PubMed Health⌕ Search

Biomedical subjects

M C Dean

Publications and source records attributed to M C Dean.

At least 19 recordsLinked to original sources
PubMed2006

Molar development in common chimpanzees (Pan troglodytes).

Numerous studies have reported on enamel and dentine development in hominoid molars, although little is known about intraspecific incremental feature variation. Furthermore, a recent histological study suggested that there is little or no time between age at chimpanzee crown completion and age at molar eruption, which is unlikely given that root growth is necessary for tooth eruption. The study presented here redefines growth standards for chimpanzee molar teeth and examines variation in incremental features. The periodicity of Retzius lines in a relatively large sample was found to be 6 or 7 days. The number of Retzius lines and cuspal enamel thickness both vary within a cusp type, among cusps, and among molars, resulting in marked variation in formation time. Daily secretion rate is consistent within analogous cuspal zones (inner, middle, and outer enamel) within and among cusp types and among molar types. Significantly increasing trends are found from inner to outer cuspal enamel (3 to 5 microns/day). Cuspal initiation and completion sequences also vary, although sequences for mandibular molar cusps are more consistent. Cusp-specific formation time ranges from approximately 2 to 3 years, increasing from M1 to M2, and often decreasing from M2 to M3. These times are intermediate between radiographic studies and a previous histological study, although both formation time within cusps and overlap between molars vary considerably. Cusp-specific (coronal) extension rates range from approximately 4 to 9 microns/day, and root extension rates in the first 5 mm of roots range from 3 to 9 microns/day. These rates are greater in M1 than in M2 or M3, and they are greater in mandibular molars than in respective maxillary molars. This significant enlargement of comparative data on nonhuman primate incremental development demonstrates that developmental variation among cusp and molar types should be considered during interpretations and comparisons of small samples of fossil hominins and hominoids.

Age Determination by Teeth↗
PubMed2005

Variation in modern human enamel formation times.

Most of what we know about the timing of human enamel formation comes from radiographic studies on children of known age. Here, we present new longitudinal data derived from a histological analysis of tooth enamel. Two samples, one from southern Africa and one from northern Europe, contained all anterior and molar tooth types. Two further samples contained only one tooth type: canines from a medieval Danish sample and third molars from a modern North American sample. Data were collected on 326 molars and 352 anterior teeth. Each tooth was sectioned and prepared for polarized light microscopy. We used daily enamel cross striations to determine cuspal enamel formation time, recorded the periodicity of long-period striae in the lateral enamel, and used this value to calculate enamel formation times for each decile of crown length. We present data that reveal some of the processes whereby differences in enamel formation times arise between our samples. Mean cuspal enamel formation times were similar in southern African and northern European anterior teeth, but differed in certain molar cusps. All the southern African anterior teeth completed enamel formation earlier. The greatest difference in mean chronological age at enamel completion was 5.2 vs. 6.2 years of age in lower canines. However, enamel completion times in the molar teeth showed few differences between the samples, with mean times for the longest forming cusps all falling between 3.0 years and 3.45 years. Our data suggest fewer differences between samples and smaller ranges of variation than in many radiographic studies and present a more realistic picture of worldwide variation in enamel formation times.

Amelogenesis↗
PubMed2005

Dental development and life history in Anapithecus hernyaki.

The sample of Anapithecus from Rudabánya, Hungary, is remarkable in preserving a large number of immature individuals. We used perikymata counts, measurements of root length and cuspal enamel thickness, and observations of the sequence of tooth germs that cross match specific developmental stages in Anapithecus to construct the first composite picture and time scale for dental development in a pliopithecoid (Catarrhini, Primates). We conclude that the age of eruption of M1 in Anapithecus was similar to various macaque species (approximately 1.45 months), but that M2 and M3 emergence were close to 2.2 and 3.2 years, respectively (both earlier than expected for similarly sized cercopithecoids). There may have been little difference in individual tooth formation times between cercopithecoids and Anapithecus, but the degree of molar overlap during M1, M2, and M3 crown development, which is extreme in Anapithecus, is fundamentally different. Overall dental development in Anapithecus was very rapid. Old World monkeys appear derived in lacking significant molar overlap, and hominoids may be derived in having longer tooth formation times, both resulting in longer overall dental development times. This is consistent with the general conclusion that the Pliopithecoidea is an outgroup to the Cercopithecoidea and the Hominoidea. On the other hand, rapid dental formation in Anapithecus may be an apomorphy indicative of an unusually rapid life history or unique pressures related to diet and maturation. Folivory and/or predation pressure may be responsible for generating selection to more rapidly erupt permanent teeth and possibly attain adult body masses in Anapithecus. Whatever the case, Anapithecus, with an M3 emergence of approximately 3.2 years, is dramatically faster than any extant catarrhine of similar body mass. This represents yet another unusual attribute of this poorly known fossil catarrhine.

