Mandibular Dentition Research Articles

Measurement of proximal enamel thickness of 182 permanent teeth

Objective: To measure the proximal enamel thickness (PET) at the mesial and distal contact areas of the permanent teeth and to provide a reference for interproximal enamel reduction (IPR). Methods: From May 2016 to February 2018, 182 isolated permanent teeth were collected and screened from patients who underwent extraction at Department of Oral and Maxillofacial Surgery, Capital Medical University School of Stomatology. These teeth were extracted for orthodontic purpose or due to severe periodontitis. The patients having teeth extracted were all Beijing residents, Han nationality, and aged (39.5±10.6) years. Ninety percent of the teeth came from patients under 50 years old. These teeth were classified according to different tooth type. The mesial and distal contact areas of these teeth were marked with fluid resin. The isolated teeth were scanned using micro-CT and the enamel thickness was measured and analyzed. The parameters measured included mesial PET (PETm), distal PET (PETd), the distance from mesial contact area to occlusal plane (CAm-OP), the distance from distal contact area to occlusal plane (CAd-OP), the distance from mesial contact area to the cementoenamel junction (CAm-CEJ), the distance from distal contact area to cementoenamel junction (CAd-CEJ) and tooth width (TWmd). Results: The PET gradually increased from the anterior tooth area [(0.63±0.16) mm] to the molar area [(1.46±0.25) mm]. The sum of the PET from the second molar to the contralateral second molar in the maxillary dentition was 31.60 mm, and that of the PET from the second molar to the contralateral second molar in the mandibular dentition was 29.68 mm. The contact areas were located on the occlusal third of the proximal walls of anterior teeth and the middle third of the proximal walls of posterior teeth. The PET were positively correlated with the tooth width between the mesial and distal contact areas (P<0.05). Conclusions: The PET was thinner in the incisor area and thicker in the molar area. IPR should be carried out close to the occlusal side of the proximal walls in anterior teeth and the cementoenamel junction side of the proximal walls in posterior teeth.

Biomechanical considerations for total distalization of the mandibular dentition in the treatment of Class III malocclusion

Class III malocclusions with mild to moderate skeletal discrepancies can be camouflaged by orthodontic tooth movement. Conventional methods using Class III elastics can correct Class III into Class I molar relationships. These mechanics show side-effects such as labioversion and intrusion of the maxillary incisors, extrusion of the maxillary molars, linguoversion and extrusion of the mandibular incisors, and intrusion of the mandibular molars along with flattening of the occlusal plane. Conventional mechanics can improve occlusal relationships and some profile esthetics but may produce detrimental smile esthetics by reducing the amount of maxillary incisor exposure. Recently, with the advent of temporary skeletal anchorage devices (TSADs), clinicians are able to achieve total distalization of the mandibular dentition and therefore improve the occlusal relationship without worsening smile esthetics. With the use of TSADs, the en masse movement of an entire dentition can be easily accomplished using a statically determinate force system, which makes treatment plans easier and treatment results more predictable. Finite element studies have identified the location of the center of resistance of the entire dentition and simulated displacement of the dentition depending on the force angulations (FAs) and have thus provided the theoretical basis for 3-dimensional tooth movement patterns. This article provides the biomechanical considerations and clinical applications of total distalization of the mandibular dentition depending on various FAs to the mandibular occlusal plane for camouflage treatment of various types of skeletal Class III malocclusions.

