Effective en-masse retraction design with orthodontic mini-implant anchorage: a finite element analysis.
BACKGROUND
The strategic design of an appliance for correcting a bialveolar protrusion by using orthodontic mini-implant anchorage and sliding mechanics must take into account the position and height of the mini-implant, the height of the anterior retraction hook and compensating curve, and midline vertical traction. In this study, we used finite element analysis to examine effective en-masse retraction with orthodontic mini-implant anchorage and sought to identify a better combination of the above factors.


METHODS
Base models were constructed from a dental study model. Models with labially and lingually inclined incisors were also constructed. The center of resistance for the 6 anterior teeth in the base model was 9 mm superiorly and 13.5 mm posteriorly from the midpoint of the labial splinting wire. The working archwires were assumed to be 0.019 x 0.025-in or 0.016 x 0.022-in stainless steel. The amount of tooth displacement after finite element analysis was magnified 400 times and compared with central and lateral incisor and canine axis graphs.


CONCLUSIONS
The tooth displacement tendencies were similar in all 3 models. The height of the anterior retraction hook and the placement of the compensating curve had limited effects on the labial crown torque of the central incisors for en-masse retraction. The 0.016 x 0.022-in stainless steel archwire showed more tipping of teeth compared with the 0.019 x 0.025-in archwire. For high mini-implant traction and 8-mm anterior retraction hook condition, the retraction force vector was applied above the center of resistance for the 6 anterior teeth, but no bodily retraction of the 6 anterior teeth occurred. For high mini-implant traction, 2-mm anterior retraction hook, and 100-g midline vertical traction condition, the 6 anterior teeth were intruded and tipped slightly labially.
Sung
Sang-Jin
SJ
Division of Orthodontics, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea. ssjmail@amc.seoul.kr
Jang
Gang-Won
GW
Chun
Youn-Sic
YS
Moon
Yoon-Shik
YS
D000539:Alveolar Process / Q000473:pathology; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D003481:Cuspid / Q000473:pathology; D003722:Dental Alloys / Q000737:chemistry; D015921:Dental Implants; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006801:Humans; D007180:Incisor / Q000473:pathology; D008954:Models, Biological; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation / Q000379:methods*; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D010513:Periodontal Ligament / Q000473:pathology; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D019227:Tooth Apex / Q000473:pathology; D019228:Tooth Crown / Q000473:pathology; D014087:Tooth Movement Techniques / Q000295:instrumentation / Q000379:methods*; D019415:Torque
D003722:Dental Alloys; D015921:Dental Implants; D013193:Stainless Steel