THE EFFECT MASTICATORY IRVING
OF EXTREME STROKES
D.M.D." New York, N. Y.
VERTICAL OVERLAP of opposing anterior teeth has been associatedwith periodontal involvement, abnormal function, improper mastication, excessive stresses,trauma, functional problems, and temporomandibular joint disturbances.‘J Chewing with mandibular movements in a vertical direction has been considered characteristic of such tooth and jaw relationships.3-6 Such chopping masticatory strokes have been credited with the development of increased vertical overlap on the one hand,7 and preventing the destruction of the periodontium on the other.s While there is some diversity of opinion as to the pathogenicity of this type of mastication, its existence in patients with deep vertical overlap has apparently been based for the most part on visual impressions. A previous study of the stability of denture basesduring function indicated that considerable movement could take place intraorally without comparable movement extraorally.Q Inasmuch as lateral mandibular movement occurs for short distances, during function, and the masking effect of the orofacial musculature is considerable, simple visual evaluation of vertical chewing would not seem to be reliable. The attachment of extension rods to orthodontic bands on anterior teeth for an accurate registration of jaw movement presents a problem of interference with occlusion in subjects with a deep vertical overlap of anterior teeth. In view of the pathologic conditions associated with such occlusions and the assumedlimited masticatory function, cinefluorography was used to study the direction of mandibular movements during mastication on subjects with deep vertical overlap of the anterior teeth.
Eight subjects with a very great vertical overlap of anterior natural teeth were studied by means of cinefluorography. Five of these subjects had lingually inclined maxillary anterior teeth that were in contact with the full length of the labial surfaces of the mandibular anterior teeth (Figs. 1 and 2). Two subjects tute
This investigation was supported in part for Dental Research, United States Public *Research Associate, Dental Department
by Research Grant D-782 from Health Service, Bethesda, Md. and the Division of Diagnostic 1035
J. Pros. Den. November-December, 1965
Fig. L-Maximal contact of the surfaces of the maxillary incisors was Fig. 2 .-A severe vertical overlap lary and mandibular incisors. vertical lead marker Fig. 3 .-A with self-curing, acrylic resin.
labial surfaces of the mandibular incisors with the lingual characteristic of 5 of the 8 subjects. without maximal labiolingual surface contact of the maxilis attached
wore small removable partial dentures. All subjects except one were 50 years of age or over. Vertical lead markers were attached anteriorly at the midlines of the maxillae and mandible (Fig. 3). Most of the lower markers were attached to the lingual surfaces of the lower anterior teeth. The markers caused no interference with closure or mandibular movements. Most subjects were given five foods to chew. These were an oatmeal cooky,* containing barium, a peeled apple, a banana, a walnut meat, and a Triscuit (a fibrous cracker). No special instructions were given to the subjects other than to eat the specific food. Mastication was recorded cinefluorographically in a posteroanterior view. Exposures were made at a speed of 15 frames per second on 35 mm. film. Then the processed films were viewed frame by frame. The total number of chewing cycles involved with the chewing of each food was recorded for each subject. All closing strokes which appeared to be in a vertical direction were counted and recorded. In addition, the position of the bolus that contained barium (oatmeal cooky) during each closing stroke was recorded as right, left, or simultaneously bilateral, depending upon the location of the bolus in the mouth. *Abbreviated
The total number of masticatory cycles involved in the study was 1,048. Most masticatory strokes contained a lateral component (Figs. 4 to 6). However, approximately 8 per cent of these cycles appeared to contain closing strokes that occurred in a vertical direction. On the 5 test foods, the highest percentage of vertical closing strokes (13 per cent) occurred with the banana, 9 per cent with the oatcake, 7 percent with the apple, 6 per cent with the walnut meat, while the Triscuit yielded the lowest quantity of such strokes at 5 per cent (Table I).
Fig. I.--selected cinefluorographic frames from opening and closing masticatorystrokes. The bolus is on the left side of the mouth. A, the mandibular marker is to the right shortly after the start of the opening stroke; B, the start of a closing stroke; C and D, the closing stroke is almost completed.
Fig. B.-Selected cineihmrographic frames from a closing masticatory stroke. The bolus is on the left side of the mouth. A, the starting of a closing stroke; B, C, and D, the mandibular marker has moved to the left during closure on the bolus; 1, a possible closure with mandibular marker on the midline and above the maxillary marker.
mastication and bolus are on the right side: B, the mastication on the left side. The mandible has moved to the left side.
