Semaphorin-RhoA signaling regulates HERS maintenance by acting against TGF-ß-induced EMT.

BACKGROUND AND OBJECTIVES: Hertwig's epithelial root sheath (HERS) plays a role in root dentin formation. It produces the epithelial rests of Malassez (ERM) for the induction of periodontal tissue development during root formation. Although ERM is thought to be caused by epithelial-mesenchymal transition (EMT), the mechanism by which HERS is maintained as epithelium is unknown. Here, we aimed to elucidate the molecular mechanisms regulating the relationship between HERS maintenance and ERM development. METHODS: To understand the relationship between HERS and ERM development during root formation, we observed the developing molar root using cytokeratin14 (CK14) Cre/tdTomato mice via stereomicroscopy. The relationship between semaphorin and transforming growth factor (TGF) signaling in the maintenance of HERS and ERM development was examined using CK14cre/R26-tdTomato mice and a HERS cell line. RESULTS: tdTomato-positive cells were observed on HERS and the migrating cells from HERS. The migrating cells showed reduced E-cadherin expression. In contrast, HERS cells expressed semaphorin receptors and active RhoA. Semaphorin signaling was associated with RhoA activation and cell-cell adhesion, while TGF-ß induced decreased E-cadherin and active RhoA expression, and consequently enhanced cell migration. CONCLUSION: HERS induces root formation by controlling epithelial maintenance and EMT through the opposing effects of semaphorin and TGF-ß signaling.

Cementum thickening leads to lower whole tooth mobility and reduced root stresses: An in silico study on aging effects during mastication.

In the course of a lifetime the crowns of teeth wear off, cementum thickens and the pulp closes-in or may stiffen. Little is known about how these changes affect the tooth response to load. Using a series of finite element models of teeth attached to the jawbone, and by comparing these to a validated model of a 'young' pig 3-rooted tooth, the effects of these structural changes were studied. Models of altered teeth show a stiffer response to mastication even when material properties used are identical to those found in 'young' teeth. This stiffening response to occlusal loads is mostly caused by the thicker cementum found in 'old' teeth. Tensile stresses associated with bending of dentine in the roots fall into a narrower distribution range with lower peak values. It is speculated that this is a possible protective adaptation mechanism of the aging tooth to avoid fracture. The greatest reduction in lateral motion was seen in the bucco-lingual direction. We propose that greater tooth motion during mastication is typical for the young growing animal. This motion is reduced in adulthood, favoring less off-axis loading, possibly to counteract natural bone resorption and consequent compromised anchoring.

Cellular and molecular mechanisms of tooth root development.

The tooth root is an integral, functionally important part of our dentition. The formation of a functional root depends on epithelial-mesenchymal interactions and integration of the root with the jaw bone, blood supply and nerve innervations. The root development process therefore offers an attractive model for investigating organogenesis. Understanding how roots develop and how they can be bioengineered is also of great interest in the field of regenerative medicine. Here, we discuss recent advances in understanding the cellular and molecular mechanisms underlying tooth root formation. We review the function of cellular structure and components such as Hertwig's epithelial root sheath, cranial neural crest cells and stem cells residing in developing and adult teeth. We also highlight how complex signaling networks together with multiple transcription factors mediate tissue-tissue interactions that guide root development. Finally, we discuss the possible role of stem cells in establishing the crown-to-root transition, and provide an overview of root malformations and diseases in humans.

Evaluation of the regenerative potential of dentin conditioning and naturally derived scaffold for necrotic immature permanent teeth in a dog model.

