- Email: [email protected]
Distribution of occlusal contacts in maximum intercuspation
PIERCEANDGOODKIND
45.
46. 47. 48. 49.
chromium release in viva: a 120-day rat study. J Biomed Mater Res 1986;20:219-33. Merritt K, Brown SA, Sharkey NA. Blood distribution of nickel, cobalt and chromium following intramuscular injection into hamsters. J Biomed Mater Res 19&1,18:991-1004. Rogers GT. In viva production of hexavalent chromium. Biomaterials 1984$244-5. Moffa JP, Beck WD, Hoke AW. Allergic response to nickel-containing dental alloys. J Dent Res 1977;56B78:No. 107. Ferguson AH, Laing MB, Hodge ES. The ionization of metal implants in living tissues. J Bone Joint Surg 1960,42:77-90. PafTenbarger GC, Caul HL. Base metal alloys for oral restorations. J Am Dent Assoc 1943;30:382.
Distribution William
of occlusal
L. Maness,
50. Rae T. The haemolytic action of particulate metals (Cd, Cr, Co, Fe, MO, Ni, Ta, Ti, Zn, Co-Cr alloy). J Path01 1978;125:81-9. 51. Arvidson K, Cottler-Fox M, Hammarlund E, Friberg U. Cytotoxic effects of cobalt-chromium alloys on fibroblasts derived from human gingiva. Stand J Dent Res 1986;95:356-63. 52. Stenberg T. Release of cobalt from cobalt chromium alloy construction in the oral cavity of man. Stand J Dent Res 1982;90:472-9. Reprint
contacts
D.D.S., M.S.,* and Robert
requests
to:
DR. LEWIS N. PIERCE 2273 GORWN AVE. ST. PAUL, MN 55108
in maximum
Podoloff,
intercuspation
S.M., B.S.M.E.**
Tufts University, School of Dental Medicine, Boston, Mass., and Tekscan Incorporated, Mass.
Boston,
This study describes the use of the T-Scan system to record and analyze tooth contact data by calculating time moment statistics in the sagittal and transverse axes of the occlusal plane and reports the results of this method to analyze the occlusion of 93 normal subjects. Results confirm the tidings of previous investigators and indicate that in a normal dentition there is a tendency for bilateral equality of the tooth contacts about the sagittal axis and that the center of effort for tooth contacts anteroposteriorly is located in the region of the first molar and is symmetrical bilaterally. Because of the rapid and accurate ability of the T-Scan system to identify the distribution of the tooth contacts, it shows great promise as a clinical diagnostic screening device for occlusion. (J PROSTAET DENT 1989$X%238-
42.)
M
any investigators have studied the distribution of tooth contacts in maximum intercuspation and have reported contact locations with respect to the tooth position.lM6The methods used to identify tooth contacts in thesestudiescan be divided into two types: qualitative and quantitative tests. Qualitative methodsare those requiring the investigator to make decisionsabout the nature of the tooth contacts. These methods involve the use of marking papers, shim stocks, occlusal waxes, silicone impressions,or combinations of these materials to identify the presenceof tooth contacts, and the results are recorded by counting the contacts and describing the tooth locations. Quantitative methodsdependon a reliable measurement system to describe the nature of the tooth contacts. Two types of quantitative systemsare reported in the literature: photocclusion,7 which describescontact. intensities, and the T-&an system,8which describesthe timing and force characteristics of tooth contacts. This article describesthe method using the T-Scan sys-
*Associate Clinical Professor, Department of Graduate and Poatgraduate Proethodontics, Tufta University, School of Dental Medicine; Chairman, Tekecan Incorporated. **Director
238
of Engineering,
Tekscan
Incorporated.
tern to analyze tooth contacts asreflected by time moment statistics and reports the results describing distribution of tooth contacts in maximum intercuspation for 93 normal patients.
