Age-Related Changes in Temporal Binding Involving Auditory and Vestibular Inputs.

Maintaining balance involves the combination of sensory signals from the visual, vestibular, proprioceptive, and auditory systems. However, physical and biological constraints ensure that these signals are perceived slightly asynchronously. The brain only recognizes them as simultaneous when they occur within a period of time called the temporal binding window (TBW). Aging can prolong the TBW, leading to temporal uncertainty during multisensory integration. This effect might contribute to imbalance in the elderly but has not been examined with respect to vestibular inputs. Here, we compared the vestibular-related TBW in 13 younger and 12 older subjects undergoing 0.5 Hz sinusoidal rotations about the earth-vertical axis. An alternating dichotic auditory stimulus was presented at the same frequency but with the phase varied to determine the temporal range over which the two stimuli were perceived as simultaneous at least 75% of the time, defined as the TBW. The mean TBW among younger subjects was 286 ms (SEM ± 56 ms) and among older subjects was 560 ms (SEM ± 52 ms). TBW was related to vestibular sensitivity among younger but not older subjects, suggesting that a prolonged TBW could be a mechanism for imbalance in the elderly person independent of changes in peripheral vestibular function.

Assessment of the activity of secondary caries lesions with short-wavelength infrared, thermal, and optical coherence tomographic imaging.

Significance: Leakage in the interfaces between restorative materials and tooth structure allows for fluid and bacterial acid infiltration, causing restoration failure due to secondary caries. Dentists spend more time replacing composite restorations than placing new ones. Previous in vitro and in vivo studies on enamel and root surfaces using shortwave-infrared (SWIR) and thermal imaging during dehydration with forced air have been promising for assessing lesion activity. Aim: We hypothesized that SWIR reflectance and thermal imaging methods can be used to monitor the activity of secondary caries lesions around composite restorations. The objective of this study was to employ these methods to measure the rate of fluid loss from lesions during dehydration with forced air to assess lesion activity. Approach: Sixty-three extracted human teeth with total of 109 suspected secondary lesions were examined using SWIR and thermal imaging during dehydration. The thickness of the highly mineralized transparent surface layer (TSL) at lesion interfaces indicative of lesion activity was measured by optical coherence tomography (OCT). Micro-computed tomography (MicroCT) was used to further confirm lesion severity and structure. OCT and MicroCT measurements of lesion structure, depth, and severity were correlated with fluid loss rates measured with SWIR reflectance and thermal imaging. Results: TSL thickness measured with OCT correlated with both SWIR reflectance and thermal measurements of rates of fluid loss ( p < 0.05 ). Increasing TSL thickness led to decreased permeability of lesions, potentially indicating full lesion arrest at TSL ≥ 70 µ m . SWIR performed better than thermal imaging for secondary lesion activity assessment, although both methods performed best on smooth surface lesions. Conclusions: Nondestructive SWIR reflectance and OCT imaging methods are promising for clinically monitoring the activity of secondary caries lesions.

Assessing lesion activity of secondary lesions on extracted teeth by thermal dehydration measurement and optical coherence tomography.

Secondary caries occurs when leakage in the interfaces between restorative materials and tooth structure allow fluid and bacterial acid infiltration. Thermal imaging coupled with dehydration can be used to measure this increase in fluid permeability for secondary lesions in teeth. Thermal imaging exploits the temperature change due to water evaporation during dehydration to measure the rate of water diffusion from porous lesion areas. Previous in vitro and in vivo thermal imaging studies on enamel and root surfaces have been promising for assessing natural lesion activity. In this study, the rates of dehydration for secondary lesions on extracted teeth were measured. The secondary lesions were also assessed by optical coherence tomography (OCT) and correlated with dehydration rates to determine lesion activity. Future studies with µCT will be used to further confirm lesion severity and structure.

Use of SWIR dehydration and OCT to assess the complete arrest of simulated incipient caries lesions.

