Congenital defects of the upper lateral incisors (ULI) Condition and measurements of the other teeth measurements of the superior arch head and face.код для вставкиСкачать
Congenital Defects of the Upper Lateral Incisors (ULI): Condition and Measurements of the Other Teeth, Measurements of the Superior Arch, Head and Face PIERRE L E BOT AND DENISE SALMON 2 Lnboratozre d’dnthropoloqze Bzologzque (Frofesseur Oliuier) Uniuersite Parzs VII - 2 , Place Jusszeu 75005 Paris, France and 2 Group de Recherche U88,Inserm, Mbthodologze lnformatzque e t Statzshyue e n Mbdectne (Professeur F Greniy) 9 1 , bd de I’HBpilnl, 75634 Parts Cvdrx 13, France ’ KEYWORDS defects Tooth agenesis . Upper lateral incisors . Congenital ABSTRACT We surveyed a French male population for the incidence of missing or reduced upper lateral incisors (ULI). In 5,738 subjects, we observed a n incidence of 1.59% with one or two reduced ULI (the other normal) and 1.90% with one or two missing ULI (the other normal or reduced), altogether, 3.49 % affected subjects. Furthermore, 250 random controls were observed. Agenesis of other teeth is more frequent in propositi. Missing third molars were 12.4% in controls, 24.0% i n propositi with reduced ULI and 39.6% i n propositi with two missing ULI. Furthermore, agenesis of incisors, canines and premolars ranges from 0.4 % in controls to 1.3% i n propositi having reduced ULI and 5.0 % in propositi with two missing ULI. So, propositi with reduced ULI are intermediate between the controls and the propositi with missing ULI with respect to the frequency of agenesis of other teeth. On the other hand, a different ranking is observed with respect to the teeth measurements: reduction of tooth size is more marked in propositi with reduced ULI than in propositi with missing ULI. The reduction mainly affects canines, incisors and to a lesser degree, premolars. Arch length and interpremolar diameters are smaller in propositi with missing ULI, compared with controls. acteristics: conoid (peg-shaped) ULI; ULI reducing in diameter from the cervix to the incisal edge; ULI with marked asymmetry in volume between the right and left sides. The control group consisted of normal subjects examined after each propositus. MATERIAL AND METHODS Thus, 200 diagnosed propositi and 250 The subjects surveyed were 5,738 males, random controls were observed, and all born in Paris, age 18 to 25, examined a t teeth of both groups examined by three the Selective Service Center at Vincennes. types of X-rays: simple intra-alveolar films This provided a large random sample with to check for the premolars or molars pregood dental health and permanent denti- sumed absent (most commonly, third motion and likely to remember any extraction. lars); occlusal films using the modified Those with absent or reduced ULI consti- Simpson method, for all the cases where tuted the experimental group. Congenital the incisors or the canines were missing; absence was verified from past dental his- Panoramic films, using the Panorex proctory and from X-rays. Reduction was de- ess for cases of presumed multiple agenefined by one or more of the following char- sis. These films made it possible to have Congenital absence of Upper Lateral Incisor teeth (ULI) has been associated with other defects. We surveyed a French population for the incidence of missing or reduced ULI and compared their dentition with controls. AM. J. PnYs. ANTHROP.,46: 237-244. 231 232 PIERRE LE BOT AND DENISE SALMON both complete arches on the same film, obviously the ideal technique for this type of study. Each tooth was coded as following: 1 = normal, erupted; 2 = reduced, erupted; 3 = congenitally absent; 4 = normal, not erupted; 5 = normal impacted; 6 = reduced not erupted, not impacted (fig. 1). Measurements Dental impressions of the two arches for all subjects were taken in alginate and cast in plaster. Dental measurements of maxillary teeth were carried out on the casts, using the method elaborated by Morrees et al. (‘57). Given the unavoidable e Fig. 1 Various possible combinations in congenital defects of ULI. Code 1 - 