Skeletal and Dental Effects of Maxillary Protraction in Patients with Angle Class III Malocclusion A Meta-Analysis

Abstract

The aim of this study was a quantitative review of the published results concerning the treatment effects of maxillary protraction in patients with Angle Class III using the meta-analysis method. 85 articles published between 1966 and 1998 were reviewed under strict, pre-defined criteria. Of these, 12 studies presenting results of cephalometric measurements were selected for further analysis. The results of different cephalometric measurements were reviewed with Dstat 1.10 software in order to calculate a standardized treatment effect variable. The homogeneity of the variances of the different effect variables as well as a composite effect were calculated. For the latter, each individual effect variable was weighted by the reciprocal of its variance, with predefined study characteristics being used for categorical model calculations. Our results showed a significant composite effect of the therapy on the skeletal components (SNA: 1.4 degrees, composite effect = 1.11; SNB: -1.3 degrees, composite effect = -0.94; ANB: 2.6 degrees, composite effect = 1.73; lower anterior face height: 1.6 mm, composite effect = 0.85) as well as on the dental components of the face (inclination of upper incisors: 1.6 degrees, composite effect = 0.37; inclination of lower incisors: -3.7 degrees, composite effect = -0.87). However, several of the individual effect variables demonstrated a significant lack of homogeneity. Study characteristics which might possibly account for this variability were the patients' ages at the start of treatment and the combination of maxillary protraction with rapid maxillary expansion. In summary, maxillary protraction was shown to have a significant treatment effect. The meta-analysis method proved to be a valuable tool in judging the current status of a given clinical therapeutic concept.

Effectiveness of maxillary protraction using a hybrid hyrax-facemask combination: A controlled clinical study

“…A meta-analysis of conventional maxillary protraction reported a mean increase in the SNA angle of 1.4u. 7 Occlusal effects related to the control group, however, appeared to be slightly higher using the conventional approach. In the study by Westwood et al, 26 the overjet improved by 4.8 mm compared with the 3.2 mm in the current investigation; the molar relationship improved by 3.8 mm compared with 3.1 mm.…”

“…[1][2][3] There is evidence that this method is particularly efficient during the early developmental phases. [4][5][6] The most efficient treatment time seems to be in the early mixed dentition, 7 although some studies also report good outcomes when treatment is started in the late mixed dentition. 8 Usually, orthopedic forces for maxillary protrusion are applied via tooth-borne devices.…”

“…Larger forward (1.0 mm) and downward (0.5 mm) movement of point A was observed in the expansion group. In a meta-analysis, Jä ger et al 7 identified a greater effect of maxillary protraction after RME. In a randomized clinical trial, however, Vaughn et al…”

Analysis of Sutural Strain in Maxillary Protraction Therapy

“…The skeletal effects of maxillary protraction therapy, however, are still largely unclear and the subject of some controversy in the literature, although there is agreement that a slight increase in both the SNA and the ANB occurs during maxillary protraction therapy. 4,10 This clearly does not prove a skeletal effect of the apparatus, however, since no differentiation was made between growth and apparatus effects in most of the papers published. Sung and Baik, 11 on the other hand, confirmed that when comparing a protraction group with a control group of the same age showing normal growth, no significant difference could be found between the groups.…”

“…3,4 By applying an anteriorly directed, orthopedic force vector to the superior dental arch, growth of the maxilla should be encouraged in an anterior direction, 5 whereby force vectors are applied to the maxillary structures by using various facial masks such as those developed by Delaire 6 or Grummons 7 or by using reverse-pull headgear. 8 As a result of the anterior directed force vectors reproaching on the dental arch, a mesial movement of the posterior teeth and a protrusion of the anterior upper jaw teeth occurs, 4,9 which facilitates a dental compensation of the skeletal dysgnathia for Class III cases. The skeletal effects of maxillary protraction therapy, however, are still largely unclear and the subject of some controversy in the literature, although there is agreement that a slight increase in both the SNA and the ANB occurs during maxillary protraction therapy.…”