The activity of alveolar bone incident to orthodontic tooth movement as studied by oxytetracycline-induced fluorescence

American Journal of ORTHODONTICS Volume

3, M A R C H , 1968

54, Number

ORIGINAL

ARTICLES

The activity of alveolar bone incident to orthodontic tooth movement as studied by oxytetracycline-induced fl uorescence* E.

KENT

UTLEY,

B.S.,

I).I).S.,M.S.

San Jose, Calif. ORTHODONTIC treatment is based on the premise that when force is delivered to a tooth and thereby transmitted to the adjacent investing tissues, certain structural alterations take place within these tissues which allow for, and contribute to, the movement of that tooth. The specific changes which occur in the investing bone tissue that surrounds the root of an orthodontically moving tooth are commonly described as follows: Resorption of the bone on the pressure side of the socket wall clears a path, or makes space available, ahead of the advancing tooth ; deposition of bone on the tension side of the socket maintains a progressively advancing socket wall behind the moving tooth. However, the changes in the investing bone tissue which take place in response to orthodontic force are not limited to resorption and deposition in areas of pressure and tension on the socket wall. The architectural pattern of the trabecular arrangement in the supportive bone surrounding the alveolus also responds to the orthodontic force and the moving tooth by adaptive alterations in its structural design. In 1892 Julius WoliF published his classic, “Das Gesetz der Transformation der Knochen,” in which he claimed to have originated the law (Wolff’s law) which stated that the internal structure of a bone was determined by the mechanical forces acting upon it. John C. KochI stated in 1917 that the inner architecture of normal boric was determined by definite and exact requirements of mathematical and mechanical laws. This thesis was written in partial fulfillment of the requirements Science degree at the University of Southern California, School ate Orthodontic Department (Harry L. Dougherty, chairman). This *Winner

research of

was supported the

1966

Milo

in part Hellman

through

a grant

Award,

American

from

the

Association

for the Master of of Dentistry, GraduTweed

Foundation. of

Orthodontists.

In 1918 William

Bayliss,” the notetl physiologist,

wrote’ :

Vital phenomena being essentially dynamic, the study of physiology consist,s in the inwstigation of changes. As .Jcnnings says, “It is of thlb vmy greatest importanw for the understanding of t.hc behaviour of organisms, to look upon t.hwn chicfly as somf~thing dynamic-as prorc~st~s rather than St IV~tUrW. AIL :tnirml its

is

sornc~thing

thxt

happens.”

This investigation, utilizing t,hc rcccntl,v discovcrccl \-it al staining prop(krt y of the tetracvcline antibiotics, demonstrates the structural dynamics and osteogenic activity of alveolar bone in its biologic: rc~ponsr to ort,hoclontic tooth movem(~nl. REVIEW EARLY

OF

THE

THEORIES

LITERATURE OF ORTHODONTIC

TOOTH

MO\‘EMEST.

In

the

first,

~lllCl+C&Il

test.

on orthodontics, published in 1.880, Norman W’. Kingsltly’” discussed alvcolai bone and its response to forces which were externally applied to the teeth. He explained the orthodont,ic movement of teeth as a result of the clast,icity of alveolar bone. In 1888 FarraP described the orthodontic movement of teeth as a result of the resorption and apposition of bone and the bending of the alveolar process. Edward H. Angle* claimed in 1907 that absorption of the alveolar process occurred in advance of the moving tooth and that deposition of bone followed behind it,, but, that, the first and principle response to orthodontic force was the bending of the alveolar process. Angle illustrated the bending of alveolar bone by noting that the bony septum closely followed a moving tooth. BreitneP refuted Angle’s theory when he sta.ted in 1940 that, during tooth movement, the bone tissue which formed the septa between t,he teeth did not travel along with the moving teeth. In&cad, he said, it was progressively reformed of entirely new boric. JTistologic invedgation of t,he effwt, of orthodontic fame on alvcolwr boric was initiated in 1904 by Carl Sandstcdt.:” He experimented on t,he terth of (logs and reported that, with the application of force, both weak and strong, there was deposition of bone on the tension side of the old socket wall. On the pr~ssn~ side the alveolar bone was equally resorbed by wea.k forces; strong forces, howcvcr, resulted in “undermining rctsorption.” Gottlicb and Orbanl’ discusser1 orthodont,ic to’ot,h movement. and agrrcd with Sandstedt on the subject. of undermining resorption. and BrodielS found that. Sandst,edt’s In 1954 Macapanpan, Weinmann, theory of undermining resorption was also valid for t,he orthodontic movement of the molar t,eeth of rats. Sicher and Weinmann,“” in 1944, found that human t.eeth moved, or drifted, throughout the life of the individual. They termed this process “physiological tooth movement” and compared it with orthodontic tooth movement.

Volume Number

54 3

Posttreatnzent

activity

of alveolar booze 169

Brash,5 in 1928, utilized vital staining techniques and demonstrated that associated with the general physiologic growth of alveolar bone there were constant additions to the walls of the alveoli and the interalveolar septa which caused a slight, but continual, eruption of the teeth. He added that the alveolus of an apparently stationary tooth was constantly altering, so that in due time it consisted of entirely new bone. INTERNBL STRUCTURAL ARCHITECTURE OF ALVEOLAR BONE. A description Of the normal structural arrangement of alveo1a.r bone was given by ParfiW in 1962. MacMillan,lg in 1926, stated that bone tissue that was under stress was characterized by an increased closeness of the spacing of trabeculae in accordance with strict principles of engineering. In 1928 he added that the texture of bone surrounding a tooth depended on the “number of pounds of pressure” exerted in the act of mastication.20 In 1926 Johnson, Appleton, and Rittershofer15 experimented on a young monkey and found that, in response to orthodontic force, the trabecular rearrangement was in the direction of tooth movement. Herzberg,13 in 1932, was the first to move a human tooth with an orthodontic appliance and study its surrounding tissue. He found that, adjacent to the tooth, spicules of bone were formed on the tension side; they were arranged parallel to the direction of the force. Gottlieb and Orbanll claimed that the trabeculae of alveolar bone were laid down at right angles to the long axis of the tooth only when the lamina dura was completely destroyed by extreme forces. Breitner’j found in 1940 that, in response to orthodontic force, alveolar bone spicules were lined up parallel, but not exactly perpendicular, to the long axis of the tooth. They were aligned, however, in the direction of the pull. In 1953 Storey36 recognized four zones of activity around a tooth which was being moved with light orthodontic forces-“on the pressure side resorption and then deposition, on the tension side deposition then resorption.” He explained that behind the (1) newly forming bone on the tension side of the socket wall was an area of (2) resorption where spongy supportive bone eventually replaced the lamina dura which progressively re-formed as it followed behind the moving tooth. On the pressure side of the socket, ahead of the area of (3) resorption was an area of (4) apposition where the lamina dura was continually being re-formed in advance of the approaching tooth. In 1958 Stafferis published a roentgenographic study in which he claimed that each person had his own characteristic inherited alveolar pattern. He found that, despite the local bone changes observed in orthodontic t.herapy, “the over-all bone pattern did not change and the original pattern characteristic of the individual person eventually manifested itself in those areas of temporary change.” MAGNITUDE OF ORTHODONTIC FORCE. The exact magnitude of force that is most ideal for physiologic tooth movement has been a subject of controversy for many years among the members of the orthodontic specialty. Farrar,Q in 1876, did not give exact force values but indicated that forces of lighter magnitude were more desirable for tooth movement. In 1929 McKeag,21 was one of the earliest investigators to propose a specific

