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Bite Opening: A Cephalometric Analysis
BITE OPENING: A CEPHALOM ETRIC ANALYSIS M. A.
B a h a d o r ,* B . S .,
D.D.S., M.S., and L. B. Iowa City, Iowa
H ig le y ,!
B.A., D.D.S., M.S.,
T is well known by the dental pro is the length, size and tonicity of the fession that a close bite may be muscle that maintains the normal length treated by various mechanical de and size of the bones, and not the reverse, vices. Not so well known are the changes as so often and erroneously thought.” that ultimately take place in the ana Mershon’s claim that only the intrusion tomic form of the head when the bite is of mandibular incisors results when a opened. The purpose of this study is to biteplate is worn is not supported by any determine, by cephalometric methods, scientific data. the changes that occur when the biteplate Wolfson3 has presented four cases in which he used a maxillary anterior splint is used to induce this opening. The literature indicates that there are to overcome the deep bite. His measure various schools of thought relative to the ments of the “dentofacial casts” seem to changes occurring when this device is indicate an intrusion of the mandibular employed. Mershon1 evidently believes incisors of as much as 4 mm. His meas that the changes can be only in the urement method can be questioned, since mandibular area, since he states that “ the this change might have taken place ow only permanent change which can be ing to vertical growth in the posterior brought about in the use of the biteplate region of the jaws or to changes in the is the depression of the anterior teeth into mandibular position, neither of which the alveoli.” This, of course, would he takes into consideration. Hemley,4 in contrast to these investi not open the bite, but would reduce the overlapping of the teeth in the anterior gators, is of the opinion that the bite can region of the dentures and therefore com be opened with little or no intrusion of pensate for the close-bite appearance of the mandibular posterior teeth. His con the dentition without increase in vertical clusions are based on twenty-two cases in dimension of the face. Mershon is of the which external measurement methods opinion that the vertical height of the were employed. With respect to mandib face is controlled by the length of the ular incisors, he states, “In only one case out of twenty-two was there any depres muscles and not by bone. He contends that, since muscle cannot sion of the mandibular incisor teeth, a be induced to lengthen, any increase in loss of one millimeter. In all the other bone length obtained during the wearing cases, there was usually no change what of the bite plate will be temporary and ever, or occasionally a slight increase in the bone will in time be returned to its height.” Hemley, in disagreement with original height owing to the pull of the Mershon, is of the opinion that even if musculature. Mershon’s opinion is sup we could depress the mandibular incisors, ported by Mackenzie2 when he states, “It once the pressure is removed these teeth would resume their original height. With *Thesis submitted in partial fulfilment of reference to Mershon’s assertion that the the requirements of the University of Iowa length and size of muscle are unchange for the degree of master of science. tProfessor of orthodontics, University of able, Hemley states that the tonicity of muscle is important, as had been origi Iowa, College of Dentistry.
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Dr. Breitner’s histologic demonstration nally stated by Mackenzie. Hemley states: “It is my contention that the in corroborates some of the effects which I fluence of the hypertonic muscles on the have recorded roentgenographically . . . I alveolar bone growth can be controlled have recorded these changes roentgenograph by the use of the biteplate. The biteplate ically in the joint, in the angle of the jaw, and in the head of the condyle. relieves the strain of the abnormal pres Hopkins,9 speaking of biteplates and sure and thus permits growth.” Strang,5 without giving scientific evidence, states in discussing Hemley’s paper,4 says: that “it opens the bite for the possible I have felt from clinical experience that vertical growth in the molar and pre the biteplate really did elevate the molars molar region so often required and so . . . that it had no effect along the lines of depressing the incisors . . . of sufficient de slowly obtained by other methods.” gree. . . . My clinical experience does not Callaway10 feels that biteplates can be agree with Dr. Mershon along this line. I used for either intrusion or extrusion of have cases in which infra-occlusion of the posterior teeth and for intrusion of man molars was present. A biteplate was used dibular incisors. He has presented some which showed a very satisfactory result ten cases without stating where the changes and fifteen years after removal of all appli might have taken place and without giv ances. Consequently, I think that there must ing actual measurements. be some mode of adjustment of these Further discussion of the works of muscles, perhaps as Hemley has spoken, in their tonicity, which permits them to allow these various men will be included in a later section of this paper after the ex the occlusal plane to be raised. perimental procedure and findings have Breitner6 has done some stimulating been presented. and interesting experiments on changing e x p e r im e n t a l p r o c e d u r e the vertical dimension or opening the bite on monkeys, and then studied the Twenty cases were finally selected for changes histologically. By placing “caps” this study. This is not a large group, but on the six maxillary anterior teeth, the it was decided that the quality of the bite was opened and, after forty-nine records was more important than the days, the posterior teeth had returned to number of cases. During the last ten occlusion again. Histologic slides showed years, the staff of the Department of changes both at the condyle and at the Orthodontics of the College of Dentistry, fossa, indicating that “the condyle ap University of Iowa, has been securing parently is growing distocranially.” There records of many more cases in which the were also changes at the angle of the biteplate was worn and which were mandible indicating a “development of a originally intended to be included in this more obtuse angle.” In a subsequent study. However, only the twenty cases paper,7 Breitner says: mentioned fulfilled all requirements. The reason for rejecting the remaining cases These bone transformations seem to indi cate that any artificial change of the vertical was that other orthodontic treatment was dimension not only influences the alveolar being carried on simultaneously with the processes, but also leads to changes in shape wearing of the biteplate or that records and position of the mandible. The bone obtained gave insufficient or incomplete transformations subsequent to raising of the data. The various reasons for opening bite might be regarded as nature’s intention the bite in the twenty selected cases were to reestablish the original vertical dimension to improve function, facilitate dental and, with it, the balance between muscular restoration, prevent further wear of the action and architecture of the bone. teeth, especially the incisors, eliminate Breitner’s earlier paper6 was discussed trauma and irritation and improve the by Reisner8 thus: appearance.
