From brain to bridge: masticatory function and dental implants

Multiple regions of sensorimotor cortex encode bite force and gape

The precise control of bite force and gape is vital for safe and effective breakdown and manipulation of food inside the oral cavity during feeding. Yet, the role of the orofacial sensorimotor cortex (OSMcx) in the control of bite force and gape is still largely unknown. The aim of this study was to elucidate how individual neurons and populations of neurons in multiple regions of OSMcx differentially encode bite force and static gape when subjects (Macaca mulatta) generated different levels of bite force at varying gapes. We examined neuronal activity recorded simultaneously from three microelectrode arrays implanted chronically in the primary motor (MIo), primary somatosensory (SIo), and cortical masticatory (CMA) areas of OSMcx. We used generalized linear models to evaluate encoding properties of individual neurons and utilized dimensionality reduction techniques to decompose population activity into components related to specific task parameters. Individual neurons encoded bite force more strongly than gape in all three OSMCx areas although bite force was a better predictor of spiking activity in MIo vs. SIo. Population activity differentiated between levels of bite force and gape while preserving task-independent temporal modulation across the behavioral trial. While activation patterns of neuronal populations were comparable across OSMCx areas, the total variance explained by task parameters was context-dependent and differed across areas. These findings suggest that the cortical control of static gape during biting may rely on computations at the population level whereas the strong encoding of bite force at the individual neuron level allows for the precise and rapid control of bite force.

Current Understanding of the Regulatory Mechanism of Tooth Root Development and Future Perspectives

Background

The purpose of this review article is to understand tooth root development and its regulation through evolution and epigenetics as well as future implications involving root regeneration and tissue engineering.

Types of Studies Reviewed

we performed a comprehensive PubMed search to review all published studies related to the molecular regulation of tooth root development and regeneration until August 2022. Articles selected include original research studies and reviews.

Results

Epigenetic regulation strongly influences dental tooth root patterning and development. One study highlights how genes such as Ezh2 and Arid1a are crucial components in the development of tooth root furcation patterning. Another study shows that loss of Arid1a ultimately leads to shortened root morphology. Furthermore, researchers are utilizing information about root development and stem cells to find alternative treatments in replacing missing teeth through a stem cell-mediated bioengineered tooth root (bio-root).

Practical Implications

Dentistry values preserving natural tooth morphology. Presently, implants are the best treatment for replacing missing teeth, but alternative future treatments might include tissue engineering/bio-root regeneration to restore our dentition.

Subjective and objective evaluation of masticatory function in patients with bimaxillary implant-supported prostheses

BACKGROUND

People perform poorly in masticatory function tests despite well-functioning prostheses. However, it is unclear whether there is an agreement between subjective and objective measures of mastication.

OBJECTIVES

To investigate the association between subjective and objective measures of masticatory function in patients with bimaxillary implant-supported prostheses.

MATERIALS AND METHODS

An experimental group (n = 25, age = 70.6 ± 7.5 years, eight women) with bimaxillary implant-supported fixed prostheses and a control group (n = 25, age = 69.0 ± 5.3, 13 women) with natural dentition were recruited. The participants in the experimental group were included if they had been using the prosthesis for at least a year and had no obvious complaints with their prostheses. The control group was people with natural dentition and without any prostheses or complaints related to the masticatory system. The masticatory function was evaluated objectively with food comminution and mixing ability tests, and subjectively with jaw function limitation scale (JLFS) and oral health impact profile (OHIP).

RESULTS

The experimental group performed poorly in both objective tests (p < .001). However, there was no significant differences between the two groups in total JFLS (p = .114) and OHIP (p = .312) scores. Though, there were certain positive correlations between the food comminution test and JFLS subdomains in the control group, and a positive correlation between food comminution test and specific subdomains of OHIP in the experimental group indicating poor correlation between the subjective and objective measures.

CONCLUSION

Although patients with implant prostheses show poor masticatory performance, there is no agreement in the objective and subjective measures of mastication.

A comparative evaluation of neurophysiological activity, active tactile sensibility and stereognostic ability of complete denture prosthesis, and implant-supported prosthesis wearer-A pilot study

AIM

The study aimed to evaluate the effect of implant-supported prosthesis in completely edentulous participants in terms of osseoperception ability, neural activity, and stereognostic ability in comparison to removable prosthetic options.

