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PubMed1993

Cervical laminectomy and foraminotomy as surgical treatment of cervical spondylosis: a follow-up study with analysis of failures.

Ninety patients were followed after undergoing multilevel cervical laminectomy for cervical myeloradiculopathy secondary to cervical stenosis. Follow-up data was obtained by chart review and phone interview for all patients; 20% were examined at follow-up as well; 77% of patients were improved, 13% without change, and 10% worse at follow-up. No patients deteriorated in the immediate postoperative period. Greater than 50% of severely disabled patients had an excellent result, and 78% improved somewhat. It is concluded that cervical laminectomy is an effective procedure for treating patients with cervical spondylosis causing myeloradiculopathy. Reasons for failure of this procedure, although rarely identified on follow-up examination, are reviewed and briefly discussed.

Adult↗
PubMed2001

A randomized study of combined botulinum toxin type A and casting in the ambulant child with cerebral palsy using objective outcome measures.

It is recognized that objective gait analysis is of great value in planning a multilevel botulinum toxin type A (BTX-A) treatment. After BTX-A treatment, objective outcome measures can provide new and interesting information for each individual child with cerebral palsy (CP). Moreover, by studying group results, we may evaluate our treatment hypotheses. The present prospective study attempts to document the effect of integrated multilevel BTX-A treatment on objective gait parameters and to define the optimal strategy for the combined treatment of BTX-A with casting in children with cerebral palsy. Objective three-dimensional gait analysis (3DGA) data were collected pre- and 2 months post-treatment, in two randomized patient groups: a first group of 17 children treated with lower leg casting prior to BTX-A injections, and a second group of 17 patients who received casting immediately after injections. The present study demonstrates that improved gait can be achieved after a multilevel BTX-A treatment, combined with casting, using a set of 90 gait parameters. The most pronounced improvement was seen at the ankle joint. The results in the knee, hip and pelvis imply that multilevel treatment of the child with CP should start at an early age, in order to prevent development of muscle contractures. Slightly more pronounced benefits, mainly in the proximal joints, were seen for the children who were casted after injections as compared to the children who were casted before injections.

Biomechanical Phenomena↗
PubMed1998

Spinal deformity and instability after multilevel cervical laminectomy for spondylotic myelopathy.

STUDY DESIGN: A retrospective radiographic and medical record analysis of 58 patients. OBJECTIVES: To describe the incidence and consequences of cervical spinal deformity and instability after multilevel laminectomy in adult patients with myelopathy caused by cervical spondylosis and to determine the usefulness of preoperative dynamic roentgenographic films in the prevention of postoperative destabilization. SUMMARY OF BACKGROUND DATA: Extensive cervical laminectomy has been widely used in the treatment of progressive myelopathy secondary to stenotic conditions. Complications of this procedure, including spinal instability, accelerated spondylotic changes, postoperative spinal deformity, and constriction of the dura mater by formation of extradural scar tissue formation have been recognized. However, the frequency of these complications is probably overestimated, and their effect on clinical outcome remains unknown. METHODS: Fifty-eight patients older than 30 years who underwent a laminectomy at more than three levels without fusion for myelopathy secondary to cervical spondylosis were reviewed retrospectively with an average follow-up of 3.6 years. Functional results were evaluated according to the Japanese Orthopaedic Association's scoring system. Lateral views in neutral position, in flexion, and in extension of the preoperative cervical roentgenograms were analyzed in comparison with the last follow-up films to identify the changes in the curvature of the cervical column, in the range of motion of the neck, and in the intervertebral angular mobility and anteroposterior displacement of the vertebral bodies and finally to quantify the incidence of spinal instability. RESULTS: In 18 patients (31%), postoperative changes in the type of cervical spine curvature developed. Fifteen patients (25%) had destabilization at one or more levels. Deformities of the cervical spine occurring after surgery do not appear to cause symptoms or neurologic abnormalities. Destabilization required repeat surgery in 3 patients. All the levels appearing to be destabilized on the postoperative films were hypermobile on the preoperative dynamic radiographs. Preoperative olisthesis Without hypermobility is not a factor of risk in postoperative destabilization. CONCLUSIONS: The use of preoperative dynamic radiographs should improve the selection of patients undergoing laminectomy for the treatment of multilevel cervical cord compression. Dynamic radiographs may also reinforce the need for such adjunctive procedures as fusion and instrumentation, to prevent postoperative destabilization. Preoperative olisthesis with hypermobility in sagittal or horizontal planes must be fused and instrumented.

