The effect of corticosteroid-induced osteoporosis on orthodontic tooth movement Michael B. Ashcraft, DDS, MS," Karin A. Southard, DDS, MS, b and Elizabeth A. Tolley, PhD ~ Little Rock, Ark., Iowa City, Iowa, and Memphis, Tenn. The purpose of this research was to study the effects of corticosteroid-induced osteoporosis on orthodontic tooth movement and relapse. Sixteen 3-month-old New Zealand white rabbits were divided into four equal groups, two treatment and two control. All treatment rabbits were administered daily injections of 15 mg/kg cortisone acetate for 4 days before and during the experimental period. An orthodontic appliance delivering a mesial force of 4 ounces was placed on the maxillary left first molar of all animals. For all groups, measurements of active tooth movement were made after 4, 7, 11, and 14 days. For two of the groups, appliances were removed on day 14, and additional measurements of relapse were made through day 21. With the use of radiodensitometric readings of the humerus bone and histology of the maxilla, osteoporosis was demonstrated in the treatment animals. Mean incremental and cumulative active tooth movement was three to four times greater (p < 0.0001) in the treatment rabbits than in the controls. The treatment group in which relapse was measured demonstrated 100% relapse on day 18, whereas the control group relapsed at a much lesser rate through day 21 and never achieved 100% relapse. Histologic findings appeared to support tooth movement results. In conclusion, the results of this study indicate that rabbits subjected to corticosteroid-induced osteoporosis undergo significantly more rapid orthodontic tooth movement and subsequent relapse than control animals. (AM J ORTHOP DENTOFAC ORTHOP 1992;102:310-9.)
I t has been well documented since 1932 that oversecretion of cortisol by the adrenal cortex causes osteoporosis. L2 Since their introduction in the mid1950s, synthetic corticosteroids have been used in therapeutic regimens for the treatment of a wide variety of ailments ranging from arthritis to renal, collagen, allergic, and neoplastic diseases. Similarly, it has been demonstrated that supraphysiologic doses of these drugs administered chronically induce the same osteoporosis found in naturally occurring states of hypercortisolism): The exact physiologic basis for corticosteroid osteoporosis is not completely understood. In general, the mechanism involves the uncoupling of the normal relationship of bone formation and resorption; bone formation is decreased while bone resorption is increased) Regarding bone formation, the effects of corticosteroids appear to be multidimensional. Evidence indicates that corticosteroids produce a direct inhibition of osteoblastic function. This inhibition is mediated through effects on osteoblasts and osteobtastic precursors that This research was supported by the Faustin Neff Weber Research Fellowship. aln private practice, Little Rock, Ark. bAssistant Professor, Department of Orthodontics, The Unive~ity of Iowa, Iowa City. CAssociate Professor, Department of Biostatistics and Epidemiology, The University of Tennessee, Memphis. 8/1130362
310
result in a decrease in total bone formation. 3'5" The effects of corticosteroids on osteoclasts are a little less clear. Studies indicate that corticosteroids produce an increased resorptive response. 3::2t4 However, the specific mechanism is not well understood and may involve a secondary hyperparathyroidism: '~'~~ The level of parathyroid hormone is frequently elevated in patients treated with corticosteroids. This elevated level of parathyroid is caused by the direct inhibition of calcium absorption by the steroid and the induction of hypercalciuria especially with high doses of corticosteroids. The end result is an increase in bone resorption)'" Very little is known about the effects of corticosteroid osteoporosis on orthodontic tooth movement. Previous researchers have not established a drug regimen for their specific animal models in which osteoporosis could be consistently demonstrated. Storey ~6studied the histology of tooth movement in rabbits and guinea pigs that received doses of cortisone acetate. However, the doses that he used in guinea pigs were most likely not large enough to induce an osteoporosis, t6 Similarly, Davidovitch ~7 studied rates of tooth movement in cats treated with daily doses of cortisone acetate. He found slower rates of tooth movement in the experimental animals but failed to confirm a state of osteoporosis. The purpose of this investigation was (1) to develop a confirmed state of corticosteroid osteoporosis in an animal model, (2) to quantify rates of active tooth
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Effect o f corticosteroids on tooth movement
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Number 4
Fig. 1. Diagram of orthodontic appliance design, which consisted of a spring that applied tension between maxillary first molar and central incisor of rabbit.
movement and relapse in the model, and (3) to examine for histologic evidence that active tooth movement a n d / o r relapse may be affected in corticosteroid treated subjects.
MATERIALS AND METHODS Selection of experimental model Researchers have used human iliac crest biopsies," guinea pigs, t8 rats, ~9':~and rabbits, ~3 to study corticosteroid osteoporosis. However, Thompson et al." were able to consistently demonstrate osteoporosis with quantitative microradiography in rabbits receiving daily 15 mglkg injections of cortisone acetate. Likewise, Storey '~ found osteoporosis after 4 days in rabbits that received a similar dose of cortisone. Therefore, 3-month-old New Zealand white rabbits were selected and administered cortisone acetate at doses of 15 mg/kg for 4 days before and during the experimental period.
