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The Influence of Orthodontic Movement on Periodontal Tissues Level Daniele Cardaropoli and Lorena Gaveglio Orthodontic forces are capable of reorganizing and remodeling the peri- odontal ligament, to facilitate tooth movement. Optimal forces will pro- duce favorable tissue responses, but whenever this balance is lost (as in the case of high force magnitudes, or in the presence of reduced peri- odontal support), the periodontal ligament may respond differently. This review highlights the responses of the periodontal ligament reactions when orthodontic forces— both normal and extreme—are applied. We also attempt to discuss how orthodontic movement differs in patients with good periodontal health and in those with periodontal disease. (Semin Orthod 2007;13:234-245.) © 2007 Elsevier Inc. All rights reserved. T he question of whether orthodontic forces may have negative effects on the periodon- tal tissues has been evaluated through a number of clinical and experimental studies. 1 This issue is of clinical relevance, since epidemiologic stud- ies have shown that the worldwide prevalence of gingival inflammation is high, and that 30% of the population has advanced periodontal dis- ease. 2,3 It is also known that the prevalence of periodontal disease in patients with a history of gingivitis is high, as is susceptibility of certain teeth. 4 Thus, it is important to identify patients who are susceptible to periodontal disease, and to control their periodontal health before start- ing orthodontic treatment. The adult patient with periodontitis usually presents with flaring of the anterior teeth, spaces, rotations, and overeruption of the den- tition. These changes in tooth position might compromise the esthetics and function of the dentition. In these situations orthodontic treat- ment may be useful in bringing back better func- tion and esthetics (Fig 1). When proper peri- odontal health and oral hygiene are maintained during the active phase of orthodontic therapy, no or only clinically insignificant lesions in the supporting tissues will occur. 5-9 However, if the oral hygiene maintenance is less effective with poor patient compliance and the presence of established periodontal inflammation during orthodontic treatment, the risk of a periodontal breakdown is markedly increased. 10-13 It should be noted, however, that the majority of the clin- ical studies evaluating the effect of orthodontic movement on the periodontal tissues have been performed in children or adolescents, who rarely are affected by destructive periodontal disease. 14 The development of destructive periodontal disease may result in the formation of suprabony pockets, with inflamed connective tissue and the dentogingival epithelium located coronal to the alveolar bone crest, or in the formation of in- frabony pockets, with the inflamed connective tissue and the dentogingival epithelium located apical to the alveolar bone crest. 15 Experimental studies involving histological analysis have re- vealed that orthodontic forces per se are un- likely to convert gingivitis into a destructive pe- riodontitis. 1,16 This finding may be related to the fact that, in the case of gingivitis, the plaque- induced inflammatory lesion is confined to the supra-alveolar connective tissue, while the tissue reactions occurring as a result of orthodontic tooth movement are confined to the connective tissue located between the root and the sur- rounding alveolar bone. Private Practice, Torino, Italy. Address correspondence to Dr. Daniele Cardaropoli, Via Balti- mora 122, 10137 Torino, Italy. Phone: 39.011.323683; E-mail: [email protected] © 2007 Elsevier Inc. All rights reserved. 1073-8746/07/1304-0$30.00/0 doi:10.1053/j.sodo.2007.08.005 234 Seminars in Orthodontics, Vol 13, No 4 (December), 2007: pp 234-245

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Page 1: The Influence of Orthodontic Movement on Periodontal ... · PDF fileThe Influence of Orthodontic Movement on Periodontal Tissues Level Daniele Cardaropoli and Lorena Gaveglio Orthodontic

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he Influence of Orthodontic Movement oneriodontal Tissues Levelaniele Cardaropoli and Lorena Gaveglio

Orthodontic forces are capable of reorganizing and remodeling the peri-

odontal ligament, to facilitate tooth movement. Optimal forces will pro-

duce favorable tissue responses, but whenever this balance is lost (as in

the case of high force magnitudes, or in the presence of reduced peri-

odontal support), the periodontal ligament may respond differently. This

review highlights the responses of the periodontal ligament reactions

when orthodontic forces— both normal and extreme—are applied. We

also attempt to discuss how orthodontic movement differs in patients

with good periodontal health and in those with periodontal disease.

(Semin Orthod 2007;13:234-245.) © 2007 Elsevier Inc. All rights reserved.

