Influence and Impact of Mandibular Ramal Dimensions on the Incidence of Lower Third Molar Impaction: A Prospective Study.

Context: The incidence of third molar impaction is very frequent in the dental arch; however, the etiology remains unclear. Assessment of ramal parameters might aid in deducing the chance of the lower third molar being impacted. Aims: To investigate the mandibular ramus features that could contribute to the etiology of mandibular third molar impaction. Settings and Design: A prospective study. Methods and Materials: In total 1,125 patients (568 males and 557 females) who satisfied the inclusion and exclusion criteria were included in the study. Six linear and four angular measurements such as ramal height, ramal width, mandibular body length, third molar width, the body of mandible width, retromolar space, angle of the impacted tooth, the angle between condyle and coronoid process, gonial angle, and inclination of the lower posterior teeth were made using digital panoramic radiographs and recorded. Also, the occurrence of impacted lower third molar was noted. Statistical Analysis Used: Comparisons between groups were done using Student's t-test. Pearson correlation was used to assess the degree of relationship between retromolar space and mandibular measurements.
Results: Control group showed significantly greater measurements in most of the variables, whereas the impacted group showed no significant difference. A significant correlation of retromolar space is found with body height, third molar width, and angle of impaction. Conclusions: The present study found that the configuration of the mandibular ramus appears to be discrete in many aspects in the erupted other than impacted lower third molars subjects, which might be a possible cause for the impaction. Copyright:

INTRODUCTION

Impaction of the mandibular third molars is a common dental anomaly where there is a failure of eruption of the tooth.[12345] Evidence for the causes of impaction of the mandibular third molars has been described in the literature. Interestingly, different populations and ethnic groups exhibit various causes for the incidence of impacted teeth.[25] The most common causes of the impaction of the mandibular third molar are the abnormal positioning of the tooth bud, lack of space in the dental arch, supernumerary tooth ankylosis of the deciduous or permanent tooth, non-resorbing bone due to local or systemic causes.[6] The main etiological factor is contributed by the bony obstruction in the pathway of eruption, or the local adjacent tooth causes hindrance.[7] The failure of the eruption could be due to many systemic and local factors, such as cleidocranial dysplasia, Down's syndrome, and arch-length deficiency.[8] Evaluation of the incidence of impacted mandibular third molars is of prime importance because of the established correlation between the development of pericoronitis, cystic lesions, and caries with impacted teeth.[9] The sequelae can be addressed well if the etiological factor is detected. Panoramic radiographs are widely used in the profession of dentistry as these give quick, low-cost, small radiation dosages, and provide a bilateral view of the mandible compared with other sophisticated diagnostic tools. It is also considered as one of the proper radiographic techniques that are used to assess lower third molar space and mandibular linear and angular dimensions. This study aims to correlate the incidence of impacted mandibular third molar teeth with mandibular ramal measurements in an orthopantomogram.

SUBJECTS AND METHODS

Patients reporting to the department of oral and maxillofacial surgery in the age group of 21 to 50 years were assessed for the presence or absence of mandibular third molars. Patients with atrophic mandible, age less than 21 years, syndromic cases (such as Down's syndrome), post-orthodontic treatment, craniofacial anomalies, incomplete root formation of the third molars, or were higher than ASA III under the Society of Anesthesiologists (ASA) classification and patients contraindicated for radiographic investigations were excluded from the study. Digital panoramic radiographs were used to assess the relationship between the ramal measurements and the third molar impaction status. A total of 3,765 patients were screened for 1 year out of which 1,125 patients (568 males and 557 females) satisfied the inclusion and exclusion criteria and hence were included in the study. Linear and angular measurements such as ramal height, ramal width, mandibular body length, third molar width, the body of mandible width, retromolar space, the angle of the impacted tooth, angle between condyle and coronoid process, gonial angle, and inclination of the lower posterior teeth were made for each OPG and recorded using the DICOM software. Also, the occurrence of impacted lower third molar was noted. The measured parameters were compared between normally erupted the third molar and impacted molars thereby an inference of whether the mandibular anatomical measurements influence the occurrence of impacted third molar can be derived.

