Dentinal Growth Research Articles

AGE and SEX COMPOSITION OF THE STRIPED DOLPHIN DIE‐OFF IN THE WESTERN MEDITERRANEAN

AbstractDuring the morbillivirus epizootic that affected the Mediterranean striped dolphins (Stenella coeruleoalba)in 1990–1992, several thous and individuals are believed to have died. In order to determine the segments of the population that were affected by the event, the sex‐ and age‐frequency distributions of the animals that were washed ashore on the Spanish coasts were studied. The age of the animals was determined by counting dentine growth layer groups in the teeth. The results obtained indicate that both sexes were affected similarly by the disease and that the population component that suffered the largest mortality was that of sexually mature individuals, although substantial mortality of calves, probably still dependent on their mothers, was also observed. Juveniles, in contrast, appeared to be only slightly affected by the epizootic. This pattern of mortality is not consistent with the epidemiology of morbillivirus infections previously observed in other mammals. Possible explanations of this particular age distribution include behavioral factors, increased susceptibility to the disease in adults due to the effects of pollution, high temperatures and decreased food availability, or allopatric geographical distribution of population components and, therefore, of their associated mortality.

Growth and reproduction of the northern right whale dolphin, Lissodelphis borealis, in the offshore waters of the North Pacific Ocean

Biological samples and data were obtained from 229 northern right whale dolphins, Lissodelphis borealis (99 males and 130 females), taken in Japanese squid driftnets in the central North Pacific Ocean, May – November of 1990 and 1991. Length and sex were recorded for an additional 188 males and 272 females. Ages were determined by counting dentinal growth layer groups. Female reproductive status was determined by macroscopic examination of ovaries; 67 were mature. Sixteen percent were pregnant, 3% were pregnant and lactating, 33% were post partum, 24% were lactating (no recent pregnancy), 10% were resting, and 14% were of unknown condition. Testis and epididymis were examined for evidence of spermatogenesis; 28 were mature. Three estimates of length at birth were 99.7, 100.6, and 103.8 cm. The gestation period was 12.1 – 12.3 months. The sex ratio at birth was not significantly different from 1.0; the male component decreased with age. Estimates of the average age at sexual maturation among males were 9.9 and 10.1 years; average length at sexual maturation was estimated at 215.1 and 214.7 cm. Mature testis masses ranged from 117.4 to 1300 g. Estimates of the average age at sexual maturation among females were 9.7 and 10.4 years; the average length at sexual maturation was estimated at 201.1 and 199.8 cm. Males reach an asymptotic length of 265 cm, females 210 cm. Ovulation rates were < 1.0/year. Calving appeared to peak in July and August; the minimum calving interval was 2 years.

Daily rates of dentine formation in macaque tooth roots

AbstractWhen tetracycline antibiotics are administered either orally or by injection they bind at the forming mineral front of the dentine and become incorporated into teeth as a permanent label. In this study, oxytetracycline was used as a label in order to investigate the growth of root dentine in macaques. There are no good data available in the literature for daily rates of root dentine formation over a prolonged period of time in either humans or macaques. Records of ten doses of oxytetracycline administered orally at irregular intervals (but at the same time of day) over a period of 10 months to a young rhesus macaque monkey (Macaca mulatta) were used to calculate the rate of dentine formation in tooth roots. Rates of dentine formation in the first portion of third permanent molar root formation, and in the apical portion of permanent canine and premolar root formation, were consistently between 3 μm and 4 μm per day. There was no evidence in this study of a gradual decrease in daily dentine formation rate from the crown to the root, or along the length of a dentine tubule through the bulk of the dentine, as has been implied previously. With the exception of faster rates recorded in cusps or slower rates recorded at the very beginning or very end of primary dentine secretion in other studies, the results of the present study suggest a consistent rate of dentine formation in permanent macaque teeth. What data there are for human dentine formation rates suggests that it is likely this finding can be extended to human dentine as well.

