The optimal activation of plastic aligner for canine distal movement: a three-dimensional finite element analysis.

This study aimed to investigate the optimal activation of plastic aligner for the canine distal movement by combining the stress and strain of periodontal ligament. Computer-aided design models of the upper canine, periodontal ligament, alveolar bone, and plastic aligner were constructed. The stresses and strains of periodontal ligament were acquired by fitting plastic aligner on the canine, which will cause the canine distal-direction movement. The activation of plastic aligner was set into 12 groups, including 0.050, 0.100, 0.125, 0.150, 0.175, 0.200, 0.225, 0.250, 0.275, 0.300, 0.350, and 0.400 mm. Assuming the volume-averaged hydrostatic stress (VAHS) ranging from 4.7 to 16 kPa to be the optimal stress, and an average strain no less than 0.3 to be the optimal strain. The optimal activation of plastic aligner was acquired based on the optimal stress and average strain. As the activation increased, the stress and strain of periodontal ligament increased visibly. The degree of activation of plastic aligner was nonlinearly and positively related to VAHS and average strain. According to the fitted curves, the activation corresponding to the optimal stress was 0.07-0.24 mm and the activation was not less than 0.21 mm based on the optimal strain. The optimal activation of plastic aligner for the canine distal movement was 0.21-0.24 mm in this study. The degree of activation affects the force system of orthodontic tooth movement, and it should be taken into consideration to obtain healthy and efficient tooth movement. The activation with 0.21-0.24 mm seems optimal for orthodontic tooth movement in the plastic aligner system in this study.

Relationship between cervical vertebral maturation and dental development in a sample of yemeni children and adolescents / Relación entre la maduración vertebral cervical y el desarrollo dental en una muestra de niños y adolescentes yemeníes

Objective: This study was conducted to investigate the relationship between dental development and cervical vertebral maturation stages in a group of Yemeni children and adolescents. Materials an Methods: The study included digital panoramic radiographs and lateral skull cephalograms obtained from 207 Yemeni subjects­122 females and 85 males aged between 8 to 18 years. Dental maturity was evaluated according to the method of Demirijian et al., calcification stages of the left mandibular canines, first and second premolars and second molars were assessed. Skeletal maturity was assessed by the cervical vertebral maturation (CVM) stages according to the method of Baccetti et al. Correlation between CVM and dental maturation was evaluated by Spearman rank-order correlation coefficient (SROCC). Results: CVM and dental calcification stages were highly correlated (p<0.001) in both genders, ranging from 0.686 to 0.873 for females and 0.787 to 0.871 for males. Calcification stages of the second molars showed the strongest correlation with CVM. Conclusion: Calcification stages of the second molar may be used as a reliable maturation indicator. Dental maturation may be applied to determine the skeletal maturity status of Yemeni children and adolescents.

Objetivo: Este estudio se realizó para investigar la relación entre el desarrollo dental y las etapas de maduración vertebral cervical en un grupo de niños y adolescentes yemeníes. Material y Métodos: El estudio incluyó radiografías panorámicas digitales y cefalogramas laterales del cráneo obtenidos de 207 sujetos yemeníes: 122 mujeres y 85 hombres de entre 8 y 18 años. La madurez dental se evaluó de acuerdo con el método de Demirijian et al. Se evaluaron las etapas de calcificación de los caninos mandibulares izquierdos, primer y segundo premolares y segundos molares. La madurez esquelética se evaluó mediante las etapas de maduración vertebral cervical (CVM) de acuerdo con el método de Baccetti et al. La correlación entre la CVM y la maduración dental se evaluó mediante el coeficiente de correlación de orden de rango de Spearman (SROCC). Resultado: Las etapas de CVM y calcificación dental estuvieron altamente correlacionadas (p<0.001) en ambos sexos, con un rango de 0.686 a 0.873 para las mujeres y 0.787 a 0.871 para los hombres. Las etapas de calcificación de los segundos molares mostraron la correlación más fuerte con CVM. Conclusión: las etapas de calcificación del segundo molar pueden usarse como un indicador de maduración confiable. La maduración dental puede aplicarse para determinar el estado de madurez esquelética de los niños y adolescentes yemeníes.