RESULTS

A total of 1,125 patients with 568 males and 557 females within the age range of 21–50 years were included in the study and their OPG was assessed. Out of 1,125 patients, 810 patients were found to have impacted lower third molars either unilaterally or bilaterally and the rest 315 patients had a normal eruption of lower third molars. The linear and angular measurements recorded were compared among impacted and normally erupted lower third molars as in Table 1.

Table 1

Comparison of linear and angular measurements between the impacted and control group

Variable	Type of impaction	Mean	SD	P
Ramus height	Normal patients	5.488	0.654	0.73
	Impacted group	5.424	0.552
Total ramus height	Normal patients	7.186	0.705	0.48
	Impacted group	7.334	0.651
Ramus width	Normal patients	3.275	0.386	0.049
	Impacted group	3.521	0.389
Mandibular body length	Normal patients	8.983	0.785	0.71
	Impacted group	9.172	1.853
Third molar width	Normal patients	1.247	0.142	0.004
	Impacted group	1.372	0.126
Retromolar space	Normal patients	1.817	0.317	0.001
	Impacted group	1.261	0.273
Body of mandible width	Normal patients	2.987	0.378	0.15
	Impacted group	2.789	0.450
Angle between condyle and coronoid process	Normal patients	38.038	4.600	0.91
	Impacted group	38.276	11.555
Angle of impaction	Normal patients	80.015	7.225	0.001
	Impacted group	66.750	12.993
Gonial angle	Normal patients	119.126	6.766	0.71
	Impacted group	119.984	7.722
Inclination of lower posterior teeth	Normal patients	82.286	4.686	0.46
	Impacted group	83.853	7.397

An independent t-test was done for comparison of all parameters among which ramal width, third molar width, retromolar space, and angle of impaction exhibited significance.

A significant correlation of retromolar space is found with body height, third molar width, and angle of impaction [Table 2].

Table 2

Pearson correlation coefficient for normal patients

Variables correlated (retromolar space vs)	Pearson’s correlation coefficient (r)	P	Strength of correlation	Significance
Ramus height	–0.126	0.66	*	*
Total ramus height	–0.105	0.72	*	*
Ramus width	–0.166	0.57	*	*
Mandibular body length	–0.772	0.001	Moderately negative	Highly significant
Third molar width	0.562	0.036	Moderate positive	Significant
Body of mandible width	–0.05	0.85	*	*
Angle between condyle and coronoid process	0.22	0.44	*	*
Angle of Impaction	–0.533	0.050	Moderately negative	Significant
Gonial angle	0.052	0.85	*	*
Inclination of lower posterior teeth	–0.44	0.112	*	*

No significant correlation of retromolar space was found with other parameters in impacted patients [Table 3].

Table 3

Pearson correlation coefficient for impacted teeth

Variables correlated (retromolar space vs)	Pearson’s correlation coefficient (r)	P	Strength of correlation	Significance
Ramus height	0.02	0.901	*	*
Total ramus height	0.027	0.87	*	*
Ramus width	0.025	0.88	*	*
Mandibular body length	0.273	0.10	*	*
Third molar width	0.043	0.80	*	*
Body of mandible width	0.23	0.16	*	*
Angle between condyle and coronoid process	0.22	0.18	*	*
Angle of impaction	–0.053	0.76	*	*
Gonial angle	–0.14	0.41	*	*
Inclination of lower posterior teeth	0.13	0.44	*	*

DISCUSSION

The mean age of the total sample was 29.2 ± 6.7 years, which is close to the average age reported for the eruption of a mandibular third molar.[101112] According to Schersten et al.,[13] 20 to 25 years is the most appropriate age for studying the incidence of mandibular third molar impaction. Based on such evidence and to minimize the influence of such factors on the measurements, the subjects included in this study were 21 years old or older, as this age essentially completes the growth and root formation of all third molars.

About the ramal dimensions, ramus height, and total ramus height did not exhibit significance in both the normal group and the impacted group. This finding contradicts the result of Capelli[14] who had recorded that long ascending ramus seems to be indicative of third molar impaction. Also, our result is in line with that of Hasan,[15] who did not find any significant difference between normal and impacted groups. In this study, the control group showed a significantly wider ramal width than the impacted group (P < 0.049). This result is found not to be in line with the results obtained by Hassan,[15] who found significantly wider ramal width in the impaction group. This difference may be due to the different measurement techniques used and sampling differences. The present study showed that the angle between the condyle and coronoid process was the same and was not significantly different in both the control group and the impacted group. This measure along with the ramus height influences the sigmoid notch depth, which in turn governs the slope of the anterior and posterior borders of the ramus.

