RECOMMENDATIONS FOR USE AND SCORING OF ORAL HEALTH IMPACT PROFILE VERSIONS.

BACKGROUND: OHIP's original seven-domain structure does not fit empirical data, but a psychometrically sound and clinically more plausible structure with the four OHRQoL dimensions Oral Function, Orofacial Pain, Orofacial Appearance, and Psychosocial Impact has emerged. Consequently, use and scoring of available OHIP versions need to be revisited. AIM: We assessed how well the overall construct OHRQoL and its four dimensions were measured with several OHIP versions (20, 19, 14, and 5 items) to derive recommendations which instruments should be used and how to score them. METHODS: Data came from the "Dimensions of OHRQoL Project" and used the project's learning sample (5,173 prosthodontic patients and general population subjects with 49-item OHIP data). We computed correlations among OHIP versions' summary scores. Correlations between OHRQoL dimensions, on one hand, and OHIP versions' domain scores or OHIP-5's items, on the other hand, were also computed. OHIP use and scoring recommendations were derived for psychometrically solid but also practical OHRQoL assessment. RESULTS: Summary scores of 5-, 14-, 19- and 49-item versions correlated highly (r = 0.91-0.98), suggesting similar OHRQoL construct measurement across versions. The OHRQoL dimensions Oral Function, Orofacial Pain, Orofacial Appearance, and Psychosocial Impact were best measured by the OHIP domain scores for Physical Disability, Physical Pain, Psychological Discomfort, and Handicap, respectively. CONCLUSION: Recommendations were derived which OHIP should be preferably used and how OHIP versions should be scored to capture the overall construct and the dimensions of OHRQoL. Psychometrically solid and practical OHRQoL assessment in all settings across all oral health conditions can be achieved with the 5-item OHIP.

Effect of dietary counselling with prosthetic restoration on fruit and vegetable intake in partially dentate patients: A prospective study.

The aim of this study was to investigate the effects of a counselling-based dietary intervention on nutritional status in partially dentate patients receiving removable partial dentures (RPDs). Thirty-eight patients [mean age (standard deviation): 73.2 (7.7) years] who were scheduled to receive RPDs at a dental hospital and were currently eating <350 g of vegetables per day were included in the study. A dentist provided basic dietary counselling aimed at increasing dietary fruit and vegetable intake and improving dietary habits. Patients received dietary counselling directly after treatment with new RPDs and at 1 week after a 1-month follow-up evaluation (T1). Food intake was assessed via a validated brief-type self-administered diet history questionnaire, and carotenoids and vitamin C in 6-hour fasting blood samples were measured before RPD administration, and at 1 (T1) and 3 months (T3) thereafter. Vegetable but not the fruit intake increased significantly at T1 and T3 compared to before treatment. Alpha carotene significantly increased at T3 while ß significantly increased both at T1 and T3 compared to before treatment (P < .05). The number of occlusal units on natural teeth was significantly positively associated with increased vegetable and ß-carotene intake (P < .05). Serum carotenoids and vitamin C levels measured with 6-hour fasting blood samples remained constant. These results suggest that basic dietary counselling may improve vegetable intake in partially dentate patients receiving RPD treatment, but did not lead to haematological changes. The presence of occlusion of remaining posterior teeth may be critical for improving vegetable intake.

Adaptive change in chewing-related brain activity while wearing a palatal plate: an functional magnetic resonance imaging study.

Prosthodontic treatment success depends on patients' ability to adapt to an altered oral environment containing removable prostheses. We investigated adaptive chewing-related brain activity changes in response to a new oral environment. Twenty-eight fully dentate subjects (mean age: 28·6 years) wore experimental denture-base palatal plates (3 mm thick), for 7 days. We measured food mixing ability and cycle time, and assessed brain activity by functional magnetic resonance imaging during chewing at pre-insertion (Day 0), and immediately (Day 1), 3 days (Day 3) and 7 days (Day 7) after insertion. Food mixing ability significantly decreased and cycle time increased on Day 1 as compared to Day 0 (P < 0·001) and tended to recover to Day 0 level by Day 7. Brain activation in the right face primary sensorimotor cortex and putamen significantly decreased on Day 1 as compared to Day 0 (P < 0·001) and recovered to Day 0 level by Day 7. Brain activation in the left face primary sensorimotor cortex, putamen, anterior cingulate gyrus (ACG) and right posterior medial frontal cortex (pMFC) significantly decreased on Day 1 as compared to Day 0 (P < 0·001) and did not recover by Day 7. Thus, oral environment changes involving palate covering affected chewing and induced adaptive brain activity changes in the face primary sensorimotor cortex and putamen, possibly associated with motor learning. As ACG and pMFC activity remained unrecovered by 7 days after plate insertion, automatisation of chewing while wearing a palatal plate may require longer adaptation periods.