Chewing with food on both sides of the mouth as evidenced by the placement of the cooky containing barium was found in two subjects during 67 and 80 per cent of the strokes, respectively (Fig. 7). However, of these masticatory strokes, only 13 and 7 per cent appeared to involve closing strokes in a vertical direction. The remaining five subjects showed the oatcake on the left side only (Table I). DISCUSSION
The assumption that chewing in a vertical direction is characteristic of subjects with extreme vertical overlap of anterior teeth would seem likely to be based upon examination of diagnostic casts, particularly those with lingually inclined maxillary anterior teeth. Following such an assumption, one might tend to see what appears to be chewing in a vertical direction in these subjects. Previous cinefluorographic studies” of denture base movement indicated that the orofacial musculature grossly masked much of the activity within the oral cavity. Therefore, clinical-visual evaluations of the direction of mandibular movement during chewing would seem to be unreliable. Cinefluorography permits visualization and differentiation of the direction of masticatory strokes without outside interference. However, coincidence of the vertical path of mandibular closure and the sagittal plane was not determined in this study. Observation by means of cinefluorography indicates that a probable reason for the side shift of the mandible during mastication is to align the full width of opposing occlusal food tables, although not necessarily with every stroke. Such alignment appears to vary according to the needs of the moment. Closing strokes, in a vertical direction also seem to provide less crushing surface by not using a perfect alignment of the food tables. Subjects with extreme vertical overlap, if restricted only to closures in a vertical direction, would have less efficient unila-teral mastication. Theoretically, they might compensate for this inefficiency by chewing on both sides of the dental arch at the same time. However, lateral shifts, of the mandible predominated even with the two subjects who displayed consider-
:. : 5 F
13 14 16
; : -0 1
to the right,
sides, are not recorded.
ZZI 1 --
EXTREME VERTICAL OVERLAP
or to both
AND BOLUS PLACEMENT WITH
it was shifted
6” 0 18
of the bolus
26 21 20 61
TABLE I. MASTICATORY STROKES IN A VERTICAL OF THE ANTERIOR TEETH
is on both
of the mouth. The this frame.
able placement of the bolus on both sides at the same time. Apparently maximal masticatory efficiency occurred on the side that had the full widths of the opposing occlusal surfaces aligned, while less efficiency occurred with the other portion of the bolus on the opposite side of the mouth. The predominance of chewing on the left side in the subjects studied i.s surprising, in view of current work in progress with other types of dentitions. The high incidence of chewing strokes in a vertical direction with bananas may be related to the reduced crushing force necessary to masticate a soft bolus of food. By way of contrast, the increased crushing force necessary for chewing a Triscuit involved a reduced incidence of masticatory strokes in a vertical direction. The protection of the periodontium that results with an absence of lateral stresses in chewing does not seem to be likely, in view of the small percentage of closing strokes that occurred in a vertical direction with subjects who have extreme vertical overlap of anterior teeth. It also does not seem likely that such masticatory strokes in a vertical direction are a factor in the development of the severe vertical overlap inasmuch as this form of mastication did not predominate. SUM
Cinefluorographic studies of the direction of jaw movement during mastication were made of a group of subjects who had a severe vertical overlap of the anterior teeth. The results indicated that: 1. Mandibular movements in a vertical direction were seldom found in 1,045 masticatory cycles in 8 subjects. 2. The smallest percentage of masticatory strokes in a vertical direction occurred with a tough fibrous food. 3. Chewing was completely unilateral and confined to the left side in 5 subjects. 4. Considerable mastication occurred bilaterally in 2 subjects. 5. Masticatory strokes in a vertical direction were not required when chewing occurred on both sides, simultaneously. 6. Chewing in a vertical direction did not seem to be a causative factor in the development of extreme vertical overlap of anterior teeth or in prevention of periodontal disturbances in these subjects. The author wishes to acknowledge the cooperation of Dr. David Tanchester, G. Jacobson, and Mrs. Frances Greenfield.
J. Pros. November-December.
1. Graber, T. M.: Orthodontics; Principles and Practice, Philadelphia, 1961, W. B. Saunders Company, p. 604. 2. Prakash, P., and Margolis, H. I.: Dento-craniofacial Relations in Varying Degrees of Overbite, Am. J. Orthodontics, 38 :657-673, 1952. 3. Shepherd, R. W.: A Further Report on Mandibular Movement, Australian D. J. 5:337342,1960. 4. Granger, E. R.: The Establishment of Occlusion, D. Clin. North America, p. 536, 1960. Guttelman, A. S.: Chop-stroke Chewers, D. Progress 1:254-257, 1961. Riesner, S. E. : Diagnosis of the Abnormalities of the T. M. Articulation, in Miller, S. C. : Oral Diagnosis and Treatment, ed. ‘2. Philadelphia, 1950, The Blakiston Company, ^ ‘)?C Hemley, S.: Orthodontic Theory and Practice, ed. 2, New York, 1953, Grune & Stratton, pp. 144-14s. Hirschfeld, L.: Minor Tooth Movement in General Practice, St. Louis, 1960, The C. V. Mosby Company p. 48. Sheppa4r$ Iis:.: Denture Base Dislodgment During Mastication, J. PROS. DEN, 13:462,
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