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ORIGINAL ARTICLE
Year : 2018  |  Volume : 6  |  Issue : 1  |  Page : 8-13

Evaluation of mesiodistal inclination of permanent maxillary and mandibular first molars in different Angle's molar relation: A cephalometric study


Department of Orthodontics and Dentofacial Orthopaedics, K.M. Shah Dental College and Hospital, Sumandeep Vidyapeeth, Vadodara, Gujarat, India

Date of Web Publication05-Nov-2018

Correspondence Address:
Dr. Dweepika Garg
C-201 Rutupearl Appt, Behind Deep Chambers, Manjalpur Road, Vadodara - 390 011, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JIHS.JIHS_5_18

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  Abstract 


Introduction: Angle's molar relationship is the most widely used classification in spite of the introduction of various other classifications. At the end of the treatment, the molars are finished in a Class I, II, or III molar relation. Thus, it is important to know the ideal inclinations of upper and lower 1st molars, thereby assisting in achieving a stable relationship. Aims and Objectives: The aim and objective of this study was to evaluate the mesiodistal inclination of permanent maxillary and mandibular first molars in Angle's Class I, II, and III molar relationships in relation to the occlusal plane. Methodology: Lateral cephalograms of 16–30-year-old individuals with Class I, II, and III molar relations were selected and traced in Dolphin imaging software, and the angle between the first molar and occlusal plane was calculated. Results: There was a statistically significant difference in the inclination of maxillary 1st molar in between Class I and Class III. No significant difference was noted in the inclination of maxillary first molar in case of Class I and Class II. In case of mandibular molars, there was a statistically significant difference in case of Class I and Class II and between Class I and Class III. Conclusion: When the end molar relationship of a case is planned to be Class I, the upper molar should be at an angle of 84.12° to the occlusal plane. When the end molar relationship of a case is planned to be Class II, the upper molar should be 84.15° to the occlusal plane. When the end molar relationship of a case is planned to be Class III, the upper molar should be inclined at an angle of 87.07° to the occlusal plane.

Keywords: Inclination, molar relation, molar tube, occlusal plane


How to cite this article:
Garg D, Goje SK. Evaluation of mesiodistal inclination of permanent maxillary and mandibular first molars in different Angle's molar relation: A cephalometric study. J Integr Health Sci 2018;6:8-13

How to cite this URL:
Garg D, Goje SK. Evaluation of mesiodistal inclination of permanent maxillary and mandibular first molars in different Angle's molar relation: A cephalometric study. J Integr Health Sci [serial online] 2018 [cited 2018 Nov 13];6:8-13. Available from: http://www.jihs.in/text.asp?2018/6/1/8/245026




  Introduction Top


For orthodontists, incisors should not be the only concern. Molars, which are used as anchorage teeth, are also important, especially the first permanent molars (PMs), the compensatory differences of which have crucial roles in growth, development, and anchorage control.[1]

In the specialty of orthodontics, the classification of malocclusion plays a very important role. It helps in the diagnosis and treatment planning of malocclusion and to determine the magnitude of the problem.[2] Second, classification facilitates communication between specialists.

Jesuino et al.[3] conducted a study to evaluate the mesiodistal root inclination of permanent incisors, canines, and first molar of Brazilian children with mixed dentition, using the horizontal reference line drawn on a panoramic radiograph.[3]

Several tools[4] have been used for assessing the inclination of teeth such as cephalometric angular measurements and conveyor and compass on dental casts. All teeth are arranged at an angle to the occlusal plane and each has an optimum inclination mesiodistally to best perform its individual and collective functions.[5] Many clinicians have developed classification system for describing the malocclusion namely Deway,[6] Anderson,[7] and Bennet.[8] However, the most universally accepted classification system still in use today is Angle's[9] method which was developed in 1889 and was based on the position of maxillary permanent first molar in the craniofacial anatomy.[2]

All teeth are essential; yet in function and influence, some are of greater importance than others, the most important of all being maxillary first molar which is often called “key to occlusion.”[2] Angle[9] in 1906 published his article where he proposed the virtues of this tooth. George Risse[2] suggested that maxillary first molars were the key to occlusion because of the following virtues:[2]

  1. Largest teeth
  2. Firmest in their attachment
  3. Have a key location in the arch
  4. Broadest spread of root and widest base
  5. Occupy normal position in the arches far more often than teeth because they are the first permanent teeth to erupt.