A digital approach to the evaluation of mandibular position by using a virtual articulator

The purpose of this technique report was to describe a fully digital technique to evaluate the mandibular position both in centric relation occlusion (CRO) and maximal intercuspation position (MIP). The procedure transfers data relative to the position of the maxillary and mandibular dentition to a virtual articulator based on a single cone beam computed tomography (CBCT) image. A CBCT scan of the patient was obtained in CRO, and the maxillary and mandibular casts were scanned both in CRO and MIP with an intraoral scanner. The model CRO scan data were registered on the dental part of the CBCT image by using a virtual articulator program, and a virtual facebow transfer process and mounting was performed. The virtual articulator was positioned in the right and left condyle medial pole and right orbitale. The mandibular position was evaluated in CRO and MIP by superimposing the data of the mandible position in both CRO and MIP. A quantitative 3D measurement was obtained by using the grid function. Based on this protocol, it is possible to use a fully digital approach to transfer the position of a patient’s maxillary dentition to a virtual articulator based on the data from a single CBCT scan and intraoral scans. This technique eliminates the traditional facebow transfer and mounting process and complicated laboratory procedures for evaluating mandibular positional changes in CRO and MIP.

The double-edged sword of calcium hydroxide in endodontics: Precautions and preventive strategies for extrusion injuries into neurovascular anatomy

BackgroundNowhere in the consideration of dental care involving endodontics does a patient become more vulnerable to potentially life-changing injuries than during a root canal procedure on the mandibular dentition that may invade and injure the neurovascular anatomy. Case DescriptionThe authors present a series of 5 cases wherein using calcium hydroxide as a disinfection strategy in endodontics caused serious neurologic injury to the treated patients. The mechanism in all cases was the inappropriate use of needle applications resulting in significant overfill into the inferior alveolar nerve space. Although calcium hydroxide has been recognized and used as a meaningful disinfectant in endodontic therapy for many years, the dangers and risks associated with a needle delivery technique are discussed and analyzed with recommendations based on current research to minimize risk. Conclusions and Practical ImplicationsA literature search revealed that the 5 cases are not solitary cases; indeed, consequences of calcium hydroxide overfills have been described before. Therefore, a clinician initiating root canal therapy on a mandibular posterior tooth should always be mindful of the vital neurovascular anatomy, which commonly approximates the ends of these roots. Preoperative cone-beam computed tomographic imaging and the thoughtful delivery of medicaments in treatment can help the clinician manage close proximity to neural anatomy and avoid potential injuries.

Emergence stages of permanent teeth in twins: A comparative study.

The relative effects of genetic factors on the timing of tooth eruption can be demonstrated through twin studies; however, twin studies on the eruption time of permanent teeth were limited. To compare the emergence stages of permanent teeth in twins and non-twin children. A total of 480 patients aged from 5.0 to 13.11years who attended to the Department of Pediatric Dentistry for any dental reason were included in the study. Twins were compared with the control group in terms of the emergence stages for all permanent teeth. At the age of 5years, girls in the control group showed statistically significant differences related to the central incisors, the first molars in the mandibular dentition and the first molars in the maxillary dentition, showing more advanced emergence stages. In the 6- to 8- and 12- to 13-year-old age groups, no gender-related differences in emergence stages were observed. Gestation age was found to have a statistically significant effect on the emergence stages of permanent teeth. There were no statistically significant differences between birthweights and tooth emergence stages in twins. Longitudinal studies are needed to determine whether there is a strong genetic effect on emergence stages of permanent teeth in twins.

Computer-Assisted Preoperative Simulations and 3D Printed Surgical Guides Enable Safe and Less-Invasive Mandibular Segmental Resection: Tailor-Made Mandibular Resection

This study aimed to present and evaluate alternative lesion-specific mandibulectomy methods for preserving the mandibular anatomical structures as compared with the conventional virtual surgical plan. Fifteen patients who received segmental mandibulectomy were included in this study, and the following parameters were evaluated: (1) the disease-free bone margin, (2) the volume and surface between the tailor-made resection simulation and conventional resection simulation, and (3) the preserved mandibular anatomical structures. In all 15 patients, disease-free bone margins were confirmed by histopathology. Volumes of conventional resection simulation and tail-made resection simulation were 49,468.66 ± 14,007.96 mm3 and 52,610.01 ± 13,755.33 mm3 and the surfaces were 20,927.38 ± 4471.70 mm2 and 22,356.49 ± 4185.73 mm2, respectively; these were statistically significant (both, p &lt; 0.001). Mandibular dentition was partially preserved in six patients. Twelve of the 15 patients had changes in defect classification with preservation of the mandibular inferior border. In conclusion, alternative lesion-specific mandibulectomy was a less invasive method for effectively removing mandibular lesions while preserving the important anatomical structures of the mandible.