COKXC ValUa for the orthodontic movement of t,eeth. 1Ie (*liljlkl(~d tllat tllc‘ init ial pressure should be 2 ounces for each tooth. Schwarz,“’ in 1932, experimented on the teeth of dogs and evaluat,cd sarious magnitudes of orthodont,ic force. Stutevillc3’ claimed in 1937 that the magnitude OS an orthodontic force was not as important as t,hc distance through which it was active. He theorized that “one could use a ton of force if it were possible, and as long as the force was not active for a great enough distance to obliterat,e the blood vessels in the periodontal membrane. , . .” In 1942 Oppenheim*” critically described the effect of continuous forces. He claimed that intermittent light forces administered over long periods of time constituted the best orthodontic treatment. Moyers and Baue? suggested in 1950 that the ideal orthodontic appliance should operate over a distance of less t,han 0.2 mm. with a force of 15 to 25 grams. Smith and Storey,34 in 1952, studied the distal movement of maxillary cuspids in orthodontic patients. They found that. there was an optimum range of pressure on the tooth-bone interface which produced the maximum rate of tooth movement. This range of force ext,ended approximately from 150 to 200 grams. For pressure below t,his “optimum range” there was practically no movement, of the cuspid tooth. When the force was increased above the optimum range, the rate of movement of t,he tooth decreased and finally approached zero in the experimental time of one week. Fur experiments of longer duration, thr teeth resumed movement, but by the process of undermining rcsorption. In 1962 Burstone’ described three phases of orthodontic tooth movement.: (1) the initial phase, which represented the displacement of the tooth in the periodontal membrane space; (2) the lag phase, a period in which the tooth did not move or had a relatively low rate of displacement; (3) the postlag phase, in which the rate of movement gradually or suddenly increased. LOCATION OF FULCRUM DURING TIPPING MOVEMENT. The location of the point about which a tooth rotates or tips when a lateral force is applied to its crown has been a topic of disagreement among orthodontists for many years. Most, of tile investigatorsI, 7, 15, 2;,,31.32, 34,3X believed that a toot,11 acted as a two-armed lever when it tipped, the apex moving in the opposite direction from the crown. Others lo, 39 claimed that a tooth acted as a one-armetl lever, tipping with it,s fulcrum at the apex of the root. In 1938 Stuteville3” used motion-picture studies and determined that t,hc center of rotation of multirooted teeth in dogs and monkeys was located at a point which was about the middle of the bony septum. MacapanpaqWeinmann, and Brodie’” while investigating the orthodontic movement of rat molars in 1954, found t,hat the location of the fulcrum in a multirooted tooth depended upon the number, relative strength, spatial arrangement, and divergence of the roots. They concluded that rat molars tipped from an axis situated somewhere in the alveolar bone beyond the apices of the roots. In 1962 Burstone? gave precise measurements for the location of the center

Volume Number

54 3

Posttreatment

activity

of alveolar

bone

171

of resistance of a single-rooted tooth with a parabolic shape. He stated that it was at a point 0.4 times the distance from the alveolar crest to the apex. VITAL STAINING : TETRACYCLINE. Several investigators,‘2, 21, 30 have indicated the possibility of using antibiotics of the tetracycline series as another type of tracer material in studies of osseous tissue. They found that, with parenteral introduction of tetracycline, it was possible to produce heavily fluorescent areas in bone which was undergoing proliferation and calcification at the time of the drug’s administration. In 1963 Bhatia and Sognnaes4 reviewed the literature on tetracycline labeling of teeth and bones. They reported that, much like the deposition of madder, tetracyclines were deposited in the calcifying tissues of the body and therefore could be employed experimentally as “indicators for development of the dental and osseous hard tissue.” They concluded that, from an experimental point of view, a new scientific tool had been provided by the fact that “tetracycline appears to be a ‘fellow traveler’ of calcium and exhibits precisely definable areas of fluorescence wherever calcification has occurred at the time of tetracycline administration.” Urist and Ibseq40 in 1963, investigated the effect of oxytetracycline (Terramycin, Pfizer) on bone tissue. They found that following an intravenous infusion, the tetracycline was deposited in high concentration in “hot spots,” or the “highly reactive, newly deposited mineral” of the skeleton. In 1964 Ibsen and Urist14 studied the biochemical properties of the tetracyclines and found that they formed stable complexes with inorganic compounds. The binding of tetracycline to new bone was explained as follows: The new bone binds tetracycline to calcium on the crystal surface of apatite because of the stable calcium-tetracycline complex. The predominant attraction of new bone relative to old bone for tetracycline can be explained on the basis of relative availability of calcium.

The use of ultraviolet light microscopy has made it possible to study tissues which totally or partially exhibit fluorescence as a result of the incorporation of tetracycline. As predicted by McLeay and WalskeZ2 in 1960, the selective fixation of the tetracycline-fluorescent complex in osseous tissue has offered many new investigative methods for the study of the “morphology of osteogenesis.” STATEMENT

OF THE

PROBLEM

The purpose of this investigation was to study the structural dynamics and osteogenic activity of alveolar bone incident to orthodontic tooth movement using forces of different magnitude. Within the scope of this study the following areas were investigated : 1. Location of the center of resistence about which a tooth rotates when a continuous force is applied to its crown. 2. A differential comparison of distance and rate of tooth movement using orthodontic forces of different magnitudes. 3. The compensatory alteration of the internal structural architecture of alveloar bone in response to orthodontic t,ooth movement.

1.72

titley METHODS

AND

JIATERIAI,I:

Twenty-one young common do1nrst.k cats wcrc usc~1as the: c~xpc~rimc~nt aI a IIimals in t.his study. The domestic cat, E’rjlis c&s, was chosen l)eCilllst! of t h(* convenient, size and accessibility of its teeth, becaus,c of the rclativ(> W+C wit,h which it is handled and housed, and bec~ausc,as l)cbbancg rcportccl in 195X. the cat, is au c~xccllent animal for experiments in ort,hodontic reseer~h. Intcrferenccs with orthodont,ic tooth movement that al*e normally present hecanse of occlusion are negligible in the cat because of thtl la& of interdigitation of the opposing t,ecth. The maxillary dent,ition overlaps the mandibular dcntition. The exact ages of the animals WWCLnot tlrtcrmined, an(l sex tliffcrenccs were not considered. 911 animals weighed betwctln 6 and !f pounds at the beginning of the study, and no significant weight changes occurretl during bhe experimental duration. The animals were fed a diet of common commercial canned cat food and water. The soft consistency of the prepa.red canned food lessened t,he possibility of damage to the appliance. The methods used in this investigation were (1) alginate impressions of the maxillary arch for pretreatment record models; (2) placement of the orthodontic appliance; (3) vital staining of calcifying tissues wit,h intraperitoneal injections of oxyt,etracycline; (4) alginate impressions of the maxillary arch for posttreatment record models; (5) roentgenograms of maxillary lateral jaw sections ; (6) determination and calculation of tooth movement from record models and roentgenograms; and (T) histologic examination of the tissues. GROUP DESIGNATIOS AND EXPERIBLENT~~I, SCHEDULE. The twenty-one experiment,al animals were divided inbo five groups, designated as Groups A, B, C, I), and E. Each animal had two maxillary cuspid teeth; thus, there was a total sample of forty-two teeth available for orthodont,ic tooth movement and subsequent histologic examination. Group A consisted of six animals in a 30 day study. Seven appliances were placed ; three delivered forces of light magnitude (40 to 60 grams), one delivered a force of medium magnitude (135 to 165 grams), and three delivered forces of heavy magnitude (400 to 560 grams). No appliances were placed on five teeth, and these were designated as controls. On the twenty-seventh and twenty-eighth days after the appliances had been placed, the oxytctracyelinc vital stain was administered by intraperitoncal injcct,ion. The animals of Group A were sac%ficed on t.he thirtict,h day. (Iroup B consisted of five animals in a short-term experiment of 3 days. Six appliances were placed; two delivered light forces, two delivered medium forces, and two delivered heavy forces. Four teeth, on which no appliances were placed, were designated as controls. Each animal received an injection of oxyt,etracycline at the time the appliances were placed. A second injection of the vital stain was given on the following day. The animals of Group B were sacrificed on the third day. Group C consisted of three animals in a 9 day study. Five appliances were placed; one delivered a light force, three delivered medium forces, and one delivered a heavy force. One tooth, on which no appliance? was pla.ced> was desig-

