This blog post is by Dr. Alfonso Caiazzo, D.D.S. and Dr. Federico Brugnami, D.D.S.
The course of treatment for predictable non-surgical orthodontics has long been established. However, it is a well-known fact that during orthodontic treatment, bone resorption usually occurs in the direction of tooth movement. Reduced volume of alveolar bone is a complicating factor for orthodontic treatment and numerous studies have shown a greater incidence of marginal bone resorption in those areas where the tooth movement was carried out towards the cortical plate. The buccal cortical plate of the alveolus has been considered inviolable for many years and it was thought that any movement beyond that line might cause bony dehiscence and eventually gingival recession.
With the introduction of periodontally accelerated osteogenic orthodontics (PAOO), this concept has been refuted in the last years and as is the case in recent research, the alveolar “envelope” or limits of alveolar housing may be more malleable than previously believed and can be virtually defined by the position of the roots.“Surgically-assisted” orthodontic treatment is referred to in many ways in literature, depending on the type of surgery that is performed. Wilckodontics, AOO, and PAOO specifically refer to corticotomy surgery when performed in combination with bone grafting, which offers the ability to increase the existing alveolar volume. Thereby, not only potentially minimizing the risk of bone dehiscence and fenestration as side effects of orthodontic movement, when occurring outside the bony envelope, but also correcting pre-existing dehiscences and fenestrations over vital root surfaces.
Gingival recession has always been of clinical concern with orthodontic treatment. In a recent publication, authors found that lingual positioning of teeth results in an increase in the gingival height on the facial aspect with a coronal migration of the soft tissue margin. In contrast, the opposite occurs when teeth are moved to a more facial position in the alveolar process. In addition, while some researchers have found that there is a higher incidence of gingival recessions in patients who are orthodontically treated for trans-verse discrepancy, others have failed to correlate expanding movement and vestibular recessions and no higher incidence of increased length of clinical crowns post therapy was found.
One hypothesis that has been widely accepted is that orthodontics per se does not directly cause recession but it creates marginal bone resorption when the tooth is moved outside the bony envelope of the alveolar process, which then leads to soft tissue migration and loss of gingival attachment. This may be observed, for example, even in untreated patients with dental crowding. In these cases, the discrepancy between tooth size and the space available may force some of the teeth outside the bony alveolar housing. A study showed that in cases of more than 5 mm of crowding, recession was twelve times more likely to occur. This clearly underlines the importance of achieving proper 3-D positioning of the roots inside the bony alveolar housing after orthodontic treatment.
A more recent study evaluated the long-term development of labial gingival recessions during orthodontic treatment and retention phase. In particular, the lower incisors seemed to be more at risk. Most studies on alveolar bone changes in patients who have undergone orthodontic treatment, in the past have used bitewings and/or periapical radiographies, thus restricting the assessments to proximal bone surfaces. Recently, CBCTs have been employed in this field and it has been demonstrated that during orthodontic tooth movement, teeth may be inadvertently repositioned beyond the bony alveolar housing with resultant dehiscences and fenestrations formation.
A further study showed a correlation between rapid palatal expansion and thinning of the vestibular plate up to almost 1 mm. A 3-dimensional positioning of the roots inside the bony envelope at the end of the treatment becomes then an asset of future orthodontic treatment planning. If the orthodontic treatment is expected to have root movement outside the bony envelope of the original anatomy, orthodontists have historically considered modifying the treatment plan. The combination of corticotomy and GBR (bone graft and membrane) increases the ability to augment the existing topographical anatomy so that such “historically considered unfavorable root movements” can be predictably completed. In recent retrospective case series, it was found that the possible detrimental effects of orthodontic movements on periodontal tissues can be overcome even when the movements are outside the original alveolar anatomy using a combination of corticotomy and grafting. If corticotomy is performed without GBR, existing alveolar bone volume in not consistently preserved.
3-D positioning of the roots inside the bony envelope at the end of the treatment is considered one of the pillars for stability of orthodontic treatment. Many orthodontists now obtain CBCT examinations prior to initiating treatment and these scans can be utilized to review the topographical anatomy of the alveolar bone housing. It has been found that corticotomy in combination with guided bone regeneration can increase the scope of conventional orthodontic treatment by allowing for expansive movements beyond the traditional envelope of predictability. The technique of corticotomy with concomitant bone grafting seems to be an effective method to minimize the risk of marginal bone resorption and fenestration when a tooth is orthodontically inclined or moved toward, or even outside, the cortical plate. In contrast, corticotomy by itself, without concomitant bone grafting does not yield similar results.
In conclusion this is retained a valid and consolidated technique with many advantages. However, every clinicians should bear in mind that, especially when facing cases involving the possible outcome of tooth roots being positioned outside the alveolar envelope, corticotomy with GBR must be considered a well grounded procedure to be adopted.
Picture 1: Initial intraoral view, upper-posterior expansion is required. The thin biotype could represent a risk for future recessions
Picture 2 and 3: Initial aspect on CBCT, the thin buccal plate could represent a risk for future bony dehiscence in case of expansion outside the bony envelope
Picture 4: Final intraoral view, the change of the biotype can be noticed despite the segmental dental expansion bilaterally at the upper premolar
Picture 5 and 6: CBCT at the end of treatment, a great quantity of grafting material covers the roots of the premolar despite the expansive movement