MATERIALS AND METHODS

A total sample of 18 patients, irrespective of gender and age were allocated into three groups according to the three-treatment protocol (upper and lower complete denture, upper complete denture opposing lower implant-retained overdenture, implant-supported fixed prosthesis in both arches). Four weeks after completion of the treatment procedure active tactile sensibility (ATS) was checked by using varying thicknesses (12, 40, 80, 100, 200 μ) of articulating foils and papers. Functional magnetic resonance imaging (fMRI) was performed to record neurophysiological activity in cerebral cortex in all the participants. Various forms of test pieces (heat cure acrylic resin) were used to evaluate stereognostic ability. Data regarding the neurophysiological activity were analyzed by using Krushkal-Wallis test and p ≤ 0.05 was considered to be statistically significant. Data from stereognostic ability test procedure and ATS were compared by using chi-squared test and p ≤ 0.05 was considered to be statistically significant.

RESULTS

Statistically significant difference was found in between the articulating foils in terms of true negative responses as the foil thickness increased in participants wearing complete denture in both the arches (p = 0.004) and implant-supported fixed prosthesis in both the arches (p = 0.010). Participants in implant-supported fixed prosthesis group showed significantly more activation in primary motor cortex (right side), somatosensory cortex (left side), angular gyrus (both sides), temporal lobe (left) compared to other groups. No significant difference found in thalamus and premotor cortex region in between the participants of different groups. No statistically significant difference found in between the groups in terms of true responses identifying correct shapes. Mean number of correct responses in stereognostic ability test were 4.16 (83.33%), 3.5 (70%), 3.83 (76.66%) for participants of complete denture group, upper complete denture opposing lower implant retained overdenture group, and implant-supported fixed prosthesis group, respectively.

CONCLUSION

Primary motor cortex, somatosensory cortex, and other regions of brain were diffusely activated in participants wearing implant-supported fixed prosthesis in both the arches. Less number of false responses were recorded in participants of implant-supported fixed prosthesis group and upper complete denture opposing lower implant-retained overdenture group in ATS test compared to participants wearing complete denture in both the arches.

A conceptual model of oro-facial health with an emphasis on function

The individual inclination to lead an autonomous life until death is associated with requirements that may be of physiological, psychosocial and environmental nature. We aim to describe a conceptual oro‐facial health model with an emphasis on oro‐facial function, taking the domains of quality of life and patient‐centred values into account. In the context of oro‐facial function, the requirements of life are met when the oro‐facial system is in a fit state. ‘Fitness of the oro‐facial system, that is oro‐facial health, is a state that is characterised by an absence of, or positive coping with physical disease, mental disease, pain and negative environmental and social factors. It will allow natural oro‐facial functions such as sensing, tasting, touching, biting, chewing, swallowing, speaking, yawning, kissing and facial expression’. In the presented conceptual model of oro‐facial health, it is postulated that each individual has present and future potentials related to biological prerequisites and resources that are developed by an individual through the course of life. These potentials form the oro‐facial functional capacity. When the individual potentials together do not meet the requirements of life anymore, dysfunction and disease result. The oro‐facial system is subject to physiological ageing processes, which will inevitably lead to a decrease in the oro‐facial functional capacity. Furthermore, comorbid medical conditions might hamper oro‐facial function and, alongside with the ageing process, may lead to a state of oral hypofunction. Currently, there is a lack of widespread, validated, easy‐to‐use instruments that help to distinguish between states of oro‐facial fitness as opposed to oral hypofunction. Clearly, research is needed to establish adequate, validated instruments alongside with functional rehabilitation procedures.

Digital Quantification of Occlusal Contacts: A Methodological Study

OBJECTIVE

To compare the reliability of digital occlusal contacts quantification and the validity of digital occlusal contacts quantification with traditional methods used for occlusal contact determination.

SUBJECTS AND METHODS

Thirty participants, all of whom were students at the Sahlgrenska Academy, University of Gothenburg in Gothenburg, Sweden, were included in the study. Three different methods were used to evaluate occlusal contacts: (I) a digital examination of the patients' casts, using the Ortho 3D Models (O3DM) software and measuring the total occlusal contact area in square millimeters (DE); (II) an examination involving the measurement of the total number of occlusal contacts on stone casts mounted in an articulator (AE); and (III) a clinical examination with the measurement of the total number of occlusal contacts with 8 μm-thick articulating foil (CE).