MATERIAL
AND
METHODS
The T-Scan system (Fig. 1) digitizes the location and timing of tooth contacts and presentsa rapid, quantitative method of describing tooth contact data. These numerical data provide accurate, analyzable, and comprehensive evaluations of tooth contact information by showing momenta of time in two axes:the sag&al axis and the transverse axis of the occlusalplane. Time moments are defined as the sum of the distances of the tooth contacts in millimeters from the X or Y axis of the occlusalplane multiplied by their relative time values (l-t. set) and divided by the sum of the onset times. By analyzing the time moments in these axes, any occlusion can be uniquely described. Ninety-three adult patients with complete natural dentitions showingno signsof occlusalcomplications were selected for the study. The subjects were primarily dental studentsfrom three separateuniversities. They were asked to sit upright in the dental chair and closeon the sensorin maximum intercuspation with normal biting pressure. Several practice closures were made until a repeatable AUGUSTlOSs
VOLUME62
NUMBER2
DISTRIBUTION
OF OCCLUSAL
Fig.
CONTACTS
1 Schematic
diagram of T-Scan system.
Fig. 2. Typical time sequence display shows tooth contacts and their relative time sequence values. Note value for duration of closure of 0.18 sec. Fig. 3. Diagram shows calculation of total left-right statistic. Calculated value for tooth contacts presented in example is TLR = -3.49 mm. Fig. 4. Diagram shows calculation of right front-back and left front-back statistics. Reference line represents transverse axis. Calculated values for RFB and LFB statistics in this example are 34.30 mm and 30.20 mm, respectively.
pattern of contact was seen on the video monitor, and at that time four closures were recorded in the time mode. In Fig. 2 a typical time sequence display shows the tooth contact position and relative timing. After data collection, a special version of the T-Scan software compiled the following descriptive statistics that determine the time moment of the occlusion in the sagittal and transverse axes.
Total
left-right
statistic
The total left-right (TLR) statistic (Fig. 3) is calculated as the sum of the distances of the contact points from the THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
midsaggittal plane with each distance weighted by the timing of the tooth contact. In this way, a subject who exhibits ideal bilateral simultaneity with equal distribution of tooth contacts will have a TLR of zero
Right front-back statistics
and left
front-back
The right front-back (RFB) and left front-back (LFB) statistics (Fig. 4) are calculated as the sum of the distances of each contact point on the respective side of the midsagittal plane from the reference point established by the sensor support (Y axis at the incisal plane). As with the TLR 239
MANESS
-aa
-aa
-1.
.
.I
”
aI
.
1.
I
m
AND
PODOLOFF
Y
”
nillAamtorm
n111iaDtorm
Fig. 5. Frequency histogram shows total left-right (TLR) tooth contact distribution. Note that curve shows statistically insignificant skew to right.
Fig. 7. Frequency histogram showsleft front-back tooth contact distribution.
RESULTS
Fig. 6. Frequency histogram shows (RFB) tooth contact distribution.
right
front-back
statistic, these distances are weighted by their onset times. Because of the way these evaluative statistics are defined, a person with ideal bilateral simultaneity and equal distribution would have equal RFB and LFB values. The actual magnitude of these statistics would be dependent on the relative distribution of the anterior and posterior tooth contacts. 240
An average of four closuresfrom 93 adult subjectswith intact dentitions were recorded and analyzed with regard to the TLR, RFB, and LFB values. For the purposesof analysis,the data were grouped into frequency rangesof 5 units. The summaryfrequency histogramsare presentedin Figs. 5 through 7 and the statistical summary data in Table I. The mean for the TLR statistic was 0.30 mm with a standard deviation of 6.48mm and a standard error of 0.68. The mean value indicated a statistically insignificant displacement to the right for the tooth contacts about the midsagittal plane. The normal probability plot is alsopresented in Fig. 8 and showsthe tendency of the TLR data to conform to a normal distribution. A one-samplenormality analysisto determine how well the TLR data conformed to a normal curve yielded a t value of 0.45 with a correspondingp > 0.60 indicating that the tooth contacts around the sagittal axis tended to be symmetric and conformed to a standardized normal distribution. The RFB statistic exhibited a meanof 28.11mm, a standard deviation of 7.23 mm, and a standard error of 0.76. The LFB statistic had a meanof 27.78mm, a standard deviation of 8.08 mm, and a standard error of 0.85. The means for the RFB and LFB statistics were also compared for differences with Student’s t-test for related samples,which yielded a value of t = 0.48 with p < 0.63, indicating that the meanswere statistically equal. Correlations betweenthe TLR, RFB, and LFB variables were examined by using the Pearsonproduct moment correlation test (Table II). No significant correlation was AUGUST
1989
VOLUME
62
NUMBER
2
DISTRIEUTION
OF OCCLUSAL
CONTACTS
I. Summary table for total left-right (TLR), right front-back (RFB), and left front-back statistics Table
Test
N
TLR RFB LFB
93 93 93
TLR vs. perfect, p > 0.63.
