- Email: [email protected]
Contributions of reformatted computed tomography and panoramic radiography in the localization of third molars relative to the maxillary sinus
Contributions of reformatted computed tomography and panoramic radiography in the localization of third molars relative to the maxillary sinus Annabelle Bouquet, DDS,a Jean-Loup Coudert, DDS, PhD,b Denis Bourgeois, MD, DDS, PhD,c Jean-Francxois Mazoyer, DDS,d and Denis Bossard, DDS,e Lyon, France LYON UNIVERSITY AND ST. JEAN MEDICAL CENTER OF LYON
Objective. The aim of this clinical study was to seek an answer to the question ofwhether CT gives better qualitative and quantitative information as compared to panoramic radiograph when deciding on extraction of upper impacted third molars. Study. The study concerned 34 third molars appearing in direct relation with the sinus on the panoramic radiograph for which a CT scan had been recommended. For each case, the panoramic radiograph was compared with the CT scan for 5 evaluation criteria. Results. The CT scan was more precise than the panoramic radiograph by 1.67 mm for measurement of the level of impaction of the third molar, by 12.448 for measurement of the third molar displacement, by 0.74 mm for bone height separating the third molar roots and the sinus, and by 2.26 mm for the length of roots in the sinus. The CT scan was equally accurate for measurement of the distance separating the crowns of second and third molars in 34 cases. Conclusions. This study confirms the gain in precision for the CT scan as compared with conventional techniques. The CT scan therefore presents advantages when considering the extraction of upper third molars by providing both qualitative and quantitative information liable to bear on the diagnosis and therapeutic management. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;98:342-7)
The removal of upper third molars is a procedure commonly performed to treat evolutive accidents of these teeth. When this surgical procedure is performed, buccosinusal communications and displacements of the tooth into the sinus may occur.1-7 Many isolated cases of displacement of the third molar have been reported in the literature.8-11 Different studies have shown that such accidents are common. The frequency reported varies from 0.6% to 3.8%.12-17 Further, a third of the oroantral communications have been reported to be caused by the extraction of maxillary sinusal teeth.18 Although a panoramic radiograph is of considerable help to the dental surgeon for a preoperative control, it may present certain deficiencies in terms of distortion and blurred images. The reformatted computed tomography (CT), linked with the evolution of technologies,
a
Resident, Division of Oral Surgery, Lyon University Dental Hospital. b Professor, Division of Oral Surgery, Lyon University Dental Hospital. c Professor, Department of Public Health, Lyon University Dental Hospital. d Resident, Department of Radiology. e Resident, St. Jean Medical Center of Lyon. Received for publication Feb 28, 2003; returned for revision Apr 4, 2003; accepted for publication Feb 24, 2004. 1079-2104/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.tripleo.2004.02.082
342
could represent in this context a quality alternative for a better management of this surgical procedure. Does the CT study give better qualitative and quantitative information as compared to panoramic radiograph when deciding on extraction of upper impacted third molars? MATERIAL AND METHODS In the surgical department of the Lyon University Faculty of Odontology, Lyon, France, 22 CT studies were prescribed in the period 1996-2002 to determine the position of the upper third molars in relation to the sinus and for which the indication for extraction was set. The study concerns 34 third molars appearing in direct relation with the sinus on the panoramic film. The patients, aged 15 to 59 years, included 13 women and 9 men. During this period, the different successive CT scans used were of the type SOMATOM + 4 A (Siemens, Erlangen, Germany). During these examinations, the maxillae were separated by a compress which the patient bites on. The reference plane was the occlusion plane of the maxilla concerned so as to limit radial artifacts to the plane of the coronal radiopaque substances. The acquisition parameters were 140 kV and 129 mA. The slice thickness was 0.5 mm, the table increment was 6 mm/ second, and the FOV was 180 mm. The reconstruction filter goes up to 90 HU. Rotation time was 1.5 seconds. The examination was performed by spiralled acquisition on contiguous sections every 1 mm. The acquisitions were completed by multiplanar reconstructions
