|Year : 2016 | Volume
| Issue : 2 | Page : 145-149
Radiographic assessment of distribution of mandibular third molar impaction: A retrospective study
Tejavathi Nagaraj, Lakshmi Balraj, Keerthi Irugu, Shruthi Rajashekarmurthy, Sreelakshmi
Department of Oral Medicine and Radiology, Sri Rajiv Gandhi College of Dental Sciences and Hospital, Bengaluru, Karnataka, India
|Date of Submission||27-Apr-2015|
|Date of Acceptance||14-Nov-2016|
|Date of Web Publication||02-Dec-2016|
Department of Oral Medicine and Radiology, Sri Rajiv Gandhi College of Dental Sciences and Hospital, Bengaluru - 560 032, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Introduction: Third molars are the most common teeth that may follow an abortive eruption path and become impacted as a result of pathology, anatomical structures or insufficient osseous space posterior to the second molars. Aims and Objectives: The present study evaluated (1) the distribution of the impaction of mandibular third molar; (2) the distribution of the patterns of impaction radiographically; and (3) the gender distribution for pattern of impaction. Materials and Methods: This hospital-based retrospective study was conducted over a course of 6 months in the Department of Oral Medicine and Radiology and presents the analysis of 122 panoramic radiographs of patients between the age group of 18-30 years. They were interpreted and assessed for the impaction of mandibular third molars. Statistical analysis was done by Chi-square test. Results: Bilateral impaction of mandibular third molar is more common than unilateral in both the sexes, with mesioangular being the most common pattern. In males, mesioangular pattern was followed by horizontal, whereas in females it was followed by vertical. Conclusion: The present study provides useful data regarding the radiographic status of impacted mandibular third molars in patients.
Keywords: Impaction, mandibular third molar, panoramic radiography
|How to cite this article:|
Nagaraj T, Balraj L, Irugu K, Rajashekarmurthy S, Sreelakshmi. Radiographic assessment of distribution of mandibular third molar impaction: A retrospective study. J Indian Acad Oral Med Radiol 2016;28:145-9
|How to cite this URL:|
Nagaraj T, Balraj L, Irugu K, Rajashekarmurthy S, Sreelakshmi. Radiographic assessment of distribution of mandibular third molar impaction: A retrospective study. J Indian Acad Oral Med Radiol [serial online] 2016 [cited 2018 Oct 22];28:145-9. Available from: http://www.jiaomr.in/text.asp?2016/28/2/145/195125
| Introduction|| |
Third molar, also known as the "wisdom tooth," is the only tooth to erupt in adolescents or even in adults. Impaction is defined as completely or partially unerupted and positioned against another tooth, bone or soft tissue, such that its further eruption would be unlikely.  Impactions may be unilateral or bilateral. Pattern of impacted third molar (Winter's classification) is determined by the angle formed between the intersected longitudinal axis of the second and third molars [Vertical impaction (10° to −10°), mesioangular impaction (11° to 79°), horizontal impaction (80° to 100°), distoangular impaction (−11° to −79°)] [Figure 1].  The present study provides useful data regarding the radiographic status of impacted mandibular third molars in patients.
| Materials and Methods|| |
This hospital-based retrospective study was conducted during a period of 6 months, from July 2014 to December 2014, in the Department of Oral Medicine and Radiology. This study represents the analysis of panoramic radiographs of those patients who were advised the same for various purposes. All panoramic radiographs were taken by ORTHOPHOS XG, by Denstply Sirona, USA, panoramic machine. Previous records of the patients were collected whose panoramic radiographs were to be assessed. A total of 122 panoramic radiographs of patients in the age group of 18-30 years were interpreted and assessed for the mandibular third molar impactions. The panoramic radiographs were chosen according to the following criteria.
- Impacted mandibular third molars with completed root formation radiographically
- Panoramic radiographs of male and female patients in the age group of 18-30 years
- No history of trauma
- Images of good quality that had the clearest reproduction of teeth without any superimposition.
