Influence of maxillary first molar rotation on the severity of dental class II malocclusion: A cross-sectional study Alexander L, ShanajD, Arun V

ORIGINAL ARTICLE

Year : 2023 | Volume : 12 | Issue : 1 | Page : 52

Influence of maxillary first molar rotation on the severity of dental class II malocclusion: A cross-sectional study

Lidhiya Alexander, Shanaj Doulath A, V Arun
Department of Orthodontics and Dentofacial Orthopaedics, Indira Gandhi Institute of Dental Sciences, Sri Balaji Vidyapeeth University, Puducherry, India

Date of Submission	06-Jan-2023
Date of Decision	03-Mar-2023
Date of Acceptance	15-Apr-2023
Date of Web Publication	04-Sep-2023

Correspondence Address:
Lidhiya Alexander
No 544/A, 3^rd Cross Street, Kalaivanar Nagar, Danvantri Post, Gorimedu, Puducherry - 605 006
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jos.jos_3_23

Abstract

AIM: The aim of the study was to evaluate and assess the influence of maxillary molar rotation on severity of dental class II malocclusion.
MATERIALS AND METHODS: The study comprised of 4 different groups namely, 1/4th class II malocclusion, 2/4th class II malocclusion, 3/4th class II malocclusion and full class II malocclusion involving sample size of 20,15,16 and 12. The samples were subjected to digital evaluation of maxillary 1st permanent molar rotation using 4 parameters namely angle of Friel, Ricketts E-Line, angle of Henry and Premolar angle.
RESULTS: The results were subjected to statistical analysis using one way ANOVA wherein group IV (Full class II malocclusion) exhibited a greater rotational value. On evaluation, angle of Friel exhibited a mean of 59.6±1.61 degrees, Ricketts E-Line was found to be 12.3±1.77mm while angle of Henry showed a mean of 19±3.19 degrees and premolar angle was 12.5±5.83 degrees.
CONCLUSION: On evaluating molar rotation using angle of Friel, Ricketts E-Line, angle of Henry and premolar angle, full cusp class II malocclusion presented higher degree of mesiopalatal rotation maxillary molar rotation. With increasing mesiopalatal rotation, the severity of molar relation also increased from 1/4th to full class II. Hence the maxillary molar spatial position along the long axis majorly influences the molar relation wherein a full cusp class II molar relation exhibits higher degree of molar rotation.

Keywords: Molar rotation, Class II malocclusion, angle of Friel, Ricketts E-Line, angle of Henry and premolar angle

How to cite this article:
Alexander L, ShanajD, Arun V. Influence of maxillary first molar rotation on the severity of dental class II malocclusion: A cross-sectional study. J Orthodont Sci 2023;12:52

How to cite this URL:
Alexander L, ShanajD, Arun V. Influence of maxillary first molar rotation on the severity of dental class II malocclusion: A cross-sectional study. J Orthodont Sci [serial online] 2023 [cited 2023 Oct 3];12:52. Available from: https://www.jorthodsci.org/text.asp?2023/12/1/52/385068

Introduction

The position of the first molar in the maxillary arch is of immense importance in the diagnosis of malocclusion and treatment planning. As stated by Edward H. Angle (1899), maxillary first permanent molar has been used to describe various occlusal malrelations and is the “key to occlusion.”^[1] Normal occlusion, as described by Angle, has the drawback of not considering the spatial axes of the molars. In general, as molars exhibit a rhomboidal shape, they occupy a large surface area.^[2] Andrews (1972) has mentioned that lack of rotation is the key to normal occlusion. Correcting the axial deviation of the molar helps in achieving sufficient arch perimeter, proper sagittal positioning, and maximum intercuspation, thereby providing long-term stability.^[3] Henry (1956) measured the angle created by the median raphe and the line drawn through the buccal cusp tips of the molar.^[4] Furthermore, Friel (1959) proposed an angle made by the median raphe and the line drawn through the mesiobuccal and mesiopalatal cusps of the molar.^[5] Orton (1966) used the angle made by two tangents, one drawn to the buccal surface of the premolar and the other through the molar.^[6] According to Ricketts (1969), a molar is considered to be positioned normal along its long axis when the line joining the distobuccal and mesiopalatal cusps of the maxillary first permanent molar passes 4 mm distal to the canine cusp tip in the opposite side.^[7] In addition, various other parameters in the form of linear and angular measurements were introduced to determine the spatial position of the molar. Cetlin and Tenhove (1993) postulated that a well-positioned maxillary first permanent molar exhibits parallelism of its buccal surfaces when viewed from the anterior aspect. Evaluation of the molar rotation is of prime importance in diagnosis and treatment planning as, when properly executed, it provides correction in the early phase of fixed orthodontic therapy. Thus, various problems, such as premature contacts and compromised inter-molar width, are minimized. A high prevalence of molar rotation in patients with class II malocclusion has been widely reported in the literature.^{[6],[8],[9],[10]} Hence, this study evaluated the rotation of maxillary first permanent molar in patients with Angles class II division 1 malocclusion to determine the correlation between molar rotation and the severity of class II malocclusion.

