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A review of maxillary expansion in relation to rate of expansion and patient's age
A review of maxillary expansion in relation to rate of expansion and patient’s age Ronald Aqusm,
A. Bell, D.D.S., M.D.* Go.
Treatment variables such as patient age, rate of expansion, magnitude of applied transverse force, appliance design, and retention protocol produce an array of interactions which affect orthopedic and orthodontic movements during maxillary expansion procedures, The purpose of this article is to review the quantitative and qualitative changes of sutural, skeletal, and dental tissues demonstrated in human and animal studies of maxillary expansion procedures. The association of the reported tissue responses with the treatment variables of patient age and rate of expansion serve as the focus of discussion. While the accumulated evidence appears to support a treatment rationale of early correction using a slow expansion procedure, individual variables must be considered in determining an expansion protocol that will optimally affect the quantity and quality of the expansion changes.
Key words: Review, maxillary, expansion, rate, age
T
he early correction of posterior cross-bites requiring maxillary expansion has been advocated to redirect the developing teeth into more normal positions,‘-” eliminate untoward temporomandibular joint positions and mandibular closure patterns,2s 5, i and make beneficial dentoskeletal changes during growth periods involving a reduced treatment complexity and time.XP”’ The purpose of this article is to review the literature concerning the quantitative and qualitative effects of maxillary expansion on connective, skeletal. and dental tissues. The role that patient age and rate of expansion may play as treatment variables in maxillary expansion procedures will serve as a focus for review and discussion.
This stage of orthodontic response appears to be essentially complete within a week.“, *L 17, l9 Subsequent orthodontic movements will occur through bodily translation as the compressed buccal alveolar plate resorbs at the root-periodontal interface from continued force application.‘*23 If the applied transverse forces are of sufficient magnitude to overcome the bioelastic strength of sutural elements, orthopedic separation of the maxillary segments can occur.‘3-‘9, 2’. a~,24x25The separation and repositioning of the palatal segments will continue until the force distribution is reduced below the tensile strength of the sutural elements.“‘. 2’. pZ,~3 25Reorganization and remodeling of the sutural connective and skeletal tissues may then proceed in the stabilization of the
REVIEW
OF LITERATURE
Increased maxillary arch width has been related to orthodontic movements, orthopedic movements, or a combination of these movements during expansion procedures.H, ‘I. I2 While the relative degree and nature of these movements is affected by various factors, the general pattern of maxillary expansion may be described. Upon the application of transverse biomechanical forces, initial changes involve the lateral tipping of the posterior maxillary teeth as the periodontal and palatal soft tissues are compressed and stretched.‘“P’” *Associate Profesor, Department cal College of Georgia.
32
of Pedodontics,
School of Dentistry,
Medi-
expanded
maxillary
arch.‘:‘,
19,
“1,
“2,
“(i.
“i
When
orthopedic separation of the maxillary segments occurs, asymmetric linear and angular responses have generally been
obseped,l3-19,
21.
2‘2.
24,
25.
‘LX-35
The
asymmetric
expansion has been attributed to variations in the rigidity of the different maxillary articulations.““. Z’sA frontal view of orthopedic sutural separation shows a lateral rotation or tipping of the palatal halves. 19,21.22.‘1. “3. :33.36 The palatal movement is greater at the alveolar crest and less at the palatal vault, presenting a triangular expansion pattern with the base near the incisors and the apex toward the nasal areal4, 15. 19, 21, 12. 24. 26, 29, X0, Xl-4i (Fig. 1,A). From an accusal view, the greatest opening of the midpalatal suture has been found anteriorly, with progressively lessseparation toward the posterior’“. :‘z :‘H,M-~“. ‘x 0002.9416/82/010032+06$00.60/0
0
1982 The C
V Mosby Co
Review
(Fig. 1,B). Inthesagittalplane,adownwardandforward displacement of the maxilla with opening of the bite has the finding is not been reported, 19,22,34,35%40-43though always demonstrated after treatment.“’ ‘i5 A significant skeletal component of the increased arch width is generally considered a desirable product of maxillary expansion procedures as orthopedic changes allow coordination of the maxillary and mandibular bases in establishing a stable correction of transverse skeletal and/or dentoskeletal malocclusions, IO. 15. 193 203 :M* 40-43 The relative amount of skeletal versus dental changes occurring in maxillary expansion procedures has been primarily related to the treatment variables of patient age and rate of expansion (that is, magnitude of applied force, appliance design). Clinicians have commonly reported difficulty in producing palatal separation following the pubertal growth orthopedic reperiod, 1.i. 29. :30. 35. W-43 while favorable sponses have been indicated prior toi’s Zy, 30, M* 4851 and
during
pubertal
growth.l.5.
29, 30, 3.5, 40-43,
of maxillary
expansion
33
0
52, 53 A
direct relationship between increased resistance to skeletal expansion and increasing patient age has been quantified”” and associated with the formation of mechanical interlockings at maxillary articulations as early the as 12 to 13 years of age.‘“, 2X, 32, 32 In addition, enhanced skeletal response in younger age groups has been associated with a greater cellular activity in the growing
suture.13.
14
19s %I.
2%. 24,
27,
31,
.iS Brin
and
co-workers ,j5 using the measurement of cyclic nucleotides as indicators of cellular activity and new bone formation, reported that the sutural bone cells of young cats were more responsive to palatal expansion forces than the corresponding cells of old animals. Ten Cate and associates” reported that the sutural tissues in young growing rats were characterized by increased fibroblastic, fibroclastic, and osteoblastic activity following rapid expansion in contrast to a less marked activity in more mature animals. The treatment variable most critically evaluated in the literature in relation to maxillary expansion changes has been the rate of expansion. In rapid expansion procedures employing jackscrew appliances (Fig. 2, A) expansion generally occurs at a rate of about 0.2 to 0.5 mm. per day during an active treatment time of 1 to 3 weeks .“;,. ZL SZ,4”-43 The individual activation schedule has been most often determined on an empirical basis, dependent on the amount of expansion desired and the patient’s tolerance. Isaacson and Ingram’” reported that single activations of jackscrew appliances produce forces in the 3- to lo-pound range, while multiple daily activations can result in cumulative loads of 20 pounds or more, Such high-magnitude forces maximize orthopedic separation of the bony segments by disruptively
Fig. 1. A, Triangular pattern of maxillary expansion in the frontal plane includes orthopedic and orthodontic movement. Orthopedic changes may involve separation at sutural sites with a lateral rotation or tipping of the palatal halves, widening of the nasal processes, and subsequent bony remodeling. Orthodontic changes may involve lateral tipping and bodily translation of maxillary teeth, transient midline diastema, and mild expansion of mandibular teeth. 6, Occlusal view of maxillary expansion illustrating midpalatal suture opening with greatest separation occurring anteriorly, lateral rotation of palatal halves, bony remodeling of maxillary elements, and lateral/rotational movement of the maxillary teeth.
