Augmented Reality Visualization for Image-Guided Surgery: A Validation Study Using a Three-Dimensional Printed Phantom.

BACKGROUND: Oral and maxillofacial surgery currently relies on virtual surgery planning based on image data (CT, MRI). Three-dimensional (3D) visualizations are typically used to plan and predict the outcome of complex surgical procedures. To translate the virtual surgical plan to the operating room, it is either converted into physical 3D-printed guides or directly translated using real-time navigation systems. PURPOSE: This study aims to improve the translation of the virtual surgery plan to a surgical procedure, such as oncologic or trauma surgery, in terms of accuracy and speed. Here we report an augmented reality visualization technique for image-guided surgery. It describes how surgeons can visualize and interact with the virtual surgery plan and navigation data while in the operating room. The user friendliness and usability is objectified by a formal user study that compared our augmented reality assisted technique to the gold standard setup of a perioperative navigation system (Brainlab). Moreover, accuracy of typical navigation tasks as reaching landmarks and following trajectories is compared. RESULTS: Overall completion time of navigation tasks was 1.71 times faster using augmented reality (P = .034). Accuracy improved significantly using augmented reality (P < .001), for reaching physical landmarks a less strong correlation was found (P = .087). Although the participants were relatively unfamiliar with VR/AR (rated 2.25/5) and gesture-based interaction (rated 2/5), they reported that navigation tasks become easier to perform using augmented reality (difficulty Brainlab rated 3.25/5, HoloLens 2.4/5). CONCLUSION: The proposed workflow can be used in a wide range of image-guided surgery procedures as an addition to existing verified image guidance systems. Results of this user study imply that our technique enables typical navigation tasks to be performed faster and more accurately compared to the current gold standard. In addition, qualitative feedback on our augmented reality assisted technique was more positive compared to the standard setup.?>.

Immediate implant-retained prosthetic obturation after maxillectomy based on zygomatic implant placement by 3D-guided surgery: a cadaver study.

BACKGROUND: The aim of this study was to introduce a complete 3D workflow for immediate implant retained prosthetic rehabilitation following maxillectomy in cancer surgery. The workflow consists of a 3D virtual surgical planning for tumor resection, zygomatic implant placement, and for an implant-retained prosthetic-obturator to fit the planned outcome situation for immediate loading. MATERIALS AND METHODS: In this study, 3D virtual surgical planning and resection of the maxilla, followed by guided placement of 10 zygomatic implants, using custom cutting and drill/placement-guides, was performed on 5 fresh frozen human cadavers. A preoperatively digitally designed and printed obturator prosthesis was placed and connected to the zygomatic implants. The accuracy of the implant positioning was obtained using 3D deviation analysis by merging the pre- and post-operative CT scan datasets. RESULTS: The preoperatively designed and manufactured obturator prostheses matched accurately the per-operative implant positions. All five obturators could be placed and fixated for immediate loading. The mean prosthetic point deviation on the cadavers was 1.03 ± 0.85 mm; the mean entry point deviation was 1.20 ± 0.62 mm; and the 3D angle deviation was 2.97 ± 1.44°. CONCLUSIONS: It is possible to 3D plan and accurately execute the ablative surgery, placement of zygomatic implants, and immediate placement of an implant-retained obturator prosthesis with 3D virtual surgical planning.The next step is to apply the workflow in the operating room in patients planned for maxillectomy.

Mixing ability test compared with a comminution test in persons with normal and compromised masticatory performance.

A mastication test was needed with a material that forms a bolus and is soft enough to be chewed by persons with compromised oral function, in particular patients confronted with oral cancer. We therefore developed a wax-mixing ability test and compared it with a comminution test using Optocal as test food. We hypothesized that the mixing ability test would be better at differentiating between groups of persons with compromised masticatory performance than the comminution test. Sixty healthy subjects were recruited in three groups of 20, matched for age and gender: a group with natural dentition; a group with full dentures; and a group with maxillary denture and implant-supported mandibular overdenture. The mixing ability test was found to discriminate better between the two full-denture groups than the comminution test.

Patient-specific pre-contouring of osteosynthesis plates for mandibular reconstruction: Using a three-dimensional key printed solution.