This study evaluated the outcome of partial exposure of dentin matrix to ethylenediaminetetraacetic acid (EDTA) and application of platelet-rich fibrin (PRF) scaffold on regeneration of necrotic immature permanent teeth in a dog model. The present study was carried out on 216 permanent immature roots in nine mongrel dogs aged 6-9 months. Pulp necrosis and periapical pathosis were induced in 180 roots. These roots were divided into five equal groups (36 roots each) according to the treatment protocol: group I: blood clot; group II: 17% EDTA solution and blood clot; group III: PRF; group IV: 17% EDTA solution and PRF; and group V: without treatment (positive control). The negative control group (group VI) represented 36 untouched normal roots for normal maturation. The groups were followed up for 1, 2 and 3 months (subgroups). Maturation of the roots was monitored by radiography and histopathology. All data were statistically analysed. Group IV exhibited the highest increase in root length and thickness, decrease in apical diameter, the highest score of vital tissue infiltration and least inflammatory scores. There was a significant difference regarding the increase in root length and thickness and decrease in apical diameter in all subgroups of the experimental and negative control groups (P ≤ .05). PRF has a better regenerative potential than the blood clot during treatment of immature permanent teeth with necrotic pulp. Inclusion of 17% EDTA solution as a final irrigation enhances the regenerative potential of both PRF and blood clot.

Evaluation of antibacterial activity of propolis on regenerative potential of necrotic immature permanent teeth in dogs.

BACKGROUND: This study evaluated the antibacterial efficiency and ability of propolis to promote regeneration of immature permanent non-vital dogs' teeth. METHODS: Ninety six immature permanent premolars teeth in 6 mongrel dogs were divided randomly into: experimental teeth (N = 72) and control teeth (N = 24). Periapical pathosis was induced in all experimental and positive control teeth. Experimental teeth were classified according to the used intra-canal medication into: group I (N = 36), propolis paste was used and group II (N = 36), triple antibiotic paste (TAP) was used. Bacteriologic samplings were collected before and after exposure to intra-canal medicaments. After the disinfection period (3 weeks), revascularization was induced in all experimental teeth. Each group was subdivided according to the root canal orifice plug into: subgroup A (N = 18), propolis paste was used and subgroup B (N = 18), mineral trioxide aggregates (MTA) was used. Each subgroup was further subdivided according to the evaluation period into 3 subdivisions (6 teeth each): subdivision 1; after 2 weeks, subdivision 2; after one month and subdivision 3; after 2 months. Positive control group had 12 teeth with induced untreated periapical pathosis. Negative control group had 12 untouched sound teeth. All teeth were evaluated with radiography and histology. The bacteriologic and radiographic data were analyzed using repeated measures ANOVA and post-hoc Tukey tests. The histologic data were analyzed using Kruskal-Wallis test, Mann-Whitney U test with Bonferroni's adjustment and Chi-square test. The significance level was set at P ≤ .05. RESULTS: There was no significant difference in the antibacterial effectiveness between TAP and propolis groups (P > .05). In all subdivisions, there was no significant difference between the experimental groups in terms of increase in root length and dentin thickness, decrease in apical closure, new hard tissue formation, vital tissue formation inside the pulp canal and apical closure scores (P > .05). CONCLUSION: Propolis can be comparable with TAP as a disinfection treatment option in regenerative endodontic. As a root canal orifice plug after revascularization of necrotic immature permanent teeth in dogs, propolis induces a progressive increase in root length and dentin thickness and a decrease in apical diameter similar to those of MTA.

Stem cell-based tooth and periodontal regeneration.

Currently regeneration of tooth and periodontal damage still remains great challenge. Stem cell-based tissue engineering raised novel therapeutic strategies for tooth and periodontal repair. Stem cells for tooth and periodontal regeneration include dental pulp stem cells (DPSCs), periodontal ligament stem cells (PDLSCs), stem cells from the dental apical papilla (SCAPs), and stem cells from human exfoliated deciduous teeth (SHEDs), dental follicle stem cells (DFSCs), dental epithelial stem cells (DESCs), bone marrow mesenchymal stem cells (BMMSCs), adipose-derived stem cells (ADSCs), embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). To date, substantial advances have been made in stem cell-based tooth and periodontal regeneration, including dentin-pulp, whole tooth, bioroot and periodontal regeneration. Translational investigations have been performed such as dental stem cell banking and clinical trials. In this review, we present strategies for stem cell-based tissue engineering for tooth and periodontal repair, and the translational studies.

