New regression formula to estimate the prenatal crown formation time of human deciduous central incisors derived from a Roman Imperial sample (Velia, Salerno, Italy, I-II cent. CE)

The characterization and quantification of human dental enamel microstructure, in both permanent and deciduous teeth, allows us to document crucial growth parameters and to identify stressful events, thus contributing to the reconstruction of the past life history of an individual. Most studies to date have focused on the more accessible post-natal portion of the deciduous dental enamel, even though the analysis of prenatal enamel is pivotal in understanding fetal growth, and reveals information about the mother's health status during pregnancy. This contribution reports new data describing the prenatal enamel development of 18 central deciduous incisors from the Imperial Roman necropolis of Velia (I-II century CE, Salerno, Italy). Histomorphometrical analysis was performed to collect data on prenatal crown formation times, daily secretion rates and enamel extension rates. Results for the Velia sample allowed us to derive a new regression formula, using a robust statistical approach, that describes the average rates of deciduous enamel formation. This can now be used as a reference for pre-industrial populations. The same regression formula, even when daily incremental markings are difficult to visualize, may provide a clue to predicting the proportion of infants born full term and pre-term in an archaeological series.

Insular dentin formation pattern in human odontogenesis in relation to the scalloped dentino-enamel junction

This study is a first report on the modality of early dentin formation in respect to the scalloped pattern of the dentino-enamel junction (DEJ). We applied scanning electron microscopy (SEM), transmission electron microscopy (TEM), histological serial sections, and three-dimensional (3D) reconstructions. TEM and SEM showed scallops and secondary scallops on the DEJ of deciduous dental primordia and on deciduous teeth with the enamel cap removed. This peculiar outline of the DEJ requires a specific dentin formation pattern; histological sections showed that dentin formation began at the brims of the scallops, seen as triangular spikes in serial sections. The dentin formation front was not uniform; instead, it was characterized by multiple, insular forming centers, as revealed by our 3D reconstructions. As thicker dentin layers formed, the islands became confluent. Factors are discussed, which may lead to crimpling of the inner enamel epithelium, and maintained as the scalloped pattern of the DEJ develops. Signaling patterns in accordance with the insular dentin formation are unknown so far.

Prenatal growth acceleration in maxillary deciduous canines of children with Down syndrome: Histological and chemical composition study

Previous studies have reported that the abnormal development of the second deciduous molar in Down syndrome and cerebral palsy begins before birth. In view of these results we have turned our attention to the earlier stages of dental development in utero, represented by the primary canine, in order to see if we can identify more precisely the origin and timing of developmental insults in these conditions. The study was carried out on exfoliated or extracted maxillary primary canines of children with Down syndrome (DS) and cerebral palsy (CP) and they were compared to a control group of children with no adverse medical history. Thin sections were made through the mid-sagittal bucco-palatinal axis. Using a light microscope, the width of prenatal enamel and postnatal enamel, defined by the neonatal line was measured on each section at a standardized location. The chemical composition of the enamel was then measured at three different locations using an energy dispersive spectrophotometer (ESR) in a high vacuum mode. The total enamel width in DS and controls was similar and greater than that of CP canines. Significantly more enamel was laid down prenatally in DS teeth than in controls or CP and it was more highly mineralized. These results for DS canines differ from those previously published for the later developing second primary molars. They support the hypothesis of accelerated growth in the early stages of intra-uterine development, prior to the establishment of reduced growth trajectories in the later stages. The results for CP teeth showed that more prenatal enamel was laid down prenatally than in controls. Mineralization in CP was poor during the first two trimesters and improved significantly during the last trimester. While this approach is retrospective, we propose that it may aid in identifying the onset of developmental anomalies of unknown etiology that are expressed in later life.

Remarks on the morphology of the human temporomandibular joint in the fetal period

Skeletons of human fetuses of different ages allow the study of the considerable transformations of the mandibular joint and the mandible in this relative short stage of life. The condyle is anchored in the mandible by a conical process. The tip of this cone extends to the anLage of the 2nd milk molar. The conical process can be recognized macroscopically up to newborn age. It can also be identified by modern imaging methods. The cone can be well distinguished from the surrounding bone of the mandible. The mandibular joints of fetuses in the 31st, the 32nd, the 39th week and of a newborn were dissected, removed, and histologically investigated. The conical process of the condyle was clearly observed. The cartilage on the condyle is characterised by a layered structure which is typical for a center of growth. In the cartilage of young fetuses, blood vessels were found, reaching from the trabecular bone to the articular space. At this stage of life, blood vessels are also present in the central part of the discus articularis.

