Takero Otsuka

Effects of Mandibular Deviation on Brain Activation During Clenching: An fMRI Preliminary Study

Abstract Using functional magnetic resonance imaging (fMRI) in eight healthy human subjects, the present study measured blood oxygenation level-dependent (BOLD) signals during clenching in a malocclusion model, using a custom-made splint that forced the mandible to a retrusive position and a splint of no modification for control, and compared the results to the BOLD signals during the corresponding resting conditions. An individual visual analog scale (VAS) score was also examined during clenching to evaluate the interactions between fMRI data and psychiatric changes. During both clenchings, activations in four brain regions (premotor cortex, prefrontal cortex, sensorimotor cortex, and insula) were seen. However, clenching in the malocclusion model, with psychological discomfort, increased additionally BOLD signals in the anterior cingulate cortex and the amygdala. Furthermore, there was a parallel relationship between BOLD signal intensities and VAS scores in these two regions. The findings may suggest the involvement of clenching with malocclusal conditions in the emotion and/or pain-related neural processing in the brain.

Chewing-induced regional brain activity in edentulous patients who received mandibular implant-supported overdentures: A preliminary report

PURPOSE We used functional magnetic resonance imaging (fMRI) to investigate the change in brain regional activity during gum chewing when edentulous subjects switched from mandibular complete dentures to implant-supported removable overdentures. METHODS Four edentulous patients (3 males and 1 female, aged 64 to 79 years) participated in the study. All subjects received a set of new maxillary and mandibular complete dentures (CD), followed by a maxillary complete denture and a new mandibular implant-supported removable overdentures (IOD). A 3-T fMRI scanner produced images of the regional brain activity for each subject that showed changes in the blood-oxygenation-level-dependent (BOLD) contrast in the axial orientation during gum-chewing with CD and IOD. RESULTS Region-of-interest analysis showed that IOD treatment significantly suppressed chewing-induced brain activity in the prefrontal cortex. The chewing-induced brain activities in the primary sensorimotor cortex and cerebellum tended to decrease with IOD treatment, however they did not reach to significance level. There was no change in brain activity in the supplementary motor area, thalamus and insula between gum chewing with CD and IOD. Group comparison using statistical parametrical mapping further showed that, within the prefrontal cortex, the neural activity of the frontal pole significantly decreased during gum-chewing with IOD when compared to that with CD (P<0.05). CONCLUSION Despite the limitation of a small sample size, these results suggest that the gum-chewing task in elderly edentulous patients resulted in differential neural activity in the frontal pole within the prefrontal cortex between the 2 prosthodontic therapies-mandibular CD and IOD.

Dental resin curing blue light induced oxidative stress with reactive oxygen species production

Dental resin curing blue light has been used in the treatment of tooth bleaching and to restore teeth with resin-based composite fillings. However, there has been little consideration of its effect on oral tissues such as dental pulp and oral mucosa. The aim of this study was to investigate whether dental resin curing blue light irradiation affects the dental pulp, especially the blood vessels that are known as the first target of reactive oxygen species (ROS), which play an important role in vascular reactivity. We found that blue light irradiation increased the level of lipid peroxidation in isolated rat aorta blood vessels by measuring malondialdehyde. Furthermore, cell proliferative activity was decreased in a time-dependent manner and apoptosis of human aorta vascular smooth muscle cells (VSMCs) was induced. These results indicated that (ROS) such as hydrogen peroxide and hydroxyl radicals were generated in VSMCs by irradiation with blue light, and they induced cytotoxicity associated with oxidative stress, which increased lipid peroxidation and apoptosis. In addition, N-acetyl-l-cysteine, which is a typical intracellular antioxidant, protected VSMCs against cytotoxicity associated with oxidative stress. These findings suggested that antioxidants may be used to prevent oxidative stress in dental pulp by repeated and/or multiple treatments with blue light irradiation in future dental treatments.

