Age effects on orthodontic treatment: Adolescents contrasted with adults Gregory S. Dyer, DDS, MS, Edward F. Harris, PhD, and James L. Vaden, DDS, MS Memphis, Tenn. Skeletodental treatment changes in 30 adolescent girls and 26 women who had Class II, Division 1 malocclusions were contrasted cephalometrically, primarily with the McNamara analysis. The data show that adult treatment does not obligate the practitioner to longer treatment. In this study, both age groups were treated in 2.5 years on the average. Apical base corrections were achieved with equal facility in both groups by the posterior remodeling of point A, and this (in conjunction with unrestrained mandibular growth) is the major source of correction in the adolescents. In adults, in whom growth is trivial, an appreciable source of sagittal correction is the steepening of the occlusal plane. Several sequelae of Class II elastLc force occurred as by-products of molar correction in the adults: increased mandibular molar eruption, increased maxillary molar intrusion, increased maxillary incisor eruption, increased mandibular incisor intrusion, and steepening of the occlusal plane. (AM J ORTHOD DENTOFACORTHOP 1991 ;100:523-30.)
T h e r e has been a substantial increase in the proportion of adult patients in orthodontic practices over the last several years. 1"3 This trend has evolved from increased experience with adult treatment, increased public awareness of the availability of treatment, and decreased numbers of preadult patients in some areas. The effect of the patient's age on the nature of correction of malocclusions has received line study, but it would seem presumptuous to think that we can simply transfer our conventional treatment to the adult condition. 4'~ In the conventional adolescent patient, a substantive degree of correction--particularly in the sagittal plane--is achieved by differential growth of the two jaws. 6 Because of physiologic differences between adolescent and adult patients, s'79 there may well be differences in the way malocclusions are corrected in these two groups. Since adults do not experience any substantive growth during treatment, combined with physiologic bone differences, this would be a reasonable hypothesis. The purpose of this investigation was to quantitate differences in the nature of the correction of malocclusion dependent on the patient's age at the time of treatment.
Bone remodeling in adulthood After skeletal maturity at approximately the age of 20 years, the amount of cortical bone in many different bones has been reported to decrease as a normal acFrom the Department of Orthodontics, College of Dentistry, University of Tennessee. 8/1/24329
companiment of the aging process,t°'12 Epker et al. la have documented a progressive thinning of cortical bone after adulthood is attained, stemming from enlargement of the marrow cavity due to a negative bone balance at the cortical-endosteal surface in excess of a positive balance at the periosteal surface. Liu et al. 14assessed alveolar bone samples obtained at autopsy and during third molar extractions. A significant decrease was seen in pore volume with increasing age along with a decrease in lacunar-canalicular pore diameter and an increase in density. This increase in alveolar bone density contrasts with several studies of bone elsewhere in the body (primarily the vertebrae) that report gradual decreases in trabecular bone density, commencing around 25 years Of age and continuing into old age.tS~7
Periodontal changes In the growing child, the tooth-supporting tissues are in a state of proliferation, i8 Within the periodontal ligament and in marrow spaces surrounding the alveolus, large numbers of connective tissue cells are actively involved in alveolar growth and remodeling. Within cancellous bone of the alveolus there is a rich blood supply to assist in metabolism, and in the medullary region the large marrow spaces provide bone trabeculae with considerable surface area that facilitates the activities of osteoblasts and osteoclasts.t9 Reitan I8 found bone resorption on the pressure side of teeth after a delay of about 4 days after the application of 50 gm of continuous force in a 39-year-old man. Bone apposition onthe tension side, however, was evident only after 8 days of force application. This lag in 523
524
Dyer, Harris, and Vaden
Am. J. Orthod.Dentofac. Orthop. December 1991
45
Adolescents
40
Adults l
35~
-13o 25 .
0.75). Comparable reductions were also observed in the SNA and the measure nasion-perpendicular to point A. None of these maxillary skeletal parameters exhibited a significantly different in-treatment change between adolescents and adults (Table III). Maxillary dental. The horizontal maxillary dental measurements, which differed at the pretreatment examination (upper molar horizontal was greater in the adults), converged enough with treatment and growth to be statistically indistinguishable at the end of treatment. Midfacial growth carried the first molar forward significantly relative to pterygoid-vertical (PtV) in the adolescents (x = 2.5 mm), whereas the absence of this growth in the adults contributed to the molar remaining in the same average position. In fact, this molar movement is probably spurious since it is unsupported through closer scrutiny. 31 Instead, the increase in upper molar horizontal almost certainly reflects growth at intermediate bony sites between PtV and the molar rather than true tooth movement. The vertical component of molar movement was also significant. Growth in the adolescents carried the molar down an average of 1.9 m m compared with the 1.0 m m of intrusion observed in the adults.
Treatment in adolescents and adults 525
Table I. Statistics regarding initial-records age, age at the end of active treatment, and treatment time of the adolescents and adults Variable Sample size
Adolescents
[
Adults
30
26
12.52 0.67 13.88 11.37
27.57 5.38 40.07 21.14
14.98 0.80 16.45 13.22
30.14 5.39 42.36 23.39
2.46 0.36 3.41 1.46
2.56 0.35 3.23 1.97
Initial records Mean age (yr) SD Maximum Minimum
End of treatment
Mean age (yr) SD Maximum Minimum Treatment time Mean duration (yr) SD Maximum Minimum
Complementary measures of the horizontal position of the upper incisor (upper incisor horizontal and upper incisor/point A) revealed a significant but similar degree of retraction of the upper incisor in the two groups. Incisor retraction helps camouflage the skeletal disharmony; the normative value for incisor/point A (point A perpendicular to the facial surface of central incisor horizontally) is 4 to 6 ram. 25 The posttreatment values for the adolescents and the adults for incisor/point A were 0.6 mm and 0.3 m m , respectively. The vertical position of the upper incisor did not change significantly in either age group. There was, however, a trend toward enhanced eruption in the adults (x = 1.6 m m for adults, 0.7 mm for adolescents). The AOBO discrepancies 3° were significantly different before treatment (~ = 3.1 mm for adolescents, 5.3 m m for adults), with each exhibiting a significant reduction during treatment. The adults displayed a much greater AOBO change during treatment, with a finished mean value of - 0 . 2 m m compared with the adolescents' 0.3 mm. One must remember that this measure is taken along Downs' occlusal plane (OP), which is considerably steepened in the adults. This change in cant of the occlusal plane will mimic an improved apical base relationship. The cant of the occlusal plane changed significantly between age grades. The adults experienced almost a fourfold increase in steepness relative to the adolescents. The application of Class II elastics during treatment is suggested to produce this response. Mandibular skeletal. Mandibular growth in the adolescents resulted in significant increases in both man-
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Am. J. Orthod. Dentofac, Orthop. December 1991
Table II, Descriptive and inferential statistics, b y age, for the skeletodental variables assessed at the start of treatment Adults (n --- 26)
Adolescents (n = 30)
F Variable
SE
X
SE
ratio¢
Maxillary skeletal
Condylion-A point SNA angle Naslon perpendiculartpoint A
93,36 81.38 - 2.17
0.81 0.75 0.63
93.33 80.40 -3.36
1.29 0.57 0.71
0,0 1,1 1.6
26.09 45,59 5.07 57.97 53.19 3.05 10,22 11.99
0.69 0.56 0,47 0.77 0.69 0.44 0.72 0.80
29,98 50.71 6.27 59.87 55.76 5,30 7.91 10.04
0.84 0.76 0.81 1.31 0.92 0,51 1.11 1.20
12.9" 30.6* 1.8 1.7 5.2* i1,1' 3.2 1,9
113.46 73.99 - 11.36 83.93 76.34
1.02 0.84 0.96 0.51 0.69
117.76 75.74 - 13.08 83,61 75.52
1.58 1.11 1,61 0.77 0.66
5.5' 1.6 0.9 0.1 0.7
--31,77 29.74 2,23 5.91 40.37 96.30 56.62
0.51 0.40 0.30 0.48 0.53 1.05 1.12
-30.62 31.84 2.91 7.83 43.59 94.69 56.10
0.66 0.80 0.40 0.69 0.87 1.53 1.54
2.0 6.0* 1.9 5.4* 10.6' 0.8 0.1
64.89 52.66 27.07 90,06 60,36
1.01 0.80 0.92 0.73 0.60
69.22 56.62 29.20 92.75 62.72
1.65 1.37 1,65 1.35 0.99
5.3* 6.7* 1.4 3.3 4.4*
Maxillary dental
Upper molar horizontal Upper molar vertical Upper incisor/point A Upper incisor horizontal Upper incisor vertical AOBO discrepancy Downs' OP to FH Functional OP to FH Mandibular skeletal
Mandibular length Corpus length Pogonion/N perpendicular Facial angle SNB angle Mandibular dental
Lower molar horizontal Lower molar vertical Lower incisor/A-pogonion Lower incisor horizontal Lower incisor vertical IMPA FMIA Vertical
Anterior facial height Posterior facial height Mandibular plane angle Facial axis angle Y axis angle *p < 0.05. tThe F ratio tests for age differences.
