Monday, January 3, 2011

Force production of the genioglossus as a function of muscle length in normal humans

  1. 1 Departments of Medicine and
  2. 3 Pediatrics, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Brunswick 08903; and
  3. 2 Department of Biomedical Engineering, Rutgers University, Piscataway, New Jersey 08554 Journal of Applied
Physiology May 2000 vol. 88 no. 5 1678-1684. 

Resting muscle length affects both maximum force production and force maintenance. The strength and force maintenance characteristics of the genioglossus as a function of resting muscle length have not been described. We hypothesized that genioglossus optimum length (L o) could be defined in vivo and that the ability of the genioglossus to sustain a given workload would decrease as resting length deviated from L o. To test this, 11 normal men repeated maximal isometric genioglossus protrusions at different muscle lengths to determineL o. L o was also obtained by using submaximal efforts while simultaneously recording electromyographic activity of the genioglossus, withL o defined as the length at which the force-to-genioglossus electromyographic activity ratio was maximum. Both methods provided similar results. Force maintenance was measured at four muscle lengths on separate days. Target efforts representing 60% of each subject's maximum at L o and lasting 5 s were performed at 12-s intervals. Time limit of endurance of the genioglossus was defined as the time from trial onset at which 90% of the target could not be maintained for three consecutive efforts. Time limit of endurance was greatest atL o and fell to 47.5% at L o + 1 cm, 53.8% at L o − 1 cm, and 47.4% atL o − 1.5 cm. We conclude thatL o of the genioglossus can be determined in vivo and that force maintenance of the genioglossus is decreased when operating length deviates from L o.

Sunday, August 22, 2010

Effect of Increased Maxillo-mandibular Relationship on Isometric Strength in TMD Patients with Loss of Vertical Dimension of Occlusion

Tariq Abduljabbar, D.D.S., M.S.; Noshir R. Mehta, D.M.D., M.S.; Albert G., Forgione, Ph.D.; R. Ernest Clark, Ph.D.; Joseph H. Kronman, D.M.D., Ph.D.; Theodore L. Munsat, M.D.; Patrick George, B.S.: Effect of Increased Maxillo-mandibular Relationship on Isometric Strength in TMD Patients with Loss of Vertical Dimension of Occlusion.  THE JOURNAL OF CRANIOMANDIBULAR PRACTICE JANUARY 1997, VOL. 15, NO. 1, pp. 57-67.

The effect on isometric strength of the shoulders and limbs while biting in habitual occlusion, on a bite-elevating appliance and on a placebo appliance was analyzed. Twenty female volunteer patients, presenting with temporomandibular pain dysfunction syndrome and obvious loss of vertical dimension, served as subjects. All were weaker to the manual application of the Isometric Deltoid Press (IDP) when biting, as opposed to maintaining the mandible in an unsupported rest position. Two intraoral appliances were fabricated for each subject: a bite-elevating appliance (BEA) set by a functional criterion of peak strength to the IDP and a placebo appliance which did not interfere with occlusion but was “set” with a mock IDP procedure. Testing was carried out by the Neuromuscular Research Testing
Laboratory of the Neurology Department of Tufts New England Medical Center. Testing was independent of the dentist who fabricated and set the appliances. A standard neuromuscular test with the Maximal Voluntary Isometric Contraction apparatus was used to assess strength of right and left shoulder, elbow and knee flexion and extension as is routinely performed with all neuromuscular disease
patients. Twelve strength tests were carried out for each of three conditions: 1. Baseline–biting in habitual occlusion; 2. Elevated–biting on the BEA; and 3. Placebo–biting with the placebo appliance inserted.  The order of conditions 2 and 3 was counterbalanced without knowledge of the subjects. Twelve repeated measures ANOVAs (each subject as their own control) were conducted for each of the 12
strength measures. All F-tests indicated a significant main effect for treatment differences (p<0.0001).  Mean strength biting on the BEA was consistantly greater (p< 0.001) than Baseline or Placebo strength.  Baseline and Placebo condition were equivalent. These findings confirmed previous observations at this TMD Center: individuals with loss of vertical dimension of occlusion respond to a bite raising appliance by increased isometric-strength.

