European Journal of Orthodontics 14 (1992) 296-301
i 1992 European Orthodontic Society
The application of computerized tomography (CT) in cases of impacted maxillary canines G. P. F. Schmuth\ M. Freisfeld, 0. K6ster*\ and H. Schuller** 'Department of Orthodontics and ""Department of Radiology, University of Bonn, Germany
A comparison is made between conventional X-rays and computerized tomography (CT) based on eight patients with thirteen impacted upper permanent canines. The use of CT yields information which is much more detailed than that observed on conventional X-rays, such as: pathological resorption on adjacent teeth caused by aberrant canines; the localization of the injury and the position of the canine in relation to one or both incisors. The amount of radiation per exposure is still rather high for the CT (Koster and Ewen, 1986). Further research is necessary in order to reduce this exposure and to determine the appropriate and most effective use of CT in the dental field. SUMMARY
Introduction
Methodology The CT examinations were performed with a Tomoscan 350 HS (Philips). A lateral scanogram was utilized for aligning the slice parallel to the hard palate. Contiguous scans with a
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The failure of the maxillary permanent canines to erupt and their consequent retention in a palatal or buccal position in relation to the dental arch result in an increased risk of resorption of the roots of the permanent incisors. The perceptibility of such root resorption is observed much more easily and in much more detail with the use of CT than with conventional X-rays (Ericson and Kurd, 1986). This fact is supported by a comparison of previous reports, based on conventional X-rays, concerning the frequency of incisor root resorption observed with the CT (Ericson and Kurol, 1987a). Several local and hereditary aetiological factors which may be responsible for impacted canines are briefly discussed. The early detection of canine aberration is important in order to avoid the risk of root resorption of the adjacent permanent incisors (Ericson and Kurol, 1987b). The usefulness of various X-ray techniques in defining the real position of the impacted canine is examined. It is proposed that the CT will prove to be the most effective in this respect, and in indicating the presence and degree of root resorption on the adjacent teeth.
Figure 1 Topogram shows situation of the CT slices.
slice thickness of 1.5 mm were made. Other technical factors included a 120 kv X-ray beam and a routine mAs of 482. The reconstruction was done by a bone detail algorithm (CF6) using high resolution technique (macroview). The pixel spacing was 0.3 mm. The images were displayed with a window of 4000 HU. A clinical examination only infrequently reveals the asymmetry of unerupted canines or the incorrect position of one or both lateral incisors. The use of CT produces a graduated grey
297
COMPUTER TOMOGRAPHY AND IMPACTED CANINES Table 1 (a) Position of 13 maxillary canines in patients ranging from 11 to 29 years of age. (b) The width of the dental follicle of malpositioned upper canines. (a) Canine malposition
(b) Width of dental follicle
Patient
Age
13
23
13/23
F.C
11 12 15 17 17 21 25 29
b b
m b
• u •
0
n.v
H.C. H.A H.N K.O
H.C. K.R. H.G. Total
0 0
%
D
•
o
m->o
m-> o
O
o 7
0
•
6
• = regular, b = buccal, m = middle, o = oral, u = uncertain, n.v. = non-visible, #$:2mm, D ^ 2 m m , O = 2 m m
Figure 2 (a) X-ray of KR: Resorption at the root of 12 is suspected (f). (b) CT of KR. no resorption of the lateral incisor root 12, only contact 13 with 12 {]).
incisor roots, while some are oriented to the vestibular aspect. This oral or vestibular orientation of impacted canines would result in an overlapping canine/incisor image on panoramic
Table 2 (a) Root resorptions on upper incisors. Comparison between conventional X-ray versus CT (b) Resorption of the deciduous canine root: conventional X-ray versus CT. (b) Deciduous canine (a) Incisors Patient
Age
Overlapping
X-ray: resorption
F.C
11 12 15
XXX
Rf
H.C. H.A. K.O. H.C. K.R. H.G.
17 17 21 25 29
C
—
63
53
63
E
R R R
R E
R X X X X X
H.N
53
w
CT
X-ray
CT: resorption
R R
X = overlapping; C = contact, E-extraction R = resorption, R?= resorption uncertain, — = no resorption.
