Bill Klaproth (Host): This is an AAOMS On The Go Podcast. Dr. Michael Miloro and Dr. Michael Han join us to discuss a study recently published in the Journal of Oral and Maxillofacial Surgery titled, What is the Linear Accuracy of Regional Voxel-Based Registration for Orthognathic Surgery Landmarks? Now, here's Dr. Michael Miloro.

Dr. Michael Miloro: Dr. Han, welcome. It's great to have you here today.

Dr. Michael Han: Thank you for having me. Nice to see you somewhere else for a change.

Dr. Michael Miloro: Exactly. So by way of introduction to this podcast, I was asked as section editor of the Orthognathic Craniofacial Section of the Journal of Oral Surgery to identify an article published in my section in 2023 to feature in the AAOMS On The Go Podcast series. I looked for an article that I felt had sound research methodology and had the potential to impact on patient care and clinical outcomes. So, I chose the article published by you, Dr. Han, et al, in the May Journal of Oral Surgery 2023 issue that was a collaboration between the University of Illinois, Chicago and Kyungpook National University in Daegu, Korea. The article is titled, What is the Linear Accuracy of Regional Voxel-Based Registration for Orthognathic Surgery Landmarks? So, let's get right into it now with Dr. Han. Dr. Han, what led you and your research collaborators to pursue this specific research topic?

Dr. Michael Han: So, we knew there were plenty of studies looking at the accuracy of orthognathic surgery, whether it's 3D planned or a custom hardware traditionally planned. There's no paucity of research in that area. But we really wanted to focus on the tools with which the accuracy was measured because, at the end of the day, accuracy data can only be as good as the tools that was used to measure that. So, I like to think of it as being analogous to study the accuracy of a caliper of a weight scale that's used to measure something. And essentially, what we tried to do was to look into any built-in errors, any inherent errors of this accuracy-measuring tool called regional voxel-based registration.

Dr. Michael Miloro: It is really interesting that you're trying to validate this technology. So, is this a followup study to any prior research in this area?

Dr. Michael Han: It actually is, that we did have a previous publication in the Journal of Oral and Maxillofacial Surgery that looked at the angular accuracy of this technique. And, you know, to give quick background, when someone says accuracy, it could mean a lot of different things, and it could be measured in angles or in millimeters, and they're not really interchangeable. So, accuracy from an angular standpoint does not mean accuracy from a linear standpoint and vice versa. So to answer our study question, we thought that it had to be done in that specific order, measure the angular accuracy and then measure the linear accuracy that's derived from that dataset.

Dr. Michael Miloro: Interesting. So for those surgeons who don't know, can you briefly describe what is regional voxel-based registration analysis and how is it used in orthognathic surgery?

Dr. Michael Han: Sure. I think we're all pretty familiar with how orthognathic surgery accuracy studies go. They do have this kind of common denominator where you overlay or superimpose pre and post-op imaging of whatever kind. And this dates back to the 2D days as well. But it's what's done afterwards that varies a lot. What regional voxel-based registration does is it superposes the jaw itself. For example, if you're trying to measure the accuracy of a Le Fort osteotomy, you're superimposing the maxilla from the post-op to the maxilla to the pre-op as opposed to superimposing the cranial base to their cranial base. And by doing that, what you get is you get a semi-automatic calculation of the rotation in degrees and the linear movements. And you can compare that to what you planned to get a pretty accurate, at least in theory, measurement of your actual surgical movements.

And when I say semi-automatic, it's semi-automatic because the operator has to delineate the jaw, basically draw the boundaries of the jaw being examined, but everything else is automated by the imaging analysis software. So, again, in a nutshell, it's an imaging analysis tool that allows you to, in theory, accurately measure the angular and linear movements of jaw surgery, and it applies to other surgeries as well.

Dr. Michael Miloro: Great. That's a great explanation for those of us who don't understand it that well. So, what are the main conclusions or takeaway or take-home points from this study?