RESULTS

The repeated digital measurements (same casts scanned multiple times) showed a significant correlation of 0.85 (p < 0.01), which shows a diagnostic consistency. Furthermore, there was a significant correlation between the results obtained with the DE method and the AE of 0.41 (p < 0.05), and between those acquired with the AE method and the CE of 0.37 (p < 0.05). However, no significant correlation was found between the DE method and the CE method with a correlation coefficient of 0.10 (p > 0.05).

CONCLUSIONS

Digital casts can be used for quantification of the total occlusal contact area (in mm²) owing to the high reliability of repeated measurements and the strong validity of the method compared to traditionally employed stone cast measurements.

Consensus on the terminologies and methodologies for masticatory assessment

A large number of methodological procedures and experimental conditions are reported to describe the masticatory process. However, similar terms are sometimes employed to describe different methodologies. Standardisation of terms is essential to allow comparisons among different studies. This article was aimed to provide a consensus concerning the terms, definitions and technical methods generally reported when evaluating masticatory function objectively and subjectively. The consensus is based on the results from discussions and consultations among world‐leading researchers in the related research areas. Advantages, limitations and relevance of each method are also discussed. The present consensus provides a revised framework of standardised terms to improve the consistent use of masticatory terminology and facilitate further investigations on masticatory function analysis. In addition, this article also outlines various methods used to evaluate the masticatory process and their advantages and disadvantages in order to help researchers to design their experiments.

The Influence of Initial Breakage on Size Reduction during Habitual Chewing of a Solid Test Food

OBJECTIVES

Food comminution during chewing is due to intra-oral particle selection and subsequent breakage. Under conditions of habitual chewing and a nearly complete selection, the influence of initial breakage on particle size reduction was studied in trials with a first chewing cycle (N = 1) from a sequence of randomized trials with various cycle numbers. Furthermore, relationships were examined between degree of fragmentation from breakage (r-fr), molar maximal bite force (MBF) and chewing efficiency (the number of cycles needed to half the initial particle size, N(1/2-Xo)).

DESIGN

Thirty-one subjects with a natural dentition chewed samples of 2 half-cubes (9.6 × 9.6x4.8 mm) of Optosil®, using sequences with 1-7 cycles, in 2-10 randomized trials; 10 trials with one cycle. Particle size distributions by underweight, characterized by median particle size, X₅₀, were obtained using sieving. N(1/2-Xo) was derived from the log(X₅₀)-log(N) relationship. and r-fr from the cumulative distribution of underweight fractions of damaged particles for N = 1. MBF was determined on both sides of the jaw using a force transducer and averaged.

CONCLUSIONS

A strong, decreasing regression occurred in X₅₀ at N = 1 with r-fr (R² = 0.934, p < 0.001). The decreasing regression of N(1/2-Xo) with r-fr was moderately strong (R² = 0.454; p < 0.001). Thus, initial size reduction is strongly determined by breakage and overall reduction partly, when chewing small amounts of particles. N(1/2-Xo) vs. MBF and r-fr vs. MBF were weakly related (R²≤0.124, p = 0.052-0.127). The lack of a pronounced relationship between r-fr and MBF suggests that either MBF is not relevant but supra-threshold force, or that another factor, occlusion, may influence breakage.

The Evolution of Neuroscience as a Research Field Relevant to Dentistry

The field of neuroscience did not exist as such when the Journal of Dental Research was founded 100 y ago. It has emerged as an important scientific field relevant to dentistry in view of the many neurally based functions manifested in the orofacial area (e.g., pain, taste, chewing, swallowing, salivation). This article reviews many of the novel insights that have been gained through neuroscience research into the neural basis of these functions and their clinical relevance to the diagnosis and management of pain and sensorimotor disorders. These include the neural pathways and brain circuitry underlying each of these functions and the role of nonneural as well as neural processes and their "plasticity" in modulating these functions and allowing for adaptation to tissue injury and pain and for learning or rehabilitation of orofacial functions.