C R C C C
R
R
ft
ft R
R
R
R R
R R
R R
R R R
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image and eliminates the blurring of structures and the overlapping of adjacent teeth seen on conventional X-rays (Linke and Pfeiler, 1987; Sitzmann, 1988). Transverse CT images, 1.5 mm in thickness, reveal circular defects on the incisor roots. These transverse sections are illustrated on a survey X-ray image in Fig. 1. Conventional X-ray images are two-dimensional and, thus, resorption on the oral or vestibular surfaces of the incisor roots cannot be detected. With panorex images, the position of impacted canines can be ascertained by the tube-shift technique. Most of the impacted canines are oriented to the oral surface of the
298
X-rays. It is this situation which is a key indicator for the use of CT. Aetiological factors in canine impacrion CT was used on eight cases with 13 aberrant canines in order to discern root resorptions not only on the lateral but also on the oral and vestibular surfaces of the affected incisors. (Table 1). Resorption was suspected in one case because
of the interruption of the lamina dura and of the periodontal space. There was almost no overlapping between the impacted canines and the incisor roots. CT did not verify the suspicion; it indicated no root resorption (Fig. 2a,b). This finding supports Ericson's and Kurd's (1987a) statement that the interruption of the lamina dura and of the periodontal space is not always associated with root resorption. Cystic degeneration of the dental follicle (more than 2-3 mm in space) has been considered a possible cause of root resorption. The amount of the consequent three-dimensional enlargement of the dental follicle cannot be estimated with the two-dimensional images of conventional X-rays (Tronje, 1982). This task is suitable for the CT. The CT examination of the eight cases in this study yielded no case in which cystic degeneration was associated with root resorption. The examination did indicate, however, that, as the age of the patient increased, a process of involution of the dental follicle took place (Table 1). As noted previously, CT reveals an accurate picture of the real position of an impacted canine. This is particularly true for contact situations between incisors and aberrant canines, especially in the oro-vestibular direction, which cannot be determined with conventional X-rays (Table 2). The failure of conventional X-rays to ascertain contact situations and consequent incisor root resorption led to the hypothesis that unresorbed deciduous canines were one possible cause of impacted permanent canines. The present study refutes this hypothesis. In two cases, one of an 11-year-old girl and the other of a 12-year-old boy, the CT image revealed root resorption of the deciduous canines, which is normal at this age. In the former case, the mesiopalatal portion of both deciduous canine roots are resorbed. The right impacted canine is positioned buccally to the rotated lateral incisor, while the left is in central position (Fig. 3a). Conventional X-ray images of the same area revealed no resorption (Fig. 3b,c). A comparison of conventional X-ray and CT images in relation to the determination of deciduous root resorption before the age of 17 years shows the same dichotomy in results (see Table 2b). The extent of overlap between impacted canines and the roots of lateral and central incisors
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Figure 3 (a) CT of FC: Resorption of mesiopalatal portion of both deciduous canine roots (f). Right ectopic canine buccal to the rotated lateral incisor, left canine in central position (|) (b) Panorex of FC: at 53, 63 no root resorption is to be seen. Ectopic 13 reaching the pulp of 12 (|) (c) Extracted 53 of FC: resorption at the mesio-palatal root surface (f).
G. P. F. SCHMUTH ET AL.
299
COMPUTER TOMOGRAPHY AND IMPACTED CANINES
Table 3
Extent of overlapping. 12
Patient
Incisor age
F.C. HC HA. H.N KO. HC. KR. H.G.
11 12 15 17 17 21 25 29
m
11 h
t
m
21 h
t
m
22 h
t
m
h
t
X X X
m = Moderate, h = half, t = total, C = contact, • = non-overlapping, X = overlapping
reveals resorption (Fig. 4a,b).
on
all
four
incisors
Discussion
The results of the present study demonstrate the significant advantage of the use of CT in cases of impacted canines. If an impacted canine causes resorption of the adjacent incisor root, a patient would be unaware of a problem with the use of conventional X-rays, even if the root is already resorbed to such a degree that the incisor may be lost. Therefore, early detection is of the greatest importance and is now possible through the application of CT, irrespective of the site of
Figure 4 (a) CT of KO: Left lateral incisor root in this area almost resorbed (f). Right central incisor shows resorption from disto-palatal (]). (b) Closer to the apex: resorption of all four incisors (|).