Appliance placement and design The rabbit maxilla was selected for appliance placement because of its known vulnerability to osteoporosis. '* The appliance was designed according to Heller and Nanda. 2~A 1.0 cm section of 0.010 • 0.045-inch closed coil spring (Rocky Mountain Orthodontics, Denver, Colo.) was affixed to the maxillary left first molar and the maxillary left central incisor with a 0.012-inch steel ligature. Retention grooves were placed with a Vz-round bur to prevent dislodgement of the steel ligatures. These grooves were placed subgingivaUy on the buccal and the palatal surfaces of the maxillary left first molar and on the mesial and distal surfaces of the maxillary left central incisor at the level of the gingiva. The mandibular central incisors were disked out of occlusion to prevent appliance breakage. The appliance was calibrated with a Dontrix force gauge (ETM, Monrovia, Calif.) to deliver a 4-ounce force and recalibrated to remain at 4 ounces at each measurement interval (Fig. 1).
Group determination Sixteen rabbits were divided equally into four groups, two treatment and two control. The two treatment groups received daily subcutaneous injections of 15 mg/kg cortisone
acetate for 4 days before and during the experimental period. The two control groups received no cortisone. An orthodontic appliance was placed on the left first molar and incisor teeth of all 16 rabbits for 14 days. One treatment group (T,) and one control group (C,) were used to measure active tooth movement for 14 days. The two other groups (T, § and (C,. ,) had appliances removed after 14 days and had relapse of active tooth movement measured for an additional 7 days.
Animal care All animals were caged individually with regulated light and temperature and fed rabbit chow, lettuce, and water ad libitum. The rabbits were weighed daily to confirm that they were healthy, and to determine the daily dosage of cortisone acetate that each rabbit in the treatment groups would receive. At the time of appliance placement and during all toothmovement measurements, each rabbit was anesthetized with 0.4 mg/kg intramuscular injections of ketamine/xylazine admixture composed of 1.5 ml Xylazine (Hayer Lockhart, Swankee, Kan.) mixed with 10 ml Ketaset (Aveco, Fort Dodge, Iowa).
Tooth movement measurements Reference points were placed in the midpalatal surfaces of the left first and second molars with a Vz-round bur. All measurements of tooth movement were made with a Great Lakes caliper (Great Lakes Orthodontics, Tonawanda, N.Y.) calibrated to 0.1 mm and that had the points filed down to fit into the reference points on the teeth. Measurements of distance between the reference points on the first and second molars were made at the time of appliance placement, days 4, 7, 11, and 14. For the two relapse groups, (T.. ,, C , . ,), measurements were also taken at days 18 and 21.
Tissue preparation At the appropriate time of sacrifice, rabbits were killed with an intravenous injection of commercial euthenasia agent, T-6I (Agrivet Co., Sommerville, N.J.). Maxillary molar segments were dissected out, fixed in 10% buffered formalin, and decalcified with Decal II (Surgipath, Grayslake, II1.). The
312
Am. J. Orthod. Oentofac. Orthop.
Ashcraft, Sottthard. a m l Tolle~'
"
October 1992
APPLIED FORCE
IL,/[
ALVEOLAR BONE FIRST MOLAR INCISOR
PERIODONTALLIGAI~NT
ALVEOLARBONE
Fig. 2. Schematic representation of rabbit maxilla demonstrating two anatomic areas examined microscopically for comparisons between groups. The bold squares represent (1) a mesiocclusal area relative to the maxillary first molar and (2) a midroot inlerproximal area of the maxillary first and second molars.
Table
I. Optical densities o f cortical b o n e taken from the right humeri o f six treatment and eight control rabbits
Treatment
I
Control
To.,t 2.31 T,+,,. 2.02 T,+,3 1.97 T,+a expired T,i 2.18 T,: expired Te 2.15 Ta 2.05
C,§ 1.77 C,§ 1.98 C,+,3 1.77 C,+a 1.91 Ca 1.65 Ca 1.98 Ca 1.91 Ca 1.85
glean 2.14' SE 0.05
glean 1.85 SE 0.04
*Significantly different from control (p < 0.003). specimens were then embedded in paraffin, sectioned parasagittally, and stained with hematoxylin and eosin. To confirm osteoporosis in the cortisone treatment groups, the right humerus was taken from each rabbit, cleaned, and dried. Each bone was oriented on an occlusal x-ray film (Eastman Kodak, Rochester, N.Y.) and radiographed, wit.h, the cone 30 mm from the film at settings of 15 mA and 50 kVp. Average
radiodensitometric readings were obtained with the 1 mm aperture at standardized locations on the cortical bone of 5 mm, 10 mm, 15 mm, and 20 mm from the junction of the head and the shaft of the humerus along the greater curve of the shaft. The humeri of treatment and control animals were tested for density differences with the standard t test and the analysis of covariance (ANCOVA).
Data analysis Linear tooth movement measurements were analyzed with SAS statistical software (SAS Institute, Inc., Cary, N.C.). The experimental design was the typical split plot two-way analysis of variance with rabbits nested within groups and repeated measurements recorded over time. Groups consisted of eight rabbits that received cortisone acetate (treatment) and eight rabbits that did not receive cortisone acetate (control). These two main groups were further subdivided into four groups of four. The analysis therefore consisted of a treatment and a control group studied only during active tooth movement (To, C,), and a treatment and a control group studied during active tooth movement and during a relapse phase (T, + ,, C, .,). The comparisons of specific interest were those between groups for each measurement period. Histologic sections of treatment and control specimens were examined microscopically. Qualitative assessment of
Volume 102 Number 4
Effect of corticosteroids on tooth nzovement
313
3.0
w --
2"51 2.0 1.5 1.0 0.5' 0.0'
u~ cc p-
9
[] CCtm~L
-0.5.
2
TREATkIENT
-1.0.
