keen
craniomandibular
erences P. Kirveskari, T. J&m&i,
DOdont,”
P. Alanen,
in children DOdont,
DSocSci,b
and
DOdonV
University of Turku, Institute of Dentistry, Turku, Finland The association between clinical signs of craniomandibular disorders (CMD) and occlusal interferences was studied longitudinally in two cohorts of children, 5 and 10 years of age at baseline, representing the nonpatient population. They were follwwed up for 5 years. The range of active participants was 96 to 106 in the younger group, and 64 to 74 in the older group. The subjects were seen annually for registration of signs of CMD and for the presence of interferences, and for a real or placebo wcclusal adjustment. The double-blind study design was applied. Baseline data showed no association between the variables studied; parts of data from second and third examinations disclosed significant associations; and fourth, fifth and sixth examinations disclosed a consistent pattern of significant associatiwns.(d PROSTHET DENT 1992;67:692-6.)
he significance of occlusal interferences in the etiology of craniomandibular disorders (CMD) has been questioned in numerous recent articles.lm7 On the other hand, contrasting findings regarding signs and symptoms of @MD and various occlusal factors have also been shown.s-l7 A recent textbookls regards occlusion as important in dental therapy, but regards the notion that occlusion is etiologic in CMD development as far from compelling. Proponents of the psychophysiologic theory of temporomandibular joint dysfunction maintain that occlusal factors either have nothing to do with the signs and symptoms of CMD,l’ or else occfusa1 changes found associated with CMD are a result of CMD rather than a cause of it.20 Moreover, the high frequencies of signs of CMD as well as reported malocclusion are regarded as misleading by Greene and Marbach,lg who argue that many of the variables registered represent normal variation. There are several theoretical pitfalls in drawing conclusions on the etiologic role of occlusion from studies of associations.17 A lack of association between signs of CMD and occlusal factors in cross-sectional studies does not exclude occlusal factors from the etiology of CMD. Neither does an existing association prove that occlusal factors have
Presented at the American Equilibration Society Meeting, Chicago, 111. Supported in part by the American Equilibration Society. aAssociate Professor, Department of Stomatognathic Physiology. SAssociate Professor, Department of Community Dentistry. CAssistant Professor, Department of Oral Development and Orthodontics.
an etiologic role. The present study examines the association between occlusal interferences and signs of CMD over a period of 6 years in two cohorts of children, half of whom underwent occlusal adjustment annually.
SUBJECTS
AND
METN
All children 5 or 10 years of age in the towaship and rural municipality of Loimaa in southwestern Finland were invited by means of a letter to their parents to participate in this study, which had been approved by tbe Ethics Committee of the District Hospital. A cohort of I5-yearolds was also included, as reported ear1ier.17 Baseline data and details of methods have been previously reported,21 and are only briefly related here. The total number of 5-year-olds was 136 (69 boys and 67 girls). Of these, 128 (67 boys and 61 girls) volunteered to participate. The corresponding figures for IO-year-olds were 116 (62 boys and 54 girls) and 109 (55 boys and 54 girls). At the first examination, one child was excluded because of a severe general health problem, and five others because of poor cooperation. Children receiving or having received orthodontic treatment are excluded from the present analysis. During the 6 years of study, 26 children dropped out, and in a few cases the recordings proved incomplete. Thus the analysis was based on a total number of children varying between 96 and 106 in the younger group and between 64 and 74 in the older group. The annual! clinical examinations were carried ou.t by one the study, who and the same author (TJ) throughout remained unaware of whether oeclusal adjustment had been performed or not. The examination included observations of muscle and joint palpatory tenderness, joint sounds, and measurements of mandibular mobility. The
CMD
AND
QCCLUSAL
lNTERFERENCJZS
---_
BL
I
II
III
OCCLUSION ADJUSTED OCCLUSION
Iv
v
NOT ADJUSTED
BL
I
II
III
IV
v
YEAR OF STUDY Fig. 1. Changes in percentage of subjects totally free from occlusal interferences nually-adjusted and placebo-adjusted groups. BL, Baseline.
last examination in the sequence was occlusal analysis including measurements of retrusive-intercuspal position (RP-IF) distance, observations of first contact on hinge closure, of the presence of mediotrusion contacts, and of postcanine laterotrusion and protrusion contacts. Immediately after the examination, the children underwent either real or mock occlusal adjustment, as determined in advance, by applying random numbers to alphabetical lists of subjects, The adjustment followed the principles of Dawsonz2 and Riise.23 The adjustment was done once a year in a maximum time of 30 minutes. The mock adjustment was performed in an identical setting; however, only nonabrasive burs were used. The associations between CMD and occlusal interferences were analyzed using the present-absent dichotomy for CMD. ‘Fhe number of interferences denotes the type of interference, not the number of teeth interfering. Thus an inter~e~e~~e-flee occlusion had to display the perception of bila.teraI contact in the RP, a maximum distance of less than 1 mm sag&ally and vertically between RP and IP, no visible lateral component of the slide RP-IP, no mediotrusion contacts, and no postcanine protrusion contacts. Laterotrusion contacts were not used in the present analysis because of the diffculties in assessing them in the mixed dentitions. The chi square test was used for statistical anaiyses.
