[Change in trigeminal mesencephalic neurons after teeth extraction in guinea pig]

Trigeminal mesencephalic (Mes V) neurons innervating the periodontal mechanoreceptor (PMR) are known to play an important role in controlling the bite force and jaw-movements during mastication. After teeth loss, the PMR disappears due to loss of the periodontal membrane. The present work is a study on whether cell death is induced in the Mes V neurons in association with teeth loss. The upper and lower incisors were extracted on the right side in 5 guinea pigs (extraction group) and the other 5 guinea pigs were kept intact (control group). In the extraction group, the animals were kept alive for 58-119 days after teeth extraction. Serial coronal sections (50 microns thick) were made of the midbrain and pons and stained with cresyl violet. The Mes V neurons were counted on every other section. In the caudal half of the Mes V nucleus, where the neurons innervating the PMR are reported to be located, the number of neurons was less on the right side than on the left side (P < 0.01) in the extraction group, while there was no difference between the right and left sides in the control group. We conclude that teeth extraction can induce cell death in the Mes V neurons innervating the PMR and produce a significant change in the brainstem mechanisms controlling mastication.