Comparison of Brain Activation via Tooth Stimulation

The aim of this study was to evaluate the sensation of each tooth type at the cortical level. The tactical sensation from teeth plays an important role in controlling the masticatory system. However, the role of each tooth type has not been determined. Functional near-infrared spectroscopy (fNIRS) was used to detect changes in cerebral blood flow in the somatosensory cortex of 12 healthy volunteers. Painless vibrotactile stimuli were applied to 8 teeth (left maxillary and mandibular incisors, canines, 1st premolars, or 1st molars). The somatosensory cortex was activated during stimulation of all teeth. A comparison of cortical activation revealed significantly greater activation during stimulation of the maxillary and mandibular first molars. However, no significant differences were seen between any other teeth. These results indicate that the first molar is the most sensitive tooth type at the cortical level, and provide basic data on the relationship between input from individual tooth type and brain activation. These data could be useful for understanding the neural mechanisms of individual tooth types.

The Amount of TMJ Displacement Correlates with Brain Activity

Abstract The aim of this functional magnetic resonance imaging (fMRI) study was to investigate the correlation between the severity of malocclusion and brain activation. The fMRI was used to measure blood-oxygenation- level-dependent (BOLD) signals of twelve healthy human subjects while they clenched in two different ways to simulate two types of malocclusion. In each malocclusion model, a custom-made splint forced the mandible to each of two retrusive positions (0.5 mm, 0.7 mm). A no-modification splint provided the control. We compared the BOLD signals measured at each clenching position with those measured during the corresponding resting conditions. The BOLD signals were significantly stronger in the amygdala and the prefrontal area (PFA) when subjects clenched in the two retrusive positions compared during clenching in the control position. In addition, the BOLD signal in the PFA increased as the simulated malocclusion became more severe. These results indicate that we may be able to objectively assess the severity of malocclusion via focus on the brain activity.

Vertical facial height and its correlation with facial width and depth: Three dimensional cone beam computed tomography evaluation based on dry skulls

IntroductionThe aim of the present study was to evaluate how vertical facial height correlates with mandibular plane angle, facial width and depth from a three dimensional (3D) viewing angle.MethodsIn this study 3D cephalometric landmarks were identified and measurements from 43 randomly selected cone beam computed tomography (CBCT) images of dry skulls from the Weisbach collection of Vienna Natural History Museum were analyzed. Pearson correlation coefficients of facial height measurements and mandibular plane angle and the correlation coefficients of height-width and height-depth were calculated, respectively.ResultsThe mandibular plane angle (MP-SN) significantly correlated with ramus height (Co-Go) and posterior facial height (PFH) but not with anterior lower face height (ALFH) or anterior total face height (ATFH). The ALFH and ATFH showed significant correlation with anterior cranial base length (S-N), whereas PFH showed significant correlation with the mandible (S-B) and maxilla (S-A) anteroposterior position.ConclusionsHigh or low mandibular plane angle might not necessarily be accompanied by long or short anterior face height, respectively. The PFH rather than AFH is assumed to play a key role in the vertical facial type whereas AFH seems to undergo relatively intrinsic growth.

The mandibular response to occlusal relief using a flat guidance splint

BackgroundThe mechanism of action of occlusal splints used for the successful treatment of temporomandibular disorders (TMD) remains unclear and controversial.AimThe aim of this study was to observe the mandibular response during sleep bruxism (SB) on the elimination of occlusal influences by using a flat anterior and lateral guidance splint (FGS).Material and methodAny changes in mandibular movement patterns and condylar position with the introduction of this tool were measured. Current SB activity on the natural dentition was evaluated using a Brux Checker® (BC) and compared with the activity after insertion of an FGS in 153 subjects.ResultThe spatial mandibular position changed individually with a tendency toward forward and downward movement. The insertion of an FGS led to a change in the topographical condyle-fossa relationship and seemed to create an “unloading” condition for the temporomandibular joint. It was found that increased angulation of the maxillar incisors was responsible for altered muscular activity during sleep.ConclusionThe masticatory organ appears to self-regulate and to provide an oral behavior modification, which may be more physiological using the FGS as a compensating factor. In this context, it is assumed that sleep bruxism in terms of parafunctional activity is a physiological function of the masticatory organ. The results of this study indicate the importance of controlling anterior guidance in the functional reconstruction of human occlusion.