Male morphological traits are heritable but do not predict reproductive success in a sexually-dimorphic primate.

Sexual selection favours traits that increase reproductive success via increased competitive ability, attractiveness, or both. Male rhesus macaque (Macaca mulatta) morphological traits are likely to reflect the effects of multiple sexual selection pressures. Here, we use a quantitative genetic approach to investigate the production and maintenance of variation in male rhesus macaque morphometric traits which may be subject to sexual selection. We collected measurements of body size, canine length, and fat, from 125 male and 21 female free-ranging rhesus macaques on Cayo Santiago. We also collected testis volumes from males. We used a genetic pedigree to calculate trait heritability, to investigate potential trait trade-offs, and to estimate selection gradients. We found that variation in most male morphometric traits was heritable, but found no evidence of trait trade-offs nor that traits predicted reproductive success. Our results suggest that male rhesus macaque morphometric traits are either not under selection, or are under mechanisms of sexual selection that we could not test (e.g. balancing selection). In species subject to complex interacting mechanisms of selection, measures of body size, weaponry, and testis volume may not increase reproductive success via easily-testable mechanisms such as linear directional selection.

Investigation of effective intrusion and extrusion force for maxillary canine using finite element analysis.

Orthodontic tooth movement is mainly regulated by the biomechanical responses of loaded periodontal ligament (PDL). We investigated the effective intervals of orthodontic force in pure maxillary canine intrusion and extrusion referring to PDL hydrostatic stress and logarithmic strain. Finite element analysis (FEA) models, including a maxillary canine, PDL and alveolar bone, were constructed based on computed tomography (CT) images of a patient. The material properties of alveolar bone were non-uniformly defined using HU values of CT images; PDL was assumed to be a hyperelastic-viscoelastic material. The compressive stress and tensile stress ranging from 0.47 to 12.8 kPa and 18.8 to 51.2 kPa, respectively, were identified as effective for tooth movement; a strain 0.24% was identified as the lower limit of effective strain. The stress/strain distributions within PDL were acquired in canine intrusion and extrusion using FEA; root apex was the main force-bearing area in intrusion-extrusion movements and was more prone to resorption. Owing to the distinction of PDL biomechanical responses to compression and tension, the effective interval of orthodontic force was substantially lower in canine intrusion (80-90 g) than in canine extrusion (230-260 g). A larger magnitude of force remained applicable in canine extrusion. This study revised and complemented orthodontic biomechanical behaviours of tooth movement with intrusive-extrusive force and could further help optimize orthodontic treatment.

Short communication: Influence of retainer configuration and loading direction on the stress distribution of lithium disilicate resin-bonded fixed dental prostheses: 3D finite element analysis.

The present study elucidates the mechanical performance of different designs of resin-bonded fixed dental prostheses made of lithium disilicate simulating masticatory loads of anterior or canine guidance. A three-dimensional model of maxilla was constructed containing central incisor and canine teeth, with edentulous space of the lateral incisor. Three designs of prosthesis were created: retained in central incisor (1-I), retained in canine (1-C) and fixed in both teeth (2-IC). The computational analysis was performed for load in canine and central incisor separately (100N, 45°). The tensile and shear stresses were calculated for the resin-bonded fixed dental prosthesis, bonding surface of each retainer and cement layer using 3D finite element analysis. The 20 highest stress values were analyzed using two-way ANOVA and post-hoc Tukey test, all with α = 5%. The computational analysis showed that 2-retainer resin-bonded fixed dental prosthesis presented the worst prognosis regardless of the mandibular movement. ANOVA showed that Mandibular movement*Retainer interaction influenced on the tensile and shear stresses values (p < 0.01). Higher stresses were observed in the connector region for all groups (13-82.2 MPa; 11-70.2 MPa). In order to reduce the stress concentration in the resin-bonded fixed dental prosthesis and the retainer made of lithium disilicate, the occlusion may serve as the selection criteria of the unitary abutment for better sustainability.

Three-dimensional finite element analysis to evaluate biomechanical effects of different alveolar decortication approaches on rate of canine retraction.

