The effects of infraocctusion: Part 1. Tilting of the adjacent teeth and local space loss Adrian Becker, BDS, LDS, DDO, ~ and Reuben M. Karnei-R'em, DMD b Jerusalenz, Israel
The normal arrangement of the transseptal fibers in the dentition is one of a completely horizontal system that links the mesial and the distal aspects of each tooth within the dental arch, from the most distal tooth of one side to the most distal tooth of the other, across the midline. This continuous fiber band is parallel to the occlusal plane, being attached to each tooth coronal to the level of the interradicular alveolar bone crest and apical to the cementoenamel junction. Alteration of the occlusal plane will be mirrored by a similar change in the plane of the transseptal fiber system. From the clinical observation of young people with infraoccluded deciduous teeth, over many years, the regular and concomittant occurrence of certain other, well-defined phenomena appears to be the rule. It was thought that these phenomena could be explained in terms of the inclusion of a vertical component (infraocclusion) into this horizontal system. Two of these phenomena are discussed here. The first and most obvious of these relates to the exaggerated tipping that affects the adjacent tooth mesially and distally. The second parameter measures the amount of actual horizontal (mesiodistal) space change that occurs locally, within the dental arch, between the two teeth adjacent to the infraoccluded tooth, measured at both the occlusal level and at the level of their root apices. With a high degree of statistical validity, it was found that infraocculsion is related to severe tilting of the two adjacent teeth toward the affected tooth, with minimal space loss in the dental arch at the occlusal level, but a wide separation of root apices. (AMJ ORTHOD DENTOFACORTHOP 1992;102:256-64.)
D e c i d u o u s molar teeth are often found with their occlusal surface below that of the neighboring teeth, long after they should have reached occlusion) 4 Many reports over the years have indicated that these infraoccluded teeth have been in occlusion and are ankylosed to the alveolar bone as a result of some disturbance in their periodontal ligament and therefore remain in a fixed position, 3,5~zwhereas those around them move occlusally with the continuous process of eruption. The result is that the infraoccluded teeth appear to become progressively more submerged in relation to their neighbors as time passes) "13:4 Histologic studies have confirmed a very high correlation between these clinical observations and ankylosis, 3,7'~~ and it is generally accepted today that ankylosis is, in fact, the cause of the altered occlusal level. Clinically, we have observed several phenomena in association with the infraocclusion of deciduous teeth, which do not appear to be coincidental, since their appearances have very commonly been seen in this context. These include the following: (1) the character of the tipping of the adjacent teeth, which appears to
From the Hebrew University-Hadassah Faculty of Dental Medicine. ~linical Associate Professor, Department of Orthodontics. ~Former undergraduate dental student, from a thesis presented in partial fulfillment of the requirements for DMD degree. 8 / 1/ 30553
256
be quite different from that associated with space closure that occurs because of the early loss of deciduous teeth, (2) marked tipping of the teeth adjacent to a severely infraoccluded tooth is frequently seen, with only a minimal degree of space closure occurring, (3) a consistent displacement of the dental midline to the side of the infraoccluded tooth, (4) a relative spacing of the teeth of the affected side of the arch, and (5) a reduction in the vertical height of the teeth neighboring an infraoccluded tooth, often with accompanying overeruption of their antagonists and consequent alteration in the occlusal plane in the opposite jaw. In normal circumstances and in the absence of infraocclusion, the teeth migrate toward a common center in the midline of the dental arch, a phenomenon known as mesial drift) 72~ The theories put forward to explain mesial drift have included (1) the existence of an anterior component of force in the permanent dentition, because of the mesial inclination of the long axes of the teeth, (2) the generation of mesial pressures from the soft tissues of the cheeks and the tongue acting on the teeth, (3) the eruptive force of the developing molars against the distal aspects of the teeth anterior to them, and (4) forces generated in the periodontium.~9"2~'29 On the basis of their studies, Moss and Picton22.24.25 have shown that approximal drift can occur in the absence of forces from the tongue, the cheeks, and the opposing teeth and is not related to tooth angulation.
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Effects of infraocclusion 257
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They concluded that the principal cause of drift lies in the periodontium 22"24"~and, having verified these conclusions experimentally, ~8:9'23"24 have implicated the tension within the transseptal fiber system as being primarily responsible. Transseptal fibers are those fibers of the gingival group of the periodontium that traverse the interproximal gingival tissue and link the approximal root surfaces of adjacent teeth. They are located immediately coronal to the alveolar septum and apical to the cementoenamel junction (CEJ). At the time of emergence into the oral cavity, well-formed transseptal fibers may be seen to extend obliquely from the CEJ of the erupting tooth toward the CEJ of the neighboring teeth. 2~ The final horizontal arrangement of these fibers indicates their function in maintaining the mesiodistal relationship between neighboring teeth and in stabilizing the teeth against separating forces. 3~They link the teeth in a continuous chain, parallel to the occlusal plane, to provide a "system-under-tension" that maintains interproximal contact between teeth) 82~ Their influence is, under these normal circumstances, manifestly and exclusively in the horizontal plane. In the presence of an infraoccluded tooth, a local change in the direction of the transseptal fibers occurs. As the neighboring teeth continue to erupt under the influence of normal physiologic forces, the transseptal fibers, which initially joined the tooth to its approximal neighbors in the horizontal plane, reorientate diagonally downward as the tooth becomes infraoccluded. This results in a decreased angle between the mesial and the distal transseptal fibers, which are also elongated two or three times their normal length (Fig. 1). As the teeth adjacent to the infraoccluded tooth continue to erupt, the transseptal fibers exert a one-sided restraining influence on each of these adjacent teeth. This influence is expressed apically and distally for a mesial neighbor and apically and mesially for a distal neighbor. Under these abnormal circumstances, a definite and distinct vertical component is introduced at one point in the originally horizontal transseptal fiber system. By virtue of the ankylotic attachment, the infraoccluded tooth is unable to respond to the upward directed force created by the stretching of the transseptal fibers attached to it and to the adjacent teeth situated on both its mesial and distal sides. Conversely, however, these adjacent teeth have a normal periodontal ligament and can respond by bone remodeling to the stimulus of what were once horizontal connecting fibers. Infraoccluded teeth have been reported as having far-reaching ramifications on the dentition.* Ac-
"3,5,1 !,14,24,33-35
AI Fig. 1. A, Normal transseptal fiber arrangement. B, Transseptal fiber arrangement in presence of infraocclusion.
cordingly, the present investigation was initiated to evaluate some of these effects and, by implication, to speculate on the possible role of the transseptal fibers as a causative agent. Perhaps the most obvious and commonly noted effect of infraocclusion, which has received much attention, is the tilting of the neighboring teeth toward the a f f e c t e d tooth. 3"5a3"14"33"36It would appear from clinical observation that the tilt of the teeth adjacent to the infraoccluded tooth seems to be more severe than that observed when the teeth on either side of an extraction site migrate toward one another. Indeed, the mental exercise of tipping both tilted teeth into the upright position, about a fulcrum placed even halfway down the root, would open up a space for the infraoccluded tooth that could be approximately 50% larger than the mesiodistal width of the tooth. One might also look at the phenomenon from a different viewpoint, namely, the relatively small amount of actual space closure that seems to occur, presents with very severe tipping of the teeth. It is the particular aspect of severe tipping of the teeth adjacent to an infraoccluded tooth that will be dealt with in this first article.
