Mastication and jaw motion of partially edentulous patients are affected by different implant‐based prostheses

The main goal of prosthetic treatment is to restore masticatory function. However, insufficient evidence supports the recommendation of one specific prosthetic intervention for partially edentulous patients. Function after the use of three different prostheses by the same partially edentulous subject. Mastication was assessed in 12 subjects (mean age 62·6 ± 7·8 years) after they had used removable partial dentures (RPDs), implant‐supported partial dentures (IRPDs) and implant‐fixed partial dentures (IFPDs). Masticatory ability (MA) was estimated by visual analogue scale questionnaire, while the mandibular chewing motion was evaluated by kinesiographic device, representing an objective measurement of masticatory function. Data were analysed by repeated‐measures anova followed by Tukey–Kramer (P < 0·05). MA improved after IRPD and IFPD use (P < 0·05). Opening, closing and total cycle time duration were reduced after both IRPD and IFPD use (P < 0·05), irrespectively the implant prosthesis type. IFPDs and IRPDs restore the masticatory function of partially edentulous patients better than RPDs.     

Posterior scissors‐bite: masticatory jaw movement and muscle activity

Scissors‐bite is a malocclusion characterised by buccal inclination or buccoversion of the maxillary posterior tooth and/or linguoclination or linguoversion of the mandibular posterior tooth. This type of malocclusion causes reduced contact of the occlusal surfaces and can cause excessive vertical overlapping of the posterior teeth. This case–control study is the first to evaluate both masticatory jaw movement and masseter and temporalis muscle activity in patients with unilateral posterior scissors‐bite. Jaw movement variables and surface electromyography data were recorded in 30 adult patients with unilateral posterior scissors‐bite malocclusion and 18 subjects with normal occlusion in a case–control study. The chewing pattern on the scissors‐bite side significantly differed from that of the non‐scissors‐bite side in the patients and of the right side in the normal subjects. These differences included a narrower chewing pattern (closing angle, P < 0·01; cycle width, P < 0·01), a longer closing duration (P < 0·05), a slower closing velocity (P < 0·01) and lower activities of both the temporalis (P < 0·05) and the masseter (P < 0·05) muscles on the working side. In 96% of the patients with unilateral posterior scissors‐bite, the preferred chewing side was the non‐scissors‐bite side (P = 0·005). These findings suggest that scissors‐bite malocclusion is associated with the masticatory chewing pattern and muscle activity, involving the choice of the preferred chewing side in patients with unilateral posterior scissors‐bite.     

Influence of surgical orthodontic treatment on masticatory function in skeletal Class III patients

Skeletal Class III patients exhibit malocclusion characterised by Angle Class III and anterior crossbite, and their occlusion shows total or partially lateral crossbite of the posterior teeth. Most patients exhibit lower bite force and muscle activity than non‐affected subjects. While orthognathic surgery may help improve masticatory function in these patients, its effects have not been fully elucidated. The aims of the study were to evaluate jaw movement and the electromyographic (EMG) activity of masticatory muscles before and after orthognathic treatment in skeletal Class III patients in comparison with control subjects with normal occlusion. Jaw movement variables and EMG data were recorded in 14 female patients with skeletal Class III malocclusion and 15 female controls with good occlusion. Significant changes in jaw movement, from a chopping to a grinding pattern, were observed after orthognathic treatment (closing angle P < 0·01; cycle width P < 0·01), rendering jaw movement in the patient group similar to that of the control group. However, the grinding pattern in the patient group was not as broad as that of controls. The activity indexes, indicating the relative contributions of the masseter and temporalis muscles (where a negative value corresponds to relatively more temporalis activity and vice versa) changed from negative to positive after treatment (P < 0·05), becoming similar to those of control subjects. Our findings suggest that orthognathic treatment in skeletal Class III patients improves the masticatory chewing pattern and muscle activity. However, the chewing pattern remains incomplete compared with controls.     