Effects of corticopuncture (CP) and low-level laser therapy (LLLT) on the rate of tooth movement and root resorption in rats using micro-CT evaluation.

The aim of this study was to compare the rate of tooth displacement, quantity of root resorption, and alveolar bone changes in five groups: corticopuncture (CP), low-level laser therapy (LLLT), CP combined with LLLT (CP + LLLT), control (C), and negative control (NC). A total of 60 half-maxilla from 30 male Wistar rats (10 weeks old) were divided randomly into five groups: three (CP, LLLT, and CP + LLLT) test groups with different stimulation for accelerated-tooth-movement (ATM), one control (C) group, and one negative control (NC) group with no tooth movement. Nickel-titanium coil springs with 50 g of force were tied from the upper left and right first molars to micro-implants placed behind the maxillary incisors. For the CP and CP + LLLT groups, two perforations in the palate and one mesially to the molars were performed. For the LLLT and CP + LLLT groups, GaAlAs diode laser was applied every other day for 14 days (810 nm, 100 mW, 15 s). The tooth displacements were measured directly from the rat's mouth and indirectly from microcomputer (micro-CT) tomographic images. Bone responses at the tension and compression sites and root resorption were analyzed from micro-CT images. The resulting alveolar bone responses were evaluated by measuring bone mineral density (BMD), bone volume fraction (BV/TV), and trabecular thickness (TbTh). Root resorption crater volumes were measured on both compression and tension sides of mesial and distal buccal roots. The tooth displacement in the CP + LLLT group was the greatest when measured clinically, followed by the CP, LLLT, and control groups (C and NC), respectively (p <0.05). The tooth movements measured from micro-CT images showed statistically higher displacement in the CP and CP + LLLT groups compared to the LLLT and control groups. The BMD, BV/TV, and TbTh values were lower at the compression side and higher at the tension side for all three test groups compared to the control group. The root resorption crater volume of the distal buccal root was higher in the control group, followed by CP, LLLT, and CP + LLLT, mostly at the compression site. Combining corticopuncture and low-level laser therapy (CP + LLLT) produced more tooth displacement and less root resorption at the compression side. The combined technique also promoted higher alveolar bone formation at the tension side.

Scanning Electron Microscopy Evaluation of Root Surfaces After Instrumentation With Two Piezoelectric Devices.

Scanning electron microscopy evaluation of root surfaces after ultrasonic instrumentation was performed with 2 different metallic tips on piezoelectric devices. Fresh extracted teeth were collected for experimental observation and randomly divided into 2 groups: Test Group, where the root surfaces were treated using an iron, rough, double nano-structural coated (T-Black), corindone-treated tip, and Control Group where the root surfaces were treated with a conventional iron smooth tip. A scanning electronic microscope analysis was performed and the surface roughness and the amount of residual debris were evaluated. Descriptive and inferential statistics were performed. Twenty specimens were analyzed, 10 per group and a total of 21.4 × 10 µm has been observed. On treated area percentage of debris after ultrasonic scaling in Test Group was 1.9 ±â€Š1.8%, while in Control Group it was 5.7 ±â€Š4.3%. Within the limits of the study, it seems that the efficacy of the novel iron, rough, double nano-structural coated (T-Black), corindone-treated structure tip showed greater performance in terms of root surface debridement than the conventional iron smooth tip. The possibility to use a single tool (ultrasonic device with a specific tip) for the root planing procedure within the nonsurgical mechanical therapy may represent a significant advantage for the clinicians. The tested novel tip seems to be able to show the requested ideal characteristics. However, further clinical studies are needed to demonstrate the in vitro results.

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.

Wnt activity is associated with cementum-type transition.