Patterns of growth in wild bottlenose dolphins, Tursiops truncatus

The growth of bottlenose dolphins is described from observations made during a capture release programme that has operated in coastal waters of the eastern Gulf of Mexico from 1970 to the present. Measurements of standard length, girth and body mass were recorded from 47 female and 49 male dolphins, some captured as many as nine times. Ages were known from approximate birth dates or estimated from counts of dentinal growth layers. In all three measurements. females grew at a faster initial rate than males, but reached asymptotic size at an earlier age. This extended period of growth in males resulted in significant sexual dimorphism in length, girth and mass at physical maturity. The growth of both sexes was well described by three‐parameter Gompertz models using either cross‐sectional data or a mixture of longitudinal and cross‐sectional data. There was considerable variation in size‐at‐age for both sexes in all year classes. Residuals of size measurements were used to derive measures of relative size for individual dolphins; most dolphins demonstrated little ontogenetic change in relative size. Body mass was adequately predicted by multiple regression equations that incorporated both length and girth as independent variables.

Sexual dimorphism in the baiji, Lipotes vexillifer

Dimorphism was detected in body length and in skull dimensions of the baiji, Lipotes vexillifer. The age of a sample comprising 22 females and 14 males was estimated. A single-phase Laird growth model was fitted to the body length versus age data for females. Two curves were required for the males, one for those with 4 dentinal growth layer groups (GLGs) and another for those above that age, i.e., with more than 4 GLGs. Males and females have about the same growth rate until they have about 4 GLGs, after which males grow more slowly than females. Sexual dimorphism was also found in 9 external measurements, based on t-tests. Analysis of covariance showed that once the effect of body length was removed, only 1 of the 9 measurements, from the tip of the upper jaw to the genital aperture, differed significantly between males and females. Differences in skull measurements resulted mainly from an early slowdown in the rate of longitudinal growth of the male, before the increase in body length slowed. Females and males could be correctly sexed by discriminant analysis using the body length, condylobasal length, and zygomatic width, and also the condylobasal length, width of the rostrum at the base, and the zygomatic width, except for one young female. Eight skull length measurements were greater in adult females than in adult males after the effect of body length was removed, and five skull width measurements were greater in males when the effect of condylobasal length was removed. Asymmetry in the position of the blowhole and in skew of the skull is pronounced and is independent of body length and sex.

AGING LIVE ANTARCTIC FUR SEALS AND SOUTHERN ELEPHANT SEALS

AbstractThis study describes a method for extracting post‐canine or incisor teeth from live antarctic fur seals (Arctocephalus gazella) and southern elephant seals (Mirounga leonina) respectively and their use to determine age in a field situation. Dental elevators were used to loosen the teeth from the alveolus and periodental ligament. Most teeth were removed within l‐2 min and a total of 214 and 81 teeth were collected by this method from antarctic fur seals and southern elephant seals respectively. No seal recaptured at intervals up to a year after a tooth was extracted showed signs of infection or distress related to removal of the tooth. Teeth were thin‐sectioned for the purpose of aging. In both species cementum growth layer groups were a more satisfactory indicator of age than dentinal growth layer groups. Estimates of age from cementum growth layers were confirmed for Antarctic fur seals using seals which had been tagged as pups up to 16 yr before sampling.

Upper Central Incisor and Canine Tooth Crown Size in 47,XXY Males

Enamel and dentin thicknesses were measured in permanent tooth crowns of 47,XXY (Klinefelter syndrome) males. In 47,XXY males, enamel thickness in maxillary central incisors was significantly greater than that in control males or females, and dentin thickness in incisors and canines was significantly greater than that in control females, but smaller than that in normal males. These findings confirm the concept that human dental growth is affected by sex chromosomes. Amelogenesis is promoted by both X and Y chromosome genes, and sexual dimorphism in average tooth size is evidently determined by a promoting effect of the Y chromosome on dentin growth, probably through cell proliferation. This effect can also explain sex predilection for males in the numbers of supernumerary and ordinary teeth.

Genetic study of dentinal growth in mandibular first molars of mice.

The dentinal growth of mandibular molars of mice could be determined by genetic and environmental factors as are other quantitative characters, such as crown size and craniofacial size. To study the relative contribution of genetic and environmental factors to dentinal growth, a partial diallel cross was carried out by the mating of one pair from each of six strains of mice. In each F1 offspring, the total amount of dentinal formation in the first molar of the right mandible was quantified as a volume by the time-marking method, using nitrilotri-acetate lead with the computerized image scanning system, and then analyzed by a quantitative genetic method. The result obtained was as follows: In either sex, both additive genetic and nonadditive genetic variance components of the accumulative volume of dentinal formation in the first molar were relatively large throughout the experimental period, while the environmental variance component was much smaller. Thus it could be concluded that the genetic factor contributed more to the whole process of dentinal growth in the first molar rather than the environmental one in this F1 population.