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varies from case to case (Table 3). The extent of the overlap depends not only on the position of the canine, but also on projection variations. The gradual overlapping begins with contact (c), reaches to the pulp (m) (see Fig. 3b), then covers the pulp (h), until there is a total overlap of the lateral incisor root (see Fig. 5a). Overlapping between impacted canines and central incisors was mostly moderate. Half overlapping was observed in one case. There are great variations in the correlation between the degree of overlapping and the probability of root resorption. (Table 4). One patient, 17-year-old K..O. who was undergoing orthodontic treatment, showed overlapping on all four incisors to a different extent. The CT
300
G. P. F. SCHMUTH ET AL.
Figure 5 (a) OPG of HA: root 12 totally overlapped by ectopic 13, and covering the pulp of 11. No resorption at the incisor teeth to detect (|) (b) CT of HA: flattened root contour palatal of 12 indicates resorption (|). (c) CT (sec reconstruction). HA: The ectopic right canine resorbing the lateral incisor some millimeters below the apex.
resorption and especially if secondary reconstructions are used. The CT study found no relationships between the extent of dental overlap when assessed by panoramic radiographs, and the amount of root resorption when assessed by means of CT scanning. A similar extent of panoramic dental overlapping showed root resorption of the lateral incisor in the CT scans of one case (Fig. 5ac), whereas the second case demonstrated a
contact between the malposed canine and the root of the upper left central incisor with no root resorption (Fig. 6a,b). Further investigations are required to determine the indications for the application of computerized tomography in the field of orthodontics, where time, cost, and radiation factors should be taken in to consideration. Until now only one case has been presented by Ericson and Kurol (1988). Conclusion
If resorption is revealed by the application of CT, orthodontic movement of the impacted canine, in order to separate it from the incisor root, could be initiated in time to prevent further root resorption. This would allow for restoration of the incisor root. Due to the radiation hazard, the application of CT should be restricted, at the present time, to cases where there is a suspicion of root resorption of the permanent incisors, caused by the adjacent impacted canines.
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Figure 6 (a) OPG of FH: root 22 (||) totally overlapped by ectopic 23, no resorption at the incisor teeth to detect (f). (b) CT of FH: no resorption of the incisor roots, but only contact of the canine crown with the central incisor root (|).
301
COMPUTER TOMOGRAPHY AND IMPACTED CANINES
Table 4 Correlation between overlapping (conventional X-ray) and root resorptions (CT). Overlapping Patient F.C. H.C. HA. HN.
K.O. H.C. K.R. H.G.
Incisor age 11 12 15 17 17 21 25 29
12
11
CT resorption 21
22
h m t h
m
t
C
m t
12 C C R R R
m m
II
21
22
C C R C
R C
C C
m = Moderate, h = half, t = total, C = contact, R = resorption
Address for correspondence
References Ericson S, Kurol J 1986 Radiographic assessment of maxillary canine eruption in children with clinical signs of eruption disturbance. European Journal of Orthodontics 8: 133-140 Ericson S, Kurol J 1987a Radiographic examination of ectopically erupting maxillary canines. American Journal of Orthodontics and Dentiofacial Orthopedics 91: 483-492
Sitzmann F 1988 Bildgebende Verfahren in der Zahn-, Mund und Kieferheilkunde. In: W. Ketterl (ed.) Grundlagen der Zahn-, Mund- und Kieferheilkunde. Bd.I, Hrsg Urban und Schwarzenberg, Wien-Innsbruck Tronje G 1982 Image distortion in rotational panoramic radiography Dento-Maxillo-Facial Radiology 11 Suppl. 3
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Dr Marita Freisfeld Poliklinik fur Kieferorthopadie Universitat Bonn WelschnonnenstraBe 17 D- 5300 Bonn 1 Germany
Ericson S, Kurol J 1987b Incisor resorption caused by maxillary cuspids, A radiographic study. Angle Orthodontist 57: 332-346 Ericson S, Kurol J 1988 CT diagnosis of ectopically erupting maxillary canines—a case report. European Journal of Orthodontics 10: 115-120 Koster O, Ewen K 1986 Zur Strahlenbelastung bei der hochauflosenden Computertomographie des Felsenbeines. Digit Bilddiagn 6. 176-180 Linke G, Pfeiler M 1987 Grundlagen und Verfahren der Rontgen-Computertomographie. In: Frommhold W (ed ) Radiologische Diagostik in Klinik und Praxis, Bd. I. Georg Thieme, Stuttgart-New York