Crown inclination had been defined by Andrews[10] in “The six keys to normal occlusion” based on his study on 120 adults with normal occlusion. Several orthodontists have found that the inclination of dentition can change appreciably according to certain factors and can exhibit regularities. Teeth could change their direction of eruption to compensate for positional changes of the jaws because the amount and direction of jaw growth show considerable variability.[1]

Changes in inclination of the first PMs are inextricably linked to changes in anchorage. Orthodontists have used various methods to make the correct changes in mesiodistal inclination of the first molars to influence anchorage preservation. Classic fixed appliances are used to put tip-backs on the posterior teeth for resisting the forward-tipping trend of the molars.

Before starting the treatment, it is better to evaluate: (i) molar inclination before treatment; (ii) the benefits of the compensatory condition of the molars themselves for anchorage preservation; and (iii) the natural pattern of differences in the axial inclination of the first molars in all types of malocclusions.[1]

Su et al.[1] evaluated the compensation trends of the inclination of first molar in Chinese population. Palatal and mandibular plane were used as reference planes. They concluded that the clinicians must avoid using a straight archwire in a 0° buccal tube on more distal-tipping first molars with regard to anchorage control.[1]

During fixed orthodontic treatment, the buccal tube is placed in reference to the occlusal plane. Therefore, taking occlusal plane as reference instead of mandibular plane or palatal plane would be better so that the buccal tube can be tipped mesially or distally, depending on the planned end relationship of molar. Hence, it will be better to know the mesiodistal inclination of molars in relation to occlusal plane, which helps in accurate positioning of buccal tube.

Kannabiran et al.[5] concluded that tip and torque modifications are suggested for the fine finishing and easy retention of occlusion in Dravidians while using straight-wire appliance.

Kamble et al.[2] assessed 103 lateral cephalograms for positional variation of permanent maxillary first molar with infrazygomatic crest in skeletal Class I, II, and III cases.

Mesiodistal root angulation alterations of the maxillary and mandibular incisors may significantly change the molar relationship.[3]

In Angle's Class I molar relation, the mesiobuccal cusp of the upper first PM lies in the buccal grove of the lower first PM. Whereas in Class II molar relation, the mesiobuccal grove of the upper first molar lies in the interdental area between the 2nd PM and 1st molar.[2] Thus, due to anatomic variations, there is change in the mesiodistal inclination of the upper first molar in Class I, II, and III cases.

Su et al.[1] concluded that compensation of molar inclination varies among different classifications of sagittal malocclusion.

After searching the literature, databases such as PubMed, Medline, EBSCO, Scopus, and LILACS, till October 2017, with no restriction on language, very few studies[1],[2],[3] are found which have evaluated the mesiodistal inclination of upper and lower first molars in Angles' Class I, II, and III cases. No study has been found which evaluated the mesiodistal inclination of upper and lower first molars in relation to the occlusal plane. Therefore, this study has been taken up. The aim of this study was to evaluate difference in the mesiodistal inclination of permanent maxillary and mandibular first molars in Angle's Class I, II, and III molar relationships in relation to the occlusal plane.


  Methodology Top


The study was conducted at the Department of Orthodontics, K. M. Shah Dental College and Hospital, Piparia, Vadodara, Gujarat, India. Ethical approval was obtained from Sumandeep Vidyapeeth Institute of Ethical Clearance.

Based on values obtained from the study done by Kamble et al.,[2] the sample size was calculated as follows:

A sample size of 150 achieves 80% power to detect an effect size (W) of 0.25 using 2 degrees of freedom by Chi-square test with a significance level (alpha) of 0.05.

Sample size n = Chi-square/W^2

Where W = 0.25

Chi-square = 9.4

df = 2.

Hence, the final sample size was 150 and sample per group was 50.

Good quality, undamaged lateral cephalograms of Angles Class I, Class II, and Class III molar relation were included in the study. The exclusion criteria were absence of permanent first molar or any tooth mesial or distal to it, lateral cephalograms showing bone loss around the first molar, any pathological lesion on the radiograph, and lower anterior crowding and cephalograms showing open bite.