overwhelming sutural tissues before substantial orthodontic movement and/or physiologic changes can occur within the tissue.‘“. ~3 4’t42 The relative skeletal and dental components produced by rapid palatal expansion have been evaluated with the use of standardized nonanatomic reference points (for example, implants) and frontal cephalograms .2ga0 KrebsZg, 3o reported average dental arch increases of 6.0 mm (0.5 to 10.3 mm. range) for twenty-three subjects aged 8 to 19 years, with the total arch increase twice that of the basal maxillary segments. Cottoni and Hicks,‘” using the Krebs data, estimated that one third to one half the achieved maxillary arch width increase was due to skeletal separation, with the remainder being of dental origin. The analysis
34
Bell
ments heal in a unique proliferative response which ultimately leads to a regeneration of the suture,“’ a stable maxillary complex is not achieved until residual forces which tend to collapse the expanded segments are dissipated. “‘. “I, 42, “3 x Insufficient retention periods have resulted in substantial, even total, skeletal relapse.‘!‘, ” Retention periods of 3 to 6 months are normally recommended to allow reorganization and stabilization of rapidly expanded maxillary sutures, I!,. “I. “2. ‘ii. 29.:jo.:I’. :C -I~,ZJ with even longer periods advocated by some clinicians, P:j,-10--,:1 Evidence of iatrogenic resorptive pro-
Fig. 2. A, Rapid ance. B, Lingual
palatal expansion emplying a jackscrew arch wire appliance of the quad-helix
applitype.
of the Krebs rapid expansion data also demonstrated that the skeletal changes accounted for approximately one half the increased arch width in 8 to 12 year-olds and about one third of the increase in 13 to 19-year-old subjects.” 20. :N The range of maxillary arch width increases reported by Kreb? X’ is representative of other quantitative amounts reported following rapid expansion procedures,:i,i. ~0~?:1,~9 Human and animal studies have documented extensive bone and sutural activity at the fine structural level during rapid maxillary expansion. Brossian and associates’” found gross separation of the palate segments, bone deposition over external surfaces of the maxillary complex, and significant deformation of maxillary bones following rapid palatal expansion in monkeys, The histologic picture of rapidly expanded sutural tissues has included reports of free-floating bone fragments and numerous microfractures,:=% x cystlike formations ‘!A s’. 22 highly vascular disorganized connective tissu; of an inflammatory nature, 13.16 I!,, 14,38,92.5.iand a rapid dystrophic ossification with immature bone tissue.“‘, “, XL 5x While the sutural connective tissue ele-
cesseson the root surfaces of anchor teeth demonstrated up to 9 months postexpansion suggest the potential for long-term activity of the residual loads.“‘, ‘?x Slow expansion procedures, such as those involving the use of lingual arch wire appliances with expansive capability (Fig. 2, B), incorporate force systems of several ounces up to approximately 2 pounds.“‘, ‘I. “. “. “’ The slow expansion procedures increase the percentage of orthodontic movements as the tensile strength of the suture elements is not overwhelmed.X. I”. Ii. I”. I” ” However, orthopedic separation of the maxillary segments has been documented as a component of slow maxillary expansion in both human’;‘, ‘j’. lx, “. iti and primate’:‘. I1 studies, particularly in younger age groups with deciduous and/or mixed dentitions. Using standardized reference procedures in analyzing serial frontal cephalograms obtained during slow expansion treatment (0.5 mm. per week), SkielleP attributed approximately 20 percent of the arch width increase to orthopedic Hicks.‘” using separation of the midpalatal suture. 2-pound forces with expansion rates of 0.4 to 1. I mm. per week, achieved maxillary arch width increases of from 3.8 to 8.7 mm. during treatment. With the use of nonanatomic reference points, Hicks’” estimated that the skeletal changes represented 24 to 30 percent of the total arch width increase in 10 to I l-year-old patients and 16 percent in the 14 to 15-year-olds. While not documenting the relative degree of orthopedic versus orthodontic changes, radiographic evidence of midpalatal suture separation during the deciduous and mixed dentitions has been demonstrated with lingual arch wire appliances of the w-arch”’ and quad-helix design.” Histologic findings, reported in conjunction with procedures, suggest that sutural sepslow expansion aration occurs at a rate which allows the maintenance of tissue integrity during adjustments to the maxillary repositioning and remodeling.lA. lH, 2’. “2. “5. ‘2,;. :I”. :I4 Ekstrom and co-workers”’ reported that the slowly expanded suture normally becomes well organized by mineralized tissue in about 30 days and is established within 3 months. Storey’” suggests that slow expansion
of 0.5 to 1.O mm. per week allows “physiologic sutural adjustments” with less traumatic disruption, a greater reparatory reaction, and greater sutural stability than rapid expansion of sutures. Other comparative effects reported include a reduced evidence of abutment tooth tipping’“. x and a reduced accumulation of residual stress loads within the expanded segments’“. x following slow maxillary expansion. In conjunction with the maintenance of sutural integrity and the reduced stress loads within the tissues, empirical observations reported by clinicians have indicated a reduced skeletal relapse potential following slow expansion procedures,14. 16. I!). 21. 22. 25. R-l,J4 Retention periods of 3 months or less appear adequate in allowing sutural regeneration and stabilization of slowly separated maxillary segments.lJ. 19,26, 4x In association with the palatal expansion of maxillary arches, various anatomic and functional changes have also been reported. An increase in nasal width has been demonstrated as a response to rapid palatal expansion.29,
:30. 35, 40-43,
4i.
