Dental status and oxidative homeostasis state in patients exposed to occupational vibration: reduced glutathione content in oral fluid.

AIM: The aim of the research involved determination of reduced glutathione content in oral fluid of patients exposed to occupational vibration depending upon their dental status. MATERIALS AND METHODS: The assessment of dental status (DS) and reduced glutathione (RG) content in oral fluid (OF) was carried out in three groups of patients: control group (n=129) included the persons exposed to occupational vibration whose results of comprehensive medical examination excluded the presence of vibration disease (VD); the second group (n=63 patients with the VD stage I) and the third group (n=66 patients with VD stage II), who underwent treatment at the clinical department of the Research Institute of Occupational Hygiene and Occupational Diseases of Kharkiv National Medical University of the Ministry of Health of Ukraine. DS determination was carried out according to the method of K. M. Kosenko (Patent No. 57512, Ukraine) for in-patients and controls (during medical checkups) using the following indices: PMA, OHI-S, DMFT, with assessment of vacuum-pressory resistance of gingival capillaries (VPRC) (according to V. I. Kulazhenko) and community periodontal index of treatment needs (CPITN). RG content (activity) in OF was determined according to Garishvili. Primary data were statistically processed with the determination of accuracy by Student's test. RESULTS: Assessment of metabolic indices, which characterize the state of oxidative homeostasis enzyme chain, showed that RG content in OF depending upon VD severity reliably (p<0.05) reduced. RG content depending upon PMA intensity in patients with VD ranged from 23.5±0.8 mg/cm3 to 28.6±0.3 U/min and was reliably (p<0.05) lower in patients with VD stage I versus controls (23.2±1.0 U/min and 26.7±0.3 U/min respectively, when PMA>2.1) and also reliably lower in patients with VD stage II versus patients with VD stage I (29.9±0.9 U/min and 26.2±0.4 U/min respectively, when PMA>1.0). RG content depending upon OHI-S values in patients with VD ranged from 33.4±1.2 U/min to 24.1±1.1 U/min and was reliably (d<0.05) lower in patients with OHI-S values equal to 1.7 U and higher versus controls (24.1±1.1 U/min and 27.1±0.2 U/min, respectively) and also reliably lower in patients with VD stage II versus patients with VD stage I (27.3±0.4 U/ min and 33.4±1.2 U/min, respectively, with OHI-S≤0.6 U). A comparative analysis showed that the activity of the enzymatic protection of the periodontal membrane could be also determined by the state of hard tissues, in particular by such DS index as DFMT. The activity of RG in VD stage I was shown to be reliably (p<0.05) reduced in patients with DFMT index exceeding 15 pts (in DFMT≤10 pts RG activity was 32.2±0.4 U/min, whereas in DFMT exceeding 15 pts it was equal to 26.7±0.6 U/min). Somewhat different pattern of RG activity in OF was found in patients with VD stage II: RG activity in OF was reduced in all DFMT values in these patients and its reduction was shown to be dependent on an increase in DMFT index. In DMFT≤10 the patients with VD stage II were found to have a reliable (p<0.05) reduction in RG activity in OF versus the control group (30.1±0.3 U/ min and 23.8±0.5 U/min, respectively) and this activity was shown to be inhibited in DFMT increase (23.8±0.5 U/min with DFMT≤10 and 19.3±0.9 U/min with DFMT≥20 pts, respectively). RG content depending upon VPRC in VD patients ranged from 29.2±0.1 U/min to 29.2±0.1 U/min and was reliably (p<0.05) lower in patients with their VPRC values ≤40 sec. Assessment of RG activity in OF of VD patients with different levels of CPITN showed that RG content in persons requiring comprehensive treatment (also including prosthetic treatment; CPITN≥3.1 pts) was reliably reduced (versus corresponding groups of patients but with low CPITN values) both in VD stages I and II (24.1±1.0 U/min and 19.3±0.9 U/min, respectively). CONCLUSIONS: Increases in the rate and expression of periodontal lesions (by PMA index) depending upon the presence and severity of VD with a proper decrease in the level of RG content in OF were registered. An activation of the enzymatic chain of antioxidant protection in patients with VD under low HI values and a simultaneous inhibition of enzymatic activity under high HI values were found out. VD stage I revealed an increased RG activity versus controls (p<0.05), while VD stage II demonstrated a reliable (p<0.05) reduction of the above activity. Moreover, an unsatisfactory state of the oral cavity hygiene contributed to enzymatic protection of their periodontium in patients with VD (irrespective of its stage). Regularities were revealed, which supported the benefit of pathogenetic relationships between the state of the periodontal microcirculatory bed and enzymatic activity of OF in patients with VD. Both patients with VD and persons, who are exposed to occupational vibration, need for diagnosis of activity of enzymes in OF since, as our analysis of findings has shown, DS indices are interdependent with activity of the enzymatic chain of the antioxidant protection of OF.

