Pressure-pain threshold determination in the oral mucosa: validity and reliability

Evaluation of Three Methods of Sensory Function Testing for the Assessment of Successful Maxillary Nerve Blockade in Horses

Maxillary nerve blocks (MNBs) commonly facilitate dental surgeries in standing horses. The goal of this prospective, blinded, cross-over design trial including 15 client-owned horses was to evaluate 3 methods of sensory function testing for confirming a successful MNB. Testing was performed bilaterally before sedation, 5 min after sedation, and 15 and 30 min after MNB with 0.5% bupivacaine and involved a needle prick dorsal to each naris, hemostat clamping of each nostril, and gingival algometry (measuring sensitivity to pain). Responses to stimulation were numerically scored and scores were summed up to a total score. Total score increases on the blocked side by ≥ 2 between baseline and 30 min Post MNB recordings signified a successful MNB. Sedation in the preceding 6 h, presence of sino-nasal disease, side of dental pathology, age, butorphanol administration, and detomidine dosing (µg/kg/min) throughout the tooth extraction procedure were recorded. In 73% of horses, MNB was successful. Sedation in the preceding 6 h (P = .732), age (P = .936), side of pathology (P = .516), and sino-nasal disease (P = .769) were not associated with total scores. Detomidine dosage and butorphanol use did not differ between horses in which the MNB was considered successful and for those in which it was not (P = .967 and P = .538, respectively). Scores obtained with gingival algometry were less closely associated with total scores (rho = .649) than those obtained with needle prick and nostril clamping (rho = .819 and .892, respectively). Therefore, needle prick and nostril clamping are considered the more reliable methods for use in clinical practice to determine the success of an MNB.

Merkel cells and keratinocytes in oral mucosa are activated by mechanical stimulation

The detection of mechanical qualities of foodstuffs is essential for nutrient acquisition, evaluation of food freshness, and bolus formation during mastication. However, the mechanisms through which mechanosensitive cells in the oral cavity transmit mechanical information from the periphery to the brain are not well defined. We hypothesized Merkel cells, which are epithelial mechanoreceptors and important for pressure and texture sensing in the skin, can be mechanically activated in the oral cavity. Using live-cell calcium imaging, we recorded Merkel cell activity in ex vivo gingival and palatal preparations from mice in response to mechanical stimulation. Merkel cells responded with distinct temporal patterns and activation thresholds in a region-specific manner, with Merkel cells in the hard palate having a higher mean activation threshold than those in the gingiva. Unexpectedly, we found that oral keratinocytes were also activated by mechanical stimulation, even in the absence of Merkel cells. This indicates that mechanical stimulation of oral mucosa independently activates at least two subpopulations of epithelial cells. Finally, we found that oral Merkel cells contribute to preference for consuming oily emulsion. To our knowledge, these data represent the first functional study of Merkel-cell physiology and its role in flavor detection in the oral cavity.

Evaluation of dental health of the adult population of Kazakhstan and solutions for improving removable prosthetics

Screening studies on dental morbidity of elderly people in the urban and rural population of the Republic of Kazakhstan were conducted. Three age groups were investigated in the districts of Almaty and Almaty oblast: middle-aged (45-59 years old), elderly (60-79 years old) and the oldest (80 years and above). A high loss of teeth was revealed, which was 79.3% in the urban and 90.6% in the rural population of the Republic of Kazakhstan, respectively. Complete absence of teeth on the upper jaw was most common in rural and city dwellers in the oldest and elderly age groups. A high frequency of complete absence of teeth was revealed in elderly rural residents (44.9%). The production of removable prostheses with a double layer base improves the quality thereof. Indications for these prostheses have been determined. In conclusion, the need for orthopedic dental care was the highest in rural areas. Complete absence of teeth on the upper jaw was most common in the oldest and elderly age groups among rural and urban dwellers. A high frequency of complete absence of teeth was revealed among elderly rural residents (44.9%). Orthopedic treatment of persons with complete absence of teeth requires improvement of this assistance. The use of removable prostheses with a two-layer base improved the quality of manufactured prostheses, providing comfort and functional efficiency for patients. Indications for the manufacture of soft-lined prostheses have been determined and clarified.