i 1992 European Orthodontic Society
The application of computerized tomography (CT) in cases of impacted maxillary canines G. P. F. Schmuth\ M. Freisfeld, 0. K6ster*\ and H. Schuller** 'Department of Orthodontics and ""Department of Radiology, University of Bonn, Germany
A comparison is made between conventional X-rays and computerized tomography (CT) based on eight patients with thirteen impacted upper permanent canines. The use of CT yields information which is much more detailed than that observed on conventional X-rays, such as: pathological resorption on adjacent teeth caused by aberrant canines; the localization of the injury and the position of the canine in relation to one or both incisors. The amount of radiation per exposure is still rather high for the CT (Koster and Ewen, 1986). Further research is necessary in order to reduce this exposure and to determine the appropriate and most effective use of CT in the dental field. SUMMARY
Introduction
Methodology The CT examinations were performed with a Tomoscan 350 HS (Philips). A lateral scanogram was utilized for aligning the slice parallel to the hard palate. Contiguous scans with a
Downloaded from by guest on January 27, 2015
The failure of the maxillary permanent canines to erupt and their consequent retention in a palatal or buccal position in relation to the dental arch result in an increased risk of resorption of the roots of the permanent incisors. The perceptibility of such root resorption is observed much more easily and in much more detail with the use of CT than with conventional X-rays (Ericson and Kurd, 1986). This fact is supported by a comparison of previous reports, based on conventional X-rays, concerning the frequency of incisor root resorption observed with the CT (Ericson and Kurol, 1987a). Several local and hereditary aetiological factors which may be responsible for impacted canines are briefly discussed. The early detection of canine aberration is important in order to avoid the risk of root resorption of the adjacent permanent incisors (Ericson and Kurol, 1987b). The usefulness of various X-ray techniques in defining the real position of the impacted canine is examined. It is proposed that the CT will prove to be the most effective in this respect, and in indicating the presence and degree of root resorption on the adjacent teeth.
Figure 1 Topogram shows situation of the CT slices.
slice thickness of 1.5 mm were made. Other technical factors included a 120 kv X-ray beam and a routine mAs of 482. The reconstruction was done by a bone detail algorithm (CF6) using high resolution technique (macroview). The pixel spacing was 0.3 mm. The images were displayed with a window of 4000 HU. A clinical examination only infrequently reveals the asymmetry of unerupted canines or the incorrect position of one or both lateral incisors. The use of CT produces a graduated grey
297
COMPUTER TOMOGRAPHY AND IMPACTED CANINES Table 1 (a) Position of 13 maxillary canines in patients ranging from 11 to 29 years of age. (b) The width of the dental follicle of malpositioned upper canines. (a) Canine malposition
(b) Width of dental follicle
Patient
Age
13
23
13/23
F.C
11 12 15 17 17 21 25 29
b b
m b
• u •
0
n.v
H.C. H.A H.N K.O
H.C. K.R. H.G. Total
0 0
%
D
•
o
m->o
m-> o
O
o 7
0
•
6
• = regular, b = buccal, m = middle, o = oral, u = uncertain, n.v. = non-visible, #$:2mm, D ^ 2 m m , O = 2 m m
Figure 2 (a) X-ray of KR: Resorption at the root of 12 is suspected (f). (b) CT of KR. no resorption of the lateral incisor root 12, only contact 13 with 12 {]).
incisor roots, while some are oriented to the vestibular aspect. This oral or vestibular orientation of impacted canines would result in an overlapping canine/incisor image on panoramic
Table 2 (a) Root resorptions on upper incisors. Comparison between conventional X-ray versus CT (b) Resorption of the deciduous canine root: conventional X-ray versus CT. (b) Deciduous canine (a) Incisors Patient
Age
Overlapping
X-ray: resorption
F.C
11 12 15
XXX
Rf
H.C. H.A. K.O. H.C. K.R. H.G.
17 17 21 25 29
C
—
63
53
63
E
R R R
R E
R X X X X X
H.N
53
w
CT
X-ray
CT: resorption
R R
X = overlapping; C = contact, E-extraction R = resorption, R?= resorption uncertain, — = no resorption.
