in a 3D printed experimental jig. Two FBGs were used in the RBC space, one that was covered with a polyimide tube and that measured only temperature, and another that was affected by both mechanical strain and temperature. Experiments to determine if the two FBG system could be used to compensate for thermal artefacts were contrived to verify that a tube-covered and bare FBG measure the same temperature effect (n = 5). In situ photo-polymerization experiments, which consisted of using controlled amounts of SureFil SDR Flow + RBC, were performed to study RBC shrinkage behavior. As-machined (n = 10) and micro-etched (n = 11) cavity analogs were used. Significant differences in FBG measurements, which could indicate the ability of FBGs to detect alterations in strain across surface preparations, were determined using one tail t-tests at 95% confidence. Finally, additional temperature experiments were conducted 5 h after initial light exposure using the same light irradiation regiment to investigate temperature effects within a cured RBC system (n = 3).For temperature measurement, the tubing-covered and bare FBGs measured temperature changes with time-lag of 3.7 ± 1.4 s (tubing-covered FBG relative to bare). For measurements in cured RBC, the bare FBG and tubing-covered FBG measured different strains, with the bare FBG measuring larger apparent strains because this FBG is affected by thermal volumetric expansion of the RBC and a temperature increase of the FBG itself. The tubing covered FBG, that is isolated from volumetric expansion effects, measured relatively less. The interpretation of these results is that thermally-compensated strain measures (in-situ) could require simultaneous use of two FBGs (one strain isolated). In situ measurements of the photo-polymerization procedure for as-machined analogs at two time-points, 500 and 1000 s, were determined to be -485.43 ± 131.06 μstrain and -524.96 ± 134.78 μstrain, respectively. For air-abraded surfaces measures were significantly lower at (p 0.001) -211.36 ± 12.38 μstrain and -228.07 ± 49.08 μstrain, respectively.To measure shrinkage strain and compensate for associated thermal effects from photo-polymerization, systems employing two FBGs, one of them isolated from thermal volumetric expansion, may be required. The presented approach proved capable of detecting significant alteration in strain across two surface preparations.

Purpose The presented study utilized an in vitro Orthodontic SIMulator (OSIM) to study how Class II elastic configuration effects the forces and moments acting on maxillary canine teeth when using a straight archwire fixed lingual appliance. Materials and methods Maxillary in-Ovation L self-ligating brackets were bonded to anatomically shaped stainless steel teeth on OSIM. A 0.016″ × 0.022″ stainless steel straight lingual archwire was used to provide a relevant arch shape and to position simulated teeth in a passive position. A mandibular typodont was positioned above the OSIM arch in a half cusp Class II malocclusion to serve as attachment points for elastics. Four different elastic configurations were tested: 1. maxillary–buccal to mandibular-buccal; 2. maxillary–lingual to mandibular–lingual; 3. maxillary–buccal to mandibular–lingual; 4. maxillary–lingual to mandibular–buccal. A new 4.5 oz 3/16″ elastic (n = 40 per configuration) was attached to the maxillary canine and mandibular first molar teeth for each trial. Forces and moments at the maxillary canine simulated center of resistance were considered. ANOVA was used to assess the effect of elastic configuration, and pairwise comparisons using Bonferroni correction were conducted to investigate configuration differences. Results Of the thirty-four pairwise comparisons, only two were statistically insignificant. Configurations 1, 2, and 4 were found to produce over 1 N of force in the desired distal direction, whereas Configuration 3 was significantly lower at 0.65 N. Conclusions Overall, the configuration of Class II elastics had a significant effect on forces and moments at maxillary canine teeth for a simulated straight archwire fixed lingual appliance.

The goal of this investigation was to adapt and incorporate a nonlinear viscoelastic material model representative of the midpalatal suture’s viscoelastic nature into finite element analysis simulations of maxillary expansion treatment. Step-wise displacements were applied to a partial skull geometry to simulate treatment using an expansion screw appliance. Four simulation cases were considered for the midpalatal and intermaxillary sutures: 1. Neglecting suture tissue; 2. Linear elastic properties; 3. Viscoelastic properties; 4. A fused intermaxillary and viscoelastic midpalatal suture. Results from simulations indicated that removal of suture tissue and inclusion of viscoelastic properties resulted in the same maxillary displacement following 29 activations of 0.125 mm applied directly to the maxilla; however, assuming a fused intermaxillary suture significantly changed maxillary displacement patterns. Initial stress results within the suture complex were significantly influenced by the inclusion of suture viscoelasticity as compared to linear elastic properties. The presented study demonstrates successful incorporation of suture viscoelasticity into finite element analysis simulations of maxillary expansion treatment, and elucidates the appropriateness of various suture material property assumptions depending desired research outcomes.