GROWTH LAYERS IN TEETH FROM KNOWN‐AGE, FREE‐RANGING BOTTLENOSE DOLPHINS

AbstractGrowth layers were examined in teeth collected from free‐ranging bottlenose dolphins, Tursiops truncatus, from Florida that have been part of a long‐term study begun in 1970; 26 of the dolphins were of known or approximately known age, and 19 were of minimum known age. A second tooth was extracted from 6 animals for examination of growth that had taken place in the interval following the initial extraction. The teeth were read for age estimates without knowledge of any data pertaining to the animals. Most of the estimated ages were the same as or close to the known and approximately known ages of the animals, ranging from 2 to 16 yr. We conclude that the structures we define as dentinal growth layer groups (GLGs) are annual, we describe sources of error in age estimates, and we provide a description of the GLG pattern that can be used by others to estimate age for dolphins.

The 1982–1983 El Niño event recorded in dentinal growth layers in teeth of Peruvian dusky dolphins (Lagenorhynchus obscurus)

Dusky dolphins (Lagenorhynchus obscurus) recorded the effects of the 1982–1983 El Niño event in the form of anomalous dentine deposited during 1983. This anomaly, which I call the El Niño mark (ENM), consists of a pair of hypocalcified incremental layers about 75 μm in width, located within the 1983 growth layer group. The anomaly was present in 15 of 18 mature females, 1 of 9 immature females, and only 1 of 14 mature and immature males. Teeth from other species inhabiting the upwelling system were examined and revealed no ENM. Dusky dolphins feed primarily on anchoveta (Engraulis ringens), the stocks of which collapsed during the 1983 El Niño; this collapse severely affected other anchoveta predators. It is possible that the ENM reflects the presumably low foraging success experienced by dusky dolphins in 1983. However, it is unclear why the ENM is present in most mature females and absent from most male specimens. The discovery of the El Niño mark in dusky dolphins provides the first convincing evidence in odontocete cetaceans of a direct environmental influence on the mineral quality of dentine deposited during a period of markedly abnormal climatic conditions.

A comparison of age determination techniques for the harbour porpoise, Phocoena phocoena L.

The maximum life-span of the harbour porpoise has been estimated at 13 years (based upon dentinal growth layer groups in the teeth) and at 21 years (based upon growth layers in the periosteal bone of the mandible). We used both techniques to estimate the ages of 120 harbour porpoises from the western North Atlantic, in an attempt to determine the relative reliability of each technique. Dentinal layering was the better predictor of body length. Mandibular layering was highly variable even within a single cross section in most specimens, as a result of both common bifurcation of the layers and destruction of the inner layers by growth and remodelling of the living bone. Furthermore, mandibular layers appear to be deposited at a rate of 2 layers/year, double the deposition rate of dentinal growth layer groups. Age estimates which assume annual deposition of mandibular layers therefore overestimate true age.

Organochlorines in bottlenose dolphinsTursiops truncatusfrom the east coast of South Africa

Concentrations of polychlorinated biphenyls (PCBs), t-DDT (DDT + DDE + DDD) and dieldrin were determined in blubber samples of 105 bottlenose dolphins inhabiting the coastal waters of the east coast of South Africa. Residue concentrations increased with age and, in males, reached levels that may impair testosterone production. In females, however, there was a decline in concentrations of all three residues in animals with between 8 and 10 dentinal growth layer groups. A significant difference was found between residue levels in females before and subsequent to their first or second ovulation, suggesting that first-born calves receive the majority of the mother's load through lactation. Evidence is presented to indicate that primiparous females impart the majority of their load within seven weeks post-partum. Levels of PCBs, t-DDT and dieldrin differed significantly in different geographical areas, suggesting a degree of isolation of sections of the population.