Volume

54

Number

3

Posttreatment

activity

173

of alveolar bone

nated as a control. The first oxytetracycline injection was given 4 days prior to placement of the appliance. A second injection of the oxytetracycline vital stain was given after the appliance had been in place for 6 days. The animals of Group C were sacrificed on the ninth day. Group D consisted of three animals in a 21 day study. Six appliances were placed; two delivered light forces, two delivered medium forces, and two dclivered heavy forces. The first injection of oxytetracycline wits given 4 days prior to placement of the appliance. After the appliance had been in position for 6, 12, and 18 days, second, third, and fourth injections of oxytetracyclinc were given, respectively. The a,nimals of Group D were sacrificed on the twenty-first day. Group E consisted of four animals in a 15 day study. Six appliances were placed; three delivered light forces, one delivered a medium force, and two deTable I. Appliance

Day 0 1 2 3 4 5 6 7 s 9 10 11 12 13 14 15 1s 17 18 19 20 21 2”d 23 24 25 26 27 28 29 30 AP = Appliance I = Oxytetracyeline 8 = Sacrifice.

placement and oxytetracyc&te

I

I

A AP

I

B AP-I I

injection

Group c

I

schedule

D

I

I

AP

AI’

I

I

S

I

Ix AP I I 1 1 I 1 1 1 I r 1 I I

S S I

I

S I I S placement. injection.

MEASUREMENT OF ORTHODONTIC WRCES. The orthodontic l’o~ws uwtl iI1 tllis study were delivered to the teeth by means of stretched latex elastics. Two sizes of elastics were used, l/4 inch light ((lat. No. 1-3, Ornico (“orp.~ (~lcntlora, Calif.) and l/b inch heavy (Cat. No. 4-13, ()~JrJCY~ Corp.) In orcier that the magnit~~tlt of force dclivcred by an appliance could be accurately calculatt~I, a graph was plotJtc’tl which determined t,he relationship ol’ Corcc delivcrecl ( grams) p
160 t 140 120-

60 40 20 12

13

14

15

16

17

l’s

lb

20

Chart 1. Magnitude of force delivered by wet and dry latex elastics per elongation by stretching. Dry elastics were measured upon removal from package; wet elastics were soaked in water for 24 hours immediately preceding measurement. A, I/* inch light (Cat. NO. 4 3, Ormco Corp.) ; B, 1A inch heavy (Cat. No. 4-13, Ormco Corp.).

Posttreatmewt

activity

of alveolar

bone

175

By using the 1/4 inch light and heavy latex elastics, either singly or in group combinations, the force delivered by an appliance was predetermined by measuring the distance the elastics were to be stretched. By this method, the magnitude of force delivered by each appliance was calculated and controlled. Three categories of force intensity were used in this study; they were de+ ignated as light magnitude (40 to 60 grams), medium magnitude ( 135 to 165 grams), and heavy magnitude (400 to 560 grams). The elastics, either singly or in group combinations, were held together by two small eyelets made from 0.014 inch round stainless steel orthodontic wire.

Fig. 1. Materials used in fabrication of maxillary cuspid preformed bands. B, Contoured 0.003 inch cuspid blanks; D, cast-metal dies of right and left maxillary cuspid teeth; 8, st,aples; PB, completed preformed bands with staples attached.

8

Fig. Fig.

2. Custom-made 3. Taking the

plastic maxillary

tray for taking alginate impression. The animal

impression is under

of maxillary arch. general anesthesia.

ANESTHESIA. The animals M’(‘I’o urrtlrr general ancsthosia while i;h(b initial impressions wcrc taken a,ntl the c~rthotlorttic appliances were placed. The anrsthetic agent, pentobarbital sodium (Uiabutol, Diamond Laboratoricts, Des Bloines, Iowa) was administered by int,rapcritoncal injection. i 60 mg. for each 5 pounds of body weight). Anesthesia was apparent within 10 to I.5 minutes and laslcd for approximately 2 hours. To encourage a more rapid recovery from the anesthesia and thereby reduce the incidence of respiratory complications, the animals which were operat,ed on during the latter portion of the investigation (Groups (I, L), and YE) received intraperitoneal injections of 10 per cent aqueous solution of pentylenetetrazol (Metrazol, Knoll Pharmaceutical Company, Orange, K. 6.) at a dosage of 200 mg, for each 5 pounds of body weight. The Metraxol was administered after placement of the appliance had been completed and acted as a respiratory and vasomotor stimulant. The animals were sacrificed with a,n overdose of the anesthetic. IMPRESSIONS AND RECORD MODELS. While the animals were under general anesthesia, impressions of the maxillary arch were taken with alginate impression material (Hydrol Jel, Professional Products Co., San Diego, Calif.) in prefabricated custom-made plastic trays (Figs. 2 and 3). The impressions were poured with a hard type gypsum dental stone (Vel Mix, Kerr Manufacturing Company, Detroit, Mich.) to lessen the possibility of breaking the long slender cuspid teeth at, the time of separa,tion of the record model from the impression (Fig. 4). lmpressions for posttreatment models were taken after the animals had bcthn sacrificed; the oral tissues had been fixed and the appliances were removed. THE APPLIANCE. Prefabricated bands for the maxillary cuspid teeth were formed from 0.003 inch stainless steel contoured cuspid blanks (Cat. No. UB-653, Unitek Corp., Monrovia, Calif.) on right and left cast-metal cuspid dies (Fig. I ). One leg of a stainles’s steel staple (Cat. No. UT-483, linitek Corp.) was spot-

Fig. 4. Record model of maxillary

arch of young domestic cat.

Volume Number

54 3

Posttreatment

activity

of alveolar

bone

177

welded on the distal surface of each band 1 mm. from the gingival margin (Figs. 1 and 6). Immediately after the initial impression had been taken, and while the animal remained under general anesthesia, a well-fitting preformed band with its staple attached was chosen (Fig. 6). The elastics were then attached to the band by slipping one of the eyelets onto the staple via the unattached leg. That leg was welded to the band, thereby securing the eyelet with its elastics to the band. The band was then cemented to the cuspid tooth. While the cement was setting, a groove was cut in the fissure which lies between the mesial buccal cusp and the distal buccal cusp of the maxillary third premolar tooth. A second but smaller groove was also cut in the distal gingival aspect of the same tooth, accentuating the undercut already present there.

6

Fig. 5. Maxillary dentition of young domestic cat. Roots of the teeth have been exposed by removal of the surrounding bone. I, Incisors; C, cuspid; Pl, first premolar; P.%‘, second premolar; P5’, third premolar; M, molar. Fig. 6. A well-fitting preformed cuspid band was chosen. Note that only one leg of the staple has been welded to the band. The band was not cemented until the elastics were secured to the band via the staple. Fig. 7. The completed cuspid-retracting appliance in place. The twisted ligature was cut and bent, placing it in a position which would not interfere with occlusion or irritate the soft tissues.

Fig. of its Fig. of of

Pig.

8

Fig.

9

8. Lateral rocntgrnogram of right si11~. of animal Al, illusi rating 1111: rvpical appearance a control side (no appliance placed 1. Noti, l:i~>!i of dist)lavt~uli~lit 11f i.11~ wspid root within socket. (See Chart 2.) 9. Lateral roentgenogrsm of Ici’t side of animal 9-4, illustral ing the typical appearance an experimental side. Note displacement, c) I’ the cuspid root within its socket and the areas compression (cj and tension (T) bctwettu the root and the sovkni. wall. (See Chart 2.)

