We thank Dr Murphy for his interest in our recent article, “Clinical application of accelerated osteogenic orthodontics and partially osseointegrated mini-implants for minor tooth movement,” in the September 2009 issue of the AJO-DO .
Dr Murphy wrote that we commited 4 errors. First, he said that we “did not need to graft the left molar site because there was sufficient bone in situ.” Although sufficient bone might have been present in the maxillary second molar region, it was thin, and we thought it prudent to add bone graft material to the indentation area.
Second, our corticotomy cuts “were too shallow to elicit the necessary mesenchymal stem cells and too coronal and too timid to induce the degree of therapeutic ‘trauma’ necessary for intrusion.” Because the bone was thin between the buccal root surface and cortical bone, it was challenging to reach deeply into medullary bone during decortication. The corticotomy was necessarily shallow to avoid damage to the root surfaces. Whether regional acceleratory phenomenon (RAP) was or was not induced is speculative, but the tooth movement response was a positive indication. It was our intent to induce rapid tooth movement without damaging the teeth. Two notable options for individual molar intrusion were considered: intrusion by compression osteogenesis, in which cortical bone at the root apex is sufficiently removed, and the bone segment and teeth are together intruded; and cortical activation, which depends on RAP. We chose the second, placed a buccal C-tube plate with a flap operation, and performed additional decortication to induce the RAP phenomenon.
Third, Dr Murphy said that our “comments that heavy forces are necessary conflicts with both prior literature” and our own words later in the article. Previous studies that RAP is also activated by normal orthodontic force are well known. However, studies are lacking regarding RAP activation by intrusion or uprighting forces. The intrusion methods used in several case reports on decortications typically applied the same amount of force on both buccal and palatal sides. The intrusion force was 150 to 250 g in those cases. Mostafa et al applied a 400-g force for displacement of a premolar in dog experiments. Whether the forces applied in our patients would also be considered “heavy” is perhaps debatable. We would like to see further studies assessing the optimal force to use after decortication.
Finally, Dr Murphy thought that our adjustments every 4 weeks were probably not frequent enough to perpetuate a therapeutic osteopenia or the so-called regional acceleratory phenomenon of Frost and Jee.
Continued tensional stress altered in frequency and magnitude via the roots every 1 to 2 weeks maintains the osteopenic state and facilitates both accelerated tooth movement and a stable posttreatment phenotype. So monthly adjustments risk recalcification in midtreatment. In our office, we initiate biomechanics 5 minutes after the last suture is placed and make biomechanical adjustments every 1 to 2 weeks. This gives us tooth movement of 1 to 2 mm per week.
As shown by Iino et al and Wilcko et al, in space closure or when tooth uprighting is needed in a mesiodistal orientation in the long axis of the alveolus, bone reduction is accomplished with an ostectomy through the entire thickness of the alveolus to include the labial and lingual cortical plates and interspersed medullary bone. The concept of corticotomy-facilitated orthodontic treatment does not also define intrabony tooth movement. Our studies might help us to know whether decortications alone have similar effects as osteoectomy.
We do appreciate these thoughtful questions by Dr Murphy. We look forward to not only future animal research and case reports, but also meta-analyses with several relative randomized clinical trials for corticotomy-facilitated orthodontic treatment to be approved as an evidence-based technique.