Papers
The following is a listing of research papers written by NDI's customers regarding .
Displaying results 1 to 5 of 5
Effect of an auditory cue on chewing cycle kinematics.
AM Wintergerst, B Hutchins, GS Throckmorton, PH Buschang
OBJECTIVES: This study analysed the systematic and random effects of a rhythmic auditory cue on chewing cycle kinematics. METHODS: The chin movements of 25 subjects (19-35 years of age) with normal class I occlusion were recorded at 100Hz (Optotrak) Northern Digital) during two natural gum chewing (2.5 g) sequences to determine the chewing rate of each subject. Another sequence was recorded with the subjects chewing at their natural rate following an audible cue. Multilevel modeling procedures were used to evaluate differences between natural chewing with and without an audible cue. RESULTS: Differences were found between experimental conditions for excursions, velocities and cycle shape. When chewing with the audible cue velocities were slower and there was less excursion of the chin marker, with the exception of initial lateral movements toward the balancing side. No differences in between-subject variability were found when chewing with or without an audible cue. Within-subject variability was 44% smaller for total cycle duration and 53% smaller for total 3D excursion when chewing with the auditory cue. CONCLUSIONS: Chewing at one's normal rate while following an auditory cue produces more consistency in chewing cycle kinematics. This method may be applicable, with some limitations, to reduce within-subject variability in chewing cycle kinematics.
The effects of bolus hardness on masticatory kinematics.
GS Throckmorton, H Hayasaki, K Anderson, PH Buschang
This study investigated how jaw kinematics, including cycle duration, three-dimensional (3-D) excursive ranges and velocities, and cycle shape, changed with increasing hardness of chewing gum. Twenty-six subjects (13 males and 13 females; mean age 23.6 +/- 2.5 years) with Class I normal occlusion were asked to chew two brands of gum with differing hardness. Jaw motion during chewing was tracked with an Optotrak camera at 100 Hz, and all movements were recorded as pure 3-D mandibular movements relative to Frankfort horizontal. Cycle duration did not change significantly with harder gum, but 3-D excursive ranges and velocities increased, except during the occlusal phases of the chewing. Cycle shape was similar for hard and soft gum, but the overall size of the cycle was larger with hard gum. These results suggest that greater muscular effort when chewing harder gum produces a greater acceleration of the mandible in all phases except when the harder gum slows the mandible during the occlusal phases.
Mandibular rest position: a reliable position influenced by head support and body posture.
EM Tingey, GS Throckmorton, PH Buschang
This prospective study was designed to establish how the positions of the molars and the condyles are related to incisor position in the mandibular rest position and how their positions are altered by changing head posture. Measurements of the mandibular rest position were taken on 24 men (age range, 23 to 35) with normal Class I occlusion, skeletal patterns, and temporomandibular joint function. The movements of 5 landmarks (lower incisor, and condyles and molars bilaterally) were tracked from maximum intercuspation into 4 independent rest positions (upright supported, upright unsupported, supine supported, and supine unsupported) using an optoelectric (Optotrak; Northern Digital, Waterloo, Ontario, Canada) computer system. The positions were based on minimal electromyographic and verbal instructions to swallow, lick the lips, and say "Mississippi." The results showed significant (P <.01) movements of the incisors, the molars, and the condyles into each of the 4 rest positions. Movements of the molars and the condyles into the supported upright posture and the unsupported upright posture differed slightly but significantly because of greater movement into the supported posture. Patterns of mandibular movement were entirely different between the upright and the supine rest positions; the mandible rotated anteriorly in the supine position and posteriorly in the upright position. We concluded that movement into the mandibular rest position from the intercuspal position is not a simple opening rotation of the mandible, and that the pattern of movement is influenced by head support and body postures.
Incisor and mandibular condylar movements of young adult females during maximum protrusion and lateratrusion of the jaw.
GS Throckmorton, H Hayasaki, KH Travers, PH Buschang
This study evaluated the correlations between condylar translation and incisor movements during maximum protrusion and lateratrusion. The sample was 27 adult females (23--35 years old), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements [linear distances (LD) and curvilinear pathways (CP)] were recorded in three dimensions for 20 s with an optoelectric (Optotrak) jaw-tracking system while each participant performed multiple maximum protrusive and lateratrusive cycles. Masticatory analysis and multilevel statistical programs computed the three-dimensional movements of the incisors and condylar hinge axis during protrusion and lateratrusion. CP of the incisor point averaged 12.0 mm (9.3 mm LD) during protrusion, 13.0 mm (11.5 mm LD) during right excursion and 12.3 mm (11.0 mm LD) during left excursion. CP of the condyles averaged 11.9--12.9 (9.2--9.5 LD) mm during protrusion. During lateratrusion the contralateral condyles moved anteroinferiorly 11.6--14.1 mm (9.5--10.2 mm LD); the ipsilateral condyles moved posterolaterally 5.8-6.8 mm (2.3--2.5 mm LD). The left condyles demonstrated more movement than the right condyles during protrusion and than the contralateral condyles during laterotrusion. Relative variation, as measured by the coefficient of variation, was greater for the movements of the ipsilateral than contralateral condyles. Incisor movements were only moderately related to condylar movements between individuals and between replicates; LDs showed stronger correlations than CPs; and correlations were stronger for lateratrusion than protrusion. While incisor and condylar movements were not affected by repeated protrusion, incisor CP (approx. 0.2 mm/cycle) and LD (approx. 0.1 mm/cycle) increased significantly with repeated excursive movements to the left and right. It was concluded that (1) incisor protrusion and lateratrusion provide moderately reliable measures of condylar translation; (2) the linear distances that the incisors move during lateratrusion provide the best measure of contralateral condylar translation; and (3) condylar movements are not affected by repeated protrusion or lateratrusion.
Associations between incisor and mandibular condylar movements during maximum mouth opening in humans.
GS Throckmorton, H Hayasaki, KH Travers, PH Buschang
This study evaluated the common clinical assumption that condylar translation and mouth opening at the incisor are closely related. The sample studied comprised 27 adult females (23-35 years), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements (straight-line distances and curvilinear pathways) were recorded in three dimensions (3D) for 20 s with an optoelectric (Optotrak(R)) jaw-tracking system while each participant performed multiple maximum opening cycles. Masticatory analysis and multilevel statistical programs computed the 3D movements of the incisors and condylar hinge axis during opening and closing. The incisor point moved an average straight-line distance of 46.6 mm during opening and 45.9 mm during closing; the lengths of the opening and closing curvilinear pathways were 48.6 and 47.7 mm, respectively. The condyles moved average straight-line distances of 11.9 and 12.2 mm during opening and closing, respectively. The condyles' curvilinear pathways during opening and closing were 14 and 14.6 mm, respectively. Ranges of condylar movement varied widely between individuals. The straight-line distances and curvilinear pathways were highly correlated for the incisors (R=0.98) and the condyles (R=0.98). Neither the straight-line distances nor curvilinear pathways of the incisors were correlated with those of the condyles. Incisor straight-line distances and curvilinear pathways were moderately correlated with mandibular rotation (R(between subjects)=0.82 and R(between repeats)=0.88). During repeated openings, both condylar and incisor excursions increased, but during repeated closings only incisor excursions increased. It is concluded that (1) maximum incisor opening does not provide reliable information about condylar translation and its use as a diagnostic indicator of condylar movement should be limited, (2) healthy individuals may perform normal opening with highly variable amounts of condylar translation, (3) the straight-line distances of the incisor and condyles provide adequate information about the length of the curvilinear pathway, and (4) variation in maximum incisor opening is largely explained by variation in the amount of mandibular rotation.
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