DENTOALVEOLAR SURGERY
Measurement of the Lingual Position of the Lower Third Molar Roots Using Cone-Beam Computed Tomography € Yusuf Emes, DDS, PhD,* Bora Oncu, DDS,y Buket Aybar, DDS, PhD,z Nazar Al-Badri, DDS,x Halim Is¸sever, MD, PhD,k Belir Atalay, DDS, PhD,{ and Serhat Yalc¸ın, DDS, PhD# Purpose:
The aim of this study was to evaluate the distance between the roots of the impacted third molars and the floor of the mouth to predict the risk of lingual root displacement during surgery.
Materials and Methods:
Thirty-one patients (5 men and 26 women) were evaluated for this study using cone-beam computed tomography (CBCT). The teeth were grouped according to their position on the orthopantomogram as vertical, mesioangular, horizontal, and distoangular. The distance between 2 points on the roots and lingual soft tissues was measured.
Results:
The average distance between the apex of the root, which is in the most lingual position, and the lingual cortical plate was 1.03 mm. The average distance between the most lingual point on the apical half of the root, which is in closer proximity, and the lingual cortical plate was 0.65 mm.
Conclusion:
The distance between the apices and the lingual plate is very short, which allows displacement of broken roots or teeth, especially when the lingual plate is perforated. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 73:13-17, 2015
Extraction of mandibular third molars is one of the most common surgical procedures in the field of oral and maxillofacial surgery.1 As in all surgical procedures, various complications related to third molar surgery have been reported in the literature.2-6 These complications include infection, alveolar osteitis, inferior alveolar nerve injury, lingual nerve injury, and clinically important hemorrhage. Mandibular fractures, osteomyelitis, and displacement of a tooth or root fragments into fascial spaces have been reported as rare complications, the incidences of which are unknown.7-24
A thin lingual cortical plate or a fenestration in the lingual cortical plate and poor surgical technique are the major factors for the displacement of teeth or tooth fragments into the lingual soft tissues. Cone-beam computed tomography (CBCT) is an imaging technique in which volumetric data from the patient are reconstructed using algorithms similar to those used in conventional CT.25 Although CBCT has a higher image noise and is not suitable for soft tissue assessment, it is widely used as a maxillofacial imaging tool owing to its high spatial resolution and lower radiation exposure compared with conventional CT.
Received from the Istanbul University, Istanbul, Turkey.
#Professor, Department of Oral and Maxillofacial Surgery, Faculty
*Associate Professor, Department of Oral and Maxillofacial
of Dentistry.
Surgery, Faculty of Dentistry.
Address correspondence and reprint requests to Dr Emes:
yResearch Assistant, Department of Oral and Maxillofacial
Department of Oral and Maxillofacial Surgery, Faculty of Dentistry,
Surgery, Faculty of Dentistry.
Istanbul University, Istanbul, Turkey; e-mail: [email protected]
zProfessor, Department of Oral and Maxillofacial Surgery, Faculty
Received September 25 2013
of Dentistry.
Accepted June 30 2014
xResearch Assistant, Department of Oral and Maxillofacial Surgery, Faculty of Dentistry.
Ó 2015 American Association of Oral and Maxillofacial Surgeons 0278-2391/14/01120-3
kProfessor, Department of Public Health, Faculty of Medicine.
http://dx.doi.org/10.1016/j.joms.2014.06.460
{Associate Professor, Department of Oral and Maxillofacial Surgery, Faculty of Dentistry.
13
14 In this pilot study, CBCT was used to evaluate the proximity of lower third molar roots to the lingual cortex, which can be used to determine the potential risk of root displacement during lower third molar surgery.