B a h a d o r a n d H ig l e y — B it e O p e n in g The plate was of the usual Hawley retainer design for the maxillary arch with either a vulcanite or an acrylic base. (Fig. i.) Stainless steel clasps were used on the first permanent molars, with a labial wire of the same material extend ing from canine to canine. Often, clasps on the first bicuspids were substituted for the labial wire. The base covered the entire palate, extending slightly beyond the first molar area. When the jaws attempted to close, the mandibular in cisors contacted the biteplate holding the jaws apart so that the maxillary posterior teeth were separated from those of the mandible by a space meeting the needs of the individual patient, but never per-
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ural growth processes would open the bite. Only after such a period of obser vation had shown no apparent improve ment was a biteplate placed in the mouth. The rapid improvement there after was convincing as to the stimulating effect of the appliance. It was interesting to note that for two patients of 10 and 11 years, the desired bite opening was obtained within two weeks, and there after the appliance was used as a re tainer only. Most of the older patients were not placed under observation be-
Fig. i.—A Hawley type bite-plate. A simi lar appliance was used to open the bite for all cases included in this study. mitted to exceed the space allowed by Fig. 2 .—A. X-ray tube, B. Casette and the physiologic rest position of the holder. C. Head positioner. mandible. There were nine females and eleven cause it was felt that they had reached males in the group. No attempt was a more or less stationary level of growth. made to compare the two sexes or to Patients wearing the biteplate were seen evaluate them separately. The age range at first every week and then every two was from 10 to 26 years, eight being weeks for observation and, when neces under 15 and twelve over 15. The treat sary, adjustment of the appliance. Each patient had at least two profile ment period varied from two to about eight months. All of the younger pa roentgenograms taken, one before the tients, those below 15 years of age, were treatment was begun and the other after placed under observation for various the desired vertical dimension was ob periods of time to determine whether nat tained. The technic and procedure for
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taking the roentgenograms was that em ployed and described by Higley.11 The technic is essentially this : The patient’s head is so positioned in a head holder (Figs. 2 and 3) that the midsagittal plane is at a fixed distance from the target and film and parallel to the film. The mid central roentgen-ray is focused to pass through the head on a transverse axis at the level of the ear holes and be at right angles to the midsagittal plane of the head and the film. By using this equip ment, it is possible to reorient the head in the same position for a series of head roentgenograms. Several years of experi-
Fig. 3 -—Head in position. mentation with this equipment has es tablished the objectivity and reliability of the method. The technic has been found to be accurate enough to allow superposition of two or more roentgeno grams or tracings of them. Since the treatment time was so short, it was found that the superstructures of the head, in the before and after treatment roentgeno grams, would be superimposed exactly. This made any change in the lower facial area quite obvious and facilitated meas urement.
In this study, the measurements were made directly on the roentgenogram. To make these measurements, the following base lines were placed under the film on the illuminating table. (Fig. 4.) (a) NS, a line from the nasion tangent to the base of the sella turcica. (b) MG, a line tangential to the lower border of the mandible at two points and at right angles to a line which is tan gential to the anterior border of the mandible at the symphysis. (c) NA, a vertical line from the nasion perpendicular to the base line NS. These base lines were considered ac ceptable, since former cranial studies have shown that growth changes in these areas would be practically nil for the duration of treatment of any individual patient in this series, or for any other individuals in this age range.12 Measurements taken before and after treatment were: (a) Total face height, (b) Posterior dental height (maxillary and mandibular). (c) Mandibular incisor height, (d) Maxillary incisor anteropos terior position, (e) Mandibular antero posterior position. No attempt was made to select the same points for measurements on all the roentgenograms. Only on those of the same patient were identical points chosen. However, comparable points were chosen for the entire group. The reason for this was that all the roentgen ograms did not show with equal clarity the same points for all the same anatomic landmarks under consideration. This procedure allowed more freedom to select the clearest, but still comparable points for measurement, and it seemed perfectly acceptable for the problem at hand to do so for the following reasons : (a) The amount of bite opening de sired in the various cases was not in tended to be comparable except in a qualitative sense. (b) The measurements of the roent genograms of before and after treatment for the same individual were intended
B a h a d o r a n d H ig l e y — B it e O p e n in g to be comparable qualitatively and quantitively. (c) Only the direction of position or growth changes was considered of sig nificance, since the amount of bite open ing had been planned to meet the needs of the individual. (d) The amount of these changes is of significance only in respect to dura tion of treatment and age of the patient. Points used in taking the measure ments were:
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and premolar tooth perpendicular to the base line MG. (c) For mandibular incisor height. From the incisal edge perpendicular to the base line MG. (d) For maxillary incisor anteropos terior position. From a point on the maxillary central incisor, perpendicular to the line NA. (e) For mandibular anteroposterior position. From a point on the symphysis per-
Fig. 4 .— Base lines used to facilitate measurement NS, a line from the nasion tangent to the base of the sella turcica. MG, a line tangential to the lower border of the mandible at two points and at right angles to a line which is tangential to the mandible at the symphysis. NA, a ver tical line from the nasion perpendicular to the base line NS. (a) For total face height. pendicular to the line NA. With reference to total face height From a point at the symphysis perpen dicular to the base line NS. (Table 1) : (b) For posterior dental height. All cases showed an increase in the 1. From a point on a maxillary molar vertical dimensions ranging from 0.1 to and premolar tooth perpendicular to the 4.3 mm. With reference to posterior height base line NS. 2- From a point on a mandibular molar (Table 1) :
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1. All cases showed increase in height for one or more of the four posterior teeth that were measured. 2. More maxillary posterior teeth showed increase in height than those of the mandible. 3. For the maxillary premolar measure ment, seventeen cases showed a height increase ranging from 0.2 to 2.0 mm., while one case showed no change and two cases showed a decrease of 0.1 mm.