INTRODUCTION: The aim of this study was to compare different corticotomy approaches and determine their biomechanical effects on rate of canine displacement when compared to conventional orthodontics. METHOD: Three-dimensional Finite Element Models with conventional non-corticotomy approach (model 1) and three corticotomy approaches ensuing buccal and palatal vertical cuts (model 2), interseptal bone reduction (model 3), buccal vertical cuts (model 4) were fabricated. Displacement of the canine and von Mises stresses in the canine and trabecular bone were calculated and compared under a distal retraction force of 1.5N. RESULTS: The maximum displacement of canine with minimum anchorage loss was seen in model 3 followed by model 2, model 4 and model 1. The maximum equivalent (von Mises) stress was concentrated mainly on the distal side of canine in model 3 and had a uniform distribution of stresses on entire root surface. CONCLUSIONS: Corticotomy approaches effectively accelerated maxillary canine retraction, exhibiting twice the rate of canine movement with minimum anchorage loss when compared to non-corticotomy approach. Corticotomy with interseptal bone reduction was most effective in terms of canine displacement and stress distribution.

The relation between structural, rugometric and fractal characteristics of hard dental tissues at micro and nano levels.

Human tooth exhibits a structure of a mixture of inorganic hydroxyapatite nanocrystals and organic phases. The aim of this study is to investigate different tissues of human canine teeth surface along with the micro structure parameters of each tissue. X-ray diffraction (XRD) is used to study the amorphous or crystalline nature of each tissue with different mineral compositions and crystalline structures where the highest crystalline quality is related to enamel. The surfaces are also examined by energy-dispersive X-ray spectrometry. Moreover, crystalline quality factor is carried out to estimate the crystallinity of the tissues. Also, based on the basic Scherrer equation, the Williamson-Hall equation is applied to extend the formula for the XRD. Enamel and cementum tissues of a typical human tooth, which look similar, are composed of a large variety of wide lines with different widths through Raman spectra analysis. In addition, the applied scanning electron microscopy extracts similar morphology for all tissues with round granular structures which are denser in the cementum. Atomic force microscopy is finally used for investigation of micro-morphologies of the different tissues and the results are compared with the fractal analysis which ends to the bifractal and anisotropic nature of enamel and cementum along with monofractal and isotropic nature of dentin.

Permanent canine eruption into the alveolar cleft region after secondary alveolar bone grafting: Are there prediction factors for impaction?

INTRODUCTION: The aims of this study were to investigate the eruption pattern of maxillary permanent canines in the alveolar cleft area after secondary alveolar bone grafting and to assess the risk indicators for canine impaction. METHODS: The sample consisted of 75 patients with unilateral cleft lip and palate who underwent secondary alveolar bone grafting with rhBMP-2 with a mean age of 9.8 years of age at 1 center. A split-mouth study design was used, with the noncleft hemiarch comprising the control group. Panoramic radiographs taken before, immediately after, and 1 year after secondary alveolar bone grafting were used to assess the following parameters in both cleft side (CS) and noncleft side: canine mesiodistal angulation, canine height relative to the occlusal plane, canine mesial displacement, and superimposition with the neighboring maxillary incisors. The frequency of associated dental anomalies was compared between patients with and without CS canine impaction. Data were evaluated using analysis of variance, t tests, Fisher tests, and multiple logistic regression analysis (P <0.05). RESULTS: On the CS, maxillary canines were usually more mesially angulated and more distant from the occlusal plane compared with the noncleft side. The prevalences of canine impaction on the CS and noncleft side were 24% and 1.3%, respectively. Maxillary impacted canines on the CS demonstrated increased mesiodistal angulation and height at all time points. No association between CS canine impaction and mesial displacement (sectors) was found. An increased prevalence of lateral incisor agenesis on the CS was observed in the subgroup with canine impaction. CONCLUSIONS: Increased mesial angulation and lateral incisor agenesis on the CS are early risk indicators for maxillary canine impaction in patients with unilateral cleft lip and palate.

Comparison of the Demirjian and Root Resorption Methods to Estimate Dental Age in Radiographic Images.