Effect of 125-150 Hz Vibrational Frequency Electric Toothbrush on Teeth and Supporting Structures: A Finite Element Method Study.

AIM AND OBJECTIVE: The aim of this finite element method (FEM) study was to assess the safety of 125-150 Hz vibrational frequency electric toothbrush on teeth and associated structures. MATERIALS AND METHODS: A three-dimensional (3D) geometric model of entire skull having maxilla, mandible, and their dentitions was created using a computed tomography (CT) image of a healthy male patient. Linear static analysis was carried out by applying 15 g of force on anterior part of maxilla and mandible from labial and lingual sides each to calculate the primary displacement (sagittal, vertical, and transversal) and principal stress levels generated on the maxillary and mandibular dentition, on the maxilla and mandible and on the whole skull. RESULTS: A force of 15 g applied to maxillary anterior teeth from labial side caused a mean deflection of 0.003 mm and stress of 0.004 MPa on the teeth and supporting structures. A force of 15 g applied to maxillary anterior teeth from palatal side caused a mean deflection of 0.017 mm and stress of 0.017 MPa on the teeth and supporting structures. A force of 15 g applied to mandibular anterior teeth from labial side caused a mean deflection of 0.078 mm and stress of 0.051 MPa on the teeth and supporting structures. A force of 15 g applied to mandibular anterior teeth from lingual side caused a mean deflection of 0.077 mm and stress of 0.051 MPa on the teeth and supporting structures. CONCLUSION: For the applied loads and boundary conditions, very small or negligible amount of stresses were observed in maxilla, mandible, and their dentitions. The vibrational frequency of 150 Hz producing 15 g of force did not produce any harmful effects on maxilla, mandible, and their dentitions. Hence, 125-150 Hz of vibrational frequency can be considered optimum. CLINICAL SIGNIFICANCE: An electric toothbrush using the vibration of 125-150 Hz produces negligible stress on teeth and associated structures.

Case report: Hand-arm vibration syndrome in a dental technician.

Occupational exposure to vibration using hand-held tools may cause hand-arm vibration syndrome (HAVS) among workers. We report the case of a 39-year-old lady with a 5-year work exposure to repetitive wrist movements and vibration from hand tools in the dental fabrication laboratory, working as a dental technician. She presented with a 3-year history of chronic pain over the wrists and positive symptoms of numbness and tingling in the hands, pain and discomfort of the fingers during cold exposure, and poor grip strength. Symptoms over the right hand were worse than the left. She is right-hand dominant. She had bilateral median nerve neuropathy at the wrist. Nerve conductive tests were consistent with minimal bilateral carpal tunnel syndrome. MRI showed evidence of soft tissue damage from repetitive strain injury of the right wrist. Neurosensory grading for hand-vibration syndrome (HAVS) using the Stockholm Workshop Scale (SWS) was performed and she was graded as Stage 1SN with numbness or tingling symptoms. Using the International Consensus Criteria (ICC) grading for HAVS, she was graded Stage N1 with numbness and/or tingling (symptoms) of finger. A workplace risk health assessment (WHRA) was performed, and exposure scores for her work tasks in dental fabrication and risk levels were determined using the HSE (Health and Safety UK) Assessment of Repetitive Tasks (ART) tool. The processes of teeth setting using dental burs (exposure score 23), divestment work with stone clippers (score 20), and use of pneumatic drills (score 21) were deemed high-risk activities for repetitive strain injury. The use of carving tools (score 12), packing with the use of flask clamps, and trimming (score 14) were classified as medium high-risk activities for repetitive strain injuries. Workplace modifications and workplace vibration exposure level monitoring protocols were subsequently established with the stabilization of the patient's symptoms.

