T-Scan Clinical Application Sheet
Centric Relation Utilizing the T-Scan II
Statement of Purpose/Treatment Significance
The importance of isolating the centric relation prematurity when performing an occlusal equilibration has
been advocated by numerous authors1-4. It is believed that when the condyles are properly positioned in centric
relation, both articular discs are properly positioned between the head of the mandibular condyle and the
superior aspect of the eminentia. At this fully seated condylar position, there is no stimulus for antagonistic
muscle hyperactivity5.
The centric relation prematurity can be located by various methods6-8 involving operator-guided mandibular
positioning. Numerous studies have shown that joint position is influenced by the method used to record
centric relation9-15. The method advocated by Dawson, known as bimanual manipulation8, has been widely
recognized and accepted as a predictable way to assure the correctness of a mandibular closure into the centric
relation position. The first occlusal contact that results from this bimanual manipulation procedure is known
as the centric relation prematurity.
To locate the centric relation prematurity, the operator relies on the patient to describe the general location of
the perceived first tooth-to-tooth contact, by "feel", as the guided mandibular closure brings the first few teeth
into contact.
The isolation of the centric relation prematurity can be accomplished more precisely by performing bimanual
manipulation in combination with a T-Scan II Real-Time Force Movie16 (recording) of the sequential tooth
contacts that result from the guided closure.
With real-time recording, it is possible to record a Force Movie16 of a guided mandibular closure into centric
relation, which describes the sequential ordering of tooth contacts. Additionally, the duration of time in which
the teeth are making occlusal contact, as they proceed from first contact in centric relation through the slide
from centric relation to maximum intercuspation until maximum intercuspation is reached, can be recorded,
and then visualized. The playback of the occlusal contact time data is presented to the operator on a sequential, frame-by-frame basis, or as a continuous movie from start to finish.
The incremental playback of a real-time recording of a guided closure into centric relation can illustrate to the
operator the location of the first tooth contact, its force content, and the length of time that it is premature to
the rest of the occlusal contacts. This information enhances the operator's ability to locate the first tooth
contact.
Contributory factors affecting successful implementation of the T-Scan II
Locating the centric relation prematurity is a "four-handed" procedure, during which the chair side assistant
holds the articulating ribbon forceps intraorally, as the operator holds the condyles on the centric relation axis
during closure.
Tekscan, Inc., 307 West First St., So. Boston, MA 02127-1309 / (617) 464-4500 / (800) 248-3669 / Fax (617) 464-4266
Updated July 2002
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The alternative technique is accomplished successfully with the chair side assistant managing the T-Scan II
recording handle (instead of articulating ribbon forceps), while the operator performs the bimanual manipulation.
Patient Preparation
Place the patient in a supine position, with their body parallel to the floor and head cradled between the arms
and midsection (see figure 1). Then practice the technique by attempting a few bimanual manipulation
closures without the presence of the T-Scan II recording handle. This will help to orient both the patient and
the operator to the technique, so that together they can repeatedly locate the centric relation position.
Figure 1
T-Scan II Preparation
Use the mouse to click the CR button on the T-Scan II toolbar (see Figure 2). This activates the centric
relation recording mode, which insures that the T-Scan II allows for adequate recording time length for the
operator to completely capture a bimanual manipulation procedure. The CR mode also raises the recording
sensitivity to compensate for the low occlusal forces that a guided closure generally produces.
Centric Relation Button
Figure 2
T-Scan Toolbar (with CR Button)
Recording technique
Prior to recording a centric relation Force Movie, the chair side assistant should place the T-Scan II recording
handle, with a sensor and arch support in place, between the maxillary Central Incisors of the patient. With
the patient lying parallel to the floor, the recording handle should be held nearly perpendicular to the floor (see
Figure 3).
2
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Updated July 2002
Figure 3
The chair side assistant commences the recording procedure by depressing, then releasing, the recording button
that is located on the top surface of the recording handle. A computer prompt sounds (to mark the beginning
of the real-time recording), after which the bimanual manipulation is commenced. After the mandible is
properly seated in the centric relation position, the mandible is closed to tooth contact with the sensor.
Locating the first centric relation contact
The playback of the recording will reveal the location, the time duration of prematurity, and the force content
of the first tooth contact. By attempting additional recordings (in the same manner as previously described),
the reproducibility of the determination of the first contact can be validated. It is recommended that at least
three bimanual manipulation recordings (Force Movies) be performed, to validate the location of the centric
relation prematurity.
