What is the effect of preterm birth on permanent tooth crown dimensions? A systematic review and meta-analysis.

BACKGROUND: The permanent tooth formation process may be disrupted in preterm infants with potential discrepancies in size and subsequent occlusal disturbances. OBJECTIVE: To systematically analyse and quantitively synthesize the available evidence regarding the impact of preterm birth on permanent tooth crown dimensions. SEARCH METHODS: Unrestricted searches in 6 databases and manual searching of the reference lists in relevant studies were performed up to March 2021 (Medline via PubMed, CENTRAL, Cochrane Database of Systematic Reviews, Scopus, Web of Science, ProQuest Dissertations and Theses Global). SELECTION CRITERIA: Observational studies investigating permanent tooth crown dimensions in preterm and control full-term born individuals. DATA COLLECTION AND ANALYSIS: Following study retrieval and selection, relevant data were extracted, and the Newcastle-Ottawa scale was used to assess the selection, comparability, and outcome domains. Exploratory synthesis and meta-regression were carried out using the random effects model. RESULTS: Three studies were located from the initially retrieved records and the assessments with the Newcastle-Ottawa scale identified issues regarding the selection and comparability domains. Overall, the mesiodistal and the buccolingual dimensions of the permanent teeth in both dental arches tended to be smaller in children born prematurely than full term children. Subgroup analyses showed statistically significant differences for the extremely preterm to control group comparisons for the incisors and the first molars. Meta-regression showed a modificatory effect of gestational age and racial background but not of birth weight and gender on tooth size. The quality of available evidence was rated at best as moderate. CONCLUSIONS: Premature birth could potentially be associated with reduced tooth-crown dimensions in some permanent teeth especially in children born extremely preterm. Although the results from these observational studies should be approached with caution until more information becomes available, the possible clinical implications in terms of diagnosis and treatment planning should be considered. REGISTRATION: PROSPERO (CRD42020182243).

Crown formation times of deciduous teeth and age at death in neolithic newborns / Tiempos de formación de la corona de los dientes deciduos y edad al morir en neonatos neolíticos

SUMMARY: The aim of the present study was to investigate the possibility of estimating crown formation times of immature deciduous teeth and age at death in Neolithic newborns. In the Neolithic-Mesolithic transition, the health of the population deteriorated. Leaving the intrauterine environment for the newborn is the first obstacle in the process of adaptation and survival in the outside world. The fetus is protected by the mother's immune system and receives the necessary nutrients through the umbilical cord, but external factors indirectly affect its development. At birth deciduous teeth are not fully formed and are only partially mineralized. Variations in the rhythmic activity of ameloblasts and the secretion of the enamel matrix lead to the formation of incremental lines in the enamel. The sample consisted of unerupted deciduous teeth removed from the baby jaws from Neolithic archaeological graves, LepenskiVir Serbia. The skeletal age of the babies was from 38 to 40 gestational weeks. The daily enamel apposition rate was obtained for each tooth. The age of individuals was estimated using crown formation time. The average value of daily secretion rates for the primary teeth from the Neolithic age was 3.78 µm. There was no statistically significant difference in age at death determined by skeletal age assessment and crown formation time. Three babies were born preterm. The results of the present study show that the calculation of the time required for the formation of deciduous tooth enamel is applicable to archaeological samples of newborns.The age estimation using crown formation time together with the analysis of other anthropological parameters, can contribute to a more accurate determination of neonatal death in anthropological, archaeological and forensic contexts.