ll-3i
A
rejated
reduction
in
nasal airway resistance has been quantitated by comparing pre-and postexpansion airway resistance,“‘-“” although this was not studied with a large sample or control group. Increasing maxillary arch width in the correction of functional posterior cross-bites may allow normal vertical closure patterns and aid in the establishment of symmetrical temporomandibular joint relationships.’ Translational movement of the deciduous dentition has been found to affect the position of underlying permanent teeth,“‘. 61 and early correction of cross-bites is thought to encourage favorable eruption of the manpatterns. I-6. K--II. 1X-51. 61-67 Expansion dibular arch in response to altered occlusion and muscle balance has been claimed to occur to a mild degree, I-). :(“, 1”+4:1,-1xalthough that has not been conclusively documented with a large sample and compared to a control group. A transient midline diastema may be evidenced during the early stages of palatal expansion,‘“, ‘o--13after which the bioelastic activity of the stretched periodontal and palatal tissues restores normal incisor alignment through mesially oriented uprighting movements. ‘S S’ The recoil tendency of the periodontal and palatal tissues and muscle actions in the lateral area are considered significant factors in returning expanded (that is, laterally tipped) posterior teeth to pretreatment angulation ranges, once retention is discontinued. “3 I93“. es+3’, “’ Even lengthy retention periods have a minimal effect in preventing some dental relapse or uprighting following maxillary
expansion.'l,
13. 18, 21. 42, 26, 29-31.
anticipation of this normal orthodontic
34, 3;i, 1X In
adjustment,
overexpansion of the desired maxillary arch width by approximately 2 to 3 mm. appears to be necessary in the expansion
protocol.9,
15. 2R, 35. 1X
An additional consideration in the stability of achieved maxillary arch expansions is the form of retention (that is, fixed versus removable). In the clinical study of slow maxillary expansion reported by Hicks,‘;’ the relapse amount was 10 to 23 percent with fixed retention, 22 to 25 percent with removable retention, and 45 percent with no retention. Other reports have similarly indicated more favorable relapse control with fixed retention appliances following maxillary expansion. 14. 3.5. 10-13. .5-l DISCUSSION
Although comparison of treatment results is complicated by differing experimental conditions, data interpretation, and the empirical nature of many reports, reviews of clinical and animal studies consistently document an enhanced orthopedic response to maxillary expansion procedures during the deciduous and mixed dentition periods. The increased sutural and skeletal response has been related to growth periods of high cellular activity with increased reparability potential and treatment prior to the formation of bony interlockings at maxillary articulations. In addition to the enhanced skeletal response, the early correction of posterior cross-bites may offer the advantages of redirecting the developing teeth into more normal positions, correcting asymmetries of condylar position, and allowing normal vertical closure of the mandible without functional shifts to avoid occlusal interferences. The long-term benefits of allowing a more harmonious occlusion may, at least theoretically, eliminate or minimize deleterious anatomic and functional growth factors. In conjunction with the enhanced response to maxillary expansion, early treatment appears to allow the use of less complex and lower-force expansion systems to achieve material increases in maxillary arch width. While the relative quantitative increments achieved with low-force, slow expansion procedures are less skeletally, they compare favorably with qualitative orthopedic/orthodontic changes reported during rapid expansion procedures in prepubertal age groups. The rate of midpalatal suture separation by slow expansion systems apparently allows a more physiologically tolerable response by the sutural elements than the disruptive nature of rapidly expanded maxillary segments. The enhanced maintenance of tissue integrity in slowly expanded sutural elements has been associated with a greater stability and less relapse potential during reor-
36
Bell
ganization of the maxillary complex. The resulting retention periods of 1 to 3 months in the slow expansion protocol are significantly shorter than the 3- to 6-month regimens recommended to sustain rapidly expanded maxillary arches. While the accumulated evidence appears to support a treatment rationale of early correction using a slow expansion procedure, individual variables must be considered in determining an expansion protocol that will optimally affect the quantity and quality of the expansive changes. Although fixed lingual arch wire expansion appliances may effectively increase maxillary arch width with a combination of orthopedic and orthodontic components during the deciduous and mixed dentitions, older patients may require the higher force systems of rapid expansion procedures or surgical intervention”*% Ii9 to achieve palatal separation. The primary consideration ultimately involves determination of the appropriate expansion protocol which would promote orthopedic movement of the maxillary segments while maintaining optimal tissue integrity and minimizing orthodontic tipping effects.
REFERENCES 1. Barnes, R. E.: The early expansion of deciduous arches and its effect on the developing permanent dentition, AM. J. ORTHOD. 42: 83, 1956. 2. Cheney, E. A.: Indications and methods for the interception of functional crossbites and interlockings, Dent. Clin. North Am.. pp. 385, July, 1959. 3. Clifford, F. 0.: Cross-bite correction in the deciduous dentition: Principles and procedures, AM. .I. ORTHOD. 59: 343, April, 1971. 4. Davis, J. M.: Why early treatment of crossbites? Dent. Digest 75: 449, 1969. 5. Harvold, E.: Some biological aspects of orthodontic treatment in the transitional dentition, AM. J. OR~HOD. 49: I, 1963. 6. Kutin, G., and Hawes, R. R.: Posterior cross-bites in the deciduous and mixed dentitions, AM. J. ORTHOD. 56: 491, 1969. 7. Myers, D. R., et al.: Condylar position in children with functional posterior crossbites: Before and after crossbite correction, Pediatr. Dent. 2: 190, 1980. 8. Moyers, R. E.: Handbook of orthodontics, ed. 3, Chicago. 1974, Yearbook Medical Publishers. 9. Sims, .I. M.: Minor tooth movement in children, St. Louis. 1972, The C. V. Mosby Company. IO. Ricketts, R. M.: Early treatment, J. Clin. Orthod. 13: 181, 1979. I I. Ficarelli, J. P.: A brief review of maxillary expansion, J. Pedodontics 3: 29, 1978. 12. Graber, T. M.: Orthodontics-Principles and practice, ed. 3. Philadelphia, 1972, W. B. Saunders Company. 13. Cleall, J. F., et al.: Expansion of the mid-palatal suture in the monkey, Angle Orthod. 35: 23, 1965. 14. Cotton, L. A.: Slow maxillary expansion: Skeletal versus dental response to low-magnitude force in Macc~ccr rnulatta, AM. J. ORTHOD. 73: I. 1978.