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left
right orbit
coronoid
notch
control
orbit
anterior n a s a l spine
left
---.g__
side
coronoid notch
Y
affected
side
Fig. 2. Tracing of panoramic radiograph.
MATERIALS AND METHODS The panoramic radiographs of more thah 100 patients with unilateral, severely infraoccluded mandibular second deciduous molars were examined for suitability for inclusion in this study. Only 17 of these patients remained after the elimination of cases because of the rigorous criteria set at the outset to ensure accuracy. Films were discarded when any of the following problems occurred: poor quality, right-left mesiodistal crown diameter discrepancies of teeth to be measured, poor definition in the anterior area, lower border of mandible not fully visible, lower border of orbits and/or coronoid (sigmoid) notches not clearly defined, anterior nasal spine unclear. The purpose of excluding cases with these insufficiencies was to allow linear and angular measurements, made on the side where the infraoccluded deciduous molar was present, to be compared with the unaffected opposite side, which would act as a control in the experiment. The 17 cases were then divided into two groups. Seven cases presented a second deciduous molar on the control side of the mandible and were labeled cases A to G. Of these, two cases, C and D, had a first deciduous molar mesial to the second on that side. The remaining 10 cases presented a second premolar on the control side and were labeled 1 to 10. Tracings were made of each radiograph (Fig. 2) to include the following structures. 1. The infraoccluded tooth and its immediate mesial and distal neighbors 2. The three homologous teeth on the contralateral side 3. The mandibular central incisors 4. The inferior border of the mandible 5. The anterior nasal spine
6. The inferior borders of the left and fight orbits 7. The left and right coronoid (sigmoid) notches In addition to determine the degree of infraocclusion and the angulation of adjacent teeth, the following registrations and measurements were made (Fig. 3). !. The long axis of each first molar and first premolar tooth was determined by first defining the midpoint of the mesiodistal diameter of the teeth at two heights (1) at the greatest crown contour and (2) at the apical third of the root. These two midpoints were then joined and extended superiorly and inferiorly. The apical third of the root was preferred to the apex because development of the root near its apex may often deviate when a tooth is tilted or vertically rotated. 2. The individual occlusal table of each molar tooth was defined by passing a line between the images of the buccal and lingual cusps, or joining cusp tips when these were coincident. The individual occlusal table of the premolar was defined by passing a line midway between the images of the buccal and lingual cusps, at right angles to the long axis of these teeth. The "midocclusal point" of each tooth was defined by the intersection between the long axis and the occlusal table. 3. The angle formed by the convergence of the long axes of the teeth, mesial and distal to each infraoccluded tooth, was measured. A similar measurement was made of the homologous teeth of the contralateral side of the arch. On the affected side, the angle was labeled x and on the contralateral, control, side the angle was labeled y. 4. The occlusal table of the mesial and distal neighbors
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259
I~
y
I I I
J
/
/
I I
I I I
',/ ~ /
/ "~\
x measured
infraocclusion
Fig. 3. Angles of convergence of the long axes of the adjacent teeth.
was described by a line joining the midocclusal points of the two teeth. The degree of infraocclusion was measured in millimeters as that length of the extension of the long axis of the infraoccluded tooth measured from its occlusal table to that of its immediate neighbors. In two cases, one of the adjacent teeth was not fully erupted at the time of radiographic examination (the first premolar in case 3 and the first molar in case D). In these cases, a line was drawn perpendicular from the fully erupted adjacent tooth to the long axis of the infraoccluded tooth and the measurement made from the intersection of these two lines to the occlusal table" With regard to the intercoronal space and interapical distance, the following registrations and measurements were also made (Fig. 4). 1. The long axis of each of the adjacent teeth was drawn. 2. The Constructed apex of each of these teeth was defined as that point on the long axis 30 mni apical to the midocclusal point. This was done for standardization and to eliminate errors because of abnormal root apex structure, since the time and direction of development of the apex varies greatly under the influence of many factors, not the least a tipping movement of the tooth. 3. The intercoronal space was defined as the distance between the most mesial point of the crown contour of the first permanent molar and the most distal point of the crown contour of the first premolar/deciduous molar on that side. 4. The interapical distance was defined as the distance between the constructed apices of these two teeth. All lengths were measured to the nearest 0.5 ram, and all angles measured to the nearest 0.5 ~ In each of the parameters determined in this series of
three studies, the measurements performed were repeated after at least 14 days had elapsed to ensure objectivity and reproducibility of the method in each case. The data were analyzed with a paired t test (one-tailed) to assess the statistical significance of all the results in this investigation, and a Pearson correlation analysis was performed to test the assumption that severity of infraocclusion was related to the degree of tilt of the adjacent teeth.
RESULTS Table I lists the cases according to the control side of the mandible. Those which presented a second deciduous molar on this unaffected side Were labeled from A to G. All those in which a second premolar had erupted on the control side were labeled from 1 to 10. The cases have been arranged in descending order of severity of infraocclusion. The tilt of the teeth adjacent to the infraoccluded tooth is greater in all instances than the tilt on the control sides. The mean increase of tilt of the combined axial inclinations of these adjacent teeth (i.e., the angle of convergence of the long axes Of the teeth adjacent to the affected tooth, angle x, Subtracted from the angle of convergence of the homologous teeth on the control side, angle y) when compared with those of the control side where a deciduous molar was present, was found to be 19.36 ~ In the group where a premolar was present on the control side, the mean increase was 13.45 ~ For both groups taken together, the increase was 15.88 ~ a result which, statistically, was highly significant (p < 0.0001). The general trend for a severer infraocclusion being
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Am. J. Orthod. Dentofac. Orthop. September 1992
intercoronal space
d istance Fig. 4. Intercoronal space and interapical distance of adjacent teeth.
Table I. Infraocclusion and tooth angulation Cases
Affected side
lnfraocclusion (ram)
Angle x (degrees)
I J
Angle y (degrees)
13 9 7 6 3.5 3 2 6.21 3.87
48 43 38 31 33.5 30 7 32.93 13.16
16 16 11 17.5 20.5 9 5 13.57 5.42
8.5 6.5 6 5 3.5 3.5 3.5 3.5 3 2.5 4.55 1.91
58.5 42.5 19.5 35 42 27 29 20.5 23 23 32.00 12.50
23 27 9 24 20 6 20 17.5 21 18 18.55 6.51
5.23 2.89
32.38 12.37
16.50 6.42
Deciduous second molar on control side A B C D E F G Mean SD (t = 4.900 p < 0.001)
right fight left fight left left left
Second premolar on control side i 2 3 4 5 6 7 8 9 10 Mean SD (t = 4 . 1 0 4 p < 0.0003)
left left right left right right left left fight left
For both groups (A to G and 1 to 10) combined Mean SD (t = 6.234 p < 0.0001)
x, The angle formed by the convergence of the long axes of the teeth immediately mesial and distal to the infraoccluded deciduous molar. y, The angle formed by the convergence of the long axes of the two homologous teeth on the control side.
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.-. 40
~
30 ,I
20
"
~10 U t-
"
0
,
I
0
,
2 Degree
I
,
I
/~ of
: ,
6
I
8
Infraocclusion
,
l
,
10
I
,
12 (in
1/+
nm)
Fig. 5. Scatterplot showing trend for severity of infraocclusion to be related to increased tilt.