RESUMEN: El objetivo del estudio fue investigar la posibilidad de estimar el tiempo de formación de la corona de los dientes deciduos inmaduros y la edad, al momento de la muerte en neonatos neolíticos. Durante la transición Neolítico-Mesolítico, la salud de la población deterioró significativamente. Para el recién nacido dejar el medio intrauterino es el primer obstáculo en el proceso de adaptación y supervivencia en el mundo exterior. El feto está protegido por el sistema inmunológico de la madre y recibe los nutrientes necesarios a través del cordón umbilical, pero factores externos afectan indirectamente su desarrollo. Al nacer, los dientes deciduos no están completamente formados y solo están parcialmente mineralizados. Las variaciones en la actividad rítmica de los ameloblastos y la secreción de la matriz del esmalte conducen a la formación de líneas incrementales en el esmalte. La muestra consistió en dientes sin erupción extraídos de las mandíbulas de neonatos de tumbas arqueológicas neolíticas, LepenskiVir Serbia. La edad esquelética de los bebés fue de 38 a 40 semanas de gestación. Se obtuvo la tasa diaria de aposición de esmalte para cada diente. La edad de los individuos se estimó utilizando el tiempo de formación de la copa. El valor promedio de las tasas de secreción diaria para los dientes temporales del Neolítico fue de 3,78µm. No hubo diferencia estadísticamente significativa en la edad al momento de la muerte determinada por la evaluación de la edad esquelética y el tiempo de formación de la corona. Tres bebés nacieron prematuros. Los resultados del presente estudio muestran que el cálculo del tiempo requerido para la formación del esmalte dental deciduo es aplicable a muestras arqueológicas de recién nacidos. La estimación de la edad utilizando el tiempo de formación de la corona junto con el análisis de otros parámetros antropológicos, puede contribuir a una mayor determinación precisa de la muerte neonatal en contextos antropológicos, arqueológicos y forenses.

Advances in the identification of deciduous molar tooth germs.

In forensic anthropology, correct identification of human deciduous teeth is of paramount importance for age-at-death estimation and relies on detailed anatomical descriptions. Yet literature is scarce on indications: details on the morphology of molar tooth germs of fetuses and newborns, developing from multiple mineralized centers that will eventually coalesce, are scant. This paper presents new anatomical elements for practitioners to identify human molar tooth germs at early developmental stages. 126 deciduous molars from 22 modern skeletons of fetuses and newborns (with a known age-at-death ranging between 0 days and 2 months and 21 days postnatal), without reported or observed dental pathological signs, were selected from the Collezione Antropologica LABANOF (CAL) documented skeletal collection. Gross anatomical descriptions of the morphology and configuration of the centers were provided, considering the number of mineralized centers, the shape and the outline of the occlusal plane at different stages. Three different developmental stages were observed in the maxillary first and second molar and the mandibular first molar, whereas in the mandibular second molar four stages were observed. For each stage, we provide additional detailed morphological descriptions, sketches outlining the shape of the tooth germ, and a picture of the tooth; also, indications for siding the teeth are presented. This information can be used by forensic anthropologists and odontologists for a proper identification when tooth germs are not found in anatomical connection within the dental sockets. Further analyses that encompass more age groups on a larger sample would allow to map the entire crown development of deciduous molars.

Molar crown formation times of fossil orangutan molars from Guangxi, China.

OBJECTIVES: We aimed to investigate molar enamel development in fossil orangutans from Guangxi and shed light on the evolution of Asian great apes. MATERIALS AND METHODS: We collected 32 fossil orangutan molars, most of which were from Guangxi apothecaries and the Guangxi Daxin Heidong cave, and prepared histological sections of each molar. We then characterized aspects of dental development, including long period line periodicity, number of Retzius lines and lateral enamel formation time, cuspal enamel thickness, and enamel formation time. RESULTS: The long period line periodicity in fossil orangutans ranged from 9 to 10 days (mean, 9.09 days). The molar lateral enamel formation time ranged from 1.48 to 3.17 years (540-1,152 days). Cuspal enamel thickness in fossil orangutan molars ranged from 949 to 2,535 µm, and cuspal enamel formation time ranged from 0.64 to 1.87 years. Molar enamel formation time of fossil orangutans ranged from 2.47 to 4.67 years. DISCUSSION: Long-period line periodicity of fossil orangutans from Guangxi was within the variation range of extant orangutans, and the average long period line periodicity (9.09 days) of fossil orangutans from Guangxi in this study was lower than the values for extant orangutans (9.5 days) and fossil orangutans (10.9 days) from Sumatra and Vietnam. Orangutan enamel thickness may have gradually decreased from the Middle Pleistocene to Holocene. Crown formation time of fossil orangutans was slightly longer than that of extant orangutans, and the M1 emergence age of fossil orangutans from Guangxi was about 4-6 years. These findings might indicate the regional difference or evolutionary changes in orangutans since Pleistocene. Dental development of the Guangxi fossil orangutans were more similar to that of Asian Miocene apes, suggesting the closer evolutionary relationship of orangutans to Miocene Asian fossil apes.