Background: Decontamination and reuse of respirators have been proposed to mitigate the shortage of respirators during pandemics. The U.S. National Institute for Occupational Safety and Health (NIO...

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

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.

There is currently a gap in the literature that quantitatively describes the complex bone microarchitecture within the diploe (trabecular bone) and cortical layers of the human calvarium. The purpose of this study was to determine the morphometric properties of the diploe 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 diploe and cortical layers. A two-way mixed (repeated measures) analysis of variance (ANOVA) was used to determine diploe 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 diploe morphometry except for fractal dimension. Trabecular thickness and separation in the diploe 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.

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.

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).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.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.The condylar segmentation technique proved to be a reliable and accurate method for evaluating condylar volume.

Introduction An Orthodontic SIMulator (OSIM) was used to investigate the propagation of forces and moments around a simulated archform for a gingival displaced canine and lingual displaced lateral incisor using fixed lingual orthodontic appliances. Methods In-Ovation L self-ligating lingual brackets were bonded to anatomically shaped teeth on the OSIM, and the teeth were positioned such that a G4 NiTi 0.016" large maxillary mushroom archwire could be ligated in passive position. Each trial consisted of two movements: a 3mm lingual displacement of the 1-2 lateral incisor at 0.2 mm increments, and a 1.5 mm gingival displacement of the 2-3 canine at 0.15 mm increments (n = 50). Anterior brackets were repositioned to accommodate G4 NiTi 0.016" universal straight archwires (n = 50). Tests were completed at 37°C, and force and moment data in all directions was collected for each tooth around the arch at all increments. Results In general, the straight archwire produced significantly larger forces and moments at the centre of resistance for teeth of interest than did mushroom archwires. Specifically, the straight archwire produced 2.62 N and 3.81 N more force in the direction of tooth movement on the tooth being moved for a gingival displaced canine and lingual displaced lateral incisor, respectively, as compared to mushroom archwires. Conclusions Results from this study suggest that mushroom archwires may provide better mechanics for movement of teeth in the anterior segment when using a round archwire; however, only biomechanical data was considered in this study and there are many factors that need to be considered in treatment planning.

Measurement of periodontal ligament (PDL) strain in an ex vivo or in vivo setting of a complete tooth-PDL-bone complex (TPBC) has yet to be achieved in the literature. The objective of this study was to investigate inter- and intra-TPBC PDL strain measurement using fibre Bragg grating (FBG) strain sensors. Second and third premolars from the left and the right side of four swine mandibles were removed to yield sixteen TPBC samples. Samples were secured in a miniature load-frame equipped with a digital actuator used to apply apical-directed displacement to the tooth. The same tooth on left and right sides of the mouth were exposed to the same loading condition over ten trials allowing for comparisons in a split-mouth study. Displacements of 0.2 and 0.3 mm were considered along with displacement rates of 0.025, 0.05, and 0.1 mm/s, yielding six loading combinations. Hypothesis testing between left and right teeth revealed FBGs did not always measure the same strain between left and right TPBCs. For all strain measures, the average coefficient of variation (CV) (all data collected) was 2.16 (range: 0.274–10.71). For repeated measures in single TPBCs, the minimum CV ranged from 0.037 to 0.449, and generally coincided with the time of maximum strain measured over the test duration. Based on the findings of this study, it is suggested that FBGs can provide repeatable ex vivo strain measures in the PDL of complete TPBCs.