15. Hicks, E. P.: Slow maxillary expansion: A clinical study of the skeletal versus dental response to low-magnitude force. AM. J. ORTHOD. 73: 121, 1978. 16. Murray, J. M., and Cleall. J. F.: Early tissue response to rapid maxillary expansion in the midpalatal suture of the rhesus moneky, J. Dent. Res. 50: 1654. 1971. 17. Starnebach. J. K., and Cleall, J. F.: Effects of splitting the midpalatal suture on the surrounding structures, Ah!. J. OKI HOD. 50: 923, 1963. IX. Starnebach, H. K., et al.: Fdcioskeletal and dental changes resulting from rapid maxillary expansion, Angle Orthod. 36: 152, 1966. 19. Storey, E.: Tissue response to the movement of bone\, AM. J. OR7HOD. 64~229, 1973. 20. Barber, A. F., and Sims, M. R.: Rapid maxillary expansion and external root resorption in man: A scanning electron microscope study, AM. J. ORTHOD. 79: 630. 1981. 21. Storey, E.: Bone changes associated with tooth movement: A histological study of the effect of force in the rabbit, guinea pig. and rat, Aust. Dent. J. 59: 147, 1955. 22. Storey, E.: Bone changes associated with tooth movement: A histological study of the effect of force for varying durations in the rabbit, guinea pig, and rat, Aust. Dent. J. 59: 209, 1955. 23. Timms, D. J., and Moss, J. P.: An histological investigation into the effects of rapid maxillary expansion on the teeth and their supporting tissues. Trans. Eur. Orthod. Sot.. pp. 263, 1971. 24. Brossman, R. E., et al.: Faciohkeletal remodeling resulting from rapid palatal expansion in the monkey. Arch. Oral Biol. 18: 987, 1973. 25. Isaacson, R. J., and Ingram, A. H.: Forces produced by rapid maxillary expansion. Il. Forces present during treatment, Angle Orthod. 34: 261, 1964. 26. Ekatrom, C., et al: Mineralization in the midpalatal suture after orthodontic expansion, A~I. J. OKTHOD. 71: 449, 1977. 27. Ten Cate. A. R., Freeman, E.. and Dickinson. J. B.: Sutural development and its response to rapid expansion, Alvl. J. ORTHOD.
71: 622,
1977.
28. Isaacson, R. J.. and Murphy, T. D.: Some effects of rapid maxillary expansion in cleft lip and palate patients. Angle Orthod 34: 143, 1964. 29. Kreba. A. A.: Expansion of the midpalatal suture studied by means of metallic implants, Acta Odontol. Stand. 17: 491. 1959. 30. Krebs, A. A.: Midpalatal suture expansion studied by the implant method over a seven-year period, Trans. Eur. Orthod. Sot. pp. 131, 1964. 31. Muguerza. 0. E., and Shapiro. P. A.: Palatal mucoperiostomy-an attempt to reduce relapse after slow maxillary expansion, AM. J. ORTHOD. 78: 548. 1980. 32. Ohshima, 0.: Effect of lateral expansion force on the maxillary suture in cynomolgus monkey. J. Osaka Dent. Univ. 6: I I. 1972. 33. Rune, B., et al.: Movement of maxillary segments after expansion and/or secondary bone grafting in cleft lip and palate-A roentgen stereogrammetric study with the aid of metallic implants, AM. J. ORTHOD. 77: 643, 1980. 34. Storey, E.: Bone changes associated with tooth movement: Histological study of the effect of age and sex in the rabbit and guinea pig, Aust. Dent. J 59: 210, 1955. 35: Wertz. R. A.: Skeletal and dental changes accompanying rapid mldpalatal suture opening, AM. J. ORTHOD. 58: 41, 1970. 36. Timms, D. J.: A study of basal movement with rapid maxillary expansion, AM. J. ORTHOD. 77: 500, 1980.
37. Davis, W. M., and Kronman, J. H.: Anatomical changes induced by splitting of the midpalatal suture, Angle Orthod. 39: 126, 1969. 38. Debbane, E. F.: A cephalometric and histologic study of the effect of orthodontic expansion of the midpalatal suture of the cat, AM. J. ORTHOD. 44: 187, 1958. 39. Gardner, E., and Kronman, J. H.: Craniofacial displacements caused by rapid palatal expansion in the rhesus monkey, AM. J. ORTHOU.
40.
41. 42. 43. 44. 45.
46. 47.
48.
49.
50.
59:
146,
72: 422,
ORTHOD.
55.
1971.
Haaa. A. J.: Rapid expansion of the maxillary dental arch and nasal cavity by opening of the midpalatal suture, Angle Orthod. 31: 73. 1961. Haaa. A. J.: The treatment of maxillary deficiency by opening the midpalatal suture, Angle Orthod. 35: 200, 1965. Haas. A. J.: Palatal expansion: Just the beginning of dentofacial orthopedics, AYI. J. ORTHOD. 57: 219, 1970. Haas. A. J.: Longterm posttreatment evaluation of rapid palatal expansion. Angle Orthod. 50: 189, 1980. Halpern, M. R.: Maxillary changes during rapid palatal expanjion, AM. J. ORTHOD. 57:90, 1970. Heflin. B. M.: A three-dimensional cephalometric study of the Influence of expansion of the midpalatal suture on the bones of the face, AM. J. ORTHOD. 57: 194, 1970. Mayoral. P., and Aristeguita, R.: What happens with palatal dysfunction (Abstr.), J. Clin. Orthod. 12: 561, 1978. Thorne. H.: Expansion of the maxilla spreading the midpalatal suture, measuring the widening of the apical base and the nasal cavity on serial roentgenograms (Abstr.), AM. J. ORTHOD. 46: 626, 1960. Bell, R. A., and LeCompte, E. J.: The effects of maxillary expansion using a quad-helix appliance during the deciduous and mixed dentitions, Aw. J. ORTHOD. 79: 152, 1981. Berlocher, W. C., et al: The effect of maxillary palatal expansion on the primary dental arch circumference, Pediatr. Dent. 2: 27. 1980. Chaconas, S. J., and de Albay Levy, J. A.: Orthopedic and orthodontic applications of the quad-helix appliance, AM. J. ORTHOD.
morphology and skeletal maturation on rapid palatal expansion in children, Trans. Eur. Orthod. Sot., pp. 499, 1972. 53. Skieller, V.: Expansion of the midpalatal suture by removable plates, analysed by the implant method, Trans. Eur. Orthod. Sot., pp. 143, 1964. 54. Korkhaus, G.: Present orthodontic thought in Germany, AM. J.
