Masahito Nakashima

Bio: Masahito Nakashima is an academic researcher from Gifu University. The author has contributed to research in topics: Estrogen & Ovariectomized rat. The author has an hindex of 2, co-authored 2 publications receiving 147 citations.

Modulation of pain by estrogens.

Abstract: It has become increasingly apparent that women suffer a disproportionate amount of pain during their lifetime compared to men. Over the past 15 years, a growing number of studies have suggested a variety of causes for this sex difference, from cellular to psychosocial levels of analysis. From a biological perspective, sexual differentiation of pain appears to occur similarly to sexual differentiation of other phenomena: it results in large part from organizational and activational effects of gonadal steroid hormones. The focus of this review is the activational effects of a single group of ovarian hormones, the estrogens, on pain in humans and animals. The effects of estrogens (estradiol being the most commonly examined) on experimentally induced acute pain vs. clinical pain are summarized. For clinical pain, the review is limited to a few syndromes for which there is considerable evidence for estrogenic involvement: migraine, temporomandibular disorder (TMD) and arthritis. Because estrogens can modulate the function of the nervous, immune, skeletal, and cardiovascular systems, estrogenic modulation of pain is an exceedingly complex, multi-faceted phenomenon, with estrogens producing both pro- and antinociceptive effects that depend on the extent to which each of these systems of the body is involved in a particular type of pain. Forging a more complete understanding of the myriad ways that estrogens can ameliorate vs. facilitate pain will enable us to better prevent and treat pain in both women and men.

Temporomandibular disorders and hormones in women.

Abstract: Temporomandibular disorders (TMD) are loosely defined as an assorted set of clinical conditions, characterized by pain and dysfunction of the masticatory system. Pain in the masticatory muscles, in th

Evaluation of bone changes in the temporomandibular joint using cone beam CT.

Abstract: Objective: The aim of this study was to assess bone changes and mobility in temporomandibular joints (TMJs) using cone beam CT (CBCT) in a population sample in Recife, PE, Brazil. Methods: The TMJ images of patients treated by a radiologist at a private dental radiology service over a period of 1 year were retrieved from the computer database and assessed using a computer with a 21-inch monitor and the iCAT Cone Beam 3D Dental Imaging System Workstation program (Imaging Sciences International, Hatfield, PA). The Pearson x 2 test was used to analyse the differences in percentage of bone changes among the categories of mobility (p # 0.05). The McNemar test was used to compare the presence of bone changes in TMJs on the right and left sides (p # 0.05). Results: An adjusted logistic regression model was used to assess the effect of age and gender on the occurrence of bone changes (p # 0.05). Bone changes were present in 227 (71%) patients. Age group and gender showed a statistically significant association with presence of bone changes (p # 0.05). There was no significant difference between the right and left sides (p 5 0.556) and in condylar mobility (p 5 0.925) with regard to the presence of degenerative bone changes. Conclusions: There is a high prevalence of degenerative bone alteration in TMJs, which is more frequent in women and mostly located in the condyle. The prevalence of degenerative bone changes increases with age. There is no correlation between condylar mobility and the presence of degenerative bony changes in TMJs. Dentomaxillofacial Radiology (2012) 41, 24–29. doi: 10.1259/dmfr/17815139

Progressive condylar resorption after mandibular advancement.

Abstract: Progressive condylar resorption is an irreversible complication and a factor in the development of late skeletal relapse after orthognathic surgery. We have evaluated cephalometric characteristics, signs and symptoms in the temporomandibular joint (TMJ), and surgical factors in six patients (one man and five women) who developed it after orthognathic surgery. The findings in preoperative cephalograms indicated that the patients had clockwise rotation of the mandible and retrognathism because of a small SNB angle, a wide mandibular plane angle, and a "minus" value for inclination of the ramus. There were erosions or deformities of the condyles, or both, on three-dimensional computed tomography (CT) taken before treatment. The mean (SD) anterior movement of the mandible at operation was 12.1 (3.9)mm and the mean relapse was -6.4 (2.5)mm. The mean change in posterior facial height was 4.5 (2.1)mm at operation and the mean relapse was -5.3 (1.8)mm. Two patients had click, or pain, or both, preoperatively. The click disappeared in one patient postoperatively, but one of the patients who had been symptom-free developed crepitus postoperatively. In the classified resorption pattern, posterior-superior bone loss was seen in three cases, anterior-superior bone loss in two, and superior bone loss in one. Progressive condylar resorption after orthognathic surgery is multifactorial, and some of the risk factors are inter-related. Patients with clockwise rotation of the mandible and retrognathism in preoperative cephalograms; erosion, or deformity of the condyle, or both, on preoperative CT; and wide mandibular advancement and counterclockwise rotation of the mandibular proximal segment at operation, seemed to be at risk. The mandible should therefore be advanced only when the condyles are stable on radiographs, and careful attention should be paid to postoperative mechanical loading on the TMJ in high-risk patients.