The dissertation presents a theoretical substantiation and a practical solution to an аctual problem – increasing the effectiveness of prevention and treatment of inferior alveolar nerve (IAN) injury in patients with skeletal malocclusions through the development of new methods of intraoperative therapy using plasma rich in growth factors and dexamethasone phosphate 0.04%.
Inferior alveolar nerve neuropathy is a serious complication in orthognathic surgery and, according to the scientific literature, occurs in 9-85% of cases. The causes of neurosensory disturbances include the close location of the osteotomy line relative to the mandibular canal during sagittal split osteotomy (SSO) of the mandible. Among the symptoms that develop as a result of this complication, patients most often report anesthesia and paresthesia, less frequently dysesthesia, hypoalgesia, hyperalgesia, allodynia, and others. In most cases, sensory function recovers spontaneously within 6 months after surgery; however, if symptoms persist after 1 year, neurosensory disorders become permanent and lead to a significant decrease in patients’ quality of life.
The study was aimed at identifying clinically and prognostically unfavorable variants of mandibular canal topography, analyzing predictors of postoperative IAN neuropathy development – the degree of IAN exposure, its localization relative to the proximal and distal mandibular fragments during SSO, the magnitude and direction of mandibular movement, developing and substantiating new methods of intraoperative therapy using topical application of dexamethasone phosphate 0.04% and application of plasma rich in growth factors, clinical assessment of neurosensory disturbances, and analysis of their correlations with laboratory indicators of growth factors (GFs).
The study design was approved by the Commission on Bioethical Examination and Ethics of Scientific Research of Bohomolets National Medical University.
The research program was structured into four interrelated stages – analytical, clinical-experimental, clinical-diagnostic, and laboratory – the sequential implementation of which ensured a comprehensive assessment of the problem from a systems-based approach and generalization of the obtained results.
At the first stage, an analysis of modern domestic and foreign literature sources was conducted regarding the incidence, cellular and molecular mechanisms of IAN injury, risk factors for neuropathy development after SSO of the mandible, and possible methods of prevention, therapy, and clinical diagnosis in the postoperative period, including their advantages and disadvantages.
The second stage was based on a prospective controlled randomized study of 44 patients aged 18 years and older (mean age 30.4±7.8 years) with various skeletal classes of malocclusion, in whom 88 mandibular SSO procedures were performed using navigational surgical guides by a single surgical team according to the same technique. For accurate assessment of IAN injury, a modified classification of nerve exposure (NE) types was applied: 1 – less than 50% of the nerve visualized in the distal bony fragment; 2 – more than 50% visualization of the nerve in the distal bony fragment; 3 – the nerve completely located in the proximal mandibular segment. The magnitude and direction of bone fragment movement were also evaluated based on cone-beam computed tomography (CBCT) data. It was established that the severity of postoperative neurosensory disturbances depended on the degree of nerve exposure, its topographic localization (ρ=0.532; p<0.001), and the magnitude of mandibular movement (ρ=0.446; p<0.001).
An algorithm of intraoperative IAN therapy was developed and implemented into the surgical protocol. After osteotomy and mobilization of the bone fragments, topical application of dexamethasone phosphate 0.4% (4 mg/1 ml) on a gauze swab for 10 minutes was applied to the exposed IAN, followed by placement of fraction 2 (F2) plasma rich in growth factors (PRGF) prepared according to the Endoret BTI technology.
The third stage included the development of a step-by-step clinical diagnostic scheme and creation of an individual patient examination chart, according to which sensory disturbances were assessed. Mapping of affected areas – dermatomes of the lower lip and chin corresponding to the innervation zones of the inferior alveolar nerve – was performed by marking between the relevant anatomical landmarks. Two zones were outlined with solid lines: on the lower lip – from the stomion (st) landmark to the mentolabial sulcus (ms), and on the chin – from ms to gnation (gn). Each zone was then divided into four segments – right and left within each zone – oriented to the facial midline and vertical lines drawn from the chelion (ch) landmarks. The area of paresthesia was determined using the light touch (LT) test on postoperative day 1, after 1 week, 1 month, 3 months, and 6 months.