Adaptation, Physiological↗
PubMed2001

Perikymata spacing and distribution on hominid anterior teeth.

We documented the spacing and distribution of perikymata on the buccal enamel surface of fossil hominin anterior teeth with reference to a sample of modern human and modern great ape teeth. A sample of 27 anterior teeth attributed to Australopithecus (5 to A. afarensis, 22 to A. africanus) and of 33 attributed to Paranthropus (6 to P. boisei, and 27 to P. robustus) were replicated and sputter-coated with gold to enable reflected light microscopy of their surface topography. Anterior teeth were then divided into 10 equal divisions of buccal crown height. The total perikymata count in each division of crown height was recorded using a binocular microscope fitted with a vernier micrometer eyepiece. Then the mean number of perikymata per millimeter was calculated for each division. Similar comparative data for a modern sample of 115 unworn human anterior teeth and 30 African great ape anterior teeth were collected from ground sections. Perikymata counts in each taxon (together with either known or presumed periodicities of perikymata) were then used to estimate enamel formation times in each division of crown height, for all anterior tooth types combined. The distributions of these estimates of time taken to form each division of crown height follow the same trends as the actual perikymata counts and differ between taxa in the same basic way. The distinction between modern African great apes and fossil hominins is particularly clear. Finally, we calculated crown formation times for each anterior tooth type by summing cuspal and lateral enamel formation times. Estimates of average crown formation times in australopiths are shorter than those calculated for both modern human and African great ape anterior teeth. The data presented here provide a better basis for exploring differences in perikymata spacing and distribution among fossil hominins, and provide the first opportunity to describe four specimens attributed to Homo in this context. Preliminary data indicate that differences may exist among the species attributed to early Homo, especially between Homo ergaster and Homo rudolfensis on the one hand, and Homo habilis sensu strico on the other.

Animals↗
PubMed2000

Effect of temperature on the separation of DNA fragments by high-performance liquid chromatography and capillary electrophoresis: a comparative study.

This study investigates the effect of experimental temperature on the separation of DNA fragments, 21-587 bp, by both high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). The results show that the temperature plays an important role in the HPLC separation of DNA fragments. The optimum temperature was found to be between 40 and 50 degrees C for HPLC, while 25 degrees C was the optimum temperature for the CE separation. Also, although CE migration times became shorter, efficiency and resolution decreased with an increase in temperature from 25 to 50 degrees C, but the separation was not significantly affected. Also, the optimum HPLC temperature might be different depending on the fragment sizes to be resolved.

Chromatography, High Pressure Liquid↗
PubMed2000

Brief communication: the timing of linear hypoplasias on human anterior teeth.

One hundred and fifteen unworn anterior teeth were sectioned longitudinally with a diamond saw and prepared for histological examination by polarized light microscopy. Incremental markings in the enamel of each tooth were used to estimate the average total crown formation times of each tooth type. The total time taken to form the crowns of each tooth type was apportioned by 1) cuspal enamel formation and 2) each tenth percentile of total tooth height. Based on these data, and on histological estimates for the time of initiation of mineralization in each anterior tooth, the following conclusions can be drawn. Little if any visible surface enamel is likely to form before the end of the first year after birth in any anterior tooth type. No relation exists between tooth crown height and the total time taken to form enamel. Anterior crown formation is nonlinear and slows towards the cervix in all teeth. The estimated mean chronological age at crown completion ranged in this study from between around 4 years for lower central incisors to around 6 years for lower canines. We suggest that these combined findings will be useful for devising more reliable ways to estimate the timing of linear enamel hypoplasias than some methods currently in use.

Dental Enamel Hypoplasia↗
PubMed1999

Morphological variation in great ape and modern human mandibles.