1977.
Harberson, V. A., and Myers, D. R.: Midpalatal suture opening during functional cross-bite correction, AM. J. ORTHOD. 74: 310, 1978. 52. Melsen. B. A.: A histological study of the influence of sutural
56. 57. 58.
59.
60. 61. 62. 63. 64.
65. 66.
67. 68.
51.
69.
46:
187,
1960.
Brin, I., et al.: Rapid palatal expansion in cats-Effect of age on sutural cyclic nucleotides, AM. J. ORTHOD. 79: 163, 1981. Schulhof, R. J.: Consideration of airway in orthodontics, J. Clin. Orthod. 12: 440, 1978. Wertz. E. A.: Changes in nasal airflow incident to rapid maxillary expansion, Angle Orthod. 38: 1, 1968. Linder-Aronson, S., and Aschan, G.: Nasal resistance to breathing and palatal height before and after expansion of the median palatine suture, Odontol. Revy 14: 254, 1963. Hershey, H. G., Stewart, B. L., and Warren, D. W.: Changes in nasal airway resistance associated with rapid maxillary expansion, AM. J. ORTHOD. 69: 274, 1976. Breitner, C.: The influence of moving deciduous teeth on the permanent successors, AM. J. ORTHOD. 26: 1152, 1940. Matthews, J. R.: Translational movement of first deciduous molars into second molar position, AM. J. ORTHOD. 55: 276, 1969. Buck, D. L.: The fixed W-arch for correction of posterior crossbites in children, J. Am. Dent. Assoc. 81:1140, 1970. Matthews, J. R.: Malocclusion in the primary dentition, Dent. Clin. North Am., pp. 466, July, 1966. Mehta, J. D., and Barnett, E. M.: Use of the lingual arch for space maintenance and minor tooth movement, J. Can. Dent. Assoc. 36: 228, 1970. Mueller, B. H., et al.: Rapid palatal expansion in the primary dentition, Texas Dent. J. 94: 6, 1976. Wickwire, N. A.: A simple technique for correction of bilateral maxillary dental constriction in the primary and mixed dentition, Dent. Clin. North Am., pp. 151, January, 1973. Wood, W.: Anterior and posterior crossbites, J. Dent. Child. 29: 280, 1962. Bell, W. H., and Turvey, T. A.: Surgical correction of posterior crossbite, J. Oral Surg. 32: 811, 1974. Kennedy, J. W., et al.: Osteotomy as an adjunct to rapid maxillary expansion, AM. J. ORTHOD. 70: 123, 1976.
A. Bell, D.D.S., M.D.* Go.
Treatment variables such as patient age, rate of expansion, magnitude of applied transverse force, appliance design, and retention protocol produce an array of interactions which affect orthopedic and orthodontic movements during maxillary expansion procedures, The purpose of this article is to review the quantitative and qualitative changes of sutural, skeletal, and dental tissues demonstrated in human and animal studies of maxillary expansion procedures. The association of the reported tissue responses with the treatment variables of patient age and rate of expansion serve as the focus of discussion. While the accumulated evidence appears to support a treatment rationale of early correction using a slow expansion procedure, individual variables must be considered in determining an expansion protocol that will optimally affect the quantity and quality of the expansion changes.
Key words: Review, maxillary, expansion, rate, age
T
he early correction of posterior cross-bites requiring maxillary expansion has been advocated to redirect the developing teeth into more normal positions,‘-” eliminate untoward temporomandibular joint positions and mandibular closure patterns,2s 5, i and make beneficial dentoskeletal changes during growth periods involving a reduced treatment complexity and time.XP”’ The purpose of this article is to review the literature concerning the quantitative and qualitative effects of maxillary expansion on connective, skeletal. and dental tissues. The role that patient age and rate of expansion may play as treatment variables in maxillary expansion procedures will serve as a focus for review and discussion.
This stage of orthodontic response appears to be essentially complete within a week.“, *L 17, l9 Subsequent orthodontic movements will occur through bodily translation as the compressed buccal alveolar plate resorbs at the root-periodontal interface from continued force application.‘*23 If the applied transverse forces are of sufficient magnitude to overcome the bioelastic strength of sutural elements, orthopedic separation of the maxillary segments can occur.‘3-‘9, 2’. a~,24x25The separation and repositioning of the palatal segments will continue until the force distribution is reduced below the tensile strength of the sutural elements.“‘. 2’. pZ,~3 25Reorganization and remodeling of the sutural connective and skeletal tissues may then proceed in the stabilization of the
REVIEW
OF LITERATURE
Increased maxillary arch width has been related to orthodontic movements, orthopedic movements, or a combination of these movements during expansion procedures.H, ‘I. I2 While the relative degree and nature of these movements is affected by various factors, the general pattern of maxillary expansion may be described. Upon the application of transverse biomechanical forces, initial changes involve the lateral tipping of the posterior maxillary teeth as the periodontal and palatal soft tissues are compressed and stretched.‘“P’” *Associate Profesor, Department cal College of Georgia.
32
of Pedodontics,
School of Dentistry,
Medi-
expanded
maxillary
arch.‘:‘,
19,
“1,
“2,
“(i.
“i
When
orthopedic separation of the maxillary segments occurs, asymmetric linear and angular responses have generally been
obseped,l3-19,
21.
2‘2.
24,
25.
