Dentition Patterns Research Articles

Tooth Eruption Sequences in Cervids and the Effect of Morphology, Life History, and Phylogeny

Tooth eruption sequences vary in a non-random way among mammalian species. Several variables have been linked to this, including tooth and jaw shape, adaptations to diet, and food processing. Likewise, changes in eruption patterns correlate with the speed of postnatal growth in some groups, the Schultz’s Rule pattern. Here, the eruption pattern of the permanent dentition in lower jaws from different cervid species have been investigated to discern the effect of these factors and phylogeny as well as to reconstruct the ancestral tooth eruption sequence of cervids. In ruminants, the different patterns of emergence of permanent teeth seem to be best explained by phylogeny. The degree of hypsodonty, age of first molar eruption, and life history parameters such as longevity and age of female sexual maturity do not explain the observed sequential differences in eruption patterns. The Parsimov-based analysis for the ancestral state resulted in a tooth eruption sequence of m1 – m2 – i1 – i2 – i3 – c – m3 – (ppp) for Cervidae; a pattern recorded in Odocoileus, Capreolus, and Hydropotes. The eruption pattern of Caenomeryx filholi, from the Oligocene of Gaimersheim, is identical to the result of the Parsimov-based analysis except for the presence of a first premolar, a tooth lost in cervids.

Effects of chewing pattern and condition of dentition on taste threshold in healthy adults

Effects of chewing pattern and condition of dentition on taste threshold in healthy adults

Wear pattern of the molar dentition of an extant and an Oligocene bat assemblage with implications on functionality

Wear stages have been defined based on dentine exposure at the lower molar surfaces for a population of the extant bat Pipistrellus pipistrellus (6 wear stages) and for a sample of the Oligocene bat Pseudorhinolophus antiquus (4 wear stages). Wear stages 1–2, which occur in juveniles, are characterised by punctual dentine exposure on the cusps and ridges. Wear stages 3–4, found in adult individuals, are characterised by connected areas of band-shaped dentine. The last two wear stages (5–6) reflect the dental condition of old (senile) individuals, with the molar surface showing wide areas of exposed dentine and the occlusal relief drastically reduced. The defined wear stages of the P. antiquus sample are comparable to stages 3–6 of P. pipistrellus. The molars of both species show wear facets with striations that go in two directions, indicating a two-phased, bucco-lingually directed masticatory movement which gains more freedom with progressive wear. This development underlines that shear-cutting dominates in the early stages of the mastication process, whereas in later stages a crushing component becomes increasingly dominant. Based on the average age determination of individuals from the defined wear stages, about 90 % of the studied P. pipistrellus population consists of juveniles (wear stages 1–2). In contrast, wear stages 3–5 (95 %) predominate in the studied sample of P. antiquus, indicating that most of the individuals were of an adult/senile age.

Maternal and early life factors of tooth emergence patterns and number of teeth at 1 and 2 years of age.

Various environmental factors have been associated with the timing of eruption of primary dentition, but the evidence to date comes from small studies with limited information on potential risk factors. We aimed to investigate associations between tooth emergence patterns and pre-conception, pregnancy and postnatal influences. Dentition patterns were recorded at ages 1 and 2 years in 2915 children born to women in the Southampton Women's Survey from whom information had been collected on maternal factors before conception and during pregnancy. In mutually adjusted regression models we found that: children were more dentally advanced at ages 1 and 2 years if their mothers had smoked during pregnancy or they were longer at birth; mothers of children whose dental development was advanced at age 2 years tended to have poorer socioeconomic circumstances, and to have reported a slower walking speed pre-pregnancy; and children of mothers of Asian ethnicity had later tooth development than those of white mothers. The findings add to the evidence of environmental impacts on the timing of the eruption of primary dentition in indicating that maternal smoking during pregnancy, socio-economic status and physical activity (assessed by reported walking speed) may influence the child's primary dentition. Early life factors, including size at birth are also associated with dentition patterns, as is maternal ethnicity.

Development and evolution of dentition pattern and tooth order in the skates and rays (batoidea; chondrichthyes).

