The main cause of LN injury is inadequate exodontia. Therefore, clinicians have to learn adequate surgical technique of the third molar and must understand the risk factors associated with injury to the LNs. The torn LN injury should recover as soon as possible with the best methods.
Slight peripheral nerve injury may be healed spontaneously without any surgical management, for example, in the phase of neurapraxia on Seddon analysis. As a common sense, in the early phase of suspicious spontaneous healing, critical examination like a clinical neurosensory testing (CNT) should be performed as soon as possible [1]. Currently, the conventional protocol for managing LN neurosensory deficiency in regard to optimal methods and the timing for surgical repair is not recognized. In the case of completely damaged case, microsurgical reconstruction should be utilized. Generally, grafting is unadvisable for LN repair because the nerve path is tortuous enough to mobilize without tension [2]. The best functional nerve recovery may occur after direct apposition [3]. When a tensionless direct suturing is not possible, nerve grafting should be considered [4, 5]. Recently, peripheral nerve defect is intended to reconstruct with allograft nerve collagen about substitutes for nerve autograft, because nerve grafts can cause sensory defects in the donor site [6]. There are various types of nerve allografts, for example, Gore-Tex and absorbable allograft tubes [7, 8]. In our case, we utilized the allograft nerve RENERVE®. Previously, meaningful animal experiment and clinical research were done clearly as follows.
Okamoto et al. studied a potential of RENERVE®. With 12 adult female beagle dogs weighting 10–12 kg, the peroneal nerve was cut to make a 30-mm defect. The nerve defect was bridged by RENERVE®. Comprehensive functional, electrophysiological, morphometrical, and histological analyses were performed for 1 year after the operation. The wet weight of the tibialis anterior muscles was only 32.4% of the healthy side at 24 weeks, which recovered to 77.4% 52 weeks after denervation. Electrophysiological evaluation of the tibialis anterior muscle belly showed a polyphasic wave 52 weeks after the implantation, which was almost half amplitude compared with that of the control. The results from this study showed the detailed process of morphological, electrophysiological, and functional recovery of the regenerated nerve, which would provide a scientific background for this novel therapy [9].
Saeki et al. made a clinical project to clarify the safety and efficacy of using RENERVE® in the treatment for nerve defects in humans. They conducted a multicenter, controlled, open-label study to compare the safety and efficacy of RENERVE® with those of the autologous nerve grafts. They included patients with sensory nerve defect of ≤ 30 mm, at the level of the wrist or a more distal location. They compared the sensory recovery using static two-point discrimination and adverse events between RENERVE® and autologous nerve grafting. As the result from these studies, the RENERVE® group included 49 patients, with a nerve defect of 12.6 mm. The autologous nerve graft group included 38 patients and nerve defect of 18.7 mm. The rate of recovery of sensory function at 12 months was 75% (36/49) for the RENERVE® group and 73.7% (28/38) in the autologous nerve group. No serious adverse events directly associated with the use of the RENERVE® were identified [10].
Time to repair played an important role in the overall surgical result, although the exact timing is still unclear. The patients with LN repair within 90 days of injury are said to have FSR within 1 year after repair in 93% of the cases [11]. Pogrel reported that microsurgical repair within 10 weeks of injury showed better results for FSR of the LN [12,13,14]. All the abovementioned opinions are in contrast with Robinson et al. Robinson et al. achieved a significant improvement in a number of sensory function categories including gustatory and functional results; however, they saw no correlation between time to repair and procedure success [15]. Minimally, we can agree with the opinion of Robinson et al. No consensus exists regarding the optimal methods and timing for disturbed lingual nerve repair. Our case had 17 years interval between the third molar teeth extraction and allograft collagen reconstruction. In spite of the extremely long span, we could get a precious result; There was recovery on gustatory sensation, 2PD, and SWT in the objective assessment, but unfortunately, in the subjective assessment, she is still angry with the first countermeasure of the dentist (Tables 1 and 2). Moreover, the important facts are the patient could be free from the heavy psychotropic drugs, which she continued to take in more than 7 years. The quality of her life was drastically refined after the operation (Fig. 4). the vein graft cuff method and the allograft collagen nerve (RENERVE®).