Previous studies have shown that optical coherence tomography (OCT) can be used to show the formation of a transparent surface zone on caries lesions indicative of remineralization. Studies have also shown that monitoring changes in the diffuse reflectivity of caries lesions during drying with air can be used to assess lesion activity and that the largest changes occur at SWIR wavelengths coincident with high water absorption at 1450 and 1950 nm. The purpose of this study was to determine when remineralization has occurred by monitoring changes in SWIR reflectance measurements and OCT images of simulated lesions over an extended time period during exposure to a remineralization solution. Eight bovine enamel surfaces each with two treatment windows were exposed to a pH cycling regimen to produce simulated lesions 50-100 µm deep. OCT at 1310 nm was used to image the samples at each time point. An extended range tungsten halogen lamp with a 1450 nm band pass filter and a broadband amplified spontaneous emission source centered near the peak of the water-absorption band at 1950 nm were used as light sources. An extended range InGaAs camera (1000-2340 nm) was used to acquire reflected light images as the samples were dried with air. After 32 days of exposure to the remineralization solution there were no further changes to the samples suggesting they had been completely arrested.

Monitoring silver diamine fluoride application with optical coherence tomography and thermal imaging: An in vitro proof of concept study.

OBJECTIVES: The purpose of this study was to show that optical coherence tomography (OCT) and thermal imaging can be used to monitor changes in the structure and activity of caries lesions over time after treatment with silver diamine fluoride (SDF). METHODS: Artificial caries lesions were formed on enamel and dentin bovine blocks. Each block was partitioned into five windows with the central three windows exposed to a demineralization solution to create lesions: one sound window served as a sound control (SC), one sound window was exposed to SDF to serve as a test control (SCT), one lesion window served as a lesion control (LC), one lesion window received one application of SDF (L1), while the other lesion window received two applications of SDF (L2). Each window was scanned using OCT before SDF application, and every week subsequently, for 12 weeks after initial SDF treatment. Changes in the mean intensity and the width of the peak of increased reflectivity due to the lesion and SDF along with the intensity at a depth of 180 µm from the surface representing optical penetration through the lesion were monitored. Changes in the heat lost, ΔQ (temperature integrated over time) of each window during drying with air were also monitored using a thermal imaging camera. Transverse microradiography (TMR), and high-resolution microscopy were also used for the analysis of selected samples. RESULTS: The reflectivity and optical penetration of sound and lesion areas of enamel and dentin manifested significant changes in OCT images after SDF application. Thermal imaging showed significant differences in ΔQ indicative of permeability changes in the sound and lesion areas of enamel and dentin after SDF application.

Treponema denticola dentilisin triggered TLR2/MyD88 activation upregulates a tissue destructive program involving MMPs via Sp1 in human oral cells.

Periodontal disease is driven by dysbiosis in the oral microbiome, resulting in over-representation of species that induce the release of pro-inflammatory cytokines, chemokines, and tissue-remodeling matrix metalloproteinases (MMPs) in the periodontium. These chronic tissue-destructive inflammatory responses result in gradual loss of tooth-supporting alveolar bone. The oral spirochete Treponema denticola, is consistently found at significantly elevated levels in periodontal lesions. Host-expressed Toll-Like Receptor 2 (TLR2) senses a variety of bacterial ligands, including acylated lipopolysaccharides and lipoproteins. T. denticola dentilisin, a surface-expressed protease complex comprised of three lipoproteins has been implicated as a virulence factor in periodontal disease, primarily due to its proteolytic activity. While the role of acylated bacterial components in induction of inflammation is well-studied, little attention has been given to the potential role of the acylated nature of dentilisin. The purpose of this study was to test the hypothesis that T. denticola dentilisin activates a TLR2-dependent mechanism, leading to upregulation of tissue-destructive genes in periodontal tissue. RNA-sequencing of periodontal ligament cells challenged with T. denticola bacteria revealed significant upregulation of genes associated with extracellular matrix organization and degradation including potentially tissue-specific inducible MMPs that may play novel roles in modulating host immune responses that have yet to be characterized within the context of oral disease. The Gram-negative oral commensal, Veillonella parvula, failed to upregulate these same MMPs. Dentilisin-induced upregulation of MMPs was mediated via TLR2 and MyD88 activation, since knockdown of expression of either abrogated these effects. Challenge with purified dentilisin upregulated the same MMPs while a dentilisin-deficient T. denticola mutant had no effect. Finally, T. denticola-mediated activation of TLR2/MyD88 lead to the nuclear translocation of the transcription factor Sp1, which was shown to be a critical regulator of all T. denticola-dependent MMP expression. Taken together, these data suggest that T. denticola dentilisin stimulates tissue-destructive cellular processes in a TLR2/MyD88/Sp1-dependent fashion.