T a b l e Ila. I n t e r c o r o n a l s p a c e a n d i n t e r a p i c a l d i s t a n c e lnterapical distance
lntercoronal space
Control side
Affected side
Control side
Deciduous second molar on control side A 40 B 41 C 38 D ** E 36.5 F 35.5 G 29 Mean 36.67 SD 4.29
29.5 30.5 28 ** 34 27 20.5 28.25 4.50
6.5 8.5 8.5 ** 10 11 11 9.25 1.75
11.5 10.5 il ** 12 11.5 I0 I 1.08 0.74
Second premolar on control side 1 44 2 38 3 32.5 4 42 5 40 6 31 7 42 8 28.5 9 29.5 10 34 Mean 36.15 SD 5.73
25.5 31 27 32 21 20.5 33 24 25.5 30 26.95 4.44
4 7 11 12.5 8 7 13 7 9 10 8.85 2.81
2.5 7 9 8 5.5 5.5 9.5 5 6 8 6.60 2.12
For both groups (A to G and 1 to 10) combined Mean 36.34 SD 5.09
27.44 4.36
9.00 2.41
8.28 2.81
Cases
Affected side
**First permanent molar was unerupted.
r e l a t e d to a m o r e p r o n o u n c e d tilt o f the n e i g h b o r i n g teeth showed a significantly positive Pearson correlation ( r = 0 . 7 3 9 , p < 0 . 0 0 0 4 ) a n d is s h o w n g r a p h i c a l l y in the s c a t t e r p l o t ( F i g . 5).
F r o m T a b l e II, it c a n b e s e e n that in c a s e s A to G , w h e r e a d e c i d u o u s m o l a r w a s p r e s e n t o n the c o n t r o l side, the i n t e r c o r o n a l s p a c e is g r e a t e r t h a n o n the affected side ( m e a n d i f f e r e n c e = - 1.83 m m ) . F o r c a s e s
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Becker and Karnei-R' en~
Table lib. The interapical distance between affected side (column 1) and control side (column 2) p< Cases A to G Cases 1 to 10 Cases A to G + I to 10 combined
8.42 9.20 8.91
3.04 5.57 4.68
6.782 5.220 7.617
0.0006 0.0003 0.0001
Table IIc. The intercoronal space between affected side (column 3) and control side (column 4)
Column3-column4 Cases A to G Cases 1 to 10 Cases A to G + I to 10 combined
[
Meo,, - 1.83 2.25 0.72
1 t o 10, however, the intercoronal space is greater on the affected side than on the control side, where a premolar is present (mean difference = 2.25 mm). In all the cases, the interapical distance was greater on the affected side, with a mean difference of 8.91 mm, Which was highly significant (p < 0,0001). DISCUSSION
9Panoramic radiographs are generally no t used as a means for making precise measurements because of a lack of standardization i.n positioning the subjects relative to the radiation source thus resulting i n dissimilar films. This would preclude comparing measurements made on one film with those on another. In the present investigation, however, comparison of measurements was made within the same film, exclusively. Given the precautions already mentioned and the fact that the sampl e showed an almost equal left and right side distribution of the infraocclusion, it was believed that a high degree of validity of results was ensured. The initial hypothesis for this investigaiion was that the presence of an infraoccluded tooth would give rise to marked and far-reaching disturbances in the alignment of the teeth b y the introduction, at one point, of a vertical component into the normally horizontally arranged transseptal fiber system. The comparison of angle s of convergence of the control sides where a premolar was present versus the control sides where a deciduous molar was present expressed a difference between the relative tilt on the control sides of the two groups, i.e., 18.55 ~ 13.57 ~ = 4.98 ~ This is an expression of the increased tilt of the teeth on the control side of the premolar group, which occurs as a result of closure of the leew~/y'SlSace at the time of the changeover from the late mixed dentition to the early permanent dentition.
I
SD 2.02 1.23 2.54
[
t -2.227 5.783 1.134
I
p< 0.04 0.0002 0.14
Table I shows that teeth adjacent to the infraoccluded tooth tilt toward the affected tooth in proportion to the degree of the infra0cclusion. Since the degree of inffaocclusion is a function of time, w e may presume that with the passage o f time, the adjacen t teeth become more tilted. The group that presented a second deciduous molar on the control side of the affected tooth presented the greate r inffaocclusion (mean of 6.21 mm) and showed a mean increased tilt of 19.36 ~ whereas the second group, with a second premolar on the control side, showed a mean infraoeclusion of only 4.55 mm and an increased tilt of only 13.45 degrees. This apparent paradox is due to the fact that, on the control side, the leeway space closure is accompanied by a tilting of the two adjacent teeth toward one another to increase the angle formed by their long axes. Thus, while the same degree of severity of tilting may be present on the affected side, the mean difference in tilt between the affected side and the control side will be altered as a result of changes on the control side during the transition from the mixed to the permanent dentition. With both groups taken together, the mean infraocclusion of 5.23 mm for the affected side produced a mean tilt that was 15.88 ~ greater than the mean for the normally developing control side. Fig. 1 is a diagrammatic illustration in which we have compared the normal horizontal arrangement of the transseptal fibers with that one would expect to find on either side of an infraoccluded tooth. Clearly, the greater the infraocclusion, the greater is the vertical component in the configuration of the transseptal fibers. This would lead us to expect a tilting effect of the adjacent teeth, since they are being pulled toward an ankylosed tooth, which is prevented from responding to the equal and opposite reactive force of the stretched fibers.