"
~
TREATMENT 9
CC~,t~
.J
-3.0
4
7
11 14 DAYS
18
21
0
5
10 15 DAYS
20
25
Fig. 3. Mean incremental active tooth movement and relapse (negative values) for each measurement period in treatment and control groups.
Fig. 4. Mean cumulative tooth movement at each measurement
indicators of formative and resorptive bone activity was determined in two anatomically defined areas (Fig. 2).
Linear measurements
RESULTS Morbidity and mortality All rabbits consumed food and water at a rate indicating that the orthodontic appliance was not an interference. Throughout the experimental period, the eight control animals gained weight. Although the eight treatment rabbits consumed food and water at rates equivalent to control animals, the treatment rabbits began to lose weight at varying times from the initiation of the cortisone injections. One treatment rabbit died from complications secondary to the cortisone treatment, and one treatment animal died in a cage-related accident.
Bone density Densitometric readings (Model TBX, Tobias Associates, Ivyland, Pa.) from the humeri indicate striking differences between the two groups (p < 0.003). The mean optical density for the cortisone treatment animals was 2.14 as compared to 1.85 for control animals. (An area of lesser density results in greater radiographic film exposure; greater radiodensitometric readings represent bone of lesser density (Table I).) Because the cortisone treated rabbits lost weight throughout the experiment, optical density readings were adjusted for humerus length with ANCOVA. The covariate was not significant, indicating that there was no relationship between optical density and length. Therefore adjusted means were virtually identical to nonadjusted means (treatment, 2.15; control, 1.82). In addition, length of the humerus was independent of both group and days in study.
period for treatment and control animals.
In all groups, tooth movement was significant (p < 0.0001). However, the rates of tooth movement differed dramatically between the cortisone treatment groups (Ta, T~ + r) and the control groups (C,, Ca + ,). These results demonstrate increased rates of active tooth movement and relapse in the cortisone treatment animals compared with the control animals during each measurement period (p < 0.0001). Mean cumulative active tooth movement for the treatment groups ranged from three to four times greater than that of control groups for each measurement interval. After the first 4 days of the relapse period (day 18), the mean total relapse in the cortisone-treated group was 100% and about 17 times greater than that of the control group. The control group continued to relapse an average of 0.3 mm over the next 3 days until day 21 (Tables II and III; Figs. 3 and 4).
Histology As previously stated, all histologic sections were compared by using two anatomic locations, interproximal to the first and second molars at the midroot level and mesial to the first molar in the coronal one-third (Fig. 2). In general, sections taken from the maxilla of the cortisone-treated rabbits revealed evidence of increased bone resorption and/or decreased bone deposition. The bone between the first and second molars typically revealed small amounts of thin trabeculae and was scalloped with osteoclast-like cells in resorptive lucunae, much in contrast to control specimens (Figs. 5, A and B, and 6). In areas of pressure along the coronal one-third of the mesial surface of the first molar, the bone also appeared to be less dense than in controls and was typically scalloped with numerous osteoclastlike ceils. In addition, there was a greater tendency to
314
Ashcraft, Southard, and Tolley
am. J. Orthod. Dentc~tc. Orthop. October 1992
Table II. Incremental active tooth movement and relapse (negative values) in millimeters at each
measurement period for all treatment and control rabbits D~"
Subject
o
14717,,i,,,
I
,4,s
18-21
Treatment T,,t T, § To+,3 T,+,4 T.t T., T~ T,4 Mean SE
0.8 1.0 0.8 0.9 0.8 0.9 0.8 0.7 0.84** 0.04
0.5 0.3 0.4 0.4 0.7 0.8 0.8 0.5 0.54** 0.04
0.4 0.5 0.3 expired 0.5 expired 0.6 0.6 0.50** 0.05
0.5 0.4 0.8
-2.2 -2.2 -2.3
0.0 0.0 0.0
0.7 0.56** 0.05
--2.28** 0.07
0.3 0.2 0.2 0.2 0.3 0.2 0.2 0.1 0.21 0.04
0.1 0.2 0.1 0.1 0.2 0.3 0. I 0.2 O. 16 0.04
0.2 O. 1 0.3 0.2
0.1 0.2 0.2 0.2 0.2 0.2
-0.1 -0.2 -0.1 -0.1 ---
0.4 0.5
m
__
-0.00"" 0.00
Control C,§ C,.,z C,.o C,§ C.t
C~ C,3 C.~ Mean SE
0.1
0.1 0.2 0.2 O. 18 0.04
-0.2 -0.3 -0.3 -0.3 ---
0.1
--
0.1 0.16 0.04
--
---
-0.12 0.06
-0.27 0.06
*Significantly different from control (p < 0.02). **Significantly different from control (p < 0.0001). JRelapse was 100% at previous measurement interval.
