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OBJECTIVE Patients with oligodontia frequently show different types of malocclusions. However, how oligodontia affects the maxillofacial growth remains uncertain. This study aimed to investigate the maxillofacial morphological characteristics in growing patients with oligodontia. SETTING AND SAMPLE POPULATION The study subjects included 33 Japanese children with non-syndromic oligodontia (14 boys and 19 girls; mean age: 10.2 years) who visited the orthodontic clinic of Fukuoka Dental College Medical and Dental Hospital from 1999 to 2019. MATERIALS AND METHODS Cephalometric analyses were performed, and the variables measured in each subject were converted into Z scores in relation to the mean and standard deviation of the Japanese norms matched for growth stage. The one-sample t-test or Wilcoxon signed-rank test was performed to compare the mean scores in the patients with oligodontia with those of the Japanese norms. RESULTS Compared with the Japanese norms, patients with oligodontia showed a smaller convexity and larger A-B plane and SNB angles. The Frankfort-mandibular plane and gonial angles were smaller, whereas the height of the ramus was larger. The vertical height of the alveolar bone in the maxillary and mandibular incisors and molar areas was smaller in patients with oligodontia. CONCLUSIONS Patients with oligodontia showed Class III skeletal tendency with mandibular prognathism and flattened mandibular plane with a smaller gonial angle. These maxillofacial morphological features can be induced by a deficiency in the vertical growth of the alveolar bone in the maxillary and mandibular molar areas due to the lack of tooth germs.

Odontomas and ameloblastic fibro-odontomas (AFOs) are the result of a developmental anomaly of odontogenic tissues. A literature review of proteins immunoexpressed in odontomas and AFOs was conducted in order to determine which proteins are involved in the pathogenesis of these lesions. AFO was changed to early odontoma in the 2017 WHO classification and will also be discussed in this article. A literature search was performed in the following electronic databases: PubMed/MEDLINE, Web of Science, Scopus, EMBASE, Lilacs, Cochrane Collaboration Library, and Science Direct. The research question was developed according to the population, intervention, comparison, and outcome (PICO) framework: Which proteins are related to the differentiation of odontomas and what is their interrelationship with AFOs? Thirty articles met all inclusion criteria and were selected for this systematic review, totaling 355 cases of odontomas and 43 cases of AFO. Similar immunoexpression was observed in odontomas and AFOs. Immunoexpression of proteins involved in cell differentiation was higher in compound odontomas than in complex odontomas. Proteins involved in histodifferentiation and enamel formation were more frequent in odontomas. The immunoexpression of enamel matrix proteins differs between odontomas and tooth germs, with their persistence being related to the development of odontomas. Compound odontomas exhibit the highest immunoexpression of proteins involved in cellular histodifferentiation and the Wnt/beta-catenin pathway is involved in tumor formation. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s12105-020-01260-x) contains supplementary material, which is available to authorized users.

The aim of the study.To reveal tooth germs structural changes induced by low doses of ionizing radiation in the experiment using light-microscopic examination. Objects and methods. The experiments were carried out on albino rats mongrel gregarious breeding. Gravid female rats were exposed to chronic irradiation on “Gammarid 192/120 unit” at 110 mR/h power of exposition for 18 days at the Institute of Radiobiology of the National Academy of Sciences of the Republic of Belarus. The total dose absorbed by the fetuses was 0.42 Gy. Results and discussion. The experiment showed a significant decrease of proliferative activity of tooth germ cells. It resulted in the decrease in size and in the number of cell layers, shape change up to the appearance of deformed tooth germs. Reducing the intensity of mitotic division also led to the lack of “concentric structures” and cell cushion-shaped thickenings in the enamel epithelium in the experiment. Conclusion. These series of experiments revealed such odontogenesis disorders that cannot be explained only by the decrease of proliferative activity.