Functional Adaptation of Oromotor Functions and Aging: A Focused Review of the Evidence From Brain Neuroimaging Research

“Practice makes perfect” is a principle widely applied when one is acquiring a new sensorimotor skill to cope with challenges from a new environment. In terms of oral healthcare, the traditional view holds that restoring decayed structures is one of the primary aims of treatment. This assumes that the patient’s oromotor functions would be recovered back to normal levels after the restoration. However, in older patients, such a structural–functional coupling after dental treatment shows a great degree of individual variations. For example, after prosthodontic treatment, some patients would adapt themselves quickly to the new dentures, while others would not. In this Focused Review, I argue that the functional aspects of adaptation—which would be predominantly associated with the brain mechanisms of cognitive processing and motor learning—play a critical role in the individual differences in the adaptive behaviors of oromotor functions. This thesis is critical to geriatric oral healthcare since the variation in the capacity of cognitive processing and motor learning is critically associated with aging. In this review, (a) the association between aging and the brain-stomatognathic axis will be introduced; (b) the brain mechanisms underlying the association between aging, compensatory behavior, and motor learning will be briefly summarized; (c) the neuroimaging evidence that suggests the role of cognitive processing and motor learning in oromotor functions will be summarized, and critically, the brain mechanisms underlying mastication and swallowing in older people will be discussed; and (d) based on the current knowledge, an experimental framework for investigating the association between aging and the functional adaptation of oromotor functions will be proposed. Finally, I will comment on the practical implications of this framework and postulate questions open for future research.

Active tactile sensibility of three-unit implant-supported FPDs versus natural dentition

Background

Splinting of the implants might improve the active tactile sensibility (ATS) of the pontic area due to cumulative effect of Osseo perception of two retainers; on the other hand, due to the lack of any supporting implant in the axis of occlusal force for the pontic area, ATS might be lower for this portion of FPDs. we evaluated the active tactile sensibility of natural teeth and three-unit implant-supported FPDs.

Material and Methods

The ATS of posterior 3-unit implant-supported FPD and contralateral teeth was measured in 50 patients, in a random order blinded to patients and assessor, carried out at two sessions. Based on the experimental range of 0 to 70 um, the sigmoid shape of psychometric curve was estimated to locate the 50% values as the ATS thresholds for each tooth or implant. Data were analyzed using unpaired t-tests.

Results

The ATS of the teeth and implants differed significantly and compared to teeth, implants exhibited significantly higher ATS thresholds in all the groups. The results of independent t-test showed the highest difference in the means of ATS between the pontic and the first molar tooth. Based on the equivalence testing approach, the 95% CIs indicated that the differences were clinically significant only in the Pontic/First Molar group.

Conclusions

In multi-unit implant-supported prostheses the tactile perception of the prosthesis that are placed on fixtures is similar to the natural teeth. In pontic areas there are significant statistical and clinical differences, with much lower tactile sensibility in pontics compared to the natural teeth. Key words:Active tactile sensibility, dental implants, interdental perception, osseoperception.

Tooth extraction and subsequent dental implant placement in Sprague-Dawley rats induce differential changes in anterior digastric myofibre size and myosin heavy chain isoform expression

OBJECTIVE

to determine if tooth loss and dental implant placement in rats induce changes in the morphological and histochemical features of the Anterior Digastric muscle.

DESIGN

Adult male Sprague-Dawley rats had their right maxillary molar teeth extracted. 'Extraction-1' and 'Extraction-2 groups were sacrificed, respectively, 4 or 8 weeks later, and an Implant group had an implant placement 2 weeks after the molar extraction, and rats were sacrificed 3 weeks later (n = 4/group). Naive rats (n = 3) had no treatment. Morphometric and immunohistochemical techniques quantified Anterior Digastric muscle myofibres' cross-sectional area (CSA) and myosin heavy chain (MyHC) isoform proportions. Significant ANOVAs were followed by post-hoc tests; p < 0.05 and 0.1 were considered to reflect levels of statistical significance.

RESULTS

In naïve rats, the peripheral regions of the Anterior Digastric muscle was dominated by MyHC-IIx/b isoform and there were no MyHC-I isoforms; the central regions dominated by MyHC-IIx/b and MyHC-IIa isoforms. Compared with naive rats, tooth extraction produced, 8 (but not 4) weeks later, a decreased proportion of fast-contracting fatigue-resistant MyHC-IIa isoform (p = 0.08), and increased proportion of fast and intermediate fatigue-resistance MyHC-IIa/x/b isoform (p = 0.03). Dental implant placement following tooth extraction attenuated the extraction effects but produced a decreased proportion of fast-contracting fatiguable MyHC-llx/b isoform (p = 0.03) in the peripheral region, and increased inter-animal variability in myofibre-CSAs.