Materials and Methods

This study was performed on 63 selected dental class II malocclusion models after receiving ethical clearance (registration no. IGIDSIEC2019NRP13PGSDODO) and informed consent from patients. Any model that deviated from class I molar relationship toward a class II condition on either side was collected and segregated into four groups based on molar relationships, as follows: 1/4^th class II (group I), 2/4^th class II (group II), 3/4^th class II (group III), and full class II (group IV) malocclusion. The sample size was calculated using 5% alpha error and 80% power for a correlation coefficient of ≥0.20. The following were the inclusion criteria: 1) presence of all permanent teeth, 2) absence of any restoration or decay, attrition, worn or missing teeth, prosthetic replacement, and supernumerary teeth, 3) absence of previous orthodontic treatment, 4) absence of crossbite, and 5) toward a class II relationship from a class I relationship. This study aimed to evaluate the relationship between the magnitude of rotation and the severity of malocclusion. The anteroposterior discrepancy of the maxillary first molar was determined based on the position and distance of the distobuccal cusp tip of the maxillary molar in relation to the mesiobuccal groove of the mandibular molar, as follows: full class II group is 1.0–3.5 mm, 3/4^th class II group is 3.5–7.0 mm, 2/4^th class II group is 3.5 mm, and 1/4^th class II group is >7 mm.^[11]

The models were digitally photographed with the leveling bubble in place, and the molar rotation was assessed [Figure 1], [Figure 2], [Figure 3]. The digitally photographed models were standardized using a ruler and landmarks [Figure 4]. Parameters of angle of Friel, Ricketts E-line, angle of Henry, and premolar angle were measured using a digital protractor and recorded [Figure 5], [Figure 6], [Figure 7], [Figure 8].^[12],[13]

Figure 1: Digital camera with leveling bubble in place

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Figure 2: Maxillary model with leveling bubble in place

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Figure 3: Digital photograph of the maxillary model

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Figure 4: Landmarks plotted on the photographed model.

RP1—Most anterior region of the palatine raphe,

RP2—Most posterior region of the palatine raphe,

MV—Tip of the mesiobuccal cusp of the maxillary first molar,

DV—Tip of the distobuccal cusp of the maxillary first molar,

MP—Tip of the mesiopalatal cusp of the maxillary first molar,

C—Tip of the cusp of the maxillary canine

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Figure 5: Plotted parameters (angle of Friel, Ricketts E-line, angle of Henry, and premolar angle) on 1/4^th class II maxillary model

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Figure 6: Plotted parameters (angle of Friel, Ricketts E-line, angle of Henry, premolar angle) on 2/4^th class II maxillary model

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Figure 7: Plotted parameters (angle of Friel, Ricketts E-line, angle of Henry, and premolar angle) on 3/4^th class II maxillary model

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Figure 8: Plotted parameters (angle of Friel, Ricketts E-line, angle of Henry, and premolar angle) on full class II maxillary model

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Results

The mean molar rotational values were statistically analyzed and tabulated for all four parameters on both sides [Table 1]. One-way analysis of variance was used to test the level of significance and was found to be statistically significant [Table 2] and [Table 3]. The groups were statistically compared using Bonferroni test. The comparison between group I and group IV showed a larger mean difference, which suggests a larger variation between 1/4^th class II and full class II malocclusion, followed by group I (1/4^th class II) and III (3/4^th class II) and group II (2/4^th class II) and group IV (full class II) [Table 4].