DEVELOPMENTAL PATTERN OF THE BONY FALX AND BONY TENTORIUM OF SPOTTED DOLPHINS (STENELLA ATTENUATA) AND THE RELATIONSHIP BETWEEN DEGREE OF DEVELOPMENT AND AGE

AbstractThe bony falx (BF) and bony tentorium (BT) of spotted dolphins (Stenella attenuata) at different growth stages were observed. The BF and BT were observed to have the shape of the entire falx cerebri (FC) and tentorium cerebelli (TC), respectively, in adults, but were not seen in fetuses at all. Partially formed BF and BT were observed in the young. The BF and BT of spotted dolphins are formed by ossification in the FC and TC in the course of aging. Based on age determination by means of dentinal growth layers of the maxillary teeth, the ossification in the FC and TC of spotted dolphins begins by about 1 yr of age, and is completed, except for the passage of nerves and blood vessels, by about 9 yr of age. The BF and BT of spotted dolphins are formed possibly by continual dietary intake of large amounts of calcium, phosphorus and vitamin D.

Morphometric and meristic comparisons of skulls of harbour porpoisePhocoena Phocoena(L.) from the North Atlantic and North Pacific

Abstract Highly significant (α = 0.01) differences in analysis of 473 skulls of harbour porpoises indicate separate eastern Pacific, western Atlantic, and eastern Atlantic populations. Including the isolated population in the Black Sea—Sea of Azov, four major populations in this species are presently definable. Small sample sizes and incomplete data prevented conclusive tests for significant differences in subpopulations within these, but there are trends which suggest some segregation of Dutch, Baltic, and eastern English (North Sea) animals might be demonstrated with large samples. Skulls of western Atlantic harbour porpoises are larger than those of eastern Atlantic animals; skulls of eastern Pacific porpoises are smaller yet. This size order is more strongly marked in males than females. Despite their smallest overall dimensions, Pacific harbour porpoise skulls are most attenuate, with significantly longer jaws and more teeth than Atlantic animals. Females exceed males in size in each population. The configuration of dentinal growth layers was consistent in specimens from the Bay of Fundy, the Baltic, North Sea, and north-west Africa, lending support to the hypothesis of endogenous control of layering, rather than exogenous control through seasonal food availability.

Dentin-predentin complex and its permeability: pathology and treatment overview.

This review paper focuses attention on tissue changes which may take place in dentin and on localized alterations in tissue formation in the predentin area. A number of reaction patterns has been described in dentin affecting both the inorganic and organic components. Dentinal tubules may become partly or completely obturated by growth of the peritubular dentin. Precipitation of mineral salts within the tubules, which may be a reprecipitation of minerals from adjacent demineralized dentin, represents a fundamentally different mode of obturation of dentinal tubules. Initially, demineralization selectively affects the peritubular dentin. If dentin is exposed to the oral environment, the surface layer may become hypermineralized. The surface layer of dentin, exposed by grinding, becomes covered by a smear layer. Displacement of the contents of the tubules or of the odontoblasts is a characteristic change in the organic components. Odontoblast destruction or degeneration will lead to a lack of, or reduced, predentin formation. Changes in the protein components which lead to alterations in dentin permeability have also been reported. The structure of the interface between dentin and localized formations of irregular secondary dentin varies considerably. If there is no tubular communication between primary and secondary dentin, the interface will act as an impermeable barrier. Changes in dentin, including irregular secondary dentin formation, affect the permeability of the tissue. Such changes are clinically important for the outcome of all types of restorative work performed on vital teeth.

Changes in the Male Reproductive Organs of the Dugong, Dugong dugon (Sirenia: Dugondidae) with Age and Reproductive Activity

The anatomy and histology of the male reproductive tract of the dugong (Dugong dugon) is described. Each testis and its adjacent epididymis lie immediately caudal to the corresponding kidney. The seminal vesicles are large but there is no discrete prostate gland and the bulbo-urethral glands are also diffuse. Both qualitative and quantitative examination of the testes and epididymides of 59 males whose ages have been estimated from tusk dentinal growth layer counts indicate that the male dugong does not produce spermatozoa continuously, despite the absence of a distinct breeding season. Individual dugongs were observed with testes at all stages between complete quiescence and full spermatogenesis, and only 10 of the 40 mature males had fully spermatogenic testes and epididymides packed with spermatozoa. Androgenic and spermatogenic activity of the testes appeared to be in phase, but the testicular histology of some old males suggested that they may have been sterile for long periods.

Development of sensory innervation in dentin.

