Dental Crown Morphology Research Articles

Multiple Accessory Cusps Expression at Mandibular Third Molar: A Unique Variation of Dental Crown Morphology - A Case Report

Accessory cusps are occasional variations in tooth morphology that can be detected clinically. Third molars have a wide range of eruption patterns and shapes but are commonly impacted. Unlike root morphology, variations in the crown morphology of the third molar have rarely been reported. Variations in crown morphology are important because they can affect clinical outcomes. Here, we present a rare case of fully erupted mandibular third molar (MTM) with multiple accessory cusps. This case report describes a case of a 31-year-old female Kenyah with a unique crown morphology of her fully erupted, vital, and functional mandibular third molar (MTM) which has multiple accessory cusps seen on the buccal surface, giving the appearance of a double tooth. Her MTM presented with an incipient caries lesion, which was managed conservatively. Documenting variations in tooth morphology is crucial for individual identification. While most people opt to have their MTMs extracted, early management of well-erupted and functional teeth should be undertaken to prevent disease progression.

Structural analysis of premolar roots in Middle Pleistocene hominins from China

This study investigates permanent maxillary and mandibular premolar root structural organization in East Asian Middle Pleistocene hominins. In addition to reporting and analyzing the linear and volumetric properties of the roots, we used a landmark-free approach to both qualify and quantify in 3D premolar root shape variation of Middle Pleistocene hominins in East Asia. Moreover, we focus on some mid-to late East Asian Middle Pleistocene hominin specimens whose taxonomic attribution is unclear. We find considerable cementum in this sample of hominins, similar to other fossil groups, but clearly different from modern humans which have a very small amount of cementum. Additionally, a smaller root pulp cavity is found in later Homo (Neanderthals and modern humans). Our analyses on the crown-root surface area ratio show that East Asian Middle Pleistocene Homo erectus as well as one late Middle Pleistocene Homo sp. specimen (PA 81 P4 from Changyang site) are distinguished from other fossil and extant groups by a relatively larger root surface, stout root branches and thick cementum deposits. This may represent a distinct East Asian H. erectus dental pattern. Geometric morphometric analyses on the external root surface reveal a general trend of shape simplification along the Homo lineage examined here, and distinguish Early Pleistocene Homo, Middle Pleistocene H. erectus, Neanderthals and modern human morphologies. The late Middle Pleistocene teeth from Changyang site (PA 76 P3 and PA 81 P4) are close to East Asian H. erectus and Neanderthals, while the mid-Middle Pleistocene P3 from Panxian Dadong falls within the modern human distribution. Combined with dental crown morphology and root number/form reported in previous studies, our results show that the external root shape can be considered a taxonomically relevant indicator. In general, an evolutionary tendency towards modern human morphology is observed in part of the East Asian Middle Pleistocene specimens, while a retention of primitive, H. erectus-like features is expressed in some late Middle Pleistocene specimens, supporting a multi-lineage and discontinuous scenario of human settlements in East Asia.

Tooth Crown Morphology in Turner and Klinefelter Syndrome Individuals from a Croatian Sample.

ObjectiveTurner syndrome (TS) and Klinefelter syndrome (KS) represent the two most common X chromosome aneuploidies, each associated with systemic disruptions to growth and development. Effects of these conditions on tooth crown morphology are explored in a sample of Croatian individuals.Materials and MethodsThe sample included 57 TS, 37 KS and 88 control individuals. Dental crown morphology was scored on dental casts according to the Turner-Scott Dental Anthropology System.ResultsIncisor shoveling and the hypocone were significantly different between TS individuals and both control and KS individuals. Individuals with TS exhibit lower grades of expression than either group. Furthermore, the number of lingual cusps on the mandibular premolars, the hypoconulid on the mandibular second molar, and cusp 7 on the mandibular first molar were significantly different, though pair-wise comparisons did not elucidate these differences. Tuberculum dentale, distal accessory ridge, and Carabelli’s trait were expressed similarly to the control. KS individuals were not significantly different from control individuals for any trait, though this may be related to sample size.ConclusionsPrevious studies suggest the loss of an X chromosome has a reducing effect on dental crown morphology, which is confirmed in this research. TS individuals exhibit generally simpler dental morphology compared to the control sample, though some traits are expressed comparably to the control sample. The effects of KS are less clear. Though previous studies suggest that the presence of an extra X chromosome increases dental crown dimensions, there was no notable effect on crown morphology in this study.