Characteristic dental pattern with hypodontia and short roots in Fraser syndrome.

Fraser syndrome (FS) is a rare autosomal recessive multiple congenital malformation syndrome characterized by cryptophthalmos, cutaneous syndactyly, renal agenesis, ambiguous genitalia, and laryngotracheal anomalies. It is caused by biallelic mutations of FRAS1, FREM2, and GRIP1 genes, encoding components of a protein complex that mediates embryonic epithelial-mesenchymal interactions. Anecdotal reports have described abnormal orodental findings in FS, but no study has as yet addressed the orodental findings of FS systematically. We reviewed dental radiographs of 10 unrelated patients with FS of different genetic etiologies. Dental anomalies were present in all patients with FS and included hypodontia, dental crowding, medial diastema, and retained teeth. A very consistent pattern of shortened dental roots of most permanent teeth as well as altered length/width ratio with shortened dental crowns of upper incisors was also identified. These findings suggest that the FRAS1-FREM complex mediates critical mesenchymal-epithelial interactions during dental crown and root development. The orodental findings of FS reported herein represent a previously underestimated manifestation of the disorder with significant impact on orodental health for affected individuals. Integration of dentists and orthodontists into the multidisciplinary team for management of FS is therefore recommended.

Comparison of actual porcine tooth crown development stages and computer image analysis.

Tooth developmental stage evaluation is important in dental and chronological age estimation, and it is important for accurate diagnoses and appropriate treatment in dental practice. It is routinely assessed by clinical observations and radiographic techniques. This study aimed at ascertaining tooth developmental stage judgments made by examiners and Mimics software according to the Nolla method with radiographs. Meanwhile, the true tooth developmental stages would be explored with histological analysis. Twenty freshly slaughtered porcine heads were collected and hemisected, and both the left and right mandibular samples were numbered. The developmental stages of the second and third permanent molars (M2 and M3) were evaluated by examiners and Mimics software analysis. The ratio of the radiopaque calcified area to the dental follicle (RCA/DF) at different stages was calculated. Both non-decalcified and decalcified samples were processed for histologic observation. The results showed significant differences between RCA/DF ratios from different developmental stages. There was a high positive correlation between the examiners' evaluation results and Mimics analysis results. Radiograph judgments and histology observation results were consistent from Stages 2-6. However, radiograph images of Stage 1 samples showed only crypts present, while under a surgical operating microscope, a bell-shaped tooth germ was observed. This was also confirmed by normal and hard tissue histology. In conclusion, radiograph judgments made by either examiners or Mimics software were both reliable. Mimics analysis can be a useful tool in evaluating tooth developmental stages. However, judgments need to be made cautiously in early developmental stages.

Histological and developmental insights into the herbivorous dentition of tapinocephalid therapsids.