Effects of infraocc/usion
Volume 102 Number 3
The point of application of the restraining force is near the CEJ, i.e., coronal to the center of resistance of the tooth, which is nearer the midpoint of the root. 37 Since tilting becomes more severe with the increase of infraocclusion, we may assume that the tilting force is unopposed or exceeds any uprighting force unless and until the infraoccluded tooth subsequently frees itself and resumes normal eruption. ~4 Table II shows that there is a significant difference on the control side in the intercoronal space between the first molar and the first premolar when a deciduous second molar is present (mean = 11.08 mm) and when a premolar is present (mean = 6.60 mm). This 4.48 mm discrepancy accounts for the leeway space, which closes spontaneously after the shedding of the deciduous molar because of the mesial migration of the first permanent molar into proximal contact with the newly erupted first premolar. As would be expected in the presence of a deciduous second molar on the control side, the intercoronal space on the affected side was smaller because of the tilting of the adjacent teeth. The reduction caused was 1.83 mm. However, when a second premolar was present on the control side, it was the control side intercoronal space that was 2.25 m m smaller than the affected side, despite the degree of tilting. This indicates that local space closure adjacent to the site of an infraoccluded tooth is considerably less than the physiologic closure of the leeway space that spontaneously occurs after exfoliation of a second deciduous molar. The interapical distance between the two teeth adjacent to the infraoccluded tooth was found to be significantly greater than the interapical distance measured on the control side, with a mean difference of 8.91 mm. This being so, we must conclude that the observed tilt is due only marginally to convergence of the crowns of the teeth adjacent to the infraoccluded tooth. It is principally the result of a considerable divergence of the root apices of these teeth. If we study Table II and consider the control sides of cases A to G (where a deciduous second molar was present) together with those of cases 1 to 10 (where a premolar was present), a comparison of the intercoronal and the interapical distances in both groups will show us the character of the movement of the molar as it closes off the leeway space from the viewpoint of this cross-sectional sample study. On the control side, the mean intercoronal distance between the first permanent molar and the first premolar, when a second premolar is present, was found to be 4.48 mm less than when a deciduous second molar was in place. The interapical distance in the presence of a deciduous molar was only 0.40 mm larger than after its shedding. This shows that
263
the entire molar translates mesially, in tipping fashion, with no distal movement of the apex to accompany the marked movement of the crown. The teeth adjacent to an infraoccluded tooth cannot translate mesially because of the l~resence of the infraoccluded tooth. The observed tilt of the teeth therefore is mainly the result of the apex of the molar becoming displaced distally and of the premolar mesially away from the infraoccluded tooth, with only very slight approximation of the crowns as they undergo what appears to be a vertical rotation, which will be discussed in another article. To move the roots of the teeth in this manner, an active force is required, which would need to find its origin in the infraoccluded tooth. CONCLUSIONS
The changes discussed here in relation to the teeth adjacent to an infraoccluded deciduous second molar indicate: (I) a greater degree of tilting when related to a severer degree of infraocclusion, (2) a greater degree of tilting than that occurring after physiologic leeway space closure, (3) a relatively limited local loss of space when compared with physiologic leeway space closure, and (4) a very large anteroposterior displacement of the apices of the teeth away from the infraoccluded tooth. REFERENCES
i. Koyoumdjisky-KayeE, Steigman S. Ethnic variability in the prevalence of submerged primary molars. J Dent Res 1982;61:1401-4. 2. Koyoumdjisky-KayeE, SteigmanS. Submergingprimarymolars in Israeli rural children. Community Dent Oral Epidemiol 1982;10:204-8. 3. Kurol J. Infraocclusionof primary molars. An epidemiol~ical, familial, longitudinal, clinical and histol~ical study. Swed Dent J (Suppl) 1984;21:1-67. 4. Steigman S, Koyoumdjisky-KayeE, Matrai Y. Submerged deciduous molars in preschool children: an epidemiologicsurvey. J Dent Res 1973;52:322-6. 5. Biederman W. The ankylosed tooth. Dent Clin North Am 1964;8:493-508. 6. Brown ID. Some further observations on submerging deciduous molars. Br J Orthod 1981;8:99-107. 7. Darling AI, Levers BGH. Submerged human deciduous molars and ankylosis. Arch Oral Biol 1973;18:1021-40. 8. DarlingAI, Levers BGH. The pattern of eruption of some human teeth. Arch Oral Biol 1975;20:89-96. 9. Darling AI, Levers BGH. The pattern of eruption. In: Colston papers--eruption and occlusion of teeth. London: Butterworth, 1976:80-96. 10. Kurol J, Magnusson BC. lnfraocclusion of primary molars: a histologie study. Scand J Dent Res 1984;92:564-76. 11. Rune B. Submerged deciduous molars. Odontol Revy 1971;22:257-73. 12. RuneB. Sarnas KV. Root resorptionand submergencein retained deciduous second molars. Eur J Orthod 1984;6:123-31. 13. Kurol J, Thilander B. Infraocclusion of primary molars with
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aplasia of the permanent successor, a longitudinal study. Angle Orthod 1984;54:283-94. Kurol J, Thilander B. Infraocclusion of primary molars and the effect on occlusal development, a longitudinal study. Eur J Orthod 1984;6:277-93. Kula K, Tatum BM, Owen D, Smith RJ, Rule J. An occlusal and cephalometrie study of children with ankylosis of primary molars. J Pedod 1984;8:146-59. Lamb KA, Reed MW. Measurement of space loss resulting from tooth ankylosis. J Dent Child 1968;35:483-6. Lebret LML. Tooth migration. In: The mechanisms of tooth support, a symposium. Bristol: John Wright, 1967:120-5. Moss JP, Picton DCA. The effect on approximal drift of cheek teeth of dividing mandibular molars of adult monkeys (Macaca irus). Arch Oral Biol 1974;19:!211-4. Moss JP, Picton DCA. Short-term changes in the mesiodistal position of teeth following removal of approximal contacts in the monkey (Macacafascicularis). Arch Oral Biol 1982;27:273-8. Picton DCA. Tooth movement as mesial and lateral drift. In: Colston papers--eruption and occlusion of teeth. London: Butterworth. 1976:108-19. Berkowitz BKB, Moxham BJ, Newman HN. The periodontal ligament in health and disease. Oxford: Pergamon Press, 1982:51-72, 197-247. Moss JP, Picton DCA. On the cause of mesial drift of the teeth in adult monkeys. In: The mechanisms of tooth suppo~, a symposium. Bristol: John Wright, 1967:140-3. Moss JP, Picton DCA. The causes of migration of teeth. Trans Third lntemat Orthod Congress. London: Crosby, Lockwood & Staples. 1973;536-43. Moss JP. A review of the theories of approximal migration of teeth. In: Colston papers--eruption and occlusion of teeth. London: Butterworth, 1976:205-12. Picton DCA, Moss JP. The relationship between the angulation of the roots and the rate of approximal drift of cheek teeth in adult monkeys. Br J Orthod 1974;1:105-10. Ten Care AR, Oral Histology: development, structure and function. St. Louis: CV Mosby, 1985:268-73.
Volume 102 Number 3 27. Van Beek H, Fidler VJ. An experimental study on the effect of functional occlusion on mesial tooth migration in macaque monkeys. Arch Oral Biol 1977;22:269-71. 28. Van Beek H. The transfer of mesial drift potential along the dental arch in macaca irus: an experimental study of tooth migration rate related to the horizontal vectors of occlusal forces. Eur J Orthod 1979;1:125-9. 29. Yilmaz RS, Darling AI, Levers BGH. Mesial drift of human teeth assessed from ankylosed deciduous molars. Arch Oral Biol 1980;25:127-3 I. 30. Parker GR. Transseptal fibers and relapse following bodily retraction of teeth: a histologic study. AM J ORTHOD 1972;61:33144. 31. Picton DCA, Moss JP. The part played by the transseptal fibre system in experimental approximal drift of the cheek teeth of monkey (macaca irus). Arch Oral Biol 1973;18:669-80. 32. Becker A. The median diastema. Dent Clin North Am 1978;22:685-710. 33. Becker A, Shochat S. Submergence of a deciduous tooth: its ramifications on the dentition and treatment of the resulting malocclusion. AM J ORTItOD 1982;81:240-4. 34. Brearley LI, McKibben DH. Ankylosis of primary teeth. I. Prevalence and characteristics. 1I. A longitudinal study. J Dent Child 1973 ;40:54-63. 35. Gellin ME. Indications and contraindications for the removal of primary teeth. Dent Clin North Am 1969;13:899-911. 36. Yilmaz RS, Darling AI, Levers BGH. Experimental tooth ankylosis and horizontal tooth movement in the pig. Arch Oral Biol 1981;26:41-7. 37. Smith RJ, Burstone CJ. Mechanics of tooth movement. Ar,l J OaTt~or, 1984;85:294-307. Reprint requests to: Dr. Adrian Becker Hebrew University-Hadassah Faculty of Dental Medicine P.O. Box 1172 Jerusalem 91010 Israel
The normal arrangement of the transseptal fibers in the dentition is one of a completely horizontal system that links the mesial and the distal aspects of each tooth within the dental arch, from the most distal tooth of one side to the most distal tooth of the other, across the midline. This continuous fiber band is parallel to the occlusal plane, being attached to each tooth coronal to the level of the interradicular alveolar bone crest and apical to the cementoenamel junction. Alteration of the occlusal plane will be mirrored by a similar change in the plane of the transseptal fiber system. From the clinical observation of young people with infraoccluded deciduous teeth, over many years, the regular and concomittant occurrence of certain other, well-defined phenomena appears to be the rule. It was thought that these phenomena could be explained in terms of the inclusion of a vertical component (infraocclusion) into this horizontal system. Two of these phenomena are discussed here. The first and most obvious of these relates to the exaggerated tipping that affects the adjacent tooth mesially and distally. The second parameter measures the amount of actual horizontal (mesiodistal) space change that occurs locally, within the dental arch, between the two teeth adjacent to the infraoccluded tooth, measured at both the occlusal level and at the level of their root apices. With a high degree of statistical validity, it was found that infraocculsion is related to severe tilting of the two adjacent teeth toward the affected tooth, with minimal space loss in the dental arch at the occlusal level, but a wide separation of root apices. (AMJ ORTHOD DENTOFACORTHOP 1992;102:256-64.)
