Method error
The Intra-rater agreement between repeated tooth agenesis pattern identification was 97.5%.
Agenesis group without considering third molars
In the 303 individuals (170 females, 133 males) of the agenesis sample, in total 799 teeth, other than third molars, were congenitally missing. In 38.6% of the sample one tooth, in 33.3% two, and in 7.9% three teeth were missing (Appendix Table 1). The incidence for missing teeth in the maxilla was 57.1%, compared to 68.6% in the mandible (p = 0.079). The most common missing tooth was the mandibular second premolar (29.3%), followed by the maxillary lateral incisor (21.0%), and the maxillary second premolar (14.0%; Table 1).
Table 1. Distribution of missing teeth across quadrant and tooth number.
Tooth number
|
Upper right
|
Upper left
|
Lower right
|
Lower left
|
Total
|
Agenesis group
|
|
|
|
|
|
1
|
3
|
2
|
29
|
30
|
64
|
2
|
85
|
83
|
15
|
18
|
201
|
3
|
14
|
13
|
5
|
4
|
36
|
4
|
20
|
21
|
15
|
15
|
71
|
5
|
60
|
52
|
117
|
117
|
346
|
6
|
5
|
4
|
9
|
7
|
25
|
7
|
13
|
14
|
15
|
14
|
56
|
8
|
101
|
105
|
104
|
108
|
418
|
Total
|
301
|
294
|
309
|
313
|
1217
|
Control group
|
|
|
|
|
|
8
|
37
|
32
|
39
|
36
|
144
|
Regarding tooth symmetry, the teeth that were most often symmetrically missing in the maxilla were the lateral incisors (19.5%) followed by the second premolars (14.2%). In the mandible, the second premolars were missing bilaterally in 25.4%, followed by the central incisors in 7.9% (Table 2).
Table 2. Frequency tables that show single tooth agenesis and the prevalence of right sided, left sided or bilateral agenesis in the whole sample (n = 606).
Maxilla
|
Tooth number
|
Present bilaterally (%)
|
Missing right side (q1) (%)
|
Missing left side (q2) (%)
|
Missing unilaterally (%)
|
Missing bilaterally (%)
|
Agenesis group
|
|
|
|
|
|
1
|
300 (99.0)
|
1 (0.3)
|
0 (0.0)
|
1 (0.3)
|
2 (0.7)
|
2
|
194 (64.0)
|
26 (8.6)
|
24 (7.9)
|
50 (16.5)
|
59 (19.5)
|
3
|
286 (94.4)
|
4 (1.5)
|
3 (1.0)
|
7 (2.5)
|
10 (3.3)
|
4
|
277 (91.4)
|
5 (1.7)
|
6 (2.0)
|
11 (3.7)
|
15 (5.0)
|
5
|
234 (77.2)
|
17 (5.6)
|
9 (3.0)
|
26 (8.6)
|
43 (14.2)
|
6
|
297 (98.0)
|
2 (0.7)
|
1 (0.3)
|
3 (1.0)
|
3 (1.0)
|
7
|
287 (94.7)
|
2 (0.7)
|
3 (1.0)
|
5 (1.7)
|
11 (3.6)
|
8
|
185 (61.1)
|
13 (4.3)
|
17 (5.6)
|
30 (9.9)
|
88 (29.0)
|
Control group
|
|
|
|
|
|
8
|
260 (85.8)
|
11 (3.6)
|
6 (2.0)
|
17 (5.6)
|
26 (8.6)
|
Mandible
|
Tooth number
|
Present bilaterally (%)
|
Missing right side (q4) (%)
|
Missing left side (q3) (%)
|
Missing unilaterally (%)
|
Missing bilaterally (%)
|
Agenesis group
|
|
|
|
|
|
1
|
268 (88.4)
|
5 (1.7)
|
6 (2.0)
|
11 (3.7)
|
24 (7.9)
|
2
|
281 (92.7)
|
4 (1.3)
|
7 (2.3)
|
11 (3.6)
|
11 (3.6)
|
3
|
297 (98.0)
|
2 (0.7)
|
1 (0.3)
|
3 (1.0)
|
3 (1.0)
|
4
|
284 (93.7)
|
4 (1.3)
|
4 (1.3)
|
8 (2.6)
|
11 (3.6)
|
5
|
146 (48.2)
|
40 (13.2)
|
40 (13.2)
|
80 (26.4)
|
77 (25.4)
|
6
|
292 (96.4)
|
4 (1.3)
|
2 (0.7)
|
6 (2.0)
|
5 (1.7)
|
7
|
283 (93.4)
|
6 (2.0)
|
5 (1.7)
|
11 (3.7)
|
9 (3.0)
|
8
|
179 (59.1)
|
16 (5.3)
|
20 (6.6)
|
36 (11.9)
|
88 (29.0)
|
Control group
|
|
