Pitted enamel hypoplasia in tuberous sclerosis

Thirty patients with tuberous sclerosis (from 29 different families) were examined for evidence of macroscopically visible pitted enamel hypoplasia. Of 23 patients with permanent teeth, 11 (48%) showed multiple enamel pits (mean 4.6 pits, range 3-9), but none were seen in six patients with deciduous teeth. Five of 563 controls (0.88%) had similar pitted enamel hypoplasia. Simple dental examination may be a useful adjunct in the assessment of patients with permanent teeth when a diagnosis of tuberous sclerosis is being considered, but is less likely to be helpful in the pre-school child.     

Developmental enamel defects in tuberous sclerosis: a clinical genetic marker?

Ten probands with tuberous sclerosis (TS) and 20 first degree relatives were examined for evidence of pitted enamel hypoplasia; 100% of TS patients had pitting, compared to 65% of relatives and 72% of 25 controls. We found that 70% of TS cases had more than 14 pits per person compared with only 5% of relatives and 4% of controls; 85% of relatives and 84% of controls had fewer than six pits per person. Our results confirm that significantly increased numbers of dental enamel pits are found in persons with TS compared to controls. These results suggest that examination for the presence or absence of dental enamel pits is not a useful screening test for first degree relatives to detect otherwise unsuspected subjects with tuberous sclerosis. However, the lack of pits in first degree relatives in our study is probably largely because none of the relatives appeared to carry the TS gene.     

Pitted enamel hypoplasia in tuberous sclerosis patients and first-degree relatives

Thirty-six families with tuberous sclerosis (TS) including 49 affected persons and 68 apparently unaffected first-degree relatives were examined for dental abnormality. Fifty unrelated controls were similarly examined. Clinically observed multiple enamel pits (pitted enamel hypoplasia) were noted in 71% of persons with typical TS and in one out of 10 "atypical" cases. Enamel pits were rarely seen, and in small numbers only, in the control series, and they were rare in the otherwise apparently normal TS first-degree relatives. However, one parent and one half-sib of persons with typical TS, but themselves without other signs of TS, were found to have multiple enamel pits. Examination for pitted enamel hypoplasia should be made in all persons suspected of having TS and in all close relatives; enamel pits are a valuable clinical sign and may identify otherwise unsuspected carriers of the gene within the family.     

Comparison between deciduous and permanent incisor teeth in morphology of bovine enamel.

Functional incisor teeth (deciduous and permanent teeth) from Bovidae (14 species) were prepared for scanning electron microscopic observation. Ultrastructural patterns of the enamel layer of deciduous and permanent incisor teeth varied (ex. prisms, arrangement pattern of matrices, and in thickness of enamel layer) in each species. The ultrastructures of prisms in longitudinal sections were classified into three types; A, radial, B, tangential, and C, mix of A and B arrangement enamel; modified Koenigswald's method (1982) in examined species. Type A was found in a large part of permanent and a small part of deciduous incisor teeth, while types B and C were mainly found in the deciduous teeth. These morphological features show the remarkable correlation between permanent and deciduous teeth.     

Effect of Down syndrome on the dimensions of dental crowns and tissues

Abnormal growth in Down syndrome (DS) is reflected by variable reduction in size and simplification in form of many physical traits. This study aimed to compare the thickness of enamel and dentine in deciduous and permanent mandibular incisor teeth between DS and non‐DS individuals and to clarify how these tissues contribute to altered tooth size in DS. Sample groups comprised 61 mandibular incisors (29 permanent and 32 deciduous) from DS individuals and 55 mandibular incisors (29 permanent and 26 deciduous) from non‐DS individuals. Maximum mesiodistal and labiolingual crown dimensions were measured initially, then the crowns were sectioned midsagittally and photographed using a stereomicroscope. Linear measurements of enamel and dentine thickness were obtained on the labial and lingual surfaces of the crowns, together with enamel and dentine–pulp areas and lengths of the dentino‐enamel junction. Reduced permanent crown size in DS was associated with a reduction in both enamel and dentine thickness. After adjustments were made for tooth size, DS permanent incisors had significantly thinner enamel than non‐DS permanent teeth. The DS permanent teeth also exhibited significant differences in shape and greater variability in dimensions than the non‐DS permanent teeth. Crown dimensions of deciduous incisors were similar in size or larger in DS compared with non‐DS deciduous teeth. Enamel and dentine thicknesses of the deciduous teeth were similar in DS and non‐DS individuals. The findings indicate that growth retardation in DS reduces both enamel and dentine deposition in the permanent incisors but not in the earlier‐forming deciduous predecessors. The results are also consistent with the concept of amplified developmental instability for dental traits in DS. Am. J. Hum. Biol. 13:690–698, 2001. © 2001 Wiley‐Liss, Inc.     

