Gnathologic assessment of centric slides in postretention orthodontic patients

CRANIOMANDIBULAR SECTION

GEORGE

FUNCTION

AND DYSFUNCTION

EDITOR

A. ZARB

Gnathologic postretention L. E. Johnston, St. Louis University

assessment of centric slides in orthodontic patients

Jr., D.D.S., Ph.D.,* and EICO Orthodontic Medical

Center, St. Louis, MO., and Medina,

Study Group of Ohio**

Ohio

A

frequent criticism of orthodontic treatment is that it often fails to produce a so-called “centric relation occlusion.“1-5 Athough the penalties for this failure are said to be severe, the dental literature reveals that anteroposterior slides are the rule instead of the exception6-13 (Table I). Large centric slides (>2 mm) are regarded as a possible factor in the cause and maintenance of joint (TMJ) disorders because they are more likely to include a significant lateral component.‘4j l5 Moreover, orthodontic therapy probably has the potential to create slides of this magnitude. Indeed, studies of the occlusion at the time of band-removal imply that contemporary methods may tend to produce discrepancies between centric relation (CR) and centric occlusion (CO) that are somewhat larger (perhaps by 0.5 to 0.7 mm) than would be expected in the absence of treatment.16-‘* Although there are reports that treatmentinduced changes of this magnitude-both positive and negative-may be transitory,‘8*‘9 and despite the rarity of naturally occurring centric relation occlusions, gnathologically oriented dentists continue to view the elimination of CO-CR slides as a key element in the prevention ot TMJ disorders. The implications of this generalization are disturbing. Recently, Sadowsky and BeGolezOexamined 75 orthodontic patients at least 10 years after treatment and compared the status of their occlusion and temporomandibular joints with that of a control group. They reported that “ . . . a high prevalence of mandibular shift from the retruded contact to the intercuspal position was evident in both groups, with the shift being significantly greater in the control group than in the ortho$ntic group.” In a subsequent report, Sadowsky and Polson2’ compared data from 199 subjects at the University of Illinois (96 orthodontic patients, 103 controls) with the results of a similar survey conducted at Eastman Dental Center in Rochester (111 orthodontic patients, 111 controls). Again, there was no evidence in either study that orthodontic therapy had produced an increase in the CO-CR distance. *Professor and Chairman, Department of Orthodontics. **David S. Fuller, D.D.S., M.S., Delorre Haddad, D.D.S., M.S., George Kho, D.D.S., C. Burwell Myers, Jr., D.D.S., Louis Seikel, D.D.S., Masid Shaheen, D.D.S.. M.S., and David Starr, D.D.S., MS., Eastman Dental Center, University of Illinois, Case Western Reserve, Ohio State University.

712

Fig.

1. Study

casts in centric

occlusion.

Vertical

lines

on canines and first molars were scribed in centric relation; their separation in centric occlusion equals anteroposterior CO-CR distance. These studies, however, would be criticized in gnathologic circles, not only for their failure to “deprogram” the muscles of mastication with occlusal splints, but also for their reliance on measurements obtained intraorally instead of from articulated casts.‘5~22~23 As noted by Roth’ (his italics), “One complicating factor that we must always keep in mind is that we simply cannot believe what we see in the mouth.” The present study was designed to test the null hypothesis that slides from CR to CO in orthodontic patients ultimately are no larger than those seen in an untreated population.

MATERIAL

AND METHODS

This study was done in conjunction with the laboratory of the sophomore occlusion course at the Ohio State University College of Dentistry. The 357 students in two consecutive sessions (1976 and 1977) were surveyed by questionnaire. The results identified 92 students as having previously undergone comprehensive (multibanded, two-arch) orthodontic therapy. A comparable number of untreated controls (83) were obtained from the remaining 265 students by selecting every third person with no history of orthodontic treatment. The mean age of the 175 subjects (men 95%) was 25 years, 6 months. Each participant wore a full-coverage maxillary occlusal splint for 2 weeks before obtaining a centric DECEMBER

