TO ASSESS POSITION OF THIRD MANDIBULAR MOLAR IN DIFFERENT SAGITTAL PATTERNS.
The purpose of this study was to determine the relationship between mandibular third molar and sagittal pattern of the patients reporting to the orthodontics department of IIDC.
Orthopentomogram (OPG) and lateral cephalograms of 50 patients ranging from age group 15 to 25 years were taken. The sample was divided into 2 groups i.e. skeletal class 2 and class 3. Four parameters were studied on these patients, which included angle between mandibular second molar(M2) and occlusal plane, angle between amdibular third molar(M3) and occlusal plane, distance between M3 and occlusal plane and retromolar distance.
The result shows difference between left and right side of angle between M2, M3 and occlusal plane but it is insignificant. The retromolar distance and the distance between M3 and occlusal plane in class 2 and 3 patients also has difference on both sides but this difference is also insignificant (p>0.05).
The study did not show any significant relation between mandibular third molar position and sagittal skeletal discrepancy in both males and females.
Key Words: Mandibular 3rd molar, retromolar area, sagittal skeletal malocclusion.
Among permanent dentition third molar has the most diversity in the size, shape and eruption timings. The crypt of mandibular third molar forms around 4 years of age with calcification beginning at the age around 8-10 years. The eruption timings for this tooth varies from person to person but mostly is around 17 to 23 years of age.1 Development of third molar has various effects on the developing dentition in human population depending upon factors like age, gender, race, genetics and environmental factors. Mandibular third molar has higher prevalence of impaction than maxillary third molar.2-3
It is not uncommon to encounter a malposed or an impacted molar that can lead to different conditions like pericoronitis, abcess, tumors that can proceed to different systemic infections.4
Impacted third molar can also affect individuals that are candidates for orthodontic treatment and orthognathic surgery.
For evaluation of position with good visualization the most common diagnostic radiograph, opg is taken in dentistry especially in orthodontics to evaluate the position of teeth with a good visualization of surrounding structures. It allows to accurately assess third molar position and pathologies with a minimal amount of radiation exposure to the patient than the other imaging techniques available.5
The impaction of third molar is multifactorial, one being insufficient retromolar space. To anticipate the tendency of molar to erupt or being impacted has a profound importance in dentistry be it in orthodontics for anchorage or prosthodontics as abutment.4
In this study, vertical position of mandibular third molar in relation to occlusal plane, angle of mandibular second molar (M2) and third molar (M3) to occlusal plane and also retromolar space present in skeletal class 2 and 3 patients was assessed. The purpose of this study is to find any disparity in third molar position among different sagittal pattern of maxilla and mandible that includes skeletal class 2 and class 3.
Approval of the study was taken from ethical committee of Islamic International Dental College and hospital. It is the retrospective carried out in Orthodontic department of Islamic International dental hospital from May 2015 to December 2015. The digital panoramic radiographs and lateral cephalograms (X-era Smart 3D panoramic imaging system) of 50 patients (class 2=25, class 3=25).
The inclusion criteria included patients ranging age 15-25 years with either skeletal class II or class III, presence of lower 8's on both sides and presence of all permanent dentition including the third molars. The list of exclusion criteria includes hypodontia, no extraction and no previous history of orthodontic treatment.
This study consisted of 2 groups based on their sagittal pattern and then following measurements were manually done on opg of these patients using acetate paper and a Dollar soft-liner 0.3 pointer.
1) Angle between longitudinal axis of M2 and occlusal plane: two lines were drawn which determined the longitudinal axis of M2. First line was drawn by tangent to mesiobuccal (MB) and mesiodistal (MD) cusps of M2 and second line was drawn perpendicular to the first line. Then angle between this longitudinal axis and occlusal plane is determined. Angle on both sides (right and left) is measured.
2) Angle between M3 and occlusal plane: similarly as described previously angle between longitudinal axis of M3 and occlusal plane is determined on both sides.
3) Retromolar distance: A perpendicular line was drawn to occlusal plane of M2 (which was a tangent to the distal part of the tooth). The distance between intersection of this line with occlusal plane and anterior border of ramus is determined.
