Axis Of Tooth Research Articles

Association of Computed Tomography Values of the Tooth Root and Alveolar Bone with Orthodontic Root Resorption

This study aimed to evaluate the effect of CT values of the tooth root and bone on root resorption using data obtained before and after orthodontic treatment. Forty-one patients with jaw deformities were divided into those with and without root resorption （n = 18 and 23, respectively）. The distance from the anatomical root apex to the edge of the incisive canal was measured using axial CT sections before active treatment. The distance from the anatomical root apex to the labial and palatal cortical bone and the CT values of the root and alveolar bone were measured and compared using sagittal CT sections. The tooth axis and vertical and lateral movements of the maxillary right central incisor were examined using lateral cephalograms before and after treatment. Root resorption group showed significantly higher CT values of alveolar bone than the control group and different axial movement of the root apex and distance between the labial cortical bone and root apex on lateral cephalograms. The risk of root resorption increased with an increase in the CT values of the alveolar bone surrounding the maxillary central incisor. The horizontal movement of the root apex was associated with the distance between the labial cortical bone and root apex, and root resorption during maxillary central incisor movement.

The Effect of Maxilla Impacted Canine Positions on Root Resorption of Adjacent Teeth Using Cone-Beam Computed Tomography Imaging

Objective. To determine the effect of the impacted position of the maxillary canine on the root resorption of the adjacent incisor using Cone-beam Computed Tomography (CBCT) imaging.Methods. This was an analytic quantitative study. The research sample determined CBCT images of treatmentpatients at the Orthodontic Specialist Policlinic in Dental Hospital of Airlangga University over a three-year period and secondary data taken from Pramita Laboratory. CBCT photos that met the inclusion criteria, including mesially impacted canine or close to central or lateral incisors with completely formed anatomy were then analyzed. Multiple linear regression was used to determine x-axis, y-axis, z-axis position of the impacted canine on the severity of root resorption of the adjacent incisor, and the effect of impacted canines on all axes simultaneously on the severity of root resorption of the adjacent incisors.Results. The position of the impacted canine in the x-axis and z-axis planes had a significant influence on the root resorption of the adjacent incisor. Meanwhile, impacted canine from the y-axis plane showed non-significant influence on the root resorption.Conclusion. The position of the impacted canine when viewed in all planes of the tooth axis has a significant effect on the severity of root resorption of the adjacent incisor

MICROSTRUCTURAL AND MICROMECHANICAL TESTS OF TITANIUM CROWNS

Fixed prosthetic restorations must meet the health requirements in terms of the protection of the tissues of the oral cavity, biomechanical requirements for optimal tissue stress and the strength and wear resistance of the structure, aesthetic requirements related to the location of the gingival margin, as well as the shape, thickness, and colour of the veneers. The aim is to evaluate the impact of manufacturing technology on the microstructure and micromechanical parameters of titanium crowns. The material of the analysis are prosthetic crowns made of Ti6Al4V alloy for the maxilla premolars and the mandible molars, produced using two technologies: Selective Laser Melting (SLM) and CAD/CAM milling. Crown structures were evaluated on the basis of examinations of the microstructure and surface layer of the chamfers, micromechanical parameters in axial sections perpendicular to the dental arches, and the accuracy of mapping the internal shape in sections with horizontal planes perpendicular to the axis of the abutment tooth. The results of this work can be used in a clinical setting. They allow the evaluation of what is the impact of the technology of producing the supporting substructure on the structure of the prosthetic crown. The strength requirements in both technologies are met, while the higher value of the microhardness of the titanium SLM substructure, compared to the milled one, increases the stiffness of the structure under conditions of biomechanical excitation. The errors in mapping the internal shape of the crowns are comparable and slightly higher during sintering.

