Sixth Cusp Research Articles

Morphometric variations and nonmetric anatomical traits or anomalies of the primary molar teeth, plus the molars' size thresholds for sex identification

IntroductionMorphological and morphometric features of the teeth are of interest to various clinical and academic dental and medical fields including prosthodontics, orthodontics, anatomy and anthropology, pathology, archeology, and forensic dentistry. These have been more or less researched in the case of the permanent dentition. However when it comes to the primary dentition, the literature is scarce and controversial. No study worldwide exists on the cutoff points (thresholds) for sex identification; no study exists on metric or nonmetric traits of deciduous teeth in Iranians. Hence, the aim of the study was to assess both the metric and nonmetric traits of primary molars, as well as their cut-off points for sex identification.MethodsIn this epidemiological cross-sectional study, pretreatment casts of 110 children (51 boys and 59 girls) aged 6 to 12 years were collected. Maxillary and mandibular first and second primary molars were evaluated regarding their metric traits (mesiodistal and buccolingual widths) and 9 nonmetric traits (Accessory cusp on the upper D, Accessory cusp on the lower D, Fifth cusp on the upper E, Carabelli’s cusp on the upper E, Protostylid on the lower E, Fifth cusp on the lower E, Sixth cusp on the lower E, Tuberculum intermedium [metaconulid] on the lower E, and Deflecting wrinkle on the lower E). ROC curves were used to identify cut-off points for sex determination as well as the usefulness of metric measurements for this purpose. Data were analyzed using independent-samples and paired-samples t-tests, McNemar, Fisher, and chi-square tests, plus Pearson and Spearman correlation coefficients (α = 0.05).ResultsAll the primary molars’ coronal dimensions (both mesiodistal and buccolingual) were extremely useful for sex identification (ROC curves, all P values ≤ 0.0000099). Especially, the mandibular primary molars (areas under ROC curves [AUCs] between 85.6 and 90.4%, P values ≤ 0.0000006) were more useful than the maxillary ones (AUCs between 80.4 and 83.1%, P values ≤ 0. 0000099). In the mandible, the first primary molar (maximum AUC = 90.4%) was better than the second molar (maximum AUC = 86.0%). The optimum thresholds for sex determination were reported. Sex dimorphism was significant in buccolingual and mesiodistal crown widths of all the primary molars (all P values ≤ 0.000132), but it was seen only in the case of 2 nonmetric traits: Deflecting wrinkle (P = 0.001) and Tuberculum intermedium (metaconulid, P = 0.029) on the lower Es, taking into account the unilateral and bilateral cases. The occurrence of nonmetric traits was symmetrical between the right and left sides (all P values ≥ 0.250). All mesiodistal and two buccolingual molar measurements were as well symmetrical (P > 0.1); however, two buccolingual measurements were asymmetrical: in the case of the maxillary E (P = 0.0002) and mandibular D (P = 0.019). There were three weak-to-moderate correlations between the nonmetric traits of the mandibular second molars (Spearman correlations between 22.7 and 37.5%, P values ≤ 0.045). Up to 6 concurrent nonmetric traits were observed in the sample, with 53.6% of the sample showing at least 2 concurrent nonmetric traits at the same time, without any sex dimorphism (P = 0.658).ConclusionSex dimorphism exists considerably in primary molars’ sizes, but it is not as prevalent in their nonmetric traits or abnormalities. Primary molars’ crown sizes are useful for sex identification; we calculated optimum cut-off points for this purpose, for the first time.

Rasgos Morfológicos Dentales Coronales en dentición temporal y permanente: Distancia biológica entre tres grupos indígenas del Amazonas Colombiano

