American Journal of ORTHODONTICS and DENTOFACIAL ORTHOPEDICS Volume 99 Number l
Founded in 1915
J a n u a r y 1991
Copyright © 1991 by Mosby-Year Book, Inc.
ORIGINAL ARTICLES
The premaxillary-maxillary suture and orthodontic mechanotherapy Rolf G. Behrents, DDS, MS, PhD,* and Edward F. Harris, PhD** Memphis, Tenn.
Even though there has been debate over whether a separate premaxilla exists in the human being, it has been suggested that the premaxillary-maxillary suture remains patent into adolescence and provides an explanation for the action of certain orthodontic and orthopedic appliances. To assess whether this suture is pertinent to an understanding of appliance effects, the skulls of 50 subadult subjects were scrutinized to determine patency with regard to age. Remnants of a premaxillary-maxillary suture may be present on the surface of the palate at all ages studied, and often this suture extends deep to the surface. However, in no case was the suture continuous so as to distinguish a distinct premaxilla. These findings disprove the claim that the premaxillary-maxiilary suture system provides an explanation for any form of orthodontic or orthopedic therapy. (AMJ ORTHOD DENTFACORTHOP 1991 ;99:1-6.)
Witzig and others t'3 have suggested that various orthodontic and orthopedic appliances are capable of translating a malposed premaxilla to a more favorable position. It has been stated that a certain type of sagittal appliance will move the premaxilla forward or upward, with the second molars serving as anchorage;' another type of sagittal appliance will pull the premaxilla forward; I and a bionator may be used to rotate a protruded premaxilla into a correct position.' The basis for this explanation involves the notion that such appliances can be used to open up the premaxillary sutures "in order to gain true orthopedic development of the premaxillary area. ''1 While speculation about the contribution of the premaxillary-maxillary sutures is attractive and may seem reasonable in light of observed
From the University of Tennessee, Department of Orthodontics. Supported by a grant from the University of Tennessee Orthodontic Alumni Foundation. *Professor and Chairman. **Associate Professor and Director of Research.
811119152
clinical results, no anatomic basis for this possibility has been established. In most mammals a suture system separates the premaxilla and the maxilla sometime during ontogeny. The suture courses facially downward from the junction of the premaxilla and the maxilla near the inferior margin of the piriform plate to the alveolar margin in the region of the canine and across the palate to the incisive foramen. Differences in the appearance of the premaxilla are often noted according to taxon. *~ Because of substantive variability in the course and the time of suture obliteration in the human being, 6 there is disagreement as to whether a premaxilla ever exists as a distinct entity in this species. 78 Doubt is based on the suggestion that a center of ossification for the premaxilla is difficult to identify embryologically. Even when existence is admitted, it is a constant finding that obliteration of the facial aspects of the suture in human beings occurs very early, with obliteration of the isthmus between the premaxillary and maxillary centers of ossification being completed during the first trimester of prenatal life. 4-5,9
2
Am. J. Orthod. Dentofac. Orthop. January 1991
Behrents and Harris
Fig. 1. A, Skull of young child showing extent of palatal portion of premaxillary-maxillary suture. B, Facial view.
Table I. Frequencies of suture closure in the premaxillary-maxillary system, by region and by age grade*
Palatal aspect Age
(yrs)
16 22 11
3-5 6-10 11-17 *Sample sizes specimens.
n
(n) vary
[
Facial aspect
buernal aspect
% Fused
n
37 59 45
10 21 9
I
% Fused
n
0 29 33
16 22 12
I
% Fused I00 95 100
by category because of inability to assess internal structures in intact skulls and absence of relevant portions of some
However, on the basis of identification of separate centers of ossification in embryos, the structural similarities among mammals, the characteristic deformities noted in bilateral facial clefts, and the persistence of suture remnants in the areas of the infraorbital foramen
and the surface of the palate, it is generally concluded that human beings do indeed exhibit a separate premaxilla during development. Less clear, however, is the time course of suture obliteration. ~° Because palatal remnants of the premaxillary-
Volume 99 Number 1
Prema-tillary-maxillary suture fi+sion
3
P
Fig. 2. A, Skull of adolescent showing that palatal sutural extensions are diminished. B, Facial view showing no evidence of facial suture.
maxillary suture may be observable into adulthood, it is believed that such a suture may be patent and provide an explanation for the action of several orthodontic treatments. METHODS AND MATERIALS
To investigate the possibility that there exists a patent suture system that would permit movement of the premaxilla, 50 skulls of subadults were scrutinized. Materials were obtained from the Hamman-Todd Osteological Collection housed in the Museum of Natural History at Case Western Reserve University and supplemented with the collection of Dr. Donald H. Enlow at Case Western Reserve. In addition, several prenatal specimens from the Hopkins Collection also at Case Western Reserve were viewed for perspective.