Adult↗
PubMed2005

Clinical and biologic factors related to oral implant failure: a 2-year follow-up study.

The purpose of this study is to evaluate urinary biomarkers of bone formation and resorption as predictive factors for oral implant failure, and to contribute to the knowledge of factors related to oral implant failure. A total of 93 patients between 18 and 85 years old, with an indication of oral implant, were eligible in this 2-year prospective, open, and nonrandomized study. Patients who had bone graft before implantation or presented with prosthetic difficulties (implant-to-crown ratio < 1, and/or unfavorable intermaxillary space) were excluded. All patients received either Frialit-2 (Friadent, Mannheim, Germany), cylinder, or screwed implants or IMZ Twin Plus (Friadent), cylinder implants, with FRIOS (Friadent) titanium coating. Serum osteocalcin, and urinary pyridinoline and deoxypyridinoline were measured, together with bone density at implant location. The primary endpoint (implant failure) was the implant removal (radiographic evidence of peri-implant bone loss and/or pockets). Factors related to implant failure were analyzed using multilevel logistic regression models to consider within-patient effects. Of the 93 patients included, 61% were female, and 16% were current smokers. A total of 266 oral implants were placed and analyzed, with a mean number of 3.1 implants by patient. Eleven and 15% of bone locations scored at D1 and D4, respectively, for the Misch bone density scoring. The majority of implants (72%) were placed more than 3 months after tooth extraction, using a Frialit-2 system in 73% of cases. The mean of osteocalcin was 17.3 (+/-9.4) ng/L; those of pyridinoline and deoxypyridinoline were 33.2 (+/-15.8) and 10.2 (+/-11.9) mmol per creatinine mmol, respectively. At one-year, 95.5% (95% confidence interval 92.5-97.5) of implants have not been removed. One year later, no further implant failed. In both univariate and multivariate analysis, osteocalcin, pyridinoline, and deoxypyridinoline were not significant predictive factors of oral implant failure. In multilevel logistic regression analysis, only tobacco consumption and single-tooth replacement or removable prosthesis were independent and significant predictive factors of oral implant failure. Serum osteocalcin, and urinary pyridinoline and deoxypyridinoline were not predictive of oral implant failure in this study. These results suggest that oral implants are more likely to fail for posterior single-tooth replacements and removable prostheses rather than for complete edentulous fixed bridgeworks or overdentures. Tobacco smoking has been identified as a major risk factor of oral implant failure.

Adolescent↗
PubMed2006

Long-term results over 10 years of anterior corpectomy and fusion for multilevel cervical myelopathy.

STUDY DESIGN: Retrospective long-term outcome analysis over more than 10 years. OBJECTIVES: To assess the long-term results of anterior corpectomy and fibular strut grafting over > or =4 disc levels for cervical myelopathy, and identify factors affecting the late deterioration in clinical outcome. SUMMARY OF BACKGROUND DATA: Few studies have shown long-term results after anterior corpectomy and strut grafting. There is little detailed information about the long-term effects of multilevel anterior corpectomy and fusion for cervical myelopathy. METHODS: A total of 31 cases were available for the 10-year follow-up after surgery (86% follow-up rate). Clinical results and radiographic measurements were obtained before surgery, 3 months after surgery, and at follow-up. RESULTS: There were 3 patients who had deterioration of the Japanese Orthopedic Association score of 1 point because of increasing hand numbness; 1 patient had adjacent disc degeneration, and 1 had pseudarthrosis without additional stenosis on magnetic resonance imaging. Adjacent disc degeneration did not affect the clinical results (P = 0.76). CONCLUSIONS: The long-term follow-up showed stable clinical results for more than 10 years, which depended on the thorough removal of the possible causes of the myelopathy, such as ossification of the posterior longitudinal ligament or a degenerated disc. Adjacent disc degeneration has minimal effects on the long-term clinical results after anterior long fusion.

Adult↗
PubMed2003

Pathologic N1 non-small cell lung cancer: correlation between pattern of lymphatic spread and prognosis.