Materials and Methods This study was approved by the ethical committee of Istanbul University (Istanbul, Turkey; project number 723). CBCT images of 32 impacted lower third molar teeth of 31 patients (5 men and 26 women) were evaluated for this study. The data were collected from images of patients who had undergone CBCT imaging for various reasons, such as impacted teeth, dental implants, and cysts of the jaws. Ectopic teeth and teeth with cystic lesions were excluded from the study. The CBCT mandibular scans were acquired using a Soredex Scanora 3D Cone Beam device (Soredex, Helsinki, Finland) operated at 85 kV and 12.5 mA using a charged coupled device sensor. The slice thickness was 0.35 mm and the thinly sliced trans-planar images were assessed using the OnDemand3DApp 1.0.9.1138 software program (Cybermed, Inc, Irvine, CA). Each measurement was performed independently and recorded twice by 2 surgeons. Then, the average of the 2 measurements was calculated and evaluated. EVALUATION OF IMAGES
In a darkened room, the CBCT images were shown in random order on a 24-inch monitor. An evaluation was performed independently by 2 trained oral and maxillofacial surgeons who were experienced in the radiographic evaluation of maxillofacial anatomy. The teeth were grouped according to their positions on the orthopantomogram as vertical, mesioangular, horizontal, and distoangular. Two measurements were performed for each tooth. If 1 tooth had more than 1 root, the root in the most lingual position was considered: 1) the distance from the root apex of the tooth, which is in the most lingual position, to the lingual cortical plate and 2) the distance from the most lingual point on the apical half of the root to the lingual cortical plate (Fig 1). STATISTICAL ANALYSIS
Comparisons between groups were performed using the c2 test and PASS 2000 (NCSS, Kaysville, UT).
Results The measurements showed an average distance of 1.03 mm between the apices of the lower third molars and the lingual soft tissues. The average distance between the most lingually positioned point on the apical half of the root and the lingual soft tissues was
CBCT MEASUREMENT OF LOWER THIRD MOLAR ROOTS
0.65 mm. The relation between the roots and the lingual soft tissues were grouped into 3 types: relation type A, in which there was an amount of bone between the root and the soft tissues (Fig 2A); relation type B, in which there was 0 mm of bone between the root and the soft tissues (Fig 2B); and relation type C, in which the root protruded into the soft tissues (Fig 2C). Four root apices had values of 0 mm (12.5% of total roots evaluated; relation type B) and 4 apices had negative measurement values (12.5% of total roots evaluated; relation type C). In total, 25% of root apices had a type B or type C relation with the floor of the mouth. When the apical halves of the roots were evaluated (distance from the most lingual point on the apical half of the root to the lingual cortical plate), 5 roots were in contact with the soft tissues (measurement, 0 mm; 15.62% of total roots evaluated; relation type B) and 5 roots protruded into the soft tissues (negative values; 15.62% of total roots evaluated; relation type C). In total, 34.38% of the roots were found to be in contact with the lingual soft tissues. Of the 31 patients evaluated, 3 patients were younger than 20 years, and only 1 tooth in these 3 patients had incomplete root formation. This tooth had a type A relation in the apices and the apical halves of the roots. The teeth also were grouped according to their positions (vertical, horizontal, mesioangular, or distoangular). When the roots were compared according to the positions of the teeth evaluated (vertical, horizontal, mesioangular, or distoangular), there were no statistically significant differences among groups in their relation to the lingual soft tissues (P = 0.453 AL distance; P = 0.548 RL distance).
Discussion Accidental displacement of lower third molars or root fragments into facial spaces is rare, and only limited information about its incidence and management is found in the literature. However, when it occurs, the most affected sites are the floor of the mouth and the submandibular and pterygomandibular spaces.26 Lingually located teeth, a thin lingual cortical plate or a fenestration in the lingual plate with tooth exposure, and application of excessive force during extraction have been reported to be among the main causes for this type of complication.1,7-26 Although displacement of teeth or teeth fragments during surgery into the surrounding tissues is a rare complication, Campbell and Costello27 stated that these complications may be underreported owing to practitioners retrieving their own displaced fragments without referral. CBCT has several advantages over conventional CT, such as lower radiation dose,25 high spatial
15
EMES ET AL
FIGURE 1. Left, Distance from the apex of the root to the lingual tissues. Right, Distance from the most lingual point on the apical half of the root to the lingual tissues. AL, distance from the root apex of the tooth in the most lingual position to the lingual cortical plate; L, lingual; RL, distance from the most lingual point on the apical half of the root to the lingual cortical plate; V, vestibule. Emes et al. CBCT Measurement of Lower Third Molar Roots. J Oral Maxillofac Surg 2015.