Table III. Cumulative tooth movement in millimeters at each measurement period for all treatment and control rabbits Day Subject
4
I
7
I
"
I
,4
I
,s
I
2,
Treatment T,+,I T,~,. T,+,3 "1".,.,4 T,I T,a, T~ T,4 Mean SE
0.8 1.0 0.8 0.9 0.8 0.9 0.8 0.7 0.84** 0.04
1.3 1.3 1.2 1.3 1.5 1.7 1.6 1.2 1.38"~ 0.04
1.7 1.8 1.5 expired 2.2 expired 2.2 1.8 1.89** 0.05
2.2 2.2 2.3
0.3 0.2 0.2 0.2 0.3 0.2 0.2 0.1 0.21 0.04
0.4 0.4 0.3 0.3 0.5 0.5 0.3 0.3 0.38 0.04
0.6 0.5 0.6 0.5 0.6 0.6 0.5 0.5 0.55 0.04
2.6
0.0 0.0 0.0
0.0 0.0 0.0
--
--
2.7 2.5 2.44** 0.05
--0.00'* 0.00
--0.00" 0.00
0.7 0.7 0.8 0.7 0.8 0.8 0.6 0.6 0.71 0.04
0.6 0.5 0.7 0.6 ----0.60 0.05
0.5 0.4 0.5 0.3 ----0.43 0.05
Control C.., C,,z C,,-,3 C,+,~ C,t C.: C~3 C~4 Mean SE
*Significantly different from control (p < 0.02). **Significantly different from control (p < 0.0001).
Volume 102 Number 4
Effect of corticosteroids on tooth movement
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Fig. 5. Photomicrographs of midroot interproximal area of the maxillary first and second molars. A, Control, 14 days; demonstrating the density of the interproximal bone (b) bounded by periodontal ligament. Bar = 1.0 mm. B, Cortisone treatment, 14 days; note the difference in the overall bone (b) density compared with the control. Bar = 1.0 ram.
observe resorption of the cementum in this location in the cortisone treatment groups (Figs. 7, A and B, and 8). In areas of tension, the bone adjacent to the distal root surface of the first molar had few osteoblasts present with evidence of little or no bone deposition in the treatment group animals. All of these findings were quite different from those of control specimens. Sections taken from the maxilla of control rabbits revealed evidence of bone resorption a n d bone deposition, but the amount of resorption appeared to be less than that observed in the cortisone treatment groups. The amount of bone, in general, appeared to be greater in the control group. Osteoclast-like cells were observed in areas of pressure along the bone surface adjacent to the mesial root of the first molar; however,
the numbers visible were fewer than those observed in the cortisone-treated animals. In contrast to treatment specimens, osteoclasts were not observed in areas of bone interproximal to the first and second molars. The bone adjacent to the distal root surface of the first molar, an area of tension, was often characterized by a border of osteoblasts along the outer surface (Fig. 9). DISCUSSION
Corticosteroids are widely used in the treatment of a variety of medical conditions. Osteoporosis, however, is a well documented side effect of these drugs which results from a pathologic dissociation of the normal processes of bone remodeling. It is recommended that patients who are taking corticosteroids for longer than
:316
Am. J. Ortbod. Dentofac. Orthop. October 1992
Ashcraft, Southard, and Toiler -
,~
{7'
..
4
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nl 9 {
?.ii99 .~ =~
Fig. 6. Photomicrograph of midroot interproximal bone of maxillary first and second molars from cortisone treatment, 14-day rabbit demonstrating numerous osteoclast-like cells (arrows). These cells were not apparent in similar sections from control rabbits. Bar = 0.5 mm.
a few months be examined for radiographic signs of osteoporosis.2-" Normal bone remodeling is fundamental to orthodontics. Very little is known about the possible effects of corticosteroid therapy on tooth movement. The prerequisite to study these effects is a good animal model demonstrating a confirmed state of osteoporosis. In this study, rabbits administered 15 mg/kg cortisone acetate daily demonstrated osteoporosis on the basis of radiodensitometric and histologic analyses. The humeris of the cortisone groups were strikingly less dense than those of controls (p < 0.003). Histologically, the bone on the pressure side of the alveolus was less dense with more osteoclast-like cells present in the treatment groups. Interproximal bone on the tension side of the alveolus had a noticeable absence of osteoblasts in the treatment groups. Furthermore, numerous osteoclast-like cells were noted interproximally in the cortisone treatment animals. The presence of osteoclast-iike cells interproximal to the first and second molars on the tension side of the alveolus indicates an influence other than the orthodontic force, specifically a cortisone influence. Linear tooth movement measurements indicated that the rate of active tooth movement was approximately three to four times greater in treatment groups than in controls (p < 0.0001). Because a general model of increased skeletal resorption has been demonstrated and is attributed to an elevation of osteoclastic, activity,
it is possible that during conditions stimulating additional resorptive influences (i.e., an orthodontic force) increased resorption might occur. The results of this research tend to support this theory. The measure of relapse indicates that the tooth movement of treatment groups was dramatically less stable than in controls (p < 0.0001). These results support the belief that if bone deposition is suppressed, then the stability of the new tooth position is in doubt. The treatment groups relapsed 100% during the first 4 days after removal of appliances. The controls relapsed at a much lesser rate (p < 0.0001) and never achieved 100% relapse during the experimental period. The histologic studies presented evidence possibly explaining these differences. The interproximal areas of the first and second molars revealed little bone was present with no indication of new bone formation in the treatment animals, whereas the same areas of controls had significantly more bone present with evidence of new bone formation. It must be kept in mind, though, that our experimental animals received relatively short-term administration of cortisone acetate ranging from 18 to 25 days. There is evidence that during the initial administration of corticosteroids, a period of very rapid bone loss occurs that may not be totally representative of longer term administration or other chronic conditions. 23 Loss of weight in the cortisone treated animals was noted. This difference in the general metabolism of the
Voh,me 102
Effect o f corticosteroids oli tooth movenlent
Number 4
317
Fig. 7. Photomicrographs of bone mesiocclusal to maxillary first molar. A, Control, 14 days; demonstrating the density of the bone (b). Bar = 1.0 ram. B, Cortisone treatment, 14 days; note the difference in the overaTI bone (b) density as compared with the control. Bar = 1.0 ram.
