Evaluation of Horizontal Distance between WALA-FA Point in Angle's Class I, Class II, and Class III Malocclusion.

INTRODUCTION: The objective of the study was to measure the horizontal distance between the FA-WALA (Facial Axis Point-William Andrews and Larry Andrews) of posterior teeth in Angle's Class I, Class II, and Class III malocclusions and to assess the depth of the Curve of Spee, to find the correlation between intercanine FA and intercanine WALA and its significance.
MATERIAL AND METHODS: Sixty pretreatment mandibular casts of patients with an age range of 18-35 years were included. A sample size of 20 was evaluated in Angle's Class I, Class II, and Class III, respectively. The WALA ridge and FA points were marked in the model and calibrated using the digital Vernier caliper.
RESULTS: There was an incremental increase in the horizontal distance from the FA-WALA in the posterior teeth. The mandibular intercanine FA-FA and intercanine WALA-WALA distance were greater in Angle's Class III group when compared to Angle's Class II. The Curve of Spee measurement was increased in Angle's Class II group, while Angle's Class III had a flat curve.
CONCLUSION: The horizontal distance between FA-WALA increased incrementally in the posterior teeth in Angle's Class I, Class II, and Class III malocclusions. In Angle's Class II malocclusion, the Curve of Spee measurement was increased and had a narrower mandibular arch. Copyright:

INTRODUCTION

The stability of orthodontic treatment depends on the mandibular arch form. WALA ridge serves as an anatomic guide for positioning the teeth as proposed by Andrews. WALA ridge is the strip of soft tissue immediately above the mucogingival junction of the mandible, at the level of the line that passes through the center of rotation of the teeth or close to it.[1] There are many variations in the dental arch forms among individuals and WALA ridge helps in customizing their arch forms.[234] Knowing the importance of WALA ridge, this study aimed at analyzing the horizontal distance between FA-WALA ridge in various malocclusions and to find its correlation with the Curve of Spee. Intercanine distance between FA-FA and WALA-WALA was evaluated to study the transverse discrepancies.

MATERIAL AND METHODS

Pretreatment mandibular dental casts of 60 patients who reported to the department of orthodontics, were selected for the study. Samples consisted of 20 each in Angle's Class I, Class II, and Class III, respectively, with the age range of 18–30 years. Inclusion criteria were patients with permanent dentition and no previous history of orthodontic treatment. Casts with dental agenesis, supernumerary teeth, mutilated dentition, and patients with craniofacial syndromes, bruxism, and attrition were excluded from the study. A single examiner marked the FA point on the tooth and WALA ridge on the mandibular model from the occlusal aspect [Figure 1]. The horizontal distance between the FA point on the posterior teeth of the mandible and WALA ridge was assessed on both sides of the mandibular arch using a modified digital Vernier caliper parallel to the occlusal plane [Figure 2]. The Curve of Spee measurement was made on the right and left sides from the cusp tip of the first premolar. Intercanine width at the region of WALA and FA was also analyzed.

Figure 1

Armamentarium (A. Measuring Scale, B. Digital vernier caliper, C. Modified Digital vernier caliper, D. Mandibular Dental cast)

Figure 2

FA-WALA Ridge measurement using modified Digital Vernier Caliper (A. Modified Digital Vernier Caliper, B. Manibular Cast)

Statistics

The data were subjected to statistical analysis. Paired t-test was done to find the significance of the mean value between the intercanine width and WALA in Angle's Class I, Class II, and Class III malocclusions. Comparison of horizontal distance of FA-WALA in posterior teeth was done with one-way analysis of variance. Post Hoc test was done to find the significance of the Curve of Spee between Angle's Class I, Class II, and Class III malocclusions.

DISCUSSION

The primary goal of orthodontic treatment relies on establishing a stable relationship with the underlying basal bone.[5] Shape, size, and position of teeth, jaw size, facial pattern, musculature, and occlusion are various factors that can cause variation. The six elements of orofacial harmony developed by Andrews act as a guideline for achieving ideal occlusion, where the teeth are positioned in harmony with the basal bone and the surrounding soft tissue. Archwires shaped differently from the WALA ridge may cause adverse effects on the gingiva, root, and alveolus. In this study, the plaster models of the mandibular arch with Angle's Class I, Class II, and Class III were analyzed. The results showed that the horizontal distance from FA-WALA in mandibular posterior teeth increased gradually from 1st premolar to 2nd molar on both sides.[6] These were similar to the previously reported studies of Andrews and Andrews, Kanashiro and Vigorito, and Ronay et al. The values in the 1st molars were 2.38 mm and 2.41 mm, 2.30 mm in Angle's Class II and Class III, respectively [Table 1]. The values are higher than the studies reported by Andrews (2.0 mm) Kong-Zarate et al. (2.12 mm), and Trivino et al. (2.21 mm). This can be explained as there was a more lingual position of the mandibular teeth than with normal occlusion. Based on this study, there was more inclination and lingual position of teeth from premolars to 1st molars, while the 2nd molar was more stable irrespective of the class of malocclusion.