|
|
|
|
8
|
255 (84.2)
|
12 (4.0)
|
9 (3.0)
|
21 (7.0)
|
27 (8.9)
|
The most common agenesis patterns in the maxilla were bilaterally missing lateral incisors (23.1%), followed by bilaterally missing second premolars (12.7%). In the mandible, the most common patterns were bilateral agenesis of second premolars in 27.9%, followed by unilateral agenesis of the right second premolar (17.3%). In the whole dentition, bilateral agenesis of maxillary lateral incisors occurred most often (11.2%), followed by bilateral agenesis of mandibular second premolars (10.2%; Table 3).
Table 3. Most common tooth agenesis patterns in the agenesis group excluding third molars.
Index
|
Frequency (%)
|
Missing teeth
|
Index
|
Frequency (%)
|
Missing teeth
|
Maxilla
|
Mandible
|
1
|
40/173 (23.1)
|
12, 22
|
1
|
58/208 (27.9)
|
35, 45
|
2
|
22/173 (12.7)
|
15, 25
|
2
|
36/208 (17.3)
|
45
|
3
|
21/173 (12.1)
|
12
|
3
|
34/208 (16.3)
|
35
|
4
|
20/173 (11.6)
|
22
|
4
|
10/208 (4.8)
|
31, 41
|
5
|
11/173 (6.4)
|
15
|
5
|
5/208 (2.4)
|
34, 35, 44, 45
or
32, 42
|
Overall
|
114/173 (65.9)
|
|
Overall
|
143/208 (68.8)
|
|
Whole dentition
|
1
|
34/303 (11.2)
|
12, 22
|
2
|
31/303 (10.2)
|
35, 45
|
3
|
29/303 (9.6)
|
45
|
4
|
27/303 (9.0)
|
35
|
5
|
18/303 (6.0)
|
22
|
Overall
|
139/303 (45.9)
|
|
Third molar agenesis in the agenesis and the control group
The prevalence of third molar agenesis in the agenesis group was 50.8%, which is significantly larger than the 20.5% in the control group (p < 0.001). 418 third molars were congenitally missing in the agenesis group (n = 303) compared to 144 in the control group (n = 303). If the probability of third molar agenesis in the agenesis group was equal to that of teeth other than third molars, this would increase the value of 144 missing third molars, observed in the control group, by 114. Consequently, 258 missing third molars would have been expected in the agenesis group. This value is significantly lower than the actual value observed (418; p < 0.001). Thus, the chance of a missing third molar in the agenesis group is increased by 38.3%, compared to controls.
In the agenesis group, there was a significant, though weak correlation, of the total number of other missing teeth to the total number of missing third molars (rho = 0.31, p < 0.001). Similarly, very weak correlations were identified when third molar agenesis was correlated to the number of other tooth agenesis within quadrants (Q1: rho = 0.16, p = 0.006; Q2: rho = 0.14, p = 0.015; Q3: rho = 0.20, p = 0.001; Q4: rho = 0.29, p = 0.001).
The frequency of bilaterally missing third molars in the agenesis group was 29% in the maxilla, as well as in the mandible. This is about three times higher than the frequency of unilaterally missing third molars (maxilla: 9.9%, p < 0.001, mandible: 11.9%, p < 0.001; Table 2). The ratio of bilateral to unilateral third molar agenesis was significantly higher in the agenesis group compared to the control group (maxilla: 2.93 vs. 1.53, respectively, p < 0.001; mandible: 2.44 vs. 1.29, respectively, p < 0.001; Table 2).