Variation in Dental Crown Morphology in Malaysian Populations

Dental crown variation was studied inthe four main population groups living in Malaysiausing dental casts (upper and lower) obtained from 790individuals. The aims of the study were to characterizevariation in 13 dental crown traits, within groups as wellas between groups, and to assess affinities between thegroups based on frequencies of occurrence of dentalfeatures. Using chi-square analysis and Fisher’s exacttest, the majority of dental traits were found to bebilaterally symmetrical and to demonstrate low sexualdimorphism. Comparisons of trait frequencies betweengroups revealed similarities between Malays, Jahai(Negritos) and Chinese who conformed to MongoloidSinodont-Sundadont dental patterns, whereas theIndians conformed to an Indo-European pattern.Phenetic distance analysis, using the mean measureof divergence, showed that Indians were markedlyseparated from the other three groups, while Malayswere closer to Jahai than to Chinese. These findingsbased on dental traits are consistent with historicalexplanations of affinities between modern Malaysianpopulations.

Short Communication: Dental Trait Variation and Age Determination Based on Dental Wear: A Preliminary Study of Javanese

This preliminary study describes the dentalcrown morphology of 14 Javanese of known sex andage. The purpose was to suggest what dental traits tolook for when studying a bigger sample from Java. Of21 traits looked for, traits occurring in the sample wereshovel shape, winging, tuberculum dentale, interruptiongroove, canine distal accessory ridge, premolar accessoryridges, premolar accessory marginal tubercles, premolarmultiple lingual cusps, cusp 5, cusp 6, Y5 pattern, cusp 7,protostylid, deflecting wrinkle, anterior fovea, hypocone,and Carrabelli’s cusp. Dental wear overestimated actualages because the observed rate of wear was less than inthe reference sample.

The Dental Traits of Indonesian Javanese

This study describes the dental crown morphology of 91 Javanese of known sex and age, in Surabaya, East Java. The purpose was to explore the dental morphology in the area of East Java, especially in Surabaya. I scored a battery of three dozen dental traits on the permanent dentition (sexes pooled). Comparisons of the trait frequencies show that this Javanese sample does not exhibit a classic combination either of the Sinodont or Sundadont dental patterns. Instead, it represents some features of each, and this probably is due to the millennia of human migrations through this region.

A geometric morphometric analysis of hominin upper premolars. Shape variation and morphological integration

This paper continues the series of articles initiated in 2006 that analyse hominin dental crown morphology by means of geometric morphometric techniques. The detailed study of both upper premolar occlusal morphologies in a comprehensive sample of hominin fossils, including those coming from the Gran Dolina-TD6 and Sima de los Huesos sites from Atapuerca, Spain, complement previous works on lower first and second premolars and upper first molars. A morphological gradient consisting of the change from asymmetric to symmetric upper premolars and a marked reduction of the lingual cusp in recent Homo species has been observed in both premolars. Although percentages of correct classification based on upper premolar morphologies are not very high, significant morphological differences between Neanderthals (and European middle Pleistocene fossils) and modern humans have been identified, especially in upper second premolars. The study of morphological integration between premolar morphologies reveals significant correlations that are weaker between upper premolars than between lower ones and significant correlations between antagonists. These results have important implications for understanding the genetic and functional factors underlying dental phenotypic variation and covariation.

Brittle Cornea Syndrome Associated with a Missense Mutation in the Zinc-Finger 469 Gene

To investigate the diverse clinical manifestations, identify the causative mutation and explain the association with red hair in a family with brittle cornea syndrome (BCS). Eight family members in three generations underwent ophthalmic, dental, and general medical examinations, including radiologic examination of the spine. Bone mineral density (BMD) and serum levels of vitamin D, parathyroid hormone, and biochemical markers for bone turnover were measured. Skin biopsies were examined by light and transmission electron microscopy. Molecular genetic studies included homozygosity mapping with SNP markers, DNA sequencing, and MC1R genotyping. At 42 and 48 years of age, respectively, both affected individuals were blind due to retinal detachment and secondary glaucoma. They had extremely thin and bulging corneas, velvety skin, chestnut colored hair, scoliosis, reduced BMD, dental anomalies, hearing loss, and minor cardiac defects. The morphologies of the skin biopsies were normal except that in some areas slightly thinner collagen fibrils were seen in one of the affected individuals. Molecular genetic analysis revealed a novel missense mutation of ZNF469, c.10016G>A, that was predicted to affect the fourth of the five zinc finger domains of ZNF469 by changing the first cysteine to a tyrosine (p.Cys3339Tyr). Both affected individuals were homozygous for the common red hair variant R151C at the MC1R locus. BCS is a disorder that affects a variety of connective tissues. Reduced BMD and atypical dental crown morphology have not been reported previously. The results confirm that BCS is associated with mutations in ZNF469. The association with red hair in some individuals with BCS is likely to occur by chance.