PURPOSE: In mandibular reconstructive surgery, the osteosynthesis plates require contouring according to the patients' individual anatomical situation. These plates are frequently contoured around a three-dimensional (3D) printed model. However, the translation to the actual patient can introduce inaccuracies and unwanted rotations in the condyles and mandibular ramus, due to malpositioning of the pre-contoured plate. MATERIALS AND METHODS: This article describes an easy-access method for exact translation of the pre-contoured plate to the patient's mandible. This is done by using 3D printed guides that allow pre-drilling of screw holes in both the contour model and the patients' mandible. The accuracy of the Key Printed Solution was analysed by comparing the anatomical landmarks on both the 3D planned and post-operative models. RESULTS: The method was applied to 4 cases. All landmarks were identified on both the 3D planning and post-operative computed tomographic data. This showed an average deviation of 1.0 mm between planning and the post-operative result. The inter-observer variation was 0.6 mm (intra-class correlation, 0.75). CONCLUSION: This article presents an easy-to-use method for pre-bending the osteosynthesis plate and subsequent accurate translation of the intended contour with corresponding screw hole locations. The method was proved to be accurate and time-efficient.

Testing of iatrogenic lingual nerve injury using a novel psychophysical method and oral reflexes.

In a case of long-term sensory loss in the tongue following third molar extraction, a novel, efficient and effective psychophysical test was used. This initial test, which includes the presentation of pairs of a real and fake stimulus, and a forced-choice response, was applied to determine whether relatively thick or thin afferent fibres of the lingual nerve were affected. The results suggested that thick fibres on the right tongue side were mainly affected. Sensory loss was confirmed and its extent assessed by a standard test determining thresholds of light touch. Furthermore, sensory function was determined by an objective test based on inhibitory reflexes in masseteric electromyographic activity following electrical stimulation of oral tissue. Reflex features that are important for within-patient diagnosis are a difference between the injured and control sides in latency of the first reflex, and also in depth-contrast in signal amplitude between both sides at the post-stimulus time of the trough of an inhibition on the uninjured side. In agreement with the findings from the psychophysical tests, the finding of the absence of an early component of both inhibitions suggested sensory loss related to dysfunction of fast-conducting, relatively thick afferent fibres of the lingual nerve. Apart from being used for medicolegal reasons, the objective reflex test may have conclusive prognostic value or may influence surgical therapeutic decisions.

Accuracy and reproducibility of a newly developed tool for volume measurements of the arm using 3D stereophotogrammetry.

BACKGROUND: Lymph edema of the arm is a common complication after breast cancer treatment. To evaluate lymph edema volume and treatment outcome, an easy to use, objective quantification method of arm volume is necessary. Most often, water displacement is used to measure arm volume, as it is an easy and robust method that can be performed at any place with a simple equipment. However, when using water displacement, no exact localization of volume difference can be seen. To accurately measure hand and forearm volumes separately, an in-house-developed device was constructed for an accurate landmark placement. METHOD: An in-house developed measurement tool was used for placing artificial landmarks proximal to the wrist crease on ten healthy subjects. Three-dimensional (3D) images of the hand and forearm were acquired, and volume measurements of the hand and forearm were performed. Measurements were repeated to investigate the intra- and inter-rater variability caused by the landmark placement. RESULTS: Measuring volume of the hand and forearm while using artificially placed landmarks turned out to be a highly reproducible, quick, and easy procedure. Both intra- and inter-rater variability showed high reproducibility for hand (ICC = 0.96 and 0.98, respectively) and forearm (ICC = 0.99 and 0.99, respectively) volumes. CONCLUSION: Measuring volumes of the hand and forearm while using artificially placed landmarks was found to be a highly reproducible, quick, and easy procedure. The device enables to analyze the localization of lymph edema in greater details.

Oral physiology and mastication.

Mastication is a sensory-motor activity aimed at the preparation of food for swallowing. It is a complex process involving activities of the facial, the elevator and suprahyoidal muscles, and the tongue. These activities result in patterns of rhythmic mandibular movements, food manipulation and the crushing of food between the teeth. Saliva facilitates mastication, moistens the food particles, makes a bolus, and assists swallowing. The movement of the jaw, and thus the neuromuscular control of chewing, plays an important role in the comminution of the food. Characteristics of the food, e.g. water and fat percentage and hardness, are known to influence the masticatory process. Food hardness is sensed during mastication and affects masticatory force, jaw muscle activity, and mandibular jaw movements. When we chew for instance a crispy food, the jaw decelerates and accelerates as a result of resistance and breakage of food particles. The characteristic breakage behaviour of food is essential for the sensory sensation. This study presents a short review of the influence of oral physiology characteristics and food characteristics on the masticatory process.

