Rethinking the bioprogressive technique for Class II correction with clear aligners
There have been many reports on the treatment of Class II malocclusion cases solely by clear aligners, showing correction of buccal occlusion as well as improvement of the overbite and overjet. In many of these reports, proclination of the mandibular incisors was a common treatment outcome, specically when Class II elastics were used to distalise maxillary molars or to correct the buccal occlusion to Class I. The only exceptions were the cases reported by Boyd1, who reported that mandibular incisor inclination improved after Class II treatment; however, the manner of this improvement was unclear. In cases where mandibular incisors are initially retroclined, it is known that Class II elastics can move mandibular incisors forward to a normal position or sometimes beyond a normal position. The challenge is usually when mandibular incisors are initially proclined, normally seen in a skeletal Class II relationship and known as dental compensation. The mandibles of growing patients can grow forward or backward according to their mandibular structure shape, in particular the mandibular condylar heads.
The bioprogressive philosophy was first discussed by Ricketts, who suggested that Class II correction in cases with mandibular retrognathism should include maxillary molar distalisation and extrusion using cervical headgear, which triggers faster forward mandibular projection/growth in growing patients. However, detailed clinical trials and meta-analysis of the proposed technique have not been published.