Age at death was obtained from autopsy records and, occasionally, supplemented by gauging dental mineralization status.ZX In both series most of the skulls were either disarticulated or had been sectioned, which permitted visualization of the deep portions of the suture system in the intermaxillary region and laterally inferior to the nasal floor. The sutural complex was divided into three aspects: (1) the palatal view, (2) the hlternal aspect just noted, and (3) the facial aspect from the nasal sill inferiorly to the alveolus. These aspects were scored separately because the system does not mature uniformly.~Z Indeed, much of the earlier controversy over the existence of a premaxilla in human beings revolved on the failure to distinguish between the facial aspect (which fuses early) and the palatal aspect (where unfused remnants may persist well into adulthood). The
4
Am. J. Orthod. Dentofac. Orthop. January 1991
Behrents and Harris
Fig. 3. View of single specimen possessing a facial remnant of a premaxillary-maxillarysuture.
Fig. 4. Lateral view of palate showing deep extension of premaxillary-maxillarysuture as it courses in incisive canal.
sample was also divided into broad age intervals (3 to 5 years, 6 to 10 years, and 11 to I7 years) to view ontogenic trends. It is well known that sutures typically initiate fusion at internal sites, with the tempo of obliteration often being slowest at the periosteal (ectocranial) surface. 6"~2~ Sutural obliteration is progressive and cumulative. ~5To be conservative, we scored a suture site as fused when all of the suture space had been ossified: while a slight indentation (a line or dimpling) typically persisted on the surface showing where the suture had been, there was complete obliteration of the bony denticles that interdigitate before synostosis.
RESULTS The facial aspect of the premaxillary-maxillary suture complex fuses and is entirely obliterated early in life (Table I; Figs. 1 and 2). Indeed, we encountered just one example.of persistence of a remnant of this suture (2%, 1/50; Fig. 3). Consequently, patency can be viewed as a minor developmental anomaly akin to persistence of the metopic suture, ~6the os japonicum, ~7 and the bipartite parietal bone. ~8 While these are interesting anatomic oddities, none of them provides a predictable site for orthopedic intervention. The internal third of the premaxillary-maxillary system obviously is the slowest to undergo fusion (Table
Volume99
Premaxillary-maxillary suture fusion
Number I
I; Fig. 4). One third of the cases in the conventional age interval for orthodontic treatment (11 to 17 years) exhibited fusion, and it may well be that, like most other facial sutures,~3t4 this portion of the complex does not routinely fuse. The palatal aspect of the system is quite variable, though there is an age-progressive trend in which half of the adolescent cases exhibited obliteration of most, if not all, of the tract from the incisive foramen to the incisor-canine junction in the alveolus. Often a remnant of this suture persists for 4 to 5 mm adjacent to the foramen, but this would not aid in orthopedically overcoming the cortical fusion of the suture elsewhere in the palate, to say nothing of the facial obliteration. DISCUSSION
These findings disturb the contentions of various authors who invoke a premaxillary-maxillary mechanism to explain treatment results. Vardimon et al.,2 in their investigations on the use of palatal expansion devices with Macacafasicularis monkeys as their model, refer to the premaxillary-maxillary suture in explaining aspects of forward and vertical displacements of the midface. Interpretations of their findings on an Old World monkey, which is known to have an unfused premaxillary suture, may not apply to human situations; clinical suggestions regarding maxillary protraction in the human being are an inappropriate extrapolation. The Vardimon report also refers to a report by Haskell and Farman. 3 Specifically, Haskell and Farman presented a hypothesis that the premaxillary-maxillary suture may be patent and could be significant in an understanding of premaxillary protraction in Class III treatments. They reviewed the important literature, but in no case did it support the contention that the premaxillary-maxillary suture system remains entirely patent at any time during postnatal life. However, they note that sutural remnants may be present. Evidence to support their conjecture was derived from observations on three specimens (two dry skulls and an occlusal radiograph intended to portray a patent suture) and the need to explain successful maxillary protraction in another case. While visualization of a partial remnant of a suture on a dry skull and a fine-lined opacity on a radiograph may be used to determine the location of a sutural remnant, location does not demonstrate patency. Furthermore, to explain the correction in the case presented, it is sufficient to invoke tipping of the maxillary anterior teeth (a condition described by the authors); demonstration of a patent suture was not accomplished. Haskell and Farman suggest that erratic treatment resuits in cases such as that presented might be due to partial patency. The meaning of this is unclear, and such patency is unmanageable as a mechanism. Apparently Witzig and Spahl t have completely ac-