Shortened dental arch and prosthetic effect on oral health-related quality of life: a systematic review and meta-analysis.

This systematic review aimed to compare oral health-related quality of life (OHRQoL) between two tooth replacement strategies - the shortened dental arch (SDA) concept and conventional treatment with removable partial dental prosthesis (RPDP) or implant-supported fixed partial dental prosthesis (IFPDP) - for distal extension of edentulous space in the posterior area. We retrieved eligible randomised controlled trials (RCTs) and non-RCTs published between 1980 and November 2016 retrieved from MEDLINE and the Cochrane Central Register of Controlled Trials. The primary outcome was OHRQoL evaluated using validated questionnaires. Two reviewers independently screened and selected the articles, evaluated the risk of bias and determined the standardised weighted mean difference (SWMD) in OHRQoL scores between the two strategies using a random effects model. Two RCTs and one non-RCT involving 516 participants were included in this review. All studies employed the oral health impact profile (OHIP) for evaluation of OHRQoL. There was no statistically significant difference in OHIP summary scores between SDA and RPDP at 6 (SWMD = 0·24) or 12 (SWMD = 0·40) months post-treatment. Only one non-RCT had reported higher OHRQoL with IFPDP than with SDA; however, because of the small sample size, there was no significant difference in OHIP summary scores between the two strategies at 6 (SWMD = -0·59) or 12 (SWMD = -0·67) months post-treatment. In terms of OHRQoL in partially dentate patients, the SDA concept appears to be as feasible as RPDP restoration. Further clinical trials are required to clarify the effect of IFPDP restoration on OHRQoL.

Oral health-related quality of life in patients with non-metal clasp dentures: a randomised cross-over trial.

We investigated the efficacy of non-metal clasp dentures (NMCDs) with regard to the oral health-related quality of life (OHRQoL) and compare the findings with those for conventional metal clasp-retained dentures (MCDs). This single-centre, randomised controlled, two-phase, open label, cross-over trial included 28 partially dentate individuals. The patients were randomised to receive MCDs followed by NMCDs, or the opposite sequence (n = 14 in each group); each denture was worn for 3 months. OHRQoL was evaluated using the Oral Health Impact Profile-Japanese version (OHIP-J) at entry (T-entry; before treatment with the first denture) and at 3 months after treatment with each denture (T3). An examiner evaluated denture stability, oral appearance and surface roughness before denture delivery (T0) and at T3 and denture hygiene at T3. A total of 24 patients completed the trial. There were no complications related to the dentures, abutment teeth or denture-bearing mucosa during the follow-up periods for both dentures. The mean OHIP summary score was lower for NMCDs than for MCDs, and the difference (9 points) was greater than the minimal important difference (6 points), indicating the difference was clinically relevant. The effect size was medium (0·70). Statistical analyses with linear mixed models found a significant effect of the denture type on the OHIP summary score and scores for the Oro-facial appearance, Oro-facial pain and Psychological impact domains (NMCD < MCD; P < 0·05). The results of our study suggest that NMCDs allow for better OHRQoL compared with MCDs.

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.

Effect of prosthetic restoration on masticatory function in patients with shortened dental arches: a multicentre study.

The aim of this multicentre study was to investigate the effect of prosthetic restoration for missing posterior teeth on mastication in patients with shortened dental arches (SDAs). Partially dentate patients who had an intact teeth in anterior region and missed distal molar(s) (2-12 missing occlusal units) classified as Kennedy Class I or Class II were recruited from seven university-based dental hospitals in Japan. Of the 125 subjects who underwent baseline (pre-treatment) and follow-up/post-treatment evaluation, 53 chose no replacement of missing teeth and 72 chose treatment with removable partial dentures (n = 53) or implant-supported fixed partial dentures (n = 19). Objective masticatory performance (MP) was evaluated using a gummy jelly test. Perception of chewing ability (CA) was rated using a food intake questionnaire. In the no-treatment group, mean MP and CA scores at baseline were similar to those at follow-up evaluation (P > 0·05). In the treatment group, mean MP after treatment was significantly greater than the pre-treatment mean MP (P < 0·05). However, the mean perceived CA in the treatment groups was similar at pre- and post-treatment (P > 0·05). In a subgroup analysis of subjects in the treatment group, subjects with lower pre-treatment CA showed a significant CA increase after treatment (P = 0·004), but those with higher pre-treatment CA showed a significant decrease in CA (P = 0·001). These results suggest that prosthetic restoration for SDAs may benefit objective masticatory performance in patients needing replacement of missing posterior teeth, but the benefit in subjective chewing ability seems to be limited in subjects with perceived impairment in chewing ability before treatment.