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using Dentascan (Siemens) software: cross-sectional reconstructions, tangential reconstructions, and panoramic-type section. Dentascan allows one to obtain sections perpendicular to the crest. The study is sent to the practitioners in the form of classical argentic reprograph plates or as a CDROM. The magnification on the panoramic radiograph is 1.3. The magnification is compensated for by dividing the measurements on the panoramic radiograph by 1.3. Evaluation of the contribution of the reformatted CT compared with the conventional panoramic radiograph rests on the comparison for each case included in the study, panoramic versus CT. The judgement criteria to evaluate the impacted teeth were: The length of the roots in the sinus (mm); ie, the root length measured between the apex of the roots and the floor of the sinus. From this length, 3 groups could be defined: Group 1 has a length in the sinus markedly >1 mm, for group 2 the length is 1 mm, and for group 3 the length is markedly \1 mm. The distance between the crown of the second molar in relation to the crown of the third molar (mm); ie, the length measured between 2 horizontals passing by the cuspid apices of the 7 and the other by the cuspid apices of the 8. Two groups are therefore defined: one where the distance is # 10 mm of bone and the other where the distance is >10 mm. The bone height separating the roots and the sinus (mm); ie, the bone thickness measured between the apex of the roots and the floor of the sinus. Three groups emerge: one where the roots are separated from the sinus only by a mucosa with no bone, one where the bone thickness is # 1mm, and one where the thickness is >1 mm. The impaction level of the wisdom teeth (mm); ie, the bone thickness situated between the cuspid apices of the third molar and the buccal mucosa. Class B concerns the submucosal teeth with no bone and class C comprises the intrabone teeth with more than 0 mm bone. The displacement of the third molar in relation to the vertical (degrees); ie, the angle measured between a vertical line and the long axis of the wisdom tooth. When the tooth is situated distally, the angle is negative, and a tooth situated mesially has a positive angle. The vertical is between 108 and +108. Statistical analysis relied on a descriptive analysis produced for the main study variables. Comparisons of means on matched series were performed (Student’s t-test). RESULTS For the impaction level of third molar (Table I), on the panoramic radiograph 15 teeth were class B
Bouquet et al 343
(submucosal) and 19 class C (intraosseous). On the CT study, 10 teeth were class B and 24 class C. For the distance separating the crowns of the second molar and the third molar, on the panoramic radiograph 14 third molar were separated by 0 to 10 mm from the second molar and 20 separated by more than 10 mm of bone. On the CT study, 21 teeth were separated by 10 mm or less and 13 teeth by more than 10 mm of bone. For the displacement of the third molar in relation to the vertical, on the panoramic radiograph 5 teeth were distally displaced, 5 vertically displaced, and 24 mesially displaced. On the CT scan, 5 teeth were distally displaced, 11 vertically displaced, 15 mesially displaced, and 3 not measurable. For the bone height separating the roots from the sinus, on the panoramic radiograph 20 teeth had a bone thickness equal to 0 mm, 7 teeth 0 and 1 mm, and 7 teeth over 1 mm. On the CT study, 4 teeth had a bone thickness of 0 mm, 22 teeth between 0 and 1 mm, and 8 teeth over 1 mm. For the length of the roots in the sinus, on the panoramic radiograph 30 teeth had a length of over 1 mm, 3 teeth equal to 1 mm, and 1 tooth over 1 mm. On the CT study, 23 teeth had a length of over 1 mm, 4 teeth equal to 1 mm, and 7 teeth above 1 mm. For the impaction level of right and left upper third molars (Table II), on the panoramic radiograph the maximum was 20 mm. On the CT study, the maximum was 7.5 mm. For the distance separating the crowns of second molar and the third molar, on the panoramic radiograph the maximum was 19 mm and on the CT study 18 mm. For the displacement of the third molar in relation to the vertical, on the panoramic radiograph the maximum was 708 and on the CT scan 648. For the bone height separating the roots from the sinus, on the panoramic radiograph the maximum was 3 mm and on the CT scan 2 mm. For the length of roots in the sinus, on the panoramic radiograph,the maximum was 13 mm and on the CT scan 15 mm. For the impaction level of the third molar (Table III), the differences obtained between panoramic radiograph and CT results were 1.67 6 0.49 mm (P \ .001). The difference obtained was significant between the 2 methods. For the distance separating the crowns of second molar and third molar, the differences obtained between panoramic radiograph and CT scan measurements were 2.2 6 5.83 mm (P [ .001). The difference obtained between the 2 methods was nonsignificant. For third molar displacement in relation to the vertical, the differences between the measurements obtained by the 2 methods were 12.44 6 2.148 (P \ .001). The difference was significant between the 2 methods. For the bone height separating the roots from the sinus, the differences between the 2 methods were
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344 Bouquet et al Table I. Position of the 34 upper-third molars Evaluation parameters
Radiographic technique
