Congenital defects of the upper lateral incisors (ULI) and the morphology of other teeth in man.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 53:479-486 (19801 Congenital Defects of the Upper Lateral Incisors (ULI) and the Morphology of Other Teeth in Man PIERRE LE BOT, ALICE GUEGUEN, AND DENISE SALMON FacultP de Chirurgie Dentaire, 1, rue Maurice Arnoux, 92120 Montrouge, France (P.L.B.), and Groupe de Recherches INSERM U 88, 91, Bd de l’Hopita1, 75634 PARIS cedex 13, France (A.G., D.S.) KEY WORDS Tooth Agenesis, Upper lateral incisors, Congenital defects, Tooth morphology ABSTRACT A sample of 192 male propositi with a t least one ULI either missing or reduced has been compared with 197 male controls in terms of the morphology of the other teeth. Every class of propositi exhibits modifications in the following characters: Significant differences between propositi and controls were found for molar cusp number and groove pattern, particularly in the lower first molar and in propositi with reduced ULI. Significant differences between propositi and controls were also found with respect to caniniform pattern of the lower first premolar. The Carabelli’s cusp is rarer in propositi. A hypothesis to account for these observations is proposed. The congenital absence of particular teeth is associated with quantitative and qualitative modifications of other teeth. This phenomenon was first observed in individuals missing the third molars (Garn and Lewis, 1962, Keene, 1965, Baum and Cohen, 1971). More recently, the number and size of teeth in individuals with congenital defects of the upper lateral incisors (ULI) have been shown to be more marked than they are in those with third molar agenesis (Le Bot and Salmon, 1977). In this study, we have analyzed morphological characters of certain teeth in these same individuals and compared them with controls. MATERIAL AND METHODS Our sample was composed of 192 propositi with a t least one maxillary lateral incisor either missing or reduced in size. Controls were 197 subjects selected at random from the same population. All were males, aged 18 to 25 years, who were examined at the Selective Service Center, Vincennes. Alginate impressions of both dental arches were obtained for each subject and cast in plaster. 0002-9483/80/5304-0479501.70:C: 1980 ALAN R. LISS. INC. Congenital absence of a tooth was verified from dental history and radiographs. Reduction in size of a maxillary lateral incisor was defined by one or more of the following characteristics: conical (peg-shaped) crown morphology; reduction in diameter from the cervix to the incisal edge; asymmetry in overall size between right and left incisors. Previous studies disclosed morphological differences in the dentition between individuals with size reduction of the maxillary lateral incisor and those with agenesis of this tooth (Le Bot and Salmon, 1977). Accordingly, the propositi were classified into three main groups and four subgroups that were determined by the morphology of the maxillary lateral incisor, as shown in Table 1. The control subjects also were classified into three subgroups according to the presence or agenesis of third molars. The morphological characters shown in Table 2 were assessed for each subject and scored according to the criteria listed. The Received February 15. 1979; accepted April 21. 1980 P. LE BOT, A. GUEGUEN. AND D. SALMON 480 rating of cusp number-groove pattern, as defined by Hellman (1928),was determined on the right side of the mandible only. For the other characters both sides of the dental arch were examined. If asymmetry was present the more “evolved score was used, that is, the lesser cusp number, the X groove pattern, the more extreme reduction of the Carabelli cusp, and for the lower first premolar, the caniniform pattern. In some instances, as reflected in the number of observations, all characters could not be scored. Furthermore, the upper and lower third molars were excluded from the study, as their morphology could not be determined with consistent reliability. For