Infrared imaging confirms the role of the transparent surface zone in arresting dental caries.

Several studies have demonstrated the potential of short wavelength infrared (SWIR) reflectance, thermal imaging and optical coherence tomography for the nondestructive assessment of the activity of caries lesions. The purpose of this study was to test the hypothesis that the activity of arrested caries lesions on the coronal surfaces of extracted teeth would be changed by reducing the thickness of the highly mineralized transparent surface layer, which was measured using polarization sensitive optical coherence tomography (PS-OCT). The lesion activity was assessed using SWIR reflectance and thermal imaging during forced air drying of the lesion before and after mechanical removal of a surface layer ~ 50-µm thick covering the lesion. Both the intensity change in SWIR reflectance images at 1500-1750-nm wavelengths after drying the lesions and the change in thermal emission measured with a thermal camera at 8-13-µm wavelengths increased significantly (P<0.05) after reducing the thickness of the mineralized surface layer in the lesions indicating the permeability of the lesion to fluids increased. These results provide further evidence that the presence of a highly mineralized outer surface layer is a key indicator of lesion arrest.

A thermal imaging handpiece for the clinical assessment of lesion activity on root surfaces via dehydration.

New imaging methods are needed to assess the activity of caries lesions on tooth surfaces. Recent studies have shown that thermal imaging of lesions on root surfaces during dehydration with air can be used to determine if the lesions are active or arrested. In this study changes in the thermal emission of root caries lesions on extracted teeth during dehydration with air was monitored using an imaging system with a miniature thermal camera and a 3D printed handpiece with an integrated air nozzle suitable for clinical use. This study evaluated the performance of the thermal camera for imaging root caries on extracted teeth prior to it's use for in vivo studies. There was a significant difference in the thermal response of sound and root lesion areas of human teeth under dehydration at constant airflow.

A SWIR imaging handpiece for the clinical assessment of lesion activity via dehydration. Preclinical Assessment.

New imaging methods are needed to assess the activity of caries lesions on tooth surfaces. Recent studies have shown that changes in the contrast of lesions during dehydration with air at SWIR wavelengths can be used to determine if lesions are active or arrested. In this study changes in the reflectance of caries lesions during dehydration with air was monitored at 1500-1750-nm on extracted teeth using an imaging system with an InGaAs camera, a light source and a 3D printed handpiece with an integrated air nozzle suitable for clinical use. Lesion structure was also assessed with optical coherence tomography and microCT for comparison. This small preclinical study demonstrated that a 3D printed appliance with integrated air for dehydration can be used to acquire SWIR dehydration curves similar to those acquired previously for benchtop imaging systems.

Frequency-dependent integration of auditory and vestibular cues for self-motion perception.