Introduction: Supernumerary teeth in cases of cleft lip and palate do not result from the division of normal germs before the formation of hard tissue. Deciduous and permanent teeth odontogenesis begins after the face has formed, either with or without the cleft. Discussion: The most acceptable hypothesis to enable understanding of the presence of supernumerary teeth on one or both sides of the cleft palate is hyperactivity of the dental lamina in its walls. This hyperactivity, with the formation of more tooth germs, must be attributed to mediators and genes related to tooth formation, under strong influence of local epigenetic factors, whose developmental environment was affected by the presence of the cleft. Conclusion: The current concepts of embryology no longer support the fusion of embryonic processes for the formation of the face, but rather the leveling of the grooves between them. All human teeth have a dual embryonic origin, as they are composed of ectoderm and mesenchyme/ectomesenchyme, but this does not make it easy for them to be duplicated to form supernumerary teeth. RESUMO Introdução: Os dentes extranumerários nas fissuras labiopalatinas não são resultado da divisão dos germes normais antes da formação do tecido duro. A odontogênese dos decíduos e permanentes inicia-se depois de formada a face, com ou sem fissuras. Discussão: A hipótese mais plausível para compreender a presença dos dentes extranumerários em um ou nos dois lados da fissura labiopalatina é a hiperatividade da lâmina dentária em suas paredes. Essa hiperatividade, com formação de mais germes dentários, deve ser atribuída aos mediadores e genes relacionados à formação dos dentes, sob forte influência de fatores epigenéticos locais, cujo ambiente de desenvolvimento foi afetado pela presença da fissura. Conclusão: Os conceitos atuais da embriologia não fundamentam mais a fusão de processos embrionários para a formação da face, e sim o nivelamento dos sulcos entre eles. Todos os dentes humanos têm uma dupla origem embrionária, pois se compõem de ectoderma e mesênquima/ectomesênquima, mas isso não facilita sua duplicação para formar dentes extranumerários.

Delayed tooth development (DTD) is the development progress of a tooth germ that takes place later due to local or general causes. This case report reviews a 16-year-old Asian adolescent whose bilateral upper second premolar germs were at Nolla’s 6 stage as shown on a panoramic radiograph. It is unusual that tooth germs of the maxillary second premolar are developed after 11 years of age. To reduce the chance of misdiagnosis, clinicians should consider the possibility of DTD if a tooth germ does not present in radiographs.

When a traumatic dental injury affects the deciduous teeth, the main management is to regularly review the patient until the successor permanent tooth erupts to avoid further consequences to the affected tooth and, especially, sequelae in the tooth germs of the successor permanent tooth. This report describes a case of a tooth extrusion in a 4-year-old male treated with a minimally invasive approach. After 4 years of follow-up, there was a mild disturbance (demarcated opacity in the vestibular surface) and a satisfactory result with normal eruption of the permanent successor tooth.

Background The egg tooth is a vital structure allowing hatchlings to escape from the egg. In squamates (snakes and lizards), the egg tooth is a real tooth that develops within the oral cavity at the top of the upper jaw. Most squamates have a single large midline egg tooth at hatching, but a few families, such as Gekkonidae, have two egg teeth. In snakes the egg tooth is significantly larger than the rest of the dentition and is one of the first teeth to develop. Results We follow the development of the egg tooth in four snake species and show that the single egg tooth is formed by two tooth germs. These two tooth germs are united at the midline and grow together to produce a single tooth. In culture, this merging can be perturbed to give rise to separate smaller teeth, confirming the potential of the developing egg tooth to form two teeth. Conclusions Our data agrees with previous hypotheses that during evolution one potential mechanism to generate a large tooth is through congrescence of multiple tooth germs and suggests that the ancestors of snakes could have had two egg teeth.

