Tissue Rearrangement During Retention OfOrthodontically Rotated Teeth *KAARE KEITAN, M.S.D., Ph.D.,Oslo, NorwayThe mechanical procedure of rotat-ing malposed teeth has seldom beenconsidered a problem in orthodontics.On the other hand, it is well knownthat the rotated tooth frequently showsa tendency to move back toward itsoriginal position after removal of theappliances. This occurs especially incases where the respective tooth hasbeen rotated rapidly and through aconsiderable number of degrees. Insome textbooks overrotation has beenrecommended as a measure againstthese secondary changes in tooth posi-tion.Other methods have been suggestedfor stabilization of rotated teeth. Hence,Skogsborg ( 1927) advocated surgicaltransection of fibrous and bone struc-tures in the septal area on both sidesof the root, after rotation, in order toprevent relapse of the tooth moved.Recently Hallett (1956) discussed theresults obtained after immediate tor-sion of twenty-three teeth, the so-called"redressement forcC" ; the teeth thusrotated had been retained by fixedsplints. The descriptions of these twomethods tend to stress that there areproblems connected with rotation ofteeth, but that these problems are re-lated chiefly to the retention period.The present investigation is based onanimal experiments arid deals withsome histologic observations made inthe supporting structures of ortho-dontically rotated teeth.Up to the present few histologic ex-* From the Xorwegian Institute of DentalResearch, Oslo.periments on rotation have been re-ported. One series was performed twen-ty years ago (Skillen Keitan 1940),the findings of which are partly dis-cussed in this study. In addition, a newseries will be described, also includingexperimental teeth that were retainedafter rotation. Except one dog, two anda half years old, the experimentalanimals were around one year old.The new series comprises sixteen ex-perimental teeth, six of which representexperiments on retention.ROTATION OF TEETHVarious factors are involved in themovement of rotation. Of these theanatomical and mechanical factorsshould be considered here. The ana-tomical factor is primarily related tothe position of the tooth, its form andsize. Except the upper central incisorand to some extent the first and secondlower premolars in man, most roots,seen in cross section, have an oval form.In the present series the upper secondincisor in the dog was selected as theexperimental tooth, the first and thirdincisors serving as control. In cross sec-tion the second incisor of the dog hasan oval contour, Fig. 1. Because of thisFig. 1 Cross sections of the first, second,:iiid third upper incisors of the dog.105 106 Reitan April, I959form a parallel movement between theroot surface and the inner alveolar bonesurface takes place chiefly on the buccaland lingual sides of the root. Anotheranatomical detail to be mentioned isthe arrangement of the periodontalfibers.G It is well known that the majorgroup of the periodontal fiber bundlesruns from the root surface to the inneralveolar surface. The free gingivalfibers, however, are attached in thegingival soft tissues and the periosteum.As shown later, this variation in theattachment of the fibers plays an im-portant part especially during the re-tention period.The mechanical factor primarily in-fluences the degree of rotation. For thesake of clarity, the root may be dividedinto two halves, one lingual and onelabial. It is found that the mechanicsof the appliance will determine whichportion of the root will be moved themost. The appliances used in the ex-periments are seen in Figure 2. TWO ofthe experimental teeth were ligated di-rectly to a 0.7 mm. labial arch. By thistype of appliance some movement wasobtained, mainly of the lingual por-tion. Traction exerted by one springwould increase the movement of thelingual portion, a method applied intwo cases. Still more rotation was ob-tained when this force was counter-acted by a spur resting on the labialsurface of the tooth, Fig. 2B.Eleven teeth were moved by springsexerting traction in opposite directions,Fig. 2 Methods applied for rotation. Upperarrow, B, indicates spur counteracting trac-tion by spring.by which a considerable rotation couldbe obtained, Fig. 2C. Each of thesesprings exerted forces around 30 g.The degree of rotation obtained variedbetween fifty and seventy degrees. Bygrinding occlusal surfaces, the toothto be rotated was kept out of occlusionas long as the experiment lasted. Figure3 represents the average degree of ro-tation. The time periods required forthis movement varied between eightto twelve weeks in the younger ani-mals. Slightly more time was requiredfor rotation of the teeth in the olderanimal, an observation which is wellFig3known from other experiments.The areas to be examined may bedivided into marginal, middle andapical