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Statement of Problem: When implants are incorporated into an existing partial removable dental prosthesis, the acrylic resin base can fracture. It is therefore essential to study the mechanical behavior of partial removable dental prostheses by using stress and deformation analysis., Purpose: The purpose of this study was to analyze the effect of the occlusal rest position on the implant-assisted partial removable dental prosthesis by finite element analysis., Material and Methods: A Faro Arm scan was used to extract the geometrical data of a human partially edentulous mandible. A standard plus regular neck (4.8×12 mm) implant and titanium matrix, tooth roots, and periodontal ligaments were modeled by using a combination of reverse engineering in Rapidform XOR2 and solid modeling with the Solid Works CAD program. The model incorporated a partial removable dental prosthesis and was loaded with standard bilateral forces. A uniform pressure was applied on the occlusal surface so as to generate an equivalent net force of 120 N for both the left and right prosthesis. The finite element analysis program ANSYS Workbench was used to analyze the stress and strain distributions in the implant-assisted partial removable dental prosthesis., Results: Maximum stresses were significantly high for the metal framework compared to the acrylic resin surface, and these stresses were different for the mesial and distal arm designs. The maximum stress in the metal framework for the mesial arm design was 614.9 MPa, and it was 796.4 MPa for the distal arm design. The corresponding stresses in the acrylic resin surface were 10.6 and 8.6 MPa., Conclusions: Within the limitation of this study, it was found that moving the position of the occlusal rest from the mesial to distal side of the abutment teeth improved the stress distribution in the metal framework and acrylic resin denture base structures., (Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

The aim of this in vitro study was to investigate the strain distribution of the compressed mandible bone under the applied restoration- removable partial denture and to compare with the same but unrestored mandible under vertical (occlusal) load and to find out whether removable partial denture-restored or unrestored mandible causes greater strain effect on supporting tissue. Four mandible models were tested during loading for the purpose of strain measuring. Digital image correlation system (GOM - German Optical Measuring, Braunschweig, Germany), used for measuring strain consists of two digital cameras and software ARAMIS (6.2.0, Braunschweig, Germany). Remaining teeth suffer from greater strain in the mandible model without removable partial denture (7.5-10%). On the contrary, mandible with removable partial denture shows the maximum strain below the denture saddle (3.5%). However, it can be noticed that the marginal bone of the second lower praemolar in both experimental models is deformed whether the mandible model has (2.8%) or has not (10%) replacement. Within the limitations of this study the higher strain is observed in mandible model without replacement and the strain is limited locally, in the bone region that surrounds remaining teeth and mental foramen.

Objective: In general, ageing is a risk factor for sensory and motor deterioration, with the rate of decline varying amongst individuals. Concerning masticatory function, missing teeth along with oral disease seem to accelerate the dysfunction. Here, we aimed to confirm whether masticatory dysfunction by ageing is inevitable. This study investigated the effect of age, gender, number of natural teeth, occlusal force and salivary flow on the masticatory performance in a large sample of elderly adults., Design: The study sample consisted of 1288 independently living people aged 60-84 years. Masticatory performance was determined by the comminuted particles of test food. Bilateral maximal occlusal force in the intercuspal position was measured with pressure sensitive sheets. Stimulated whole saliva was collected., Results: Masticatory performance was significantly correlated to age, number of residual teeth, occlusal force and stimulated salivary flow rate by Pearson's correlation test. The multiple linear regression analysis showed that, with other variables controlled, masticatory performance was significantly associated with the number of residual teeth (β=0.456, P<0.001), occlusal force (β=0.244, P<0.001) and stimulated salivary flow rate (β=0.069, P=0.003). Age was not related to masticatory performance (β=-0.007, P=0.753)., Conclusions: Declines in the number of residual teeth, occlusal force and salivary flow were associated with a reduction of masticatory performance in older adults. If tooth loss is not considered as an attribute of physiological ageing, then ageing by itself may not be a risk factor for masticatory dysfunction., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Purpose: Eichner Indices (A, B, and C), especially the Eichner subgroups (A1-A3, B1-B4, C1-C3), have not been validated in relation to oral functions. The purpose of this study was to investigate the association of posterior occlusal contact loss with occlusal force and masticatory performance in subjects who had a normal dentition or partially edentulous arches restored with removable prostheses., Materials and Methods: The study sample consisted of 1,288 independently living patients over the age of 60 years. Subjects were grouped into 10 subgroups by posterior occlusal contacts according to the Eichner Index. Bilateral maximum occlusal force in the intercuspal position was measured using pressure-sensitive sheets. Masticatory performance was determined by the concentration of dissolved glucose obtained from comminuted gummy jellies., Results: Occlusal force and masticatory performance were significantly associated with posterior occlusal contacts. Occlusal force measured in subgroups A2 to B2 and B3 to C3 did not differ statistically, although overall occlusal force decreased significantly as the loss of occlusal contacts increased. Similarly, masticatory performance was reduced with decreasing occlusal contact, although the decline was more gradual. Masticatory performance among subgroups A1 to B1, A3 to B2, B2 to B3, B4 to C2, and C1 to C3 did not differ significantly., Conclusions: The Eichner Index subgroups were significantly associated with reduced oral functions, even if the teeth were restored with removable prostheses. Preservation of occlusal contacts of the bilateral (B2) and unilateral (B3) premolars was critical for occlusal force and masticatory performance, respectively.

