Bone Changes in the TMJ as Illustrated on MRI

In this article, we will present some research reports that provide an opinion on whether there is indeed a growth and development spurt of the mandibular head in the MRI-rendered bony changes of the temporomandibular joint.

Distinguishing between two types of bone addition images

　According to an article1) that examined the relationship between the appearance of MR double contour images on MRI and growth spurt in the TMJ (mandibular head), MR double contour images are bone remodeling images of the mandible, which are bone addition images seen in the mandible after TMJ disk dislocation is repaired. There are two types of double contour images: one is a clear double contour image and the other is a high-signal cap-like image around the mandible head. (Paper 2)

In paper 1), however, we focused on the cap-shaped bone remodeling image and named it the double contour-like structure image (DCLS) to distinguish between the two types.

Research Results

　The study used MRI to observe the mandibular head of 71 healthy subjects (9 to 62 years old), 21 of whom were 9 to 14 years old, 25 of whom were 15 to 24 years old, and 25 of whom were 25 to 62 years old. The examination items were the presence of double contour-like structure (DCLS) images, bone marrow signals, and the relationship with the eruption of the maxillary second molars.

The bone marrow signal on MRI is lower at younger ages due to less fat (red marrow), and higher at older ages due to more fat (yellow marrow).

The results showed that at ages 9-14 years: DCLS was present in 17 of 42 joints, and not in older ages. The results showed that 94% of the DCLS group had no second molar eruption, and 72% of the absent group had yellow marrow.

　These results suggest that DCLS is a physiological phenomenon that occurs in growing normal subjects before the eruption of the maxillary second molars and that this phenomenon is depicted in the images before the yellow bone marrow develops. Since DCLS has also been observed to disappear afterward, it is considered to be a bone remodeling image observed during the growth and development spurt of the mandibular head.

　In the field of orthopedics, it has already been reported that a similar high-signal image appears on MRI of growing knee cartilage, and the medical community understands that this is a bone remodeling image caused by a growth spurt in the knee.

　After reading this paper, we believe that the effect and timing of use of the removable orthodontic device (activator), which we thought was a change in the dentition, needs to be examined. In addition, it is necessary to distinguish the two types of bony changes of the mandibular head, the double contour image, and the double contour-like structure image, and to consider them. Although both types of images can be seen in the mandible after disk reconstruction, Morimoto et al. differentiated between them, probably because they suggested that although these are ossification images of the same mandible, the difference in their imaging findings is due to a different ossification style. (Paper 3)

　We, the Institute of Orthodontics (IOS), are committed to disseminating correct knowledge and accurate information about orthodontic treatment based on international evidence to a wide audience, from the general public to dentists.

______________________________________________________________________________________________________________________________________

References)

1) Morimoto et al. Detection and significance of the characteristic magnetic resonance signals of mandibular condyles in children.

Oral surg Oral Med Oral Oath Vol,97,No.2

2) K Yano, K.Nishikawa, T.Sano, T.Okano .Relationship between appearance of a double contour on the mandibular condyle and the change in articular disc position after splint therapy.Oral Surg Oral Med Oral Pathol Oral Radiol Endod 108(4): e30-4 ,2009 oct

3) Yano Keisuke Nishikawa Keiichi Sano Tsukasa Okano Tomohiro Changes in MR imaging findings before and after treatment in TMJ with double contour image after splint therapy

Nichijinshi, 18:(3)181-186.2006