Microstructure and chemical composition of primary teeth in children with Down syndrome and cerebral palsy

This study was designed to test the hypothesis that prenatal growth insults leave permanent signs in the developing primary teeth that can be identified in later life. To test this hypothesis we examined exfoliated and extracted lower second primary molars of children with Down syndrome (DS) and cerebral palsy (CP). Teeth of children with no adverse medical history were used as a control group. Informed consent of parents and children was obtained in all cases. On each tooth two thin sections were cut, one bisecting the mesial cusps and one bisecting the distal cusps. Using a light microscope, the width of prenatal enamel and postnatal enamel was measured on each section at standardized locations from the dentin-enamel junction (DEJ) with the neonatal line used to distinguish between prenatal and postnatal enamel. Chemical analysis of each section was carried out using an energy dispersive spectrophotometer (ESR). The Ca/P ratios of enamel and dentin for each cusp were calculated and intercusp and intergroup differences analysed using non-parametric statistical tests. The results showed that significantly less enamel was laid down prenatally in DS and CP teeth than in the control group and that the enamel of the mesial cusps in these groups was less highly mineralised than that of the controls. The results also showed that in DS teeth growth and mineralisation of all cusps was affected. Based on these findings we propose that analysis of exfoliated deciduous teeth in developmentally challenged children may help in identifying the onset and severity of growth insults in utero and its impact on later development.

Origin of the deciduous upper lateral incisor and its clinical aspects

The upper lateral incisor in humans is often affected by dental anomalies that might be explained developmentally. To address this question, we investigated the origin of the deciduous upper lateral incisor (i2) in normal human embryos at prenatal weeks 6-8. We used serial frontal histological sections and computer-aided 3D reconstructions. At embryonic days 40-42, two thickenings of the dental epithelia in an "end-to-end" orientation were separated by a groove at the former fusion site of the medial nasal and maxillary processes. Later, these dental epithelia fused, forming a continuous dental lamina. At the fusion site, i2 started to develop. The fusion line was detectable on the i2 germ until the 8th prenatal week. The composite origin of the i2 may be associated with its developmental vulnerability. From a clinical aspect, a supernumerary i2 might be a form of cleft caused by a non-fusion of the dental epithelia.

[Tissue engineering of dentin-pulp complex-like structures by human dental mesenchymal cells]

OBJECTIVE

To establish three-dimensional culture model of human dental mesenchymal cells and bioengineer in vivo with ceramic bovine bone (CBB) and Collagraft as scaffolds.

METHODS

Human dental mesenchymal cells induced upon stimulation of bFGF and IGF-1 or TGF-beta(1) were implanted onto CBB and Collagraft containing the same kinds of growth factors respectively. Then cell/scaffold constructs were transplanted into nude mice to establish in vivo culture model of dental mesenchymal cells. Control groups were set up at the same time. After 4 weeks or 10 weeks, the implants were taken out for histological and immunohistochemical analysis.

RESULTS

Within 10-week implant tissues, typical dentin-pulp complex-like structures were generated in scaffolds containing growth factors. Human dentin sialoprotein (DSP) was expressed in the newly formed dentin. This phenomenon wasn't observed in control groups and 4-week implants.

CONCLUSIONS

Dentin-pulp complex-like structures could be bioengineered successfully with human dental mesenchymal cells and CBB or Collagrafts containing growth factors in nude mice.

Runx2 (Cbfa1) inhibits Shh signaling in the lower but not upper molars of mouse embryos and prevents the budding of putative successional teeth

Heterozygous mutations in the RUNX2 (CBFA1) gene cause cleidocranial dysplasia, characterized by multiple supernumerary teeth. This suggests that Runx2 inhibits successional tooth formation. However, in Runx2 knockout mice, molar development arrests at the late bud stage, and lower molars are more severely affected than upper ones. We have proposed that compensation by Runx3 may be involved. We compared the molar phenotypes of Runx2/Runx3 double-knockouts with those of Runx2 knockouts, but found no indication of such compensation. Shh and its mediators Ptc1, Ptc2, and Gli1 were down-regulated only in the lower but not the upper molars of Runx2 and Runx2/Runx3 knockouts. Interestingly, in front of the mutant upper molar, a prominent epithelial bud protruded lingually with active Shh signaling. Similar buds were also present in Runx2 heterozygotes, and they may represent the extension of dental lamina for successional teeth. The results suggest that Runx2 prevents the formation of Shh-expressing buds for successional teeth.