Dental absence interferes in the physiological functioning of the masticatory system, promoting occlusal and functional alterations. The purpose of this study was to verify maximal bite force and maximal bite force correlated with electromyographic activity in 14 partially edentulous and 14 dentate individuals. Bite force in right and left molar and incisor regions were registered using a dynamometer with capacity of up to 1000N, adapted for oral conditions and at the same time electromyography was performed using Myosystem-Br1 with electrodes positioned on right and left masseter and temporalis muscles, and one reference electrode on the frontal bone. The highest value out of three recordings was considered the individual's maximal bite force. Statistical analysis of the bite force data was performed by means of t-test and Pearson's bivariate correlation test was used for the analysis between bite and electromyographic activity using SPSS 12.0 software. Dentate individuals showed greater maximal bite force in the three regions. Correlations between electromyographic activity and bite force in the dentate group obtained positive coefficients for every muscle in the right molar region, for the left temporalis in the left molar region, and for every muscle in the incisive region. For the partially edentulous group, only the left temporalis muscle presented a positive correlation in the right molar region, there was positive correlation for the right masseter and right and left temporalis in the left molar region, and, in the incisive region, every muscle presented negative correlation. These data evidence the strong influence of dental loss over the maximal bite force and small correlation between bite force and electromyographic activity.

Goal: This study tests the hypothesis of loading-dependence on the temporomandibular joint during clenching on the particular of experimentally partial edentate conditions., Methodology: A complete and detailed finite element model of the temporomandibular joint (TMJ) was used. The closing movement of the mouth was reproduced by contracting the closing muscles of the masticatory system. Electromyography (EMG) data were taken from 10 healthy, dentulate volunteers, both with and without intraoral appliances. The intraoral appliances served to mimic nine partially edentulate (PE) conditions for each volunteer. The EMG data were fed into the finite element model (FEM) for each condition and the loading of the joint was analyzed., Results: The results obtained show that muscular activity decreases when the contact between teeth disappears. In particular, the numerical results showed that when there is no contact between the posterior teeth an overload of the joints appeared. Moreover, the existence of a unilateral unique molar induced asymmetric overloading in the TMJ disc without posterior contact., Conclusions: During clenching, a uniform distribution of the dental contact along the maxillar arches prevents the TMJ from overloading. In contrast, severe partial edentation seems to induce overloading of the TMJ with severity depending on the type of contact.