Mandibular movements and bite force in Alzheimer's disease before and after new denture insertion

Chewing impairment has been observed in elders with Alzheimer's disease (AD); however, it is unknown whether oral rehabilitation can improve their masticatory function. This study evaluated the influence of new removable prostheses on chewing function of patients with AD. Participants using removable dentures were divided into two groups: patients with mild AD (77·2 ± 5·8 years, n = 16) and controls (76·0 ± 4·4, n = 16). All participants received general dental treatment and new total and/or partial removable prostheses. After 2 months of adaptation to the new dentures, chewing was evaluated by the following parameters: masticatory cycle time (CT), cycle velocity (CV), and opening (OA) and closing mandibular angles (CA), registered by a kinesiographic device. Maximum bite force (MBF) was assessed using a strain sensor. Evaluations were performed at baseline and after insertion of the new prostheses. A mixed model (α = 5%) was used for within‐ and between‐subject analyses. After insertion of new prostheses, CT was reduced, and CV and MBF were increased in both groups (P < 0·05). There were no changes in OA or CA (P > 0·05). Compared to controls, elders with AD showed higher CT and reduced MBF and CV both at baseline and after insertion of new prostheses (P < 0·05). However, OA and CA did not differ between groups (P > 0·05). Insertion of new removable prostheses improved masticatory function in elders with and without AD, but patients with mild AD still had reduced chewing parameters compared to controls.     

Evaluation of psychological guidance impact on complete denture wearer's satisfaction

The purpose of this study was to evaluate the impact of psychological intervention on edentulous patients’ satisfaction with complete clinically satisfactory complete dentures. The survey was conducted in China Medical University involving 84 individuals receiving complete dentures at this institution from August 2013 to March 2014. Participants were randomly allocated to intervention and control groups consisting of 42 subjects, respectively. In the intervention group, individuals received oral health education and psychological intervention before and after the whole process. In the control group, 42 cases received doctor's regular advice after treatment. Satisfaction regarding aesthetic, speech, mastication, retention and comfort was rated in the first and third month after prosthesis treatment. Patients overall aesthetic, speech, mastication and retention were significantly improved in both intervention and control groups in 3 months later after prosthesis treatment when compared with the first month (P < 0·05). No significant difference existed for comfort in control group. Patient scores on aesthetic, speech, mastication and retention at both first and third month evaluations (P < 0·05) differed between the control and intervention groups. However, there was no difference for their scores related to comfort (P > 0·05) in first and third month. The study concludes that psychological intervention plays a significant role in improving patient satisfaction with complete dentures.     

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.     

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

Summary 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.     

Effect of mouth breathing on masticatory muscle activity during chewing food

The aim of this study was to examine the effect of mouth breathing on masticatory muscle activity during chewing food. Masseter muscle activity during chewing of a rice ball was recorded in 45 adult volunteers (three women), identified as nose breathers. Surface electrodes were placed on the skin according to the orientation of the masseter muscle to record the activity of this muscle while the subjects chewed the food until swallowing. Each activity was recorded twice, once with nose breathing and once with mouth breathing induced by nasal obstruction. The integrated and mean electromyography values for mouth breathing were significantly lower than the values for nose breathing (P < 0·05). The resting and total duration of chewing were significantly prolonged (P < 0·05) and the active duration significantly shorter (P < 0·05) when breathing through the mouth compared with the nose. Significantly more chewing strokes were counted for mouth breathing compared with nose breathing (P < 0·05). Taken together, the results indicate that mouth breathing decreases chewing activity and reduces the vertical effect upon the posterior teeth.     

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.     

Effect of dentist's clinical experience on treatment satisfaction of a complete denture

The relationship between the prosthodontic experience of dentists and satisfaction of complete denture wearers remains unknown. To investigate whether a prosthodontist's clinical experience affects treatment satisfaction of a complete denture wearer. From April 2004 to July 2006, we conducted a randomised controlled trial at two centres, including 74 edentulous patients; of these, 32 and 30 were randomly allocated to the ED or ID group, respectively. All the patients rated their satisfaction with dentures, including general satisfaction and satisfaction of chewing ability, speaking, cleaning, stability, retention, comfort and aesthetics. These satisfaction ratings were measured by a 100‐mm visual analog scale (VAS). Perceived chewing ability to foods, divided into five grades, was measured using a questionnaire. The mastication index (MI) was calculated for each grade. General satisfaction and satisfaction of speaking, stability and retention were significantly higher in the ED than in the ID group (P = 0·049, 0·003, 0·019 and 0·041, respectively). No significant difference existed between the MI of the ED (71·3 ± 18·4) and ID group (64·1 ± 16·53). However, the perceived chewing ability of grade 5 food, whose texture was the hardest among all the grades, was significantly higher in the ED group than in the ID group. Within its limitations, this study showed that a clinician's prosthodontic experience affects a complete denture wearer's satisfaction ratings.     