2 A - Right normal, left reduced Code 2 - 1 B - Right reduced, left normal Code 2 - 2 C - Right reduced, left reduced Code 1 - 3 D - Right normal, left missing Code 3 - 1 E - Right missing, left normal Code 2 - 3 F - Right reduced, left missing Code 3 - 2 G - Right missing, left reduced Code 3 - 3 H - Right missing, left missing CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS TABLE 1 Upper lateral incisos (ULI) defects, by type in 5,738 subjects ULI dfects Code Right ULI Left 90 in POPU- R L No. lation 1 2 2 Reduced 2 Normal Normal 1 Reduced 2 Reduced Reduced 1 or 2 reduced ULI (the other normal) 28 37 0.49 0.45 0.64 91 1.59 Missing 3 Normal Normal 1 Missing Missing 3 Reduced Reduced 2 Missing Missing 3 Missing 1 or 2 missing ULI (the other normal or reduced) 16 14 18 12 49 0.28 109 1.90 200 3.49 1 3 2 3 3 All propositi ULI 26 0.24 0.31 0.21 0.85 R, right; L, left; 1, normal, erupted tooth; 2, reduced, erupted tooth; 3, missing tooth: No., number of observed propositi. 233 molars have been excluded from these comparisons because of the inherent uncertainty regarding the cause of absence. After regrouping the eight categories of propositi, we obtained three large classes and six subclasses: Class 1: Controls having both ULI normal (class l a : controls with four third molars present; class l b : controls lacking at least one third molar). Class 2: Propositi having one (class 2a) or both (class 2b) ULI reduced. Class 3: Propositi lacking one (class 3a) or both (class 3b) ULI; in the former case, the other ULI may be either normal or reduced. Only in the case of the third molars (tables 2, 3) did the data fall into the predicted states, i.e. code 1 to 6. For the other teeth (table 4), only their presence or absence was taken into consideration. 1. Relationship between agenesis of the ULI and agenesis of the inaccuracy of dental measurements the third molars use of very precise measuring instruments is pointless. A specially adapted sliding The grouped results (table 3) show that, caliper with ground tips accurate to 0.01 for the controls, 12.4% of the third molars mm was used in this study. were lacking, while for the propositi having We also measured the following: trans- absence of both ULI (class 3b), 39.6% of verse diameters of the upper arch between the third molars were absent. This differthe first premolars (grooves), between the ence is highly significant (X2 = 87.8, 3 first molars (grooves), and between the d.f.,p < 0.001). second molars (buccal surface); length: A more detailed analysis (table 2) shows between the distal surface of the second that the position of the affected ULI (left molars and the central incisors; head: or right), has no influence whatsoever on maximum length (glabella opisthocranion), the third molar. This is important because maximum width; face: height (gnathion- it shows that the malformation is not spenasion) and bizygomatic width. cific to a particular side. Symmetry is thus almost perfect between the two sides of the RESULTS arch. Third molars are absent more freThe condition of ULI in the 200 propositi quently in the lower arch than in the upis shown in table 1. Thus 109 (or 1.90% of per for all classes of subjects (table 3). the population) had one or both ULI missThe situation “tooth not erupted and ing and the other normal or reduced, while impacted” (code 5, i.e., that it is mechanthe remaining 91 (or 1.59% of the popula- ically impossible for the third molar to astion) had one or both ULI reduced and the sume its normal position in the arch) is other normal. No impacted ULI were found. almost always observed in the mandible, We found no difference between the left these teeth being most often impacted in and the right sides; the slightly higher a horizontal position. We note (table 2) incidence of the malformation on the left that this anomaly is equally frequent in side is not statistically significant. class 1 (controls, 5.2% of examined teeth) class 2 (4.4%) and class 3 (4.5%). I. The frequency of congenital defects of In the same way, the case “impacted other teeth in propositi and controls