BJLTS The impact of the arm& adjustment on occlusion, as inspected 12 months after the adjustment, was small on the individual level. It was impossible to distinguish between the adjusted and nonadjusted subjects without a thorough examination of occlusal surfaces for traces of grinding. However, some evidence of a reduction in the number of interferences was present. Thus the number of subjects to-
THE
JOt’RNAL
OF PROSTHETIC
DENTISTRY
in an-
tally free from interferences tended to be greater in the adjusted group than in the nonadjusted group (Fig. 1). The association between the number of interferences and the presence of signs of CMD is presented in 2 x 2 contingency tables year by year for both cohorts and for pooled cohorts (Table I). Baseline data showed no association, parts of the second and third year show significant association, and fourth, fifth, and sixth year data show significant association in a consistent pattern, The same pattern was present in both sexes when analyzed separately. Contrasting the extremes of variation (two-point design), the total material yielded a statistically significant association in the first year of data collection. The association was strong in the sixth-year data (Table II). DISCUSSlON Several methodologic problems typical of clinical studies have a bearing in the interpretation of results. Repeatability of the clinical procedures, symptom fluctuation, possible shifts in tooth position associated with adjustment, shedding of deciduous teeth, and eruption of permanent teeth are examples of factors affecting the observed results. However, in view of the doable-blind design of the study, the possible biasing effect of these factors would rather give rise to a false negative than to a false positive result. On the basis of the results presented in our earlier report on 15-year-olds, we suggested that the lack of association between interferences and CMD in cross-sectional studies may be ascribed to methodologic reasons.17 For a meaningful statistical analysis of association, sufficient variation must be present in the study population. We submit that the variation in interferences is insufhcjent unless special measures are taken in collecting data. Random samples of
693
children
Association between number of occlusal interferences examined annually: Chi square test Age
group
5 yr
and clinical signs of CMD in two cohorts of nonpatient Age
signs No. of interferences
group
Total
10 yr
Signs
Signs
Absent
Present
Absent
Present
Absent
Present
7 5
18 27
8 21
69 68
15 26
1 14
17 25
10 21
57 76
10 22
31 17
6 17
62 57
4 28
28 13
7 22
61 45
9 35
28 12
9 15
55 38
13 29
20 13
10 21
56 31
BL
o-3 4-6
51 41
I
o-3 4-6
40 51
2
o-3 4-6
31 40
3
o-3 4-6
33 32
4
O-3 4-6
27 26
5
o-3 4-6
36 18
NS
NS
p = 0.014
NS
p = 0.035
NS
NS
p = 0.0054
p = 0.0006
11 50 6, = 0.000002
p = 0.02
p = 0.001
16 39 p = 0.0075
p = 0.007
p = 0.004
1J. 35
18 50 p = 0.00008
p = 0.043
23 50 p = 0.00006
BL, Baseline; NS, not statistically significant.
Table II. Distribution of clinical signs of CMD at beginning and at end of study in subsamples showing low number and high number of interferences (two-point design): Cohorts pooled, chi square test Signs Year
No. of interferences
of CMD
Absent
Present
3 24
3%
o-1 5-6
22 44
5
o-1 5-6
28 24
p = 0.028 7 39 p = 0.0001 Abbreviations as in Table I.