C R C C C
R
R
ft
ft R
R
R
R R
R R
R R
R R R
Downloaded from by guest on January 27, 2015
image and eliminates the blurring of structures and the overlapping of adjacent teeth seen on conventional X-rays (Linke and Pfeiler, 1987; Sitzmann, 1988). Transverse CT images, 1.5 mm in thickness, reveal circular defects on the incisor roots. These transverse sections are illustrated on a survey X-ray image in Fig. 1. Conventional X-ray images are two-dimensional and, thus, resorption on the oral or vestibular surfaces of the incisor roots cannot be detected. With panorex images, the position of impacted canines can be ascertained by the tube-shift technique. Most of the impacted canines are oriented to the oral surface of the
298
X-rays. It is this situation which is a key indicator for the use of CT. Aetiological factors in canine impacrion CT was used on eight cases with 13 aberrant canines in order to discern root resorptions not only on the lateral but also on the oral and vestibular surfaces of the affected incisors. (Table 1). Resorption was suspected in one case because
of the interruption of the lamina dura and of the periodontal space. There was almost no overlapping between the impacted canines and the incisor roots. CT did not verify the suspicion; it indicated no root resorption (Fig. 2a,b). This finding supports Ericson's and Kurd's (1987a) statement that the interruption of the lamina dura and of the periodontal space is not always associated with root resorption. Cystic degeneration of the dental follicle (more than 2-3 mm in space) has been considered a possible cause of root resorption. The amount of the consequent three-dimensional enlargement of the dental follicle cannot be estimated with the two-dimensional images of conventional X-rays (Tronje, 1982). This task is suitable for the CT. The CT examination of the eight cases in this study yielded no case in which cystic degeneration was associated with root resorption. The examination did indicate, however, that, as the age of the patient increased, a process of involution of the dental follicle took place (Table 1). As noted previously, CT reveals an accurate picture of the real position of an impacted canine. This is particularly true for contact situations between incisors and aberrant canines, especially in the oro-vestibular direction, which cannot be determined with conventional X-rays (Table 2). The failure of conventional X-rays to ascertain contact situations and consequent incisor root resorption led to the hypothesis that unresorbed deciduous canines were one possible cause of impacted permanent canines. The present study refutes this hypothesis. In two cases, one of an 11-year-old girl and the other of a 12-year-old boy, the CT image revealed root resorption of the deciduous canines, which is normal at this age. In the former case, the mesiopalatal portion of both deciduous canine roots are resorbed. The right impacted canine is positioned buccally to the rotated lateral incisor, while the left is in central position (Fig. 3a). Conventional X-ray images of the same area revealed no resorption (Fig. 3b,c). A comparison of conventional X-ray and CT images in relation to the determination of deciduous root resorption before the age of 17 years shows the same dichotomy in results (see Table 2b). The extent of overlap between impacted canines and the roots of lateral and central incisors
Downloaded from by guest on January 27, 2015
Figure 3 (a) CT of FC: Resorption of mesiopalatal portion of both deciduous canine roots (f). Right ectopic canine buccal to the rotated lateral incisor, left canine in central position (|) (b) Panorex of FC: at 53, 63 no root resorption is to be seen. Ectopic 13 reaching the pulp of 12 (|) (c) Extracted 53 of FC: resorption at the mesio-palatal root surface (f).
G. P. F. SCHMUTH ET AL.
299
COMPUTER TOMOGRAPHY AND IMPACTED CANINES
Table 3
Extent of overlapping. 12
Patient
Incisor age
F.C. HC HA. H.N KO. HC. KR. H.G.
11 12 15 17 17 21 25 29
m
11 h
t
m
21 h
t
m
22 h
t
m
h
t
X X X
m = Moderate, h = half, t = total, C = contact, • = non-overlapping, X = overlapping
reveals resorption (Fig. 4a,b).
on
all
four
incisors
Discussion
The results of the present study demonstrate the significant advantage of the use of CT in cases of impacted canines. If an impacted canine causes resorption of the adjacent incisor root, a patient would be unaware of a problem with the use of conventional X-rays, even if the root is already resorbed to such a degree that the incisor may be lost. Therefore, early detection is of the greatest importance and is now possible through the application of CT, irrespective of the site of
Figure 4 (a) CT of KO: Left lateral incisor root in this area almost resorbed (f). Right central incisor shows resorption from disto-palatal (]). (b) Closer to the apex: resorption of all four incisors (|).