dibular and corpus lengths (2.5 rnm and 1.6 ram). The small increase i n facial angle ( F H - N P ) in the adolescents, coupled with the slight decrease in the adults, resulted in a significant difference in the amounts of intreatment change. P o g o n i o n to n a s i o n - p e r p e n d i c u l a r and the SNB angle did not change significantly, either within or among groups. M a n d i b u l a r d e n t a l . The lower molar moved vertically and horizontally i n both the adolescents and the adults with appreciably greater forward m o v e m e n t in the adolescents relative to pogonion. Thus, by this measure, the adolescents exhibited about twice as much sagittal m o l a r correction because of the mesial movement of the lower molar (about 4 m m versus 2 ram;
p < 0.05). The significant vertical eruption of the molars in each group was statistically similar in the adolescents and the adults (3.1 m m and 2.4 m m , respectively). Vertical eruption in the adults must be due to an extrusive component in the mechanics since it cannot be solely accounted for b y growth. This may be a sequela of Class II elastic force. Average changes in horizontal measures of lower incisor position did not differ between ages, but there were significant changes within each age group. The incisor was retracted toward the A-pogonion line an average of 0.6 m m in the adolescents and 1.2 m m in the adults. The lower incisor was positioned significantly more posteriorly after treatment in the adolescents, but one should recall the AP line is influenced by point A
Volume lO0 Number 6
Treatment in adolescents and adults
527
Table III. Descriptive and inferential statistics, by age, for the changes during treatment (posttreatment -- pretreatment c o n d i t i o n s ) t Adolescents Variable
x
SE
Maxillary skeletal Condylion-A point SNA angle Nasion perpendicular/point A
- 1.70 - 1.75 - 1.95
0.47 0.28 0.38
2.47 1.89 4.47 5.91 0.73 2.79 1.73 0.46
Maxillary dental Upper molar horizontal Upper molar vertical Upper incisor/point A Upper incisor horizontal Upper incisor vertical AOBO discrepancy Downs' OP to FH Functional OP to FH Mandibular skeletal Mandibular length Corpus length Pogonion/N perpendicular Facial angle SNB angle Mandibular dental Lower molar horizontal Lower molar vertical Lower incisor/A-pogonion Lower incisor horizontal Lower incisor vertical IMPA FMIA Vertical Anterior facial height Posterior facial height Mandibular plane angle Facial axis angle Y axis angle
Adults --" x
SE
3.6" 6.3* 5.1"
- 1.41 - 1.22 - 1.40
0,67 0.43 0.50
2.1" 2.8* 2.8*
0.1 1.1 0.8
0.40 0.41 0.54 0.61 0.50 0.47 0.55 0.66
6.1" 4,6' 8.2* 9.7" 1.5 6,0" 3.2* 0.7
-0.08 - 0.98 - 5.95 - 7,47 1.64 - 5,50 7.15 4.42
0.48 0.38 0.64 0.75 0.67 0.66 1.03 1.13
0.2 2.6 9.2* 9.9" I_.5 8.4* 6.9* 3.9*
16.8" 26.1" 3.1 2.7 1.2 12.0" 23.2* 14.8"
2.47 1.59 0.56 0.51 -0,10
0.56 0.41 0.57 0.28 0.27
4.4* 3.8* 1.0 1.8 0.3
- 0.54 0.33 - 0.94 -0,38 -0.48
0.61 0.39 0,78 0.33 0.3l
0.9 0.9 1.2 1_.1 1.5
13.2" 4.8* 2.5 4.1" 0.9
3.87 3.11 - 0.60 1,49 -1.54 - 0.59 0.53
0.39 0.31 0.28 0.36 0.39 1.35 1.28
10.0' 9.9* 2.2* 4.1" 4.0* 0.4 0.4
2.49 2.43 - 1.16 0.51 -3.76 - 0,47 -0.10
0.38 0.37 0.29 0.35 0.43 1.02 0,97
6,6* 6,6* 3.9" 1.5 8.7" 0.5 0.1
6.5* 2.0 1,9 3.7 14.7" 0.0 0.1
2.51 2.15 0,06 0.62 0.47
0.50 0.62 0.31 0.41 0.28
2.5* 3.5* 0.2 1.5 1.6
0.93 - 0.93 0.57 0.58 0.26
0.60 0.57 0.45 0.40 0.42
1.5 1.6 1.3 1.4 0.6
4.1" 13.1" 0.9 0.0 0.2
-
t
.
.
.
.
i
ratio F
*p < 0,05. ]'Age-specific one-sample t tests (t) were calculated testing whether the mean cephalometric change differs from zero. The F ratio assesses whether there is a significant difference between the age-specific mean values.
position, which is m o v i n g posteriorly in relation to the mandible ( A O B O and A N B changes, Table III). Significant intrusion of the incisor occurred in both the adolescents and the adults with m e a n changes of 1,5 m m and 3.8 ram, respectively, m e a s u r e d relative to the mandibular plane. This t w o f o l d greater average change in the adults is a statistically significant differe n c e in treatment response. Vertical dimension. The adolescents exhibited significant growth during treatment as measured by anterior and posterior facial heights. These two measures constitute the only significant age-dependent differences in treatment response as measured a m o n g the five vertical variables.