Numerical study of the stress state on the oral mucosa and abutment tooth upon insertion of partial dentures in the mandible

The introduction of a removable partial denture onto the dental arch significantly influences the mechanical stress characteristics of both the jawbone and oral mucosa. The aim of this study was to analyze the stress state caused by biting forces upon insertion of partial dentures into the assembly, and to understand the influence of the resulting contact pressure on its retention behavior. For this purpose, a numerical model of a removable partial denture is proposed based on 3D models developed using computer tomography data of the jawbone and the removable partial denture. The denture system rests on the oral mucosa surface and three abutment teeth. The application of bite forces on the denture generated a stick condition on the loaded regions of the denture-oral mucosa interface, which indicates positive retention of the denture onto the oral mucosa surface. Slip and negative retention were observed in the regions of the contact space that were not directly loaded. The contact pressures observed in the regions of the oral mucosa in contact with the denture were below the clinical pressure pain threshold value for soft tissue, which potentially lowers the risk of pain being experienced by denture users. Further, the variation of the retention behavior and contact pressures across different regions of the denture assembly was observed. Thus, there is a need for adhesives or restraining mechanisms for the denture system in order to avoid bending and deformation of sections of the denture as a consequence of the applied bite force.

Orofacial quantitative sensory testing: Current evidence and future perspectives

BACKGROUND AND OBJECTIVE

Orofacial quantitative sensory testing (QST) is an increasingly valuable psychophysical tool for evaluating neurosensory disorders of the orofacial region. Here, we aimed to evaluate the current evidence regarding this testing method and to discuss its future clinical potential.

DATA TREATMENT

We conducted a literature search in Medline, Embase and Scopus for English-language articles published between 1990 and 2019. The utilized search terms included QST, quantitative, sensory testing and neurosensory, which were combined using the AND operator with the terms facial, orofacial, trigeminal, intraoral and oral.

RESULTS

Our findings highlighted many methods for conducting QST-including method of levels, method of limits and mapping. Potential stimuli also vary, and can include mechanical or thermal stimulation, vibration or pinprick stimuli. Orofacial QST may be helpful in revealing disease pathways and can be used for patient stratification to validate the use of neurosensory profile-specific treatment options. QST is reportedly reliable in longitudinal studies and is thus a candidate for measuring changes over time. One disadvantage of QST is the substantial time required; however, further methodological refinements and the combination of partial aspects of the full QST battery with other tests and imaging methods should result in improvement.

CONCLUSIONS

Overall, orofacial QST is a reliable testing method for diagnosing pathological neurosensory conditions and assessing normal neurosensory function. Despite the remaining challenges that hinder the use of QST for everyday clinical decisions and clinical trials, we expect that future improvements will allow its implementation in routine practice.

Verification of the reliability of current perception threshold and pain threshold testing by application of an electrical current stimulus to mandibular mucosa in young adults

BACKGROUND

There is little evidence regarding the reliability of CPT and PT measurements to gauge mandibular perception. Thus, this study aimed to evaluate the test-retest reliability of CPT and PT values obtained from the mandibular oral mucosa and to test the bilateral differences in CPT and PT values obtained from the mental foramen region and buccal shelf region by a single operator.

METHODS

CPT and PT values were obtained from the mental foramen and buccal shelf regions of 20 volunteers (10 males and 10 females; average age: 26.4 ± 2.6 years) by using the Neurometer CPT/C® device to deliver electrical stimulation.

RESULTS

Relative and absolute reliabilities were confirmed over two measurements of CPT and PT over a 7- to 10-day measurement interval. Intra-class correlation coefficients (ICCs) for CPT and PT table obtained from the mental foramen region were >0.8, while most ICC for the buccal shelf region were <0.8. Standard error of measurement, minimal detectable change and Bland-Altman analyses showed that the CPT and PT measurements had no systematic error and could serve as useful methods. At all frequencies, the bilateral difference in CPT and PT values at the mental foramen and buccal shelf region was not significant.

CONCLUSION

CPT and PT measurements using a custom-made device that applied an electrical current to the mental foramen region have appropriate reliability to assess intra-oral sensitivity to electrical stimulation in young adults.

Receptivity of the mandible versus the maxilla to external stimuli in patients with complete dentures

PURPOSE

This study aimed to investigate whether the mandible is more receptive to external stimuli than the maxilla in patients with complete dentures by comparing regional current perception thresholds (CPTs) and pain threshold (PTs).

