Interrelationships of dental maturity, skeletal maturity, height and weight from age 4 to 14 years.

The correlations of dental mineralization stages, skeletal mineralization, body-height and weight were determined for each year between age 4 and 14 for 121 boys and 111 girls of the serial experimental group of the Burlington Growth Centre. Dental development related more strongly to morphological development than to skeletal development in both sexes, and skeletal age was more strongly related to morphological age than to dental stage. The relationship of individual teeth to skeletal age, height and weight were different but consistent in a sex-specific pattern. In males, both skeletal mineralization and dental mineralization, particularly of the first molars, were more closely related to height than to weight. In the females, skeletal and dental mineralization, especially of the second molars, were more closely related to weight from age 7 than to height. These relationships were significant in both pre-adolescent and adolescent years. In both these periods, skeletal age and body size related most strongly to late stages of tooth formation. Hence, from an early age, the stages of dental, skeletal and morphological maturation were significantly interrelated in a pattern that was specific for individual teeth and for sex.     

Dental and skeletal growth in early fossil hominins

Early fossil hominins have often been assigned a chronological age on the basis of modern human data for tooth eruption. Better data and more sophisticated methods are now available to estimate their chronological age from modern human standards for stages of mineralization of individual teeth developing within the jaws. However, while comparisons with modern human dentitions are interesting, they can also be misleading as early hominin teeth and dentitions did not grow like modern human teeth. Chronological age can also be estimated using the microanatomy of tooth enamel and root dentine. Counts of incremental markings in enamel predict much younger ages at death for early fossil hominins than those based on modern human radiographic standards of dental development. Comparative evidence from the skeleton suggests that a greater proportion of adult body mass and stature was achieved earlier in the growth period of fossil hominins than it is in modern humans. The combined skeleto-dental evidence provides the basis for a hypothesis that the earliest hominins grew more like modern great apes, but that Homo erectus had a slightly more prolonged period of growth, and which was still not totally modern human-like in its pattern or timing.     

New systems for dental maturity based on seven and four teeth

An updated system for estimating dental maturity is presented. It extends the original system (Demirjian et al., 1973) based on radiographs of 7 teeth by including two extra stages, and by enlarging the standardizing sample to include 2407 boys and 2349 girls. Percentile standards from ages 2·5 to 17·0 years are presented separately for boys and girls.

Scoring systems and percentile standards are presented for two different sets of 4 teeth and a comparison of all three systems is made. It is suggested that these systems may measure somewhat different aspects of dental maturity.     

Dental age assessment for Kuwaiti children using Demirjian's method

Background: Dental age can be estimated based on the level of tooth mineralization during the developmental process. Various methods of determining chronological and radiographical stages have been used for dental age estimation.

Aim: To test the validity of the standards of dental maturation of Demirjian and Goldstein (Ann Hum Biol 3:411–421, 1976) when applied to Kuwaiti children.

Subjects and methods: The sample was selected from healthy Kuwaiti children attending the routine and emergency dental clinics of the Faculty of Dentistry, Kuwait University. Good quality rotational pantomographs were obtained for 509 children (263 girls and 246 boys) between 3 and 14 years. Maturation of the seven permanent teeth on the left side of the mandible was determined according to the crown and root development stages described by Demirjian et al. (Hum Biol 45:211–227, 1973).

Results: There were statistically significant differences in the mean of dental maturation between Kuwaiti and French–Canadian children (p<0.0001). Kuwaiti children were dentally delayed compared to the Canadian standards (mean dental maturation difference of 0.69 year, SD=1.25 years, CI=0.58–0.80). The mean delay in girls was 0.67 year (SD=1.30 years, CI=0.51–0.83) and in boys it was 0.71 year (SD=1.18 years, CI=0.56–0.86). Using a non-linear regression model, function formulae were developed for Kuwaiti girls and boys.

Conclusion: The standards of dental maturation described by Demirjian and Goldstein (1976) may not be suitable for Kuwaiti children.     