‘LX-35
The
asymmetric
expansion has been attributed to variations in the rigidity of the different maxillary articulations.““. Z’sA frontal view of orthopedic sutural separation shows a lateral rotation or tipping of the palatal halves. 19,21.22.‘1. “3. :33.36 The palatal movement is greater at the alveolar crest and less at the palatal vault, presenting a triangular expansion pattern with the base near the incisors and the apex toward the nasal areal4, 15. 19, 21, 12. 24. 26, 29, X0, Xl-4i (Fig. 1,A). From an accusal view, the greatest opening of the midpalatal suture has been found anteriorly, with progressively lessseparation toward the posterior’“. :‘z :‘H,M-~“. ‘x 0002.9416/82/010032+06$00.60/0
0
1982 The C
V Mosby Co
Review
(Fig. 1,B). Inthesagittalplane,adownwardandforward displacement of the maxilla with opening of the bite has the finding is not been reported, 19,22,34,35%40-43though always demonstrated after treatment.“’ ‘i5 A significant skeletal component of the increased arch width is generally considered a desirable product of maxillary expansion procedures as orthopedic changes allow coordination of the maxillary and mandibular bases in establishing a stable correction of transverse skeletal and/or dentoskeletal malocclusions, IO. 15. 193 203 :M* 40-43 The relative amount of skeletal versus dental changes occurring in maxillary expansion procedures has been primarily related to the treatment variables of patient age and rate of expansion (that is, magnitude of applied force, appliance design). Clinicians have commonly reported difficulty in producing palatal separation following the pubertal growth orthopedic reperiod, 1.i. 29. :30. 35. W-43 while favorable sponses have been indicated prior toi’s Zy, 30, M* 4851 and
during
pubertal
growth.l.5.
29, 30, 3.5, 40-43,
of maxillary
expansion
33
0
52, 53 A
direct relationship between increased resistance to skeletal expansion and increasing patient age has been quantified”” and associated with the formation of mechanical interlockings at maxillary articulations as early the as 12 to 13 years of age.‘“, 2X, 32, 32 In addition, enhanced skeletal response in younger age groups has been associated with a greater cellular activity in the growing
suture.13.
14
19s %I.
2%. 24,
27,
31,
.iS Brin
and
co-workers ,j5 using the measurement of cyclic nucleotides as indicators of cellular activity and new bone formation, reported that the sutural bone cells of young cats were more responsive to palatal expansion forces than the corresponding cells of old animals. Ten Cate and associates” reported that the sutural tissues in young growing rats were characterized by increased fibroblastic, fibroclastic, and osteoblastic activity following rapid expansion in contrast to a less marked activity in more mature animals. The treatment variable most critically evaluated in the literature in relation to maxillary expansion changes has been the rate of expansion. In rapid expansion procedures employing jackscrew appliances (Fig. 2, A) expansion generally occurs at a rate of about 0.2 to 0.5 mm. per day during an active treatment time of 1 to 3 weeks .“;,. ZL SZ,4”-43 The individual activation schedule has been most often determined on an empirical basis, dependent on the amount of expansion desired and the patient’s tolerance. Isaacson and Ingram’” reported that single activations of jackscrew appliances produce forces in the 3- to lo-pound range, while multiple daily activations can result in cumulative loads of 20 pounds or more, Such high-magnitude forces maximize orthopedic separation of the bony segments by disruptively
Fig. 1. A, Triangular pattern of maxillary expansion in the frontal plane includes orthopedic and orthodontic movement. Orthopedic changes may involve separation at sutural sites with a lateral rotation or tipping of the palatal halves, widening of the nasal processes, and subsequent bony remodeling. Orthodontic changes may involve lateral tipping and bodily translation of maxillary teeth, transient midline diastema, and mild expansion of mandibular teeth. 6, Occlusal view of maxillary expansion illustrating midpalatal suture opening with greatest separation occurring anteriorly, lateral rotation of palatal halves, bony remodeling of maxillary elements, and lateral/rotational movement of the maxillary teeth.
overwhelming sutural tissues before substantial orthodontic movement and/or physiologic changes can occur within the tissue.‘“. ~3 4’t42 The relative skeletal and dental components produced by rapid palatal expansion have been evaluated with the use of standardized nonanatomic reference points (for example, implants) and frontal cephalograms .2ga0 KrebsZg, 3o reported average dental arch increases of 6.0 mm (0.5 to 10.3 mm. range) for twenty-three subjects aged 8 to 19 years, with the total arch increase twice that of the basal maxillary segments. Cottoni and Hicks,‘” using the Krebs data, estimated that one third to one half the achieved maxillary arch width increase was due to skeletal separation, with the remainder being of dental origin. The analysis
34
Bell
ments heal in a unique proliferative response which ultimately leads to a regeneration of the suture,“’ a stable maxillary complex is not achieved until residual forces which tend to collapse the expanded segments are dissipated. “‘. “I, 42, “3 x Insufficient retention periods have resulted in substantial, even total, skeletal relapse.‘!‘, ” Retention periods of 3 to 6 months are normally recommended to allow reorganization and stabilization of rapidly expanded maxillary sutures, I!,. “I. “2. ‘ii. 29.:jo.:I’. :C -I~,ZJ with even longer periods advocated by some clinicians, P:j,-10--,:1 Evidence of iatrogenic resorptive pro-
Fig. 2. A, Rapid ance. B, Lingual
palatal expansion emplying a jackscrew arch wire appliance of the quad-helix
applitype.