tooth capable of normal evolution” (code The first and second upper and lower 4, table 2) has nearly the same frequency L ULI 2 1 2 3 1 3 2 3 6 6 1 4 2 5 7 2 10 98 52 L 3 7 1 4 4 4 7 3 16 98 58 Up 7 8 1 0 5 7 6 4 12 1 1 0 2 0 0 1 2 1 7 113 103 51 59 4 7 1 0 5 5 7 2 11 R Up L Lo R Lo L 1 0 0 2 0 2 0 1 3 6 Up (2 ) 0 0 0 0 0 0 0 0 9 5 4 0 2 3 2 0 18 0 0 0 0 0 0 0 5 4 4 0 4 2 4 18 31 41 0 29 0 43 1 0 R L Up L LoUp 6 6 4 4 9 1 1 1 0 3 3 3 5 6 5 19 21 29 55 35 51 L Lo Lo R Congenitally absent (3) La R Reduced erupted R L Up R Lo 8 8 11 7 6 5 7 17 4 6 4 5 12 15 9 11 1 5 9 4 4 3 3 1 117 116 77 69 66 52 Up (4) L 3 6 8 5 2 3 3 87 47 Lo 1 non-erupted Normal R ULI, right ULI; L ULI, left ULI; R Up, right upper; L Up, left upper; R Lo, right lower; L Lo, left lower. ULI 1 2 2 1 3 2 3 3 R Controls Propositi R Up erupted (1) Normal Third molor status TABLE 2 9 1 R 0 0 0 0 0 0 2 0 Up 0 0 0 0 0 0 1 0 0 1 0 Up L 0 4 2 1 2 2 1 0 2 2 1 1 2 1 0 5 28 12 21 19 L Lo Lo R impacted (5) Normal 2 R 3 0 1 0 1 0 0 3 3 0 Up 1 0 0 0 0 0 0 0 1 0 0 1 1 0 0 0 1 1 3 3 R Lo 1 L Up Reduced not erupted not impacted (6) 0 0 0 0 0 0 0 1 3 1 L Lo Total 15 12 48 14 24 20 30 11 250 174 subject W 0 +I 235 CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS TABLE 3 Distribution of missing third molars Missing third molars Total of examined subjects Total of examined third molars R Up L Up R Lo LLO 9% 250 1,000 29 31 29 35 12.4 74 296 18 13 21 19 24.0 52 208 7 10 13 13 20.7 48 192 18 18 21 19 39.6 ~ ~~~~ Number ~ Controls class 1 Propositi with 1 or 2 reduced ULI class 2 Propositi with 1 missing ULI class 3a F'ropositi with 2 missing ULI class 3b R ULI, right ULI; L ULI, left ULI; R Up, right upper; L Up, left upper; R Lo, right lower; L Lo, left lower. in the three classes: class 1 , 40.8% of examined teeth; class 2, 38.2% and class 3, 32.25 % . 2 . Relationship between agenesis of ULI and agenesis of the incisors, canines and premolars In table 4, we regrouped the findings for absence of all these teeth, except the ULI and molars. The differences in frequency of agenesis of these teeth between the classes of subjects appear to be even more striking than for the third molars, since agenesis varies from 0.4% for controls (class 1) to 5 % for propositi, with two teeth absent (class 3b). Nevertheless, the increase could be due to the presence of a few cases having multiple agenesis. Thus, in effect, subjects have substantial multiple agenesis, among them an individual who lacked 14 teeth, These individuals always lacked the ULI; they were all propositi. On the other hand, if we only take into consideration the iiumber of affected subjects, the differences between the groups remain highly significant ( 4 % , class 1 and 26.5%, class 3b). There is thus both a qualitative and quantitative effect. As a result of these findings, we can thus rank teeth according to the frequency of agenesis. In 250 controls, we observed 12.8% oflower third molars absent, 12.0% of upper third molars absent, 2.0% of lower second premolars absent. In 5,738 subjects sampled, we noted 1.6% with ULI missing. In the 250 controls, we found less than 1% with other teeth absent in decreasing order (lower central incisors, upper second premolars, upper canine, lower lateral incisor, upper first premolar, lower canine and lower first premolar). 11. Measurements of other teeth, head and face in propositi and controls Reduction of most of the dental measurements is in the following order: controls l a , controls l b , propositi of classes 3a, 3b, 2a and 2b (tables 5, 6). The reduction studied tooth by tooth is not always significantly different. Nevertheless, the sum of the buccolingual diameters ( S B.L. diameters) of the teeth in the upper arch is significantly smaller (p < 0.01) in the propositi. This is also true for the sum of the mesiodistal diameters (2 M.D. diameters). These results confirm that reduction affects all the teeth. The question to be raised now is the following: does this reduction affect all the measurements? Is the entire dentition smaller but in the same proportion, or are the relative values of each tooth modified? A. Mesiodistal diameters Figure 2, where the measurements are given in absolute values, immediately provides an answer to our question. It is evident that all of the teeth are not equally affected, neither in absolute values, nor still less, in proportion. We found no statistically significant difference between the measurements of the 1,376 896 784 56 49 4,000 Number of examined teeth 86 250 Number of examined subjects 3 1 0 0 3 5 0 0 R Lo 1 1 2 Lo Lo 0 L R No missing upper central incisor was observed. 