Efficacy of intraarch mechanics using differential moments for achieving anchorage control in extraction cases,☆☆,,★★

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Abstract

A prospective survey was conducted to test the hypothesis that maximum anchorage can be achieved in the maxillary arch by controlling forces and moments using intraarch mechanics while retracting canines into first premolar extraction sites. The sample consisted of 24 patients (mean age 18 years, 9 months) who required the extraction of two maxillary first premolars, with or without extractions in the mandibular arch. Movements of the first molars, canines, and incisors were evaluated with 6 cephalometric variables and 10 study model variables. T tests were used to assess differences between pretreatment and postretraction tooth positions. Cephalometrically, the maxillary first molars (left and right sides combined) moved mesially ONLY 0.7 mm (SD 0.43; p < 0.008). All other cephalometric variables showed no significant differences between the two time points. From the study models, the molars moved mesially ONLY 0.5 mm on both the right and left sides (right side SD = 0.43 and left side SD = 0.38; p < 0.005), while the canines were retracted on average 5.8 mm on the right side and 5.6 mm on the left. The molars and canines showed significant mesiopalatal and distolingual rotations, respectively. Many of the study model and cephalometric variables were significantly correlated to one another. This study questions the need to use adjunctive appliances, which directs a distal force to the posterior teeth, if horizontal molar anchorage control is a treatment objective. By controlling forces and moments, using intraarch mechanics while retracting maxillary canines into first premolar extraction sites, minimal molar anchorage loss occurred. (Am J Orthod Dentofac Orthop 1997;112:441-8.)

Section snippets

MATERIALS AND METHODS

The study design was a prospective longitudinal investigation with one observation subsequent to the initial observation. No plan for unbiased allocation by randomization was followed because patients were selected on the basis of anchorage needs, and there was no comparison group selected.

The sample consisted of 24 subjects (14 females, 10 males) from the orthodontic department, University of Illinois at Chicago. Ages ranged between 12 years, 5 months, to 43 years, 10 months, with a mean

RESULTS

On average, canine retraction time was 7.1 months with a range of 3 to 12 months. In three patients, complete retraction of the canines was not performed because treatment needs at that time necessitated that the posterior teeth be allowed to move mesially to complete the space closure. The data for the latter three cases were included in the study, because it was decided the findings would not be influenced.

The means and standard deviations for the cephalometric variables are listed in Table I

DISCUSSION

The current study primarily evaluated anchorage control of the molars in the anteroposterior dimension. The horizontal, vertical, and angular positions of the incisors and molars were measured both before treatment and after canine retraction to determine whether the auxiliary arch wire produced side effects (particularly molar extrusion, incisor intrusion, and incisor proclination) that could be unfavorable in some cases. No statistically significant differences were found in the vertical and

CONCLUSIONS

  • 1.

    Maxillary canines can be retracted into extraction sites with minimal (clinically insignificant) horizontal anchorage loss of the molars by controlling forces and moments.

  • 2.

    These results suggest that cervical headgear, Nance holding arches, and other adjunctive appliances are not necessary for horizontal molar anchorage control in the maxillary arch.

  • 3.

    When using these mechanics, marked mesiopalatal molar and distopalatal canine rotation occurred, which indicated the need for counteractive forces

References (21)

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    Iwasaki et al36 recently demonstrated this relationship clinically. Differences between controlled and uncontrolled tipping are clinically relevant because rates of tooth movement can be slowed or increased, relatively, by moving teeth in different ways (ie, uncontrolled tipping, controlled tipping, and translation).28,29 Importantly, post-hoc tests showed that our study had insufficient power to rule out a difference between jaws in the amounts of canine cusp retraction.

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This article is based on research by Dr. Rajcich submitted as partial fulfillment of the requirements for the Degree of Master of Science in Oral Sciences in the Graduate College of the University of Illinois at Chicago, 1996.

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aProfessor.

Reprint requests to: Dr. Cyril Sadowsky, University of Illinois at Chicago, 801 S. Paulina, Chicago, IL 60612.

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