In the tooth agenesis group, symmetrical third molar agenesis occurred in a similar manner within jaws (29% within each jaw), between jaws (right side: 24%, left side: 24%), or crossed quadrant (q1 vs. q3: 22.1%; q2 vs q4: 24.4%) (p > 0.05; Table 4). The same was true for the control groups (p > 0.05; Table 4), though the prevalence of all respective symmetrical patterns was much lower (range: 6.6 - 8.9%, p < 0.001).
Table 4. Symmetry of tooth agenesis patterns.
Pattern symmetry
|
Comparison
|
|
Symmetry I (%)
|
Symmetry II (%)
|
|
|
No 3rd - Agenesis
|
26.7
|
46.8
|
Maxilla
|
Right vs. left side
|
3rd - Agenesis
|
29.0
|
74.6
|
|
|
3rd - Control
|
8.6
|
60.5
|
|
|
No 3rd - Agenesis
|
30.0
|
43.8
|
Mandible
|
Right vs. left side
|
3rd - Agenesis
|
29.0
|
71.0
|
|
|
3rd - Control
|
8.9
|
56.3
|
|
|
No 3rd - Agenesis
|
6.9
|
8.8
|
Left side
|
Upper left vs. lower left
|
3rd - Agenesis
|
24.1
|
52.1
|
|
|
3rd - Control
|
6.6
|
41.7
|
|
|
No 3rd - Agenesis
|
7.9
|
9.8
|
Right side
|
Upper right vs. lower right
|
3rd - Agenesis
|
24.4
|
56.5
|
|
|
3rd - Control
|
8.6
|
52.0
|
|
|
No 3rd - Agenesis
|
6.9
|
8.71
|
Crossed q1 vs q3
|
Upper right vs. lower left
|
3rd - Agenesis
|
22.1
|
47.2
|
|
|
3rd - Control
|
6.6
|
37.7
|
|
|
No 3rd - Agenesis
|
7.6
|
9.5
|
Crossed q2 vs q4
|
Upper left vs. lower right
|
3rd - Agenesis
|
24.4
|
54.8
|
|
|
3rd - Control
|
6.6
|
39.2
|
Symmetry I: percentage relative to the whole sample (n = 303) without considering the patterns of no missing teeth as symmetrical. Symmetry II: percentage relative to subsample of subjects with missing teeth in the respective area (i.e. maxilla, mandible etc.).
In both groups, there was no statistically significant difference between the number of missing third molars in the different quadrants (Chi square test, p > 0.05; Table 1). The agenesis group differed significantly from the control group in the distribution of the number of missing third molars (p < 0.001). There is a clear tendency towards more missing third molars in the agenesis group compared to the controls. The agenesis group has 1.55, 2.14, 3.80, and 3.48 times higher possibility of having one, two, three, or four missing third molars respectively, when compared to the control group (Figure 1).
Appendix Table 2 shows the most common patterns of tooth agenesis in the agenesis group, including third molars. In the maxilla, the lateral incisors were most commonly missing in 14.1%, followed by bilaterally missing third molars in 13.6% of the sample. In the mandible, the second premolars were most commonly missing bilaterally in 12.8% of the sample, followed by unilateral second premolar agenesis.
Appendix Table 3 shows the most common patterns of third molar agenesis in control subjects where agenesis was observed. In the maxilla, as well as in the mandible, bilateral third molar agenesis was the most common pattern (60.5% and 56.3%, respectively). In the entire dentition, the most common pattern was the four missing third molars (17.4%), followed by bilateral third molar agenesis in the mandible, in 14.5%. Appendix Table 4 shows the most common patterns of third molar agenesis in the agenesis group, where third molar agenesis was observed. In this group also, bilateral third molar agenesis was the most common pattern within jaws (74.6% and 71.0%, in the maxilla and the mandible, respectively). Furthermore, in the entire dentition, the most common pattern was also in this group the four missing third molars (38.3%), followed by bilateral third molar agenesis in the mandible (12.3%).