DISCUSSION T h e histologic picture o f a l v e o l a r structures in the adult is different than that o f the adolescent. B o n e is more dense, and there is a d e c r e a s e in p o r e v o l u m e and a decrease in the lacunar-canalicular pore d i a m e t e r ? 4 T h e s e age-progressive trends differ f r o m those docum e n t e d for bones outside the c r a n i o f a c i a l c o m p l e x J 5"~7 In addition, the p e r i o d o n t a l e n v i r o n m e n t in the adult is more or less in a state o f rest, I~''9 and the adults require a l o n g e r hyalinization p e r i o d , as w e l l as a l o n g e r mobilization period, to prepare the tissues for orthodontic c h a n g e s ) 6,37 T h e present study is u n i q u e in its quantification of treatment o u t c o m e s b e t w e e n h o m o g e n e o u s adolescent
528
Dyer, Harris, and Vaden "
Am. ,I. Orthod. Detttofac. Orthop. December 1991
Fig. 2. Schematic of consequences of Class II eIastics observed in adult series, involving steepening of occlusal plane through intrusion of upper molar and mandibular incisor and extrusion of lower molar and maxillary incisor. Ideally, this Class II elastic effect can be offset through the concomitant use of vertical elastics in the anterior along with HPHG attached to hooks on the anterior portion of the maxillary arch wire.
(x = 12.5 years) and adult (x = 27.6 years) samples treated by one practitioner with the same mechanics to correct a Class II, Division 1 malocclusion. On the other hand, several of these findings have been adumbrated by the extensive research of Johnston 6 on younger and older adolescents: When there was no reasonable expectation of g r o w t h . . , the major source of the molar correction was tooth movement [i.e., bodily and tipping movements]. It is difficult to escape the feeling that this mix of changes is less desirable than those generally achieved in children.
Age related changes during treatment
Maxillary skeletal. The two age groups experienced comparable reductions in midfacial depth. This is reasonable since retraction of the maxillary incisors greatly influences point A. It is believed that the effects of high-pull headgear (HPHG) and closing loop mechanics are responsible for this outcome. The posteriorly directed movement of point A in both age groups resulted in similar in-treatment changes in all four of the maxillary skeletal measures. It is not known how much effect H P H G had on maxillary growth because the maxilla was significantly displaced anteriorly in both age groups. Behrents "~'3uhas documented continued growth of the craniofacial complex through adulthood as a discernible quantity over a period of years, but the amount observed in this study was greater than anticipated.
Maxillaly dental. The maxillary molar exhibited significant differences in the magnitude and direction of in-treatment change. Growth is largely responsible for the downward-forward displacement of the maxillary molar in the adolescent in combination with anchorage loss. Johnston 6 has described comparable changes in which the maxillary molar always came farther forward in a premolar-extraction group than in Class II untreated controls. Adolescents can afford this loss of anchorage since the lower molar would more than make up for this through the combined translatory effect of mandibular growth and mesial orthodontic movement. Adults cannot afford any anchorage loss, as there is only so much available space in the mandibular arch for mesial movement of the mandibular molar to aid in the molar correction. The lack of overt growth in the adults places a higher demand on the precision of the mechanics used in gaining molar correction. Prolonged use of Class II elastic force was evident in the treatment changes observed in the maxillary arch of the adults (Fig. 2). There was significant molar intrusion. The incisors were extruded and were uprighted twice as much as in the adolescents. This greater change in inclination represents a loss of torque in the anterior segment, as expected from the accompanying findings. The adults' fourfold increase in steepness of the Downs OP is another sequela of prolonged Class II elastic
Volume lO0 Number 6
force. In contrast, the adolescents displayed stability of the functional OP, which is in agreement with Johnston's findings. 6 The steepening of Downs' OP in the adults accounts for the significant reduction in AOBO; one can change the AOBO discrepancy just by altering the cant of the occlusal plane. Consequently, the reduction in AOBO observed in the adolescents is a reasonable finding, whereas this measure can be misleading in the adult if taken in isolation. Mandibular dental. The similar amounts of vertical eruption in the two age groups result from different mechanisms. Vertical growth of the alveolar process is responsible for the adolescents' eruption. In contrast, the extrusive component of the Class II force caused the vertical displacement in adults. There was more anchorage preparation in the adolescents as indicated by the greater distal inclination of the mandibular molar, even though one would anticipate a greater need for anchorage preparation in the adults because of the required Class II force. Two explanations come to mind: (1) The desired anchorage preparation was achieved but was obscured by the subsequent prolonged Class II force, or (2) anchorage preparation was attempted but not obtained to the extent observed in the adolescents. Vertical dimension. As mentioned, except for the anticipated growth in the adolescents (significant increases in anterior and posterior facial heights), all the vertical measures remained stable throughout treatment. Resultant eruption of the mandibular molar was accompanied by intrusion of the maxillary molar, which aided in minimizing any vertical skeletal change even though the occlusal plane steepened. It is obvious why Melsen 23 concluded that one of the major differences in the treatment of adults is the demand for vertical control. She pointed out that condyIar growth and vertical development of the alveolar process during adolescence allowed tooth movement to be partly extrusive. In the adult, by contrast, extrusion in the posterior segment will lead to an opening of the bite through downward-backward autorotation, that is, an increase in lower anterior face height. It is indeed fortunate, as observed by Musich, 5 that adults are generally more compliant, motivated, and follow prescribed mechanotherapy very well. One way to work harder is to increase the duration, but this is not what happened. It is believed that adults constitute a more restrictive sample and exhibit greater cooperation because they are self-selecting in contrast to adolescents, whose parents are generally making the decision to seek treatment.as'4° This is also in keeping with the finding of Chiappone 4~ that progress can be made as fast or faster in adults because of greater compliance. Class H elastic force. Greater use of Class II elastic
Treatment in adolescents a n d adults
529
force had to be employed to compensate for the absence of substantive growth in adults and because comparable amounts of mesial mandibular molar movement (orthodontic movement) were observed in the two age groups. 3~ As mentioned previously, the clinician cannot afford any loss of anchorage in the maxillary arch; loss necessitates the application of even more Class II elastic correction. A Class 1I force complex24 is used to counteract the unfavorable sequelae of using Class II elastic force alone. This complex consists of Class II elastics, anterior vertical elastics, and HPHG. The anterior vertical elastics counteract the vertical component of the Class II elastics in conjunction with the HPHG, which counterbalances the downward pull on the maxillary arch exerted by the anterior vertical elastics. This force complex, in conjunction with adequate mandibular arch anchorage preparation, is intended to result in mesial bodily movement of the mandibular dental unit. With this in mind, one must determine why the multiple sequelae of Class II elastic force were observed in the adults. Inspection of the treatment records for these eases establishes a clear-cut difference. Adults began wearing Class II elastics much earlier in treatment (about 1 year) and continued wearing them for an average of 13 months. Adolescents, in contrast, began wearing elastics later in treatment (about 16 months) and wore them for a much shorter interval (~ = 3.6 months). There is, then, virtually a fourfold difference in duration that accounts for the observed skeletodental differences between age groups. Since there is no predictable substantive growth in adults, steepening of the occlusal plane is going to be a common consequence of correcting sagittal disharmonies except in instances of exceptional HPHG application. MAJOR FINDINGS
Differences are documented in the nature of orthodontic correction depending on patient age, either adolescent (x = 12.5 years) or adult (x = 27.6 years). i. Adult treatment does not necessarily equate to a longer duration of treatment; in fact, average treatment times in the two age groups were comparable at 2.5 years. 2. The AOBO discrepancy was significantly reduced in adults and adolescents but by different mechanisms. Correction was achieved in the adolescents by the posterior movement of point A, whereas steepening of Downs' occlusal plane accounted for the reduction in adults. 3. Measures of vertical dimension in the adults remained unchanged during treatment, reflecting the effective absence of growth.