Effect of implant‐supported prosthesis on the bite force and masticatory efficiency in subjects with shortened dental arches

The aim of the study was to assess changes in bite force and masticatory efficiency in shortened dental arch (SDA) subjects rehabilitated with implant‐supported restoration for 1st molar. Ten SDA subjects with bilaterally missing mandibular molars (experimental group) were recruited. In each subject, one tapered threaded implant was placed bilaterally in 1st mandibular molar region and restored. Masticatory efficiency was evaluated objectively by measuring the released dye from chewed raw carrots, with a ‘spectrophotometer’ at 530 nm preoperatively and at 3 months after restoration. Bite force was evaluated using ‘bite force measuring appliance’ preoperatively, at 6 weeks and at 3 months after restoration. Ten completely dentate‐matched subjects (in terms of age, sex, height and weight) acted as control. The results revealed that as compared with the control group, the experimental group showed significantly less (P < 0·05) mean maximum bite force at pre‐restoration and at 6 weeks after restoration. Although at 3 months the mean maximum bite force value was less than the control group but the mean difference was statistically insignificant. The mean difference of masticatory efficiency between control and experimental group was statistically significant (P < 0·05) before restoration, but was statistically insignificant at 3 months after restoration. Thus it was concluded that after the restoration of mandibular arch with implant‐supported prosthesis, both bite force and masticatory efficiency of all SDA subjects increased and were comparable to that of matched completely dentate subjects after 3 months.     

First molar cross‐bite is more closely associated with a reverse chewing cycle than anterior or pre‐molar cross‐bite during mastication

A posterior cross‐bite is defined as an abnormal bucco‐lingual relationship between opposing molars, pre‐molars or both in centric occlusion. Although it has been reported that patients with unilateral posterior cross‐bite often show unique chewing patterns, the relationship between the form of cross‐bite and masticatory jaw movement remains unclear in adult patients. The objective of this study was to investigate masticatory jaw movement among different forms of cross‐bite. One hundred and one adults were recruited in this study: 27 had unilateral first molar cross‐bite (MC group); 28, unilateral pre‐molar cross‐bite (PC group); 23, anterior cross‐bite (AC group); and 23, normal occlusion (control group). Masticatory jaw movement of the lower incisor point was recorded with six degrees of freedom jaw‐tracking system during unilateral mastication. Our results showed that the reverse chewing ratio during deliberate unilateral mastication was significantly larger in the MC group than in the PA (P < 0·001), AC (P < 0·001) and control (P < 0·001) groups. These findings suggest that compared to the anterior or pre‐molar cross‐bite, the first molar cross‐bite is more closely associated with a higher prevalence of a reverse chewing cycle.     

Changes in masticatory function after injection of botulinum toxin type A to masticatory muscles

This study examined changes in masticatory function after botulinum toxin type A (BTX‐A) injection using objective and subjective tests during 12 weeks. Also, we compared differences in masticatory function between group in which only masseter muscle (M group) was injected and group in which masseter and temporal muscle (M‐T group) were injected. Forty subjects were assigned into two groups; M group (n = 20) and the M‐T group (n = 20). The Meditoxin^® was used as BTX‐A injection. The mixing ability index (MAI) was used as the objective indicator, and visual analogue scale (VAS) and food intake ability (FIA) index were used as subjective indicators. Overall, the masticatory function drastically declined after 4 weeks and gradually recovered with time. Compared with the pre‐injection state, the masticatory function decreased by 89·2% (MAI), 12·2% (FIA) and 32·2% (VAS) 4 weeks after the injection (P < 0·05). When the results between M group and M‐T group were compared, scores of VAS and FIA were significantly different 4 weeks after the injection (P < 0·05), but the MAI score showed no significant difference between two groups. In conclusion, this study showed that masticatory function was significantly decreased after BTX‐A injection into the masticatory muscle after 4 and 8 weeks from injection. However, masticatory efficiency measured using MAI could completely recover after 12 weeks. Furthermore, after 8 weeks from the injection, the masticatory function measured after injection into only the masseter muscle was similar to that measured after injection into both masseter and temporal muscle.     

