Discussion
TMA, luxation injuries, orthodontic, tooth
REGRESSION
Although BF changes during extrusion and intrusion orthodontic forces have been previously reported [In the current orthodontic practice, 0.017 × 0.025-inch SS, 0.019 × 0.025-inch SS, and 0.21 × 0.025 TMA AWs are used for COS leveling during orthodontic treatment. The reported stiffness values for 0.019 × 0.025-inch SS AW are higher than 0.021 × 0.025-inch-TMA AW which means the amount of the delivered force when using 0.19 × 0.025-inch SS is higher [In the current study, only subjects with good oral hygiene and healthy periodontium were included. The oral health status during the study was maintained by giving the patients oral hygiene instructions both verbally and using social media [It has been demonstrated that tooth morphology affects the distribution, the amount of orthodontic force, and the developed strain within the PDL [Different types of tooth movement were reported during leveling the COS in subjects with different vertical proportions. Rozzi et al. [Within the first 20 min of force application, BF showed more reduction in the extrusion subgroup as compared to the intrusion subgroup. Although intrusion is associated with more crushing of cells and vessels in the apical tissues than luxation injuries, and more detrimental effect on the vasculature of the pulp [In the current study, significant BF recovery occurred within 48 h of force application (intrusion and extrusion) in group 1, while it continued to increase in the premolar extrusion subgroups in 0.019 × 0.25-inch SS and 0.21 × 0.025-inch TMA AWs and in the intrusion subgroup in the TMA AW group. The continued BF increase after 1 week of extrusive force application in groups 2 and 3 could be explained by the higher force applied to the teeth using the larger dimension AWs in groups 2 and 3. Also, the less AW/bracket play in group 3 may have produced more frictional forces.These results agree with previous studies [These results were also inconsistent with studies that used NiTi AWs; McDonald and Pitt Ford [When comparing BF changes between the 3 AWs, only the canines showed significant differences. The canines showed more BF changes (more BF reduction during the first 20 min and more recovery during the first 48 h) when the SS AWs were used. This may be due to higher forces applied to the canines when using the stiffer SS AWs. Also, the position of the canines in the middle of the lower arch connecting the intrusion and extrusion parts of the reverse COS AWS may have subjected the canines to more complex types of orthodontic forces.When the type of force was compared between the 3 AWs, premolars subgroup showed more BF return toward their baseline value in group 2 (0.019 × 0.025-inch SS AW) as compared to group 3 (TMA AW) within the first 48 h of force application. As the premolars are in the deepest point of the accentuated COS, they are subjected to more extrusive forces when COS is placed in the AW. This indicates that the premolars in SS group may have been subjected to more insults due to higher forces that necessitated an increase in BF changes to help in recovery.In the current study, 1 month after force application, BF increased beyond its original value. This was contrary to the previous studies [Regression analysis revealed an association between BF changes with the type of tooth and the amount of COS depth changes. The change of the COS reflects the outcome of orthodontic force application. Therefore, it is expected to detect changes in the pulp as a result of this force. Based on the above results, it seems prudent to evaluate the amount of change in COS required and to select the type of AW that may produce the least amount of force to avoid detrimental pulpal effects during extrusion.Limitations of the current study include the following: BF measurements were carried out during active orthodontic treatment, and teeth were not in a fixed position, the extrusive and intrusive forces were applied to teeth with different morphology, and the presence of the orthodontic appliance limits the measurement area and hinders the placement of a black rubber dam sheet during BF measurements to reduce signals from the gingival blood vessels [