Presence of enamel on the incisors of the llama (Lama glama) and alpaca (Lama pacos)

Attempts have been made to define the relationships among the South American camelids, the guanaco, llama, alpaca, and vicuna, by comparing the morphology of their incisors. The alpaca has been reported to have an incisor morphology similar to the vicuna, lacking enamel on the lingual surface. The llama and guanaco are said to have enamel on both the labial and lingual surface of their incisor teeth. These comparisons have been based on gross morphological observations and not on histologic analysis. This study was undertaken to determine whether or not alpaca teeth have enamel on the lingual surface. The cross-sectional histologic anatomy of the incisor teeth was compared in two closely related South American camelid species, the llama (Lama glama), and the alpaca (Lama pacos). Thick sections (300 μm) and scanning electron microscopy were the techniques utilized. The mandibular first, second, and third incisors were examined in four llamas and five alpacas. A substantial layer of enamel was present on all surfaces of all llama incisors. The enamel layer on the labial surface of the alpaca incisors closely resembled that found in the llama. The enamel layer on the lingual surface of the alpaca incisors, although greatly reduced, was distinctly present. Alpacas may be more closely related to guanacos and llamas than to vicunas. A histologic study of vicuna incisors would help to better define the relationships of the four camelids. Anat Rec. 249:441–449, 1997. © 1997 Wiley-Liss, Inc.     

Cementum-like tissue deposition on the resorbed enamel surface of human deciduous teeth prior to shedding

Prior to the shedding of human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentin, and this resorption occasionally extends coronally from the dentinoenamel junction into the enamel. After the end of resorption, however, the resorbed enamel surface is repaired by the deposition of a cementum-like tissue. Using this phenomenon as an observation model, in this study we examined the sequence of cellular and extracellular/matrix events involved in the enamel resorption repair by light and electron microscopy. As the odontoclast terminated its resorption activity, it detached from the resorbed enamel surface; thereafter, numerous mononuclear cells were observed along the resorbed enamel surface. Most of these mononuclear cells made close contact with the resorbed enamel surface, and coated pits or patches were observed on their plasma membrane facing this surface. Furthermore, they frequently contained thin needle- or plate-like enamel crystals in their cytoplasmic vacuoles as well as secondary lysozomes. Following the disappearance of these monononuclear cells, the resorbed enamel surface now displayed a thin coat of organic matrix. Ultrastructurally, this organic layer was composed of a reticular and/or granular organic matrix, but contained no collagen fibrils. Energy-dispersive X-ray microanalysis of this thin organic layer in undecalcified sections revealed small spectral peaks of Ca and P. Cementum-like tissue initially formed along this thin organic layer, increased in width, and appeared to undergo mineralization as time progressed. The results of our observations demonstrate that regardless of type of matrix of dental hard tissues, tooth repair may be coupled to tooth resorption, and suggest that mononuclear cells and an organic thin layer found on the previously resorbed enamel surface may play an important role in the repair process initiated after resorption of the enamel.     

In Vivo Microstructural Analysis of Enamel in Permanent and Deciduous Teeth

Confocal microscope was used to analyze human enamel from 10 deciduous and 10 permanent teeth. Optically sectioned images were obtained. A more intense autofluorescence was found in primary teeth. This finding might be due to the greater presence of organic substances in deciduous enamel. The mean prism diameter measurement in permanent teeth enamel was 3.150?µm and 2.602?µm in deciduous teeth. The mean prism diameter in deciduous teeth was statistically least. The results indicate that a confocal microscope may be of help in analyzing and defining the microscopic features of human enamel.     

Immunocytochemical localization of amelogenins in the deciduous tooth germs of the human fetus

The immunocytochemical localization of amelogenins in the developing deciduous tooth germs of 6-month-old human fetuses was investigated by the protein A-gold method using an antiserum against porcine 25K amelogenin. The inner enamel epithelial cells and underlying matrix showed no amelogenin-like immunoreactivity. Distinct immunoreactivity was initially shown by fine fibrils found beneath the intact basal lamina of preameloblasts at the early differentiation stage. At the late differentiation stage, amelogenin-like immunoreactivity was shown by a fine granular material within the extracellular matrix as well as by the Golgi apparatus, secretory granules, lysosomal structures, coated vesicles, and coated pits of preameloblasts with a disrupted basal lamina. At the formative stage, the localization of immunoreactivity in secretory ameloblasts was similar to that in preameloblasts during the late differentiation stage. However, immunopositive coated vesicles and coated pits were only found at the early stage of matrix formation. The calcified enamel matrix and stippled material showed intense immunoreactivity. Immunocytochemical labeling of the enamel matrix appeared as a gradient, decreasing from the enamel surface to the dentinoenamel junction. No maturation stage of ameloblasts existed in the tooth germs examined. In predentin and dentin, amelogenin-like immunoreactivity was occasionally detected on odontoblasts and their processes, but odontoblasts and cells of the stratum intermedium contained no immunoreactive elements. These findings confirmed that the secretory ameloblast in the human deciduous tooth germ is responsible for the synthesis and secretion of enamel proteins.     