Objetivos: Determinar la frecuencia y variabilidad de doce rasgos morfológicos dentales coronales (Winging, incisivos centrales y laterales en pala, doble pala, cúspide de Carabelli, patrón cuspídeo, número de cúspides, cresta distal del trigónido, pliegue acodado, protostílido, cúspide 6 y cúspide 7), en dientes temporales (ui1/ui2/um2/lm2) y permanentes (UI1/UI2/ UM1/LM1), para comprender la influencia étnica y la distancia biológica de tres grupos indígenas del Amazonas Colombiano. Material y métodos: Se realizó un estudio descriptivo cuantitativo para observar la frecuencia y variabilidad de doce rasgos morfológicos dentales coronales mediante los sistemas Hanihara, Dahlberg, Sciulli, Grine y ASUDAS en 96 modelos de niños de ambos sexos, en dentición mixta y pertenecientes a los grupos Ticuna, Huitoto y Cocama. Resultados: Fueron observadas altas frecuencias de winging, incisivos centrales y laterales en pala, de las formas surco y fosa de la cúspide de Carabelli, patrón cuspídeo Y6 o Y7, pliegue acodado, protostílido y cúspide 6, típicas de la morfología dental del complejo dental Mongoloide - subdivisión Sinodonte. Se apreciaron frecuencias significativas del patrón cuspídeo +6 y +7, y de la cúspide, 7 lo cual sugiere mestizaje. Existe afinidad biológica entre las tres etnias, y fue demostrada la simetría bilateral y ausencia de dimorfismo sexual.

DECIDUOUS HUMAN TEETH FROM THE UPPER PALEOLITHIC SITE OF YUDINOVO, WESTERN RUSSIA

Population affinities of the Timonovka-Yudinovo Upper Paleolithic people are reconstructed on the basis of three isolated deciduous teeth––a lower lateral incisor, lower and upper second molars, likely representing three individuals––from Yudinovo in the middle Desna basin (15–12 ka BP), found in 1987–1996. Based on measurements and descriptive traits and computed microtomography, the teeth were compared with those from other Upper Paleolithic sites in northern Eurasia. The principal component analyses of metric and nonmetric traits revealed similar patterns. To minimize random variation, results of both analyses were integrated. Results indicate affi nity with Pavlov people in Central Europe. The diagnostic trait combination includes weak expression of the Carabelli cusp on the upper second molar, accessory sixth cusp on the lower second molar, large bucco-lingual diameter of both molars, and moderate mesio-distal diameter of the lower second molar. These results support the view that the Timonovka-Yudinovo tradition is related to eastern Gravette.

Результаты изучения молочных зубов с верхнепалеолитической стоянки Юдиново (Среднее Подесенье)

Population affinities of the Timonovka-Yudinovo Upper Paleolithic people are reconstructed on the basis of three isolated deciduous teeth––a lower lateral incisor, lower and upper second molars, likely representing three individuals––from Yudinovo in the middle Desna basin (15–12 ka BP), found in 1987–1996. Based on measurements and descriptive traits and computed microtomography, the teeth were compared with those from other Upper Paleolithic sites in northern Eurasia. The principal component analyses of metric and nonmetric traits revealed similar patterns. To minimize random variation, results of both analyses were integrated. Results indicate affi nity with Pavlov people in Central Europe. The diagnostic trait combination includes weak expression of the Carabelli cusp on the upper second molar, accessory sixth cusp on the lower second molar, large bucco-lingual diameter of both molars, and moderate mesio-distal diameter of the lower second molar. These results support the view that the Timonovka-Yudinovo tradition is related to eastern Gravette.

Dental anthropology of a Brazilian sample: Frequency of nonmetric traits

Dental elements are valuable tools in a study of ancient populations and species, and key-features for human identification; among the dental anthropology field, nonmetric traits, standardized by ASUDAS, are closely related to ancestry. This study aimed to analyze the frequency of six nonmetric traits in a sample from Southeast Brazil, composed by 130 dental casts from individuals aged between 18 and 30, without foreign parents or grandparents. A single examiner observed the presence or absence of shoveling, Carabelli's cusp, fifth cusp, 3-cusped UM2, sixth cusp, and 4-cusped LM2. The frequencies obtained were different from the ones shown by other researches to Amerindian and South American samples, and related to European and sub-Saharan frequencies, showing the influence of this groups in the current Brazilian population. Sexual dimorphism was found in the frequencies of Carabelli's cusp, 3-cusped UM2, and sixth cusp.

