Clinical Application and Advancement Procedure
1. Working bites should be taken in a comfortably achievable protrusive position for the patient and open 6mm at the posteriors. The centrelines should be coincident if possible. If the patient cannot give a repeatable centric position then proceed as for Class 2 Div 2 cases.
2. For severe Class 2 Div 2 cases where a working bite cannot be taken due to a deep anterior overbite, the models may be articulated in RCP and then opened up on the articulator to give clearance for the screws and the lower model slid forward on the articulator fork to give the start position. You will need to advise your technician accordingly. Advancement can then follow the proclination and alignment of the upper incisors. (NB Screw positioning can sometimes be difficult to judge in these cases)
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3. To advance the appliance, after cleaning any debris from the screw heads, the screws are removed (Fig. 1) and spacers of appropriate length slid onto the screws (Fig. 2) before replacing them in the appliance (Fig. 3). Screws must be fully tightened to prevent them from working loose during use.
4. Spacers should normally only be applied to a maximum of 50% of the screw length i.e. 6mm for 12mm screws, 8mm for 16mm screws etc. Any greater percentage advancement may lead to fracturing of the screw housings and blocks. Ideally longer screws should be used once the 5mm and 9 mm marks have been reached respectively.
5. If necessary the 20mm screws may be advanced to 12mm in final stages.
6. Asymmetric advancement can be achieved and centrelines corrected, by applying unequal spacers.
7. Avoid damaging the screw heads as this will cause premature lower block wear.
8. If severe block wear is apparent then screw positioning and screw head condition should be checked. Block wear can also occur if low quality self-cure acrylic is used.
9. Some block wear is inevitable in those patients who have a tendency to bruxing.
10. Remember that if screws are converging then the amount of advancement achieved will not equal applied spacer length.
11. Never try to advance the appliance without using spacers and fully re-tightening the screws.
12. All components are classified for single use only.