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Introduction: Orthodontically induced inflammatory root resorption (OIIRR) constitutes an undesirable risk connected to orthodontic treatment. Finite element analysis (FEA) is a powerful tool to study the risk of OIIRR. However, its efficiency in predicting OIIRR depends on the insertion of the correct inputs and the selection of an output coherent with the clinical failure mechanism.Methods: By combining a systematic review with a 3-dimensional FEA, this article discusses which are the implications of using certain periodontal ligament (PDL) properties (linear and nonlinear models) and failure criteria. Six orthodontic loading regimes were simulated in a maxillary premolar: pure intrusion, buccal tipping, and their combination applied with either a light (25 cN) or a heavy (225 cN) force. Three stress parameters in the PDL were compared: von Mises stress, minimum principal stress, and hydrostatic stress (σH).Results: The comparison between linear and nonlinear models showed notable differences in stress distribution patterns and magnitudes. For the nonlinear PDL, none of the light-force models reached the critical compressive hydrostatic stress of 4.7 kPa, whereas all the heavy-force models reached it. In addition, the regions of critical compressive σH matched with the regions with resorption craters in clinical studies. In linear models, the σH critical value of 4.7 kPa was reached even in the light-force scenario.Conclusions: Only compressive hydrostatic stress in PDL satisfied the requirements to be used as an FEA indicator of OIIRR. However, the requirements were satisfied only when a nonlinear PDL model was considered. [ABSTRACT FROM AUTHOR]

To assess the torsional load transfer of various commercially available stainless-steel wires used for fixed retainers. An in vitro study using a robotic device. Department of Pediatric Oral Health and Orthodontics, University of Basel. A 10° proclination of a maxillary lateral incisor of a 2-2 retainer was simulated with a robotic device. Eight stainless-steel wires with different shapes (round or rectangular), types (plain, braided, coaxial or chain) and dimensions were selected to measure the torsional load transfer at the adjacent central incisor. The influence of annealing was also tested. The 0.016 × 0.016 and Bond-A-Braid™ wires (0.02645 × 0.01055-inch, 8-stranded, braided) showed the largest relative torsional load transfer (3.7% and 3.3%, respectively). The two multistranded wires - Triple Flex™ and Respond® - showed the smallest values of 1.0% and 0.7%, respectively. The spiral direction of these two multistranded wires affected the load transfer, the twisting showing larger torsional load transfer than the untwisting one. The effective torsional load transfer depends on the dimension, shape and type of a wire. Plain and braided retainers were more predictable in torsional load transfer than multistranded retainers, which may have stored more energy in the area between the composite bonding sites. This may explain the unexpected complications reported in multistranded retainers. [ABSTRACT FROM AUTHOR]

To compare a fluorescence-aided identification technique (FIT) with a conventional light source (CLS) for removing composite during debonding of brackets with respect to time needed, composite remnants, and tooth substance loss. Twelve maxillary models with 10 bovine teeth each were digitally surface-scanned and metal brackets were bonded on each tooth with Opal Seal and Opal Bond. Two operators: an experienced orthodontist (A) and an undergraduate student (B) received six models each and were asked to remove the composite remnants with a tungsten carbide bur and Sof-Lex discs by both a conventional light source (CLS group, n = 3), and fluorescent inducing light (FIT group, n = 3). The time taken was recorded, and a postoperative scan was digitally superimposed on the preoperative scan to quantify number of teeth with composite remnants and volume and thickness of enamel loss and composite remnants. Chi-square test and independent t-tests were performed to compare methods with a significance level of 5%. Compared to CLS, both operators needed significantly less time when using the FIT method and degree of enamel loss, height, and volume of composite remnants and total remaining composite remnants were significantly reduced. By FIT, the volume of enamel loss was significantly reduced for operator A only. Operator B removed the same enamel volume with either method. Cleanup after orthodontic debonding with the FIT was superior regarding time needed and removal of composite remnants. Total enamel loss reduction was operator-dependent. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the force systems produced by transpalatal arches (TPAs) activated according to the six classes of geometries described by Burstone and Koenig. Materials and Methods: Sixty appliances were tested for first-order activations using a mechanical force testing system. The TPAs were first checked for passivity in sagittal, transverse, and vertical planes at the measuring machine. Then 10 appliances per group were activated using a millimeter template to obtain the six classes of geometries, and the activated appliances were inserted into lingual tubes of the Force System Identification machine that recorded the deactivation forces and moments delivered by both terminal ends of the TPAs. Results: The overall force system with the actual values of forces and moments recorded by each type of activation was illustrated and compared with the mathematical model reported by Burstone and Koenig. Although a great consistency of the direction of forces and moments were observed, the theoretically feasible force systems could not be fully accomplished by the TPA activated for the six classes of geometries. Conclusion: The first-order activations of the TPA can deliver predictable force systems in respect to the direction of forces and moments attainable, but some unexpected forces and moments are also produced. Careful clinical monitoring is, therefore, strongly recommended when using this statically indeterminate system. [ABSTRACT FROM AUTHOR]

The article presents the study on the three-dimensional (3D) evaluation of condylar and mandibular growth among patients with juvenile idiopathic arthritis (JIA) with unilateral temporomandibular joint who were treated with distraction splint. The cone-beam computed tomography (CBCT) scans and reconstruction of 3D models were conducted. The results were outlined and conclude on the effect of orthopedic functional treatment on condylar adaptation and modeling.