Tooth germs undergo a series of dynamic morphologic changes through bud, cap, and bell stages, in which odontogenic epithelium continuously extends into the underlying mesenchyme. During the transition from the bud stage to the cap stage, the base of the bud flattens and then bends into a cap shape whose edges are referred to as “cervical loops.” Although genetic mechanisms for cap formation have been well described, little is understood about the morphogenetic mechanisms. Computer modeling and cell trajectory tracking have suggested that the epithelial bending is driven purely by differential cell proliferation and adhesion in different parts of the tooth germ. Here, we show that, unexpectedly, inhibition of cell proliferation did not prevent bud-to-cap morphogenesis. We quantified cell shapes and actin and myosin distributions in different parts of the tooth epithelium at the critical stages and found that these are consistent with basal relaxation in the forming cervical loops and basal constriction around enamel knot at the center of the cap. Inhibition of focal adhesion kinase, which is required for basal constriction in other systems, arrested the molar explant morphogenesis at the bud stage. Together, these results show that the bud-to-cap transition is largely proliferation independent, and we propose that it is driven by classic actomyosin-driven cell shape–dependent mechanisms. We discuss how these results can be reconciled with the previous models and data.

In this study, we attempted to localize the immunoreactivities of podoplanin/E11/gp38 and CD44, a counterpart possessing a high affinity to podoplanin/E11/gp38, as well as endomucin-immunoreactive blood vessels in the regions of odontoblast layers and the underlying sub-odontoblastic layers in murine tooth germs. Endomucin-reactive small blood vessels were scattered throughout the dental papillae of the tooth germs at postnatal day 1 but came to be localized close to the odontoblast/sub-odontoblastic layers until day 3. After postnatal day 5, small blood vessels were seen in odontoblast cell layers, while blood vessels with relatively larger diameters were seen forming in sub-odontoblastic layers. Immunoreactivities of podoplanin/E11/gp38 and CD44 were not detectable in the cells of dental papillae facing the inner enamel epithelium at postnatal day 1. However, at around postnatal days 3-5, podoplanin/E11/gp38 was localized in the odontoblast layer but not in the sub-odontoblastic layer, whereas CD44 was observed in the sub-odontoblastic layer but not in the odontoblast layer. The exclusive immunolocalization of podoplanin/E11/gp38 and CD44 in the odontoblast layers and sub-odontoblastic layers was seen after postnatal day 3 of the tooth germs, when the mesenchymal cells of dental papillae have already differentiated into mature odontoblasts at the cusp tip. Taken together, it seems likely that endomucin-reactive small blood vessels extended to the podoplanin/E11/gp38-positive odontoblast layers, whereas endomucin-reactive large blood vessels were already present in CD44-immmunopositive sub-odontoblastic layer, indicating the cellular regulation on the vascularization of endomucin-reactive endothelial cells during odontogenesis of the tooth germs.

Biological hard tissue structures can only be fully comprehended through a thorough understanding of developmental mechanisms. This is possible to achieve by studying living animals. We limit our coverage here to dental tissues in extant mammals. We describe mammalian tooth germs, the embryonic origins of dentine, enamel and cementum and the basics of tooth form. We explore the histology of dental tissues in respect to variability in cell behaviors, matrix and mineralization strategies, their periodic and sometimes aperiodic growth expression and the adaptive structural patterns that emerge. We also relay the advantages and pitfalls of preparation and imaging methods particularly useful to the paleohistologist. We are particularly focused on the sophisticated heterodont dentitions of mammals among the gnathostomes. Yet, the diversity explored here is expected to be a vast underestimation of the real variability among living and extinct mammals.

The transparency of soft tissue in Xenopus laevis tadpoles and the anterior-posterior orientation of their developing tooth germs in the upper jaw offer a unique opportunity for the in vivo charting of the first 15-20 days of the developing dentition. Twenty-two X. laevis tadpoles were anesthetized daily and their mouths opened to record the first appearance, position, and development of tooth germs in the upper jaw. The initiation patterns revealed considerable variability between animals, and even between the jaw quadrants in the same animal. This variability appears within a structural boundary and the results are consistent with the presence of an odontogenic band. The final length of dental rows far exceeded the jaw growth for each quadrant during the recording period. This in vivo investigation underlines the limits of cross-sectional studies, and in particular the assumption that tooth germs initiate at the same position in the dental row. The tooth germ initiation patterns in this study did not align with the predictions of standard models for the development of the dentition-Zahnreihen, Clone, and New Progress Zone theories.