Impaction level of right and left third molars (mm) Panoramic radiography CT scan Distance between crowns of second and third molars (mm) Panoramic radiography CT scan Displacement of the third molar in relation to vertical (degrees) Panoramic radiography CT scan Bone height separating roots from sinus (mm) Panoramic radiography CT scan Length of roots in sinus (mm)
Group 1
Group 2
Class B
Class C
15
19
10 Distance # 10 mm
Group 3
Group 4
24 Distance [ 10 mm
14
20
21 Distal displacement
13 Vertical
Mesial displacement
Not measurable
5
5
24
0
5 Bone thickness = 0 mm 20
11 0 \ bone thickness # 1 mm 7
15 bone t hickness > 1 mm 7
3
4 Length > 1 mm
22 Length = 1 mm
8 Length \ 1 mm
Panoramic radiography CT scan
30
3
1
23
4
7
Table II. Description analysis of the minima, maxima, and means for each evaluation criterion Panoramic radiography Evaluation parameters
M
m
Mean 6 SD
Impaction level of right and left third molars (mm) Displacement of the third molar in relation to vertical (degrees) Length of roots in sinus (mm) Bone height separating roots from sinus (mm) Distance between crowns of second and third molars (mm)
20 70
0 0
3.7 6 5 25 6 15.7
13 3 19
0 0 0
4.9 6 3.7 0.6 6 0.85 10.8 6 4.3
0.74 6 0.11 mm (P \ .001). The difference was significant. For the length of roots in the sinus, the differences were 2.26 6 0.32 mm (P \ .001). The difference was significant. Case of Mr. X, 27 years A panoramic radiograph and a CT scan were taken. It can be noticed that the panoramic radiograph presents some drawbacks. Indeed, the third dimension escapes analysis, and mesiodistal evaluation is possible but approximate. Third molar displacement in relation to the vertical is inexact. On the panoramic
CT scan M
m
Mean 6 SD
7.5 64
0 0
3.2 6 2.9 19.9 6 18.4
15 2 18
0 0 2
4.6 6 4.2 0.7 6 0.62 10.1 6 4.1
radiograph, the left third molar appears vertical (Fig 1), whereas on the CT it is situated mesially by 308 (Fig 2). CT clearly shows the presence of the roots of the left third molar in the sinus with a length of 9 mm, while it is only 2 mm on the panoramic radiograph. The 3-D reconstruction (Fig 3) provides more precise information in the localization of the third molar relative to the maxillary sinus. DISCUSSION When deciding on avulsion of the third molar in the maxillary region, one should examine attentively all the area around it for this region has complex anatomical
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Bouquet et al 345
Table III. Recapitulation of the statistical analysis concerning the comparison of means on matched series Evaluation parameters
Mean difference 6 Standard Deviation
Impaction level of right and left third molars Distance between crowns of second and third molars Displacement of the third molar in relation to vertical Bone height separating roots from sinus Length of roots in sinus
1.63 2.2 12.44 0.74 2.26
6 6 6 6 6
0.49 mm 5.83 mm 2.148 0.11 mm 0.32 mm
Significance threshold P \ .001* P [ .001** P \ .001* P \ .001* P \ .001*
*Significant difference. **Nonsignificant difference.
Fig 1. Panoramic radiograph of impacted upper third molar. It appears vertical and its roots extend 2 mm into the sinus.
structures.19-21 Thus, panoramic radiograph presents certain drawbacks: Superposition of structures, which become uninterpretable when conditions are pathological and the structures deviate from the normal.22 Formation of ghost images on the side opposite the object.23-24 Mesiodistal and vertical enlargement. Third dimension not appearing. Blurring of some structures. Spreading of a curved structure over a plane. Evaluation of maxillary sinuses necessarily illusory when one compares the reduced width of the section thickness and the mean depth of a sinus (40 to 50 mm).25 The data of our study (Table I) clearly point up the fact that, in certain cases, the CT study allowed invalidation of the direct relation between the root of the tooth and the sinus. Indeed, 30 panoramic
radiographs showed the sinus projecting on to the roots of the teeth, thereby leading it to be supposed that the roots penetrate into the sinus, whereas the CT showed the sinus in front of the roots in 7 of these 30 cases. On the other hand, the apices of the third molar roots vaguely overlapped the sinus on the panoramic radiograph whereas on the CT these roots could be clearly seen penetrating the sinus, covered with a fine film of bone. Without the CT, the surgeon would have taken far fewer precautions and that might have resulted in an oroantral communication or, worse, a projection of the tooth into the sinus. Table II shows the differences between the results obtained by panoramic radiograph and those by CT. Thus, the maximal displacement was 708 for the panoramic radiograph and 648 for the CT. The tooth appeared more inclined on the panoramic. The deformations on the panoramic radiograph are due to the projection of a volume on to a plane surface. Such deformations are not seen on the CT. For the parameter
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346 Bouquet et al
Fig 2. Tangential CT scan of the left impacted upper third molar, situated 308 mesially and the roots of which extend 9 mm into the sinus.