Investigating the effect of hot and cold polyurethane foam on reducing whole body vibration of forklift operators.

BACKGROUND: Vibration is one of the harmful factors for forklift drivers. The use of non- standard seats and not paying attention to how the seats are maintained can be affected by the amount of vibration transmitted to the person. OBJECTIVE: This study investigates the amount of vibration transmitted from the forklift and the effect of different types of polyurethane foam in reducing the vibration transmitted from the forklift seat. METHODS: This descriptive-analytical study was performed on 38 forklifts in 4 diesel models with the same weight class. The amount of vibration transmitted from forklift seats according to ISO2631 standard, taking into account the effect of various factors such as foam type (hot and cold), thickness (6-12 cm), load and year Function was measured. The amount of vibration caused by the forklift on the seat and under the seat was evaluated using ISO7096 standard. RESULTS: The average total vibration of the whole body in all foams in no-load mode is more than with load. The transmission vibration of cold polyurethane foam is less than that of hot polyurethane foam. With increasing thickness, the efficiency of cold polyurethane foam increases by 12 cm and in the loaded state 40.63% and in the unloaded state 49.58% in reducing the vibration transmitted to drivers. CONCLUSION: The results of this study show that cold foam has better effectiveness and efficiency than hot polyurethane foam. Also, the thicker the foam, the less vibration is transmitted to the driver.

The relationship between resonance frequency analysis (RFA) and lateral displacement of dental implants: an in vitro study.

This in vitro investigation was conducted to study the relationship between resonance frequency analysis (RFA) and lateral displacement measurements of dental implants. A total of 30 implant sites were prepared in nine fresh bovine bone specimens. The bone density around each preparation was determined by using cone beam computerized tomography (CBCT) and imaging software. Dental implants were then inserted during continuous registration of insertion torque. RFA measurements were performed in perpendicular and parallel to the long axis of the specimens. The bone blocks were embedded in plaster and fixated in a specially designed rig for displacement measurements. A lateral force of 25 N was applied via an abutment perpendicular and parallel to each implant and the displacement measured in µm. In addition, a flex constant (µm N(-1) ) was calculated for each measurement. There was a significant inverse correlation between RFA and lateral implant displacement (µm) measurements and between RFA measurements and the flex constant in both perpendicular and parallel directions in bone (P ≤ 0·001). Moreover, both RFA and displacement measurements correlated with bone density (P ≤ 0·001). It is concluded that RFA measurements reflect the micromobility of dental implants, which in turn is determined by the bone density at the implant site.

A comparative study of the Osstell™ versus the Osstell Mentor™ to evaluate implant stability in human cadaver mandibles.

The aim of this study was to assess the primary stability of dental implants by resonance frequency analysis (RFA) using the Osstell™ and Osstell Mentor™ devices and to investigate the reproducibility and comparability of the results obtained with these devices. Twenty-four Straumann implants (Straumann AG, Basel, Switzerland) were placed in the anterior mandible of 12 fresh edentulous human cadaver mandibles. The implant stability quotients (ISQs) were measured with the Osstell™ and Osstell Mentor™ when implants were inserted at 50% of their length and following their complete insertion. The Osstell™ device measured lower scores compared with the Osstell Mentor™. This was significant for the full position (mean difference = 9·9), t (11) = 7·4, P < 0·001 and for the halfway position (mean difference = 5·9), t (11) = 2·41, P = 0·03. In conclusion, the Osstell™ produced relatively lower ISQ scores than the Osstell Mentor™.

Effect of vibration on orthodontic tooth movement in a double blind prospective randomized controlled trial.