Table 1

Comparison of FA–WALA distance in posterior teeth in Angle’s Class I, Class II, and Class III malocclusions

Tooth	Mean±SD			P
	Angle’s Class I malocclusion	Angle’s Class II malocclusion	Angle’s Class III malocclusion
1st premolar	0.61±0.41	0.45±0.38	0.37±0.25	0.0115 (S)
2nd premolar	1.01±0.48	0.98±0.41	0.68±0.33	0.0006 (S)
1st molar	1.87±0.52	1.67±0.45	1.51±0.32	0.0015 (S)
2nd molar	2.38±0.57	2.41±0.58	2.30±0.4	0.06571
Total	1.47±0.85	1.38±0.86	1.35±0.82	0.0268 (S)

SD: Standard deviation, S: Significant

Andrews described the six keys of occlusion and found that the Curve of Spee ranged from mild to flat in subjects with proper occlusion. The curve of Spee provides posterior disocclusion and anterior tooth guidance with mandibular forward movement.[7] The depth of the Curve of Spee8 increased with the eruption of second molars and slightly decreased during adolescence and remained stable in adulthood. The Curve of Spee and WALA-FA point is subjected to occlusal variations. The Curve of Spee was measured from the cusp tip of 1st premolars on both sides. Interpretation of the results of our study revealed that the depth of the Curve of Spee was greatest in the Angle's Class II malocclusion group, followed by Angle's Class I, and Angle's Class III having the least amount of depth. The increase in the depth of the Curve of Spee in Angle's Class II was attributed to the unopposed eruption of teeth in lower anteriors due to increased overjet.[9] The results were similar to the study by Veli, Ozturk, and Uysal et al.

Intercanine width FA-FA and intercanine WALA-WALA

Transverse dimensions of the mandibular arch form in subjects across different malocclusions were assessed in canine-canine FA and canine-canine WALA points.10 The arch form was established based on mandibular canines and molars.[11] The mandibular intercanine width was significantly larger in Angle's Class III group12 than in Angle's Class II which indicates a restricted growth in this region of Angle's Class II malocclusion.[1314] Angle's Class I malocclusion had a wider width of mandibular arch than in Angle's Class II malocclusion.15 Increased intercanine width in Angle's Class III can be imputed to the increased growth potential of mandible even in transverse dimension.16 The disparity in age or severity of malocclusion may cause differences in studies.

CONCLUSION

The horizontal distance from the FA-WALA in posterior teeth increased incrementally in Angle's Class I, Class II, and Class III malocclusions. The WALA-FA distance showed the difference between classes for all teeth except 2nd molars. The Curve of Spee was deepest in Angle's Class II malocclusion[17] [Table 2] and intercanine FA and WALA width was widest for Angle's Class III malocclusion [Table 3].[18] The WALA ridge helps in determining the faciolingual position of the posterior teeth and identifies the transverse dimension.[19]

Table 2

Comparison of the Curve of Spee between Angle’s Class I, Class II, and Class III malocclusions

Parameter	Mean±SD			P
	Class I	Class II	Class III
Curve of Spee	1.425±0.65	1.81±0.45	1.17±0.34	0.0466 (S)

SD: Standard deviation, S: Significant

Table 3

Comparison of intercanine width (FA-FA) and WALA-WALA (intercanine width) between Angle’s Class I, Class II, and Class III malocclusions

Malocclusion	Mean±SD
	FA-FA (intercanine width)	WALA-WALA (intercanine width)
Angle’s Class I	30.97±2.78	31.76±2.82 (S)
Angle’s Class II	28.59±3.58	29.61±3.43 (S)
Angle’s Class III	35.98±1.69	36.78±1.62 (S)

SD: Standard deviation, S: Significant

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.