Shark and ray (elasmobranch) dentitions are well known for their multiple generations of teeth, with isolated teeth being common in the fossil record. However, how the diverse dentitions characteristic of elasmobranchs form is still poorly understood. Data on the development and maintenance of the dental patterning in this major vertebrate group will allow comparisons to other morphologically diverse taxa, including the bony fishes, in order to identify shared pattern characters for the vertebrate dentition as a whole. Data is especially lacking from the Batoidea (skates and rays), hence our objective is to compile data on embryonic and adult batoid tooth development contributing to ordering of the dentition, from cleared and stained specimens and micro-CT scans, with 3D rendered models. We selected species (adult and embryonic) spanning phylogenetically significant batoid clades, such that our observations may raise questions about relationships within the batoids, particularly with respect to current molecular-based analyses. We include developmental data from embryos of recent model organisms Leucoraja erinacea and Raja clavata to evaluate the earliest establishment of the dentition. Characters of the batoid dentition investigated include alternate addition of teeth as offset successional tooth rows (versus single separate files), presence of a symphyseal initiator region (symphyseal tooth present, or absent, but with two parasymphyseal teeth) and a restriction to tooth addition along each jaw reducing the number of tooth families, relative to addition of successor teeth within each family. Our ultimate aim is to understand the shared characters of the batoids, and whether or not these dental characters are shared more broadly within elasmobranchs, by comparing these to dentitions in shark outgroups. These developmental morphological analyses will provide a solid basis to better understand dental evolution in these important vertebrate groups as well as the general plesiomorphic vertebrate dental condition.

Patterning of mammalian heterodont dentition within the upper and lower jaws.

Mammalian heterodont dentition is differentiated into incisors, canines, premolars, and molars in the mesial-distal direction, in both the upper and lower jaws. Although all the lower teeth are rooted in the mandible, the upper incisors are rooted in the premaxilla and the upper canine and the teeth behind it are in the maxilla. The present study uncovers ontogenetic backgrounds to these shared and differing mesiodistal patterns of the upper and lower dentition. To this end, we examined the dentition development of the house shrew, Suncus murinus, instead of the rodent model animals because the dentition of this primitive eutherian species includes all the tooth classes, and no toothless diastema region. In the shrew, the upper incisor-forming region extended over the medial nasal prominence and the mesial part of the maxillary prominence. Consequently, the maxillary and mandibular prominences were in a mirror-image relationship in terms of the mesiodistally differentiated tooth-forming regions and of the complementary gene expression pattern, with Bmp4 in the mesial and Fgf8 in the distal regions. This suggests shared molecular mechanisms regulating tooth class differentiation between the upper and lower jaws. However, the premaxillary bone appeared within the mesenchyme of the medial nasal prominence, but grew distally beyond the former epithelial boundary with the maxillary prominence to form, finally, the incisive (premaxillary-maxillary) suture just mesial to the canine. Therefore, the developmental locations of the upper incisors are not inconsistent with the classical osteological criterion of the upper canine by comparative odontologists.

Unusual pharyngeal dentition in the African Chedrin fishes (Teleostei: Cyprinindae): Significance for phylogeny and character evolution

The dentition of cyprinid fishes is restricted to the right and left fifth ceratobranchials, which form the lower pharyngeal jaw (LPJ). The African members of the cyprinid subfamily Danioninae are nested within the tribe Chedrini. We compare the pharyngeal dentitions of African and of Asian Chedrini (Danioninae), including Danio rerio (Danionini), considering the following morphological characters: the pattern of dentition, the number of pharyngeal tooth rows, the curving and inclination of the tooth crowns, and the ratio of the tooth-bearing area to the length of the LPJ. Similar to a previous genetic based study a close relationship is proposed among the African genera Engraulicypris, Mesobola, and Rastrineobola, and among Leptocypris, Neobola, and Chelaethiops, all of which were formerly assigned as ‘Neobolines’. Species of Rastrineobola, Engraulicypris, Mesobola, and Neobola develop an additional (fourth) row of pharyngeal teeth. The dentition of Rastrineobola argentea (Pellegrin, 1904) and the shape of the LPJ of Engraulicypris sardella (Günther, 1868) characterize these two species as specialized within the Chedrini. An additional pharyngeal tooth row also occurs infrequently in the zebrafish D. rerio (Hamilton, 1822). The ‘fourth’ row of this fish species is possibly the result of a different process for acquiring four rows of pharyngeal teeth, likely by the splitting of one tooth row.

Distalization pattern of whole maxillary dentition according to force application points.