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40

00

0.5

1.0

1.5

2.0

2.5

3.0

mm Fig. 2. Frequency distribution of slides from CO to CR (average of canine, molar, and incisor measurements by two examiners) for 92 subjects with a history of orthodontic treatment (Cl) and 83 co&rols (m). relation wax interocclusal record (Aluwax, Aluwax , Dental Products, Grand Rapids, Mich.) according to the method of Dawson.24 A facebow with an arbitrary hinge axis was then used to mount each student’s casts in CR on a semiadjustable articulator (Model 8500, Whip-Mix Corp., Louisville, KY.). Each mounting was verified by the class instructor, Dr. Richard W. Huffman, who then permitted us to gather data for this study. With the casts in CR, a straight edge and a sharp pencil were used to mark fine vertical lines bilaterally on the upper and lower canines and first molars. The casts were then placed in CO, and the CO-CR difference was obtained by measuring (to the nearest 0.5 mm) the anteroposterior separation of the four sets of reference lines (Fig. 1) and the change in horizontal overlap (measured at the left central incisors). In addition, these five measures were averaged to provide a single estimate of the CO-CR slide in each of the subjects. All of the measurements were duplicated blindly and independently by two observers (Drs. Delorre Haddad and George Kho). Finally, the articulators were photographed in CO to provide a standardized (1:l) record of the entire sample. The data were graphed, and standard descriptive statistics (means and standard deviations) were calculated for each of the two sets of data. Completely randomized t-tests were then used to test the null hypothesis of equal means (HO: orthodontics minus control = 0) for the five measures of CO-CR difference and for the individual average of the five measures.

RESULTS The mean CO-CR difference (averaged over the five measures and two examiners) for the orthodontic patients had a frequency distribution similar to that of the untreated controls (Fig. 2). Approximately half of both samples had slides smaller than 0.75 mm, although THE

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Table I. CO-CR difference: results

summary Sample

Study

Year

N

Kydd & Sander6 Ingervall’

1961 1964

Hodge & Mahan’ Beaton & Cleall’ Calagna et al.‘O Rieder” Total

1967 1973 1973 1978

14 36 29 101 48 15 323 566

*Inferred

from

frequency

Age Adults Children Adults Adults Children Adults Adults

of past

Difference (in mm) 0.87 0.85 0.89 0.44 0.68 0.70 0.66’ 0.65

distribution.

the control group featured a few more subjects with a centric relation occlusion. When measurements are made to the nearest 0.5 mm, this category would include slides from 0 to 0.25 mm. Descriptive statistics for the slides measured by the two examiners are summarized in Table II. The means and standard deviations are almost identical, as verified by a total lack of statistically significant differences between the subjects with a history of orthodontic treatment and the comparable group of controls (Table III).

DISCUSSION Although the present findings beg the question of the ultimate significance of small slides from CR to CO, it is clear that our data lend little support to the popular contention that “orthodontics” produces a long-term increase in the CO-CR distance: for the data of both ‘examiners, the control and experimental groups had practically identical slides, regardless of measurement site. Moreover, the mean slide for both groups was comparable to previous estimates for untreated subjects. Although the present means for both groups are slightly 713

JOHNSTON

Table II. CO-CR difference:

means and standard

deviations

(in mm)

Measurement

site

Canines Group Examiner Control

Orthod

Molars

Incisors

Right

Left

Right

Left

Individual ave. of 5 sites

Mean SD Mean SD

0.7 0.7 0.7 0.6

0.7 0.7 0.8 0.7

0.8 0.8 0.7 0.7

0.8 0.7 0.7 0.6

0.8 0.8 0.6 0.7

0.7 0.7 0.7 0.6

Mean SD Mean SD

0.7 0.6 0.8 0.8

0.8 0.7 0.9 0.9

1.0 0.8 0.9 0.8

0.9 0.7 0.9 0.9

0.9 0.8 0.8 0.8

0.9 0.7 0.9 0.8

N

Statistic

83

1

Orthod Examiner Control

92 2 82 89

Table III. CO-CR difference:

f-scores for comparisons

between

orthodontic

Measurement

*All

Statistic

Incisors

Right

Left

Right

Left

1

173

2

173

Mean diff. t-Score* Mean diff. t-Score*

0.0 -0.2 0.1 1.2

0.1 0.5 0.1 0.5

-0.1 -0.9 -0.1 -1.0

-0.0 -0.4 0.0 0.1

-0.1 -1.6 -0.1 -0.9

nonsignificant

means

Molars

df

Individual ave. of 5 sites -0.0 -0.8 -0.0 -0.1

@ > .05).

