Light forces during leveling and aligning

If premolars are extracted in deep-bite cases, it is normally to reduce anterior protrusion or eliminate anterior crowding, or a combination of the two. If there is anterior protrusion without crowding, it is possible to retract the anterior segments en masse. Alternatively, the canines can be retracted alone, followed by retraction of the incisors. If the latter decision is made, extreme care must be taken not to tip the cupids distally because this results in extrusion of the incisors and further bite deepening (Fig. 6.20). For this reason, the authors prefer to carry out en masse retraction of the anterior six teeth with a rectangular steel wire after arch leveling and overbite control.

In cases with anterior crowding, it is necessary to retract canines at least until there is enough space for proper incisor alignment. In the lower arch, this is the authors' preferred treatment method. After crowding has been eliminated in the lower incisor region and the case has been leveled to the rectangular steel wire stage, then en masse movement is carried out. In the upper arch, it is not only important to retract canines until crowding is eliminated, but also to attempt to maintain a Class I canine relationship. Therefore, in certain cases, the canines may be retracted a greater distance to maintain this Class I position. This may result in some spacing mesial to the canines (Case JN, p. 123). It has been observed in many cases that the contact of the lower canine against the upper canine serves to distalize the upper canine. This additional source of anchorage is helpful in the overall management of the upper anterior segment. The upper arch can then be retracted en masse using rectangular stainless steel wires.

There is a tendency for incisors and canines to tip mesially after placement of the opening archwires, due to the built-in tip features of the preadjusted appliance system. Canine -iacebacks (p. 15) should be used to resist this mesial tipping of the canines and to retract these teeth effectively without distal tipping. Elastic forces should be avoided, because they can result in excessive distal tipping of the canines. This can lead to posterior bite opening, and the overall reaction has been called the 'roller coaster' effect (Fig. 6.20), which increases overall treatment time.

Fig. 6.20 Canine elastic retraction forces should be avoided because they can result in distal tipping of the canines, leading to the 'roller coaster' effect. This increases overall treatment time.

Fig. 6.21 Unfavorable distal tipping of the lower canines at the start of treatment. Greater care and time will be required to ensure good overbite control.

Fig. 6.22 Unfavorably angled canines can cause unwanted extrusion of the incisors after placement of the initial archwires.

Fig. 6.21 Unfavorable distal tipping of the lower canines at the start of treatment. Greater care and time will be required to ensure good overbite control.

Fig. 6.22 Unfavorably angled canines can cause unwanted extrusion of the incisors after placement of the initial archwires.

Lacebacks (p. 100) initially compress the periodontal ligament space on the distal aspect of the canine, leading to slight tipping. T his is followed by adequate time for uprighting, in response to the leveling effect of the archwire. T his uprighting occurs with a laceback, but it is not seen if elastic chains are used, because they give a continuous force which does not allow time for rebound to occur.

The discussion thus far has assumed a favorable initial position of the canines with the crowns at slight or moderate anterior inclination. However, if canines show unfavorable angulation at the start of treatment (Fig. 6.21), much greater care is needed to ensure good overbite control. Figure 6.22 shows how preadjusted brackets on unfavorably angled canines can cause unwanted extrusion of incisors after the initial archwires have been placed. The authors normally prefer to bracket the incisors that are in reasonably good alignment and include them in the initial archwires. This provides greater stability to the arch form and minimizes distal tipping of the canines. However, when canines are unfavorably angled, it may be beneficial to avoid bracketing the incisors until the canine roots have been retracted, providing more favorable angulation of the canine slots. This method minimizes the inevitable tendency for bite deepening in such cases. An alternative technique involves placing a bend in the archwire, mesial to the canines, to prevent a slight intrusive force on the incisors while the canine roots are being moved distally.

In summary, it is clear that there are many factors which can lead to bite deepening during the initial leveling stage. Effective overbite control requires the use of light forces, with minimal activation and adequate rebound time. Lacebacks have proven to be the most effective way of controlling canine position and movement, and hence the overbite, in these cases.

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