The objective was to explore how clinically relevant machining process and heat treatment influence damage accumulation and strength degradation in lithium silicate-based glass ceramics machined in the fully crystallized state.A commercial zirconia-reinforced lithium silicate (ZLS) glass ceramic with a fully developed microstructure (Celtra® Duo) was studied. Disk-shaped specimens (nominal 10 mm diameter and 1 mm thickness) were fabricated either using a CAD-CAM process, creating a clinically relevant dental restoration surface, or were sectioned from water-jet cut cylindrical blocks with their critical surfaces consistently polished. Bi-axial flexure strength (BFS) was determined in a ball-on-ring configuration, and fractographic analysis was performed on failed specimens. XRD, AFM and SEM measurements were conducted before and after heat treatment. For each sample group, BFS was correlated with surface roughness. A two-way ANOVA and post-hoc Tukey tests were used to determine differences in BFS between machining and heat treatment groups (ɑ = 0.05).A two-way ANOVA demonstrated that BFS was influenced by fabrication route (p0.01) with CAD-CAM specimens exhibiting significantly lower mean BFS. A factorial interaction was observed between heat treatment and machining route (p0.01), where a significant strengthening effect of post-manufacture heat treatment was noted for CAD-CAM specimens but not sectioned and polished samples. CAD-CAM specimens exhibited sub-surface lateral cracks alongside radial cracks near fracture origin which were not observed for polished specimens. BFS did not correlate with surface roughness for polished specimens, and no change in microstructure was detectable by XRD following heat treatment.The mechanical properties of the ZLS ceramic material studied were highly sensitive to the initial surface defect integral associated with manufacturing route and order of operations. CAD-CAM manufacturing procedures result in significant strength-limiting damage which is likely to influence restoration performance; however, this can be partially mitigated by post-machining heat treatment.

Objective The structure of the polymer phase of dental resin-based-composites is highly sensitive to photo-polymerisation variables. The objective of this study was to understand how different polymer structures, generated with different photo-polymerisation protocols, respond to thermal perturbation. Methods Experimental resins were prepared from a series of Bis-GMA/TEGDMA blends (40/60, 50/50 and 60/40 wt.%), with either Camphorquinone/DMAEMA or Lucirin TPO as the photo-initiator system. Resins were photo-polymerised, in a disc geometry, at either relatively ‘high’ (3000 mW cm−2 for 6 s) or ‘low’ (300 mW cm−2 for 60 s) irradiances ensuring matched radiant exposures (18 J cm−2). Specimens were heated, from 20−160 °C at a rate of 5 °C min−1, whilst simultaneous synchrotron X-ray scattering measurements were taken at 5 °C increments to determine changes in polymer chain segment extension and medium-range order as a function of temperature. For each unique resin composition (n = 3), differential scanning calorimetry was used to measure glass transition temperatures using the same heating protocol. A paired t-test was used to determine significant differences in the glass transition temperature between irradiance protocols and photo-initiator chemistry at ɑ = 0.05. Results Resins pre-polymerised through the use of TPO and or high irradiances demonstrated a reduced rate of chain extension indicative of lower thermal expansion and a larger decrease in relative order when heated below the glass transition temperature. Above the transition temperature, differences in the rate of chain extension were negligible, but slower converted systems showed greater relative order. There was no significant difference in the glass transition temperature between different photo-initiator systems or irradiance protocols. Significance The evolution of chain extension and medium-range order during heating is dependent on the initial polymer structure which is influenced by photo-polymerisation variables. Less ordered systems, generated at faster rates of reactive group conversion displayed reduced chain extension below the glass transition temperature and maintained lower order throughout heating.

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.

Objective: To critically synthesize the literature surrounding segmentation of the mandibular condyle using three-dimensional imaging modalities. Specifically, analyzing the reliability and accuracy of methods used for three-dimensional condyle segmentation. Methods: Three electronic databases were searched for studies reporting the reliability and accuracy of various methods used to segment mandibular condyles from three-dimensional imaging modalities. Two authors independently reviewed articles for eligibility and data extraction. Results: Nine studies fulfilled the inclusion criteria. Eight studies assessed the condylar segmentation from CBCT images and limited studies were available on non-CBCT three-dimensional imaging modalities. Threshold-based volume segmentation, manual segmentation, and semi-automatic segmentation techniques were presented. Threshold-based volume segmentation reported higher accuracy when completed by an experienced technician compared to clinicians. Adequate reliability and accuracy were observed in manual segmentation. Although adequate reliability was reported in semi-automatic segmentation, data on its accuracy were lacking. Conclusion: A definitive conclusion with regards to which current technique is most reliable and accurate to efficiently segment the mandibular condyle cannot be made with the currently available evidence. This is especially true in terms of non-CBCT imaging modalities with very limited literature available.