normal population must be very large before the number of subjects representing absence (or low occurrence) of interferences becomes adequate for statistical purposes. Application of the two-point design is meaningful and often more fruitful than including the whole distribution in the analysis, as shown by Solberg et a1.s However, in studies requiring clinical examinations, the sample sizes tend to remain too small with respect to the observed frequency of the absence or minimal presence of interferences. While the present data yielded a significant association in pooled cohorts even before intervention (Table II), a correspond-
694
ing association was present only after intervention in the cohort of 15year-olds reported previously.17 Our decision to try to introduce the missing part of the variation-that is subjects not exposed to the presumed risk factor-into manageable samples by way of occlusal adjustment, was based on the fact that we could foresee no significant harmful effects. During the 6 years of study, a few subjects mentioned experiencing transient sensitivity in their teeth after the occlusal adjustment. One girl refused to present herself for the sixth examination unless we promised not to grind her teeth. She had experienced a lengthy period of soreness in her teeth each time after we had ground them. We did as she wished, examined her, and reassured her that her teeth were in excellent condition. She belonged to the placebo treatment group? as did most of those who mentioned having experienced dental symptoms after the adjustment. We conclude that virtually no harmful effects detectable in thorough examinations could be found in subjects who underwent the occlusal adjustment. Similar conclusions have also been presented by others.22-25 In general, the placebo treatment was also harmless except for the few subjects developing transient subjective symptoms. The present study is a powerful test of at least two pet arguments put forward by the proponents of the psychophysiologic theory. If the variables studied-occlusal interferences and signs of CMD-for the most part at least
MAY
?992
VOLUME
67
NUMBER
5
represent normal variation,lg one must predict that a reduction in ““interferences” will have no systematic effect on the distribution of the “signs” of CMD. Our results were at variance with that conclusion. The main argument concerns the very existence of the association between these interferences and CMD. One view is that the association only exists in the minds of clinicians.lg Another view is that eventual occlusal changes can emerge as a result of CMD.20 Accordingly, an association could. be present in patients but not in nonpatient populations. Again, both of these views are at variance with our results. Our samples represented a young nonpatient population. The frequency of the separate clinical signs was in general too low for a statistical analysis of association. Only muscular tenderness was tested separately and was found to be associated with the number of interferences, in accordance with the pattern present for any clinical sign representing CMD. Seligman and Pullinger16 demonstrated significant associations between occlusal factors and temporomandibular joint (TMJ) disorders but not with myalgia. We suggest that the link between occlusion and myalgia at a relatively early age should also be considered when hypotheses on the etiology of CMD are discussed. Our results do not really address the causal question. The number of occlusal interferences and clinical signs of CMD are crude variables. However, interferences appear to be part of an effective causal complex that enables disclosure of the association. It is of particular interest that a recently introduced occlusal variable, the difference in the number of occlusal contacts between light and hard pressure,26 could be effectively applied to the analysis of associationsz7T 28Clearly, occlusal adjustment affects not only the number of interferences but also many other characteristics such as size, type, location, and any combination of these. But even if we do not know what exactly constitutes the effective causal complex, our results appear to contradict the argument that an eventual association can only reflect the effects of dysfunction on occlusion. It is sometimes possible to deduce the predominant order of the appearance of the presumed cause and effect in repeated cross-sectional studies of one and the same sample. In our samples, the shift from having interferences but no signs into having both interferences and signs of CMD was far more common than the shift from having signs but no interferences into having both. That would seem to favor the order of events in which interferences precede signs. However, the small number of subjects showing no interferences precludes an effective analysis. Nelkimo2g considered occlusal factors to be important in the etiology of CMD, although he found little support for his opinion from the epidemiologic literature. In the absence of convincing evidence, Carlsson and Droukas30 deemed occlusal factors to be at best of little importance.
THEJOURNAL
OFPROSTHETICDENTISTRY
Contrary to the conclusions of those authorsi who do not regard occlusion as playing a significant role in CMD development, we interpret our results as suggesting a need for reappraisal of the role of occlusal factors in the etiology of CMD. CONCLUSIONS Within the contex of this research design and the duration of this study, the following conclusions are drawn: 1. Occlusal adjustment resulting in a modest decrease in the number of occlusal interferences was sufficient to disclose a significant association between the number of occlusal interferences and clinical signs of CMD in two nonpatient child populations. 2. The concept of “occlusal interference” as employed in this study appears to include elements of pathophysiologic significance. Occlusal interferences are therefore unlikely to represent only normal variation. 3. The clinical signs of CMD used in this study, or at least some of them, cannot be regarded as representing normal variation if the term is understood so that only variables beyond its limits can have anything to do with the development of pathofunction. 4. The elimination of anatomically minor occlusal interferences does not entail harmful effects. We thank the District Health Authorities of Loimaa, Finland, for permission to carry out our study in the local health center, and Dr. &no Nummila and the personnel of the health center for practical assistance. REFERENCES 1. Rieder CE, Martinoff JT. The prevalence of mandibuiar dysfunction. Part II. A multiphasic dysfunction prc6le. J PROSTHET DEW 1983;50:237-44. 2. Droukas B, Lindee C, Carlsson GE. Relationship between occlusal factors and signs and symptoms of mandibular dysfunctions. Acta Odonto1 Stand 1984;42:277-83. 3. Bush FM. Malocclusion, masticatory muscle and temporomandibular joint tenderness. J Dent Res 1985;64:129-33. 4. Lieberman MA, Gazit E, Fuchs C; Lilos P. Mandibular dysfunction in 10.18-year-old6 as related to morphologic malocclusion. J Oral Rehabil 1985;12:209-14. 5. De Laat A, van Steenberghe D. Occlusal relationships and temporomandibular joint dysfunction. Part II. Correlation between occlusal and articular parameters and symptoms of TMJ dysfunction by means of stepwise logistic regression. J PROSTHETDENT 1986;55:116-21. 6. Seligman DA, Pullinger AG, Solberg WK. The pxevaience of dental attrition and its association with factors of age,gender, occlusion and TMJ symptomatology. J Dent Res 1988;67:1323-33. 7. Seligman DA, Pullinger AG, Solberg WK. Temporomandibular disorders. Part III. Occiusal and articular factors associated with muscle tenderness. J PROSTHETDENT 1988;59:483-9. 8. Solberg WK, Woo MW, Houston JB. Prevalence of mandibular dysfunction in young adults. J Am Dent Assoc 1979;98:25-34. 9. Ingervall B, Mohlin B, Thilander B. Prevalence of symptoms of functional disturbances of the masticatory system of Swedish men. J Oral Rehabil 1980;7:185-97. 10. Ledermsn KH, Clayton JA. Restored occlusions. Fart IX. The relationship of clinical and subjective symptoms to varying degrees of TMJ dysfunction. J PROSTHETDENT 1982;47:303-9.
