Journal of Dentistry, 4, 42-44
Congenitally missing third molars in a British population D. L. Shinn, Orthodontic
BDS, FDS, Darth RCS
Department,
Liverpool Dental Hospital, Liverpool
ABSTRACT
The radiographic records of 2500 orthodontic patients in the south of England were examined for congenitally missing third molar teeth. The incidence of congenitally missing third molars was found to be 12.72 per cent.
INTRODUCTION THERE has
been a recent tendency to extract second molar teeth in cases of mild crowding to allow well-positioned third molars to erupt into position with minimal active orthodontic treatment (Wilson, 1966; Cryer, 1967; McBride and Huggins, 1970). When the extraction of first permanent molars is considered to be advisable it is normally carried out at an early age (Wilkinson, 1942). Since both these lines of treatment are dependent upon the presence of third molar teeth, it seemed worth while to investigate the incidence of their agenesis. A survey of the literature has revealed studies by Goblirsch (1930), Banks (1934), Hellman (1936), Brekhus et al. (1944), Nanda (1954), Nanda and Chawla (1959), Garn et al. (1963), Keene (1964) and Thompson et al. (1974). A wide range of values for third molar agenesis was found (Table 1). There have been only two previous British studies. Gravely (1965) obtained his results by extrapolation of a graph, and Lavelle et al. (1970) reported mandibular third molar agenesis alone.
Hants Hospital, Southampton; 1103 (44.12 per cent) were male, and 1397 (55.88 per cent) were female. The data were collected from the patients’ radiographic records, the views most frequently used being lateral oblique (bimolar) and Panorex. To a lesser extent lateral skull, postero-anterior skull and intra-oral periapical films were also used. The commencement of calcification of third molars is quite variable. Scott and Symons (1971) stated that calcification of the upper third molars commences at 7-9 years, and lower third molars at 8-10 years of age. However, it is relatively common for their development not to be evident on radiographic examination until several years after this. To take cases of late development into account, a tooth was not considered to be congenitally absent unless there was no sign of its development at 14 years of age or over. Where a tooth was found to be absent the patient’s records were carefully examined to exclude the possibility of previous extraction of either the third molar or one of the other molar teeth, as early extraction of a first molar followed by forward drifting of the second and third molars could give the appearance of third molar agenesis. If there was any reasonable doubt that a tooth was not congenitally missing the case was excluded from the survey, and because of this the figures that are given are a conservative estimate.
METHODS
RESULTS
The subjects of the present survey consisted of 2500 patients who had been referred to the Orthodontic Department at the Royal South
The results showed that 129 males (11.69 per cent) and 189 females (13.53 per cent) had missing third molars (Table Z). Thus, altogether
Shinn
: Congenitally
Table /.-Incidence
Missing Third Molars
of congenitally missing third molars reported in the literature
Author
Incidence
Material
Goblirsch (1930) Banks (1934) Hellman (1936)
Brekhus et al. (1944) Nanda (1954) Nanda and Chawla (1959) Garn et al. (1963) Keene (1964) Gravely (1965) Lavelle et al. (1970)
Thompson et al. (1974) Shinn (1975)
Table //.-Distribution
43
(%I
2112 American whites 461 American whites Unspecified number of Tasmanian skulls Unspecified number of Hungarian skulls 433 Columbia University students Male Female 11487 Patients 200 Female Boston hygienists 650 Male Indian patients 650 Female Indian patients 476 Orthodontic patients 195 US naval recruits 550 Children (aged 6-l 5 years) 400 Cases (mandible only) Male Female 521 Burlington Growth Centre patients 2500 Orthodontic patients Male Female
9.0 19.7 0.0 49.0 21.67 30.81 0.609 9.0 10.9 14.5 16.4 27.0 14-15 13.7 16.9 22.3 11.69 13.53
of congenitally missing third molars between the sexes
No. of missing third molars
No.
1 2 3 4
43 45 14 27
33.34 34.88 IO.85 20.93
65 64 21 39
34.39 33.86 11.11 20.64
108 109 35 66
33.96 34.28 11.01 20.75
129
100~00
189
100.00
318
100.00
Total
Males %
Females No. %
318 patients or 12.72 per cent had missing third molars. On statistical examination using the x2 test the difference between the sexes was found to be not significant (P>O.O5). Some patients had more than one third molar missing. The total number of individual missing third molar teeth was 695, consisting of 283 (40.71 per cent) teeth from males, and 412 (59.29 per cent) teeth from females. The distribution of multiple agenesis of third molar teeth was analysed and showed a remarkable similarity between males and females (Table ZZ). In both sexes those missing 1 tooth and those missing 2 teeth were each responsible for just over one-third of the entire group, the balance being made up of those
Total No.