each character the x2 test was used in two types of comparisons: between the main groups of controls and propositi (groups 1, 2, 3, and 4, and between subgroups l a , 2b, and 3b. In the latter comparison these subgroups were representative of more extreme tooth morphology; la-controls with complete dentition, 2b-propositi with two reduced incisors, and 3b-propositi with bilateral agenesis of the incisor. Some cell sizes were to small for x2 analysis, and in these instances subjects were pooled to increase the group size. For the mandibular first molar (Table 3), subjects scored as five or six cusps were pooled for the x2 analysis, as were subjects with groove patterns + and X. The same procedure was followed for the analysis of the maxillary second molar (Table 6), where Carabelli scores two and three were pooled, and for the analysis of the mandibular second molar (Table 4), where scores for all propositi were pooled. The xZ test was not applied to the cusp number-groove pattern categories of Hellman (1928) or to the cusp number ratings of the maxillary first molar. RESULTS Results are presented in Tables 3-7 according to tooth examined and morphological categories. Each group and subgroup of propositi exhibited modifications of all dental characters, which are sumarized as follows. (Table 4) and the upper second molar (Table6), but in these instances there were no marked differences between the groups of propositi. In the upper first molar only two propositi, each with size reduction of the lateral incisor, displayed a reduction in cusp number from the usual pattern of four cusps displayed by all remaining subjects (Table 5 ) . There were no significant differences between groups or subgroups with regard to cusp number of the lower second premolar (Table7). Groove pattern I t is generally assumed that the order of groove pattern, Y, +, and X, ranges from a more archaic to a more evolved morphology. Propositi exhibited significantly higher frequencies of the evolved pattern than did the controls. This trend was evident in all groups of propositi for both the mandibular first and second molars (Tables 3 and 4). Cusp number-groove pattern Even greater differences between groups were noted in the Hellman classification, which associates cusp number and groove pattern. In the mandibular first molar, the Y5 pattern, which included Y6 ratings, diminished in frequency from controls through group 3 propositi to group 2 propositi, who displayed the lowest frequencies (Table 3). Similar trends were observed in the mandibular second molar, where the + 4 pattern was more frequent in all groups of propositi than in controls (Table 4). However, for this tooth the differences between groups of propositi were not so clear-cut. Carabelli complex Although the Carabelli cusp occurred less frequently in all groups of propositi, the differences between controls and propositi were not significant for either the first molar or the second (Tables 5 and 6). Morphology of the lower first premolar Propositi were more prone to caninification, with differences in frequencies between conCusp number trols and all groups or subgroups of propositi In the lower first molar cusp number was highly significant (Table 7 ) .Propositi with size significantly reduced in the propositi com- reduction or agenesis of the maxillary lateral pared with controls, and, furthermore, the incisor were equally affected. lowest cusp number was found in propositi DISCUSSION with size reduction of the maxillary lateral incisor (Table 3). I t is generally assumed that a lowered cusp A similar reduction in cusp number for pro- number in hominids corresponds to a more positi was observed in the lower second molar evolved tooth morphology and, similarly, that TOOTH MORPHOLOGY AND ULI ANOMALIES 481 TABLE 1. Classification of 197 control subjects and 192propositi according to dental criteria Main Group Subgroup Number Criteria Controls 1 197 134 46 17 la lb lc Normal maxillary I2 Complete dentition Agenesis of one or more M3 Radiographs unavailable to assess M3 Propositi 