Orientation and eruptive patterns of the mandibular second premolar Nick D. Spyropoulos, FACULTY
OF DENTISTRY,
DDS, DrOdont,a Athens, Greece UNIVERSITY
OF ATHENS
Distal migration of the mandibular second premolar into a first molar extraction site is a clinical finding often correlated with the early loss of a permanent mandibular first molar. Signs of this tendency can be detected radiographically as early as 6 to 7 years of age when the mineralization of the crown of the mandibular second premolar is almost complete. The results of a study of 2000 panoramic dental radiographs of children, aged 8 to 18 years, are reported. (ORAL SURC ORAL MED ORAL PATHOL 1990;69:642-6)
A
space between mandibular premolars with the secondpremolar located next to the secondpermanent molar is often observed clinically (Fig. 1). The cause of such a wide interpremolar space may at first seem obscure, but careful evaluation of the patient’s history usually reveals loss of the ipsilateral mandibular permanent first molar tooth, at an early age. Several case reports with respect to this dental malalignment have appeared in the literature.‘-‘3 Apparently, developing mandibular second premolar teeth often exhibit a distal angulation in the bud stage and becomeupright as they contact the mesial surface of the permanent first molar during eruption (Fig. 2). Early loss of the permanent first molar will, therefore, predispose to interpremolar spacing in the mandible 638.11 The prevalence of distal positioning of the mandibular secondpremolar tooth after extraction of the first molar has been studied by Matteson and coworkers. 13 However, neither distal angulation of the second premolar bud nor the age of the patients at the time of first molar extraction was determined in that study. Thus, the relationship between mandibular second premolar bud angulation and distal migration after first molar loss could not be studied in relation to the age of the patient, since the sample used consisted only of a random adult population. Inasmuch as the prevalence of mandibular first permanent molar loss in Greek populations is relatively high in comparison to similar American
=As.sistant Professor of Oral Diagnosis. 7/16/18243 642
populations, l 4 it was decided to investigate the hypothesis that the distal migration of secondpremolars in Greek children and age at time of first permanent molar extraction are associated. This report presents the results of this study. MATERIAL
AND METHODS
Two thousand panoramic radiographs from Greek children were examined. Subject age ranged from 8 to 18 years. The sample included 620 boys and 1380 girls. The greater number of girls was due to the fact that this was a sample attending an orthodontic office during the last 8 years. All of the radiographs selected for the study had been made under the same conditions, and were evaluated on the basis of the following variables: the presenceof unerupted mandibular secondpremolars, the absenceof the permanent mandibular first molar, and, in cases of permanent mandibular first molar absence, determination of the age at loss, where adequately documented. For all unerupted mandibular second premolars, the angulation and direction of eruption were evaluated on the basis of the inclination of the long axis of the tooth in relation to the apparent true vertical position. This true vertical position was determined on the panoramic film by drawing a perpendicular to the line tangent to the lower border of the mandible at the mesial root of the adjacent molar tooth (Fig. 3). The position and angulation of all the erupted mandibular second premolars were recorded. Whenever a permanent mandibular first molar tooth was missing, the position and inclination of the mandibular second premolar was evaluated in relation to the mesial root
Mandibular
Volume69 Number5
Fig.
second premolar
orientation
643
2. Panoramicradiograph showingbilateral distal angulation of mandibular secondpremolarbuds.
Fig.
3.
Panorakc radiograph showingdistal angulation of mandibular secondpremolar buds.
of the respective mandibular second molar. Evaluation of the buccolingual tipping of these teeth was not possible on the panoramic film. To test the validity of the method, a random sample of 30 radiographs was examined by the author twice with a l-month interval between the two examinations. The two observations were consistent at a 93% level. In all caseswhere there was loss of the permanent mandibular first molar, the age at loss was ascertained
from the patient’s records or history. All observations were recorded on special forms from which statistical analysis of the data was performed. RESULTS
There were 3898 mandibular second premolar teeth present on the 2000 radiographs, 1476 (38%) unerupted. Of these, 98 (7%) showed distal angulation, whereas only three (0.2%) showed a mesial angulation (Table I). Fifty-nine of the unerupted second
644
SpJ'ropodOs
ORAL SURG ORAL
MED ORAL PATHOL May 1990
Fig. 4. Relationship between age of mandibular permanent first molar and prevalence of distally tipped mandibular second premolars.