5
cepted the hypothesis that the premaxillary-maxillary suture system is patent even into older adolescence. In their textual and illustrative descriptions of the mode of action of the sagittal and bionator appliances, repeated reference is made to orthopedic protraction of the premaxilla by opening the premaxillary sutures or by using the suture as a point of rotation. Such contentions do not reflect biologic reality. The mode of action of these appliances clearly rests on general expansion mechanisms where the teeth are tipped into position. This is also the conclusion of Owen t9 and Johnston z° in reports on the action of the sagittal appliance. According to the findings in this study, in order for the premaxillary-maxillary suture to be important in an understanding of the effects of a sagittal appliance at the time when the second molars have erupted (and are thus available for anchorage), it would be necessary for the obliterated sutures to be fractured. Such an event would be a profound experience for the patient and the practitioner alike. Furthermore, such an opening has never been demonstrated in a person, even with such simple techniques as documentation with an occlusal radiograph (as is often done during intermaxillary and midpalatine suture expansion). In summary, this conjecture cannot be accepted. It is hoped that these data will put to rest the contention that the premaxillary-maxillary suture is of significance in an understanding of the effects of various orthopedic protraction appliances. The clinical effects must be explained by means of alternative interpretations. In this regard, it is quite likely that, when such appliances are used, the incisors are simply being pushed anteriorly. If this is, in fact, the case, dehiscences of the labial plate of the alveolus and resorption of the labial surface of the tooth roots should be consequential concerns. CONCLUSION
Because major segments of the premaxillarymaxillary suture system have fused and are largely obliterated postnatally, in this context sutural remodeling cannot be exploited as an explanation for the action of various orthodontic and orthopedic appliances. REFERENCES
I. Witzig JW, Spahl TJ. The clinical managementof basic maxillofacial orthopedic appliances. Vol I. Mechanics. Littleton: PSG Publishing 1987:226-8, 236-7, 240. 2. Vardimon AD, Graber TM, Voss LR, Verrusio E. Magnetic versus mechanicalexpansionwith different force thresholds and points of force application. AM J OR'rrtoDDENTOFACOR'I'HOP 1987;92:455-65. 3. Haskell BS, Farman AG. Exploitation of the residual premaxillary-maxillarysuture site in maxillary protraction: an hypothesis. Angle Orthod 1985;55:108-19.
6
Behrents and Harris
4. Ashley-Montagu MF. The premaxilla in primates. Q Rev Biol 1935;10:32-59, 181-208. 5. Noback CR, Moss ML. The topology of the human premaxillary bone. Am J Phys Anthropol 1953;11:181-8. 6. McKern TW, Stewart TD. Skeletal age changes in young American males analyzed from the standpoint of age identification. Natick, Mass.: U.S. Army technical report EP-45, Quartermaster Research and Development Center, Environmental Protection Research Division, 1957. 7. Wood NK. The premaxilla: embryological evidence that it does not exist in man. Anat Rec 1967;158:485-90. 8. Wood NK. Osteogenesis of the human upper jaw: proof of the non-existence of a separate pre-maxillary centre. Arch Oral Biol 1969;14:1331-41. 9. Remmelink IlL The postnatal development of the human maxillary sutural surfaces [Thesis]. Groningen, The Netherlands: The University of Groningen, 1985. 10. Schwartz JH. Dentofacial growth and development in Homo sapiens: Evidence from perinatal individuals from Punic Carthage. Anat Anz 1982;152:1-26. 11. Moorrees CFA, Fanning EA, Hunt EE Jr. Age variation of formation stages for ten permanent teeth. J Dent Res 1963;42:1490502. 12. Krogman WM. The human skeleton in forensic medicine. Springfield: Charles C Thomas, 1962. 13. Todd TW, Lyon DW Jr. Cranial suture closure: its progress and age relationship. Part IV. Ectocranial closure in adult males of Negro stock. Am J Phys Anthropol (o.s.) t925;8:149-68. 14. Kokick VG. Age changes in the human frontozygomatic suture from 20 to 95 years. AM J OR~[OD 1976;69:411-30.