Recent evidence has shown that auditory information may be used to improve postural stability, spatial orientation, navigation, and gait, suggesting an auditory component of self-motion perception. To determine how auditory and other sensory cues integrate for self-motion perception, we measured motion perception during yaw rotations of the body and the auditory environment. Psychophysical thresholds in humans were measured over a range of frequencies (0.1-1.0 Hz) during self-rotation without spatial auditory stimuli, rotation of a sound source around a stationary listener, and self-rotation in the presence of an earth-fixed sound source. Unisensory perceptual thresholds and the combined multisensory thresholds were found to be frequency dependent. Auditory thresholds were better at lower frequencies, and vestibular thresholds were better at higher frequencies. Expressed in terms of peak angular velocity, multisensory vestibular and auditory thresholds ranged from 0.39°/s at 0.1 Hz to 0.95°/s at 1.0 Hz and were significantly better over low frequencies than either the auditory-only (0.54°/s to 2.42°/s at 0.1 and 1.0 Hz, respectively) or vestibular-only (2.00°/s to 0.75°/s at 0.1 and 1.0 Hz, respectively) unisensory conditions. Monaurally presented auditory cues were less effective than binaural cues in lowering multisensory thresholds. Frequency-independent thresholds were derived, assuming that vestibular thresholds depended on a weighted combination of velocity and acceleration cues, whereas auditory thresholds depended on displacement and velocity cues. These results elucidate fundamental mechanisms for the contribution of audition to balance and help explain previous findings, indicating its significance in tasks requiring self-orientation.NEW & NOTEWORTHY Auditory information can be integrated with visual, proprioceptive, and vestibular signals to improve balance, orientation, and gait, but this process is poorly understood. Here, we show that auditory cues significantly improve sensitivity to self-motion perception below 0.5 Hz, whereas vestibular cues contribute more at higher frequencies. Motion thresholds are determined by a weighted combination of displacement, velocity, and acceleration information. These findings may help understand and treat imbalance, particularly in people with sensory deficits.

SWIR, Thermal and CP-OCT imaging probes for the in vivo assessment of the activity of root caries lesions.

New imaging technologies are needed for the clinical assessment of lesions on root surfaces. It is not sufficient to simply detect caries lesions; methods are needed to assess lesion depth, structural composition and activity to determine if chemical intervention has the potential to be effective and if remineralization has occurred. Lesions were monitored using CP-OCT during lesion dehydration to assess the lesion structure and any shrinkage. Thermal imaging at 6-10 µm wavelengths and short wavelength-IR imaging at 1450-1750-nm were used to monitor thermal emission during lesion dehydration to assess lesion activity. Imaging probes were custom fabricated for clinical use. We present the first clinical results of a small feasibility study employing CP-OCT, thermal and SWIR imaging to assess lesion activity in vivo on thirty test subjects with suspected root caries lesions.

A dual handheld SWIR transillumination/reflectance probe for imaging lesions on tooth occlusal and proximal surfaces.

We developed a clinical probe capable of acquiring simultaneous short wavelength infrared (SWIR) reflectance and occlusal transillumination images of lesions on tooth proximal and occlusal surfaces to reduce the potential of false positives. The dual probe is 3D-printed and the imaging system uses a Ge-enhanced camera and fiber-optic light sources that use SWIR light at 1300-nm for occlusal transillumination and SWIR 1450-nm light for reflectance measurements. The purpose of this study was to test the performance of the probe on extracted teeth prior to commencing clinical studies. The dual probe was used to image extracted teeth with proximal and occlusal lesions. SWIR images of each tooth were compared with micro-CT images to assess performance.

The Relationship of Dehydration Rate and Transparent Surface Layer Thickness for Coronal Lesions on Extracted Teeth.

Transparent remineralized surface zones found on natural caries lesions may reduce the permeability to water and plaque generated acids. Near-IR (NIR) reflectance imaging coupled with dehydration can be used to measure changes in the fluid permeability of lesions in enamel and dentin. Previous work demonstrated a negative association between the surface zone thickness and the rate of dehydration in simulated enamel lesions. In this study, the rates of dehydration and thickness of transparent surface layer of coronal lesions of extracted teeth were measured and correlated. Reflectance imaging at NIR wavelengths from 1695-1750 nm, which coincides with higher water absorption and manifests the greatest sensitivity to contrast changes during dehydration measurements, was used to image these enamel lesions. The remineralized surface layer thickness was determined using optical coherence tomography (OCT).

Lesion Dehydration Rate Changes with the Surface Layer Thickness during Enamel Remineralization.