Geometric morphometric analysis of the crown morphology of the lower first premolar of hominins, with special attention to Pleistocene Homo

This article is the third of a series that explores hominin dental crown morphology by means of geometric morphometrics. After the analysis of the lower second premolar and the upper first molar crown shapes, we apply the same technique to lower first premolar morphology. Our results show a clear distinction between the morphology seen in earlier hominin taxa such as Australopithecus and African early Homo, as well as Asian H. erectus, and more recent groups such as European H. heidelbergensis, H. neanderthalensis, and H. sapiens. The morphology of the earlier hominins includes an asymmetrical outline, a conspicuous talonid, and an occlusal polygon that tends to be large. The morphology of the recent hominins includes a symmetrical outline and a reduced or absent talonid. Within this later group, premolars belonging to H. heidelbergensis and H. neanderthalensis tend to possess a small and mesiolingually-displaced occlusal polygon, whereas H. sapiens specimens usually present expanded and centered occlusal polygons in an almost circular outline. The morphological differences among Paranthropus, Australopithecus, and African early Homo as studied here are small and evolutionarily less significant compared to the differences between the earlier and later homin taxa. In contrast to the lower second premolar and the upper first molar crown, the inclusion of a larger hominin sample of lower first premolars reveals a large allometric component.

Defining new dental phenotypes using 3-D image analysis to enhance discrimination and insights into biological processes

AimsIn studying aetiological interactions of genetic, epigenetic and environmental factors in normal and abnormal developments of the dentition, methods of measurement have often been limited to maximum mesio-distal and bucco-lingual crown diameters, obtained with hand-held calipers. While this approach has led to many important findings, there are potentially many other informative measurements that can be made to describe dental crown morphology. Advances in digital imaging and computer technology now offer the opportunity to define and measure new dental phenotypes in 3-D that have the potential to provide better anatomical discrimination and clearer insights into the underlying biological processes in dental development. Over recent years, image analysis in 2-D has proved to be a valuable addition to hand-measurement methods but a reliable and rapid 3-D method would increase greatly the morphological information obtainable from natural teeth and dental models. Additional measurements such as crown heights, surface contours, actual surface perimeters and areas, and tooth volumes would maximise our ability to discriminate between samples and to explore more deeply genetic and environmental contributions to observed variation. The research objectives were to investigate the limitations of existing methodologies and to develop and validate new methods for obtaining true 3-D measurements, including curvatures and volumes, in order to enhance discrimination to allow increased differentiation in studies of dental morphology and development. The validity of a new methodology for the 3-D measurement of teeth is compared against an established 2-D system. The intra- and inter-observer reliability of some additional measurements, made possible with a 3-D approach, are also tested. Methods and resultsFrom each of 20 study models, the permanent upper right lateral and upper left central incisors were separated and imaged independently by two operators using 2-D image analysis and a 3-D image analysis system. The mesio-distal (MD), labio-lingual (LL) and inciso-gingival (IG) dimensions were recorded using our 2-D system and the same projected variables were also recorded using a newly developed 3-D system for comparison. Values of Pearson's correlation coefficient between measurements obtained using the two techniques were significant at the 0.01 probability level for variables mesio-distal and incisal-gingival with labio-lingual significant at the 0.05 level for the upper left side only, confirming their comparability. For both 2-D and 3-D systems the intra- and inter-operator reliability was substantial or excellent for variables mesio-distal, labio-lingual, incisal-gingival actual and projected and actual surface area. The reliability was good for inter-operator reliability measurement of the labio-lingual dimension using 3-D. ConclusionsWe have developed a new 3-D laser scanning system that enables additional dental phenotypes to be defined. It has been validated against an established 2-D system and shown to provide measurements with excellent reliability, both within and between operators. This new approach provides exciting possibilities for exploring normal and abnormal variations in dental morphology and development applicable to research on genetic and environmental factors.

Complex segregation analysis of dental morphological variants.