Diagnosis and Treatment Considerations of Orthodontic Miniscrews in Camouflage Treatment of Adult Class III Malocclusions by Distalization of the Mandibular Dentition- A Review of Literature

Class III malocclusions pose a challenge to the orthodontist, and conventional treatment options to treat this condition in an adult patient include orthognathic surgery, or orthodontic camouflage. Up until a few years ago, orthodontic camouflage for correction of a Class III problem involved retroclination of the lower anterior teeth and proclination of the upper anterior teeth. The advent of skeletal anchorage systems has opened up new vistas in camouflaging Class III malocclusion due to mandibular prognathism. This article reviews the various treatment planning considerations, both clinical and radiographic, for camouflage of Class III malocclusion by miniscrew assisted distalization of the mandibular dentition, and also discusses treatment options, procedures, biomechanics and possible pitfalls.

Safe regions of miniscrew implantation for distalization of mandibular dentition with CBCT

BackgroundTo assess the anatomy of the mandibular buccal shelf (MBS) with cone-beam computed tomography (CBCT) and to identify the region of miniscrew implantation for the distalization of mandibular dentition.Materials and methodsThe MBS was assessed in 80 patients at four regions as follows: (i) between the buccal root of the mandibular second premolar and the mesiobuccal root of the first molar (L5b–L6mb), (ii) between the mesiodistal root of the first molar (L6mb–L6db), (iii) between the distobuccal root of the first molar and the mesiobuccal root of the second molar (L6db–L7mb), and (iv) between the mesiodistal roots of the second molar (L7mb–L7db). The buccal alveolar bone thickness, the narrowest inter-radicular space at the buccal side of the roots, and the distance between the implantation site and the mandibular neural tube were measured at horizontal planes of 3, 5, 7, and 9 mm from the alveolar crest.ResultsThe buccal alveolar bone thickness increased from the premolar to the molar and from the crest edge to the mandibular roots. The L7mb–L7db region had the thickest buccal alveolar bone of 7.61 mm at a plane of 9 mm. The buccal inter-radicular spaces were smallest in the L7mb–L7db region and greatest in the L6db–L7mb region. The distances from the implantation site to the mandibular neural tube at planes of 3, 5, 7, and 9 mm were all > 13 mm from the L6 region to the L7 region.ConclusionsThe L6db–L7mb region should be the first choice for miniscrew implantation in the MBS for the distalization of mandibular dentition.

Class III malocclusion camouflage treatment in adults: A Systematic Review

Objective: To evaluate the effects of camouflage treatment of Class III malocclusion in adults. Methods: An electronic search was performed in MEDLINE/PubMed, Embase, Scopus, Web of Science, Google Scholar, Lilacs, and Cochrane databases, without limitations regarding publication year or language. Studies evaluating nongrowing individuals with Class III malocclusion undergoing orthodontic camouflage treatment with any orthodontic technique, including extraction and non-extraction approaches, were considered. Study selection, data extraction, and risk of bias assessment according to a modified Downs and Black checklist were performed by two independent reviewers. A third evaluator was included if disagreements emerged. Results: Nine studies were included in the review. Eight presented high risk of bias. Different methods for Class III malocclusion correction were described and included maxillary and mandibular premolar extractions, mandibular incisor extraction, Class III elastics and distalization of the mandibular dentition. Extractions in the mandibular arch resulted in lingual tipping and retrusion of the mandibular incisors, and labial tipping and protrusion of the maxillary incisors. The use of Class III intermaxillary elastics promoted proclination of the maxillary incisors, extrusion of the maxillary molars, distal tipping of the mandibular molars, extrusion of the mandibular incisors, and clockwise rotation of the mandible. Distalization of the mandibular dentition resulted in distal tipping of the mandibular molars, retroclination and retraction of the mandibular incisors, and counter clockwise rotation of the mandible. Conclusions: Treatment changes are influenced by the method used to correct the Class III malocclusion and are primarily dentoalveolar