OBJECTIVES: Patients with N1 non-small cell lung cancer represent a heterogeneous population with varying long-term survivals. Prognosis and pattern of recurrence seem to be particularly affected by the level of lymph node involvement. METHODS: From 1990 to 1995, a total of 1954 consecutive patients underwent surgical resection for non-small cell lung cancer: 549 (28%) had ipsilateral pulmonary lymph node metastases (N1). The hospital survivors (n = 535) were reviewed. Three levels of lymph node metastases (hilar, interlobar, and lobar) were identified according to the new Regional Lymph Node Classification for Lung Cancer Staging and differentiated from lymph node involvement on the basis of direct invasion. RESULTS: 1 The overall 5-year survival of patients with N1 disease was 40%. Survival was related in the univariate analysis to T classification, level-type of N1 involvement, number of involved nodes, multilevel involvement, Karnofsky Index, R status, and adjuvant therapy. In the multivariate analysis, only T classification and level-type of N1 involvement clearly showed statistical power (P =.000 and P =.001, respectively). The pattern of cancer relapse according to level-type of N1 involvement differed significantly: hilar N1 disease recurred at distant sites in 41% of patients and locoregionally in 12% of patients, whereas N1 disease by direct invasion occurred in 24% and 17% of patients, respectively (P =.030). CONCLUSIONS: Metastases to ipsilateral hilar, interlobar, or both, lymph nodes are associated with a poorer prognosis compared with metastases in intralobar lymph nodes or with lymph node involvement by means of direct invasion. Although surgical resection remains the mainstay of treatment, the high rate of tumor recurrence in both groups mandates further randomized studies with multimodality therapy approaches.

Adult↗
PubMed2000

Outdoor air concentrations of nitrogen dioxide and sulfur dioxide and prevalence of wheezing in school children.

We report analysis of data on outdoor air pollution and respiratory symptoms in children collected in the Czech part of the international Small Area Variations in Air pollution and Health (SAVIAH) Project, a methodological study designed to test the use of geographical information systems (GIS) in studies of environmental exposures and health at small area level. We collected the following data in two districts of Prague: (1) individual data on 3,680 children (response rate 88%) by questionnaires; (2) census-based socio-demographic data for small geographical units; (3) concentrations of nitrogen dioxide (NO2) and sulfur dioxide (SO2) measured by passive samplers in three 2-week surveys at 80 and 50 locations, respectively. We integrated all data into a geographical information system. Modeling of NO2 and SO2 allowed estimation of exposure to outdoor NO2 and SO2 at school and at home for each child. We examined the associations between air pollution and prevalence of wheezing or whistling in the chest in the last 12 months by logistic regression at individual level, weighted least squares regression at small area (ecological) level and multilevel modeling. The results varied by the level of analysis and method of exposure estimation. In multilevel analyses using individual data, odds ratios per 10 microg/m3 increase in concentrations were 1.16 (95% CI = 0.95-1.42) for NO2, and 1.08 (95% CI = 0.97-1.21) for SO2. While mapping of spatial distribution of NO2 and SO2 in the study area appeared valid, the interpolation from outdoor to personal exposures requires consideration.

Air Pollutants↗
PubMed2001

Multilevel performance probability: a meta-analytic integration of expectancy and self-efficacy.

A meta-analysis of one approach to measuring expectancy and self-efficacy was conducted. Although used for over 25 years, this measure has yet to be named or integrated across the two theoretical domains. We proposed to label this measure a Multilevel Performance Probability and conducted a meta-analysis. The search for empirical tests of expectancy and self-efficacy using this procedure yielded 16 studies with ratings which could be subjected to meta-analysis. Five studies with 8 tests were taken from expectancy studies and 11 studies with 47 tests from studies of self-efficacy. In total, the analyses involved 7,444 subjects across 55 tests of the Multilevel Performance Probability to performance relationship. Examination of the measure as a predictor of performance gave a mean r of .51 (p<.001) which is in the same direction and larger than values from other meta-analyses conducted within each of the two theoretical domains (rs of .21 and .38).

Humans↗
PubMed2004

Meta-regression detected associations between heterogeneous treatment effects and study-level, but not patient-level, factors.

OBJECTIVE: Two investigations evaluate Bayesian meta-regression for detecting treatment interactions. STUDY DESIGN AND SETTING: The first compares analyses of aggregate and individual patient data on 1,860 subjects from 11 trials testing angiotensin converting enzyme (ACE) inhibitors for nondiabetic kidney disease. The second explores meta-regression for detecting treatment interaction on 671 covariates, including the baseline risk, from 232 meta-analyses of binary outcomes compiled from the Cochrane Collaboration and the medical literature. RESULTS: In the ACE inhibitor study, treatment effects were homogeneous so meta-regression identified no interactions. Analysis of individual patient data using a multilevel model, however, discovered that treatment reduced glomerular filtration rate (GFR) more among patients with higher baseline proteinuria. The second investigation found meta-regression most effective for detecting treatment interactions with study-level factors in meta-analyses with >10 studies, heterogeneous treatment effects, or significant overall treatment effects. Under all three conditions, 46% of meta-regressions produced strong interactions (posterior probability >0.995) compared with 6% otherwise. Baseline risk was associated with the odds ratio in 6% of meta-analyses, half the rate found using maximum likelihood. CONCLUSION: Meta-regression can detect interactions of treatment with study-level factors when treatment effects are heterogeneous. Individual patient data are needed for patient-level factors and homogeneous effects.