Adult mandibles of 317 modern humans and 91 great apes were selected that showed no pathology. Adult mandibles of Pan troglodytes troglodytes, Pongo pygmaeus pygmaeus and Gorilla gorilla gorilla and from 2 modern human populations (Zulu and Europeans from Spitalfields) were reliably sexed. Thirteen measurements were defined and included mandibular height, length and breadth in representative positions. Univariate statistical techniques and multivariate (principal component analysis and discriminant analysis) statistical techniques were used to investigate interspecific variability and sexual dimorphism in human and great ape mandibles, and intraspecific variability among the modern human mandibles. Analysis of interspecific differences revealed some pairs of variables with a tight linear relationship and others where Homo and the great apes pulled apart from one another due to shape differences. Homo and Pan are least sexually dimorphic in the mandible, Pan less so than Homo sapiens, but both the magnitude of sexual dimorphism and the distribution of sexually dimorphic measurements varied both among and between modern humans and great apes. Intraspecific variation among the 10 populations of modern humans was less than that generally reported in studies of crania (74.3% of mandibles were correctly classified into 1 of 10 populations using discriminant functions based on 13 variables as compared with 93% of crania from 17 populations based on 70 variables in one extensive study of crania). A subrecent European population (Poundbury) emerged as more different from a recent European population (Spitalfields) than other more diverse modern populations were from each other, suggesting considerable morphological plasticity in the mandible through time. This study forms a sound basis on which to explore mandibular variation in Neanderthals, early Homo sapiens and other more ancient fossil hominids.

Adult↗
PubMed1998

Caroline Crachami, the Sicilian dwarf (1815-1824): was she really nine years old at death?

Caroline Crachami (C.C.) considered to have had the Seckel syndrome was one of the most extreme cases of dwarfism ever recorded. Reputedly born in Sicily in 1815, she attracted much attention when exhibited in England before her death on 3 June 1824. Although she is said to have been 9 years old at death, published descriptions give her a dental age varying from 2 to 7 years. Examination of her skull in the Royal College of Surgeons of England demonstrated a more or less erupted complete deciduous dentition, with no erupted permanent teeth. Radiographs showed agenesis of several permanent teeth. It was concluded that the dental age of C.C. was 3 years (+/- 6 months). Perikymata were evident in the surface enamel encircling the crown of the partially exposed maxillary left first permanent molar. Their distribution and spacing were normal, with no evidence of developmental retardation. The distance between the periradicular bands in the root near the cement-enamel junction was also normal. We conclude that the dental age of C.C. was similar to her chronological age and that at death she was about 3 and not 9 years old. The reason that she was said to be nearly 9 when exhibited in England we believe was related to financial considerations, as people would be generally less impressed with a dwarf only 3 years old. The new age we give C.C. has implications on the diagnosis of her medical condition.

Age Determination by Skeleton↗
PubMed1998

Comparative dental development and microstructure of Proconsul teeth from Rusinga Island, Kenya.

Eighteen histological sections were prepared from eleven teeth attributed to Proconsul heseloni and two molar teeth attributed to Proconsul nyanzae. Measurements of spacings and counts of daily incremental markings in both enamel and dentine were possible in the majority of these tooth sections. Measurements of the spacings and angles to the enamel dentine junction (EDJ) of regular striae of Retzius and of equivalent markings in dentine were also made. In addition to these measurements, counts of perikymata were made on replicas of all other Proconsul teeth housed in the National Museum of Kenya, Nairobi, that preserved good perikymata on any aspect of their tooth surface. The sequence of crown formation in Proconsul and the crown formation times of the enamel and dentine were estimated from these data. In addition, the rates of root extension were estimated using the formula derived for this purpose by Shellis (Archs. oral Biol. 29, 697-705, 1984) and estimates of the total period of root formation subsequently made for premolar and molar teeth based on measurements of root length. A composite chart of dental development for P. heseloni is presented which suggests M3 root completion was between six and seven years of age. In general Proconsul molar teeth have high stria angles to the EDJ, a high ratio of enamel formed with respect of dentine formed at the same time, median values of rates of enamel formation close to the EDJ in excess of 4 microns per day and the occasional presence of "S-shaped" striae in the lateral enamel. There is no evidence to suggest that Proconsul from Rusinga Island, Kenya, had relatively thin enamel on molar or premolar teeth. When all of these data are considered in a comparative context, Proconsul emerges overall as hominoid-like in its enamel and dentine microstructure and as most similar to Pongo but with some features shared with Pan and Homo. Similar data for other Miocene primates will have considerable bearing on how these data are interpreted. These new data on dental microanatomy and on dental development in Proconsul make a further contribution to our understanding of the total morphological picture of this early Miocene primate.