Application of computer-aided virtual mandibular position in the simultaneous treatment of children with temporomandibular joint ankylosis and jaw deformity

Objective To evaluate the feasibility of computer-aided design virtual mandibular position in the simultaneous treatment of children with temporomandibular joint ankylosis (TMJA) and jaw deformity. Methods The children with unilateral TMJA were surgically treated from January 2016 to June 2017 in the Department of Oral and Maxillofacial Surgery. The image data of jaw and dentition were imported into the computer software to simulate the surgical procedure. An osteotomy of the affected side was performed to remove ankylosed bone mass. Then the mandible was rotated around the unaffected condyle to eliminate the chin deviation by the virtual plan. An open bite was thus created on the affected side to provide space for vertical midfacial growth. In the virtual mandibular position, the affected ramus was reconstructed with costochondral grafting. Finally, digital occlusal splint was designed and prefabricated by 3D printing. During surgery, temporomandibular joint ankylosis was released and mandibular position was guided in place by the digital occlusal splint. In the new mandibular position, costochondral grafting was completed. After the surgery, the occlusal splint was wired to the mandibular dentition and would be gradually adjusted by grinding off the maxillary side to promote downward growth of the maxilla until the open bite was eliminated. The ramus height and chin deviation were measured before and one week after the surgery to validate the method. Comparisons of the measurements were made by means of a repeatedmeasures analysis of variance (ANOVA) (P=0.05). Pairwise multiple comparisons were conducted using the Bonferroni correction (P=0.05). Results Five patients were included in this study. Under the guidance of the digital occlusal splint, the mandible could reach the preoperative designed position smoothly in all the cases. The chin deviations were (0.58±0.20) mm in the virtual plan before surgery, and (0.70±0.27) mm after surgery, which were not significant statistically (P>0.05). The ramus heights on the affected side were (48.19±3.20) mm in the virtual plan before surgery, and (48.17±3.62) mm after surgery, which were not significant statistically (P>0.05). Conclusion It is feasible and reliable in the simultaneous treatment of TMJA with jaw deformity under the guidance of virtual mandibular position.

Orthognathic Treatment Using Combination Surgery (Unilateral Sagittal Ramus Osteotomy and Unilateral Intraoral Vertical Ramus Osteotomy) for Skeletal Class III Malocclusion Patient with Facial Asymmetry

This case report describes a successful orthognathic treatment using a combination surgery; unilateral sagittal ramus osteotomy (USSRO) and unilateral intraoral vertical ramus osteotomy (UIVRO). A 23-year-old male patient showing skeletal class III malocclusion with mandibular asymmetry visited our orthodontic department. Characteristics of his facial asymmetry was translation of the mandibular dentition to the left side, without yawing or canting of both jaws. After pre-surgical orthodontic treatment, orthognathic surgery with LeFort I osteotomy in the maxilla and combination surgery in the mandible was performed (USSRO on non-deviation side and UIVRO on deviation side). After 18-month of overall treatment, facial appearance and malocclusion were improved. The combination surgery (USSRO + UIVRO) could be a predictable and better treatment option that overcome the limitations of conventional orthognathic surgery for skeletal class III malocclusion with asymmetry.

Camouflage of Skeletal Class III Malocclusion in an Adult Male Using Miniscrew Anchorage From the External Oblique Ridge in Conjunction With Face Mask Wear

This article reports the successful camouflage of skeletal Class III malocclusion in a 20-year-old man through distalization of the mandibular dentition using miniscrew anchorage from the external oblique ridges of the mandible. In addition, maxillary face mask wear assisted in the closure of maxillary spacing without retroclination of maxillary incisors. This combination may be effective in the management of adult Class III skeletal malocclusions that are amenable to camouflage therapy.