Mean (mm)
SD (mm)
SE
00.30 28.11
6.48 7.23
0.68 0.76
27.78
8.08
0.85
t = 0.45; DF, 92; p > 0.60. RFB
vs. LFB,
t = 0.48;
DF, 92;
II. Pearsonproduct moment correlations for TLR, RFB, and LFB variables Table
TLR
TLR RFB LFB **Significant,
RFB
LFB
-0.163
0.196
----...i----
0.625**
-u
p < 0.01.
-4
.
*
I
found between the TLR and the RFB and LFB statistics, but the RFB and LFB measuresdemonstrated a high degree of correlation (p < 0.01).
Fig. 8. Normally distributed probability plot for TLR time moment statistic.
DISCUSSION
to demonstrate relative bilateral symmetry of the tooth contacts describedby time moments, the TLR value may provide a rapid initial screening device for the patient’s occlusion, especially when used in combination with the total duration of closure statistic.g The total duration of closure statistic is a calculation of the total elapsed time from first contact to last and is always reported by the TScan system for any closure. The total duration of closurestatistic and its relationship to muscleincoordination hasonly recently beendescribed, but a distinct relationship appearsto exist betweenthe repeatability of total duration valueson closurein maximum intercuspation and muscular incoordination. Researchin this field is in progressasare further studies to determine the TLR values for patients exhibiting symptoms of muscle dysfunction, for comparisonof tooth contact asymmetry.
Contact
distribution
about
the sagittal
axis
The distribution of tooth contacts about the sagittal axis of the occlusalplane, as describedby the TLR statistic in 93 normal patients, demonstratesthat there is a tendency for tooth contacts to be symmetric about the axis as reflected by the TLR mean of 0.30 mm. Perfect symmetry would have had a mean of 0 mm. This finding supports the conclusionsof Neff et al.5when they describedthe asymmetry coefficient, which wasa calculation made from the contact intensities as they varied about the sagittal axis of the occlusalplane with photocelusion. Using this method, they found a high degree of symmetry of the tooth contacts about the sagittal axis with most contacts being in the posterior region. Riise and Ericksson3in a study of contact distribution in adults found that a significant number of subjects had at least 60% of their tooth contacts on oneside with light and hard pressureand that the differenceswere randomly distributed betweenthe right and left sides.Thesefindings do not support the tendency for a symmetric distribution about the sagittal axis. The TLR, however, not only measuresthe total number of contacts, but alsotheir relationship to a fixed reference plane (sagittal axis) multiplied by their relative time values. This statistic results in a time moment or a timeweighted average of the occlusal contacts, and therefore addsanother dimensionto the description of occlusaldata. Becauseof the tendency for a normal patient population THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Distribution
of anteroposterior
contact
The mean values for the RFB and LFB statistic in the normal samplewere 28.11 and 27.78,respectively, placing most of the force of occlusionin the region of the second premolar and first molar.‘OThe Student t-test showedthe RFB and LFB meansto be equal (p > 0.05), indicating that the tooth contacts on the right and left sides,asmeasured anteroposteriorly from the transverse axis, tended to be bilaterally symmetric. These findings are consistent with those of other investigators1-5who found that there were more contacts in the molar and premolar regions than in the anterior teeth in normal young adult and adult popu241
MANESS
lations and supports the conclusion that the center of effort for mastication is in the region of the first molar. A strong correlation was found between the RFB and LFB statistics, which is almost expected in a normal patient population from the results of some previous investigators. However, the correlations that may exist in abnormal patient populations show the direction for future studies, especially as the TLR varies from symmetry.