Table
1.Angulation of unerupted second premolar
teeth Total
Permanent first molars missing
1476 (38%)
(2)
Distal angulation
Mesial angulation
(O.i%)
premolars (4%) were associated with a missing permanent mandibular first molar tooth (Table I). Of the 2422 erupted second premolars (62%), 160 (7%) were associated with missing, and presumably extracted, permanent first mandibular molars. Of these 160 cases, 72 (45%) were in females and 88 (55%) were in males. Of these 160 second premolars, 18 (11%) showed distal migration. Their distribution was 10 in females (56%) and 8 in males (44%) (Table 11). In the total sample, there were 2 19 missing permaL~~~ii~ilandi’ouiar first molars. Forty-nine (22%) of the associated second premolars had a distal angulation,
migration, or drift. For the 38 instances in which time of extraction of the permanent mandibular first molar was adequately documented, a histogram was developed to graphically illustrate the correlation between age at molar loss and the prevalence of distally oriented or drifted second premolars (Fig. 4). This histogram demonstrates that the modal age at the time of first permanent molar loss was 9 through 11 years. Comparison of proportions (Colton 197415) revealed a significant difference in the incidence of distal drifting of second premolars associated with missing permanent mandibular first molars in the erupted and unerupted second premolar groups (Table III). The number of erupted teeth demonstrating distal migration was less than predicted by the null hypothesis. DISCUSSION
It is known that migration of unerupted and drifting of erupted teeth can be influenced by several factors including the molar occlusal relationship, early
Mandibular
Volume 69 Number 5
Fig.
second premolar
orientation
645
5. Details from two panoramicradiographsshowinghorizontally placedimpactedsecondpremolars.
loss of a deciduous predecessor,early loss of adjacent permanent teeth, the space available in the arch, and the stage of development of the specific tooth at the time of loss of adjacent teeth. For the mandibular secondpremolar, one of the factors permitting distal migration is the early loss of the permanent mandibular first molar (Matteson and coworkers 1982).13 This is possibly due to a tendency for distal angulation of the secondpremolar during development and its apparent need to lean against the permanent mandibular first molar to make itself upright during eruption. Matteson and coworkers13 found a 5% to 10% risk of distal premolar migration when permanent mandibular first molars were extracted at an early age. The current statistical analysis for comparison of proportions revealed that in the erupted premolar group, distally oriented second premolars are found less often than expected compared to the unerupted group. This is probably due to distally oriented second premolar buds eventually becoming upright if the permanent first molar is present in the arch until full eruption of the premolar. Hence, in caseswhere the permanent mandibular first molars are badly decayed they should still be retained, if possible, until the second premolars attain a vertical eruption pattern. However, if the distal inclination of the unerupted premolar is exaggerated, with a low position of the bud, or if the first molar is lost early enough, the result may be an impaction of the premolar adjacent to the second or even to the third permanent molar (Fig. 5). As previously mentioned, distal migration and drifting of the mandibular second premolar may be caused or permitted to occur by many other factors that it was not possible to evaluate in this investigation. The current study supports a recommendation for evaluation of the orientation of the mandibular sec-
Table
II. Erupted second premolar teeth
-_r
2422 (62%)
160 (7%)
F (4%)
M
18 (11%)
(2) F $.:I,,
M (44p4%)
Table Ill. Comparison of proportions of orientation of second premolars associated with missing molars Erupted Orientation
No.
Distal orientation Vertical orientation Total Proportion
18 142 160
%c (critical
Unerupted 970
(11) (89) 11.25
No.