Fig 3. A 3-dimensional CT scan reconstruction of impacted left upper third molar, second molar, left maxillary sinus (blue) and bone (brown).
‘‘distance separating the crowns of second and third molars,’’ the 2 methods have the same performance. For the other 4 criteria, the difference is significant. Panoramic radiograph is less reliable and gives less accurate measurements. In the context of this study (Table III), the CT proved more accurate by 1.67 mm than panoramic radiograph for the measurement of the impaction level of third molar. The CT was equally good as the panoramic radiograph for measurement of the distance separating the 2 crowns for 34 cases. The CT was more exact by 12.448 than panoramic radiograph for measurement of the bone height separating the third molar roots and the sinus. The CT was also more accurate by 2.26 mm for the length of roots in the sinus. For the parameter ‘‘distance separating second and third molars’’ (Table III), the 2 methods gave similar results. They were equally good for 34 cases, but that does not mean that for a larger number of cases the difference would not be significant. For the other 4 parameters, the CT was better than
panoramic radiograph with measurements that were more exact and closer to anatomical reality. The CT study, by showing with greater precision the anatomical situation, is an aid for diagnosis and therapy. The procedures performed during extraction can be carried out with a better mental visualization of the anatomical obstacles and of the 3-dimensional position of the third molar. This study confirms the gain in precision with the CT in relation to conventional techniques. The CT study therefore is of interest for the extraction of upper third molars by the contribution of both quantitative and qualitative information that may influence diagnosis and therapy. Indeed, of the 34 cases of extraction of a sinusal third molar where a CT was realized, no buccosinusal communication and no sinusal projection resulted. Further, statistical analysis confirmed the clinical study. Indeed, it demonstrated that CT is more precise for the different measurements than is panoramic radiography. Only 1 parameter gave similar results. Panoramic radiograph is equally as reliable as CT study for the criterion ‘‘distance separating the crowns of second and third molar.’’ The 3-dimensional reconstruction allows greater accuracy of measurements and an improved visualization of the anatomical situation of the third molar.
REFERENCES 1. Thoma KH. Oral surgery. 5th ed. St Louis: Mosby; 1969. p. 308-9. 2. Atterbury R. Maxillary sinus perforation. CDS Rev 1991;84: 32-7. 3. Bradley PF. Foreign bodies in the para-nasal sinuses as a complication of facial injuries. Br J Oral Surg 1971;8:192. 4. Harrisson FDM. Oro-antral fistula. Br J Clin Pract 1961;15:169. 5. Sailer HF. Oral surgery for the general dentist. Color atlas of dental medicine. Stuttgart: Thie`me; 1999. 6. Parker W, Dunn JK. Foreign bodies of dental origin in maxillary sinus. Acta otolaryngol (Suppl 84):1. 7. Weisenbauch JM. The impacted third molar. Complications and their treatement. J Md State Dental Assoc 1977;20.