Objective The fabrication of all-ceramic restorations using Computer Aided Design and Computer Aided Manufacturing (CAD–CAM) most commonly involves subtractive machining which results in strength-limiting, surface and sub-surface damage in the resultant prosthesis. The objective was to explore how clinically relevant machining-process variables, and material variables, affect damage accumulation in lithium silicate glass-ceramics. Methods Three commercial lithium silicate glass-ceramics (IPS e.max® CAD, Celtra® Duo and Vita Suprinity®) were selected. For each material, two groups of disk-shaped specimens were fabricated (n = 15), using a CAD–CAM process, creating surfaces equivalent to those generated for a dental restoration, or alternatively, using a highly controlled laboratory process generating disk-shaped test specimens with a consistent polished surface. Bi-axial flexure strength (BFS) was determined in a ball-on-ring configuration and fractographic analyses performed. For each material BFS was correlated with machining sequence and with surface roughness. Results BFS was significantly influenced by material substrate (p Significance All CAD–CAM specimens showed evidence of machining introduced damage in the form of median and radial cracks at sites either coincident with, or peripheral to the failure origin. Subtractive machining introduced significant strength limiting damage that is not eliminated by heat treatments applied for either microstructure development (IPS e.max® CAD and Vita Suprinity®) or annealing/crack blunting (Celtra® Duo).

Previously, dental stone has been utilized in mechanical testing of the periodontal ligament, which connects the tooth to the alveolar bone. This was achieved by casting swine mandibles in dental stone for displacement controlled testing. The stone was used as a riding base to hold the mandible in place. However, this was done in dry, ex vivo conditions, failing to simulate the natural presence of vascular fluid in the periodontal ligament. While this can be simulated with submersion in saline, the mechanical response of dental stone to saline is currently unknown, and thus cannot yet be used to secure the mandible in saline. To identify differences in the strength of dental stone after submersion in saline, Coecal Type III Dental Stone samples were cast in a 3D printed mold, then submerged in 0.9% NaCl solution for varying time periods: 0 hours, 0.5 hours, 1 hour, 4 hours, and 24 hours. Samples were then removed from the solutions, patted dry, and placed in an Instron ElectroPuls E3000 for compression tests. The Instron preloaded samples to 3 N, displaced them to 0.1 mm at 0.025 mm/s, held them for 10 s, then offloaded at 0.025 mm/s. This cycle was repeated five times per test, with each sample undergoing two tests. Results showed that the last three cycles of each test were most consistent, and were the only ones considered in further analysis of results. The average peak force and average force during the 10 s hold of each test were compared across submersion times, and, considering standard deviation, showed no consistent differences. A linear regression was completed to determine statistical differences between the force values. The p-values of the average peak force and average force were 0.624 and 0.892 respectively, approaching the required value of 1, and therefore failed to reject the null hypothesis, representing no significant difference in the average force across submersion times. As a result, it can be assumed that submersion in saline has no effect on the strength of dental stone. These results can be applied to further research on the periodontal ligament, involving submersion of the swine mandible in saline solutions.

Objective: To investigate the influence of a rotational second-order bracket-archwire misalignment on the loads generated during third-order torque procedures. Specifically, torque in the second- and third-order directions was considered. Materials and Methods: An orthodontic torque simulator (OTS) was used to simulate the third-order torque between Damon Q brackets and 0.019 × 0.025-inch stainless steel archwires. Second-order misalignments were introduced in 0.5° increments from a neutral position, 0.0°, up to 3.0° of misalignment. A sample size of 30 brackets was used for each misalignment. The archwire was then rotated in the OTS from its neutral position up to 30° in 3° increments and then unloaded in the same increments. At each position, all forces and torques were recorded. Repeated-measures analysis of variance was used to determine if the second-order misalignments significantly affected torque values in the second- and third-order directions. Results: From statistical analysis of the experimental data, it was found that the only statistically significant differences in third-order torque between a misaligned state and the neutral position occurred for 2.5° and 3.0° of misalignment, with mean differences of 2.54 Nmm and 2.33 Nmm, respectively. In addition, in pairwise comparisons of second-order torque for each misalignment increment, statistical differences were observed in all comparisons except for 0.0° vs 0.5° and 1.5° vs 2.0°. Conclusion: The introduction of a second-order misalignment during third-order torque simulation resulted in statistically significant differences in both second- and third-order torque response; however, the former is arguably clinically insignificant.