Evidence for reperfusion injury in cortical bone as a function of crush injury ischemia duration: a rabbit bone chamber study.

A model for critical limb ischemia was produced by occluding femoral vessels in 24 rabbits with a pneumatic cuff for 0, 2, 4, or 6 hours. Immediate sequelae and subsequent creeping substitution of cortical bone were observed in vivo using an implanted tibial window, the optical bone chamber implant (with intravital microscopy), and then by light and fluorescence microscopy of fluorochrome-labeled and surface-stained ground sections of retrieved implants. Six rabbits were used as controls (0 h) for each ischemia treatment, and the animals were monitored for 5 weeks postocclusion. A subpopulation of 13 implants was retrieved after euthanization and then histologically assessed for bone necrosis and remodeling. The hypothesis tested was that reperfusion injury during the 24 h after occluder release (reperfusion phase), and vessel perfusion/caliber, angiogenesis, and net bone resorption during the 5 subsequent weeks (creeping substitution phase), would exhibit ischemia duration-dependent effects. All animals could bear weight on the affected limb to ambulate by 1 week posttreatment. Two-way analysis of variance (ANOVA) comparison of the resulting data confirmed a significant difference between control and ischemia-treated rabbits for: (1) vessel perfusion/reperfusion; (2) vessel caliber; and (3) net bone resorption. Vascular responses to 4 vs. 6 h of ischemia were not significantly different, but net bone resorption was strictly ischemia duration-dependent. The conclusion that reperfusion injury was the mechanism spreading ischemia to more vessels was supported by a decrease in reperfusion and caliber of vessels, and an increase in vascular permeability and leukocyte adherence during the reperfusion phase. It is postulated that reperfusion injury produces a secondary ischemia that amplifies the occlusion-created primary ischemia and, in the present work, may have been succeeded by progressive episodes of ischemia, similar to the infarction pattern of ischemic hearts.

Mechanisms underlying the effects of remote noxious stimulation and mental activities on exteroceptive jaw reflexes in man.

Successive inhibitory, excitatory, inhibitory and excitatory reflexes (the Q, R, S and T waves of the post-stimulus electromyographic complex (PSEC)), evoked by applying non-painful taps to an incisor tooth, were recorded from the jaw-closing muscles of 15 subjects. The effects on these reflexes of the subjects undertaking mental exercises (MEx) in the form of arithmetic calculations were compared with those of remote noxious stimulation (RNS; application of 3 degrees C to a hand). This was done to investigate whether the previously established effects of RNS were likely to be related to a change in the subject's mental state and/or to direct nociceptive mechanisms. Both MEx and RNS caused increases in EMG activity around the Q-R and S-T transitions of the PSEC, which resulted principally from shortenings of the inhibitory Q and S waves. Reducing the intensity of the tap stimuli, which mimicked condition-induced disinhibition, caused shortenings of the inhibitory waves at latencies similar to the shortenings induced by MEx or RNS. The magnitude of the RNS-induced effect on the ST segment of the PSEC was greater (P<0.01) than that on the QR segment. By contrast, MEx induced similar effects on both segments. Regression analyses were performed for the relationship between condition-induced changes in amplitude of the excitatory waves and their control amplitudes. These analyses were performed to reveal any condition-induced inhibition or facilitation of the tap-induced influences on the motoneurons. Overall, the evidence suggested that: (1) mental exercise induced a similar degree of inhibition of the two tap-induced inhibitory jaw reflexes and a facilitation of the excitatory ones, and (2) remote noxious stimulation induced an inhibition of the second tap-induced inhibitory reflex which was greater than that of the first one, and an inhibition of the first excitatory reflex. Thus, although factors related to altered mental activity could play a role in the modulation of jaw reflexes by RNS, the differences between the effects of MEx and RNS suggest that alternative or complementary mechanisms are also likely to be involved.

Analysis of differences between conditioned and control reflex series in EMG recordings.

Two methods are presented for the data analysis of signals derived by subtracting conditioned from control reflex data in full-wave rectified and averaged electromyographic (EMG) signals. The first method uses the ratios of the mean amplitudes and standard errors of the mean (S.E.M.s) (i.e. Student's t values) of a series of data points in such a difference signal, and deals with the detection of latencies of reflex components which are susceptible to a conditioning stimulus or experimental situation. The second method applies a modified cumulative sum (CUSUM) technique to full-wave rectified difference signals. This modified CUSUM technique determines the magnitude of the effects of the conditioning situation above that expected due to chance fluctuations, taking into account the effect of reflex modulations on such chance fluctuations in a post-stimulus period. The modified CUSUM technique proved particularly useful when various subtle but consistent, opposing changes occurred sequentially in the conditioned series thus yielding a complicated pattern of effects in a difference signal, with a low signal-to-noise ratio.