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he question of whether orthodontic forcesmay have negative effects on the periodon-

al tissues has been evaluated through a numberf clinical and experimental studies.1 This issue

s of clinical relevance, since epidemiologic stud-es have shown that the worldwide prevalence ofingival inflammation is high, and that 30% ofhe population has advanced periodontal dis-ase.2,3 It is also known that the prevalence oferiodontal disease in patients with a history ofingivitis is high, as is susceptibility of certaineeth.4 Thus, it is important to identify patientsho are susceptible to periodontal disease, and

o control their periodontal health before start-ng orthodontic treatment.

The adult patient with periodontitis usuallyresents with flaring of the anterior teeth,paces, rotations, and overeruption of the den-ition. These changes in tooth position mightompromise the esthetics and function of theentition. In these situations orthodontic treat-ent may be useful in bringing back better func-

ion and esthetics (Fig 1). When proper peri-dontal health and oral hygiene are maintaineduring the active phase of orthodontic therapy,

Private Practice, Torino, Italy.Address correspondence to Dr. Daniele Cardaropoli, Via Balti-

ora 122, 10137 Torino, Italy. Phone: �39.011.323683; E-mail:[email protected]

© 2007 Elsevier Inc. All rights reserved.1073-8746/07/1304-0$30.00/0

rdoi:10.1053/j.sodo.2007.08.005

34 Seminars in Orthodontics, Vol 13, No

o or only clinically insignificant lesions in theupporting tissues will occur.5-9 However, if theral hygiene maintenance is less effective withoor patient compliance and the presence ofstablished periodontal inflammation duringrthodontic treatment, the risk of a periodontalreakdown is markedly increased.10-13 It shoulde noted, however, that the majority of the clin-

cal studies evaluating the effect of orthodonticovement on the periodontal tissues have been

erformed in children or adolescents, whoarely are affected by destructive periodontalisease.14

The development of destructive periodontalisease may result in the formation of suprabonyockets, with inflamed connective tissue and theentogingival epithelium located coronal to thelveolar bone crest, or in the formation of in-rabony pockets, with the inflamed connectiveissue and the dentogingival epithelium locatedpical to the alveolar bone crest.15 Experimentaltudies involving histological analysis have re-ealed that orthodontic forces per se are un-ikely to convert gingivitis into a destructive pe-iodontitis.1,16 This finding may be related tohe fact that, in the case of gingivitis, the plaque-nduced inflammatory lesion is confined to theupra-alveolar connective tissue, while the tissueeactions occurring as a result of orthodonticooth movement are confined to the connectiveissue located between the root and the sur-

ounding alveolar bone.

4 (December), 2007: pp 234-245

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235Orthodontic Forces and Periodontal Ligament

Orthodontic movement creates clinical, cel-ular, and molecular level changes in the alve-lar bone. In periodontal pressure sites, boneesorption occurs by osteoclasts, while in theeriodontal tension sites, bone apposition oc-urs by osteoblasts. Orthodontically generatedental movement thus is strictly related to phys-

ological processes of cellular activity, both inhe soft connective tissue and in the alveolarone compartments.17

This article will review experimental and clin-cal reports that may be helpful in trying tonderstand the effect of orthodontic movementn periodontal tissue levels, and to determinehen abnormal force application can create aisk for further periodontal breakdown.

eriodontal Responses to Orthodonticorce Application

lassically, when an orthodontic force is ap-

igure 1. (A-D) Adult patient affected by a chronic pef bone support. After surgical periodontal treatment,ote the esthetic improvement obtained at the end o

Color version of figure is available online.)

lied, tooth movement will occur in the direc- s

ion of the force, by narrowing the periodontaligament (PDL) at the site of compression, withubsequent bending and resorption of the alve-lar bone. In this way teeth can be moved a smallistance, until the resisting bone stops the move-ent. This resistance is eventually overcome by

he ensuing resorption of the bone opposite theompressed PDL. At sites of force-induced ten-ion in the PDL, a concomitant apposition ofone will occur, until the PDL has regained itsormal width. Thus, tooth movement occurs as airect outcome of force-induced tissue remodel-

ng around the dental root. Such a remodelingequires the presence of cells capable of resorb-ng and forming the extracellular matrix (ECM)f the PDL and alveolar bone. When this mech-nism is kept under control, initial anatomicimitations such as sinuses, sutures, or corticalarriers can be exceeded, and tooth movementan be performed even through the maxillary

ntitis showing flaring of the anterior teeth due to lossodontic therapy was started to realign migrated teeth.atment together with a healthy periodontal support.