Evaluation of dentoskeletal effects of surgically assisted rapid maxillary expansion using computed tomography

Introduction: Patients with transverse maxillary deficiency may have unilateral or bilateral posterior crossbite, crowded and rotated teeth and narrow palate. The treatment for adults is surgically assisted rapid maxillary expansion, a procedure that results in changes not only to bones, but also to teeth, nasal cavity, air space, lips and surrounding soft tissues. Objective: This study evaluated dentoskeletal changes in patients that underwent surgically assisted rapid maxillary expansion (SARME). Methods: Cone beam computed tomography (CBCT) scans were obtained before and after SARME. The thickness of buccal and lingual cortical bone and the angle of the long axis of posterior maxillary teeth were measured. Data were analyzed statistically. Results showed changes in thickness of buccal and lingual cortical bone and tooth movement and tipping. Conclusion: Tooth tipping increased and buccal bone thickness decreased, although osteotomies were used.

Comparison of Root Parallelism in Extraction Cases Treated with Clear Aligners vs. Fixed Appliances

In the process of orthodontic treatment, root parallelism is related to the relapse of extraction spaces, black triangles, and periodontal health. However, there are few studies on root parallelism in extraction cases with different types of appliances. The objective was to compare the root parallelism in extraction cases treated with clear aligners vs. those treated with fixed appliances by measuring the differences per extraction site and to access the root-movement control capacity of both orthodontic appliances. A retrospective study was conducted on cases in which the first premolars were extracted, treated by clear aligner appliance (“Invisalign” system, 28 patients) or fixed appliance (30 patients). The angulations of the tooth axis (canines, the second premolars, the first molars, and the second molars) were measured to analyze and compare the difference in root parallelism between the two orthodontic appliances. The percentage of root parallelism between the canine and second premolar in both groups had no significant difference. However, judging from the average angle difference value, the fixed appliance might have a greater range in root angulation adjustment than the aligner. In the angulation categories, the aligner mainly showed root apical divergence, while the fixed appliance mainly showed root apical convergence. The dental crown of the molars was mainly non-tipping in both groups, but it could be observed that the dental crown of the maxillary molars had a tendency toward mesial inclination. In conclusion, the same root parallelism and root inclination were obtained in tooth extraction cases whether treated by clear aligners or fixed appliances. This study provides clinicians with more information on the performance of clear aligners and fixed appliances.

CONCEPTUAL FEATURES OF OCCLUSAL BALANCE IN THE DEVELOPMENT AND PATHOLOGY OF LOCALIZED AND GENERALIZED DISEASES OF PARODONTAL TISSUES IN PATIENTS WITH PARTIAL TOOTH LOSS DURING ORTHOPEDIC REHABILITATION BOTH ON THE NATURAL TEETH AND THOSE ON DENTAL IMPLANT

The biomechanical component is an important aspect of orthopedic rehabilitation in the case of parodontal tissue pathology, which involves the most accurate reproduction of not only the shape of the tooth but also the location (functional axis) and the relationships of occlusal surfaces. At the same time, it is important to understand that the functional axis of the tooth and the areas of occlusal contacts are very dynamic and depend on the strength and character of masticatory movements. Therefore, the force vectors on the tooth axis continuously change in the articulation cycle, which helps to change the force of the occlusal interaction of the dentitions and the direction on the periodontium itself and the bone tissue of the jaws.
 Aim: To explain the importance of restoration of functional occlusal relationships in patients with localized and generalized diseases of parodontal tissues, on the example of partial tooth loss with rational orthopedic rehabilitation on natural teeth and dental implants.
 Materials and methods. Clinical examination of patients with localized and generalized parodontal tissue diseases. Orthopantomography – for visualization of the general state of the dentofacial system. In complicated cases, computer tomography with 3D replication was used to make a diagnosis and choose a treatment method. Adjustable articulators have been configured for individual functions together with CAD/CAM technology for the production of rational orthopedic restorations.
 Study results and discussion. 10 patients after orthopedic treatment (13 orthopedic restorations on their natural abutment teeth and dental implants) were admitted to the Dental Medical Center of Danylo Halytsky Lviv National Medical University with complaints of difficult mastication, increased mobility of orthopedic restorations, and halitosis. During clinical examination and taking history, it was found that all patients with parodontal tissue pathology underwent local orthopedic treatment on their natural abutment teeth consisting of 3 bridgework (23% (p<0.05)) and 4 single (31% (p<0.05)) orthopedic restorations and 9 dental implants, which corresponded to 3 bridgework (23% (p<0.05)) and 3 single (23% (p<0.05)) orthopedic restorations, which were used from 6 to 12 months. The signs of disocclusion and overloading were found on the laterotrusion side when checking the static and dynamic occlusion according to the concepts of group management and canine protection. As a result of orthopedic rehabilitation in a virtual articulator adjusted for individual function, functional occlusion was normalized, pathological dental mobility, signs of peri-implantitis, and inflammatory processes of the supporting teeth were eliminated for 10 patients (13 orthopedic restorations) with localized and generalized diseases of parodontal tissues and partial loss of teeth. After 12 months, control clinical examination with additional examination methods of patients with parodontal tissue pathology corresponded to the stabilization of the pathological process both on their natural abutment teeth and on dental implants with normative osseointegration.
 Conclusion. Therefore, the shape and size of restored functional occlusal relationships in adjustable articulators configured for individual function using modern CAD/CAM technologies ensure the balancing of force vectors on teeth and dental implants in parodontal tissue pathology.
 Directions for future research. Unfortunately, modern technologies are not available to all patients and medical institutions of health care of Ukraine due to their high cost. Consequently, a significant number of orthopedic restorations are manufactured in commercial technical laboratories or manually by dental technicians in municipal health care facilities. Therefore, scientific publications must be aimed at attracting and implementing modern technologies in health care educational institutions for further scientific and practical development.

