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Resorption of maxillary lateral incisors caused by ectopic eruption of the canines
Resorption of maxillary lateral incisors caused by ectopic eruption of the canines A clinical and radiographic analysis of predisposing factors Sune Ericson, DDS, Odont. Dr.,* and Jiiri Kurol, DDS, Odont. Dr.** JSnkiiping,
Sweden
Factors predisposing to resorption of adjacent permanent lateral incisors caused by ectopic eruption of maxillary canines were evaluated. The subjects consisted of two groups: one with 40 lateral incisors with resorption caused by ectopic eruption and a control group of 118 ectopic eruption cases with no lateral incisor resorption. The mean age of the children in the two groups differed by only 0.7 of a year and ranged from 10.0 to 15.0 years, covering the normal eruption period of the maxillary canine. Resorption of lateral incisors was three times as common in girls as in boys. The resorption cases showed a more advanced dental development, a more medial canine position,in the dental arch, and a slightly more mesial horizontal path of eruption (an average of 100) than that of the control cases. Factors such as the width of the dental follicle and proclination or distal tilting of the lateral incisor showed no correlation to the resorption. Potential resorption cases are always those in which the canine cusp in periapical and panoramic films is positioned medially to the midline of the lateral incisor. Such situations should be carefully investigated with polytomography if necessary. The risk of resorption also will increase with a more mesial horizontal path of eruption. From 10 years of age or younger, annual clinical examination by palpation of the canine eruption path is recommended. This clinical examination should be supplemented with a stepwise extended radiographic procedure in cases in which ectopic eruption of the maxillary canines is suspected. (AM J ORTHOD
DENTOFAC
ORTHOP
1988:94:503-l
3.)
T
he permanent maxillary canine is frequently misplaced in relation to other teeth in the maxilla. The prevalence of noneruption and ectopic eruption of this tooth has been reported to be 0.9% to 2.0% in samples not previously selected for orthodontic treatment.‘,’ The canine is most frequently found palatal to the lateral incisor and buccally in only about 15% of cases,2-4 Ectopic eruption of maxillary canines may lead to impaction and/or resorption of neighboring permanent teeth.‘*‘,” However, in most studies of the eruption of the maxillary canines, the latter complication is sparsely reported. This might give the impression that resorption caused by the eruption of the maxillary canine is rare and of minor clinical importance, however unfortunate in the individual case. The lesions often are difficult to diagnose with ordinary radiographic techniques because most of the resorptions are located palatally or buccally in the middle third of the root of the adjacent lateral incisor. Often they are concealed by overlapping of the canine in the periapical radiographs.” In a recent epidemiologic study of maxillary canine From the Departments of Maxilla-Facial Radiology* Institute for Postgraduate Dental Education.
and Orthodontics.**
The
eruption in which uninterpretable areas caused by overlapping on the intraoral radiographs were examined by polytomography, it was found that resorption of lateral incisors occurred in 12% of cases after ectopic eruption of maxillary canines, suggesting a total prevalence of 0.7% for resorbed lateral incisors in the lo- to 13-year age group.’ During eruption of the maxillary canines, these teeth are in very close contact with the lateral incisors due to the anatomy in this region,’ and it has been shown in radiographs that the lamina dura often is missing.‘,6 Furthermore it is believed that in situations of resorption, there must be close contact between the canine and lateral incisor, rather than mediation of the resorption by swelling of the dental follicle.‘.’ The importance of the dental follicle in the tooth eruption process has been shown in animal experiments.” However, it is not clear what the predisposing causative factors in this incisor resorption process are and in what positions and situations an ectopically erupting or misplaced canine is liable to resorb the adjacent teeth. This investigation was undertaken in an attempt to elucidate the role of various causative factors in the resorption of lateral incisors caused by ectopic eruption of maxillary canines. A further aim was to evaluate the 503
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Fig. 1. Records of female subject, aged 10 years 10 months. Lateral (A and B) and occlusal (C and D) views of the dentition and dental arches show crowding and lack of space. Extraction of first premolars was indicated and the patient was referred for orthodontic treatment. Note the buccal position of the maxillary canines. E, Axial-vertex intraoral radiograph at 11 years 3 months of age shows the position of the maxillary canines relative to the dental arch. In the Orthopantomograph F, the medial position of the canine crowns and degree of mesial path of eruption are seen. In the periapical dental films (G and H), an overlapping of the canine over the lateral incisor is seen together with an unbroken mesiodistal root contour. The lamina dura is missing. Because of this and the close relation between the canine and lateral incisor as seen in E, further radiographic investigation is indicated. (Which one of the lateral incisors is resorbed?)
strength of various possible predisposing factors singularly associated with the resorption of lateral incisors by comparing resorption cases with nonresorption cases after ectopic eruption of the maxillary canine.
eruption. The two groups were investigated in an identical manner, both clinically and radiographically. In no case had the canine erupted into the oral cavity. The primary canine was missing in 30% of the subjects.
SUBJECTS
Resorption
The material for this study was derived from two groups: a group with resorption of the maxillary permanent lateral incisor associated with ectopic eruption of the maxillary canine and a control group in whom the incisor was not resorbed because of the ectopic
This group comprised 40 consecutively collected cases with resorbed lateral incisors with varying degrees of resorption. No evidence of traumatic injuries to the incisors was found. A detailed presentation of the location and extent of resorption on the lateral incisors
group
Resorption
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polytomograms (I and J) show that the girl’s right lateral incisor is buccally in close relation to the canine crown and a resorption cavity ~&WOWS) is seen extending into the pulp. On the left side, there is close contact between the lateral incisor root and canine crown but without resorption. The girl showed a lack of interest and was reluctant to wear a visible fixed orthodontic appliance. In K, the extracted lateral incisor on the right side shows a buccal resorption in the middle third of the root and the radiograph L shows the full extent of buccal root resorpQon. Note the conformity of information between the polytomogram (I) and the radiograph (L). For reasons of symmetry, both lateral incisors were extracted, and in M and N the clinical and radiographic frontal views of both the resorbed and normal lateral incisors are seen. The intraoral photograph (0) of the maxillary dental arch shows the result 8 months after extraction at 12 years 0 months of age.
Fig. 1 (Cont’d). The sagittal
has been given previously.’ In 34 of the 40 lateral incisors (85%), the erupting canine was found in an ectopic position lingually, distolingually, or buccally to the resorbed incisor root. In six cases the canine position was distal to the lateral incisor root. In 45% of the lateral incisors, the resorption extended into the pulp. Control group The material for the control group was collected from material presented earlie?.6.‘o in a series of studies on normal and ectopic canine eruption. This group consisted of 118 cases of nonerupted maxillary canines with an ectopic path of eruption, but without causing resorption of the lateral incisor roots. From the radiographs it could be seen that the two materials were very similar and comparable with regard to the position of the canine crown relative to the adjacent teeth in the dental arch. In 83% of cases, the canine crowns showed lingual, distolingual, or buccal positions relative to the incisor root. Buccal positions were noted for 15% of the canines (as compared with 18% in the resorption group). Age The age of the subjects ranged from 10.1 to 14.9 years in the resorption group and from 10.0 to 15 .O
years in the control group. The mean age in the resorption group was 12.1 + 1.2 years; in the control group, the mean age was 11.3 t 1.O years. This minor difference in age (mean 0.7 years) between the two groups was not statistically significant. METHODS Radiographic
examination
The radiographic examination was performed according to defined criteria and an earlier described stepwise procedure.‘.‘” In addition to conventional intraoral periapical films in different projections., an intraoral occlusal film was exposed in an axial-vertex projection, with the x-ray beam parallel to the long axis of the incisors. An orthopantogram and lateral head film also were obtained. In those cases in which the canines could not be projected free from the lateral incisors and the overlapping made it impossible to rule out resorption, the lateral incisors were polytomographed (for a detailed description, see Ericson and Kurol’.‘). A. complete radiographic examination is illustrated in Fig. 1. The panoramic image was obtained with a Siemens Orthopantomograph (OP-3)” modified with a collimator system and rotating anode. The patient was carefully *Siemens Corporation,
Icrlin,
N I.