Craniofacial and dental phenotype of Smith-Magenis syndrome

The aim of this study was to assess and characterize dental and craniofacial findings in individuals with a confirmed diagnosis of Smith-Magenis syndrome (SMS). Extraoral and intraoral examination including dental and craniofacial radiographs and three-dimensional facial photoimaging were performed for 15 cases between ages 4 and 19 years old. Tooth agenesis (13/15 cases) affecting primarily the mandibular second premolars and taurodontism (13/15 cases) were common findings. Dilaceration of the tooth roots was present in one-third of the cases. At least one dental anomaly was present in each case. These findings occur with greater frequency than in the general population (P < 0.001). An age-related increase in decayed and restored teeth was found. Poorer oral hygiene, increased dental plaque, and increased gingival inflammation progressed from childhood to teenage years. Radiographic findings suggest the prognathic appearance is not caused by excessive mandibular growth. Other findings including protrusion of the mandibular anterior teeth, increased bony chin size, and macroglossia were noted, which may contribute to the prognathic appearance. The high prevalence of dental anomalies (>90%) further expands the phenotype and indicates that dental evaluation may aid in the diagnosis of SMS.     

Dental age estimation in a group of Kenyan children using Willems’ method: a radiographic study

Background: Radiographic study of developing teeth provides a reliable indication of chronological age. In Kenya, dentists are often required to estimate age. However, there is a paucity of publications on the performance of dental age estimation methods.

Aim: To determine the accuracy of Willems’ method of dental age estimation.

Subjects and methods: A cross-sectional study was done at The University of Nairobi Dental Hospital. Panoramic radiographs of children aged 3.00–16.99 years old were studied. Dental age was estimated according to Willems’ method and compared to chronological age and the difference compared to zero using a t-test.

Results: Radiographs of 187 (47%) females and 214 (53%) males were analysed. Willems’ method significantly over-estimated the mean overall age by –0.24?±?1.17 years (p?p?=?.254); however, age in boys was significantly over-estimated by –0.37?±?1.14 years (p?Conclusions: Willem’s model over-estimated dental age slightly and the method performed better in estimating the age of girls compared to boys. The majority of the children had their age estimated within 1 year of their chronological age. This suggests that Willems’ method is suitable for estimating the ages of individual children in Kenya.     

Novel and Bizarre Abnormalities of the Tooth Row in Side-Blotched Lizards (Uta) and Rock Lizards (Petrosaurus)

Multiple tooth rows along the dentary or maxilla are present in many bony and cartilaginous fishes but occur infrequently in amniotes. Although two partially overlapping rows of teeth or a few doubled tooth positions were both previously reported in extant and extinct lizards, multiple rows of teeth across the entire dental or maxillary shelf were not previously documented in any lizard taxon. Here, we report one specimen of the side-blotched lizard Uta stansburiana and two specimens of the rock lizard Petrosaurus mearnsi that have two or more marginal tooth rows that overlap for most of the dental shelf. We also describe several other phrynosomatid lizard specimens with one or two doubled tooth positions per marginal tooth-bearing skeletal element. We examined 520 total specimens of pleurodont iguanian lizards and verified that aberrant tooth row and tooth position morphologies were almost exclusively present in phrynosomatid lizards. We hypothesize that developmental irregularities in the number of odontogenic bands or in the function of zones of inhibition may have resulted in the observed tooth row abnormalities. The expression of multiple tooth rows or doubled tooth positions may be phylogenetically informative morphologies of phrynosomatid lizards. This bears further investigation from developmental, genetic, ecological, and phylogenetic perspectives. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:2014–2025, 2020. © 2019 American Association for Anatomy     

The influence of wisdom tooth impaction on root formation.

The development of wisdom teeth occurs within a definite period of time. The correlation of wisdom tooth development and chronological age has been frequently used for several purposes, e. g. the start of orthodontic treatment, estimates of age or, for legal and anthropological purposes. Wisdom teeth are frequently impacted in the bone. It has been argued that the impaction of wisdom teeth can cause a delay in root development. This thesis could have bearing on age estimations in teenagers and young adults and the timing of dental treatment. The aim of this study was to determine whether the impaction of wisdom teeth influences the velocity of root formation. MATERIAL AND METHODS: The dental x-rays (orthopantomograms) of 1053 outpatients were evaluated (age: 14 to 24 years). The condition "impacted" or "not impacted" was registered for each wisdom tooth present. The impaction types were further classified. The data were then calculated using statistical tools. RESULTS: The correlation between the developmental stages of wisdom teeth and the chronological age is high. However, neither any impaction type nor the whole group of retained wisdom teeth showed a statistically significant different course of root development compared to the root development of non-retained wisdom teeth. DISCUSSION: This study provides evidence for the lack of bearing of wisdom teeth topography on the growth stages of the dental roots within definite time intervals, based on the evaluation of orthopantomograms only. Obviously, the variations of root formation in the selected chronological periods are greater than the variations attributable to possible periods of delay in root formation of retained wisdom teeth. These results could have some importance for the fields of dental anthropology and dentistry.     