The pattern of impaction was determined by measuring the angle formed between the lines intersecting the long axis of the second and third molars. The angle thus formed was used to interpret the mesial or distal inclination in relation to second molar [Figure 2]. The third molars that had reached the occlusal plane in relation to the second molar were considered to be normally erupted teeth. The results were analyzed by Chi-square test by an expert statistician using Statistical Package for Social Sciences Software (SPSS) version 11.0, (IBM Corporation, New York, U.S). A P value of ≤0.001 was considered to be statistically significant.
- Agenesis of mandibular third molars
- Third molar tooth buds or third molars having underdeveloped roots (i.e., radiographically less than two-third root formation)
- Patients with history of extraction of mandibular third molars, mandibular fractures or orthodontic treatments
- Patients with developmental anomaly, congenital or systemic disease, and/or major pathology in the mandible that has/had caused severe bone resorption/destruction, bone expansion, root resorption, and tooth migration, cysts and tumors involving orofacial structures
- Impacted teeth other than mandibular third molars.
|Figure 2: Determination of the pattern of impaction based on the angulation|
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| Results|| |
A total of 122 panoramic radiographs for impacted mandibular third molars were studied and recorded by performing Chi-square test. They were then classified according to sex; 71 (58.2%) were males and 51 (41.8%) females [Table 1]. Bilateral impactions, with a frequency of 68 (55.7%), were more common than unilateral impactions (on either left / right side) with a frequency of 54 (44.3%) [Table 2]. The most common pattern of impaction seen in both unilateral as well as bilateral impactions was mesioangular, which was statistically significant (P < 0.001) followed by equal number of vertical and horizontal types (27.8%) in unilateral impactions. In bilateral impactions, mesioangular (47.1%) was followed by vertical (29.4%) and horizontal (15.4%). The least common pattern in both unilateral and bilateral was distoangular [Table 3]. In the present study, bilateral impactions were studied in detail for gender distribution of type of impaction. Gender distribution for common pattern of bilateral impaction was mesioangular, both in males (51.7%) and in females (43.6%), followed by horizontal pattern in males (27.6%) and vertical pattern in females (39.7%), which was statistically significant with P < 0.001 [Table 4].
|Table 3: Different patterns of impaction in bilateral and unilateral impactions |
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| Discussion|| |
Embedded teeth are those individual teeth which remain unerupted usually due to a lack of eruptive forces, lack of space either due to small jaws or large teeth, or incomplete mandibular forward and downward growth, or can be hereditary.  In early 1954, Mead  defined an impacted tooth as a tooth that is prevented from erupting into position because of malposition, lack of space or other impediments. Later, Peterson  characterized impacted teeth as those teeth that fail to erupt into the dental arch within the expected time. In 2004, Farman  stated that impacted teeth are those whose eruption is prevented due to a physical barrier within the path of eruption.
In general, third molars have been found to erupt between the ages of 17 and 21 years. Furthermore, the time of third molar eruption has been reported to vary with race.  The average age for the eruption of mandibular third molars in males is approximately 3-6 months ahead of females.  Lack of space is the major cause for abortive eruption. As an associated complication, it can also cause incisor crowding, resorption of adjacent tooth roots, inflammatory processes (pericoronitis), and temporomandibular joint dysfunction. 
Studies conducted by Kramer and Williams reported that maxillary third molar is commonly impacted (62.57%) compared to mandibular third molars (47.44%). Impaction of mandibular third molar is more symptomatic and disturbs an individual's routine.  Impaction of mandibular third molars is a common condition related with the difficulty of extraction and risk of various associated complications such as pain, swelling, inferior alveolar nerve damage, alveolitis, incomplete root removal, bleeding, delayed healing, postoperative infection and bony spicules. 
The location and configuration of impacted third molar, adjacent teeth, surrounding bone and mandibular canal are important in imaging diagnosis for the proper surgical operation planning. Periapical radiographs have been used for many years to assess the jaws during impacted teeth surgery.  During the last decade, many dental practices replaced the film with digital imaging systems.  Cone beam computed tomography (CBCT) has been advocated as the method of choice only when there is a need to obtain a three dimensional view of the mandibular third molar and adjacent anatomical structures. , At present, orthopantomography is the radiographic technique of choice to evaluate impacted mandibular third molars. The estimated specificity for radiographic signs, as predictor of nerve injury ranges from 96 to 98%.  The radiation dose of a panoramic radiograph is lower than that from four periapical views and the diagnostic yield is higher. 
