Initial pulp changes during orthodontic movement: histomorphological evaluation

Abstract

This study evaluated pulp changes in molars of rats submitted to tooth movement by application of a 0.4 N force. Twenty-five adult male Wistar rats (Rattus norvegicus, albinus) were randomly assigned to 5 groups (n=5), being one control group not submitted to force application, and four study groups of 6, 12, 24 and 72 h of force application. The study groups received a 5-mm long nickel-titanium closed coil spring, placed from the right maxillary first molar to the maxillary incisors of each animal. The coil spring was used for mesial inclination of the first molar. After the specific period of tooth movement of each study group, the animals were sacrificed and specimens containing the teeth submitted to movement were processed and stained with hematoxylin and eosin for histological analysis under light microscopy. The results demonstrated alteration of the odontoblastic layer, with hypertrophy of odontoblasts especially at the mesial area of the coronal pulp, edema of the pulp connective tissue in the central area of the pulp, and vascular alteration with accumulation of erythrocytes and leukocytes inside the vessels, especially at the mesial root of the moved teeth. These changes were less remarkable for the 72-h period. Thus, it may be concluded that tooth movement yielded pulpal tissue alterations compatible with an inflammatory process, which are reversible if the aggression is not more intense than the physiological limit of tissue tolerance.

Effects of Low-Level Laser Therapy and Orthodontic Tooth Movement on Dental Pulps in Rats

“…The pulp region that pre-sented the greatest alteration was the mesial surface, accompanying the pressure side of the orthodontically induced tooth movement. 7,8 The cell-free zone of Weil was absent in the initial periods of group I, which is in agreement with the results of previous studies, 1,7,8 especially where there were more accentuated alterations of the odontoblastic layer. The cell-free zone of Weil was restored at the 7-day period with normalization of the odontoblastic layer.…”

“…7,8 Alterations consistent with inflammatory process events were found in all evaluation periods. The increase in the number of blood cells, erythrocytes, and leukocytes in the blood vessels and in the connective pulp tissue 7,8 reveals a chemotactic reaction and the presence of tissue-irritating agents in this area. 23 Cell migration and liquid accumulation in the pulp tissue are part of the inflammatory process, whose main triggering event is the alteration of pulpal blood flow.…”

“…14,20 The alterations in the odontoblastic layer observed in group I are consistent with the consensual outcomes reported in previous studies. 1,7,8 In the earliest periods of group II, this layer was completely disorganized, similar to group I. The pulp region that pre-sented the greatest alteration was the mesial surface, accompanying the pressure side of the orthodontically induced tooth movement.…”

“…13,14,18,20,21 The literature has shown controversial results with respect to pulpal alterations caused by orthodontic tooth movement, mainly those regarding revascularization, which may be explained by differences in the methodological designs. 1,[5][6][7][8] The analysis of the results of group II was complex because of the small number of studies addressing the pulpal responses resulting from LLLT application. Most studies refer to high-power laser irradiation, temperature changes, 11,22 and the presence of free radicals in the tooth pulp.…”

“…Root resorption can be reversible or a degenerative process that could result in necrosis, depending on the orthodontic force application. Studies on tooth movement in rats have demonstrated early pulp hyperemia 6 and tissue alterations consistent with inflammatory processes, 7,8 which are, however, reversible if the aggression does not exceed the physiologic limit of tolerance of the pulp tissue.…”