Hızlı üst çene genişletmesi ve yüz maskesi kombine uygulamasının mandibular dentisyona etkisi

Amaç: Bu çalışmanın amacı, Hızlı Üst Çene Genişletmesi (HÜÇG) ve Yüz maskesi (YM) kombine uygulamasının mandibular dentisyona etkisini değerlendirmektir. Gereç ve Yöntem: Bu retrospektif çalışmada daimi dişlenme döneminde olan, ortalama iskelet yaşı 12 yıl 1 ay olan, posterior çapraz kapanış ve maksiller retrognatinin eşlik ettiği iskeletsel Sınıf 3 anomaliye (ANB&amp;lt;0) sahip olup tedavi protokolü gereği yapıştırmalı tip Hyrax vidalı HÜÇG aygıtı ile Petit tip YM’nin kombine uygulandığı 25 bireye (10 kız, 15 erkek) ait tedavi başı ve sonu sefalometrik film ve ortodontik modeller değerlendirildi. HÜÇG-YM kullanımı ortalama 8.7 aydı. Ortodontik modellerin 3D görünümünde 3Shape Ortho Analyzer 2013-1 programıyla alt çenede intermolar, interkanin genişlik, ark derinliği ve alt anterior bölge kanin-kanin arası çapraşıklık miktarı Little düzensizlik indeksi (LDİ) metodu kullanılarak ölçüldü. Lateral sefalometrik filmlerde alt keser eğimi (IMPA açısı) ölçüldü. Verilerin istatistiksel olarak değerlendirilmesinde eşleştirilmiş t-testi kullanıldı. İstatistiksel anlamlılık değeri p&amp;lt;0.01 olarak kabul edildi. Bulgular: Kombine uygulama sonunda alt dental arkta intermolar genişlikte ortalama 1.38 mm anlamlı artış bulundu (p&amp;lt;0.001). Buna karşılık, interkanin genişliğinde değişim saptanmadı. Ark derinliğinde ise 1.45 mm anlamlı azalma (p&amp;lt;0.001) ve LDİ değerinde 1.46 mm anlamlı artış görüldü (p&amp;lt;0.01). Alt keser eğiminde (IMPA açısı) istatistiksel olarak anlamlı değişim saptanmadı. Sonuç: HÜÇG-YM kombine uygulaması sonunda alt çenede oluşan intermolar genişlikteki artış ark boyunu arttırırken, buna karşılık ark derinliğindeki azalma ark boyunu azaltmaktadır. Klinisyenler bu kombine uygulamayla alt çenede kesici dişlerde çapraşıklık miktarının artabileceğini göz önünde bulundurmalıdır.

A cone-beam computed tomography analysis of angulation and inclination of whole tooth and clinical crown in adults with normal occlusion.

To identify the mesiodistal angulation and faciolingual inclination of whole tooth and clinical crown in Chinese young adults with normal occlusion, by examining CBCT digitalized images. Forty-two volunteers, who presented with normal occlusion and without previous orthodontic treatment, were selected for this study. The subjects were advised to take dental CBCT and the digital images of the dentition were obtained. The widely recognized University of Southern California (USC) root vector analysis was adopted to detect the angulation and inclination of the whole tooth, as well as of the clinical crown. No statistically significant difference was detected between male and female subjects. The fluctuations of the angulation and the inclination of the whole tooth from anterior to posterior in both arches manifested distinctive trends. The changes in maxillary dentition seem relatively marked, whereas those in mandibular dentition show less obvious, demonstrating moderate fluctuation both in angulation or inclination. The angulation and inclination of clinical crown are obtained and are shown positively correlated with that of each whole tooth. The normal range of the mesiodistal angulation and faciolingual inclination of whole tooth and clinical crown in Chinese adults with normal occlusion are identified. This study could establish clinical standards for designing 3D dental data-based orthodontic appliances for Chinese, and for providing the guidance for orthodontic treatment.

