INTRODUCTION:

The size of our jaw is relatively smaller compared to neolistic man. Due to change of diet habits, there is decrease in jaw size. In the present population, the type of food we take is generally soft; subsequently the masticatory force needed to chew food is enormously diminished. So, evolution makes our jaw become smaller in size as the use of masticatory functional force is lesser. This reduced jaw size causes a decrease in the space to accommodate the full set of dentitions¹. As the third molar in permanent dentition is the last tooth to be erupted, the lack of space causes uneruption². This impaction often cause problems like caries, pulp diseases, pericoronitis, periodontitis, pathological resorption of mandibular second molar, cyst formation, odontogenictumours, crowding of teeth and temporomandibular joint dysfunction^3,4.

The most frequently impacted tooth in dental arch is the mandibular third molar and it shows a great variability in their path of formation and their course of eruption^5,6. The various local factors influencing the impaction includes unfavorable angulations, irregular eruption pathway, lack of space in the dental arch, delayed eruption, density of soft and hard tissues covering above, reduced resorption at the front of the ramus and vertical growth of the condyle^6-8. The angulation of the third molar also plays an important role in this impaction^9,10. If the long axis of third molar is parallel to the plane of occlusion, it is believed that the chances of the molar erupting into functional occlusion will be greatly increased ^9,11,12.

The gonial angle (GA) will also predict the prevalence of impaction of third molar^11,13. As the GA increases, the chances of eruption of third molar also increase as it may affect the retromolar space ^13-15. Furthermore, when GA increases there is a chance of an increase in retromolar space¹¹. Thus, the purpose of this research is to evaluate whether retromolar pad length, mesiodistal width of lower third molar, third molar angulation, angulation of second molar, mesioangular slope of third molar against mandibular second molar, GA, and anteroposterior length of arch affect the impaction of mandibular third molar prevalence among outpatients of AIMST dental clinic.

MATERIALS AND METHODS:

About 200 participants with full dentition and bilaterally present mandibular third molars (aged between 17 and 40) made up the sample. The study was carried out on the patient's records where OPGS were available in AIMST Dental Faculty Oral Surgery Department. Ethical clearance was obtained from the AIMST University Human Ethics Committee before commencement of the study.

Samples were divided into two groups: Group A and Group B. Group A: fully erupted till functional point of mandibular third molars. Group B: unerupted/erupted but not till functional point due to abnormal orientation of mandibular third molars.

Using an X-ray viewer, the panoramic radiographs were traced over acetate paper with a matte finish. The measurements were taken by a panel of three observers, further measurements were taken utilizing a ruler with an accuracy till 0.1 mm. OPGs with full developed roots of erupted and impacted third molars (3 Ms), first and second molars that are alignment properly within the arch were included in the study. Grossly decayed 3Ms with spatial relationships that are challenging to evaluate, 3Ms with partially developed root, mesially drifted 3Ms, individuals with dental and medical anomalies, clinical records without OPG, individuals with absence of first and second molar, pathological conditions like cysts or extensive caries pertaining to mandibular second and third molars and those with poor quality DPTs were excluded from the study.

Figure 1: Measurements used for dental pantomograph analysis.

J x is a point at the junction of the body and anterior border of the mandibular ramus. D7 x is a point located at distal surface of the lower second molar. M8 x is a point located at the mesial surface of the lower third molar. D8 x is a point located at the distal surface of the lower third molar. MDW is the mesio-distal crown width of third molar, measured as the greatest distance between the mesial (M8) and distal (D8) surfaces of the crown. RMS is the distance between the distal contact point and the junction of the anterior border of the ramus with the body of the mandible (point J). α angle is the third molar angulation, the angle formed as a result of a line bisecting the third molar from the midpoint and lower border of the mandible. β angle is the measurements of mesioangular slope of the third molar, which is an angle formed between the intersected long axes of the second and third molars drawn through the midpoint of the occlusal surface and the midpoint of the bifurcation. θ angle is second molar angulation, the angle resulting from a line bisecting the second molar from the midpoint and lower border of the mandible. γ angle is gonial angle, the angle between the tangential line of the posterior border of the mandible and the tangential line of the lower border of the mandibular body was measured. AP is anterior-posterior distance of the arch. The anterior end of the dental arch is represented by the interdental alveolar crest between the central incisors and the posterior end of the arch is represented by the mesial edge of the retromolar pad ^3,8,11.

