Effect of Bone-anchored Protraction on Maxillary Growth in the Young Child

Overview

Class III malocclusions may originate in a retrognathic maxilla, a prognathic mandible or both. Young patients with class III malocclusion and maxillary hypoplasia are conventionally treated with a protraction facemask in order to stimulate forward growth of the upper jaw. This treatment option is often inducing unwanted side effects including mesial migration of the teeth in the upper jaw and clockwise rotation of the mandible. Because skeletal effects are often difficult to achieve with this approach, more pronounced class III malocclusions cannot be addressed by face mask therapy. These children cannot be treated during childhood and end up in major orthognathic surgery at full-grown age. To be able to treat also the more pronounced class III malocclusion and to minimize dentoalveolar compensations new treatment methods were developed which uses skeletal anchorage.

Rationale: Class III malocclusions may originate in a retrognathic maxilla, a prognathic mandible or both. Young patients with class III malocclusion and maxillary hypoplasia are conventionally treated with a protraction facemask or reverse twin block appliance in order to stimulate forward growth of the upper jaw. This treatment option is often inducing unwanted side effects including mesial migration of the teeth in the upper jaw and clockwise rotation of the mandible. Because skeletal effects are often difficult to achieve with this approach, more pronounced class III malocclusions cannot be addressed by face mask therapy. These children cannot be treated during childhood and end up in major orthognathic surgery at full-grown age. To be able to treat also the more pronounced class III malocclusion and to minimize dentoalveolar compensations new treatment methods were developed which uses skeletal anchorage. In maxillary deficiency cases it's common to have the deficiency anteroposteriorly as well as transversely. Opening of the midpalatal suture by rapid expansion can correct the transverse hypoplasia and may produce more anterior movement of the maxilla. The proposed technique enables to start skeletal anchorage treatment at an earlier age, which also has the potential of more growth modification during treatment. Objective: To compare a new technique of skeletal traction with incorporation of maxillary expansion to conventional treatment protocols. Study design: This is a RCT Study population: Healthy human volunteers (7- 14 yrs old) with class III malocclusion due to maxillary deficiency. Intervention: The intervention consists of the application of a mentoplate (anchored with screws to the bone) in the lower jaw and two screws in the upper jaw (palate). Expansion in the upper jaw is achieved by a classic Hyrax appliance, connected to these screws. Anterior movement of the maxilla is subsequently accomplished by intermaxillary elastic traction to the mentoplate. Control group (conventional treatment): Anterior movement of the maxilla accomplished by elastic traction to a face mask Main study parameters/endpoints: The main study parameter is the difference in the amount of forward growth of the upper jaw and mid-face (measured with a cone beam CT) compared to the growth that is observed with conventional treatment. A cone beam CT will be made before the start of traction therapy (baseline) and after 1 year of therapy to evaluate the amount of expansion and forward growth of the maxilla. One last cone beam CT will be produced at the end of growth, 5 years after start of the orthodontic traction, to evaluate the long-term stability of the obtained advancement. Other end-points will be patients' satisfaction and complication-rate.