resolution,28 better-quality view of the dental structures,29,30 and lower cost. CBCT has been proposed as a more accurate method of imaging the relation between the inferior alveolar nerve and the third molar, because it provides the dentist with more accurate information than conventional imaging techniques.31 The accuracy of CBCT images is a matter of question, and several studies have been conducted to determine the accuracy of CBCT in evaluating the location
of the inferior alveolar nerve.32 Tantanapornkul et al32 reported a sensitivity of 93% and a specificity of 23% in determining the inferior alveolar nerve exposure during third molar removal. In a similar study, Ghaeminia et al31 reported a sensitivity of 96% and a specificity of 23%. These advantages of CBCT formed the basis of the present study. A review of the literature disclosed no studies performed on this subject. In this study, the relation
FIGURE 2. A, Type A relation, in which there is bone between the root and the floor of the mouth. B, Type B relation, in which the root communicates with but does not protrude into the floor of the mouth. C, Type C relation, in which the root does not protrude into the soft tissues. Emes et al. CBCT Measurement of Lower Third Molar Roots. J Oral Maxillofac Surg 2015.
16 between the roots of the impacted lower third molars and the floor of the mouth was evaluated. A second point, other than the root apex, also was taken into consideration, because the authors believe that a fenestration in the apex region is not the only predisposing factor in the occurrence of root displacement into the soft tissues. The present findings show that 25% of the apices of impacted teeth were in contact with the mouth floor. If a root in the lingual position is fractured during lower third molar surgery, there may not be enough bone volume between the fractured segment and the floor of the mouth. Further, there may be a fenestration in the lingual cortical plate, which renders the root in contact with the lingual soft tissues. Therefore, an improperly applied force vector by the surgeon can displace the root fragment into the soft tissues. Recently, Gerlach et al33 compared the measurements of CBCT images with histologic sections in 2 cadaver skulls and recommended that a deviation of 0.76 mm could be considered when evaluating CBCT images to prevent injury to the inferior alveolar nerve. The present results show a bone thickness ranging from 0.65 to 1.03 mm lingual to the lower third molar roots. Actual bone thickness may be even thinner than the average measurements made on CBCT images, considering the conclusions stated by Gerlach et al. Only 1 of the 32 evaluated teeth had an incomplete root formation, and this tooth had a type A relation in the root apices and the apical halves of the roots. The sample of teeth with underdeveloped roots in the present study was insufficient to compare distances between teeth with developed apices and those with underdeveloped apices for their relations with the lingual soft tissues. The presence of a lingual undercut is an anatomic property that also can affect the distance between the third molar roots and the lingual soft tissues, depending on the vestibular and lingual position and the axis of the tooth. Lingual undercuts can be observed in the posterior mandible. Although the presence of a lingual undercut was not evaluated in this study, a presence of 36 to 39% in the molar region has been reported in the literature.34,35 Braut et al32 conducted a study using CBCT and evaluated the buccal and lingual bone thickness in the posterior mandible. That study showed an increase in buccal bone thickness in the molar tooth region compared with the premolar region; however, no such differences were observed for lingual bone thickness. The aim of this pilot study was to measure the anatomic proximity of the roots of impacted third molars to the lingual soft tissues to evaluate the possible risk of displacement of fractured root segments lingually. It must be noted that the authors of this study
CBCT MEASUREMENT OF LOWER THIRD MOLAR ROOTS
do not advocate the use of CBCT before all impacted third molar surgeries. This is the reason the radiographs of patients who were examined for conditions other than impacted third molars were used in the present study. Because the evaluated teeth were not subjected to surgery, it would be proper to state that the present findings support only a theoretical risk of lingual root displacement during extraction. Although the sample is small, the larger percentage of contact between the root and the floor of the mouth implies that practitioners should be very careful when dealing with fractured roots of third molars. Further studies comparing CBCT findings with actual measurements on cadavers may help resolve the problems regarding this risk.