The developmental relationship between the deciduous dentition and the oral vestibule in human embryos

In humans, there is no consensus about the developmental relationship between the deciduous dentition and the oral vestibule separating the teeth from the lips and cheeks. The classical concept assumes that two horseshoe-shaped epithelial structures exist: the dental lamina, giving rise to single tooth primordia, and the vestibular lamina running parallel and externally to it, giving rise to the oral vestibule. The aim of this study was to investigate the development of the dental and vestibular laminae in the upper jaw and to determine their developmental relationship in humans from embryonic week 6 to 9. Although a thickening of the vestibular epithelium was always present on serial histological sections, computer-aided three-dimensional reconstructions did not show any continuous vestibular lamina. Several discontinuous epithelial structures (bulges and ridges) occurred transiently at different stages of oral vestibule development. Along the mesiodistal axis, the dental and vestibular epithelia were regionalized in parallel: in the incisive, canine, and 1st and 2nd molar regions. The vestibular ridges fused with the dental lamina distally to the deciduous canine, 1st molar and 2nd molar. These interactions between the developing teeth and vestibular structures are reminiscent of the situation in some reptiles, where single teeth are paired one-to-one with single tooth glands.

Variation in elemental intensities among teeth and between pre- and postnatal regions of enamel

Microspatial analyses of the trace element composition of dental enamel are made possible using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Fine spatial resolution, multielement capabilities, and minimal sample destruction make this technique particularly well-suited for documenting the distribution of elements in sequentially calcifying layers of enamel. Because deciduous enamel forms from week 13 in utero up to 9 months postnatally (thereafter essentially becoming inert), the application of LA-ICP-MS allows for the retrospective measurement of prenatal and early postnatal trace-element uptake during a critical period of child development. In this study, we compared intra- and intertooth intensities of 25Mg, 57Fe, 66Zn, 68Zn, 88Sr, 138Ba, and 208Pb via LA-ICP-MS of 38 exfoliated deciduous incisors and canines donated by 36 participants in the Solís Valley Mexico Nutrition Collaborative Research Support Program (NCRSP). Pre- and postnatal comparisons within teeth showed significant increases (P < 0.001) and greater variation in the abundance of all isotopes in postnatal enamel, with the exception of a decrease in 25Mg (P < 0.001) and constant values for 88Sr (P = 0.681). Conversely, comparisons by tooth type and mouth quadrant revealed few significant differences between teeth of the same individual. We argue that more variation in the trace element composition of teeth occurs across developmental areas within a tooth than among different teeth of the same person. This study further demonstrates that sequentially calcifying areas of enamel have different chemical concentrations. The results support the use of microspatial analyses of enamel for understanding changes in nutrition, pollution, and residence.

Development of innervation in primary incisors in the foetal period

Sections from the frontal part of the mandible of 43 human foetuses from 9 to 39 weeks of prenatal age, which contained two, three and sometimes four lower incisors were immunohistochemically examined using protein gene product and neuron specific enolase (NSE) antibodies in order to establish the time of appearance of nerve fibres in the developing tooth germ and to define their topography. Nerve fibres were first detected in the dental follicle in the 11th week of intrauterine life. Their presence in the dental papilla was confirmed in the 18th week when the first layers of dentine and enamel were deposited. In the 24th week of intrauterine life, the nerve fibres first reached the subodontoblastic region. In the subsequent weeks, an increase in the number of nerve fibres accompanying blood vessels in the central portion of the dental papilla resulted in the formation of neuro-vascular bundles. Moreover, the progressive deposition of enamel and dentine was accompanied by branching of papillary nerves, which thereby formed a fan-pattern. In the foetal period, no evidence was found for the formation of a subodontoblastic plexus. However, we did observe single nerve fibres in close proximity to the odontoblast layer at the end of intrauterine life. Nerve fibres were not detected in either predentine or dentine throughout foetal life.

