Effect of miniscrew placement torque on resistance to miniscrew movement under load
Michelle Marie McManus, Fang Qian, Nicole M. Grosland, Steve D. Marshall, and Thomas E. Southard. Am J Orthod Dentofacial Orthop 2011;140:e93-e98
I ntroduction: The primary stability of orthodontic anchorage miniscrews is believed to result from mechanical interlock, with success based upon a number of variables, including screw diameter, angle of placement, monocortical vs bicortical placement, placement through attached or unattached soft tissue, presence or absence of a pilot hole, periscrew inflammation, and maximum placement torque. The purpose of this ex-vivo study was to further explore the relationship between maximum placement torque during miniscrew placement and miniscrew resistance to movement under load. Methods: Ninety-six titanium screws were placed into 24 hemi-maxillae and 24 hemi-mandibles from cadavers between the first and second premolars by using a digital torque screwdriver. All screws were subjected to a force parallel to the occlusal plane, pulling mesially until the miniscrews were displaced by 0.6 mm. The Spearman rank correlation test was used to evaluate whether there was an increasing or a decreasing relationship between maximum placement torque of the screws, miniscrew resistance to movement, and bone thickness. A paired-sample t test and the nonparametric Wilcoxon signed rank test were used to compare maximum placement torque, bone thickness, and miniscrew resistance to movement between coronally positioned and apically positioned screws in the maxilla and the mandible, and between screws placed in the maxilla vs screws placed in the mandible. Additionally, 1-way analysis of variance (ANOVA) with the post-hoc Tukey-Kramer test was used to determine whether there was a significant difference in miniscrew resistance to movement for screws placed with maximum torque of <5 Ncm, 5 to 10 Ncm, and >10 Ncm. Results: The mean difference in miniscrew resistance to movement between maximum placement torque groupings, <5 Ncm, 5 to 10 Ncm, and >10 Ncm, increased throughout the deflection range of 0.0 to 0.6 mm. As deflection increased to 0.12 to 0.33 mm, the mean resistance to movement for miniscrews with maximum placement torque of 5 to 10 Ncm was statistically greater than for screws with maximum placement torque <5 Ncm ( P <0.05). As deflection increased to 0.34 to 0.60 mm, the mean resistance to movement for miniscrews with maximum placement torque of 5 to 10 Ncm and >10 Ncm was significantly greater than for screws with maximum placement torque <5 Ncm ( P <0.05). At no deflection was there a significant difference in resistance to movement between the 2 miniscrew groups with higher placement torque values of 5 to 10 Ncm and >10 Ncm. Conclusions: Ex vivo, the mean resistance to movement of miniscrews with higher maximum placement torque was greater than the resistance to movement of those with lower maximum placement torque.
Comparative assessment of conventional and self-ligating appliances on the effect of mandibular intermolar distance in adolescent nonextraction patients: A single-center randomized controlled trial
Nikolaos Pandis, Argy Polychronopoulou, Christos Katsaros, and Theodore Eliades. Am J Orthod Dentofacial Orthop 2011;140:e99-e105
I ntroduction: Our aim in this study was to compare intermolar widths after alignment of crowded mandibular dental arches in nonextraction adolescent patients between conventional and self-ligating brackets. Methods: Fifty patients were included in this randomized controlled trial according to the following inclusion criteria: nonextraction treatment in both arches, eruption of all mandibular teeth, no spaces in the mandibular arch, mandibular irregularity index from canine to canine greater than 2 mm, and no therapeutic intervention planned involving intermaxillary or other intraoral or extraoral appliances including elastics before the end of the observation period. The patients were randomized into 2 groups: the first received a conventional appliance, and the other a passive self-ligating appliance, both with a 0.022-in slot. The amount of crowding of the mandibular dentition at baseline was assessed by using the irregularity index. Intermolar width was investigated with statistical methods of linear regression analysis. On an exploratory basis, the effect of appliance type on intercanine width was also assessed. Additionally, the effects of appliance type on time to alignment and crowding on time to alignment were assessed by using the Cox proportional hazards model. Results: No evidence of difference in intermolar width was found between the 2 bracket systems (β = 0.30; 95% CI, −0.3 to 0.9; P = 0.30). No evidence of difference in intercanine width was observed between the 2 bracket systems (β = 0.33; 95% CI, −0.8 to 0.1; P = 0.15). The time to reach alignment did not differ between appliance systems (hazard ratio, 0.68; 95% CI, 0.4 to 1.2; P = 0.21), whereas the amount of crowding was a significant predictor of the required time to reach alignment (hazard ratio, 0.88; 95% CI, 0.8 to 0.9; P = 0.02). Conclusions: The use of conventional or self-ligating brackets does not seem to be an important predictor of mandibular intermolar width in nonextractions patients when the same wire sequence is used.
Comparative assessment of conventional and self-ligating appliances on the effect of mandibular intermolar distance in adolescent nonextraction patients: A single-center randomized controlled trial
Nikolaos Pandis, Argy Polychronopoulou, Christos Katsaros, and Theodore Eliades. Am J Orthod Dentofacial Orthop 2011;140:e99-e105
I ntroduction: Our aim in this study was to compare intermolar widths after alignment of crowded mandibular dental arches in nonextraction adolescent patients between conventional and self-ligating brackets. Methods: Fifty patients were included in this randomized controlled trial according to the following inclusion criteria: nonextraction treatment in both arches, eruption of all mandibular teeth, no spaces in the mandibular arch, mandibular irregularity index from canine to canine greater than 2 mm, and no therapeutic intervention planned involving intermaxillary or other intraoral or extraoral appliances including elastics before the end of the observation period. The patients were randomized into 2 groups: the first received a conventional appliance, and the other a passive self-ligating appliance, both with a 0.022-in slot. The amount of crowding of the mandibular dentition at baseline was assessed by using the irregularity index. Intermolar width was investigated with statistical methods of linear regression analysis. On an exploratory basis, the effect of appliance type on intercanine width was also assessed. Additionally, the effects of appliance type on time to alignment and crowding on time to alignment were assessed by using the Cox proportional hazards model. Results: No evidence of difference in intermolar width was found between the 2 bracket systems (β = 0.30; 95% CI, −0.3 to 0.9; P = 0.30). No evidence of difference in intercanine width was observed between the 2 bracket systems (β = 0.33; 95% CI, −0.8 to 0.1; P = 0.15). The time to reach alignment did not differ between appliance systems (hazard ratio, 0.68; 95% CI, 0.4 to 1.2; P = 0.21), whereas the amount of crowding was a significant predictor of the required time to reach alignment (hazard ratio, 0.88; 95% CI, 0.8 to 0.9; P = 0.02). Conclusions: The use of conventional or self-ligating brackets does not seem to be an important predictor of mandibular intermolar width in nonextractions patients when the same wire sequence is used.
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