A new method for assessment of dental maturity using the individual curve of number of erupted permanent teeth

A new method for the evaluation of dental age in healthy children, using the curve of the total number of erupted permanent teeth, is presented. The method is based on the observation that the curves of the total number of teeth erupted are parallel and similar in shape in different individuals provided that logarithms are used for both age and number of erupted teeth. The chronological age for a specific reference point on the eruption curve was determined graphically in individual subjects. At this age each child has reached the same degree of dental maturity. A group of 133 healthy boys and 137 girls was examined annually for seven years. The mean age at the reference point of the tooth eruption curve was 8.75 years for the boys and 8.44 years for the girls.     

Sibling correlations for skeletal age assessments by the Fels method

Sibling correlations are reported for Fels skeletal ages from 2,622 mixed longitudinal hand-wrist radiographs of 285 boys and 276 girls. Because the observed correlations were irregular across age, they were smoothed by using kernel regression. The brother-sister correlations were generally lower than those for the other types of silbling pairs, but they were similar to the brother-brother correlations after 11 years. The sister-sister correlations were considerably higher than the brother-brother and brother-sister correlations after 12 years. The present data do not provide clear evidence of involvement of the X chromosome in the timing of skeletal maturation, but after 12 years the present data suggest such an involvement.     

Complex patterns of tooth replacement revealed in the fruit bat (Eidolon helvum)

How teeth are replaced during normal growth and development has long been an important question for comparative and developmental anatomy. Non‐standard model animals have become increasingly popular in this field due to the fact that the canonical model laboratory mammal, the mouse, develops only one generation of teeth (monophyodonty), whereas the majority of mammals possess two generations of teeth (diphyodonty). Here we used the straw‐coloured fruit bat (Eidolon helvum), an Old World megabat, which has two generations of teeth, in order to observe the development and replacement of tooth germs from initiation up to mineralization stages. Our morphological study uses 3D reconstruction of histological sections to uncover differing arrangements of the first and second‐generation tooth germs during the process of tooth replacement. We show that both tooth germ generations develop as part of the dental lamina, with the first generation detaching from the lamina, leaving the free edge to give rise to a second generation. This separation was particularly marked at the third premolar locus, where the primary and replacement teeth become positioned side by side, unconnected by a lamina. The position of the replacement tooth, with respect to the primary tooth, varied within the mouth, with replacements forming posterior to or directly lingual to the primary tooth. Development of replacement teeth was arrested at some tooth positions and this appeared to be linked to the timing of tooth initiation and the subsequent rate of development. This study adds an additional species to the growing body of non‐model species used in the study of tooth replacement, and offers a new insight into the development of the diphyodont condition.     

Biomechanical Evaluation of Equine Masticatory Action: Position and Curvature of Equine Cheek Teeth and Age‐Related Changes

The equine cheek tooth battery is part of a very dynamic system. The aim of this study was to investigate whether the curvature and position of the teeth are also involved in such dynamical processes. The alveolar crest was labelled with a radiodense marker (48 cadaver heads, 15 skulls) and laterolateral radiographs were taken. Then a geometrical method was elaborated to determine a cheek tooth's curvature and its position by means of specific angles. This method respects the remarkable changes of the equine dentition throughout life by considering two items: (1) the alveolar crest was taken as a constant landmark, (2) the central axis of the curved dental crown was determined by calculation of a linear regression equation. This equation considered several geometrically determined points on the curved dental crown which had been marked in the radiographs. Our study yielded the following results: Mandibular cheek teeth became more curved with age, but their positions (represented by the so‐called mesio‐occlusal angle between tooth and alveolar crest) did not change significantly. In maxillary cheek teeth, however, the mesio‐occlusal angle became larger with age (indication of change of dental position), while their curvature did not change. Even though changes of the dental position were not always statistically significant, they are discussed as being biologically/functionally relevant. The mandibular anticlinal tooth, i.e. the tooth positioned at a mesio‐occlusal angle of about 90°, was not in contact with the maxillary anticlinal tooth. Interestingly, the maxillary anticlinal tooth is known to cause most clinical dental problems. Anat Rec, 291:565–570, 2008. © 2008 Wiley‐Liss, Inc.     