Purpose: Eating, which includes chewing and swallowing, is an oral function that influences quality of life. Though the swallowing ability of maxillectomy patients was reported in our previous study, the chewing function has not been fully reported to date. Thus, the purpose of this study was to evaluate the chewing function of obturator prosthesis wearers by measurement of masticatory performance and occlusal force. The relationship of these 2 measurements was also investigated., Materials and Methods: Twenty maxillofacial obturator prosthesis wearers undergoing periodic checkup at the maxillofacial rehabilitation clinic in Kyushu University Hospital were recruited for this study. Additionally, 20 young, healthy individuals were recruited as controls. Data on masticatory performance, which was measured by a sieve method using hydrocolloid material, and maximum occlusal force, which was measured by the Dental Prescale System (Fuji Film), were obtained for each participant., Results: The mean of masticatory performance was 2.6 (SD 1.2) on a 1.40-mm mesh. There was no significant difference in masticatory performance between the patient group and the controls. The mean maximum occlusal force of the patient group was 625.9 N (SD 299.1 N), which was significantly lower than that of the control group. There was no significant correlation between masticatory performance and maximum occlusal force for the patient group in this study (P = .3726)., Conclusion: Masticatory performance of obturator prosthesis wearers with dentate or partially edentulous maxillae was not different from that of young, healthy individuals, though maximum occlusal force of these patients was lower than that of controls.

Due to large individual differences of masticatory function, an inter-individual comparison between denture patients and complete dentate people would be insufficient. This cross-sectional study aimed to evaluate patients' masticatory performance (determined by Mixing Ability Index, MAI) and bite force (determined by maximum bite force, MBF) after removable partial denture (RPD) treatment by comparing those of the RPD replaced side with those of their own opposite dentulous side, and to evaluate influence of bite force on masticatory performance in different dentitions. Subjects included patients with unilateral distal extension RPDs (n=28). Apart from the RPD replaced area on one-side, all subjects had intact dentitions. Both masticatory parameters were evaluated separately on each chewing side. MAls and MBFs obtained from the RPD replaced side (0.65 +/- 0.50 and 220 +/- 155 N, mean +/- SD) were significantly lower than those from the dentulous side (1.06 +/- 0.64 and 450 +/- 268 N; Wilcoxon signed-ranks, P < 0.001). MBF significantly influenced MAI in both RPD replaced (Univariate linear regression; R2 = 0.17, P < -0.001) and dentulous sides (R2 = 0.51, P < 0.001). After RPD treatment, masticatory performance and bite force of RPD replaced side were lower than those of their own dentulous side. The influence of the bite force on masticatory performance in RPD replaced side was less significant than that in the dentulous side.

Objective: To evaluate the effects of age and dental status on chewing performance in humans., Design: Electromyography recordings (EMG) were made during chewing of six foods (rice, beef, cheese, crispy bread, apple, and peanuts) to compare the masticatory patterns of four subject groups with different ages and dental status., Subjects: Nineteen elders (mean age 67.2 years) classified into three categories according to their number of opposing post-canine teeth pairs (i.e. functional units) and a control group of 10 young adults (mean age 26.5 years) with a high number of functional units., Main Outcome Measures: Number of chewing cycles, chewing time, total muscle activity and muscle activity per chew, burst and inter-burst durations, maximum and mean voltages from EMG recordings., Results: Time-related EMG parameters increased from young subjects to elderly subjects with high, middle and low dental status. Parameters related to EMG voltages per chew decreased in the same order among the different groups of subjects. These tendencies were observed for all the studied products. Subjects with weak muscle contraction may compensate for their poor chewing performance by lengthening both chewing cycle and sequence duration. Additional alterations in the chewing patterns were observed when age effect was associated with a dental status degradation in terms of number of functional units., Conclusion: Impairment in mastication for the elderly is due to both ageing and decreasing number of functional pairs of post-canine teeth.