Torque movement of the upper anterior teeth using a clear aligner in cases of extraction: a finite element study

BackgroundClear aligner treatment has become popular over recent years. It is necessary to identify methods by which we could avoid the bowing effect in extractions with clear aligner. The present study was to identify the appropriate method to design torque movement involving the upper anterior teeth of extraction cases, in order to maintain or improve the axis and torque of the upper anterior teeth with a clear aligner during movement and closure of the extraction space.ResultsAs the height of the power ridge increased, the rotation angle of the upper central incisor in the sagittal direction decreased gradually and the location of the rotation center changed significantly; the rotation center moved in the apical direction and then changed to the crown side. The highest von-Mises stress of the upper central incisor root, periodontal ligaments, and alveolar bone, showed little change as the power ridge height increased. When the axial inclination of the upper central incisor was normal (U1-SN = 105°), the tendency of movement for the upper central incisor approached translation with a power ridge height of 0.7 mm (corresponding distorted angle: 5.8415). When the axial inclination of the upper central incisor was oversized (U1-SN = 110°), the axial inclination of the upper central incisor reduced to normal following completion of the anterior segment retraction with a power ridge of 0.4 mm (corresponding distorted angle: 3.4265).ConclusionAnalysis indicates that pure palatal tipping movement of the upper anterior teeth is generated without torque control, thus resulting in the bowing effect. The required torque control of the upper anterior teeth with oversize axial inclination is weaker than that of the upper anterior teeth with normal axial inclination because limited torque loss is expected for oversize axial inclination teeth. Variation sensitivity of the rotation center should be considered carefully due to biological problems when designing translation of the upper anterior teeth with normal axial inclination.

Reconstruction of dental roots for implant planning purposes: a feasibility study

PurposeModern virtual implant planning is a time-consuming procedure, requiring a careful assessment of prosthetic and anatomical factors within a three-dimensional dataset. In order to facilitate the planning process and provide additional information, this study examines a statistical shape model (SSM) to compute the course of dental roots based on a surface scan.Material and methodsPlaster models of orthognathic patients were scanned and superimposed with three-dimensional data of a cone-beam computer tomography (CBCT). Based on the open-source software “R”, including the packages Morpho, mesheR, Rvcg and RvtkStatismo, an SSM was generated to estimate the tooth axes. The accuracy of the calculated tooth axes was determined using a leave-one-out cross-validation. The deviation of tooth axis prediction in terms of angle or horizontal shift is described with mean and standard deviation. The planning dataset of an implant surgery patient was additionally analyzed using the SSM.Results71 datasets were included in this study. The mean angle between the estimated tooth-axis and the actual tooth-axis was 7.5 ± 4.3° in the upper jaw and 6.7 ± 3.8° in the lower jaw. The horizontal deviation between the tooth axis and estimated axis was 1.3 ± 0.8 mm close to the cementoenamel junction, and 0.7 ± 0.5 mm in the apical third of the root. Results for models with one missing tooth did not differ significantly. In the clinical dataset, the SSM could give a reasonable aid for implant positioning.ConclusionsWith the presented SSM, the approximate course of dental roots can be predicted based on a surface scan. There was no difference in predicting the tooth axis of existent or missing teeth. In clinical context, the estimation of tooth axes of missing teeth could serve as a reference for implant positioning. However, a higher number of training data must be achieved to obtain increasing accuracy.