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236 Cardaropoli and Gaveglio

When orthodontic treatment is commenced,force system should be planned to reach the

roposed objectives. Increasing or decreasingorce levels, are always associated with a tissueeaction. Under normal conditions, chewingnd phonetic forces act on teeth surfaces, but noental movement results, since teeth are placed

n a so-called neutral zone. Moreover, this equi-ibrium is also maintained by means of an activetabilization, mediated by the metabolic activityf the PDL. To overcome this equilibrium andove a tooth, a minimal force of 5 to 10 g/cm2

s required.19 Dental movements can be classi-ed as movement “with the bone” or “through

he bone.” To achieve “with the bone” move-ent, frontal (direct) resorption of the bone in

he direction of the movement should occur,ith a balance between resorption and apposi-

ion. With excessive force application, indirectesorption occurs in areas surrounding the com-ressed, necrotic (hyalinized) PDL, and toothovement will be of “through the bone” type,ith only small amounts of bone apposition.20,21

owever, once the bony barrier is dissolved, theooth moves rapidly in the direction of the force,hile the PDL in the tension sites is stretched,nd bone apposition proceeds vigorously.

When an orthodontic force is applied, a cas-ade of events initiated by mechanical deforma-ion of cells and ECM takes place. The mechan-cal deformation of cells, their change in shapeovoid or round), and the release of arachidoniccid from the cell surface and its metabolismhrough either the lipooxygenase or cyclooxy-enase pathway leads to release of first messen-ers (prostaglandins and leukotrienes), which inurn activate or stimulate the release of second

essengers (cyclic AMP, inositol phosphate, dia-yl glycerol, and mitogen-activated tyrosine ki-ases). These second messengers evoke cellulareactions, such as bone and PDL remodeling. Inddition, pressure generated in the PDL altershe vascular support, contributing to the cellulareactions and remodeling changes.

In the presence of heavy and intermittentorces, as are produced during mastication, aental response is completed within a few sec-nds. These heavy intermittent forces cause an

nstantaneous microdeformation of the alveolarone since the fluid component of the PDLannot be compressed. After 1 to 2 seconds,

uid leaks out of the periodontal ligament and a

he teeth are deflected in the PDL space. Aftern additional 3 to 5 seconds, this fluid leaks outf the ligament, which generates compressionnd pain, leading to a cessation of any damagingorce. However, the pattern of the tissue re-ponse to orthodontic forces differs and can beelated to the intensity of the applied force. Itiffers in accordance with the magnitude of thepplied orthodontic force, whether light oreavy. When light forces are used, a deforma-

ion of the alveolar bone develops within 1 sec-nd, since the PDL fluids cannot be com-ressed. After 1 to 2 seconds, the fluids leak outf the ligament, allowing the tooth to move inhe ligament space. After 3 to 5 seconds the PDLlood vessels will be compressed in pressure sitesnd stretched in tension sites. Within a few min-tes, a decrease of the Po2 (partial pressure ofxygen) will develop, along with an increase inhe concentrations of prostaglandins and cyto-

igure 2. Cat maxillary canine after 7 days of orthodon-ic treatment showing compressed PDL and undermin-ng resorption. Tissue section stained with hematoxylin

nd eosin. (Color version of figure is available online.)
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237Orthodontic Forces and Periodontal Ligament

ines. After a few hours, metabolic alterationsill increase the incidence and rate of cellularifferentiation, and after 2 days, noticeable ini-

iation of tooth movement can be found. Thisrocess occurs predominantly due to the load-

nduced bone remodeling performed by a com-ined activity of both osteoclasts and osteoblasts.his kind of tissue reaction will generate a directone resorption (Fig 2), with a synchronizationf tissue resorption and apposition in PDL pres-ure and tension sites (Fig 3), respectively.