The present study was conducted to document the distribution of impaction, its unilateral or bilateral involvement, as well as its pattern. Out of a total of 122, the orthopantomographs were classified according to sex; 71 (58.2%) were males and 51 (41.8%) were females. There was not much sexual difference in the current study in relation to prevalence of third molar impaction, which was in agreement with Kramer and Williams and raised the question against Hellmen's statement that jaws of the female stopped growing, when third molar just started to erupt, whereas in males the growth of the jaws continued beyond the time of third molar and hence, he proposed that impaction of third molar is common in females than in males. 
In the present study, even though bilateral impactions with a frequency of 68 (55.7%) were more common than unilateral impactions with a frequency of 54 (44.3%), the difference was not statistically significant. This may be due to the small sample size of the study. This finding was in agreement with the study conducted by Guthua and Mwaniki  in 1992 that reported 68.2% bilateral impactions.
As already stated in literature by many authors and in many studies by Linden et al.,  Hattab et al.,  Knutsson et al.,  and Sedaghatfar et al.,  maximum number of third molar impactions were found to be mesioangular. In the present study also, the most common pattern of impaction seen in both unilateral as well as bilateral impactions was mesioangular, which was statistically significant (P < 0.001). It appears that mesioangular impactions are probably the most common type which may be due to their late development and maturation, path of eruption, and lack of space in mandible at later age.  However, this result was not in accordance with the study conducted by Gupta et al.  and Hazza'a et al.  because they found the highest number of vertically placed third molars followed by mesioangular, distoangular and horizontal patterns. These variations in angular position of mandibular third molars may be because of the fact that the studied population in each study was quite different from each other.
In the present study, we observed that mesioangular was followed by equal number of vertical and horizontal types (27.8%) in unilateral impactions and by vertical (29.4%) and horizontal (15.4%) in bilateral cases. In the present study, gender distribution for the pattern of impaction was also investigated. Mesioangular was the most common pattern seen in both males (51.7%) and females (43.6%). Mesioangular was followed by horizontal pattern in males (27.6%) and vertical pattern in females (39.7%) which was statistically significant (P < 0.001). These values are in accordance with the study conducted by Ramamurthy et al.  and not in agreement with study by Al-Bahrani et al.  where mesioangular impactions were the most common in both genders followed by distoangular in males (36%) and vertical in females (16%). Literature reports are insufficient to correlate the gender difference in the pattern of third molar impaction.
In bilateral impactions, we also observed the distribution of impaction patterns based on angulation. Most common pattern was mesioangular (17.2%) on either side, followed by mesioangular-vertical impactions (10.7%) on both side and vertical pattern on either side (9%). These patterns have been newly analyzed in the present study and further studies are required to establish its clinical significance.
| Conclusion|| |
Radiographic diagnosis of the presence, position and degree of third molar formation is a crucial part of integral treatment planning. Panoramic radiographs can be used as valuable predictor of the outcome of the impacted mandibular third molars position as they appear to have quite good cost-information ratio. From the above study it can be concluded that
The only limitation of present study is its small sample size. However, this study can be added to future comprehensive studies involving impacted mandibular third molars to set a gold standard for early prediction, evaluation and to avoid all possible complications post-disimpaction procedures.
- Bilateral impactions are more common than unilateral,
- Mesioangular is the most common pattern of impaction in both unilateral and bilateral impactions, and
- Common pattern of impaction was mesioangular, in both the sexes, followed by horizontal pattern in males and vertical pattern in females.
The present study reveals valuable insights on the information concerning various patterns of impacted mandibular third molars. Type of impaction and its effect on the surrounding tissues can be determined using radiographs. Classification of mandibular third molar impaction enables the clinician to determine the degree of difficulty in removal of the impacted tooth, to choose the optimal treatment and to avoid a majority of possible complications.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]