Correlation of ANB, Beta and Yen angle with soft tissue profile angle in class I and class II patients: A retrospective cephalometric study.

INTRODUCTION

An aesthetically pleasing and balanced face is one of the objectives of orthodontic treatment.Facial harmony is determined by the skeleton and its overlying soft tissue.¹ Class I, Class II and Class III are the three types of skeletal malocclusions categorised based on anatomical relationship between maxilla and mandible.² The anteroposterior relationship of maxilla to mandible is an important diagnostic criterion for treatment planning. This can be diagnosed from clinical observation, but accurate evaluation is only possible with cephalometric interpretation. Cephalometrics was introduced by Broadbent in 1931 which offers a possibility to evaluatemaxillo- mandibular discripancy.³

Soft tissue assessment in orthodontic patients plays a crucial role in appropriate treatment planning. Maxillo-mandibular discrepancy effectssoft tissue facial drape of an individual. Skeletal Class II condition exhibits a convex facial profile whereas Class I subject presents a straight profile.⁴ Soft tissue significance in evaluating facial aesthetics has been studiedby many investigators and have inferred that‘soft tissue is independent from the underlying hard tissue’. Therefore,the demand for precisesoft tissue cephalometricanalysis is essential for proper diagnosis of a case.^5,6,7

The study of hard and soft tissue parameters using cephalometric analysis is considered a better pathway for proper diagnosis and implementing accurate treatment plan.^8,9,10

Cephalo metrically, Riedel’s ANB angle formed by connecting Point A(deepest point of the anterior maxilla), B(deepest point in the symphysis) and N(anterior most point of the frontonasal suture) helps to evaluateanteroposterior apical base form.1^0-13 (Fig1)

Beta angle is made of, three skeletal landmarks-points A, point B and apparent axis of the condyle-point C (postero superior point on the condyle) and these landmarks are found to be independent of cranial reference planesor functional occlusalplane. Angle formed by between A-B line and point A perpendicular to C-B line (Condylion-B point) is the Beta angle.¹⁴ (Fig2).

YEN angle developed in 2009 is formed by joining Point S (deepest point in sellaturcica), M (which is the midpoint of the anterior maxilla) and G (which is the centre at the bottom of Symphysis.)¹⁵ (Fig3)

All the three angular parameters described above helpsin assessing the maxillo– mandibular relationship.

Parameters of soft tissue assessment and their ideal range enables us in planning orthodontic treatment to evaluate facial aesthetics.¹⁶ In 1980, Legan and Burstone introduced profile angle for soft tissue also called angle of convexity.¹⁷ (Fig 4) The study intended to correlate ANB, Beta and YEN anglewith profile angle in paients with Class I and Class II malocclusion in Gulbarga population.

MATERIALS AND METHOD

This study was carried out on pretreatment records containing high definition radiographs of 140 patients. Records were collected from the record room of Orthodontic department of the Institution.

Profile angle was traced manually on all the 140 cephalograms. Profile angle is the inferior angle formed by joining following soft tissue points:

Glabella (G),

Subnasale (Sn),

Pogonion (Pog)

Depending upon the profile angle, subjects were grouped into ;

• Group I - 70 Class Imalocclusion patients (165 -175 degree)

• Group II -70 Class II malocclusion patients (< 165 degree). Subjects were selected based on following inclusion criteria.

• Age between 18 to 25 years

• Patients who have not undergone orthodontic treatment.

• No history of trauma

• No congenital facial anomaly

Cephalograms were traced manually by single examiner to avoid inter examiner bias,using a sharp 3H pencil on acetate tracing paper with the help of X-ray viewer. The landmarks ANB, Beta and YENangle wereidentified, drawn and measured. These were recorded on data recording sheets. (Fig 1,2,3)

STATISTICAL ANALYSIS

Statisticalanalysis was performed using SPSS software v.23.0. and Microsoft office 2007.

P value (P<0.005) was considered to calculate statistically significant difference between ANB, Beta and YEN angle in patients with Class I and Class II malocclusions. The three angles correlation with profile angle was carried out using Karl Pearson correlation test.

RESULTS

Patients with Class I and II malocclusion presented significant difference between them (Table I) (Fig 4). Karl Pearson correlation presented a decreased R value signifying minimum correlation between soft profile angle and skeletal angular measurements (Table II). A moderately positive correlation of YEN angle with profile angle was noted. Class II subjects presents a soft tissue drape whichis least correlated with increase in ANB angle.