Tissue engineering offers to restore the lost tooth using a biological analogue grown from the tooth germ. These technologies provide long-term cultivation of the germ in bioreactor in vitro. The subsequent transfer and growth of the in vitro grown tooth in the jaw is hampered by difficulty of integration of the new tooth with the host tissue. We suggested that growing tooth by homotopic transplantation in situ, that is, immediately in the jaw passing the in vitro stage will help to solve these problems. The aim of the work was to test the hypothesis. The principal possibility of transfer of the tooth germ directly into the jaw and cultivation in situ eliminating the stage in vitro is shown. The results showed a good integration of the grown teeth with the jaw without signs of inflammation and with the appearance of blood vessels in the pulp. At the same time, the results also showed the necessity to improve the preparation of tooth germs for transplantation and surgical procedures.Тканевая инженерия предлагает восстанавливать утраченный зуб с помощью биологического аналога, выращенного из зачатка зуба. Эти технологии предусматривают длительное культивирование зачатка in vitro в биореакторе. Последующие перенос и рост выращенного in vitro зуба в челюсти затруднены сложностью интеграции нового зуба с тканью хозяина. Мы предположили, что выращивание зуба с помощью гомотопической трансплантации зачатка in situ, т.е. сразу в челюсть, минуя стадию in vitro, поможет решить эти проблемы. Цель работы - проверка этой гипотезы. Показана принципиальная возможность переноса зачатка зуба сразу в челюсть, и выращивания in situ, исключая этап in vitro. Результаты показали хорошую интеграцию выросших зубов с тканями челюсти, без признаков воспаления и появлением в пульпе кровеносных сосудов. Вместе с тем результаты также показали необходимость совершенствования подготовки зачатка зуба к пересадке и хирургическим манипуляциям.

The appearance pattern of pharyngeal tooth germs was investigated in the larval Japanese dace, Tribolodon hakonensis, which has a bilaterally asymmetrical dentition. Teeth develop in a series of replacement waves beginning with the initial central tooth (Ce) and continuing with teeth of anterior (An) and posterior (Po) positions relative to the initial one. Identified by wave number (n) and tooth position (r), according to the formula n-1 [r], tooth germs appeared in the order of tooth 0 [Ce0], 1 [Po1], 1 [Anl], 2 [Ce0], 2 [An2], 3 [Po1], 3 [An1], 4 [Ce0], 4[An2], 5 [Po1], 5 [An1], 5 [An3], 6 [Ce0], 6 [An2] during the larval period. Dentition on the right side, however, lacks the first tooth at position An2 (tooth 2 [An2]) and teeth at position An3. Tooth germs on the first, second, and third replacement waves appeared simultaneously on the arches of both sides. During following waves, tooth germs on the left side appeared later than those on the right. Delay of tooth germ appearance On the left side is interpreted as an inhibitory influence of existing tooth germs in accordance with Osborn's (Proc. R. Soc. Lond. Ser. B 179:261--289, '71) theory. The delay of tooth germ appearance on the left arch is most pronounced on the seventh replacement wave. Teeth of the right major row in adults of this species are replaced more frequently than those of the left major row, apparently in correlation with the absence of the first larval tooth at position An2 and teeth at position An3. It is hypothesized that cyprinids evolved the minor rows and specialized teeth of their adult dentition as apomorphic characteristics by the process of neoteny.