Ligature wire 0.010 inch, was looped over and around the clistal buccal cusp and into the prepared grooves of the third premolar tooth. The elastics were stretched between the cuspid and the third premolar and secured in position with the ligature wire (Fig. 7). OXYTETRACYCLINE VITAL STAIN. The vital stain, oxytetracycline (Terramycin, Pfizer Laboratories, New York, N. Y. )? was administered by intraperitoneal injection (50 mg. for each 7 pounds of body weight). A summary of the vital stain injection schedule for Ciroups A, 13, (‘, I>! and E is given in Table I. R~ENTGEN~GRA~vI~ AND TRACINGS. Lateral maxillary ja.w sections containing the cuspid and all buccal teeth were cut to a buccolingual t,hickness of 7 to 8 mm. Each section was individually placed directly on a dental x-ray film packet for the roentgenographic exposure. The film used was Du Pont dental x-ray film, Type D-l. The exposure was 10 seconds at 15 Ma. and 55 kv., with a 12 inch long cone and a source-film distance of 15 inches.

Posttreatmcnd

activity

of alveolar hose

179

Fi,g. 10

Fig. 11

Fig. Note

10. Lateral roentgenogram lack of displacement of

of left side of animal the cuspid root within

A-6; control its socket.

side

(no

appliance

placed).

Fig. 11. Lateral roentgenogram of right experimental side of animal A-6. The third had been orthodontically extracted from its bony socket. The appliance had initially a magnitude of force in the heavy range (525 grams).

premolar delivered

Tooth movement calculations were made by comparing and superimposing the roentgenographic tracings of the right and left maxillary jaw sections (Figs. 8 through 15 and Charts 2, 3, and 4). The tracings were superimposed on the first premolar, the nasal border of the premaxilla, the incisors, and the plane of the alveolar crest. HISTOLOGIC PROCEDURE. The tissue sections of tooth and alveolar bone were embedded under vacuum (25 to 28 inches Hg) in blocks of styrene base plastic (Clarocast, Fry Plastics Co., Los Angeles, Calif.). Sagittal and cross sections, 150 microns in thickness, were cut with a diamond abrasive wheel on a Bronwill thin sectioning machine. The undecalcified sections were mounted on glass slides and examined microscopically under incandescent light and ultraviolet light. The ultraviolet light source was a mercury vapor type high-pressure burner with an HGl filter. The color microphotographs were taken with Kodacolor-X color negative film (Eastman Kodak Company, Rochester, N. Y.) at an exposure of 1 second.

Fig.

ld

Fig.

13

FINDINGS

Sixteen of the original twenty-one animals successfully completed the experimental phase without complications. Each animal maintained a good appetite and showed no apparent sign of the appliance interfering with eating. The cats remained friendly during the duration of the experiment, despite the repeated intraperitoneal injections. Comparative examination of the pretreatment and posttreatment record models revealed that, following the placement of an appliance there was a distal movement of the crown of the cuspid tooth as well as an extrusion and mesial movement of the third premolar. In eight of the twenty-one experimental animals in this study cuspid-retracting appliances were placed on one side only and the opposite side was maintained as a control. By superimposing the roentgenographic tracings of the experimental side over the control side, it was found that as the crown of the cuspid tooth moved in a distal direction, the apex moved in a mesial direction (Figs. 8 through 15 and Charts 2 and 3).

Volume Number

54 3

Posttreatment

activity

of alveohr

bo9z.e 18 1

E

I

‘ig.

Fig. 14. Lateral roentgenogram of right side of animal A-l. The appliance magnitude of force in the heavy range for 30 days. Note similarity in detail in the lateral roentgenogram of the left side (Fig. 15). (See Chart 4.)

to

Fig. 15. magnitude the lateral

15

delivered a that seen

Lateral roentgenogram of left side of animal A-l. The appliance delivered of force in the light range for 30 days. Note similarity in detail to that seen roentgenogram of the right side (Fig. 14). (See Chart 4.)

a in

LOCATION OF THE CENTER OF ROTATION. The specific locations of the centers of resistance about which the teeth rotated were also determined by superimposing the experimental and control roentgenographic tracings (Chart 2). The centers of rotation were found to lie within the middle fifth of the root, but not in the same position for all maxillary cuspid teeth. A summary of the specific locations of the centers of rotation for the cuspid teeth is given in Table VII. Histologically, the position of the center of resistance about which a multirooted premolar tooth rotated was found to be located between the roots at a point within the bony septum. No correlation was found to exist between the magnitude of force delivered to a tooth and the location of its center of rotation. DISTANCEANDRATEOF TOOTH MOVEMENT. Linear measurements of the distance of tooth movement were determined for the eight animals in which the cuspidretracting appliances had been placed on one side only and the opposite side had been maintained as a control.

182

fit/C??/

Chart 2. Superimposed tracings of right and left lateral maxillary jaw roentgenograms (magnification, x3) of animal A-4. (See Figs. 8 and 9.) Solid line represents control side (right) ; broken line represents experimental side (left). R, Center of rotation. Chart 3. Superimposed tracings of right and left lateral maxillary jaw roentgenograms (magnification, x3) of animal C-l. (See Figs. 12 and 13.) Solid line represents control side (left) ; broken line represents experimental side (right). D, Distance of cuspid movement. Chart .4. Superimposed tracings of right and left lateral maxillary jaw roentgenograms (magmfication, x3) of animal A-l. Note lack of differentiation between tracings of right and left cuspids, demonstrating identical tooth movement regardless of magnitude of orthodontic force. (See Figs. 14 and 15.) Solid line represents left side (light force) ; broken line represents right side (heavy force).

Table II. Force delivered

by appliance movement, Group A animals

Force Animal

Side

1

Left Right

2

3

and difSerentia1 compariso~~t of cuspid Poroe at applh.ce placement

desig-

natiorb*

Force

0wpia

movement

(grams)

L H

48 510

44 440

No difference

Left Right

c M

(Died 165

day) 145

Right moved 1.5 mm. more than left

Left Rig11 t

L c

52

(Died

day)

Left moved 3.5 mm. more than right

Left Right

L C

(Died

day)

Left moved 3.0 mm. more than right

5

Left Bight

H C

6

Left Right

C H

Note:

Cuspid

*Force

movement

designation:

was L =

on the fifth

58 on

the

seventh

on

the

seventh

50

54

measured

at tip

Light;

M =

16. The

400

525

175t

Left moved 0.8 mm. more than right Right moved 4.0 mm. more than left

of cusp. H =

heavy; premolar

Table III.

ad

diflerential

Animal

No. 6 sacrificed force from the

on day appliance.

460

third

tAnima1 with the

medium; right

Force delivered by appliance movement, Group B animals

C =

control.

was

orthodontically

extrbed

comparison

of cuspid

Side

nation*

Force at appliance placement (gram)

1

Left Right

M H

160 560

140 470

No difference

2

Left Right

M L

135 48

115 42

No difference

3

Left Right

L H

40 560

36 510

No

difference

4

Left Right

c c

No

difference

5

Left Right

C C

No

difference

Foroe

*Force

cwmpCzrtiolt0f

(grams)

4

Note:

Differential

at sacrifice animal

of

Cuspid

movement

designation:

L

was =

desig-

measured

Light;

M =

at tip medium;

Force

at sacrifice of animal (gram)

of cusp. H =

heavy;

C =

control.

Difewntial compan-rison 0f 0thspia movement

1

Left Right,

c! M

Right, 160

105

7.0

ihan

No tliffercnce

56

16

No difference

165

140

Left Right

M 1T

160 475

3

Left Right

I, M

*Force

movement

designation:

was

L =

measured

Light;

M =

at tip medium;

Table V. Force delivered by uppliaw~ movement, Group D animals

of

cusp. H =

heavy;

C =

control.

and cliffewltial Force at appliance placenmbt

Form designation*

compa,rison of cuspid

Force at sawifice

of

atimal

Di~erential

comparison of ompid movement

Animal

Side

1

Left Right

L M

48

44

135

125

Left Right

I, II

48

45 3 15

No difference

425

Left Right

M II

155

140

No difference

500

430

2

3

Note: Cuspid “Force

movement

designation:

was L =

measured

Light;

M =

(grams)

at tip medium;

more

left

1 “(‘I 450

2

Note: Cuspid

moved mm.

