[Paper Review] The Relationship Between Forward Movement of the Chin Bone and Soft Tissue Movement: After Chin Advancement Surgery, How Will My Face Actually Change?

Hello, I’m Dr. Jo Hyun-woo of Ipto Plastic Surgery.

When someone has chin surgery, patients occasionally ask, “How will my face actually change?”

When I get that question, I usually say that if there is little soft tissue, the change will appear sufficiently in proportion to how much the bone moves, and if there is a lot of fat or other soft tissue, the bone movement may not be fully reflected. But the exact amount is not known. That is what I usually explain.

While reading papers, I found one related to this topic, so I’d like to review it.

This paper was written by a Canadian dentist and published in an American dental journal in June 2022.

It seems that studies like this are more common in dentistry, probably because facial contour surgery and orthognathic surgery are often performed by dentists in the U.S. and Canada.

The title is, quite literally, “Measurements of Changes in Soft Tissue and Hard Tissue After Functional Chin Surgery.”

The authors say they conducted the study on a total of 75 patients who had completed orthodontic treatment.

They divided them into three age groups: under 15, 15 to 18, and 19 or older, and observed changes by taking X-rays before surgery, immediately after surgery, after surgery, and two years later.

It is generally said that when the mouth does not close well and the chin is retruded (a weak chin), closing the mouth causes the chin to appear flatter due to contraction of the labiomental muscle. Therefore, correcting this by advancing the chin is said to improve it.

These measurement lines look extremely complicated.

This is a figure often used in double-jaw surgery and various other measurements.

For the chin height measured by the authors, the red line is used, and for the forward measurement, the blue circle represents the bone, and the red circle represents the soft tissue. That is probably all you need to know.

There is also an explanation of each point shown just before.

It brings back memories of studying hard for the resident exam.

Next, this table shows the average values measured in patients before surgery.

A very complicated table appears here.

It lists how the various marks shown earlier changed after surgery.

Based on all of these numbers, the table that can be considered the conclusion of this paper appears.

This table shows the amount of change in soft tissue and hard tissue before and after surgery.

Based on the observation of various values, the conclusion drawn from the significantly changed results was:

The horizontal hard-tissue change was stable for nongrowing patients, and the horizontal soft-tissue change was 92% of hard-tissue.

The authors are saying that soft tissue moves by about 90% of the hard tissue.

There are various variables, and this study separated age and sex, but it says that in patients whose growth had finished, this is the type of change seen with chin advancement surgery.

When I first read the paper, it seemed complicated, but the conclusion is actually this simple.

The paper also shows patient cases.

This is a case in which a long, retruded chin was advanced forward and upward.

The authors say that when surgery is done at a young age, the shape of the chin gradually improves as the patient grows.

From my perspective, there do not seem to be many cases with a lot of soft tissue in this paper.

So I think that is why the conclusion was that the change was expressed at nearly 92% of the bone advancement.

Finally, they say that when chin advancement surgery is performed, the open mouth also closes, and the bone undergoes remodeling.

I also think this is something worth reflecting on carefully, so reading this paper was very helpful.

Today, I reviewed a paper that looks extremely complicated.

The conclusion is that after chin advancement surgery, the amount reflected in the soft tissue is about 92%.

I have always been curious about how much advancement would be achieved numerically, and I think this paper helped answer that question for me as well.

I hope this paper helps answer some of your questions too.

Thank you.