A transparent highly mineralized outer surface zone is formed on caries lesions during remineralization that reduces the permeability to water and plaque generated acids. However, it has not been established how thick the surface zone should be to inhibit the penetration of these fluids. Near-IR (NIR) reflectance coupled with dehydration can be used to measure changes in the fluid permeability of lesions in enamel and dentin. Based on our previous studies, we postulate that there is a strong correlation between the surface layer thickness and the rate of dehydration. In this study, the rates of dehydration for simulated lesions in enamel with varying remineralization durations were measured. Reflectance imaging at NIR wavelengths from 1400-2300 nm, which coincides with higher water absorption and manifests the greatest sensitivity to contrast changes during dehydration measurements, was used to image simulated enamel lesions. The results suggest that the relationship between surface zone thickness and lesion permeability is highly non-linear, and that a small increase in the surface layer thickness may lead to a significant decrease in permeability.

Association between objectively measured chewing ability and frailty: A cross-sectional study in central Thailand.

AIM: Limited data are available on the association between oral function and frailty, especially in developing countries. Additionally, the association between objectively assessed chewing function and frailty has not been well studied. The present cross-sectional study tested the hypothesis that objectively measured poor chewing ability is associated with frailty in community-dwelling older Thai adults. METHODS: The study population comprised 141 people in Nakhon Pathom, Thailand (median age 72 years). Demographic and clinical data were collected at a community center. Participants were asked to chew a gum designed for assessing chewing ability. The differences in gum color before and after chewing (ΔE*ab) were calculated and used as the exposure variable, where a lower ΔE*ab indicates lower chewing ability. Frailty phenotypes were defined by weakness, slowness, weight loss, low physical activity level and exhaustion components, and used as the outcome variable. Participants with three or more components were considered frail, and those with one or two components were considered pre-frail. Ordinal logistic regression analyses were carried out to assess the association of objective chewing ability with frailty. RESULTS: Of the 141 participants, 32 (22.7%) were categorized as frail and 78 (55.3%) as pre-frail. In the analysis adjusted for demographic and health characteristics, the adjusted odds ratio of the presence and severity of frailty was significantly higher in participants with lower ΔE*ab (adjusted odds ratio for one decrease in ΔE*ab 1.05, 95% confidence interval 1.01-1.10, P = 0.03). CONCLUSIONS: Objectively measured chewing ability was significantly associated with frailty in community-dwelling older Thai adults. Geriatr Gerontol Int 2018; 18: 860-866.

Influence of multi-wavelength laser irradiation of enamel and dentin surfaces at 0.355, 2.94, and 9.4 µm on surface morphology, permeability, and acid resistance.

OBJECTIVE: Ultraviolet (UV) and infrared (IR) lasers can be used to specifically target protein, water, and mineral, respectively, in dental hard tissues to produce varying changes in surface morphology, permeability, reflectivity, and acid resistance. The purpose of this study was to explore the influence of laser irradiation and topical fluoride application on the surface morphology, permeability, reflectivity, and acid resistance of enamel and dentin to shed light on the mechanism of interaction and develop more effective treatments. METHODS: Twelve bovine enamel surfaces and twelve bovine dentin surfaces were irradiated with various combinations of lasers operating at 0.355 (Freq.-tripled Nd:YAG (UV) laser), 2.94 (Er:YAG laser), and 9.4 µm (CO2 laser), and surfaces were exposed to an acidulated phosphate fluoride gel and an acid challenge. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, polarized light microscopy, near-IR reflectance, fluorescence, polarization sensitive-optical coherence tomography (PS-OCT), and surface dehydration rate measurements. RESULTS: Different laser treatments dramatically influenced the surface morphology and permeability of both enamel and dentin. CO2 laser irradiation melted tooth surfaces. Er:YAG and UV lasers, while not melting tooth surfaces, showed markedly different surface roughness. Er:YAG irradiation led to significantly rougher enamel and dentin surfaces and led to higher permeability. There were significant differences in acid resistance among the various treatment groups. CONCLUSION: Surface dehydration measurements showed significant changes in permeability after laser treatments, application of fluoride and after exposure to demineralization. CO2 laser irradiation was most effective in inhibiting demineralization on enamel while topical fluoride was most effective for dentin surfaces. Lasers Surg. Med. 49:913-927, 2017. © 2017 Wiley Periodicals, Inc.