References 1. Huang IY, Wu CW, Worthington P: The displaced lower third molar: A literature review and suggestions for management. J Oral Maxillofac Surg 65:1186, 2007 2. Boffano P, Ferretti F, Giunta G, et al: Surgical removal of a third molar at risk for mandibular pathologic fracture: Case report and clinical considerations. Oral Surg Oral Med Oral Pathol Oral Radiol 114:e1, 2012 3. Lata J, Tiwari AK: Incidence of lingual nerve paraesthesia following mandibular third molar surgery. Natl J Maxillofac Surg 2:137, 2011 4. Aznar-Arasa L, Figueiredo R, Gay-Escoda C: Iatrogenic displacement of lower third molar roots into the sublingual space: Report of 6 cases. J Oral Maxillofac Surg 70:e107, 2012 5. Figueiredo R, Valmaseda-Castell on E, Formoso-Senande MF, et al: Delayed-onset infections after impacted lower third molar extraction: Involved bacteria and sensitivity profiles to commonly used antibiotics. Oral Surg Oral Med Oral Pathol Oral Radiol 114:43, 2012 6. Yalcin S, Aktas I, Emes Y, et al: Accidental displacement of a highspeed handpiece bur during mandibular third molar surgery: A case report. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 105:e29, 2008 7. Bui CH, Seldin EB, Dodson TB: Types, frequencies and risk factors for complications after third molar extraction. J Oral Maxillofac Surg 61:1379, 2003 8. Sisk AL, Hammer WB, Shelton DW, et al: Complications following removal of impacted third molars: The role of the experience of the surgeon. J Oral Maxillofac Surg 44:855, 1986 9. Benediktsdottir IS, Wenzel A, Peterson JK, et al: Mandibular third molar removal: Risk indicators for extended operating time, postoperative pain and complications. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 97:438, 2004 10. Chiapasco M, De Cicco L, Marrone G: Side effects and complications associated with third molar surgery. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 76:412, 1993 11. De Boer MP, Raghoebar GM, Staganga B: Complications after third molar extraction. Quintessence Int 26:779, 1995 12. Goldberg MH, Nemarich AN, Marco WP: Complications after mandibular third molar surgery: A statistical analysis of 500 consecutive procedures in private practice. J Am Dent Assoc 111:277, 1985 13. Osborn TP, Frederickson G Jr, Small IA, et al: A prospective study of comparisons related to mandibular third molar surgery. J Oral Maxillofac Surg 43:767, 1985 14. Bloomer CR: Alveolar osteitis prevention by immediate placement of medicated packing. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 90:282, 2000 15. Bruce RA, Frederickson GC, Small GS: Age of patients and morbidity associated with mandibular third molar surgery. J Am Dent Assoc 101:240, 1980
EMES ET AL 16. Libersa P, Roze D, Cachart T, et al: Immediate and late mandibular fractures after third molar removal. J Oral Maxillofac Surg 60:163, 2002 17. Alling C, Alling R: Indications for management of impacted teeth, in Alling C, Helfrick I, Alling R (eds). Impacted Teeth. Philadelphia, PA, Saunders, 1993. pp 43–64 18. Bataineh AB: Sensory nerve impairment following mandibular third molar surgery. J Oral Maxillofac Surg 59:1012, 2001 19. Lopes V, Mumenya R, Feinmann C, et al: Third molar surgery: An audit of the indications for surgery, post-operative complaints and patient satisfaction. Br J Oral Maxillofac Surg 33:33, 1995 20. Middlehurst RJ, Barker GR, Rood JP: Postoperative morbidity with mandibular third