Am. J. Orthod. Dentofae. Orthop. January 1991 15. McKem TW. Estimation of skeletal age: from puberty to about 30 years of age. In: Stewart TD, ed. Personal identification in mass disasters. Washington, D.C.: National Museum of Natural History, 1970:41-56. 16. Woo J-K. Racial and sexual differences in the frontal curvature and its relation to metopism. Am J Phys Anthropol 1949;7:21526. 17. Elliot Smith G, Wood-Jones F. Report on the human remains. Archaeological Survey of Nubia, Report of 1907-1908. 1910; 11:1-375. 18. Hrdlicka A. Divisions of the parietal bone in man and other mammals. Bull Am Mus Nat Hist 1903;19:231-386. 19. Owen AH III. The maxillary sagittal appliance: a clinical study. At~t J ORTIIODDENTOFACORTHOP 1987;9h271-85. 20. Johnston LE Jr. A comparative analysis of Class I1 treatments. In: Vig PS and Ribbens KA, eds. Science and clinical judgment in orthodontics. Monograph 19, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan. 1986:103-148. Reprhlt requests to: Dr. Rolf G. Behrents Department of Orthodontics College of Dentistry The University of Tennessee 875 Union Ave. Memphis, TN 38163
AAO MEETING CALENDAR
1991--Seattle, Wash., May 11 to 15, Seattle Convention Center 1992--St. Louis, Mo., May 10 to 13, St. Louis Convention Center 1993--Toronto, Canada, May 16 to 19, Metropolitan Toronto Convention Center 1994--Orlando, Fla., May 1 to 4, Orange County Convention and Civic Center 1995--San Francisco, Calif., May 7 to 10, Moscone Convention Center 1996-- Denver, Colo., May 12-15, Colorado Convention Center
Founded in 1915
J a n u a r y 1991
Copyright © 1991 by Mosby-Year Book, Inc.
ORIGINAL ARTICLES
The premaxillary-maxillary suture and orthodontic mechanotherapy Rolf G. Behrents, DDS, MS, PhD,* and Edward F. Harris, PhD** Memphis, Tenn.
Even though there has been debate over whether a separate premaxilla exists in the human being, it has been suggested that the premaxillary-maxillary suture remains patent into adolescence and provides an explanation for the action of certain orthodontic and orthopedic appliances. To assess whether this suture is pertinent to an understanding of appliance effects, the skulls of 50 subadult subjects were scrutinized to determine patency with regard to age. Remnants of a premaxillary-maxillary suture may be present on the surface of the palate at all ages studied, and often this suture extends deep to the surface. However, in no case was the suture continuous so as to distinguish a distinct premaxilla. These findings disprove the claim that the premaxillary-maxiilary suture system provides an explanation for any form of orthodontic or orthopedic therapy. (AMJ ORTHOD DENTFACORTHOP 1991 ;99:1-6.)
Witzig and others t'3 have suggested that various orthodontic and orthopedic appliances are capable of translating a malposed premaxilla to a more favorable position. It has been stated that a certain type of sagittal appliance will move the premaxilla forward or upward, with the second molars serving as anchorage;' another type of sagittal appliance will pull the premaxilla forward; I and a bionator may be used to rotate a protruded premaxilla into a correct position.' The basis for this explanation involves the notion that such appliances can be used to open up the premaxillary sutures "in order to gain true orthopedic development of the premaxillary area. ''1 While speculation about the contribution of the premaxillary-maxillary sutures is attractive and may seem reasonable in light of observed
From the University of Tennessee, Department of Orthodontics. Supported by a grant from the University of Tennessee Orthodontic Alumni Foundation. *Professor and Chairman. **Associate Professor and Director of Research.