CONCLUSIONS

Given the crucial role that the Anterior Digastric muscle plays in many vital oral functions (e.g., chewing, swallowing), these changes may contribute to the changes in oral sensorimotor functions that occur in humans following such treatments.

Mastication Evaluation With Unsupervised Learning: Using an Inertial Sensor-Based System

There is a direct relationship between the prevalence of musculoskeletal disorders of the temporomandibular joint and orofacial disorders. A well-elaborated analysis of the jaw movements provides relevant information for healthcare professionals to conclude their diagnosis. Different approaches have been explored to track jaw movements such that the mastication analysis is getting less subjective; however, all methods are still highly subjective, and the quality of the assessments depends much on the experience of the health professional. In this paper, an accurate and non-invasive method based on a commercial low-cost inertial sensor (MPU6050) to measure jaw movements is proposed. The jaw-movement feature values are compared to the obtained with clinical analysis, showing no statistically significant difference between both methods. Moreover, We propose to use unsupervised paradigm approaches to cluster mastication patterns of healthy subjects and simulated patients with facial trauma. Two techniques were used in this paper to instantiate the method: Kohonen’s Self-Organizing Maps and K-Means Clustering. Both algorithms have excellent performances to process jaw-movements data, showing encouraging results and potential to bring a full assessment of the masticatory function. The proposed method can be applied in real-time providing relevant dynamic information for health-care professionals.

Effects of orofacial myofunctional therapy on masticatory function in individuals submitted to orthognathic surgery: a randomized trial

Objectives

The esthetic and functional results of orthognathic surgery of severe dentofacial deformities are predictable, however there are differences regarding the effects on stomatognathic system. The aim was to investigate the effects of orofacial myofunctional therapy (OMT) on the masticatory function in individuals with dentofacial deformity submitted to orthognathic surgery (OGS).

Material and Methods

Forty-eight individuals (18-40 years) were evaluated, 14 undergoing OMT (treated group-TG), 10 without this treatment (untreated group-UTG) and 24 in a control group with normal occlusion; for clinical aspects the data of an individual was missed (n=46). Chewing was performed using the Expanded protocol of orofacial myofunctional evaluation with scores (OMES-E). Muscle tone and mobility were also analyzed before (P0), three (P1) and six months (P2) after OGS. Surface electromyography of the masseter and temporalis muscles was performed, considering the parameters amplitude and duration of act and cycle, and the number of masticatory cycles. The OMT consisted of ten therapeutic sessions along the postoperative period. The results were compared using parametric and non-parametric tests.

Results

TG showed higher scores in P1 and P2 than P0; for the masticatory type the scores in P2 were significantly higher than P0. In addition, the proportion of individuals with adequate tone of lower lip and adequate tongue mobility for TG increased significantly from P1 and P2 in relation to P0. The EMG results showed a decrease in act and cycle duration in P2 in relation to P0 and P1 for the TG; furthermore the values were close to controls. An increase in the number of cycles from P0 to P2 was also observed, indicating faster chewing, which may be attributed to an improvement of balanced occlusion associated with OMT.

Conclusion

There were positive effects of OMT on the clinical and electromyography aspects of chewing in individual submitted to orthognathic surgery.

Selection in mixtures of food particles during oral processing in man

OBJECTIVES

Two processes underlie food comminution during chewing: (1) selection, i.e. every particle has a chance of being placed between the teeth and being subjected to (2) breakage. Selection decreases with particle number by saturation of breakage sites, and it depends on competition between smaller and larger particles for breakage sites. Theoretical models were tested which describe competition between various sizes X. In the one-way model, small particles cannot compete with larger ones because of their smaller height. In the two-way model, small particles may compete when piled between antagonistic teeth.

DESIGN

Five subjects participated in one-chew experiments on cubes made of Optosil^®. The critical particle number (n_c(X)) at which saturation starts, and the number of breakage sites (n_b(X)) were determined by varying particle numbers (n_X) for single-sized cubes of 1.7-6.8mm. Using n_c(X) and n_b(X), the models predicted relationships between number of selected particles (n_s(X)) and n_X in one-chew experiments using simple mixtures with only two sizes. A fixed number (mean 6 or 26) of larger cubes (X=6.8 or 3.4mm) was mixed with various numbers (16-1024) of smaller cubes (X=4.8, 2.4 or 1.7mm), thus varying the factors X, n_X, and possible particle piling (for X<4mm).