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Table I. Analyzed factors and their statistical correlation to resorption of maxillary lateral incisors caused by ectopic eruption of the canine in a group of 40 resorbed incisors (I) and a group of 118 nonresorption cases (II) after ectopic eruption I-II Variables Sex
Degree of canine maturation Canine position relative to the midline of the dental arch (transverse plane) Canine position relative to the lateral incisor root (transverse plane) Medial position of the canine cusp: -Panoramic image (frontal plane) -Axial projection (transverse plane) Angle of canine mesial eruption to midline, (Y (panoramic image) Angle of canine mesial eruption to long axis of lateral, p (panoramic image) Angle of canine eruption in sagittal plane, 6 (lateral head film) Angle of canine mesial inclination to midline, y (axial projection) Degree of vertical eruption: -Panoramic image (d,) -Lateral head film (d,) Distance from canine cusp to APg line (lateral head film) Proclined lateral incisor Distal tipping of lateral incisor Enlarged follicular width Apical canine root deflection Degree of resorption of primary canine KEY:
Level of significance
test values
x2 = 3.77 (DF 1) x2 = 14.31 (DF 1) x2 = 1.80 (DF 3)
Power (phi or Cramer’s
NS
0.16 0.31 -
x2 = 1.83 (DF 4)
NS
-
x2 = 23.07 (DF 4) x2 = 24.67 (DF 4) t = 4.62 (DF 154) t = 2.93 (DF 154)
p 5 0.0001
0.39 0.40 0.12 0.05
t = 0.13 (DF 156) t = 3.89 (DF 156) t = 2.10 (DF 154) t = 1.23 (DF 156) t = 2.03 (DF 156) x2 = 0.04 (DF 1) x2 = 0.14 (DF I) x* = 0.00 x2 = 1.90 (DF 1) x2 = 6.67 (DF 3)
p 5 0.05 p 5 0.002
p I 0.0002 p~O.ooo
p 5 0.004
p 5 0.000
0.09
p 5 0.04
0.02
NS
V)
NS p 5 0.04
NS NS NS NS NS
0.02 -
x2 = Chi-square analysis; t = Student’s t test; DF = degrees of freedom; p = probability; NS = nonsignificant.
Table II. Distribution of the most medial position of the cusp of the ectopically erupting maxillary canine (sectors l-5) as projected in the orthopantogram (%) Canine Group
Resorption (n = 40) Control (n = 118)
position
in sector
5
4
3
2
I
3 33
31 39
42 20
I9 7
5 0.8
oriented to the x-ray machine and clinical measurements of the mesiodistal width of the maxillary incisors were made and compared with the orthopantograms to ensure an optimal position of the x-rayed object within the image-processing layer. The lateral head films were obtained with a focus distance of 155 cm and with the beam of the x ray directed through the external auditory meatus.” Analyzed factors
of development
(mineralization)
Total (%)
100 100
Level of significance p cc
0.001
-Path of eruption in all three planes -Position of the canine relative to the lateral incisor in all
three planes The development (degree of maturation) of the maxillary canine has been presented in two degrees: 1. The root is longer than the canine crown. 2. The root is shorter than the canine crown. The positions, measured distances, and degrees can be seen from Figs. 2 through 6. Lateral
Twenty-four variables were analyzed. The data were transferred to magnetic tape and analyzed by computer. The SPSS computer program” was used. This presentation focuses on the following factors: Canine -Degree
(%)
incisor
The position of the lateral incisor within the dental arch was clinically assessedand registered as normal or distally tipped, proclined or not proclined.
Dental age was determined according to a method developed by Gustafson and Koch.13 The tested variables are presented in Table I. Space loss was measured with sliding calipers and
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Fig. 3. Schematic illustration of the canine position in an axialFig. 2. Schematic illustration of the projection of the canine in the panoramic image and sectors (7 through 5) of the most medial position of the crown.
vertex intraoral radiograph and sectors (7 through 5) of the most medial position of the canine cusp.
amounted to 1 to 3 mm in three cases in the resorption group. Statistical methods Conventional methods have been used for statistical analysis.‘* Distributions have been studied by means of the chi-square test with the Yates correction; differences in means between two groups have been analyzed by means of Student’s t test with n-2 degrees of freedom. For those variables in which statistical significance was found, the association was further analyzed, and the strength of the statistical associations from obtained differences was estimated and expressed with the coefficient phi and Cramer’s V for the chi-square tests” and with the coefficient omega for Student’s t test.14 Any influence of sample size on statistical significance was hereby eliminated. The coefficients assumed a value between 0 and 1, depending on the strength of the statistical association (Table I), where 0 means complete independence and 1.00 a complete association . The reliability of the radiographic methods was estimated according to Guilford’s definitionI by studying the variance between two determinations. No error exists when the reliability coefficient is 1.OO. The coefficient varied between 0.92 and 0.94. RESULTS The main results are presented in Table I, together with an estimate of the strength of the statistical associations of variables between the two groups.
Resorption of maxillary lateral incisors was found to be more common in girls than in boys. The sex ratio
Fig. 4. Schematic illustration of the inclination of the maxillary canine to the midline (a) and long axis of the lateral incisor (p) in the panoramic image.
was 3 : 1 in the resorption group and 6: 5 in the control group. The factor related to sex accounts for about 16% (phi 0.16) of the variance of the score. Compared with some of the other significant variables, sex was of comparatively little importance (Table I). Canine tooth development The canine tooth development (measuring the length of the root) was more advanced in the resorption group than in the control group (Table I). In cases with resorption, more than half of the root had developed in nine of 10 cases as compared with a 6:5 ratio for controls of the same age. Children in the resorption group had a dental age close to the mean’* (mean k 1 year) in 97% of the
50%
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0A Lye A 80.
80.
40. -
NL
20
Fig. 5. A, Schematic illustration of the maxillary canine inclination lo the midline (y) in an intraoral axis-vertex projection. B, Diagram showing median values (Md) of the eruption angles (CXand p) in the resorption group (R) and control group (C), the range for 50% of the observations, and the total range.
cases. For children in the control group, the corresponding figure was 90%. Position Position of the canine crown relative to the dental arch (transverse plane). The position of the cusp of the
maxillary canine crown in relation to the midline of the dental arch or relative to the lateral incisor (both in buccal and lingual positions) did not significantly differ between the two groups (Table I). Medial position of the canine cusp (transverse and frontal planes). A detailed analysis showed that the
cusp of the maxillary canine was positioned more mesially in the resorption group than in the control group (Tables I and II). This difference was statistically significant. An estimate of this variable showed that it accounts for approximately 40% of the variance of obtained scores. The projection of the canine position in the orthopantogram and in the axial-vertex projection showed similar patterns. The distribution of the position of the cusp of the maxillary canine in the orthopantogram can be seen from Fig. 2 and TablebII.
Fig. 6. A, Degree of vertical eruption of the maxillary canine (6) registered as a distance d, in the panoramic image. B, Degree of vertical eruption of the maxillary canine registered as a distance d2 in the lateral head film. AU, Nasal line; OL, occlusal line; Afg, line from the A point to the pogonion. Also shown is the angle between NL and the long axis of the maxillary canine.