ObjectiveThe purpose of this study was to observe stress distribution and displacement patterns of the entire maxillary arch with regard to distalizing force vectors applied from interdental miniscrews.MethodsA standard three-dimensional finite element model was constructed to simulate the maxillary teeth, periodontal ligament, and alveolar process. The displacement of each tooth was calculated on x, y, and z axes, and the von Mises stress distribution was visualized using color-coded scales.ResultsA single distalizing force at the archwire level induced lingual inclination of the anterior segment, and slight intrusive distal tipping of the posterior segment. In contrast, force at the high level of the retraction hook resulted in lingual root movement of the anterior segment, and extrusive distal translation of the posterior segment. As the force application point was located posteriorly along the archwire, the likelihood of extrusive lingual inclination of the anterior segment increased, and the vertical component of the force led to intrusion and buccal tipping of the posterior segment. Rotation of the occlusal plane was dependent on the relationship between the line of force and the possible center of resistance of the entire arch.ConclusionsDisplacement of the entire arch may be dictated by a direct relationship between the center of resistance of the whole arch and the line of action generated between the miniscrews and force application points at the archwire, which makes the total arch movement highly predictable.

Developmental integration in a functional unit: deciphering processes from adult dental morphology.

The evolution of mammalian dentition is constrained by functional necessity and by the non-independence of morphological structures. Efficient chewing implies coherent tooth coordination from development to motion, involving covariation patterns (integration) within dental parts. Using geometric morphometrics, we investigate the modular organization of the highly derived vole dentition. Integration patterns between and within the upper and lower molar rows are analyzed to identify potential modules and their origins (functional and developmental). Results support an integrated adult dentition pattern for both developmental and functional aspects. The integration patterns between opposing molar pairs suggest a transient role for the second upper and lower molars during the chewing motion. Upper and lower molar rows form coherent units but the relative integration of molar pairs is in contradiction with existing developmental models. Emphasis on the first three cusps to grow leads to a very different integration pattern, which would be congruent with developmental models. The early developmental architecture of traits is masked by later stages of growth, but may still be deciphered from the adult phenotype, if careful attention is paid to relevant features.

Molecular characterization of dental development in a toothed archosaur, the American alligatorAlligator mississippiensis

Few skeletal structures are as informative of the adaptive natural history of vertebrate animals as their teeth. Understanding principles of tooth development is key to understanding evolution of the vertebrate dentition in general and emergence of multiple specialized tooth types in particular. Morphological and phylogenetic considerations suggest that crocodilians have the most primitive mode of dentition within extant tetrapods, displaying simple, conical, socketed, and continuously replaced teeth. Previous histological studies revealed several dental fates, including functional and non-functional teeth (rudiments) in the developing alligator embryos. We analyze expression of key odontogenic regulators and markers to better characterize the molecular patterning of crocodilian dentition. Importantly, we demonstrate that the morphologically distinct tooth types in Alligator mississippiensis are distinguishable by differences in their developmental programs. We also present evidence showing that tooth maturation is accompanied by dynamic gene expression in the epithelial and mesenchymal cells involved in tooth development. Our data reveal a significant morphological and genetic variation in early dental fates. We believe that this underlying developmental variation reflects modularity, or the ability of teeth to develop semi-autonomously along the alligator jaw. We propose that such modularity may have been a crucial for adaptive evolution within Amniota, allowing for the progressive modifications to tooth replacement, number, and shape.

Description of a new subspecies, Macrobrachium aemulum madhusoodani (Decapoda: Palaemonidae) from Neyyar River, Kerala, S. India.

Macrobrachium aemulum madhusoodani, a new subspecies of M. aemulum (Nobili, 1906) is described and illustrated. The distinctive characters of the subspecies are: rostral formula 9-13/2, second pereiopods dissimilar in shape and unequal in size, movable finger of larger second pereiopod with 2 large denticles on the proximal part and 6 weak denticles on distal part. Similar pattern of dentition is present on immovable finger also. In second small pereiopod, fingers stout, equal, unarmed with distinct gap in between when closed. Numerous stiff setae present on cutting edges of fingers. Telson extends beyond the level of the outer lateral spine of the uropodal exopod. Some of the distinctive morphometric and meristic characters of the specimens did not conform to that collected and described from New Caledonia by Nobili (1906) and recorded from India by Jayachandran and Joseph (1988). Since the features cannot be reckoned as mere growth variations, it is described herein as a new subspecies.