BACKGROUND AND OBJECTIVE: Cellular and acellular cementum and the cells that form them are postulated to have different characteristics, and the relationship between these two tissues is not well understood. Based on the hypothesis that Wnt signaling is involved in the determination of cementum type, we examined Wnt activity along the tooth root and analyzed cementum formation in genetic mutant models. MATERIAL AND METHODS: We generated mutant models with Wnt signaling upregulation (OC Catnblox(ex3)/+ ), downregulation (OC Wlsfl/fl ), and a compound mutant (Enpp1asj/asj ;OC Catnblox(ex3)/+ ) to compare cementum apposition patterns of ectonucleotide diphosphatase/phosphodiesterase (Enpp1) mutant (Enpp1asj/asj ). The analysis of structural morphology and histology was performed with hematoxylin and eosin and immunohistochemical staining and scanning electron microscopy. RESULTS: The cementum type of upper apical region of tooth roots in the molar is altered from the cellular form at the initial stage to the acellular form at the late stage of cementum formation. However, the basal part of this apical region is not altered and retains cellular cementum characters with strong Wnt activity. In the genetic mutant models for Wnt upregulation, cellular cementum is formed at the cervical region instead of acellular cementum. However, Enpp1 mutant mice have clearly different characteristics with cellular-type cementum even with dramatically increased cervical cementum matrix. In addition, we found that acellular-type formation could be altered into cellular-type formation by analyzing Wnt upregulation and compound mutant models. CONCLUSIONS: Cementum type is not determined by its specific location and could be transformed with Wnt activity during cementum formation.

Differences between biological and chronological age-at-death in human skeletal remains: A change of perspective.

OBJECTIVES: This analysis seeks to determine whether differences between real and estimated chronological age (CA) with biological age (BA) in skeletal individuals reflect variability in aging. MATERIAL AND METHODS: A total of 87 individuals of two samples, ranging from 20 to 94 years old, were analyzed. One, partially documented, belongs to a Mexican skeletal collection dating to the 20th century; the other is an assemblage of prehispanic individuals from different archaeological sites. In all specimens, the tooth annulation method (TCA) was applied to estimate CA, while-excluding individuals older than 80 years-auricular surface (AS) and pubic symphysis (PS) methods were used to estimate BA. Statistical analyses were conducted to identify correlations and significance of the differences between CA vs. TCA, CA vs. AS/PS, TCA vs. AS/PS. Sex of individuals was assessed for its influence in aging. RESULTS: The use of TCA to estimate CA was successful for most individuals. A strong correlation was found between CA vs. TCA, CA vs. AS/PS, TCA vs. AS/PS and their differences were significant but variation in these were found when assessed by separate age groups. Sex did not influence such differences. DISCUSSION: TCA can be used to estimate CA and its differences with BA, being less than 10 years, are similar to those found in living populations. Differences between CA and BA are due to intra-population variability, which could be the consequence of individual differences in aging. More research is needed to have confidence that under- and overestimations of BA are indicators of aging variability at the level of the individual.

Enhanced regeneration potential of mobilized dental pulp stem cells from immature teeth.

OBJECTIVES: We have previously demonstrated that dental pulp stem cells (DPSCs) isolated from mature teeth by granulocyte colony-stimulating factor (G-CSF)-induced mobilization method can enhance angiogenesis/vasculogenesis and improve pulp regeneration when compared with colony-derived DPSCs. However, the efficacy of this method in immature teeth with root-formative stage has never been investigated. Therefore, the aim of this study was to examine the stemness, biological characteristics, and regeneration potential in mobilized DPSCs compared with colony-derived DPSCs from immature teeth. MATERIALS AND METHODS: Mobilized DPSCs isolated from immature teeth were compared to colony-derived DPSCs using methods including flow cytometry, migration assays, mRNA expression of angiogenic/neurotrophic factor, and induced differentiation assays. They were also compared in trophic effects of the secretome. Regeneration potential was further compared in an ectopic tooth transplantation model. RESULTS: Mobilized DPSCs had higher migration ability and expressed more angiogenic/neurotrophic factors than DPSCs. The mobilized DPSC secretome produced a higher stimulatory effect on migration, immunomodulation, anti-apoptosis, endothelial differentiation, and neurite extension. In addition, vascularization and pulp regeneration potential were higher in mobilized DPSCs than in DPSCs. CONCLUSIONS: G-CSF-induced mobilization method enhances regeneration potential of colony-derived DPSCs from immature teeth.