METHODS

A single operator obtained measurements from maxillae at the incisor foramen and the left side of the greater palatine foramen region and the mandible at the left side of the mental foramen region, using the Neurometer CPT/C device, CPT and PT values from the oral mucosa of 20 edentulous individuals wearing complete dentures were analyzed. Participant characteristics such as mucosal thickness, occlusal force, age, and sex. Mucosal thickness over target regions and occlusal force were measured by the same operator using Krupp SDM and Occlusal Force-Meter GM10s devices. Differences in CPT and PT among the three measurement regions were tested with an analysis of covariance, and post hoc t-tests with the Bonferroni correction.

RESULTS

There were no significant differences between the mental foramen, incisor papilla, and greater palatine regions CPT values. PTs obtained at all current frequencies (2000Hz, 250Hz, and 5Hz) were lowest in the mental foramen region and highest in the greater palatine region. Covariates including sex, mucosal thickness, and occlusal force had no significant influence on CPT or PT values at all frequencies.

CONCLUSIONS

The mandible exhibits higher receptivity to external pain stimuli than the maxilla.

Anesthetic efficacy of an inferior alveolar nerve block in soft tissue and correlation between soft tissue and pulpal anesthesia

OBJECTIVES

This study was aimed at evaluating the anesthetic success rates in various regions of soft tissue after inferior alveolar nerve (IAN) block and comparing the success rates of soft tissue anesthesia with those of pulpal anesthesia to find correlations.

MATERIALS AND METHODS

Fifty-nine dental students received an IAN block injection. A total of four test sites were used for soft tissue anesthesia using a pressure algometer (PA): the corner of the lower lip vermilion border (LL); the buccal-attached gingiva of the lateral incisor (BGI), the molar (BGM), and the lingual gingiva (LG). The lateral incisor (LI) and the first molar (M1) were evaluated for pulpal anesthesia using an electric pulp tester. To evaluate whether soft tissue anesthesia can be an indicator of pulpal anesthesia, the positive predictive value (PPV) and negative predictive value (NPV) were calculated.

RESULTS

The highest success rate for soft tissue anesthesia was seen on the LG (93.9%), followed by LL (79.6%), BGI (53.1%), and BGM (14.3%). The PPVs of LL for the M1 and Ll were 74.4 and 59.0%. The NPVs for the M1 and LI were much higher in the LL (90.0 and 100%, respectively) than in the BGI (56.5 and 69.6%, respectively).

CONCLUSIONS

The highest success rate was found in the LG. Lip numbness was not an indicator of pulpal anesthesia of M1 and LI. However, if the LL was not anesthetized, the probabilities of failed pulpal anesthesia were very high in the LI and M1.

CLINICAL RELEVANCE

The clinicians need to consider not doing an additional lingual nerve block after IAN block.

Quantitative sensory testing for assessment of somatosensory function in human oral mucosa: a review

OBJECTIVE

This narrative review provides an overview of the quantitative sensory testing (QST) to assess somatosensory function in human oral mucosa.

MATERIAL AND METHODS

A literature search was conducted in the PubMed database to identify studies in vivo on human oral mucosa using QST methods. A list of 149 articles was obtained and screened. A total of 36 relevant articles remained and were read in full text. Manual search of the reference lists identified eight additional relevant studies. A total of 44 articles were included for final assessment.

RESULTS

The included studies were divided into six categories according to the study content and objective. In each category, there was a great variety of aims, methods, participants and outcome measures. The application of QST has nevertheless helped to monitor somatosensory function in experimental models of intraoral pain, effects of local anesthesia, after oral and maxillofacial surgery and after prosthodontic and orthodontic treatment.

CONCLUSIONS

QST has been proved to be sufficiently stable and reliable, and valuable information has been obtained regarding somatosensory function in healthy volunteers, special populations and orofacial pain patients. However, as most of the studies were highly heterogeneous, the results are difficult to compare quantitatively. A standardized intraoral QST protocol is recommended and expected to help advance a mechanism-based assessment of neuropathies and other intraoral pain conditions.

Assessment of periodontal mechano-nociceptive function in healthy Chinese individuals

OBJECTIVE

Few clinical techniques are available for the description of mechano-nociceptive function in human periodontal tissues. The objective of this study was to test a new technique for assessment of periodontal mechano-nociceptive function by direct application of controlled forces to the teeth and quantify site, side and gender differences in healthy individuals.

DESIGN

Twenty healthy young adults (ten males and ten females) participated. A handheld pressure algometer was used to assess pressure pain threshold (PPT) on the maxillary and mandibular central incisors, canines and first premolars on the left and the right side from two directions: lateral and vertical. Statistical analysis was performed using analyses of variance (ANOVA) with repeated measures to compare data.