695
11. Nilner M. Relationships between oral parafunctions and functional disturbances and diseases of the stomatognathic system among children aged 7-14 years. Acta Gdontol Stand 1983;41:167-72. 12. Nilner M. Relationships between oral parafunctions and functional disturbances in the stomatognathic system among 15- to 18-year-olds. Acta Odontol Stand 1983;41:19’7-201. 13. Egermark-Eriksson I, Ingervall B, Carlsson GE. The dependence of mandibular dysfunction in children on functional and morphologic malocclusion. Am J Crthod 1983;83:187-94. 14. Egermark-Eriksson I, Carlsson GE, Magnusson T. A long-term epidemiologic study of the relationship between occlusal factors and mandibular dysfunction in children and adolescents. J Dent Res 1987;66:6771. 15. Puhinger AG, Seligman DA, Solberg WK. Temporomandibular disorders. Part II. Occlusal factors associated with temporomandibular joint tenderness and dysfunction. J PROSTHET DENT 1988;59:363-7. 16. Seligman DA, Pullinger AG. Association of occlusal variables among refined TM patient diagnostic groups. J Craniomandib Disord Facial Oral Pain 1989;3:227-36. 17. Kirveskari P, .Alanen P, Jsimsa T. Association between craniomandibular disorders and occlusal interferences. J PROSTHET DENT 1989;62:66-9.
18. Mohl ND, Zarb GA, Carlsson GE, Rugh JD. A textbook of occlusion. Chicago: Quintessence Publishing Co, Inc, 1988. 19. Greene CS, Marbach JJ. Epidemiologic studies of mandibular dysfunction: a critical review. J PROSTHET DENT 1982;48:184-90. 20. La&in DM. Etiology of the pain-dysfunction syndrome. J Am Dent Assoc 1969;79:147-53. 21. Kirveskari P, Alanen P, J&n& T. Functional state of the stomatognathic system in 5-, PO-and 15-year-old children in southwestern Finland. Proc Finn Dent Sot 1986;82:3-8.
22. Dawson PE. Evaluation, diagnosis and treatment of occlusal problems. 2nd ed. St. Louis: CV Mosby Co, 1989. 23. Riise C. Rational performance of occlusal adjustment. J PR~STHET DENT 1982;48:319-27.
24. Rsmfjord SP, Ash MM. Occlusion. 3rd ed. Philadelphia: WB Saunders Co, 1983. 25. Kirveskari P, Le Bell Y, Salonen M, Forssell II, Gram L. Effect of elimination of occlusal interferences on signs and symptoms of craniomandibular disorder in young adults. J Oral Rehabil 1989;16:21-6. 26. 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. 27. Wanman A, Agerberg G. Recurrent headaches and craniomandibular disorders in adolescents: a longitudinal study. 3 Craniomandib Disord Facial Oral Pain 1987;1:229-36. 28. W&man A, Agerberg 6. Fatigue in the jaws: a longitudinal study in adolescents. J Craniomandib Disord Facial Oral Pain 1988;2:29-34. 29. Helkimo M. Epidemiological surveys of dysfunction of the masticatory system. In: Zarb GA, Carlsson GE, eds. Temporomandibular joint function and dysfunction. Copenhagen: Munksgaard, 1979:175-92. 30. Carlsson GE, Droukas BC. Dental occlusion and the health of the masticatory system. J Craniomandib Pratt 1984;2:341-7. Reprint requests to: DR. PENTTI KIRVESKARI INSTITUTE OF DENTISTRY UNIVERSITY OF TURKU SF-20520 TKJRWJ FINLAND
craniomandibular
erences P. Kirveskari, T. J&m&i,
DOdont,”
P. Alanen,
in children DOdont,
DSocSci,b
and
DOdonV
University of Turku, Institute of Dentistry, Turku, Finland The association between clinical signs of craniomandibular disorders (CMD) and occlusal interferences was studied longitudinally in two cohorts of children, 5 and 10 years of age at baseline, representing the nonpatient population. They were follwwed up for 5 years. The range of active participants was 96 to 106 in the younger group, and 64 to 74 in the older group. The subjects were seen annually for registration of signs of CMD and for the presence of interferences, and for a real or placebo wcclusal adjustment. The double-blind study design was applied. Baseline data showed no association between the variables studied; parts of data from second and third examinations disclosed significant associations; and fourth, fifth and sixth examinations disclosed a consistent pattern of significant associatiwns.(d PROSTHET DENT 1992;67:692-6.)