Significance
of the time
moment
statistic
Time moment statistics, as described, are a measure of the distribution of tooth contacts with respect to the sagittal and transverse axes of the occlusal plane multiplied by their relative onset times and reflected by the TLR, RFB, and LFB values. The TLR, RFB, and LFB values, when used in combination, can uniquely identify an occlusion and describe the tendency to conform to the values of the normal population, resulting in an estimate of the symmetry and distribution of the tooth contacts. By using the time moment statistic, the investigator is able to understand the distribution of tooth contacts as they are weighted by their contact order and identify patients with asymmetric occlusal patterns. Because this measure reflects the presence of significant prematurities, it adds a dynamic aspect to the description of occlusal contact distribution. In a clinical situation where there are equal contacts bilaterally, but one side is substantially premature, a measurement system that can only identify the presence or absence of tooth contacts, such as marking paper, would conclude that the distribution was equal. This information, although important, ignores the clinical significance of the tooth contact data that is reflected by time moment statistics and has undeniable clinical significance as an estimate of bilateral simultaneity.
CONCLUSIONS This study had two objectives. The first objective was to present a digital measurement system and a set of statistics to identify occlusion contacts as described by time moments in the sagittal and transverse axes of the occlusal plane. The second objective was to present the results describing the distribution of tooth contacts in maximum intercuspation for 93 normal patients by using this method. From the information gathered, it is possible to make the following conclusions:
242
AND
PODOLOFF
1. The distribution of occlusal contacts in maximum intercuspation described by the T-Scan system conforms to the conclusions of other investigators using other methods. 2. There is a strong tendency for tooth contacts in maximum intercuspation to be symmetric about the sagittal axis of the occlusal plane as reflected by the time moment statistic (TLR). 3. The location of the center of effort for the anteroposterior tooth contacts measured from the transverse axis of the occlusal plane, as reflected by the time moment statistics RFB and LFB, is in the second premolar-first molar region and is bilaterally symmetric in a normal dentition. 4. The method of data collection offered by the T-Scan and the TLR, RFB, and LFB statistics describing the time moments in the sagittal and transverse axes of the occlusal plane show great promise as a clinical screening device for easily identifying the distribution of tooth contacts. We thank Dr. Peter Neff, Georgetown University, and Dr. George Maryniuk, University of North Carolina, School of Dentistry, Chapel Hill, for their support in the data collection effort.
REFERENCES 1. Beyron H. Occhrsal relations and mastication in Australian aborigines. Acta Odontol &and 1964,22:597-678. 2. Riise C. A clinical study of the number of occlusal tooth contacts in the intercuspal position at light and hard pressure in adults. J Oral Rehabil 1982;9:469-77. 3. Riise C, Ericksson SG. A clinical study of the distribution of occlusal tooth contacts in the intercuspal position at light and hard pressure in adults J Oral Rehabil 1983;10:473-86. 4. Berry DC, Singh BP. Diurnal variations in occlusal contacts. J PROSTHET DENT
1983;50:386-91.
5. Neff P, Binderman I, Arcan M. The diagram of contact intensities: a basic characteristic of occlusion. J PROSTHJST DENT 1985;53:697-702. 6. Amsterdam M, Purdum LC, Purdum KL. The occlusalgraph: a graphic representation of photocclusion data. J PROSTHET DENT 1987;57:94-8. 7. Arcan M, Zandman F. Mechanics of contact and memorized birefringence. Seances Acad Sci 1980;290:B-17. 8. Maness W, Benjamin M, Podoloff R, Bobick A, Golden R. Computerized occlusal analysis: a new technology. Quint Internat 1987;4:287-92. 9. Maness W. Comparison of the duration of occlusal contacts during habitual closure using the digital occlusal sensor [Abstract]. J Dent Res 1986;65:141. 10. Mack PJ. Maxillary arch and central incisor dimensions in a Nigerian and British population sample. J Dent 1981;9:67-70.