Circumstances favoring jaw tumors in Burkitt''s lymphoma

In Burkitt's lymphoma, dental structures may provide the route for Epstein-Barr virus (EBV) in saliva to penetrate the jaws, thereby promoting tumor formation. In children, EBV could enter tooth sockets exposed following deciduous tooth loss and thereby contact jaw marrow lymphocytes stimulating neoplastic transformation. Marrow contact by EBV probably also occurs through carious teeth. Jaw tumors are rare in adults because their jaw marrow is no longer hematopoietic and so lacks the lymphoid substrate for the virus. In adults, jaw marrow lymphocytosis, as accompanies infectious mononucleosis and perhaps malaria, or which could develop around the roots of carious teeth having chronic periapical infection, could provide the substrate for EBV. EBV could then contact the jaw marrow lymphocytes when teeth are extracted and so favor jaw tumor development. Therefore, prevention of dental caries might reduce jaw tumor prevalence in Burkitt's lymphoma except among children ages 6-13 whose jaw marrow would unavoidably become infected by salivary EBV when the latter is present at the time of deciduous tooth loss.     

Eruption age of teeth in Nigeria

Present study was carried out on 1,022 boys and 646 girls of various age groups. In this study, an attempt has been made to estimate the eruption age of teeth in various age groups, ranging from 6 to 23 years in Northern Nigerian population. From the data collected a mean have been provided for the eruption age of each tooth. The differences noticed in the eruption ages between boys and girls are not very marked. However, a few points of interest may be mentioned. The lateral incisor, first premolar and Canine erupt earlier amongst girls. The first molar and the central incisor seem to erupt earlier among boys than girls. The teeth of the lower jaw erupt before those of the upper jaw. The Nigerian's wisdom teeth erupt with some constancy between 14-21st years. The third molar tooth fails to erupt in 5% individuals. The second premolar was absent in 0.5% populations.     

Dental Maturation,Eruption, and Gingival Emergence in the Upper Jaw of Newborn Primates

In this report we provide data on dental eruption and tooth germ maturation at birth in a large sample constituting the broadest array of non‐human primates studied to date. Over 100 perinatal primates, obtained from natural captive deaths, were screened for characteristics indicating premature birth, and were subsequently studied using a combination of histology and micro‐CT. Results reveal one probable unifying characteristic of living primates: relatively advanced maturation of deciduous teeth and M1 at birth. Beyond this, there is great diversity in the status of tooth eruption and maturation (dental stage) in the newborn primate. Contrasting strategies in producing a masticatory battery are already apparent at birth in strepsirrhines and anthropoids. Results show that dental maturation and eruption schedules are potentially independently co‐opted as different strategies for attaining feeding independence. The most common strategy in strepsirrhines is accelerating eruption and the maturation of the permanent dentition, including replacement teeth. Anthropoids, with only few exceptions, accelerate mineralization of the deciduous teeth, while delaying development of all permanent teeth except M1. These results also show that no living primate resembles the altricial tree shrew (Tupaia) in dental development. Our preliminary observations suggest that ecological explanations, such as diet, provide an explanation for certain morphological variations at birth. These results confirm previous work on perinatal indriids indicating that these and other primates telegraph their feeding adaptations well before masticatory anatomy is functional. Quantitative analyses are required to decipher specific dietary and other influences on dental size and maturation in the newborn primate. Anat Rec, 298:2098–2131, 2015. © 2015 Wiley Periodicals, Inc.     

