Initial forces experienced by the anterior and posterior teeth during dental-anchored or skeletal-anchored en masse retraction in vitro

Abstract

Objective: To investigate initial forces acting on teeth around the arch during en masse retraction using an in vitro Orthodontic SIMulator (OSIM). Materials and Methods: The OSIM was used to represent the full maxillary arch in a case wherein both first premolars had been extracted. Dental and skeletal anchorage to a posted archwire and skeletal anchorage to a 10-mm power arm were all simulated. A 0.019 3 0.025-inch stainless steel archwire was used in all cases, and 15-mm light nickel-titanium springs were activated to approximately 150 g on both sides of the arch. A sample size of n¼40 springs were tested for each of the three groups. Multivariate analysis of variance (a ¼ 0.05) was used to determine differences between treatment groups. Results: In the anterior segment, it was found that skeletal anchorage with power arms generated the largest retraction force (P , .001). The largest vertical forces on the unit were generated using skeletal anchorage, followed by skeletal anchorage with power arms, and finally dental anchorage. Power arms were found to generate larger intrusive forces on the lateral incisors and extrusive forces on the canines than on other groups. For the posterior anchorage unit, dental anchorage generated the largest protraction and palatal forces. Negligible forces were measured for both skeletal anchorage groups. Vertical forces on the posterior unit were minimal in all cases (,0.1 N). Conclusions: All retraction methods produced sufficient forces to retract the anterior teeth during en masse retraction. Skeletal anchorage reduced forces on the posterior teeth but introduced greater vertical forces on the anterior teeth. (Angle Orthod. 2017;87:549-555)

Stress distribution analysis in anterior teeth caused by several retraction mechanics

“…In this study, the strains dissipated in the posterior segments were not evaluated because the contralateral posterior segment of the arc-shaped photoelastic model interposed between the light source and the area supposed to be observed, blocking the correct formation of photoelastic fringes. Several orthodontic anchorage techniques are available according to the required anchorage, 1 , 2 , 4 - 8 , 10 - 18 , 22 , 27 regardless of using sliding mechanics or loops. Absolute anchorage is not necessarily recommended for all retraction techniques; however, absolute anchorage intends to standardize and reduce the stresses on posterior segment and concentrate these stresses on the anterior teeth roots.…”

“…Absolute anchorage is not necessarily recommended for all retraction techniques; however, absolute anchorage intends to standardize and reduce the stresses on posterior segment and concentrate these stresses on the anterior teeth roots. 27 Future studies can be considered to assess the differences in stress dissipation in the anterior and posterior teeth when using different retraction techniques without absolute anchorage.…”

“…A transparent acrylic resin base fitted to the photoelastic model was used to simulate an absolute anchorage in the posterior segment, intending to concentrate all the resulting retraction forces in the anterior area of the arch. 27 A mini-implant was placed on each side in the distal area of the base and attached to the mandibular first molar tube with a metallic ligature.…”

Simulation of orthodontic force of archwire applied to full dentition using virtual bracket displacement method

“…Badawi et al designed a promising system to accurately measure the six degrees of freedom of orthodontic forces applied on all teeth by fixed appliances. The designed system was successfully used to study orthodontic force on full dentition with an archwire in several treatment scenarios . These in vitro measurement systems provide useful tools for the clinical estimation of orthodontic force.…”

“…The designed system was successfully used to study orthodontic force on full dentition with an archwire in several treatment scenarios. [16][17][18][19][20] These in vitro measurement systems provide useful tools for the clinical estimation of orthodontic force. However, it is timeconsuming and costly to physically produce the oral treatment condition in vitro for accurate measurement.…”