The Effect of Removable Partial Dentures on Alveolar Bone Resorption: A Retrospective Study with Cone‐Beam Computed Tomography

Purpose: The aim of this study was to compare vertical and horizontal mandibular alveolar bone resorption by measuring bone morphological variation in Kennedy Class II removable partial denture (RPD) wearers and non‐wearers using cone‐beam computed tomography (CBCT). Materials and Methods: In total, 124 sites in the CBCT scans of 62 (29 RPD non‐wearers, 33 RPD wearers) Kennedy Class II patients were analyzed retrospectively. Three‐dimensional representations of the mandible with superimposed cross‐sectional slices were developed with the CBCT scans to evaluate the mandibular alveolar height and width by measuring distances between the mandibular canal, mylohyoid ridge, alveolar crest, and lower border of the mandible in four regions (eight sites) of Kennedy Class II non‐wearers and wearers of RPDs. Results: Mandibular alveolar bone height and width were significantly lower in edentulous sites when compared with dentate sites in both Kennedy Class II non‐wearers and wearers of RPDs (p < 0.05). Additionally, mean vertical and horizontal mandibular bone resorption was significantly higher in RPD wearers than in non‐wearers (p < 0.05). Conclusions: Vertical and horizontal alveolar bone resorption was found to be higher in the RPD wearing patients when comparing the dentate and edentulous sites.     

Electromyographic assessment of jaw muscles in patients with All‐on‐Four fixed implant‐supported prostheses

This study evaluated the electromyographic (EMG) characteristics of masticatory muscles in patients with fixed implant‐supported prostheses according to All‐on‐Four^® principles and in control healthy dentate subjects. Twenty‐six subjects aged 50–74 years were examined. Eighteen were edentulous and had been successfully rehabilitated with (i) mandibular All‐on‐Four^® implant‐supported fixed prostheses and maxillary complete dentures (10 patients) and (ii) mandibular and maxillary All‐on‐Four^® implant‐supported fixed prostheses (eight patients). Eight reference subjects had natural dentition. Surface EMG recordings of the masseter and temporalis muscles were performed during maximum voluntary teeth clenching and during unilateral gum chewing. All values were standardised as percentage of a maximum clenching on cotton rolls. During clenching, a good global neuromuscular equilibrium was found in all participants. During chewing, all groups had similar values of working‐side muscle activities and of chewing frequency. No significant differences in the analysed EMG parameters were found between the patients with mandibular and maxillary All‐on‐Four^® implant‐supported prostheses and the reference subjects. In contrast, standardised pooled muscle activities and standardised muscular activities per cycle were larger in patients with a maxillary removable prosthesis than in control subjects (Kruskal–Wallis test, P < 0·01). Also, patients wearing a complete maxillary denture showed a poor neuromuscular coordination with altered muscular pattern and lower values of the index of masticatory symmetry than dentate control subjects (P < 0·01). EMG outcomes suggest that All‐on‐Four^® implant‐supported prostheses may be considered a functionally efficient treatment option for the rehabilitation of edentulous patients with reduced residual bone volume.     

Measurement of jerk‐cost using a triaxial piezoelectric accelerometer for the evaluation of jaw movement smoothness

Summary Jerk‐cost as a measure of jaw movement smoothness has been used to evaluate the masticatory function of patients with tooth loss and malocclusion. Jerk‐cost measuring systems have thus far been unable to determine the jerk‐cost of each chewing phase over time. The purposes of this study were (i) to develop a new method for measuring momentary jerk‐cost of the jaw movement using a small triaxial piezoelectric accelerometer and (ii) to test the hypothesis that the lowest smoothness is seen during jaw‐opening phase. The accelerometer was attached to the skin of the mentum of each subject. Vertical jaw displacement, acceleration, the jerk, and the time differential of jerk‐cost during gum chewing were analysed as a function of time in five normal dentate subjects (n = 5). The system revealed intra‐class correlation coefficients of intra‐examiner, inter‐examiner, and test–retest consistency of substantially high values (0·80–0·88). In all subjects, the highest jerk‐cost was observed in the opening phase of each chewing cycle when the gum was parting from the teeth; the lowest jerk‐cost was observed in the intercuspal phase throughout the chewing cycle, thus confirming the hypothesis. Significant differences were observed between the opening, closing, and intercuspal chewing phases (N = 5, P = 0·007). The smoothness measurement system used in this study evaluated the momentary smoothness of each chewing phase in the masticatory cycle. The system may serve as a diagnostic tool to evaluate the smoothness of the jaw movement in general dental practice.     