higher than the average of the reports in the literature (Table I), the slight increase is probably a function of the use of an occlusal splint before recording centric relation, a technique that is generally thought to “unmask” the full extent of a centric slide.’ Indeed, the present results match almost perfectly the data of Calagna et al.,‘O who also used occlusal splints. The present results also confirm the recent report that orthodontic patients ultimately have slides that are no larger than those of untreated controls.20 Similar studies conducted at the time of band removal, however, produced markedly different results. Specifically, the average centric slide immediately after treatment is twice as large, 1.3 to 1.6 mm. 16-‘* Barring untoward sampling and/or technical variation, these findings imply that, in growing patients, increased centric slides may ultimately be expected to return to a more “normal” size, perhaps as a result of dentoalveolar compensation25 or excess adolescent condylar growth. Conversely, when centric slides are completely eliminated by full-mouth reconstruction, they tend to reappear in later years.” Indeed, Mellion’* followed up 20 orthodontic patients from band-removal through the first 6 months of retention and found a highly significant, systematic reduction in variance: large slides became smaller; small slides became larger. A generalized tendency for CO-CR changes-both increases and decreases-to relapse implies that a COCR difference may be an intrinsic feature of the individ714

and control

site

Canines Examiner

ET AL

ual envelope of motion in populations that retain their cusps throughout life. As noted by Celenza”: “ . . . We must not confuse the centric position we choose for prosthetic construction with that centric occlusion position we find occurring naturally. The former is a mechanical substitute which is, hopefully, physiologically acceptable, and the latter is intimately related to adapted [sic] factors over% long period of time.” The inference that each individual may have a characteristic and physiologically significant CO-CR difference implies that occlusal treatments, especially in nongrowing patients, be designed not to eliminate moderate centric slides, but rather to avoid any increase. Accordingly, the following hypotheses warrant prospective analysis.: 1. The magnitude of the CO-CR difference is intrinsic to the individual and thus may be constant throughout a patient’s life. 2. In growing (and therefore “adaptable”) patients, therapeutic changes in the CO-CR difference will tend to revert to their individual pretreatment values. SUMMARY

AND

CONCLUSIONS

After 2 weeks of “deprogramming” with an occlusal splint, 92 subjects with a history of comprehensive orthodontic therapy had an average centric slide that was comparable not only to that of an untreated control group, but also to equivalent estimates reported in the literature. It is suggested that for modern man a CO-CR DECEMBER

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difference may be a normal, physiologically significant by-product of the nature and pattern of mandibular function and the tooth attachment mechanism. Moderate changes in the magnitude of a given patient’s centric slide would therefore be expected to regress, not to the population mean, but rather to the CO-CR difference that was present before treatment.

13.

REFERENCES

16.

Roth RH. Functional occlusion Orthod 1981;15:32-40. Roth RH. Functional occlusion J Clin Orthod 1981;15:100-23. Roth RH. Functional occlusion J Clin Orthod 1981;15:174-9. Brandt S. JCO/interviews: Dr. occlusion and TMJ dysfunction.

1. 2. 3. 4.

for

the orthodontist.

Part

II.

for the orthodontist.

Part

III.

40:419-25.

Ingervall B. Retruded contact position of the mandible. a comparison between children and adults. Odont Revy 1964; 15: 130-49. Hodge LC Jr, Mahan PE. A study of mandibular movement from centric occlusion to maximum intercuspation. J PROSTHET

7.

8.

DENT

1967;18:19-30.

Beaton WD, Cleall JF. CineRuorographic and study of Class I ;acceptable occlusion. Am J Orthod

9.

cephalometric 19?3;64:469-

The prevalence and in a survey population.

magnitude of mandibular J PROSTHET DENT 1978;

39~324-9.

12.

21.