regions, Fig. 4. In the freegingival fiber group of the marginalregion, a marked displacement andstretching of fibrous structures was ob-served in all cases. Because the freegingival fibers are continuous with thewhole fiber system of this area, stretch-ing will cause displacement of fibrousstructure at some distance from therotated tooth, Fig. 5. This seemed tobe caused primarily by the fiber groupattached to the lingual or labial sur-faces of the root, Fig. 6. It was evenfound that tension had been exertedon the epithelial processes, which wereinclined as a result of traction by sub-jacent fibrous structures.In the middle region, usually bone Vol. 29, No. 2Retention107Fig. 4resorption was observed in two pres-sure areas, while there was stretchingof periodontal fibers and bone forma-tion in two corresponding tension areas,Fig. 7. Great variations existed in thedegree of tissue response on the pres-sure sides. In a few experiments ofshort duration compressed cell-freefiber bundles were found in one pres-sure area and direct bone resorptionin the other. Frequently direct bone re-sorption was observed in areas wherethe root was moved parallel to the boneFig. 5fibers following rotation of teeth.The arrangement of free gingivalFig. 6 Cross section of the marginal region,well-spaced teet.h. A, fiber bundles adjacentto the rotated toot.h, arranged obliquely. B,normal arrangement of periodontal fibers ad-jacent to the conitrol ltooth, U. D, undistinct,layer between stretched and relaxed fiberbundles.surface or where the pressure wasmoderated because the tooth movedcontacted the proximal tooth. A typicaldirect bone resorption of the lingualarea is seen in Fig. 8. Indirect resorp-tion had taken place more frequentlyin the labial than in the lingual pres-sure areas. Because an indirect resorp-tion process will last for two to threeweeks,5 undermining of compressedareas was completed in all experimentsof longer duration. Shallow root re-sorptions were observed in some casestogether with an extensive underminingof bone tissue. Two teeth, not includedin this series and rotated nearly go",exhibited corners that were flattenedby resorption during tooth movement,Fig. 9. Such aftereffects of an indirectbone resorption can hardly be avoidedand represent a typical reaction follow- 108ReitanApril, 1959Fig. i'-.%bove. Section of the middle region. A, resting lines between old and newlyforttied bone, B. C, thin bone layer bcti\ een control tooth and rit:tted tooth.Fig. S-Belo~v. Cross section of R pressure :;rea. A, thin cementum liue along the rootsurface ; the tooth moved as indicatect by :irrow. 13, protruding boiic spicule under directresorption by large osteoclasts, C. Vol. 29, No. 2Retention109on the tension side, Fig. 10, while verylittle cementum had been deposited onthe pressure side, Fig. 8.Fig. 9 R, amount of root substance re-moved by resorption following extensiverotation.ing an extensive rotation of teeth. Insome instances resorbed areas of theroot were already repaired by cellularcementum.The changes taking place on thetension sides were greatly influencedby the traction exerted on fiber bundles.A demarcation or resting line was ob-served between old and new bone lay-ers. New bundle bone and osteoid tis-sue were found arranged in tongue-like spicules along stretched fibers, Fig.10. Hence opposition of new bone isstimulated by the traction exerted byfiber bundles3 This traction will alsostimulate formation of cellular cemen-tum along the root surface. In somecases a marked increase in the thick-ness of the cementum layer was foundFig. 10 Tension side, middle region ofupper second incisor in older animal. A, lineindicating thickness of ceuientuni layer; B,demarcation line between old cementum andrapidly formed new cementum layer ; C,zoue with proliferating cells; D, new bonespicules formed as a result of tooth move-ment.In the apical region the supportingfibers were arranged obliquely. Amoderate increase of new bone layerswas observed in certain areas of theinner bone wall.Since rotation causes extensivechanges in the alveolar bone, withelongation of fiber bundles in the per-iodontal membrane as well as stretch-ing and displacement of the freegingival fibers, it is obvious that therotated tooth must be retained whilerearrangement of these structures takesplace. In experiments on retention oneshould be able to observe the length oftime required for a rearrangement ofthe structures involved.RETENTION AFTER ROTATIONThe retention appliance consisted ofbands cemented on the first and secondupper incisors. The rotated tooth wasmaintained in position by two shortpieces of wire, one soldered to thelingual sides and one to the labial sidesof the bands. The end of the labialsection rested on the labial surface ofthe third incisor. In cases where thetooth had been rotated in the