2 86 2a 2b 34 Size reduction of one or more maxillary I2 Unilateral size reduction of maxillary I2 Bilateral size reduction of maxillary I2 80 31 49 Agenesis of one or both maxillary I2 Unilateral agenesis of maxillary I2 Bilateral agenesis of maxillary I2 26 Agenesis of one and size reduction of the other maxillary I2 52 3 3a 3b 4 TABLE 2. Morphological characters observed and scoring methods Teeth Max. Man. Man. Man. Character M1, M2 P2, M1, M2 M1, M2 M1, M2 Scoring method Cusp number Count of cusp number Three categories: Y, + , X' Four categories: Y5, +5, Y4, +42 Max. M1, M2 Groove pattern Groove pattern, cusp number Carabelli complex Man. PI Cusp morphology 1 = no trace 2 = groove, pit, or slight elevation 3 = pronounced cusp Molariform = well-developed lingual cusp Caniniform = diminution of lingual cusp - ' After Jorgensen 11955). After Hellman 119281. the order Y, + , X ranges from a more archaic to a more highly evolved pattern (i.e., the strongest distal drift of the buccal cusp). Our results exhibit a significant decrease of cusp number in propositi with agenesis of ULI. This decrease affects the lower first molar most and, to a lesser degree, the lower second molar and the upper second molar. The upper first molar is rarely affected, and the lower second premolar also exhibits no difference between controls and propositi. I t may be noticed that propositi with reduced ULI seem more prone to these reductions in cusp number in the lower first molar and are the only class exhibiting three cusps in the upper first molar. As for groove pattern, a trend from a more archaic to a more evolved pattern is observed between controls and propositi. The Hellman scheme, which combines these two morphological characters, reveals the same trend towards the more highly evolved pattern in propositi, especially in M1 and in propositi class 2. Similar studies have been carried out by Keene (1965) and Davies (1968). who compared controls to subjects with agenesis of one or more third molars. They found a significant reduction of first and second molar cusp number in the agenesis group. In this study we treated controls with one or more missing third molars as a separate class (class lb), but except for the second upper molar, we did not find differences between our third molar agenesis group (class l b ) and controls with full dentition (class la). This difference between Keene's (1965) and Davies' (1968) results and our own may be explained by several factors. Keene, in fact, notes that in the class of subjects with M3 agenesis, 7.5% had other congenitally missing teeth, whereas our class of control l b subjects with M3 agenesis pos- 48 33 75 29 46 22 2b 3 3a 3.b 4 ~ 54.5 57.6 65.5 52.2 36.4 50.0 44.4 71.1 71.2 68.9 Y5 22.7 29.3 31.0 28.3 33.3 29.2 30.9 19.6 19.7 20.0 +5 18.2 9.3 3.5 13.0 6.1 14.6 11.1 4.1 3.8 4.4 Y4 4.6 4.0 0.0 6.5 24.2 6.2 13.6 5.2 5.3 6.7 62.7 65.5 60.9 68.2 22 36.4 64.6 53.1 73.7 72.7 73.2 Y 75 29 46 33 48 81 194 132 45 + 4 Number 27.3 32.0 27.6 34.8 57.6 33.3 43.2 24.7 25.8 24.5 + % Subjects 4.5 5.3 6.9 4.3 6.0 2.1 3.7 1.6 1.5 2.2 X Jorgensen classification’ ________ 22 75 29 46 33 51 84 194 132 45 Number 22.7 13.3 3.5 19.6 30.3 19.6 23.8 9.3 9.1 11.1 4 77.3 82.7 86.2 80.4 69.7 78.4 75.0 85.0 86.4 80.0 5 0.0 4.0 10.3 0.0 0.0 2.0 1.2 5.7 4.5 8.9 6 Cusp number’ YO Subjects 4.8 4.9 5.1 4.8 4.1 4.8 4.8 5.1 5.0 5.0 number Mean CUSP = 15.571. ’Cusp number Differences between main f l u u p s 1. 2. 3, and 4 significant a t p < 0.01 If Ix’ = 11,631: differences between subgroups l a , 2h. and 3b significant a t p < 0.01 (x’ = 10.59) ‘Groove pattern (Jorgensen 19561. Differences hctween main groups I , 2 . 3 , and 4 significant a t p < 0.01 (s2= 11.62);differences between suhgroups l a , 2h, and 3h significant a t p < 0.001 81 2 194 132 45 Number ~- 2a Propositi 1 la lb Controls Group % Subjects Hellman classification ______ TABLE -3. Analysis of the mandibular first molar shoioing percentages of controls and propositi according to classification of grooue pattern and cusp number p ? 