Oral pressure receptors mediate a series of inhibitory and excitatory periods in the masseteric poststimulus EMG complex following tapping of a tooth in man.

Poststimulus EMG complexes (PSECs), consisting of a series of inhibitory and excitatory waves in full-wave rectified and averaged electromyogram (EMG), were elicited in the masseter muscles of 7 subjects following controlled tapping of a tooth, at a controlled clenching level. Applying local anaesthesia to this tooth decreased the total surface of the waves, on average by 89%. The excitatory and the inhibitory waves were similarly affected, indicating that mainly pressure receptors in the periodontium mediate the entire PSEC. In 4 subjects, who were exposed to acoustic noise to exclude a contribution of acoustic receptors, the recovery of the PSEC waves from local anaesthesia was tracked. In 3 subjects, one wave (the first inhibitory or the first excitatory one, respectively) recovered differently from the other waves, indicating that they are not necessarily mediated by one type of afferent axons. The evidence, nevertheless, suggests that the different PSEC waves in man reflect the projection of the periodontal afferents upon several brain structures, involved in the control of the activity of the masseteric motorneurones, as: inhibitory and excitatory control requires different groups of interneurones; and a mediation of the first inhibitory wave by slower conducting axons than the second inhibitory wave, or a mediation of both waves by axons of similar type, is not compatible with common interneurones.

Interactive periodontal and acoustic influences on the masseteric post-stimulus electromyographic complex in man.

Post-stimulus electromyogram (EMG) complexes (PSECs) were studied in the full-wave rectified and averaged EMGs of the masseter muscles in 15 subjects, who clenched at a controlled level. The PSECs, a series of downward- and upward-going waves reflecting inhibitory and excitatory influences upon the masseteric motoneurones, were elicited by mechanical stimulation of a tooth. The stimuli selectively activated mechanoreceptors in the periodontium and, by bone-conduction, acoustic receptors. Application of acoustic masking during the periods of stimulation revealed a series of inhibitory and excitatory acoustic influences in the PSEC, which were absent after local electrical stimulation of receptors in the periodontium or their afferents. By applying local anaesthesia to the periodontium of a mechanically stimulated tooth, the durations of the acoustic influences were on the average reduced by 76%. In subjects whose PSECs consistently included a second inhibitory period, the duration of the acoustic influences with respect to that of the PSEC (30%) was larger than otherwise (13%), suggesting a central gating of periodontal pathways which can block both periodontal and acoustic influences. The acoustic influences, of which the appearance in the PSEC largely depends upon activated periodontal pathways, represent a new finding of audio-motor reflexes.

Effects of remote noxious stimulation on exteroceptive reflexes in human jaw-closing muscles.

Reflexes evoked by applying non-painful taps to an incisor tooth were recorded from the jaw closing masseter and temporal muscles of 21 human subjects. A series of inhibitory, excitatory, inhibitory and excitatory waves (the 'Q, R, S and T' waves of the post-stimulus electromyographic complex (PSEC)) occurred in full-wave rectified and averaged electromyograms. Conditioning by remote noxious stimulation (RNS; application of 3 degrees C water to a hand) usually produced increases in activity at the Q-R and S-T transitions of the PSEC (at mean latencies of 24 and 54 ms respectively), which resulted principally from a shortening of the inhibitory Q and S waves. Changes in the amplitudes of the excitatory R and T waves were also found. The effects of RNS were quantified by integrating records of the difference between conditioned and control PSECs. The RNS-induced effect on the entire PSEC was significantly (P < 0.01) greater when the reflexes were evoked by applying hard (7.4 mN.s) as opposed to soft (3.4 mN.s) taps to the tooth. However the ratio between the effects on the ST and QR segments did not differ significantly between these two intensities of tap stimuli. RNS-induced sensations of pain and increases in systemic arterial blood pressure were not correlated with the RNS-induced effects on the different segments of the PSEC. The results suggest that RNS may affect particularly those elements of the PSEC evoked by higher threshold afferents and that the effects are mediated by mechanisms acting directly at the brainstem level and are not secondary to pain or autonomic responses.

Functional properties of area 19 as compared to area 17 of the cat.