(grams)

No difference

of cusp. H =

heavy;

(1 =

control.

Each animal demonstrated an independent rate of tooth movement. Animal C-l experienced the greatest distance and the most rapid rate of cuspid tooth movement. With the applia,nce delivering a magnitude of force in the medium range, the tip of the right cuspid moved 7 mm. in 9 days, a rate of 0.8 mm. per day (Figs. 12 and 13, Chart 3). The shortest distance and the slowest rate of cuspid tooth movement were seen in animal A-5. With the appliance delivering a magnitude of force in the heavy range, the tip of the left cuspid moved 0.8 mm. in 30 days, a rate of 0.03 mm. per day. A summary of the magnitudes of force delivered by the appliances and the resulting distances and rates of cuspid tooth movement is given in Table VIII. No correlation was found to exist between the rate of cuspid tooth movement and the magnitude of force delivered by the appliance.

Volume Number

54 3

Posttreatment

Table VI. Force delivered by appliance movement, Group E animals

Foroe

activity

and diflerential Force at appliance pl.acemen”t

desig-

of alveolar bone

Force of

comparison

at sacrifice animal

185

of cuspid

Diferential comparison of 0tbspia movement

nation"

(gr@msl

(grams)

Left Right

L M

52 160

48 150

No difference

2

Left Right

L H

48 500

42 450

No difference

3

Left Right

H C

460

370

Left moved 1.8 mm. more than right

4

Left Right

c

(IDied

L

54

Animal

Side

1

Note:

Cuspid

*Force

movement

desigrmtion:

Table VII.

L

Location

was measured =

Light;

of center

Animal Average

ancl side

(grams)

I

A-2-R A-3-L A-4-L A-5-L A-6-R C-l-R E-3-L E-4-R *Root tLocation distance

force

I

155 55 52 430 350 133 415 52

length of from

=

Distance

at tip

M =

of

medium;

H =

of rotation

from

third

day) 50

Right moved 1.6 mm. more than left

cusp. heavy;

of maxillary

C =

control.

ousti

Duration

Tooth

of

length

Root length”

cm.1

(mm.)

force (aawl

5 7 7 30 16 9 15 3

center of rotation alveolar crest to

on the

alveolar

20.6 18.2 17.0 18.5 19.7 19.8 19.7 17.0 crest

is determined apex.

to apex by

Location of ceder of rotationt

10.6 9.6 8.8 8.8 10.4 9.9 9.3 7.9

0.4 0.5 0.6 0.4 0.6 0.5 0.4 0.6

of tooth.

multiplying

value

shown

in

column

times

Cuspid-retracting appliances were placed on both right and left sides in eleven of the twenty-one experimental animals. The appliance on one side delivered a force of different intensity than the appliance on the opposite side. The evaluation of tooth movement for these animals was based on a differential comparison of the right and left sides. Superimposition of the roentgenographic tracings of these eleven animals revealed that the cuspid teeth of both right and left sides of the same animal moved equal distances, regardless of the different magnitudes of force which were delivered by the right and left appliances. A typical example of this finding is illustrated in Figs. 14 and 15 and Chart 4.

Fig. 16. Undecalctied cross section of right maxillary cuspid tooth bone, distal surface of root at level near the alveolar crest, area illustrating appearance under incandescent light. (Magnification, 27, showing the same tissue section under ultraviolet light. II. G, cementurn; I(, bone; PDM, periodontal membrane space; MnS, direction of tooth movement.

and surrounding alvcola~ of tension in auimal +;:-a: x10.) Compare with Fig. Dentine; I’, dental pu111; medullary spaw: Ar~or~:,

A summary of the differential comparisons of cuspid movement per magnitude of force delivered is given in Tables II, III, IV, V, and VI. FLUORESCENT MICROSCOPY. Microscopic examination of the undecalcified tissue sections demonstrated that in all animals in which cuspid-ret,racting appliances were placed there was a tipping displacement of the cuspid teeth within their sockets. The coronal portion of the root moved in a distal direction, and the apical portion of the root moved in a mesial direction. The control teeth were not displaced within their sockets, and their encircling periodontal membrane space was of uniform thickness.

Volume Number

54 3

Posttreatment

activity

of alveolar

bone

187

The microscopic appearance of the undecalcified tissue sections under incandescent light is illustrated in Fig. 16. Under ultraviolet light, the tissue sections from each group of experimental animals exhibited varying intensities and patterns of fluorescence which were representative and characteristic of the particular vital staining schedule of that specific group. Within each group, the fluorescence -of the alveolar bone surrounding the experimental teeth was compared with the fluorescence of the alveolar bone which surrounded the control teeth. Group A-Experimental sections. Well-defined fluorescence was seen on the surface of the socket wall mesial to the coronal half of the root and distal to the apical half of the root, the areas of tension (Fig. 17). High-power magnification revealed two distinct areas of fluorescence directly opposite each other on the opposing surfaces of the tooth-bone interface in the areas of compression between the root and t,he socket wall (Fig. 19). In a similar area of compression from section A-l-R, bony projections which extended out from the surface of the socket wall and into the periodontal space appeared to be in contact with the root of the tooth. These bony projections and that portion of the root surface which they appeared to contact exhibited distinct fluorescence (Fig. 20). Group A-Control sections. The alveolar bone surrounding the control teeth did not exhibit definable fluorescence. The supportive bone which surrounded the sockets of the control teeth demonstrated only slight traces of fluorescence (Fig. 18). Group B-Experimental sections. The experimental teeth of Group B were displaced in their sockets, but the degree of fluorescence was almost identical to the fluorescence of the control sections. Fluorescence on the opposing surfaces of the tooth-bone interface in the areas of compression were demonstrated, but with much less frequency than in Group A. Group B-Control sections. The sections of t,issue from the control teeth of Group B demonstrated the same fluorescence as did the control sections of Group A. Groups C and D-Experimedal sections. The histologic findings for the sections of tissue from Groups C and D were almost identical. The only difference was that the animals of Group C had received two injections of the vital stain and therefore exhibited patterns of fluorescing lines in groups of two; the animals of Group D received four injections of the vital stain and therefore exhibited patterns of fluorescing lines in groups of four. Otherwise, the histologic findings were identical. Sagittal sections through the center of the experimental teeth demonstrated a series of converging fluorescent lines within the lamina dura at each of the areas of tension on the socket wall (Figs. 21 and 22). Mesial to the tooth the lines began at the coronal portion of the socket and continued apically for a distance of approximately half the length of the socket, where they met at a common point of convergence. Distal to the tooth the lines began at the apical portion of the socket and continued coronally for a distance of approximately half the length of the socket,

Fig.

Pig. 29

E5gs. 17-20. For legends, see opposite page.

Volume

54

Posttreatment

Number 3

Fig. 17. Undecalcified sagittal section of left maxillary bone, mesial surface of root in area of tension in Magnification, x6.) Compare with Fig. 18, showing D, Dentine; C, cementum; B, bone; PDM, periodontal BC, Alveolar crest; S, premaxilla-maxillary suture; F, movement.

activity

of alveolar bone

189

cuspid tooth and surrounding alveolar animal A-5. (Ultraviolet light source. right side (control) of same animal. membrane space; MS, medullary space; fluorescence; Arrow, direction of tooth

Fig. 18. Undecalcified bone, mesial surface placed) of animal showing left side PDM, periodontal maxillary suture;

sagittal section of right maxillary cuspid tooth and surrounding alveolar of root in region of alveolar crest (control tissue section, no appliance A-5. (Ultraviolet light source. Magnification, x6.) Compare with Fig. 17, (experimental) side of same animal. D, Dentine; C, cementum; B, bone; ktC, alveolar crest; S, premaxillamembrane space; ;KS, medullary space; F, fluorescence.