Tapinocephalids were one of the earliest therapsid clades to evolve herbivory. In acquiring derived tooth-to-tooth occlusion by means of an exaggerated heel and talon crown morphology, members of this family have long been considered herbivorous, yet little work has been done to describe their dentition. Given the early occurrence of this clade and their acquisition of a dentition with several derived features, tapinocephalids serve as an important clade in understanding adaptations to herbivory as well as macroevolutionary patterns of dental trait acquisition. Here we describe the histology of tapinocephalid jaws and incisors to assess adaptations to herbivory. Our results yield new dental characters for tapinocephalids including a peculiar enamel structure and reduced enamel deposition on the occlusal surface. These traits are convergent with other specialized herbivorous dentitions like those found in ornithischian dinosaurs and ungulates. Furthermore, these results demonstrate that while acquiring some specializations, tapinocephalids also retained plesiomorphic traits like alternate, continuous replacement. We interpret these findings as an example of how different combinations of traits can facilitate a derived and specialized dentition and then discuss their implications in the acquisition of a mammal-like dentition.

Incidental observation of pre-eruptive intracoronal resorption after seven years.

Pre-eruptive intracoronal resorption (PIER) can be described by the presence of coronal radiolucency in a unerupted tooth. Upon eruption, the resorbed dentine might leave the occlusal layer of enamel unsupported and susceptible to fracture, potentially exposing the pulp chamber and root canals to the oral flora. With current case studies showing unfavourable endodontic and restorative consequences of PIER lesions when left untreated, this case report presents an unchanged lesion, 7 years following initial identification.

Three-Dimensional Assessment of Crown Size and Eruption Space for Developing Third Molars: Data Collection Techniques Based on Cone-Beam Computed Tomography (CBCT).

Third molar development and eruption are two related areas of major interest in dental research into the etiology of "wisdom tooth" impaction. Third molars are not only an excellent model for studying dental development but also of fundamental clinical importance because they are very frequently impacted. Because the third molar is located in the distal-most region of the oral cavity, clinical access is relatively challenging. With the increasingly widespread use of cone-beam computed tomography (CBCT) in dentistry, studies and measurements of the third molar and its eruption area have become considerably easier to do. Here we present a novel CBCT-based measurement methodology we developed for our recent investigations that we hope will also be useful for the broader dental research community.

First systematic assessment of dental growth and development in an archaic hominin (genus, Homo) from East Asia.

Several human dental traits typical of modern humans appear to be associated with the prolonged period of development that is a key human attribute. Understanding when, and in which early hominins, these dental traits first appeared is thus of strong interest. Using x-ray multiresolution synchrotron phase-contrast microtomography, we quantify dental growth and development in an archaic Homo juvenile from the Xujiayao site in northern China dating to 161,000-224,000 years or 104,000-125,000 years before present. Despite the archaic morphology of Xujiayao hominins, most aspects of dental development of this juvenile fall within modern human ranges (e.g., prolonged crown formation time and delayed first molar eruption). For its estimated age-at-death (6.5 years), its state of dental development is comparable to that of equivalently aged modern children. These findings suggest that several facets of modern human dental growth and development evolved in East Asia before the appearance of fully modern human morphology.

The pay-off of hypsodonty - timing and dynamics of crown growth and wear in molars of Soay sheep.

BACKGROUND: Several lineages of herbivorous mammals have evolved hypsodont cheek teeth to increase the functional lifespan of their dentition. While the selective drivers of this trend and the developmental processes involved have been studied in greater detail, thus far no quantitative information is available on the relationship between additional investment into tooth growth and the resulting extension of the functional period of these teeth. To achieve this, we performed a detailed analysis of molar crown growth in known-age Soay sheep repeatedly injected with different fluorochromes. RESULTS: Our study revealed that in sheep molars especially the formation of the crown base portion is prolonged in comparison with other herbivorous artiodactyl species. Our results demonstrate that growth of the crown base accounted for more than half of the total crown formation time (CFT) of the anterior lobes of the first (approx. 220 days of total CFT of 300 days), second (approx. 260 of 460 days) and third (approx. 300 of at least 520 days) molars, and that the formation of this crown portion occurred largely after the teeth had already reached functional occlusion. By combining data on wear-related changes in crown morphology from the literature with the reconstructed additional investment into the crown base portion, it was possible to relate this additional investment to a prolongation of the functional periods of the molars ranging from 4 years in the M1 to 6 years in the M3. CONCLUSIONS: Our results allow to establish a quantitative link between an additional investment into molar crown growth of sheep and the extension of the functional period of these teeth. The reported findings enable an assessment of the adaptive value, in terms of increased longevity, of an additional investment into crown elongation in a mammalian herbivore.