From Tables II and III, it can be seen that the number of resorbed lateral incisors increased as a result of a more medial position of the canine cusp. The difference between the two groups in this respect is significant and the strength of this relationship is high (Table I). In the resorption group, canines in the most medial sectors (1 through 3) in the orthopantogram comprised 65% of the material, whereas the corresponding figure for the control material was 28% (Table II). The corresponding figures for the axial-vertex projection were 60% and 28%, respectively (Table III). It is worth noting that when the cusp of the canine was positioned mesially to the lateral incisor (in sectors 1 and 2), the risk of complications increased three times, and every
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Table III. Distribution of the most medial position of the cusp of the ectopically erupting canine in an axial-vertex projection (%) Canine Group
Resorption Control
5
(n = 40) (n =
118)
position
in sectors
(YG)
4
3
2
I
Total
0
41
33
18
8
100
31
40
20
7
1
100
Level of srgnifcance
(o/o)
F’ < 0.001
Table IV. The vertical inclination (“) of the eruption path of the canine in the orthopantogram measured to the midline (a) and to the long axis of the lateral incisor (@)-Mean, standard error, and standard deviation I
Group
x
Resorption (n = 40) Control (n = 118) Level of significance
29.5 18.6
SE
t 2
2.5 I.0 p < 0.001
second lateral incisor was found to be resorbed with canines in this medial position. Inclination Vertical inclination of the canine path of eruption. The vertical inclination of the canine was analyzed both from the orthopantogram and from the lateral head film (Figs. 4 and 6). Inclination of the canine in the frontal plane. In the orthopantogram, the inclinations of the eruption path to the midline (a) and to the long axis of the lateral incisor (p) were measured. The mean values and standard deviations for these two angles are shown in Table IV. When measured to the midline ((-u-29.5” and 18.6”, respectively) and also to the long axis of the laterals (p 39.1” and 31. l”, respectively), the inclination of the erupting canine was more horizontal (average 10”) than that of the control group. This difference between the two groups was statistically significant and more pronounced for the inclination to the midline (CL).The range in individual variation was considerable, however, and the strength of the association was thus found to be fairly low-5% to 12% (Table I). For the vertical inclination angles a and p, the medians and the 50% quartiles were calculated (diagram shown in Fig. 5, B). The inclination angle (Y ranged from 8” to 80” in the resorption group and from 0” to 59” in the control group, the median values being 28” and 17”, respectively. It was found that 25% to 75% of the observations could be found between 18” and 40” and between 10” and 25”, respectively. This indi-
SD
x
15.4 Il.5
39.1 31.1
-c 2
SE
SD
2.5 1.3 p < 0.01
15.5 14.2
cates that the risk of resorption increases by 50% when the eruption inclination exceeds 25” as compared with the controls. The corresponding value for the vertical eruption inclination to the lateral incisor (p) is 28”. This is valid for the positions (buccolingually) as expressed in the orthopantograms. Inclination of the canine in the sagittal plane. The sagittal inclination of the path of eruption (6) was measured in lateral head films (Fig. 6); no statistically significant differences were found between the two groups. Inclination of the canine in the horizontal plane. The degree of mesial orientation of the canine was analyzed by measuring the angle (y) between the projections of the long axis of the canine and the midline of the maxilla in the axial-vertex occlusal film (Fig. 5). The values are presented in Table V. In the resorption group, the mesial inclination of the canine to the midline in the horizontal plane was more pronounced (34.5”) than in the control group (16.4”). This difference between the groups was statistically significant. Canine eruption in the vertical dimension The degree of vertical canine eruption was analyzed by measuring the distance (d,) from the canine cusp to the occlusal plane in the orthopantogram (Fig. 6). The results can be seen in Table VI; they show a statistically significant but small difference between the two groups. However, the strength of the statistically significant association is low. When calculating means and 50% quartiles, no definite difference could be found between the two groups.
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Table V. The mesial inclination of the canine to the midline (6) of the canine in an axial-vertex projection-Mean, standard error, and standard deviation 6 x
Group Resorption Control
(n = 40) (n = 118)
SE
SD
34.5
k
4.5
29
16.4
”
2.2
24
Level of significance
p < 0.001
Table Vi. The distance from the canine cusp to the occlusal line in orthopantograms (d,) and lateral head films (d,)-Mean, standard error, and standard deviation d, (orthopantogram) Group
x
Resorption (n = 40) Control (n = 118)
14.1 15.6
t 2
Level of significance
dz (lateral
SE
SD
x
0.6 0.3
4.5 3.8
10.7 11.4
* -t
p < 0.05
headjlm) SE
SD
0.5 0.3
3.6 3.4
NS
Tabts WI. Distribution of the degree of root resorption of the primary canine (1 and 2) or absence (3) (0 denotes no resorption) .53”163” Group Resorption Control
(n = 40) (n =
118)
of resorption
(%)
0
1
2
3
35
17.5
17.5
30
100
34
34
18
14
100
Canine position in the sagittai plane The canine position in the sagittal plane was measured as the distance between the cusp and the line APg (A point to pogonion) in lateral head films (Fig. 6). A small but not statistically significant difference was found between the two groups.
Total (%)
Level of significance NS
No such association was found (Fig. 7, Table VII). In one third of the resorption cases, normal resorption of the primary canine root was found. The position of the lateral incisor relative to the dental arch
The influence of the dental follicular width (measured in intraoral periapical radiographs with calipers) was analyzed by comparing two groups, one with a maximum width of 3 mm or more and another with a maximum width less than 3 mm. The distributions were then tested between the resorption group and the control group and no difference was found. In intraoral radiographs, the dental follicles exceeded 3 mm in 23% and 24% of the subjects in the resorption and control groups, respectively.
When compared to adjacent incisors clinically, in the axial-vertex projection, and in the orthopantogram, the position of the lateral incisor relative to the dental arch was registered as (1) proclined or normal and (2) distal tipping or normal for the two groups (Table I). No association was found between the position of the lateral incisor and the lateral incisor root resorption. In the resorption group, 16% of the lateral incisors were proclined and 27% were distally tilted; the corresponding figures for the control group were 18% and 23%, respectively. Most proclinations were associated with buccal positions of the canine.
Resorption of the primary canine root
DISCUSSION
The association between lateral incisor resorption and the degree of the so-called physiologic root resorption or absence of the primary canine was tested.
Root resorption of permanent incisors caused by an erupting maxillary canine is an underestimated prob1em.6 Immediate therapeutic measures often are needed
The width of the dental follicle
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to avoid worsening of the situation and subsequent prolonged and expensive orthodontic treatment. Several predisposing and singularly associated factors involved in the resorption of incisors due to canine ectopic eruption have been identified in this study and their importance evaluated. The possibility of any covariation of the analyzed factors has not been assessed and needs further study. The subjects in this study were younger than those in other reports because of the screening procedure used.” The age ranges of the resorption and control groups (10 to 15 years) cover the entire normal eruption period of the canine and differ on average only 0.7 of a year. Furthermore the number of subjects is large for this uncommon complication. This material therefore may be considered representative for identification of factors associated with resorption of lateral incisors caused by ectopic eruption of maxillary canines. The conventional clinical and radiographic methods used are representative of an everyday clinical situation and have been used to present an analysis that facilitates the everyday use of the results. Of the radiographic methods used, the intraoral periapical and axial-vertex projections in occlusal films and the panoramic image were the most efficient in identifying differences in position between the resorption and control groups. Used together, these three methods describe the displaced canine in three dimensions and can be expected to have a sufficient degree of accuracy in describing the relationship of the canine to the adjacent incisor and to other anatomic structures. The detailed analysis of the results also showed good agreement among these methods (Tables III through V). The lateral head tilm was less efficient in this respect because of the overlapping of the two sides, which made identification of the specific canine difficult. The curve of the dental arch in the canine region was also a factor. The posterior-anterior (PA) skull radiograph was not used in this study since it has been shown by Coupland,” that this radiograph is comparable to the orthopantogram in the presentation of the position of the canine. The orthopantogram was chosen because it better describes the dental situation in the anterior region without disturbing the overlap and can be obtained at many orthodontic departments, whereas the PA skull radiograph is not as available. Most panographic machines give approximately comparable images in the central part of the cut, provided that the orientation of the patient is correct.” In all radiographic techniques, there is some degree of distortion. Comparing the position of the canine in two series of observations in this study, the distortion factor did not influence the main results in a decisive way because the same methods were used and the two groups showed similar locations of the canine relative
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DEGREE OF RESORPTION TOOTH 53/63
--____--__ __________ 0 ---____ _ _-_-_-__-_ 1 __-____ ~ -- - ____-_--_ 2 --_---_ - --------3 (missing)
Fig. 7. Schematic illustration of the degree of root resorption of the primary canines.
to the dental arch. Guilford’s coefficient of reliabilityI was high for all measurements of both inclination and distance in the panoramic and vertex images, indicating that the errors of the methods were low as compared with the total variance of the measured variables. The results show that ectopic eruption per se does not increase the risk of resorption unless accompanied by other factors. The factors that most increased the risk were a more medially positioned canine crown, a more advanced degree of canine development, and an increased mesial inclination of the path of eruption. Of the angles of eruption, (Yand y had greater power than p, which would indicate that tipping of the lateral incisors to a certain extent moderates the risk of resorption. Townend” has reported that canines causing resorption appeared to be more vertical, which is contrary to the findings of this study. Female sex also was associated with the occurrence of resorption as indicated earlier by Howard’ and Sasakura and associates.‘” The estimates of the strength of the statistical associations do not give much consideration to mutual relationship and covariations. It may well be that a discriminant analysis could better explain the strength of these associations. Of the clinical factors that may influence resorption during ectopic eruption of the canines, we gave particular attention to the lateral incisor’s proclination and tipping, the width of the canine’s dental follicle, and the degree of primary canine root resorption. No significant associations could be demonstrated in this study. This is in contrast to earlier observations and opinions in which such factors have been stated to be associated with resorption, -namely, tipping of lateral incisors,2o an enlarged canine follicle in some resorption cases,’ and delayed resorption and exfoliation of the primary canine.“‘.”
