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Abstract
To test the null hypothesis that force decay would not affect the processes of resorption and repair of root surface, a randomized controlled clinical trial was conducted. Twenty one prospective orthodontic patients requiring the extraction of mandibular first premolars as part of their treatment plan were recruited according to strict selection criteria. The participants were assigned to three groups according to the period of force application — a five- week, a seven-week and a nine-week group.
The first premolar on one side was selected at random. An experimental orthodontic appliance was used to deliver 75 cN of a buccal tipping intrusive force using a NiTI coil spring. The force was not reactivated; hence each period would correspond to one activation cycle. At the end of the experiment, the first premolars were extracted. Seven non-moved contralateral premolars were selected randomly to serve as control material. The test and control premolars were examined using scanning electron microscope.
Significantly less surface resorption was registered in the five-week test group. The seven-week and nine-week test group showed no statistically significant difference in surface resorption. Apical resorption scores were strongly associated with the experimental periods. Only partial repair of resorption lacunae was evident in the seven-week and nine-week group, involving both cellular and acellular cementum.
Thenull hypothesis was rejected; force decay was associated with changes In the root sur ces, name[j resorpti&i ancf’repair. Sveii èk appeared to be sufficient for the process of root resorption to cease, however a