Estimating age using permanent molars and third cervical vertebrae shape with a novel semi-automated method.

Estimating chronological age accurately in young adults is difficult and additional methods are required to increase the accuracy. This study explored a new semi-automated method to assess shape change of third cervical vertebra (C3) with age in the living; comparing this as a method to determine whether individuals could be categorised into being less than 18 years of age (<18), or at least 18 years of age (≥18) with tooth formation of the second and third mandibular molars (M2 and M3). The sample was panoramic and lateral skull radiographs of 174 dental patients (78 males, 96 females aged 15-22 years). Twelve variables were compared in two age categories: younger than 18 and at least 18 years of age in males and females separately using a t-test. Tooth formation of M2 and M3 was assessed. Mean values of eight variables of C3 in males and one variable in females were significantly different between the two age categories (p < 0.05). Results for males showed that the best age indicator for age ≥18 was the ratio between height and width of C3 and for females, the ratio between diagonals. Results for molars showed that M2 was mature in 69% of males and 83% of females, within the expected age range of 14-16 years. M3 was highly variable ranging from stages 6-14 for both; M3 was missing in 24% of males and 28% of females and mature in 14% of males and 15% of females. The conclusion was that shape change of C3 has potential as an additional method to group individuals <18 and ≥ 18 years of age.

Evaluation of Teeth Development in Unilateral Cleft Lip and Palate Patients in Mixed Dentition by Using Medical Image Control Systems.

OBJECTIVES: The aim of this study was to evaluate the crown and root development in patients with cleft lip and palate using medical software programmes. MATERIALS AND METHODS: In our study, 25 patients with mixed dentition unilateral cleft lip and palate were examined with cone-beam computed tomography (CBCT). The tomography images obtained as high resolution medical images on the computer control system (MIMICS 15.0, Materialise, Leuven, Belgium and SOLIDWORKS 2014 Premium, Concord, Massachusetts) were converted to three-dimensional volumetric images. These three-dimensional images of the cleft on the sides of the teeth in the crown and root growth were measured by mesiodistal length and crown/root rate with volume and area. These measurements were compared with a control group of healthy individuals. RESULTS: There were no statistically significant differences in the volume, surface area and MD size, crown/root ratio of central incisor, canine, first premolar and second premolar teeth within defect, and healthy teeth. However, it was found that there was a significant difference between the volume, surface area and MD size, and crown/root ratio of the lateral teeth in each group. CONCLUSION: In particular, among patients with cleft lip and palate, on obtaining a solid model of the tooth structure by using these programs, tooth development can be examined in more detail, diagnosis can be made more reliable, as well as in treatment planning. We believe that these programs can be used to resolve certain limitations such as a lack of an application to be used in routine dental treatment and in particular the need to do more study.

Age Estimation of Infants Through Metric Analysis of Developing Anterior Deciduous Teeth.

This study provides regression equations for estimation of age of infants from the dimensions of their developing deciduous teeth. The sample comprises 97 individuals of known sex and age (62 boys, 35 girls), aged between 2 days and 1,081 days. The age-estimation equations were obtained for the sexes combined, as well as for each sex separately, thus including "sex" as an independent variable. The values of the correlations and determination coefficients obtained for each regression equation indicate good fits for most of the equations obtained. The "sex" factor was statistically significant when included as an independent variable in seven of the regression equations. However, the "sex" factor provided an advantage for age estimation in only three of the equations, compared to those that did not include "sex" as a factor. These data suggest that the ages of infants can be accurately estimated from measurements of their developing deciduous teeth.

