[Paper Review] If the jawbone gets smaller, how much smaller does my face actually become?

Hello, this is Director Jo Hyun-woo of Ipcheok Plastic Surgery.

Today, I’d like to talk about something many patients are curious about, as well as a paper I recently read.

The title of the paper is

In Korean, it is a paper that measured three-dimensional changes in soft tissue after square jaw surgery.

Although it was written by a hospital in Shanghai, China, I’ll go over the content from the standpoint of the fairly authoritative journal, Journals of Oral Maxillofac Surgery.

They measured the volume of the masseter and temporalis muscles in 29 patients who underwent surgery from 2019 to 2020,

and, using CT, observed changes in the patients’ soft tissue by applying various 3D indices.

Before surgery, they say the bone was cut using a guide plate like the one marked with arrows here.

Looking at the shape of the cut bone, there is a severe second angle remaining, and it looks quite unrefined, so once again it is clear that Korean surgeons really do perform these surgeries well.^^

This is the actual post-surgery bone shape and the guide plate.

The two shapes are similar, but they are quite different from Korean surgeries, which are based on long-curve resection.

Another unusual part was how they measured how much the soft tissue changed in terms of facial appearance.

In the figure, the green area shows a reduction in volume, and red indicates a greater reduction in volume, they say.

Based on the surgical results, the amount of square jaw before and after surgery was greatly reduced.

In the soft tissue evaluation, the square jaw area appears green and gradually red, showing that there were significant changes.

This table shows the results.

It shows that the surface area and volume of the square jaw region decreased before and after surgery.

They decreased by 12.8% and 18.4%, respectively. But the interesting point is the increase in the volume of the temples.

The surface area and volume increased by 12.0% and 10.7%, and these were said to be statistically significant.

I hadn’t really thought that square jaw surgery would make the temples look wider, but the data above seems like something worth considering.

This is the data observing changes in muscle mass after surgery.

They report that even without surgical manipulation such as masseter muscle resection, the muscle mass decreases as the square jaw angle is cut.

The muscle surface area decreased by 10.99%, and muscle volume also decreased by 18%.

It seems that the muscles on the side without bone have atrophied.

They speculate that this may be because of reduced masseter activity and because the patient did not open the mouth widely.

The reason why temporalis muscle volume increased is not clear, but they think it may be a compensatory action to maintain chewing function as the masseter becomes smaller.

What I was most curious about was how much the facial soft tissue shrinks in proportion to the amount of bone removed.

Table 5 above shows this.

However, the table only says that the bone volume decreased and the face also became smaller.

I think this part of the paper is a little disappointing.

So far, it seems there are no papers that precisely show how much changes in bone surgery are related to changes in soft tissue.

Of course, textbooks include numerical values for soft tissue changes according to bone changes after orthognathic surgery, but it does not seem to be specifically defined for cheekbone surgery or square jaw surgery.

Naturally, for people with very little soft tissue fat or muscle, changes in the bone will appear directly as changes in the face.

And it is true that for people with more fat or muscle, the degree of change is smaller.^^

I’ve reviewed the paper at length.

What did you think of this paper review? If you’re interested, I’ll try reviewing another interesting paper next time, explaining it in an easy way.

Thank you.