molar surgery: A comparison of two techniques. J Oral Maxillofac Surg 46:474, 1988 21. Mason DA: Lingual nerve damage following lower third molar surgery. Int J Oral Maxillofac Surg 17:290, 1988 22. Blackburn CW, Bramley PA: Lingual nerve damage associated with removal of lower third molars. Br Dent J 167:103, 1989 23. Robinson PP, Smith KG: Lingual nerve damage during lower third molar removal: A comparison of two surgical methods. Br Dent J 180:456, 1996 24. Haug RH, Perrott DH, Gonzalez MC, et al: The American Association of Oral and Maxillofacial Surgeons age-related third molar study. J Oral Maxillofac Surg 63:1106, 2005 25. Ludlow JB, Davies-Ludlow LE, Brooks SL, et al: Dosimetry of three CBCT devices for oral and maxillofacial radiology: CB Mercuray, NewTom 3G and i-CAT. Dentomaxillofac Radiol 35: 219, 2006 26. Xavier CB, Gonc¸alves FR, Batista SH, et al: Spontaneous migration of third molar following displacement to pterygomandibular fossa. J Oral Maxillofac Surg 69:1004, 2011 27. Campbell A, Costello BJ: Retrieval of a displaced third molar using navigation and active image guidance. J Oral Maxillofac Surg 68:480, 2010
17 28. Araki K, Maki K, Seki K, et al: Characteristics of a newly developed dentomaxillofacial X-ray cone beam CT scanner: System configuration and physical properties. Dentomaxillofac Radiol 33:51, 2004 29. Hashimoto K, Kawashima S, Kameoka S, et al: Comparison of image validity between cone beam computed tomography for dental use and multidetector row helical computed tomography. Dentomaxillofac Radiol 36:465, 2007 30. Loubele M, Guerrero ME, Jacobs R, et al: Comparison of jaw dimensional and quality assessments of bone characteristics with cone-beam CT, spiral tomography and multi-slice spiral CT. Int J Oral Maxillofac Implants 22:446, 2007 31. Ghaeminia H, Meijer GJ, Soehardi A, et al: Position of the impacted third molar in relation to the mandibular canal. Diagnostic accuracy of cone beam computed tomography compared with panoramic radiography. Int J Oral Maxillofac Surg 38:964, 2009 32. Tantanapornkul W, Okouchi K, Fujiwara Y, et al: A comparative study of cone-beam computed tomography and conventional panoramic radiography in assessing the topographic relationship between the mandibular canal and impacted third molars. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 103:253, 2007 33. Gerlach NL, Ghaeminia H, Bronkhorst EM, et al: Accuracy of assessing the mandibular canal on cone-beam computed tomography: A validation study. J Oral Maxillofac Surg 72: 666, 2014 34. Braut V, Bornstein MM, Lauber R, et al: Bone dimensions in the posterior mandible: A retrospective radiographic study using cone beam computed tomography. Part 1—Analysis of dentate sites. Int J Periodontics Restorative Dent 32:175, 2012 35. Watanabe H, Mohammad Abdul M, Kurabayashi T, Aoki H: Mandible size and morphology determined with CT on a premise of dental implant operation. Surg Radiol Anat 32: 343, 2010
Measurement of the Lingual Position of the Lower Third Molar Roots Using Cone-Beam Computed Tomography € Yusuf Emes, DDS, PhD,* Bora Oncu, DDS,y Buket Aybar, DDS, PhD,z Nazar Al-Badri, DDS,x Halim Is¸sever, MD, PhD,k Belir Atalay, DDS, PhD,{ and Serhat Yalc¸ın, DDS, PhD# Purpose:
The aim of this study was to evaluate the distance between the roots of the impacted third molars and the floor of the mouth to predict the risk of lingual root displacement during surgery.