Purpose: To compare the accuracy of dental age (DA) estimates in children using the Demirjian method and the proportion of root resorption in primary teeth.Methods: Panoramic images from 497 children aged three to 11.99 years were evaluated. Individuals were classified in five groups of two-year age intervals. Seven permanent teeth in the left mandible were scored based on diagrams developed by Demirjian. The proportion of root resorption was determined in the primary mandibular left canine and primary second molar, and age was estimated according to the length of root resorption (one quarter, one half, three quarters).Results: The Demirjian method tended to overestimate DA, except for the 10- to 11.99 year-old category in girls. The greatest overestimation was in four- to 5.99 year-old children. Except for the youngest category, the difference between DA and chronological age, according to the Demirjian method, decreased with increasing age in both sexes. The root resorption method tended to underestimate age, except for canine root resorption in boys.Conclusion: Estimated DA was closest to chronological age when the former was based on canine root resorption. Both the Demirjian and root resorption methods were effective and can be used to determine age in children.

A biomechanical case study on the optimal orthodontic force on the maxillary canine tooth based on finite element analysis.

Excessive forces may cause root resorption and insufficient forces would introduce no effect in orthodontics. The objective of this study was to investigate the optimal orthodontic forces on a maxillary canine, using hydrostatic stress and logarithmic strain of the periodontal ligament (PDL) as indicators. Finite element models of a maxillary canine and surrounding tissues were developed. Distal translation/tipping forces, labial translation/tipping forces, and extrusion forces ranging from 0 to 300 g (100 g=0.98 N) were applied to the canine, as well as the force moment around the canine long axis ranging from 0 to 300 g·mm. The stress/strain of the PDL was quantified by nonlinear finite element analysis, and an absolute stress range between 0.47 kPa (capillary pressure) and 12.8 kPa (80% of human systolic blood pressure) was considered to be optimal, whereas an absolute strain exceeding 0.24% (80% of peak strain during canine maximal moving velocity) was considered optimal strain. The stress/strain distributions within the PDL were acquired for various canine movements, and the optimal orthodontic forces were calculated. As a result the optimal tipping forces (40-44 g for distal-direction and 28-32 g for labial-direction) were smaller than the translation forces (130-137 g for distal-direction and 110-124 g for labial-direction). In addition, the optimal forces for labial-direction motion (110-124 g for translation and 28-32 g for tipping) were smaller than those for distal-direction motion (130-137 g for translation and 40-44 g for tipping). Compared with previous results, the force interval was smaller than before and was therefore more conducive to the guidance of clinical treatment. The finite element analysis results provide new insights into orthodontic biomechanics and could help to optimize orthodontic treatment plans.

Interrelationships Between Morphometric, Densitometric, and Mechanical Properties of Teeth in 5-Month-Old Polish Merino Sheep.

Interrelationships between morphological, densitometric, and mechanical properties of deciduous mandibular teeth (incisors, canine, second premolar) were investigated. To perform morphometric, densitometric, and mechanical analyses, teeth were obtained from 5-month-old sheep. Measurements of mean volumetric tooth mineral density and total tooth volume were performed using quantitative computed tomography. Microcomputed tomography was used to measure total enamel volume, volumetric enamel mineral density, total dentin volume, and volumetric dentin mineral density. Maximum elastic strength and ultimate force of teeth were determined using 3-point bending and compression tests. Pearson correlation coefficients were determined between all investigated variables. Mutual dependence was observed between morphological and mechanical properties of the investigated teeth. The highest number of positive correlations of the investigated parameters was stated in first incisor indicating its superior predictive value of tooth quality and masticatory organ function in sheep. Positive correlations of the volumetric dentin mineral density in second premolar with final body weight may indicate predictive value of this parameter in relation with growth rate in sheep. Evaluation of deciduous tooth properties may prove helpful for breeding selection and further reproduction of sheep possessing favorable traits of teeth and better masticatory organ function, leading to improved performance and economic efficiency of the flock.

A Volumetric Assessment Using Computed Tomography of Canine and First Molar Roots in Dogs of Varying Weight.