RESULTS:

The minimum, maximum value, mean and standard deviation (SD) of the third molar angulation (α angle), mesioangular slope of the third molar (β angle),second molar angulation (θ angle), gonial angle (γ angle) these angles were involved for the erupted third molar (group A) and impacted third molar (group B). Then measurements of mesio-distal crown width (MDW) of third molar, retromolar space (RMS) and anterior-posterior distance of the arch (AP) of the erupted third molar (group A) and impacted third molar (group B) can be seen as in Table 1. A comparison of variables of Group A and B and significance of each variable were presented in Table 2.

Table 1: Descriptive Statistics of Group A and Group B

Parameters	Range		Mean± SD
Parameters	Minimum	Maximum	Mean± SD
Group A (Erupted mandibular third molar)
α Angle (°)	28.5	107	84.32 ± 11.59
β Angle (°)	-14	67	7.14± 9.64
θ Angle (°)	71	106.5	88.32 ± 7.59
γ Angle (°)	100	143	123.02 ± 7.60
MDW (mm)	10	17	14.15 ± 1.28
RMS (mm)	12	32	19.09 ± 2.97
AP Length (mm)	42.5	75	58.88 ± 6.23
Group B (Impacted mandibular third molar)
α Angle (°)	7.5	111	64.15 ± 30.92
β Angle (°)	-24	101.5	29.54 ± 35.77
θ Angle (°)	-20	108	86.58± 15.06
γ Angle (°)	74	141	120.08 ± 8.31
MDW (mm)	10	17	14.47 ± 1.17
RMS (mm)	8	21	13.54± 2.96
AP Length (mm)	46	76.5	62.31 ± 5.75

Table 2: Comparison of variables of Group A and B and significance of variable difference

Paramaters	Group A mean	Group B mean	Difference of mean	P value
α Angle (°)	84.32	64.15	-20.17	<0.001
β Angle (°)	7.14	29.54	22.4	<0.001
θ Angle (°)	88.32	86.58	-1.74	0.302
γ Angle (°)	123.02	120.08	-2.94	0.010
MDW (mm)	14.15	14.47	0.32	0.067
RMS (mm)	19.09	13.54	-5.55	<0.001
AP Length (mm)	58.88	62.31	3.43	0.007

For the third molar angulation, the minimum value was 28.5° in the erupted group and in impacted group the minimum value was 7.5°. A marked difference of 21° was seen in the minimum value. The maximum value was 107° in erupted group and 111° in impacted group with similar values. The mean value in erupted group was 84.32° with a standard deviation of 11.59° and 64.15° in impacted group with a standard deviation of 30.92°. There was a significant difference in the mean of both groups for 20.17°. The p value was < 0.001. Since the p value was less than 0.05, this difference was considered to be extremely statistically significant. Mandibular third molar distribution according to alpha angle was elucidated in figure 2.

Figure 2: Distribution of mandibular third molar in groups according to Alpha angle

For the mesioangular slope of the mandibular third molar to mandibular second molar, the minimum value was -14° in the erupted group and in impacted group was -24°. A difference of 10° was seen in the minimum value. The maximum value in erupted group was 67° and 101.5° in impacted group, showing a relatively large difference of 34.5° compared to third molar angulation. The mean value in erupted group was 7.14° with a standard deviation of 9.64° and 29.54 in impacted group with a standard deviation of 35.77°. There was a marked difference of mean 22.40° and p value was 0.001. p value which is less than 0.05 implies this parameter extremely significant in impaction of mandibular third molar. Mandibular third molar distribution according to beta angle was interpreted in figure 3.

Figure 3: Distribution of mandibular third molar in groups according to Beta Angle

For the second molar angulation, the minimum value was 71° in the erupted group and in impacted group was -20°. Even larger difference in minimum value of 91 ° was seen here. The maximum value in erupted group was 106.5° and 108° in impacted group without much divergence. The mean value in erupted group was 88.32°±7.59 and 86.58°±15.06° in impacted group. The difference of mean was 1.74° and p value was 0.302. The p value is more than 0.05, in this way the difference was considered to be not statistically significant.

Moving on to the gonial angle (γ angle), the minimum value was 100° in the erupted group and in impacted group was 74°. 26° of difference can be appreciated. The maximum value in the erupted group was 143° and 141° in impacted group. The mean value in the erupted group was 123.02°±7.60 and 120.08°±8.31 in impacted group. The difference of mean was 2.94° and p value was 0.01. Since the p value is less than 0.05, this difference is considered to be very statistically significant. Mandibular third molar distribution according to gamma angle was summarized in figure 4.

