The effect of masticatory behaviour on generalized attention in heathy volunteers.

AIM: As our society ages, the number of people living with dementia also steadily increases. Some work has focused on masticatory behaviour as a form of daily health care that could help prevent cognitive impairment and dementia. However, it is not yet clear how masticatory behaviour influences various cognitive functions. Therefore, the purpose of this study was to examine the effect of masticatory behaviour on the decline of generalized attention, an important cognitive function. METHODS: Participants were 35 healthy, dentulous individuals without stomatognathic abnormalities (24 men, 11 women; mean age: 56.8 ± 4.8 years). All participants completed three interventions: mastication, foot-stepping, and none (control). Pre- and post-intervention measures of generalized attention were measured by using neuropsychological tests to examine general attention; the results were then compared. Simultaneously, during the generalized attention task, the functional activity of the prefrontal cortex was observed on functional near-infrared spectroscopy. RESULTS: Response time of generalized attention improved in both the masticatory and foot-stepping interventions. There was a transient increase in oxyhaemoglobin activity in the right and left prefrontal cortices in the masticatory intervention. CONCLUSIONS: Masticatory behaviour may be involved in a partial improvement of generalized attention and may induce prefrontal cortex activity in middle-aged and older adults.

Loss of molars early in life develops behavioral lateralization and impairs hippocampus-dependent recognition memory.

BACKGROUND: Using senescence-accelerated mouse prone 8 (SAMP8), we examined whether reduced mastication from a young age affects hippocampal-dependent cognitive function. We anesthetized male SAMP8 mice at 8 weeks of age and extracted all maxillary molar teeth of half the animals. The other animals were treated similarly, except that molar teeth were not extracted. At 12 and 24 weeks of age, their general behavior and their ability to recognize novel objects were tested using the open-field test (OFT) and the object-recognition test (ORT), respectively. RESULTS: The body weight of molarless mice was reduced significantly compared to that of molar-intact mice after the extraction and did not recover to the weight of age-matched molar-intact mice throughout the experimental period. At 12 weeks of age, molarless mice showed significantly greater locomotor activity in the OFT than molar-intact mice. However, the ability of molarless mice to discriminate a novel object in the ORT was impaired compared to that of molar-intact mice. The ability of both molarless and molar-intact SAMP8 mice to recognize objects was impaired at 24 weeks of age. These results suggest that molarless SAMP8 mice develop a deficit of cognitive function earlier than molar-intact SAMP8 mice. Interestingly, both at 12 and 24 weeks of age, molarless mice showed a lateralized preference of object location in the encoding session of the ORT, in which two identical objects were presented. Their lateralized preference of object location was positively correlated with the rightward turning-direction preference, which reached statistical significance at 24 weeks of age. CONCLUSIONS: Loss of masticatory function in early life causes malnutrition and chronic stress and impairs the ability to recognize novel objects. Hyperactivation and lateralized rotational behavior are commonly observed with dysfunction of the dopaminergic system, therefore, reduced masticatory function may deplete the mesolimbic and mesocorticolimbic dopaminergic systems to impair the cognitive functions of selective attention and recognition memory in the prefrontal cortex and the hippocampus.

Patient satisfaction with conventional dentures vs. digital dentures fabricated using 3D-printing: A randomized crossover trial.

PURPOSE: Evidence regarding the performance of digital dentures (DDs) fabricated using 3D printing is insufficient. This study aimed to evaluate patient satisfaction with conventional dentures (CDs) and DDs fabricated using 3D printing. METHODS: This randomized controlled trial was conducted between November 2017 and May 2020. In the CD-DD group, CDs were fabricated before DDs, while the protocol was reversed in the DD-CD group. The primary outcome was patient satisfaction, quantified using a 100-mm visual analog scale, which assessed chewing efficiency, pain, stability, retention, comfort, esthetics, ease of cleaning, phonetics, and general satisfaction. Secondary outcomes were quality of life (QOL), number of visits, time required for definitive denture fabrication, number of adjustment appointments, and time required for denture stabilization after denture delivery. RESULTS: Patient satisfaction with CDs was superior in terms of phonetics, ease of cleaning, stability, comfort, and general satisfaction. Secondary outcomes such as social disability and the number of clinic visits were significantly lower in patients with DDs. However, the two groups showed no significant differences in the other outcomes. Although patient satisfaction with DDs was inferior to that with CDs, 20% of patients preferred and used DDs (12 patients preferred CDs, and three patients opted for DDs). CONCLUSION: Although patient satisfaction or QOL with DDs may be somewhat inferior to that with CDs, 20% of patients preferred and used DDs daily. Thus, DDs fabricated using 3D printing may have comparable practicality and efficacy to CDs.