The study models were assessed from the archives of pretreatment orthodontic records of the patients. The study models with ideal posterior intercuspation were identified and their lateral cephalograms were included in the study. A total of fifty lateral cephalograms of Class I [Figure 1] and [Figure 2], fifty Class II [Figure 3] and [Figure 4], and fifty Class III [Figure 5] and [Figure 6] cases were recruited retrospectively based on the inclusion criteria.
Figure 1: The long axis of the upper first molar was constructed from the apex of mesiobuccal root of the first molar and its mesiobuccal cusp using the software. The line was extended until it intersected the occlusal plane. Then, the superior inside angle was measured

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Figure 2: The long axis of the lower first molar was constructed by joining the apex of the mesiobuccal root with mesiobuccal cusp. The lines were extended until they intersected the occlusal plane. Then, the inferior inside angle was measured. A case of Class I molar relation

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Figure 3: Inclination of the upper molar measured in a case of Class II molar relation

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Figure 4: Inclination of the lower molar measured in a Class II molar relation

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Figure 5: Inclination of the upper molar measured in case of Class III molar relation

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Figure 6: Inclination of the lower molar measured in a Class III molar

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The soft copy of the lateral cephalograms was digitized using Dolphin cephalometric software (Vadodara, Gujarat, India). Occlusal plane was traced by drawing a line passing through the intercuspation of the upper and lower teeth. The long axis of the upper first molar was constructed from the apex of the mesiobuccal root of the first molar and its mesiobuccal cusp using the software [Figure 1]. The line was extended until it intersected the occlusal plane. Then, the superior inside angle was measured. Similarly, long axis of the lower first molar was constructed by joining the apex of the mesiobuccal root with the mesiobuccal cusp [Figure 2]. The lines were extended until they intersected the occlusal plane. Then, the inferior inside angle was measured. The data obtained were subjected to statistical analysis.


  Results Top


In patients with Class I molar relation, the mean inclination of maxillary molar is 84.12° and mean inclination of mandibular molar is 85.23 [Table 1].
Table 1: One-way ANOVA

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In patients with Class II molar relation, the mean inclination of maxillary molar is 84.15 and mean inclination of mandibular molar is 81.71 [Table 1].

In patients with Class III molar relation, the mean inclination of maxillary molar is 87.07 and mean inclination of mandibular molar is 81.25 [Table 1].

Post hoc test was used and multiple comparisons were done [Table 2]. When the inclination of maxillary molar was compared between Class I and Class II, the P value obtained was 0.999, showing that the data obtained were not statistically significant. This indicates that there is no difference in the inclination of maxillary molar in cases of Class I and Class II molar relation [Table 3].
Table 2: Tukey's post hoc multiple comparison tests

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Table 3: Paired sample t-test

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When the inclination of maxillary molar was compared between Class I and Class III, the P value obtained was 0.002 [Table 2], showing that the data obtained were statistically significant. This indicates that there is a significant difference in the inclination of maxillary molar in cases of Class I and Class III molar relation.

When the inclination of mandibular molar was compared between Class I and Class II, the P value obtained was 0.003 [Table 2], showing that the data obtained were statistically significant. This indicates that there is a significant difference in the inclination of mandibular molar in cases of Class I and Class II molar relation.

When the inclination of mandibular molar was compared between Class I and Class III, the P value obtained was 0.001 [Table 2], showing that the data obtained were statistically significant. This indicates that there is a significant difference in the inclination of mandibular molar in cases of Class I and Class III molar relation.

In Class I molar relation, the mean difference in the inclination of maxillary and mandibular first molar was 1.10, with P = 0.225 [Table 3]. This shows that there is no significant difference in the inclination of upper and lower molars in Class I cases.

In Class II molar relation, the mean difference in the inclination of maxillary and mandibular first molar was −2.44, with P = 0.008 [Table 3]. This shows that there is a statistically significant difference in the inclination of upper and lower first molars in Class II cases.

In Class III molar relation, the mean difference in the inclination of maxillary and mandibular first molar was −5.81, with P < 0.001 [Table 3]. This shows that there is a statistically significant difference in the inclination of upper and lower first molars in Class III cases.