We have labeled dental nerves of 3-week- to 1-year-old rats by axonal transport of radioactive protein in order to detect nerves in developing dentin by autoradiography. We found that, in addition to nerve growth, two processes determine adult dentinal nerve location: (1) enclosure of nerves within circumpulpal dentinal tubules during the last few weeks of dentinogenesis, beginning at the tip of the pulp horn and spreading to include most coronal dentin; and (2) gradual loss of the nerves near the tip of the cusp because of dentinal attrition and replacement by noninnervated, reparative dentin. Several days before a molar erupts, nerves at the tip of the cusp have already begun to be enclosed by dentin; 2-3 weeks later, when dentinogenesis at the cusp tip slows down, most of the innervation for that region has been established, nerves extend up to 160 micron into dentin, and the molar has reached the stage of functional occlusion. Soon after initial occlusion, the process of dentinal attrition and replacement by noninnervated reparative dentin begins; however, simultaneous dentinogenesis in more apical regions produces new innervated dentin. We studied nerve position in relation to dentin growth lines and found that there is a long-term association of nerve endings with specific sites in the dentinal tubules. The similarities between the development of dentinal innervation in rat molars and in human permanent teeth are discussed; it is found that as teeth mature and become more sensitive to painful stimuli, the density of dentinal nerves increases.

Dentinal dysplasia: endodontic treatment, with case report

Various characteristics of dentinal dysplasia include defective root formation, aberrant growth of dentin within the pulp chamber, and formation of periapical abscesses and cysts. No relationship to any systemic condition has been discovered. The case of a young adult male treated endodontically is described in this article. Up to this time, extraction has been the only reported treatment for this rare hereditary disease. Various characteristics of dentinal dysplasia include defective root formation, aberrant growth of dentin within the pulp chamber, and formation of periapical abscesses and cysts. No relationship to any systemic condition has been discovered. The case of a young adult male treated endodontically is described in this article. Up to this time, extraction has been the only reported treatment for this rare hereditary disease.

A calcitonin-like action of prostaglandin E 1

The pharmacological effects of PGE 1 (6 and 9 days, 21,250 μg/kg per day subcutaneously) upon the growth and the bone resorption of mammals were studied using the proximal tibia and upper incisor of immature rats along with lead acetate as a time marker, and upon the serum calcium and inorganic phosphorus levels. The following results were obtained. 1. PGE 1 hardly affected the body weight or the weight of organs of the rats but apparently inhibited the longitudinal growth of proximal tibia in a dose related manner. 2. PGE 1 clearly inhibited not only the longitudinal growth (incisor growth) but also the appositional growth (dentin formation) of incisal dentin. 3. The grade of the inhibitory effect on the growth was in the order of bone growth >dentin formation >incisor growth. 4. The occurrence of osteoporosis due to a low calcium diet was inhibited by the simultaneous administration of PGE 1, the mechanism being considered to be mainly due to the inhibitory effect on the bone resorption. 5. PGE 1 lowered the level of serum calcium and the lowering effect was not observed in the thyro-parathyroidectomized rat. From the facts that the above effects were exactly the same as those of calcitonin (1), the possibility that the subcutaneous injection of PGE 1 may induce a calcitonin-like action, a part of which may dependent on the calcinonin secretion is suggested.

Age determination of harbour porpoise, Phocoena phocoena (L.), in the western North Atlantic.

Age, based on analysis of dentinal growth layers, was determined in a sample of 121 harbour porpoises, Phocoena phocoena (L.), from western North Atlantic waters. One growth layer, consisting of a thick opaque zone and a relatively thin translucent zone, is deposited each year.Mean thicknesses of opaque and translucent zones in males and females were 347 μm, 114 μm, 432 μm, and 125 μm, respectively. Significant reduction in thicknesses of growth layers with age was found in both sexes, the major contribution in both cases being progressive reduction in thickness of the opaque zones. Translucent-zone thickness decreased with age in males, but significantly increased in thickness in females. Formation of the opaque zone occurs from June through February, and formation of the translucent zone from January to early September. This overlap is attributed to the protracted calving season of this population, and precludes any simple relationship between food supply and zonation, as proposed by others. Age–length relationships based on numbers of dentinal layers were calculated for males and females using regression analysis. Best fits of body length (b) against age (expressed by completed dentinal layers) (d) were obtained from the curvilinear equations: d = [b/(−1.30b + 209.35)] −1 for males, and d = [b/(−0.84b + 156.15)] −1 for females.