Clinical procedures for revitalization: current knowledge and considerations.

Revitalization or regenerative treatment approaches in teeth with incomplete root formation and pulp necrosis have become part of the therapeutic endodontic spectrum and should be considered as an alternative to conventional apexification. Ideally, regenerative endodontic procedures allow not only for a resolution of pain, inflammation and periapical lesions, but also for the formation of an immunocompetent tissue inside the root canal which can reconstitute the original biological structure and function of dental pulp and thus lead to an increase in root length, and thickness and strength of previously thin, fracture-prone dentine walls. Common features of regenerative procedures performed in immature teeth with pulp necrosis include (i) minimal or no instrumentation of the dentinal walls, (ii) disinfection with irrigants, (iii) application of an intracanal medicament, (iv) provocation of bleeding into the canal and creation of a blood clot, (v) capping with calcium silicate, and (vi) coronal seal. Although case reports and case series provide promising results, the protocol for regenerative endodontic treatment is not fully established; questions remain regarding the terminology, patient selection and informed consent as well as procedural details, especially on the choice of irrigants, intracanal medicaments and materials for cavity sealing. Animal studies document repair rather than regeneration, which opens the discussion on prognosis and outcome, especially the biological versus the patient-based outcome. This review will provide an overview of the current state of regenerative endodontic therapies, discuss open questions and provide recommendations based on the recent literature.

Actin stabilization induces apoptosis in cultured porcine epithelial cell rests of Malassez.

AIM: To test whether actin stabilization by jasplakinolide induces inhibition of cell viability and apoptosis in epithelial cell rests of Malassez (ERM). METHODOLOGY: ERM derived from porcine were spread in a 96-well dish (5 × 10(4) /well) using Dulbecco's modified Eagle's medium. The actin-specific stabilization reagent, jasplakinolide, was incorporated into the culture medium and incubated for 24 h. To evaluate cell viability, the WST-1 assay was carried out and absorption (450 nm) was measured. To detect apoptotic cells, monoclonal antibody to single-strand DNA (ssDNA) was used and absorption (405 nm) was measured. Actin stabilization and apoptosis induced by jasplakinolide were morphologically investigated by staining with Alexa Fluor 568 phalloidin and observed under a fluorescent microscope. As a negative control, DMSO was used instead of jasplakinolide. Differences between the jasplakinolide-treated group and the control group were analysed statistically using the Student's t-test. RESULTS: Cell viability decreased in a concentration-dependent manner, and cell viability in the jasplakinolide-treated ERM was lower than that in nontreated ERM (n = 16, P < 0.01). Apoptotic cells in the jasplakinolide-treated ERM were more frequently detected compared to that in nontreated ERM (n = 16, P < 0.01). Morphologically, shrinkage, irregular forms and fragmentation of nuclei suggesting apoptotic bodies were observed in jasplakinolide-treated ERM, whilst actin filaments were extended in non-treated ERM. CONCLUSION: Actin stabilization by jasplakinolide inhibited cell viability and induced apoptosis in epithelial cell rests of Malassez.

Ideal orthodontic alignment load relationships based on periodontal ligament stress.