To determine whether shortened dental arches (SDAs) cause functional overloading of the teeth and the temporomandibular joints, which has been implicated in periodontal diseases and temporomandibular disorders, we investigated the influences of SDA on occlusal and joint loads. Bite force and masticatory muscle electromyograms were recorded in five dentate subjects who clenched maximally on intra-oral appliances, creating symmetrical SDAs experimentally. Muscular forces estimated from the recorded electromyograms were fed into a finite element jaw model for calculating bite forces and joint loads. Comparison between the measured and the calculated bite forces ensured that the joint loads were representative. The bite force on each tooth increased with missing molar occlusions, while joint loads decreased. The bite force per root surface area was always greatest on the most posterior tooth, and these values were most constant. The findings provide no evidence that SDA causes overloading of the joints and the teeth, which suggests that neuromuscular regulatory systems are controlling maximum clenching strength under various occlusal conditions.

Purpose: Forceful clenching in the intercuspal position has the potential to cause significant mandibular displacement. Such a displacement can be expected to be exaggerated in patients without molar support. The appropriate clenching level for intercuspal position registration or evaluation in these patients has never been clarified. The aim of this study was to clarify the effect of clenching level and absence of posterior occlusal support on mandibular displacement., Materials and Methods: Thirteen women with a unilateral edentulous area posterior to the first premolar were enrolled in this study. They were asked to perform intercuspal clenching at various occlusal force levels, and 3-D mandibular displacements were measured by an optoelectronic method. The effects of "clenching force level" and "side of molar tooth loss" on the displacements of the condylar and second molar points were analyzed., Results: The mandible was elevated without substantial horizontal displacements during each clenching task. The effect of clenching level on vertical mandibular displacement was significant, with a clenching level > or = 50% of maximal voluntary contraction causing significantly greater elevations (P < .05). Clenching > or = 50% of maximal voluntary contraction caused consistent tipping of the mandible, with greater elevation on the edentulous side (P < .05)., Conclusion: The clenching level should not surpass 50% of maximal voluntary contraction for registration or evaluation of intercuspal position in Kennedy Class II patients.

Three-dimensional mandibular displacement related to loss of posterior occlusal support was investigated. Five subjects, whose mandibular premolars and molars needed to be restored, were selected. Their experimental prostheses were removed in sequence from the most posterior to anterior. The more the absence of posterior occlusal support increased, the more condylar displacements were increased. On the other hand, maximum bite forces were decreased, by removing each prosthesis in sequence from posterior to anterior. These results suggest that condylar position would be easily displaced with low level bite force following loss of posterior occlusal support.

Objective: The aim of the present study was to analyse the relationship between masticatory ability (self-assessed masticatory ability and bite force) and intake of energy, nutrients and food items in a population sample of elderly subjects., Design and Subjects: From a population sample of 80-year-old people, 160 individuals (74 men and 86 women) took part in an odontological study., Main Outcome Measures: A dental examination including bite force recording, a questionnaire focusing on self-assessed masticatory ability, and a dietary interview., Setting: Department of Geriatric Medicine, Göteborg University, Sweden., Results: The dental status among the participants varied much (from edentulous in both jaws--22%--to more than 20 natural teeth--30%). The mean maximum bite force was higher in men (165 N) than in women (105 N). Bite force was significantly correlated to the Eichner index and to the number of teeth. One third of the subjects reported no masticatory problem, whereas 18% identified > or = 3 such problems. The intake of energy and nutrients varied much but the means were well above recommended values. The correlations between dental status and bite force on one side and dietary intake on the other side were in general weak and most often statistically non-significant. Impaired general health and reduced dentition were both associated with more masticatory problems., Conclusion: The examined sample of 80-year-old subjects had a great variation in dental status, bite force and self-assessed masticatory ability, but these factors had only a minor influence on dietary selection and intake, which on average were well above recommended values.

The aim of this study was to create a standard for occlusal support in the diagnosis and evaluation of prosthetic treatment. In experimental occlusion, the maximal bite force of eight normal dentates was measured by pressure-sensitive film over the whole dentition using splints divided into nine pieces. The occlusal contact was altered by exchanging splint pieces according to the shortened dental arch concept. The occlusal load center (OLC) was located on a graph set up with reference to the size of the individual dental arch. The occlusal supporting index (SI) and the rehabilitation index (RI) were calculated from the locations of the OLC corresponding to each occlusal contact. Differences in numbers and distribution of occlusal stops could clearly be distinguished by the location of the OLC. Though the SI showed a strong positive correlation with maximal bite force, it is proposed that the number of occlusal stops, or occlusal units, provides the most effective index for quantitative parameters of occlusal support in clinical use. From the standpoint of bite force, analysis of the RI is suggested as a useful method of objectively evaluating the recovery of occlusal support with prosthetic treatment.