  Discussion Top


This study was carried out with the aim of evaluating the difference in the mesiodistal inclination of permanent maxillary and mandibular first molars in Angle's Class I, II, and III molar relationships in relation to the occlusal plane. The molar tube is placed in reference to the occlusal plane. Till now, no study had measured the inclination of molars in relation to the occlusal plane. Therefore, this study was taken up.

Lateral cephalograms of 16–30-year-old individuals with Class I, II, and III molar relations were taken and were digitized using Dolphin cephalometric software. 4-point angle was taken. Only angular values were noted. No calibration was required.

All the values obtained were subjected to statistical analysis. Thus, the ideal inclination of upper and lower molar was identified. Hence, while ending a case in Class I, II, or III molar relationship, the inclination of maxillary and mandibular molar should be calculated in relation to the occlusal plane. If it is not in the range of being ideal, then the molar tube can be tipped as per requirement to obtain the required inclination.

In Angle's Class I molar relation, the mesiobuccal cusp of the upper first PM lies in the buccal grove of the lower first PM. Whereas in Class II molar relation, the mesiobuccal grove of the upper first molar lies in the interdental area between the 2nd PM and 1st molar. Thus, due to anatomic variations, there is change in the mesiodistal inclination of the upper first molar in Class I, II, and III cases.

This will help in achieving proper inclination of molar at the end of the treatment. Thus, due to anatomical variations in the molar relations, its inclination varies in Class I, II, and III molar relationships. To achieve ideal inclination of first molar after the treatment, proper positioning of molar tube is a necessity. Thus, by knowing the variations which need to be done while bonding the first molar, it is possible to achieve good cusp-to-fossa relation, thereby stabilizing the occlusion. Hence, once we decide the molar relation in which we plan to end the case, the molar tube should be positioned accurately.


  Conclusion Top


After appraising the inclination of molars, it can be concluded that:

  1. When the end molar relationship of a case is planned to be Class I, the upper molar should be at an angle of 84.12° to the occlusal plane
  2. When the end molar relationship of a case is planned to be Class II, the upper molar should be 84.15° to the occlusal plane
  3. When the end molar relationship of a case is planned to be Class III, the upper molar should be inclined at an angle of 87.07° to the occlusal plane
  4. This helps in achieving an ideal cusp-to-fossa relationship, thereby stabilizing the occlusion.


Financial support and sponsorship

This is a self-funded study.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Su H, Han B, Li S, Na B, Ma W, Xu TM, et al. Compensation trends of the angulation of first molars: Retrospective study of 1403 malocclusion cases. Int J Oral Sci 2014;6:175-81.  Back to cited text no. 1
    
2.
Kamble R, Hazarey A, Hazarey P, Singh J. Assessment of positional variation of maxillary permanent first molar with respect to the infrazygomatic crest(key ridge) in skeletal class I, II and III cases. World J Dent 2013;228-34.  Back to cited text no. 2
    
3.
Jesuino FA, Costa LR, Valladares-Neto J. Mesiodistal root angulation of permanent teeth in children with mixed dentition and normal occlusion. J Appl Oral Sci 2010;18:625-9.  Back to cited text no. 3
    
4.
Nouri M, Abdi AH, Farzan A, Mokhtarpour F, Baghban AA. Measurement of the buccolingual inclination of teeth: Manual technique vs. 3-dimensional software. Am J Orthod Dentofacial Orthop 2014;146:522-9.  Back to cited text no. 4
    
5.
Kannabiran P, Thirukonda GJ, Mahendra L. The crown angulations and inclinations in Dravidian population with normal occlusion. Indian J Dent Res 2012;23:53-8.  Back to cited text no. 5
  [Full text]  
6.
Dewey M. Classification of malocclusion. Int J Orthod 1915;1:133-47.  Back to cited text no. 6
    
7.
Anderson GM. Practical Orthodontics. 9th ed. St. Louis: CV Mosby; 1960. p. 144-50.  Back to cited text no. 7
    
8.
Bennet NG. Report of the committee of orthodontic classification. Oral Health 1912;2:321-7.  Back to cited text no. 8
    
9.
Angle EH. Classification of malocclusion. Dent Cosmos 1899;41:248-64, 350-7.  Back to cited text no. 9
    
10.
Andrews LF. The six keys to normal occlusion. Am J Orthod 1972;62:296-309.  Back to cited text no. 10
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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