Effect of prosthetic restoration on oral health-related quality of life in patients with shortened dental arches: a multicentre study.

The aim of this multicentre prospective study was to investigate the effect of prosthetic restoration for missing posterior teeth in patients with shortened dental arches (SDAs). SDA patients with 2-12 missing occlusal units (a pair of occluding premolars corresponds to one unit, and a pair of occluding molars corresponds to two units) were consecutively recruited from seven university-based dental hospitals in Japan. Patients chose no replacement of missing teeth or prosthetic treatment with removable partial dentures (RPDs) or implant-supported fixed partial dentures (IFPDs). Oral health-related quality of life (OHRQoL) was measured using the oral health impact profile (Japanese version - OHIP-J) at baseline and follow-up/post-treatment evaluation. Of the 169 subjects who completed baseline evaluation, 125 subjects (mean age; 63.0 years) received follow-up/post-treatment evaluation. No-treatment was chosen by 42% (53/125) of the subjects, and 58% (72/125) chose treatment with a RPD (n = 53) or an IFPD (n = 19). In the no-treatment (NT) group, the mean OHIP summary score at baseline was similar to that at follow-up evaluation (P = 0.69). In the treatment (TRT) group, the mean OHIP summary score decreased significantly after the RPD treatment (P = 0.002), and it tended to decrease, though not statistically significant (P = 0.18), after the IFPD treatment. The restoration of one occlusal unit was associated with a 1.2-point decrease in OHIP summary score (P = 0.034). These results suggest that the replacement of missing posterior teeth with RPDs or IFPDs improved OHRQoL. Prosthetic restoration for SDAs may benefit OHRQoL in patients needing replacement of missing posterior teeth.

Influence of intra-oral sensory impairment by anaesthesia on food comminution and mixing in dentate subjects.

Sensory input from sensory receptors regarding food morsels can affect jaw motor behaviours during mastication. The aim was to clarify the effects of intra-oral sensory input on the food-comminuting and food-mixing capacities of dentate subjects. Eleven dentate subjects without sensory dysfunction in their oro-facial region participated in this study. Local anaesthesia was achieved on the periodontal structures and on the oral mucosa of the subjects' preferred chewing side by injecting a lidocaine solution with adrenalin. At baseline (control) and after anaesthesia, data on the subjects' food-comminuting and food-mixing capacities were gathered. The food-comminuting capacity was quantified by measuring the degree of pulverisation of peanuts (objective hardness; 45.3 [Newton, N]) after a prescribed 20 chewing strokes. The food-mixing capacity was measured as the degree of immixture of a two-coloured paraffin wax cube after 10 chewing strokes. Wax cubes of three different hardness levels were used (soft, medium and hard: 20.3, 32.6 and 75.5 [N], respectively) and were chewed in random order. After anaesthesia, the subjects' food-comminuting capacity significantly decreased (P < 0.001), as did the food-mixing capacity for each hardness level of the wax cubes (P < 0.01). A significant correlation was observed between the objective hardness values and the anaesthesia effects for the food-mixing capacity (P < 0.05), indicating that after anaesthesia, deterioration of the mixing capacity increased as the hardness increased. In conclusion, intra-oral sensory input can affect both food-comminuting and food-mixing capacities.

Influence of posterior dental arch length on brain activity during chewing in patients with mandibular distal extension removable partial dentures.