RESULTS

There were significant gender differences of PPT for both lateral (P_lateral=0.007) and vertical (P_vertical=0.001) directions with lower thresholds in females (higher sensitivity) than in males. A significant site effect (P_lateral=0.002, P_vertical<0.001) was observed with less sensitivity at the first premolar compared to the anterior teeth. No significant right-to-left side differences (P=0.082) were found for the PPTs. There were significant PPT differences between maxillary and mandibular teeth (P_lateral=0.020, P_vertical=0.041,) and significant differences between lateral and vertical direction (P<0.001).

CONCLUSION

The novel application of PPTs directly to the teeth indicated an adequate and practical method with potential value for clinical assessment of painful conditions affecting the periodontal ligament.

Factors associated with mucosal pain in patients with partial removable dental prostheses

The aim of this study was to investigate factors associated with mucosal pain in patients with partial removable dental prostheses (PRDPs). In this hospital-based cross-sectional study, 333 patients wearing 500 PRDPs (mean age 71·4 years, men 33·3%) were consecutively recruited from prosthetic clinic of a dental hospital in Japan. Subjects rated pain intensity and frequency of denture-bearing mucosa. An examiner recorded age, gender and systemic diseases as well as dental, mucosa, denture, sensory, behavioural- and psychological-related characteristics that were possibly associated with the mucosal pain. Multivariate analyses were performed to analyse factors related to mucosal pain. Pain intensity was rated as more than score 0 (presence) in 34·2% (171/500) PRDPs, and pain was experienced after denture delivery in 42·8% (214/500) PRDPs. Logistic regression analyses showed that younger age, mucosal damage, poor mucosal condition, bone prominence, poor residual ridge, higher pain sensitivity, presence of awake bruxism, perception of oral dryness, interim denture wear and high number of missing teeth were significant independent predictors for the presence of the mucosal pain intensity and/or frequency (P < 0·05). Multiple factors are associated with mucosal pain in patients with PRDPs. Oral mucosal characteristics, age, pain sensitivity and behavioural factors seem to be more critical for mucosal pain than distribution of missing teeth and number of abutment teeth.

Biomechanics of oral mucosa

The prevalence of prosthodontic treatment has been well recognized, and the need is continuously increasing with the ageing population. While the oral mucosa plays a critical role in the treatment outcome, the associated biomechanics is not yet fully understood. Using the literature available, this paper provides a critical review on four aspects of mucosal biomechanics, including static, dynamic, volumetric and interactive responses, which are interpreted by its elasticity, viscosity/permeability, apparent Poisson's ratio and friction coefficient, respectively. Both empirical studies and numerical models are analysed and compared to gain anatomical and physiological insights. Furthermore, the clinical applications of such biomechanical knowledge on the mucosa are explored to address some critical concerns, including stimuli for tissue remodelling (interstitial hydrostatic pressure), pressure–pain thresholds, tissue displaceability and residual bone resorption. Through this review, the state of the art in mucosal biomechanics and their clinical implications are discussed for future research interests, including clinical applications, computational modelling, design optimization and prosthetic fabrication.

Test-retest reliability of a new technique with pressure algometry applied to teeth in healthy Chinese individuals

Pressure pain thresholds (PPTs) have been shown to be useful measures of mechanical pain sensitivity in deep tissues. However, clinical methods for measuring mechanical allodynia or hyperalgesia in teeth have not been reported. The aim of this study was to assess the reliability of PPTs in periodontal ligament of healthy Chinese participants. Twenty healthy young adults participated. Pressure pain thresholds were measured at six teeth and in two directions. The tests included three consecutive trials, in two separate sessions, which were performed on the first day by one examiner. After 1-3 wk, an identical protocol was carried out by two examiners, also in two separate sessions. There were no significant differences between repeated measures for all teeth. The PPTs had excellent reliability with high intraclass coefficients (ICCs) across different sessions (ICC: 0.871-0.956), days (ICC: 0.879-0.951), and examiners (ICC: 0.845-0.950). Pressure pain thresholds applied to the teeth have excellent intra- and inter-examiner agreement in healthy participants. This method may be proposed as an easy and reliable technique to assess mechanical pain sensitivity (e.g. mechanical allodynia and hyperalgesia) in the periodontal ligament, which is associated with endodontic or periodontal conditions.