Statement of Problem: Patients who have lost moderate posterior tooth support may also lose clenching force as a result of sensitivity to increased loading to the remaining teeth and possibly a loss of muscle strength, because clenching forces are limited to avoid stress to the remaining teeth. Few studies have correlated moderate posterior tooth loss with maximum clenching force., Purpose: The purpose of this pilot study was to test the hypothesis that moderate loss of posterior tooth support will have a significant effect on maximum clenching force., Material and Methods: The maximum clenching force of 44 adults, ages 28 to 76 (mean 46), with posterior tooth loss was compared with the maximum clenching force of a control group of 20 healthy full dentition adults, ages 18 to 55 (mean 30), by use of a bilateral strain-gauged transducer. The transducer consisted of 2 stainless steel plates separated by a steel sphere that balanced occlusal forces between right and left sides. Acrylic resin pads were fabricated for each patient to protect the cusps of the teeth. The overall accuracy was found to be within 2.3% of full scale over a range of 0 to 4000 N (0 to 900 lbs). The calibration reliability of the system was checked frequently by use of a dead weight of 222 N (50 lbs). Clenching forces were supported by first and second molars and second premolars when possible. The instrumentation, methods, and operator were the same for both groups. A 2-tailed Student t test (alpha=0.01) and a pooled estimate of the mean were used to determine possible statistical significance. To test for possible correlations between clenching force and lost tooth support and between clenching force and age, a linear regression correlation coefficient R was calculated., Results: For the 44 subjects with posterior tooth loss, the mean clenching force was 462 N (104 lbs), with a range of 98 to 1031 N (22 to 232 lbs). This compares with a mean of 720 N (162 lbs) with a range of 244 to 1243 N (55 to 280 lbs) for the full-dentition subjects. A 2-tailed t test showed that the average difference of 258 N (58 lbs) between the 2 groups was significant (P< or =.01). There was only a moderate negative association between clenching strength and loss of mandibular tooth support (R = -0.35). Clenching force was not well correlated with age as indicated by low R values (R = 0.21, missing tooth group and R = -0.03, full dentition group)., Conclusion: Within the limitations of this study the maximum clenching force was less (P< or =.01), by 258 N (58 lbs) on average, in subjects with moderate loss of posterior tooth support. Loss of maximum clenching force was associated with a modest negative correlation to the number of missing teeth in the mandibular arch (R = -0.35). The range of clenching force was surprisingly large for both the missing tooth (98 to 1031 N) and full dentition (244 to 1243 N) groups.

Masticatory performance results from a complex interplay of direct and indirect effects, yet most studies employ univariate models. This study tested a multivariate model of masticatory performance for dentate subjects. Explanatory variables included number of functional tooth units, bite force, sex, age, masseter cross-sectional area, presence of temporomandibular disorders, and presence of diabetes mellitus. The population-based sample consisted of 631 dentate subjects aged 37-80 years. Covariance structure analysis showed that 68% of the variability in masticatory performance could be explained by the combined effects of the explanatory variables. Age and sex did not show a strong effect on masticatory performance, either directly or indirectly through masseter cross-sectional area, temporomandibular disorders, and bite force. Number of functional tooth units and bite force were confirmed as the key determinants of masticatory performance, which suggests that their maintenance may be of major importance for promoting healthful functional status.

The purpose of the present study was to (1) determine the standard value of maximum bite force and to (2) compare the maximum bite force of the elderly between healthy and frail subjects. Subjects included 349 healthy elderly individuals (149 males, 200 females) and 24 frail elderly individuals (seven males, 17 females) ranging from 65 to 74 years of age. Maximum bite force was evaluated using a Dental Prescale system. The maximum bite force of the healthy subjects was significantly higher than that of the frail subjects in both males (P=0.020) and females (P=0.015). However, no significant difference was observed in the number of present teeth between the healthy and frail subjects. Median of maximum bite force in healthy males was 408.0 N, and that of the healthy females was 243.5 N. These results suggest that the frail elderly have latent bite force problems.