6. For the mandibular molar measure ment, fourteen cases showed an increase ranging from 0.1 to 2.3 mm., while two cases showed no change and four showed a decrease ranging from 0.1 to 0.6 mm. Additional measurements in the posterior area may have proved of value since un even vertical change in the teeth is evi dent. With reference to mandibular incisal height (Table 1) :
Fig. 5 .— Profile roentgenogram of a patient before opening the bite. 4. For the maxillary molar measure ment, nineteen cases showed an increase ranging from 0.1 to 2.0 mm., while one case showed a decrease of 0.2 mm. 5. For the mandibular premolar meas urement, thirteen cases showed an in crease ranging from 0.1 to 2.4 mm., while three cases showed no change and four cases showed a decrease ranging from 0.2 to 0.7 mm.
Eight cases showed a height increase, in six of which it was 0.4 mm. or less in amount, while in two it equaled 1.1 mm. Six cases showed no change at all and six others showed a decrease ranging from 0.2 to 0.9 mm. With reference to maxillary incisor anteroposterior position (Table 1) : Three cases showed a slight protrusive change ranging from 0.3 to 0.6 mm.,
B a h a d o r a n d H ig l e y — B it e O p e n in g while two cases showed no change and fourteen cases showed a retrusive change ranging from o. i to 3.4 mm. With reference to mandibular antero posterior position (Table 1) : Fifteen cases showed a retrusion rang ing from 0.2 to 2.6 mm., while one case showed no change and four cases showed a slight protrusion ranging from o. 1 to 0.7 mm.
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interdigitation requirements of various teeth and changes in the mandibular position. Before treatment is complete, the dental vertical change is not equal for all areas, but it is difficult to de termine what is responsible for this. Figure 5 shows before and after treat ment roentgenograms of a patient from this series. The major dental and facial changes are obvious.
Fig. 6.—Profile roentgenogram of the same patient as shown in Figure 5 but after opening the bite. The changes in the lower facial area are obvious. DISCUSSION In Table 2 are shown the total verti cal facial height increase, the sum of This investigation reveals an increase the increase in the premolar area of the in the posterior dental area in all cases. maxillae and the mandible and the in It also shows that there was little change crease in the molar area of the maxilla in the mandibular incisal height level. and the mandible. With very few ex Hemley4 had found the latter to be true, ceptions, the total facial height increase but his measurements for posterior height and posterior dental height increase cor increase were taken only in the mandible, respond, although they are not exactly and therefore he did not mention any the same, perhaps because of the peculiar increase for the maxillary posterior area.
0.0
0
0.1
—
1.3 0.7 0.2 1.3
0.2 2.0 0.8
0.7 0.1 0.7
1.0 1.1
+ 0
0.2
—
0.2 1. 2 0.1
0.1 0.2
2.4
0.6
+
0.0 0.0
0
1.4 0.4
1.0
0.6
1.1
2.3 0.3
+
0 .1
0.3 0.2 0.7 0.3
0.5
—
0.0
0
0.4 0.4
—
1.4 0.4
1.1
+
0.0
0.0 0.0
0.0
0.0
0
+
0.9 0.7 0.2
0.6
0.6
0.4 0.3
—
Mandibular Incisal
0.0
0.0
0
0.1
+
0.0
0
0.6 0.6 2.6
0.5
1.0 1.0
2.3
0.6 0.2
— 0.4
Mandibular
0.7 0.7 0.4 0.9
0.2
0.8
— 3.4 0.1 0.9
Maxillary Incisal
13 14 IS 16 17 18 19
A m e r ic a n
0.2 0.6 1.5 2.3 0.6 0.2 0.6 0.1 1.1 0.4 0.1 0.2 2.8 0.2 0.4 0.7 0.3 1.5 1.1 3.0 1.0 0.4 0.0 0.1 0.0 1.2 0.30.1 1.5 1.8 2.4 2.2 1.4 0.1 4.3 1.1 0.7 0.4 0.4 0.4 0.0 0.3 2.2 0.7 0.8 0.3 0.3 1.2 1.1 0.9 0.9 1.7 0.2 1.2 0.9 0.4 1.5 0.3 0.4 1.1 20 *Differences in measurements taken before and after treatment of each patient. Height changes are shown in all but the last two columns, which present an teroposterior changes.
0.8 0.2 0.2
1.3 0.3
1. 2
0.6
2.0
0.7
0.8
+
Mandibular Molar
th e
0.1 1.2 0.6 0.2
—
Mandibular Premolar
(M m .)
of
10 11 12
1.3 2.8 1.7
0
Maxillary Molar
e ig h t a n d A n te ro p o s te rio r C h an g es
Jo u rn al
3 4 5 6 7 8 9
2.0 2.6 1.2 0.8 1.1
+
Maxillary Premolar
1. — H
The
1 2
Case
Total Face
T a b le
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B a h a d o r a n d H ig l e y — B it e O p e n in g This study also showed that, while the vertical dimension of the face was in creased, there were anteroposterior changes in the mandible, mostly retrusion, and also retrusion of the maxillary incisors in most cases. Hemley’s work did not include the positional changes of the mandible, which certainly affect the vertical change of the face. With the evidence presented in this study, it is difficult to agree with Mershon that “there is nothing known to science which will correct a true closeT able 2.— C hanges in H e ig h t (M m .)