100.0 0.0 0.0 0.0 23 4 ~ 94.9 90.0 98.0 3.8 6.7 2.0 1.3 3.3 0.0 0.0 23 79 30 49 0.0 1.3 0.0 2.0 6.1 5.9 6.0 6.7 6.8 6.5 Y 60.9 51.9 56.7 49.0 45.4 51.0 48.8 69.7 71.2 69.6 i 39.1 46.8 43.3 49.0 48.5 43.1 45.2 23.6 22.0 23.9 X 25 80 31 49 33 52 85 196 133 46 Number ~ Cusp number' 100.0 98.7 96.8 100.0 94.0 98.1 96.5 88.3 89.0 89.1 4 0.0 1.3 3.2 0.0 6.0 1.9 3.5 11.7 11.0 10.9 5 % Subjects Mean 4.0 4.0 4.0 4.0 4.1 4.0 4.0 4.1 4.1 4.1 cusp number (x'= 'Groove pattern (Jorgensen 1955).Differences between main groups 1. 2. 3, and 4 significant at p < 0.001 lx2 = 20.38);differences between subgroups l a , Zh, and 3h significant at p < 0.001 16.73). 'Cusp number. Differences between main groups 1. 2.3, and 4 sibmificant at p < 0.001 (x2 = 13.751; differences between subgroups la, 2b. and 3b significant at p < 0.05 (xz= 5.14). 0.0 0.0 79 30 49 3 33 87.8 3a 3b 6.1 6.1 0.0 33 2b 84 51 8.0 195 132 46 Number 70Subjects Jorgensen classification' 92.0 7.2 2.4 0.0 0.0 90.4 75.4 76.5 73.9 +4 0.0 13.3 12.9 15.2 Y4 50 10.3 9.8 8.7 - +5 83 1.0 0.8 2.2 Y5 2 195 132 46 Number 2a Propositi 1 la lb Controls Group % Subjects Hellman classification TABLE 4. Analysis of the mandibular second molar showing percentages of controls and propositi according to classification of groove pattern and cusp number P E P. LE BOT, A. GUEGUEN, AND D. SALMON 484 TABLE 5. Analysis of the maxillary first molar showing percentages of controls and propositi according to classification of the Carabelli complex and cusp number Carabelli complex' % Subjects Group Number 1 Cusp Number % Subjects 2 3 Number Mean 4 3 cusp number Controls 196 134 46 33.2 32.8 37.0 48.5 47.8 50.0 18.3 19.4 13.0 197 134 46 0.0 0.0 2a 2b 85 51 34 36.5 29.4 47.1 55.3 62.8 44.1 8.2 7.8 8.8 3 3a 3b 4 78 30 48 26 41.0 43.3 39.6 38.4 46.2 40.0 50.0 30.8 1 la lb 0.0 100.0 100.0 100.0 4.0 4.0 4.0 86 52 34 2.3 1.9 2.9 97.7 98.1 97.1 4.0 4.0 4.0 12.8 16.7 10.4 79 31 48 0.0 0.0 0.0 100.0 100.0 100.0 4.0 4.0 4.0 30.8 26 0.0 100.0 4.0 Propositi 2 'Carabelli complex. Differences between main groups 1, 2 . 3 , and 4 non-significant (x' = 11.63): difterences between subgroups l a . 2h. and 3h nonsignificant If = 4.841. TABLE 6. Analysis of the maxillary second molar showing percentages of controls and propositi according to classification of the Carabelli complex and cusp number - Carabelli complex' % Subjects Group Number 1 Cusp Number' % Subjects 2 3 Number 3 Mean 4 CUSD number Controls 197 134 46 32.5 31.3 41.3 67.5 68.7 58.7 3.7 3.7 3.6 0.0 86 52 34 41.9 36.5 50.0 58.1 63.5 50.0 3.6 3.6 3.5 7.7 6.7 8.3 1.3 0.0 2.1 79 31 48 43.0 35.5 47.9 57.0 64.5 52.1 3.6 3.7 3.5 20.0 0.0 25 40.0 60.0 3.6 la lb 197 134 46 88.3 91.0 87.0 11.7 9.0 13.0 0.0 0.0 Propositi 2 2a 2b 85 51 34 87.1 82.4 94.1 12.9 17.6 5.9 0.0 0.0 3 3a 3b 78 30 48 91.0 93.3 89.6 4 25 80.0 1 0.0 'Carabelli complex. Differences hetween main groups 1. 2. :i. and 4 non-significant I\' = 2.291: differences hrtween subgroups l a , 2h. and 3h nonmgnificant ( \ * = 0.521. 'Cusp number. Differences between suhgroups 1. 2. :iand . 4 non significant 11' = 3.911: differences hetwpen YuhLToupn la. 2h. and 3h signifi< o.ns I \ ' = 6.601 cant sessed all their other teeth. Moreover, Keene (1965) considered separately subjects whose M3 agenesis was located in the maxilla and those whose M3 agenesis occurred in the mandible. Onthe other hand, Davies (19681,who set M3 agenesis apart from agenesis of other teeth, obtained results more consistent with ours. In the first lower molar he found 25.3%of subjects missing the fifth cusp (hypoconulid)in the class with agenesis of one or more teeth other than third molars, versus 8% in the class of subjects possessing the full dental complement.We find 19.6%of these subjects missing the fifth cusp in class 3b propositi versus 9.1% in full dentition controls. Because of the assignment of his propositi, 485 TOOTH MORPHOLOGY AND ULI ANOMALIES T A B L E 7. Analysis of the mandibular premolars showing percentages of controls and propositi according to classification of morphology and cusp number First premolar-morphology' _____ Group Number B Subjects Caniniform Molariform Second premolar-cusp number' % Subjects Mean Number 2 3 cusp number Controls 1 196 133 46 13.8 I 0.5 13.0 86.2 89.5 87.0 194 132 45 54.6 54.5 55.6 45.4 45.5 44.4 2.5 2.5 2.4 2 2a 2b 85 51 34 38.8 33.3 47.1 61.2 66.7 52.9 83 49 34 48.2 49.11 47.1 51.8 51.0 52.9 2.5 2.5 2.5 3 3a 3b 80 31 49 37.5 22.6 46.9 62.5 77.4 53.1 78 31 47 57.7 58.1 57.5 42.3 41.9 42.5 2.4 2.4 2.4 4 23 26.1 71.9 23 47.8 52.2 2.5 la lb Propositi ____. 