Adult↗
PubMed2003

A discrete-time multilevel mixture model for event history data with long-term survivors, with an application to an analysis of contraceptive sterilization in Bangladesh.

Event history models typically assume that the entire population is at risk of experiencing the event of interest throughout the observation period. However, there will often be individuals, referred to as long-term survivors, who may be considered a priori to have a zero hazard throughout the study period. In this paper, a discrete-time mixture model is proposed in which the probability of long-term survivorship and the timing of event occurrence are modelled jointly. Another feature of event history data that often needs to be considered is that they may come from a population with a hierarchical structure. For example, individuals may be nested within geographical regions and individuals in the same region may have similar risks of experiencing the event of interest due to unobserved regional characteristics. Thus, the discrete-time mixture model is extended to allow for clustering in the likelihood and timing of an event within regions. The model is further extended to allow for unobserved individual heterogeneity in the hazard of event occurrence. The proposed model is applied in an analysis of contraceptive sterilization in Bangladesh. The results show that a woman's religion and education level affect her probability of choosing sterilization, but not when she gets sterilized. There is also evidence of community-level variation in sterilization timing, but not in the probability of sterilization.

Adolescent↗
PubMed1994

Multilevel time series models with applications to repeated measures data.

The analysis of repeated measures data can be conducted efficiently using a two-level random coefficients model. A standard assumption is that the within-individual (level 1) residuals are uncorrelated. In some cases, especially where measurements are made close together in time, this may not be reasonable and this additional correlation structure should also be modelled. A time series model for such data is proposed which consists of a standard multilevel model for repeated measures data augmented by an autocorrelation model for the level 1 residuals. First- and second-order autoregressive models are considered in detail, together with a seasonal component. Both discrete and continuous time are considered and it is shown how the autocorrelation parameters can themselves be structured in terms of further explanatory variables. The models are fitted to a data set consisting of repeated height measurements on children.

Adolescent↗
PubMed2000

Application of stratum-specific likelihood ratios in mental health screening.

BACKGROUND: The accuracy of a diagnostic procedure is commonly assessed by measuring sensitivity, specificity and positive and negative predictive values. Likelihood ratios provide an alternative method for describing these results, though they are typically reported only for dichotomized outcomes. However, likelihood ratios can also be applied to ordinal or continuous results. METHODS: The present paper discusses the application of stratum-specific likelihood ratios in a primary care setting using the General Health Questionnaire (GHQ-12) and the Symptom Check List 90-R (SCL-90-R). A randomly selected sample (n = 408) of adult outpatients from primary care offices in Düsseldorf was screened using the German versions of the GHQ-12 and the SCL-90-R. RESULTS: Logistic regression analysis indicated that stratum-specific or multilevel likelihood ratios preserve more information than a fixed threshold approach with a single cutoff point. For each test, five clinically useful strata with monotonically increasing stratum-specific likelihood ratios were selected. CONCLUSIONS: Stratum-specific likelihood ratios have enormous practical value, and they are becoming an important way of expressing and comparing the usefulness of different tests. Stratum-specific likelihood ratios reduce the spectrum bias that might arise if only two categories (cases and non-cases) are chosen. Additionally, multilevel likelihood ratios can be used as bedside information to obtain the post-test probability from the pre-test probability of the disorder.

Adult↗
PubMed1999

Quality of life after infrainguinal bypass grafting surgery. Dutch Bypass Oral Anticoagulants or Aspirin (BOA) Study Group.