%
31 28 59
(53) (47) 52.5
ratio) = 6.658. p
OF DENTISTRY,
DDS, DrOdont,a Athens, Greece UNIVERSITY
OF ATHENS
Distal migration of the mandibular second premolar into a first molar extraction site is a clinical finding often correlated with the early loss of a permanent mandibular first molar. Signs of this tendency can be detected radiographically as early as 6 to 7 years of age when the mineralization of the crown of the mandibular second premolar is almost complete. The results of a study of 2000 panoramic dental radiographs of children, aged 8 to 18 years, are reported. (ORAL SURC ORAL MED ORAL PATHOL 1990;69:642-6)
A
space between mandibular premolars with the secondpremolar located next to the secondpermanent molar is often observed clinically (Fig. 1). The cause of such a wide interpremolar space may at first seem obscure, but careful evaluation of the patient’s history usually reveals loss of the ipsilateral mandibular permanent first molar tooth, at an early age. Several case reports with respect to this dental malalignment have appeared in the literature.‘-‘3 Apparently, developing mandibular second premolar teeth often exhibit a distal angulation in the bud stage and becomeupright as they contact the mesial surface of the permanent first molar during eruption (Fig. 2). Early loss of the permanent first molar will, therefore, predispose to interpremolar spacing in the mandible 638.11 The prevalence of distal positioning of the mandibular secondpremolar tooth after extraction of the first molar has been studied by Matteson and coworkers. 13 However, neither distal angulation of the second premolar bud nor the age of the patients at the time of first molar extraction was determined in that study. Thus, the relationship between mandibular second premolar bud angulation and distal migration after first molar loss could not be studied in relation to the age of the patient, since the sample used consisted only of a random adult population. Inasmuch as the prevalence of mandibular first permanent molar loss in Greek populations is relatively high in comparison to similar American
=As.sistant Professor of Oral Diagnosis. 7/16/18243 642
populations, l 4 it was decided to investigate the hypothesis that the distal migration of secondpremolars in Greek children and age at time of first permanent molar extraction are associated. This report presents the results of this study. MATERIAL
AND METHODS
Two thousand panoramic radiographs from Greek children were examined. Subject age ranged from 8 to 18 years. The sample included 620 boys and 1380 girls. The greater number of girls was due to the fact that this was a sample attending an orthodontic office during the last 8 years. All of the radiographs selected for the study had been made under the same conditions, and were evaluated on the basis of the following variables: the presenceof unerupted mandibular secondpremolars, the absenceof the permanent mandibular first molar, and, in cases of permanent mandibular first molar absence, determination of the age at loss, where adequately documented. For all unerupted mandibular second premolars, the angulation and direction of eruption were evaluated on the basis of the inclination of the long axis of the tooth in relation to the apparent true vertical position. This true vertical position was determined on the panoramic film by drawing a perpendicular to the line tangent to the lower border of the mandible at the mesial root of the adjacent molar tooth (Fig. 3). The position and angulation of all the erupted mandibular second premolars were recorded. Whenever a permanent mandibular first molar tooth was missing, the position and inclination of the mandibular second premolar was evaluated in relation to the mesial root
Mandibular
Volume69 Number5
Fig.
second premolar
orientation
643
2. Panoramicradiograph showingbilateral distal angulation of mandibular secondpremolarbuds.
Fig.
3.
Panorakc radiograph showingdistal angulation of mandibular secondpremolar buds.
of the respective mandibular second molar. Evaluation of the buccolingual tipping of these teeth was not possible on the panoramic film. To test the validity of the method, a random sample of 30 radiographs was examined by the author twice with a l-month interval between the two examinations. The two observations were consistent at a 93% level. In all caseswhere there was loss of the permanent mandibular first molar, the age at loss was ascertained
from the patient’s records or history. All observations were recorded on special forms from which statistical analysis of the data was performed. RESULTS
There were 3898 mandibular second premolar teeth present on the 2000 radiographs, 1476 (38%) unerupted. Of these, 98 (7%) showed distal angulation, whereas only three (0.2%) showed a mesial angulation (Table I). Fifty-nine of the unerupted second
644
SpJ'ropodOs
ORAL SURG ORAL
MED ORAL PATHOL May 1990
Fig. 4. Relationship between age of mandibular permanent first molar and prevalence of distally tipped mandibular second premolars.