Figure 4: Distribution of mandibular third molar in groups according to Gamma Angle

For the third molar mesio-distal crown width (MDW), the minimum value in both erupted group and impacted group was 10mm. The maximum value in both erupted group and impacted group is also the same, which was 17mm. However, the mean and standard deviation varies a by a little amount. The mean value in erupted group was 14.15mm ±1.28 and 14.17mm±1.17 in impacted group. The difference of mean was 0.31mm and p value was 0.06. For the p value is more than 0.05, this difference is considered to be insignificant.

For the retromolar space, the minimum value was 12mm in the erupted group and in impacted group was 8mm; the difference seen was 4mm. The maximum value in erupted group and impacted group are 32mm and 21mm respectively. The mean value in erupted group was 19.09mm±2.97 and 13.54mm±2.96 in impacted group. The difference of mean was 5.55mm and p value was <0.001. Considering the p value is less than 0.05, this difference was considered to be statistically significant. Mandibular third molar distribution according to retromolar space was illustrated in figure 5.

Figure 5: Distribution of mandibular third molar in groups according to retromolar space

For the anterior-posterior distance of the arch (AP length), the minimum value was 42.5mm in the erupted group and in impacted group was 46mm. A difference of 3.5mm was observed. The maximum value only differs by 1.5mm between the two groups which is 75mm in erupted group and 76.5mm in impacted group. The mean value in erupted group was 58.88mm±6.23 and 62.31mm±5.75 in impacted group. Mean difference was 3.43mm and p value was 0.007. p value of less than 0.05, this difference was considered to statistically significant. Mandibular third molar distribution according to anterior posterior length was explicated in figure 6. In our study, mandibular third molar anglulation, mesioangular slope of mandibular third molar, gonial angle, retromolar space length and anterior-posterior mandibular length are significant parameters that govern the impaction of mandibular third molar.

Figure 6: Distribution of mandibular third molar according to anterior posterior length

DISCUSSION:

Impacted third molars leads to pain, re-infection and decay of second molars may occur. A minor surgical procedure to remove the impacted third molars is the ideal treatment procedure. Less surgical and postoperative complications will be seen if removed early⁷. Hence, early prophylactic removal is the ideal treatment procedure advised^2,
9.Germectomy is simple, short and relatively atraumatic surgical intervention for removing impacted third molar according to a study done by Ricketts et al. ⁷.

A number of studies has been carried out to predict the probability of third molar eruption. One among those studies was carried out by Henry and Morant, suggested the third molar space index to predict the third molar eruption. On the flip side, Schulhof used centre of ramus (Xi) point to measure the available space for the mandibular third molar eruption. Few studies utilized lateral cephalometric radiograph but, studies by Olive¹⁶ and Larheim¹⁷ have shown that panoramic radiographs are reliable indicator to evaluate third molar angulations, due to fewer superimposition compared to lateral cephalometric radiograph³. Thus, we choose to use OPG to assess the factors that influencing the impaction of third molar in our study.

Before 20 years of age it’s difficult to conclude whether the third molar will erupt or impact. Various measurement differences on radiographs of impacted and erupted lower third molars will help for early prediction of lower third molar eruption or impaction ^3,18.Beyond 40 years of age, it is more likely that a third molar of an individual might have been extracted¹⁹. Facial growth pattern, direction of tooth eruption and root configuration are the most common influencing factors for third molar impaction²⁰. Niedzielska et al in the year 2006 conducteda study on 64 patients showed Ganss ratio , third molar inclination to mandibular base and second molar are the predictors for the lower third molar alignment in the dental arch using a panoramic radiograph²¹.

Based on our findings that were in correlation with this study discussed above, in group A (erupted third molar), 17% had third molar angulation <74° while 83% of mandibular third molar had >74°.On the other side, in group B (Impacted third molar), 52% had third molar angulation <74° while 48% had >74°. When alpha angle is <74°, there is higher probability towards impaction of lower third molar while for alpha angle >74°, there is higher probability towards eruption of third molar. This result was supported by a study conducted by Amin et al in the year 2008¹⁰which showed a notable difference on third molar angulation to lower border of mandible. The mean of vertically erupted teeth were 73.9 (±8.16) degrees and 50.10 (±15.99) degrees in mesially impacted teeth. To conclude, the greater the angle between the base of the mandible with the third molar more the chances of eruption. The same study also reported that inclination of third molar, angulation of third molar with base of mandible and retromolar space are variables which determines the impaction of mandibular third molar¹⁰.