It is well known that shortened dental arch decreases masticatory function. However, its potential to change brain activity during mastication is unknown. The present study investigates the effect of a shortened posterior dental arch with mandibular removable partial dentures (RPDs) on brain activity during gum chewing. Eleven subjects with missing mandibular molars (mean age, 66.1 years) on both sides received experimental RPDs with interchangeable artificial molars in a crossover trial design. Brain activity during gum chewing with RPDs containing (full dental arch) and lacking artificial molars (shortened dental arch) was measured using functional magnetic resonance imaging. Additionally, masticatory function was evaluated for each dental arch type. Food comminuting and mixing ability and the perceived chewing ability were significantly lower in subjects with a shortened dental arch than those with a full dental arch (P < 0.05). Brain activation during gum chewing with the full dental arch occurred in the middle frontal gyrus, primary sensorimotor cortex extending to the pre-central gyrus, supplementary motor area, putamen, insula and cerebellum. However, middle frontal gyrus activation was not observed during gum chewing with the shortened dental arch. These results suggest that shortened dental arch affects human brain activity in the middle frontal gyrus during gum chewing, and the decreased middle frontal gyrus activation may be associated with decreased masticatory function.

Association between occlusal curvature and food comminution and mixing in human young adults with permanent dentitions.

OBJECTIVE: Occlusal curvatures in human adult dentition such as the curve of Spee, curve of Wilson and Monsons's sphere provide clinical guidance for prosthetic rehabilitation and orthodontic treatment. However, association between occlusal curvature and masticatory function is not known. The aim of this study was to investigate the association between occlusal curvature and food comminuting and food mixing ability in human young adults with permanent dentitions. DESIGN: Fifty young adults with complete dentitions (mean age, 25.0 years) participated in the study. Occlusal curvature was determined by a three-dimensional analysis of the mandibular arch according to the Broadrick flag method. Food comminuting ability was assessed using a masticatory performance test with peanuts as test food and it was scored as median particle size. Food mixing ability was assessed using a mixing ability test with a two-coloured wax cube and it was scored as mixing ability index. RESULTS: A linear regression analysis identified the sphere radius of occlusal curvature as significant predictor for both median particle size and mixing ability index after controlling for maximum bite force (P<0.001). These results indicated that subjects with a flatter curvature (larger sphere) in the mandibular arch showed better food comminuting and mixing ability. Coefficient of determination (R(2)) of occlusal curvature related to median particle size and mixing ability index was comparable to that of maximum bite force. CONCLUSION: Occlusal curvature seems to be associated with food comminuting and mixing ability in human young adults with permanent dentitions.

A structural equation model to investigate the impact of missing occlusal units on objective masticatory function in patients with shortened dental arches.

The aim of this study was to investigate the impact of missing occlusal units (MOUs) on objective masticatory function with respect to food comminuting and mixing ability. Sixty partially dentate patients (mean age, 64·1 years) with shortened dental arches participated in the study. Food comminuting ability was assessed using a masticatory performance test with peanuts as a test food. Food mixing ability was assessed using a mixing ability test with a two-coloured wax cube. Maximum bite force (MBF) was measured using a pressure-sensitive film as a mediator for food comminuting and mixing ability. A structural equation model was constructed based on a hypothesis that MOUs would be associated with reduced MBF and impairment of food comminuting and mixing ability. Structural equation modelling analysis found significant direct effects of MOU on median particle size and mixing ability index (MAI) (P < 0·001). In addition, MOU had significant indirect effects on median particle size and MAI with MBF as a mediator (P < 0·05). These results suggest that decrease in occlusal platform area and reduced MBF because of MOUs are associated with the impairment of food comminution and mixing in patients with shortened dental arches.

Factors related to prosthetic restoration in patients with shortened dental arches: a multicentre study.

The aim of this study was to identify the factors related to prosthetic restoration in patients with shortened dental arches (SDA). SDA patients with 2-12 missing occlusal units were consecutively enrolled from seven university-based dental hospitals in Japan. Of the 145 subjects (mean age; 63·4 years), 41% chose no treatment and 59% sought to replace their edentulous spaces with removable partial dentures or implant-supported fixed partial dentures. Restoration decisions were related to tooth loss patterns. Only 3% of subjects missing just second molar(s) sought to receive prosthetic treatment, while the percentage increased to 58% in subjects who were missing first and second molars and 93% in subjects missing premolar(s). Logistic regression analyses found that young age, increased number of missing occlusal units, asymmetric arch and presence of chewing complaint were significant predictors for prosthetic restoration (P<0·05). Increased number of missing occlusal units and asymmetric arch were significant predictors for the presence of chewing complaint (P<0·05). These results suggest that perceived impairment of chewing ability owing to missing occlusal units is a critical factor for prosthetic restoration in SDA patients.

A structural equation model relating objective and subjective masticatory function and oral health-related quality of life in patients with removable partial dentures.