Biomechanical analysis for total mesialization of the mandibular dentition: A finite element study.

To clarify the mechanics of tooth movement in mesialization of the whole mandibular dentition when changing the force angulation. A finite element method was used to simulate long-term movements of the whole mandibular dentition. Tooth movement was simulated by accumulating the initial displacement, which was produced by elastic deformation of the periodontal ligament. Mesial forces of 3N were applied to the second molar bracket at -30°, -15°, 0°, 15° and 30° to the occlusal plane. The whole dentition and occlusal plane were rotated depending on the direction of the force with respect to the centre of resistance (CR). At a force angulation of -30°, the line of action of the force passed near the CR, and the whole dentition translated without rotation of the occlusal plane. The second molar tipped buccally due to a clearance gap between the archwire and bracket slot. When increasing a force angulation from -30°, the line of action of the force passed above the CR, and thereby, the occlusal plane rotated clockwise. This rotation of the whole dentition induced tipping of the individual teeth. Buccal tipping of the molar due to an elastic deformation of the archwire was prevented by using a lingually pre-bent archwire. Careful selection of force angulation and biomechanics is essential to obtain proper tooth movement in total mesialization of the mandibular dentition.

TAD driven whole dentition distalization with special considerations for incisal/gingival display and occlusal canting

Many orthodontists face difficulties in aligning incisors in an esthetically critical position, because the individual perception of beauty fluctuates with time and trend. Temporary anchorage device (TAD) can aid in attaining this critical incisor position, which determines an attractive smile, the amount of incisor display, and lip contour. Borderline cases can be treated without extraction and the capricious minds of patients can be satisfied with regard to the incisor position through whole dentition distalization using TAD. Mild to moderate bimaxillary protrusion cases can be treated with TAD-driven en masse retraction without premolar extraction. Patients with Angle's Class III malocclusion can be the biggest beneficiaries because both sufficient maxillary incisal display, through intrusion of mandibular incisors, and distalization of the mandibular dentition are successfully achieved. In addition, TAD can be used to correct various other malocclusions, such as canting of the occlusal plane and dental/alveolus asymmetry.

Complete permanent mandibular dentition of early Homo from the upper Burgi Member of the Koobi Fora Formation, Ileret, Kenya

The KNM-ER 64060 dentition derives from a horizon that most likely dates to between 2.02 and 2.03 Ma. A proximate series of postcranial bones (designated KNM-ER 64061) derives from the same siltstone unit and may be associated with the dentition, but their separation on the surface of the site leaves some room for doubt. KNM-ER 64060 is one of fewer than ten hominin specimens from the Early Pleistocene of East Africa that comprises a full or nearly complete mandibular dentition. Its taxonomic attribution is potentially significant, especially if the postcranial elements are related. At least three, and probably four hominin species, including Paranthropus boisei and Homo erectus (= H. ergaster), are known at about this time in East Africa. Other penecontemporaneous fossils have been referred to a single, highly variable species, H. habilis, or two taxa, namely H. habilis and H. rudolfensis. Although the weight of evidence supports the attribution of these specimens to two species, there is notable lack of agreement over the assignation of individual fossils. We take a conservative approach and group all such specimens under the designation “early Homo sp.” for comparative purposes. KNM-ER 64060 is clearly attributable to Homo rather than Paranthropus. The preponderance of the evidence suggests that the affinities of KNM-ER 64060 are with fossils assigned to the early Homo sp. category rather than with H. erectus. This is indicated by the overall sizes of the KNM-ER 64060 canine, premolar and molar crowns, the size relationships of the P3 to P4, the relative narrowness of its premolar crowns, the cusp proportions of the M1 and especially those of the M2 and M3, and seemingly the possession of a two-rooted P4. Some of these comparisons suggest further that among the fossils comprising the early Homo sp. sample, the KNM-ER 64060 dentition exhibits greater overall similarity to specimens such as OH 7 and OH 16 that represent Homo habilis sensu stricto.