PURPOSE: The purpose of this study was to compare quality of life in patients with and without various ischemic complications after infrainguinal bypass grafting surgery for occlusive vascular disease. METHODS: A sample of patients (n = 746) randomized in the Dutch BOA study (n = 2645), a multicenter trial that compared the effectiveness of oral anticoagulant therapy with aspirin in the prevention of infrainguinal bypass graft occlusions, was entered in this study. On the basis of clinical outcomes of the trial, the patients were grouped as follows: patients with patent grafts (n = 409); patients with nontreated graft occlusions, subdivided into an asymptomatic group (n = 32) and a symptomatic group (n = 65); patients with subsequent revascularizations (n = 194); patients with amputations (n = 36); and patients with failed secondary revascularizations followed by secondary amputation (n = 38). In case an outcome event occurred, the patients were regrouped accordingly. Every half year, the patients completed a Short Form-36 and a EuroQol questionnaire. A multilevel model was used for repeated measure analysis. RESULTS: The mean follow-up time was 21 months. The quality of life in patients with nontreated asymptomatic occlusions was roughly similar to the quality of life in patients with patent grafts. Patients with symptomatic nontreated occlusions had the lowest outcome with regard to pain as compared with the other groups. Furthermore, physical and social functioning was lower for these patients than for patients with patent grafts. Revascularizations, successful or not, negatively affected pain, social functioning, and physical and emotional role. After successful revascularization, some improvement was observed in pain, physical and social functioning, and general and mental health as compared with the group with nontreated symptomatic occlusions. Amputation deteriorated physical functioning strikingly, especially after failed secondary revascularization. These patients also had the lowest scores of all the groups in the dimensions of social functioning, physical and emotional role, and mental health. EuroQol score showed deterioration of quality of life after all events, except for asymptomatic occlusions. The same patterns emerged if we stratified our analysis according to the indication for the initial operation: claudication or limb salvage. Quality of life was constant over time in all the groups in the observed period. CONCLUSION: Quality of life in patients with asymptomatic occluded grafts is similar to quality of life in patients with patent grafts. Revascularization of symptomatic occluded grafts improves quality of life to a certain extent. Amputation, in particular after failed secondary revascularization, seemed to be the lowest possible outcome. The results of the Short Form-36 and EuroQol measurements were in line with the clinical expectations. The association of disease severity with scores on the instruments supports the construct validity of these outcome measures for an objective assessment of quality of life in controlled studies.

Aged↗
PubMed2004

Short-term outcome of multilevel surgical intervention in spastic diplegic cerebral palsy compared with the natural history.

Outcome in 24 ambulant children with spastic diplegic cerebral palsy, in whom multilevel surgical intervention was recommended following gait analysis, is reviewed. Twelve children had surgical intervention (treatment group; eight males, four females; mean age 9 years 10 months, SD 3 years 4 months) while the other 12 did not (control group; five males, seven females; mean age 10 years 1 month, SD 2 years 11 months). All children had interval three-dimensional gait analyses (mean time between analyses: control group, 14.1 months; treatment group, 17.9 months). At follow-up the control group (mean age 11 years 9 months) showed a significant increase in minimum hip and knee flexion in stance which was not related to age, the interval between analyses, changes in the passive joint range of motion, nor changes in anthropometric measurements. The treatment group (mean age at follow-up 11 years 3 months) showed a significant improvement in minimum knee flexion and in ankle dorsiflexion in stance. Parents of nine children said their child's walking distance had increased following intervention. Of five children using posterior walkers preoperatively, two continued to use them postoperatively; two were using crutches or sticks and the remaining child walked independently. Two children who walked independently preoperatively used sticks postoperatively for community ambulation. The deterioration seen in the kinematics of the control group suggests that previous outcome studies comparing postoperative gait with preoperative gait have underestimated the immediate effects of surgery. It also raises concerns about the long-term effects of surgical intervention.

Ankle↗
PubMed2006

Active and passive dispersal of an invading land snail in Mediterranean France.

1. Land snail dispersal abilities are considered poor; however, the current invasion of the French Mediterranean region by Xeropicta derbentina (Krynicki 1836), as well as the past invasions of this region by several other species, seems to contradict this view. 2. Using a multilevel approach, from individual experimentation to landscape analysis, the dispersal abilities and mechanisms allowing the passive dispersal of X. derbentina are studied. 3. The colonization of Provence occurred by stratified diffusion, where short-range active dispersal occurs side by side with long-range passive dispersal. 4. Active dispersal is not as limited as previously thought. In the field, the capture-mark-recapture method recorded a maximum distance covered of 42 m in 6 months within a radius of 38 m from the original release point. 5. Temperature and humidity, and therefore the time of year, influence the main type of dispersal. Dispersal is active during wet periods and essentially passive in dry and hot months. 6. Heat avoidance behaviour is one of the mechanisms allowing passive dispersal. 7. Passive dispersal via human activities is the main determinant of X. derbentina distribution within the landscape. In comparison to other species, X. derbentina is found more often in the vicinity of a communication route. 8. These results show that land snails can cover large distances in a lifetime. The potential for active and passive dispersal described in this paper enables X. derbentina to be a successful invasive species and explains the rapid spread and current distribution of this species.