Early development of the tush and the tusk of the African elephant (Loxodonta africana)

This early development was studied from a serial histological sections of eight elephant embryos with masses varying between 1 and 240 g. The tush and the tusk develop from one tooth germ in a deciduous to permanent tooth relation. In order to study the mineralization of the dental organ of the tush and cap and bell stage of the tusk, embryos older than 3-months' gestation (weighing more than 250 g) would be required.

Prenatal development of the alveolar bone of human deciduous incisors and canines

The formation of the human alveolar process around the incisors and canines is a hitherto unreported aspect of fetal oral development. The question is how, where, and when the alveolar process is formed. The purpose of this study was to elucidate the questions where and when and hence to analyze the pattern of formation of the alveolar bone around developing human deciduous canine and incisor teeth. The study was conducted with material selected from a sample of 61 normal human fetuses, legally or spontaneously aborted. Fertilization ages ranged from 9 to 22 weeks, crown-rump Length from 25 to 205 mm, and foot length from 4 to 34 mm. From this material, 7 maxillae and 10 mandibles were selected for the study according to developmental stages of the canines and incisors and according to the orientation of the histological sections. The skeletal investigation consisted of macroscopic and microscopic analysis of the mandibles and maxillae. The investigations revealed the absence of bone between the central and lateral incisors in the mandibles and maxillae of fetuses below the ages of 21 and 22 weeks, respectively. In three specimens, alveolar bone between the central and lateral incisors was recorded (21, 21, and 22 weeks of fertilization). Absence of bone labial to the canine was recorded in all fetuses investigated. In all other regions, alveolar bone occurred as a regular finding. The present study has shown that alveolar bone formation is strictly coordinated with tooth formation. Alveolar bone occurs later in the area labial to the canine and in the region between the central and lateral incisors than it does in other areas associated with the incisor/canine regions. Knowledge of this pattern in the formation of the alveolar process seems to be of importance for a future elucidation of how the alveolar process is initially formed.

Hyaluronan in human deciduous tooth germs in the bell stage. Histochemistry and immunohistochemistry

The primary aim of the present study was a localization of hyaluronan (HA) in human deciduous tooth germs in the bell stage. HA was compared to the content of chondroitin sulfates (CSs). HA was detected with a biotin-labeled HA-binding protein (HABP) and CS with a monoclonal antibody. As controls, enzyme digestions were carried out. Furthermore, the glycosaminoglycans were investigated histochemically with enzyme digestions followed by alcian blue staining. The investigation showed a considerable content of HA in the stellate reticulum, although CS was also found, primarily when treatment with protease was omitted. The dental papilla contained both HA and CS, while the predentin and the dentin contained only CS. The enamel did not contain any CS, but some staining with HABP was observed along the borderline between the ameloblasts and the enamel. The significance of HA in the stellate reticulum is discussed. The importance of carrying out investigations with and without protease digestions is stressed.

A scanning electron-microscopic study of developing human deciduous enamel on the dependence of the outline of surface pits on the angle of observation

On the developing enamel surfaces of fetal human deciduous teeth, many of the surface pits were arcade-shaped with the arcade preferentially pointing in a cervical direction. The configuration of the interprism ridges between the pits contributed to this appearance. Surface cracks allowed verification of an incisal inclination of the subsurface prisms. This apparent paradox was solved when the specimens were tilted so that the pits were viewed in the directions of the prisms, giving the pits a compressed arcade-shape with the arcades pointing incisally. It is recommended that care should be exercised and due attention paid to the angle of observation when determining the orientation of pit arcades. Pit entry direction seems to be a more reliable feature for inferring the direction of tangential ameloblast movement.

Aspects of teeth from archaelogic sites in Sweden and Denmark

The purpose of this study was to examine ground sections of primary second molars and permanent first molars from the same jaws. Teeth from 11 individuals were collected from archaeologic sites in Sweden and Denmark. Longitudinal buccolingual sections were examined in a polarization light microscope and in a Philips scanning electron microscope (SEM). The seven teeth from Sweden appeared to have been subjected to environmental influences at their burial site, which had affected both the dentin and the enamel. The teeth from the Danish sites had a normal color, and no disintegration of the dentin was seen. The general morphologic appearance was normal in all primary and permanent teeth. The position of the neonatal line indicated a normal full-term gestational age. The observed accentuated incremental lines in both the primary and permanent enamel suggested periods of dietary changes, possibly related to periods of illness. SEM images of the surface area of the Swedish teeth showed an extremely porous enamel surface with severe changes in the prism structure as an effect of acid penetration. The Danish teeth did not show any marked changes in the enamel.