D e c i d u o u s molar teeth are often found with their occlusal surface below that of the neighboring teeth, long after they should have reached occlusion) 4 Many reports over the years have indicated that these infraoccluded teeth have been in occlusion and are ankylosed to the alveolar bone as a result of some disturbance in their periodontal ligament and therefore remain in a fixed position, 3,5~zwhereas those around them move occlusally with the continuous process of eruption. The result is that the infraoccluded teeth appear to become progressively more submerged in relation to their neighbors as time passes) "13:4 Histologic studies have confirmed a very high correlation between these clinical observations and ankylosis, 3,7'~~ and it is generally accepted today that ankylosis is, in fact, the cause of the altered occlusal level. Clinically, we have observed several phenomena in association with the infraocclusion of deciduous teeth, which do not appear to be coincidental, since their appearances have very commonly been seen in this context. These include the following: (1) the character of the tipping of the adjacent teeth, which appears to
From the Hebrew University-Hadassah Faculty of Dental Medicine. ~linical Associate Professor, Department of Orthodontics. ~Former undergraduate dental student, from a thesis presented in partial fulfillment of the requirements for DMD degree. 8 / 1/ 30553
256
be quite different from that associated with space closure that occurs because of the early loss of deciduous teeth, (2) marked tipping of the teeth adjacent to a severely infraoccluded tooth is frequently seen, with only a minimal degree of space closure occurring, (3) a consistent displacement of the dental midline to the side of the infraoccluded tooth, (4) a relative spacing of the teeth of the affected side of the arch, and (5) a reduction in the vertical height of the teeth neighboring an infraoccluded tooth, often with accompanying overeruption of their antagonists and consequent alteration in the occlusal plane in the opposite jaw. In normal circumstances and in the absence of infraocclusion, the teeth migrate toward a common center in the midline of the dental arch, a phenomenon known as mesial drift) 72~ The theories put forward to explain mesial drift have included (1) the existence of an anterior component of force in the permanent dentition, because of the mesial inclination of the long axes of the teeth, (2) the generation of mesial pressures from the soft tissues of the cheeks and the tongue acting on the teeth, (3) the eruptive force of the developing molars against the distal aspects of the teeth anterior to them, and (4) forces generated in the periodontium.~9"2~'29 On the basis of their studies, Moss and Picton22.24.25 have shown that approximal drift can occur in the absence of forces from the tongue, the cheeks, and the opposing teeth and is not related to tooth angulation.
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Effects of infraocclusion 257
Number 3
They concluded that the principal cause of drift lies in the periodontium 22"24"~and, having verified these conclusions experimentally, ~8:9'23"24 have implicated the tension within the transseptal fiber system as being primarily responsible. Transseptal fibers are those fibers of the gingival group of the periodontium that traverse the interproximal gingival tissue and link the approximal root surfaces of adjacent teeth. They are located immediately coronal to the alveolar septum and apical to the cementoenamel junction (CEJ). At the time of emergence into the oral cavity, well-formed transseptal fibers may be seen to extend obliquely from the CEJ of the erupting tooth toward the CEJ of the neighboring teeth. 2~ The final horizontal arrangement of these fibers indicates their function in maintaining the mesiodistal relationship between neighboring teeth and in stabilizing the teeth against separating forces. 3~They link the teeth in a continuous chain, parallel to the occlusal plane, to provide a "system-under-tension" that maintains interproximal contact between teeth) 82~ Their influence is, under these normal circumstances, manifestly and exclusively in the horizontal plane. In the presence of an infraoccluded tooth, a local change in the direction of the transseptal fibers occurs. As the neighboring teeth continue to erupt under the influence of normal physiologic forces, the transseptal fibers, which initially joined the tooth to its approximal neighbors in the horizontal plane, reorientate diagonally downward as the tooth becomes infraoccluded. This results in a decreased angle between the mesial and the distal transseptal fibers, which are also elongated two or three times their normal length (Fig. 1). As the teeth adjacent to the infraoccluded tooth continue to erupt, the transseptal fibers exert a one-sided restraining influence on each of these adjacent teeth. This influence is expressed apically and distally for a mesial neighbor and apically and mesially for a distal neighbor. Under these abnormal circumstances, a definite and distinct vertical component is introduced at one point in the originally horizontal transseptal fiber system. By virtue of the ankylotic attachment, the infraoccluded tooth is unable to respond to the upward directed force created by the stretching of the transseptal fibers attached to it and to the adjacent teeth situated on both its mesial and distal sides. Conversely, however, these adjacent teeth have a normal periodontal ligament and can respond by bone remodeling to the stimulus of what were once horizontal connecting fibers. Infraoccluded teeth have been reported as having far-reaching ramifications on the dentition.* Ac-
"3,5,1 !,14,24,33-35
AI Fig. 1. A, Normal transseptal fiber arrangement. B, Transseptal fiber arrangement in presence of infraocclusion.
cordingly, the present investigation was initiated to evaluate some of these effects and, by implication, to speculate on the possible role of the transseptal fibers as a causative agent. Perhaps the most obvious and commonly noted effect of infraocclusion, which has received much attention, is the tilting of the neighboring teeth toward the a f f e c t e d tooth. 3"5a3"14"33"36It would appear from clinical observation that the tilt of the teeth adjacent to the infraoccluded tooth seems to be more severe than that observed when the teeth on either side of an extraction site migrate toward one another. Indeed, the mental exercise of tipping both tilted teeth into the upright position, about a fulcrum placed even halfway down the root, would open up a space for the infraoccluded tooth that could be approximately 50% larger than the mesiodistal width of the tooth. One might also look at the phenomenon from a different viewpoint, namely, the relatively small amount of actual space closure that seems to occur, presents with very severe tipping of the teeth. It is the particular aspect of severe tipping of the teeth adjacent to an infraoccluded tooth that will be dealt with in this first article.
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left
right orbit
coronoid
notch
control
orbit
anterior n a s a l spine
left
---.g__
side
coronoid notch
Y
affected
side
Fig. 2. Tracing of panoramic radiograph.