4) Distance between M3 and occlusal plane: The distance between crown of M3 and occlusal plane is measured in mm.
For statistical purpose SPSS version 21.0 was used and independent sample T test was applied. A p value of <0.05 was considered significant.
A sample consisted of 50 patients (76% females and 24% males) that came to the orthodontics department of Islamic International Dental Hospital (IIDH). The mean and standard deviation of age group and gender is given in Table 1 and 2 respectively. Independent sample T test was applied.
The angle between M2 and occlusal plane was insignificant on left and right side (p on left= 0.4; p on right=0.6). The angle between M3 and occlusal plane was insignificant on left and right side (p on left=0.4; p on right=0.6). The retromolar distance was insignificant on left and right side (p on left= 0.9; p on right=0.3). Distance between M3 and occlusal plane was insignificant on left and right side (p on left= 0.18; p on right=0.09).
The reason for impaction of mandibular third molar is mostly due to lack of retromolar space as found by Bjork's study that was 17% to 22%.6 The retromolar space can b assessed by measuring the distance between distal surface of mandibular second molar and anterior border of mandibular ramus. However, in this study the retromolar distance was insignificant (10.4% and 10.8%). Comparing to the results of Qamaruddin et al the retromolar distance came out to be significant on both sides (16% n 11%). The patients in this study were divided into 2 groups on basis of eruption status of mandibular third molar.
The angle between M2 and M3 has significant role as it defines the chances of eruption of third mandibular molar. The more the angulation between M2 and M3 the more chances of impaction of third molar as explained by Qamaruddin et al. Farzmegan et al conducted a study in which there was a significant difference in angle between M2 and M3 on left side (p=0.017) which was in contrast to our study which showed the insignificant difference on both sides (p value for M2 and M3 with occ on left was 0.4 and p value on right side for both was 0.6).
As opposed to our study Farzmegan used angle between M2 and M3. A study carried out by Abbas Shokri et al that use beta angle showed insignificant result in all 3 sagittal groups (class 1=, class 2=, class 3=) 3.
Farzamegan et al carried out the study which determined no significant difference in distance measured between occclusal plane and third molar but this study was carried out in patients with vertical discrepancies.4
Our study showed similar results as the former study but it was determined in patients with sagittal discrepancy. The significance of this distance is established by the evidence, which shows that a farther the tooth is from the occlusal plane more chances of third molar impaction and vice versa.
There is no study available on sagittal pattern regarding these variables in this local study is first of its kind. There is still a lot of debate regarding third molar impaction and its effects on outcome of orthodontic treatment. The advantage of this study to orthodontists is that it helps them in determining the position of mandibular third molar and also helps them with the decision of extraction of third molar in different sagittal patterns.
The current study showed no significant relationship between different parameters in assessing position of mandibular third molar in class 2 and class 3 patients in both genders.
1 Rezwana Begum Moh, Ravichandra Kognati, Siva V Kalyan Digital radiographic evaluation of mandi 3rd molar for age estimation, J Forensic Dent Sci, 2014; 6(3); 191-96.
2 Nasreen Amanat, Daud Mirza, Kulsoom Fatima, Pattern of 3rd molar impaction;frequency and types among patients PODJ vol 34, No. 1 (March 2014).
3 Abbas Shokri, Majid Mahmoudzadeh, Maryam Baharvand et al. Imaging Sci in Dent 2014; 44; 61-65.
4 Fahimeh Farzanegan, Ali Goya Evaluation of mandibular 3rd molar positions in various vertical skeletal malocclusion, JDMT, Vol 1, No. 2, Dec 2012.
5 Smith AC, Barry SE, Chiong AY, et al. Inferior alveolar nerve damage following removal of mandibular third molar teeth. A prospective study using panoramic radiography. Aust Dent. 1997; 42: 149.
6 Irfan Qamaruddin, Wasif Qayyum, Syed Mahmood Haider et al difference in various measurements on panoramic radiograph among erupted and impacted 3rd molar groups, JPMA Vol 62, No. 9, Sept 2012.
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|Publication:||Pakistan Oral and Dental Journal|
|Date:||Dec 31, 2016|
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