Novel fast-setting calcium silicate cement with fluoride (CSC) has been developed for potential applications in tooth crown. The aim of this study was to test the diametral tensile strength (DTS) of different CSC compositions in humid condition on day1, 28, and 180. We tested 'bond CSC' with 3.5% fluoride and no radiocontrast, 'CSC' with 3.5% fluoride and 10% radiocontrast, 'ultrafast CSC' with 3.5% fluoride and 20% radiocontrast, 'high fluoride CSC' with 15% fluoride and 25% radiocontrast, Biodentine, and MTA. We filled the cements after mixing to cylindrical molds. Specimens were stored in >95% humidity. DTS was measured at each time point. CSC compositions had statistically higher DTS compared to MTA and Biodentine on day1. Bond CSC showed higher DTS versus all cements, except CSC, at all time points. DTS of all cements, except Biodentine, significantly increased in humid condition on day28 and day180 compared to day1. [ABSTRACT FROM AUTHOR]

Objective: Movements of teeth splinted by fixed retention wires after orthodontic treatment have been observed. The aetiological factors for these movements are unknown. The aim of thisin vitrostudy was to compare the resistance to torque of different stainless steel wires commonly used for fixed retainers in orthodontics.Materials and Methods: Torquing moments acting on a retainer wire were measured in a mechanical force testing system by applying buccal crown torque to an upper lateral incisor in both a 3-teeth and in a 2-teeth setup. Seven stainless steel wires with different shape, type (plain, braided, coaxial, or chain) and dimensions were selected for this study.Results: For a torquing angle of 16.2° in the 3-teeth setup torsion moments can vary between 390 cNmm and 3299 cNmm depending on the retainer wire. For the 2-teeth setup the torsion moments are much smaller. Exposure to the flame of a butane-gas torch for 10 seconds to anneal the wire reduces the stiffness of the retainer wire.Conclusions: Clinicians must select wires for fixed retainers very carefully since the difference in resistance to torque is large. A high level of torque control can be achieved with a plain 0.016 × 0.016-inch or a braided 0.016 × 0.022-inch stainless steel wire. A tooth attached by a retainer wire to only one neighbouring tooth is less resistant to torque than a tooth connected to two neighbouring teeth. Annealing a retainer wire with a flame reduces the stiffness of the wire markedly and can lead to a non-uniform and non-reproducible effect. [ABSTRACT FROM PUBLISHER]

Objective: The aim of this study was to assess the amount of torsional play in 32 commercially available self-ligating and conventional 0·018-inch and 0·022-inch bracket systems in relation to 0·017×0·022-inch and 0·019×0·025-inch stainless steel wires, respectively, and compare the results with the theoretical amount of play for the given bracket/wire combinations. Methods: Torque moments were measured in a mechanical force testing system by twisting straight pieces of stainless steel wire seated in the bracket slot in increments of 0·5° until a full torsional expression was registered. Five upper central incisor brackets from each of the 32 different bracket systems were selected for the study. Results: The result from the laboratory testing clearly showed that wire/slot play was larger than anticipated from the nominal values, especially regarding the 0·022-inch brackets and particularly in relation to the passive self-ligating brackets. The play ranged from 19·8 to 36·1° of play for the most imprecise bracket system. Conclusions: The result does not favour the use of self-ligating brackets when focussing on torque control. The actual play is larger due to oversized slots and the inability of self-ligation brackets to press the archwire into the bottom of the slot. In conventional brackets, the initial torque moment is generated by the steel ligatures pressing the arch wire against the bottom of the slot. The oversize of the slot is thus less critical in relation to the conventional than in relation to the passive self-ligation bracket. [ABSTRACT FROM AUTHOR]