Animals↗
PubMed2004

Neighbourhood deprivation and incidence of coronary heart disease: a multilevel study of 2.6 million women and men in Sweden.

STUDY OBJECTIVE: To examine whether neighbourhood deprivation predicts incidence rates of coronary heart disease, beyond age and individual income. DESIGN: Follow up study from 31 December 1995 to 31 December 1999. Women and men were analysed separately with respect to incidence rates of coronary heart disease. Multilevel logistic regression was used in the analysis with individual level characteristics (age, individual income) at the first level and level of neighbourhood deprivation at the second level. Neighbourhood deprivation was measured at small area market statistics level by the use of Care Need Index. SETTING: Sweden. PARTICIPANTS: All women and men aged 40-64 in the Swedish population, in total 2.6 million people. MAIN RESULTS: There was a strong relation between level of neighbourhood deprivation and incidence rates of coronary heart disease for both women and men. In the full model, which took account of individual income, the risk of developing coronary heart disease was 87% higher for women and 42% higher for men in the most deprived neighbourhoods than in the most affluent neighbourhoods. For both women and men the variance at neighbourhood level was over twice the standard error, indicating significant differences in coronary heart disease risk between neighbourhoods. CONCLUSIONS: High levels of neighbourhood deprivation independently predict coronary heart disease for both women and men. Both individual and neighbourhood level approaches are important in health care policies.

Adult↗
PubMed2005

Prosocial behavior: multilevel perspectives.

Current research on prosocial behavior covers a broad and diverse range of phenomena. We argue that this large research literature can be best organized and understood from a multilevel perspective. We identify three levels of analysis of prosocial behavior: (a) the "meso" level--the study of helper-recipient dyads in the context of a specific situation; (b) the micro level--the study of the origins of prosocial tendencies and the sources of variation in these tendencies; and (c) the macro level--the study of prosocial actions that occur within the context of groups and large organizations. We present research at each level and discuss similarities and differences across levels. Finally, we consider ways in which theory and research at these three levels of analysis might be combined in future intra- and interdisciplinary research on prosocial behavior.

Altruism↗
PubMed1997

Effects of food texture and sample thickness on mandibular movement and hardness assessment during biting in man.

This study was designed to investigate the relationship among jaw movements, physical characteristics of food, and sensory perception of hardness in man. Vertical movements of the mandible were recorded with an infrared tracking device in humans during biting on two test foods, carrot and cheese. Samples of standard length (2 cm) and width (2 cm) were prepared in three different thicknesses (0.5, 1.0, and 1.5 cm). Nine subjects were asked to perform two types of bite with their incisor teeth. In the first, they cut through the food, then stopped and spat out the pieces (bite alone); in the second, biting was followed by mastication and swallowing (bite+chew). The 12 conditions (thickness x3, food x2, and bite x2) were presented in a random order within each block, and blocks were repeated five times (60 trials per subject). Subjects also estimated the hardness of the samples twice for each condition on visual analogue scales (VAS) 100 mm long. The duration, vertical amplitude, and maximum vertical velocity of the mandible during biting were calculated by computer for the three phases of the movements (opening, and fast and slow closing). Multilevel statistical models were used for data analysis. The estimated hardness scores associated with the first bite of thin carrot (59.0 VAS units) was significantly greater than for cheese (16.8 VAS units). The type of bite had no significant effect on these scores, but the estimate of hardness was significantly greater for the thickest sample (+13.3 VAS units). Food type had its strongest effect on the slow-closing phase. In particular, the peak velocity that followed the fracturing of the food sample was much greater for carrot than for cheese (thin, 34.1 mm.s-1 vs. 26.6 mm.s-1), and the difference between foods increased with thickness. The amplitude of opening was significantly greater for the thickest sample than for the other two. There were no significant relationships between VAS scores and the movement parameters. These results suggest that, when humans bite food: (1) changing the thickness of food has a greater effect on movement parameters than changing from soft to hard food, (2) the parameters of biting change little if biting is followed by mastication, (3) hardness perception is dependent on the thickness of food, (4) hardness perception is not different when food is removed from the mouth than when it is chewed and swallowed, and (5) there is no relationship between any of the parameters of movement that change with food type and the perceived hardness of food.

Adult↗