Out of a total of 139 area 19 cells, 87 were examined quantitatively for their responses to stimuli moving at a wide range of velocities. The results were compared with those obtained on a sample of 106 area 17 cells (out of a total of 172) tested in the same way. It was found that both areas 19 and 17 prefer slow stimulus movement. However, area 17 responded well to velocities up to 4 degrees/s while response amplitudes of area 19 cells started to decrease for stimulus velocities over 0.3 degrees/s. In both areas, responsiveness to fast stimuli improved at higher eccentricities. The most frequently encountered velocity type in area 19 was the 'velocity broad band' (VBB) type, lacking velocity preference, while the rarest type was the 'velocity tuned' (VT) type. As in area 17 very few area 19 cells were found to prefer high velocities (velocity high pass type, VHP) and those that were encountered had peripheral receptive fields (RFs). Cells preferring exclusively low velocities (velocity low pass type, VLP) were less frequent in area 19 than in area 17 and were considerably more sluggish. Area 19 was also less direction and orientation selective than area 17. In contrast, end-stopping was very common in area 19 (66%) and more units were binocular as compared to area 17. On average firing rate during optimal stimulation was lower in area 19 than in area 17. These results are consistent with the notion that area 19 receives predominantly W-type input and is involved in form discrimination (low spatial frequencies) during fixation.

Receptive field structure of area 19 as compared to area 17 of the cat.

A total of 139 cells from area 19 along with a comparison sample of 172 cells from area 17 were classified using a system proposed by Orban and Kennedy, following Henry and consisting of 4 basic cell 'families', namely S, C, A and B, each having an end-stopped member: HS, HC, HA and HB. The two basic parameters separating the 4 families are firstly spatial overlap of ON and OFF subregions and secondly receptive field (RF) width. Spatial overlap was studied quantitatively in a number of these cells using multiple presentations of stationary slits or moving light and dark edges. RF width was determined quantitatively using bars moving at different velocities across the RF. It was found that cells with spatially nonoverlapping and overlapping subregions are present in both areas. S and HS cells, which show similarities with simple cells, were encountered in area 19 but they constituted only 18% of the population as opposed to 55% in area 17. C and HC cells, reminiscent of complex cells, were about as common in area 19 as in area 17. In both areas C cells were the only group which consistently discharged equally well or better in response to diffuse light turned on and off than when presented with light bars. A and B families formed a minority in both areas. Area 19 contained a larger proportion of nonoriented and undriveable units, as well as a special category of cells preferring stimuli with a width larger than the length ('rectangle cells'). RF width was generally larger in area 19 than in area 17 and its distribution in area 19 showed distinct peaks. In the part of area 19 subserving central vision these peaks appeared with a periodicity of 0.8 degrees, suggesting that cells in this zone are supplied by one or more rows of a uniform set of afferents having a RF center diameter of about 0.8 degrees. The identification of this population as W-relay cells is supported by the long latencies found in cells from this part of area 19. It is concluded that basic principles underlying the structure of the RF are similar in both areas 19 and 17.

A computer simulation of the influence of selection and breakage of food on the chewing efficiency of human mastication.

The reduction of food particle sizes during mastication is considered to be the composite result of a selection and breakage process. The chance of a food particle being selected between the teeth was assumed to increase as a power function of the particle's size, whereas the breakage of food particles was described by a cumulative distribution function. The selection and breakage functions were combined with matrix algebra, resulting in a matrix model. By use of this model, particle-size distributions could be calculated after various numbers of chewing cycles. From these distributions, the decrease of the median particle size was determined as a function of the number of chewing cycles. The calculations were performed for various sets of physiologically relevant selection and breakage variables. The number of chewing cycles, N1/2, needed for the initial particle size to be halved was taken as an indication of chewing efficiency. This number varied approximately inversely with both the selection coefficient and the breakage variable. The initial particle size appeared to have the largest influence on N1/2. The theoretical results from the simulation study were also compared with data obtained from experiments on human chewing efficiency.

The effect of an occlusal stabilization splint and the mode of visual feedback on the activity balance between jaw-elevator muscles during isometric contraction.