Our study finding states, Group A had 91% with mesioangular slope angle of <18° while 9% of mandibular third molar had >18°. In group B, 52% had beta angle <18° while 48% had beta angle >18°. Therefore, beta angle <18°, there is higher probability towards eruption of lower third molar while for beta angle >18°, there is higher probability towards impaction of third molar. This finding correlates with report by Amin et al 2008 [10] which states that greater the angulation made by the long axis of mandibular third molar and mandibular second molar, the greater the chances of impaction. Another study by Imtiaz Ahmed et al 2011²² states that teeth were favourable to erupt had initial angulation below 30º relating to long axis of second molar and third molar. The smaller the initial angulation, greater the chance of tooth to develop a small angulation that is favourable for eruption.

In group A, 41% had gonial angle of <121⁰ while 59% of mandibular third molar >121⁰. Whereas in group B, 52% had gonial angle of <121⁰ and 48% had >121⁰. Thus, for gamma angle <121⁰, there is higher probability towards impaction of lower third molar while for gamma angle >121⁰, there is higher probability towards eruption of third molar. This is against the report done by Amin et al 2008 stating that impaction of third molar are independent of gonial angle¹⁰. Besides that, Hattab et al 1997 reported similar findings that acute GA seen in impacted group²³.A study by Mollaoglu and his colleague in the year 2002 reported ,there was a notable difference in the GA among male and female patients who had third molars erupted, On the contrary, it did not vary much between the impacted and erupted group^24-26.

Retromolar space in group A had 5% which was <16mm while 95% of mandibular third molar had retromolar space >16mm. On the other hand, for group B, 73% had retromolar space <16mm while 27% had retromolar space >16mm. Hence, for retromolar space <16mm, there is higher probability towards impaction of lower third molar while for retromolar space >16mm, there is higher probability towards eruption of third molar. Retromolar space has been identified as an important factor that is responsible for mandibular third molar impaction. This was in line with the earlier reports which stated, decrease in retromolar space is the significant factor that causes impaction of mandibular third molar³.

It has been reported that mean retromolar space in mesially impacted teeth was 11.50 mm and in vertically erupted teeth was 15.80 mm¹⁰. In our study, we did not categories impacted and erupted group according to skeletal class I, class II and class III. There are some research saying that retromolar space shortage is due to skeletal problem and it lead to impaction of third molar. For instance, the study on mandibular third molar space in different antero-posterior skeletal patterns⁸, found that retromolar space width was lower in Class III subjects compared with Class I and Class II. There was a elevated incidence of lower third molar impaction seen among the subjects with a Class III skeletal pattern even though the length of mandible is longer in class III compared to class I and class II.

From the group A, 58% had anterior posterior length <60mm while 42% of mandibular third molar had anterior posterior length >60mm. In group B, 29% had anterior posterior length <60mm while 71% had anterior posterior length >60mm. This implies that for anterior posterior length <60mm, there is higher probability towards eruption of lower third molar while for anterior posterior length >60mm, there is higher probability towards impaction of third molar.

The mandibular length (Go-Gn) which corresponds to the anterior posterior length of mandible has shown that mean of the anterior posterior length of mandible is longer in group A than in group B. However, this result was not significant based on their p value, and concluded no significant differences were found between the erupted and impacted groups for any mandibular length⁸. In contrast, the findings were significant that the longer the anterior posterior length of mandible, the higher the prevalence of lower third molar impaction based on our study findings. This was in line with the study carried out by Behbehani et al. (2006), where the mandibular length deficiency was related with risk of impaction18.

CONCLUSIONS:

The impaction of third molar is greatly associated with angulation of third molar (α angle), mesioangular slope of the third molar (β angle) and retromolar space (RMS). The probabilty of impaction of third molar increased when the α angle of third molar is less (than 74⁰). When the β angle of third molar is more (than 18⁰), the probability of impaction of third molar increased. The probability of impaction of third molar increases as the RMS decreases (<16mm). The GA (γ angle) and anterior posterior distance of arch (AP length) are also associated with impaction of third molar but not as much as the α angle, β angle and RMS. As the γ angle decreases (<121⁰), the probability of impaction of third molar increases. The probability of impaction increased when the AP length of the arch increases (>60mm). Based on the result obtained, the second molar angulation (θ angle) and third molar mesio-distal crown width (MDW) does not influence the impaction of third molar. In conclusion, a higher incidence of third molar impaction occurs in decreased α angle, decreased RMS, decreased γ angle, increased β angle and increased AP length.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 18.04.2023 Modified on 23.05.2023

Research J. Pharm. and Tech 2023; 16(6):2979-2984.

DOI: 10.52711/0974-360X.2023.00492