MATERIALS AND METHODS The panoramic radiographs of more thah 100 patients with unilateral, severely infraoccluded mandibular second deciduous molars were examined for suitability for inclusion in this study. Only 17 of these patients remained after the elimination of cases because of the rigorous criteria set at the outset to ensure accuracy. Films were discarded when any of the following problems occurred: poor quality, right-left mesiodistal crown diameter discrepancies of teeth to be measured, poor definition in the anterior area, lower border of mandible not fully visible, lower border of orbits and/or coronoid (sigmoid) notches not clearly defined, anterior nasal spine unclear. The purpose of excluding cases with these insufficiencies was to allow linear and angular measurements, made on the side where the infraoccluded deciduous molar was present, to be compared with the unaffected opposite side, which would act as a control in the experiment. The 17 cases were then divided into two groups. Seven cases presented a second deciduous molar on the control side of the mandible and were labeled cases A to G. Of these, two cases, C and D, had a first deciduous molar mesial to the second on that side. The remaining 10 cases presented a second premolar on the control side and were labeled 1 to 10. Tracings were made of each radiograph (Fig. 2) to include the following structures. 1. The infraoccluded tooth and its immediate mesial and distal neighbors 2. The three homologous teeth on the contralateral side 3. The mandibular central incisors 4. The inferior border of the mandible 5. The anterior nasal spine
6. The inferior borders of the left and fight orbits 7. The left and right coronoid (sigmoid) notches In addition to determine the degree of infraocclusion and the angulation of adjacent teeth, the following registrations and measurements were made (Fig. 3). !. The long axis of each first molar and first premolar tooth was determined by first defining the midpoint of the mesiodistal diameter of the teeth at two heights (1) at the greatest crown contour and (2) at the apical third of the root. These two midpoints were then joined and extended superiorly and inferiorly. The apical third of the root was preferred to the apex because development of the root near its apex may often deviate when a tooth is tilted or vertically rotated. 2. The individual occlusal table of each molar tooth was defined by passing a line between the images of the buccal and lingual cusps, or joining cusp tips when these were coincident. The individual occlusal table of the premolar was defined by passing a line midway between the images of the buccal and lingual cusps, at right angles to the long axis of these teeth. The "midocclusal point" of each tooth was defined by the intersection between the long axis and the occlusal table. 3. The angle formed by the convergence of the long axes of the teeth, mesial and distal to each infraoccluded tooth, was measured. A similar measurement was made of the homologous teeth of the contralateral side of the arch. On the affected side, the angle was labeled x and on the contralateral, control, side the angle was labeled y. 4. The occlusal table of the mesial and distal neighbors
Voh,,,e 102
Effects of infraocch~sion
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259
I~
y
I I I
J
/
/
I I
I I I
',/ ~ /
/ "~\
x measured
infraocclusion
Fig. 3. Angles of convergence of the long axes of the adjacent teeth.
was described by a line joining the midocclusal points of the two teeth. The degree of infraocclusion was measured in millimeters as that length of the extension of the long axis of the infraoccluded tooth measured from its occlusal table to that of its immediate neighbors. In two cases, one of the adjacent teeth was not fully erupted at the time of radiographic examination (the first premolar in case 3 and the first molar in case D). In these cases, a line was drawn perpendicular from the fully erupted adjacent tooth to the long axis of the infraoccluded tooth and the measurement made from the intersection of these two lines to the occlusal table" With regard to the intercoronal space and interapical distance, the following registrations and measurements were also made (Fig. 4). 1. The long axis of each of the adjacent teeth was drawn. 2. The Constructed apex of each of these teeth was defined as that point on the long axis 30 mni apical to the midocclusal point. This was done for standardization and to eliminate errors because of abnormal root apex structure, since the time and direction of development of the apex varies greatly under the influence of many factors, not the least a tipping movement of the tooth. 3. The intercoronal space was defined as the distance between the most mesial point of the crown contour of the first permanent molar and the most distal point of the crown contour of the first premolar/deciduous molar on that side. 4. The interapical distance was defined as the distance between the constructed apices of these two teeth. All lengths were measured to the nearest 0.5 ram, and all angles measured to the nearest 0.5 ~ In each of the parameters determined in this series of
three studies, the measurements performed were repeated after at least 14 days had elapsed to ensure objectivity and reproducibility of the method in each case. The data were analyzed with a paired t test (one-tailed) to assess the statistical significance of all the results in this investigation, and a Pearson correlation analysis was performed to test the assumption that severity of infraocclusion was related to the degree of tilt of the adjacent teeth.
RESULTS Table I lists the cases according to the control side of the mandible. Those which presented a second deciduous molar on this unaffected side Were labeled from A to G. All those in which a second premolar had erupted on the control side were labeled from 1 to 10. The cases have been arranged in descending order of severity of infraocclusion. The tilt of the teeth adjacent to the infraoccluded tooth is greater in all instances than the tilt on the control sides. The mean increase of tilt of the combined axial inclinations of these adjacent teeth (i.e., the angle of convergence of the long axes Of the teeth adjacent to the affected tooth, angle x, Subtracted from the angle of convergence of the homologous teeth on the control side, angle y) when compared with those of the control side where a deciduous molar was present, was found to be 19.36 ~ In the group where a premolar was present on the control side, the mean increase was 13.45 ~ For both groups taken together, the increase was 15.88 ~ a result which, statistically, was highly significant (p < 0.0001). The general trend for a severer infraocclusion being
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Am. J. Orthod. Dentofac. Orthop. September 1992
intercoronal space
d istance Fig. 4. Intercoronal space and interapical distance of adjacent teeth.
Table I. Infraocclusion and tooth angulation Cases
Affected side
lnfraocclusion (ram)
Angle x (degrees)
I J
Angle y (degrees)
13 9 7 6 3.5 3 2 6.21 3.87
48 43 38 31 33.5 30 7 32.93 13.16
16 16 11 17.5 20.5 9 5 13.57 5.42
8.5 6.5 6 5 3.5 3.5 3.5 3.5 3 2.5 4.55 1.91
58.5 42.5 19.5 35 42 27 29 20.5 23 23 32.00 12.50
23 27 9 24 20 6 20 17.5 21 18 18.55 6.51
5.23 2.89
32.38 12.37
16.50 6.42
Deciduous second molar on control side A B C D E F G Mean SD (t = 4.900 p < 0.001)
right fight left fight left left left
Second premolar on control side i 2 3 4 5 6 7 8 9 10 Mean SD (t = 4 . 1 0 4 p < 0.0003)
left left right left right right left left fight left
For both groups (A to G and 1 to 10) combined Mean SD (t = 6.234 p < 0.0001)
x, The angle formed by the convergence of the long axes of the teeth immediately mesial and distal to the infraoccluded deciduous molar. y, The angle formed by the convergence of the long axes of the two homologous teeth on the control side.
Effects o f infraocclusion
Volume 102 Number 3
261
.-. 40
~
30 ,I
20
"
~10 U t-
"
0
,
I
0
,
2 Degree
I
,
I
/~ of
: ,
6
I
8
Infraocclusion
,
l
,
10
I
,
12 (in
1/+
nm)
Fig. 5. Scatterplot showing trend for severity of infraocclusion to be related to increased tilt.