2 reduced ULI class 2 Prop0 siti with 1 missing ULI class 3a Propositi with 2 missing ULI class 3b Controls class 1 Propositi with 1 or Classes 2 2 4 0 0 0 2 3 0 L Up 1 0 0 0 R Lo Missing canine 0 0 Up Lo 0 R L Missing Missing central lateral incisor incisor 0 1 0 0 Lo I, 0 1 1 1 Up R 0 ~ 1 1 1 L Up 0 0 1 0 Lo R Missing first premolar Number of missing teeth (excluding molars) TABLE 4 0 0 1 0 2 4 0 0 R Up L Lo 1 3 4 3 5 4 R Lo 1 1 L Up 4 Missing second premolar L 5 3 6 Lo 1 13 10 1 10 Number 4 % 1.4 5.0 26.5 1.3 0.4 5% Missing teeth 17.9 12.8 Affected subjects z z 0 vl M vl +9 2 M tr 3 > W 0 ri m r m zM CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS 237 11 10 I I I I 1 9 I i F F A I I I I I 7 I I I I I 6 I Lentrill Zncisor 1 I I I \: ! P> I I I I I i I Canine '\ ?-- I I I I 1 2 I I A. J I I 1 First rrenciar Fig. 2 I I Iecond PPemolar I I I I L I I irst Mrllar Second molar Mesiodistal diameters of the upper maxilla. left and right side or a trend in this differ- controls 1 a, controls 1b, propositi of classes ence. This thus allows us to restrict our 3a, 2a, 3b and 2b. Analysis of variance beattention to the teeth situated on the right tween the three classes: controls, propositi side of the maxilla. 2 and propositi 3 showed that the reduction If we classify these teeth in decreasing gradient is, in decreasing order: PI, P2, MI, order of the absolute difference in tooth M2, both in absolute values, and also prosize between the three classes of controls portionally. So,premolars are clearly more and propositi, we obtain: C, Pl, I], M2, P2, reduced (F = 27 and 22 for 2 and 389 df, MI. p < 0.001) than are molars (F = 7.5 and Nevertheless, this difference is not sig- 3.3 for 2 and 385 df, p < 0.01 and p < nificant for M1 (F = 1.26, 2 and 362 df) 0.05). Furthermore, we note that the bucand the significant differences observed colingual diameters are proportionally more between the three classes for the five others reduced than the mesiodistal ones. We also note that M1 is more reduced MD diameters may be ranked in the following decreasing order: C, P1, P2, 11, M2 (F than M2 in contrast with our findings for from 28 to 7.2, 2 and 383 to 411 df) point- the mesiodistal diameters. It appears further that in the domain ing out that the ordering of the proportional reductions of these diameters is dif- of dental measurements the propositi of ferent from the ordering of absolute dif- class 2 (i.e., those having a reduction of ferences. So there is a strong constraint the ULI) have a more extreme phenotype with respect to canines, incisors and pre- than the propositi of class 3 (i,e., those molars; the molars, on the other hand, are having an absence of the ULI). In contrast to the results involving agenesis of the less affected. other teeth, class 2 does not represent an B. Buccolingual diameters intermediary between the controls and the As for the mesiodistal diameters, we propositi that carry the phenotype for abfound a reduction in size, but in a slightly sence. In particular, we observe that the different ranking, i.e. by decreasing order: teeth most often affected by reduction are N 81.63 (6.28) 22 84.44 (6.33) 81 85.02 (6.58) 35 85.80 (6.41) 109 87.66 (5.85) 30 87.95 (5.57) 135 74.95 (4.79) 22 76.96 (4.57) 78 76.97 (4.90) 35 77.74 (5.33) 110 80.76 (4.65) 30 81.45 (4.48) 139 MD MD 65.00 (4.81) 22 67.58 (4.96) 79 67.00 (4.65) 35 68.50 (4.97) 102 71.27 (4.68) 29 72.07 (4.61) 132 MD P' 82.31 (5.13) 22 86.83 (6.28) 81 85.60 (7.13) 35 87.43 (7.11) 106 89.72 (6.79) 29 92.60 (6.07) 133 BL Each cell gives, from first to third lines, the