Reprint requests tot DR. WILJ.UM L. MANFS LEWIS WI-LUG BAY 237 BOSTON, MA 02110
AUGUST
1989
VOLUME
62
NUMBER
2
45.
46. 47. 48. 49.
chromium release in viva: a 120-day rat study. J Biomed Mater Res 1986;20:219-33. Merritt K, Brown SA, Sharkey NA. Blood distribution of nickel, cobalt and chromium following intramuscular injection into hamsters. J Biomed Mater Res 19&1,18:991-1004. Rogers GT. In viva production of hexavalent chromium. Biomaterials 1984$244-5. Moffa JP, Beck WD, Hoke AW. Allergic response to nickel-containing dental alloys. J Dent Res 1977;56B78:No. 107. Ferguson AH, Laing MB, Hodge ES. The ionization of metal implants in living tissues. J Bone Joint Surg 1960,42:77-90. PafTenbarger GC, Caul HL. Base metal alloys for oral restorations. J Am Dent Assoc 1943;30:382.
Distribution William
of occlusal
L. Maness,
50. Rae T. The haemolytic action of particulate metals (Cd, Cr, Co, Fe, MO, Ni, Ta, Ti, Zn, Co-Cr alloy). J Path01 1978;125:81-9. 51. Arvidson K, Cottler-Fox M, Hammarlund E, Friberg U. Cytotoxic effects of cobalt-chromium alloys on fibroblasts derived from human gingiva. Stand J Dent Res 1986;95:356-63. 52. Stenberg T. Release of cobalt from cobalt chromium alloy construction in the oral cavity of man. Stand J Dent Res 1982;90:472-9. Reprint
contacts
D.D.S., M.S.,* and Robert
requests
to:
DR. LEWIS N. PIERCE 2273 GORWN AVE. ST. PAUL, MN 55108
in maximum
Podoloff,
intercuspation
S.M., B.S.M.E.**
Tufts University, School of Dental Medicine, Boston, Mass., and Tekscan Incorporated, Mass.
Boston,
This study describes the use of the T-Scan system to record and analyze tooth contact data by calculating time moment statistics in the sagittal and transverse axes of the occlusal plane and reports the results of this method to analyze the occlusion of 93 normal subjects. Results confirm the tidings of previous investigators and indicate that in a normal dentition there is a tendency for bilateral equality of the tooth contacts about the sagittal axis and that the center of effort for tooth contacts anteroposteriorly is located in the region of the first molar and is symmetrical bilaterally. Because of the rapid and accurate ability of the T-Scan system to identify the distribution of the tooth contacts, it shows great promise as a clinical diagnostic screening device for occlusion. (J PROSTAET DENT 1989$X%238-
42.)
M
any investigators have studied the distribution of tooth contacts in maximum intercuspation and have reported contact locations with respect to the tooth position.lM6The methods used to identify tooth contacts in thesestudiescan be divided into two types: qualitative and quantitative tests. Qualitative methodsare those requiring the investigator to make decisionsabout the nature of the tooth contacts. These methods involve the use of marking papers, shim stocks, occlusal waxes, silicone impressions,or combinations of these materials to identify the presenceof tooth contacts, and the results are recorded by counting the contacts and describing the tooth locations. Quantitative methodsdependon a reliable measurement system to describe the nature of the tooth contacts. Two types of quantitative systemsare reported in the literature: photocclusion,7 which describescontact. intensities, and the T-&an system,8which describesthe timing and force characteristics of tooth contacts. This article describesthe method using the T-Scan sys-
*Associate Clinical Professor, Department of Graduate and Poatgraduate Proethodontics, Tufta University, School of Dental Medicine; Chairman, Tekecan Incorporated. **Director
238
of Engineering,
Tekscan
Incorporated.
tern to analyze tooth contacts asreflected by time moment statistics and reports the results describing distribution of tooth contacts in maximum intercuspation for 93 normal patients.