A set of 20 morphological variants of the dental crowns and four characteristics of the jaws are tested for probable mode of inheritance using the complex segregation analysis method of Morton et al. (Am. J. Hum. Genet. 23:602-611, 1971). Models tested include three two-allele single-locus models (dominant, codominant, and recessive) and a model employing the polychotomized normal distribution of liability (an additive polygenic model), with transmissibility estimated via maximum likelihood. Most of the traits studied are observed using ordinal scales with several grades, and many are tested using more than one dichotomy of their scale. These multiple analyses allow for an examination of such factors as trait incidence on the results of the statistical analysis. The results of the analysis yield propositions of major genes for 13 of the 24 traits examined. Two traits give good evidence of being polygenic in origin. The remaining nine characters present methodological problems that do not allow for a definite conclusion on their mode of inheritance at this time. The ability to test varying levels of transmissibility in the polygenic model allows for an estimation of the percentage of trait variance determined by familial factors. Estimates of transmissibility for all characters examined range from 0 to 1, with a mean of 0.36. These findings may suggest a large environmental role in the development of dental crown morphology. However, the possibility exists that difficulties in the ability to classify the expression of certain traits consistently result in overestimates of the environmental influences on the development of those characters.

Root canal anatomy of mandibular first premolars in a southern Chinese population

Abstract Racial differences in dental crown morphology have long been recognized, but the frequency of genetically determined variations in the root canal anatomy of teeth has not been fully established. There is, therefore, a need to study the morphology of non‐Caucasoid teeth to establish the existence and prevalence of racially determined root canal variations. In this study 100 mandibular first premolars of Chinese origin were accurately identified and radiographed in vitro to establish the frequency of root canal bifurcation. Thirty‐six per cent of the sample presented with more than one canal. The division of these canals occurred at various levels of the root, and in all but one of the teeth the canals remained separate.

Root form and canal anatomy of mandibular first molars in a southern Chinese population

Abstract Racial differences in dental crown morphology have long been recognised, but the diverse aspects of root form and canal anatomy of human teeth have not received the same attention. The majority of books on dental anatomy fail to supply detailed information of the features of root and root canal morphology that occur at particularly high frequency in Mongoloid populations. These features have not been systematically documented and the implications that these variations may have upon clinical endodontics have not been fully reported. In this study 100 mandibular first molars extracted from Hong Kong Chinese patients were examined visually and radiographically. For each tooth, the number of roots, root canals, and apical foramina were noted. Fifteen per cent of the mandibular first molars examined were found to be 3‐rooted. Forty‐five per cent of the sample displayed 2 distal canals and 28% of the teeth had 2 separate distal apical foramina. The frequency of the second distal canal is higher than the previously reported findings for non‐Mongoloid groups.

Root form and canal anatomy of mandibular second molars in a Southern Chinese population

Racial differences in dental crown morphology have long been recognized, but the frequency of genetically determined variations in root form and canal anatomy has not been established. Features of root and root canal morphology occurring at particularly high frequency in Mongoloid populations have not been systematically documented. The implications that such features may have upon clinical endodontics have not been fully reported. In this study 100 mandibular second molars extracted from Hong Kong Chinese patients were examined visually and radiographically. For each tooth, the number of roots, root canals, and apical foramina were noted. Fifty-two percent of the mandibular second molars examined were found to have complete root fusion and 55% of the teeth were found to have only two canals. The high prevalence of fusion of roots in this sample of Chinese teeth emphasizes the way in which racial divergence may have a direct influence upon the endodontic morphology of the teeth of the adult dentition.

Root form and canal anatomy of maxillary first premolars in a southern Chinese population.

Abstract Racial differences in dental crown morphology have long been recognized, but the frequency of genetically determined variations in root form and canal anatomy has not been established. Features of root and root canal morphology that occur at particularly high frequency in Mongoloid populations have not been systematically documented, and the implications that such features may have upon clinical endodontics have not been fully reported. In this study 100 maxillary first premolars extracted from Hong Kong Chinese patients were examined visually and radiographically. For each tooth, the number of roots, root canals, and apical foramina were noted. Sixty per cent of the maxillary first premolars examined were found to be single‐rooted, but only 13% were found to have a single canal. The high frequency of single‐rooted teeth with two canals suggests that the single‐rooted condition represents a fusion, occurring in the relatively recent past, of two original roots.

The oral and dental manifestations of trisomy D syndrome

The oral and dental findings in two cases of trisomy D are reported and the oral findings are compared with those of other workers. The marked abnormalities of dental morphology found in these cases, together with the knowledge that abnormalities of dental morphology occur frequently in trisomy G, suggest that an extra autosomal chromosome tends to affect dental morphogenesis. This conclusion is in keeping with the observation of Kraus and his colleagues that prenatal disturbances may affect dental crown morphology.