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Among possible causative factors in ectopic eruption and impaction of maxillary canines, lack of space and crowding in the canine region have been proposed to influence ectopic eruption.‘~3~5~20~22 It has been suggested, however, that most such patients have sufficient space. 6~2’~23-25 In this study of resorbed lateral incisors, lack of space was found in only three of the 40 cases and was apparently of minor importance. For diagnostic awareness, it is important to note that the relative prevalence of the most common site of resorption was not greater in palatal positions (which is a far more common ectopic position compared with buccal ones). However, it is interesting that resorption was far more common in the middle third of the root than in the cervical and apical thirds, which is contrary to Kettle,” who believed apical resorption to be more common. Thus this midroot location of resorption in the sagittal and vertical dimensions means that, because of overlapping, diagnosis from intraoral or even panoramic films is not always reliable. The importance of polytomography in diagnosing resorption in these cases has been evaluated earlier by Ericson and Kurol.6 Polytomography, which is gaining increasing use for localizing unerupted teeth,2.6.8.26 should be considered when resorptions cannot be ruled out from routine intraoral films. Another possible tool is computed tomography.*’ An advanced canine root development was significantly correlated to resorption on adjacent incisors as was a more medial position of the canine crown. Both of these factors may be assumed to be age-related. It may therefore be concluded that early diagnosis of ectopic eruption and potential resorptive situations should reduce the number of complications. Annual clinical investigation, including palpation of the canine region and relating this to the patient’s somatic and dental maturity, may show cause for a radiographic investigation of the canine position starting at 10 years of age at the latest,*.” and may help to reduce the number of complications caused by eruption disturbances. This is especially important because it has been stated that lateral incisor resorption is unpredictable*’ and rapid.5.20.29.31 It is noteworthy that in the resorption group, one third of the primary canines showed normal physiologic root resorption. Thus the discovery of such normal primary root resorption is no guarantee that the canine is free from complications. Resorption may occur as early as 10 years of age but the prevalence of such unfortunate resorption and the degree of resorption seem to be 10w.~ Therefore general radiographic screening at this age is not recommended for both practical and ethical reasons. Our opinion is that the use of radiographic diagnostic meth-
Dentofac. Orthop. December 1988
ods should be based on individual indications according to our previously suggested clinical and radiographic procedures. *.I0 It is customary in scientific articles to express associations with some sort of statistical significance, usually in the form of certain previously chosen levels of statistical significance-for example, *** = p < 0.001. However, the occurrence of such a significant result discloses nothing about the strength of the association among the tested variables.‘4 For this reason we have performed an analysis of the statistical power of the associations to evaluate the most important single factors that are easily recognized by the clinician. It is also our opinion that it is very important, especially when studying causative factors, to analyze the strength of the associations in addition to the significance. This study could in this respect point out three powerful factors-namely, more advanced canine development, a more medial position of the canine cusp, and mesial inclination of the canine to the midline exceeding 25” as measured on the orthopantogram. CONCLUSION In general, the results show that the typical candidate for resorption of the lateral incisors during ectopic eruption is a girl approximately 11 to 12 years of age, with (1) a well-developed canine root, (2) the canine cusp erupted medially to the long axis of the adjacent lateral incisor, and (3) the canine in a mesial angle of eruption to the midline exceeding 25”. However, because the pattern is not uniform and resorption also may occur in apparently normal eruption situations, the risk of resorption in children with displaced canines must not be neglected. REFERENCES 1. Thilander B, Jakobsson SO. Local factors in impaction of maxillary canines. Acta Odontol Stand 1968;26:145-68. 2. Ericson S, Kurol J. Radiographic assessment of maxillary canine eruption in children with clinical signs of eruption disturbance. Eur J Orthod 1986;8:133-40. 3. Hitchin AD. The impacted maxillary canine. Br Dent J 1956;100:1-14. 4. Rayne J. The unerupted maxillary canine. Dent Pratt 1969; 19:194-204. 5. Howard RD. The displaced maxillary canine positional variations associated with incisor resorption. Trans Br Sot Study Orthod 1970-1;57:149-57. 6. Ericson S, Kurol J. Radiographic examination of ectopically erupting maxillary canines. AM J ORTHOD DENTOFAC ORTHOP 1987;91:483-92. 7. van der Linden FPGM, Dutterloo HS. Development of the human dentition. An atlas. Hagerstown, Maryland: Harper & Row, 1976. 8. Ericson S, Kurol J. Resorption of permanent incisors due to eruption of maxillary canines. A radiographic study. Angle Orthod 1987;57:332-46.
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9. Marks SC Jr, Cahill DR. Regional control by the dental follicle of alterations in alveolar bone metabolism during tooth eruption. J Oral Path01 1987:16:164-9. 10. Ericson S, Kurol J. Longitudinal study and analysis of clinical supervision of maxillary canine eruption. Community Dent Oral Epidemiol 1986;14:172-6. Il. Iikubo M. Korsell S, Omnell K-A. Description of a new cephalostat and its performance. Dentomaxillofac Radio1 1975: 4~25-9. K, Bent DH. Statis12. Nie N, Hull CH, Jenkins JG, Steinbrenner tical package for the social sciences. 2nd ed. New York: McGraw-Hill, 1975. 13. Gustafson G, Koch G. Age estimation up to 16 years of age based on dental development. Odontol Revy 1974;25:297-306. 14. Hays WL. Statistics for the social sciences. 2nd ed. New York: Holt, Rinehart & Winston, 1973:414-24. 15. Guilford JP. Introduction to analysis of variance. In: Fundamental statistics in psychology and education. 4th ed. New York: McGraw-Hill, 1965:268-303. 16. Coupland MA. Localisation of misplaced maxillary canines. Orthopantomograph and P.A. skull views compared. Br J Orthod 1984:11:27-32. 17. McDavid WD. Tronje G, Welander U, Morris CR, Nummikoski P. Imaging characteristics of seven panoramic X-ray units. J Int Assoc Dent Maxillofac Radio1 1985[suppl 81. 18. Townend PI. Resorption of the roots of upper incisor teeth due to misplaced canine teeth. Trans Br Sot Study Orthod 1967: 74-7. 19. Sasakura H. Yoshida T, Murayama S, Hanada K, Nakajima T. Root resorption of upper pennanent incisor caused by impacted canine. An analysis of 23 cases. Int J Oral Surg 1984;13:299306. 20. Kettle MA. Treatment of the unerupted maxillary canine. Trans Br Sot Study Orthod 1957:74-84.
21. 22. 23.
24.
25. 26.
27. 28. 29. 30. 3 1.
Dewel BF. The upper cuspid. Its development and impaction. Angle Orthod 1949;19:79-90. Bass TB. Observations on the misplaced upper canine tooth. Dent Pratt 1967;18:25-33. Trlnkmann J. Zur Indikation der operativen Freilegung und Anschlingung retinierter oberer Schneideund Eckzlhne. Dtsch Zahnaerztl Z 1967;22:695-8. Richardson A, McKay C. Delayed eruption of maxillary canine teeth. Part 1. Aetiology and diagnosis. Proc Br Paedod Sot 1982;12:15-25. Jacoby H. The etiology of maxillary canine impactions. t\M J ORTHOD 198384: 125-32. Cugat Femandez de la CA, Asensi CC, Gascon MF. Aplicacion de la tomogralia multidirectional al estudio de piezas dentarias incluidas. Acta Estomatokjgica Valenciana 1986; I :3- 10. Ericson S, Kurol J. CT diagnosis of ectopicaily erupting maxillary canines. A case report. Eur J Orthod 1988: 10: 115-2 1. Hotz R. Orthodontics in daily practice. Bern, Switzerland: Hans Huber, 1974:340-53. Moss JP. The unerupted canine. Dent Pratt 1972:22:241-8. Kisling E, Ravn E. Two cases of marked pressure resorption in maxillary incisors. Tandlaegebladet 1977;81: 153-5. Brown ID, Matthews RW. Apical resorption of a maxillary lateral incisor from a misplaced canine in 17-year old. A case report. Br J Orthod 1981;8:3-5.
