Physical properties of root cementum: Part 18. The extent of root resorption after the application of light and heavy controlled rotational orthodontic forces for 4 weeks: A microcomputed tomography study

Effect of supplemental vibrational force on orthodontically induced inflammatory root resorption: A multicenter randomized clinical trial

“…[6][7][8][9] The aetiology of OIIRR is believed to be multifactorial with many factors influencing outcome, including root morphology, 10 history of dentoalveolar trauma, 4 patient age 6 and the presence of any underlying systemic inflammatory condition, such as asthma or allergy. [11][12][13] Factors related to orthodontic treatment include the level and direction of force, [14][15][16][17][18] type of force 19,20 and contact of tooth roots with cortical bone. 7,21 However, the specific role relating to many of these factors is poorly understood and there is only good evidence that heavier orthodontic forces cause greater OIIRR than light forces 22 and that increased treatment time positively correlates to increased OIIRR.…”

Mechanical Performance of Nickel-titanium Archwires

“…Assuming this limit, just Tp HA lot 686025 (39.9gf) was able to release this strength on the unloading baseline. However, many authors have stated that 25gf should be considered as a light force and a heavy force limit was calculated multiplying by 9 this lower baseline, leading to a 225gf, which is a much higher level than observed in all wires tested during unloading [25][26][27]29 . It should also be considered that an orthodontic appliance is not composed just of one wire solely, but by an interaction of brackets and wires, which result in a multipoint load system when the wire is completely tied.…”

“…Continuous forces, such as those produced by NiTi alloys, are more effective for tooth movement, but may induce root resorption because of the long times of force application involved 23 . It is described elsewhere that there is a tendency to consider that the optimal forces for clinical tooth movement are characterized by a maximal cellular response, including apposition and resorption of supporting tissues, while maintaining the vitality of the surrounding tissues 25,26 . The optimal compression on periodontal tissue should be in the range between 7 × 10 -4 MPa (7 g/cm 2 ) and 2.6 × 10 -3 MPa (26 g/cm 2 ) [26][27][28] .…”

“…It is described elsewhere that there is a tendency to consider that the optimal forces for clinical tooth movement are characterized by a maximal cellular response, including apposition and resorption of supporting tissues, while maintaining the vitality of the surrounding tissues 25,26 . The optimal compression on periodontal tissue should be in the range between 7 × 10 -4 MPa (7 g/cm 2 ) and 2.6 × 10 -3 MPa (26 g/cm 2 ) [26][27][28] . Above 2.6 × 10 -3 MPa, over compression of periodontal capillaries may cause local ischemia that could lead to tissue hyalinization 25,29 .…”

“…Root resorption may be a side effect of the cellular activity associated with the removal of necrotic tissue from the hyalinized zone 25 . For comparison purpose, we assume, based on literature, that an optimal force to induce physiologic turnover on the mineralized tissues coupled with a maxillary premolar is around 50g (49cN) 23,26 . According to Table 1, just Tp HA Lot 686025 group stayed below this limit (39.9 gf), all other groups exceeded this value, although some groups (Mt HA lot 310, Tp HA lot 1758052, Sc HA lot 9003, GAC HA lot H359, 3M, Orthometric lot 310 and TP lot 3429007) remained below 70gf.…”