Fig. 19. Undecalcified bone, distal surface Magnification, x6.) space; BC, alveolar

sagittal section of left maxillary cuspid tooth and surrounding alveolar root in area of compression in animal A-l. (Ultraviolet light source. D, Dentine; B, bone; PDM, periodontal membrane space; MS, medullary crest; F, fluorescence; Arrow, direction of tooth movement. of

Fig. 20. Undecalcified sagittal section of right maxillary cuspid tooth and surrounding alveolar bone, distal surface of root in area of compression in animal A-l. (Ultraviolet light source. Magnification, x6.) D, Dentine; B, bone; PDM, periodontal membrane space; MS, me&&q space; F, fluorescence; Arrow, direction of tooth movement.

Fig. 21. Undecalcified sagittal section of left maxillary cuspid tooth and surrounding alveolar bone, distal surface of root in animal D-l. (Ultraviolet light source. Magnification, x3.5.) D, Dentine; P, dental pulp; B, bone; PDM, periodontal membrane space; MS, medullary space; C, area of compression; T, area of tension; P, fluorescence; Arro,w, direction of tooth movement.

where they met at a common point. of con~crgence. The points of convergent on the opposite sides of the socket were on the same horizontal level. Distinct and repeated patterns of fluorescence were YPCII in t,he supportive bone in forms of wavy parallel lines (Fig. 23) a.nd concentric circles within circles (Fig. 24). Fluorescence was also seen on the opposing surfaces of t,lie tooth-bone interface in the areas of compression of the socket wall. The premolar teeth and the surrounding alveolar boric of animal D-3 wcrc also sectioned. The bony septum between the second and third premolars demonstrated a series of parallel fluorescing lines on its mesial surface (Fig. 25). A similar pattern of fluorescence was seen in the bony septum between the roots of the second premolar (Fig. 26). &oups C ad D--Control scctl:orcs. Fluorescence of the lamina. dura was limited to single line which extended the length of the entire soeket. A few fluorescing concentric rings were sc.cn within the supportive bone but with less frequency than in the experimental sections.

Volume

54

Nunt ber 3

E

Fig.

24. Undecalcified cross section of alveolar bone in apical h of animal C-2. (Ultraviolet light source. Magnification, :e; S, premaxilla-maxillary suture; P, fluorescence.

region x6.)

of left maxillary cuspid 1 I?, Bone; MS, med .ullary

25. Undecalcified sagittal section of right maxillary second and third premolar Fig. teeth and surrounding alveolar bone of animal D-3. (Ultraviolet light source. Magnification I, x6.) premolar; Ps, third premolar; PDH, periodontal membrane space; B, PC Second T, area of tension; P, fluorescence; Arrow, direction of tooth moveC, a rea of compression; meu

192

utzey

Group E-~F:zyerbn e?i.td sdions. ‘I’he sections of IM~I.: t&such surrolultliing the experimental teeth of Croup 1.1 tlrmonstratcd l~l~illimt prttc~lms (II’ ilrtcascl yellow fluorescence. &St prominclnt was the hand of Iwigkt ftuorcw~cwc~t~ wit It i tl the lamina dura in the arcas of tension on the socket. ~111 i Figs. 5, 2X, ;I tl( I t’!) 1. Distinct areas of fluorescence wercl seen on the> opposing surfacrrs ot’ t hv tooth-bone interface in the arcas of compression of the socket \valI i b’igs. :M and 31). Within the supportive bone, areas of fluorescence were observed in the interior of the medullary spaces on the surface nearest the root of t,he approaching tooth; some individual trabeculae exhibited fluorescence (F’ig. 31). Many configurations of bright fluorescence were seen throughout, the supportive bone which surrounded the alveolar socket. Group E-Control sections. Fluorescence of the lamina dura was limited to a bright yellow line which outlined the surface of the Mire socket wall (Fig. 32). The supportive bone surrounding the control teeth exhibited more ffuorescence than the control sections of the other groups, but much less fluorescence than the supportive bone of the experimental sections of Group E. DISCUSSION

The young common domestic cat proved to be an excellent research animal for investigations related to experimental orthodontic tooth movement. The convenient size, shape, lack of occlusal interference, and accessibility of the teeth were factors which facilitated the placement and manipulation of t,he cuspid-retracting appliances. LOCATION OF THE CENTER OF ROTATION. The findings of this investigation demonstrated that when a distal force was applied to the maxillary cuspid tooth of a young cat the crown moved in a distal direction and the apex moved in a mesial direction. However, the centers of rotation for these teeth (with almost identical shapes) were not always located in exactly the same position, The

Fig. bone x6.) VR,

26. Unclecalcified sagittal section of left maxillary second premolar tooth and alveolar within the bifurcation of the roots in animal D-3, (Ultraviolet light source. Magnification, T, area of tension; PDM, periodontal membrane space; B, Bone; C, area of compression; mesial root; DR, distal root; P, fluorescence; Arrow, direction of tooth movement.

Fig. 27. Undeealcified cross section of right maxillary cuspid tooth and surrounding alveolar bone, mesial surface of root in area of tension in animal E-2. (Ultraviolet light source. Magnification, x3.5.) Compare with Fig. 16, showing same tissue section under incandescent light. D, Detitine; P, dental pulp; B, bone; PDX, periodontal membrane space; MS, medulF, fluorescence; Awow, direction of tooth movelary space; S, premaxilla-maxillary suture; ment. Fig. 30. Undecalcified sagittal section of right maxillary cuspid tooth and surrounding bone, distal surface of root in area of compression in animal E-l. (Ultraviolet light Magnification, x10.) D, Dentine; C, cementum; B, bone; PDM, periodontal membrane AfS, medullary space; F, fluorescence; Arrow, direction of tooth movement.

alveolar source. space;

Volume Number

Figs.

Posttreatment

54 3

26, 27, and

30. For

legends,

see opposite

page.

activity

of alveolar bone

19 3

Fig.

Volume

54

Number

3

Posttreatment

uctivity

of

alveolar

bone

$8

Fig. 28. Undecakified sagittal bone, mesial surface of root D, Dentine; P, dental pulp; space; C, area of compression; movement.

IY 3

Fig.

section of left maxillary cuspid tooth and surrounding alveolar in animal E-3. (Ultraviolet light source. Magnification, x6.) B, bone; PDM, periodontal membrane space; dlS, medullary T, area of tension; F, fluorescence; Arrow, direction of tooth

Fig. 29. Undecalcified cross section of left maxillary cuspid tooth and surrounding bone, apical region of root in area of tension in animal E-2. (Ultraviolet light Magnification, x6.) D, Dentine; I’, dental pulp; B, bone; PDM, periodontal membrane MS, medullary space; F, fluorescence; Arrow, direction of tooth movement.

alveolar source. space;

maxillary cuspid teeth of young cats were found to rotate about a point located between 0.4 and 0.6 times the distance from the alveolar crest to the apex (that is, within the middle fifth of the root). Burstone? claimed that the fulcrum, or center of rotation, of a single-rooted tooth with a parabolic shape was located at a point 0.4 times the distance from the alveolar crest to the apex. Histologic studies revealed that the centers of rotation for multirooted premolar teeth of cats were located between the roots at a point at about the middle of the bony septum. This observation was in agreement with the findings reported by Stuteville38 when he studied the centers of rotation for multirooted teeth of dogs and monkeys. Macapanpan, Weinmann, and Brodiels claimed that multirooted rat molars tipped from a point situated somewhere in the alveolar bone beyond the apices of the roots. New bone formation represented by patterns of yellow fluorescence on the socket walls in the areas of tension provided histologic confirmation of the tipping movement of the experimental teeth. The points of convergence of the fluorescing lines in the experimental animals of Groups C and D represented

d

19 6

I .tl(,!j

31

Fig. 31. Undeealcified bone, distal surface Magnification, x3.5.) space; MS, medullary ment.

of

crow section of right maxillary cuspid tooth and surrounding alveolar root in arca of cornpwssion in animal l’:-2. (IXravidet light source. I), Dentine; I’, dental pulp; B, hone; PDJI, periodontal membrane space ; 2’. trabccula; I;‘, flnorcscence; AVOU~. direction of tooth move-

Fig. 32. Undecalcified sagittal sect.ion of right maxillary cuspid tooth and surrounding alveolar bone, distal surface of root in region of alreolar crrst (control tissue section, no appliance placed) in animal E-3. (Ultraviolet light source. Magnification, x3.5.) D, Ikntinc; .P, dental &is, medullary space ; AC, alveolar crest ; pulp; B, bone; PDH, periodontal membrane space; F, fluorescence.