Dr. Michael Han: So, historically, this regional voxel-based registration was, in theory, considered to be the most accurate because it wasn't susceptible to a lot of pitfalls or errors. But with this study, we were able to confirm via scientific data analysis, the previous theory, that indeed regional voxel-based registration was accurate. So specifically, the inaccuracies derived from this method itself was less than 0.3 millimeters, which is less than a size-- well, it's a size of a voxel, and that's the threshold that we use to determine accuracy and inaccuracy. However, it did depend on which landmark you're evaluating. For example, one landmark, the gonial angle, the inaccuracy was up to 0.4 millimeters, so it did exceed our study threshold. But whether or not that's clinically significant, I think that's up to the interpretation of the reader of the study.

Dr. Michael Miloro: Yeah. Thanks for that explanation, Dr. Han. So, what were the limitations of this study?

Dr. Michael Han: Some of the landmarks that were evaluated were dental landmarks like canine cuspid and mesiobuccal, distobuccal molars. So as clinicians, we know that sometimes if you have bruxism or you did occlusal collaboration or there's interval trauma between the pre-op scan and the post-op scan, that could change. And that's one thing that we didn't account for in our study, so that's a potential confounder to the data that we have. And then, the sample size was 28, which one may deem rather small. But we had the, privilege of working with a statistician from the conception of this study all the way to the analysis. And when we crunched the numbers, it was considered to be sufficiently powered to answer a clinical question.

Dr. Michael Miloro: So, how are these results relevant to the specialty of oral and maxillofacial surgery?

Dr. Michael Han: I think being up-to-date with surgical accuracy studies, really is important because at the individual level, it allows you to assess your techniques and your protocols and whatnot. It's a self-quality control measure and, as a specialty, allows us to look for opportunities to improve in the context of orthognathic surgery, for example, designs and custom hardware or different protocols and things like that. And I think whether you're a clinician or a researcher, the relevance of this study is that it will allow you to better appraise the literature on accuracy studies, meaning that data generated from regional voxel-based registration could now be interpreted with good confidence that there are minimal artifacts from the analysis methods themselves.

Dr. Michael Miloro: Sounds good. So, how can the average oral and maxillofacial surgeon apply these findings to their everyday practice and can be used with different VSP, virtual surgical planning, software programs?

Dr. Michael Han: Right. I think on the surface, this is a really dry topic that could seem a little distant from everyday practice. But as I mentioned, I think the individual surgeon benefits greatly from staying up-to-date with accuracy data. And then, since now accuracy data's essentially all without exception digital and 3D, just having a better appreciation for the finer nuances of data analysis is very important. And on a broader level, I think it would bring a greater awareness to the different types of assessment tools. You know, I think we all agree that this specialty is ever-evolving. And to actually follow, you'll have to stay abreast to do developments, and that holds true for surgical accuracy and related studies. So, it's the hope of myself and the rest of the research team that the results of this study could be utilized in that fashion.

Dr. Michael Miloro: Yeah. I completely agree with you on that point. So, are there any future studies planned?

Dr. Michael Han: Yeah. We actually have already finished a followup study. It's the same study, same sequence of investigation that looked at segmental Le Fort osteotomies and also genioplasty. The significance being that these are osteotomies that create smaller jaw segments and that potentially could have different accuracy when you're studying regional voxel-based registration. So, we already have the data analyzed and ready, and we're very eager to, one day make that public.

Dr. Michael Miloro: Well, that's excellent. You know, I really want to thank you for being here today and sharing your thoughts on your research with us, and it's been great talking to you.

Dr. Michael Han: Well, thank you so much for having me. Great opportunity.

Bill Klaproth (Host): And once again, that's Dr. Michael Miloro and Dr. Michael Han. And for more information, please visit aaoms.org/joms, that's J-O-M-S. Aaoms.org, A-A-O-M-S.org/joms, J-O-M-S. And if you enjoyed this podcast, please share it on your social media and be sure to subscribe so you don't miss an episode. Thanks for listening.