OBJECTIVES: To test the hypothesis that periodontal ligament (PDL) stress relationships that yield resistance numbers representing load proportions between different teeth depend on alignment load type. MATERIALS AND METHODS: Finite element models of all teeth, except the third molars, were produced. Four different types of loads were applied, and the third principal stresses of different teeth in standardized areas of most compression were calculated. Based on these results, resistance numbers, representing the load proportions for each tooth derived from PDL stress, were determined. RESULTS: The third principal stress values for typical alignment loads in the areas of most stress were very different for different load types for each tooth. Differences in resistance numbers between teeth also varied with different loads. CONCLUSION: Resistance numbers, that is, load proportion numbers between teeth to achieve similar stress at the compressive PDL zone, depend on the type of applied load.

A finite element analysis of the maxillary first molar PDL with maxillary protraction in a mixed dentition Class III malocclusion.

OBJECTIVES: To analyze the stress distribution on the PDL of the maxillary first molar in a mixed dentition Class III malocclusion, using a Hyrax-type appliance and maxillary protraction. SETTING AND SAMPLE POPULATION: A Class III malocclusion in the mixed dentition was reconstructed based on CBCT images. MATERIAL AND METHODS: The 3D FEM comprised the maxilla, alveolar bone, right first permanent molar teeth, and PDL and consisted of 1 133 497 nodes and 573 726 elements. Maxillary protraction force was applied to a hook positioned close to the deciduous canines with 600 g and at 15°, 30°, and 45° downward angles to the maxillary occlusal plane. RESULTS: Analysis was carried out from the top and buccal view of the sagittal plane. The magnitude of the stresses at 15°, 30°, and 45° of protraction angulation resulted in the highest stress magnitude being in the region between the distobuccal and palatal roots, as well as on the distal surface of the mesial root. The vector direction in this area showed traction and mesial movement. With 30° and 45° protraction angulations, the stress was located only between the distobuccal and palatal roots, and the vector direction was more extrusive at 15°. CONCLUSIONS: The suggested orthodontic movement is in the mesial direction with a small amount of extrusion with 15° angulation and greater extrusion with 30° and 45°.

Mechanical environment change in root, periodontal ligament, and alveolar bone in response to two canine retraction treatment strategies.

OBJECTIVE: To investigate the initial mechanical environment (ME) changes in root surface, periodontal ligament (PDL), and alveolar bone due to two treatment strategies, low or high moment-to-force ratio (M/F). SETTING AND SAMPLE POPULATION: Indiana University-Purdue University Indianapolis. Eighteen patients who underwent maxillary bilateral canine retraction. MATERIAL AND METHOD: Finite element models of the maxillary canines from the patients were built based on their cone beam computed tomography scans. For each patient, the canine on one side had a specially designed T-loop spring with the M/F higher than the other side. Four stress invariants (1st principal/dilatational/3rd principal/von Mises stress) in the tissues were calculated. The stresses were compared with the bone mineral density (BMD) changes reported previously for linking the ME change to bone modeling/remodeling activities. The correlation was tested by the mixed-model anova. RESULTS: The alveolar bone in the direction of tooth movement is primarily in tension, while the PDL is in compression; the stresses in the opposite direction have a reversed pattern. The M/F primarily affects the stress in root. Three stress invariants (1st principal/3rd principal/dilatational stress) in the tooth movement direction have moderate correlations with BMD loss. CONCLUSIONS: The stress invariants may be used to characterize what the osteocytes sense when ME changes. Their distributions in the tissues are significantly different, meaning the cells experience different stimuli. The higher bone activities along the direction of tooth movement may be related to the initial volumetric increase and decrease in the alveolar bone.

Finite Element Analysis of Bone Stress for Miniscrew Implant Proximal to Root Under Occlusal Force and Implant Loading.