he significance of occlusal interferences in the etiology of craniomandibular disorders (CMD) has been questioned in numerous recent articles.lm7 On the other hand, contrasting findings regarding signs and symptoms of @MD and various occlusal factors have also been shown.s-l7 A recent textbookls regards occlusion as important in dental therapy, but regards the notion that occlusion is etiologic in CMD development as far from compelling. Proponents of the psychophysiologic theory of temporomandibular joint dysfunction maintain that occlusal factors either have nothing to do with the signs and symptoms of CMD,l’ or else occfusa1 changes found associated with CMD are a result of CMD rather than a cause of it.20 Moreover, the high frequencies of signs of CMD as well as reported malocclusion are regarded as misleading by Greene and Marbach,lg who argue that many of the variables registered represent normal variation. There are several theoretical pitfalls in drawing conclusions on the etiologic role of occlusion from studies of associations.17 A lack of association between signs of CMD and occlusal factors in cross-sectional studies does not exclude occlusal factors from the etiology of CMD. Neither does an existing association prove that occlusal factors have
Presented at the American Equilibration Society Meeting, Chicago, 111. Supported in part by the American Equilibration Society. aAssociate Professor, Department of Stomatognathic Physiology. SAssociate Professor, Department of Community Dentistry. CAssistant Professor, Department of Oral Development and Orthodontics.
an etiologic role. The present study examines the association between occlusal interferences and signs of CMD over a period of 6 years in two cohorts of children, half of whom underwent occlusal adjustment annually.
SUBJECTS
AND
METN
All children 5 or 10 years of age in the towaship and rural municipality of Loimaa in southwestern Finland were invited by means of a letter to their parents to participate in this study, which had been approved by tbe Ethics Committee of the District Hospital. A cohort of I5-yearolds was also included, as reported ear1ier.17 Baseline data and details of methods have been previously reported,21 and are only briefly related here. The total number of 5-year-olds was 136 (69 boys and 67 girls). Of these, 128 (67 boys and 61 girls) volunteered to participate. The corresponding figures for IO-year-olds were 116 (62 boys and 54 girls) and 109 (55 boys and 54 girls). At the first examination, one child was excluded because of a severe general health problem, and five others because of poor cooperation. Children receiving or having received orthodontic treatment are excluded from the present analysis. During the 6 years of study, 26 children dropped out, and in a few cases the recordings proved incomplete. Thus the analysis was based on a total number of children varying between 96 and 106 in the younger group and between 64 and 74 in the older group. The annual! clinical examinations were carried ou.t by one the study, who and the same author (TJ) throughout remained unaware of whether oeclusal adjustment had been performed or not. The examination included observations of muscle and joint palpatory tenderness, joint sounds, and measurements of mandibular mobility. The
CMD
AND
QCCLUSAL
lNTERFERENCJZS
---_
BL
I
II
III
OCCLUSION ADJUSTED OCCLUSION
Iv
v
NOT ADJUSTED
BL
I
II
III
IV
v
YEAR OF STUDY Fig. 1. Changes in percentage of subjects totally free from occlusal interferences nually-adjusted and placebo-adjusted groups. BL, Baseline.
last examination in the sequence was occlusal analysis including measurements of retrusive-intercuspal position (RP-IF) distance, observations of first contact on hinge closure, of the presence of mediotrusion contacts, and of postcanine laterotrusion and protrusion contacts. Immediately after the examination, the children underwent either real or mock occlusal adjustment, as determined in advance, by applying random numbers to alphabetical lists of subjects, The adjustment followed the principles of Dawsonz2 and Riise.23 The adjustment was done once a year in a maximum time of 30 minutes. The mock adjustment was performed in an identical setting; however, only nonabrasive burs were used. The associations between CMD and occlusal interferences were analyzed using the present-absent dichotomy for CMD. ‘Fhe number of interferences denotes the type of interference, not the number of teeth interfering. Thus an inter~e~e~~e-flee occlusion had to display the perception of bila.teraI contact in the RP, a maximum distance of less than 1 mm sag&ally and vertically between RP and IP, no visible lateral component of the slide RP-IP, no mediotrusion contacts, and no postcanine protrusion contacts. Laterotrusion contacts were not used in the present analysis because of the diffculties in assessing them in the mixed dentitions. The chi square test was used for statistical anaiyses.