The purpose of the present study was to investigate the effect of vibration on orthodontic tooth movement and safety assessment based on our previous basic research in animal experiments. A double-blind prospective randomized controlled trial using split-mouth design was conducted in patients with malocclusion. The left and right sides of maxillary arch were randomly assigned to vibration (TM + V) and non-vibration (TM) groups. After leveling, vibrations (5.2 ± 0.5 g-forces (gf), 102.2 ± 2.6 Hertz (Hz)) were supplementary applied to the canine retracted with 100 gf in TM + V group for 3 min at the monthly visit under double-blind fashion, and the canine on the other side without vibration was used as TM group. The amount of tooth movement was measured blindly using a constructed three-dimensional dentition model. The amount of canine movement per visit was 0.89 ± 0.55 mm in TM group (n = 23) and 1.21 ± 0.60 mm in TM + V group (n = 23), respectively. There was no significant difference of pain and discomfort, and root resorption between the two groups. This study indicates that static orthodontic force with supplementary vibration significantly accelerated tooth movement in canine retraction and reduced the number of visits without causing side effects.

Investigating the efficacy of vibration anesthesia to reduce pain from cosmetic botulinum toxin injections.

BACKGROUND: Many analgesic modalities have been employed with limited success to alleviate the pain associated with botulinum toxin type A (BTX-A) injections. Vibration is an effective method of reducing pain during facial cosmetic injections, but it has not been previously studied in the context of clinical cosmetic procedures. OBJECTIVES: The authors evaluate the safety and efficacy of vibration-assisted anesthesia for reducing pain associated with BTX-A injections. METHODS: In this prospective study, 50 patients received BTX-A injections for cosmetic rhytid reduction. Injections were given in a split-face design that was randomly assigned. A vibration stimulus was coadministered with BTX-A injections on one side, while the other side of each patient's face received BTX-A injections alone. Patients completed a questionnaire immediately posttreatment and were contacted for follow-up three to four weeks later. RESULTS: Patients reported less injection pain on the vibration-treated half of the face as compared to the control side (an average of 1.3 vs 2.4 on a five-point scale; P = .000). Overall, 86% of patients preferred to receive vibration with their next BTX-A treatment. There was no significant difference between first-time and repeat BTX-A patients in terms of preference for vibration. Five of 50 patients experienced transient side effects perceived to be associated with vibration, including tingling teeth, increased bruising, and headaches. Of the patients who did not request vibration with subsequent BTX-A injections, none cited decreased BTX-A efficacy as the reason for their preference. CONCLUSIONS: Vibration is a safe and effective means of reducing patient discomfort during BTX-A injections for cosmetic rhytid reduction and may have applications in other cosmetic procedures.

Effect of the thickness of polyurethane foams at the seat pan and the backrest on fore-and-aft in-line and vertical cross-axis seat transmissibility when sitting with various contact conditions of backrest during fore-and-aft vibration.

Ride comfort in vehicles can be affected by seat properties. While previous studies focused on the vertical whole-body vibration, this study was designed to understand the influence of the foam thickness at the seat pan and at the backrest on seat transmissibilities with fore-and-aft vibration. Twelve subjects sitting with or without a vertical backrest were exposed to random fore-and-aft vibration between 1 and 15 Hz with the magnitude of 0.5 ms-2 r.m.s.. It was found that there was no significant difference in the primary resonance frequencies in the fore-and-aft in-line and vertical cross-axis transmissibilities to the seat pan and to the backrest. The resonance frequency in the fore-and-aft in-line transmissibilities to the seat pan and the backrest decreased with increasing thickness of foam at the seat pan and the backrest. Altering the thickness of foam at the seat pan was more effective than changing that at the backrest.

Vibration transmissibility and apparent mass changes from vertical whole-body vibration exposure during stationary and propelled walking.

Whole-Body Vibration (WBV) is an occupational hazard affecting employees working with transportation, construction or heavy machinery. To minimize vibration-induced pathologies, ISO identified WBV exposure limits based on vibration transmissibility and apparent mass studies. The ISO guidelines do not account for variations in posture or movement. In our study, we measured the transmissibility and apparent mass at the mouth, lower back, and leg of participants during stationary and propelled walking. Stationary walking transmissibility was significantly higher at the lumbar spine and bite bar at 5 and 10 Hz compared to all higher frequencies while the distal tibia was lower at 5 Hz compared to 10 and 15 Hz. Propelled walking transmissibility was significantly higher at the bite bar and knee at 2 Hz than all higher frequencies. These results vary from previously published transmissibility values for static participants, showing that ISO standards should be adjusted for active workers.

Whole-body vibration exposure of roller compactor operators: characteristics and effect of waste rubber in damping the vibration.