Downloaded from by guest on January 27, 2015
varies from case to case (Table 3). The extent of the overlap depends not only on the position of the canine, but also on projection variations. The gradual overlapping begins with contact (c), reaches to the pulp (m) (see Fig. 3b), then covers the pulp (h), until there is a total overlap of the lateral incisor root (see Fig. 5a). Overlapping between impacted canines and central incisors was mostly moderate. Half overlapping was observed in one case. There are great variations in the correlation between the degree of overlapping and the probability of root resorption. (Table 4). One patient, 17-year-old K..O. who was undergoing orthodontic treatment, showed overlapping on all four incisors to a different extent. The CT
300
G. P. F. SCHMUTH ET AL.
Figure 5 (a) OPG of HA: root 12 totally overlapped by ectopic 13, and covering the pulp of 11. No resorption at the incisor teeth to detect (|) (b) CT of HA: flattened root contour palatal of 12 indicates resorption (|). (c) CT (sec reconstruction). HA: The ectopic right canine resorbing the lateral incisor some millimeters below the apex.
resorption and especially if secondary reconstructions are used. The CT study found no relationships between the extent of dental overlap when assessed by panoramic radiographs, and the amount of root resorption when assessed by means of CT scanning. A similar extent of panoramic dental overlapping showed root resorption of the lateral incisor in the CT scans of one case (Fig. 5ac), whereas the second case demonstrated a
contact between the malposed canine and the root of the upper left central incisor with no root resorption (Fig. 6a,b). Further investigations are required to determine the indications for the application of computerized tomography in the field of orthodontics, where time, cost, and radiation factors should be taken in to consideration. Until now only one case has been presented by Ericson and Kurol (1988). Conclusion
If resorption is revealed by the application of CT, orthodontic movement of the impacted canine, in order to separate it from the incisor root, could be initiated in time to prevent further root resorption. This would allow for restoration of the incisor root. Due to the radiation hazard, the application of CT should be restricted, at the present time, to cases where there is a suspicion of root resorption of the permanent incisors, caused by the adjacent impacted canines.
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Figure 6 (a) OPG of FH: root 22 (||) totally overlapped by ectopic 23, no resorption at the incisor teeth to detect (f). (b) CT of FH: no resorption of the incisor roots, but only contact of the canine crown with the central incisor root (|).
301
COMPUTER TOMOGRAPHY AND IMPACTED CANINES
Table 4 Correlation between overlapping (conventional X-ray) and root resorptions (CT). Overlapping Patient F.C. H.C. HA. HN.
K.O. H.C. K.R. H.G.
Incisor age 11 12 15 17 17 21 25 29
12
11
CT resorption 21
22
h m t h
m
t
C
m t
12 C C R R R
m m
II
21
22
C C R C
R C
C C
m = Moderate, h = half, t = total, C = contact, R = resorption
Address for correspondence
References Ericson S, Kurol J 1986 Radiographic assessment of maxillary canine eruption in children with clinical signs of eruption disturbance. European Journal of Orthodontics 8: 133-140 Ericson S, Kurol J 1987a Radiographic examination of ectopically erupting maxillary canines. American Journal of Orthodontics and Dentiofacial Orthopedics 91: 483-492
Sitzmann F 1988 Bildgebende Verfahren in der Zahn-, Mund und Kieferheilkunde. In: W. Ketterl (ed.) Grundlagen der Zahn-, Mund- und Kieferheilkunde. Bd.I, Hrsg Urban und Schwarzenberg, Wien-Innsbruck Tronje G 1982 Image distortion in rotational panoramic radiography Dento-Maxillo-Facial Radiology 11 Suppl. 3
Downloaded from by guest on January 27, 2015
Dr Marita Freisfeld Poliklinik fur Kieferorthopadie Universitat Bonn WelschnonnenstraBe 17 D- 5300 Bonn 1 Germany
Ericson S, Kurol J 1987b Incisor resorption caused by maxillary cuspids, A radiographic study. Angle Orthodontist 57: 332-346 Ericson S, Kurol J 1988 CT diagnosis of ectopically erupting maxillary canines—a case report. European Journal of Orthodontics 10: 115-120 Koster O, Ewen K 1986 Zur Strahlenbelastung bei der hochauflosenden Computertomographie des Felsenbeines. Digit Bilddiagn 6. 176-180 Linke G, Pfeiler M 1987 Grundlagen und Verfahren der Rontgen-Computertomographie. In: Frommhold W (ed ) Radiologische Diagostik in Klinik und Praxis, Bd. I. Georg Thieme, Stuttgart-New York