Animals↗
PubMed1998

Comparative observations on the spacing of short-period (von Ebner's) lines in dentine.

The spacing of short-period incremental markings in dentine was measured in longitudinal ground sections and in longitudinal demineralized silver-stained sections of permanent human canines and premolars. Measurements were made (i) within 50 microm from the granular layer of Tomes (GLT), (ii) between 100 and 200 microm from the GLT, and (iii) in the axial plane of the tallest cusps. Median values for the spacing of calcospheritic lines closest to the GLT in the ground sections increased from 1.8 to 2.8 microm as the lines gradually coalesced into a laminar pattern beyond the GLT pulpally. Median values for the spacing of short-period lines in the cuspal dentine, where dentine formation is known to be fastest, were 4.1 microm. Markings in the demineralized sections were between 25 and 39% closer together, presumably due to contraction and shrinkage during specimen preparation. The spacings of short-period incremental lines measured on ground sections of non-human primate dentine (gibbon, siamang, orang) and on pig dentine, all between 100 and 200 microm from the GLT, clustered between 2.5 and 3.5 microm. Apart from gibbon dentine (in which spacings were closer together in this position than in the others), the distribution of measurements was not significantly different in pig, orang or human dentine. However, none of the data for the comparative samples presented here revealed spacings of short-period lines anywhere close to the 16 microm previously reported for circumpulpal dentine in animals. These data suggest that there may be many other animals where the mode and, to some extent, rate of dentine mineralization close to the root surface follows a common pattern. While data for the spacing of incremental markings in dentine provide no evidence for their periodicity, it is clear that the measurements made in the ground sections match the reported daily rates of mineralization at these locations, whereas those in demineralized silver-stained sections do not. Tissue shrinkage is probably a better explanation for this than the generally accepted view that they represent 12 h increments of dentine mineralization. This study provides a better basis for identifying and describing these lines, and for distinguishing them from other kinds of incremental markings in dentine.

Animals↗
PubMed1997

A comparison of two prophylaxis angles: disposable and autoclavable.

In a clinical trial, the authors evaluated the effectiveness of stain, plaque and debris removal, as well as patient and hygienist acceptance, of the disposable prophylaxis angle vs. the autoclavable prophylaxis angle. Thirty patients received a dental prophylaxis by hygienists for up to 45 minutes. A clinician performed blinded pre- and post-prophylaxis evaluations for stain, plaque and debris. A matched pairs t-test determined significant differences (P < .05) between groups. Significantly less stain, plaque and debris remained following use of the disposable vs. the autoclavable angle.

Dental Equipment↗
PubMed1996

The relation between long-period incremental markings in dentine and daily cross-striations in enamel in human teeth.

Ground sections of human permanent teeth were chosen where fluorescent labels in the dentine, resulting from repeated doses of tetracycline antibiotic, were unambiguously associated with accentuated markings in the enamel developing at the same time. Counts of daily cross-striations in enamel were continued from one tooth to another in a developmental sequence over a period of some 1200 days such that the time interval between doses of tetracycline could be calibrated. Long-period incremental markings in the dentine, spaced on average between 15 and 30 microns apart (and first described by Andresen in 1898) were easily visible in the coronal dentine when the ground sections were viewed with polarized light. The total number of long-period incremental markings in the dentine between the consecutive fluorescent labels was also counted. A regression plot of daily incremental lines in enamel against long-period lines in dentine demonstrated a regular and consistent relation between the two (r = 0.997) over a 1200-1300-day period. These data support the hypothesis that long-period markings in dentine are in fact regular incremental markings with a constant periodicity in an individual. They also suggest that regular long-period markings in dentine can be used to reconstruct the timing of tooth growth or to retrieve developmental information about dentine formation rates in forensic, archaeological and palaeontological studies with some confidence.

Anti-Bacterial Agents↗
PubMed1993

Increasing human tooth length between birth and 5.4 years.

Most previous studies of tooth development have used fractional stages of tooth formation to construct growth standards suitable for aging juvenile skeletal material. A simple alternative for determining dental age is to measure tooth length throughout development. In this study, data on tooth length development are presented from 63 individuals of known age at death, between birth and 5.4 years, from an archeological population recovered from the crypt of Christ Church, Spitalfields, London. Isolated developing teeth (304 deciduous, 269 permanent) were measured in millimeters and plotted against individual age. Regression equations to estimate age from a given tooth length, are presented for each deciduous maxillary and mandibular tooth type and for permanent maxillary and mandibular incisors, canines, and first permanent molars. Data on the earliest age of root completion of deciduous teeth and initial mineralization and crown completion of some permanent teeth in this sample are given, as well as the average crown height and total tooth length from a small number of unworn teeth. This method provides an easy, quantitative and objective measure of dental formation appropriate for use by archeologists and anthropologists.

