Setting up Stage I

CHAPTER 8 Setting up Stage I

Getting Stage I up and running is exactly the same with Plus as with the previously familiar Rx-1 brackets. The subsequent adjustments and checks are the same too.

The description that follows shows how to set up a case along the lines illustrated in the previous chapter. The malocclusion features a marked increase in overjet, an increased overbite, plus severe upper and lower anterior crowding. The reader is invited to assume that the typodont does not have a greatly raised maxillary–mandibular planes angle or a severe increase in lower facial height, and is therefore suitable for Class II intermaxillary elastic traction. Four first premolars are extracted (Fig. 8.1).

A question commonly asked is why such a case cannot be started more simply by means of nickel–titanium aligning archwires, before proceeding to stainless arches. The answer is that, while such wires do an excellent job aligning teeth, they are unable to control the vertical dimension, and particularly the molars, in the way that stainless steel can; neither can they support the use of intermaxillary elastics. The outcome would therefore be some loss of anchorage, by mesial molar migration, and a delay in implementing overbite and overjet reduction. Both are telling disadvantages in the more severe cases, particularly in the child patient. Besides, with experience, the following method becomes easy to carry out and, once set up, is easy to adjust and maintain without a change of archwires, over the 6 months or so necessary to obtain all first stage objectives.

The base archwire

.016 inch round high tensile stainless steel is the ideal archwire for Stage I, in both arches. This has the necessary resilience to withstand forces of occlusion, combined with the flexibility required to align mild tooth-to-tooth irregularities. It is particularly suitable for bite opening, offering a good range of action without excessive forces. The long established Special Plus grade Wilcock Australian wire continues to perform well, as does the more recent Bow-Flex® wire from TP Orthodontics (La Porte, Indiana, USA) (Fig. 8.2).

The ‘horseshoe shaped’ archform, as used in straight-wire techniques, is not appropriate for the early stages of Tip-Edge, since use of an anchorage bend requires a straight posterior leg. Combining a buccal archwire curvature with a vertical anchor bend will cause the wire to ‘wriggle’ and rotate within the buccal tube, which will invite some molar rotation. Even if an initial molar rotation is present, a straight leg is the rule. No toe-in, in any shape or form, should ever be combined with an anchor bend.

The anterior curvature is interrupted by the ‘cuspid circles’, each of which should be placed mesial to its respective canine bracket. How close to the bracket will vary, according to alignment and available space. If the labial segment is crowded, the canines will need to drift distally to accommodate instanding teeth, so that the circles may be immediately mesial to the canine brackets at the start of treatment. This will minimize the need for subsequent repositioning of the circles distally along the arch. Conversely, if the incisors are spaced, it makes better sense to site the circles further mesially, to allow for the mesial movement of the canines, relative to the archwire, as the anterior space is gathered up.

Once the anteriors are aligned and in contact, the correct position for the circles will be just mesial to the canine brackets. However they should not be more than 2 mm in front of the brackets, bearing in mind that in the aligned segment the circles will be ligated to the canines by elastomeric modules (as described later in this chapter) which, if too stretched, could provoke mesial canine rotations.

If bending an archwire up by hand, begin with the anterior curvature. Each circle should then be formed so that the posterior section loops to the labial of the anterior segment and not vice versa. It should also be noted that the anterior archform curvature extends distal to the circles, across the face of the canines (Fig. 8.3).

When using Class II elastics and anchor bends, it is good practice to incorporate some overall expansion in the lower arch, as both components exert some elevating effect on the molar tube, which may cause some lingual crown deflection. Five millimetres of expansion each side, measured across the molars, is generally adequate (Fig. 8.4), but this may be increased up to twice this amount in difficult deep bite cases. Even this does not amount to a strong expanding force in so light a wire. Since the upper molars will not be carrying intermaxillary elastics, only a marginal degree of archwire expansion will be required here (Fig. 8.5), simply to counteract the effect of the anchor bend.

A considerable amount of clinical time can be saved by using preformed archwires, which are fabricated from .016 inch Bow-Flex wire (Fig. 8.6). These are size graded according to the distance in millimetres between the cuspid circles, which can be ascertained in the mouth with a flexible plastic ruler, between the mesial surfaces of both canine brackets (Fig. 8.7). As a check, the circles can be tried across the front of the mouth without inserting the posterior archwire legs, before removing the sticky identification label. Arch length and arch width can then be tailored accordingly.

Dec 31, 2014 | Posted by in Orthodontics | Comments Off on Setting up Stage I
Premium Wordpress Themes by UFO Themes