Expression of new genes in vertebrate tooth development and p63 signaling.

p63 is an evolutionarily ancient transcription factor essential to vertebrate tooth development. Our recent gene expression screen comparing wild-type and "toothless" p63-/- mouse embryos implicated in tooth development several new genes that we hypothesized act downstream of p63 in dental epithelium, where p63 is also expressed. Via in situ hybridization and immunohistochemistry, we probed mouse embryos (embryonic days 10.5-14.5) and spotted gar fish embryos (14 days postfertilization) for these newly linked genes, Cbln1, Cldn23, Fermt1, Krt15, Pltp and Prss8, which were expressed in mouse and gar dental epithelium. Loss of p63 altered expression levels but not domains. Expression was comparable between murine upper and lower tooth organs, implying conserved gene functions in maxillary and mandibular dentitions. Our meta-analysis of gene expression databases supported that these genes act within a p63-driven gene regulatory network important to tooth development in mammals and more evolutionary ancient vertebrates (fish, amphibians). Cbln1, Cldn23, Fermt1, Krt15, Pltp, and Prss8 were expressed in mouse and fish dental epithelium at placode, bud, and/or cap stages. We theorize that these genes participate in cell-cell adhesion, cell polarity, and extracellular matrix signaling to support dental epithelium integrity, folding, and epithelial-mesenchymal cross talk during tooth development.

Timing of Development of the Permanent Mandibular Dentition: New Reference Values from the Fels Longitudinal Study.

Estimating chronological age or assessing the rate of maturation in immature individuals is an important task in biological anthropology and clinical practice. One of the most reliable ways of doing this is by evaluating one's dental development, specifically tooth mineralization. However, few chronologies include reference values for very young children, and few provide an extensive documentation of the range of variation surrounding the reported reference values. We present a new chronology of development of permanent mandibular canine and postcanine teeth from birth through age 28 years, based on over 6,000 radiographs of 590 participants of the Fels Longitudinal Study, recorded between 1940 and 1982. Tooth mineralization was scored following the 14-stage system of Moorrees, Fanning, and Hunt (Moorrees et al., 1963a) with an additional crypt stage. We calculated ages of attainment, as well as average age in stage, using transition analysis. We find that variation increases throughout ontogeny for all teeth, though it is generally comparable between girls and boys. The tempo of dental development tends to be faster in girls. Compared to the classic chronology of Moorrees et al. (1963a), partly based on Fels radiographs, in our sample the development of crowns tends to occur at earlier, and development of roots at increasingly later ages. Our results are more similar to chronologies based on more recent, clinical samples (Liversidge, 2009), though the development of tooth roots in our sample occurs at older ages. Anat Rec, 302:1733-1753, 2019. © 2019 American Association for Anatomy.

Biomechanical analysis for total distalization of the mandibular dentition: A finite element study.

The aim of this finite element study was to analyze and clarify the mechanics of tooth movement patterns for total distalization of the mandibular dentition based on force angulation. Long-term orthodontic movement of the mandibular dentition was simulated by accumulating the initial displacement of teeth produced by elastic deformation of the periodontal ligament. Displacement of each tooth was caused by movement of the whole dentition, elastic deflection of the archwire, and clearance gap between the archwire and bracket slot. The whole dentition was rotated clockwise or counterclockwise when the line of action of the force passed below or above the center of resistance. Elastic deflection of the archwire induced a lingual tipping of the anterior teeth. It became larger when increasing the magnitude of angulation. The archwire could be rotated within the clearance gap between the archwire and the bracket slot, and thereby the teeth tipped. Mechanics of total mandibular distalization was clarified. Selective use of force angulation with a careful biomechanical understanding can achieve proper distalization of the whole mandibular dentition.