%
missing 3 teeth (11 per cent) and 4 teeth (21 per cent). The distribution of the missing third molars between the four quadrants of the mouth was analysed (Table III). The only difference shown to be statistically significant was in males, who showed maxillary third molar agenesis more frequently in the right than in the left side (P
Congenitally missing third molars in a British population D. L. Shinn, Orthodontic
BDS, FDS, Darth RCS
Department,
Liverpool Dental Hospital, Liverpool
ABSTRACT
The radiographic records of 2500 orthodontic patients in the south of England were examined for congenitally missing third molar teeth. The incidence of congenitally missing third molars was found to be 12.72 per cent.
INTRODUCTION THERE has
been a recent tendency to extract second molar teeth in cases of mild crowding to allow well-positioned third molars to erupt into position with minimal active orthodontic treatment (Wilson, 1966; Cryer, 1967; McBride and Huggins, 1970). When the extraction of first permanent molars is considered to be advisable it is normally carried out at an early age (Wilkinson, 1942). Since both these lines of treatment are dependent upon the presence of third molar teeth, it seemed worth while to investigate the incidence of their agenesis. A survey of the literature has revealed studies by Goblirsch (1930), Banks (1934), Hellman (1936), Brekhus et al. (1944), Nanda (1954), Nanda and Chawla (1959), Garn et al. (1963), Keene (1964) and Thompson et al. (1974). A wide range of values for third molar agenesis was found (Table 1). There have been only two previous British studies. Gravely (1965) obtained his results by extrapolation of a graph, and Lavelle et al. (1970) reported mandibular third molar agenesis alone.
Hants Hospital, Southampton; 1103 (44.12 per cent) were male, and 1397 (55.88 per cent) were female. The data were collected from the patients’ radiographic records, the views most frequently used being lateral oblique (bimolar) and Panorex. To a lesser extent lateral skull, postero-anterior skull and intra-oral periapical films were also used. The commencement of calcification of third molars is quite variable. Scott and Symons (1971) stated that calcification of the upper third molars commences at 7-9 years, and lower third molars at 8-10 years of age. However, it is relatively common for their development not to be evident on radiographic examination until several years after this. To take cases of late development into account, a tooth was not considered to be congenitally absent unless there was no sign of its development at 14 years of age or over. Where a tooth was found to be absent the patient’s records were carefully examined to exclude the possibility of previous extraction of either the third molar or one of the other molar teeth, as early extraction of a first molar followed by forward drifting of the second and third molars could give the appearance of third molar agenesis. If there was any reasonable doubt that a tooth was not congenitally missing the case was excluded from the survey, and because of this the figures that are given are a conservative estimate.
METHODS
RESULTS
The subjects of the present survey consisted of 2500 patients who had been referred to the Orthodontic Department at the Royal South
The results showed that 129 males (11.69 per cent) and 189 females (13.53 per cent) had missing third molars (Table Z). Thus, altogether
Shinn
: Congenitally
Table /.-Incidence
Missing Third Molars
of congenitally missing third molars reported in the literature
Author
Incidence
Material
Goblirsch (1930) Banks (1934) Hellman (1936)
Brekhus et al. (1944) Nanda (1954) Nanda and Chawla (1959) Garn et al. (1963) Keene (1964) Gravely (1965) Lavelle et al. (1970)
Thompson et al. (1974) Shinn (1975)
Table //.-Distribution
43
(%I
2112 American whites 461 American whites Unspecified number of Tasmanian skulls Unspecified number of Hungarian skulls 433 Columbia University students Male Female 11487 Patients 200 Female Boston hygienists 650 Male Indian patients 650 Female Indian patients 476 Orthodontic patients 195 US naval recruits 550 Children (aged 6-l 5 years) 400 Cases (mandible only) Male Female 521 Burlington Growth Centre patients 2500 Orthodontic patients Male Female
9.0 19.7 0.0 49.0 21.67 30.81 0.609 9.0 10.9 14.5 16.4 27.0 14-15 13.7 16.9 22.3 11.69 13.53
of congenitally missing third molars between the sexes
No. of missing third molars
No.
1 2 3 4
43 45 14 27
33.34 34.88 IO.85 20.93
65 64 21 39
34.39 33.86 11.11 20.64
108 109 35 66
33.96 34.28 11.01 20.75
129
100~00
189
100.00
318
100.00
Total
Males %
Females No. %
318 patients or 12.72 per cent had missing third molars. On statistical examination using the x2 test the difference between the sexes was found to be not significant (P>O.O5). Some patients had more than one third molar missing. The total number of individual missing third molar teeth was 695, consisting of 283 (40.71 per cent) teeth from males, and 412 (59.29 per cent) teeth from females. The distribution of multiple agenesis of third molar teeth was analysed and showed a remarkable similarity between males and females (Table ZZ). In both sexes those missing 1 tooth and those missing 2 teeth were each responsible for just over one-third of the entire group, the balance being made up of those
Total No.
%
missing 3 teeth (11 per cent) and 4 teeth (21 per cent). The distribution of the missing third molars between the four quadrants of the mouth was analysed (Table III). The only difference shown to be statistically significant was in males, who showed maxillary third molar agenesis more frequently in the right than in the left side (P