OOOOE Volume 98, Number 3 8. Barclay JK. Root in the maxillary sinus. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1987;64:162-4. 9. Major A. A dental root in the ostium of the maxillary antrum. Br J Oral Maxillofac Surg 1985;23:67-73. 10. Patel M. Accidental displacement of impacted maxillary third molars. Br Dent J 1994;177:57-9. 11. Oberman M, Horowitz I, Ramon Y. Accidental displacement of impacted maxillary third molars. Int J Oral Maxillofac Surg 1986; 15:756-8. 12. Killey HC, Kay LW. Possible sequelae when a tooth or root is disloged into the maxillary sinus. Br Dent J 1964;116:73-7. 13. Lee FMS. The displaced root in the maxillary sinus. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1970;29:491-504. 14. Chiapasco M, Decicco L. Marrone. Side effects and complications associated with third molar surgery. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1993;76(4):412-20. 15. Hirata Y. A clinical investigation of oro-maxillary sinus-perforation due to tooth extraction. Kokubyo Gakkaı¨ Zasshi 2001;68: 249-53. 16. Wachter R. Complication of surgical wisdom tooth removal of the maxilla. Fortschr Kiefer Gesichtschir 1995;40:128-33. 17. Sisk AL, Hammer WB, Shelton WD, Joy ED. Complications following removal of impacted third molars: the role of the experience of the surgeon. J Oral Maxillofac Surg 1986;44:855-9. 18. Killey HC, Kay LW. Teeth or roots in the maxillary sinus. Bristol: Wright; 1975. p. 71-89.
Bouquet et al 347 19. Terakado M. Diagnostic imaging with newly developed ortho cubic super-high resolution computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:509-18. 20. DelBalso AM, Hall RE, MarGarone JE. Radiographic evaluation of maxillofacial imaging. Philadelphia: Saunders; 1990. p. 35-49. 21. Poyton HG, Pharoah MJ. Oral radiology. Toronto: Decker; 1989. p. 74-81. 22. Langlais RP. Diagnostic imaging of the jaws. Malvern: Williams & Wilkins; 1995. 23. Higashi T, Iguchi M. ‘‘Ghost images’’ in panoramic radiograph. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1983;55:221. 24. Knight N. Reverse images and ghost of Panorex radiograph. J Am Soc Prev Dent 1973;3:53. 25. Langland OE, Sippy FH. Anatomic structures as visualized on the orthopantomogram. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1968;26:475.
Reprint requests: Dr. Annabelle Bouquet SCTD, Service de Chirurgie 6-8 place Depe´ret 69007 LYON France [email protected]
Objective. The aim of this clinical study was to seek an answer to the question ofwhether CT gives better qualitative and quantitative information as compared to panoramic radiograph when deciding on extraction of upper impacted third molars. Study. The study concerned 34 third molars appearing in direct relation with the sinus on the panoramic radiograph for which a CT scan had been recommended. For each case, the panoramic radiograph was compared with the CT scan for 5 evaluation criteria. Results. The CT scan was more precise than the panoramic radiograph by 1.67 mm for measurement of the level of impaction of the third molar, by 12.448 for measurement of the third molar displacement, by 0.74 mm for bone height separating the third molar roots and the sinus, and by 2.26 mm for the length of roots in the sinus. The CT scan was equally accurate for measurement of the distance separating the crowns of second and third molars in 34 cases. Conclusions. This study confirms the gain in precision for the CT scan as compared with conventional techniques. The CT scan therefore presents advantages when considering the extraction of upper third molars by providing both qualitative and quantitative information liable to bear on the diagnosis and therapeutic management. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;98:342-7)
The removal of upper third molars is a procedure commonly performed to treat evolutive accidents of these teeth. When this surgical procedure is performed, buccosinusal communications and displacements of the tooth into the sinus may occur.1-7 Many isolated cases of displacement of the third molar have been reported in the literature.8-11 Different studies have shown that such accidents are common. The frequency reported varies from 0.6% to 3.8%.12-17 Further, a third of the oroantral communications have been reported to be caused by the extraction of maxillary sinusal teeth.18 Although a panoramic radiograph is of considerable help to the dental surgeon for a preoperative control, it may present certain deficiencies in terms of distortion and blurred images. The reformatted computed tomography (CT), linked with the evolution of technologies,
a
Resident, Division of Oral Surgery, Lyon University Dental Hospital. b Professor, Division of Oral Surgery, Lyon University Dental Hospital. c Professor, Department of Public Health, Lyon University Dental Hospital. d Resident, Department of Radiology. e Resident, St. Jean Medical Center of Lyon. Received for publication Feb 28, 2003; returned for revision Apr 4, 2003; accepted for publication Feb 24, 2004. 1079-2104/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.tripleo.2004.02.082