Mandibular volume and tooth root volumes were shown to increase at different rates at locations containing the roots of the canine (C) and mesial and distal roots of the first molar (M1). Thirty-six dogs were included in this study. Data were generated using computed tomography at locations of the mandible involving the roots of the C and M1 teeth. Software was used to trace the external surface of the mandible, calculating the volume of the mandible at each location. Similar techniques were used to trace and calculate the volume of the C and M1 roots. Mandible volume, tooth root volume, and root percentage of mandible volume were analyzed and compared using the slopes of the best fit line. At the M1 mesial and distal roots, mandible volume ( P < .001) and root volume ( P < .001) were both noted to increase, with increasing weight at different rates. The rate of change in the root percentage by weight of M1 roots was not different ( P = .214). Each location demonstrated a different increasing rate of change for mandibular volume and increasing root volume. Results show that as patient's weight increases, the mandible and root volumes increase at different rates. Root percentage by volume at all three locations was noted to decrease by the same rate. Canine and M1 roots are proportionally larger than the supporting mandibular bone in smaller patients. Care should be taken to recommend periodontal disease prevention for owners of small dogs and consideration made when performing extractions or other surgery that may destabilize the mandible.

Mechanical behavior of endodontically restored canine teeth: Effects of ferrule, post material and shape.

OBJECTIVE: To assess the effect of a ferrule design with specific post material-shape combinations on the mechanical behavior of post-restored canine teeth. METHODS: Micro-CT scan images of an intact canine were used to create a 3-D tessellated CAD model, from which the shapes of dentin, pulp and enamel were obtained and geometric models of post-endodontically restored teeth were created. Two types of 15mm post were evaluated: a quartz fiber post with conical-tapered shape, and a carbon (C) fiber post with conical-cylindrical shape. The abutment was created around the coronal portion of the posts and 0.1mm cement was added between prepared crown and abutment. Cement was also added between the post and root canal and a 0.25mm periodontal ligament was modeled around the root. Four models were analysed by Finite Element (FE) Analysis: with/without a ferrule for both types of post material and shape. A load of 50N was applied at 45° to the longitudinal axis of the tooth, acting on the palatal surface of the crown. The maximum normal stress criterion was adopted as a measure of potential damage. RESULTS: Models without a ferrule showed greater stresses (16.3MPa) than those for models with a ferrule (9.2MPa). With a ferrule, stress was uniformly distributed along the abutment and the root, with no critical stress concentration. In all models, the highest stresses were in the palatal wall of the root. Models with the C-fiber post had higher stress than models with the quartz fiber posts. The most uniform stress distribution was with the combination of ferrule and quartz fiber post. SIGNIFICANCE: The FE analysis confirmed a beneficial ferrule effect with the combination of ferrule and quartz fiber post, with tapered shape, affording no critical stress concentrations within the restored system.

Mechanical load exerted by PET-G aligners during mesial and distal derotation of a mandibular canine : An in vitro study.

INTRODUCTION: The six force-moment (F/M) components exerted by aligners of different thickness during simulated mesiorotation and distorotation of a mandibular canine were studied. MATERIALS AND METHODS: An acrylic mandibular model with a separated right canine mounted on a hexapod via a 3D F/M sensor was used. Duran+® aligners (Scheu Dental, Germany) of thickness 0.5, 0.625, and 0.75 mm were fabricated on plaster models with the measurement tooth in its neutral position. The F/M values were recorded during progressive mesiorotation or distorotation of tooth 43 in 1° steps up to ±15°, corresponding to 0.5 mm displacements of the tooth's interdental contacts. Each rotation step included renewed seating of the aligner on the acrylic model. Three aligners were tested three times each for each thickness and direction of rotation. RESULTS: The median rotational moments for the 0.5 mm aligner and 15° distorotation of tooth 43 was 27.49 Nmm (interquartile range, IQR 1.45 Nmm). The corresponding values for the 0.625 and 0.75 mm aligners were 41.04 Nmm (IQR 5.62 Nmm) and 42.48 Nmm (IQR 2.17 Nmm), respectively. The average rotational moments for distorotation were 15% higher than for mesiorotation (p = 0.01). Relatively high collateral F/M components, specifically an intrusive force and labiolingual and mesiodistal tipping moments, were observed. CONCLUSION: To avoid overloading of periodontal structures, derotation of lower canines should be limited to 10° per setup step, leading to rotational moments of about 15 Nmm. The mechanical behavior of the 0.625 and 0.75 mm aligners were similar; thus, it may be omitted from the aligner sequence. Further studies are required to investigate specific aligner modifications or attachments for minimizing collateral F/M components or unwanted movements, respectively, during canine derotation.