811119152
clinical results, no anatomic basis for this possibility has been established. In most mammals a suture system separates the premaxilla and the maxilla sometime during ontogeny. The suture courses facially downward from the junction of the premaxilla and the maxilla near the inferior margin of the piriform plate to the alveolar margin in the region of the canine and across the palate to the incisive foramen. Differences in the appearance of the premaxilla are often noted according to taxon. *~ Because of substantive variability in the course and the time of suture obliteration in the human being, 6 there is disagreement as to whether a premaxilla ever exists as a distinct entity in this species. 78 Doubt is based on the suggestion that a center of ossification for the premaxilla is difficult to identify embryologically. Even when existence is admitted, it is a constant finding that obliteration of the facial aspects of the suture in human beings occurs very early, with obliteration of the isthmus between the premaxillary and maxillary centers of ossification being completed during the first trimester of prenatal life. 4-5,9
2
Am. J. Orthod. Dentofac. Orthop. January 1991
Behrents and Harris
Fig. 1. A, Skull of young child showing extent of palatal portion of premaxillary-maxillary suture. B, Facial view.
Table I. Frequencies of suture closure in the premaxillary-maxillary system, by region and by age grade*
Palatal aspect Age
(yrs)
16 22 11
3-5 6-10 11-17 *Sample sizes specimens.
n
(n) vary
[
Facial aspect
buernal aspect
% Fused
n
37 59 45
10 21 9
I
% Fused
n
0 29 33
16 22 12
I
% Fused I00 95 100
by category because of inability to assess internal structures in intact skulls and absence of relevant portions of some
However, on the basis of identification of separate centers of ossification in embryos, the structural similarities among mammals, the characteristic deformities noted in bilateral facial clefts, and the persistence of suture remnants in the areas of the infraorbital foramen
and the surface of the palate, it is generally concluded that human beings do indeed exhibit a separate premaxilla during development. Less clear, however, is the time course of suture obliteration. ~° Because palatal remnants of the premaxillary-
Volume 99 Number 1
Prema-tillary-maxillary suture fi+sion
3
P
Fig. 2. A, Skull of adolescent showing that palatal sutural extensions are diminished. B, Facial view showing no evidence of facial suture.
maxillary suture may be observable into adulthood, it is believed that such a suture may be patent and provide an explanation for the action of several orthodontic treatments. METHODS AND MATERIALS
To investigate the possibility that there exists a patent suture system that would permit movement of the premaxilla, 50 skulls of subadults were scrutinized. Materials were obtained from the Hamman-Todd Osteological Collection housed in the Museum of Natural History at Case Western Reserve University and supplemented with the collection of Dr. Donald H. Enlow at Case Western Reserve. In addition, several prenatal specimens from the Hopkins Collection also at Case Western Reserve were viewed for perspective.
Age at death was obtained from autopsy records and, occasionally, supplemented by gauging dental mineralization status.ZX In both series most of the skulls were either disarticulated or had been sectioned, which permitted visualization of the deep portions of the suture system in the intermaxillary region and laterally inferior to the nasal floor. The sutural complex was divided into three aspects: (1) the palatal view, (2) the hlternal aspect just noted, and (3) the facial aspect from the nasal sill inferiorly to the alveolus. These aspects were scored separately because the system does not mature uniformly.~Z Indeed, much of the earlier controversy over the existence of a premaxilla in human beings revolved on the failure to distinguish between the facial aspect (which fuses early) and the palatal aspect (where unfused remnants may persist well into adulthood). The
4
Am. J. Orthod. Dentofac. Orthop. January 1991
Behrents and Harris
Fig. 3. View of single specimen possessing a facial remnant of a premaxillary-maxillarysuture.
Fig. 4. Lateral view of palate showing deep extension of premaxillary-maxillarysuture as it courses in incisive canal.
sample was also divided into broad age intervals (3 to 5 years, 6 to 10 years, and 11 to I7 years) to view ontogenic trends. It is well known that sutures typically initiate fusion at internal sites, with the tempo of obliteration often being slowest at the periosteal (ectocranial) surface. 6"~2~ Sutural obliteration is progressive and cumulative. ~5To be conservative, we scored a suture site as fused when all of the suture space had been ossified: while a slight indentation (a line or dimpling) typically persisted on the surface showing where the suture had been, there was complete obliteration of the bony denticles that interdigitate before synostosis.