of the Krebs rapid expansion data also demonstrated that the skeletal changes accounted for approximately one half the increased arch width in 8 to 12 year-olds and about one third of the increase in 13 to 19-year-old subjects.” 20. :N The range of maxillary arch width increases reported by Kreb? X’ is representative of other quantitative amounts reported following rapid expansion procedures,:i,i. ~0~?:1,~9 Human and animal studies have documented extensive bone and sutural activity at the fine structural level during rapid maxillary expansion. Brossian and associates’” found gross separation of the palate segments, bone deposition over external surfaces of the maxillary complex, and significant deformation of maxillary bones following rapid palatal expansion in monkeys, The histologic picture of rapidly expanded sutural tissues has included reports of free-floating bone fragments and numerous microfractures,:=% x cystlike formations ‘!A s’. 22 highly vascular disorganized connective tissu; of an inflammatory nature, 13.16 I!,, 14,38,92.5.iand a rapid dystrophic ossification with immature bone tissue.“‘, “, XL 5x While the sutural connective tissue ele-
cesseson the root surfaces of anchor teeth demonstrated up to 9 months postexpansion suggest the potential for long-term activity of the residual loads.“‘, ‘?x Slow expansion procedures, such as those involving the use of lingual arch wire appliances with expansive capability (Fig. 2, B), incorporate force systems of several ounces up to approximately 2 pounds.“‘, ‘I. “. “. “’ The slow expansion procedures increase the percentage of orthodontic movements as the tensile strength of the suture elements is not overwhelmed.X. I”. Ii. I”. I” ” However, orthopedic separation of the maxillary segments has been documented as a component of slow maxillary expansion in both human’;‘, ‘j’. lx, “. iti and primate’:‘. I1 studies, particularly in younger age groups with deciduous and/or mixed dentitions. Using standardized reference procedures in analyzing serial frontal cephalograms obtained during slow expansion treatment (0.5 mm. per week), SkielleP attributed approximately 20 percent of the arch width increase to orthopedic Hicks.‘” using separation of the midpalatal suture. 2-pound forces with expansion rates of 0.4 to 1. I mm. per week, achieved maxillary arch width increases of from 3.8 to 8.7 mm. during treatment. With the use of nonanatomic reference points, Hicks’” estimated that the skeletal changes represented 24 to 30 percent of the total arch width increase in 10 to I l-year-old patients and 16 percent in the 14 to 15-year-olds. While not documenting the relative degree of orthopedic versus orthodontic changes, radiographic evidence of midpalatal suture separation during the deciduous and mixed dentitions has been demonstrated with lingual arch wire appliances of the w-arch”’ and quad-helix design.” Histologic findings, reported in conjunction with procedures, suggest that sutural sepslow expansion aration occurs at a rate which allows the maintenance of tissue integrity during adjustments to the maxillary repositioning and remodeling.lA. lH, 2’. “2. “5. ‘2,;. :I”. :I4 Ekstrom and co-workers”’ reported that the slowly expanded suture normally becomes well organized by mineralized tissue in about 30 days and is established within 3 months. Storey’” suggests that slow expansion
of 0.5 to 1.O mm. per week allows “physiologic sutural adjustments” with less traumatic disruption, a greater reparatory reaction, and greater sutural stability than rapid expansion of sutures. Other comparative effects reported include a reduced evidence of abutment tooth tipping’“. x and a reduced accumulation of residual stress loads within the expanded segments’“. x following slow maxillary expansion. In conjunction with the maintenance of sutural integrity and the reduced stress loads within the tissues, empirical observations reported by clinicians have indicated a reduced skeletal relapse potential following slow expansion procedures,14. 16. I!). 21. 22. 25. R-l,J4 Retention periods of 3 months or less appear adequate in allowing sutural regeneration and stabilization of slowly separated maxillary segments.lJ. 19,26, 4x In association with the palatal expansion of maxillary arches, various anatomic and functional changes have also been reported. An increase in nasal width has been demonstrated as a response to rapid palatal expansion.29,
:30. 35, 40-43,
4i.
ll-3i
A
rejated
reduction
in
nasal airway resistance has been quantitated by comparing pre-and postexpansion airway resistance,“‘-“” although this was not studied with a large sample or control group. Increasing maxillary arch width in the correction of functional posterior cross-bites may allow normal vertical closure patterns and aid in the establishment of symmetrical temporomandibular joint relationships.’ Translational movement of the deciduous dentition has been found to affect the position of underlying permanent teeth,“‘. 61 and early correction of cross-bites is thought to encourage favorable eruption of the manpatterns. I-6. K--II. 1X-51. 61-67 Expansion dibular arch in response to altered occlusion and muscle balance has been claimed to occur to a mild degree, I-). :(“, 1”+4:1,-1xalthough that has not been conclusively documented with a large sample and compared to a control group. A transient midline diastema may be evidenced during the early stages of palatal expansion,‘“, ‘o--13after which the bioelastic activity of the stretched periodontal and palatal tissues restores normal incisor alignment through mesially oriented uprighting movements. ‘S S’ The recoil tendency of the periodontal and palatal tissues and muscle actions in the lateral area are considered significant factors in returning expanded (that is, laterally tipped) posterior teeth to pretreatment angulation ranges, once retention is discontinued. “3 I93“. es+3’, “’ Even lengthy retention periods have a minimal effect in preventing some dental relapse or uprighting following maxillary
expansion.'l,
13. 18, 21. 42, 26, 29-31.