Case 1 2
3 4 S 6 7 8 9 10 11 12
13 14 15 16 17 18 19
20
Total Facial 2.8 2.6 1. 2 0.8 1.1
1.3 1.7
2.8
0.1 1. 2 0.6 0.2
2.3 0.4 3.0 1.2 4.3 2.2 1.7 0.4
Maxillary Maxillary Premolar Molar plus plus Mandibular Mandibular Premolar Molar 2 .1 1.4 3.4 3.1 2 .1 1.0 0.7 0.1 0.1 0.7 1.2 0.2 2.4 3.4 1.2 1.4 0.2 0.0 0.6 0.9 0.5 0.4 0..2 0.3 1.5 0.7 0.5 0.1 1.8 1.9 0 .1 0.3 3.5 3.6 1.1 0.7 1.2 2.0 1.8 1.5
bite during development or after ma turity.” 1 His definition of “ true closebite” is as follows: “In the true close-bite, the posterior teeth are short, the rami are short and the maxillomandibular muscles are correspondingly short and in har mony with the rest of the organism.”1 Granted that the muscles are not able to increase in length, there remains the pos sibility that they may still have some un consumed potentiality for growth, since all other structures, as he implies, have
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been retarded in growth. Once these other structures have been stimulated to grow to reach their optimum, the muscles also may grow to a corresponding opti mum length. Again, if the muscle had reached its optimum length while the other structures were retarded, it could be possible that the musculature is re laxed and folded upon itself and would therefore allow an unfolding and increase in tonicity as the bite was opened. Fur thermore, it is possible to make use of the “physiologic rest position” of the mandi ble or the space between the upper arid lower posterior teeth when the jaws are at rest. If the amount of the bite open ing does not exceed the amount allowed by the physiologic rest position, this should not be incompatible even with Mershon’s opinion of opening the bite, since the length of the muscles have re mained unaltered. That is exactly what was done in the treatment of cases used for this study- In no case was the amount of bite opening more than the space al lowed by the physiologic rest position. None of the patients at any time, during or after treatment, complained of any facial muscular pain or discomfort. If this limit of bite opening has been exceeded, as may have been the case in Breitner’s experiments with monkeys, this statement of his can be considered: “. . . a disharmony of muscular forces acting upon the skeleton is created, which necessarily leads to bone transforma tions.” His histologic findings on adult monkeys can be regarded as acceptable with respect to being able to induce some changes in the mandibular form with various orthodontic devices.7’ 13 However, in the human being, it has not been demonstrated clinically or otherwise that the mandible can be mechanically altered in its shape after adulthood or even earlier. If there are changes, they might be so slight as to be demonstrable only by histologic methods, which it is difficult, if not impossible, to apply to human beings. In the pres
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ent study, it is felt that any change in 4 . Increase in the vertical dimension the mandibular form is not gross enough was accompanied by changes in the man to be included within the reliability of dibular position. Fifteen cases showed the cephalometric technic. Nevertheless, retrusion, four slight protrusion and one Breitner’s studies13 indicate that it may no change at all. be possible to obtain major growth 5. Maxillary incisor teeth showed re changes in the jaws as a whole and not trusion in fourteen patients, protrusion depend alone on tooth movements to in four and no change in two. The value of the biteplate for increas remedy facial deformities. Measurable change in the position of the mandible ing the vertical dimension has been dem was obtained in this series, but it was onstrated. It is now necessary to investi not determined just where the changes gate the permanence of the result after took place or what was their nature. removal of the appliance. Such a study is now in progress. sum m ary
The literature presents a number of viewpoints, which may be divided into various schools of thought in determin ing the changes that occur when the bite is opened: 1. That the results obtained in bite opening are due only to intrusion of the mandibular incisors and there is no change in the posterior dental or other areas of the jaws. 2. That there is little if any intrusion of mandibular incisors and the increase in the vertical dimension of the pos terior region of the jaws is responsible for opening the bite. 3. That there are changes in the mandibular form in addition to other changes as evidenced by animal experi mentation. c o n c l u s io n s
i - Various amounts of bite opening were obtained in all of twenty cases un der study. 2. A few cases showed very slight in trusion of the mandibular incisor teeth. The majority of cases showed either no change in height or some slight extrusion of these teeth. 3. Most of the vertical increase was shown in the posterior dental region. More cases showed vertical increase in the maxillary posterior teeth than in the same area of the mandibular arch.
1.
b ib l io g r a p h y
M er sh o n , J. V.: Possibilities and Limi
tations in Treatment of Close-Bite. Internat. J. Orthodontia, 2 3 :5 8 1 -589, June 19 3 7 . 2 . M ackenzie , W. C.: Action of Muscles, Including Muscle Rest and Muscle Reeduca tion. New York: Paul B. Hoeber, 1 9 1 8 , p. 5 . 3 . W o lfso n , A bra h a m : Deep Bites in Adults. Am. J. Orthodontics, 2 4 : 12 0 - 128, February 1938 . 4 . H emley , S a m u e l : Bite Plates, Their Application and Action. Am. J. Orthodon tics, 2 4 : 7 2 1 -736, August 1938 . 5 . S trang , R o b er t : Disc, of Hemley, Refer ence 4 . 6 . B reitner , C ar l : Bone Changes Result ing from Experimental Orthodontic Treat ment. Am. J. Orthodontics, 2 6 :5 2 1 -545 , June 1940 . 7 . Idem: Further Investigations of Bone Changes Resulting from Experimental Ortho dontic Treatment. Am. J. Orthodontics, 27: 605 -632 , November 1 9 4 1 . 8. R eisn er , S. E.: Disc, of Breitner, Refer ence 6. 9 . H o pk in s , S. C.: Bite Planes. Am. J. Orthodontics, 2 6 : 107 - 1 1 9 , February 1940 . 10 . C allaw ay , G. S.: Use of Bite Plates. Am. J. Orthodontics, 2 6 : 12 0 - 124 , February 1940 . 1 1 . H igley , L. B.: Head Positioner for Scientific Radiographic and Photographic Purposes. Internat. J. Orthodontia, 2 2 :699, July 1936 . 1 2 . B roadbent , B. H .: Face of Normal Child. Angle Orthodontist, 7 : 18 3 , No. 4 , 19371 3 . B reitner , C a r l : Alteration of Occlusal Relations Induced by Experimental Procedure. Am. J. Orthodontics, 2 9 :277 -289, June 1943 .