'Man. PI morphology. Differences between main groups 1. 2. 3, and 4 significant a t p < 0.001 (x2 = 28.511: ditferences between subgroups l a . Zb, and 3b significant a t p < 0.001 lx* = 36.691. 'Man P2 cusp number. Differences between main groups I. 2, 3. and 4 non-significant lx2 = 1.891; differences between subgroups l a , 2b. and 3b non-significant (x' = 0.90). Keene (1965) found significant differences between his classes of subjects with regard to Carabelli's trait, whereas we did not find any difference in our l b controls. In subjects with the same agenesis of M3, Garn et al. (1966) could not find any marked difference with respect to his controls and suggested that further exploration in cases of hypodontia be u n d e r t a k e n . Conversely, our r e s u l t s demonstrate that a relationship exists between ULI congenital defects and Carabelli's trait. Carabelli's trait is less marked in propositi 2b (2 ULI reduced) than in controls with full dentition. These results lead to the following conclusion: Congenital defects of ULI are associated with morphological changes in other parts of the dentition, and the effects appear to be greater than those observed in cases of third molar agenesis. I t is of some interest to note the marked morphological defect of the first lower premolar in ULI propositi, whereas the second lower premolar remains more stable. In our preceding study (Le Bot and Salmon, 1977)we have already observed that the first upper premolar was more variable in size than the second. These facts are in agreement with Butler's model (1939),which associates molars and premolars in a single morphogenetic field in mammals. According to this hypothesis, the first molar is the most stable tooth, the key-tooth, neighbouring teeth becoming more variable the farther away they are from this key-tooth. However, the high frequency of second lower premolar agenesis in hominids is not explained by this theory. In contrast, Dahlberg (1945) distinguishes between the molar field and the premolar field in man, considering the fact that in both fields the most distal tooth is the least stable. Our results disagree with this hypothesis. Another striking fact in our results is that ULI reduction is associated with modifications of size and morphology that are more pronounced than the corresponding modifications observed in ULI agenesis. We can explain this difference with the hypothesis of Sofaer et al. (1971). According to this, the agenesis of a tooth may give an increased growth potential to other teeth belonging to the same morphogenetic field. A compensatory effect may occur. This hypothesis tallies well with the otherwise paradoxical fact observed by ourselves and others: M 1 measurements are greater in subjects with M3 agenesis than in controls (Garn and Lewis 1970, Hanihara 1970). In the present study and in our previous one (Le Bot and Salmon, 1977),we observed an increasing alteration of dentition in the following order: controls with full dentition, controls 486 P. LE BOT, A. GUEGUEN, AND D. SALMON with one or more missing third molars, propositi with one ULI missing, propositi with two ULI missing, propositi with one ULI reduced, propositi with two ULI reduced, This was observed on most mesiodistal and buccolingual diameters and also on morphological characters. This trend is statistically significant. CONCLUSIONS We propose the following model for the morphological simplification of man’s dentition observed in our propositi sample. This modification may be described in the following sequence: Initially, a change in developmental timing