Whole-body vibration (WBV) exposure of 12 roller compactor operators were measured to investigate the characteristics of WBV transmitted to the roller compactor operators and to assess their level of exposure to WBV. All of the subjects were in the seated position and vibration transmission at the interface between the operator and seat was measured. Operators showed a dominant WBV transmission in the vertical direction. Eight-hour exposure and the vibration dose value were used to assess operators' exposure to WBV. In total, 75% of operators had high or moderate potential health risk defined in the health guidance caution zone specified in Standard No. ISO 2631-1:1997. A rubber mat produced with waste rubber sludge was used to investigate the effect of damping the vibration transmitted to the operator. The rubber mat damped the WBV transmission in all three directions: 18% in vertical, 5% in lateral and 2% in fore-and-aft directions.

Vibration warning design for reaction time reduction under the environment of intelligent connected vehicles.

Scenario-based warnings for road safety can be provided in the environment of intelligent connected vehicles via Bluetooth earphones or smart wristbands; designing an optimal means of presentation to drivers is an important point of consideration. Vibration warnings have been widely studied owing to their unique benefits. This experimental study aims to identify suitable body parts for vibration warnings during driving. The independent variables were the vibration position (three levels of stimulus, i.e., wrist, shin, and upper jaw) and response effector (two levels, i.e., hand and foot). Experiment Tasks 1 and 2 measured participants' simple reaction time and choice reaction time, respectively, when providing vibration warnings in non-driving situations. The results demonstrate that the vibration on the upper jaw has the shortest simple reaction time and choice reaction time. The effect of stimulus-response consistency on choice reaction time was insignificant. Task 3 was similar to Task 2, with the exception of simulated driving. Compared to the result in Task 2, the choice reaction time in Task 3 was approximately 200 ms longer. Vibration of the upper jaw was reported to have the highest perceived intensity and preference. Based on the study results, the design implications for wearable vibration warnings of collision avoidance systems are presented.

Vibration Exposure and Transmissibility on Dentist's Anatomy: A Study of Micro Motors and Air-Turbines.

The use of dental hand pieces endanger dentists to vibration exposure as they are subjected to very high amplitude and vibration frequency. This paper has envisaged a comparative analysis of vibration amplitudes and transmissibility during idling and drilling with micro motor (MM) and air-turbine (AT) hand pieces. The study aims to identify the mean difference in vibration amplitudes during idling, explore different grasp forces while drilling with irrigant injection by the dentist, and various vibration transmission of these hand pieces. The study utilized 22 separate frequency resonances on two new and eight used MMs and two new and eight used ATs of different brands by observing the investigator at 16 different dentist clinics. The study adopted a descriptive research design with non-probability sampling techniques for selecting dentists and hand pieces. Statistical methods like Levene Test of Homogeneity, Welch ANOVA, independent t-test, and Games-Howell test were utilized with SPSS version 22 and MS-Excel. The results reveal that vibration amplitudes and vibration transmissibility when measured at position 2 are higher than in another position 1. Vibrations during idling for used MMs are more than AT hand pieces, and the used MM (MUD) and used AT (AUA) hand pieces differ due to their obsolescence and over-usage. Vibration amplitudes increase every time with the tightening of grasping of the hand piece. Vibration amplitudes for each grasping style of MM hand piece differ from all other grasping styles of AT hand pieces. Routine exposure to consistent vibrations has ill physical, mental, and psychological effects on dentists. The used hand pieces more hazardous as compared to newer ones. The study suggests that these hand pieces must be replaced periodically, sufficient to break between two operations, especially after every hand piece usage. Hence, the present research work can be further extended by creating some control groups among dentists and then studying the vibration amplitude exposure of various dental hand pieces and subsequent transmissibility to their body parts.

Effect of Hand Held Vibrating Tools on Nerve Conduction Study in Dental Residents.