Fixed orthodontic appliances cause pain and disturbance in somatosensory function

This study aimed to assess the short-term effects of orthodontic pain on quantitative sensory testing (QST) in subjects receiving fixed orthodontic treatment. Twenty patients and 12 healthy volunteers (as controls) participated. All 20 patients had bonded AO self-ligating brackets, with a 0.014 super elastic nickel-titanium arch wire placed in the brackets. Pain [self-reported on a visual analog scale (VAS)], and thermal and mechanical thresholds, were tested at six time points--before (baseline), and 2 h, 24 h, 7 d, 14 d, and 30 d after, force application--in the treatment group. The attached gingiva adjacent to the left upper central incisor (21 gingiva) was hypersensitive to cold stimuli (i.e. increased cold detection thresholds were detected) in the treatment group. The pressure pain thresholds of the left upper central incisor (21) and 21 gingiva were significantly reduced. Our results suggest clear signs of sensitization of the trigeminal nociceptive system up to 1 month after force application and orthodontic pain. Quantitative assessment of somatosensory function may help to provide a better understanding and profiling of the underlying neurobiological mechanisms related to orthodontic pain.

Shape Optimization for Additive Manufacturing of Removable Partial Dentures--A New Paradigm for Prosthetic CAD/CAM

With ever-growing aging population and demand for denture treatments, pressure-induced mucosa lesion and residual ridge resorption remain main sources of clinical complications. Conventional denture design and fabrication are challenged for its labor and experience intensity, urgently necessitating an automatic procedure. This study aims to develop a fully automatic procedure enabling shape optimization and additive manufacturing of removable partial dentures (RPD), to maximize the uniformity of contact pressure distribution on the mucosa, thereby reducing associated clinical complications. A 3D heterogeneous finite element (FE) model was constructed from CT scan, and the critical tissue of mucosa was modeled as a hyperelastic material from in vivo clinical data. A contact shape optimization algorithm was developed based on the bi-directional evolutionary structural optimization (BESO) technique. Both initial and optimized dentures were prototyped by 3D printing technology and evaluated with in vitro tests. Through the optimization, the peak contact pressure was reduced by 70%, and the uniformity was improved by 63%. In vitro tests verified the effectiveness of this procedure, and the hydrostatic pressure induced in the mucosa is well below clinical pressure-pain thresholds (PPT), potentially lessening risk of residual ridge resorption. This proposed computational optimization and additive fabrication procedure provides a novel method for fast denture design and adjustment at low cost, with quantitative guidelines and computer aided design and manufacturing (CAD/CAM) for a specific patient. The integration of digitalized modeling, computational optimization, and free-form fabrication enables more efficient clinical adaptation. The customized optimal denture design is expected to minimize pain/discomfort and potentially reduce long-term residual ridge resorption.

Biomechanical factors related to occlusal load transfer in removable complete dentures

Owing to economic conditions, removable dentures remain popular despite the discomfort and reduced chewing efficiency experienced by most denture wearers. However, there is little evidence to confirm that the level of mucosal load exceeds the pressure pain threshold. This discrepancy stimulated us to review the current state of knowledge on the biomechanics of mastication with complete removable dentures. The loading beneath dentures was analyzed in the context of denture foundation characteristics, salivary lubrication, occlusal forces, and the biomechanics of mastication. The analysis revealed that the interpretation of data collected in vivo is hindered due to the simultaneous overlapping effects of many variables. In turn, problems with determining the pressure beneath a denture and analyzing frictional processes constitute principal limitations of in vitro model studies. Predefined conditions of finite element method simulations should include the effects of oblique mastication forces, simultaneous detachment and sliding of the denture on its foundation, and the stabilizing role of balancing contacts. This review establishes that previous investigations may have failed because of their unsubstantiated assumption that, in a well-working balanced occlusion, force is only exerted perpendicular to the occlusal plane, allowing the denture to sit firmly on its foundation. Recent improvements in the simulation of realistic biomechanical denture behavior raise the possibility of assessing the effects of denture design on the pressures and slides beneath the denture.

Enhanced therapeutic alliance modulates pain intensity and muscle pain sensitivity in patients with chronic low back pain: an experimental controlled study

BACKGROUND

Physical therapy influences chronic pain by means of the specific ingredient of an intervention as well as contextual factors including the setting and therapeutic alliance (TA) between provider and patient.

OBJECTIVE

The purpose of this study was to compare the effect of enhanced versus limited TA on pain intensity and muscle pain sensitivity in patients with chronic low back pain (CLBP) receiving either active or sham interferential current therapy (IFC).