T a b l e Ila. I n t e r c o r o n a l s p a c e a n d i n t e r a p i c a l d i s t a n c e lnterapical distance
lntercoronal space
Control side
Affected side
Control side
Deciduous second molar on control side A 40 B 41 C 38 D ** E 36.5 F 35.5 G 29 Mean 36.67 SD 4.29
29.5 30.5 28 ** 34 27 20.5 28.25 4.50
6.5 8.5 8.5 ** 10 11 11 9.25 1.75
11.5 10.5 il ** 12 11.5 I0 I 1.08 0.74
Second premolar on control side 1 44 2 38 3 32.5 4 42 5 40 6 31 7 42 8 28.5 9 29.5 10 34 Mean 36.15 SD 5.73
25.5 31 27 32 21 20.5 33 24 25.5 30 26.95 4.44
4 7 11 12.5 8 7 13 7 9 10 8.85 2.81
2.5 7 9 8 5.5 5.5 9.5 5 6 8 6.60 2.12
For both groups (A to G and 1 to 10) combined Mean 36.34 SD 5.09
27.44 4.36
9.00 2.41
8.28 2.81
Cases
Affected side
**First permanent molar was unerupted.
r e l a t e d to a m o r e p r o n o u n c e d tilt o f the n e i g h b o r i n g teeth showed a significantly positive Pearson correlation ( r = 0 . 7 3 9 , p < 0 . 0 0 0 4 ) a n d is s h o w n g r a p h i c a l l y in the s c a t t e r p l o t ( F i g . 5).
F r o m T a b l e II, it c a n b e s e e n that in c a s e s A to G , w h e r e a d e c i d u o u s m o l a r w a s p r e s e n t o n the c o n t r o l side, the i n t e r c o r o n a l s p a c e is g r e a t e r t h a n o n the affected side ( m e a n d i f f e r e n c e = - 1.83 m m ) . F o r c a s e s
262
Am. J. Orthod.Dentofac.Orthop. September1992
Becker and Karnei-R' en~
Table lib. The interapical distance between affected side (column 1) and control side (column 2) p< Cases A to G Cases 1 to 10 Cases A to G + I to 10 combined
8.42 9.20 8.91
3.04 5.57 4.68
6.782 5.220 7.617
0.0006 0.0003 0.0001
Table IIc. The intercoronal space between affected side (column 3) and control side (column 4)
Column3-column4 Cases A to G Cases 1 to 10 Cases A to G + I to 10 combined
[
Meo,, - 1.83 2.25 0.72
1 t o 10, however, the intercoronal space is greater on the affected side than on the control side, where a premolar is present (mean difference = 2.25 mm). In all the cases, the interapical distance was greater on the affected side, with a mean difference of 8.91 mm, Which was highly significant (p < 0,0001). DISCUSSION
9Panoramic radiographs are generally no t used as a means for making precise measurements because of a lack of standardization i.n positioning the subjects relative to the radiation source thus resulting i n dissimilar films. This would preclude comparing measurements made on one film with those on another. In the present investigation, however, comparison of measurements was made within the same film, exclusively. Given the precautions already mentioned and the fact that the sampl e showed an almost equal left and right side distribution of the infraocclusion, it was believed that a high degree of validity of results was ensured. The initial hypothesis for this investigaiion was that the presence of an infraoccluded tooth would give rise to marked and far-reaching disturbances in the alignment of the teeth b y the introduction, at one point, of a vertical component into the normally horizontally arranged transseptal fiber system. The comparison of angle s of convergence of the control sides where a premolar was present versus the control sides where a deciduous molar was present expressed a difference between the relative tilt on the control sides of the two groups, i.e., 18.55 ~ 13.57 ~ = 4.98 ~ This is an expression of the increased tilt of the teeth on the control side of the premolar group, which occurs as a result of closure of the leew~/y'SlSace at the time of the changeover from the late mixed dentition to the early permanent dentition.
I
SD 2.02 1.23 2.54
[
t -2.227 5.783 1.134
I
p< 0.04 0.0002 0.14
Table I shows that teeth adjacent to the infraoccluded tooth tilt toward the affected tooth in proportion to the degree of the infra0cclusion. Since the degree of inffaocclusion is a function of time, w e may presume that with the passage o f time, the adjacen t teeth become more tilted. The group that presented a second deciduous molar on the control side of the affected tooth presented the greate r inffaocclusion (mean of 6.21 mm) and showed a mean increased tilt of 19.36 ~ whereas the second group, with a second premolar on the control side, showed a mean infraoeclusion of only 4.55 mm and an increased tilt of only 13.45 degrees. This apparent paradox is due to the fact that, on the control side, the leeway space closure is accompanied by a tilting of the two adjacent teeth toward one another to increase the angle formed by their long axes. Thus, while the same degree of severity of tilting may be present on the affected side, the mean difference in tilt between the affected side and the control side will be altered as a result of changes on the control side during the transition from the mixed to the permanent dentition. With both groups taken together, the mean infraocclusion of 5.23 mm for the affected side produced a mean tilt that was 15.88 ~ greater than the mean for the normally developing control side. Fig. 1 is a diagrammatic illustration in which we have compared the normal horizontal arrangement of the transseptal fibers with that one would expect to find on either side of an infraoccluded tooth. Clearly, the greater the infraocclusion, the greater is the vertical component in the configuration of the transseptal fibers. This would lead us to expect a tilting effect of the adjacent teeth, since they are being pulled toward an ankylosed tooth, which is prevented from responding to the equal and opposite reactive force of the stretched fibers.
