Correlation of Inter Canine Width with Basal Plane Angle in Patients Seeking Orthodontic Treatment

Keywords

Arch Width; Basal Plane Angle; Inter-Canine Width; Lateral Cephalometry; Canine Width.

Introduction

Lateral cephalometry has been widely used in clinical orthodontics to assess the skeletal, dental, and soft tissue relationships of craniofacial complex [1]. Proper knowledge of facial structures is very important to achieve ideal facial profile and pleasing esthetic harmony [2]. In this new era, facial harmony is of paramount value especially to orthodontists [3]. Before treating an orthodontic patient, every aspect of treatment should be planned in a way that not only to correct the malocclusion but also to improve facial esthetics and profile. That is why during treatment planning, orthodontists have to have certain diagnostic aids to assess various diagnostic parameters [4]. Various cephalometric analyses have been done to study the relationship of teeth with each other and with skeletal bases in the sagittal and vertical planes. Basal plane angle of face can be determined by a number of factors, among which PP-MP angle is one of the most important [5]. Facial types are determined by different parameters, such as ratio between the lower and upper anterior facial height, the angle formed between the mandibular plane and the base of the skull, and the gonial angle [6].

Usually patients with high PP-MP angle tends to have a long, narrow face, and one with low PP-MP angle often has a short, broad face [7, 8]. A study was done to assess the relationship between dental arch width and vertical facial morphology [9]. Ricketts et al. (1982), Enlow and Hans (1996) and Wagner and Chung (2005) reported that a long-faced individuals usually have narrow transverse dimension and a short-faced individuals have wider transverse dimension [9]. Howes (1957) found that steep MP individuals generally had larger teeth and narrower and shorter arches than flat mandibular plane individuals when measured from the buccal cusp tips of the maxillary first premolars.

Clinically, preformed arch wires are routinely used by many orthodontists regardless of the facial type and gender of the patients. The purpose of the present study was to investigate the correlation of dental arch width with basal plane angle. This will help us to determine which arch wires to be used in individual facial types.

Material and Methods

A cross sectional study was conducted in the Department of Orthodontics and Dentofacial Orthopaedics, Saveetha Dental College and Hospitals, Chennai, India. 50 patients seeking orthodontic treatment were selected for the study. The subjects were selected based on following inclusion and exclusion criteria:

Inclusion criteria

• Male and female patients having permanent dentition up to first permanent molar
• No supernumerary tooth
• No permanent tooth extraction before the study (excluding 3rd molar)
• No skeletal asymmetry

Exclusion criteria

• Patients who had received previous orthodontic treatment
• unilateral or bilateral posterior cross bites

Patients history was taken and clinical examination was done to confirm the inclusion criteria. Alginate impressions of patients were taken and casts were poured out of them. A digital Vernier calliper was used to record the measurements on dental cast. The inter-canine width of maxilla and mandible was recorded.The inter canine width was measured from cusp tip of canine to the cusp tip of the other canine.(Figure 1)

Lateral cephalograms was taken and each radiographic film was traced on Facad® Software. For each individual PP-MP angle was measured.The collected data was co-related,each patients intercanine width was co-related to the basal plane angle.

Result

A total of 50 untreated adults were selected in this cross-sectional study to find out the correlation between inter-canine width and basal plane angle in patients seeking orthodontic treatment. The minimum age was above 16 years whereas the maximum age of patients was 32 years with a mean age of 16.62 ± 4.974 years.

The distribution of PP-MP angle showed that the mean PP-MP angle was 24.98 ± 7.61 with a minimum angle of 15.23 degrees and maximum of 40.34degrees. There were 18 (36%) persons who had low PP-MP angle (< 22), 14(28%) had normal PP-MP angle (23-27) and 18 (36%) participants of the study had high PPMP angle(>27).(Table-1)

To find out the correlation of PP-MP angle with inter-canine width of maxilla and inter-canine width of mandible, Pearson correlation analysis was applied. Which showed that there was statistically significant and strong correlation of -0.919 between PP-MP angle and inter-canine width of maxilla, but a weak co-relation of -0.419 between the basal plane angle inter-canine width of mandible in this study (Table -2).

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Figure 1:

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Figure 1. Inter-canine width as measure on dental cast using vernier calliper.

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Table 1:

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Table 1. Basal Plane Angle amongst three growth patterns.

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Table 2:

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Table 2. Co-relation between inter-canine width of maxilla and mandible to bass-plane angle.

Discussion

Correction of vertical dysplasia is very important in achieving a balanced profile after orthodontic treatment. As per the results of this study mean inter-canine width decrease as the basal plane angle increases, hence individualised arch forms should be used in patients with variable vertical pattern. This confers to the basic law of stability according to which arch dimensions should not be changed especially across the canines. Use of arch expansion mechanics in patients with increased PP-MP angle should be at all avoided or used with maximum caution. In comparison with a study performed by Forster et al for the maxillary arch, there was a statistically significant inverse relationship between the mandibular plane angle and dental arch widths. However, statistical analysis showed that the r value was small, which suggests that the correlation was not very strong [15]. Similarly in this study, results showed that there was statistically significant and strong correlation between PP-MP angle and inter-canine width of maxilla. Our study did not compare the difference of arch widths on basis of gender, like the previous studies by Howes, 1957; Isaacson et al, 1971; Nasby et al, 1972; Schulhof et al, 1978 but another study investigated untreated adult males and females separately which showed a significant differences in maxillary and mandibular arch widths in males and females [17, 18].

Musculature has a possible link in this close relationship between the transverse dimension and vertical facial morphology. There are a number of studies have illustrated the influence [19] of masticatory muscles on craniofacial growth. The general agreement is that individuals with strong or thick mandibular elevator muscles tend to exhibit wider transverse head dimensions (Ringqvist, 1973; Ingervall and Helkimo, 1978; Weijs and Hillen, 1984; Kiliaridis and Kalebo, 1991; Van Spronsen et al., 1991; Bakke et al. , 1992; Kiliaridis, 1995) [20, 21]. Strong masticatory musculature is often associated with a brachyfacial pattern (short face). This muscular hyperfunction causes an increased mechanical loading of the jaws. This, in turn, may cause an induction of sutural growth and bone apposition which then results in increased transverse growth of the jaws and bone bases for the dental arches.

In terms of the difference in arch width between males and females, Wei (1970) evaluated PA cephalograms of Chinese adults and noted gender differences in maxillary and mandibular intercanine widths [22]. Eroz et al. (2000) reported that in children, males had significantly larger intermolar widths than females [23]. Ideally, this type of study should have been conducted on patients with ideal dentitions without any crowding or spacing [23]. However, due to difficulties in finding ideal untreated subjects and subsequent limitations in sample size, the degree of crowding and spacing was not included in the accepted criteria.

Conclusion

The following conclusion can be made from this study: Since dental arch width is associated with facial vertical morphology, using individualised arch wires according to each patient’s pre-treatment arch form and inter canine widths is suggested during orthodontic treatment.