Clinical Example
Bimanual manipulation Force Movies of a 31 year-old female Prosthodontist, who exhibited the signs and
symptoms often associated with chronic Myofascial Pain Dysfunction Syndrome, were taken. Her symptoms
were characterized as mostly muscle contraction type, combined with mild TM Joint clicking and popping.
Diagnostic load testing was accomplished to confirm the absence of non-adapted internal derangement in either
temporomandibular joint.
To begin testing, the patient was properly positioned. Initial training bimanual manipulation procedures were
practiced by the operator and the patient, until the patient consistently reported her awareness of a repeatable
first tooth contact. The patient reported that tooth #3 was consistently striking before all others.
With CR mode activated, the T-Scan II handle was inserted intraorally, and an initial centric relation bimanual
manipulation procedure was accomplished, using the sensor. The procedure was repeated three times for
validation and reproducibility. The T-Scan II consistently located the palatal occlusal slope on tooth #12 as
the first tooth contact that showed a moderate force level (see Figures 4 & 5). The first contact was
consistent in all three movies.
In figure 4, tooth #12 becomes forceful (the red contact) and tooth #14 approaches moderate force levels (the
yellow contact) in advance of the earliest contacts on tooth #3 (the blue contact).
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Updated July 2002
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CR prematurity
Palatal occlusal slope #12
Earliest forceful contacts
on left side of arch
Figure 4
Figure 5
In each of the centric relation recordings accomplished with bimanual manipulation, the first tooth contact on
tooth #12 consistently preceded the appearance of light force on tooth #3 by an average of 1.1 seconds. The
patientís perception of the first tooth contact was incorrect repeatedly. Figure 6 shows that the first contact is
much lighter in color intensity than those tooth contacts that occur later.
Figure 6
Conclusions
Locating the Centric Relation Prematurity by performing Bimanual Manipulation in combination with the TScan II can significantly improve the precision of the procedure. With the real-time recording capability of the
T-Scan II, tooth contact timing data can be sampled in .01 second increments. These fractional time increments will predictably reveal the correct sequence of tooth contact that results from performing the Bimanual
Manipulation. Therefore, the first tooth contact can be isolated with improved predictability over the alternative methodology (without computer analysis), which relies on the patientís subjective occlusal assessments.
4
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Updated July 2002
References
1. Dawson, PE. Diagnosis and Treatment of Occlusal Problems, ed. 2. St. Louis, CV Mosby Co. 1989.
2. Schuyler, CH. Fundamental principles in the correction of occlusal disharmony, natural and artificial.
JADA, Pp. 1193-1202, July, 1935
3. Glickman, l. Clinical Periodontology, ed. 4, Philadelphia, 1972, W.B. Saunders Co.
4. Long, JH. Occlusal adjustment. JPD 30:706-714, 1973.
5. Dawson, PE. Diagnosis and Treatment of Occlusal Problems. ed. 2. St Louis, CV Mosby Co. 1989.
Pp. 31.
6. Long, JH. Location of the terminal hinge axis by intraoral means. JPD 23:11, 1970.
7. Lucia, VO. A technique for recording centric relation. JPD 14:492, 1964.
8. Dawson, PE. Diagnosis and Treatment of Occlusal Problems, ed. 2. St. Louis, CV Mosby Co. 1989.
Pp. 41-47.
9. Kantor, ME, Silverman, SI, Garfinkel, L. Centric-relation recording techniques - a comparative
investigation. JPD 1972; 28:593-600.
10. Hobo, S., Iwara, T. Reproducibility of mandibular centricity in three dimensions. JPD 1985;53:64954.
11. Roblee, RD. The determination of the accuracy of six maxillomandibular relation techniques. [Thesis]
Waco, TX: Baylor University, 1989.
12. Wessberg GA, Epker, BN, Elliott AC. Comparison of mandibular rest position induced by phonetics,
transcutaneous electrical stimulation, and masticatory electromyography. JPD 1983;49:100-5.
13. Remien, JC 2nd, Ash M Jr. "Myo-monitor centric: an evaluationî. JPD 1974;31:137-45.
14. Bessette RW, Quinlivan JT. Electromyographic evaluation of the MyoMonitor. JPD 1973;30:19-24.
15. Dao TT, Feine JS, Lund JP. Can electrical stimulation be used to establish a physiologic occlusal
position? JPD 1988;60:509-14.
16. Maness, W.L., Force Movie. A time and force view of occlusion. Compendium 1989:10;404-8.
Tekscan, Inc., 307 West First St., So. Boston, MA 02127-1309 / (617) 464-4500 / (800) 248-3669 / Fax (617) 464-4266
Updated July 2002
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