530
Dyer, Harris, and Vaden
. Several dental sequelae of Class II elastic force were observed in fhe adult series: increased mandibular molar eruption, increased maxillary molar intrusion, increased maxillary incisor eruption, increased mandibular incisor intrusion, and steepening of the occlusal plane. REFERENCES 1. Williams RL, Shilliday DJ, Kress W, et al. The American Association of Orthodontists study of the availability of orthodontic services. AM J ORTHOD 1975;68:326-38. 2. Gottlieb EL, Vogels DS. 1983 JCO orthodontic practice study. Part I. Trends. J Clio Orthod 1984;18:t67-73. 3. Gottlieb EL, Vogels DS. 1983 ]'CO orthodontic practice study. Part lI. Practice success. J Clin Orthod 1984;18:247-53. 4. Vaoarsdall RL, Maslch DR. Adult orthodontic treatment. In: Graber TM, Swain B, eds. Orthodontics: current principles and techniques. St. Louis: CV Mosby, 1985;791-856. 5. Musich DR. Assessment and description of the treatment needs of adult patients evaluated for orthodontic therapy: characteristics of solo provider group. Int J Adult Orthod Orthog Surg 1986; 1:55-67. 6. Johnston LE Jr. A comparative analysis of Class H treatments. In: Carlson DS, ed. Science and clinical judgement in orthodontics: Monograph 19, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan, 1986:103-48. 7. Franks AST, Hedeg~rd B. Geriatric dentistry. Oxford: Blackwell Scientifie Publications, 1973:3-48. 8. Levitt HL. Adult orthodontics. J C/in Orthod 1971;5:130-5. 9. Aekerman JL. The challenge of adult orthodontics. J Clin Orthod 1985;12:43-~. 10. Lindhal O, Lindgren GA. Grading of osteoporosls in autopsy specimens. Acta Orthop Stand 1962;32:85-93. 1 I. Merz AL, Trotter M, Peterson RR. Estimation of skeletal weight in the living. Am J Phys Anthropol 1956;14:589-609. 12. Trotter M, Peterson RR. Ash weight of human skeletons in per cent of their dry, fat free weight. Anal Roe 1955;123:341-8. 13. Epker BN, Kelin M, Frost HM. Magnitude and location of cortical bone loss in human rib with aging. Clio Orthop 1965; 41:198-203. 14. Liu CC, Baylink DJ, Wergedal JE, Allenbach ItM, Sipe J. Pore size measurements and some age-related changes in human alveolar bone and rat femur. J Dem Res 1977;56:143-50. 15. Arnold JS. Focal excessive endosteal resorption in aging and senile osteoporosis. In: Barzel U, ed. Osteoporosis. New York: Grune & Stratton, 1970:114-24. 16. Dequeker J, Remans J, Franssen R, Woes J. Aging patterns of trabecular and cortical bone and relationship. Calcif Tissue Res 197l;7:23-31. 17. Havivi E, ReshefA, Schwarz A, et al. Comparison of metacarpal bone loss with physical and chemical characteristics of vertebrae and ribs. Israel J Med Sci 1971;7:1055-8. 18. Reitan K, Tissue reaction as related to the age factor. Dent Rec 1954;74:271-9. 19. ReRan K. Biomechanical principles and reactions. In: Graber TM, ed. Current orthodontic concepts and techniques. Philadelphia: WB Sounders, 1969:56-159. 20. Bond JA. The child versus the adult. Dent Clio North Am 1972; 16(3):401-12. 21. Graber TiM. Orthodontics principles and practice. 3rd ed. Philadelphia: WB Sounders, 1972;488-527. 22. BaiTer HG. The adult orthodontic patient. AM ]. ORTHOD 1977;72:617-40.
Am. J. Orthod. Dentofac. Orthop. December 1991
23. Melsen B. Adult orthodontics: factors differentiating the selection of biomeehanics in growing and adult individuals, lot Jr Adult Orthod Orthog Surg 1988;3:167-77. 24. Merrifield LL. The sequential directional force edgewise tech~ nique. In: Johnston LE, ed. New vistas in orthodontics. Philadelphia: Lea & Febiger, 1985:184-208. 25. McNamara JA. A method of cephalometric evaluation. AM J ORTHOD 1984;86:449-69. 26. McNamara JA, Bookstein FL, Shaughnessy TG. Skeletal and dental changes following functional regulator therapy on Class II patients. AM J OR'r~OD 1985;88:91-110. 27. Downs WB. Variations in facial relationships: their significance in treatment and prognosis. AM J ORTHOD 1948;34:812-40. 28. Steiner CC. Cephalometrics for you and me. AM J ORTHOD 1953 ;39:729-55. 29. Rickens RM. The influence of orthodontic treatment on facial growth and development. Angle Orthod 1960;30:103-33. 30. Jacobson A. The "Wits" appraisal of jaw disharmony. AM J O~T}tOD 1975;67:125-38. 31. Harris EF, Dyer GS, Vaden JL. Age effects On orthodontic treatment: assessments from the Johnston analysis. AM J ORTHOD DENTOFACORTHOP [in press]. 32. Dixon WJ, Brown MB, eds. Biomedical computer programs P-series, BMDP-81. Los Angeles: University of California Press, 1981. 33. Sokal RR, Rohlf FJ. Biometry: the principles and practice of statistics in biologic research. 2nd ed. San Francisco: WH Freeman, 1981:583-91. 34. Merrifield LL. Edgewise sequential directional force technology. J Tweed Int Found 1986;4:22-37. 35. Riolo ML, Moyers RE, McNamara JA Jr, Stuart HW. An atlas of craniofaeial growth; standards from the University SchoOl Growth Study, the University of Michigan. Ann Arbor: Center for Human Growth and Development, University of Michigan, 1974. 36. Weiss RC. Physiology of adult tooth movement. Dent Clio North Am 1972;16(3):449-57. 37. Grant DA, Ben~iek S. The periodontium of aging humans. J Periodontol 1972;43:660-73. 38. Behrents RG. Aging of the craniofacial skeleton. Monograph 17, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan, 1985. 39. Behrents RG, An arias of growth in the aging craniofacial skeleton. Monograph 18, Craniofaeial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan, 1986. 40. Baldwin DC, Barnes ML. Psychosocial factors motivating orthodontic treatment (Abstract). J Dent Res 1965;44:153. 4l. Baldwin DC, Barnes ML. Patterns of motivation in families seeking orthodontic treatment (Abstract). J Dent Res 1966; 45:142. 42. Dorsey J, Korabik K. Social and psychological motivations for orthodontic treatment. AM J OItT~OD 1977;72:460-5. 43. Chiappone RC. Special considerations for adult orthodontics. J Clin Orthod 1976;10:535-45. Reprint requests to: Dr. Edward F. Harris Department of Orthodontics College of Dentistry University of Tennessee 875 Union Ave. Memphis, TN 38163
T h e r e has been a substantial increase in the proportion of adult patients in orthodontic practices over the last several years. 1"3 This trend has evolved from increased experience with adult treatment, increased public awareness of the availability of treatment, and decreased numbers of preadult patients in some areas. The effect of the patient's age on the nature of correction of malocclusions has received line study, but it would seem presumptuous to think that we can simply transfer our conventional treatment to the adult condition. 4'~ In the conventional adolescent patient, a substantive degree of correction--particularly in the sagittal plane--is achieved by differential growth of the two jaws. 6 Because of physiologic differences between adolescent and adult patients, s'79 there may well be differences in the way malocclusions are corrected in these two groups. Since adults do not experience any substantive growth during treatment, combined with physiologic bone differences, this would be a reasonable hypothesis. The purpose of this investigation was to quantitate differences in the nature of the correction of malocclusion dependent on the patient's age at the time of treatment.