Dental Morphological Markers as a Proxy for Ethnicity in Robinson Crusoe Islanders

*,**,***,**** ***** *** ****** ; ****** *** ** SUMMARY: Chilean Robinson Crusoe Island is a semi-isolated location with unusually high rates of both consanguinity and language disorder. The current population of 633 inhabitants is descended almost exclusively from the colonization at the end o f the 19th century, as there were few preceding immigrations to the island. This study investigates the genetic composition and degree of miscegenation within the island population, using dental morphological markers. The universe of island children was studied (n= 128, 3 to 15 years of age) using clinical exams, dental cast, and identification of each individual within a previously-constructed extensive genealo gy for the island. The frequencies for Carabelli's cusp (61.7%), shovel-shaped incisor (9.4%), and sixth cusp (2.3%), along with the absen ce of seventh cusp, are consistent with a primarily Caucasian population. The estimated degree of miscegenation suggests an Amerindia n component of 4.3%, which is consistent with the extensive known genealogies of the founders. Characterizing the genetic profile of Robinson Crusoe Island, a location with a remarkably high prevalence of language disorder, facilitates the comparison of the ge netic variants underlying this pathology with those identified in European populations.

Morphological changes in the crown of mandibular molars with an additional distolingual root

ObjectiveThe mandibular molars typically have two roots placed mesiodistally, but they occasionally have an additional distolingual (DL) root. This study was to determine the morphological characteristics of the crown of such mandibular molars. DesignRadiographic records and study models were collected from a Korean population (n=86 patients). Each molar was assigned to either the experimental group (i.e. with a DL root) or the control group (i.e. without a DL root; n=41 patients) based on the radiographic findings. The intercuspal distances of the first permanent molars (total, n=100; control/experimental, n=50/50) and primary second molars (46, 23/23), and the largest buccolingual/mesiodistal widths of those molars and primary first molars (42, 21/21) were measured for molars with and without a DL root. In addition, the correlation between the existence of a sixth cusp and a DL root was examined. ResultsThe crowns of first permanent and primary second molars with DL roots had significantly larger intercuspal distances between the distobuccal–distolingual cusp tips and a larger distal-area buccolingual width than those without the DL root (t-test; p<0.05). There was no significant correlation between the existence of a sixth cusp and the presence of a DL root. ConclusionsThe existence of a DL root was associated with larger buccolingual dimensions, especially in the distal area.

Variation in the number of cusps of lower first and second molars M1 and M2

Aim: To find the existence of variability in the number of primary cusps of the lower first and second molars M1 and M2. Materials and methods: The study was conducted on the models of 400 orthodontic patients (164 males and 236 females). Results: It was found that the lower molars M1 in the group is least subject to reduction so that the majority of patients within gender groups (75.61% boys and 66.95% girls), have the presence of all five basic cusps type M1-5. Type M1-4, where there is complete absence of hypoconulid has 21.35% 32.63% boys and girls. The presence of the sixth cusp is found at 3.05% and 0.42% of boys of girls. Type M2-4 dominated in both sexes (86.59% boys and 91.1% girls), while type M2-5 found in much smaller percentage (13.41% boys and 8.9% girls). Conclusion: The subjects of our sample are characterized by a high percentage of the presence of M1 with five cusps (70.5%) and M2 with 4 cusps (89.25%). It has been established the total absence of only distovestibular cusp-hypoconulid.

下顎第2乳臼歯エナメル象牙境の形態学的研究

Morphologies of the DEJ which might have phylogenetically primitive characters are important for understanding the phylogeny of the human teeth. Morphological traits on the outer enamel surface (OES) can be observed clearly on the dentino-enamel junction (DEJ) as a distinct ridge or a process even if they are not distinct on the OES. We observed ten characters on the OES and DEJ of lower second deciduous molars (m2), and examined significant differences of these frequencies between the DEJ and OES. We also compared the frequencies of occurrence with the lower permanent first molar (M1) and searched for morphological relationship among four surfaces by distance analysis.The following results were obtained;1. On the buccal surface of m2, frequencies of occurrence of characters on the DEJ were almost higher than on the OES. And on the DEJ, frequencies of occurrence of the buccal marginal ridge (mesial) and protostylid of the m2 were higher than in M1.2. On the occlusal surface of the DEJ of m2, frequency of occurrence of metaconid distal accessory tubercle forming the seventh cusp was higher than on the OES. Frequencies of occurrence of the middle trigonid crest, distal trigonid crest, sixth cusp, seventh cusp and mesial accessory tubercle of the m2 were higher than in M1.3. The distance analysis indicated that there was a strong resemblance between the DEJ of m2 and of M1, and between the OES of m2 and of M1. This study suggested that the frequencies of primitive crown characters were retained most in the DEJ of the m2 among four surfaces in the m2-M1 series.