The Effect of Composite Thickness on the Stress Distribution Pattern of Restored Premolar Teeth with Cusp Reduction.

PURPOSE: Different thicknesses of restorative material can alter the stress distribution pattern in remaining tooth structure. The assumption is that a thicker composite restoration will induce a higher fracture resistance. Therefore, the present study evaluated the effect of composite thickness on stress distribution in a restored premolar with cusp reduction. MATERIALS AND METHODS: A 3D solid model of a maxillary second premolar was prepared and meshed. MOD cavities were designed with different cusp reduction thicknesses (0, 0.5, 1, 1.5, 2.5 mm). Cavities were restored with Valux Plus composite. They were loaded with 200 N force on the occlusal surface in the direction of the long axis. Von Mises stresses were evaluated with Abaqus software. RESULTS: Stress increased from occlusal to gingival and was maximum in the cervical region. The stressed area in the palatal cusp was more than that of the buccal cusp. Increasing the thickness of composite altered the shear stress to compressive stress in the occlusal area of the teeth. CONCLUSION: The model with 2.5 mm cusp reduction exhibited the most even stress distribution.

Long-term results of secondary alveolar bone grafting using a technique to harvest pure calvarial cancellous bone: Evaluation based on plain radiography and computed tomography.

BACKGROUND: We introduce a method to extract the maximum amount of cancellous bone from the calvarium and analyze the outcomes using plain radiography and computed tomography. METHODS: We retrospectively analyzed the medical records of patients who underwent secondary alveolar bone grafts using a maximal harvesting technique for calvarial cancellous bone. Bone survival was determined based on Enemark's grading system using plain radiographs. Alveolar thickness and height were analyzed by computed tomography and compared with radiographic measurements. RESULTS: Our study enrolled 27 patients, 22 unilateral and 5 bilateral, for a total of 32 alveolar clefts. The mean age at surgery was 9.04 ± 0.41 years (range: 6-12 years). Donor sites were successfully recovered without complications, such as hematomas, seromas, infections, or tears in the dura mater. The mean follow-up duration for obtaining plain radiographs was 6.90 ± 0.61 years (range: 2.0-18.50 years). The mean follow-up duration for computed tomography was 6.51 ± 0.99 years (range: 2.0-14.83 years). A canine tooth erupted in 30 cases. Success (Enemark's grades I or II) was achieved in 26 cases. Alveolar height was strongly correlated with the Enemark scale results (γ = 0.878, p < 0.001), but alveolar thickness was not correlated (γ = 0.4575, p = 0.08). CONCLUSION: Our cancellous bone harvesting technique resulted in successful graft survival without serious complications, including dural or brain injuries. Although the ilium is widely accepted as the optimal donor site for secondary alveolar bone grafting, the calvarium could be an alternative donor site that results in equivalent outcomes.

Applications of cone-beam computed tomography to assess the effects of labial crown morphologies and collum angles on torque for maxillary anterior teeth.

INTRODUCTION: Currently, cone-beam computed tomography (CBCT) has been widely used because of its capacity to evaluate the anatomic structures of the maxilla, mandible, and teeth in 3 dimensions. However, articles about the use of CBCT to evaluate the relationships between the morphology of individual teeth and torque expression remain rare. In this study, we aimed to determine the influence of labial crown morphologies and collum angles on torque for maxillary anterior teeth using CBCT. METHODS: A total of 206 extracted maxillary anterior teeth were selected to establish scanning models using dental wax, and they were scanned by CBCT. Three-dimensionally reconstructed images and median sagittal sections of the teeth were digitized and analyzed with AutoCAD software (Autodesk, San Rafael, Calif). The angle α, formed by the intersection of the tangent at a certain vertical height on the labial surface from the incisal edge with the crown long axis, and the collum angle, were measured. RESULTS: The variations in angle α at different heights from the incisal edge for the same type of tooth were statistically significantly different (P <0.001). Moreover, the variations between collum angles and 0° for any type of maxillary anterior tooth were statistically significant (P <0.01). CONCLUSIONS: This study suggested that there are great differences in labial crown morphologies and collum angles for maxillary anterior teeth between persons, indicating that the morphologies of these teeth do play important roles in torque variations.

