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ePaper created 2017-03-17, 13:11:17 | version 1.38.0
| industry report rapid overbite correction Figs. 2a & b: Severe overbite of 120 % associated with CNS-muscle hyperactivity and skeletal vertical mandibular overclosure (VMO). Freeway space at rest was excessive of 10 mm at the molars (Figs. 4a & b) where the norm is 3 mm. Fig. 2a Fig. 2b ments. New tools to address deep overbite are de- sirable (Fig. 1). Research has verifi ed deep overbites are also highly susceptible to one of the highest levels of relapse.1-6 One of the main reasons ap- pears to be centred around increased muscle hy- peractivity that has long been associated with the cause of deep overbite. However, this muscle hyperactivity is secondary to our current clinical perception. The central nervous systems (CNS) plays a higher role through CNS hyperactivity, tension, or stress that is a precursor to producing muscle hyperactivity (in conjunction with other implicating factors such as dental interferences, crossbites and TMD). Due to the primary nature of the CNS ethology, today the differentiating term CNS-muscle hyperactivity is preferred to the blended and often lost term of neuromuscular activity used in the past. The genetic CNS disposi- tion and personality of the patient is a primary factor compared to simply muscle hyperactivity in severe overbite. A good medical and social history is vital in the diagnosis of patient disposition such as a Type A (e. g. proactive, ambitious, over- achiever) for instance, prior to treatment planning and prior to retaining deep overbite long-term. Figs. 3a–d: The fi rst generation BT1 was a rigid one-piece (a). The BT1 prototypes are shown in test-polycar- bonate with a positioning instrument used in the vertical groove (b). Anterior guidance is produced by the curved design of the BiTurbo2 (c). The vertical groove permits easier debonding when needed, than past solid form bite supports (d). Fig. 3a Fig. 3b Fig. 3c Fig. 3d 32 ortho 1 2017 CNS-muscle hyperactivity may additionally infl u- ence the malalignment of the dentition. In vertical mandibular overclosure into the maxilla, termed VMO, found in Class II division 1 malocclusion with severe overjet, the lower incisal edge can be crowded by the cingulum of the upper incisor. In fact, lower incisal edges have been found to impinge the palatal gingiva in severe overbite (Figs. 2a & b). Secondly, VMO also provides less space for the dentition vertically where tongue space is also restricted, which can re- sult in proclination of the lower incisors into the strong perioral musculature. Thirdly, it is clinically signifi cant that muscle hyperactivity be viewed from the labial and lingual since it includes the masse- ter-medial pterygoid sling and temporalis, but also tongue hyperactivity associated with buccal segment intrusion. In the transverse dimension, it is not unu- sual to fi nd the lateral borders of the confi ned tongue to be scalloped with dental impressions as it attempts to fi nd space by spreading out and pressing onto the occlusal surfaces of the lingual cusps during swal- lowing and at rest, associated with further buccal segment intrusion. Aetiology of deep overbite includes: 1. CNS hyperactivity, tension or stress 2. Masticatory muscle hyperactivity, particularly the elevators masseter and temporalis muscles 3. Facial muscle hyperactivity such as the orbicularis oris in Class II division 2 patients affecting upper central incisors 4. Skeletal restriction of the dentoalveolar growth of the buccal segments 5. Skeletal upward and forward or counter clockwise growth of the mandible at the chin (brachycephalics) 6. Dental interferences, crossbites, missing buccal dental units, TMD and severe posterior enamel wear reducing the posterior vertical support of the den- tition related to CNS-muscle hyperactivity. Several appliances have been developed to control the CNS-muscle hyperactivity including traditional removable or cemented anterior bite planes soldered to molar bands, and bondable resin or brackets on the palatal of the upper incisors or molars. The resin bite ramps were easily worn and swallowed by the patient, often requiring resin additions, and when placed at