resulting in delayed tooth eruption may lead to progressive simplification of dental morphology. The second step, in the lower molars, is a modification of the groove pattern tending from Y through to X. Concomitantly, the cusp number decreases. By associating the two characters, we may observe successively Y5 + 5 , Y4 + 4 . This phenomenon may be described as a distal drift of buccal cusps with groove reorganisation. The distal drift leads to hypoconulid reduction and secondly to hypoconulid loss. I t is associated with a mesial drift of lingual cusps, and then the groove pattern modification is accelerated. In the maxilla, we will observe the reduction and, later on, the disappearance of the hypocone. A reduction then appears and accompanies this second step. I t is a differential reduction of mesiodistal and buccolingual diameters, the latter being the more affected. Some teeth will be more affected, following a gradient that we have previously described. A stronger constraint will determine dwarfism firstly of the third molar and secondly of the ULI. The bilateral reduction of this latter tooth marks the end of the reduction of dentition. The next step will be the disappearance of some teeth, according to the following order: third molar, second lower premolar, ULI. But the paradox is that this last step will be associated with quantitative and qualitative modifications less marked than in the preceding step. We previously mentioned that + Sofaer et al.’s (1971) hypothesis may explain this phenomenon. So the trend will continue from presence to reduction and, later on, the loss of some teeth (particularly third molars and the upper lateral incisor), even if certain crown components do not follow this progression. This evolutionary scheme attempts to explain the different studies on agenesis. Further investigations will be necessary to settle some points, in particular with respect to eruption timing. However, Firschs (1965)conclusions concerning phylogenesis seem to corroborate our hypotheses. LITERATURE CITED Baum, BJ, Cohen, M. (1971) Agenesis and tooth size in the permanent dentition. Angle Orthodont., 41;lOO-102. Butler, PM (1939)Studies of the mammalian dentition. Differentiation of the post-canine dentition. Proc. Zool. SOC. Lond. B., 109t1-36. Dahlberg, AA (1945) The changing dentition of man. J. Amer. Dent. Assoc., 32.676-690. Davies, PL (19681Relationship of cusp reduction to the permanent mandibular first molar to agenesis to teeth. J. Dent. Res., 47t499. Frisch, J E (1965) Trends in the evolution of the hominoid dentition. Bibliotheca Primatologia. Fasc. 3. S. Karger. Basel. Switzerland. Garn, SM, and Lewis, AB (1962) The relationship between third molar agenesis and reduction in tooth number. Angle Orthodont., 3214-18. Garn. SM, and Lewis, AB (1970)The gradient and the pattern of crown size reduction in simple hypodontia. Angle Orthodont., 40:51-58. Garn, SM, Lewis, AB, Kerewsky, RS, and Dahlberg. AA(1966) Genetic independence of Carabelli’s trait from tooth size or crown morphology. Arch. Oral Biol., 11:745-747. Hanihara, K (1970)Upper lateral incisor variability and the size of the remaining teeth. J. Anthropol. SOC.Nippon. Hellman, M (1928) Racial characteristics in human dentition. Part 1. A racial distribution of the Dryopithecus pattern and its modifications in the lower molar teeth of man. Proceedings of the American Philosophical Society (Philadelphia)1967:157-174. Jorgensen, KD (1955) The Dryopithecus pattern in recent Danes and Dutchmen. J. Dent. Res.. 434:195-208. Keene. HJ (1965) The relationship between third molar agenesis and the morphological variability of the molar teeth. Angle Orthodont.. 35:289-298. Le Bot, P. and Salmon, D (1977) Congenital defects of the upper lateral incisors (ULI):condition and measurements of the other teeth, measurements of the superior arch, head and face. Am. J. Phys. Anthropol., 46t231-244. Sofaer, JA. Chung, CS, Niswander, JD, Runck. DW (1971) Development interaction size and agenesis among permanent maxillary incisors. Hum. Biol.. 43:22-35.