Obstacles to space closure

In almost all cases, space closure is easy and proceeds uneventfully. Only rarely are problems encountered. If it appears that space is not closing as it should (about 1 mm per month typically), the spaces should be carefully measured at successive visits. If they are not reducing, or if wire is not appearing gradually from the distal of the molar tube, then possible obstacles should be evaluated before resorting to different mechanics:

• Inadequate leveling. The working rectangular wires need to be in place for at least I month with passive ties (p. 255), to ensure proper leveling and freedom from posterior torque pressure. Also, it is important not to attempt overbite correction using reverse curve in the lower archwire at the same time as attempting space closure. Overbite control should be achieved before space closure.

• Damaged brackets. Lower first molar brackets can be damaged and partly closed down by excessive biting forces. As a short-term measure, the wire may be thinned in that area, but it is belter to replace the molar attachment. The use of first molar non-convertible lubes is recommended, as these are not susceptible to damage in the same way as first molar convertible tubes, and they have other advantages (pp 53 & 54).

• Incorrect force levels. Forces above the recommended levels can cause tipping and friction, and thus prevent space closure. Inadequate force may sometimes be a cause of slow- or non-space closure in adult treatment. Force levels need to be in balance with archwire size and stiffness. If they are not in balance, archwire deflection and unwanted friction can occur. It has been shown that archwire deflection causes friction8,9. Also, recent research in Japan10 has measured the amount of deflection of rectangular archwires in response to typical space closure force. It has been shown that on average 47% more deflection occurs with a .016/.022 wire compared with a .010/.025 wire (Fig. 9.26).

• Interference from opposing teeth (Fig. 9.27). This can prevent lower space closure, and it is necessary to carefully check the occlusion. In the past this was often related to vertical bracket-positioning errors in the upper arch. The use of gauges has reduced ihese errors, and interference is seldom an obstacle now.

Fig. 9.26 Force levels need to be in balance during space closure and sliding mechanics. A .019/ 025 steel rectangluar wire is recommended in the .022 slot.

Fig. 9.26 Force levels need to be in balance during space closure and sliding mechanics. A .019/ 025 steel rectangluar wire is recommended in the .022 slot.

Fig. 9.27 Space closure can be prevented by interference from opposing teeth. In this illustration, the bracket on the upper premolar is placed too far gingivally, and the premolar crown is preventing full closure of lower space.

• Soft tissue resistance. Gingival overgrowth in the extraction sites can prevent space closure, and can cause space to re-open after appliance removal (Fig. 9.11, p. 253). It can also be a problem when closing an upper midline diastema. Care is needed to maintain good oral hygiene and avoid loo rapid space closure, as these can contribute to local gingival overgrowth. In a few cases, local surgery to soft tissue may be indicated.

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