Background Mismatch repair proteins (MMRPs) are a group of nuclear enzymes that participate in the repair of base mismatches that occur during DNA replication in all proliferating cells. The most studied MMRPs are hMSH2 and hMLH1, which are known to be highly expressed in normal tissues. A loss of MMRPs leads to the accumulation of DNA replication errors in proliferating cells. Ki-67 is a biomarker regarded to be the gold-standard tool for determining cell proliferation by immunohistochemical methods. The aim of this study was to investigate the immunohistochemical expression of hMLH1, hMSH2 and Ki-67 proteins in ameloblastomas and tooth germs, to contribute to the understanding of the development of this odontogenic neoplasm. Material and Methods Immunohistochemical assays to determine the presence of proteins hMSH2, hMLH1 and Ki-67 were performed in 80 ameloblastomas (40 solid and 40 unicystic) and five tooth germs. Results Unicystic ameloblastomas showed higher MMRP expression (hMLH1: 62.5 ± 43.4; hMSH2: 83.3 ± 47.8) than did solid ameloblastomas (hMLH1: 59.4 ± 13.5; hMSH2: 75.8 ± 40.2). Additionally, the cell proliferation index assessed by Ki-67 was inversely proportional to the expression of MMRP. Comparison between tooth germs and ameloblastoma revealed significantly higher expression of hMLH1, hMSH2 and Ki-67 in tooth germs (p=0.02). Conclusions The differences of MMRP and Ki-67 immunoexpression between ameloblastomas and tooth germ suggest that alterations in the MMRP mechanisms could participate in the biological behavior of ameloblastomas. Key words:hMLH1, hMSH2, Ki-67, Ameloblastomas, Tooth germs.

Introduction Nomads move from one settlement to another, thus it has been difficult to have adequate documentation about their oral health and that of their children. Aim To investigate the perception and practices of nomadic Fulani women toward their children’s oral health. Methodology A cross-sectional study was conducted among 197 Fulani women using a structured interviewer administered questionnaire. Results Perceived causes of tooth decay included tooth germs/worms (23.9%) and sugar (5.1%), and 32.0%, 15.2%, and 5.1%, respectively, self-medicated children with antibiotics, traditional concoctions/herbs, and analgesics for tooth decay. Two fifths (40.1%) attributed bleeding gums to tooth germs/worms. Polyurethane foam (46.7%), toothbrush (32.0%), finger (18.8%), and wooden twigs (2.5%) were aids used for cleaning children’s teeth. Conclusions These mothers have suboptimal oral health knowledge, attitudes, and practices toward their children’s oral health. There is a need for urgent intervention among this group of people.

Ectodermal dysplasia (ED) is an anomaly determined by genetic factors that alter ectodermal structures such as skin, hair, nails, glands, and teeth. Children affected by this condition require extensive, comprehensive, and multidisciplinary treatment. An 8-year-old female patient visited the Dentistry Clinic of the Federal University of Santa Catarina with the chief complaint of multiple missing teeth. The mother reported that the patient had ED. Clinical and radiographic examination revealed the congenital absence of several primary and permanent teeth and tooth germs. Subsequent oral rehabilitation comprised the application of a maxillary denture and mandibular implant-supported fixed prosthesis. The child was also supplied with a wig for further enhancement of esthetics aimed at improving her emotional wellbeing. Psychological follow-up and speech therapy were also provided. After 4 years of follow-up, implant-supported oral rehabilitation has proved to be a satisfactory treatment option, allowing restoration of masticatory, phonetic, and esthetic function, as well as an improvement in the patient's self-esteem and social wellbeing.

The presence of bilateral fusion of teeth in permanent dentition is an unusual and rare condition. It is a developmental anomaly characterized by the union of two separate tooth germs during formation. The case of a 9 year old boy with fusion of permanent maxillary central incisors with associated bilateral disto-palatal rotation was examined. The fused maxillary incisors were treated conservatively using an aesthetic restorative material. The purpose of this report is to review the literature related to bilateral fused maxillary permanent teeth and its aesthetic treatment. Keywords: Bilateral fusion, fused teeth, maxillary incisors, treatment

