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Introduction: A former study on orthopantomograms from young children with abnormal dental development (not canine ectopia) demonstrated that the tooth bud of the mandibular canine, compared to a stable longitudinal canine axis, could be located normally, anteriorly or posteriorly, with close relation to the first premolar., Aim: The aim of the present study is to analyse on orthopantomograms if the canine axis can demonstrate where the ectopic mandibular canine started tooth formation., Materials: The material consists of orthopantomograms with ectopic mandibular canines and presence of primary mandibular canines from 47 cases (29 cases 9-21 years old and 18 cases with unknown ages). The primary canines demonstrated from minor apical resorption to more severe apical resorption., Methods: Based on canine maturity, location of the canine axes and the interrelationships between the roots of the permanent canine and first premolar, the location from where the canine started tooth formation was determined. Canine maturity. Maturity stage below half root length and maturity stage above half root length revealed that 11 ectopic canines had less than half root length and 36 cases more than half root length. Canine axes. The canine axis, through the length of the primary canines Ax, is inserted on drawings of the orthopantomograms using the tracing programme Inkscape®. Interrelationship between roots. By visual inspection, the distance between the canine and first premolar was designated close distance, normal distance and extended distance., Results: The results are divided into 3 groups. Group 1: The initial site of the permanent ectopic canine is located within the canine axis (6 cases). Group 2: The initial site of the permanent ectopic canine is located posterior to the canine axis (36 cases). Group 3: The initial site of the permanent ectopic canine is located anterior to the canine axis (5 cases)., Conclusion: The study explained that the canine axis could divide cases of ectopic canines into three groups according to the location from where tooth formation starts. For getting closer to the pattern of the ectopic canine eruption, it is necessary to analyse series of orthopantomograms taken from the same individual over several years., (© 2024. The Author(s).)

Objectives: To evaluate dental maturity in the mandibular canine/premolar and molar innervation fields in children with agenesis of the 2nd mandibular premolar and to associate these findings with normal control material., Setting and Sample Population: Department of Orthodontics, Institute of Odontology, University of Copenhagen. Eighty-three panoramic radiographs (27 girls and 31 boys with agenesis of one mandibular 2nd premolar and 17 girls and eight boys with agenesis of both mandibular 2nd premolars) represented all mandibular second premolar agenesis cases from a material of 2847 radiographs., Material and Methods: On each radiograph, dental maturity of all available mandibular premolars, canines and 2nd molars was evaluated and categorized in maturity stages according to Haavikko whose material served as control material. Descriptive statistics given by sample mean, standard deviation and range for each tooth stratified by gender and agenesis. Ninety-five percentage confidence limits and T-statistics were used. p-values <5% were considered significant., Results: In unilateral agenesis, the canines are specifically delayed in both girls and boys, with a larger delay in girls (p=0.009). The second molar is not delayed in boys (p=0.98) but is in girls (p=0.04). The differences in delay for the canine compared to the second molar are significant for both girls and boys. The results show a considerable delay in tooth maturation within the canine/premolar innervation field predominantly in girls. The 2nd molar is delayed in girls but not in boys., (© 2010 John Wiley & Sons A/S.)

The aim of this study was to analyse the correlation between external and internal mandibular morphology in adult or adolescent normal anthropological mandibles. Lateral radiographs of 31 symmetrical mandibles were analysed. The external morphology was defined by the gonial and beta-angles. In order to analyse internal morphology, a metallic pin was placed in the mental canal on the left side before radiography. The angle between the mental and the mandibular canals was termed the 'mental angle' and that expressing the curvature of the mandibular canal, the 'mandibular angle'. Spearman correlation analysis was used to investigate the relationships between the angles. Internal morphology: a statistically significant correlation was found between the mental and mandibular angles (correlation coefficient: -0.60, P=0.0004). When the mental angle was narrow, the mandibular angle tended to be wide, while a wide mental angle was interrelated with a narrow mandibular angle. External morphology: a statistically significant correlation was found between the mandibular and gonial angles (correlation coefficient: 0.57, P=0.0009). A weaker correlation was also found between the mandibular and beta-angles. The findings show that the internal courses of the mandibular and mental canals are interrelated. They also indicated that the course and morphology of the mandibular canal are interrelated with external mandibular morphology.