B a h a d o r ,* B . S .,
D.D.S., M.S., and L. B. Iowa City, Iowa
H ig le y ,!
B.A., D.D.S., M.S.,
T is well known by the dental pro is the length, size and tonicity of the fession that a close bite may be muscle that maintains the normal length treated by various mechanical de and size of the bones, and not the reverse, vices. Not so well known are the changes as so often and erroneously thought.” that ultimately take place in the ana Mershon’s claim that only the intrusion tomic form of the head when the bite is of mandibular incisors results when a opened. The purpose of this study is to biteplate is worn is not supported by any determine, by cephalometric methods, scientific data. the changes that occur when the biteplate Wolfson3 has presented four cases in which he used a maxillary anterior splint is used to induce this opening. The literature indicates that there are to overcome the deep bite. His measure various schools of thought relative to the ments of the “dentofacial casts” seem to changes occurring when this device is indicate an intrusion of the mandibular employed. Mershon1 evidently believes incisors of as much as 4 mm. His meas that the changes can be only in the urement method can be questioned, since mandibular area, since he states that “ the this change might have taken place ow only permanent change which can be ing to vertical growth in the posterior brought about in the use of the biteplate region of the jaws or to changes in the is the depression of the anterior teeth into mandibular position, neither of which the alveoli.” This, of course, would he takes into consideration. Hemley,4 in contrast to these investi not open the bite, but would reduce the overlapping of the teeth in the anterior gators, is of the opinion that the bite can region of the dentures and therefore com be opened with little or no intrusion of pensate for the close-bite appearance of the mandibular posterior teeth. His con the dentition without increase in vertical clusions are based on twenty-two cases in dimension of the face. Mershon is of the which external measurement methods opinion that the vertical height of the were employed. With respect to mandib face is controlled by the length of the ular incisors, he states, “In only one case out of twenty-two was there any depres muscles and not by bone. He contends that, since muscle cannot sion of the mandibular incisor teeth, a be induced to lengthen, any increase in loss of one millimeter. In all the other bone length obtained during the wearing cases, there was usually no change what of the bite plate will be temporary and ever, or occasionally a slight increase in the bone will in time be returned to its height.” Hemley, in disagreement with original height owing to the pull of the Mershon, is of the opinion that even if musculature. Mershon’s opinion is sup we could depress the mandibular incisors, ported by Mackenzie2 when he states, “It once the pressure is removed these teeth would resume their original height. With *Thesis submitted in partial fulfilment of reference to Mershon’s assertion that the the requirements of the University of Iowa length and size of muscle are unchange for the degree of master of science. tProfessor of orthodontics, University of able, Hemley states that the tonicity of muscle is important, as had been origi Iowa, College of Dentistry.
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Dr. Breitner’s histologic demonstration nally stated by Mackenzie. Hemley states: “It is my contention that the in corroborates some of the effects which I fluence of the hypertonic muscles on the have recorded roentgenographically . . . I alveolar bone growth can be controlled have recorded these changes roentgenograph by the use of the biteplate. The biteplate ically in the joint, in the angle of the jaw, and in the head of the condyle. relieves the strain of the abnormal pres Hopkins,9 speaking of biteplates and sure and thus permits growth.” Strang,5 without giving scientific evidence, states in discussing Hemley’s paper,4 says: that “it opens the bite for the possible I have felt from clinical experience that vertical growth in the molar and pre the biteplate really did elevate the molars molar region so often required and so . . . that it had no effect along the lines of depressing the incisors . . . of sufficient de slowly obtained by other methods.” gree. . . . My clinical experience does not Callaway10 feels that biteplates can be agree with Dr. Mershon along this line. I used for either intrusion or extrusion of have cases in which infra-occlusion of the posterior teeth and for intrusion of man molars was present. A biteplate was used dibular incisors. He has presented some which showed a very satisfactory result ten cases without stating where the changes and fifteen years after removal of all appli might have taken place and without giv ances. Consequently, I think that there must ing actual measurements. be some mode of adjustment of these Further discussion of the works of muscles, perhaps as Hemley has spoken, in their tonicity, which permits them to allow these various men will be included in a later section of this paper after the ex the occlusal plane to be raised. perimental procedure and findings have Breitner6 has done some stimulating been presented. and interesting experiments on changing e x p e r im e n t a l p r o c e d u r e the vertical dimension or opening the bite on monkeys, and then studied the Twenty cases were finally selected for changes histologically. By placing “caps” this study. This is not a large group, but on the six maxillary anterior teeth, the it was decided that the quality of the bite was opened and, after forty-nine records was more important than the days, the posterior teeth had returned to number of cases. During the last ten occlusion again. Histologic slides showed years, the staff of the Department of changes both at the condyle and at the Orthodontics of the College of Dentistry, fossa, indicating that “the condyle ap University of Iowa, has been securing parently is growing distocranially.” There records of many more cases in which the were also changes at the angle of the biteplate was worn and which were mandible indicating a “development of a originally intended to be included in this more obtuse angle.” In a subsequent study. However, only the twenty cases paper,7 Breitner says: mentioned fulfilled all requirements. The reason for rejecting the remaining cases These bone transformations seem to indi cate that any artificial change of the vertical was that other orthodontic treatment was dimension not only influences the alveolar being carried on simultaneously with the processes, but also leads to changes in shape wearing of the biteplate or that records and position of the mandible. The bone obtained gave insufficient or incomplete transformations subsequent to raising of the data. The various reasons for opening bite might be regarded as nature’s intention the bite in the twenty selected cases were to reestablish the original vertical dimension to improve function, facilitate dental and, with it, the balance between muscular restoration, prevent further wear of the action and architecture of the bone. teeth, especially the incisors, eliminate Breitner’s earlier paper6 was discussed trauma and irritation and improve the by Reisner8 thus: appearance.