average teeth (N). Propositi class 2b Propositi class 2a Propositi class 3b Propositi class 3a Controls Ib Controlsla X S.D. C I' 86.81 (5.32) 22 88.81 (6.20) 77 88.40 (7.28) 35 90.52 (7.23) 101 92.28 (7.75) 28 94.63 (6.10) 128 BL 103.90 (6.39) 22 104.59 (5.92) 72 105.57 (6.78) 35 104.87 (6.65) 95 106.07 (6.13) 28 105.93 (5.97) 113 MD MI 111.27 (5.40) 22 113.05 (5.91) 75 112.65 (7.23) 35 113.23 (7.42) 99 114.10 (6.43) 28 116.18 (6.32) 122 BL 95.77 (6.36) 22 96.67 (5.74) 76 97.48 (6.62) 35 98.24 (7.40) 98 100.73 (6.54) 30 100.28 (6.81) 132 MD M2 112.18 (6.86) 22 113.75 (7.44) 74 113.48 (8.86) 35 114.64 (9.17) 102 113.48 (7.14) 29 116.68 (8.44) 131 BL 969.63 (48.92) 22 991.32 (48.30) 61 994.05 (52.26) 35 1,001.12 (53.55) 75 1,035.50 (47.47) 24 1.026.49 (43.84) 100 ZMD 785.54 (40.54) 22 803.78 (44.95) 61 800.05 (50.75) 35 810.58 (52.52) 75 824.26 (51.10) 23 838.26 (42.99) 100 ZBL (within 0.1 mm), the standard deviation (S.D.) (within 0 . 1 mm), and the number of examined 63.04 (4.44) 22 65.30 (4.89) 73 65.08 (4.13) 35 66.47 (4.90) 100 68.41 (5.32) 29 68.66 (4.96) 127 MD P2 Dental measurements TABLE S CONGENITAL DEFECTS OF ULI: OTHER 239 TEETH OBSERVATIONS TABLE 6 Arch head arid fnce m e a s u r e m e n t s Upper arch He ad ~ Controls ff la S.D. N Face First width Second width Third width Length Length Width Length Width 364.34 (24.13) 135 481.76 (29.89) 105 626.07 (31.28) 130 474.16 (25.76) 130 195.71 (7.13) 100 155.72 (5.57) 100 139.99 (4.78) 100 121.32 (7.08) 100 363.41 (22.30) 29 481.07 (32.67) 28 622.10 (25.05) 30 473.26 (27.20) 30 191.67 (6.83) 31 153.74 (5.84) 31 138.58 (4.73) 31 119.67 (5.99) 31 351.37 (28.67) 110 472.30 (31.03) 104 617.23 (34.99) 110 453.54 (28.13) 108 93.82 (6.82) 75 155.05 (5.81) 75 138.72 (4.74) 75 119.72 (5.88) 75 344.14 (30.25) 35 471.14 610.54 (29.48) 449.05 (26.44) 94.48 (7.42) 35 154.62 (5.66) 35 139.22 (4.86) 35 120.57 (6.14) 35 365.35 (23.57) 81 485.93 (28.02) 72 620.89 (33.37) 79 483.12 (28.44) 81 194.37 (5.90) 61 155.21 (5.02) 61 139.72 (4.11) 61 119.19 (4.80) 61 365.86 (24.68) 22 486.38 (28.13) 21 625.04 (22.87) 22 455.77 (33.40) 22 194.22 (4.65) 22 154.54 (4.55) 22 140.50 (2.80) 22 118.50 (4.86) 22 ~ Controls lb Propositi class 3a Propositi class 3b (30.38) 35 35 35 Propositi class 2a h p o sit i class 2b Each cell gives from first to third lines, the average ( g ) (within 0.1 mm for arch measurements, within mm for head and face measurements) the standard deviation (S.D.) (same remarks) and the number of examined subjects (N) not the same as those affected by agenesis. The average measurements of each subgroup of subjects (tables 5 , 6; fig. 2) show the following results: the dental measurements of the controls of class 1b fall between those of the controls of class l a and those of the propositi except for the first and second molars, the measurements of which are slightly greater for the controls l b than for the controls la. On the other hand, propositi class 3b have clearly smaller tooth measurements than propositi class 3a. Similarly, propositi of class 2b have smaller teeth than propositi of class 2a. Moreover, their measurements are far inferior to those of the other classes, so that they have the smallest teeth in the sample. We find at the level of these subgroups the same process as in principal classes, and with the same hierarchy. Thus, clearly, the phenomenon “agenesis” is distinct from the phenomenon “reduction”. C . Measurements of arch head and face As for the dimensions of the arches, the comparison of each group of propositi with the controls gives the following results: the differences between propositi and controls, with respect to the average length of the arch, are all highly significant; the differences between controls and propositi class 3 (with ULI absent) are always significant, in decreasing order from the first to the third diameters; the differences between controls and propositi class 2 (with reduction of the ULI) are not significant with respect to the transverse diameters. Analysis of variance between the three groups confirms these results: p < 0.001 for the arch length