Materials and Methods:
Thirty-one patients (5 men and 26 women) were evaluated for this study using cone-beam computed tomography (CBCT). The teeth were grouped according to their position on the orthopantomogram as vertical, mesioangular, horizontal, and distoangular. The distance between 2 points on the roots and lingual soft tissues was measured.
Results:
The average distance between the apex of the root, which is in the most lingual position, and the lingual cortical plate was 1.03 mm. The average distance between the most lingual point on the apical half of the root, which is in closer proximity, and the lingual cortical plate was 0.65 mm.
Conclusion:
The distance between the apices and the lingual plate is very short, which allows displacement of broken roots or teeth, especially when the lingual plate is perforated. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 73:13-17, 2015
Extraction of mandibular third molars is one of the most common surgical procedures in the field of oral and maxillofacial surgery.1 As in all surgical procedures, various complications related to third molar surgery have been reported in the literature.2-6 These complications include infection, alveolar osteitis, inferior alveolar nerve injury, lingual nerve injury, and clinically important hemorrhage. Mandibular fractures, osteomyelitis, and displacement of a tooth or root fragments into fascial spaces have been reported as rare complications, the incidences of which are unknown.7-24
A thin lingual cortical plate or a fenestration in the lingual cortical plate and poor surgical technique are the major factors for the displacement of teeth or tooth fragments into the lingual soft tissues. Cone-beam computed tomography (CBCT) is an imaging technique in which volumetric data from the patient are reconstructed using algorithms similar to those used in conventional CT.25 Although CBCT has a higher image noise and is not suitable for soft tissue assessment, it is widely used as a maxillofacial imaging tool owing to its high spatial resolution and lower radiation exposure compared with conventional CT.
Received from the Istanbul University, Istanbul, Turkey.
#Professor, Department of Oral and Maxillofacial Surgery, Faculty
*Associate Professor, Department of Oral and Maxillofacial
of Dentistry.
Surgery, Faculty of Dentistry.
Address correspondence and reprint requests to Dr Emes:
yResearch Assistant, Department of Oral and Maxillofacial
Department of Oral and Maxillofacial Surgery, Faculty of Dentistry,
Surgery, Faculty of Dentistry.
Istanbul University, Istanbul, Turkey; e-mail: [email protected]
zProfessor, Department of Oral and Maxillofacial Surgery, Faculty
Received September 25 2013
of Dentistry.
Accepted June 30 2014
xResearch Assistant, Department of Oral and Maxillofacial Surgery, Faculty of Dentistry.
Ó 2015 American Association of Oral and Maxillofacial Surgeons 0278-2391/14/01120-3
kProfessor, Department of Public Health, Faculty of Medicine.
http://dx.doi.org/10.1016/j.joms.2014.06.460
{Associate Professor, Department of Oral and Maxillofacial Surgery, Faculty of Dentistry.
13
14 In this pilot study, CBCT was used to evaluate the proximity of lower third molar roots to the lingual cortex, which can be used to determine the potential risk of root displacement during lower third molar surgery.