B a h a d o r a n d H ig l e y — B it e O p e n in g The plate was of the usual Hawley retainer design for the maxillary arch with either a vulcanite or an acrylic base. (Fig. i.) Stainless steel clasps were used on the first permanent molars, with a labial wire of the same material extend ing from canine to canine. Often, clasps on the first bicuspids were substituted for the labial wire. The base covered the entire palate, extending slightly beyond the first molar area. When the jaws attempted to close, the mandibular in cisors contacted the biteplate holding the jaws apart so that the maxillary posterior teeth were separated from those of the mandible by a space meeting the needs of the individual patient, but never per-
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ural growth processes would open the bite. Only after such a period of obser vation had shown no apparent improve ment was a biteplate placed in the mouth. The rapid improvement there after was convincing as to the stimulating effect of the appliance. It was interesting to note that for two patients of 10 and 11 years, the desired bite opening was obtained within two weeks, and there after the appliance was used as a re tainer only. Most of the older patients were not placed under observation be-
Fig. i.—A Hawley type bite-plate. A simi lar appliance was used to open the bite for all cases included in this study. mitted to exceed the space allowed by Fig. 2 .—A. X-ray tube, B. Casette and the physiologic rest position of the holder. C. Head positioner. mandible. There were nine females and eleven cause it was felt that they had reached males in the group. No attempt was a more or less stationary level of growth. made to compare the two sexes or to Patients wearing the biteplate were seen evaluate them separately. The age range at first every week and then every two was from 10 to 26 years, eight being weeks for observation and, when neces under 15 and twelve over 15. The treat sary, adjustment of the appliance. Each patient had at least two profile ment period varied from two to about eight months. All of the younger pa roentgenograms taken, one before the tients, those below 15 years of age, were treatment was begun and the other after placed under observation for various the desired vertical dimension was ob periods of time to determine whether nat tained. The technic and procedure for
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taking the roentgenograms was that em ployed and described by Higley.11 The technic is essentially this : The patient’s head is so positioned in a head holder (Figs. 2 and 3) that the midsagittal plane is at a fixed distance from the target and film and parallel to the film. The mid central roentgen-ray is focused to pass through the head on a transverse axis at the level of the ear holes and be at right angles to the midsagittal plane of the head and the film. By using this equip ment, it is possible to reorient the head in the same position for a series of head roentgenograms. Several years of experi-
Fig. 3 -—Head in position. mentation with this equipment has es tablished the objectivity and reliability of the method. The technic has been found to be accurate enough to allow superposition of two or more roentgeno grams or tracings of them. Since the treatment time was so short, it was found that the superstructures of the head, in the before and after treatment roentgeno grams, would be superimposed exactly. This made any change in the lower facial area quite obvious and facilitated meas urement.
In this study, the measurements were made directly on the roentgenogram. To make these measurements, the following base lines were placed under the film on the illuminating table. (Fig. 4.) (a) NS, a line from the nasion tangent to the base of the sella turcica. (b) MG, a line tangential to the lower border of the mandible at two points and at right angles to a line which is tan gential to the anterior border of the mandible at the symphysis. (c) NA, a vertical line from the nasion perpendicular to the base line NS. These base lines were considered ac ceptable, since former cranial studies have shown that growth changes in these areas would be practically nil for the duration of treatment of any individual patient in this series, or for any other individuals in this age range.12 Measurements taken before and after treatment were: (a) Total face height, (b) Posterior dental height (maxillary and mandibular). (c) Mandibular incisor height, (d) Maxillary incisor anteropos terior position, (e) Mandibular antero posterior position. No attempt was made to select the same points for measurements on all the roentgenograms. Only on those of the same patient were identical points chosen. However, comparable points were chosen for the entire group. The reason for this was that all the roentgen ograms did not show with equal clarity the same points for all the same anatomic landmarks under consideration. This procedure allowed more freedom to select the clearest, but still comparable points for measurement, and it seemed perfectly acceptable for the problem at hand to do so for the following reasons : (a) The amount of bite opening de sired in the various cases was not in tended to be comparable except in a qualitative sense. (b) The measurements of the roent genograms of before and after treatment for the same individual were intended
B a h a d o r a n d H ig l e y — B it e O p e n in g to be comparable qualitatively and quantitively. (c) Only the direction of position or growth changes was considered of sig nificance, since the amount of bite open ing had been planned to meet the needs of the individual. (d) The amount of these changes is of significance only in respect to dura tion of treatment and age of the patient. Points used in taking the measure ments were:
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and premolar tooth perpendicular to the base line MG. (c) For mandibular incisor height. From the incisal edge perpendicular to the base line MG. (d) For maxillary incisor anteropos terior position. From a point on the maxillary central incisor, perpendicular to the line NA. (e) For mandibular anteroposterior position. From a point on the symphysis per-
Fig. 4 .— Base lines used to facilitate measurement NS, a line from the nasion tangent to the base of the sella turcica. MG, a line tangential to the lower border of the mandible at two points and at right angles to a line which is tangential to the mandible at the symphysis. NA, a ver tical line from the nasion perpendicular to the base line NS. (a) For total face height. pendicular to the line NA. With reference to total face height From a point at the symphysis perpen dicular to the base line NS. (Table 1) : (b) For posterior dental height. All cases showed an increase in the 1. From a point on a maxillary molar vertical dimensions ranging from 0.1 to and premolar tooth perpendicular to the 4.3 mm. With reference to posterior height base line NS. 2- From a point on a mandibular molar (Table 1) :
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1. All cases showed increase in height for one or more of the four posterior teeth that were measured. 2. More maxillary posterior teeth showed increase in height than those of the mandible. 3. For the maxillary premolar measure ment, seventeen cases showed a height increase ranging from 0.2 to 2.0 mm., while one case showed no change and two cases showed a decrease of 0.1 mm.