342
could represent in this context a quality alternative for a better management of this surgical procedure. Does the CT study give better qualitative and quantitative information as compared to panoramic radiograph when deciding on extraction of upper impacted third molars? MATERIAL AND METHODS In the surgical department of the Lyon University Faculty of Odontology, Lyon, France, 22 CT studies were prescribed in the period 1996-2002 to determine the position of the upper third molars in relation to the sinus and for which the indication for extraction was set. The study concerns 34 third molars appearing in direct relation with the sinus on the panoramic film. The patients, aged 15 to 59 years, included 13 women and 9 men. During this period, the different successive CT scans used were of the type SOMATOM + 4 A (Siemens, Erlangen, Germany). During these examinations, the maxillae were separated by a compress which the patient bites on. The reference plane was the occlusion plane of the maxilla concerned so as to limit radial artifacts to the plane of the coronal radiopaque substances. The acquisition parameters were 140 kV and 129 mA. The slice thickness was 0.5 mm, the table increment was 6 mm/ second, and the FOV was 180 mm. The reconstruction filter goes up to 90 HU. Rotation time was 1.5 seconds. The examination was performed by spiralled acquisition on contiguous sections every 1 mm. The acquisitions were completed by multiplanar reconstructions
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using Dentascan (Siemens) software: cross-sectional reconstructions, tangential reconstructions, and panoramic-type section. Dentascan allows one to obtain sections perpendicular to the crest. The study is sent to the practitioners in the form of classical argentic reprograph plates or as a CDROM. The magnification on the panoramic radiograph is 1.3. The magnification is compensated for by dividing the measurements on the panoramic radiograph by 1.3. Evaluation of the contribution of the reformatted CT compared with the conventional panoramic radiograph rests on the comparison for each case included in the study, panoramic versus CT. The judgement criteria to evaluate the impacted teeth were: The length of the roots in the sinus (mm); ie, the root length measured between the apex of the roots and the floor of the sinus. From this length, 3 groups could be defined: Group 1 has a length in the sinus markedly >1 mm, for group 2 the length is 1 mm, and for group 3 the length is markedly \1 mm. The distance between the crown of the second molar in relation to the crown of the third molar (mm); ie, the length measured between 2 horizontals passing by the cuspid apices of the 7 and the other by the cuspid apices of the 8. Two groups are therefore defined: one where the distance is # 10 mm of bone and the other where the distance is >10 mm. The bone height separating the roots and the sinus (mm); ie, the bone thickness measured between the apex of the roots and the floor of the sinus. Three groups emerge: one where the roots are separated from the sinus only by a mucosa with no bone, one where the bone thickness is # 1mm, and one where the thickness is >1 mm. The impaction level of the wisdom teeth (mm); ie, the bone thickness situated between the cuspid apices of the third molar and the buccal mucosa. Class B concerns the submucosal teeth with no bone and class C comprises the intrabone teeth with more than 0 mm bone. The displacement of the third molar in relation to the vertical (degrees); ie, the angle measured between a vertical line and the long axis of the wisdom tooth. When the tooth is situated distally, the angle is negative, and a tooth situated mesially has a positive angle. The vertical is between 108 and +108. Statistical analysis relied on a descriptive analysis produced for the main study variables. Comparisons of means on matched series were performed (Student’s t-test). RESULTS For the impaction level of third molar (Table I), on the panoramic radiograph 15 teeth were class B
Bouquet et al 343
(submucosal) and 19 class C (intraosseous). On the CT study, 10 teeth were class B and 24 class C. For the distance separating the crowns of the second molar and the third molar, on the panoramic radiograph 14 third molar were separated by 0 to 10 mm from the second molar and 20 separated by more than 10 mm of bone. On the CT study, 21 teeth were separated by 10 mm or less and 13 teeth by more than 10 mm of bone. For the displacement of the third molar in relation to the vertical, on the panoramic radiograph 5 teeth were distally displaced, 5 vertically displaced, and 24 mesially displaced. On the CT scan, 5 teeth were distally displaced, 11 vertically displaced, 15 mesially displaced, and 3 not measurable. For the bone height separating the roots from the sinus, on the panoramic radiograph 20 teeth had a bone thickness equal to 0 mm, 7 teeth 0 and 1 mm, and 7 teeth over 1 mm. On the CT