Comparison of anchorage reinforcement with temporary anchorage devices or a Herbst appliance during lingual orthodontic protraction of mandibular molars without maxillary counterbalance extraction

BACKGROUND Orthodontic protraction of mandibular molars without maxillary counterbalance extraction in cases of aplasia or extraction requires stable anchorage. Reinforcement may be achieved by using either temporary anchorage devices (TAD) or a fixed, functional appliance. The objective was to compare the clinical effectiveness of both methods by testing the null-hypothesis of no significant difference in velocity of space closure (in mm/month) between them. In addition, we set out to describe the quality of posterior space management and treatment-related factors, such as loss of anchorage (assessed in terms of proportions of gap closure by posterior protraction or anterior retraction), frequencies of incomplete space closure, and potential improvement in the sagittal canine relationship. METHODS Twenty-seven subjects (15 male/12 female) with a total of 36 sites treated with a lingual multi-bracket appliance were available for retrospective evaluation of the effects of anchorage reinforcement achieved with either a Herbst appliance (n(subjects) = 15; 7 both-sided/8 single-sided Herbst appliances; n(sites) = 22) or TADs (n(subjects )= 12; 2 both-sided; 10 single-sided; n(sites) = 14). Descriptive analysis was based on measurements using intra-oral photographs which were individually scaled to corresponding plaster casts and taken on insertion of anchorage mechanics (T1), following removal of anchorage mechanics (T2), and at the end of multi-bracket treatment (T3). RESULTS The null-hypothesis was rejected: The rate of mean molar protraction was significantly faster in the Herbst-reinforced group (0.51 mm/month) than in the TAD group (0.35). While complete space closure by sheer protraction of posterior teeth was achieved in all Herbst-treated cases, space closure in the TAD group was achieved in 76.9% of subjects by sheer protraction of molars, and it was incomplete in 50% of cases (mean gap residues: 1 mm). Whilst there was a deterioration in the canine relationship towards Angle-Class II malocclusion in 57.14% of space closure sites in TAD-treated subjects (indicating a loss of anchorage), an improvement in canine occlusion was observed in 90.9% of Herbst-treated cases. CONCLUSION Subjects requiring rapid space closure by molar protraction in combination with a correction of distal occlusion may benefit from using Herbst appliances for anterior segment anchorage reinforcement rather than TAD anchorage.