Cutting bone and treatment time?

A range of techniques geared at reducing orthodontic treatment time has been proposed in recent years. The most popular are the use of vibratory stimulation, lasers and even surgery.  The surgical options vary from minor flapless procedures to more involved surgery. For example, bone grafting and corticotomy. Researchers have published several prospective studies (and an even higher number of systematic reviews) on these approaches. Most studies point to no apparent benefit with limited consideration being given to harms, or patient experiences and views.

I have to preface this post by stating that I have a slightly wizened (and perhaps incorrect) view of surgical adjuncts. I believe that the potential risk and impact outweighs the benefit. It appears that significant acceleration may necessitate a degree of intervention that I would rather not subject my patients to. At the same time, the less invasive approaches may need to be repeated more often than either my patient, their parents or I would wish. I have not used surgical acceleration for many years. I would need some convincing that this is the right thing to do even on an individual basis, let alone as a blanket approach.

A team from Jeddah, Saudi Arabia did this study.  The Angle Orthodontist published the paper. The authors aimed to assess the effect of piezocision on the rate and nature of en-masse retraction following removal of maxillary premolars. They also considered possible adverse effects of piezocision, including root resorption and pain experience.

What did they do?

They did a two-group parallel randomised controlled trial with a 1:1 allocation as follows:

Participants: Class II division 1 with mild maxillary arch crowding or a well-aligned upper arch. Subjects were aged from 16 to 26 years with excellent periodontal support and health

Intervention: They made vertical incisions below the buccal interdental papillae using a scalpel under local anaesthetic. They then used a piezo surgical knife to create cortical alveolar incisions to a depth of about 3mm. Extractions were performed simultaneously with corticotomy undertaken in all extraction socket walls. They also removed bone distal to the canine root with a piezotome. Finally, they advised Paracetamol (500 mg) 6-hourly for 2 days following the procedure.

Control: They removed maxillary first premolars only. It is unclear as to whether they recommended analgesia.

Primary outcome: Space closure over 4 months

Secondary outcomes: Incisor inclination and root length changes after 4 months of space closure, and pain experience up to 2 days following either extractions only or extractions allied to piezocision corticotomy.

They analysed data from twenty-three participants.  This included 11 in the piezocision group and 12 controls. They used a sealed envelope system to conceal group allocation with data analysts blinded to group allocation. Mini-implants were placed in the maxillary second premolar-first molar region at the outset in both groups to facilitate maximum retraction of the maxillary anteriors. They started space closure one week after the extractions in both groups on an 0.018x 0.025-inch SS base wire with NiTi closing coils used to apply 250g of force bilaterally. They did not report the data collection intervals; however, the analysis was undertaken based on records obtained at 4 months, including repeat CBCT scans and digital models.

What did they find?

They found that more efficient incisor retraction and space closure for the piezocision group. Specifically, incisor retraction of 4.8mm was observed in the piezocision group with 50% less (2.4mm) arising in the control group (P< 0.001). Surprisingly, they found less root resorption on several teeth in the piezocision group. Finally, they reported that the pain scores were higher over the first 24 hours in the piezocision group; however, no differences were observed after that.

What did I think?

This was an ambitious study. They did this study carefully with efforts made to minimise bias by carrying out robust randomisation and allocation procedures and blinding of assessors. The magnitude of space closure overall (0.6 to 1.2mm per month) was generally in keeping with similar studies that have not involved the use of adjunctive surgery.

They reported a  sample size calculation; however, they did this post-hoc using generic effect sizes. As a result, it is less meaningful. Furthermore, the sample size is very small, indeed. The authors suggest that the numbers analysed were sufficient to highlight clinically relevant differences in treatment time. While this may be the case (and significant results were indeed obtained), higher numbers would help make the findings more credible by offsetting the effects of individual variation and other confounders. Furthermore, a larger sample would have permitted the use of more detailed statistical analyses to account for the possible confounding effects of age variation (as both adolescents and adults were included) as well as variation in other important variables including vertical skeletal dimensions.

I struggled to see the value of taking repeated CBCT scans at such short time intervals (4 months). I also doubt that they could make such firm conclusions can be made concerning root resorption at such an early stage in treatment, particularly with low numbers of participants. In terms of the pain experience, they measured this for both groups following premolar extraction (allied to the piezocision in the intervention group). It is, therefore, not possible to pinpoint the effect of the surgery, in isolation. It would be intuitive to expect that the surgical procedure would lead to more pain, and this effect might have been more apparent had extractions not been performed simultaneously in both groups.

Clinical aspects of the trial

From a clinical perspective, I was a little surprised to see force levels as high as 250g per side recommended for space closure as 150g is ample in previous studies. It is essential to highlight that the surgical procedure also involved the removal of bone distal to the root of the canine; as such, the method used was more invasive than isolated piezocision. As a result, any effect of piezocision may have been amplified by the resulting reduction in boney resistance.

What can we conclude?

Based on a very small sample, the use of piezocision allied to local bone removal may accelerate space closure for up to 4 months. However, because of the limitations above, I don’t think we can be confident of this. As such, I continue to feel that the benefit of surgery in terms of reducing treatment time is unclear. The effect of surgery on patient experiences also requires more attention. Orthodontics is a relatively benign process. Our patients like it that way; indeed, it may explain much of our success as a speciality. For now, at least, I intend to keep it that way.

Padhraig Fleming