Reprint requests to: Dr. Jiiri Kurol Department of Orthodontics The Institute for Postgraduate Jimvagsgatan 9 S-552 55 Jijnkoping Sweden
Dental
Education
Sweden
Factors predisposing to resorption of adjacent permanent lateral incisors caused by ectopic eruption of maxillary canines were evaluated. The subjects consisted of two groups: one with 40 lateral incisors with resorption caused by ectopic eruption and a control group of 118 ectopic eruption cases with no lateral incisor resorption. The mean age of the children in the two groups differed by only 0.7 of a year and ranged from 10.0 to 15.0 years, covering the normal eruption period of the maxillary canine. Resorption of lateral incisors was three times as common in girls as in boys. The resorption cases showed a more advanced dental development, a more medial canine position,in the dental arch, and a slightly more mesial horizontal path of eruption (an average of 100) than that of the control cases. Factors such as the width of the dental follicle and proclination or distal tilting of the lateral incisor showed no correlation to the resorption. Potential resorption cases are always those in which the canine cusp in periapical and panoramic films is positioned medially to the midline of the lateral incisor. Such situations should be carefully investigated with polytomography if necessary. The risk of resorption also will increase with a more mesial horizontal path of eruption. From 10 years of age or younger, annual clinical examination by palpation of the canine eruption path is recommended. This clinical examination should be supplemented with a stepwise extended radiographic procedure in cases in which ectopic eruption of the maxillary canines is suspected. (AM J ORTHOD
DENTOFAC
ORTHOP
1988:94:503-l
3.)
T
he permanent maxillary canine is frequently misplaced in relation to other teeth in the maxilla. The prevalence of noneruption and ectopic eruption of this tooth has been reported to be 0.9% to 2.0% in samples not previously selected for orthodontic treatment.‘,’ The canine is most frequently found palatal to the lateral incisor and buccally in only about 15% of cases,2-4 Ectopic eruption of maxillary canines may lead to impaction and/or resorption of neighboring permanent teeth.‘*‘,” However, in most studies of the eruption of the maxillary canines, the latter complication is sparsely reported. This might give the impression that resorption caused by the eruption of the maxillary canine is rare and of minor clinical importance, however unfortunate in the individual case. The lesions often are difficult to diagnose with ordinary radiographic techniques because most of the resorptions are located palatally or buccally in the middle third of the root of the adjacent lateral incisor. Often they are concealed by overlapping of the canine in the periapical radiographs.” In a recent epidemiologic study of maxillary canine From the Departments of Maxilla-Facial Radiology* Institute for Postgraduate Dental Education.
and Orthodontics.**
The
eruption in which uninterpretable areas caused by overlapping on the intraoral radiographs were examined by polytomography, it was found that resorption of lateral incisors occurred in 12% of cases after ectopic eruption of maxillary canines, suggesting a total prevalence of 0.7% for resorbed lateral incisors in the lo- to 13-year age group.’ During eruption of the maxillary canines, these teeth are in very close contact with the lateral incisors due to the anatomy in this region,’ and it has been shown in radiographs that the lamina dura often is missing.‘,6 Furthermore it is believed that in situations of resorption, there must be close contact between the canine and lateral incisor, rather than mediation of the resorption by swelling of the dental follicle.‘.’ The importance of the dental follicle in the tooth eruption process has been shown in animal experiments.” However, it is not clear what the predisposing causative factors in this incisor resorption process are and in what positions and situations an ectopically erupting or misplaced canine is liable to resorb the adjacent teeth. This investigation was undertaken in an attempt to elucidate the role of various causative factors in the resorption of lateral incisors caused by ectopic eruption of maxillary canines. A further aim was to evaluate the 503
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Fig. 1. Records of female subject, aged 10 years 10 months. Lateral (A and B) and occlusal (C and D) views of the dentition and dental arches show crowding and lack of space. Extraction of first premolars was indicated and the patient was referred for orthodontic treatment. Note the buccal position of the maxillary canines. E, Axial-vertex intraoral radiograph at 11 years 3 months of age shows the position of the maxillary canines relative to the dental arch. In the Orthopantomograph F, the medial position of the canine crowns and degree of mesial path of eruption are seen. In the periapical dental films (G and H), an overlapping of the canine over the lateral incisor is seen together with an unbroken mesiodistal root contour. The lamina dura is missing. Because of this and the close relation between the canine and lateral incisor as seen in E, further radiographic investigation is indicated. (Which one of the lateral incisors is resorbed?)
strength of various possible predisposing factors singularly associated with the resorption of lateral incisors by comparing resorption cases with nonresorption cases after ectopic eruption of the maxillary canine.
eruption. The two groups were investigated in an identical manner, both clinically and radiographically. In no case had the canine erupted into the oral cavity. The primary canine was missing in 30% of the subjects.
SUBJECTS
Resorption
The material for this study was derived from two groups: a group with resorption of the maxillary permanent lateral incisor associated with ectopic eruption of the maxillary canine and a control group in whom the incisor was not resorbed because of the ectopic
This group comprised 40 consecutively collected cases with resorbed lateral incisors with varying degrees of resorption. No evidence of traumatic injuries to the incisors was found. A detailed presentation of the location and extent of resorption on the lateral incisors
group
Resorption
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polytomograms (I and J) show that the girl’s right lateral incisor is buccally in close relation to the canine crown and a resorption cavity ~&WOWS) is seen extending into the pulp. On the left side, there is close contact between the lateral incisor root and canine crown but without resorption. The girl showed a lack of interest and was reluctant to wear a visible fixed orthodontic appliance. In K, the extracted lateral incisor on the right side shows a buccal resorption in the middle third of the root and the radiograph L shows the full extent of buccal root resorpQon. Note the conformity of information between the polytomogram (I) and the radiograph (L). For reasons of symmetry, both lateral incisors were extracted, and in M and N the clinical and radiographic frontal views of both the resorbed and normal lateral incisors are seen. The intraoral photograph (0) of the maxillary dental arch shows the result 8 months after extraction at 12 years 0 months of age.
Fig. 1 (Cont’d). The sagittal
has been given previously.’ In 34 of the 40 lateral incisors (85%), the erupting canine was found in an ectopic position lingually, distolingually, or buccally to the resorbed incisor root. In six cases the canine position was distal to the lateral incisor root. In 45% of the lateral incisors, the resorption extended into the pulp. Control group The material for the control group was collected from material presented earlie?.6.‘o in a series of studies on normal and ectopic canine eruption. This group consisted of 118 cases of nonerupted maxillary canines with an ectopic path of eruption, but without causing resorption of the lateral incisor roots. From the radiographs it could be seen that the two materials were very similar and comparable with regard to the position of the canine crown relative to the adjacent teeth in the dental arch. In 83% of cases, the canine crowns showed lingual, distolingual, or buccal positions relative to the incisor root. Buccal positions were noted for 15% of the canines (as compared with 18% in the resorption group). Age The age of the subjects ranged from 10.1 to 14.9 years in the resorption group and from 10.0 to 15 .O
years in the control group. The mean age in the resorption group was 12.1 + 1.2 years; in the control group, the mean age was 11.3 t 1.O years. This minor difference in age (mean 0.7 years) between the two groups was not statistically significant. METHODS Radiographic
examination
The radiographic examination was performed according to defined criteria and an earlier described stepwise procedure.‘.‘” In addition to conventional intraoral periapical films in different projections., an intraoral occlusal film was exposed in an axial-vertex projection, with the x-ray beam parallel to the long axis of the incisors. An orthopantogram and lateral head film also were obtained. In those cases in which the canines could not be projected free from the lateral incisors and the overlapping made it impossible to rule out resorption, the lateral incisors were polytomographed (for a detailed description, see Ericson and Kurol’.‘). A. complete radiographic examination is illustrated in Fig. 1. The panoramic image was obtained with a Siemens Orthopantomograph (OP-3)” modified with a collimator system and rotating anode. The patient was carefully *Siemens Corporation,
Icrlin,
N I.