DESIGN

An experimental controlled study with repeated measures was conducted. Participants were randomly divided into 4 groups: (1) AL (n=30), which included the application of active IFC combined with a limited TA; (2) SL (n=29), which received sham IFC combined with a limited TA; (3) AE (n=29), which received active IFC combined with an enhanced TA; and (4) SE (n=29), which received sham IFC combined with an enhanced TA.

METHODS

One hundred seventeen individuals with CLBP received a single session of active or sham IFC. Measurements included pain intensity as assessed with a numerical rating scale (PI-NRS) and muscle pain sensitivity as assessed via pressure pain threshold (PPT).

RESULTS

Mean differences on the PI-NRS were 1.83 cm (95% CI=14.3-20.3), 1.03 cm (95% CI=6.6-12.7), 3.13 cm (95% CI=27.2-33.3), and 2.22 cm (95% CI=18.9-25.0) for the AL, SL, AE, and SE groups, respectively. Mean differences on PPTs were 1.2 kg (95% CI=0.7-1.6), 0.3 kg (95% CI=0.2-0.8), 2.0 kg (95% CI=1.6-2.5), and 1.7 kg (95% CI=1.3-2.1), for the AL, SL, AE, and SE groups, respectively.

LIMITATIONS

The study protocol aimed to test the immediate effect of the TA within a clinical laboratory setting.

CONCLUSIONS

The context in which physical therapy interventions are offered has the potential to dramatically improve therapeutic effects. Enhanced TA combined with active IFC appears to lead to clinically meaningful improvements in outcomes when treating patients with CLBP.

Influence of denture supporting tissue properties on pressure-pain threshold--measurement in dentate subjects

PURPOSE

The present study was designed to clarify the relationship between the properties of the palatal mucosa and the pressure-pain threshold.

METHODS

Three parts of the palatal mucosa of 17 dentate subjects were measured: the median part of the palate, the lateral part of the first molar, and the midpoint between these two parts. The subjects were instructed to press a pushbutton when he or she felt pressure-pain. The probe pressure was gradually increased (1N/s). The thickness (T) (mm) and elasticity (E) (MPa) were used as the parameters of the properties of the palatal mucosa, whereas pressure (P) (MPa), compressibility (C) (%), and subsidence (S) (mm) were used as the parameters of the pressure-pain threshold. The Shapiro-Wilk test was used to consider the data of distribution of normality for each measurement point, as obtained from the 17 subjects. A Kruskal-Wallis test and a Wilcoxon signed rank test were performed for multiple comparisons, the Bonferroni method was used to compensate for the P-value. Spearman's rank correlation coefficient was calculated.

RESULTS

T correlated with the values of S at the median points (P=0.001) and midpoints (P=0.011).

CONCLUSION

Thickness can be an index of the amount of relief where pain is caused easily. In addition, modulus of elasticity is important as an indicator of the bearing ability of denture support tissues, it is necessary to consider how to evaluate the modulus of elasticity and to evaluate the relationship between the parameters of the pain threshold.

Guidelines and recommendations for assessment of somatosensory function in oro-facial pain conditions--a taskforce report

The goals of an international taskforce on somatosensory testing established by the Special Interest Group of Oro-facial Pain (SIG-OFP) under the International Association for the Study of Pain (IASP) were to (i) review the literature concerning assessment of somatosensory function in the oro-facial region in terms of techniques and test performance, (ii) provide guidelines for comprehensive and screening examination procedures, and (iii) give recommendations for future development of somatosensory testing specifically in the oro-facial region. Numerous qualitative and quantitative psychophysical techniques have been proposed and used in the description of oro-facial somatosensory function. The selection of technique includes time considerations because the most reliable and accurate methods require multiple repetitions of stimuli. Multiple-stimulus modalities (mechanical, thermal, electrical, chemical) have been applied to study oro-facial somatosensory function. A battery of different test stimuli is needed to obtain comprehensive information about the functional integrity of the various types of afferent nerve fibres. Based on the available literature, the German Neuropathic Pain Network test battery appears suitable for the study of somatosensory function within the oro-facial area as it is based on a wide variety of both qualitative and quantitative assessments of all cutaneous somatosensory modalities. Furthermore, these protocols have been thoroughly described and tested on multiple sites including the facial skin and intra-oral mucosa. Standardisation of both comprehensive and screening examination techniques is likely to improve the diagnostic accuracy and facilitate the understanding of neural mechanisms and somatosensory changes in different oro-facial pain conditions and may help to guide management.