RESULTS The facial aspect of the premaxillary-maxillary suture complex fuses and is entirely obliterated early in life (Table I; Figs. 1 and 2). Indeed, we encountered just one example.of persistence of a remnant of this suture (2%, 1/50; Fig. 3). Consequently, patency can be viewed as a minor developmental anomaly akin to persistence of the metopic suture, ~6the os japonicum, ~7 and the bipartite parietal bone. ~8 While these are interesting anatomic oddities, none of them provides a predictable site for orthopedic intervention. The internal third of the premaxillary-maxillary system obviously is the slowest to undergo fusion (Table
Volume99
Premaxillary-maxillary suture fusion
Number I
I; Fig. 4). One third of the cases in the conventional age interval for orthodontic treatment (11 to 17 years) exhibited fusion, and it may well be that, like most other facial sutures,~3t4 this portion of the complex does not routinely fuse. The palatal aspect of the system is quite variable, though there is an age-progressive trend in which half of the adolescent cases exhibited obliteration of most, if not all, of the tract from the incisive foramen to the incisor-canine junction in the alveolus. Often a remnant of this suture persists for 4 to 5 mm adjacent to the foramen, but this would not aid in orthopedically overcoming the cortical fusion of the suture elsewhere in the palate, to say nothing of the facial obliteration. DISCUSSION
These findings disturb the contentions of various authors who invoke a premaxillary-maxillary mechanism to explain treatment results. Vardimon et al.,2 in their investigations on the use of palatal expansion devices with Macacafasicularis monkeys as their model, refer to the premaxillary-maxillary suture in explaining aspects of forward and vertical displacements of the midface. Interpretations of their findings on an Old World monkey, which is known to have an unfused premaxillary suture, may not apply to human situations; clinical suggestions regarding maxillary protraction in the human being are an inappropriate extrapolation. The Vardimon report also refers to a report by Haskell and Farman. 3 Specifically, Haskell and Farman presented a hypothesis that the premaxillary-maxillary suture may be patent and could be significant in an understanding of premaxillary protraction in Class III treatments. They reviewed the important literature, but in no case did it support the contention that the premaxillary-maxillary suture system remains entirely patent at any time during postnatal life. However, they note that sutural remnants may be present. Evidence to support their conjecture was derived from observations on three specimens (two dry skulls and an occlusal radiograph intended to portray a patent suture) and the need to explain successful maxillary protraction in another case. While visualization of a partial remnant of a suture on a dry skull and a fine-lined opacity on a radiograph may be used to determine the location of a sutural remnant, location does not demonstrate patency. Furthermore, to explain the correction in the case presented, it is sufficient to invoke tipping of the maxillary anterior teeth (a condition described by the authors); demonstration of a patent suture was not accomplished. Haskell and Farman suggest that erratic treatment resuits in cases such as that presented might be due to partial patency. The meaning of this is unclear, and such patency is unmanageable as a mechanism. Apparently Witzig and Spahl t have completely ac-
5
cepted the hypothesis that the premaxillary-maxillary suture system is patent even into older adolescence. In their textual and illustrative descriptions of the mode of action of the sagittal and bionator appliances, repeated reference is made to orthopedic protraction of the premaxilla by opening the premaxillary sutures or by using the suture as a point of rotation. Such contentions do not reflect biologic reality. The mode of action of these appliances clearly rests on general expansion mechanisms where the teeth are tipped into position. This is also the conclusion of Owen t9 and Johnston z° in reports on the action of the sagittal appliance. According to the findings in this study, in order for the premaxillary-maxillary suture to be important in an understanding of the effects of a sagittal appliance at the time when the second molars have erupted (and are thus available for anchorage), it would be necessary for the obliterated sutures to be fractured. Such an event would be a profound experience for the patient and the practitioner alike. Furthermore, such an opening has never been demonstrated in a person, even with such simple techniques as documentation with an occlusal radiograph (as is often done during intermaxillary and midpalatine suture expansion). In summary, this conjecture cannot be accepted. It is hoped that these data will put to rest the contention that the premaxillary-maxillary suture is of significance in an understanding of the effects of various orthopedic protraction appliances. The clinical effects must be explained by means of alternative interpretations. In this regard, it is quite likely that, when such appliances are used, the incisors are simply being pushed anteriorly. If this is, in fact, the case, dehiscences of the labial plate of the alveolus and resorption of the labial surface of the tooth roots should be consequential concerns. CONCLUSION
Because major segments of the premaxillarymaxillary suture system have fused and are largely obliterated postnatally, in this context sutural remodeling cannot be exploited as an explanation for the action of various orthodontic and orthopedic appliances. REFERENCES
I. Witzig JW, Spahl TJ. The clinical managementof basic maxillofacial orthopedic appliances. Vol I. Mechanics. Littleton: PSG Publishing 1987:226-8, 236-7, 240. 2. Vardimon AD, Graber TM, Voss LR, Verrusio E. Magnetic versus mechanicalexpansionwith different force thresholds and points of force application. AM J OR'rrtoDDENTOFACOR'I'HOP 1987;92:455-65. 3. Haskell BS, Farman AG. Exploitation of the residual premaxillary-maxillarysuture site in maxillary protraction: an hypothesis. Angle Orthod 1985;55:108-19.