DISCUSSION

Cephalogram is an useful diagnostic tool in orthodontic practice which was introduced in 1931 by Broadbent.³ Most of the orthodontic problems occur in sagittal plane therefore analysis of jaws in anteroposterior plane is most important. Wylie assessed the maxillamandibular relationship in sagittal plane for the first time, since then numerous analysis have been introduced.¹⁸

Arnett and Bregman introduced soft tissue parameters in assessing facial harmony. Harmony and balance between different facial landmarks enhances the facial presentation of an individual. Facial Profile angle is one of the commonly used parameterin analysing facial aesthetics.This angle is formed between the lines joining three soft tissue points Glabella,Subnasale and Pogonion.¹⁹This study was attempted to correlate the skeletal angular parameters ANB, Beta, and Yen angles with profile angle of soft tissue in Class I and Class IImalocclusion patients.

Our study concluded that ANB, Beta, and YEN angle are not significantly correlated with profile angle, which connotes that soft tissue presentation in individuals with both Class I and Class II malocclusion does not depend on the underlying skeletal abnormality.

 Popular parameter to analyse the skeletal discrepancies in sagittal planeis ANB angle. In Class II patients, ANB value was found to benegatively correlated with profile angle in our study . This could be attributed to the soft tissue thickening 4 to mask the underlying skeletal abnormality.Another possible factor could be the lack of reliability of ANB angle as sagittaldysplasiaindicator. Brown, Chang and Rotberg et alfound that changes in SN plane was mainly due to superioanterior movement of nasion with growth which questions reliability of ANB measurement. Growth rotation and vertical growth also influence the interpretation of ANB according to Jacobson.^20,21,22,23

ANB angle may vary in case of

1) Jaws rotations occuring during growth period

2) Variation in the distance between points A(deepest point in the anterior part of maxilla) and B(deepest point in the anterior part of symphysis) reflected during vertical jaw growth.

3) Vertical growth reflected in the distance between points N (anterior most point of frontonasal suture) and B; and

4) Length of anterior cranial base andanteroposterior position of nasion. Vertical positioning of Nasion in the downward or upward direction will increase or decrease ANB angle, respectively.¹³

In ourstudy,Beta angle exhibited a weak positive correlation with soft tissue drape in both Class I and IIsubjects. Beta angle being independent of cranial landmarks could be claimed as a reason to prove its predictability in assessing sagittal discrepancies compared to ANB angle. This was supported by Baik, VerveridouandFida who reported less variability in Beta angle.^14,24 Doshiet al also found Beta angle more accurate in diagnosing Class II patients in Indian population. But Beta angle and mandibular plane anglewere found to be positively correlated ,indicating the variation that could occur in the angle during jaw rotations.²⁵ This statement was in close association with Sundereshwaran et al where the author mentioned that rotation of mandible in clockwise pattern affects the predictability of Beta angle as an assessment tool of sagital discrepancies.²⁶

YEN angle manifested moderate positive correlation with profile angle in Class Icategory. This could be explained in context of its reliability compared to the other two angles. This finding is in collaboration with the findings ofVenkata et al and Doshiet al who found YEN angle to be a reliablemeasurement as it involves Sella as its landmark, which is claimed to be least affected by variations in facial height and jaw rotations.^27,25,15 (Table 2)

This retrospective study performed to evaluatethe influence of hard tissue alignment upon soft tissue drapeof patients with Class I and Class II malocclusion showed that soft tissue pattern is not always correlated with the skeletal discrepancies.This is associated with the compensation presented by the soft tissue to hide the underlying skeletal deterioration. Though compensation by means of soft tissue thickening affects the credibility of all three angles in correlating with soft tissue of the subjects, YEN angle could present a moderately positive correlation with profile angleof soft tissue.

Interestingly, this study enlightenson the soft tissue paradigm. A new way of looking at treatment goals has emerged in which there is a paradigm shift from Angle’s to the soft tissue paradigm which states that both the goals and limitation of modern orthodontic treatment are determined not only by teeth and bones but also by clinical profile of the face.So, treatment of malocclusion should focus on theassessment of clinical facial profile and its adaptation separately apart from the hard tissue findings. Keeping this in mind during orthodontic treatment planning is critically important.²

Figure legends

1. ANB angle 12

2. Beta angle 14,25

3. Yen angle 25

4. Soft tissue profile angle 19

Table legends

1. P values to compare angles between Class I and Class II patients

2. Karl Pearson correlation coefficient between soft tissue profile angle and ANB, Beta and Yen angle.