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Table I. Analyzed factors and their statistical correlation to resorption of maxillary lateral incisors caused by ectopic eruption of the canine in a group of 40 resorbed incisors (I) and a group of 118 nonresorption cases (II) after ectopic eruption I-II Variables Sex
Degree of canine maturation Canine position relative to the midline of the dental arch (transverse plane) Canine position relative to the lateral incisor root (transverse plane) Medial position of the canine cusp: -Panoramic image (frontal plane) -Axial projection (transverse plane) Angle of canine mesial eruption to midline, (Y (panoramic image) Angle of canine mesial eruption to long axis of lateral, p (panoramic image) Angle of canine eruption in sagittal plane, 6 (lateral head film) Angle of canine mesial inclination to midline, y (axial projection) Degree of vertical eruption: -Panoramic image (d,) -Lateral head film (d,) Distance from canine cusp to APg line (lateral head film) Proclined lateral incisor Distal tipping of lateral incisor Enlarged follicular width Apical canine root deflection Degree of resorption of primary canine KEY:
Level of significance
test values
x2 = 3.77 (DF 1) x2 = 14.31 (DF 1) x2 = 1.80 (DF 3)
Power (phi or Cramer’s
NS
0.16 0.31 -
x2 = 1.83 (DF 4)
NS
-
x2 = 23.07 (DF 4) x2 = 24.67 (DF 4) t = 4.62 (DF 154) t = 2.93 (DF 154)
p 5 0.0001
0.39 0.40 0.12 0.05
t = 0.13 (DF 156) t = 3.89 (DF 156) t = 2.10 (DF 154) t = 1.23 (DF 156) t = 2.03 (DF 156) x2 = 0.04 (DF 1) x2 = 0.14 (DF I) x* = 0.00 x2 = 1.90 (DF 1) x2 = 6.67 (DF 3)
p 5 0.05 p 5 0.002
p I 0.0002 p~O.ooo
p 5 0.004
p 5 0.000
0.09
p 5 0.04
0.02
NS
V)
NS p 5 0.04
NS NS NS NS NS
0.02 -
x2 = Chi-square analysis; t = Student’s t test; DF = degrees of freedom; p = probability; NS = nonsignificant.
Table II. Distribution of the most medial position of the cusp of the ectopically erupting maxillary canine (sectors l-5) as projected in the orthopantogram (%) Canine Group
Resorption (n = 40) Control (n = 118)
position
in sector
5
4
3
2
I
3 33
31 39
42 20
I9 7
5 0.8
oriented to the x-ray machine and clinical measurements of the mesiodistal width of the maxillary incisors were made and compared with the orthopantograms to ensure an optimal position of the x-rayed object within the image-processing layer. The lateral head films were obtained with a focus distance of 155 cm and with the beam of the x ray directed through the external auditory meatus.” Analyzed factors
of development
(mineralization)
Total (%)
100 100
Level of significance p cc
0.001
-Path of eruption in all three planes -Position of the canine relative to the lateral incisor in all
three planes The development (degree of maturation) of the maxillary canine has been presented in two degrees: 1. The root is longer than the canine crown. 2. The root is shorter than the canine crown. The positions, measured distances, and degrees can be seen from Figs. 2 through 6. Lateral
Twenty-four variables were analyzed. The data were transferred to magnetic tape and analyzed by computer. The SPSS computer program” was used. This presentation focuses on the following factors: Canine -Degree
(%)
incisor
The position of the lateral incisor within the dental arch was clinically assessedand registered as normal or distally tipped, proclined or not proclined.
Dental age was determined according to a method developed by Gustafson and Koch.13 The tested variables are presented in Table I. Space loss was measured with sliding calipers and
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Fig. 3. Schematic illustration of the canine position in an axialFig. 2. Schematic illustration of the projection of the canine in the panoramic image and sectors (7 through 5) of the most medial position of the crown.
vertex intraoral radiograph and sectors (7 through 5) of the most medial position of the canine cusp.
amounted to 1 to 3 mm in three cases in the resorption group. Statistical methods Conventional methods have been used for statistical analysis.‘* Distributions have been studied by means of the chi-square test with the Yates correction; differences in means between two groups have been analyzed by means of Student’s t test with n-2 degrees of freedom. For those variables in which statistical significance was found, the association was further analyzed, and the strength of the statistical associations from obtained differences was estimated and expressed with the coefficient phi and Cramer’s V for the chi-square tests” and with the coefficient omega for Student’s t test.14 Any influence of sample size on statistical significance was hereby eliminated. The coefficients assumed a value between 0 and 1, depending on the strength of the statistical association (Table I), where 0 means complete independence and 1.00 a complete association . The reliability of the radiographic methods was estimated according to Guilford’s definitionI by studying the variance between two determinations. No error exists when the reliability coefficient is 1.OO. The coefficient varied between 0.92 and 0.94. RESULTS The main results are presented in Table I, together with an estimate of the strength of the statistical associations of variables between the two groups.
Resorption of maxillary lateral incisors was found to be more common in girls than in boys. The sex ratio
Fig. 4. Schematic illustration of the inclination of the maxillary canine to the midline (a) and long axis of the lateral incisor (p) in the panoramic image.
was 3 : 1 in the resorption group and 6: 5 in the control group. The factor related to sex accounts for about 16% (phi 0.16) of the variance of the score. Compared with some of the other significant variables, sex was of comparatively little importance (Table I). Canine tooth development The canine tooth development (measuring the length of the root) was more advanced in the resorption group than in the control group (Table I). In cases with resorption, more than half of the root had developed in nine of 10 cases as compared with a 6:5 ratio for controls of the same age. Children in the resorption group had a dental age close to the mean’* (mean k 1 year) in 97% of the
50%
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Dentofac. Orthop. December 1988
0A Lye A 80.
80.
40. -
NL
20
Fig. 5. A, Schematic illustration of the maxillary canine inclination lo the midline (y) in an intraoral axis-vertex projection. B, Diagram showing median values (Md) of the eruption angles (CXand p) in the resorption group (R) and control group (C), the range for 50% of the observations, and the total range.
cases. For children in the control group, the corresponding figure was 90%. Position Position of the canine crown relative to the dental arch (transverse plane). The position of the cusp of the
maxillary canine crown in relation to the midline of the dental arch or relative to the lateral incisor (both in buccal and lingual positions) did not significantly differ between the two groups (Table I). Medial position of the canine cusp (transverse and frontal planes). A detailed analysis showed that the
cusp of the maxillary canine was positioned more mesially in the resorption group than in the control group (Tables I and II). This difference was statistically significant. An estimate of this variable showed that it accounts for approximately 40% of the variance of obtained scores. The projection of the canine position in the orthopantogram and in the axial-vertex projection showed similar patterns. The distribution of the position of the cusp of the maxillary canine in the orthopantogram can be seen from Fig. 2 and TablebII.
Fig. 6. A, Degree of vertical eruption of the maxillary canine (6) registered as a distance d, in the panoramic image. B, Degree of vertical eruption of the maxillary canine registered as a distance d2 in the lateral head film. AU, Nasal line; OL, occlusal line; Afg, line from the A point to the pogonion. Also shown is the angle between NL and the long axis of the maxillary canine.
