So close, but yet so far

Accelerated tooth movement has been the goal of many orthodontists and the topic of interest for many researchers, ourselves included. For any treatment modality to be validated, reproducibility must be achieved, and we laud the authors for attempting to reproduce partly a pioneering study on micro-osteoperforations published by Alikhani et al in 2013. Since then, micro-osteoperforations have been shown to significantly accelerate tooth movement in both animal and human studies. Therefore, we read this article with great interest (Alkebsi A, Al-Maaitah E, Al-Shorman H, Alhaija EA. Three-dimensional assessment of the effect of micro-osteoperforations on the rate of tooth movement during canine retraction in adults with Class II malocclusion: a randomized controlled clinical trial. Am J Orthod Dentofacial Orthop 2018; 153:771-85). Although the authors demonstrated that micro-osteoperforations are safe, are not significantly painful, and produce no greater risk of root resorption, we have some concerns and reservations regarding their conclusion that micro-osteoperforations do not significantly accelerate tooth movement.

As written, the “Material and methods” section appears to be valid for testing the effects of micro-osteoperforations on the primary and secondary outcomes listed. However, upon closer examination, it is clear from the data that the rigor of the testing methods was not fully realized. The authors stated that their superimpositions were based on the “stable reference landmark [in] the rugae area,” which they indicated in Figure 4. With best-fit color matching (Fig 4, C ), we were struck by the authors’ use of the strong red of the reference rugae. As the authors stated, “red [is] the worst” fit, indicating the most movement between baseline and the subsequent time point. Thus, the authors’ selected “stable” reference point on which all superimpositions were based is demonstrably unstable, making canine movement measurements from superimpositions (Table II) inaccurate and unusable for analysis.

Figures 4 and 5 are remarkable for their clear demonstration that, at baseline, not only have the canines already moved a significant distance, but also there is a clear difference in how far the right and left canines have moved. Since the subject in these figures had supposedly not received micro-osteoperforations before baseline, how did the authors account for these findings? Moreover, compare Figures 4 and 5 with Figure 3, E , which the authors used to demonstrate the lack of differential canine retraction in the split-mouth design. How did the authors account for the finding that the canine positions at baseline in 1 subject look suspiciously like a subsequent time point after canine retraction in another subject, unequal distances notwithstanding? In our opinion, the authors’ failure to account for, or even acknowledge, these differences invalidates the study and their conclusion that micro-osteoperforations do not accelerate tooth movement. Since the authors used these data to take issue almost exclusively with the conclusion of Alikhani et al that micro-osteoperforations do safely accelerate tooth movement, it is important to emphasize that all canines in that study were adjacent to the lateral incisors before retraction, ensuring that 1 canine did not have a “head start” on the other, as appears to be the case in the current study.

Further evidence that the superimposition data are unreliable comes from the authors’ conclusion that while true “bodily movement” was not achieved, tipping and rotation of the canine were not significant and did not affect the results of their study. We are curious to know why the measurements of canine movement using the 3-dimensional superimposition cast analysis (Table II) and the intraoral measurements (Table III) differ by such large values. The authors mentioned that the intraoral measurements were made from the maxillary mesial wing of the canine bracket to the maxillary distal wing of the second premolar bracket. At all 3 time points, there seems to be almost a 1-mm or more discrepancy between the 2 methods, even though the intraoral measurement method has a reliability coefficient of 1 and the authors stated a strong positive correlation between the 2 methods. If both methods were strongly correlated with excellent reliability and tipping, and rotation was not significant, why did the data from the 2 methods measuring the amount of canine movement differ that much?

We would also like to reiterate to the authors that, although wire dimensions are a mitigating factor in tipping during orthodontic tooth movement, tipping essentially results from a moment created when a force is not directed through the center of resistance—not the wire dimension. The authors further mentioned that in the article by Alikhani at el, 0.016 × 0.022-in stainless steel wire was used, which could result in tipping movements and potential false positives; however, they failed to mention that tipping in that study was also measured and determined to be nonsignificant.

The authors mentioned that 8 patients received glass ionomer cement to raise their bites because occlusal interferences were detected. The authors must comment on this change in the study design, because it introduced the confounding variables of changing the occlusion and occlusal forces in 8 patients but not the remaining 24. Clearly, any statistical differences between these 8 patients vs the 24 who did not receive bite raisers must be assessed.

Our understanding of the biology of tooth movement has progressed remarkably over the years, and we have moved away from solely a simplistic view of “pressure-tension theory” to analyzing tooth movement at cellular and molecular levels. A recent article in the AJO-DO exploring age-dependent tooth movement analyzed at the level of inflammatory markers showed interesting biologic processes that control tooth movement with an interplay between inflammatory markers, osteoclasts, bone density, and architecture. Critically, that same article highlighted significant differences in the rate of tooth movement between adolescents and young adults, indicating that grouping subjects in the 2 age groups is no longer a valid experimental design option. The present study enrolled subjects aged 16 to 24.6 years (mean age, 19.26 ± 2.48) and grouped them together for data analysis. The study of Alikhani et al was conducted on adults only.

Lastly, as the authors admitted in their limitations, inflammatory markers were not measured during this study. We found this to be a severe omission in the study design, since inflammatory marker levels are strongly correlated with the rate of tooth movement. The authors further mentioned that perhaps 3 micro-osteoperforations were insufficient to trigger the inflammatory response to activate the regional acceleratory phenomenon or even cytokine expression. Without quantitative inflammatory marker data, these speculations serve no purpose and highlight the gap in the study design. Equally important, this question about inflammation should always be asked from a patient-centric perspective: “what is the safest and least-invasive method to elicit an inflammatory response great enough to significantly affect tooth movement in this patient?” This is an important question because there is a clear saturation point beyond which increased inflammatory marker levels produce no additional tooth acceleration. Patients respond differently to an equal force. Based on the authors’ speculation then, do we universally apply 4, 10, or 20 micro-osteoperforations or raise a full flap and perform full-length alveolar decortication to ensure the fastest rate of tooth movement for any patient? More research is needed. An increase in inflammation does increase the rate of tooth movement, and we are finalizing a manuscript on a clinical trial that correlates this with the number of micro-osteoperforations.

We wish that the authors of this article had included some biologic analysis in their research on micro-osteoperforations and tooth movement. This article provides the “what” of micro-osteoperforation effects, but stops short of the “why.” We cannot help but think that the authors were so close, but yet so far.

The viewpoints expressed are solely those of the author(s) and do not reflect those of the editor(s), publisher(s), or Association.

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Dec 8, 2018 | Posted by in Orthodontics | Comments Off on So close, but yet so far
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