6. For the mandibular molar measure ment, fourteen cases showed an increase ranging from 0.1 to 2.3 mm., while two cases showed no change and four showed a decrease ranging from 0.1 to 0.6 mm. Additional measurements in the posterior area may have proved of value since un even vertical change in the teeth is evi dent. With reference to mandibular incisal height (Table 1) :
Fig. 5 .— Profile roentgenogram of a patient before opening the bite. 4. For the maxillary molar measure ment, nineteen cases showed an increase ranging from 0.1 to 2.0 mm., while one case showed a decrease of 0.2 mm. 5. For the mandibular premolar meas urement, thirteen cases showed an in crease ranging from 0.1 to 2.4 mm., while three cases showed no change and four cases showed a decrease ranging from 0.2 to 0.7 mm.
Eight cases showed a height increase, in six of which it was 0.4 mm. or less in amount, while in two it equaled 1.1 mm. Six cases showed no change at all and six others showed a decrease ranging from 0.2 to 0.9 mm. With reference to maxillary incisor anteroposterior position (Table 1) : Three cases showed a slight protrusive change ranging from 0.3 to 0.6 mm.,
B a h a d o r a n d H ig l e y — B it e O p e n in g while two cases showed no change and fourteen cases showed a retrusive change ranging from o. i to 3.4 mm. With reference to mandibular antero posterior position (Table 1) : Fifteen cases showed a retrusion rang ing from 0.2 to 2.6 mm., while one case showed no change and four cases showed a slight protrusion ranging from o. 1 to 0.7 mm.
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interdigitation requirements of various teeth and changes in the mandibular position. Before treatment is complete, the dental vertical change is not equal for all areas, but it is difficult to de termine what is responsible for this. Figure 5 shows before and after treat ment roentgenograms of a patient from this series. The major dental and facial changes are obvious.
Fig. 6.—Profile roentgenogram of the same patient as shown in Figure 5 but after opening the bite. The changes in the lower facial area are obvious. DISCUSSION In Table 2 are shown the total verti cal facial height increase, the sum of This investigation reveals an increase the increase in the premolar area of the in the posterior dental area in all cases. maxillae and the mandible and the in It also shows that there was little change crease in the molar area of the maxilla in the mandibular incisal height level. and the mandible. With very few ex Hemley4 had found the latter to be true, ceptions, the total facial height increase but his measurements for posterior height and posterior dental height increase cor increase were taken only in the mandible, respond, although they are not exactly and therefore he did not mention any the same, perhaps because of the peculiar increase for the maxillary posterior area.
0.0
0
0.1
—
1.3 0.7 0.2 1.3
0.2 2.0 0.8
0.7 0.1 0.7
1.0 1.1
+ 0
0.2
—
0.2 1. 2 0.1
0.1 0.2
2.4
0.6
+
0.0 0.0
0
1.4 0.4
1.0
0.6
1.1
2.3 0.3
+
0 .1
0.3 0.2 0.7 0.3
0.5
—
0.0
0
0.4 0.4
—
1.4 0.4
1.1
+
0.0
0.0 0.0
0.0
0.0
0
+
0.9 0.7 0.2
0.6
0.6
0.4 0.3
—
Mandibular Incisal
0.0
0.0
0
0.1
+
0.0
0
0.6 0.6 2.6
0.5
1.0 1.0
2.3
0.6 0.2
— 0.4
Mandibular
0.7 0.7 0.4 0.9
0.2
0.8
— 3.4 0.1 0.9
Maxillary Incisal
13 14 IS 16 17 18 19
A m e r ic a n
0.2 0.6 1.5 2.3 0.6 0.2 0.6 0.1 1.1 0.4 0.1 0.2 2.8 0.2 0.4 0.7 0.3 1.5 1.1 3.0 1.0 0.4 0.0 0.1 0.0 1.2 0.30.1 1.5 1.8 2.4 2.2 1.4 0.1 4.3 1.1 0.7 0.4 0.4 0.4 0.0 0.3 2.2 0.7 0.8 0.3 0.3 1.2 1.1 0.9 0.9 1.7 0.2 1.2 0.9 0.4 1.5 0.3 0.4 1.1 20 *Differences in measurements taken before and after treatment of each patient. Height changes are shown in all but the last two columns, which present an teroposterior changes.
0.8 0.2 0.2
1.3 0.3
1. 2
0.6
2.0
0.7
0.8
+
Mandibular Molar
th e
0.1 1.2 0.6 0.2
—
Mandibular Premolar
(M m .)
of
10 11 12
1.3 2.8 1.7
0
Maxillary Molar
e ig h t a n d A n te ro p o s te rio r C h an g es
Jo u rn al
3 4 5 6 7 8 9
2.0 2.6 1.2 0.8 1.1
+
Maxillary Premolar
1. — H
The
1 2
Case
Total Face
T a b le
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B a h a d o r a n d H ig l e y — B it e O p e n in g This study also showed that, while the vertical dimension of the face was in creased, there were anteroposterior changes in the mandible, mostly retrusion, and also retrusion of the maxillary incisors in most cases. Hemley’s work did not include the positional changes of the mandible, which certainly affect the vertical change of the face. With the evidence presented in this study, it is difficult to agree with Mershon that “there is nothing known to science which will correct a true closeT able 2.— C hanges in H e ig h t (M m .)