Effects of infraocc/usion
Volume 102 Number 3
The point of application of the restraining force is near the CEJ, i.e., coronal to the center of resistance of the tooth, which is nearer the midpoint of the root. 37 Since tilting becomes more severe with the increase of infraocclusion, we may assume that the tilting force is unopposed or exceeds any uprighting force unless and until the infraoccluded tooth subsequently frees itself and resumes normal eruption. ~4 Table II shows that there is a significant difference on the control side in the intercoronal space between the first molar and the first premolar when a deciduous second molar is present (mean = 11.08 mm) and when a premolar is present (mean = 6.60 mm). This 4.48 mm discrepancy accounts for the leeway space, which closes spontaneously after the shedding of the deciduous molar because of the mesial migration of the first permanent molar into proximal contact with the newly erupted first premolar. As would be expected in the presence of a deciduous second molar on the control side, the intercoronal space on the affected side was smaller because of the tilting of the adjacent teeth. The reduction caused was 1.83 mm. However, when a second premolar was present on the control side, it was the control side intercoronal space that was 2.25 m m smaller than the affected side, despite the degree of tilting. This indicates that local space closure adjacent to the site of an infraoccluded tooth is considerably less than the physiologic closure of the leeway space that spontaneously occurs after exfoliation of a second deciduous molar. The interapical distance between the two teeth adjacent to the infraoccluded tooth was found to be significantly greater than the interapical distance measured on the control side, with a mean difference of 8.91 mm. This being so, we must conclude that the observed tilt is due only marginally to convergence of the crowns of the teeth adjacent to the infraoccluded tooth. It is principally the result of a considerable divergence of the root apices of these teeth. If we study Table II and consider the control sides of cases A to G (where a deciduous second molar was present) together with those of cases 1 to 10 (where a premolar was present), a comparison of the intercoronal and the interapical distances in both groups will show us the character of the movement of the molar as it closes off the leeway space from the viewpoint of this cross-sectional sample study. On the control side, the mean intercoronal distance between the first permanent molar and the first premolar, when a second premolar is present, was found to be 4.48 mm less than when a deciduous second molar was in place. The interapical distance in the presence of a deciduous molar was only 0.40 mm larger than after its shedding. This shows that
263
the entire molar translates mesially, in tipping fashion, with no distal movement of the apex to accompany the marked movement of the crown. The teeth adjacent to an infraoccluded tooth cannot translate mesially because of the l~resence of the infraoccluded tooth. The observed tilt of the teeth therefore is mainly the result of the apex of the molar becoming displaced distally and of the premolar mesially away from the infraoccluded tooth, with only very slight approximation of the crowns as they undergo what appears to be a vertical rotation, which will be discussed in another article. To move the roots of the teeth in this manner, an active force is required, which would need to find its origin in the infraoccluded tooth. CONCLUSIONS
The changes discussed here in relation to the teeth adjacent to an infraoccluded deciduous second molar indicate: (I) a greater degree of tilting when related to a severer degree of infraocclusion, (2) a greater degree of tilting than that occurring after physiologic leeway space closure, (3) a relatively limited local loss of space when compared with physiologic leeway space closure, and (4) a very large anteroposterior displacement of the apices of the teeth away from the infraoccluded tooth. REFERENCES
i. Koyoumdjisky-KayeE, Steigman S. Ethnic variability in the prevalence of submerged primary molars. J Dent Res 1982;61:1401-4. 2. Koyoumdjisky-KayeE, SteigmanS. Submergingprimarymolars in Israeli rural children. Community Dent Oral Epidemiol 1982;10:204-8. 3. Kurol J. Infraocclusionof primary molars. An epidemiol~ical, familial, longitudinal, clinical and histol~ical study. Swed Dent J (Suppl) 1984;21:1-67. 4. Steigman S, Koyoumdjisky-KayeE, Matrai Y. Submerged deciduous molars in preschool children: an epidemiologicsurvey. J Dent Res 1973;52:322-6. 5. Biederman W. The ankylosed tooth. Dent Clin North Am 1964;8:493-508. 6. Brown ID. Some further observations on submerging deciduous molars. Br J Orthod 1981;8:99-107. 7. Darling AI, Levers BGH. Submerged human deciduous molars and ankylosis. Arch Oral Biol 1973;18:1021-40. 8. DarlingAI, Levers BGH. The pattern of eruption of some human teeth. Arch Oral Biol 1975;20:89-96. 9. Darling AI, Levers BGH. The pattern of eruption. In: Colston papers--eruption and occlusion of teeth. London: Butterworth, 1976:80-96. 10. Kurol J, Magnusson BC. lnfraocclusion of primary molars: a histologie study. Scand J Dent Res 1984;92:564-76. 11. Rune B. Submerged deciduous molars. Odontol Revy 1971;22:257-73. 12. RuneB. Sarnas KV. Root resorptionand submergencein retained deciduous second molars. Eur J Orthod 1984;6:123-31. 13. Kurol J, Thilander B. Infraocclusion of primary molars with
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26.
Becker and Karnei-R'em
aplasia of the permanent successor, a longitudinal study. Angle Orthod 1984;54:283-94. Kurol J, Thilander B. Infraocclusion of primary molars and the effect on occlusal development, a longitudinal study. Eur J Orthod 1984;6:277-93. Kula K, Tatum BM, Owen D, Smith RJ, Rule J. An occlusal and cephalometrie study of children with ankylosis of primary molars. J Pedod 1984;8:146-59. Lamb KA, Reed MW. Measurement of space loss resulting from tooth ankylosis. J Dent Child 1968;35:483-6. Lebret LML. Tooth migration. In: The mechanisms of tooth support, a symposium. Bristol: John Wright, 1967:120-5. Moss JP, Picton DCA. The effect on approximal drift of cheek teeth of dividing mandibular molars of adult monkeys (Macaca irus). Arch Oral Biol 1974;19:!211-4. Moss JP, Picton DCA. Short-term changes in the mesiodistal position of teeth following removal of approximal contacts in the monkey (Macacafascicularis). Arch Oral Biol 1982;27:273-8. Picton DCA. Tooth movement as mesial and lateral drift. In: Colston papers--eruption and occlusion of teeth. London: Butterworth. 1976:108-19. Berkowitz BKB, Moxham BJ, Newman HN. The periodontal ligament in health and disease. Oxford: Pergamon Press, 1982:51-72, 197-247. Moss JP, Picton DCA. On the cause of mesial drift of the teeth in adult monkeys. In: The mechanisms of tooth suppo~, a symposium. Bristol: John Wright, 1967:140-3. Moss JP, Picton DCA. The causes of migration of teeth. Trans Third lntemat Orthod Congress. London: Crosby, Lockwood & Staples. 1973;536-43. Moss JP. A review of the theories of approximal migration of teeth. In: Colston papers--eruption and occlusion of teeth. London: Butterworth, 1976:205-12. Picton DCA, Moss JP. The relationship between the angulation of the roots and the rate of approximal drift of cheek teeth in adult monkeys. Br J Orthod 1974;1:105-10. Ten Care AR, Oral Histology: development, structure and function. St. Louis: CV Mosby, 1985:268-73.
Volume 102 Number 3 27. Van Beek H, Fidler VJ. An experimental study on the effect of functional occlusion on mesial tooth migration in macaque monkeys. Arch Oral Biol 1977;22:269-71. 28. Van Beek H. The transfer of mesial drift potential along the dental arch in macaca irus: an experimental study of tooth migration rate related to the horizontal vectors of occlusal forces. Eur J Orthod 1979;1:125-9. 29. Yilmaz RS, Darling AI, Levers BGH. Mesial drift of human teeth assessed from ankylosed deciduous molars. Arch Oral Biol 1980;25:127-3 I. 30. Parker GR. Transseptal fibers and relapse following bodily retraction of teeth: a histologic study. AM J ORTHOD 1972;61:33144. 31. Picton DCA, Moss JP. The part played by the transseptal fibre system in experimental approximal drift of the cheek teeth of monkey (macaca irus). Arch Oral Biol 1973;18:669-80. 32. Becker A. The median diastema. Dent Clin North Am 1978;22:685-710. 33. Becker A, Shochat S. Submergence of a deciduous tooth: its ramifications on the dentition and treatment of the resulting malocclusion. AM J ORTItOD 1982;81:240-4. 34. Brearley LI, McKibben DH. Ankylosis of primary teeth. I. Prevalence and characteristics. 1I. A longitudinal study. J Dent Child 1973 ;40:54-63. 35. Gellin ME. Indications and contraindications for the removal of primary teeth. Dent Clin North Am 1969;13:899-911. 36. Yilmaz RS, Darling AI, Levers BGH. Experimental tooth ankylosis and horizontal tooth movement in the pig. Arch Oral Biol 1981;26:41-7. 37. Smith RJ, Burstone CJ. Mechanics of tooth movement. Ar,l J OaTt~or, 1984;85:294-307. Reprint requests to: Dr. Adrian Becker Hebrew University-Hadassah Faculty of Dental Medicine P.O. Box 1172 Jerusalem 91010 Israel