treatment animals, in addition to the specific osteoporotic effects, may have influenced the rates of tooth movement. For example, the contribution of generally altered protein synthesis or other metabolic activity cannot be excluded. In this study, all treatment animals very clearly demonstrated evidence of osteoporosis. Further speculation concerning these results may lead to the question of a possible relationship between a subclinical osteoporosis and effects on orthodontic tooth movement. That is, there may be effects on bone cell function that alter the
normal response to orthodontics without overt osteoporosis. Similarly, more adults, especially women, are seeking orthodontic treatment. Consideration of the effects of postmenopausal osteoporosis (and other osteoporoses) is warranted because although the pathogenesis of this condition is not well understood, the condition involves similar effects on bone remodeling. 6.24 Perhaps, even early subclinical effects of this condition unknowingly impact our practice because the onset of " bone loss in women may actually precede menopause,
318
Ashcraft, Southard, and Tolley
Am..I. O~hod. Dentofac. O~n~ot~. October 1992
9
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I t has been well documented since 1932 that oversecretion of cortisol by the adrenal cortex causes osteoporosis. L2 Since their introduction in the mid1950s, synthetic corticosteroids have been used in therapeutic regimens for the treatment of a wide variety of ailments ranging from arthritis to renal, collagen, allergic, and neoplastic diseases. Similarly, it has been demonstrated that supraphysiologic doses of these drugs administered chronically induce the same osteoporosis found in naturally occurring states of hypercortisolism): The exact physiologic basis for corticosteroid osteoporosis is not completely understood. In general, the mechanism involves the uncoupling of the normal relationship of bone formation and resorption; bone formation is decreased while bone resorption is increased) Regarding bone formation, the effects of corticosteroids appear to be multidimensional. Evidence indicates that corticosteroids produce a direct inhibition of osteoblastic function. This inhibition is mediated through effects on osteoblasts and osteobtastic precursors that This research was supported by the Faustin Neff Weber Research Fellowship. aln private practice, Little Rock, Ark. bAssistant Professor, Department of Orthodontics, The Unive~ity of Iowa, Iowa City. CAssociate Professor, Department of Biostatistics and Epidemiology, The University of Tennessee, Memphis. 8/1130362
310
result in a decrease in total bone formation. 3'5" The effects of corticosteroids on osteoclasts are a little less clear. Studies indicate that corticosteroids produce an increased resorptive response. 3::2t4 However, the specific mechanism is not well understood and may involve a secondary hyperparathyroidism: '~'~~ The level of parathyroid hormone is frequently elevated in patients treated with corticosteroids. This elevated level of parathyroid is caused by the direct inhibition of calcium absorption by the steroid and the induction of hypercalciuria especially with high doses of corticosteroids. The end result is an increase in bone resorption)'" Very little is known about the effects of corticosteroid osteoporosis on orthodontic tooth movement. Previous researchers have not established a drug regimen for their specific animal models in which osteoporosis could be consistently demonstrated. Storey ~6studied the histology of tooth movement in rabbits and guinea pigs that received doses of cortisone acetate. However, the doses that he used in guinea pigs were most likely not large enough to induce an osteoporosis, t6 Similarly, Davidovitch ~7 studied rates of tooth movement in cats treated with daily doses of cortisone acetate. He found slower rates of tooth movement in the experimental animals but failed to confirm a state of osteoporosis. The purpose of this investigation was (1) to develop a confirmed state of corticosteroid osteoporosis in an animal model, (2) to quantify rates of active tooth
Voh,me 102
Effect o f corticosteroids on tooth movement
311
Number 4
Fig. 1. Diagram of orthodontic appliance design, which consisted of a spring that applied tension between maxillary first molar and central incisor of rabbit.
movement and relapse in the model, and (3) to examine for histologic evidence that active tooth movement a n d / o r relapse may be affected in corticosteroid treated subjects.
MATERIALS AND METHODS Selection of experimental model Researchers have used human iliac crest biopsies," guinea pigs, t8 rats, ~9':~and rabbits, ~3 to study corticosteroid osteoporosis. However, Thompson et al." were able to consistently demonstrate osteoporosis with quantitative microradiography in rabbits receiving daily 15 mglkg injections of cortisone acetate. Likewise, Storey '~ found osteoporosis after 4 days in rabbits that received a similar dose of cortisone. Therefore, 3-month-old New Zealand white rabbits were selected and administered cortisone acetate at doses of 15 mg/kg for 4 days before and during the experimental period.
Appliance placement and design The rabbit maxilla was selected for appliance placement because of its known vulnerability to osteoporosis. '* The appliance was designed according to Heller and Nanda. 2~A 1.0 cm section of 0.010 • 0.045-inch closed coil spring (Rocky Mountain Orthodontics, Denver, Colo.) was affixed to the maxillary left first molar and the maxillary left central incisor with a 0.012-inch steel ligature. Retention grooves were placed with a Vz-round bur to prevent dislodgement of the steel ligatures. These grooves were placed subgingivaUy on the buccal and the palatal surfaces of the maxillary left first molar and on the mesial and distal surfaces of the maxillary left central incisor at the level of the gingiva. The mandibular central incisors were disked out of occlusion to prevent appliance breakage. The appliance was calibrated with a Dontrix force gauge (ETM, Monrovia, Calif.) to deliver a 4-ounce force and recalibrated to remain at 4 ounces at each measurement interval (Fig. 1).