Despite developments in polycrystalline ceramics, glassy dental-ceramic materials provide the optimum cosmetic option in most clinical situations to mimic the natural dentition. The clinical success of glassy dental-ceramic materials is often attributed to resin-adhesive bonding techniques. In this study we explore whether shrinkage stresses generated on photo-polymerisation of the resin-cement are sufficient to induce ceramic surface defect stabilization, and we quantify the transient nature of the induced stresses.Stress-induced changes in a feldspathic ceramic over a range of thicknesses (0.5-2.0mm: n=20 per thickness) were measured using a profilometric technique at baseline for each disc-shaped specimen (mean of the maximum deflection (δA repeated measures ANOVA and post-hoc Bonferroni tests determined that δA link between shrinkage stresses associated with the photo-polymerization of dental resin-based cements and the reinforcement of dental porcelain has clearly been established.

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.

The interrelation between creep and relaxation response of a nonlinear material is a widely studied topic with major implications in the study of viscoelasticity. When considering maxillary expansion, a common orthodontic treatment, a variety of appliances and protocols may be utilized placing the midpalatal suture in a creep or relaxation scenario; hence, it is imperative to fully understand the suture׳s viscoelastic behavior in prediction of patient response to maxillary expansion. The presented study considers four approaches to a full creep–relaxation model, including both separable and inseparable functions. Each model is fit to rabbit midsagittal suture creep data from the literature and then transformed into its subsequent relaxation form for evaluation. Due to a lack of experimental relaxation data in the literature for this tissue, an additional study considering medial collateral ligament data was used to further evaluate ideal model candidates based on the initial analysis. Results from the study presented here show that the suture׳s creep behavior is best described through functions with variable stress exponents. In addition, the four models tested were found to give a physically reasonable range of relaxation predictions. Such findings further highlight the necessity to explore the creep–relaxation behavior of a material using a variety of approaches when building a comprehensive viscoelastic model.

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.

Resume L’objectif global de cette revue etait d’observer comment les proprietes materielles de la suture palatine mediane non fusionnees ont ete abordees par les chercheurs utilisant l’analyse des elements finis (AEF) pour etudier l’expansion maxillaire. La litterature disponible sur Scopus, PubMed et Biosis a ete passee en revue. A la fin de cette revue, il a ete trouve que les chercheurs supposaient la suture etre vide, possedant les memes proprietes elastiques que l’os, ou ayant des proprietes elastiques semblables aux tissus mous. Par une analyse simplifiee du complexe maxillaire pendant l’expansion, il est demontre que la suture peut exercer une influence significative sur le resultat du traitement. En consequence, malgre les contributions utiles faites par les etudes anterieures, il serait opportun d’incorporer un modele plus representatif de la suture mediopalatine dans les simulations par elements finis.

Maxillary expansion treatment is a commonly used procedure by orthodontists to widen a patient's upper jaw. As this is typically performed in adolescent patients, the midpalatal suture, connective tissue adjoining the two maxilla halves, remains unfused. Studies that have investigated patient response to expansion treatment, generally through finite element analysis, have considered this suture to behave in a linear elastic manner or it was left vacant. The purpose of the study presented here was to develop a model that could represent the midpalatal suture's viscoelastic behavior. Quasilinear viscoelastic, modified superposition, Schapery's, and Burgers modeling approaches were all considered. Raw data from a previously published study using New Zealand White Rabbits was utilized for model parameter estimation and validation. In this study, Sentalloy(®) coil springs at load levels of 0.49N (50g), 0.98N (100g), and 1.96N (200g) were used to widen the midsagittal suture of live rabbits over a period of 6 weeks. Evaluation was based on a models ability to represent experimental data well over all three load sets. Ideally, a single set of model constants could be used to represent data over all loads tested. Upon completion of the analysis it was found that the modified superposition method was able to replicate experimental data within one standard deviation of the means using a single set of constants for all loads. Future work should focus on model improvement as well as prediction of treatment outcomes.

