Physiologic Anchorage Control by Tian Min Xu

Author:Tian Min Xu
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Periods after extraction

First premolars extraction (mm)

Second premolars extraction (mm)

0–30 days

0.56 ± 0.50

0.37 ± 0.24

30–60 days

0.36 ± 0.28

0.39 ± 0.21

60–90 days

0.27 ± 0.20

0.27 ± 0.24

90–120 days

0.18 ± 0.15

0.16 ± 0.14

120–150 days

0.12 ± 0.14

0.06 ± 0.11

150–180 days

0.06 ± 0.11

0.12 ± 0.11

180–210 days

0.02 ± 0.13

0.03 ± 0.00

210–240 days

0.00 ± 0.04

0.07 ± 0.03

What are the possible forces which cause drifting? The stability of dentition is based on forces equilibrium acting on it, which includes bite forces from opposing teeth, forces from adjacent teeth, or from the tongue, cheeks, and lips. Supporting forces from the periodontal ligament and the alveolar bone also contribute to the equilibrium. But when a tooth is taken out, the above equilibrium is broken, some sorts of changes certainly will happen to achieve a new balance.

The anterior component of the occlusal force is speculated to be one of the reasons that drift the teeth when the adjacent teeth are missing [14]. But animal studies [15] have found that the occlusal force would not always accelerate the physiological drift of teeth after extraction, sometimes it may hamper the drift, and there were also studies [15, 16] shown that reduced occlusal force facilitated tooth movement. The controversial outcomes may be resulted from the various directions of the occlusal force, depending on the malocclusion, the contact areas, the cusps abrasion, and so on.

Since the 1960s, animal tests conducted by Murphey, Bulter, Picton, Moss, Xu, and Liu et al. [17–20] have confirmed the physiological drift and concluded that the contractive force came from the healing transseptal fiber after tooth extraction may be one of the possible causes. Murphey studied [17] on Macaca irus reported that after the lower right first molar was extracted, the second premolar, which had an original mesial space, moved mesially in the first 2 weeks and then turned back and moved toward the distal. This finding was nearly the same as one of the animal samples in Bulter’s study [18]. The reversal of mesial migration of this particular specimen of No. 6 was found coincided with the transseptal fiber reorganizing across the distal alveolar crest. Meanwhile there were two other specimens observed as no reversal of the mesial drifting, of which the transseptal fibers revealed incomplete reorganization. Bulter explained that when the distal transseptal fiber were destructed immediately after the extraction, the second premolar was pulled by fibers in the mesial, but after about 2 weeks when the transseptal fiber reorganized and extended across the interseptal bone crest into the extraction site, the contractive force from the new healing transseptal fibers was higher than the traction force from the mesial, so the premolar started to move distally.

Picton and Moss conducted a series of studies [15, 16, 19, 21] on Macaca irus. They [21] found that after the removal of tooth contacts, the distance between pairs of adjacent teeth reduced in only 2 h. It was proposed that the transseptal fiber system produced approximation of the adjacent teeth. By observing the drift of teeth with or without contact with the opposing cusps

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