Frequencies of Occurrence of Accessory Tubercles and Other Traits in the Lower Deciduous Second Molar.

The frequencies of occurrence of anomalous traits or tubercles on the lower second deciduous molar were investigated with the use of moire contourgraphy. A molar with negligible attrition was fixed in the tricuspal position where the position of the protoconid, metaconid and hypoconid were in a horizontal plane. A moire photograph in the pitch of 0.2 mm was thus obtained and examined. The frequency of occurrence of a tubercle was counted in three grades according to its contour patterns. The traits and their sex-pooled frequencies were as follows (n=45): (1) Mesial Accessory Tubercle, 17.8%;(2) Metaconid Mesial Accessory Tubercle, 8.9%;(3) Metaconid Distal Accessory Tubercle, 57.8%; (4) Distal Trigonid Crest, 17.8%;(5) Deflecting Wrinkle, 46.7%;(6) Sixth Cusp, 35.5%; (7) Entoconid Mesial Accessory Ridge, 0%; (8) Protostylid, 73.3%. The incidences of the traits were compared with those in the permanent first molars previously studied. The traits nos. 2, 3, 4 and 8 were significantly more frequent in the deciduous molars than in the permanent ones when tested by χ2 test. On the other hand, the frequencies of trait nos. 1, 5, 6 and 7 were not significantly different between both molars. Three of four traits showing significant difference located around the metaconid, which indicated the high morphological variability of the metaconid in the deciduous lower second molar.

Expression of the entoconulid (sixth cusp) on mandibular molar teeth of an Australian aboriginal population

The expression and genetic basis of the entoconulid (sixth cusp) on mandibular molars were examined in a geographically isolated group of aboriginals from Yuendumu in the Northern Territory of Australia. Four grades of trait expression, ranging from trace to small, medium, and large cusps, were defined on dental casts of 399 subjects. Frequencies of occurrence were among the highest reported in human populations. Approximately 80% of dm2s showed the trait, whereas frequencies in the permanent dentition ranged from around 50% on M2 to 70% on M1 and 80% on M3. The degree of expression increased distally along the molar series, with only 3% of dm2s showing large cusps compared with 25% of M3s. Fluctuating asymmetry was highest for M2 and lowest for dm2. No strong evidence for sexual dimorphism in occurrence or degree of expression was found. Based on a quasi-continuous threshold model, a genetic contribution to entoconulid variability was observed that was strongest for M1. Significant associations were noted between entoconulid expression on mandibular molars and metaconule expression on maxillary molars, indicating that similar developmental mechanisms may influence these traits. The entoconulid and the metaconule both provide additional bulk on the distal occlusal surface of molar teeth, an area subjected to early wear during mastication in aboriginals.

Sixth and seventh cusp on lower molar teeth of Malawians in East-Central Africa.

The expressions of both sixth cusp (C6) and seventh cusp (C7) among the Malawians in East-Central Africa are described and compared with those of other African, Mongoloid, and Caucasoid populations. The subjects consisted of 99 males and 95 females. Scoring was performed using dental hard stone casts according to Turner's standard plaques. A sexual dimorphism in the occurrence of each trait was found to be not significant by chi-square test. The frequency of C6 in Malawians is remarkably lower than that in Mongoloid populations, and is located at the low range of frequency of C6 in the Caucasoid racial variation. On the other hand, C7 was observed more frequently in Malawian samples than in Mongoloid and Caucasoid populations. This tendency is in accordance with findings by Hellman on West African Negroes and by Hanihara on Bantu and American Negroes. Therefore, it is likely that C7 should be one of the components of the “Negroid dental complex”. In general, the Malawians were similar to other African groups with the exception of the Teso in the occurrence of both traits. Concerning the frequency order between first and second lower molars in the Malawians, C6 and C7 appeared more often in first lower molars than in second lower molars. These results concerning C6 seriously question the validity of the “field concept” in relation to the human dentition.