Patients with removable partial dentures or complete dentures do not demonstrate masticatory function to the same level as patients with a full set of natural teeth. The purpose of this study was to characterize the relationship between reduction of masticatory function, in terms of masticatory performance and bite force, and the existence of remaining natural occlusal supports as assessed by the Eichner index. One hundred and eighteen removable partial denture and complete denture wearers were selected for analyses. These subjects were divided into four groups depending upon the number of occlusal supports. Seventy dentate subjects with full occlusal support were designated as a comparison group. Bilateral bite force was measured at the first molar region in all subjects. Masticatory performance was assessed using the modified Masticatory Performance Index. Peanuts were used as the test food. Both bite force and masticatory performance were significantly associated with group classification. Moreover, both bite force and masticatory performance of the four denture groups were significantly reduced compared to the comparison group and this tendency was remarkable for the denture groups without occlusal support. These results suggest that the existence of functional tooth units may be a key factor in preservation of masticatory function.

The aim of this in vivo study was to compare the precision of control of jaw closing forces through implants versus natural teeth. Ten partially dentate subjects with fixed implant prostheses in their mandibles took part in the study. A force transducer was used to assess the ability of the subjects to follow pre-determined jaw closing cycles. The error in tracking the target increased as the force increased for both implant and tooth sites. Within the range of forces tested, there was no significant difference in the error between the implant and natural tooth sites.

It has been suggested that the provision of dental implants can improve the oral function of subjects with severely resorbed mandibles, possibly restoring function to the level experienced by satisfied wearers of conventional complete dentures. Nevertheless, a quantitative comparison has never been made and can be drawn from the literature only with difficulty, since studies differ greatly in methodology. To make such a comparison, we measured bite force and chewing efficiency by using identical methods in subjects with overdentures, complete full dentures, and natural dentitions. Our results indicated that bite forces achieved with overdentures on dental implants were between those achieved with artificial and natural dentitions. Chewing efficiency was significantly greater than that of subjects with full dentures (low mandible), but was still lower than that of subjects with full dentures (high mandible) and overdentures on bare roots. Differences in the height of the mandible revealed significant differences in chewing efficiency between the two full-denture groups. Furthermore, subjects with a shortened dental arch exerted bite forces similar to those of subjects with a complete-natural dentition, but their chewing efficiency was limited due to the reduced occlusal area. For all groups combined, a significant correlation was found between maximum bite force and chewing efficiency. Nearly half of the variation in chewing efficiency was explained by bite force alone.

This study aimed (1) to investigate the influences of sex, age and number of teeth on biting ability through a descriptive survey, and (2) to compare the biting ability between the subjects with and without mobile teeth in a case-control study. A total of 687 subjects cooperated in the descriptive survey. Each subject bit on a pressure detecting sheet with their maximum biting force. Three indices of biting ability: biting pressure (MPa), biting force (N) and occlusal contact area (mm2) were calculated from the impressed marks on the sheet using a high vision video processor system. These indices were correlated well with the number of teeth according to the multiple regression analysis. In the case-control study, matching procedures with sex, age and number of teeth were performed between the subjects with and without mobile teeth. No differences in the three indices were observed between the two well-balanced groups. The results showed that the number of teeth is most important to maintain biting ability, and that the presence of mobile teeth does not always reduce biting ability.