The Midline Mandibular Lingual Canal: Importance in Implant Surgery

The study aims to determine if midline mandibular dental implants pose a risk for the midline lingual canal (MLC). Cone beam computed tomography was used to scan 122 mandibles (31 black males; 28 black females; 32 white males and 31 white females). Midsagittal sections in the reconstructed images were made. A measurement of 6 mm across bucco-lingually was delineated as the minimum dimensions for implant placement. In dentate cases with a bucco-lingual distance in excess of 6 mm, the measurement was across the apex of the socket to determine the bone dimension available below the socket for implant placement. From these markers a vertical line was dropped to the MLC to measure the available bone. The MLC was a consistent finding. A statistical significant difference in bone availability among the sexes and dentition pattern was found, indicating that midline implants in edentulous females posed a risk of injury to the vessels of the MLC. Implants in the position of lower central incisors are regarded as a safe procedure. Clinicians should however take note of the position of the midline mandibular lingual canal and approach this area with caution, especially if the alveolar ridge is to be reduced before implant placement.

Age determination of the Mongolian wild ass (Equus hemionus Pallas, 1775) by the dentition patterns and annual lines in the tooth cementum

Based on 440 skulls recently collected from two areas of the wild ass population in Mongolia, the time course of tooth eruption and replacement was investigated. The dentition pattern allows identification of age up to five years. We also conclude that annual lines in the tooth cementum can be used to determine the age in years for wild asses older than five years after longitudinal tooth sections were made with a low-speed precision saw. The first upper incisor proved to be most suitable for age determination, although the starting time of cement deposition is different between the labial and lingual sides of the tooth. The accurate age of the wild ass can be determined from the number of annual lines and the time before the first formation of the cementum at the respective side of the tooth.

The Role of Modularity in the Evolution of Primate Postcanine Dental Formula: Integrating Jaw Space With Patterns of Dentition

The assembly of a phenotype into modules or developmental fields, which are semiautonomous units in development and function, seems to be one of the strategies to increase the capacity to produce phenotypic variation. In mammals the upper dentition is formed on two distinct developmental units, wherein incisors are formed on the primary palate, which is derived from the embryonic frontonasal process, and the other teeth (canine, premolar, and molar) are formed on the alveolar bone, which is derived from the maxillary process (termed herein as PALATE2). The aim of the present work was to analyze the variations in size and number of premolar and molar teeth in primate dentition and to correlate these morphometrical parameters with the relative size of these tooth classes with respect to PALATE2. Furthermore, we seek to understand to what extent the changes in the relative size of premolar and molar fields can influence the size of each tooth within its respective field, and how these parameters connect with the variations in the dental formula that occurred during primate evolution. The data presented here not only indicate that premolar and molar fields can be seen as submodules of a larger and hierarchically superior module (i.e., PALATE2) but also present quantitative parameters that allow us to understand how variations in the relative size of premolar and molar teeth connect with the variations in the dental formula that occurred during primate evolution.

Evaluation of the evolution of jaw morphology in New World hirudiniform leeches, with a description of a new blood-feeding species of Oxyptychus (Annelida:Hirudiniformes) from the Peruvian Amazon

Morphological characters of well-established taxonomic utility are infrequently examined for their relative phylogenetic consistency. Second only to characters of reproductive anatomy, jaw morphology and dentition commonly are employed as diagnostic characters for hirudiniform leeches, yet these features are highly variable across the group. Patterns of change were investigated for number of jaws and number of denticles per jaw in a phylogenetic context across 17 hirudiniform leeches representing three families. Phylogeny reconstruction employed 16 morphological characters, as well as two nuclear and two mitochondrial loci, and was evaluated with parsimony and likelihood. Rather than constrain the ancestral number of denticles to extant states, this meristic was optimised with squared-change parsimony. The degree to which dentition patterns were explained by phylogenetic relationships was assessed against a null distribution defined by permutation of extant states across terminals. Dentition was found to be non-randomly explained by phylogeny and, thus, corroborative of relationships among hirudiniform leeches as well as of the uniqueness of a new species of Oxyptychus described here from the Peruvian Amazon.