In contrast, when heavy forces are applied toeeth, alveolar bone deformation will developithin 1 second, since the PDL fluids cannot beompressed. After 2 seconds, the fluids leak outf the ligament, allowing the teeth to move inhe ligament space. After 3 to 5 seconds, theDL blood vessels will be occluded, and within

ew minutes, the blood supply to compressedreas of the ligament will stop altogether. Withinfew hours, signs of cellular death will appear in

hese zones, with the development of necrosis,hich resembles the appearance of hyaline car-

igure 3. Cat maxillary canine after 7 days of orthodf new alveolar bone formation. Tissue section stainevailable online.)

ilage when viewed with a microscope (the so- s

alled hyalinized zone). After 3 to 5 days, newellular differentiation starts, along with the be-inning of indirect bone resorption in all areasurrounding the hyalinized zone (Fig 4). One toweeks later, the lamina dura will be removed,

acilitating tooth movement.Based on these findings, it can be concluded

hat light forces are more efficient in developingontinuous tooth movement, preserving bothone and PDL from necrosis. With light forces,ooth movement begins after about 2 days ofreatment, and this early movement can some-imes exceed 0.5 mm. The movement then con-inues, and if an appropriate system of forcepplication is continued, a 2-mm space changeay be detected after about 3 weeks. In contrast,

ooth movement with heavy forces will not beontinuous, but will occur with alternating peri-ds of movement and a break, because of theeed for resorption of the necrotic areas. How-ver, it is difficult to quantify the amount oforce delivered to each tooth, and to determinehether it should be categorized as “light,” since

treatment showing PDL tension site and beginningh hematoxylin and eosin. (Color version of figure is

onticd wit

uch quantification may depend on various pa-

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ameters, such as root surface area, tooth anat-my, and the extent of periodontal supporteight. In the case of periodontal disease with lossf attachment, a “normal” force may be “excessive”

n relation to the existing support of the teeth,hich often leads to tissue hyalinization, excessiveone resorption, and further periodontal break-own. It is obvious that in the case of severe peri-dontal disease, this scenario could even lead toooth loss. To provide a numeric quantificationseful for the clinician, it is suggested that a forceot greater than 10 to 15 g should be applied to aaxillary incisor with loss of periodontal support,

o minimize further tissue breakdown.19

Tooth movement in regions outside the alve-lar process is undesirable and may occur due ton altered and poorly designed force system.orce distribution in tissues surrounding dentaloots is controlled by the force magnitude, and

igure 4. Cat maxillary canine after 7 days of orth-dontic treatment showing compressed PDL and di-ect alveolar bone resorption. Tissue section stainedith hematoxylin and eosin. (Color version of figure

s available online.)

y the moment/force ratio at the center of re- m

istance of the root. The force magnitude, espe-ially at the onset of treatment and in adultatients, should be very low, to avoid areas ofyalinization and to promote proliferation oferiodontal cells,22 while the moment/force ra-

io should be high,23 to achieve a good distribu-ion of the forces along the PDL. Adult age pere is not a contraindication for therapy, evenhough tissue response to orthodontic forces,ncluding cell mobilization, activation, and re-ponses, is slow when compared with those ofhildren. This difference can be attributed toeduced cellular activity with tissues rich in col-agen in adult subjects. In adults, hyalinizedones can form readily in pressure sites, tempo-arily preventing the tooth from moving in thentended direction.23 Eventually, these necroticones are eliminated through resorption by os-eoclasts and macrophages derived from the ad-acent marrow spaces, followed by regenerationf the PDL.24

In summary, when strong/heavy forces arepplied, the compressed PDL is crushed, result-ng in local ischemia and hyalinization, whichelay tooth movement. When even moderateorces are applied, the PDL may become stran-ulated, resulting in a delay in bone resorption.owever, light forces will produce only a partialDL ischemia, along with direct bone resorp-ion, resulting in a continuous tooth movement.

rthodontic Movement of Teeth withoss of Periodontal Support

eriodontitis is a multifactorial disease, whichevelops as a result of bacterial infection, super-

mposed on a genetic predisposition. Orthodon-ic forces per se are unlikely to convert gingivitisnto a destructive periodontitis, but poorly exe-uted orthodontic therapy in patients with peri-dontitis can easily lead to further periodontalreakdown (Fig 5). The combination of inflam-ation with occlusal trauma or dental move-ent will produce a rapid destruction of the

upport apparatus. The loss of alveolar bone ineriodontitis patients results in an apical dis-lacement of the center of resistance of the

nvolved teeth, making bodily movement (trans-ation) very difficult. The subsequent effect ishat the teeth become prone to tipping. In ad-ition to these mechanical difficulties, the for-

ation of a hyalinized zone adjacent to a peri-
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239Orthodontic Forces and Periodontal Ligament

dontally compromised tooth can be deleterious,ince regeneration of the PDL does not occurn the presence of a bacterial infection, resulting inxtensive loss of alveolar bone (Fig 6). Thus, inase of a deep periodontal infection, teethhould be moved only after proper periodontalherapy has been performed, and deep infectionas been eliminated.25,26