Table 1: Mean and standard deviation

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Table 2: Analysis of variance—right

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Table 3: Analysis of variance—left

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Table 4: Comparison (right and left)—(Bonferroni)

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Discussion

The rotational position of the maxillary first molar is of great clinical importance in providing a well-aligned maxillary-to-mandibular arch and also fulfils Andrews six keys to occlusion. Dahlquist has previously observed that sex distribution is unnecessary for this type of study; hence, equal sex distribution was not considered in the present investigation. On evaluating the right and left sides of the models, no significant difference was evident in the indicators included in the study, which agrees with the findings of a study by Junqueira et al. published in 2011. Several authors have described various indicators to evaluate the position of the molar around the spatial axis. Henry, in the year 1956, proposed an angle to quantify the rotational position of the maxillary molar by constructing the angle formed by the two planes, namely the median raphe and buccal cusp tips of molars.^[14],[15] Similarly, in 1959, Friel considered the median raphe as the reference plane and presented an angle with the line joining the mesiobuccal and mesiopalatal cusp tips. Orton, in 1966, put forth an angle created by the tangent drawn from the buccal surfaces of the premolars to the molars. In 1969, Ricketts suggested a line (joining the distobuccal and mesiopalatal cusps of the maxillary molar), which on bisecting the distal aspect of the contralateral canine, is aptly positioned around its axis in the maxillary dental arch.^[16] According to Van der Linden, the raphe line and median palatal rugae points are stable anatomic landmarks for evaluating the rotational position.^{[12],[13],[14]}

Some studies have evaluated the positioning of the molar in the occlusal aspect of the arch; however, no association has been reported in the literature between molar rotation and its influence on molar relation. In this study, mesiopalatal molar rotation was highly prevalent in all four groups. The individual mean values for the four groups were evaluated for the tested parameters, namely angle of Henry, angle of Friel, Ricketts E-line, and premolar angle [Table 1]. The findings were in accordance with the study performed by Lima.^[11],[17] In this study, the mean value for the angle of Friel decreased from group I (1/4^th class II) to group IV (full class II), which indicates an increase in molar rotation on both sides. The other three parameters, that is, Ricketts E-line, angle of Henry, and premolar angle, increased from group I to group IV, which signifies that the molar rotation increases with the increase in molar class II relations from 1/4^th class II to full class II malocclusion. Hence, molar rotation influences the severity of class II malocclusion. On evaluating individual parameters, the mean and standard deviation for the angle of Friel were found to be 56.66 ± 1.66 degrees on the right side and 56.58 ± 2.53 degrees on the left side for group 4 and 65.1 ± 2.38 degrees on the right side and 65 ± 2.10 degrees on the left side for group 1, which shows increased mesiopalatal rotation. Similarly, the mean and standard deviation for Ricketts E-line were found to be 5.5 ± 0.94 mm on the right side and 4.65 ± 0.98 mm on the left side for group I and 12.33 ± 1.77 mm on the right side and 12 ± 1.41 mm on the left side for group IV. Angle of Henry was found to be 11.7 ± 1.59 degrees on the right side and 12.25 ± 1.91 degrees on the left side for group I and 19 ± 3.19 degrees on the right side and 19.66 ± 4.77 degrees on the left side for group IV. Premolar angle was found to be 4.7 ± 1.8 degrees on the right side and 6 ± 2.16 degrees on the left side for group I and 12.5 ± 5.83 degrees on the right side and 10.6 ± 4.16 degrees on the left side for group IV. In this study, on an average, not much difference was noted between the right and left sides, which is in line with the results of Scanavini et al., and Lamons FF, Holmes, who stated that there is no statistical difference between the right and left molar positioning.^[9],[18] Further studies with a larger sample size that consider the arch form and other related parameters affecting the positioning of maxillary molars are needed. Inter-examiner reliability check is required on a larger scale to standardize the method of assessing and quantifying the molar rotation.

Conclusion

Based on the methodology adapted in this study, the following conclusions could be drawn:

All class II malocclusions generally exhibit mesiopalatal rotation of maxillary first permanent molars.
The mean values for the parameter angle of Friel decline in terms of rotational values from group I to group IV, which indicates a drop in molar rotation toward group IV. This finding suggests a positive correlation between the magnitude of molar rotation and the severity of class II malocclusion.
The mean values for the parameters Ricketts E-line, angle of Henry, and premolar angle were observed to increase from group I to group IV, which demonstrates an increase in molar rotation with an increase in the severity of class II malocclusion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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