BACKGROUND: Repetitive exposure to vibration has been shown to induce peripheral nerve dysfunction. Dentists are exposed to handheld vibrating tools in their daily clinical practice. Most of the studies are done in dentists who have symptoms such as paresthesia and numbness of the hands. Thus, we conducted the study to explore the effect of vibration on nerve conduction variables in apparently healthy asymptomatic dental residents. METHODS: This cross-sectional study enrolled 22 dental residents and age matched 22 medical residents as controls. Nerve conduction study was performed in median and ulnar nerves of both hands. RESULTS: Anthropometric and cardiorespiratory variables were comparable between the groups. There were no statistically significant differences between dental and medical residents in the sensory conduction variables (right median onset latency=2.05±0.27 vs 1.91±0.21, p value=0.07; right median amplitude =27.80±8.11 vs 29.55±7.04, p=0.45; right median conduction velocity = 59.54±7.05 vs 61.06±5.15, p= 0.42) and motor conduction variables (right median distal latency = 2.87±0.38 vs 2.87±0.38, p= 0.94; right median distal amplitude=10.71±2.19 vs 11.10±2.37, p=0.58; right median conduction velocity= 70.57±13.16 vs 68.53±7.73, p= 0.54) of median and ulnar nerves. Further, there was no significant difference between the dominant and non-dominant hands of dental residents. CONCLUSIONS: Hand held vibration tools did not alter nerve conduction study parameters of dental residents.

Vibrations produced during erbium:yttrium-aluminum-garnet laser irradiation.

The purpose of this study was to evaluate vibrations induced by an erbium:yttrium-aluminum-garnet (Er:YAG) laser in the non-contact mode and compare the vibrations with different pulse durations and energy parameters. The experiment was conducted on an extracted tooth built up in silicone impression material. The vibrations were measured by piezoelectric accelerometer for a super-short pulse (SSP), a very short pulse (VSP), and a short pulse (SP) at a frequency of 5 Hz for 1 s. For VSP and SP, the energy parameters tested were 200 mJ, 300 mJ, and 400 mJ. Measurements were performed 15 times for each individual irradiation energy level. The highest values of vibrations were measured for SP (0.160 +/- 0.04 m/s(2)), and the lowest were measured for VSP mode at the energy parameter 200 mJ (0.05 +/- 0.02 m/s(2)). There was a statistically significant (P < 0.01) difference between the various laser pulse modes (SSP, VSP, SP) at different energy parameters. At energy levels of 300 mJ and 400 mJ, the least amount of vibration during cavity preparations with the non-contact Er:YAG laser was produced by SSP mode.

Occupational changes in manual tactile sensibility of the dentist.

The aim of this study was to find out if the use of vibrating tools (drill, ultrasonic scaler ...) in dental practice has negative side effects on the manual tactile sensibility of the dentist. The sensory tests were performed on 50 subjects, who were allocated to three different groups according to their occupation and the length of their working experience. The first test group consisted of 20 dentists, who had more than 25 years of work experience. As a control group, 20 non-dentists were recruited to obtain a similar age distribution as the former test group. A final group consisted of 10 dentists with more than 1 year of work experience. All subjects underwent three tests: light-touch sensation test, two-point discrimination test and thermal sensation test on the thumb and the index finger of the working and non-working hands. Results showed significant differences, especially for the light-touch sensation test. The study showed more specifically that the tactile sensibility of the working hand of the dentists with more than 25 years of work experience was significantly diminished with respect to the non-working hand and to the working hand of non-dentists. In the test group of young dentists, there was no noticeable reduction of manual tactile sensibility.

Syndromes from segmental vibration and nerve entrapment: observations on case definitions for carpal tunnel syndrome.