RESULTS

The one-way model was largely followed with small numbers of smaller particles and the two-way model with large numbers.

CONCLUSIONS

The two-way model applies to chewing a food which yields a loose aggregation of different-sized particles following an initial phase, whereas other circumstances may be favourable for the one-way model. As conditions of a food bolus can be approached by embedding hard Optosil particles in a soft medium, the models will, apart from dentistry, be of interest for controlling flavour release in food engineering.

Mandibular movements in older people with rheumatoid arthritis

OBJECTIVE

The aim of this study was to compare the mandibular movements in older people with and without temporomandibular disorder (TMD) associated with rheumatoid arthritis (RA).

STUDY DESIGN

Thirty partially or completely edentulous older adults (65.33 ± 4.7 years) were assigned to 2 groups: (1) with RA and TMD and (2) without RA and TMD. Chewing movements of the jaws during mastication of the test material (Optocal) and the range of mandibular movements were evaluated by using the JT-3-D kinesiographic device before and after new removable prosthesis insertion. Multiple comparisons were made with analysis of variance (ANOVA) and the Tukey-Kramer test.

RESULTS

Comparisons between the 2 groups before and after new prosthesis insertion revealed that the RA and TMD group had reduced opening angles (P < .05) during chewing. After insertion of new prostheses, both groups showed increased opening and closing angles during chewing (P < .05). The mandibular range of motion results showed that patients with RA and TMD exhibited lower aperture and laterality movements (P < .05) compared with controls before and after new prosthesis insertion. However, there was an increase in aperture, lefty laterality, and protrusion values after new prosthesis insertion in both groups.

CONCLUSIONS

TMD associated with RA may impair mandibular movements. Well-fitted prostheses may improve mandibular movements in older adults, especially those with RA.

Short-term follow-up of masticatory adaptation after rehabilitation with an immediately loaded implant-supported prosthesis: a pilot assessment

Background

When teeth are extracted, sensory function is decreased by a loss of periodontal ligament receptions. When replacing teeth by oral implants, one hopes to restore the sensory feedback pathway as such to allow for physiological implant integration and optimized oral function with implant-supported prostheses. What remains to be investigated is how to adapt to different oral rehabilitations.

The purpose of this pilot study was to assess four aspects of masticatory adaptation after rehabilitation with an immediately loaded implant-supported prosthesis and to observe how each aspect will recover respectively.

Methods

Eight participants with complete dentures were enrolled. They received an implant-supported acrylic resin provisional bridge, 1 day after implant surgery. Masticatory adaptation was examined by assessing occlusal contact, approximate maximum bite force, masticatory efficiency of gum-like specimens, and food hardness perception.

Results

Occlusal contact and approximate maximum bite force were significantly increased 3 months after implant rehabilitation, with the bite force gradually building up to a 72% increase compared to baseline. Masticatory efficiency increased by 46% immediately after surgery, stabilizing at around 40% 3 months after implant rehabilitation. Hardness perception also improved, with a reduction of the error rate by 16% over time.

Conclusions

This assessment demonstrated masticatory adaptation immediately after implant rehabilitation with improvements noted up to 3 months after surgery and rehabilitation. It was also observed that, despite gradually improved bite force in all patients, masticatory efficiency and food hardness perception did not necessarily follow this tendency. The findings in this pilot may also be used to assess adaptation of oral function after implant rehabilitation by studying the combined outcome of four tests (occlusal contact, maximum bite force, masticatory efficiency, and food hardness perception).

