Optimum pure intrusion of a mandibular canine with the segmented arch in lingual orthodontics

Abstract

Background:

Approximately 50% patients with a deep bite possess anatomically extruded mandibular canines.

Objective:

The objective of this study was to specify an optimum toe (Θ) of the vertical segment of a cantilever from the distal aspect to achieve pure intrusion of a mandibular canine with the segmented arch in lingual orthodontics (LiO).

Methods:

The geometrical model of a mandibular canine was developed to compute the required values of Θ (positive values – toe-in, negative values – toe-out). Different positions of the cantilever attachment on the lingual bracket top (occlusal) surface were considered according to different heights (h) from the cusp of a canine i.e. 2, 3, 4 and 5 mm in each case of horizontal distance (x) from canine surface i.e. 2 and 3 mm. In $\mathit{x}=2\text{mm}$ case, the required values of Θ at $\mathit{h}=2\mathrm{,}3\mathrm{,}4\text{and}5\text{mm}$ were $-5$ °, 0°, $+6$ ° and $+11$ ° respectively. While, in $\mathit{x}=3\text{mm}$ case, the required values of Θ at $\mathit{h}=2\mathrm{,}3\mathrm{,}4\text{and}5\text{mm}$ were 0°, $+5$ °, $+12$ ° and $+17$ ° respectively.

Results:

In finite element analysis (FEA), the computed values of Θ were verified by displaying the results of a mandibular canine movement in the form of vectors of nodal displacements along with undeformed and deformed models.

Conclusions:

In the cases of $\mathit{x}=2\text{mm}\text{and}3\text{mm}$ , no toe angles were required at heights $\mathit{h}=3\text{mm}\text{and}2\text{mm}$ respectively. Hence, these can be considered as better positions of the cantilever attachment than others.