Objectives: The purpose was to examine human osteoblasts immunohistochemically in order to clarify the significance of the innervation for alveolar bone growth., Setting and Sample Population: Unstained sections available from 21 normal human mandibles (foetal gestational ages: 14-22 weeks)., Material and Methods: Before sectioning in 1980-1990, the mandibular tissue had been fixed in 4% neutral-buffered formaldehyde for 5 days. Tissue blocks were then decalcified in equal parts of 2% citric acid and 20% sodium citrate for 7-15 days, dehydrated, embedded in paraffin, and sagittally cut into 4-mum-thick serial sections and mounted on Superfrost Plus microscope slides. Sections were dried overnight at 40 degrees C. In the present study, paraffin sections were deparaffinized and treated with Tris-EDTA (Merck, Germany), pH 9.0, and immunohistochemically tested with polyclonal rabbit anti-PGP 9.5, and the EnVision +/HRP dual link (K4065; DAKO Denmark A/S, Denmark) method., Results: A pronounced protein gene product (PGP) 9.5 activity was registered in osteoblasts from alveolar bone in all specimens. In all cases, the activity was intense at the top of and labially to the alveolar bone, while less or no activity was observed on the inner lingual aspects of the alveolar processes. Osteoclasts and osteocytes reacted vaguely or negatively., Conclusion: As the present study has demonstrated that human osteoblast activity in the alveolar bone seemingly responds to innervation, it is suggested that the peripheral nervous system via the trigeminal ganglion regulates compensatory and dysplastic alveolar bone formation.

Objectives: To explore the relationship between mandibular dental maturation and the pattern of jaw innervation., Setting and Sample Population: The sample included 365 panoramic radiographs taken in the period 1965-1969 in a Danish municipality., Design: For assessing dental maturity, the seven left mandibular teeth (M2, M1, P2, P1, C, I2, I1) were given a dental maturity score according to a method introduced by Demirjian. Spearman correlation coefficients between the maturity score of an index tooth (one of each teeth) and the maturity score of the 6 other teeth was calculated and illustrated., Results: All the correlation coefficients were larger than 0.5 indicating a rather high level of association between the development of mandibular teeth in the same individual. Thus, associations between the pattern of dental maturation and jaw innervation were not obvious., Conclusion: When the correlation between the dental maturity stages was analysed, no significant relation was found between dental maturation and jaw innervation in the mandible. This is interesting considering the results presented in a recent study, which showed that the clinical observed tooth eruption was closely related to the pattern of jaw innervation. Those authors suggested that the factors influencing the eruption might be associated with jaw innervation. In our study, the stepwise dental maturation process, however, is not equally associated with jaw innervation.

The purpose of the present study was to investigate whether the course of Meckel's cartilage could reveal the mandibular movements during the elevation and fusion of the soft tissue palatal shelves. Histological sections, cut serially in the horizontal plane from 64 human mandibles, 16-104 mm CRL, were analyzed. The course of the anterior and medial part of Meckel's cartilage changed markedly during the three palatal stages, i.e., before, during, and after palate formation. The medial part changed during these stages from a straight course through a curled, S-shaped course to a crochet-hook-shaped course. The anterior part of Meckel's cartilage developed from a separation in the symphysis menti region to a fusion and later to a separation again. It is suggested that these changes in the course of Meckel's cartilage are due to different muscle activities. It is supposed that during the palatal developmental stages the activity of the geniohyoid and genioglossus muscles caused the mandibular retraction and the widening of the angulation between the bilateral hemimandibles. The S-shape of Meckel's cartilage is a result of these movements. Later mandibular proclination and narrowing of the bilateral hemimandibles resulted in an anterior mechanical fusion of Meckel's cartilage due to the activity of the mylohyoid muscle. This stage is followed by a retraction and re-widening of the angulation between the bilateral bony components, which disrupts the fusion of Meckel's cartilage in the symphysis menti region. Thus, the course of Meckel's cartilage revealed the mandibular movements in the sagittal and transverse planes during palate formation.

The purpose of this study was to describe the prenatal formation of the human mandibular canal. Since bony canals develop in prenatal life around the nerve paths, it was assumed that the canal pattern could reflect the pattern of innervation of the dentition. Mapping of this early canal pattern does not appear to have been undertaken before. The material consisted of anthropological mandibles from the National Institute of Anthropology and History, Mexico City. A total of 302 human hemimandibles from the latter half of the prenatal period was investigated. The length, measured from the mental symphysis to the mandibular condyle, ranged from 28 to 60 mm. The dento-alveolar maturity was classified in two stages according to the appearance of alveolar sockets of deciduous and first permanent molars. The mandibles were radiographed with guttapercha points inserted into the canal openings (foramina) on the lingual surfaces of the mandibular rami. The study showed that the canal to the incisors appeared first, followed by the canal to the primary molars, and last by the one or more canals to the first permanent molars. In the most mature group, three different canals always occurred in each hemimandible. The canals were directed from the lingual surface of the mandibular ramus toward the different tooth groups. The inferior alveolar nerve presumably occurs in the mandible as three individual nerve paths originating at different stages of development. It is suggested that rapid prenatal growth and remodeling in the ramus region result in a gradual coalescence of the canal entrances that is obvious at birth. It is hypothesized that the pattern of tooth agenesis within the three groups of teeth is related to the three separate paths of innervation of the dentition.