MATERIAL
AND
METHODS
The T-Scan system (Fig. 1) digitizes the location and timing of tooth contacts and presentsa rapid, quantitative method of describing tooth contact data. These numerical data provide accurate, analyzable, and comprehensive evaluations of tooth contact information by showing momenta of time in two axes:the sag&al axis and the transverse axis of the occlusalplane. Time moments are defined as the sum of the distances of the tooth contacts in millimeters from the X or Y axis of the occlusalplane multiplied by their relative time values (l-t. set) and divided by the sum of the onset times. By analyzing the time moments in these axes, any occlusion can be uniquely described. Ninety-three adult patients with complete natural dentitions showingno signsof occlusalcomplications were selected for the study. The subjects were primarily dental studentsfrom three separateuniversities. They were asked to sit upright in the dental chair and closeon the sensorin maximum intercuspation with normal biting pressure. Several practice closures were made until a repeatable AUGUSTlOSs
VOLUME62
NUMBER2
DISTRIBUTION
OF OCCLUSAL
Fig.
CONTACTS
1 Schematic
diagram of T-Scan system.
Fig. 2. Typical time sequence display shows tooth contacts and their relative time sequence values. Note value for duration of closure of 0.18 sec. Fig. 3. Diagram shows calculation of total left-right statistic. Calculated value for tooth contacts presented in example is TLR = -3.49 mm. Fig. 4. Diagram shows calculation of right front-back and left front-back statistics. Reference line represents transverse axis. Calculated values for RFB and LFB statistics in this example are 34.30 mm and 30.20 mm, respectively.
pattern of contact was seen on the video monitor, and at that time four closures were recorded in the time mode. In Fig. 2 a typical time sequence display shows the tooth contact position and relative timing. After data collection, a special version of the T-Scan software compiled the following descriptive statistics that determine the time moment of the occlusion in the sagittal and transverse axes.
Total
left-right
statistic
The total left-right (TLR) statistic (Fig. 3) is calculated as the sum of the distances of the contact points from the THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
midsaggittal plane with each distance weighted by the timing of the tooth contact. In this way, a subject who exhibits ideal bilateral simultaneity with equal distribution of tooth contacts will have a TLR of zero
Right front-back statistics
and left
front-back
The right front-back (RFB) and left front-back (LFB) statistics (Fig. 4) are calculated as the sum of the distances of each contact point on the respective side of the midsagittal plane from the reference point established by the sensor support (Y axis at the incisal plane). As with the TLR 239
MANESS
-aa
-aa
-1.
.
.I
”
aI
.
1.
I
m
AND
PODOLOFF
Y
”
nillAamtorm
n111iaDtorm
Fig. 5. Frequency histogram shows total left-right (TLR) tooth contact distribution. Note that curve shows statistically insignificant skew to right.
Fig. 7. Frequency histogram showsleft front-back tooth contact distribution.
RESULTS
Fig. 6. Frequency histogram shows (RFB) tooth contact distribution.
right
front-back
statistic, these distances are weighted by their onset times. Because of the way these evaluative statistics are defined, a person with ideal bilateral simultaneity and equal distribution would have equal RFB and LFB values. The actual magnitude of these statistics would be dependent on the relative distribution of the anterior and posterior tooth contacts. 240
An average of four closuresfrom 93 adult subjectswith intact dentitions were recorded and analyzed with regard to the TLR, RFB, and LFB values. For the purposesof analysis,the data were grouped into frequency rangesof 5 units. The summaryfrequency histogramsare presentedin Figs. 5 through 7 and the statistical summary data in Table I. The mean for the TLR statistic was 0.30 mm with a standard deviation of 6.48mm and a standard error of 0.68. The mean value indicated a statistically insignificant displacement to the right for the tooth contacts about the midsagittal plane. The normal probability plot is alsopresented in Fig. 8 and showsthe tendency of the TLR data to conform to a normal distribution. A one-samplenormality analysisto determine how well the TLR data conformed to a normal curve yielded a t value of 0.45 with a correspondingp > 0.60 indicating that the tooth contacts around the sagittal axis tended to be symmetric and conformed to a standardized normal distribution. The RFB statistic exhibited a meanof 28.11mm, a standard deviation of 7.23 mm, and a standard error of 0.76. The LFB statistic had a meanof 27.78mm, a standard deviation of 8.08 mm, and a standard error of 0.85. The means for the RFB and LFB statistics were also compared for differences with Student’s t-test for related samples,which yielded a value of t = 0.48 with p < 0.63, indicating that the meanswere statistically equal. Correlations betweenthe TLR, RFB, and LFB variables were examined by using the Pearsonproduct moment correlation test (Table II). No significant correlation was AUGUST
1989
VOLUME
62
NUMBER
2
DISTRIEUTION
OF OCCLUSAL
CONTACTS
I. Summary table for total left-right (TLR), right front-back (RFB), and left front-back statistics Table
Test
N
TLR RFB LFB
93 93 93
TLR vs. perfect, p > 0.63.