6
Behrents and Harris
4. Ashley-Montagu MF. The premaxilla in primates. Q Rev Biol 1935;10:32-59, 181-208. 5. Noback CR, Moss ML. The topology of the human premaxillary bone. Am J Phys Anthropol 1953;11:181-8. 6. McKern TW, Stewart TD. Skeletal age changes in young American males analyzed from the standpoint of age identification. Natick, Mass.: U.S. Army technical report EP-45, Quartermaster Research and Development Center, Environmental Protection Research Division, 1957. 7. Wood NK. The premaxilla: embryological evidence that it does not exist in man. Anat Rec 1967;158:485-90. 8. Wood NK. Osteogenesis of the human upper jaw: proof of the non-existence of a separate pre-maxillary centre. Arch Oral Biol 1969;14:1331-41. 9. Remmelink IlL The postnatal development of the human maxillary sutural surfaces [Thesis]. Groningen, The Netherlands: The University of Groningen, 1985. 10. Schwartz JH. Dentofacial growth and development in Homo sapiens: Evidence from perinatal individuals from Punic Carthage. Anat Anz 1982;152:1-26. 11. Moorrees CFA, Fanning EA, Hunt EE Jr. Age variation of formation stages for ten permanent teeth. J Dent Res 1963;42:1490502. 12. Krogman WM. The human skeleton in forensic medicine. Springfield: Charles C Thomas, 1962. 13. Todd TW, Lyon DW Jr. Cranial suture closure: its progress and age relationship. Part IV. Ectocranial closure in adult males of Negro stock. Am J Phys Anthropol (o.s.) t925;8:149-68. 14. Kokick VG. Age changes in the human frontozygomatic suture from 20 to 95 years. AM J OR~[OD 1976;69:411-30.
Am. J. Orthod. Dentofae. Orthop. January 1991 15. McKem TW. Estimation of skeletal age: from puberty to about 30 years of age. In: Stewart TD, ed. Personal identification in mass disasters. Washington, D.C.: National Museum of Natural History, 1970:41-56. 16. Woo J-K. Racial and sexual differences in the frontal curvature and its relation to metopism. Am J Phys Anthropol 1949;7:21526. 17. Elliot Smith G, Wood-Jones F. Report on the human remains. Archaeological Survey of Nubia, Report of 1907-1908. 1910; 11:1-375. 18. Hrdlicka A. Divisions of the parietal bone in man and other mammals. Bull Am Mus Nat Hist 1903;19:231-386. 19. Owen AH III. The maxillary sagittal appliance: a clinical study. At~t J ORTIIODDENTOFACORTHOP 1987;9h271-85. 20. Johnston LE Jr. A comparative analysis of Class I1 treatments. In: Vig PS and Ribbens KA, eds. Science and clinical judgment in orthodontics. Monograph 19, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan. 1986:103-148. Reprhlt requests to: Dr. Rolf G. Behrents Department of Orthodontics College of Dentistry The University of Tennessee 875 Union Ave. Memphis, TN 38163
AAO MEETING CALENDAR
1991--Seattle, Wash., May 11 to 15, Seattle Convention Center 1992--St. Louis, Mo., May 10 to 13, St. Louis Convention Center 1993--Toronto, Canada, May 16 to 19, Metropolitan Toronto Convention Center 1994--Orlando, Fla., May 1 to 4, Orange County Convention and Civic Center 1995--San Francisco, Calif., May 7 to 10, Moscone Convention Center 1996-- Denver, Colo., May 12-15, Colorado Convention Center