Table
1.Angulation of unerupted second premolar
teeth Total
Permanent first molars missing
1476 (38%)
(2)
Distal angulation
Mesial angulation
(O.i%)
premolars (4%) were associated with a missing permanent mandibular first molar tooth (Table I). Of the 2422 erupted second premolars (62%), 160 (7%) were associated with missing, and presumably extracted, permanent first mandibular molars. Of these 160 cases, 72 (45%) were in females and 88 (55%) were in males. Of these 160 second premolars, 18 (11%) showed distal migration. Their distribution was 10 in females (56%) and 8 in males (44%) (Table 11). In the total sample, there were 2 19 missing permaL~~~ii~ilandi’ouiar first molars. Forty-nine (22%) of the associated second premolars had a distal angulation,
migration, or drift. For the 38 instances in which time of extraction of the permanent mandibular first molar was adequately documented, a histogram was developed to graphically illustrate the correlation between age at molar loss and the prevalence of distally oriented or drifted second premolars (Fig. 4). This histogram demonstrates that the modal age at the time of first permanent molar loss was 9 through 11 years. Comparison of proportions (Colton 197415) revealed a significant difference in the incidence of distal drifting of second premolars associated with missing permanent mandibular first molars in the erupted and unerupted second premolar groups (Table III). The number of erupted teeth demonstrating distal migration was less than predicted by the null hypothesis. DISCUSSION
It is known that migration of unerupted and drifting of erupted teeth can be influenced by several factors including the molar occlusal relationship, early
Mandibular
Volume 69 Number 5
Fig.
second premolar
orientation
645
5. Details from two panoramicradiographsshowinghorizontally placedimpactedsecondpremolars.
loss of a deciduous predecessor,early loss of adjacent permanent teeth, the space available in the arch, and the stage of development of the specific tooth at the time of loss of adjacent teeth. For the mandibular secondpremolar, one of the factors permitting distal migration is the early loss of the permanent mandibular first molar (Matteson and coworkers 1982).13 This is possibly due to a tendency for distal angulation of the secondpremolar during development and its apparent need to lean against the permanent mandibular first molar to make itself upright during eruption. Matteson and coworkers13 found a 5% to 10% risk of distal premolar migration when permanent mandibular first molars were extracted at an early age. The current statistical analysis for comparison of proportions revealed that in the erupted premolar group, distally oriented second premolars are found less often than expected compared to the unerupted group. This is probably due to distally oriented second premolar buds eventually becoming upright if the permanent first molar is present in the arch until full eruption of the premolar. Hence, in caseswhere the permanent mandibular first molars are badly decayed they should still be retained, if possible, until the second premolars attain a vertical eruption pattern. However, if the distal inclination of the unerupted premolar is exaggerated, with a low position of the bud, or if the first molar is lost early enough, the result may be an impaction of the premolar adjacent to the second or even to the third permanent molar (Fig. 5). As previously mentioned, distal migration and drifting of the mandibular second premolar may be caused or permitted to occur by many other factors that it was not possible to evaluate in this investigation. The current study supports a recommendation for evaluation of the orientation of the mandibular sec-
Table
II. Erupted second premolar teeth
-_r
2422 (62%)
160 (7%)
F (4%)
M
18 (11%)
(2) F $.:I,,
M (44p4%)
Table Ill. Comparison of proportions of orientation of second premolars associated with missing molars Erupted Orientation
No.
Distal orientation Vertical orientation Total Proportion
18 142 160
%c (critical
Unerupted 970
(11) (89) 11.25
No.
%
31 28 59
(53) (47) 52.5
ratio) = 6.658. p