Ultraviolet light treatment for the restoration of age-related degradation of titanium bioactivity.

PURPOSE: To examine the bioactivity of differently aged titanium (Ti) disks and to determine whether ultraviolet (UV) light treatment reverses the possible adverse effects of Ti aging. MATERIALS AND METHODS: Ti disks with three different surface topographies were prepared: machined, acid-etched, and sandblasted. The disks were divided into three groups: disks tested for biologic capacity immediately after processing (fresh surfaces), disks stored under dark ambient conditions for 4 weeks, and disks stored for 4 weeks and treated with UV light. The protein adsorption capacity of Ti was examined using albumin and fibronectin. Cell attraction to Ti was evaluated by examining migration, attachment, and spreading behaviors of human osteoblasts on Ti disks. Osteoblast differentiation was evaluated by examining alkaline phosphatase activity, the expression of bone-related genes, and mineralized nodule area in the culture. RESULTS: Four-week-old Ti disks showed = or < 50% protein adsorption after 6 hours of incubation compared with fresh disks, regardless of surface topography. Total protein adsorption for 4-week-old surfaces did not reach the level of fresh surfaces, even after 24 hours of incubation. Fifty percent fewer human osteoblasts migrated and attached to 4-week-old surfaces compared with fresh surfaces. Alkaline phosphatase activity, gene expression, and mineralized nodule area were substantially reduced on the 4-week-old surfaces. The reduction of these biologic parameters was associated with the conversion of Ti disks from superhydrophilicity to hydrophobicity during storage for 4 weeks. UV-treated 4-week-old disks showed even higher protein adsorption, osteoblast migration, attachment, differentiation, and mineralization than fresh surfaces, and were associated with regenerated superhydrophilicity. CONCLUSIONS: Time-related degradation of Ti bioactivity is substantial and impairs the recruitment and function of human osteoblasts as compared to freshly prepared Ti surfaces, suggesting a "biologic aging"-like change of Ti. UV treatment of aged Ti, however, restores and even enhances bioactivity, exceeding its innate levels.

Comparison of cerebral cortex activation induced by tactile stimulation between natural teeth and implants.

BACKGROUND: The purpose of this study was to assess the cortical-level sensory differences between natural teeth with a periodontal membrane and dental implants. MATERIAL AND METHODS: We used functional near-infrared spectroscopy (fNIRS) to measure brain activity in the cerebral cortex of 12 patients who had both natural teeth and dental implants in the lower molar region. Painless vibratory tactile stimulation was performed on both the natural teeth and the dental implants. RESULTS: Activation was seen in the somatosensory cortex during stimulation of both natural teeth and dental implants. A comparison of cortical activation showed no significant differences between natural teeth and dental implants. CONCLUSIONS: These results indicate the possible existence of sensory input to the cerebral cortex via dental implants as well as natural teeth, and thus suggest that may not only the periodontal membrane be involved in the signaling pathway. The data from this experiment may help us for understanding the neural mechanisms underlying natural teeth and dental implants. Key words:fNIRS, natural teeth, implants, brain activity, somatosensory cortex.

Influence of ultraviolet irradiation treatment on porcelain bond strength of titanium surfaces.

To determine the effect of titanium (Ti) surface modification by ultraviolet irradiation (UVI) on the bond strength between Ti and porcelain. Grade 2 Ti plates were allotted to five groups: sandblasted (SA), 15 min UVI (UV), SA+5 min UVI (SA+UV5), SA+10 min UVI (SA+UV10), and SA+15 min UVI (SA+UV15). After surface treatment, porcelain was added. A precious metal (MC) was used for comparison with Ti. The effects of 24-h storage at room temperature versus thermal cycling only at 5 and 55°C in water were evaluated. Subsequently, the tensile strength of each sample was tested. Data were analyzed using one-way analysis of variance and the Tukey test. In both the room temperature and thermal cycling groups, the MC and SA+15 min UVI samples showed significantly greater bond strengths than the other samples (p<0.05). UVI processing efficiently increases the bond strength between porcelain and the Ti surface.

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.