From Tables II and III, it can be seen that the number of resorbed lateral incisors increased as a result of a more medial position of the canine cusp. The difference between the two groups in this respect is significant and the strength of this relationship is high (Table I). In the resorption group, canines in the most medial sectors (1 through 3) in the orthopantogram comprised 65% of the material, whereas the corresponding figure for the control material was 28% (Table II). The corresponding figures for the axial-vertex projection were 60% and 28%, respectively (Table III). It is worth noting that when the cusp of the canine was positioned mesially to the lateral incisor (in sectors 1 and 2), the risk of complications increased three times, and every
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Table III. Distribution of the most medial position of the cusp of the ectopically erupting canine in an axial-vertex projection (%) Canine Group
Resorption Control
5
(n = 40) (n =
118)
position
in sectors
(YG)
4
3
2
I
Total
0
41
33
18
8
100
31
40
20
7
1
100
Level of srgnifcance
(o/o)
F’ < 0.001
Table IV. The vertical inclination (“) of the eruption path of the canine in the orthopantogram measured to the midline (a) and to the long axis of the lateral incisor (@)-Mean, standard error, and standard deviation I
Group
x
Resorption (n = 40) Control (n = 118) Level of significance
29.5 18.6
SE
t 2
2.5 I.0 p < 0.001
second lateral incisor was found to be resorbed with canines in this medial position. Inclination Vertical inclination of the canine path of eruption. The vertical inclination of the canine was analyzed both from the orthopantogram and from the lateral head film (Figs. 4 and 6). Inclination of the canine in the frontal plane. In the orthopantogram, the inclinations of the eruption path to the midline (a) and to the long axis of the lateral incisor (p) were measured. The mean values and standard deviations for these two angles are shown in Table IV. When measured to the midline ((-u-29.5” and 18.6”, respectively) and also to the long axis of the laterals (p 39.1” and 31. l”, respectively), the inclination of the erupting canine was more horizontal (average 10”) than that of the control group. This difference between the two groups was statistically significant and more pronounced for the inclination to the midline (CL).The range in individual variation was considerable, however, and the strength of the association was thus found to be fairly low-5% to 12% (Table I). For the vertical inclination angles a and p, the medians and the 50% quartiles were calculated (diagram shown in Fig. 5, B). The inclination angle (Y ranged from 8” to 80” in the resorption group and from 0” to 59” in the control group, the median values being 28” and 17”, respectively. It was found that 25% to 75% of the observations could be found between 18” and 40” and between 10” and 25”, respectively. This indi-
SD
x
15.4 Il.5
39.1 31.1
-c 2
SE
SD
2.5 1.3 p < 0.01
15.5 14.2
cates that the risk of resorption increases by 50% when the eruption inclination exceeds 25” as compared with the controls. The corresponding value for the vertical eruption inclination to the lateral incisor (p) is 28”. This is valid for the positions (buccolingually) as expressed in the orthopantograms. Inclination of the canine in the sagittal plane. The sagittal inclination of the path of eruption (6) was measured in lateral head films (Fig. 6); no statistically significant differences were found between the two groups. Inclination of the canine in the horizontal plane. The degree of mesial orientation of the canine was analyzed by measuring the angle (y) between the projections of the long axis of the canine and the midline of the maxilla in the axial-vertex occlusal film (Fig. 5). The values are presented in Table V. In the resorption group, the mesial inclination of the canine to the midline in the horizontal plane was more pronounced (34.5”) than in the control group (16.4”). This difference between the groups was statistically significant. Canine eruption in the vertical dimension The degree of vertical canine eruption was analyzed by measuring the distance (d,) from the canine cusp to the occlusal plane in the orthopantogram (Fig. 6). The results can be seen in Table VI; they show a statistically significant but small difference between the two groups. However, the strength of the statistically significant association is low. When calculating means and 50% quartiles, no definite difference could be found between the two groups.
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Table V. The mesial inclination of the canine to the midline (6) of the canine in an axial-vertex projection-Mean, standard error, and standard deviation 6 x
Group Resorption Control
(n = 40) (n = 118)
SE
SD
34.5
k
4.5
29
16.4
”
2.2
24
Level of significance
p < 0.001
Table Vi. The distance from the canine cusp to the occlusal line in orthopantograms (d,) and lateral head films (d,)-Mean, standard error, and standard deviation d, (orthopantogram) Group
x
Resorption (n = 40) Control (n = 118)
14.1 15.6
t 2
Level of significance
dz (lateral
SE
SD
x
0.6 0.3
4.5 3.8
10.7 11.4
* -t
p < 0.05
headjlm) SE
SD
0.5 0.3
3.6 3.4
NS
Tabts WI. Distribution of the degree of root resorption of the primary canine (1 and 2) or absence (3) (0 denotes no resorption) .53”163” Group Resorption Control
(n = 40) (n =
118)
of resorption
(%)
0
1
2
3
35
17.5
17.5
30
100
34
34
18
14
100
Canine position in the sagittai plane The canine position in the sagittal plane was measured as the distance between the cusp and the line APg (A point to pogonion) in lateral head films (Fig. 6). A small but not statistically significant difference was found between the two groups.
Total (%)
Level of significance NS
No such association was found (Fig. 7, Table VII). In one third of the resorption cases, normal resorption of the primary canine root was found. The position of the lateral incisor relative to the dental arch
The influence of the dental follicular width (measured in intraoral periapical radiographs with calipers) was analyzed by comparing two groups, one with a maximum width of 3 mm or more and another with a maximum width less than 3 mm. The distributions were then tested between the resorption group and the control group and no difference was found. In intraoral radiographs, the dental follicles exceeded 3 mm in 23% and 24% of the subjects in the resorption and control groups, respectively.
When compared to adjacent incisors clinically, in the axial-vertex projection, and in the orthopantogram, the position of the lateral incisor relative to the dental arch was registered as (1) proclined or normal and (2) distal tipping or normal for the two groups (Table I). No association was found between the position of the lateral incisor and the lateral incisor root resorption. In the resorption group, 16% of the lateral incisors were proclined and 27% were distally tilted; the corresponding figures for the control group were 18% and 23%, respectively. Most proclinations were associated with buccal positions of the canine.
Resorption of the primary canine root
DISCUSSION
The association between lateral incisor resorption and the degree of the so-called physiologic root resorption or absence of the primary canine was tested.
Root resorption of permanent incisors caused by an erupting maxillary canine is an underestimated prob1em.6 Immediate therapeutic measures often are needed
The width of the dental follicle
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to avoid worsening of the situation and subsequent prolonged and expensive orthodontic treatment. Several predisposing and singularly associated factors involved in the resorption of incisors due to canine ectopic eruption have been identified in this study and their importance evaluated. The possibility of any covariation of the analyzed factors has not been assessed and needs further study. The subjects in this study were younger than those in other reports because of the screening procedure used.” The age ranges of the resorption and control groups (10 to 15 years) cover the entire normal eruption period of the canine and differ on average only 0.7 of a year. Furthermore the number of subjects is large for this uncommon complication. This material therefore may be considered representative for identification of factors associated with resorption of lateral incisors caused by ectopic eruption of maxillary canines. The conventional clinical and radiographic methods used are representative of an everyday clinical situation and have been used to present an analysis that facilitates the everyday use of the results. Of the radiographic methods used, the intraoral periapical and axial-vertex projections in occlusal films and the panoramic image were the most efficient in identifying differences in position between the resorption and control groups. Used together, these three methods describe the displaced canine in three dimensions and can be expected to have a sufficient degree of accuracy in describing the relationship of the canine to the adjacent incisor and to other anatomic structures. The detailed analysis of the results also showed good agreement among these methods (Tables III through V). The lateral head tilm was less efficient in this respect because of the overlapping of the two sides, which made identification of the specific canine difficult. The curve of the dental arch in the canine region was also a factor. The posterior-anterior (PA) skull radiograph was not used in this study since it has been shown by Coupland,” that this radiograph is comparable to the orthopantogram in the presentation of the position of the canine. The orthopantogram was chosen because it better describes the dental situation in the anterior region without disturbing the overlap and can be obtained at many orthodontic departments, whereas the PA skull radiograph is not as available. Most panographic machines give approximately comparable images in the central part of the cut, provided that the orientation of the patient is correct.” In all radiographic techniques, there is some degree of distortion. Comparing the position of the canine in two series of observations in this study, the distortion factor did not influence the main results in a decisive way because the same methods were used and the two groups showed similar locations of the canine relative
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DEGREE OF RESORPTION TOOTH 53/63
--____--__ __________ 0 ---____ _ _-_-_-__-_ 1 __-____ ~ -- - ____-_--_ 2 --_---_ - --------3 (missing)
Fig. 7. Schematic illustration of the degree of root resorption of the primary canines.
to the dental arch. Guilford’s coefficient of reliabilityI was high for all measurements of both inclination and distance in the panoramic and vertex images, indicating that the errors of the methods were low as compared with the total variance of the measured variables. The results show that ectopic eruption per se does not increase the risk of resorption unless accompanied by other factors. The factors that most increased the risk were a more medially positioned canine crown, a more advanced degree of canine development, and an increased mesial inclination of the path of eruption. Of the angles of eruption, (Yand y had greater power than p, which would indicate that tipping of the lateral incisors to a certain extent moderates the risk of resorption. Townend” has reported that canines causing resorption appeared to be more vertical, which is contrary to the findings of this study. Female sex also was associated with the occurrence of resorption as indicated earlier by Howard’ and Sasakura and associates.‘” The estimates of the strength of the statistical associations do not give much consideration to mutual relationship and covariations. It may well be that a discriminant analysis could better explain the strength of these associations. Of the clinical factors that may influence resorption during ectopic eruption of the canines, we gave particular attention to the lateral incisor’s proclination and tipping, the width of the canine’s dental follicle, and the degree of primary canine root resorption. No significant associations could be demonstrated in this study. This is in contrast to earlier observations and opinions in which such factors have been stated to be associated with resorption, -namely, tipping of lateral incisors,2o an enlarged canine follicle in some resorption cases,’ and delayed resorption and exfoliation of the primary canine.“‘.”