The aim of this study was to investigate the relationships between objective masticatory function with respect to masticatory performance and food mixing ability, patients' perception of chewing ability and oral health-related quality of life (OHRQoL). Partially dentate patients with removable partial dentures (n = 131, mean age 67·1 year) participated in the study. Four tests were performed to evaluate objective and subjective masticatory function and OHRQoL. Masticatory performance and food mixing ability were assessed using peanuts or a two-coloured wax cube as test items. Patients' perception of chewing ability was rated using a food intake questionnaire. OHRQoL was measured using the Japanese version of the oral health impact profile. A structural equation model was constructed based on hypothesis in which objective masticatory function would be related to OHRQoL via perceived chewing ability as a mediator. Structural equation modelling analysis found a statistically significant medium effect of perceived chewing ability on OHRQoL and statistically significant medium or small effects of masticatory performance on perceived chewing ability and OHRQoL (P < 0·05); however, the effect of food mixing ability on perceived chewing ability or OHRQoL was not statistically significant (P > 0·05). A fit index indicated that the model fitted well to the data (Goodness-of-fit index = 0·99). These results suggest that perceived chewing ability is a critical factor for OHRQoL and that masticatory performance rather than food mixing ability is important for perceived chewing ability and OHRQoL in patients with removable partial dentures.

Microbiological risk for periodontitis of abutment teeth in patients with removable partial dentures.

Tannerella forsythia, Porphyromonas gingivalis and Treponema denticola are identified as the red complex which exists in high proportions in periodontally diseased patients. The aim of this study was to assess the microbiological risk for periodontitis of abutment teeth in subjects wearing removable partial dentures (RPDs) by measuring the red complex using BANA-ZymeTM test. Thirty-eight subjects (mean age: 62.2 years) with Kennedy Class II partially edentulous arch participated in this study. The red complex and clinical parameters, such as plaque index, gingival index, probing depth and tooth mobility were recorded at abutment teeth in contact with the direct retainer of unilaterally designed RPDs and the corresponding non-abutment teeth on the opposite side. Mean scores for the red complex, plaque index, gingival index and tooth mobility of the abutment teeth were significantly greater than those of the non-abutment teeth (P < 0.01). No significant mean difference in pocket depth was found between the abutment and non-abutment teeth. Logistic regression analysis revealed that abutment teeth, high scores of plaque index and a maintenance interval longer than 6 months were significant predictors for positive red complex scores (P < 0.05). These results suggest that the microbiological risk for periodontitis of abutment teeth is greater than that for non-abutment teeth in RPD wearers.

Comparisons between a mixing ability test and masticatory performance tests using a brittle or an elastic test food.

A variety of chewing tests and test items have been utilized to evaluate masticatory function. The purpose of this study was to compare a mixing ability test with masticatory performance tests using peanuts or gummy jelly as test foods. Thirty-two completely dentate subjects (Dentate group, mean age: 25.1 years) and 40 removable partial denture wearers (RPD group, mean age: 65.5 years) participated in this study. The subjects were asked to chew a two-coloured paraffin wax cube as a test item for 10 strokes. Mixing Ability Index (MAI) was determined from the colour mixture and shape of the chewed cube. Subjects were asked to chew 3 g portions of peanuts and a piece of gummy jelly for 20 strokes, respectively. Median particle size of chewed peanuts was determined using a multiple-sieving method. Concentration of dissolved glucose from the surface of the chewed gummy jelly was measured using a blood glucose meter. Pearson's correlation coefficient was used to test the relationships between the MAI, median particle size and the concentration of dissolved glucose. Mixing Ability Index was significantly related to median particle size (Dentate group: r = -0.56, P < 0.001, RPD group: r = -0.70, P < 0.001), but not significantly related to glucose concentration (Dentate group: r = 0.12, RPD group: r = 0.21, P > 0.05). It seems that ability of mixing the bolus is more strongly related to the ability of comminuting brittle food than elastic food.

Association between food mixing ability and electromyographic activity of jaw-closing muscles during chewing of a wax cube.

The purpose of this study was to clarify association between food mixing ability and activity of jaw-closing muscles during chewing of a wax cube. Twenty subjects with complete dentitions (mean age 24.1 years) were directed to chew a two-coloured paraffin wax cube for 10 strokes on preferred chewing side. Surface electromyograms (EMG) were recorded from the right and left masseter and anterior temporalis muscles during chewing of the wax cube. Maximum voltage, duration and muscle work for burst of each chewing cycle were measured on integrated EMG in each muscle. Food mixing ability was estimated as mixing ability index determined from the colour mixture and shape of the chewed wax cube. Some EMG parameters of all muscles except for masseter muscle on non-chewing side showed significant positive correlations with the mixing ability index (r = 0.45-0.56, P < 0.05). However, most of the EMG parameters correlated with one another. As a result, only muscle work of masseter muscle on the chewing side was identified as a significant predictor accounting for 28% interindividual variation in the mixing ability index (P < 0.01). These results suggest that activity of jaw-closing muscles during chewing the wax cube seems to be weakly related to food mixing ability.