Volume Number

54 3

Posttreatment

activity

of

alveolar

bone

1

Y7

the horizontal level at which the center of rotation was located. This level also represented an imaginary line which, on sagittal sections, horizontally separated the areas of tension and compression on the socket wall into separate quadrants (Fig. 9). The location of the center of resistance about which a tooth rotated was found to be independent of the magnitude of force delivered to that tooth. DISTANCE AND RATE OF TOOTH MOVEMENT. When orthodontic forces of the same magnitude were delivered to the maxillary cuspid teeth of the experimental animals, the resulting rates of tooth movement, were consistently different for each animal. A differential comparison of tooth movement with various magnitudes of force demonstrated that both right and left maxillary cuspid teeth of the same animal moved equal distances, regardless of the different magnitudes of force’ delivered by the right and left appliances (Figs. 14 and 15, Chart 4). These results were in disa,greement with the findings of Smith and Storey,“’ who claimed that there was an optimum range of pressure on the tooth-bone interface which produced the maximum rate of tooth movement. For pressures below this optimum range, they claimed that there was practically no movement ; when the force was increased above the optimum range, the rate of tooth movement decreased and finally approached zero. Within the limits of this investigation, it was demonstrated that the rate of cuspid tooth movement in young cats was not related to the magnitude of the orthodontic force delivered. Tooth movement was the result of a specialized activity of the investing alveolar bone which occurred in response to an applied force but was independent of the magnitude of that force. FLUORESCENT MICROSCOPY. Vital staining with oxytetracycline proved to be an excellent and accurate method for labeling the formation of new bone during its process of calcification. The areas of new bone formation, normally not distinguishable from “old” bone, demonstrated a brilliant yellow fluorescence when viewed under ultraviolet light. All other tissues appeared as different shades of blue and green. The patterns of fluorescence seen on the coronal half of the mesial wall of the socket and on the apical half of the distal wall of the socket represented new bone formation in the areas of tension “behind” the moving tooth and histologically confirmed the tipping motion. Only slight traces of fluorescence were seen in the experimental sections from Group B. This indicated that definable calcification of new bone had not occurred within the first 3 days following the application of the orthodontic force. The experimental sections from Group A demonstrated noticeably more fluorescence than the experimental sections of Group B. This comparative difference indicated that there was a greater activity of new bone formation in the tissues which had been subjected to the orthodontic force over a longer period of time. The sagittal sections of tissue from the experimental animals of Groups C and II demonstrated a series of converging fluorescent lines within the lamina

durn at each of the areas of tension (III I he socket. u all. ‘L’hcst: lines r~eprcsentccl the progressive new surfaces, or advancing “frontiers,” of the socket \~~;I11:IS it formed a.nd followed “behind” the moving tooth. The control sections of Groups (I, I), and 15 cxhibit,ed a single Line of fluorescence which outlined t,he surface of the entire sock(bt wall. This single line represented the formation of new boil? on the inner surl’acc of the socket wall and confirmed the findings of Brash,:’ who reported that. constant additions to the walls of the alveoli occurred throughout the life of an animal. The fluorescing concentric rings which were SWI in tilt? t,issue sections from Groups C and I> represented the developmental stages of o&eons within the alveolar bone, much in the same way ilti rings in a trot‘ trunk represent its progressive stages of devclopmcnt The fluorescing lines on the me&I surfaces of the bony septa between the second and third premolars and between the roots of the second premolar of animal D-3 indicated that as the teeth moved in response to the force from the appliance the bony septa had also progressively advanced, maintaining their positions between the root.s of the teeth. As the new bone formed on the mesial surfaces of the septa, it was labeled with t,he oxytetracycline. Fluorescence on the opposing surfaces of the tooth-bone interface in the region of compression on the socket wall indicated that calcification was occurring on the surfaces of the lamina dura and the ccmentum of the root. The experimental sections of tissue from the (:ronp E animals exhibited brilliant patterns of intense, yellow fh~orescence. A brightly fluorescing band within the lamina dura in the areas ot’ tension on the socket wall represented the new bone of the advancing lamina dura which had formed “behind” the moving tooth during the 15 days following placement of the orthoclontic appliance. The areas o’f fluorescence observed in the interior of the medullary spaces on the surface of the bone nearest the root rcpresent,etl the lamina dura. as it formed “ahea.d” of the advancing tooth. The relative absence of fluorescence within the control se&ions and t,he prominent areas of fluorescence seen throughout the supportive bone surrounding the experimental teeth demonstrated t hcl general increased activity of alveolar bone in response to orthodont,ic t,ooth movement and it,s accompanying forces. SUMMARY

AND

CONCLUSIONS

The activity of alveolar bone incident to ort,hodontic tooth movement was studied in twenty-one young domestic cats. Thirty maxillary cuspid teeth were moved in a distal direction by forces of different magnitude delivered from orthodontic appliances. Twelve teeth on which no applianc.es were placed were retained as controls. Three ra,nges of force intensity were used in t,his investigation. They were designated as light magnitude (40 to 60 grams), medium magnitude (135 to 165 grams), and heavy magnitude (400 to 560 grams). The distance and rate of tooth movement which occurred in response to the different magnitudes of force were determined. Also, the cent,ers of resistance about which the teeth tipped were located.

Volume Number

54 3

Posttreatment

activity

of alveolar bone

IYY

The animals were divided into five groups designated as Groups A, B, C, D, and E. Each group had its own experimental duration and schedule for oxytetracycline vital staining. 1. Comparison of the pretreatment and posttreatment record models revealed that the cuspid teeth moved distally and the third premolars extruded and moved mesially. 2. Superimposition of the tracings of the lateral jaw roentgenograms revealed that while the crowns of the cuspid teeth moved in a distal direction, the apices moved in an opposite direction. 3. The center of resistance about which the experimental teeth tipped was located at various positions within the middle fifth of the root. 4. The location of the center of rotation was not related to the magnitude of force delivered by the appliance. 5. The maxillary cuspids of both the right and left sides of the same animal moved equal distances regardless of the different magnitudes of force which were delivered by the right and left appliances. 6. The rates of cuspid tooth movement were not related to the magnitude of force delivered by the appliance. Each animal exhibited its own individual rate of tooth movement, regardless of the intensity of the orthodontic force. ‘7. Fluorescent microscopy revealed that the intraperitoneally injected oxytetracycline was incorporated into calcifying tissues. Any new bone formation which occurred during the time of uptake of the vital stain was represented and identified by its yellow fluorescence when viewed under ultraviolet light. 8. The patterns of fluorescence seen on the coronal half of the mesial wall of the socket and on the apical half of the distal wall represented new bone formation in the areas of tension “behind” the moving tooth. This fluorescing pattern also confirmed the tipping movement of the teeth. 9. Fluorescence at the tooth-bone interface in the areas of compression on the socket wall represented calcification which was occurring on the surfaces of the lamina dura and the cementum of the root in positions directly opposite each other. 10. Areas of fluorescence observed in the medullary spaces on the surface nearest the advancing tooth represented the lamina dura as it formed “ahead” of the tooth. This, together with the fluorescence on the inner socket wall in the areas of tension, illustrated how the lamina dura was continually maintained around a moving tooth. 11. Tissue sections from Groups C and D demonstrated a series of converging fluorescent lines within the lamina dura in the areas of tension on the socket wall. These lines represented the calcifying “frontier” of the socket wall at its various stages of developmental formation while it formed and followed “behind” the moving tooth. 12. The points of convergence of the fluorescing lines in the experimental animals of Groups C and D represented histologically the horizontal level at which the center of rotation was located, 13. Various patterns of fluorescence in the supportive bone surrounding the