섬유성이형성증은 정상적인 골조직이 섬유성 조직으로 대체되는 특징을 가진 질환으로 해면골 내에 불규칙한 골소 주가 형성되며 상악과 하악을 포함하여 두개 안면골에 흔하 게 나타난다. 골의 크기와 모양 변화를 초래하는 양성 섬유골성 병소이며 체세포의 Gsα유전자 변이와 연관되어 나타 나는 것으로 알려져 있다. 1938년 Lichtenstein과 1942 년 Jaffe에 의해 보고되었으며 양성 골 종양의 5-7% 정도 를 차지하고 어느 연령에서나 발병할 수 있으나 특히 3세15세 사이에서 가장 많이 발병하는 것으로 알려져 있다. 섬유성이형성증의 임상적 특징으로는 우연히 발견되는 경우가 많으며 대부분 통증이 없어 환자가 병소를 인지하지 못하는 경우가 많다. 그러나 병소가 진행되면서 기형, 골 통 증, 피로 골절 및 병적 골절이 발생할 수 있으며 피부에 cafe′-au-lait 반점이 발견되기도 한다. 방사선학적으로 경 계가 불분명한 방사선 투과상과 불투과상이 혼재되어 있으 며 간유리 모양의 패턴을 나타내는 것이 특징이다. 조직학 적으로 미성숙한 골소주가 중국문자모양으로 관찰된다. 본 증례는 만 7세 여환이 하악 좌측 유구치 부위 잇몸이 부었다는 주소로 연세대학교 치과대학병원 소아치과에 내 원한 환아로 섬유성이성형증에 의한 안면비대칭이 관찰되 어 보고하고 그에 따른 합병증을 논의해보고자 한다.

Objective: This study aimed to determine changes in odontogenesis arising from prenatal and postnatal protein-calorie malnutrition. Materials and methods: Twelve adult Wistar rats were selected; 8 females and 4 males. The females were divided into two groups, one of which received a normoproteic diet (NG) and the other received a hypoproteic diet (HG). After the birth of the litters, 24 pups were randomly separated from each group. The animals were sacrificed, 12 at five-days old and 12 at eight-days old, and their jaws were subjected to histological preparation to obtain cuts of tooth germs. Forty-eight slides were selected that presented the germs properly cut (24 from each group), which were analyzed by microscopy and measured by a calibrated examiner. The differences between means were verified by the nonparametric Mann-Whitney test. Results: The results showed that at 5 days the differences in thickness of enamel and dentin were statistically significant between NG (84.08 ± 28.9 and 141.51 ± 33.2; p = 0.026) and HG (47.26 ± 43.8 and 91.19 ± 54.7; p = 0.006). At 8 days of life there were no significant differences between the groups. Conclusion: The results showed evidence of the impact of malnutrition on the thickness of dental tissues. It is suggested that further work is carried out in this line of research with more complex designs.

Objective: The purpose of this study was to estimate the feasibility and accuracy of mesio-distal width measurements with magnetic resonance imaging (MRI) in comparison to conventional 3D imaging techniques [multi-slice CT (MSCT), cone-beam CT (CBCT), and µCT]. The measured values of the tooth widths were compared to each other to estimate the amount of radiation necessary to enable orthodontic diagnostics. Material and Methods: Two pig skulls were measured with MSCT, CBCT, µCT, and MRI. Three different judges were asked to determine the mesio-distal tooth width of 14 teeth in 2D tomographic images and in 3D segmented images via a virtual ruler in every imaging dataset. Results: Approximately 19% (27/140) of all test points in 2D tomographic slice images and 12% (17/140) of the test points in 3D segmented images showed a significant difference ( P ≤ 0.05). The largest significant difference was 1.6mm ( P < 0.001). There were fewer significant differences in the measurement of the tooth germs than in erupted teeth. Conclusions: Measurement of tooth width by MRI seems to be clinically equivalent to the conventional techniques (CBCT and MSCT). Tooth germs are better illustrated than erupted teeth on MRI. Three-dimensional segmented images offer only a slight advantage over 2D tomographic slice images. MRI, which avoids radiation, is particularly appealing in adolescents if these data can be corroborated in further studies.