and bipremolar diameter, p < 0.05 for the inter first molar diameter, no significant difference for the inter second molar diameter. As for the head and face measurements, the differences are far less clear; average measurements in the propositi are smaller than those of the controls particularly for facial height, and to a lesser degree for head length. Analysis of variance between the three groups did not show any significant difference. We should note, however, 240 PIERRE LE BOT AND DENISE SALMON TABLE 7 Percentage of agenesis and reduction of upper lateral incisors from the Literature Authors Rose, '06 Rose, '06 Rose, '06 HrdliEka, '21 HrdliEka, '21 Campbell, '34 Dolder, '36 Montagu, '40 Brekhus et al..'44 Rantenen, '53 Grahnen, '56 Grahnen, '56 Clayton, '56 Brown, '57 Meskin and Gorlin, '63 Davies, '67 Number of subjects examined 10,238 European males 8,618 European females 12,250 European militaries 500 White male Americans 500 White female Americans 2,000 Americans of both sexes 10,000 Swiss of both sexes 528 American males 11,487 Americans of both sexes 2,200 Finnish students 531 Scandinavian males Group A 475 Scandinavian females 547 Scandinavian males Group 475 Scandinavian females 3,557 Americans of both sexes 5,276 Americans of both sexes 5,165 American male students 3,124 American female students 1,220 Australian males 950 Australian females } } (non-aborigene) Le Bot, present study Percent of agenesis Percent of reduction 1.1 1.9 1.7 1.4 3.0 1.75 0.54 2.6 0.96 1.0 1.5 2.3 1.8 3.4 2.8 1.0 0.87 2.5 0.52 1.0 1.6 1.7 1.7 1.3 2.6 0.94 0.76 1.28 1.55 0.83 0.96 1.0 2.1 1.3 1.91 1.58 5,738 Parisian recruited males (non-selected) 14-years-old, the minimum age for proper study of third molars. Aside from the fact that their sample was composed of orthoDISCUSSION dontic patients, which could have biased Of several studies relating to congenital the results, their methods are comparable dental abnormalities, that most similar to to ours. They found, as we do, that agenesis of ours is that of Meskin and Gorlin ('63), carried out at the University of Minnesota third molars is more frequent in the manat Minneapolis. Their study included both dible than in the maxilla. They also obmale and female students but we restrict served symmetry between the left and the the comparison between their study and right side. On the other hand, these auour exclusively male sample. The differ- thors noted that the propositi with no third ences are marked in all of the categories. molar had, with respect to the other teeth, On the other hand, Rose's ('06) percent- 13 times more agenesis than did the conages (table 7) for Europeans are very close trols who had third molars. In our study to ours. the propositi with absent or reduced ULI Until this type of study is normalized, had, with respect to the other teeth (not comparisons are not valid. Nevertheless, including the third molar), 32 times more Meskin and Gorlin appear to have followed agenesis than the controls with normal the same protocol as ours and we are of ULI. the opinion that the divergence in the reMoreover, the controls observed by Garn sults are worthy of note, although not ex- ('62) had agenesis that usually involved plicable at this time. the ULI and the second premolars. SimilarIt is also very interesting to compare our ly in our study the controls most often preresults with those of a similar study car- sented agenesis of the third lower molars ried out by Garn et d. ('62) on the third and second lower premolars. But, with remolar. They compared a group of 100 sub- spect to the date of eruption of the teeth, jects that lacked at least one third molar our findings were not consistent with Garn's with a group of 398 controls that had all conclusions. He observed indeed, a delay third molars present as verified by X-rays. in the dental development of the subjects The subjects were young, but were at least having third molar agenesis, a maximum that variability is clearly smaller for the propositi affected with reduction. 