Mean (mm)
SD (mm)
SE
00.30 28.11
6.48 7.23
0.68 0.76
27.78
8.08
0.85
t = 0.45; DF, 92; p > 0.60. RFB
vs. LFB,
t = 0.48;
DF, 92;
II. Pearsonproduct moment correlations for TLR, RFB, and LFB variables Table
TLR
TLR RFB LFB **Significant,
RFB
LFB
-0.163
0.196
----...i----
0.625**
-u
p < 0.01.
-4
.
*
I
found between the TLR and the RFB and LFB statistics, but the RFB and LFB measuresdemonstrated a high degree of correlation (p < 0.01).
Fig. 8. Normally distributed probability plot for TLR time moment statistic.
DISCUSSION
to demonstrate relative bilateral symmetry of the tooth contacts describedby time moments, the TLR value may provide a rapid initial screening device for the patient’s occlusion, especially when used in combination with the total duration of closure statistic.g The total duration of closure statistic is a calculation of the total elapsed time from first contact to last and is always reported by the TScan system for any closure. The total duration of closurestatistic and its relationship to muscleincoordination hasonly recently beendescribed, but a distinct relationship appearsto exist betweenthe repeatability of total duration valueson closurein maximum intercuspation and muscular incoordination. Researchin this field is in progressasare further studies to determine the TLR values for patients exhibiting symptoms of muscle dysfunction, for comparisonof tooth contact asymmetry.
Contact
distribution
about
the sagittal
axis
The distribution of tooth contacts about the sagittal axis of the occlusalplane, as describedby the TLR statistic in 93 normal patients, demonstratesthat there is a tendency for tooth contacts to be symmetric about the axis as reflected by the TLR mean of 0.30 mm. Perfect symmetry would have had a mean of 0 mm. This finding supports the conclusionsof Neff et al.5when they describedthe asymmetry coefficient, which wasa calculation made from the contact intensities as they varied about the sagittal axis of the occlusalplane with photocelusion. Using this method, they found a high degree of symmetry of the tooth contacts about the sagittal axis with most contacts being in the posterior region. Riise and Ericksson3in a study of contact distribution in adults found that a significant number of subjects had at least 60% of their tooth contacts on oneside with light and hard pressureand that the differenceswere randomly distributed betweenthe right and left sides.Thesefindings do not support the tendency for a symmetric distribution about the sagittal axis. The TLR, however, not only measuresthe total number of contacts, but alsotheir relationship to a fixed reference plane (sagittal axis) multiplied by their relative time values. This statistic results in a time moment or a timeweighted average of the occlusal contacts, and therefore addsanother dimensionto the description of occlusaldata. Becauseof the tendency for a normal patient population THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Distribution
of anteroposterior
contact
The mean values for the RFB and LFB statistic in the normal samplewere 28.11 and 27.78,respectively, placing most of the force of occlusionin the region of the second premolar and first molar.‘OThe Student t-test showedthe RFB and LFB meansto be equal (p > 0.05), indicating that the tooth contacts on the right and left sides,asmeasured anteroposteriorly from the transverse axis, tended to be bilaterally symmetric. These findings are consistent with those of other investigators1-5who found that there were more contacts in the molar and premolar regions than in the anterior teeth in normal young adult and adult popu241
MANESS
lations and supports the conclusion that the center of effort for mastication is in the region of the first molar. A strong correlation was found between the RFB and LFB statistics, which is almost expected in a normal patient population from the results of some previous investigators. However, the correlations that may exist in abnormal patient populations show the direction for future studies, especially as the TLR varies from symmetry.