When comparing mandibular body length (Go–mandibular midpoint, M) between groups, no statistically significant difference was found. This is in line with the results of previous studies of Dierkes[16] and Kaplan[17] but disagrees with the findings of Hassan,[15] Broadbent,[18] Björk,[19] and Capelli[14] who reported significant smaller mandibular length in the impacted third molars subjects.

The results of the present study showed that the mean retromolar space measured from a line tangent to the descending anterior border of the ramus to the distal surface of the second molar (M2–Z) was found to be 18.17 ± 3.17 mm in the control group, and 12.61 ± 2.73 mm in the impacted group. The retromolar space was significantly larger in the erupted group than in the impacted group (P < 0.001). Uthman[20] measured the retromolar space on panoramic radiographs and concluded that this distance should be higher than 11 mm for females and 12 mm for males; this is within the range of the present investigation for men and women in the control group.

Our mean value of both groups (18.17 ± 3.17 mm in the control group and 12.61 ± 2.73 mm in the impacted group) was more than that reported by Hattab and Alhaija[12] for Jordanians (14.4 ± 2.4 mm for the erupted group and 11.06 ± 2.6 mm for the impacted group) and Qamruddin et al.[21] for Pakistanis (16.3 ± 2.5 mm for the normal group and 11.2 ± 3.6 for the impacted group).

In contrast, Behbehani et al.[22] using lateral cephalograms suggested that the eruption space could be a good predictor for third molar eruption when measured to Ricketts' Xi point rather than to the anterior border of the ramus. They believed that it might be due to the large method error, and the complexity of locating the anterior border of the ramus on the lateral cephalograms, especially with double contours of the right and left sides in projection. In the present study, the eruption space was measured from the distal surface of the second molar to the anterior border of the ramus (M2–Z). Our finding is in line with the previous report that panoramic radiographs can offer better measurement due to the simplicity of locating the anterior border of the ramus and the absence of double counters between the right and left sides and less method error.[23] The average space/crown width was 12.47 ± 1.42 mm for the control group and 13.72 ± 1.26 mm for the impacted group. This result is close to the value obtained by Hattab and Alhaija[12] for Jordanian subjects, and that might be due to the similarity of the inclusion criteria and ethnic background. Previous reports[1224] indicated that when the ratio of retromolar space to third molar crown width is at least 1, 69% of third molars erupt. This study showed a moderately positive correlation between third molar width and retromolar space.

Based on the results of the present study, there was no significant difference between groups about the gonial angle in contrary to Gunaid et al. 2019[25] in which the control group showed a smaller gonial angle than the impacted group. Some studies reported smaller and acuter gonial angles among the impacted group compared with the normal group.[2426] Our finding disagrees with the results obtained by Behbehani et al.[22] who reported that small mandibular plane and gonial angles are associated with an increased risk for mandibular impaction.

Regarding the angulations of lower posterior teeth, the mandibular first molar inclinations were found to be as upright in the impacted group as compared with the control group, resulting in no significance between retromolar space and the angulation of lower posterior molars. This contradicts with Gunaid et al.[25] where their study proves that the less retromolar space due to more inclined posteriors might lead to insufficient space required for the eruption of third molars in the impacted group. It has been demonstrated that the higher the inclination of the posterior teeth, the greater is the probability of impaction.[1127282930] Our results support the findings of Capelli,[14] Hassan,[8] Shiller,[28] Richardson,[31] and Begg[32] in that the initial angulation of the lower third molar to the mandibular plane can be a factor in predicting impaction.

The present study showed no correlation between the size of the gonial angle and the impaction of the third molars. In spite of the limitation of this study of using two-dimensional radiographs, some obvious variations between groups included in this study are possibly helpful during prediction and treatment planning. However, further research using a contemporary approach such as cone beam computed tomography to elucidate the difference between groups is recommended.

CONCLUSION

The present study found that the configuration of the mandibular ramus appears to be discrete in many aspects in the erupted other than impacted lower third molar subjects, which might be a possible cause for the impaction.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.