Strain analysis of maxillary complete denture with three-dimensional finite element method

STATEMENT OF PROBLEM

The fracture of maxillary complete dentures has been reported as the most common prosthesis failure.

PURPOSE

The purpose of this study was to evaluate strain distribution in dentures during application of occlusal load with 3-dimensional (3-D) finite element analysis (FEA).

MATERIAL AND METHODS

A maxillary complete denture was converted into a 3-D numerical model by an advanced topometric sensor digitizer (ATOS). The denture surfaces were scanned with fringes. Ten measurements were made for each scan of the denture in top, left, right, back, and front orientations by tilting the scanning table. The individual scans were merged by the digitizing software into a single image. A haptic device with a freeform system (PHANTOM) was used to create the mucosa in contact with the intaglio surface of the denture model. Supporting bone was then constructed from the mucosa model. The posterior teeth were loaded with an occlusal force of 230 N, and the basal bone was constrained for performing FEA.

RESULTS

The highest tensile and compressive strains were found at the incisal and labial frenal notches, respectively. Strains on the intaglio surface of the denture were primarily compressive. The buccal flange exhibited tensile strains in the horizontal direction but compressive strains in the vertical direction. The labial flange showed compressive strains in both directions. The posterior border of the denture flexed away from the mucosa during occlusal loading.

CONCLUSIONS

Three-dimensional FEA provided different views of strain distribution in the denture and indicated that denture failure was unlikely to occur at the shallow labial frenal notch because the strain is compressive. The high tensile strain concentration at the incisal notch is likely to be the cause of denture fracture during clinical service.

Reliability of intraoral quantitative sensory testing (QST)

The German Research Network on Neuropathic Pain (DFNS) has recommended a protocol with 13 quantitative sensory testing (QST) measures for detecting somatosensory abnormalities. Reliability is an important scientific property and has been adequately tested for cutaneous QST. This study evaluates intraoral sites for which no reliability trials have yet been published. Inter- and intra-examiner reliability of 13 QST measures at intra- and extraoral trigeminal sites were investigated. Twenty-one healthy volunteers from Malmö University, Malmö, Sweden (13 women and 8 men, mean age 40.4 years, range 24-71) participated. Two independent examiners previously trained in the DFNS QST protocol examined the participants using the entire protocol. Each participant was examined twice on the same day, once by each examiner (inter-examiner reliability). After 1-3 weeks, one examiner re-examined all participants (intra-examiner reliability). The measurements were made on the skin of the right cheek, the tip of the tongue, and bilaterally on the gingival mucosa of the upper premolar region. The intraclass correlation coefficient (ICC) or kappa was used to calculate variations. Most tests had acceptable to excellent inter-examiner (ICC 0.41-0.89) and intra-examiner (ICC 0.43-0.87) reliability. For each test, inter- and intra-examiner reliabilities at intra- and extraoral sites were similar. No significant differences between right and left sides were found intraorally. We conclude that inter- and intra-examiner reliabilities of most QST measures are acceptable for assessing somatosensory function in the orofacial region.

Prototyping artificial jaws for the robotic dental testing simulator

This paper presents a robot periphery prototyped for the six-degrees-of-freedom robotic dental testing simulator, simulating the wear of materials on dental components, such as individual teeth, crowns, bridges, or a full set of teeth. The robot periphery consists of the artificial jaws and compliance module. The jaws have been reverse engineered and represent a human-like mandible and maxilla with artificial teeth. Each clinically fabricated tooth consists of a crown and glass ceramic roots which are connected using resin cement. Normal clinical occlusion of the artificial jaws assembly was emulated by a dental articulator based on 'Andrew's six keys to occlusion'. The radii of the von Spee curve, the Monson curve, and the Wilson curve were also measured as important jaw characteristic indicators to aid normal occlusion. A compliance module had to be built between the lower jaw and the robot platform to sustain the fluctuating forces that occur during normal chewing in the occlusal contact areas, where these high bite forces are major causes of dental component failure. A strain gauge force transducer has been integrated into the machined lower jaw, underneath the second molars, to measure axial biting forces applied to the posterior teeth. The experiments conducted have shown that the sensor is able to sense small changes in the compression force satisfactorily, when applied perpendicular to the occlusal surfaces of the teeth.