Objective: To compare the accuracy and reproducibility of measurements performed on digital virtual models with those taken on plaster casts from models poured immediately after the impression was taken, the 'gold standard', and from plaster models poured following a 3-5 day shipping procedure of the alginate impression. Design: Direct comparison of two measuring techniques. Setting: The study was conducted at the Department of Orthodontics, School of Dentistry, University of Aarhus, Denmark in 2006/2007. Participants: Twelve randomly selected orthodontic graduate students with informed consent. Methods: Three sets of alginate impressions were taken from the participants within 1 hour. Plaster models were poured immediately from two of the sets, while the third set was kept in transit in the mail for 3-5 days. Upon return a plaster model was poured as well. Finally digital models were made from the plaster models. A number of measurements were performed on the plaster casts with a digital calliper and on the corresponding digital models using the virtual measuring tool of the accompanying software. Afterwards these measurements were compared statistically. Results: No statistical differences were found between the three sets of plaster models. The intraand inter-observer variability are smaller for the measurements performed on the digital models. Conclusions.' Sending alginate impressions by mail does not affect the quality and accuracy of plaster casts poured from them afterwards. Virtual measurements performed on digital models display less variability than the corresponding measurements performed with a calliper on the actual models. [ABSTRACT FROM AUTHOR]

Introduction: Changes in the stress/strain distribution in the periodontium after the application of orthodontic forces trigger remodeling processes that make tooth movement possible. The type of orthodontic tooth movement is linked to the force system applied to the bracket. By combining moments and forces, often expressed as the moment-to-force (M/F) ratio, it is possible to determine the prescribed type of tooth movement. According to classical theory, fixed values for M/F are associated with specific tooth movements. Methods: A segment of a mandible containing the canine and the first premolar obtained from autopsy was scanned with microcomputed tomography, and a finite element model was generated. In a series of finite element analyses simulating teeth subjected to various orthodontic loading regimens, the influences of the M/F ratio and the force magnitude were examined. Results: By applying a range of values of M/F, different types of tooth movement were generated, although the classic prescription of the M/F ratio suggested in the literature could not be confirmed. Due to the nonlinear behavior of the periodontal ligament, loading modes with a constant M/F ratio, yet varying the force magnitude, resulted in different types of tooth movement. Conclusions: The material properties of the periodontal ligament, the morphology of the root, and the alveolar bone are patient specific. Therefore, the M/F values generally advocated to obtain orthodontic tooth movement should be used only as guidelines. To be effective and accurate, the force system selected for a specific tooth movement must be monitored and the outcome compared with the predicted tooth movement. [Copyright &y& Elsevier]

Orthodontic literature is dominated by the pressure-tension theory with regard to the tissue reaction following mechanical loading of teeth. The present article discusses the reaction of the alveolar bone to the perturbation generated by different orthodontic force levels. Orthodontists generally relate the pressure zone to resorption and the tension zone to apposition. Conversely, orthopedic surgeons know that unloading generates a negative balance of the ongoing bone remodeling and that loading will result in a positive balance leading to increased bone density. Research based on histological analysis of monkey teeth, which were loaded with different force levels, demonstrated that direct resorption could be a response to a relatively lower force level. Undermining resorption, on the other hand, is a repair mechanism attempting to remove the alveolar bone underlying the ischemic periodontal ligament (PDL). The osteocyte lacunae in this bone appear empty as a sign of apoptosis or necrosis of the osteocytes. Finite element analysis (FEA) based on microcomputed tomography (μCT) and using material properties reflecting the physiological values of the PDL and alveolar bone demonstrated that the classical pressure-tension theory could not be corroborated. However, the studies did confirm that the reaction of the alveolar wall can be caused by the changes in strain occurring during various types of loading. The FEA also demonstrated that the localization of the center of resistance depends not only on the anatomical relationship of the tooth, PDL, and surrounding bone, but also on the difference in microanatomy at the different levels of the alveolus as well as the force magnitude that is applied. [Copyright &y& Elsevier]

Introduction: The aims of this study were to assess the correlation between facial hard and soft tissue asymmetry in patients with juvenile idiopathic arthritis, to identify valid soft tissue points for clinical examination, and to assess the smallest clinically detectable level of dentofacial asymmetry.Methods: Full-face cone-beam computed tomography scans and 3-dimensional photographs were used to assess facial hard and soft tissue asymmetry in 21 patients with juvenile idiopathic arthritis. A survey was conducted to assess how asymmetry is perceived observationally based on cone-beam computed tomography scans and 3-dimensional photographs.Results: Significant linear correlations were seen between the hard and soft tissue landmark deviations at both the transverse and vertical positions. Among medial soft tissue points, glabella had the smallest deviation and pogonion the largest deviation from the midsagittal plane. Professionals could identify facial asymmetry based on images beyond a cutoff threshold of 2 mm for both pogonion and gonion.Conclusions: Soft tissue pogonion and gonion were identified as the most appropriate landmarks to clinically predict hard tissue facial asymmetry. Facial asymmetries are most pronounced in the lower facial third in patients with juvenile idiopathic arthritis. Professionals can accurately identify asymmetry exceeding 2 mm. [ABSTRACT FROM AUTHOR]