Extra-oral devices can be used for distal movement as well as anchorage reinforcement. For anchorage control wearing the headgear at night-time only is usually enough. In order to produce distal movement, the patient should wear the appliance in excess of 12 hours usually for the evenings as well as at nighttime. While some practitioners increase the force levels for distal movement purposes, it is our experience that this is not necessary and a force of approximately 250-300 g per side is adequate for both distal movement and anchorage control.
Many devices have been described to reduce or eliminate the need for headgear. These are however of limited use and can only produce a very small amount of extra space. If these gadgets are used without anchorage re-enforcement unwanted mesial movement of the anchor teeth could occur. Figures 14a-c shows one example known as a Jones jig. To produce distal movement of the molars the anchorage is reinforced with an anterior trans-palatal arch. A jig incor-
Fig. 14a-c A Jones jig for distal movement of the molars (14a). A palatal arch is fitted to the first premolars to increase the anterior anchorage. A jig is then inserted into the buccal arch wire and headgear tubes. An open nickel titanium coil spring is then slid over the shaft of the jig and compressed by sliding a collar onto the shaft and tying it to the premolar (14b). This then uses the upper premolars and palatal vault to distalise the molars (14c). Note the simultaneous mesial movement of the first premolars which is a sign of anchorage loss
porating a nickel-titanium coil spring is inserted into molar tubes and tied into the premolar bands. The molars are distalised using the anterior teeth from premolar to premolar as the anchorage block. It is important to note the loss of anchorage that is occurring as demonstrated by the simultaneous mesial movement of the first premolars. Once distal movement of the molars has been achieved the anchorage reinforcement can be transferred to the molars (palatal arch or Nance button) and the premo-lars, canines and incisors retracted. True anchorage re-enforcement with these devices is difficult to achieve and headgear, or implants must still be considered the mainstay of producing effective distal movement.
Thanks to Mr. R Cousley for figure 6 and Mr. JKinelan for figures 14a-c
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