Group determination Sixteen rabbits were divided equally into four groups, two treatment and two control. The two treatment groups received daily subcutaneous injections of 15 mg/kg cortisone
acetate for 4 days before and during the experimental period. The two control groups received no cortisone. An orthodontic appliance was placed on the left first molar and incisor teeth of all 16 rabbits for 14 days. One treatment group (T,) and one control group (C,) were used to measure active tooth movement for 14 days. The two other groups (T, § and (C,. ,) had appliances removed after 14 days and had relapse of active tooth movement measured for an additional 7 days.
Animal care All animals were caged individually with regulated light and temperature and fed rabbit chow, lettuce, and water ad libitum. The rabbits were weighed daily to confirm that they were healthy, and to determine the daily dosage of cortisone acetate that each rabbit in the treatment groups would receive. At the time of appliance placement and during all toothmovement measurements, each rabbit was anesthetized with 0.4 mg/kg intramuscular injections of ketamine/xylazine admixture composed of 1.5 ml Xylazine (Hayer Lockhart, Swankee, Kan.) mixed with 10 ml Ketaset (Aveco, Fort Dodge, Iowa).
Tooth movement measurements Reference points were placed in the midpalatal surfaces of the left first and second molars with a Vz-round bur. All measurements of tooth movement were made with a Great Lakes caliper (Great Lakes Orthodontics, Tonawanda, N.Y.) calibrated to 0.1 mm and that had the points filed down to fit into the reference points on the teeth. Measurements of distance between the reference points on the first and second molars were made at the time of appliance placement, days 4, 7, 11, and 14. For the two relapse groups, (T.. ,, C , . ,), measurements were also taken at days 18 and 21.
Tissue preparation At the appropriate time of sacrifice, rabbits were killed with an intravenous injection of commercial euthenasia agent, T-6I (Agrivet Co., Sommerville, N.J.). Maxillary molar segments were dissected out, fixed in 10% buffered formalin, and decalcified with Decal II (Surgipath, Grayslake, II1.). The
312
Am. J. Orthod. Oentofac. Orthop.
Ashcraft, Sottthard. a m l Tolle~'
"
October 1992
APPLIED FORCE
IL,/[
ALVEOLAR BONE FIRST MOLAR INCISOR
PERIODONTALLIGAI~NT
ALVEOLARBONE
Fig. 2. Schematic representation of rabbit maxilla demonstrating two anatomic areas examined microscopically for comparisons between groups. The bold squares represent (1) a mesiocclusal area relative to the maxillary first molar and (2) a midroot inlerproximal area of the maxillary first and second molars.
Table
I. Optical densities o f cortical b o n e taken from the right humeri o f six treatment and eight control rabbits
Treatment
I
Control
To.,t 2.31 T,+,,. 2.02 T,+,3 1.97 T,+a expired T,i 2.18 T,: expired Te 2.15 Ta 2.05
C,§ 1.77 C,§ 1.98 C,+,3 1.77 C,+a 1.91 Ca 1.65 Ca 1.98 Ca 1.91 Ca 1.85
glean 2.14' SE 0.05
glean 1.85 SE 0.04
*Significantly different from control (p < 0.003). specimens were then embedded in paraffin, sectioned parasagittally, and stained with hematoxylin and eosin. To confirm osteoporosis in the cortisone treatment groups, the right humerus was taken from each rabbit, cleaned, and dried. Each bone was oriented on an occlusal x-ray film (Eastman Kodak, Rochester, N.Y.) and radiographed, wit.h, the cone 30 mm from the film at settings of 15 mA and 50 kVp. Average
radiodensitometric readings were obtained with the 1 mm aperture at standardized locations on the cortical bone of 5 mm, 10 mm, 15 mm, and 20 mm from the junction of the head and the shaft of the humerus along the greater curve of the shaft. The humeri of treatment and control animals were tested for density differences with the standard t test and the analysis of covariance (ANCOVA).
Data analysis Linear tooth movement measurements were analyzed with SAS statistical software (SAS Institute, Inc., Cary, N.C.). The experimental design was the typical split plot two-way analysis of variance with rabbits nested within groups and repeated measurements recorded over time. Groups consisted of eight rabbits that received cortisone acetate (treatment) and eight rabbits that did not receive cortisone acetate (control). These two main groups were further subdivided into four groups of four. The analysis therefore consisted of a treatment and a control group studied only during active tooth movement (To, C,), and a treatment and a control group studied during active tooth movement and during a relapse phase (T, + ,, C, .,). The comparisons of specific interest were those between groups for each measurement period. Histologic sections of treatment and control specimens were examined microscopically. Qualitative assessment of
Volume 102 Number 4
Effect of corticosteroids on tooth nzovement
313
3.0
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18
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Fig. 3. Mean incremental active tooth movement and relapse (negative values) for each measurement period in treatment and control groups.
Fig. 4. Mean cumulative tooth movement at each measurement
indicators of formative and resorptive bone activity was determined in two anatomically defined areas (Fig. 2).
Linear measurements
RESULTS Morbidity and mortality All rabbits consumed food and water at a rate indicating that the orthodontic appliance was not an interference. Throughout the experimental period, the eight control animals gained weight. Although the eight treatment rabbits consumed food and water at rates equivalent to control animals, the treatment rabbits began to lose weight at varying times from the initiation of the cortisone injections. One treatment rabbit died from complications secondary to the cortisone treatment, and one treatment animal died in a cage-related accident.