Changes in mineral distribution and concentration during enamel development in the deciduous human maxillary and mandibular teeth

The present study describes the detailed changes in mineral concentration in developing human enamel across the different stages of development from early formation to maturation in the human maxillary and mandibular deciduous teeth. The results indicate a stage in the development of enamel in each of the deciduous human teeth in which the tissue becomes porous due to a loss of matrix protein which is subsequently replaced by mineral during the maturation process with the enamel finally becoming fully mineralized and hard. The time of appearance of this porous stage varies in the different deciduous teeth. The importance of this stage with regards to enamel susceptibility to metabolic influences is discussed.     

Speech production errors in adults with and without Down syndrome following verbal,written, and pictorial cues

Adults with Down syndrome and adults with developmental delays not related to Down syndrome were asked to read, repeat, and formulate speech from a picture following the presentation of 2- and 4-word and picture sequences. The speech sequences were produced either immediately after stimulus presentation or following a 5-sec response delay. Overall, participants with Down syndrome produced more memory errors than persons without Down syndrome. Participants with Down syndrome also committed more speech production errors than the other participants, but only when they were required to repeat what they had heard, or to formulate speech from pictures. The speech production performance of the two groups was equivalent in the read condition. These results are discussed with reference to Elliott, Weeks, and Elliott's (1987) model of cerebral specialization, and to verbal short-term memory in persons with Down syndrome.     

Hunter-Schreger Band patterns in human tooth enamel

Using light microscopy, we examined Hunter‐Schreger Band (HSB) patterns on the axial and occlusal/incisal surfaces of 160 human teeth, sectioned in both the buccolingual and mesiodistal planes. We found regional variations in HSB packing densities (number of HSBs per mm of amelodentinal junction length) and patterns throughout the crown of each class of tooth (maxillary and mandibular: incisor, canine, premolar, and molar) examined. HSB packing densities were greatest in areas where functional and occlusal loads are greatest, such as the occlusal surfaces of posterior teeth and the incisal regions of incisors and canines. From this it is possible to infer that the behaviour of ameloblasts forming enamel prisms during amelogenesis is guided by genetic/evolutionary controls that act to increase the fracture and wear resistance of human tooth enamel. It is suggested that HSB packing densities and patterns are important in modern clinical dental treatments, such as the bonding of adhesive restorations to enamel, and in the development of conditions, such as abfraction and cracked tooth syndrome.     

Development and size of the teeth of Macaca mulatta

A cross-sectional sample of 151 skulls from Macaca mulatta of known age and similar rearing in U.S. Primate Centers was analyzed to determine age-related “norms” of stages of development and size of teeth. The stages of development from the follicle of a deciduous incisor in the fetus to completion of the root with apex closed of the permanent third molar were related to age. The age range observed for eruption of each tooth was noted and related to its stage of development. The crown of each erupted tooth was found to be completely developed, but growth of its root continued for a longer, indeterminate period. When a deciduous tooth was exfoliated, the crown of the permanent successor was found to be completed and root growth had begun. Measurements of both mesiodistal and faciolingual diameters and of crown length of the teeth in situ and of total length and root length on roentgenograms were examined for sexual dimorphism. The faciolingual diameter of the deciduous mandibular second incisor and of both second molars showed the greatest sexual dimorphism among both diameters of all deciduous teeth. The mesiodistal and faciolingual diameters of the mandibular premolars were found to be the best dimensions in discriminant functions for identifying sex in the absence of permanent canines.     

Enamel biorhythms of humans and great apes: the Havers‐Halberg Oscillation hypothesis reconsidered