Widespread Volumetric Brain Changes following Tooth Loss in Female Mice

Tooth loss is associated with altered sensory, motor, cognitive and emotional functions. These changes vary highly in the population and are accompanied by structural and functional changes in brain regions mediating these functions. It is unclear to what extent this variability in behavior and function is caused by genetic and/or environmental determinants and which brain regions undergo structural plasticity that mediates these changes. Thus, the overall goal of our research program is to identify genetic variants that control structural and functional plasticity following tooth loss. As a step toward this goal, here our aim was to determine whether structural magnetic resonance imaging (sMRI) is sensitive to detect quantifiable volumetric differences in the brains of mice of different genetic background receiving tooth extraction or sham operation. We used 67 adult female mice of 7 strains, comprising the A/J (A) and C57BL/6J (B) strains and a randomly selected sample of 5 of the 23 AXB-BXA strains (AXB1, AXB4, AXB24, BXA14, BXA24) that were produced from the A and B parental mice by recombinations and inbreeding. This panel of 25 inbred strains of genetically diverse inbred strains of mice is used for mapping chromosomal intervals throughout the genome that harbor candidate genes controlling the phenotypic variance of any trait under study. Under general anesthesia, 39 mice received extraction of 3 right maxillary molar teeth and 28 mice received sham operation. On post-extraction day 21, post-mortem whole-brain high-resolution sMRI was used to quantify the volume of 160 brain regions. Compared to sham operation, tooth extraction was associated with a significantly reduced regional and voxel-wise volumes of cortical brain regions involved in processing somatosensory, motor, cognitive and emotional functions, and increased volumes in subcortical sensorimotor and temporal limbic forebrain regions including the amygdala. Additionally, comparison of the 10 BXA14 and 21 BXA24 mice revealed significant volumetric differences between the two strains in several brain regions. These findings highlight the utility of high-resolution sMRI for studying tooth loss-induced structural brain plasticity in mice, and provide a foundation for further phenotyping structural brain changes following tooth loss in the full AXB-BXA panel to facilitate mapping genes that control brain plasticity following orofacial injury.

Fine motor control of the jaw following alteration of orofacial afferent inputs

Objective

The study was designed to investigate if alteration of different orofacial afferent inputs would have different effects on oral fine motor control and to test the hypothesis that reduced afferent inputs will increase the variability of bite force values and jaw muscle activity, and repeated training with splitting of food morsel in conditions with reduced afferent inputs would decrease the variability and lead to optimization of bite force values and jaw muscle activity.

Material methods

Forty-five healthy volunteers participated in a single experimental session and were equally divided into incisal, mucosal, and block anesthesia groups. The participants performed six series (with ten trials) of a standardized hold and split task after the intervention with local anesthesia was made in the respective groups. The hold and split forces along with the corresponding jaw muscle activity were recorded and compared to a reference group.

Results

The hold force and the electromyographic (EMG) activity of the masseter muscles during the hold phase were significantly higher in the incisal and block anesthesia group, as compared to the reference group (P < 0.001). However, there was no significant effect of groups on the split force (P = 0.975) but a significant decrease in the EMG activity of right masseter in mucosal anesthesia group as compared to the reference group (P = 0.006). The results also revealed that there was no significant effect of local anesthesia on the variability of the hold and split force (P < 0.677). However, there was a significant decrease in the variability of EMG activity of the jaw closing muscles in the block anesthesia group as compared to the reference group (P < 0.041), during the hold phase and a significant increase in the variability of EMG activity of right masseter in the mucosal anesthesia group (P = 0.021) along with a significant increase in the EMG activity of anterior temporalis muscle in the incisal anesthesia group, compared to the reference group (P = 0.018), during the split phase.

Conclusions

The results of the present study indicated that altering different orofacial afferent inputs may have different effects on some aspects of oral fine motor control. Further, inhibition of afferent inputs from the orofacial or periodontal mechanoreceptors did not increase the variability of bite force values and jaw muscle activity; indicating that the relative precision of the oral fine motor task was not compromised inspite of the anesthesia. The results also suggest the propensity of optimization of bite force values and jaw muscle activity due to repeated splitting of the food morsels, inspite of alteration of sensory inputs.

Clinical relevance

Skill acquisition following a change in oral sensory environment is crucial for understanding how humans learn and re-learn oral motor behaviors and the kind of adaptation that takes place after successful oral rehabilitation procedures.

Population response characteristics of intrinsic signals in the cat somatosensory cortex following canine mechanical stimulation

Intrinsic signal optical imaging has been widely used to measure functional maps in various sensory cortices due to better spatial resolution and sensitivity for detecting cortical neuroplasticity. However, application of this technique in dentistry has not been reported. In this study, intrinsic signal optical imaging was used to investigate mechanically driven responses in the cat somatosensory cortex, when punctate mechanical stimuli were applied to maxillary canines. The global signal and its spatial organization pattern were obtained. Global signal strength gradually increased with stimulus strength. There was no significant difference in response strength between contralateral and ipsilateral mechanical stimulation. A slightly greater response was recorded in the sigmoidal gyrus than in the coronal gyrus. The cat somatosensory cortex activated by sensory inputs from mechanical stimulation of canines lacks both topographical and functional organization. It is not organized into columns that represent sensory input from each tooth or direction of stimulation. These results demonstrate that intrinsic signal optical imaging is a valid tool for investigating neural responses and neuroplasticity in the somatosensory cortex that represents teeth.