Materials and Methods This study was approved by the ethical committee of Istanbul University (Istanbul, Turkey; project number 723). CBCT images of 32 impacted lower third molar teeth of 31 patients (5 men and 26 women) were evaluated for this study. The data were collected from images of patients who had undergone CBCT imaging for various reasons, such as impacted teeth, dental implants, and cysts of the jaws. Ectopic teeth and teeth with cystic lesions were excluded from the study. The CBCT mandibular scans were acquired using a Soredex Scanora 3D Cone Beam device (Soredex, Helsinki, Finland) operated at 85 kV and 12.5 mA using a charged coupled device sensor. The slice thickness was 0.35 mm and the thinly sliced trans-planar images were assessed using the OnDemand3DApp 1.0.9.1138 software program (Cybermed, Inc, Irvine, CA). Each measurement was performed independently and recorded twice by 2 surgeons. Then, the average of the 2 measurements was calculated and evaluated. EVALUATION OF IMAGES
In a darkened room, the CBCT images were shown in random order on a 24-inch monitor. An evaluation was performed independently by 2 trained oral and maxillofacial surgeons who were experienced in the radiographic evaluation of maxillofacial anatomy. The teeth were grouped according to their positions on the orthopantomogram as vertical, mesioangular, horizontal, and distoangular. Two measurements were performed for each tooth. If 1 tooth had more than 1 root, the root in the most lingual position was considered: 1) the distance from the root apex of the tooth, which is in the most lingual position, to the lingual cortical plate and 2) the distance from the most lingual point on the apical half of the root to the lingual cortical plate (Fig 1). STATISTICAL ANALYSIS
Comparisons between groups were performed using the c2 test and PASS 2000 (NCSS, Kaysville, UT).
Results The measurements showed an average distance of 1.03 mm between the apices of the lower third molars and the lingual soft tissues. The average distance between the most lingually positioned point on the apical half of the root and the lingual soft tissues was
CBCT MEASUREMENT OF LOWER THIRD MOLAR ROOTS
0.65 mm. The relation between the roots and the lingual soft tissues were grouped into 3 types: relation type A, in which there was an amount of bone between the root and the soft tissues (Fig 2A); relation type B, in which there was 0 mm of bone between the root and the soft tissues (Fig 2B); and relation type C, in which the root protruded into the soft tissues (Fig 2C). Four root apices had values of 0 mm (12.5% of total roots evaluated; relation type B) and 4 apices had negative measurement values (12.5% of total roots evaluated; relation type C). In total, 25% of root apices had a type B or type C relation with the floor of the mouth. When the apical halves of the roots were evaluated (distance from the most lingual point on the apical half of the root to the lingual cortical plate), 5 roots were in contact with the soft tissues (measurement, 0 mm; 15.62% of total roots evaluated; relation type B) and 5 roots protruded into the soft tissues (negative values; 15.62% of total roots evaluated; relation type C). In total, 34.38% of the roots were found to be in contact with the lingual soft tissues. Of the 31 patients evaluated, 3 patients were younger than 20 years, and only 1 tooth in these 3 patients had incomplete root formation. This tooth had a type A relation in the apices and the apical halves of the roots. The teeth also were grouped according to their positions (vertical, horizontal, mesioangular, or distoangular). When the roots were compared according to the positions of the teeth evaluated (vertical, horizontal, mesioangular, or distoangular), there were no statistically significant differences among groups in their relation to the lingual soft tissues (P = 0.453 AL distance; P = 0.548 RL distance).
Discussion Accidental displacement of lower third molars or root fragments into facial spaces is rare, and only limited information about its incidence and management is found in the literature. However, when it occurs, the most affected sites are the floor of the mouth and the submandibular and pterygomandibular spaces.26 Lingually located teeth, a thin lingual cortical plate or a fenestration in the lingual plate with tooth exposure, and application of excessive force during extraction have been reported to be among the main causes for this type of complication.1,7-26 Although displacement of teeth or teeth fragments during surgery into the surrounding tissues is a rare complication, Campbell and Costello27 stated that these complications may be underreported owing to practitioners retrieving their own displaced fragments without referral. CBCT has several advantages over conventional CT, such as lower radiation dose,25 high spatial
15
EMES ET AL
FIGURE 1. Left, Distance from the apex of the root to the lingual tissues. Right, Distance from the most lingual point on the apical half of the root to the lingual tissues. AL, distance from the root apex of the tooth in the most lingual position to the lingual cortical plate; L, lingual; RL, distance from the most lingual point on the apical half of the root to the lingual cortical plate; V, vestibule. Emes et al. CBCT Measurement of Lower Third Molar Roots. J Oral Maxillofac Surg 2015.