From a clinical point of view, in many patientsith a periodontally involved dentition the mi-ration of the anterior teeth leads to spacingnd eruption, resulting in serious functional andsthetic problems. In these cases, orthodonticsan be a reliable therapeutic treatment, becauset does not result in a decrease of the marginalone level, provided gingival inflammation isontrolled (Fig 7). Proper and timely combina-ion of orthodontic and periodontal treatmentas been shown to improve reduced periodontalonditions, suggesting the possibility for a long-

igure 5. (A-D) Detrimental effects of a poorly executpace opening due to periodontal disease. Orthodonation of the periodontal infection and adequate pla

ooth alignment. Surgical opening of the site showedown and esthetic complications. (Color version of fi

erm success.25 Best results are obtained when e

rthodontic movements are performed withight forces, and the line of action of the forceassing close to the center of resistance.26 Theentral point for the effectiveness of such treat-ents is in the ability of the procedure used to

emove subgingival plaque and calculus fromhe root surface. Following these guidelinesrthodontic treatment is no longer contraindi-ated when major marginal bone loss has oc-urred due to periodontal disease. The treat-ent of patients with severe periodontal disease

s now being performed with interdisciplinaryeamwork between the orthodontist and the pe-iodontist, to improve the possibilities of savingnd restoring a deteriorated dentition.

he Influence of Orthodontic Forces onhe Inflamed Periodontal Ligament

he development of destructive periodontal dis-

eatment. Patient presented with tooth migration andreatment has been performed without proper elimi-ontrol. Note the deepened periodontal pocket afterre bone loss resulting in further periodontal break-is available online.)

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ockets, that is, angular bony defects with thenflamed connective tissue and the dentogingi-al epithelium located apical to the crest of thelveolar bone. Furthermore, infrabony pocketsay be created by orthodontic tipping or intrud-

ng movements of teeth harboring bacterial

igure 6. (A-D) Adult patient with malocclusion whdontal and mucogingival evaluation. After the aligneveloped, which can be attributed to uncontrolled lab

evel, with the bone dehiscence. The situation wasegeneration and connective tissue graft. (Color versi

igure 7. (A-C) Interdisciplinary treatment of an adurgical periodontal treatment, osseointegrated implissing teeth and orthodontic treatment was perform

nterior teeth were splinted by means of resin-bonded

nline.)

laque, or both.27 Experimental studies haveemonstrated an aggravating effect on the pro-ression of periodontal disease when trauma,aused by “jiggling” forces, was superimposed oneriodontal lesions associated with angular bonyefects. This effect may indicate an increased

derwent orthodontic therapy without a proper peri-t of the two lower central incisors, a deep recessionovement. The intrasurgical view show the hard tissue

tly improved by the combination of guided tissuef figure is available online.)

atient with chronic periodontitis. After proper non-were inserted in the posterior areas to replace thealign the migrated dentition. At the end of therapy,

land-type bridges. (Color version of figure is available

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241Orthodontic Forces and Periodontal Ligament

isk for progression of plaque-associated peri-dontal disease, when orthodontic mechanics ispplied to a tooth, which already has angularefects.28,29 However, a similar study performed

n monkeys failed to demonstrate additional lossf connective tissue attachment when jigglingrauma was superimposed on periodontally dis-ased sites.30

