14: Class III Correctors

CHAPTER 14

Class III Correctors

Peter Ngan

The skeletal Class III malocclusion is characterized by mandibular prognathism, maxillary deficiency, or a combination of both. These patients may have a retrusive nasomaxillary area and a prominent lower third of the face. Intraorally, patients usually present with a Class III molar relationship and a reverse overjet depending on the severity of the skeletal discrepancy.

Many treatment approaches have been advocated for Class III patients, ranging from early orthopedic intervention to camouflage and definitive surgical intervention. Methods designed to intercept the developing malocclusion have included maxillary expansion and protraction with a facemask, chin cup and fixed orthodontic appliance therapy. In this chapter, an attempt is made to answer a few frequently asked questions related to the use of these Class III correctors, including the indications for treatment, treatment timing, and the response of these appliances to treatment.

1 What is pseudo Class III malocclusion, and how can these patients benefit from early treatment?

Patients with pseudo Class III malocclusion often present with anterior crossbites that are caused by a premature tooth contact or improper inclinations of the maxillary and mandibular incisors (< ?xml:namespace prefix = "mbp" />Fig. 14-1). Elimination of the centric occlusion/centric relation discrepancy may avoid abnormal wear and traumatic occlusal forces to the affected teeth, avoid potential adverse growth influences in the maxilla and mandible, and improve maxillary lip posture and facial appearance.1

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FIG 14-1 A-C, Patients with a pseudo Class III malocclusion can often present with an anterior crossbite (A and B) that can be manipulated back to an end-to-end incisal relationship in centric relation (C).

Correction of single or multiple anterior teeth in crossbite can be accomplished by using a fixed or removable appliance with an inclined plane, removable appliance with auxiliary spring, and lingual arch with finger springs (Fig. 14-2).2

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FIG 14-2 A-C, Correction of an anterior dental crossbite (A) with a fixed lingual arch and finger springs (B). C, Posttreatment photo.

2 What is a Delaire facemask?

The Delaire protraction facemask is used in the treatment of patients with Class III malocclusion and a maxillary deficiency.3 Oppenheim4 was first to suggest that one could not control the growth or anterior displacement of the mandible and suggested moving the maxilla forward in an attempt to counterbalance mandibular protrusion. Petit5 later modified Delaire’s basic concept by increasing the amount of force generated by the appliance, thus decreasing the overall treatment time.

The protraction facemask is made of two pads that contact the soft tissue in the forehead and chin region (Fig. 14-3). The pads are connected by a midline framework and are adjustable through the loosening and tightening of a set screw. An adjustable anterior wire with hooks is also connected to the midline framework to accommodate a downward and forward pull on the maxilla with elastics. To minimize the opening of the bite as the maxilla is repositioned, the protraction elastics are attached near the maxillary canines with a downward and forward pull of 30 degrees to the occlusal plane (Fig. 14-4). Maxillary protraction generally requires 300 to 600 g of force per side, depending on the age of the patient. Patients are instructed to wear the facemask for 12 hours a day.

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FIG 14-3 The protraction facemask uses the forehead and chin as anchorage to protract the maxilla forward and downward.

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FIG 14-4 A, Protraction elastics are attached to the intraoral anchorage appliance near the maxillary canines region with a downward and forward pull of 30 degrees to the occlusal plane. B, The force vectors that minimize tilting of the palatal plane.

3 When is facemask therapy indicated?

The facemask is most effective in the treatment of mild to moderate skeletal Class III malocclusions with a retrusive maxilla and a hypodivergent growth pattern. Patients presenting with some degree of anterior mandibular shift on closure and a moderate overbite have a more favorable prognosis (Fig. 14-5, A-H). The correction of anterior crossbite and mandibular shift results in a downward and backward rotation of the mandible that diminishes its prognathism (Fig. 14-5, I-P).

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FIG 14-5 A-H, Eight-year-old patient with a Class III malocclusion and a deficient maxilla treated with maxillary expansion and protraction. A and B, Facial photos. C-G, Intraoral photos.H, Cephalometric radiograph. I-P, Posttreatment photographs showing an improvement in facial profile and correction of the anterior crossbite with 8 months of maxillary protraction. I and J, Facial photos. K-O, Intraoral photos. P, Cephalometric radiograph.

4 Is expansion necessary for protraction facemask treatment?

Various appliances have been used as anchorage for maxillary protraction, including palatal arches and banded and bonded expansion appliances (Fig. 14-6). Several circummaxillary sutures play an important role in the development of the nasomaxillary complex, including the frontomaxillary, nasomaxillary, zygomaticotemporal, zygomaticomaxillary, pterygopalatine, intermaxillary,/>

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Jan 1, 2015 | Posted by in Orthodontics | Comments Off on 14: Class III Correctors
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