Dental Occlusal Changes Induce Motor Cortex Neuroplasticity

Modification to the dental occlusion may alter oral sensorimotor functions. Restorative treatments aim to restore sensorimotor functions; however, it is unclear why some patients fail to adapt to the restoration and remain with sensorimotor complaints. The face primary motor cortex (face-M1) is involved in the generation and control of orofacial movements. Altered sensory inputs or motor function can induce face-M1 neuroplasticity. We took advantage of the continuous eruption of the incisors in Sprague-Dawley rats and used intracortical microstimulation (ICMS) to map the jaw and tongue motor representations in face-M1. Specifically, we tested the hypothesis that multiple trimming of the right mandibular incisor, to keep it out of occlusal contacts for 7 d, and subsequent incisor eruption and restoration of occlusal contacts, can alter the ICMS-defined features of jaw and tongue motor representations (i.e., neuroplasticity). On days 1, 3, 5, and 7, the trim and trim-recovered groups had 1 to 2 mm of incisal trimming of the incisor; a sham trim group had buccal surface trimming with no occlusal changes; and a naive group had no treatment. Systematic mapping was performed on day 8 in the naive, trim, and sham trim groups and on day 14 in the trim-recovered group. In the trim group, the tongue onset latency was shorter in the left face-M1 than in the right face-M1 ( P < .001). In the trim-recovered group, the number of tongue sites and jaw/tongue overlapping sites was greater in the left face-M1 than in the right face-M1 ( P = 0.0032, 0.0016, respectively), and the center of gravity was deeper in the left than in the right face-M1 ( P = 0.026). Therefore, incisor trimming and subsequent restoration of occlusal contacts induced face-M1 neuroplasticity, reflected in significant disparities between the left and right face-M1 in some ICMS-defined features of the tongue motor representations. Such neuroplasticity may reflect or contribute to subjects’ ability to adapt their oral sensorimotor functions to an altered dental occlusion.

Chewing Maintains Hippocampus-Dependent Cognitive Function

Mastication (chewing) is important not only for food intake, but also for preserving and promoting the general health. Recent studies have showed that mastication helps to maintain cognitive functions in the hippocampus, a central nervous system region vital for spatial memory and learning. The purpose of this paper is to review the recent progress of the association between mastication and the hippocampus-dependent cognitive function. There are multiple neural circuits connecting the masticatory organs and the hippocampus. Both animal and human studies indicated that cognitive functioning is influenced by mastication. Masticatory dysfunction is associated with the hippocampal morphological impairments and the hippocampus-dependent spatial memory deficits, especially in elderly. Mastication is an effective behavior for maintaining the hippocampus-dependent cognitive performance, which deteriorates with aging. Therefore, chewing may represent a useful approach in preserving and promoting the hippocampus-dependent cognitive function in older people. We also discussed several possible mechanisms involved in the interaction between mastication and the hippocampal neurogenesis and the future directions for this unique fascinating research.

Validation of the Orofacial Esthetic Scale in the general population

Background

The Orofacial Esthetic Scale (OES) is an eight-item instrument to assess how patients perceive their dental and facial esthetics. In this cross-sectional study we investigated dimensionality, reliability, and validity of OES scores in the adult general population in Sweden.

Methods

In a random sample of the adult Swedish population (response rate: 39%, N=1159 subjects, 58% female, mean age (standard deviation): 49.2 (17.4) years), dimensionality of OES was investigated using factor analytic methods to determine how many scores are needed to characterize the construct. Reliability of scores was calculated using Cronbach’s alpha. Score validity was determined by correlating the OES summary score with a global indicator of orofacial esthetics (OE).

Results

Factor analyses provided support that a single score can sufficiently characterize OE. A Cronbach’s alpha of 0.93 indicated excellent reliability. A validity coefficient of r=0.89 (95% confidence interval: 0.87-0.90) indicated that OES summary scores correlated highly with a global OE assessment.

Conclusions

The OES is a promising instrument to measure the construct OE. Factor analyses supported that this construct can be assessed with one score, offering a feasible and acceptable standardized assessment of OE. The present study extends the OES use to the general population, an important target population for assessment of orofacial esthetics.