The effect of bodily movement of teeth intonfrabony periodontal defects has been evalu-ted in an experimental study in monkeys.31 Thetudy reported that no deleterious effect wasbserved on the level of the connective tissuettachment. The angular defect was eliminatedy the orthodontic treatment but no gain inttachment level was obtained. There remainednly a thin epithelial lining covering the rooturface. However, in this study periodontal treat-ent was performed before the orthodontic

ooth movement was instituted, and the animalsere subjected to plaque control measures dur-

ng the entire course of the experiment.31 Innother study performed in 4 beagle dogs, an-ular bony defects were prepared at the mesialspect of the third premolars and an experimen-al periodontitis was induced. Orthodontic tooth

ovement was performed, to move one premo-ar into and through the angular bony defect.linical, radiographic, and histological evalua-

ions revealed that it was possible to establishnd maintain an infrabony pocket with a subcr-stal, plaque-induced inflammatory lesion dur-ng the entire course of the study. While theontrol teeth had maintained their attachmentevels, the orthodontically moved teeth did showdditional loss of attachment. It was concludedhat orthodontic therapy involving bodily tooth

ovement may enhance the rate of destructionf the connective tissue attachment in teeth with

nflamed, infrabony pockets. The risk for addi-ional attachment loss is particularly evidenthen the tooth is moved into the infrabonyocket.32 In another experimental study ononkeys, in which bodily movement of teeth

nto infrabony lesions was performed, results in-icated the possibility to obtain reattachment of

he periodontium after tooth movement.33

Clinical studies that have examined the effectf orthodontic movement in periodontal pa-ients with infrabony defects also abound in theiterature. A combined therapy, made of open

ap surgery and orthodontic intrusion, resulted o

n the realignment of the treated teeth withadiological bone fill, gain in clinical attach-ent level and probing pocket depth reduc-

ion, confirming the possibility of achieving anal healthy periodontium. These clinical stud-

es demonstrated that it is possible to performooth movement into infrabony defects in pa-ients with advanced periodontal disease, butmphasizing the importance of preorthodonticeriodontal therapy.34,35

A common problem in adult patients whoave periodontal disease is the migration, overe-uption, and spacing of incisors. These posi-ional changes can be the result of the lack ofquilibrium between the periodontal supportnd the forces acting on the teeth. Anterioreeth are specifically prone to overeruption,ince they are not protected by occlusal forcesnd have no anteroposterior contacts inhibitingigration. Moreover, masticatory forces are pre-

ominantly directed anterolaterally and therexists little resistance, particularly in cases ofncreased overjet. With progressive bone loss,he center of resistance moves more apically,nd the forces acting on the crowns generate arogressive displacement. From a functionalnd esthetic point of view, the intrusion of theseeeth seems to be the logical solution34 even ifrthodontic treatment, involving intrusive move-ents, does include a risk for an aggravation

f the periodontal condition.36 These types ofovements might have some beneficial effect on

linical crown lengths and marginal bone levelsFig 8).34 Furthermore, histological investiga-ions suggest that orthodontic intrusion mayead to new attachment formation: an experi-

ental study on monkeys demonstrated newonnective tissue attachment formed during thentrusion of periodontally involved teeth. It isossible that once the gingival infection is elim-

nated and the root surfaces are thoroughlycaled, it is possible for a new cementum layer toorm on the former infected root surface.37 Innother study, performed with the help of met-ic and histological analyses in monkeys, it wasound that only about 60% of the distance

oved is covered by the gingiva when the teethre intruded with a continuous force of 80 to00 g.38

In contrast to the latter, an experiment per-ormed on dogs demonstrated that intrusive

rthodontic forces are prone to shift supragin-
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ival plaque into a subgingival position, andhereby result in formation of an infrabonyocket.27 However, contraindication of intrusiveovement should not be a major concern if aeticulous oral hygiene and a healthy gingival

tatus are maintained. Once the periodontalreatment leads to a healthy gingival conditionnd susceptibility is controlled, and if the ap-lied orthodontic forces are well calibrated, it isossible to intrude teeth with periodontal bone

oss. This intrusion may lead to a certain gain inonnective tissue attachment.34,36,37

The orthodontically induced extrusion ofeeth can be indicated to increase the clinicalrown length of teeth, or to reduce differencesn alveolar bone levels. The so called forcedruption has been described for the treatmentf infrabony pockets, in which the extrusiveovement leads to a coronal positioning of

ntact connective tissue attachment, to shallowut the bony defect.39 One contraindication tohis technique is that, following the extrusion,he teeth will be in supraocclusion and therown will need to be shortened, often requiringndodontic therapy and prosthetic restorationFig 9 A-F).