In vitro accuracy of digital and conventional impressions in the partially edentulous maxilla

ObjectivesThis in vitro study compared the dimensional accuracy of conventional impressions (CI) with that of digital impressions (DI) in a partially edentulous maxilla. DIs were made by two intraoral scanners, Omnicam (OC) and Primescan (PS).Materials and methodsCI and both intraoral scanners were used to take 30 impressions of two identical reference models. CIs were poured with type 4 gypsum and the saw-cut models were digitized. The reference models simulated a maxilla with six prepared teeth that accommodated a cross-arch fixed partial denture. Center points of five precision balls and center points at the margin level of each prepared tooth were used to detect changes in dimensions and tooth axis between the reference model and the scans.ResultsFor DI, the largest deviations (176 µm for OC and 122 µm for PS) occurred over the cross-arch. For CI, the largest deviation (118 µm) occurred over the anterior segment. For shorter distances up to a quadrant, DI was superior to CI. For longer scan distances, DI was comparable (2 sextant and anterior segment) or inferior (cross-arch) to CI. Vertical and tooth axis deviations were significantly smaller for CI than for DI (p < 0.001).ConclusionsThe impression method affected the impression accuracy of a partially edentulous maxilla with prepared teeth. DI is recommended for scans up to a quadrant. Larger scan volumes are not yet suitable for fabricating a fixed partial denture because of the high scatter of accuracy values.Clinical relevanceIn contrast to conventional impressions, digital impressions lead to comparable or better results concerning scans up to a quadrant. Consequently, for larger scan volumes, several smaller scans should be performed or, if restoration-related not possible, it is recommended to take conventional impressions.

Heritability of maxillary dental cephalometric variables among monozygotic twins, dizygotic twins and their siblings.

The purpose of this study was to investigate the heritability of dental cephalometric variables by analyzing vertical linear measurements and angular measurements of the upper incisor, canine, and first molar. Among the 553 Korean patients who participated in twin studies conducted at Samsung Medical Center, 150 patients had their lateral cephalometric radiograph data included in this study. The group was comprised of 36 monozygotic (MZ) twins (males, 16 pairs; females, 20 pairs), 13 dizygotic (DZ) twins (males, 7 pairs; females, 6 pairs), and 26 same-sex sibling pairs (males, 11 pairs; females, 15 pairs). All patients were over 20years old with a mean age of 39.75years. Lateral cephalometric diagrams and linear measurements (6 vertical factors, 6 horizontal factors) were taken. Three axial planes were measured for each tooth; intraclass correlation coefficients (ICCs) were obtained for each group and heritability was calculated using Falconer's method. ICCs of vertical linear measurements (average 0.837, P < 0.01) and the tooth axis of the central incisor and canine (average 0.679, P < 0.001) were higher in the MZ group compared to the DZ and sibling groups; thus, these variables showed high heritability. Orthodontic treatment aiming to alter the tooth axis of the maxillary central incisor or canine or other vertical factors with greater heritability can be difficult, requiring strategic treatment planning to achieve desired treatment outcome and stability. The active early treatment to gain tooth eruption space can lead to normal tooth position.

Evaluation of the impact of reference tooth morphology and alignment on model measurement accuracy.