22.

23.

25.

1973;30:598-604.

Rieder CE. displacement

20.

1986;56:230-7.

Ramfjord SP, Ash MM. Occlusion, 3rd ed. Philadelphia: WB Saunders Co, 1983;155-7. Solberg WK, Seligman DA. Temporomandibular orthopedics: a new vista in orthodontics. In Johnston LE, ed. New vistas in orthodontics. Philadelphia: Lea & Febiger, 1985;148-83. Eggleston WB Jr, Eckleberry JW. An electromyographic and functional evaluation of treated orthodontic cases [hlasrer’s thesis]. Ann Arbor, Mich., liniversity of hlichigan, 1961. Hall KC. The spatial relationship between centric occlusion and centric relation during contemporary Class II therapy [Master’s thesis]. St Louis, Mo: St Louis University, 1979. Mellion JT. The relationship between orthodontic relapse and the magnitude of centric slides: a clinical and cephalometric study during the first six months of retention [Master’s thesis]. St Louis, MO: St Louis University, 1980. Celenza FV. The centric position: replacement and character. J PROSTHET DENT 1973;30:591-8. Sadowsky C, BeCole EA. Long-term status of temporomandibular joint function and functional occlusion after orthodontic treatment. Am J Orthod 1980;78:201-12. Sadowsky C, Poison AM. Temporomandibular disorders and functional occlusion after orthodontic treatment: results of two long-term studies. Am J Orthod 1984;86:386-90. Crispin B J, Myers GE, Cla) ton JA. Effects of occlusal therapy on pantographic reproducibility of mandibular border movements. J PROSTHET DENT 1978;40:29-34. Kantor ME, Silverman SI, Garfinkel L. Centric relation recording techniques: a comparative investigation. J PROSTHET DENT 1973;30:604-6.

Calagna LJ, Silverman SI, Garfinkel L. Influence of neuromuscular conditioning on centric registrations. J PROSTHET DEET

11.

19.

24.

79.

10.

17.

Eugene H. Williamson on J Clin Orthod 1981;15:333-

50.

6.

15.

18.

Williamson EH. Occlusal concepts in orthodontic diagnosis and treatment. In -Johnston LE, ed. New vistas in orthodontics. Philadelphia: Lea & Febiger, 1985;122-47. Kydd WL, Sarder A. A study of posterior mandibular movements from intercuspal occlusal position. J Dent Res 1961;

5.

DENT 14.

J Clin

for the orthodontist.

Rosner D, Goldberg GF. Condylar retruded contact position and intercuspal position correlation in dentulous patients. Part I: three-dimensional analysis of condylar registrations. J PROSTHET

Hoffman PJ, Silverman SI, Garfinkel L. Comparison of condylar position in centric relation and in centric occlusion in dentulous subjects. J PROSTHET DENT 1973;30:582-8.

Dawson PE. Evaluation, diagnosis, and treatment of ocrlusal problems. St Louis: CV Mosby Co, 1974;54-61. Solow B. The dentoalveolar compensatory mechanism: background and clinical implications. Br J Orthod 1980;7:145-61.

Reprint reqtmlsto: DR. LYSLE E. JOHNSTON, JR. ST. LOUIS UNIVERSITY MEDICAL DEPARTMENT OF ORTHODONTICS ST. LOUIS,

MO

CENTER

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The relationship between the disk and the lateral pterygoid muscle in the human temporomandibular joint T. M. Wilkinson, University

of Adelaide,

B.D.S., M.Sc., M.D.S.* Department

of Dentistry, Adelaide,

I

South Australia

n understanding the biomechanics of any articular joint, the nature of the insertion of the muscles into that joint and their relation to the capsule, ligaments, and disk must be understood. In a joint as widely studied as

‘Senior THE

Lecturer.

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OF PROSTHETIC

DENTISTRY

the temporomandibular joint (TMJ), it is surprising that controversy still exists in regard to the insertion of the superior head of the lateral pterygoid muscle and in its relationship to these periarticular structures. Some authors report that the superior head of the lateral pterygoid muscle inserts only into the capsule and disk,‘,* whereas the most common description is that this 715