THE CVM METHOD AND THE IDEAL TIME FOR ORTHODONTIC TREATMENT.

The timing of treatment of Class II (protrusive top teeth &/or retruding lowers) patients has been debated for many years in orthodontics with some claiming you need to treat early, even as young as 5-8 (discussed in a previous Blog) or 9-10 or wait until 12-13! Several indicators have been used to assess the ideal timing and a more recent one is the Cervical Vertebral Maturation method (CVM) which uses the maturational stages of the cervical vertebrae in the neck on a cephalogram x-ray.

The CVM method was first developed by Don Lamparski along with Maria O'Reilly at the University of Pittsburgh where I trained and was later modified. However to be useful a method needs to be reliable and valid. One article demonstrated <50% intra-rater agreement (in other words less than half the time you agree with your own assessment). Another demonstrated that the CVM method offered no advantage over chronological age. Two recent papers concluded "CVM method could not accurately identify themandibular growth peak" or "...cannot predict craniofacial growth in girls with Class II malocclusion.". But let's say you do identify the ideal timing of treatment using the CVM method with the Herbst the study found ~1.9mm of advancement of Pogonion. However another study in adults (who are not growing) found they could still gain 1.3mm of advancement of Pogonion  so the ideal timing was only 0.6mm better and that is also assuming the change holds up long term which we know from other trials it doesn't.

The timing of orthodontic treatment is an interesting topic and really revolves around the issue of whether we can ‘modify growth’ of the mandible or not. Based upon the available quality scientific evidence it seems we can temporarily accelerate mandibular growth (Lysle Johnston’s ‘mortgage on growth’) but not achieve a significant long-term change and so the final outcome is mostly dento-alveolar/tooth movement. Studies supporting a change are retrospective in nature and/or use a historical control which is ~60 years old and not valid for comparison as trials using historical controls show larger treatment effects. In contrast the prospective RCT’s (UK, UNC, Florida) show no difference between treating early or in adolescence and this is supported by the Cochrane Review on the topic. The long-term ‘amount’ of change is similar regardless of the timing of treatment so it is more the ‘efficiency’ of the change/how quickly that is achieved that is affected by timing. Therefore the importance of determining the ideal timing of treatment with any method seems of minimal significance to the final outcome.

Finally I would like to thank Maria and all my other instructors at the Univ of Pittsburgh. I was so incredibly fortunate to have such wonderful mentors and friends.



Dr Peter Miles is the orthodontist at Newwave Orthodontics in Caloundra, Australia and was a part-time lecturer at the University of Queensland for 11 years and is a visiting lecturer at Seton Hill University in the USA. Peter is one of the editors and authors of the orthodontic textbook, 'Evidence-Based Clinical Orthodontics'.