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14 Removable Orthodontic Appliances
been completed. Reitan (1967) has shown that retain the tooth with a passive appliance for a
if a tooth is not retained immediately after period of between 3 and 6 months until the
active movement, tension within the periodon- remodelling changes are completed.
tal ligament may be sufficient to reverse the Rotations are particularly liable to relapse
direction of movement for a short period. and over-rotation of the tooth is sometimes
During the retention period, the periodontal recommended, however, this is difficult to
ligament becomes adapted to the new tooth achieve with removable appliances. Pericision
position. At resorption sites, osteoclastic activ- may be undertaken as a measure to reduce the
ity ceases and the surface is repaired by the relapse of rotations (Pinson and Strahan, 1973).
apposition of new bone. At sites of apposition, Provided that the patient has a good gingival
the loose woven bone, which was laid down state and it is carefully and skilfully carried out,
during tooth movement, is remodelled and it is not damaging and is quite effective (Figure
replaced by mature bony trabeculae. 2.9). However, it does not always eliminate
It is sometimes suggested that if the tooth has relapse. The routine that we recommend for
been moved to a stable position, retention will rotations is to carry out pericision and then to
not be necessary. It is a basic principle of ortho- retain full time for 6 months followed by at
dontic treatment that teeth should be moved to least a year of night-time retention.
positions where long-term stability can be
expected. However, unless the tooth movement
is held by the occlusion, as when an incisor is References
moved over the bite, it is normally prudent to
Christiansen, R.L.. Burstone, C.J. (1969) Centres of rota-
tion within the periodontal space. American Journal of
Orthodontics, 55: 353-369
Hill, P.A. (1998) Bone remodelling. British Journal of
Orthodontics, 25; 101-107
McDonald, F. (1993) Electrical effects at the bone surface.
European Journal of Orthodontics. 15: 175-183
Pinson, R.R., Strahan. J.D. (1973) The effect on the relapse
of orthodontically rotated teeth of surgical division of
the gingival fibres: pericision. British Journal of Ortho-
dontics, 1: 87-92
Reitan, K. (1967) Clinical and histologic observations on
tooth movement during and after orthodontic treat-
ment. American Journal of Orthodontics, 53: 721-745
Sandy, J.R., Famdale. R.W., Meikle. M. (1993) Recent
advances in understanding mechanically induced bone
remodelling and their relevance to orthodontic theory
and practice. American Journal of Orthodontics and
Dentofacial Orthopaedics, 103: 212-222

Further reading
Figure 2.9 Pericision, showing the line of incision to Yettram. A.L., Wright, K.W.J., Houston, WJ.B, (1977) Centre
sever the supra-alveolar fibres to reduce rotational of rotation of a maxillary central incisor under orthodontic
relapse. loading. British Journal of Orthodontics. 4: 23-27