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Among possible causative factors in ectopic eruption and impaction of maxillary canines, lack of space and crowding in the canine region have been proposed to influence ectopic eruption.‘~3~5~20~22 It has been suggested, however, that most such patients have sufficient space. 6~2’~23-25 In this study of resorbed lateral incisors, lack of space was found in only three of the 40 cases and was apparently of minor importance. For diagnostic awareness, it is important to note that the relative prevalence of the most common site of resorption was not greater in palatal positions (which is a far more common ectopic position compared with buccal ones). However, it is interesting that resorption was far more common in the middle third of the root than in the cervical and apical thirds, which is contrary to Kettle,” who believed apical resorption to be more common. Thus this midroot location of resorption in the sagittal and vertical dimensions means that, because of overlapping, diagnosis from intraoral or even panoramic films is not always reliable. The importance of polytomography in diagnosing resorption in these cases has been evaluated earlier by Ericson and Kurol.6 Polytomography, which is gaining increasing use for localizing unerupted teeth,2.6.8.26 should be considered when resorptions cannot be ruled out from routine intraoral films. Another possible tool is computed tomography.*’ An advanced canine root development was significantly correlated to resorption on adjacent incisors as was a more medial position of the canine crown. Both of these factors may be assumed to be age-related. It may therefore be concluded that early diagnosis of ectopic eruption and potential resorptive situations should reduce the number of complications. Annual clinical investigation, including palpation of the canine region and relating this to the patient’s somatic and dental maturity, may show cause for a radiographic investigation of the canine position starting at 10 years of age at the latest,*.” and may help to reduce the number of complications caused by eruption disturbances. This is especially important because it has been stated that lateral incisor resorption is unpredictable*’ and rapid.5.20.29.31 It is noteworthy that in the resorption group, one third of the primary canines showed normal physiologic root resorption. Thus the discovery of such normal primary root resorption is no guarantee that the canine is free from complications. Resorption may occur as early as 10 years of age but the prevalence of such unfortunate resorption and the degree of resorption seem to be 10w.~ Therefore general radiographic screening at this age is not recommended for both practical and ethical reasons. Our opinion is that the use of radiographic diagnostic meth-
Dentofac. Orthop. December 1988
ods should be based on individual indications according to our previously suggested clinical and radiographic procedures. *.I0 It is customary in scientific articles to express associations with some sort of statistical significance, usually in the form of certain previously chosen levels of statistical significance-for example, *** = p < 0.001. However, the occurrence of such a significant result discloses nothing about the strength of the association among the tested variables.‘4 For this reason we have performed an analysis of the statistical power of the associations to evaluate the most important single factors that are easily recognized by the clinician. It is also our opinion that it is very important, especially when studying causative factors, to analyze the strength of the associations in addition to the significance. This study could in this respect point out three powerful factors-namely, more advanced canine development, a more medial position of the canine cusp, and mesial inclination of the canine to the midline exceeding 25” as measured on the orthopantogram. CONCLUSION In general, the results show that the typical candidate for resorption of the lateral incisors during ectopic eruption is a girl approximately 11 to 12 years of age, with (1) a well-developed canine root, (2) the canine cusp erupted medially to the long axis of the adjacent lateral incisor, and (3) the canine in a mesial angle of eruption to the midline exceeding 25”. However, because the pattern is not uniform and resorption also may occur in apparently normal eruption situations, the risk of resorption in children with displaced canines must not be neglected. REFERENCES 1. Thilander B, Jakobsson SO. Local factors in impaction of maxillary canines. Acta Odontol Stand 1968;26:145-68. 2. Ericson S, Kurol J. Radiographic assessment of maxillary canine eruption in children with clinical signs of eruption disturbance. Eur J Orthod 1986;8:133-40. 3. Hitchin AD. The impacted maxillary canine. Br Dent J 1956;100:1-14. 4. Rayne J. The unerupted maxillary canine. Dent Pratt 1969; 19:194-204. 5. Howard RD. The displaced maxillary canine positional variations associated with incisor resorption. Trans Br Sot Study Orthod 1970-1;57:149-57. 6. Ericson S, Kurol J. Radiographic examination of ectopically erupting maxillary canines. AM J ORTHOD DENTOFAC ORTHOP 1987;91:483-92. 7. van der Linden FPGM, Dutterloo HS. Development of the human dentition. An atlas. Hagerstown, Maryland: Harper & Row, 1976. 8. Ericson S, Kurol J. Resorption of permanent incisors due to eruption of maxillary canines. A radiographic study. Angle Orthod 1987;57:332-46.
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9. Marks SC Jr, Cahill DR. Regional control by the dental follicle of alterations in alveolar bone metabolism during tooth eruption. J Oral Path01 1987:16:164-9. 10. Ericson S, Kurol J. Longitudinal study and analysis of clinical supervision of maxillary canine eruption. Community Dent Oral Epidemiol 1986;14:172-6. Il. Iikubo M. Korsell S, Omnell K-A. Description of a new cephalostat and its performance. Dentomaxillofac Radio1 1975: 4~25-9. K, Bent DH. Statis12. Nie N, Hull CH, Jenkins JG, Steinbrenner tical package for the social sciences. 2nd ed. New York: McGraw-Hill, 1975. 13. Gustafson G, Koch G. Age estimation up to 16 years of age based on dental development. Odontol Revy 1974;25:297-306. 14. Hays WL. Statistics for the social sciences. 2nd ed. New York: Holt, Rinehart & Winston, 1973:414-24. 15. Guilford JP. Introduction to analysis of variance. In: Fundamental statistics in psychology and education. 4th ed. New York: McGraw-Hill, 1965:268-303. 16. Coupland MA. Localisation of misplaced maxillary canines. Orthopantomograph and P.A. skull views compared. Br J Orthod 1984:11:27-32. 17. McDavid WD. Tronje G, Welander U, Morris CR, Nummikoski P. Imaging characteristics of seven panoramic X-ray units. J Int Assoc Dent Maxillofac Radio1 1985[suppl 81. 18. Townend PI. Resorption of the roots of upper incisor teeth due to misplaced canine teeth. Trans Br Sot Study Orthod 1967: 74-7. 19. Sasakura H. Yoshida T, Murayama S, Hanada K, Nakajima T. Root resorption of upper pennanent incisor caused by impacted canine. An analysis of 23 cases. Int J Oral Surg 1984;13:299306. 20. Kettle MA. Treatment of the unerupted maxillary canine. Trans Br Sot Study Orthod 1957:74-84.
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Dewel BF. The upper cuspid. Its development and impaction. Angle Orthod 1949;19:79-90. Bass TB. Observations on the misplaced upper canine tooth. Dent Pratt 1967;18:25-33. Trlnkmann J. Zur Indikation der operativen Freilegung und Anschlingung retinierter oberer Schneideund Eckzlhne. Dtsch Zahnaerztl Z 1967;22:695-8. Richardson A, McKay C. Delayed eruption of maxillary canine teeth. Part 1. Aetiology and diagnosis. Proc Br Paedod Sot 1982;12:15-25. Jacoby H. The etiology of maxillary canine impactions. t\M J ORTHOD 198384: 125-32. Cugat Femandez de la CA, Asensi CC, Gascon MF. Aplicacion de la tomogralia multidirectional al estudio de piezas dentarias incluidas. Acta Estomatokjgica Valenciana 1986; I :3- 10. Ericson S, Kurol J. CT diagnosis of ectopicaily erupting maxillary canines. A case report. Eur J Orthod 1988: 10: 115-2 1. Hotz R. Orthodontics in daily practice. Bern, Switzerland: Hans Huber, 1974:340-53. Moss JP. The unerupted canine. Dent Pratt 1972:22:241-8. Kisling E, Ravn E. Two cases of marked pressure resorption in maxillary incisors. Tandlaegebladet 1977;81: 153-5. Brown ID, Matthews RW. Apical resorption of a maxillary lateral incisor from a misplaced canine in 17-year old. A case report. Br J Orthod 1981;8:3-5.
Reprint requests to: Dr. Jiiri Kurol Department of Orthodontics The Institute for Postgraduate Jimvagsgatan 9 S-552 55 Jijnkoping Sweden
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