Medical-grade collagen peptide in injectables provides antioxidant protection

Abstract Medical-grade collagen peptide is used as an additive agent in pharmaceutical formulations; however, it is unknown as to whether the compound exerts antioxidant effects in vitro. In this study, we evaluated the antioxidant effects of medical-grade collagen peptide on reactive oxygen species such as hydroxyl radical, superoxide anion radical and singlet oxygen using electron spin resonance and spin trapping. We confirmed that medical-grade collagen peptide directly inhibited hydroxyl radical generated by the Fenton reaction or by ultraviolet irradiation of hydrogen peroxide, and singlet oxygen. In addition, an antioxidant effect of medical-grade collagen peptide on singlet oxygen was observed in peptide fractions 12–22. The total amount of antioxidant amino acids (Gly, Hyp, Glu, Ala, Cys, Met and His) constituted more than half of the total amino acids in these fractions. These results suggest that the observed antioxidant properties of medical-grade collagen peptide are due to the compound containing antioxidant amino acids. Medical-grade collagen peptide, which is used in pharmaceuticals, and especially in injectables, could provide useful antioxidant properties to protect the active ingredient from oxidation.

Influence of restoration adjustments on prefrontal blood flow: A simplified NIRS preliminary study

ObjectiveThe aim of this study was to examine, after setting several restorations, the influence of adjusted occlusal interference during gum chewing on blood flow in the prefrontal area as determined using near-infrared spectroscopy.Material and methodsThe physiological rate was assessed using a visual analog scale (VAS) questionnaire. We selected 16 patients who desired prosthetic restorative treatment on the lateral dentition, and eight healthy volunteers. Subjects were divided into three eight-person groups. One group received restorations on the premolar area (PA), another group received restorations on the molar area (MA), and the control group (CT) received no prosthetic restorations. The spectroscope was fastened to the frontal region of the head after placement of the final restoration, but before adjustment.ResultsPre-adjustment (first gum chewing for CT) blood flow in the prefrontal cortex was measured during gum chewing. Blood flow was again measured during gum chewing after the restoration (second gum chewing for CT) had been adjusted in accordance with the subjective assessment of the patient while wearing the device. The VAS provided quantification of comfort during gum chewing before and after restoration adjustment. For the PA and MA groups, adjusting restorations decreased discomfort significantly during gum chewing. Moreover, in the MA group, prefrontal blood flow was significantly reduced, and blood flow correlated with discomfort.ConclusionsActivation of the prefrontal area may provide an objective criterion for judging the functionality of occlusion after prosthetic occlusal reconstruction and/or orthodontics.

Effect of articulatory rehabilitation after oral cancer surgery on higher brain activation

The present study aimed to verify the importance of postoperative articulatory rehabilitation in patients with oral cancer and to clarify the neurological changes underlying articulatory functional recovery. A longitudinal assessment of oral function and accompanying brain activity was performed using non-invasive functional magnetic resonance imaging (fMRI). We assessed 13 patients with cancers of the tongue and oral floor before and after ablative surgery. Articulatory function was assessed preoperatively and postoperatively using a conversation intelligibility test and the Assessment of Motor Speech for Dysarthria test. Patients also performed a verbal task during fMRI scans. The assessments were then repeated after the patients had undergone 4-6 months of articulatory rehabilitation therapy. Compared to pretreatment levels, articulatory rehabilitation resulted in a significant increase in activation in the supplementary motor cortex, thalamus, and cingulate cortex. The present study offers a quantitative assessment of the effects of speech rehabilitation by investigating changes in brain activation sites.