Kimiko Nomura

Influence of the incompletely erupted lower third molar on mandibular angle and condylar fractures.

BACKGROUND Several studies have shown an increased risk of mandibular angle fractures by the presence of the lower third molar (M3), especially the incompletely erupted M3. The presence of M3s might influence condylar fractures, which is one of the most common fracture sites, as well as the angle fracture. METHODS Six hundred ninety-two mandibular sides among 346 patients with mandibular fracture were analyzed. They were classified into two groups according to the presence of incompletely erupted M3s and were analyzed according to fracture site, age, and cause of injury. RESULTS Among these patients with mandibular fractures, the frequency of occurrence of the mandibular angle fracture was higher in the group with incompletely erupted M3s (p < 0.0001) and that of the condylar fracture was higher in the group without it (p < 0.001). CONCLUSION The result of this retrospective investigation shows that an incompletely erupted M3 decreases the risk of condylar fractures and increases the risk of mandibular angle fractures.

Differential discharge patterns of rhythmical activity in trigeminal motoneurons during fictive mastication and respiration in vitro

Rhythmical activity in trigeminal motoneurons (TMNs) was studied in an in vitro neonatal rat brainstem preparation that retains functionally active circuits for oral-motor behaviors. Whole-cell current-clamp recording from TMNs demonstrated rhythmical activities during both spontaneously generated respiratory activity and neurochemically induced rhythmical oral-motor activity. TMNs showed spontaneous rhythmical (0.08 +/- 0.04 Hz) activities of burst-firing pattern during inspiration synchronized with inspiratory activities recorded in hypoglossal nerves. During rhythmical oral-motor activity induced by bath application of N-methyl-d,l-aspartic acid and the GABA(A) receptor antagonist bicuculline methiodide, TMNs showed only a rhythmical (5.6 +/- 0.8 Hz) pattern of single-spike discharge. TMNs never showed a burst-firing pattern during rhythmical oral-motor activity even when membrane potentials were shifted either to depolarized or hyperpolarized levels. Rhythmical activity in TMNs exhibited different discharge patterns between rhythmical oral-motor activity and respiratory activity generated in vitro.

Temporal patterns of trigeminal respiratory activity in rat brainstem-spinal cord in vitro

Respiratory activity in trigeminal (V) motoneurons was studied in rhythmically active en bloc brainstem-spinal cord preparations isolated from neonatal rats (P0-P3). In the majority of preparations (83%), the temporal pattern of V activity consisted of spontaneous inspiratory phasic discharge with onset delayed or coincident with onset of phrenic motoneuron discharge. Blockade of alpha-2 noradrenergic receptor activation shifted onset of V respiratory discharges earlier than phrenic discharges, while elevation of extracellular potassium concentration or blockade of GABAergic and glycinergic inhibitory synaptic transmission had little effect on temporary pattern of V respiratory discharges. We conclude V motoneurons in the in vitro preparation generate respiratory activity during inspiratory phase, and their temporal patterns are modulated by inhibitory noradrenergic synaptic transmission.

Oral-motor patterns of rhythmic trigeminal activity generated in fetal rat brainstem in vitro

Development of neural circuits generating fetal oral-motor activity was characterized in an in vitro isolated brainstem block preparation. Rhythmical trigeminal activity (RTA) at E20-E21 resembled either the pattern or rhythm of neonatal RTA. Conversely, at E18-E19, RTA displayed a different pattern of discharge from neonatal RTA, and output was not regular but intermittent with another slow rhythm.

Inhibition of Trigeminal Respiratory Activity by Suckling

The trigeminal motor system is involved in many rhythmic oral-motor behaviors, such as suckling, mastication, swallowing, and breathing. Despite the obvious importance of functional coordination among these rhythmic activities, the system is not well-understood. In the present study, we examined the hypothesis that an interaction between suckling and breathing exists in the brainstem, by studying the respiratory activity in trigeminal motoneurons (TMNs) during fictive suckling using a neonatal rat in vitro brainstem preparation. The results showed that fictive suckling, which was neurochemically induced by bath application of N-methyl-D,L-aspartate and bicuculline-methiodide, or by local micro-injection of the same drugs to the trigeminal motor nucleus, inhibited the inspiratory activities in both respiration TMNs and respiratory rhythm-generating neurons. Under patch-clamp recording, fictive suckling caused membrane potential hyperpolarization of respiration TMNs. We conclude that the brainstem preparation contains an inhibitory circuit for respiratory activity in the trigeminal motor system via the rhythm-generating network for suckling. Abbreviations: BIC, bicuculline methiodide; GABA, gamma aminobutyric acid; NMA, N-methyl-D,L-aspartate; NMDA, N-methyl-D-aspartate; and TMN, trigeminal motoneuron.

Regulation of Trigeminal Respiratory Motor Activity in the Brainstem

The trigeminal motor system participates in the control of respiration as well as suckling and mastication. However, the central mechanism underlying respiratory activity in trigeminal motoneurons is not well-understood. In this study, we aimed to elucidate brainstem circuitry for rhythm generation and signal transmission of trigeminal respiratory activity in in vitro neonatal rat brainstem-spinal cord preparations. We further examined the role of midline-crossing trigeminal interneurons in the bilateral synchronization of respiratory and suckling activity in trigeminal motor nerves. The results of brainstem-sectioning experiments indicated that respiratory rhythms were generated in the medulla and ipsilaterally transmitted to trigeminal motoneurons in the pons. We conclude that the trigeminal motor system, as well as the hypoglossal and phrenic motor system, is regulated by medullary respiratory networks, and that pontine interactions between bilateral trigeminal interneurons are not critical for the generation or synchronization of trigeminal respiratory activity, but are crucial for trigeminal suckling activity.