Influence of Multi-Wavelength Laser Irradiation of Enamel and Dentin Surfaces on Surface Morphology and Permeability.

UV and IR lasers can be used to specifically target protein, water, and the mineral phase of dental hard tissues to produce varying changes in surface morphology. In this study, we irradiated enamel and dentin surfaces with various combinations of lasers operating at 0.355, 2.94, and 9.4 µm, exposed those surfaces to topical fluoride, and subsequently evaluated the influence of these changes on surface morphology and permeability. Digital microscopy and surface dehydration rate measurements were used to monitor changes in the samples overtime. The surface morphology and permeability (dehydration rate) varied markedly with the different laser treatments on enamel. On dentin, fluoride was most effective in reducing the permeability.

Vestibular perception and the vestibulo-ocular reflex in young and older adults.

OBJECTIVES: Quantification of the perceptual thresholds to vestibular stimuli may offer valuable complementary information to that provided by measures of the vestibulo-ocular reflex (VOR). Perceptual thresholds could be particularly important in evaluating some subjects, such as the elderly, who might have a greater potential of central as well as peripheral vestibular dysfunction. The authors hypothesized that perceptual detection and discrimination thresholds would worsen with aging, and that there would be a poor relation between thresholds and traditional measures of the angular VOR represented by gain and phase on rotational chair testing. DESIGN: The authors compared the detection and discrimination thresholds of 19 younger and 16 older adults in response to earth-vertical, 0.5 Hz rotations. Perceptual results of the older subjects were then compared with the gain and phase of their VOR in response to earth-vertical rotations over the frequency range from 0.025 to 0.5 Hz. RESULTS: Detection thresholds were found to be 0.69 ± 0.29 degree/sec (mean ± standard deviation) for the younger participants and 0.81 ± 0.42 degree/sec for older participants. Discrimination thresholds in younger and older adults were 4.83 ± 1.80 degree/sec and 4.33 ± 1.57 degree/sec, respectively. There was no difference in either measure between age groups. Perceptual thresholds were independent of the gain and phase of the VOR. CONCLUSIONS: These results indicate that there is no inevitable loss of vestibular perception with aging. Elevated thresholds among the elderly are therefore suggestive of pathology rather than normal consequences of aging. Furthermore, perceptual thresholds offer additional insight, beyond that supplied by the VOR alone, into vestibular function.

Temporal integration of auditory and vestibular stimuli.

OBJECTIVES/HYPOTHESIS: Integration of balance-related cues from the vestibular and other sensory systems requires that they be perceived simultaneously despite arriving asynchronously at the central nervous system. Failure to perform temporal integration of multiple sensory signals represents a novel mechanism to explain symptoms in patients with imbalance. This study tested the ability of normal observers to compensate for sensory asynchronies between vestibular and auditory inputs. STUDY DESIGN: Double-blinded experimental design. METHODS: We performed whole-body rotations about the earth-vertical axis following a raised-cosine trajectory at 0.5 and 1.0 Hz to several peak velocities up to a maximum of 180°/s in five normal subjects. Headphones were used to present a diotic auditory stimulus at various times relative to the onset of the rotation. Subjects were required to indicate which cue occurred first. RESULTS: The vestibular stimulus needed to be presented 61 milliseconds (at a stimulus frequency of 0.5 Hz) and 19 milliseconds (at 1.0 Hz) before the auditory stimulus. Stimuli presented within a window of 300 milliseconds (at 0.5 Hz) to 200 milliseconds (at 1.0 Hz) were judged to be simultaneous. CONCLUSIONS: The central nervous system must accommodate for delays in perception of vestibular and other sensory cues. Inaccurate temporal integration of these inputs represents a novel explanation for symptoms of imbalance.