Age Determination by Teeth↗
PubMed1993

Histological reconstruction of dental development and age at death of a juvenile Paranthropus robustus specimen, SK 63, from Swartkrans, South Africa.

There has been disagreement about whether the earliest hominids grew in a similar manner to great apes or modern humans. This has important biological implications, since it may have been inappropriate to apply modern human developmental standards to early hominids. The aim of the present study was to combine data from replicas of tooth surfaces, computed tomographic (CT) scans, and radiographs with data from a histological section of the canine crown, in order to provide a complete description of tooth crown and tooth root development in a single early hominid specimen (SK 63). Although partially destructive in nature, we have been able to determine the most reliable data yet for aspects of dental development in an important juvenile early hominid specimen. Appositional enamel formation time in the permanent right canine was estimated at between 305 and 418 days, imbricational enamel formation time at 819 days, and total crown formation time at between 3.18 and 3.48 years. The most likely age at death was estimated at around 4 years with a range of ages calculated between 3.18 and 4.23 years based on differences in timing of initial mineralization of the canine and differences in appositional enamel formation times. Crown formation times of the lower central and lateral incisors were estimated between 2.35-2.68 years and 2.57-2.91 years, respectively. Crown formation time of the first permanent molar was estimated at 2.4 years. Wear facets on the first permanent molars indicate that gingival emergence had occurred sometime prior to death, between 3 and 4 years of age. Estimates of root extension rates in the first permanent molars and in the permanent incisors are fast, and either within or above ranges of rates estimated for modern great apes. While we recognize that data for one individual may not be representative of data for a whole population of early hominids, the data for age at death, for age of M1 emergence, and for root extension rates presented here accord with those known for modern great apes and fall beyond the known ranges for modern humans.

Age Determination by Teeth↗
PubMed1991

Tooth crown heights, tooth wear, sexual dimorphism and jaw growth in hominoids.

The aim of this review is to bring together data that link tooth morphology with tooth function and tooth growth: We aim to show how the microanatomy of hominoid teeth is providing evidence about rates of tooth growth that are likely to be a consequence of both masticatory strategy and social behaviour. First, we present data about incisor and molar tooth wear in wild short chimpanzees that demonstrate how crown heights are likely to be related to relative tooth use in a broad sense. Following this we review recent studies that describe the microanatomy of hominoid tooth enamel and show how these studies are providing evidence about tooth crown formation times in hominoids, as well as improving estimates for the age at death of certain juvenile fossil hominids. Next, we outline what is known about the mechanisms of tooth growth in the sexually dimorphic canine teeth of chimpanzees and compare these patterns of growth with tooth growth patterns in the canines of three fossil hominids from Laetoli, Tanzania. Finally, we discuss how selection pressures that operate to increase or reduce the size of anterior teeth interact with jaw size. We argue that the space available to grow developing teeth in the mandibles of juvenile hominoids is determined by the growth patterns of the mandibles, which in turn reflect masticatory strategy. The consequences of selection pressure to grow large or small anterior teeth are likely to be reflected in the times at which these teeth are able to emerge into occlusion.

Animals↗
PubMed1989

The developing dentition and tooth structure in hominoids.

This review of hominoid dental development is presented in two parts. The first section reviews (1) the general relationship between dental development and life history in hominoids; (2) the methods used to document dental development, and (3) the nature of incremental growth markings in hominoid teeth. The second section builds on this and reviews the contributions to hominoid dental development that have been made by (1) studies of tooth emergence; (2) studies of tooth calcification stages, and (3) histological studies of incremental growth markings made either from sections of teeth or replicas of early hominid teeth prepared for scanning electron microscopy.

Animals↗
PubMed1988

Distinct dental development patterns in early fossil hominids.

New studies on the jaws of hominids, based on incremental growth markings in teeth, can now provide an absolute timescale with which to calibrate dental developmental events such as tooth emergence. These new estimates of crown-formation times and the observed sequences of dental development are different in the hominids Australopithecus and Paranthropus. Early hominids evidently had shorter periods of dental development than modern humans and therefore a less prolonged infancy.

Animals↗