The effect of interocclusal appliances on temporomandibular joints as assessed by 3D reconstruction of MRI scans

Magnetic resonance imaging (MRI) enables simultaneous visualization of hard and soft tissues. The aims of the present study were to computer generate three-dimensional (3D) images, reconstructed from MRI scans of normal temporomandibular joints (TMJ), to assess the relative positions of the disc, condyle and articular surface of the temporal bone and to study the effect of two mandibular group function interocclusal appliances (IOAs). Bilateral MRI scans of 2 mm slice thickness were generated for the TMJs of 12 asymptomatic subjects with the image acquisition coils orientated in a corrected oblique sagittal plane. MRI scans were generated for all subjects with 3 mm interincisal distance IOAs, while a subgroup (n = 4) was also scanned with a 5 mm interincisal IOA in situ. An average of 10 slices through each TMJ were generated for the closed mouth and IOA positions. Three-dimensional reconstruction was performed on a 486 IBM compatible computer using a suite of nine programs not commercially available. Three-dimensional images allowed visualization of composite images of joint relationships. Subjective assessment indicated that joint relations in 3D were more informative than multiple separate 2D MRI scans. With the 3 mm IOA in situ, the disc was positioned posteriorly and superiorly to the condyle in three of 12 cases. In four of 12 cases the condyle, and in two of 12 cases both the disc and condyle, were positioned anteriorly and inferiorly. With the 5 mm IOA changes in condyle/disc and condyle/fossa relationships were more variable. It was concluded that 3D images of TMJs enabled the assessment of the positional changes of the condyle/disc and condyle/fossa relationships as altered by IOAs. However, the role of IOAs on the internal arrangements within the TMJ remains variable and is deserving of further study.