Comparison of food mixing ability among mandibulectomy patients.

Many papers have been published on surgical mandibulectomy and reconstruction. However, only a few reports refer to masticatory function after prosthodontic treatment in mandibulectomy patients. The aim of this study was to investigate the masticatory function of mandibulectomy patients. Twenty-three subjects (10 males and 13 females, with an average age of 63 years) participated in this study: 11 subjects who had undergone unilateral marginal mandibulectomy, six subjects with unilateral segmental mandibulectomy with reconstruction and six subjects with hemimandibulectomy without reconstruction. Mixing Ability Index (MAI) was used to measure masticatory function on the non-defect side and on the defect side with a prosthesis installed. Comparisons were carried out among the marginal, segmental and hemimandibular groups and between the non-defect side and the defect side. Consequently, our study indicates these results. On the non-defect side, a significant difference was found between the marginal and the segmental groups, and between the marginal and the hemimandibular groups. In the marginal and the segmental groups, a significant difference was found between the non-defect and the defect sides. In conclusion, our study suggests that MAI is an adequate tool to study the masticatory function in mandibulectomy patients, the masticatory function of the mandibulectomy patients is more impaired than that of the ordinary removable partial denture patients, and that surgical intervention affects the masticatory function on not only the defect side but also the non-defect side in mandibulectomy patients.

Association between food mixing ability and mandibular movements during chewing of a wax cube.

The purpose of this study was to clarify whether masticatory movements during chewing of a wax cube associate with food mixing ability. Twenty-six dentate subjects (mean age 25.3 years) were directed to chew a two-coloured paraffin wax cube for 10 strokes on preferred chewing side. Mixing Ability Index (MAI) was determined from the colour mixture and shape of the chewed wax cube. MAI was employed as an estimate of food mixing ability. Mandibular movements during chewing of the wax cube were recorded using a six-degrees-of freedom jaw movements recording system, and motion of a lower incisal point of the mandible was computed. Twelve parameters of masticatory movements in relation to mandibular excursion, angle, velocity, cycle duration, duration of each phase were measured for each masticatory cycle. In addition, unilateral maximum biting was performed, and the maximum force during biting was measured using a force-transducer. A multiple regression analysis identified vertical amplitude, closing duration, closing angle and maximum bite force as significant predictors accounting for 63% of inter-subject variation (adjusted R(2)) in the MAI (P < 0.05). Only some parameters of masticatory movements seem to have an influence on the MAI in dentate subjects.

Objective and subjective hardness of a test item used for evaluating food mixing ability.

The aim of this study was to compare objective and subjective hardness of selected common foods with a wax cube used as a test item in a mixing ability test. Objective hardness was determined for 11 foods (cream cheese, boiled fish paste, boiled beef, apple, raw carrot, peanut, soft/hard rice cracker, jelly, plain chocolate and chewing gum) and the wax cube. Peak force (N) to compress each item was obtained from force-time curves generated with the Tensipresser. Perceived hardness ratings of each item were made by 30 dentate subjects (mean age 26.9 years) using a visual analogue scale (100 mm). These subjective assessments were given twice with a 1 week interval. High intraclass correlation coefficients (ICCs) for test-retest reliability were seen for all foods (ICC > 0.68; P < 0.001). One-way anova found a significant effect of food type on both the objective hardness score and the subjective hardness rating (P < 0.001). The wax cube showed significant lower objective hardness score (32.6 N) and subjective hardness rating (47.7) than peanut (45.3 N, 63.5) and raw carrot (82.5 N, 78.4) [P < 0.05; Ryan-Einot-Gabriel-Welsch (REGW)-F]. A significant semilogarithmic relationship was found between the logarithm of objective hardness scores and subjective hardness ratings across twelve test items (r = 0.90; P < 0.001). These results suggest the wax cube has a softer texture compared with test foods traditionally used for masticatory performance test, such as peanut and raw carrot. The hardness of the wax cube could be modified to simulate a range of test foods by changing mixture ratio of soft and hard paraffin wax.