study, 4 teeth had a bone thickness of 0 mm, 22 teeth between 0 and 1 mm, and 8 teeth over 1 mm. For the length of the roots in the sinus, on the panoramic radiograph 30 teeth had a length of over 1 mm, 3 teeth equal to 1 mm, and 1 tooth over 1 mm. On the CT study, 23 teeth had a length of over 1 mm, 4 teeth equal to 1 mm, and 7 teeth above 1 mm. For the impaction level of right and left upper third molars (Table II), on the panoramic radiograph the maximum was 20 mm. On the CT study, the maximum was 7.5 mm. For the distance separating the crowns of second molar and the third molar, on the panoramic radiograph the maximum was 19 mm and on the CT study 18 mm. For the displacement of the third molar in relation to the vertical, on the panoramic radiograph the maximum was 708 and on the CT scan 648. For the bone height separating the roots from the sinus, on the panoramic radiograph the maximum was 3 mm and on the CT scan 2 mm. For the length of roots in the sinus, on the panoramic radiograph,the maximum was 13 mm and on the CT scan 15 mm. For the impaction level of the third molar (Table III), the differences obtained between panoramic radiograph and CT results were 1.67 6 0.49 mm (P \ .001). The difference obtained was significant between the 2 methods. For the distance separating the crowns of second molar and third molar, the differences obtained between panoramic radiograph and CT scan measurements were 2.2 6 5.83 mm (P [ .001). The difference obtained between the 2 methods was nonsignificant. For third molar displacement in relation to the vertical, the differences between the measurements obtained by the 2 methods were 12.44 6 2.148 (P \ .001). The difference was significant between the 2 methods. For the bone height separating the roots from the sinus, the differences between the 2 methods were
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344 Bouquet et al Table I. Position of the 34 upper-third molars Evaluation parameters
Radiographic technique
Impaction level of right and left third molars (mm) Panoramic radiography CT scan Distance between crowns of second and third molars (mm) Panoramic radiography CT scan Displacement of the third molar in relation to vertical (degrees) Panoramic radiography CT scan Bone height separating roots from sinus (mm) Panoramic radiography CT scan Length of roots in sinus (mm)
Group 1
Group 2
Class B
Class C
15
19
10 Distance # 10 mm
Group 3
Group 4
24 Distance [ 10 mm
14
20
21 Distal displacement
13 Vertical
Mesial displacement
Not measurable
5
5
24
0
5 Bone thickness = 0 mm 20
11 0 \ bone thickness # 1 mm 7
15 bone t hickness > 1 mm 7
3
4 Length > 1 mm
22 Length = 1 mm
8 Length \ 1 mm
Panoramic radiography CT scan
30
3
1
23
4
7
Table II. Description analysis of the minima, maxima, and means for each evaluation criterion Panoramic radiography Evaluation parameters
M
m
Mean 6 SD
Impaction level of right and left third molars (mm) Displacement of the third molar in relation to vertical (degrees) Length of roots in sinus (mm) Bone height separating roots from sinus (mm) Distance between crowns of second and third molars (mm)
20 70
0 0
3.7 6 5 25 6 15.7
13 3 19
0 0 0
4.9 6 3.7 0.6 6 0.85 10.8 6 4.3
0.74 6 0.11 mm (P \ .001). The difference was significant. For the length of roots in the sinus, the differences were 2.26 6 0.32 mm (P \ .001). The difference was significant. Case of Mr. X, 27 years A panoramic radiograph and a CT scan were taken. It can be noticed that the panoramic radiograph presents some drawbacks. Indeed, the third dimension escapes analysis, and mesiodistal evaluation is possible but approximate. Third molar displacement in relation to the vertical is inexact. On the panoramic
CT scan M
m
Mean 6 SD
7.5 64
0 0
3.2 6 2.9 19.9 6 18.4
15 2 18
0 0 2
4.6 6 4.2 0.7 6 0.62 10.1 6 4.1
radiograph, the left third molar appears vertical (Fig 1), whereas on the CT it is situated mesially by 308 (Fig 2). CT clearly shows the presence of the roots of the left third molar in the sinus with a length of 9 mm, while it is only 2 mm on the panoramic radiograph. The 3-D reconstruction (Fig 3) provides more precise information in the localization of the third molar relative to the maxillary sinus. DISCUSSION When deciding on avulsion of the third molar in the maxillary region, one should examine attentively all the area around it for this region has complex anatomical
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Bouquet et al 345
Table III. Recapitulation of the statistical analysis concerning the comparison of means on matched series Evaluation parameters
Mean difference 6 Standard Deviation
Impaction level of right and left third molars Distance between crowns of second and third molars Displacement of the third molar in relation to vertical Bone height separating roots from sinus Length of roots in sinus
1.63 2.2 12.44 0.74 2.26
6 6 6 6 6
0.49 mm 5.83 mm 2.148 0.11 mm 0.32 mm
Significance threshold P \ .001* P [ .001** P \ .001* P \ .001* P \ .001*
*Significant difference. **Nonsignificant difference.