Bone density Densitometric readings (Model TBX, Tobias Associates, Ivyland, Pa.) from the humeri indicate striking differences between the two groups (p < 0.003). The mean optical density for the cortisone treatment animals was 2.14 as compared to 1.85 for control animals. (An area of lesser density results in greater radiographic film exposure; greater radiodensitometric readings represent bone of lesser density (Table I).) Because the cortisone treated rabbits lost weight throughout the experiment, optical density readings were adjusted for humerus length with ANCOVA. The covariate was not significant, indicating that there was no relationship between optical density and length. Therefore adjusted means were virtually identical to nonadjusted means (treatment, 2.15; control, 1.82). In addition, length of the humerus was independent of both group and days in study.
period for treatment and control animals.
In all groups, tooth movement was significant (p < 0.0001). However, the rates of tooth movement differed dramatically between the cortisone treatment groups (Ta, T~ + r) and the control groups (C,, Ca + ,). These results demonstrate increased rates of active tooth movement and relapse in the cortisone treatment animals compared with the control animals during each measurement period (p < 0.0001). Mean cumulative active tooth movement for the treatment groups ranged from three to four times greater than that of control groups for each measurement interval. After the first 4 days of the relapse period (day 18), the mean total relapse in the cortisone-treated group was 100% and about 17 times greater than that of the control group. The control group continued to relapse an average of 0.3 mm over the next 3 days until day 21 (Tables II and III; Figs. 3 and 4).
Histology As previously stated, all histologic sections were compared by using two anatomic locations, interproximal to the first and second molars at the midroot level and mesial to the first molar in the coronal one-third (Fig. 2). In general, sections taken from the maxilla of the cortisone-treated rabbits revealed evidence of increased bone resorption and/or decreased bone deposition. The bone between the first and second molars typically revealed small amounts of thin trabeculae and was scalloped with osteoclast-like cells in resorptive lucunae, much in contrast to control specimens (Figs. 5, A and B, and 6). In areas of pressure along the coronal one-third of the mesial surface of the first molar, the bone also appeared to be less dense than in controls and was typically scalloped with numerous osteoclastlike ceils. In addition, there was a greater tendency to
314
Ashcraft, Southard, and Tolley
am. J. Orthod. Dentc~tc. Orthop. October 1992
Table II. Incremental active tooth movement and relapse (negative values) in millimeters at each
measurement period for all treatment and control rabbits D~"
Subject
o
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18-21
Treatment T,,t T, § To+,3 T,+,4 T.t T., T~ T,4 Mean SE
0.8 1.0 0.8 0.9 0.8 0.9 0.8 0.7 0.84** 0.04
0.5 0.3 0.4 0.4 0.7 0.8 0.8 0.5 0.54** 0.04
0.4 0.5 0.3 expired 0.5 expired 0.6 0.6 0.50** 0.05
0.5 0.4 0.8
-2.2 -2.2 -2.3
0.0 0.0 0.0
0.7 0.56** 0.05
--2.28** 0.07
0.3 0.2 0.2 0.2 0.3 0.2 0.2 0.1 0.21 0.04
0.1 0.2 0.1 0.1 0.2 0.3 0. I 0.2 O. 16 0.04
0.2 O. 1 0.3 0.2
0.1 0.2 0.2 0.2 0.2 0.2
-0.1 -0.2 -0.1 -0.1 ---
0.4 0.5
m
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Control C,§ C,.,z C,.o C,§ C.t
C~ C,3 C.~ Mean SE
0.1
0.1 0.2 0.2 O. 18 0.04
-0.2 -0.3 -0.3 -0.3 ---
0.1
--
0.1 0.16 0.04
--
---
-0.12 0.06
-0.27 0.06
*Significantly different from control (p < 0.02). **Significantly different from control (p < 0.0001). JRelapse was 100% at previous measurement interval.
Table III. Cumulative tooth movement in millimeters at each measurement period for all treatment and control rabbits Day Subject
4
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Treatment T,+,I T,~,. T,+,3 "1".,.,4 T,I T,a, T~ T,4 Mean SE
0.8 1.0 0.8 0.9 0.8 0.9 0.8 0.7 0.84** 0.04
1.3 1.3 1.2 1.3 1.5 1.7 1.6 1.2 1.38"~ 0.04
1.7 1.8 1.5 expired 2.2 expired 2.2 1.8 1.89** 0.05
2.2 2.2 2.3
0.3 0.2 0.2 0.2 0.3 0.2 0.2 0.1 0.21 0.04
0.4 0.4 0.3 0.3 0.5 0.5 0.3 0.3 0.38 0.04
0.6 0.5 0.6 0.5 0.6 0.6 0.5 0.5 0.55 0.04
2.6
0.0 0.0 0.0
0.0 0.0 0.0
--
--
2.7 2.5 2.44** 0.05
--0.00'* 0.00
--0.00" 0.00
0.7 0.7 0.8 0.7 0.8 0.8 0.6 0.6 0.71 0.04
0.6 0.5 0.7 0.6 ----0.60 0.05
0.5 0.4 0.5 0.3 ----0.43 0.05
Control C.., C,,z C,,-,3 C,+,~ C,t C.: C~3 C~4 Mean SE
*Significantly different from control (p < 0.02). **Significantly different from control (p < 0.0001).