24 1 CONGENITAL DEFECTS OF ULI: OTHER TEETH OBSERVATIONS TABLE 8 Other teeth modifications in propositi w i t h absent ULI and propositi with reduced ULI (3) Propositi with absent ULI (2) Propositi with reduced ULI Proportional reduction of the sum of mesiodistal diameters of propositi relative to controls’ diameters Proportional reduction of the sum of buccolingual diameters of propositi relative to controls’ diameters Percentage of agenesia of third molars 2.4% 3.3% 30 % 3% 3.4% 4.1% 24 % 1.3% delay for the posterior teeth particularly with respect to the last of the series. According to these data, we should have seen a large number of affected third molars. But such was not the case in our study where the average age of the subjects was 19; there is a striking similarity in the eruption dates of the third molars in the propositi and in the controls. Moreover, Bailit et al. (‘68) in a study on the relationship between hypodontia and the age of dental eruption also showed no relationship between the two phenomena. Our goal was to study the ULI and to compare our propositi with the controls. However, combinations of agenesis in the controls are of a general nature. In agenesis in decreasing order of fi-equency, other workers found some different results. All of them found the third molars in first place as we did. Second place is occupied by ULI for Brekhus et al. (‘44), Cohen and Anderson (‘31), Goldman (‘62), Mosmann (‘63), Poulton and Pruzanski (‘58), Rosenweig and Garbarski (‘65), and by the second lower premolars for Grahhen (‘56), Sabres and Bartholdi (‘62), Volk (‘631, Gysel (‘57), Monteil (‘68) and the present work. Our results show, as do those of Garn, that the third molars, the ULI and the second lower premolars can be absent independently of one another. On the other hand, the absence of at least one of these three teeth appears to be necessary for agenesis affecting the rest of the dentition. Thus, according to our data, agenesis of a particular tooth is not an isolated phenomenon. The dentition as a whole is affected by a process that has a tendency to reduce the number of elements and acts selectively on the most vulnerable points of the dentition. The reduction of a tooth Percentage of ageneda of 11 C PI p2 thus appears to be intermediate between presence and absence. On the other hand, comparisons of dental measurements show that for each group of propositi these measurements were reduced compared with all controls. The results do not conform to the classic notion that the most distal of each type of tooth is the least stable. In fact, P1is clearly more reduced than P2. Thus, where ULI are involved, we found a new dental profile characterized by a differential reduction in all of the dental measurements, greatest by far, with the premolars and canines. In the premolars and molars, to this reduction in size is added a modification in shape in the direction of a greater proportional reduction in the buccolingual diameters. The classes of subjects fall into the following order in diameters of the other teeth: controls class la, controls class l b , propositi class 3 (with absence of the ULI) and propositi class 2 (with reduction of the ULI). Indeed, propositi class 2 are intermediate between the controls and propositi class 3 in the frequency of agenesis of the other teeth. But dental measurements of the propositi class 2 have a phenotype more extreme than the propositi class 3. The classic hypothesis that the reduction of a tooth is an intermediate phenomenon between its presence or its absence is thus subject to question. These observations can be summarized as follows: agenesis of the ULI is associated with agenesis of other teeth and with a reduction in their measurements. On the other hand, reduction of the ULI is associated above all with a reduction in the measurements of all of the other teeth and even an absence of certain of these. Table 8 summarizes this situation by giving for each group of propositi the characteristics of agenesis of the other 242 PIERRE LE BOT AND DENISE SALMON teeth as well as the reduction on the sum of the mesiodistal and buccolingual diameters of the other teeth. It