Bone remodeling in adulthood After skeletal maturity at approximately the age of 20 years, the amount of cortical bone in many different bones has been reported to decrease as a normal acFrom the Department of Orthodontics, College of Dentistry, University of Tennessee. 8/1/24329
companiment of the aging process,t°'12 Epker et al. la have documented a progressive thinning of cortical bone after adulthood is attained, stemming from enlargement of the marrow cavity due to a negative bone balance at the cortical-endosteal surface in excess of a positive balance at the periosteal surface. Liu et al. 14assessed alveolar bone samples obtained at autopsy and during third molar extractions. A significant decrease was seen in pore volume with increasing age along with a decrease in lacunar-canalicular pore diameter and an increase in density. This increase in alveolar bone density contrasts with several studies of bone elsewhere in the body (primarily the vertebrae) that report gradual decreases in trabecular bone density, commencing around 25 years Of age and continuing into old age.tS~7
Periodontal changes In the growing child, the tooth-supporting tissues are in a state of proliferation, i8 Within the periodontal ligament and in marrow spaces surrounding the alveolus, large numbers of connective tissue cells are actively involved in alveolar growth and remodeling. Within cancellous bone of the alveolus there is a rich blood supply to assist in metabolism, and in the medullary region the large marrow spaces provide bone trabeculae with considerable surface area that facilitates the activities of osteoblasts and osteoclasts.t9 Reitan I8 found bone resorption on the pressure side of teeth after a delay of about 4 days after the application of 50 gm of continuous force in a 39-year-old man. Bone apposition onthe tension side, however, was evident only after 8 days of force application. This lag in 523
524
Dyer, Harris, and Vaden
Am. J. Orthod.Dentofac. Orthop. December 1991
45
Adolescents
40
Adults l
35~
-13o 25 .
0.75). Comparable reductions were also observed in the SNA and the measure nasion-perpendicular to point A. None of these maxillary skeletal parameters exhibited a significantly different in-treatment change between adolescents and adults (Table III). Maxillary dental. The horizontal maxillary dental measurements, which differed at the pretreatment examination (upper molar horizontal was greater in the adults), converged enough with treatment and growth to be statistically indistinguishable at the end of treatment. Midfacial growth carried the first molar forward significantly relative to pterygoid-vertical (PtV) in the adolescents (x = 2.5 mm), whereas the absence of this growth in the adults contributed to the molar remaining in the same average position. In fact, this molar movement is probably spurious since it is unsupported through closer scrutiny. 31 Instead, the increase in upper molar horizontal almost certainly reflects growth at intermediate bony sites between PtV and the molar rather than true tooth movement. The vertical component of molar movement was also significant. Growth in the adolescents carried the molar down an average of 1.9 m m compared with the 1.0 m m of intrusion observed in the adults.
Treatment in adolescents and adults 525
Table I. Statistics regarding initial-records age, age at the end of active treatment, and treatment time of the adolescents and adults Variable Sample size
Adolescents
[
Adults
30
26
12.52 0.67 13.88 11.37
27.57 5.38 40.07 21.14
14.98 0.80 16.45 13.22
30.14 5.39 42.36 23.39
2.46 0.36 3.41 1.46
2.56 0.35 3.23 1.97
Initial records Mean age (yr) SD Maximum Minimum
End of treatment
Mean age (yr) SD Maximum Minimum Treatment time Mean duration (yr) SD Maximum Minimum
Complementary measures of the horizontal position of the upper incisor (upper incisor horizontal and upper incisor/point A) revealed a significant but similar degree of retraction of the upper incisor in the two groups. Incisor retraction helps camouflage the skeletal disharmony; the normative value for incisor/point A (point A perpendicular to the facial surface of central incisor horizontally) is 4 to 6 ram. 25 The posttreatment values for the adolescents and the adults for incisor/point A were 0.6 mm and 0.3 m m , respectively. The vertical position of the upper incisor did not change significantly in either age group. There was, however, a trend toward enhanced eruption in the adults (x = 1.6 m m for adults, 0.7 mm for adolescents). The AOBO discrepancies 3° were significantly different before treatment (~ = 3.1 mm for adolescents, 5.3 m m for adults), with each exhibiting a significant reduction during treatment. The adults displayed a much greater AOBO change during treatment, with a finished mean value of - 0 . 2 m m compared with the adolescents' 0.3 mm. One must remember that this measure is taken along Downs' occlusal plane (OP), which is considerably steepened in the adults. This change in cant of the occlusal plane will mimic an improved apical base relationship. The cant of the occlusal plane changed significantly between age grades. The adults experienced almost a fourfold increase in steepness relative to the adolescents. The application of Class II elastics during treatment is suggested to produce this response. Mandibular skeletal. Mandibular growth in the adolescents resulted in significant increases in both man-
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Am. J. Orthod. Dentofac, Orthop. December 1991
Table II, Descriptive and inferential statistics, b y age, for the skeletodental variables assessed at the start of treatment Adults (n --- 26)
Adolescents (n = 30)
F Variable
SE
X
SE
ratio¢
Maxillary skeletal
Condylion-A point SNA angle Naslon perpendiculartpoint A
93,36 81.38 - 2.17
0.81 0.75 0.63
93.33 80.40 -3.36
1.29 0.57 0.71
0,0 1,1 1.6
26.09 45,59 5.07 57.97 53.19 3.05 10,22 11.99
0.69 0.56 0,47 0.77 0.69 0.44 0.72 0.80
29,98 50.71 6.27 59.87 55.76 5,30 7.91 10.04
0.84 0.76 0.81 1.31 0.92 0,51 1.11 1.20
12.9" 30.6* 1.8 1.7 5.2* i1,1' 3.2 1,9
113.46 73.99 - 11.36 83.93 76.34
1.02 0.84 0.96 0.51 0.69
117.76 75.74 - 13.08 83,61 75.52
1.58 1.11 1,61 0.77 0.66
5.5' 1.6 0.9 0.1 0.7
--31,77 29.74 2,23 5.91 40.37 96.30 56.62
0.51 0.40 0.30 0.48 0.53 1.05 1.12
-30.62 31.84 2.91 7.83 43.59 94.69 56.10
0.66 0.80 0.40 0.69 0.87 1.53 1.54
2.0 6.0* 1.9 5.4* 10.6' 0.8 0.1
64.89 52.66 27.07 90,06 60,36
1.01 0.80 0.92 0.73 0.60
69.22 56.62 29.20 92.75 62.72
1.65 1.37 1,65 1.35 0.99
5.3* 6.7* 1.4 3.3 4.4*
Maxillary dental
Upper molar horizontal Upper molar vertical Upper incisor/point A Upper incisor horizontal Upper incisor vertical AOBO discrepancy Downs' OP to FH Functional OP to FH Mandibular skeletal
Mandibular length Corpus length Pogonion/N perpendicular Facial angle SNB angle Mandibular dental
Lower molar horizontal Lower molar vertical Lower incisor/A-pogonion Lower incisor horizontal Lower incisor vertical IMPA FMIA Vertical
Anterior facial height Posterior facial height Mandibular plane angle Facial axis angle Y axis angle *p < 0.05. tThe F ratio tests for age differences.