REFERENCES

I. Angle, Edward H. : Treatment of Malowlusion of t,hc Teeth, cd. 7, l’lril:~tlelphia, l!bOi, S. S. White Dental Manufacturing Company, Chap. 6. ed. 2, London, 1918, Longmans, Green 2. Bayliss, TV. M.: Principles of General Physiology, & co. 3. Bell, W. R.: A Study of Applied Force as Rt~latetl to the lisr: of Elastics and (‘oil Springs. Angle Orthodontist 11: 151, 1951. 4. Bhatia, Harbans L., and Sognnaex, Reidar E’.: Tetracycline Discoloration and Labelling of Teeth and Bones: A Review, J. South. California D. A. 31: 215, 1963. 5. Brash, James C.: The Growth of the Alveolar Bone and Its Relation to the JIoverncnts of the Teeth, Including Eruption, INT. J. ORTHODONTIA 14: 196, 487, 192X. 6. Hreitner, C. : Bone Changes Resulting From Experimental Orthodontic ‘l’rratmcnt, Aar. J. ORTHODONTICS & ORAL SURG. 26: 521, 1940. 7. Burstone, Charles J.: The Biomechanics of Tooth Movement, 11~ Kraus, H. H., and Riedel, K. A. (editors) : Vistas in Orthodontics, Philadelphia, 1962, Lea & F’ebigzr, chap. 5, 1,. 197. A Cephalometric and Histologic Study of the Effwt ot’ Orthodontic 8. Debbane, E. F.: Expansion of the Midpalatal Suture of the (‘at, Anr. .T. OIZTHWOKTI~~F; 44: 187, 1958. 9. Farrar, J. N.: An Tnquiry Into Physiological and Pathological Changes in Animal Tissues in Regulating Teeth, Dental Cosmos 18: 13, 1876. 10. Farrar, J. N.: Philosophy of Correcting Irregularities of the Teeth, Dental Cosmos 30: 496, 1888. 11. Gottlieb, B., and Orban, B.: Die Vcranderungen der Ge\velje ljei I%ermassiger BeansJ. ORTHWXK)WT~A 28: 895, 1932.) pruchung der Zahne. (Cited by Bodecker, C. E’.: Im. 12. Harris, W. H.: A Microscopic Method of Determining Rates of’ Bone Growth, J. Bone KJoint Surg. 42B: 856, 1.960. 13. Herzberg, B. L.: Bone Changes Inc,ident to Orthodontic Tooth Movement in Man, .J. Am. Dent. A. 19: 1777, 1932. 14. Ibsen, Kenneth H., and Urist, Marshall R.: The Biochemistry and the Physiology of the Tetracyclines : With Special Reference to Mineralized Tissues, Clinical Ort~hopaf~~liw. No. 32, Philadelphia, 1964, J. B. Lippincott Company. 15. Johnson, A. L., Appleton, J. L., and Rittershofer, L. S.: Tissue Changcx Ir~rolvetl in Tooth Movement, INT. J. ORTHODONTIA 12: 889, 1926. 16. Kingsley, Norman W.: Oral Deformities, Nw York, 1880, 1). Appleton & (‘0. of Bone Architecture, Am. .J. Anat. 21: Iii, 191i. 17. Koch, J. C.: The Laws 18. Macapanpan, L., Weinmann, J. P., and Brodie, A. G.: F:arly Tiww Chang;(as P’ollowing Tooth Movement in Rats, Angle Orthodontist 24: 79, 1951. 19. MacMillan, H. W. : Structural Characteristics of the Alveolar Process, I~‘T. .J. 0a~~01n~~~r.4 12: 722, 1926.

Volume 54 Num her 3 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30.

31. 32. 33. 34. 35. 36. 37.

38. 3Q. 46. 41.

Posttreatment

activity

of alveolar oone

zu~

MacMillan, H. W.: Nonuse in the Development and Resistance of the Alveolar Process, J. Am. Dent. A. 15: 511, 1928. McKeag, H. T.: Physical Laws and the Design of Orthodontic Appliances, D. Record 49: 273, 1929. Fluorescence in Bone Lesions, J. Bone McLeay, J. F., and Walske, B. R.: Tetracycline & Joint Surg. 49A: 940, 1960. Merrill, Reed M.: Physical Behavior and Change of Rubber Bands Under Simulated Oral Conditions, Master’s Thesis, University of Southern California, 1963. of the Tetracyclines, J. Milch, R. A., Rall, D. P., and Tobie, J. E.: Bone Localization Nat. Cancer Inst. 19: 87, 1957. Moyers, R. E., and Bauer, J. L.: The Periodontal Response to Various Tooth Movements, Aix J. ORTHODONTICS 36: 572, 1950. Oppenheim, Albin: Human Tissue Response to Orthodontic Intervention of Short and Long Duration, Aix. J. ORTHODONTICS & ORAL SURG. 28: 263, 1942. Oppenheim, Albin : A Possibility for Physiological Orthodontic Movement, A&c. J. ORTHODONTICS & ORAL SURG. 30: 277, 1944. Parfitt, G. J.: An Investigation of the Normal Variations in Alveolar Bone Trabeculation, ORAL AURG., ORAL MED. & ORAL PATH. 15: 1453, 1962. Paulich, Frank: Measuring of Orthodontic Forces, Ahr. J. ORTHODONTICS & ORAL SURG. 25: 817, 1939. and Persistence of Rall, D. P., Loo, T. L., Lane, M., and Kelly, M. G.: Appearance Fluorescent Material in Tumor Tissue After Tetracycline Administration, J. Nat. Cancer Inst. 19: 79, 1957. Beitrage zur Theorie der Zahnregulierung, Nord. Tandl. Titlskr. Sandstedt, C.: Einige 5: 236, 1904. Schwarz, A. M.: Tissue Changes Incident to Orthodontic Tooth Movement, 1NT. J. ORTHODONTIA 18: 331, 1932. Richer, Harry, and Weinmann, J. P.: Bone Growth and Physiologic Tooth Movement, AK J. ORTHODONTICS & ORAL SURG. 30: 109, 1944. Smith, R., and Storey, E.: The Importance of Force in Orthodontics, Australian J. Dent. 56: 291, 1952. Stafferi, E. G.: A Radiographic Study of Alveolar Bone Patterns, AM. J. ORTHODONTICS 44: 66, 1958. Storey, E.: Bone Changes Associated With Tooth Movement-A Radiographic Study, Australian J. Dent. 57: 57, 1953. Stuteville, 0. H.: Injuries of the Teeth and Supporting Structures Caused by Various Orthodontic Appliances, and Methods of Preventing These Injuries, J. Am. Dent. A. 24: 1494, 1937. StutevilIe, 0. H.: A Summary R,evitw of Tissue Changes Incident to Tooth Movement, Angle Orthodontist 8: 1, 1938. Talbot, Eugene S.: Irregularities of the Teeth and Their Treatment, Philadelph$ 1888, P. Blakiston, Son, and Company. Urist, M. R., and Ibsen, K. H.: Chemical Reactivity of Mineralized Tissue With Osytetracycline, Arch. Path. 76: 484, 1963. Wolff, Julius: Das Gesetz der Transformation der Knochen, Berlin, 1892. Cited by Evans. F. G., in Glasser, 0.: Stress and Strain in Bones, Springfield, Ill., 1957, Charles C Thomas, Publisher. 15955

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