BackgroundThe development of personalized and high-precision dental treatment is inseparable from the accurate measurement and analysis of the model. Compared with traditional plaster models, digital models allow dentists to obtain richer and more detailed inspection results. However, the measurement of digital models in clinical practice usually ignores the influence of the overall three-dimensional (3D) structure of teeth and tooth arrangement on the measurement results. The purpose of this study was to evaluate the effect of calibrated tooth axis and tooth arrangement on tooth width and arch length.MethodsA total of 110 digital models from 80 participants were used to measure teeth width and dental arch length using the following methods: Method A, simple positioning of the proximal and distal of teeth; Method B: calibration of the clinical crown axis; and Method C: calibration of the overall 3D axis of the teeth. The Measurand model included pre- and post-orthodontic models of the same patients to assess the impact of tooth alignment on outcomes.ResultsIn the aligned dentition, whether the tooth axis was calibrated had no effect on the measurement results. On unaligned dentitions, calibrating the pinion allowed for more accurate measurements, with Method C the closest to the true size. Furthermore, the arrangement of teeth affected the measurement, but there was no continuous linear correlation with arch length discrepancy (ALD).ConclusionsClinicians should choose appropriate measurement methods according to actual needs when performing model measurement, and should pay attention to the influence of tooth axis, tooth shape, and arrangement on the measurement results.

Application Research of Tooth Arrangement Based on Rotation Matrix Calculation and Resistance Detection in Oral.

The goal of this research was to provide a new approach for analyzing orthodontic teeth arrangement inside oral depending on the rotation matrix computation and resistance detection. The present method includes the following operations within a certain therapy period: first three-dimensional positions of the tooth were evaluated with a pierced laser beam and a three-dimensional system of surface-scanning. Second, the three-dimensional shape data was automatically registered at maxillary 1st molars, and methods of coordinate had been normalized. Third, a translation vector and rotation matrix had been evaluated from automatic registration of two position data of a particular tooth. Fourth, the limited spiral axes of teeth had been measured as the zero rotational dislocation locus; and impressions for a model of the dental cast had been taken at five different points: shortly before and after device was fitted, and ten days, one month, and two months after the treatment started. The results showed that existing analysis approach could more quickly classify a specific tooth's movement by spinning all over and translating along a finite helical axis. It can provide statistical visual three-dimensional data on complex tooth arrangement throughout orthodontic therapy.

Investigation the angulation of maxillary impacted canines by using cone-beam computed tomography

Aim: This study aimed to evaluate the angulation and localization of unilaterally impacted canines by using CBCT. Methodology: Seventy-two images were included in the study based on the inclusion criteria. Demographic information (age and gender), localization and angulation of the impacted canine teeth were recorded. Canine angulation was measured between the two lines drawn on the coronal section of CBCT, with the first line drawn from the crista galli to the anterior nasal spine and the second line drawn along the long axes of the impacted canine teeth. Results: The mean age was 35.42±12.29 years in men and 31.10±11.09 years in women. In women, 16 of the impacted canines were on the right and 23 were on the left side, while in men, 21 of them were on the right and 12 were on the left side. Mean angulation was 34.6° (range, 17.6°-64.4°) for women and 36.2° (range, 21.4°-56.3°) for men. A weak negative correlation was found between patient age and angulation (p=0.49, rho = - 0.233). Conclusion: Angulation of maxillary impacted canines is an important predictive factor in orthodontic treatment. In the present study, no significant difference was found between angulation and canine localization and gender. How to cite this article: Laçin N, Yalçın M. Investigation the angulation of maxillary impacted canines by using cone-beam computed tomography. Int Dent Res 2022;12(1):9-13. https://doi.org/10.5577/intdentres.2022.vol11.no1.2 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Post-treatment Stability in Orthodontic Retention with Twistflex Retainers—Do Patients Benefit from Additional Removable Retainers?