BJLTS The impact of the arm& adjustment on occlusion, as inspected 12 months after the adjustment, was small on the individual level. It was impossible to distinguish between the adjusted and nonadjusted subjects without a thorough examination of occlusal surfaces for traces of grinding. However, some evidence of a reduction in the number of interferences was present. Thus the number of subjects to-
THE
JOt’RNAL
OF PROSTHETIC
DENTISTRY
in an-
tally free from interferences tended to be greater in the adjusted group than in the nonadjusted group (Fig. 1). The association between the number of interferences and the presence of signs of CMD is presented in 2 x 2 contingency tables year by year for both cohorts and for pooled cohorts (Table I). Baseline data showed no association, parts of the second and third year show significant association, and fourth, fifth, and sixth year data show significant association in a consistent pattern, The same pattern was present in both sexes when analyzed separately. Contrasting the extremes of variation (two-point design), the total material yielded a statistically significant association in the first year of data collection. The association was strong in the sixth-year data (Table II). DISCUSSlON Several methodologic problems typical of clinical studies have a bearing in the interpretation of results. Repeatability of the clinical procedures, symptom fluctuation, possible shifts in tooth position associated with adjustment, shedding of deciduous teeth, and eruption of permanent teeth are examples of factors affecting the observed results. However, in view of the doable-blind design of the study, the possible biasing effect of these factors would rather give rise to a false negative than to a false positive result. On the basis of the results presented in our earlier report on 15-year-olds, we suggested that the lack of association between interferences and CMD in cross-sectional studies may be ascribed to methodologic reasons.17 For a meaningful statistical analysis of association, sufficient variation must be present in the study population. We submit that the variation in interferences is insufhcjent unless special measures are taken in collecting data. Random samples of
693
children
Association between number of occlusal interferences examined annually: Chi square test Age
group
5 yr
and clinical signs of CMD in two cohorts of nonpatient Age
signs No. of interferences
group
Total
10 yr
Signs
Signs
Absent
Present
Absent
Present
Absent
Present
7 5
18 27
8 21
69 68
15 26
1 14
17 25
10 21
57 76
10 22
31 17
6 17
62 57
4 28
28 13
7 22
61 45
9 35
28 12
9 15
55 38
13 29
20 13
10 21
56 31
BL
o-3 4-6
51 41
I
o-3 4-6
40 51
2
o-3 4-6
31 40
3
o-3 4-6
33 32
4
O-3 4-6
27 26
5
o-3 4-6
36 18
NS
NS
p = 0.014
NS
p = 0.035
NS
NS
p = 0.0054
p = 0.0006
11 50 6, = 0.000002
p = 0.02
p = 0.001
16 39 p = 0.0075
p = 0.007
p = 0.004
1J. 35
18 50 p = 0.00008
p = 0.043
23 50 p = 0.00006
BL, Baseline; NS, not statistically significant.
Table II. Distribution of clinical signs of CMD at beginning and at end of study in subsamples showing low number and high number of interferences (two-point design): Cohorts pooled, chi square test Signs Year
No. of interferences
of CMD
Absent
Present
3 24
3%
o-1 5-6
22 44
5
o-1 5-6
28 24
p = 0.028 7 39 p = 0.0001 Abbreviations as in Table I.