Maximal occlusal force and oral tactile sensibility were recorded in (1) a group of partially edentulous patients restored with ITI implants supporting fixed prostheses or single crowns and (2) a control group consisting of fully dentate subjects with healthy natural teeth. Maximal occlusal force was measured with a miniature force transducer placed between antagonistic implant/tooth pairs in the test group and antagonistic teeth in the control group. The detection threshold of minimal pressure (ie, passive tactile sensibility) was recorded with dynamometers, and minimal perceived thickness (active tactile sensibility) was assessed using steel foils with a thickness from 100 to 10 microns. Highest maximal occlusal force was measured in fully dentate subjects on second premolars (average 450 N). A significant reduction on the first premolars (300 N) was observed. With fixed prostheses supported by implants, the average value of maximal occlusal force was distinctly lower, about 200 N for first premolars and for molars, and 300 N for second molars. The maximum force was again found on second premolars. The detection threshold of minimal pressure was significantly higher on implants than on natural teeth. The average number of wrong assessments when testing steel foils was 3.2 for antagonistic implant/tooth pairs and 2.6 for natural teeth. The comparison of test sides (with implants) and control sides (without implants) in patients of the test group did not reveal significant differences of measurements. It seems that patterns of oral function depend primarily on the state of dentition, type of prosthodontic restorations, and on psychological aspects, and secondarily on the presence of implants.

Several studies have shown that swinglock removable partial dentures are effective for stability of the abutment teeth and the surrounding tissues including alveolar bone. This efficacy has been thought to be due to the dynamic structure of the swinglock attachment. Individual biting force was measured to determine the physiological efficacy of teeth splints by use of the attachment. The results showed that individual biting forces with the swinglock removable partial denture were 10-25% higher than those without the denture. Furthermore, statistical analysis showed that the individual biting forces with the swinglock removable partial denture were significantly higher. The swinglock attachment can stabilize partially edentulous dentition by splinting all residual teeth. In addition, when physical forces are applied to the abutment teeth and the artificial teeth, this attachment can deliver and distribute the stress to the other abutment teeth and alveolar mucosa. The present findings suggest that the swinglock attachment augments the ability to withstand physical forces such as those occurring during biting and mastication.

A sustained submaximal (50%) clenching effort was performed in four patient groups to establish whether implant-supported prosthetic reconstructions influence myoelectrical signal parameters. The first group consisted of patients with natural teeth in both jaws. The other three groups consisted of patients who were edentulous in both jaws: one group had complete dentures; one had an overdenture in the mandible on two implants connected by a bar; and the third had an implant-supported fixed prosthesis in either the maxilla or the mandible. Surface electromyography indicated an increased myoelectrical output level that paralleled a higher bite force level for implant-supported reconstructions compared with complete dentures. Power spectrum analysis revealed a downward shift of the mean power frequency during sustained clenching in all groups except the implant-supported fixed prosthesis. The absence of a spectral shift in the latter group probably reflected a fear of biting too hard and fracturing the prosthesis.

Surgical resection of a segment or loss of mandibular continuity can adversely affect most of the structures essential for maximum occlusal force. Five subjects who had partial mandibular resections for treatment of squamous cell carcinoma were studied. Occlusal force was recorded before and after cancer treatment and following prosthetic rehabilitation. A gnathodynamometer was used to record anterior occlusal force. Five edentulous and five dentate cancer-free subjects matched for age were studied to establish comparable normative data. The null hypothesis that partial mandibular resection would not affect maximum occlusal force was rejected (p = 0.0101). Mandibular resection did alter maximum occlusal force. The impact of the decrease in maximum occlusal force on masticatory function is yet to be determined.

Three-dimensional finite element models of a partially edentulated human mandible were generated to calculate the mechanical response to simulated isometric biting and mastication loads. The level of mesh refinement was established via a convergence test and showed that a model with over 30,000 degrees of freedom was required to obtain analysis accuracy. The functional loading cases included muscle loading based on an algorithm that assigns muscle forces in accordance with muscle cross-sectional area, while maintaining static equilibrium. Results were found for isometric application of unilateral and bilateral bite and mastication loading, and two different sets of displacement boundary conditions were imposed at the condyles. The mechanical response is shown in terms of displacements, principal strains, and a new measure called the 'mechanical intensity scalar'. For each load case studied, there was substantial bending in the molar region of the corpus and high tensile strains in the anterior portion of the ramus.