Mineralized nodule formation by human dental papilla cells in culture

Human dental papilla cells were enzymatically separated from deciduous tooth germs of an 8-month-old embryo legally aborted. The second passage cells were cultured up to 35 days in 3 groups. The beta-GP group was cultured in the Dulbecco MEM containing ascorbic acid and beta-glycerophosphate supplemented with 15% fetal bovine serum. The Dex group was in the same medium, in addition containing dexamethasone. The control group contained none of the 3 chemicals. Mineralized nodules were formed after 15 days in the beta-GP and Dex groups. Only in the presence of ascorbic acid and organic phosphate did they mineralize. The addition of dexamethasone caused a significant increase in the number of nodules. By electron microscopy, the nodules contained needle-shaped crystals associated with a network of collagen fibrils. Calcium and phosphorus were detected by energy-dispersive X-ray microanalysis in the nodules. Furthermore, the crystalline material exhibited a pattern consistent with hydroxyapatite and dentin when examined by X-ray diffractometry. Cells showed high levels of alkaline phosphatase activity, which was increased 2-3 times in the presence of the 3 chemicals. These results indicated that human dental papilla cells have the ability to form dentin in culture. The formation of mineralized nodules by human dental papilla in vitro provides a useful model for studying the morphogenesis and differentiation of dental papilla ectomesenchyme.

Studies on the reduction indices of the deciduous teeth of Chinese living in Taiwan

The reduction index of deciduous teeth was investigated statistically. Materials used were plaster casts of the deciduous dentition taken from Chinese children living in Taiwan. The reduction indices showed no sexual differences. In the maxillary teeth, reduction indices of the bucco-lingual diameters (BL) had the largest values, followed by those of the mesio-distal diameters (MD), and those of the crown area (AREA) which were the least. In contrast to the maxillary teeth, in the mandibular teeth, the reduction indices of MD and those of BL had nearly the same values although the reduction indices of MD were slightly larger than those of BL in females (p < 0.05). With respect to the difference between the maxilla and the mandible, in deciduous incisors the reduction index of MD in the mandible was larger than that in the maxilla (p < 0.01). While in BL the reverse relation was noted. In the deciduous molars the reduction indices of BL and AREA in the maxilla were larger than those in the mandible (p < 0.01). The reduction indices showed no significant difference among the Mongoloid populations sampled. This result may be explained by the primitiveness of deciduous teeth.

[Morphological changes in the primordia of the deciduous teeth during an exacerbated course of the antenatal period]

Histologic examination of 380 rudimentary deciduous teeth of 91 stillborn babies or corpses of newborns dead within 16 days after birth and comparison of the results with clinical data brought the authors to a conclusion that the diagnosis of enamel hypoplasia is erroneous because all dental tissues are involved during this condition. Pathohistologic changes in the enamel, dentin, and tissues adjacent to dental rudiment are described in detail, all these tissues developing under unfavorable conditions of antenatal odontogenesis.

Development of the rabbit craniomandibular joint in association with tooth eruption

The adult rabbit craniomandibular joints (CMJs) are stress-bearing joints. The two CMJs and the teeth form an articular triad. In early fetal life the developing triad consists of the CMJ primordia, the tooth germs for the entire set of deciduous teeth, as well as the posterior extensions of the dental lamina, which will give rise to the permanent teeth with no deciduous predecessors. During postnatal life, before occlusion is established, there is a remodelling stage in which the CMJ builds up its matrix components such as collagenous and elastic fibres, proteoglycans and type II collagen. Remodelling gradually diminishes into the maintenance stage once occlusion is fully established and after eruption of the first and second molars. Chondrocytes first appear in the CMJ articular disc during the second week of postnatal development. These cells localize in the band areas of the disc and establish an extensive cartilaginous matrix 3-4 weeks postnatally. This study supports the concept that the full development of a fibrocartilaginous articular disc, rich in proteoglycans, occurs as adult occlusion is established.

[Embryologic studies on the development of tooth form]

3-dimensional reconstructions were made from serial sections of human embryos in order to trace back the development of the anlagen of the deciduous dentition. It could be shown that in the stage the late cap/early bell back contours of the inner enamel epithelium resemble the outlines of the later completed tooth. It is discussed that the shape of the earlier stages may set the preconditions for the further formation processes resulting in the occlusal morphology.