アカゲザル (Macaca mulatta) の乳歯形態について

Investigations of the teeth of the primates are invaluable for the phylogenetic study of the teeth of the mammals. Furthermore, the fact that the milk teeth are more primitive compared with the permanent teeth makes the morphological study of the milk teeth of the primates essential for the phylogenetic study. Because of the foregoing viewpoint, the teeth in position of forty-eight skulls of rhesus monkeys, in possession of the department, were measured and examined morphologically. Rhesus monkeys belong to the cercopithecids of the primates and, their tooth formura is the same as that of the humans in both milk and permanent teeth. Morphologically, their teeth are closely allied to the humans. The results were as follows : 1. The development of the cingulum in the anterior teeth region was extremely little labially but rather advanced lingually. The development was prominent particularly at the central milk incisor and milk canine of the maxilla and at the milk canine of the mandible. 2. The development of the cingulum of the milk molar was not recognized lingually but was apparent buccally. Equivalents of the human molar tubercles were observed particularly at the first milk molar in the maxilla and mandible, not only at the mesial tooth neck but also at the distal tooth neck. 3. The occlusal forms of the milk molars in the maxilla and mandible showed bilophodonty as the molars of other cercopithecids. 4. The number of cusp of the milk molars was four in all cases, but the second milk molars of the mandible showed a trend for a slight degree of differentiation in the hypoconulid. 5. The form of the occlusal surface grooves was Type + for the first milk molar and mostly Type X for the second milk molar in the maxilla, and, in the mandible, Type + for the first milk molar and either Type + or X for the most of the second milk molars. Typc Y was extremely few. This differed greatly from the humans whose milk molars are mostly Type Y. 6. Supernumerary tubercles of the milk molar were extremely few. Occurrence of Carabelli's tubercles was 9.4% at the maxillary second milk molar, protostylid 2.1% and the sixth cusp 5.3% at the mandibular second milk molar. 7. According to the measurements of the crowns, the maxillary second milk molar was the largest of the milk teeth and the mandibular lateral milk incisor the smallest. Comparison by crown index of the rates of the mesiodistal diameter to buccolingual diameter of the crowns with those of the human milk teeth revealed little difference in the rates between them in the anterior portion. In the molar portion, however, the rate of the mesiodistal diameter of rhesus monkeys to the buccolingual diameter was extremcly greater characteristically in comparison with the humans'. 8. In the comparison between the mesial and distal buccolingual diameter of the milk molar crowns, the mesial buccolingual diameter was greater in the maxilla and the distal buccolingual diameter was greater in the mandible. Of the mandibular first milk molar in particular, the distal buccolingual diameter was significantly longer compared with the mesial buccolingual diameter. 9. In the relation of the size between the milk central incisor and milk lateral incisor, the milk lateral incisor was smaller in the maxilla, as in the humans, and the mesiodistal diameter of the milk central incisor was shorter in the mandible and the labiolingual diameter of the milk lateral incisor was shorter. 10. The second milk molar was larger in size than the first milk molar in both the maxilla and mandible in all cases.

Splinting electrical burns of the mouth in children : COLCLEUGH R. G. and RYAN J. E. Dent Abstr.22 (1977) 48

The mandibular molars typically have two roots placed mesiodistally, but they occasionally have an additional distolingual (DL) root. This study was to determine the morphological characteristics of the crown of such mandibular molars.Radiographic records and study models were collected from a Korean population (n = 86 patients). Each molar was assigned to either the experimental group (i.e. with a DL root) or the control group (i.e. without a DL root; n = 41 patients) based on the radiographic findings. The intercuspal distances of the first permanent molars (total, n = 100; control/experimental, n = 50/50) and primary second molars (46, 23/23), and the largest buccolingual/mesiodistal widths of those molars and primary first molars (42, 21/21) were measured for molars with and without a DL root. In addition, the correlation between the existence of a sixth cusp and a DL root was examined.The crowns of first permanent and primary second molars with DL roots had significantly larger intercuspal distances between the distobuccal–distolingual cusp tips and a larger distal-area buccolingual width than those without the DL root (t-test; p < 0.05). There was no significant correlation between the existence of a sixth cusp and the presence of a DL root.The existence of a DL root was associated with larger buccolingual dimensions, especially in the distal area.