Serial sections of eleven human mandibles of embryos and fetuses ranging in size from 18 mm CRL to 66 mm CRL were computer-graphically reconstructed. The extension of the Meckel cartilage and the mandibular bony structures were morphometrically studied. In emphasis the study encompassed measurements portraying length, width, dorsal opening angle, and the position of the mental foramen. In addition five mandibles of human embryos and fetuses with a size range between 30 and 50 mm CRL were radiographically examined. Results showed that in the younger specimens between 21 and 29 CRL size development of the structures of the mandible and the development of overall fetal body size take place independently from each other. During further development a change in the form of the mandible from a wide V over an acute V to a more rounded U form was observed.

A Danish anthropological collection of medieval human skeletons excavated in 1986 involves a mandible (No. 212) from an adult female born without the lower alveolar nerve and mandibular canal. It is believed that the defect has resulted in lack of tooth development on the affected side and that the mylohyoid nerve has partially compensated for this defect by development of teeth in localized areas. The defective mandibular dentition has caused a compensatory development of the alveolar process in the maxilla. The missing occlusal support has altered muscular traction on the mandible. This has caused an alteration in mandibular shape. Whether the asymmetric development of the mandible is caused by muscular dysfunction, by failure in angular growth apposition, or by a combination of these factors is discussed. The case presents valuable data in the ongoing discussion about the interaction between nerve tissue and tooth formation and about the interaction between occlusion, jaw morphology, and muscular traction. The study shows how archeological material in an interdisciplinary cooperation between archeological, embryological and orthodontic research can contribute to the clarification of current biological problems.

The formation and early prenatal location of the human mental foramen was investigated on 43 human fetuses. Histochemical methods supplemented by macroscopic visualization were used. Similar studies on the mental foramen were not available in the literature. The study demonstrated constancy in the developmental sequence of the bony structures in the region of the mental foramen. The formation of the mental foramen was described and related to general developmental parameters such as CRL and CNO values (skeletal maturity indexes of the hand and foot). The study indicated that the very early position of the mental foramen was in the region of the interstitial bone between the primary canine and the primary first molar. A positional change in the dorsal direction was described during the first half of the prenatal period.

On the basis of morphological and histochemical studies of 71 human mandibles from the former half of prenatal life, five stages (D I to D V) in the development of the deciduous mandibular incisors are described. These stages are related partly to general parameters of fetal development, such as M age (menstrual age), CRL (crown-rump length), CNO (composite number of ossified bones in hand and foot) and partly to stages in the skeletal development of the symphysis menti (SM I to SM V). The investigation revealed close relationship between the development of the deciduous mandibular incisors and the skeletal development of the deciduous mandibular incisors and the skeletal development of the mandible in the region of the incisors. No such relationship was found between the development of the deciduous mandibular incisors and general parameters of fetal development.

In 51 human fetuses from the first half of the prenatal period, developmental stages in the symphysis menti and the mandibular condyle were assessed by histochemical reactions. The study showed the association between the timing of the developmental stages in the two mandibular growth zones.

Structured Abstract Authors – Kjær I, Nolting D Objectives – The purpose was to examine human osteoblasts immunohistochemically in order to clarify the significance of the innervation for alveolar bone growth. Setting and Sample Population – Unstained sections available from 21 normal human mandibles (foetal gestational ages: 14–22 weeks). Material and Methods – Before sectioning in 1980–1990, the mandibular tissue had been fixed in 4% neutral-buffered formaldehyde for 5 days. Tissue blocks were then decalcified in equal parts of 2% citric acid and 20% sodium citrate for 7–15 days, dehydrated, embedded in paraffin, and sagittally cut into 4-μm-thick serial sections and mounted on Superfrost® Plus microscope slides. Sections were dried overnight at 40°C. In the present study, paraffin sections were deparaffinized and treated with Tris-EDTA (Merck, Germany), pH 9.0, and immunohistochemically tested with polyclonal rabbit anti-PGP 9.5, and the EnVision™+/HRP dual link (K4065; DAKO Denmark A/S, Denmark) method. Results – A pronounced protein gene product (PGP) 9.5 activity was registered in osteoblasts from alveolar bone in all specimens. In all cases, the activity was intense at the top of and labially to the alveolar bone, while less or no activity was observed on the inner lingual aspects of the alveolar processes. Osteoclasts and osteocytes reacted vaguely or negatively. Conclusion – As the present study has demonstrated that human osteoblast activity in the alveolar bone seemingly responds to innervation, it is suggested that the peripheral nervous system via the trigeminal ganglion regulates compensatory and dysplastic alveolar bone formation. [ABSTRACT FROM AUTHOR]