Formation and early prenatal location of the human mental foramen

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.

The origin of tooth number of the human deciduous dentition: a hypothesis

The constant number of 5 teeth per quadrant in the human deciduous dentition is seen to be a result of the mitotic activity within the dental lamina which leads to a constant number of centers in which cells are compressed together. These centers in which, due to the compression, the cells become narrow and cylindrical and, due to subsequent bulging, wedge-shaped, are the prerequisite for the formation of the constant number of five tooth buds per quadrant.

A histological study of the chronology of initial mineralization in the human deciduous dentition

Accurate dating of initial mineralization in the dentition was derived from fetuses aged according to the maternal history, assessment of gestational age by obstetricians, paediatricians and pathologists, histological evaluation of their cerebellar and renal development, and accurate measurements of crown-rump length, skull circumference, brain and body weight. Serial sections of the jaws of 121 fetuses ranging from 10 to 26 weeks post-menstrual age first showed mineralized dentine in the deciduous central incisor at 15-19 weeks, in the lateral incisor at 16-21 weeks, in the canine at 19-22 weeks, in the deciduous first molar at 16-19 weeks and in the second molar at 20-22 weeks. These age ranges differ from those for initial mineralization common in textbooks, particularly for the molars.

Scanning electron microscopy of developing human deciduous incisor teeth

The mineralized parts of the teeth of 17 human fetal dentitions, aged 15-38 weeks, were measured mesio-distally and occluso-cervically. The growth pattern of the incisors, with particular emphasis on the changes at the developing incisal edge was studied. Contralateral teeth in the same arch developed at approximately the same rate and with mirror-image morphology. Mineralization started in the upper and lower central incisors, followed by the corresponding lateral incisors. It then progressed at approximately the same rate for both incisors. At first, mesio-distal enamel growth was more significant, but was surpassed by occluso-cervical development later. Five development stages were identified as the incisors developed from a central lobe to the mature form. The main component of growth for the mesial lobe was in the incisal direction, and for the distal lobe in a distal direction, resulting in the characteristic approximal asymmetry of these teeth.

Crown area as an indicator of changing crown size in human pre-natal teeth

This study deals with correlations of tooth size in human primary teeth. Traditionally, mesiodistal or buccolingual measurements have been used to express crown size. However, in this study, crown area was used as a reference parameter. Graphic reconstructions of 38 histologically prepared human fetuses with Crown-Rump Length (CRL) between 54 and 280 mm were used to obtain linear and area measurements. Based on clinical records and physical examinations, these fetuses were considered typical-for-age, or "normal". Correlation matrices indicated high levels of concordance among all developing deciduous tooth crowns and arch measurements. It was concluded that crown area is a statistically better trait to use in comparison of teeth rather than the traditional mesiodistal measurement.

Development of deciduous and permanent dentition in Tarsius and its phylogenetic significance

The earliest stages of development and differentiation of deciduous and permanent teeth were studied in prenatal and perinatal tarsiers. Both deciduous and successional teeth develop at loci for I1, I2, C, P2-4. Relationships among the dental lamina, enamel organs, and successional lamina were used to determine tooth homologies. During the second half of prenatal life, dP2 and dI2 undergo abnormal development. Their dentin becomes fragmented, and these teeth are shed or resorbed without eruption during the perinatal period. Our study provides evidence of an intermediate phase in evolutionary tooth loss. These findings do not corroborate recent hypotheses of primate phylogeny based mainly on tooth eruption patterns.

Deciduous tooth dimensions in fetal rhesus monkeys from mothers with induced diabetes

Thirty-four measurements of the deciduous dentition in 21 fetal rhesus monkeys from diabetic mothers (FDM) and 36 nondiabetic fetuses were compared in order to assess the effects of induced maternal diabetes on the teeth of third-trimester fetuses. After exclusion of 14 variates due to significant age-related variation, univariate statistical analysis suggested a trend toward smaller teeth in the FDMs. Multivariate discriminant function analysis indicated not only a clear separation between the two groups, with molar breadths and some incisor length and breadths serving as the best discriminators, but also that the deciduous dental dimensions in FDMs are smaller than in nondiabetic fetuses.