dibular and corpus lengths (2.5 rnm and 1.6 ram). The small increase i n facial angle ( F H - N P ) in the adolescents, coupled with the slight decrease in the adults, resulted in a significant difference in the amounts of intreatment change. P o g o n i o n to n a s i o n - p e r p e n d i c u l a r and the SNB angle did not change significantly, either within or among groups. M a n d i b u l a r d e n t a l . The lower molar moved vertically and horizontally i n both the adolescents and the adults with appreciably greater forward m o v e m e n t in the adolescents relative to pogonion. Thus, by this measure, the adolescents exhibited about twice as much sagittal m o l a r correction because of the mesial movement of the lower molar (about 4 m m versus 2 ram;
p < 0.05). The significant vertical eruption of the molars in each group was statistically similar in the adolescents and the adults (3.1 m m and 2.4 m m , respectively). Vertical eruption in the adults must be due to an extrusive component in the mechanics since it cannot be solely accounted for b y growth. This may be a sequela of Class II elastic force. Average changes in horizontal measures of lower incisor position did not differ between ages, but there were significant changes within each age group. The incisor was retracted toward the A-pogonion line an average of 0.6 m m in the adolescents and 1.2 m m in the adults. The lower incisor was positioned significantly more posteriorly after treatment in the adolescents, but one should recall the AP line is influenced by point A
Volume lO0 Number 6
Treatment in adolescents and adults
527
Table III. Descriptive and inferential statistics, by age, for the changes during treatment (posttreatment -- pretreatment c o n d i t i o n s ) t Adolescents Variable
x
SE
Maxillary skeletal Condylion-A point SNA angle Nasion perpendicular/point A
- 1.70 - 1.75 - 1.95
0.47 0.28 0.38
2.47 1.89 4.47 5.91 0.73 2.79 1.73 0.46
Maxillary dental Upper molar horizontal Upper molar vertical Upper incisor/point A Upper incisor horizontal Upper incisor vertical AOBO discrepancy Downs' OP to FH Functional OP to FH Mandibular skeletal Mandibular length Corpus length Pogonion/N perpendicular Facial angle SNB angle Mandibular dental Lower molar horizontal Lower molar vertical Lower incisor/A-pogonion Lower incisor horizontal Lower incisor vertical IMPA FMIA Vertical Anterior facial height Posterior facial height Mandibular plane angle Facial axis angle Y axis angle
Adults --" x
SE
3.6" 6.3* 5.1"
- 1.41 - 1.22 - 1.40
0,67 0.43 0.50
2.1" 2.8* 2.8*
0.1 1.1 0.8
0.40 0.41 0.54 0.61 0.50 0.47 0.55 0.66
6.1" 4,6' 8.2* 9.7" 1.5 6,0" 3.2* 0.7
-0.08 - 0.98 - 5.95 - 7,47 1.64 - 5,50 7.15 4.42
0.48 0.38 0.64 0.75 0.67 0.66 1.03 1.13
0.2 2.6 9.2* 9.9" I_.5 8.4* 6.9* 3.9*
16.8" 26.1" 3.1 2.7 1.2 12.0" 23.2* 14.8"
2.47 1.59 0.56 0.51 -0,10
0.56 0.41 0.57 0.28 0.27
4.4* 3.8* 1.0 1.8 0.3
- 0.54 0.33 - 0.94 -0,38 -0.48
0.61 0.39 0,78 0.33 0.3l
0.9 0.9 1.2 1_.1 1.5
13.2" 4.8* 2.5 4.1" 0.9
3.87 3.11 - 0.60 1,49 -1.54 - 0.59 0.53
0.39 0.31 0.28 0.36 0.39 1.35 1.28
10.0' 9.9* 2.2* 4.1" 4.0* 0.4 0.4
2.49 2.43 - 1.16 0.51 -3.76 - 0,47 -0.10
0.38 0.37 0.29 0.35 0.43 1.02 0,97
6,6* 6,6* 3.9" 1.5 8.7" 0.5 0.1
6.5* 2.0 1,9 3.7 14.7" 0.0 0.1
2.51 2.15 0,06 0.62 0.47
0.50 0.62 0.31 0.41 0.28
2.5* 3.5* 0.2 1.5 1.6
0.93 - 0.93 0.57 0.58 0.26
0.60 0.57 0.45 0.40 0.42
1.5 1.6 1.3 1.4 0.6
4.1" 13.1" 0.9 0.0 0.2
-
t
.
.
.
.
i
ratio F
*p < 0,05. ]'Age-specific one-sample t tests (t) were calculated testing whether the mean cephalometric change differs from zero. The F ratio assesses whether there is a significant difference between the age-specific mean values.
position, which is m o v i n g posteriorly in relation to the mandible ( A O B O and A N B changes, Table III). Significant intrusion of the incisor occurred in both the adolescents and the adults with m e a n changes of 1,5 m m and 3.8 ram, respectively, m e a s u r e d relative to the mandibular plane. This t w o f o l d greater average change in the adults is a statistically significant differe n c e in treatment response. Vertical dimension. The adolescents exhibited significant growth during treatment as measured by anterior and posterior facial heights. These two measures constitute the only significant age-dependent differences in treatment response as measured a m o n g the five vertical variables.