Changes in electroencephalographic activities following pressure stimulation in humans

We investigated brain activity in response to orofacial pain in 20 healthy subjects in order to characterize the relationship between pain and changes in brain function. First, the pressure pain threshold (PPT) at the styloid process of the temporal bone (Libman's point) of 20 subjects was measured by a pressure algometer. Second, electroencephalographic (EEG) changes of 20 subjects before and after 10 s of constant pressure stimulation at Libman's point were measured. These 20 subjects were divided into two groups: 10 subjects with higher PPT (high group) and 10 subjects with lower PPT (low group). EEG change in beta activity after stimulation was greater in the low group than the high group, and there was a significant negative correlation between this change and PPT, with even minor constant stimulation inducing larger EEG change in individuals highly receptive to pain. The present study demonstrated that a relative reduction in beta activity after pain stimulation was more remarkable in subjects with lower PPT than in subjects with higher PPT, and that this change was closely related to a hemispheric balance, with even minor constant stimulation inducing changes in brain waves in individuals highly sensitive to pain.

Mapping, profiling and clustering of pressure pain threshold (PPT) in edentulous oral mucosa

OBJECTIVES

Edentulous oral mucosa involves different tissue types, various innervation and wound healing process. We hypothesized that pressure pain threshold (PPT) of edentulous oral mucosa varies significantly among different regions. The objective of this study is to examine regional differences and correlations of PPT in edentulous oral mucosa.

METHODS

Pain threshold (PPT) was measured at 112 sites in 15 edentulous patients using an electric-controlled pressure algometer. PPT mapping was created by the level of PPT, and PPT clustering was undertaken based on the inter-site correlation of PPT.

RESULTS

PPT increased from the anterior to posterior alveolus in both maxilla and mandible, but decreased from the anterior palate to the posterior palate. PPT decreased from the ridge crest to the buccal vestibule. The inter-site difference was four fold within the maxilla and 2.4 fold within the mandible. Principal component analysis applied on PPT inter-site correlation matrix revealed that the maxilla and mandible could be differentiated statistically. The maxilla and mandible were divided into three and four clusters, respectively.

CONCLUSION

These results demonstrate that different areas of edentulous oral mucosa have different PPT and that the PPT varies proportionally in selected areas, providing useful diagnostic and therapeutic information in removable prosthodontics and a new opportunity for understanding pain underneath the denture.

Reproducibility Indices Applied to Cervical Pressure Pain Threshold Measurements in Healthy Subjects

OBJECTIVES

To apply various statistical indices for reproducibility analysis of pressure pain threshold measurements and to derive a preferred pressure pain threshold measurement protocol based on these indices.

METHODS

The pressure pain threshold of 3 pairs of right and left homologous cervical region sites were measured in 20 healthy subjects (10 women, 10 men) using a hand-held pressure algometer. Measurements took place on 2 occasions (test 1 and test 2) separated by a mean interval of 1 week. On each testing session, the site-related pressure pain thresholds were measured 3 times each according to 2 different protocols. Protocol A consisted of a repetitive order, namely 3 consecutive measurements at each site before proceeding to the next, whereas protocol B consisted of an alternate order in which 3 consecutive rounds of all individually tested sites took place. For test 1, protocol A was followed by protocol B with an hour interval. For test 2, the reverse order took place.

RESULTS

The findings revealed no significant differences between the two protocols and indicated a significant rise (P < 0.0001) in the absolute scores from test 1 to test 2 in both protocols. Absolute values (mean +/-SD) derived from the entire sample of pressure pain threshold sites ranged from 140 +/- 60 to 198.7 +/- 95 kPa (1.60 +/- 0.6 to 1.99 +/- 0.95 kg/cm, respectively). No significant gender or side differences were noted. Pearson r as well as the intraclass correlation coefficient revealed good to excellent reproducibility for both protocols and for all sites measured: r = 0.79-0.94 and intraclass correlation coefficient(3,3) = 0.85-0.96, respectively. To define site-specific cutoff values indicating change at the 95% confidence level, 1.96*SEM was calculated, and its values ranged from 31.6 to 58.2 kPa, which correspond to 16.8% to 32.8% of the absolute mean values. In addition, the limits of agreement, which depict the individual test-retest differences relative to their mean, indicated a heteroscedastic trend.

DISCUSSION

The two protocols yielded very similar results. However, on the grounds of patient's comfort and compliance as well as facility of application, protocol B stands out as the more preferred between the two.