[Structural organization of the microcirculatory bed of the primordia of human deciduous teeth]

By means of injection and noninjection techniques structural organization of microcirculatory bed in the deciduous (milk) teeth germs have been studied in human fetuses, newborns and children. A definite dependence of the angioarchitectonics on the developmental stage of every tooth has been stated. Morphological differentiation of separate parts of the microcirculatory ways in the dental papilla is connected with dentinogenesis, and in the dental saccule--with amelogenesis, periodontum and alveolar wall formation. Those dental germ zones which have a peculiar functional importance (peripheral parts of the dental papilla, dental saccule in the area of the epithelial dental organ) are characterized by the presence of certain structural-functional apparatuses which provide increasing contact areas between blood and the tissues. Intraorganic circulatory bed of the dental papilla consists of identically constructed vascular complexes. The conformity coefficient between the arteriolar inlet and the venular outlet of the dental papilla microcirculatory ways during dentinogenesis is between 0.16--0.3. It has been stated that devices regulating the blood stream in the deciduous tooth germs (anastomoses, sphincters, arcades, etc.) are forming during the antenatal and early postnatal periods.

Adjacency effects in developmental correlations among tooth organs in human fetuses

This study explores whether the "distance gradient" model shown for embryonic development and postnatal tooth growth is also characteristic of the fetal period. Histologic data and ratings from 26 human fetuses show that, unlike the embryonic and postnatal periods, changes occurring in two tooth germs are significantly alike, regardless of the number of intervening teeth.

Development of deciduous mandibular incisors related to developmental stages in the mandible

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.

Crown size-arch space relationships during human prenatal dental development

As shown in composite reconstructions made from optically-projected measurements of 10mu frontal maxillofacial sections of 20 histologically normal fetuses and embryos in the 70-255 mm CRL range, individual differences in relative tooth size and interdental spacing are evident by 10.5-11 weeks of gestation, and age-corrected crown-size correlations (r=0.40) approximate those in postnatal life. Despite an eight-fold increase in crown dimensions, interdental spacing remains approximately constant after 150 mm CRL, suggesting that the tooth organs or the periodontal membranes are able to maintain spacing, into the third trimester.

The early innervation of the developing deciduous teeth

Ingrowth of dental nerve fibres into the mesenchyme of the tooth-bearing areas of the mouth takes place at an relatively early stage, when the dental laminae are forming but the tooth buds are undeveloped. By the time a developing tooth has reached the cap and bell stages small nerve bundles have begun to enter the mesenchyme from which the dental papilla and sac arise.

Forensic dentistry and the human dentition in individual age estimations

The forensic dentist can estimate the age of an individual by observing the developing dentition. Systematic observations can provide accurate age estimations depending of the criteria used and the experience and training of the dentist. Anatomical, histological, and radiographic examinations of the teeth are of great value. Admittedly, some of the aforementioned methods are complicated and require prolonged time periods to perform. Alternative methods of age estimation may be required when rapid results are demanded by the police or other agencies. It is, however, the obligation of the forensic dentist to provide the precise age data. Therefore, all available resource materials must carefully evaluated, including the possible factors that may cause variations. Only after data is carefully evaluated can the error in age estimations be reduced.

Deciduous tooth chronology in the mandible of the domestic pig

Fetuses of known age, collected from 20 days' gestation to term, were used to characterize the chronology of deciduous tooth development within the right mandible of swine. Tooth development was first observed at 32 days' embryonic development, with the differentiation of the deciduous third molar. Bud stages for the remaining deciduous teeth differentiated within the period of 32 to 38 days of embryonic development. Although the initial histological appearance of these teeth covered a short period of time, it was apparent that each tooth continued to develop at its own rate. The deciduous second incisor and first molar reached a stage of enamel formation by the 80th and 86th day of fetal development. This is a much later stage than previously recorded for beginning enamel formation. The stages of tooth development and enamel formation for each tooth are summarized. A previous report on the distribution of the dental lamina and deciduous tooth development in the mandible of the domestic pig combined with the information presented in this report on tooth chronology provide much of the information required for future studies using the domestic pig in dental research. A fetus observed at the 74th day of development demonstrated a tooth bud for the deciduous first premolar. The development of this tooth was followed closely throughout the remainder of fetal development with the cap stage representing its most definitive form at 110 days' development. The suggested deciduous origin for this tooth could result in a reevaluation of the nomenclature for the dental formula of swine.