DISCUSSION T h e histologic picture o f a l v e o l a r structures in the adult is different than that o f the adolescent. B o n e is more dense, and there is a d e c r e a s e in p o r e v o l u m e and a decrease in the lacunar-canalicular pore d i a m e t e r ? 4 T h e s e age-progressive trends differ f r o m those docum e n t e d for bones outside the c r a n i o f a c i a l c o m p l e x J 5"~7 In addition, the p e r i o d o n t a l e n v i r o n m e n t in the adult is more or less in a state o f rest, I~''9 and the adults require a l o n g e r hyalinization p e r i o d , as w e l l as a l o n g e r mobilization period, to prepare the tissues for orthodontic c h a n g e s ) 6,37 T h e present study is u n i q u e in its quantification of treatment o u t c o m e s b e t w e e n h o m o g e n e o u s adolescent
528
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Am. ,I. Orthod. Detttofac. Orthop. December 1991
Fig. 2. Schematic of consequences of Class II eIastics observed in adult series, involving steepening of occlusal plane through intrusion of upper molar and mandibular incisor and extrusion of lower molar and maxillary incisor. Ideally, this Class II elastic effect can be offset through the concomitant use of vertical elastics in the anterior along with HPHG attached to hooks on the anterior portion of the maxillary arch wire.
(x = 12.5 years) and adult (x = 27.6 years) samples treated by one practitioner with the same mechanics to correct a Class II, Division 1 malocclusion. On the other hand, several of these findings have been adumbrated by the extensive research of Johnston 6 on younger and older adolescents: When there was no reasonable expectation of g r o w t h . . , the major source of the molar correction was tooth movement [i.e., bodily and tipping movements]. It is difficult to escape the feeling that this mix of changes is less desirable than those generally achieved in children.
Age related changes during treatment
Maxillary skeletal. The two age groups experienced comparable reductions in midfacial depth. This is reasonable since retraction of the maxillary incisors greatly influences point A. It is believed that the effects of high-pull headgear (HPHG) and closing loop mechanics are responsible for this outcome. The posteriorly directed movement of point A in both age groups resulted in similar in-treatment changes in all four of the maxillary skeletal measures. It is not known how much effect H P H G had on maxillary growth because the maxilla was significantly displaced anteriorly in both age groups. Behrents "~'3uhas documented continued growth of the craniofacial complex through adulthood as a discernible quantity over a period of years, but the amount observed in this study was greater than anticipated.
Maxillaly dental. The maxillary molar exhibited significant differences in the magnitude and direction of in-treatment change. Growth is largely responsible for the downward-forward displacement of the maxillary molar in the adolescent in combination with anchorage loss. Johnston 6 has described comparable changes in which the maxillary molar always came farther forward in a premolar-extraction group than in Class II untreated controls. Adolescents can afford this loss of anchorage since the lower molar would more than make up for this through the combined translatory effect of mandibular growth and mesial orthodontic movement. Adults cannot afford any anchorage loss, as there is only so much available space in the mandibular arch for mesial movement of the mandibular molar to aid in the molar correction. The lack of overt growth in the adults places a higher demand on the precision of the mechanics used in gaining molar correction. Prolonged use of Class II elastic force was evident in the treatment changes observed in the maxillary arch of the adults (Fig. 2). There was significant molar intrusion. The incisors were extruded and were uprighted twice as much as in the adolescents. This greater change in inclination represents a loss of torque in the anterior segment, as expected from the accompanying findings. The adults' fourfold increase in steepness of the Downs OP is another sequela of prolonged Class II elastic
Volume lO0 Number 6
force. In contrast, the adolescents displayed stability of the functional OP, which is in agreement with Johnston's findings. 6 The steepening of Downs' OP in the adults accounts for the significant reduction in AOBO; one can change the AOBO discrepancy just by altering the cant of the occlusal plane. Consequently, the reduction in AOBO observed in the adolescents is a reasonable finding, whereas this measure can be misleading in the adult if taken in isolation. Mandibular dental. The similar amounts of vertical eruption in the two age groups result from different mechanisms. Vertical growth of the alveolar process is responsible for the adolescents' eruption. In contrast, the extrusive component of the Class II force caused the vertical displacement in adults. There was more anchorage preparation in the adolescents as indicated by the greater distal inclination of the mandibular molar, even though one would anticipate a greater need for anchorage preparation in the adults because of the required Class II force. Two explanations come to mind: (1) The desired anchorage preparation was achieved but was obscured by the subsequent prolonged Class II force, or (2) anchorage preparation was attempted but not obtained to the extent observed in the adolescents. Vertical dimension. As mentioned, except for the anticipated growth in the adolescents (significant increases in anterior and posterior facial heights), all the vertical measures remained stable throughout treatment. Resultant eruption of the mandibular molar was accompanied by intrusion of the maxillary molar, which aided in minimizing any vertical skeletal change even though the occlusal plane steepened. It is obvious why Melsen 23 concluded that one of the major differences in the treatment of adults is the demand for vertical control. She pointed out that condyIar growth and vertical development of the alveolar process during adolescence allowed tooth movement to be partly extrusive. In the adult, by contrast, extrusion in the posterior segment will lead to an opening of the bite through downward-backward autorotation, that is, an increase in lower anterior face height. It is indeed fortunate, as observed by Musich, 5 that adults are generally more compliant, motivated, and follow prescribed mechanotherapy very well. One way to work harder is to increase the duration, but this is not what happened. It is believed that adults constitute a more restrictive sample and exhibit greater cooperation because they are self-selecting in contrast to adolescents, whose parents are generally making the decision to seek treatment.as'4° This is also in keeping with the finding of Chiappone 4~ that progress can be made as fast or faster in adults because of greater compliance. Class H elastic force. Greater use of Class II elastic
Treatment in adolescents a n d adults
529
force had to be employed to compensate for the absence of substantive growth in adults and because comparable amounts of mesial mandibular molar movement (orthodontic movement) were observed in the two age groups. 3~ As mentioned previously, the clinician cannot afford any loss of anchorage in the maxillary arch; loss necessitates the application of even more Class II elastic correction. A Class 1I force complex24 is used to counteract the unfavorable sequelae of using Class II elastic force alone. This complex consists of Class II elastics, anterior vertical elastics, and HPHG. The anterior vertical elastics counteract the vertical component of the Class II elastics in conjunction with the HPHG, which counterbalances the downward pull on the maxillary arch exerted by the anterior vertical elastics. This force complex, in conjunction with adequate mandibular arch anchorage preparation, is intended to result in mesial bodily movement of the mandibular dental unit. With this in mind, one must determine why the multiple sequelae of Class II elastic force were observed in the adults. Inspection of the treatment records for these eases establishes a clear-cut difference. Adults began wearing Class II elastics much earlier in treatment (about 1 year) and continued wearing them for an average of 13 months. Adolescents, in contrast, began wearing elastics later in treatment (about 16 months) and wore them for a much shorter interval (~ = 3.6 months). There is, then, virtually a fourfold difference in duration that accounts for the observed skeletodental differences between age groups. Since there is no predictable substantive growth in adults, steepening of the occlusal plane is going to be a common consequence of correcting sagittal disharmonies except in instances of exceptional HPHG application. MAJOR FINDINGS
Differences are documented in the nature of orthodontic correction depending on patient age, either adolescent (x = 12.5 years) or adult (x = 27.6 years). i. Adult treatment does not necessarily equate to a longer duration of treatment; in fact, average treatment times in the two age groups were comparable at 2.5 years. 2. The AOBO discrepancy was significantly reduced in adults and adolescents but by different mechanisms. Correction was achieved in the adolescents by the posterior movement of point A, whereas steepening of Downs' occlusal plane accounted for the reduction in adults. 3. Measures of vertical dimension in the adults remained unchanged during treatment, reflecting the effective absence of growth.