oppositedirection, the end of the lingual sectionrested on the lingual surface of thethird incisor. An examination of thesupporting structures of retained teethmay be applied to the same areas asmentioned previously, Le. the marginal,middle and apical regions. Two kinds oftissues are of special interest, the fiberbundles of the periodontal membraneand the newly formed bone tissue.Fibrous tissw. As seen from TableI six teeth were retained for periodsvarying from 15 to 232 days. Rear-rangement of fibrous tissue means thatthe periodontal fiber bundles are againrunning more or less perpendicularfrom the root surface, as seen in the I IO Reitan April, 1959Marginalloath Retention Regiont2 15 days2t 28 days IRearrangement of Fibrous TissueMiddle ApicalRe,@on Region+ 4.Table I + indicates partly, ++ fairlywell, and +++ completely rearrangedfibrous Itissue afrter retention.supporting structures of the controlteeth. In Table I the marginal regioncomprises the areas of the gingivalfree and transversal fibers. It was foundthat no rearrangement of fibrous struc-tures had taken place in the marginalregion after retention periods of 15 and28 days. The periodontal fibers wererunning obliquely, partly parallel to theroot surface. In the other cases somerearrangement was observed, chieflyon the mesial and distal sides of theroot. It was noted that the fiberbundles attached to the labial andlingual sides of the root were still un-der tension.In areas where the teeth were wellspaced, the transversal fiber group wasarranged in two layers, one runningobliquely from the experimental tooth,the other perpendicular from the sur-face of the control tooth. A similar ar-rangement is seen in Fig. 6. In otherareas where the tooth position wasnarrow, silver impregnation stainingwould disclose that the transversalfiber bundles were elongated and run-ning obliquely from the rotated toothto the control tooth. In areas closeto the bone crest the transversal fibersgradually assumed a more normal ar-rangement. It is of interest to notethat the free fiber bundles of the teeth,retained for 147 and 232 days, still re-mained stretched in accordance withthe previous movement of rotation.This especially applies to the fiber bun-dles attached to the labial and lingualsurfaces of the root,, Fig. 11.In the middle region of the root(Table I) the periodontal fibers werestill arranged obliquely after a reten-tion period of 15 days. After 28 days thefiber bundles were fairly well rear-ranged. This applies to the retentionperiods of 57 and 83 days as well.Complete rearrangement was found af-ter periods of 147 and 232 days.In the apical region a rearrange-ment similar to that observed in themiddle region had taken place. Figure12 shows an area from the labial sideof the root retained for 147 days. Theorientation of these periodontal fiberscan hardly be distinguished from thatof a control area.BONE TISSUEThe observations made of bonechanges are listed in Table 11. In allregions very little rearrangement wasobserved after a retention period of15 days, with partial rearrangementafter 28 days; a more advanced bonereorganization had occurred in theother cases. It was seen in the first sec-tion of this study that new bone wasformed along stretched fiber bundles.This tongue-like bone formation wasobserved in the experiments on reten-tion after periods of 15 days. After re-tention for 28 days new bone had beenRearrangement of Bone TissueI ; I57days I + I ++ I ++ 1Table II + indicates partly, ++ fairlywell, and +++ completely rearranged bonetissue after retention.83 days ++ ++ ++147 days ++ ++ +++232 days ++ +++ +++ Vol. 29. No. 2RetentionFig. 11 - Above. Margiiial regicin, cross section of rotated tooth, A, retained for 232 dags;H, elongated and stretched fiber bundles; C, thin cenieiituiii layer along the root surface.Fig. 12-Below. Apical region, cross section of ,tooth retained for 147 days; A, cementumlayer of root surface; B, rearranged fiber bundles of periodontal membrane; C, rearrangedalveolar bone tissue. 112ReitanApril, 1959Fig. 13 A, illust.rating how boiic spiculesare formed along stretclietl fiber bundles ;B, rearraiigcmeiit of boiie tissue folloiviiigretention of the tooth iiioved.added between these first bone spicules.Figure 10 shows an area of the tensionside in one of the non-retained cases.In a corresponding area of the toothretained for 57 days, new bone hadfilled out the spaces between thesespicules. The transformation of bonestructures may be illustrated as seen inFig. 