BackgroundThe aim of this study was to use three-dimensional datasets to identify associations between treatment for adult crowding using Invisalign and interproximal enamel reduction (IER) and changes in the bone volume.MethodsA total of 60 digital cone beam computed tomography (CBCT) scans from 30 patients (28 women, two men; 30 CBCTs pretreatment, 30 posttreatment) were examined retrospectively in order to record bone volume three-dimensionally before and after treatment. The patients’ average age was 36.03 ± 9.7 years. The data were collected and analyzed using the computer programs Mimics 15.0 and OsiriX. Differences in bone between T0 and T1 were analyzed with IBM SPSS 21.0 using the Wilcoxon test for paired samples.ResultsAnalysis of the orovestibular bone volume showed highly significant changes (bone change P <0.001) only in the mandible where more expansion of the dental arch was carried out using proclination or protrusion. The bone lamella was thinner buccally and thicker lingually. In general, bone increases in the oral direction were slightly greater than bone losses in the vestibular direction. No significant changes were detected in the maxilla (bone change P = 0.13). Significant vertical bone loss in the bone height was detected in both the maxilla and the mandible. The largest bone loss was observed in the vestibular direction in the mandible, at a high level of significance (P <0.001).ConclusionsParticularly in the mandible, therapeutic reduction of the vertical and sagittal bone volume shows that caution should be used in the treatment of tertiary crowding with proclination and expansion. The cortical walls appear to represent the limits for orthodontic tooth movement, at least in adult female patients.

BackgroundThe aim of this study was to use three-dimensional datasets to identify associations between treatment for adult crowding, using Invisalign aligner and interproximal enamel reduction (IER), and changes in the volume of interradicular bone.MethodsA total of 60 cone-beam computed tomography (CBCT) scans from 30 adult patients (28 women, two men; 30 CBCTs pre-treatment, 30 post-treatment) were examined retrospectively in order to measure bone volume three-dimensionally. The patients’ average age was 36.03 ± 9.7 years. The interradicular bone volume was measured with OsiriX at four levels in the anterior tooth areas of the maxilla and mandible. Differences in bone between T0 and T1 were analyzed with IBM SPSS 21.0 using the Wilcoxon test for paired samples.ResultsOverall, a slight increase in the quantity of bone was found (0.12 ± 0.73 mm). There was a highly significant increase in bone in the mandible (0.40 ± 0.62 mm; P <  0.001), while in the maxilla there was a slight loss of bone, which was highly significant in the apical third (− 0.16 ± 0.77 mm; P = 0.001).ConclusionsOverall, treatment for adult crowding using an aligner and IER appears to have a positive effect on interradicular bone volume, particularly in patients with severe grades of the condition (periodontally high-risk dentition). This effect is apparently independent of IER. This is extremely important with regard to the treatment outcome, since IER and root proximity have been matters of debate in the literature and teeth should remain firmly embedded in their alveolar sockets.