resolution,28 better-quality view of the dental structures,29,30 and lower cost. CBCT has been proposed as a more accurate method of imaging the relation between the inferior alveolar nerve and the third molar, because it provides the dentist with more accurate information than conventional imaging techniques.31 The accuracy of CBCT images is a matter of question, and several studies have been conducted to determine the accuracy of CBCT in evaluating the location
of the inferior alveolar nerve.32 Tantanapornkul et al32 reported a sensitivity of 93% and a specificity of 23% in determining the inferior alveolar nerve exposure during third molar removal. In a similar study, Ghaeminia et al31 reported a sensitivity of 96% and a specificity of 23%. These advantages of CBCT formed the basis of the present study. A review of the literature disclosed no studies performed on this subject. In this study, the relation
FIGURE 2. A, Type A relation, in which there is bone between the root and the floor of the mouth. B, Type B relation, in which the root communicates with but does not protrude into the floor of the mouth. C, Type C relation, in which the root does not protrude into the soft tissues. Emes et al. CBCT Measurement of Lower Third Molar Roots. J Oral Maxillofac Surg 2015.
16 between the roots of the impacted lower third molars and the floor of the mouth was evaluated. A second point, other than the root apex, also was taken into consideration, because the authors believe that a fenestration in the apex region is not the only predisposing factor in the occurrence of root displacement into the soft tissues. The present findings show that 25% of the apices of impacted teeth were in contact with the mouth floor. If a root in the lingual position is fractured during lower third molar surgery, there may not be enough bone volume between the fractured segment and the floor of the mouth. Further, there may be a fenestration in the lingual cortical plate, which renders the root in contact with the lingual soft tissues. Therefore, an improperly applied force vector by the surgeon can displace the root fragment into the soft tissues. Recently, Gerlach et al33 compared the measurements of CBCT images with histologic sections in 2 cadaver skulls and recommended that a deviation of 0.76 mm could be considered when evaluating CBCT images to prevent injury to the inferior alveolar nerve. The present results show a bone thickness ranging from 0.65 to 1.03 mm lingual to the lower third molar roots. Actual bone thickness may be even thinner than the average measurements made on CBCT images, considering the conclusions stated by Gerlach et al. Only 1 of the 32 evaluated teeth had an incomplete root formation, and this tooth had a type A relation in the root apices and the apical halves of the roots. The sample of teeth with underdeveloped roots in the present study was insufficient to compare distances between teeth with developed apices and those with underdeveloped apices for their relations with the lingual soft tissues. The presence of a lingual undercut is an anatomic property that also can affect the distance between the third molar roots and the lingual soft tissues, depending on the vestibular and lingual position and the axis of the tooth. Lingual undercuts can be observed in the posterior mandible. Although the presence of a lingual undercut was not evaluated in this study, a presence of 36 to 39% in the molar region has been reported in the literature.34,35 Braut et al32 conducted a study using CBCT and evaluated the buccal and lingual bone thickness in the posterior mandible. That study showed an increase in buccal bone thickness in the molar tooth region compared with the premolar region; however, no such differences were observed for lingual bone thickness. The aim of this pilot study was to measure the anatomic proximity of the roots of impacted third molars to the lingual soft tissues to evaluate the possible risk of displacement of fractured root segments lingually. It must be noted that the authors of this study
CBCT MEASUREMENT OF LOWER THIRD MOLAR ROOTS
do not advocate the use of CBCT before all impacted third molar surgeries. This is the reason the radiographs of patients who were examined for conditions other than impacted third molars were used in the present study. Because the evaluated teeth were not subjected to surgery, it would be proper to state that the present findings support only a theoretical risk of lingual root displacement during extraction. Although the sample is small, the larger percentage of contact between the root and the floor of the mouth implies that practitioners should be very careful when dealing with fractured roots of third molars. Further studies comparing CBCT findings with actual measurements on cadavers may help resolve the problems regarding this risk.
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