Teething is a dynamic and continuous phenomenon that begins in odontogenesis, where tooth germs are detached from the dental lamina. Any alteration of the enamel structure may be due to environmental or hereditary factors, which intervenes during the formation of the ameloblasts and may cause defects in the quantity and shape of the enamel or in quality and color. Molar Incisor Hypomineralization (HMI) describes the clinical appearance of hypomineralized enamel of systematic origin that affects one or more of the first permanent molars, sometimes affected or not the incisors. La dentición es un fenómeno dinámico y continuo que inicia en la odontogénesis, donde los gérmenes dentarios se desprenden de la lámina dental. Cualquier alteración de la estructura del esmalte puede ser debido a factores ambientales o hereditarios, que interviene durante la formación de los ameloblastos pudiendo provocar defectos de cantidad y de forma del esmalte o en calidad y color del mismo. La Hipomineralización Molar Incisivo (HMI) describe la apariencia clínica del esmalte hipomineralizado de origen sistemático que afecta a uno o mas de los primeros molares permanentes, algunas veces afectado o no los incisivos.

Fusion is a common dental anomaly affecting both primary as well permanent dentitions. Fusion is the union between two normally separated tooth germs. The problems associated with fused teeth are esthetics, arch symmetry, spacing, and malocclusion. These problems require cosmetic and orthodontic consideration.

A few decades ago, relatively little was known concerning the pre-eruptive spatial development of permanent molars. The material that formed the basis for this study consisted of 114 dry human mandibles of young children and adolescents. Measurements were made on radiographs of the bony crypts in which the tooth germs had existed ante mortem and the pattern of spatial development was studied macroscopically and histologically. The findings revealed a consistent developmental pattern, in which the means of expansion of the crypts of the second and third molars, prior to crown-calcification, displayed strong similarities. The displacements as they were indicated by the measurements on the radiographs were confirmed by the macro- and micro-morphological study of the bone surfaces. The mesio-distal relationship of adjacent crypts appeared to be influenced by morphological characteristics of the mandible early on in their development. New insights have not been achieved subsequently, up to the present day, because little follow-up research into the spatial development of the bony crypts has been undertaken.

Pediatric mandibular fracture needs special consideration by clinicians. The management of pediatric mandibular fracture differs from that in adults considering the presence of tooth germs and the potential for mandibular growth. One of the most common forms of conservative management for pediatric mandibular fractures is the use of cap splint along with circummandibular wiring. The conventional workflow prior to performing surgery with this technique is impression taking and dental model fabrication. Additionally, it is also recommended that mock surgery should be performed to achieve proper reduction before acrylic splint fabrication. However, these procedures are effortful and time consuming when performed under general anesthesia during surgery and require additional sedation if performed prior to surgery. The aim of this case report is to describe a simpler preoperative digital workflow for the treatment of pediatric mandibular fractures, in which closed reduction is achieved with a three-dimensional printed cap splint stabilized with circummandibular wiring under general anesthesia.

The diphyodont tooth replacement in mammals is characterized by a single replacement of a deciduous dentition by a permanent dentition. Despite its significance in mammalian biology and paleontology, little is known about the developmental mechanisms regulating the diphyodont replacement. Because the mouse never replaces its teeth, this study used the house shrew, Suncus murinus, as a model to investigate the control of the diphyodont replacement of a deciduous dentition by successions and additions of permanent teeth. Using morphological and gene expression analyses of serial sections, we have demonstrated the development of the upper dentition of the house shrew. In this species, the deciduous tooth germs are formed but soon become vestigial, whereas the successional and accessional (molar) germs are subsequently formed and developed. There are distinct Shh expression domains in the deciduous, successional, and accessional tooth germs, and those of the latter two germs are identified from the appearance of their primary enamel knots. The developmental sequence of tooth germs in the house shrew indicates that two adjacent primary enamel knots of the successional and accessional germs do not develop simultaneously, but with a constant time lag. We suggest that this mode of tooth succession and accession can be explained by a sequential inhibitory cascade model in which the timing of initiation and the spacing of tooth development are determined by the inhibition from the primary enamel knots of developmentally preceding adjacent tooth germs.