The Effect of Vertical Dimension and Mandibular Position on Isometric Strength of the Cervical Flexors

Hala AL-Abbasi, B.D.S., M.S., D.Sc.; Noshir R. Mehta, D.M.D., M.D.S., M.S.; Albert G. Forgione, Ph.D.; R. Ernest Clark, Ph.D.; The Effect of Vertical Dimension and Mandibular Position on Isometric Strength of the Cervical Flexors. THE JOURNAL OF CRANIOMANDIBULAR PRACTICE APRIL 1999, VOL. 17, NO. 2, pp. 85-92.
This study compared the peak isometric strength of the cervical flexors in deep bite temporomandibular dysfunction (TMD) patients while biting in four bite positions: habitual occlusion, edgeto-edge, lateral shift and retruded. These values were then compared to those of the same subjects’ bite positions elevated to a functional criterion (maximum isometric strength of the deltoid muscles). The mean height increase was 2.4 mm with a range of 1.5-3.8 mm. Fifteen of eighteen deep bite subjects met an inclusionary criterion, at least 13.3 Newtons (N) stronger cervical muscle strength with mandible relaxed open than habitual bite. Peak strength biting edge-to-edge was significantly greater than biting in habitual occlusion. Strength was found to increase significantly when biting in each of four mandibular
positions when the bite was elevated to the functional criterion. The greatest strength was obtained from elevated habitual and edge-to-edge positions. The findings are of clinical significance, suggesting that cervical muscle isometric strength is affected by bite position and vertical dimension of occlusion. The results suggest that when biting, individuals with deep bite may be functioning at about 60% of their
potential cervical flexor, isometric strength. The interaction between occlusal position, vertical dimension and cervical muscle function suggests a craniomandibular-cervical masticatory system.

Examination of the Relationship Between Mandibular Position and Body Posture

Kiwamu Sakaguchi, D.D.S., Ph.D.; Noshir R. Mehta, D.M.D., M.D.S., M.S.; Emad F. Abdallah, D.M.D., M.S.; Albert G. Forgione, Ph.D.; Hiroshi Hirayama, D.D.S., D.M.D., M.S.; Takao Kawasaki, D.D.S., Ph.D.; Atsuro Yokoyama, D.D.S., Ph.D.; Examination of the Relationship Between Mandibular.  The Journal of  Craniomandibular Practice, October 2007, Vol. 25, No. 4. pp. 237-249.

The purpose of this study was to evaluate the effect of changing mandibular position on body posture and reciprocally, body posture on mandibular position. Forty-five (45) asymptomatic subjects (24 males and 21 females, ages 21-53 years, mean age 30.7 years) were included in this study and randomly assigned to one of two groups, based on the table of random numbers. The only difference between group I and group II was the sequence of the testing. The MatScan (Tekscan, Inc., South Boston, MA) system was used to measure the result of changes in body posture (center of foot pressure: COP) while subjects maintained the following 5 mandibular positions: 1) rest position, 2) centric occlusion, 3) clinically midlined jaw position with the labial frena aligned, 4) a placebo wax appliance, worn
around the labial surfaces of the teeth and 5) right eccentric mandibular position. The T-Scan II (Tekscan, Inc., South Boston, MA) system was used to analyze occlusal force distribution in two postural positions, with and without a heel lift under the right foot. Total trajectory length of COP in centric occlusion was shorter than in the rest position (p<0.05). COP area in right eccentric mandibular position was larger than in centric occlusion (p<0.05). When subjects used a heel lift under the right foot, occlusal forces shifted to the right side compared to no heel lift (p<0.01). Based on these findings, it was concluded that changing mandibular position affected body posture. Conversely, changing body posture affected mandibular position.

Effects of different jaw relations on postural stability in human subjects

P. Bracco, A. Deregibus*, R. Piscetta: Biomedical Sciences and Human Oncology Department, University of Torino, C.so Dogliotti 14, I-10126 Torino, Italy, Received 22 August 2003; received in revised form 24 November 2003; accepted 27 November 2003
Authors investigated the effects of different jaws relations on body posture in a sample of 95 subjects. All subjects underwent a
posturometric and stabilometric analysis using a computerized footboard. Tests were performed in three mandibular positions: centric
occlusion, rest position and myocentric position, respectively determined by teeth engagement, joints position, and muscles contraction. All subjects showed variations of body posture in the different mandibular positions. Statistical analysis (analysis of variance for repeated
measures) confirmed that postural variations in different jaws relations were significant: in particular, the SKN multiple comparison test
showed that myocentric position improved postural balance on frontal plane with respect to the other jaw positions considered.

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