The aim of the present study was to gain an insight into the influence of a vertical bite-rise (clenching in intercuspal occlusion vs. clenching on an occlusal stabilization splint), the mode of visual feedback (VF; obtained from the compound masseter signal, from the compound anterior temporalis signal, or from the compound signal of both masseter and anterior temporalis muscles) and the EMG clenching level (10% MVC and 50% MVC) on the muscle balance between the masseter and the anterior temporalis muscles. The muscle balance was quantified as the logarithmic value of the ratio between the summated mean rectified EMG activity of the masseter muscles and this activity of the anterior temporalis muscles. The muscle balance was influenced significantly by the mode of VF (p < 0.01), the muscle balance shifting toward the group of muscles from which VF was obtained. When VF was obtained from the masseter muscles, a decrease in the anterior temporalis EMG activity was observed when the vertical dimension was increased (p < 0.05-0.01). When VF was obtained from the anterior temporalis muscles, the activity of the masseter muscles was raised with respect to that of the anterior temporalis muscles during clenching with a vertical bite-rise (p < 0.05-0.01). When VF was obtained from both groups of muscles, the masseteric EMG activity increased, whereas the anterior temporalis EMG activity decreased. Hence, regardless of the mode of VF, a relatively lower activity level of the anterior temporalis muscles was achieved after insertion of an occlusal stabilization splint.(ABSTRACT TRUNCATED AT 250 WORDS)

Rate modulation of jaw-elevator motor units as revealed from the low-frequency power spectrum of the surface electromyogram in myogenous CMD patients.

The firing pattern of the motor units (MUs) in jaw-elevator muscles was studied within a wide range of isometric contraction levels by means of changes in the frequency and broadness of the primary peak in the low-frequency (5-40 Hz) power spectral density function of the surface EMG. EMG was recorded from both masseter and anterior temporal muscles in 11 myogenous CMD patients as well as in 11 gender- and age-matched controls who clenched in intercuspal occlusion under the control of visual feedback at various levels (0.5-67% MVC for the various muscles studied). The EMG was digitized for 12 periods of 1.6 s per condition; the power spectrum was averaged and smoothed for the various clenching levels. Linear regression analysis showed that the positive slope in the peak frequency (PF)/% MVC relationship, a measure of rate modulation of the MUs, did not differ significantly between patients and controls. At a low clenching level, PF was smaller (p < 0.01) for the anterior temporal muscles of the patients, suggesting lower firing rates for a wide range of clenching levels of the patients because of a similar rate modulation for patients and controls. Furthermore, the variance in the slope values was larger (p < 0.05) for the masseteric muscles of the patients, which may be explained by more heterogeneity of the masseteric rate modulation in the patient group. The broadness of the primary peak was smallest at a low clenching level (p < 0.001) for the anterior temporal muscles of the patients, suggesting a more uniform firing rate or more synchronization between MUs.

The effect of particle size reduction on the jaw gape in human mastication.

Eight subjects participated in chewing experiments to examine how the jaw gape in consecutive chewing cycles depends on the dimensions and the volume of the food bolus. Different volumes of chewing-gum and a silicone rubber (Optosil) were used. The initial particle size of Optosil was also varied. With the aid of a sieving procedure, the size distribution of Optosil particles was determined after different numbers of chewing cycles. The maximum size of a chewing-gum bolus along three orthogonal axes was determined after a random number of chewing cycles for all the volumes of chewing-gum offered. The jaw gape was measured by means of an optical motion analysis system and calibrated at the level of the first molars. The maximum jaw gape and the gape at the first fall in mandibular velocity after the onset of jaw-closing were determined for different chewing cycles from the position signal and its time derivative. For each volume of chewing gum offered to the subject, the average of the maximum gapes attained in the subsequent cycles of jaw movement was related to the characteristic height of a bolus of that volume; maximum velocity of closing appeared to occur while the antagonistic teeth were already penetrating the gum bolus. The increase in the maximum jaw gape, the gape at the velocity maximum, and the height of the gum bolus, as a function of the volume of chewing-gum, could be well-described by a power function of the volume. The exponent of the power function for both jaw gapes was only slightly smaller than the exponent obtained for the bolus height.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of selection changes and breakage functions during chewing in man.

Food comminution in man was studied in terms of intra-oral selection and breakage processes, with a silicone rubber used as test food, aided by a sieving procedure and simultaneous form- and color-labeling of particles. The subjects chewed on mixtures of particles with a specific form (either cubes or half-cubes). In addition, seven particle sizes, within a range of 1.2 to 8.0 mm, each had a specific color. Damaged cubes or half-cubes revealed their chance of being selected for breakage. The color of the fragments indicated their original size, and thus the breakage distribution of selected particles. The selection chance increased as a power function of particle size. The degree of fragmentation was, in general, maximal for a particle size of about 4 mm. Our double-labeling technique permits a detailed unraveling of anatomical and physiological variables in the chewing process.