13. After retention periods of 147and 232 days a still more complete re-organization of bone tissue had takenplace, Fig. 12.DISCUSSIONIn a discussion of the present findingsone may question to what extent thesupporting structures of animals canbe compared with human tissues. Itappears that the arrangement of thesupporting structures in man and thedog is fairly similar. The changes tak-ing place in the alveolar bone are alsoquite similar. The periodontal fiberbundles, however, are coarser in thedog than in man and the bone tissuein the dog is frequently denser. Oneshould also remember that in practicerotated teeth are usually moved to aposition of greater mechanical ad-vantage. The opposite is frequently thecase in experimental tooth movement.These reservations must be taken intoconsideration when experiments on ro-tation are evaluated.It has been shown in the series ofretained cases that the arrangement ofthe structures in the gingival fibergroup is different from that seen inother areas. The persistence of stretch-ing and displacement of fiber bundlesin the marginal region indicates thatcomplete rearrangement of the support-ing structures requires a longer periodof retention than 232 days.Why free gingival fibers remain ina stretched position may be explainedby the fact that they are attached toa movable fibrous system which, tosome extent, may be displaced even atsome distance from the tooth moved.In addition, the supra-alveolar struc-tures contain elastic fibers which mayyield to traction during rotation. Theresult of this will be a tissue that willremain stretched during the retentionperiod. Forces leading to contractionof these fiber bundles will enter intoaction at the moment the tooth is re-leased, by which relapse of the toothmoved may occur.On the other hand, the periodontalfibers, running from the root surfaceto the bone surface will be fairly wellrearranged after a retention period oftwenty-eight days. It is therefore notlikely that relapse of a retained toothis caused by contraction of principdfibers, but primarily by a persistingdisplacement of supra-alveolar struc-tures in the marginal region.In his articles on this problem, Skogs-borg (1932) advocated transection offibers and bone structures in the septalareas of the tooth moved. Accordingto the present findings this is certain-ly necessary if the rotated tooth is notretained at all. Because contraction ofthe gingival fibers may be strongenough to cause resorption of new bonelayers adjacent to the rotated tootheven after a retention period, it wouldseem advisable in extreme cases totransect stretched fibers in the marginalregion. Surgical transection of bonestructures would hardly be necessaryfollowing a retention period. Vol. 29, No. 2RetentionI13The easiest way, however, to solvethe problem of rotating teeth wouldbe to correct the tooth position as earlyas possible, preferably before the apicalportion of the root is developed. Newperiodontal fibers would then be form-ed after rotation and thus prevent re-lapse of the tooth moved.SUMMARYExperiments on rotation and reten-tion of rotated teeth in young dogsreveal that some of the gingival fiberbundles will remain displaced andstretched even after a retention periodof 232 days. Periodontal fibers runningfrom the root to the bone surface willbe rearranged within a retention periodof 28 days. Relapse of the rotatedtooth after retention seems to be causedprimarily by a contraction of displacedgingival fibers and other supra-alveolarstructures. According to these findingsoverrotation of teeth would seem ad-visable in order to ensure a correct toothposition after the retention period. Itwould also be an advantage to transectstretched fibers around the tooth mov-ed. Early correction of a rotated toothposition would prevent relapse of thetooth moved because new fiber bun-dles, formed in the apical region: wouldassist in retaining the rotated teeth.Rad h uspat c 12 8REFERENCES1. Erikson, B. E., Kaplan, H. and Aisen-berg, M.S. : Orthodontics and TranseptalFibers. Am. J. Orth. 4 Oral Surg., 31,1, 1945.2. Hallett, G. E. M.: Immediate Torsion:A Preliminary Report on Twenty-threeCases. Dent. Practztioner 7 : 108, 1936.3. Macapanpan, L. C., Weinmann, J. P.and Brodie, A. G. : Early Tissue Changesfollowing Tooth Movement in Rats,Angle Ortho. 24: 79, 19.54.4. Reitan, K.: The Initial Tissue ReactionIncident to Orthodon'ic Tooth Movement.Acta Odoat. Scand. Supplenicntum 6,1951..). ~ Some factors netermining the Evaluation of Forces in Orthodontics.6.7.8.9.10.Ani. 1. Ortho. 43: 32, 1957.Siclitr, H.: The Principal Fibers of tlicPeriodontal Membrane. Tlic Bur, 55: `7,1954.Skillen, W. G. and Reitan, K.: TissueChmges Following Rotation of Teethin the Dog. Angle Ortlro. 10: 140, 1940.Skogsborg, C. : The Permanent Retentionof the Teeth After Orthodontic Trent-ment. Dental Cos~iios 69: 11 17-1129,1927.Septotomy in Connection with Ortho-dontic Treatment. Zwt. J. Ortko. 18 :1044-1057, 1932.Thompson, H. E., Myers, H. I.. W:iter-man, J. M. and Flanaqan, V. D : Pie-liminary Macroscopic Observations Con-cerning the Potentiality of Supra-alveo-Ixr Collagenous Fibers in Orthodonti:%Am. J. Ortho. 44: 486, 1958.