ObjectivesTo evaluate post-treatment movements of lower anterior teeth during orthodontic retention in patients with fixed twistflex retainers versus those with combined fixed and removable retainers.Materials and MethodsThis study was based on a retrospective data analysis of 57 adult patients during orthodontic retention. They were assigned to two groups: In group 1 (n = 30) the lower jaw was provided with twistflex retainers only and in group 2 (n = 27) with a twistflex combined with a removable retainer for night-time use. Orthodontic study models of the lower jaw were digitalized and superimposed. Tooth movements were analyzed at the retainer bonding (t0) and follow-up appointment ≥ six months later (t1). Rotational tooth movements (°) were measured around the x-axis (mesial/distal direction), the y-axis (buccal/lingual direction) and the z-axis (longitudinal direction, tooth axis). Translational tooth movements (mm) were registered along the x-axis (buccal/lingual direction), the y-axis (mesial/distal direction) and the z-axis (apical/coronal direction).ResultsCanine and incisor position changes during orthodontic retention were more pronounced in group 1 compared to group 2 except for canine rotations around the z-axis. In both groups in most of the cases stable lower incisor alignment could be found, but the proportion was significant higher in group 2 (group 1: 56.7% vs. group 2: 81.5%). Severe misalignment was present in 13.3% of the participants of group 1 and only in 7.4% of group 2. The extent of canine tipping and movements along the x- and y-axis in severe misalignment cases was significantly lower in group 2 compared to 1.ConclusionsLower incisor alignment was more stable in patients with combined fixed and removable retainers compared to fixed retainers only.Clinical RelevanceBased on the present findings, the routinely application of supplementary removable retainers can be recommended to enhance anterior tooth alignment in patients with fixed twistflex retainers.

TAD-Net: tooth axis detection network based on rotation transformation encoding

The tooth axes, defined on 3D tooth model, play a key role in digital orthodontics, which is usually used as an important reference in automatic tooth arrangement and anomaly detection. In this paper, we propose an automatic deep learning network (TAD-Net) of tooth axis detection based on rotation transformation encoding. By utilizing quaternion transformation, we convert the geometric rotation transformation of the tooth axes into the feature encoding of the point cloud of 3D tooth models. Furthermore, the feature confidence-aware attention mechanism is adopted to generate dynamic weights for the features of each point to improve the network learning accuracy. Experimental results show that the proposed method has achieved higher detection accuracy on the constructed dental data set compared with the existing networks.

Influence of one-wall remaining coronal tooth with resin abutment and fiber post on static and dynamic fracture resistance.

The objective of this study was to determine the influence of height and thickness of the one wall remaining coronal tooth structure on the fracture resistance of an endodontically treated root with resin abutment build-up using resin composite and fiber-reinforced resin composite post. Static and dynamic fracture tests were performed by placing the remaining tooth wall on the tensile side and applying loads at an angle of 30° from the tooth axis. Superior static fracture resistance was observed when the wall remaining on the tooth had a height and thickness greater than 1.0 mm. The dynamic fatigue test showed high loading capacity or fracture resistance in specimens with large height and thickness. The dynamic fatigue test showed the influence of the remaining tooth structure on fracture resistance clearly. In conclusion, the static and dynamic fracture resistances increased with the height and thickness of the one wall remaining tooth structure.

Construction of an end-to-end regression neural network for the determination of a quantitative index sagittal root inclination.

Immediate implant placement in the esthetic area requires comprehensive assessments with nearly 30 quantitative indexes. Most artificial intelligence (AI)-driven measurements of quantitative indexes depend on segmentation or landmark detection, which require extra labeling of images and contain possible intraclass errors. For the initial attempt, the method was tested on sagittal root inclination measurement. This study had developed an accurate and efficient end-to-end model incorporating a convolutional neural network (CNN) based on unlabeled cone-beam computed tomography (CBCT) images for immediate implant placement diagnosis and treatment. The model took pretrained ResNeXt101 as the backbone and was constructed based on 2,920 CBCT images with corresponding angles of the tooth axis and bone axis. The performance of our CNN model was evaluated on a separate test set. Our model exhibited high prediction accuracy in sagittal root inclination measurements, as evidenced by the low mean average error of 2.16°, the high correlation coefficient of 0.915 to manual measurement, and the narrow 95% confidence interval shown by Bland-Altman plots. The intraclass correlation coefficient further confirmed the measurement accuracy of our model was comparable with that of junior clinicians. The model took merely 0.001 seconds for each CBCT image, making it highly efficient. To better understand the model's quality, we visualized our end-to-end CNN model through Guided Backpropagation, Grad-CAM, and Guided Grad-CAM, and confirmed its effectiveness in region recognition. We succeeded in taking the first step in constructing the end-to-end immediate implant placement AI tool through sagittal root inclination measurements without intermediate steps and extra labeling on images.