A case of buccolingually compressed lower second premolar of a Hawaiian

The observations and measurements were made on the buccolingually compressed lower second premolars of a Hawaiian. The results are summarized as follows:The buccolingually compressed lower second premolars were exceedingly large in the mesiodistal crown diameter, while in the buccolingual crown diameter they approximately showed the average size. As shown in the figure 1, bilateral second premolars were strongly compressed buccolingually in the occlusal surface itself.It might be suggested that both the enlargement of the mesiodistal crown diameter and the compression of the buccolingual crown diameter should result from the atavism.The mesiodistal crown diameters of the remaining premolars of this case were fairly large as compared with the average size of the Hawaiian. In this case, the central tubercle, Carabelli's cusp and sixth cusp were observed on the lower second premolars, upper molars and lower molars respectively.

A Morphological Study of Enamel-Dentin Border on the Japanese Dentition

We have reported on the pattern of the enamel-dentin border of the incisors, canines, premolars and maxillary molars in this journal (vol. 73, no. 3, vol. 75, no. 4, 5, vol. 77, no. 3, vol. 79, no. 4). The present article is the description on the mandibular molars as the sixth chapter of our work. The materials used in this study were 114 mandibular first molars and 77 second molars.The results were summarized as follows:1. On the enamel-dentin border, the mesial, distal and cervical margins of buccal surface may be surrounded by the distinct ridges separated from the surface itself by clear grooves (Fig. 1.). The mesial marginal ridge starts as a continuation of the cervical ridge, rises in an occlusal direction and terminates on the mesial occlusal marginal ridge. The distal marginal ridge starts as a continuation of the cervical ridge, runs along the buccal slope of the hypoconid in a disto-occlusal direction and terminates on the tip of the hypoconulid. The frequencies of the buccal marginal ridge are shown in table 1. The enamel-dentin border has a higher frquency of well developed marginal ridge than the enamel surface. The frequencies of the buccal cervical ridge on enamel-dentin border are shown in table 2. The first molar has markedly higher frequencies of the marginal and cervical ridges than the second molar. Buccal ridges may be homologous with the buccal cingulum and its ascending portion observed in the mandibular molar of Teilhardina or recent gorilla.2. In almost all cases the enamel-dentin borders of the teeth with protostylid show the well developed buccal cingulum (Fig. 4). In many cases this cingulum shows a cingulum-protoconid crest. The enamel-dentin borders of the teeth without protostylid on the enamel surface show a more or less distinct cingulum on nearly 28-56 per cent of the cases. The degree of development of the protostylid on enamel surface and that of the buccal cingulum are significantly correlated with each other under 1 per cent level. The evidence adduced above suggests that the protostylid represents a fairly young specialization and a last product of the buccal cingulum.3. On the enamel-dentin border, the tip of the metaconid and the protoconid may be connected by the so-called distal trigonid crest. The distal trigonid crest was originally reported by WEIDENREICH (1937), who found this crest in the deciduous lower second molar of Sinanthropus. It is very probable that this crest has reduced from fairly early times in the course of human evolution. The frequencies of this crest on enamel-dentin border are 46.4% in Mr and 20.8% in M2. However, there are varieties in the type of this crest. We classified the distal trigonid crest (transverse ridge) into five types as shown on figure 11. The percentage frequencies of the transverse ridge are shown in table 8.4. The sixth cusp is one of the accessory cusps which occasionally appears between the hypoconulid and the entoconid. The percentage frequencies of the sixth cusp on the enamel surface are shown in table 9. On the enamel-dentin border, the sixth cusp is indistinct, while the spine of the occlusal marginal ridge may be present on the place where the sixth cuspshould be.5. The seventh cusp occasionally appears between the metaconid and the entoconid. It seems to be identical to the tuberculum accessorium mediale internum defined by SELENKA (1898). The percentage frequencies of the seventh cusp on the enamel surface are shown in table 10. On the enamel-dentin border, the seventh cusp is indistinct, while the spine of the occlusal lingual margin may be present on the place where the seventh cusp should be. 6. The A-type of metaconid ridge on enamel-dentin border (Fig. 8), triangular ridge of metaconid and deflecting wrinkle are intimately correlated with one another. There are negative correlations between these three traits and the distal accessory ridge of the metaconid.