Oral health‐related quality of life in patients with tooth wear

The aim of this study was to investigate the impact of tooth wear (TW) on patients' oral health‐related quality of life. A total of 198 participants were included in the study. They belonged to the following four different diagnostic categories: 51 patients with TW, 46 patients with painful temporomandibular disorders (TMD), 43 complete denture wearers and 58 healthy controls. The Dutch version of the Oral Health Impact Profile (OHIP‐NL) was used to assess the patients' oral health‐related quality of life. The results of the study show that patients with TW have an impaired oral health‐related quality of life compared with healthy controls (P < 0·001). Furthermore, the impact of TW and of edentulousness do not differ significantly, while both of these oral conditions seem to have a lower impact on quality of life compared with painful TMD (P < 0·05). It was concluded that TW has a negative impact on patients' quality of life. This impact is comparable with that of edentulousness.     

Gastric emptying rate in subjects with malocclusion examined by [13C] breath test

Masticatory function is significantly lower in individuals with malocclusion than in those with normal occlusion. Although several studies suggest that masticatory function influences gastrointestinal digestive function, the relationship between malocclusion and gastrointestinal symptoms has not been studied extensively. We hypothesised that insufficient masticatory function would increase the functional burden of the stomach and have some influence on the gastrointestinal system. The purpose of this study was to investigate masticatory function and gastric emptying rate in subjects with malocclusion. Eleven healthy dentate female volunteers and eleven female patients with maloc‐clusion underwent a ¹³C‐acetate breath test with a liquid meal. Maximum ¹³CO₂ exhalation time (T_max) was compared statistically between both groups. Masticatory function was assessed by colour‐changeable chewing gum. In addition, the frequency scale for the symptoms of gastroeso‐phageal reflux disease (FSSG) and questionnaires on food intake were given to both groups. The mean T_max of the malocclusion group was significantly longer than that of the normal occlusion group (P = 0·007). Masticatory performance, measured by colour‐changeable gum and questionnaires, was significantly lower in the malocclusion group than in the normal occlusion group (P = 0·023, P = 0·003). There was no significant difference in the FSSG results between the two groups (P = 0·262). This study suggested that there was a correlation between malocclusion and gastric emptying function in women.     

总义齿、覆盖义齿和种植覆盖义齿修复后咀嚼效率和下颌运动型的比较

目的　比较总义齿 (completedenture ,CD )、覆盖义齿 (completeoverdenture ,COD )和种植覆盖义齿 (implant supportedoverdenture ,IOD)修复后患者的咀嚼效率和下颌运动轨迹的差异。 方法　分别选取CD、COD和IOD修复后患者各 14名 ,在义齿正常戴用半年后测量患者的咀嚼效率和下颌运动轨迹。对下颌运动轨迹从规则程度、末端集中性、额状面的分型和咀嚼运动中的接触滑动4个方面进行评价 ,测试用食物为杏仁和小枣。结果　IOD组患者咀嚼枣和杏仁的效率均显著高于CD组 (P <0 0 1) ;COD组患者咀嚼杏仁的效率显著高于CD组 (P <0 0 1)。COD组患者咀嚼枣的效率高于CD组 ,且IOD组患者咀嚼枣和杏仁的效率高于COD组 ,但其间差异无显著性。IOD组患者下颌运动轨迹的规则程度显著优于CD组 (P <0 0 5 ) ,末端轨迹集中性也显著优于CD组 (P <0 0 1)。结论　IOD和COD修复有利于提高无牙颌患者或口内只保留个别残根患者的咀嚼效率。IOD修复患者较CD修复患者具有更加规则的下颌运动型。