OBJECTIVES: The purpose of this paper is to assess the overlap and stability of two different case definitions of carpal tunnel syndrome CTS. The analysis considers the association between different case definitions and objective tests (sensory nerve conduction velocities, SNCVs and vibrotactile perception thresholds, TTS), and the natural history of CTS, in the context of two vibration-exposed cohorts. METHODS: Clinical CTS cases were defined in two ways: (1) by the study physician using fixed criteria, and; (2) by questionnaire and hand diagram. SNCV in median and ulnar nerves was measured for digital, transpalmar, and transcarpal segments, and conventionally as from wrist-digit. Skin temperature was assessed as a point measurement by thermistor and regionally by thermal imaging. VTTs were determined at the bilateral fingertips of the third and fifth digits using a tactometer meeting the requirements of ISO 13091-1 (ISO 2001). The subjects were cohorts of shipyard workers in 2001 and 2004, and dental hygienists in 2002 and 2004. RESULTS: Results are reported for 214 shipyard workers in 2001 and 135 in 2004, and for 94 dental hygienists in 2002 and 66 in 2004. In 2001, 50% of shipyard workers were diagnosed as CTS cases by at least one of the diagnostic schemes, but only 20% were positive by both criteria. Among study physician diagnosed cases, 64% were CTS negative in 2001, 76% were negative in 2004, 13% were positive in both years, 22% became negative after being positive, and 11% became positive after being negative. For only study physician diagnosed CTS did VTTs differ between cases differ and non-cases in digit 3; there was no such distinction in digit 5. The dental hygienists had little CTS. CONCLUSION: Clinical case definitions of CTS based on diagrams and self-assessment, and clinical evaluation have limited overlap. Combining clinical criteria to create a more narrow or specific case definition of CTS does not appear to predict SNCV. The natural history of CTS suggests a protean disorder with considerable flux in case status over time.

Musculoskeletal symptoms in New Zealand dental therapists: prevalence and associated disability.

OBJECTIVE: To determine the prevalence and associations of disability due to musculoskeletal symptoms among practising New Zealand dental therapists. DESIGN: Cross-sectional survey of a random sample of dental therapists. METHOD: A postal questionnaire was sent out to all 483 registered dental therapists who were New Zealand Dental Therapists' Association (NZDTA) members in 2005. RESULTS: Usable responses were obtained from 323 therapists (98.8% female; mean age 49.2; age range 23 to 72). The most commonly reported problems in the previous year were neck (56.8%), lower back (54.0%) or shoulder symptoms (52.4%). Fewer of those working regularly with a dental assistant reported shoulder symptoms, but they had a higher prevalence of hip/thigh symptoms. Overall, the prevalence of disability ranged from approximately one in five (neck) to one in three (elbows or lower back) of those reporting symptoms. CONCLUSIONS: The prevalence of musculoskeletal symptoms among New Zealand dental therapists is high, with neck, shoulder and lower back symptoms being particularly common. The impact of those symptoms on sufferers' daily lives is considerable. Both therapists and employers need to examine ways of minimising musculoskeletal stress in order to minimise the incidence of new cases, and to support sufferers so that they are not lost prematurely from a workforce group which is already struggling to maintain sufficient practising numbers.

The Hand-Arm Vibration International Consortium (HAVIC): prospective studies on the relationship between power tool exposure and health effects.

OBJECTIVES: The Hand-Arm Vibration International Consortium (HAVIC) is a collaboration of investigators from Europe and North America studying health effects from hand-arm vibration (HAV). Features include prospective design, cross-cohort exposure, and health assessment methods. METHODS: Two new cohorts (dental hygienists and dental hygiene students), two existing cohorts (Finnish forest workers, and Swedish truck cab assemblers), and a previous population (US shipyard workers) are included. Instruments include surveys, quantitative medical tests, physical examination, and work simulation and data logging to assess exposure. New methods were developed for nerve conduction and data logging. RESULTS: Findings on the relationship between nerve conduction and skin temperature in HAV-exposed subjects resulted in a new approach to subject warming. CONCLUSIONS: Integrating established cohorts has advantages over de novo cohort construction. Complex laboratory tests can be successfully adapted for field use.

Mode superposition transient dynamic analysis for dental implants with stress-absorbing elements: a finite element analysis.

The purpose of this study was to analyze the dynamic behavior of a dental implant with a stress-absorbing element, using dynamic analysis. Two model types, stress-absorbing model with a resilient stress absorber made of polyoxymethylene and non-stress-absorbing model with rigid titanium, were employed. In both model types, the implant was 4.0 mm in diameter and 13.0 mm in length and placed in the mandibular first molar region. Shapes of the finite element implant and implant-bone were modeled using computer-aided design. All calculations for the dynamic analysis were performed using the finite element method. It was found that the stress-absorbing model had a lower natural frequency than the non-stress-absorbing model. In addition, the stress-absorbing model had a higher damping effect than the non-stress-absorbing model. It was concluded that mode superposition transient dynamic analysis is a useful technique for determining dynamic behavior around dental implants.