Root resorption associated with maxillary buccal segment intrusion using variable force magnitudes

OBJECTIVES

To compare the root resorption resulting from miniscrew-supported maxillary posterior dentoalveolar intrusion using two different force magnitudes.

MATERIALS AND METHODS

Adult patients with skeletal open bite, indicated for maxillary posterior dentoalveolar intrusion, were recruited and randomly assigned to the comparison or intervention groups. The comparison group involved applying 200 g of intrusive force per segment, which measured 20 g per root, while this force was 400 g per segment in the intervention group, measuring 40 g per root.

RESULTS

Twenty participants were included in the final analysis after 2 patients dropped out, 1 in each group, to end up with 10 subjects (200 roots) per group. There was statistically significant root resorption of 0.84 ± 0.96 mm and 0.93 ± 1.00 mm in the comparison and the intervention groups, respectively. However, there was no statistically significant difference between the groups.

CONCLUSIONS

Root resorption inevitably took place in association with orthodontic intrusion. However, increasing the magnitude of the intrusive force did not increase the amount of root resorption, either statistically or clinically.

Force magnitude as a variable in maxillary buccal segment intrusion in adult patients with skeletal open bite

OBJECTIVES

To compare the effects of two different force magnitudes on maxillary posterior segment intrusion using mini-screws. The null hypothesis was that there would be no difference between the two force magnitudes.

MATERIALS AND METHODS

Adult patients with skeletal open bite and a dental open bite ranging from 3 to 8 mm were recruited for this trial. The comparator group had 200 g of intrusive force applied for posterior segment intrusion, whereas 400 g of force was applied in the intervention group. Primary outcomes were the amount of posterior teeth intrusion and anterior open bite closure.

RESULTS

Twenty-two subjects were randomized to include 11 participants in each group. One participant dropped out in each group, leaving us with 10 subjects to be analyzed per group. There was statistically significant posterior teeth intrusion of 2.42 ± 2.06 and 2.26 ± 1.87 mm for the comparator and intervention groups, respectively, with no difference between them. Statistically significant open bite closure was achieved in both groups, measuring 2.24 ± 1.18 and 3.15 ± 1.06 mm in the comparator and intervention groups, respectively, with no difference between them.

CONCLUSIONS

Both the 200 g and 400 g intrusive forces yielded similar outcomes in terms of posterior teeth intrusion and anterior open bite closure.

Adherence to instructions and fluctuation of force magnitude in cervical headgear therapy

OBJECTIVES

To investigate how patients adhere to instructions and how force magnitude fluctuates and influences the use of cervical headgear (CHG) therapy.

MATERIALS AND METHODS

In this controlled clinical trial, subjects (n = 40) were treated with CHG with light (L, 300 g) or heavy (H, 500 g) force. Patients were asked to wear CHG for 10 hours per day for 10 months (ie, during sleep), but the importance for treatment of wearing CHG also in the evening hours was emphasized. Adherence to instructions and force magnitude in CHG use were monitored by electronic module (Smartgear, Swissorthodontics, Switzerland).

RESULTS

Force magnitude can be set at a certain level, L or H, even if great individual variability is seen in all subjects (0-900 g). Children in the L group used CHG longer per day than those in the H group (9.3 hours ±1.5 hours and 7.8 hours ± 2.1 hours, respectively, P = .002). During evening hours, CHG was used more ( P = .02) in the L group than in the H group. In both groups, CHG was used less in the evening hours during school breaks than in the evening hours during school ( P < .001).

CONCLUSIONS

Children with lower force in CHG seem to adhere better to the instructions for CHG use. Daily rhythm also influences the time of appliance use regardless of force magnitude. The force can be set to a certain magnitude level, even though there is substantial individual variability.

Towards a standardized reference point indentation testing procedure

We study the reference point indentation (RPI) technique which has a potential to directly measure mechanical properties of bone in patients. More specifically, we tested 6 month swine femoral cortical bone at mid-diaphysis region to investigate the effect of several testing variables on the RPI outputs. They include the force magnitude, preconditioning, variation within a sample and between samples, number of cycles, indentation surface (transverse versus longitudinal, polished versus unpolished), and micro-computed tomography radiation exposure. The force magnitude variation test shows that all RPI parameters increase linearly with the increasing force magnitude except the indentation distance increase which shows a cubic trend with a plateau for force magnitudes between 4N and 8N. Preconditioning does not affect the trends for a force magnitude variation test. The cycle variation test shows that most RPI parameters reach either a maximum or minimum at 15-20 cycles. Transverse surface measurements are more consistent than the longitudinal surface measurements, but a rough surface and periosteum on the longitudinal surface could account for this difference. Exposure to the micro-computed tomography radiation in general does not have effect on the RPI measurements. For the 6 month swine femoral cortical bone, testing using 6N force and 20 cycles with preconditioning on an unpolished longitudinal surface is recommended. This study advances our knowledge on how the RPI testing variables influence the RPI outputs and provides guidance on the RPI measurements. It may also serve as a framework for developing a standardized testing procedure for the RPI technique.