Recent decline in age at menarche: The Fels Longitudinal Study

A number of recent reports suggest that the average age at menarche of US girls has declined over the past 20 years. Because the putative declines in the age at menarche are concurrent with increases in childhood body mass index (BMI), it has been suggested that these two trends may be causally linked. We examined differences in mean age of menarche in Fels Longitudinal Study girls who were born in six 10‐year birth cohorts (1930s, 1940s, 1950s, 1960s, 1970s, and 1980s) and simultaneous cohort changes in mean BMI measured cross‐sectionally at selected ages from 3–35 years (n = 371). Girls born in the 1980s had a mean age at menarche of 12.34 years, which was ～3–6 months earlier than that of girls born previously (P < 0.001). While the mean BMI values at ages 25 and 35 generally increased from the 1930s to the 1970s, the mean BMI during childhood and adolescence remained constant across the six birth cohorts. In summary, we found no evidence that the recent decline in the age at menarche in the Fels Longitudinal Study girls was reflected in concurrent increases in BMI at any point in childhood or adolescence. Conversely, girls born in the 1960s and 1970s have subsequently become heavier in young and mid‐adulthood than were girls from earlier birth cohorts, without any concurrent change in the mean age at menarche over that time period. These two findings suggest that population‐level shifts in BMI and the timing of menarche are largely independent, although sometimes coincident, processes. Am. J. Hum. Biol. 16:453–457, 2004. © 2004 Wiley‐Liss, Inc.     

Squamate egg tooth development revisited using three-dimensional reconstructions of brown anole (Anolis sagrei,Squamata, Dactyloidae) dentition

The egg tooth is a hatching adaptation, characteristic of all squamates. In brown anole embryos, the first tooth that starts differentiating is the egg tooth. It develops from a single tooth germ and, similar to the regular dentition of all the other vertebrates, the differentiating egg tooth of the brown anole passes through classic morphological and developmental stages named according to the shape of the dental epithelium: epithelial thickening, dental lamina, tooth bud, cap and bell stages. The differentiating egg tooth consists of three parts: the enamel organ, hard tissues and dental pulp. Shortly before hatching, the egg tooth connects with the premaxilla. Attachment tissue of the egg tooth does not undergo mineralization, which makes it different from the other teeth of most squamates. After hatching, odontoclasts are involved in resorption of the egg tooth's remains. This study shows that the brown anole egg tooth does not completely conform to previous reports describing iguanomorph egg teeth and reveals a need to investigate its development in the context of squamate phylogeny.     

贵州地区氟斑牙前牙色度值与年龄及性别的关系

背景：国内外多数研究认为牙齿颜色会因年龄的改变而变化。 目的：分析氟斑牙色度值与年龄及性别的关系。 方法：从贵州省氟中毒人群中随机抽取氟斑牙患者317例,共计634颗上颌中切牙,用Shade Eye-NCC电脑测色仪测定患者氟斑牙色度学各要素(明度L*、色相a*、彩度b*)值,采用SPSS 15.0统计软件进行统计分析。 结果与结论：①氟斑牙色度值在不同性别间的差异有非常显著性意义(P < 0.01)。男性L*值略低于女性,a*、b*值则高于女性。②氟斑牙色度值在不同年龄组间的差异有显著性意义(P < 0.05)。L*值与年龄呈负相关关系,a*、b*值与年龄呈正相关关系。说明氟斑牙色度值在不同性别和年龄间有差异,男性氟斑牙颜色较女性暗且偏红偏黄,随着年龄增加,牙齿颜色逐渐变暗、偏黄。     

Tooth-bone morphogenesis during postnatal stages of mouse first molar development

The first mouse molar (M1) is the most common model for odontogenesis, with research particularly focused on prenatal development. However, the functional dentition forms postnatally, when the histogenesis and morphogenesis of the tooth is completed, the roots form and the tooth physically anchors into the jaw. In this work, M1 was studied from birth to eruption, assessing morphogenesis, proliferation and apoptosis, and correlating these with remodeling of the surrounding bony tissue. The M1 completed crown formation between postnatal (P) days 0-2, and the development of the tooth root was initiated at P4. From P2 until P12, cell proliferation in the dental epithelium reduced and shifted downward to the apical region of the forming root. In contrast, proliferation was maintained or increased in the mesenchymal cells of the dental follicle. At later stages, before tooth eruption (P20), cell proliferation suddenly ceased. This withdrawal from the cell cycle correlated with tooth mineralization and mesenchymal differentiation. Apoptosis was observed during all stages of M1 postnatal morphogenesis, playing a role in the removal of cells such as osteoblasts in the mandibular region and working together with osteoclasts to remodel the bone around the developing tooth. At more advanced developmental stages, apoptotic cells and bodies accumulated in the cell layers above the tooth cusps, in the path of eruption. Three-dimensional reconstruction of the developing postnatal tooth and bone indicates that the alveolar crypts form by resorption underneath the primordia, whereas the ridges form by active bone growth between the teeth and roots to form a functional complex.