Stress patterns in conical teeth of reptiles and mammals: experimental and finite element analyses

A 3-Dimensional Finite Element Analysis (FEA) of conical teeth of reptiles and some mammals, suggests that under a vertical loading condition along the longer axis of tooth, horizontal tensile stresses are produced. In dental enamel, these stresses are distributed mainly in two horizontal directions, i.e. in X direction and in Z direction. The empirical observation of stresses possibly leading to the vertical failure of the teeth was obtained through Universal Testing Machine (UTM) using recent unicuspid teeth of crocodiles, varanus and canines of pig, cat and dog. The horizontal development of Hunter Schreger Bands (HSBs) has been observed in the enamel of canines of herbivore and carnivore mammals, which seems to be an effective structural strategy to counter splitting of tooth enamel under vertical loading. In contrast, the unicuspid teeth of reptiles lack the HSBs, and are more susceptible to failure. However, as reptilian teeth are continuously replaced, the damage is negligible.

Primary stability analysis of the torque-resistant orthodontic miniscrew anchorage

Though miniscrews are widely used as a temporary anchorage device, research focusing on the primary stability of miniscrew loading torque force is limited. This study is aimed to design a novel torque-resistant miniscrew used as orthodontic anchorage (TRO-screws) and to compare the difference of primary stability between TRO-screws and commercial miniscrew anchorage (COM-screws) using torque tests and resonance frequency analysis (RFA). Fresh swine ribs were cut into pieces of 20 mm × 13 mm × 11 mm, and each piece was implanted with one screw after a 1.5 mm-deep hole with a diameter of 1.0 mm was pre-drilled. There were 20 TRO-screws and 20 COM-screws. Maximum insertion torque (MIT) and maximum removal torque (MRT) were measured. The implant stability quotient (ISQ) was recorded parallel to and perpendicular to the long axis of teeth respectively. The measurement was repeated three times for each direction, and the ISQ values were averaged and recorded as the ISQpar, ISQper, and ISQm. The mean values of MIT for TRO-screws and COM-screws were 11.86±1.58 N cm and 10.36±1.42 N cm. The mean values of MRT for TRO-screws and COM-screws were 8.45±2.24 N cm and 6.76±1.78 N cm. The mean values of ISQ for TRO-screws and COM-screws were 61.80±2.9 and 58.15±2.98. These indicated that TRO-screws were more stable than COM-screws. We found that the primary stability of the TRO-screw was better than that of the COM-screw.

Assessment of simulated vs actual orthodontic tooth movement with a customized fixed lingual appliance using untreated posterior teeth for registration and digital superimposition: A retrospective study

With the advancement of computer-aided design and computer-aided manufacturing (CAD-CAM), digital setups that simulate the outcome of orthodontic treatment are frequently used. Incognito appliance system is a lingual orthodontic system that uses digital setups. A limitation to previous studies evaluating CAD-CAM simulated outcomes is the lack of stable reference points to superimpose on. The purpose of this study was to compare the simulated vs actual outcomes with the Incognito Lite appliance system. Thirty-four final models were compared with their corresponding setup models exported from the Incognito Web site. Final surface 3-dimensional imaging software was used to digitally measure differences between the simulated and actual treatment outcomes using a digital registration and superimposition method that utilizes the unmoved posterior teeth as reference points. Differences between simulated and actual tooth movement were significant in the translational parameter, with a maximum average discrepancy in the maxillary central incisors of 1.0±0.6mm(P<0.0001) and 0.8±0.4mm(P<0.0001) for mandibular central incisors. Discrepancies between simulated and actual tooth movements decreased from anterior to posterior. The first bicuspids moved the least for both maxillary and mandibular teeth (range of 0.4 mm-0.7mm). The differences for rotational parameters were statistically insignificant with a mesiodistal tip of 1.6°-3.6°, buccal-palatal torque 2.3°-4.4° and rotation around the tooth axis 2.3°-5.0°. Incognito Lite simulated tooth movements were achieved for rotation, tip, and torque (±3°). However, significant discrepancies were found between simulated and actual tooth position for translation (0.6-1.0mm).