anticipation of this normal orthodontic
34, 3;i, 1X In
adjustment,
overexpansion of the desired maxillary arch width by approximately 2 to 3 mm. appears to be necessary in the expansion
protocol.9,
15. 2R, 35. 1X
An additional consideration in the stability of achieved maxillary arch expansions is the form of retention (that is, fixed versus removable). In the clinical study of slow maxillary expansion reported by Hicks,‘;’ the relapse amount was 10 to 23 percent with fixed retention, 22 to 25 percent with removable retention, and 45 percent with no retention. Other reports have similarly indicated more favorable relapse control with fixed retention appliances following maxillary expansion. 14. 3.5. 10-13. .5-l DISCUSSION
Although comparison of treatment results is complicated by differing experimental conditions, data interpretation, and the empirical nature of many reports, reviews of clinical and animal studies consistently document an enhanced orthopedic response to maxillary expansion procedures during the deciduous and mixed dentition periods. The increased sutural and skeletal response has been related to growth periods of high cellular activity with increased reparability potential and treatment prior to the formation of bony interlockings at maxillary articulations. In addition to the enhanced skeletal response, the early correction of posterior cross-bites may offer the advantages of redirecting the developing teeth into more normal positions, correcting asymmetries of condylar position, and allowing normal vertical closure of the mandible without functional shifts to avoid occlusal interferences. The long-term benefits of allowing a more harmonious occlusion may, at least theoretically, eliminate or minimize deleterious anatomic and functional growth factors. In conjunction with the enhanced response to maxillary expansion, early treatment appears to allow the use of less complex and lower-force expansion systems to achieve material increases in maxillary arch width. While the relative quantitative increments achieved with low-force, slow expansion procedures are less skeletally, they compare favorably with qualitative orthopedic/orthodontic changes reported during rapid expansion procedures in prepubertal age groups. The rate of midpalatal suture separation by slow expansion systems apparently allows a more physiologically tolerable response by the sutural elements than the disruptive nature of rapidly expanded maxillary segments. The enhanced maintenance of tissue integrity in slowly expanded sutural elements has been associated with a greater stability and less relapse potential during reor-
36
Bell
ganization of the maxillary complex. The resulting retention periods of 1 to 3 months in the slow expansion protocol are significantly shorter than the 3- to 6-month regimens recommended to sustain rapidly expanded maxillary arches. While the accumulated evidence appears to support a treatment rationale of early correction using a slow expansion procedure, individual variables must be considered in determining an expansion protocol that will optimally affect the quantity and quality of the expansive changes. Although fixed lingual arch wire expansion appliances may effectively increase maxillary arch width with a combination of orthopedic and orthodontic components during the deciduous and mixed dentitions, older patients may require the higher force systems of rapid expansion procedures or surgical intervention”*% Ii9 to achieve palatal separation. The primary consideration ultimately involves determination of the appropriate expansion protocol which would promote orthopedic movement of the maxillary segments while maintaining optimal tissue integrity and minimizing orthodontic tipping effects.
REFERENCES 1. Barnes, R. E.: The early expansion of deciduous arches and its effect on the developing permanent dentition, AM. J. ORTHOD. 42: 83, 1956. 2. Cheney, E. A.: Indications and methods for the interception of functional crossbites and interlockings, Dent. Clin. North Am.. pp. 385, July, 1959. 3. Clifford, F. 0.: Cross-bite correction in the deciduous dentition: Principles and procedures, AM. .I. ORTHOD. 59: 343, April, 1971. 4. Davis, J. M.: Why early treatment of crossbites? Dent. Digest 75: 449, 1969. 5. Harvold, E.: Some biological aspects of orthodontic treatment in the transitional dentition, AM. J. OR~HOD. 49: I, 1963. 6. Kutin, G., and Hawes, R. R.: Posterior cross-bites in the deciduous and mixed dentitions, AM. J. ORTHOD. 56: 491, 1969. 7. Myers, D. R., et al.: Condylar position in children with functional posterior crossbites: Before and after crossbite correction, Pediatr. Dent. 2: 190, 1980. 8. Moyers, R. E.: Handbook of orthodontics, ed. 3, Chicago. 1974, Yearbook Medical Publishers. 9. Sims, .I. M.: Minor tooth movement in children, St. Louis. 1972, The C. V. Mosby Company. IO. Ricketts, R. M.: Early treatment, J. Clin. Orthod. 13: 181, 1979. I I. Ficarelli, J. P.: A brief review of maxillary expansion, J. Pedodontics 3: 29, 1978. 12. Graber, T. M.: Orthodontics-Principles and practice, ed. 3. Philadelphia, 1972, W. B. Saunders Company. 13. Cleall, J. F., et al.: Expansion of the mid-palatal suture in the monkey, Angle Orthod. 35: 23, 1965. 14. Cotton, L. A.: Slow maxillary expansion: Skeletal versus dental response to low-magnitude force in Macc~ccr rnulatta, AM. J. ORTHOD. 73: I. 1978.
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28. Isaacson, R. J.. and Murphy, T. D.: Some effects of rapid maxillary expansion in cleft lip and palate patients. Angle Orthod 34: 143, 1964. 29. Kreba. A. A.: Expansion of the midpalatal suture studied by means of metallic implants, Acta Odontol. Stand. 17: 491. 1959. 30. Krebs, A. A.: Midpalatal suture expansion studied by the implant method over a seven-year period, Trans. Eur. Orthod. Sot. pp. 131, 1964. 31. Muguerza. 0. E., and Shapiro. P. A.: Palatal mucoperiostomy-an attempt to reduce relapse after slow maxillary expansion, AM. J. ORTHOD. 78: 548. 1980. 32. Ohshima, 0.: Effect of lateral expansion force on the maxillary suture in cynomolgus monkey. J. Osaka Dent. Univ. 6: I I. 1972. 33. Rune, B., et al.: Movement of maxillary segments after expansion and/or secondary bone grafting in cleft lip and palate-A roentgen stereogrammetric study with the aid of metallic implants, AM. J. ORTHOD. 77: 643, 1980. 34. Storey, E.: Bone changes associated with tooth movement: Histological study of the effect of age and sex in the rabbit and guinea pig, Aust. Dent. J 59: 210, 1955. 35: Wertz. R. A.: Skeletal and dental changes accompanying rapid mldpalatal suture opening, AM. J. ORTHOD. 58: 41, 1970. 36. Timms, D. J.: A study of basal movement with rapid maxillary expansion, AM. J. ORTHOD. 77: 500, 1980.
37. Davis, W. M., and Kronman, J. H.: Anatomical changes induced by splitting of the midpalatal suture, Angle Orthod. 39: 126, 1969. 38. Debbane, E. F.: A cephalometric and histologic study of the effect of orthodontic expansion of the midpalatal suture of the cat, AM. J. ORTHOD. 44: 187, 1958. 39. Gardner, E., and Kronman, J. H.: Craniofacial displacements caused by rapid palatal expansion in the rhesus monkey, AM. J. ORTHOU.
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morphology and skeletal maturation on rapid palatal expansion in children, Trans. Eur. Orthod. Sot., pp. 499, 1972. 53. Skieller, V.: Expansion of the midpalatal suture by removable plates, analysed by the implant method, Trans. Eur. Orthod. Sot., pp. 143, 1964. 54. Korkhaus, G.: Present orthodontic thought in Germany, AM. J.
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Harberson, V. A., and Myers, D. R.: Midpalatal suture opening during functional cross-bite correction, AM. J. ORTHOD. 74: 310, 1978. 52. Melsen. B. A.: A histological study of the influence of sutural
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