Reconstructing molar growth from enamel histology in extant and extinct Equus.

The way teeth grow is recorded in dental enamel as incremental marks. Detailed analysis of tooth growth is known to provide valuable insights into the growth and the pace of life of vertebrates. Here, we study the growth pattern of the first lower molar in several extant and extinct species of Equus and explore its relationship with life history events. Our histological analysis shows that enamel extends beyond the molar's cervix in these mammals. We identified three different crown developmental stages (CDS) in the first lower molars of equids characterised by different growth rates and likely to be related to structural and ontogenetic modifications of the tooth. Enamel extension rate, which ranges from ≈400 µm/d at the beginning of crown development to rates of ≈30 µm/d near the root, and daily secretion rate (≈17 µm/d) have been shown to be very conservative within the genus. From our results, we also inferred data of molar wear rate for these equids that suggest higher wear rates at early ontogenetic stages (13 mm/y) than commonly assumed. The results obtained here provide a basis for future studies of equid dentition in different scientific areas, involving isotope, demographic and dietary studies.

Tooth coronal index and pulp/tooth ratio in dental age estimation on digital panoramic radiographs-A comparative study.

BACKGROUND: Assessment of an age of an individual whether living or dead through teeth is one of the most reliable and simple method to calculate age than skeletal remains especially when they are in poor conditions. OBJECTIVES: The study was carried out with aim of (i) to evaluate reliability of dental age assessment through two different methods for adults i.e. tooth coronal index and pulp/tooth ratio using digital panoramic radiographs and (ii) to compare these methods for their accuracy in age determination. MATERIALS AND METHODS: The digital panoramic radiographs of 180 subjects of Chhattisgarh aged 15-70 years were selected for the study. The measurements were performed on the JPEG images of selected panoramic radiographs by using Adobe Acrobat 7.0 professional software. For tooth coronal index (TCI), height of the crown i.e. coronal height (CH) and the height of the coronal pulp cavity i.e. coronal pulp cavity height (CPCH) of mandibular second premolars and first molars was measured in millimeter (mm) and then TCI was calculated for each tooth and calculated age was compared with chronological age. For pulp/tooth ratio, the measurements of pulp chamber height (PCH) and crown root trunk height (CRTH) were performed on the mandibular first and second molar teeth, the pulp chamber crown root trunk height ratios (PCTHR) of selected tooth were calculated. The acquired data were subjected to Pearson correlation test, unpaired t test and Analysis of Variance (ANOVA) analysis. RESULTS: Results suggested that TCI (mandibular first molar r=-0.178), second premolar (r=-0.187) and PCTHR(mandibular first molar r=-0.921, second molar r=-0.901) correlated negatively with chronological age suggesting decrease in size of pulp cavity. Mandibular first molar was found to be most reliable tooth to estimate dental age. CONCLUSION: The study showed that both PCTHR and TCI have negative association with chronological age. PCTHR showed slightly higher negative correlation and proved as a better tool for age estimation than TCI. Statistically significant differences were observed between chronological and calculated age by both methods thus emphasizing the need for future clinical trials.

Changes in the buccolingual inclination of first molars with growth in untreated subjects: A longitudinal study.