Two new species of Paraliparis (Scorpaeniformes: Liparidae) from the Ross Sea (Antarctica)

Liparidae from stomachs of Antarctic toothfish Dissostichus mawsoni Norman, 1937 (Nototheniidae) caught in the Ross Sea (Pacific sector of Antarctica) have been identified. Two new species of deep-water liparids of the genus Paraliparis Collett, 1879—P. caninus sp. nov. (at a depth of 1182–1651 m) and P. vipera sp. nov. (1700 m)—were described. Both species that turned out to be most similar to P. neelovi Andriashev, 1982, from the Kerguelen area (the Indo-Oceanic sector of the South Ocean) are combined with it into a species group “P. neelovi.” According to meristic characters, pattern of dentition, and the size of gill opening, species of “P. neelovi” are close to the species group “P. copei.” In collections from a depth of 1700 m, also two individuals of P. andriashevi Stein et Tompkins, 1989, known previously from only two types from the northern boundary of the Ross Sea were found. The new finding supports species validity and extends the known limits of its range. The wide distribution of bathybenthal Paraliparis having low fecundity and leading a near-bottom mode of life can be explained by the presence of mesopelagic juveniles and their dispersal via currents.

Dental agenesis patterns of permanent teeth in Apert syndrome

Dental agenesis may either occur as an isolated trait (non-syndromic) or as a component in a congenital syndrome. The aim of the present study was to identify the prevalence of dental agenesis for each type of tooth and to look for dental agenesis patterns in persons with Apert syndrome. Serial panoramic radiographs of 23 individuals (five male patients and 18 female patients) were examined. Third molars were excluded. The prevalence of agenesis for at least one tooth was 34.8%. Up to two missing teeth were found for individuals with Apert syndrome. Maxillary lateral incisors and mandibular second premolars were the most frequently missing teeth. Four different dental agenesis patterns of the entire dentition were identified by using the tooth agenesis code (TAC). Two patterns occurred more frequently, both of which were symmetrical. One involved the simultaneous absence of teeth 12 and 22, and the other showed agenesis of teeth 35 and 45. In conclusion, patients with Apert syndrome were found to exhibit a high prevalence of dental agenesis. All dental agenesis patterns in which more than one tooth was missing were symmetrical.

Influence of masticatory exercises using hard chewing gum on chewing pattern and first molar of mixed dentition

Abstract: Masticatory exercise for a set period of time improves maximum bite force and labial-closure strength and changes masticatory patterns. The purpose of this study was to investigate the ef...

Modularity in the mammalian dentition: mice and monkeys share a common dental genetic architecture

The concept of modularity provides a useful tool for exploring the relationship between genotype and phenotype. Here, we use quantitative genetics to identify modularity within the mammalian dentition, connecting the genetics of organogenesis to the genetics of population-level variation for a phenotype well represented in the fossil record. We estimated the correlations between dental traits owing to the shared additive effects of genes (pleiotropy) and compared the pleiotropic relationships among homologous traits in two evolutionary distant taxa-mice and baboons. We find that in both mice and baboons, who shared a common ancestor >65 Ma, incisor size variation is genetically independent of molar size variation. Furthermore, baboon premolars show independent genetic variation from incisors, suggesting that a modular genetic architecture separates incisors from these posterior teeth as well. Such genetic independence between modules provides an explanation for the extensive diversity of incisor size variation seen throughout mammalian evolution-variation uncorrelated with equivalent levels of postcanine tooth size variation. The modularity identified here is supported by the odontogenic homeobox code proposed for the patterning of the rodent dentition. The baboon postcanine pattern of incomplete pleiotropy is also consistent with predictions from the morphogenetic field model.

New Rheophilic Species of Electric Knifefish from the Rapids and Waterfalls of the Lower Rio Xingu, Brazil (Gymnotiformes: Apteronotidae)

Sternarchogiton zuanoni, a new species of electric knifefish, is described from the rapids and waterfalls of Cachoeira de Kaituká along the Rio Xingu at Altamira, Pará, Brazil. The new species is diagnosable from congeners by a unique combination of morphometric and meristic features, details of pigmentation, the pattern of dentition on the dentary, the possession of an edentulous premaxilla, and an unelaborated lower lip. The description of S. zuanoni brings the number of species in the genus to five. The presence of S. labiatus in the Río Orinoco basin is documented and a key to the species of the genus is provided.