Abstract
Anchorage loss is very disturbing for orthodontists and patients during orthodontic treatment, which usually results in bad treatment effects. Despite the same treatment strategy, different patients show different tendencies toward anchorage loss, which influences the treatment results and should preferably be predicted before the treatment is begun. However, relatively little research has been conducted on which patients are more likely to lose anchorage. The mesial tipping of the first molar marks the onset of anchorage loss, and changes in the angulation of the first molar are closely related to anchorage loss. This cross-sectional study aimed to determine how the mesiodistal angulation of the upper first molars changes during general orthodontic treatment and to identify the individual physiologic factors leading to these changes in a large sample of 1403 patients with malocclusion. The data indicate that the upper first molars tend to be tipped mesially during orthodontic treatment, and this constitutes a type of anchorage loss that orthodontists should consider carefully. Compared to treatment-related factors, patients' physiologic characteristics have a greater influence on changes in the angulation of the upper first molars during orthodontic treatment. The more distally tipped the upper first molars are before treatment, the more they will tip mesially during treatment. Mesial tipping of the upper first molars, and therefore, anchorage loss, is more likely to occur in adolescents, males, patients with class II malocclusion and patients who have undergone maxillary premolar extraction. This finding is of clinical significance to orthodontists who wish to prevent iatrogenic anchorage loss by tipping originally distally tipped upper molars forward, and provides a new perspective on anchorage during orthodontic treatment planning.
Highlights
As early as 1728, the French dental pioneer Fauchard proposed that if mechanical forces were used during dental treatment, adequate tooth anchorage must be provided [1]
The results of independent-samples t-tests and analysis of variance (ANOVA) are summarized in Table 2 and Figure 2
The average change in upper first molars (UMs)/palatal plane (PP) among adults was close to 0u, which means that the UM/PP in adults was nearly unchanged throughout orthodontic treatment
Summary
As early as 1728, the French dental pioneer Fauchard proposed that if mechanical forces were used during dental treatment, adequate tooth anchorage must be provided [1]. Owing to certain anatomical characteristics, anchorage loss occurs much more in the upper jaw than in the lower jaw This dilemma compels us to consider the role of the upper first molars (UMs) in anchorage control. Orthodontists once tried to achieve ‘‘proper’’ upper molar angulation; today, they seem to accept the fixed angulation achieved using pre-adjusted buccal tubes or brackets. This standard prescription is applied to a wide variety of malocclusions, even though the different initial molar angulations and their changes during orthodontic treatment presumably have a significant effect on anchorage and on the results of treatment
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