Objective: To investigate initial forces acting on teeth around the arch during en masse retraction using an in vitro Orthodontic SIMulator (OSIM). Materials and Methods: The OSIM was used to represent the full maxillary arch in a case wherein both first premolars had been extracted. Dental and skeletal anchorage to a posted archwire and skeletal anchorage to a 10-mm power arm were all simulated. A 0.019 × 0.025-inch stainless steel archwire was used in all cases, and 15-mm light nickel-titanium springs were activated to approximately 150 g on both sides of the arch. A sample size of n = 40 springs were tested for each of the three groups. Multivariate analysis of variance (α = 0.05) was used to determine differences between treatment groups. Results: In the anterior segment, it was found that skeletal anchorage with power arms generated the largest retraction force (P < .001). The largest vertical forces on the unit were generated using skeletal anchorage, followed by skeletal anchorage with power arms, and finally dental anchorage. Power arms were found to generate larger intrusive forces on the lateral incisors and extrusive forces on the canines than on other groups. For the posterior anchorage unit, dental anchorage generated the largest protraction and palatal forces. Negligible forces were measured for both skeletal anchorage groups. Vertical forces on the posterior unit were minimal in all cases ( Conclusions: All retraction methods produced sufficient forces to retract the anterior teeth during en masse retraction. Skeletal anchorage reduced forces on the posterior teeth but introduced greater vertical forces on the anterior teeth.

Introduction: The focus of the presented study was to investigate the effect of buccal–lingual (B-L) orthodontic bracket slot dimension on third-order torque mechanics. Materials and methods: Three types of orthodontic brackets and two archwire sizes were considered. Ortho Classic H4 (0.026″ B-L slot, passive), Ormco Damon Q (0.028″ B-L slot, passive), and In-Ovation R (0.028″ slot, active) brackets were tested using 0.017″ × 0.025″ and 0.019″ × 0.025″ beta-titanium archwires. An in vitro orthodontic torque simulator (OTS) was used to rotate archwires relative to a single bracket while recording forces and moments in three directions. For each bracket-archwire combination, a total of n = 47 samples were tested. Repeated measures analysis of variance between brackets was conducted for third-order torque values at 3° increments between 9° and 30° during loading and unloading for each archwire size. Results: Statistically significant differences between H4 and Q brackets were only found for 0.017″ × 0.025″ archwires during loading, and 0.019″ × 0.025″ archwires during unloading. Conversely, differences between H4 and R brackets were found for both archwires during loading and unloading phases. Finally, when using a 0.017″ × 0.025″ archwire the H4 brackets reached the 5 Nmm threshold before R and Q brackets; however, there was little difference found when using a 0.019″ × 0.025″ archwire. Conclusions: The concept of using a smaller B-L bracket slot dimension in orthodontic treatment showed it may theoretically allow for more options, primarily using smaller archwires to correct third-order rotational misalignments. However, it is suspected that bracket material limitations and added loading on the door currently prevent this from being clinically applicable.

Conventional applications of two-dimensional tubular braided composites mostly require closed-mesh braiding; however, some stiffness-critical applications may require use of open-mesh braiding. Most likely candidates for the open-mesh braided composites are in the medical field, such as braided catheters and stents. Analytical and experimental investigation of the open-mesh braided tubular composites is very limited in the open literature; therefore, this study is an initial attempt to close this gap. The article investigates elastic properties of the open-mesh braided composites (e.g., braided catheters) and open-mesh composites with holes (i.e., stent-like structures). Analytical results are also compared with that of experimental results. Findings may be used in design of braided medical tubular composites. POLYM. COMPOS., 31:2017–2024, 2010. © 2010 Society of Plastics Engineers

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.

Introduction This in-vitro study presents the development and validation of an artificial tooth-periodontal ligament-bone complex (ATPBC) and comparison of its behavior with that of rigid dowels during third-order torque simulation. Methods ATPBCs were coupled using a 1:1 mixture of room-temperature vulcanization silicone and gasket sealant to act as a periodontal ligament simulant (PDLS). PDLS thicknesses ranging from 0.2 to 0.7 mm, in increments of 0.1 mm (n = 5 for each thickness), were tested using a linear crown displacement procedure. A suitable PDLS thickness was selected for use in third-order torque simulations to compare ATPBC (n = 29) and rigid (n = 24) dowel behavior. Their results were compared for archwire rotations up to 20° for both loading and unloading curves with repeated-measures analysis of variance. Results When used in third-order torque simulations, the ATPBC dowels with a 0.5-mm PDLS thickness showed a statistically significant difference from rigid dowels ( P = 0.020), with a 95% confidence interval (0.254, 2.897 N·mm) and a mean difference of 1.575 N·mm. Conclusions Inclusion of a PDLS in an ATPBC resulted in a statistical difference when compared with rigid dowels; however, the region where behavior differed was at low angles of archwire rotation, and the resultant torque was arguably outside a clinically relevant range.

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