normal population must be very large before the number of subjects representing absence (or low occurrence) of interferences becomes adequate for statistical purposes. Application of the two-point design is meaningful and often more fruitful than including the whole distribution in the analysis, as shown by Solberg et a1.s However, in studies requiring clinical examinations, the sample sizes tend to remain too small with respect to the observed frequency of the absence or minimal presence of interferences. While the present data yielded a significant association in pooled cohorts even before intervention (Table II), a correspond-
694
ing association was present only after intervention in the cohort of 15year-olds reported previously.17 Our decision to try to introduce the missing part of the variation-that is subjects not exposed to the presumed risk factor-into manageable samples by way of occlusal adjustment, was based on the fact that we could foresee no significant harmful effects. During the 6 years of study, a few subjects mentioned experiencing transient sensitivity in their teeth after the occlusal adjustment. One girl refused to present herself for the sixth examination unless we promised not to grind her teeth. She had experienced a lengthy period of soreness in her teeth each time after we had ground them. We did as she wished, examined her, and reassured her that her teeth were in excellent condition. She belonged to the placebo treatment group? as did most of those who mentioned having experienced dental symptoms after the adjustment. We conclude that virtually no harmful effects detectable in thorough examinations could be found in subjects who underwent the occlusal adjustment. Similar conclusions have also been presented by others.22-25 In general, the placebo treatment was also harmless except for the few subjects developing transient subjective symptoms. The present study is a powerful test of at least two pet arguments put forward by the proponents of the psychophysiologic theory. If the variables studied-occlusal interferences and signs of CMD-for the most part at least
MAY
?992
VOLUME
67
NUMBER
5
represent normal variation,lg one must predict that a reduction in ““interferences” will have no systematic effect on the distribution of the “signs” of CMD. Our results were at variance with that conclusion. The main argument concerns the very existence of the association between these interferences and CMD. One view is that the association only exists in the minds of clinicians.lg Another view is that eventual occlusal changes can emerge as a result of CMD.20 Accordingly, an association could. be present in patients but not in nonpatient populations. Again, both of these views are at variance with our results. Our samples represented a young nonpatient population. The frequency of the separate clinical signs was in general too low for a statistical analysis of association. Only muscular tenderness was tested separately and was found to be associated with the number of interferences, in accordance with the pattern present for any clinical sign representing CMD. Seligman and Pullinger16 demonstrated significant associations between occlusal factors and temporomandibular joint (TMJ) disorders but not with myalgia. We suggest that the link between occlusion and myalgia at a relatively early age should also be considered when hypotheses on the etiology of CMD are discussed. Our results do not really address the causal question. The number of occlusal interferences and clinical signs of CMD are crude variables. However, interferences appear to be part of an effective causal complex that enables disclosure of the association. It is of particular interest that a recently introduced occlusal variable, the difference in the number of occlusal contacts between light and hard pressure,26 could be effectively applied to the analysis of associationsz7T 28Clearly, occlusal adjustment affects not only the number of interferences but also many other characteristics such as size, type, location, and any combination of these. But even if we do not know what exactly constitutes the effective causal complex, our results appear to contradict the argument that an eventual association can only reflect the effects of dysfunction on occlusion. It is sometimes possible to deduce the predominant order of the appearance of the presumed cause and effect in repeated cross-sectional studies of one and the same sample. In our samples, the shift from having interferences but no signs into having both interferences and signs of CMD was far more common than the shift from having signs but no interferences into having both. That would seem to favor the order of events in which interferences precede signs. However, the small number of subjects showing no interferences precludes an effective analysis. Nelkimo2g considered occlusal factors to be important in the etiology of CMD, although he found little support for his opinion from the epidemiologic literature. In the absence of convincing evidence, Carlsson and Droukas30 deemed occlusal factors to be at best of little importance.
THEJOURNAL
OFPROSTHETICDENTISTRY
Contrary to the conclusions of those authorsi who do not regard occlusion as playing a significant role in CMD development, we interpret our results as suggesting a need for reappraisal of the role of occlusal factors in the etiology of CMD. CONCLUSIONS Within the contex of this research design and the duration of this study, the following conclusions are drawn: 1. Occlusal adjustment resulting in a modest decrease in the number of occlusal interferences was sufficient to disclose a significant association between the number of occlusal interferences and clinical signs of CMD in two nonpatient child populations. 2. The concept of “occlusal interference” as employed in this study appears to include elements of pathophysiologic significance. Occlusal interferences are therefore unlikely to represent only normal variation. 3. The clinical signs of CMD used in this study, or at least some of them, cannot be regarded as representing normal variation if the term is understood so that only variables beyond its limits can have anything to do with the development of pathofunction. 4. The elimination of anatomically minor occlusal interferences does not entail harmful effects. We thank the District Health Authorities of Loimaa, Finland, for permission to carry out our study in the local health center, and Dr. &no Nummila and the personnel of the health center for practical assistance. REFERENCES 1. Rieder CE, Martinoff JT. The prevalence of mandibuiar dysfunction. Part II. A multiphasic dysfunction prc6le. J PROSTHET DEW 1983;50:237-44. 2. Droukas B, Lindee C, Carlsson GE. Relationship between occlusal factors and signs and symptoms of mandibular dysfunctions. Acta Odonto1 Stand 1984;42:277-83. 3. Bush FM. Malocclusion, masticatory muscle and temporomandibular joint tenderness. J Dent Res 1985;64:129-33. 4. Lieberman MA, Gazit E, Fuchs C; Lilos P. Mandibular dysfunction in 10.18-year-old6 as related to morphologic malocclusion. J Oral Rehabil 1985;12:209-14. 5. De Laat A, van Steenberghe D. Occlusal relationships and temporomandibular joint dysfunction. Part II. Correlation between occlusal and articular parameters and symptoms of TMJ dysfunction by means of stepwise logistic regression. J PROSTHETDENT 1986;55:116-21. 6. Seligman DA, Pullinger AG, Solberg WK. The pxevaience of dental attrition and its association with factors of age,gender, occlusion and TMJ symptomatology. J Dent Res 1988;67:1323-33. 7. Seligman DA, Pullinger AG, Solberg WK. Temporomandibular disorders. Part III. Occiusal and articular factors associated with muscle tenderness. J PROSTHETDENT 1988;59:483-9. 8. Solberg WK, Woo MW, Houston JB. Prevalence of mandibular dysfunction in young adults. J Am Dent Assoc 1979;98:25-34. 9. Ingervall B, Mohlin B, Thilander B. Prevalence of symptoms of functional disturbances of the masticatory system of Swedish men. J Oral Rehabil 1980;7:185-97. 10. Ledermsn KH, Clayton JA. Restored occlusions. Fart IX. The relationship of clinical and subjective symptoms to varying degrees of TMJ dysfunction. J PROSTHETDENT 1982;47:303-9.