Because of the narrow interradicular spaces and varying oral anatomies of individual patients, there is a very high risk of root proximity during the mini implants inserting. The authors hypothesized that normal occlusal loading and implant loading affected the stability of miniscrew implants placed in proximity or contact with the adjacent root. The authors implemented finite element analysis (FEA) to examine the effectiveness of root proximity and root contact. Stress distribution in the bone was assessed at different degrees of root proximity by generating 4 finite element models: the implant touches the root surface, the implant was embedded in the periodontal membrane, the implant touches the periodontal surface, and the implant touches nothing. Finite element analysis was then carried out with simulations of 2 loading conditions for each model: condition A, involving only tooth loading and condition B, involving both tooth and implant loading. Under loading condition A, the maximum stress on the bone for the implant touching the root was the distinctly higher than that for the other models. For loading condition B, peak stress areas for the implant touching the root were the area around the neck of the mini implant and the point of the mini implant touches the root. The results of this study suggest that normal occlusal loading and implant loading contribute to the instability of the mini implant when the mini implant touches the root.

Biomechanical effects of corticotomy approaches on dentoalveolar structures during canine retraction: A 3-dimensional finite element analysis.

INTRODUCTION: Corticotomy has proven to be effective in facilitating orthodontic tooth movement. There is, however, no relevant study to compare the biomechanical effects of different corticotomy approaches on tooth movement. In this study, a series of corticotomy approaches was designed, and their impacts on dentoalveolar structures were evaluated during maxillary canine retraction with a 3-dimensional finite element method. METHODS: A basic 3-dimensional finite element model was constructed to simulate orthodontic retraction of the maxillary canines after extraction of the first premolars. Twenty-four corticotomy approach designs were simulated for variations of position and width of the corticotomy. Displacement of the canine, von Mises stresses in the canine root and trabecular bone, and strain in the canine periodontal ligament were calculated and compared under a distal retraction force directed to the miniscrew implants. RESULTS: A distal corticotomy cut and its combinations showed the most approximated biomechanical effects on dentoalveolar structures with a continuous circumscribing cut around the root of the canine. Mesiolabial and distopalatal cuts had a slight influence on dentoalveolar structures. Also, the effects decreased with the increase of distance between the corticotomy and the canine. No obvious alteration of displacement, von Mises stress, or strain could be observed among the models with different corticotomy widths. CONCLUSIONS: Corticotomies enable orthodontists to affect biomechanical responses of dentoalveolar structures during maxillary canine retraction. A distal corticotomy closer to the canine may be a better option in corticotomy-facilitated canine retraction.

Finite element method analysis of the periodontal ligament in mandibular canine movement with transparent tooth correction treatment.

BACKGROUND: This study used the 3D finite element method to investigate canine's displacements and stresses in the canine's periodontal ligament (PDL) during canine's translation, inclination, and rotation with transparent tooth correction treatment. METHODS: Finite element models were developed to simulate dynamic orthodontic treatments of the translation, inclination, and rotation of the left mandibular canine with transparent tooth correction system. Piecewise static simulations were performed to replicate the dynamic process of orthodontic treatments. The distribution and change trends of canine's displacements and stresses in the canine's PDL during the three types of tooth movements were obtained. RESULTS: Maximum displacements were observed at the crown and middle part in the translation case, at the crown in the inclination case, and at the crown and root part in the rotation case. The relative maximum von Mises and principal stresses were mainly found at the cervix of the PDL in the translation and inclination cases. In the translation case, tensile stress was mainly observed on the mesial and distal surfaces near the lingual side and compressive stress was located at the bottom of the labial surface. In the inclination case, tensile stress was mainly observed at the labial cervix and lingual apex and compressive stress was located at the lingual cervix and labial apex. In the rotation case, von Mises stress was mainly located at the cervix and inside the lingual surface, tensile stress was located on the distal surface, and compressive stress was detected on the mesial surface. The stress and displacement value rapidly decreased in the first few steps and then reached a plateau. CONCLUSIONS: Canine's movement type significantly influences the distribution of canine's displacement and stresses in the canine's PDL. Changes in canine's displacement and stresses in the canine's PDL were exponential in transparent tooth correction treatment.