is as though missing one tooth diminishes the impact of reduction of the other teeth. We thus have a clear but localized effect in the measurements in the case of absence and a constraint less spectacular, but more general, in the case of reduction. The conoid ULI represents an extreme of reduction. A simple asymmetry between the two teeth with diastema, often minor, may represent the beginning of the phenomenon. Thus the actual frequency of reduced ULI is very much higher than our minimum figures. We took the measurements of the upper arch at the level of the teeth. The arch system permits an equilibrium between muscular forces, on the condition that dental points of contact exist. The absence or reduction of the ULI alters this equilibrium by diastema; and thus allows the facial muscles to exert pressure towards the interior to the extent that the lower arch permits it. Thus, the mechanical explanation alone suffice to justify the differences observed at the level of the dental arch. How bone and tooth dimensions are related is presented in a companion paper (Salmon and Le Bot, ’77). Where mechanical constraints do not come into play, the related arch measurements are independent of dental measurements. Other studies to be compared with our results are those of Baum and &hen (‘7la,b), Garn and Lewis (‘70), Hanihara (‘70), Keene (‘65), and Sofaer et al. (‘71). Garn and Lewis (‘70), on a sample of 658 subjects of both sexes from Southwestern, Ohio, found, as we did, that the mesiodistal diameters are reduced in the following order: controls, propositi with missing third molars, propositi with multiple agenesis. In both the studies the molars are the least affected. Garn even found that the molars were larger in his sample of multiple agenesis than in controls. We also observed that among our controls who had an agenesis of the third molar, diameters of the first and second molars increased when compared with the controls having all their third molars. Garn and Lewis (‘70) concluded that those affected by congenital agenesis show a regularly decreasing gra- dient from central incisors to molars. Any gradient in our sample from front to back is not apparent. Indeed, in our subjects, the canines and the premolars are reduced most. On both studies, the reduction in the size of the teeth is not related to the immediate vicinity of the missing teeth. The scheme remains roughly the same whether the third molar or an ULI is absent. According to Garn et al. (‘61) dental development of the propositi is delayed with posterior-anterior gradient especially affecting the third molar, second premolar and the ULI. In particular, the frequency of the sequences of P2M2 should be considerably higher among the propositi. According to Garn’s hypothesis, the third molars should be affected most since they are at the end of the series, and the last teeth in the arch. Our results completely invalidate this prediction since we found, on the contrary, a remarkable identity in the age of eruption of this tooth in both our propositi and our controls. Hanihara (’70) isolated 60 Pima Indians with normal ULI, and 23 with reduced ULI, and showed for the propositi both a reduction in the measurements of the central incisors, canines and premolars and an increase in the measurements of the molars. Once again homogeneity of these findings underscore the particularity of these molars. Baum and Cohen (‘71a) also compared dental measurements of two samples of European ancestry from northeastern U.S.A.: controls and propositi affected by agenesis of any tooth. They found as we did, a strong reduction of canines in propositi. However, contrary to our results, they observed a strong reduction in mesiodistal diameters in first molars and only a slight reduction for buccolingual diameters in other teeth. Sofaer et al. (’71) proposed an interesting hypothesis concerning interaction between developing human teeth, especially incisors. Our present results don’t permit us to verify this hypothesis. LITERATURE CITED Bailit, H . L., L. A. 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