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11. Nilner M. Relationships between oral parafunctions and functional disturbances and diseases of the stomatognathic system among children aged 7-14 years. Acta Gdontol Stand 1983;41:167-72. 12. Nilner M. Relationships between oral parafunctions and functional disturbances in the stomatognathic system among 15- to 18-year-olds. Acta Odontol Stand 1983;41:19’7-201. 13. Egermark-Eriksson I, Ingervall B, Carlsson GE. The dependence of mandibular dysfunction in children on functional and morphologic malocclusion. Am J Crthod 1983;83:187-94. 14. Egermark-Eriksson I, Carlsson GE, Magnusson T. A long-term epidemiologic study of the relationship between occlusal factors and mandibular dysfunction in children and adolescents. J Dent Res 1987;66:6771. 15. Puhinger AG, Seligman DA, Solberg WK. Temporomandibular disorders. Part II. Occlusal factors associated with temporomandibular joint tenderness and dysfunction. J PROSTHET DENT 1988;59:363-7. 16. Seligman DA, Pullinger AG. Association of occlusal variables among refined TM patient diagnostic groups. J Craniomandib Disord Facial Oral Pain 1989;3:227-36. 17. Kirveskari P, .Alanen P, Jsimsa T. Association between craniomandibular disorders and occlusal interferences. J PROSTHET DENT 1989;62:66-9.
18. Mohl ND, Zarb GA, Carlsson GE, Rugh JD. A textbook of occlusion. Chicago: Quintessence Publishing Co, Inc, 1988. 19. Greene CS, Marbach JJ. Epidemiologic studies of mandibular dysfunction: a critical review. J PROSTHET DENT 1982;48:184-90. 20. La&in DM. Etiology of the pain-dysfunction syndrome. J Am Dent Assoc 1969;79:147-53. 21. Kirveskari P, Alanen P, J&n& T. Functional state of the stomatognathic system in 5-, PO-and 15-year-old children in southwestern Finland. Proc Finn Dent Sot 1986;82:3-8.
22. Dawson PE. Evaluation, diagnosis and treatment of occlusal problems. 2nd ed. St. Louis: CV Mosby Co, 1989. 23. Riise C. Rational performance of occlusal adjustment. J PR~STHET DENT 1982;48:319-27.
24. Rsmfjord SP, Ash MM. Occlusion. 3rd ed. Philadelphia: WB Saunders Co, 1983. 25. Kirveskari P, Le Bell Y, Salonen M, Forssell II, Gram L. Effect of elimination of occlusal interferences on signs and symptoms of craniomandibular disorder in young adults. J Oral Rehabil 1989;16:21-6. 26. 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. 27. Wanman A, Agerberg G. Recurrent headaches and craniomandibular disorders in adolescents: a longitudinal study. 3 Craniomandib Disord Facial Oral Pain 1987;1:229-36. 28. W&man A, Agerberg 6. Fatigue in the jaws: a longitudinal study in adolescents. J Craniomandib Disord Facial Oral Pain 1988;2:29-34. 29. Helkimo M. Epidemiological surveys of dysfunction of the masticatory system. In: Zarb GA, Carlsson GE, eds. Temporomandibular joint function and dysfunction. Copenhagen: Munksgaard, 1979:175-92. 30. Carlsson GE, Droukas BC. Dental occlusion and the health of the masticatory system. J Craniomandib Pratt 1984;2:341-7. Reprint requests to: DR. PENTTI KIRVESKARI INSTITUTE OF DENTISTRY UNIVERSITY OF TURKU SF-20520 TKJRWJ FINLAND