Significance
of the time
moment
statistic
Time moment statistics, as described, are a measure of the distribution of tooth contacts with respect to the sagittal and transverse axes of the occlusal plane multiplied by their relative onset times and reflected by the TLR, RFB, and LFB values. The TLR, RFB, and LFB values, when used in combination, can uniquely identify an occlusion and describe the tendency to conform to the values of the normal population, resulting in an estimate of the symmetry and distribution of the tooth contacts. By using the time moment statistic, the investigator is able to understand the distribution of tooth contacts as they are weighted by their contact order and identify patients with asymmetric occlusal patterns. Because this measure reflects the presence of significant prematurities, it adds a dynamic aspect to the description of occlusal contact distribution. In a clinical situation where there are equal contacts bilaterally, but one side is substantially premature, a measurement system that can only identify the presence or absence of tooth contacts, such as marking paper, would conclude that the distribution was equal. This information, although important, ignores the clinical significance of the tooth contact data that is reflected by time moment statistics and has undeniable clinical significance as an estimate of bilateral simultaneity.
CONCLUSIONS This study had two objectives. The first objective was to present a digital measurement system and a set of statistics to identify occlusion contacts as described by time moments in the sagittal and transverse axes of the occlusal plane. The second objective was to present the results describing the distribution of tooth contacts in maximum intercuspation for 93 normal patients by using this method. From the information gathered, it is possible to make the following conclusions:
242
AND
PODOLOFF
1. The distribution of occlusal contacts in maximum intercuspation described by the T-Scan system conforms to the conclusions of other investigators using other methods. 2. There is a strong tendency for tooth contacts in maximum intercuspation to be symmetric about the sagittal axis of the occlusal plane as reflected by the time moment statistic (TLR). 3. The location of the center of effort for the anteroposterior tooth contacts measured from the transverse axis of the occlusal plane, as reflected by the time moment statistics RFB and LFB, is in the second premolar-first molar region and is bilaterally symmetric in a normal dentition. 4. The method of data collection offered by the T-Scan and the TLR, RFB, and LFB statistics describing the time moments in the sagittal and transverse axes of the occlusal plane show great promise as a clinical screening device for easily identifying the distribution of tooth contacts. We thank Dr. Peter Neff, Georgetown University, and Dr. George Maryniuk, University of North Carolina, School of Dentistry, Chapel Hill, for their support in the data collection effort.
REFERENCES 1. Beyron H. Occhrsal relations and mastication in Australian aborigines. Acta Odontol &and 1964,22:597-678. 2. Riise C. A clinical study of the number of occlusal tooth contacts in the intercuspal position at light and hard pressure in adults. J Oral Rehabil 1982;9:469-77. 3. Riise C, Ericksson SG. A clinical study of the distribution of occlusal tooth contacts in the intercuspal position at light and hard pressure in adults J Oral Rehabil 1983;10:473-86. 4. Berry DC, Singh BP. Diurnal variations in occlusal contacts. J PROSTHET DENT
1983;50:386-91.
5. Neff P, Binderman I, Arcan M. The diagram of contact intensities: a basic characteristic of occlusion. J PROSTHJST DENT 1985;53:697-702. 6. Amsterdam M, Purdum LC, Purdum KL. The occlusalgraph: a graphic representation of photocclusion data. J PROSTHET DENT 1987;57:94-8. 7. Arcan M, Zandman F. Mechanics of contact and memorized birefringence. Seances Acad Sci 1980;290:B-17. 8. Maness W, Benjamin M, Podoloff R, Bobick A, Golden R. Computerized occlusal analysis: a new technology. Quint Internat 1987;4:287-92. 9. Maness W. Comparison of the duration of occlusal contacts during habitual closure using the digital occlusal sensor [Abstract]. J Dent Res 1986;65:141. 10. Mack PJ. Maxillary arch and central incisor dimensions in a Nigerian and British population sample. J Dent 1981;9:67-70.
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AUGUST
1989
VOLUME
62
NUMBER
2