530
Dyer, Harris, and Vaden
. Several dental sequelae of Class II elastic force were observed in fhe adult series: increased mandibular molar eruption, increased maxillary molar intrusion, increased maxillary incisor eruption, increased mandibular incisor intrusion, and steepening of the occlusal plane. REFERENCES 1. Williams RL, Shilliday DJ, Kress W, et al. The American Association of Orthodontists study of the availability of orthodontic services. AM J ORTHOD 1975;68:326-38. 2. Gottlieb EL, Vogels DS. 1983 JCO orthodontic practice study. Part I. Trends. J Clio Orthod 1984;18:t67-73. 3. Gottlieb EL, Vogels DS. 1983 ]'CO orthodontic practice study. Part lI. Practice success. J Clin Orthod 1984;18:247-53. 4. Vaoarsdall RL, Maslch DR. Adult orthodontic treatment. In: Graber TM, Swain B, eds. Orthodontics: current principles and techniques. St. Louis: CV Mosby, 1985;791-856. 5. Musich DR. Assessment and description of the treatment needs of adult patients evaluated for orthodontic therapy: characteristics of solo provider group. Int J Adult Orthod Orthog Surg 1986; 1:55-67. 6. Johnston LE Jr. A comparative analysis of Class H treatments. In: Carlson DS, ed. Science and clinical judgement in orthodontics: Monograph 19, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan, 1986:103-48. 7. Franks AST, Hedeg~rd B. Geriatric dentistry. Oxford: Blackwell Scientifie Publications, 1973:3-48. 8. Levitt HL. Adult orthodontics. J C/in Orthod 1971;5:130-5. 9. Aekerman JL. The challenge of adult orthodontics. J Clin Orthod 1985;12:43-~. 10. Lindhal O, Lindgren GA. Grading of osteoporosls in autopsy specimens. Acta Orthop Stand 1962;32:85-93. 1 I. Merz AL, Trotter M, Peterson RR. Estimation of skeletal weight in the living. Am J Phys Anthropol 1956;14:589-609. 12. Trotter M, Peterson RR. Ash weight of human skeletons in per cent of their dry, fat free weight. Anal Roe 1955;123:341-8. 13. Epker BN, Kelin M, Frost HM. Magnitude and location of cortical bone loss in human rib with aging. Clio Orthop 1965; 41:198-203. 14. Liu CC, Baylink DJ, Wergedal JE, Allenbach ItM, Sipe J. Pore size measurements and some age-related changes in human alveolar bone and rat femur. J Dem Res 1977;56:143-50. 15. Arnold JS. Focal excessive endosteal resorption in aging and senile osteoporosis. In: Barzel U, ed. Osteoporosis. New York: Grune & Stratton, 1970:114-24. 16. Dequeker J, Remans J, Franssen R, Woes J. Aging patterns of trabecular and cortical bone and relationship. Calcif Tissue Res 197l;7:23-31. 17. Havivi E, ReshefA, Schwarz A, et al. Comparison of metacarpal bone loss with physical and chemical characteristics of vertebrae and ribs. Israel J Med Sci 1971;7:1055-8. 18. Reitan K, Tissue reaction as related to the age factor. Dent Rec 1954;74:271-9. 19. ReRan K. Biomechanical principles and reactions. In: Graber TM, ed. Current orthodontic concepts and techniques. Philadelphia: WB Sounders, 1969:56-159. 20. Bond JA. The child versus the adult. Dent Clio North Am 1972; 16(3):401-12. 21. Graber TiM. Orthodontics principles and practice. 3rd ed. Philadelphia: WB Sounders, 1972;488-527. 22. BaiTer HG. The adult orthodontic patient. AM ]. ORTHOD 1977;72:617-40.
Am. J. Orthod. Dentofac. Orthop. December 1991
23. Melsen B. Adult orthodontics: factors differentiating the selection of biomeehanics in growing and adult individuals, lot Jr Adult Orthod Orthog Surg 1988;3:167-77. 24. Merrifield LL. The sequential directional force edgewise tech~ nique. In: Johnston LE, ed. New vistas in orthodontics. Philadelphia: Lea & Febiger, 1985:184-208. 25. McNamara JA. A method of cephalometric evaluation. AM J ORTHOD 1984;86:449-69. 26. McNamara JA, Bookstein FL, Shaughnessy TG. Skeletal and dental changes following functional regulator therapy on Class II patients. AM J OR'r~OD 1985;88:91-110. 27. Downs WB. Variations in facial relationships: their significance in treatment and prognosis. AM J ORTHOD 1948;34:812-40. 28. Steiner CC. Cephalometrics for you and me. AM J ORTHOD 1953 ;39:729-55. 29. Rickens RM. The influence of orthodontic treatment on facial growth and development. Angle Orthod 1960;30:103-33. 30. Jacobson A. The "Wits" appraisal of jaw disharmony. AM J O~T}tOD 1975;67:125-38. 31. Harris EF, Dyer GS, Vaden JL. Age effects On orthodontic treatment: assessments from the Johnston analysis. AM J ORTHOD DENTOFACORTHOP [in press]. 32. Dixon WJ, Brown MB, eds. Biomedical computer programs P-series, BMDP-81. Los Angeles: University of California Press, 1981. 33. Sokal RR, Rohlf FJ. Biometry: the principles and practice of statistics in biologic research. 2nd ed. San Francisco: WH Freeman, 1981:583-91. 34. Merrifield LL. Edgewise sequential directional force technology. J Tweed Int Found 1986;4:22-37. 35. Riolo ML, Moyers RE, McNamara JA Jr, Stuart HW. An atlas of craniofaeial growth; standards from the University SchoOl Growth Study, the University of Michigan. Ann Arbor: Center for Human Growth and Development, University of Michigan, 1974. 36. Weiss RC. Physiology of adult tooth movement. Dent Clio North Am 1972;16(3):449-57. 37. Grant DA, Ben~iek S. The periodontium of aging humans. J Periodontol 1972;43:660-73. 38. Behrents RG. Aging of the craniofacial skeleton. Monograph 17, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan, 1985. 39. Behrents RG, An arias of growth in the aging craniofacial skeleton. Monograph 18, Craniofaeial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan, 1986. 40. Baldwin DC, Barnes ML. Psychosocial factors motivating orthodontic treatment (Abstract). J Dent Res 1965;44:153. 4l. Baldwin DC, Barnes ML. Patterns of motivation in families seeking orthodontic treatment (Abstract). J Dent Res 1966; 45:142. 42. Dorsey J, Korabik K. Social and psychological motivations for orthodontic treatment. AM J OItT~OD 1977;72:460-5. 43. Chiappone RC. Special considerations for adult orthodontics. J Clin Orthod 1976;10:535-45. Reprint requests to: Dr. Edward F. Harris Department of Orthodontics College of Dentistry University of Tennessee 875 Union Ave. Memphis, TN 38163