OBJECTIVES: To assess longitudinal changes in the buccolingual inclination of the maxillary and mandibular first molars in untreated male and female subjects. MATERIALS AND METHODS: Forty-seven male and 48 female subjects whose longitudinal dental casts were available at ages 6-16 years, with normal maxillary and mandibular arch forms were included. The original casts at ages 6, 7, 8, 9, 10, 12, 14, and 16 years were digitized and standardized. Measurements were recorded as the differences in cusp heights in the vertical dimension for the mandibular and maxillary first molars using OrthoInsight software. RESULTS: On average, for boys from age 6 to 16 years, both maxillary and mandibular first molars uprighted with age. Maxillary molars uprighted 0.403 mm on the left and 0.418 mm on the right; mandibular molars uprighted 0.441 mm on the left and 0.589 mm on the right. Similarly, for girls from age 6 to 16, both maxillary and mandibular molars uprighted with age. Maxillary molars uprighted 0.67 mm on the left and 0.574 mm on the right; mandibular molars uprighted 0.358 mm on the left and 0.329 mm on the right. CONCLUSIONS: Maxillary molars erupted with buccal crown inclination at age 6 in both boys and girls and uprighted lingually with growth. At age 16, maxillary molars were not completely upright but rather maintained some buccal crown inclination. Mandibular molars erupted with lingual crown inclination at age 6 and uprighted buccally with age. At age 16, mandibular molars were not completely upright but rather maintained some lingual inclination.

The impact of premature birth on the permanent tooth size of incisors and first molars.

BACKGROUND: Scientific evidence is insufficient to answer the question of whether premature birth causes altered tooth-crown dimensions. OBJECTIVE: To evaluate permanent tooth-crown dimensions in prematurely born children and to compare the findings with full-term born controls. SUBJECTS AND METHODS: Preterm children of 8-10 years of age were selected from the Swedish Medical Birth Register. One group consisted of 36 extremely preterm children (born before the 29th gestational week); the other group included 37 very preterm children (born during gestational weeks 29-32). The preterm children were compared with 41 matched full-term born children. Clinical examination and study casts were performed on all children. Permanent maxillary and mandibular first molars, central incisors, and laterals were measured with a digital sliding caliper on study casts. The tooth-crowns were measured both mesio-distal and bucco-lingual. RESULTS: Both the mesio-distal and bucco-lingual measurements in the maxillary and mandibular first molars had a significantly smaller width in the extremely preterm group compared with the full-term group. The central incisors and lower laterals were significantly smaller mesio-distally in the extremely preterm group compared to the full-term group. A reduction in tooth size of 4-9% was found between the extremely preterm group and the full-term group for both boys and girls. The maxillary first molars and mandibular left first molar were also smaller mesio-distally in the extremely preterm group compared to the very preterm group. The results indicate that the more preterm the birth, the smaller the tooth-crown dimensions. Independent of gestational age girls had generally smaller teeth than boys. CONCLUSION: Premature birth is associated with reduced tooth-crown dimensions of permanent incisors and first molars.

Crown heights in the permanent teeth of 47,XYY males.

OBJECTIVE: The results in human sex chromosome aneuploidies had shown that the extra Y chromosome increases permanent and deciduous tooth crown sizes in the mesiodistal and labiolingual directions. The hypothesis of the study was that the additional Y chromosome increases the permanent tooth crown growth in a vertical dimension. We also aimed to observe possible sex difference in the permanent tooth crown height. MATERIAL AND METHODS: Data on 15 47,XYY males or males with an extra Y chromosome, nine male relatives (five brothers and four fathers) and 45 male and 48 female population controls had been gathered previously for Professor Lassi Alvesalo's KVANTTI Research Project. The measurements from panoramic radiographs were performed of all the applicable teeth, except the third molars on both sides of the jaws with a sliding digital calliper. RESULTS: All the mean tooth crown heights in the 47,XYY males were larger than in the male population controls and the differences were statistically significant in six teeth in the maxilla and 10 teeth in the mandible. Apart from few teeth, the crown heights in the 47,XYY males were larger than in their male relatives, but the difference between these groups was significant only in one tooth. The differences between sexes were statistically significant in eight teeth in the maxilla. CONCLUSIONS: Based on previous investigations and this work, it is evident that the impact of the extra Y chromosome during tooth crown development is holistic, increasing permanent tooth sizes in three dimensions in a balanced manner.

Cellular and molecular mechanisms of tooth root development.

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