The Havers‐Halberg Oscillation (HHO) hypothesis links evidence for the timing of a biorhythm retained in permanent tooth enamel (Retzius periodicity) to adult body mass and life history traits across mammals. Potentially, these links provide a way to access life history of fossil species from teeth. Recently we assessed intra‐specific predictions of the HHO on human children. We reported Retzius periodicity (RP) corresponded with enamel thickness, and cusp formation time, when calculated from isolated deciduous teeth. We proposed the biorhythm might not remain constant within an individual. Here, we test our findings. RP is compared between deciduous second and permanent first molars within the maxillae of four human children. Following this, we report the first RPs for deciduous teeth from modern great apes (n = 4), and compare these with new data for permanent teeth (n = 18) from these species, as well as with previously published values. We also explore RP in teeth that retain hypoplastic defects. Results show RP changed within the maxilla of each child, from thinner to thicker enameled molars, and from one side of a hypoplastic defect to the other. When considered alongside correlations between RP and cusp formation time, these observations provide further evidence that RP is associated with enamel growth processes and does not always remain constant within an individual. RP of 5 days for great ape deciduous teeth lay below the lowermost range of those from permanent teeth of modern orangutan and gorilla, and within the lowermost range of RPs from chimpanzee permanent teeth. Our data suggest associations between RP and enamel growth processes of humans might extend to great apes. These findings provide a new framework from which to develop the HHO hypothesis, which can incorporate enamel growth along with other physiological systems. Applications of the HHO to fossil teeth should avoid transferring RP between deciduous and permanent enamel, or including hypoplastic teeth.     

Mental retardation in Down syndrome: a hydrogen sulfide hpothesis

Mental retardation is progressive in Down syndrome: individuals are born with normal intelligence which starts to decline linearly within the first year. This phenomenon can be observed with phenylalanine in patients with phenylketonuria, therefore it is compatible with metabolic intoxication. The toxic compound could be hydrogen sulfide. The amount of the compound is probably increased in Down syndrome by increasing active cystathionine beta synthase. This heuristic hypothesis requires further investigation.     

The distribution of proliferating cells during odontogenesis in the incisor teeth of Plecoglossus altivelis

To examine the distribution of enameloid and proliferating cells during odontogenesis in the incisor teeth of Plecoglossus altivelis, we investigated the distribution of enameloid using alizarin red S and the distribution of bromodeoxyuridine (BrdU)-immunoreactive cells during odontogenesis of the teeth of the fish. Enameloid was present over the entire surface layer of the incisor teeth. BrdU-immunoreactive cells were observed in the inner and outer enamel epithelium, the odontoblasts, and dental papilla cells around the regions currently being formed. These findings suggest that ameloblasts and odontoblasts actively divide around the region currently being formed, suggesting that enameloid and dentin are made in cooperation by ameloblasts and odontoblasts.     

经典型苯丙酮尿症合并21-三体综合征患儿一例临床研究

目的对一例经典型苯丙酮尿症合并21-三体综合征患儿的临床特征进行研究。方法采用BH4负荷试验结合尿喋呤谱和红细胞二氢喋啶还原酶(DHPR)活性测定的方法对高苯丙氨酸血症进行诊断分型;G显带技术分析外周血染色体核型。结果①患儿诊断为经典型苯丙酮尿症。②患儿外周血染色体核型为47,XX,+21,诊断为21-三体综合征。结论苯丙酮尿症可能合并有其他遗传代谢性疾病,临床诊断须全面。     

Neopterin and the risk of dementia in persons with Down syndrome

Persons with Down syndrome show an altered immune response and an increased susceptibility to Alzheimer's disease. In a prospective study, we examined whether the plasma neopterin level, a marker for cell-mediated immune activation and inflammation, is associated with an increased risk of dementia in persons with Down syndrome. Plasma concentrations of neopterin were determined in a population-based study of 394 persons with Down syndrome, who were screened annually for dementia. We used Cox proportional hazards model to determine risk of dementia. Demented persons with Down syndrome have a significantly (p = 0.05) higher plasma neopterin concentration than the non-demented. In the non-demented without autoimmune disorders, in those with a plasma level of neopterin above median, the risk to develop dementia increased to 1.83 (95% confidence interval: 1.04–3.20). High plasma neopterin level is an independent determinant of the risk of dementia in persons with Down syndrome.     

Enamel Structure and Composition in the Tricho-Dento-Osseous Syndrome

Tricho-dento-osseous syndrome (TDO) is an autosomal dominant disorder characterized by curly hair, hypoplastic enamel, taurodontism, and dense bone. The purpose of this investigation was to characterize the enamel defects in a TDO population in North Carolina. Twelve TDO teeth and 12 normal teeth were examined. The enamel thickness was decreased in all TDO teeth ranging from having no enamel to about 60% the thickness of normal teeth. Half of the TDO teeth had primarily prismless enamel while the remainder had at least occasional areas of prismatic enamel. TDO enamel crystallites appeared similar to normal crystallites with TEM. The mineral per volume of TDO enamel (n =9) (68.5%) was significantly less, on average, compared with normal enamel (n=8) (84.5). The genetic mutation responsible for the TDO phenotype results in alteration of a developmental pathway(s) common to hair, teeth and bone. This further illustrates that these embryologically diverse tissues share common developmental controls at the molecular level.