Volume 102 Number 4
Effect of corticosteroids on tooth movement
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Fig. 5. Photomicrographs of midroot interproximal area of the maxillary first and second molars. A, Control, 14 days; demonstrating the density of the interproximal bone (b) bounded by periodontal ligament. Bar = 1.0 mm. B, Cortisone treatment, 14 days; note the difference in the overall bone (b) density compared with the control. Bar = 1.0 ram.
observe resorption of the cementum in this location in the cortisone treatment groups (Figs. 7, A and B, and 8). In areas of tension, the bone adjacent to the distal root surface of the first molar had few osteoblasts present with evidence of little or no bone deposition in the treatment group animals. All of these findings were quite different from those of control specimens. Sections taken from the maxilla of control rabbits revealed evidence of bone resorption a n d bone deposition, but the amount of resorption appeared to be less than that observed in the cortisone treatment groups. The amount of bone, in general, appeared to be greater in the control group. Osteoclast-like cells were observed in areas of pressure along the bone surface adjacent to the mesial root of the first molar; however,
the numbers visible were fewer than those observed in the cortisone-treated animals. In contrast to treatment specimens, osteoclasts were not observed in areas of bone interproximal to the first and second molars. The bone adjacent to the distal root surface of the first molar, an area of tension, was often characterized by a border of osteoblasts along the outer surface (Fig. 9). DISCUSSION
Corticosteroids are widely used in the treatment of a variety of medical conditions. Osteoporosis, however, is a well documented side effect of these drugs which results from a pathologic dissociation of the normal processes of bone remodeling. It is recommended that patients who are taking corticosteroids for longer than
:316
Am. J. Ortbod. Dentofac. Orthop. October 1992
Ashcraft, Southard, and Toiler -
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Fig. 6. Photomicrograph of midroot interproximal bone of maxillary first and second molars from cortisone treatment, 14-day rabbit demonstrating numerous osteoclast-like cells (arrows). These cells were not apparent in similar sections from control rabbits. Bar = 0.5 mm.
a few months be examined for radiographic signs of osteoporosis.2-" Normal bone remodeling is fundamental to orthodontics. Very little is known about the possible effects of corticosteroid therapy on tooth movement. The prerequisite to study these effects is a good animal model demonstrating a confirmed state of osteoporosis. In this study, rabbits administered 15 mg/kg cortisone acetate daily demonstrated osteoporosis on the basis of radiodensitometric and histologic analyses. The humeris of the cortisone groups were strikingly less dense than those of controls (p < 0.003). Histologically, the bone on the pressure side of the alveolus was less dense with more osteoclast-like cells present in the treatment groups. Interproximal bone on the tension side of the alveolus had a noticeable absence of osteoblasts in the treatment groups. Furthermore, numerous osteoclast-like cells were noted interproximally in the cortisone treatment animals. The presence of osteoclast-iike cells interproximal to the first and second molars on the tension side of the alveolus indicates an influence other than the orthodontic force, specifically a cortisone influence. Linear tooth movement measurements indicated that the rate of active tooth movement was approximately three to four times greater in treatment groups than in controls (p < 0.0001). Because a general model of increased skeletal resorption has been demonstrated and is attributed to an elevation of osteoclastic, activity,
it is possible that during conditions stimulating additional resorptive influences (i.e., an orthodontic force) increased resorption might occur. The results of this research tend to support this theory. The measure of relapse indicates that the tooth movement of treatment groups was dramatically less stable than in controls (p < 0.0001). These results support the belief that if bone deposition is suppressed, then the stability of the new tooth position is in doubt. The treatment groups relapsed 100% during the first 4 days after removal of appliances. The controls relapsed at a much lesser rate (p < 0.0001) and never achieved 100% relapse during the experimental period. The histologic studies presented evidence possibly explaining these differences. The interproximal areas of the first and second molars revealed little bone was present with no indication of new bone formation in the treatment animals, whereas the same areas of controls had significantly more bone present with evidence of new bone formation. It must be kept in mind, though, that our experimental animals received relatively short-term administration of cortisone acetate ranging from 18 to 25 days. There is evidence that during the initial administration of corticosteroids, a period of very rapid bone loss occurs that may not be totally representative of longer term administration or other chronic conditions. 23 Loss of weight in the cortisone treated animals was noted. This difference in the general metabolism of the
Voh,me 102
Effect o f corticosteroids oli tooth movenlent
Number 4
317
Fig. 7. Photomicrographs of bone mesiocclusal to maxillary first molar. A, Control, 14 days; demonstrating the density of the bone (b). Bar = 1.0 ram. B, Cortisone treatment, 14 days; note the difference in the overaTI bone (b) density as compared with the control. Bar = 1.0 ram.
treatment animals, in addition to the specific osteoporotic effects, may have influenced the rates of tooth movement. For example, the contribution of generally altered protein synthesis or other metabolic activity cannot be excluded. In this study, all treatment animals very clearly demonstrated evidence of osteoporosis. Further speculation concerning these results may lead to the question of a possible relationship between a subclinical osteoporosis and effects on orthodontic tooth movement. That is, there may be effects on bone cell function that alter the
normal response to orthodontics without overt osteoporosis. Similarly, more adults, especially women, are seeking orthodontic treatment. Consideration of the effects of postmenopausal osteoporosis (and other osteoporoses) is warranted because although the pathogenesis of this condition is not well understood, the condition involves similar effects on bone remodeling. 6.24 Perhaps, even early subclinical effects of this condition unknowingly impact our practice because the onset of " bone loss in women may actually precede menopause,
318
Ashcraft, Southard, and Tolley
Am..I. O~hod. Dentofac. O~n~ot~. October 1992
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