Fig 1. Panoramic radiograph of impacted upper third molar. It appears vertical and its roots extend 2 mm into the sinus.
structures.19-21 Thus, panoramic radiograph presents certain drawbacks: Superposition of structures, which become uninterpretable when conditions are pathological and the structures deviate from the normal.22 Formation of ghost images on the side opposite the object.23-24 Mesiodistal and vertical enlargement. Third dimension not appearing. Blurring of some structures. Spreading of a curved structure over a plane. Evaluation of maxillary sinuses necessarily illusory when one compares the reduced width of the section thickness and the mean depth of a sinus (40 to 50 mm).25 The data of our study (Table I) clearly point up the fact that, in certain cases, the CT study allowed invalidation of the direct relation between the root of the tooth and the sinus. Indeed, 30 panoramic
radiographs showed the sinus projecting on to the roots of the teeth, thereby leading it to be supposed that the roots penetrate into the sinus, whereas the CT showed the sinus in front of the roots in 7 of these 30 cases. On the other hand, the apices of the third molar roots vaguely overlapped the sinus on the panoramic radiograph whereas on the CT these roots could be clearly seen penetrating the sinus, covered with a fine film of bone. Without the CT, the surgeon would have taken far fewer precautions and that might have resulted in an oroantral communication or, worse, a projection of the tooth into the sinus. Table II shows the differences between the results obtained by panoramic radiograph and those by CT. Thus, the maximal displacement was 708 for the panoramic radiograph and 648 for the CT. The tooth appeared more inclined on the panoramic. The deformations on the panoramic radiograph are due to the projection of a volume on to a plane surface. Such deformations are not seen on the CT. For the parameter
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Fig 2. Tangential CT scan of the left impacted upper third molar, situated 308 mesially and the roots of which extend 9 mm into the sinus.
Fig 3. A 3-dimensional CT scan reconstruction of impacted left upper third molar, second molar, left maxillary sinus (blue) and bone (brown).
‘‘distance separating the crowns of second and third molars,’’ the 2 methods have the same performance. For the other 4 criteria, the difference is significant. Panoramic radiograph is less reliable and gives less accurate measurements. In the context of this study (Table III), the CT proved more accurate by 1.67 mm than panoramic radiograph for the measurement of the impaction level of third molar. The CT was equally good as the panoramic radiograph for measurement of the distance separating the 2 crowns for 34 cases. The CT was more exact by 12.448 than panoramic radiograph for measurement of the bone height separating the third molar roots and the sinus. The CT was also more accurate by 2.26 mm for the length of roots in the sinus. For the parameter ‘‘distance separating second and third molars’’ (Table III), the 2 methods gave similar results. They were equally good for 34 cases, but that does not mean that for a larger number of cases the difference would not be significant. For the other 4 parameters, the CT was better than
panoramic radiograph with measurements that were more exact and closer to anatomical reality. The CT study, by showing with greater precision the anatomical situation, is an aid for diagnosis and therapy. The procedures performed during extraction can be carried out with a better mental visualization of the anatomical obstacles and of the 3-dimensional position of the third molar. This study confirms the gain in precision with the CT in relation to conventional techniques. The CT study therefore is of interest for the extraction of upper third molars by the contribution of both quantitative and qualitative information that may influence diagnosis and therapy. Indeed, of the 34 cases of extraction of a sinusal third molar where a CT was realized, no buccosinusal communication and no sinusal projection resulted. Further, statistical analysis confirmed the clinical study. Indeed, it demonstrated that CT is more precise for the different measurements than is panoramic radiography. Only 1 parameter gave similar results. Panoramic radiograph is equally as reliable as CT study for the criterion ‘‘distance separating the crowns of second and third molar.’’ The 3-dimensional reconstruction allows greater accuracy of measurements and an improved visualization of the anatomical situation of the third molar.
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Reprint requests: Dr. Annabelle Bouquet SCTD, Service de Chirurgie 6-8 place Depe´ret 69007 LYON France [email protected]