Clinical and radiographic assessment of maxillary canine eruption status in a group of 11- to 14-year-old Irish children.

OBJECTIVE: The aim of this study was to investigate the prevalence of potentially ectopic maxillary canines and associated dental features in a group of 11- to 14-year-old children. PARTICIPANTS: Examination took place of a normal dlistribution of Irish schoolchildren age between I11 and 14 years in order to record the number of subjects with indications for radiographic investigation of . potentially ectopic maxillary canines. METHODS: Those subjects identified subsequently underwent radiographic examination and the number of subjects with potentially ectopic maxillary canines was established. Correlations within the latter sub-sample with anomalous or missing laterals, type of occlusion and female:male ratio were investigated. RESULTS: A total of 480 children were screened. Of the children aged 11 to 14 years, 32 (6.6%) had clinical indications for radiographic examination of potentially ectopic maxillary canines according to the criteria that had been set out. There were 11 maxillary canines, in 10 subjects, that had an unfavourable position for eruption and were considered to be potentially ectopic, and so 1.1% of the maxillary canines reviewed in this study showed a potential ectopic eruption position. CONCLUSIONS: The prevalence of potentially ectopic maxillary canines and associated dental features in an Irish population was found to be similar to those in other countries, and the practice of careful supervision and early diagnosis of any eruption disturbances of the permanent maxillary canines continues to be considered important due to the risks associated with their eruption.

Study of force loss due to friction comparing two ceramic brackets during sliding tooth movement.

OBJECTIVE: To compare the percentage of force loss generated during canine sliding movements in newly introduced ceramic brackets with metal brackets. MATERIALS AND METHODS: Two types of ceramic brackets, namely polycrystalline alumina (PCA) ceramic brackets (Clarity Advanced) and monocrystalline alumina (MCA) ceramic brackets (Inspire Ice) were compared with stainless steel (SS) brackets (Victory Series). All bracket groups (n = 5 each) were for the maxillary canines and had a 0.018-inch slot size. The brackets were mounted on an Orthodontic Measurement and Simulation System (OMSS) to simulate the canine retraction movement into the first premolar extraction space. Using elastic ligatures, 0.016 × 0.022″ (0.40 × 0.56 mm) stainless steel archwires were ligated onto the brackets. Retraction force was applied via a nickel-titanium coil spring with a nearly constant force of approximately 1 N. The OMSS measured the percentage of force loss over the retraction path by referring to the difference between the applied retraction force and actual force acting on each bracket. Between group comparisons were done with one-way analysis of variance. RESULTS: The metal brackets revealed the lowest percentage of force loss due to friction, followed by the PCA and MCA ceramic bracket groups (67 ± 4, 68 ± 7, and 76 ± 3 %, respectively). There was no significant difference between SS and PCA brackets (p = 0.97), but we did observe significant differences between metal and MCA brackets (p = 0.03) and between PCA and MCA ceramic brackets (p = 0.04). CONCLUSION: PCA ceramic brackets, whose slot surface is covered with an yttria-stabilized zirconia-based coating exhibited frictional properties similar to those of metal brackets. Frictional resistance resulted in an over 60 % loss of the applied force due to the use of elastic ligatures.

Population response characteristics of intrinsic signals in the cat somatosensory cortex following canine mechanical stimulation.

Intrinsic signal optical imaging has been widely used to measure functional maps in various sensory cortices due to better spatial resolution and sensitivity for detecting cortical neuroplasticity. However, application of this technique in dentistry has not been reported. In this study, intrinsic signal optical imaging was used to investigate mechanically driven responses in the cat somatosensory cortex, when punctate mechanical stimuli were applied to maxillary canines. The global signal and its spatial organization pattern were obtained. Global signal strength gradually increased with stimulus strength. There was no significant difference in response strength between contralateral and ipsilateral mechanical stimulation. A slightly greater response was recorded in the sigmoidal gyrus than in the coronal gyrus. The cat somatosensory cortex activated by sensory inputs from mechanical stimulation of canines lacks both topographical and functional organization. It is not organized into columns that represent sensory input from each tooth or direction of stimulation. These results demonstrate that intrinsic signal optical imaging is a valid tool for investigating neural responses and neuroplasticity in the somatosensory cortex that represents teeth.