Case 1 2
3 4 S 6 7 8 9 10 11 12
13 14 15 16 17 18 19
20
Total Facial 2.8 2.6 1. 2 0.8 1.1
1.3 1.7
2.8
0.1 1. 2 0.6 0.2
2.3 0.4 3.0 1.2 4.3 2.2 1.7 0.4
Maxillary Maxillary Premolar Molar plus plus Mandibular Mandibular Premolar Molar 2 .1 1.4 3.4 3.1 2 .1 1.0 0.7 0.1 0.1 0.7 1.2 0.2 2.4 3.4 1.2 1.4 0.2 0.0 0.6 0.9 0.5 0.4 0..2 0.3 1.5 0.7 0.5 0.1 1.8 1.9 0 .1 0.3 3.5 3.6 1.1 0.7 1.2 2.0 1.8 1.5
bite during development or after ma turity.” 1 His definition of “ true closebite” is as follows: “In the true close-bite, the posterior teeth are short, the rami are short and the maxillomandibular muscles are correspondingly short and in har mony with the rest of the organism.”1 Granted that the muscles are not able to increase in length, there remains the pos sibility that they may still have some un consumed potentiality for growth, since all other structures, as he implies, have
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been retarded in growth. Once these other structures have been stimulated to grow to reach their optimum, the muscles also may grow to a corresponding opti mum length. Again, if the muscle had reached its optimum length while the other structures were retarded, it could be possible that the musculature is re laxed and folded upon itself and would therefore allow an unfolding and increase in tonicity as the bite was opened. Fur thermore, it is possible to make use of the “physiologic rest position” of the mandi ble or the space between the upper arid lower posterior teeth when the jaws are at rest. If the amount of the bite open ing does not exceed the amount allowed by the physiologic rest position, this should not be incompatible even with Mershon’s opinion of opening the bite, since the length of the muscles have re mained unaltered. That is exactly what was done in the treatment of cases used for this study- In no case was the amount of bite opening more than the space al lowed by the physiologic rest position. None of the patients at any time, during or after treatment, complained of any facial muscular pain or discomfort. If this limit of bite opening has been exceeded, as may have been the case in Breitner’s experiments with monkeys, this statement of his can be considered: “. . . a disharmony of muscular forces acting upon the skeleton is created, which necessarily leads to bone transforma tions.” His histologic findings on adult monkeys can be regarded as acceptable with respect to being able to induce some changes in the mandibular form with various orthodontic devices.7’ 13 However, in the human being, it has not been demonstrated clinically or otherwise that the mandible can be mechanically altered in its shape after adulthood or even earlier. If there are changes, they might be so slight as to be demonstrable only by histologic methods, which it is difficult, if not impossible, to apply to human beings. In the pres
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ent study, it is felt that any change in 4 . Increase in the vertical dimension the mandibular form is not gross enough was accompanied by changes in the man to be included within the reliability of dibular position. Fifteen cases showed the cephalometric technic. Nevertheless, retrusion, four slight protrusion and one Breitner’s studies13 indicate that it may no change at all. be possible to obtain major growth 5. Maxillary incisor teeth showed re changes in the jaws as a whole and not trusion in fourteen patients, protrusion depend alone on tooth movements to in four and no change in two. The value of the biteplate for increas remedy facial deformities. Measurable change in the position of the mandible ing the vertical dimension has been dem was obtained in this series, but it was onstrated. It is now necessary to investi not determined just where the changes gate the permanence of the result after took place or what was their nature. removal of the appliance. Such a study is now in progress. sum m ary
The literature presents a number of viewpoints, which may be divided into various schools of thought in determin ing the changes that occur when the bite is opened: 1. That the results obtained in bite opening are due only to intrusion of the mandibular incisors and there is no change in the posterior dental or other areas of the jaws. 2. That there is little if any intrusion of mandibular incisors and the increase in the vertical dimension of the pos terior region of the jaws is responsible for opening the bite. 3. That there are changes in the mandibular form in addition to other changes as evidenced by animal experi mentation. c o n c l u s io n s
i - Various amounts of bite opening were obtained in all of twenty cases un der study. 2. A few cases showed very slight in trusion of the mandibular incisor teeth. The majority of cases showed either no change in height or some slight extrusion of these teeth. 3. Most of the vertical increase was shown in the posterior dental region. More cases showed vertical increase in the maxillary posterior teeth than in the same area of the mandibular arch.
1.
b ib l io g r a p h y
M er sh o n , J. V.: Possibilities and Limi
tations in Treatment of Close-Bite. Internat. J. Orthodontia, 2 3 :5 8 1 -589, June 19 3 7 . 2 . M ackenzie , W. C.: Action of Muscles, Including Muscle Rest and Muscle Reeduca tion. New York: Paul B. Hoeber, 1 9 1 8 , p. 5 . 3 . W o lfso n , A bra h a m : Deep Bites in Adults. Am. J. Orthodontics, 2 4 : 12 0 - 128, February 1938 . 4 . H emley , S a m u e l : Bite Plates, Their Application and Action. Am. J. Orthodon tics, 2 4 : 7 2 1 -736, August 1938 . 5 . S trang , R o b er t : Disc, of Hemley, Refer ence 4 . 6 . B reitner , C ar l : Bone Changes Result ing from Experimental Orthodontic Treat ment. Am. J. Orthodontics, 2 6 :5 2 1 -545 , June 1940 . 7 . Idem: Further Investigations of Bone Changes Resulting from Experimental Ortho dontic Treatment. Am. J. Orthodontics, 27: 605 -632 , November 1 9 4 1 . 8. R eisn er , S. E.: Disc, of Breitner, Refer ence 6. 9 . H o pk in s , S. C.: Bite Planes. Am. J. Orthodontics, 2 6 : 107 - 1 1 9 , February 1940 . 10 . C allaw ay , G. S.: Use of Bite Plates. Am. J. Orthodontics, 2 6 : 12 0 - 124 , February 1940 . 1 1 . H igley , L. B.: Head Positioner for Scientific Radiographic and Photographic Purposes. Internat. J. Orthodontia, 2 2 :699, July 1936 . 1 2 . B roadbent , B. H .: Face of Normal Child. Angle Orthodontist, 7 : 18 3 , No. 4 , 19371 3 . B reitner , C a r l : Alteration of Occlusal Relations Induced by Experimental Procedure. Am. J. Orthodontics, 2 9 :277 -289, June 1943 .