Depending on the different clinical situa-ions, on occasion it may be desirable to have theeriodontium follow the tooth in the extrusiveovement, while in other situations it may be

esirable to move a tooth out of the periodontalupport. An experimental study on monkeys re-ealed that free gingiva moved about 90% andttached gingiva about 80% of the extruded dis-

igure 8. (A and B) Adult patient with pathologiconsurgical periodontal therapy, orthodontic treatmeelped in reintrusion of the tooth, with a perfect reeduction with a physiologic sulcus. (Color version of

ance. The width of the attached gingiva and the d

linical crown length increased significantly,hile the position of the mucogingival junctionas unchanged.40 Therefore, the extrusion of a

ingle tooth that would be extracted at a laterime can be a reliable method to improve the

arginal bone levels, when implant placement istreatment option. The supporting soft tissuesill move vertically with the corresponding toothuring the forced eruption, so as to create the

deal conditions for implant placement.41 Onhe other hand, in teeth with crown-root frac-ure at a subgingival level, the target of the treat-

ent may be to force the tooth to erupt out ofhe periodontium to perform a prosthetic reha-ilitation. In the latter situation, the extrusiveovement should be combined with gingival

berotomy. This excision of the coronal portionf the fiber attachment around the tooth shoulde performed once every 14 days, so that theooth can be moved out of the bone withoutffecting the bony and gingival levels of theeighboring teeth.42,43

rthodontic Movement and Anatomicimitations

rthodontic treatment may on occasion be per-ormed in adult patients who have partiallydentulous dentitions (as the result of agenesisr previous extractions), and in these circum-tances there may be anatomic limitations thatan complicate tooth movement. Atrophic boneidges, with a reduction of the horizontal volume,re not a limit to orthodontic tooth movement if

th extrusion of a maxillary central incisor. After aas initiated using light and continuous forces, whichment, esthetic harmony, and clinical crown lengthre is available online.)

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istological observations have confirmed that ifight forces are applied and teeth are moved

ore bodily into an area of reduced boneeight, a thin bone plate is recreated ahead of

he moving teeth.44 The same conclusions cane reached regarding the possibility of moving aooth through anatomic limitations such as si-us, suture, or cortical barriers. Limitation of

ooth movement in regions outside the alveolarrocess, as the maxillary sinus, is the result of anabnormal force system,” but if a proper distri-ution of the forces along the periodontal liga-ent can be obtained, the limitations of the

ortical bone of the alveolar process or the max-llary sinus can be overcome.

A clinical study in humans has demonstratedhe movement of a premolar into the maxillaryinus. After 6 months of active orthodontics, theadiographic evaluation of the displacement re-

igure 9. (A-F) Patient presenting crown-root fracturehe root canal and orthodontic extrusion initiated per

nd of treatment a permanent ceramic crown was inserte

ealed that bodily movement was achieved, withhe translation of the root in the distal direction,ithout any vertical displacement. Direct resorp-

ion allowed the movement even if the sinusoor seemed to set a limit to it. After the distalovement, the direct remodeling caused a dis-

lacement of the lamina dura, leading to a com-lete remodeling of the sinus contours. Theooth maintained normal vital response to pulpesting during this period. It seems that theooth did not fall into the sinus but moved withts supporting bone, without experiencing lossf connective tissue attachment. Moreover, thisontrolled movement left the bone necessary formplant insertion into the alveolus of the dis-laced tooth.45 Hence, based on the findings in

he studies referred to, it seems reasonable tossume that a tooth moved through the maxil-ary sinus will maintain the original height of the

subgingival level. A gold-alloy post was cemented intoing circumferential fiberotomy every 2 weeks. At the

at aform

d. (Color version of figure is available online.)

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244 Cardaropoli and Gaveglio

upporting apparatus, the connective tissue at-achment, and the alveolar bone height.

onclusions

he orthodontic treatment of patients with de-eriorated dentitions requires an interdiscipli-ary team approach that involves different den-

al specialties to obtain satisfactory functionalnd esthetic outcome. Orthodontic therapy isased on the principle of displacing teeth bypplying mechanical forces and remodeling theDL and alveolar bone. Clinical and histologicalvidence support the need for using light con-inuous forces during orthodontic treatment.ight forces evoke direct bone resorption, a so-alled with-the-bone resorption, in the directionf the movement, with a balance between re-orption and apposition. In contrast, heavyorces create blood vessel strangulation with sub-equent necrosis (hyalinization) in PDL com-ression zones. This kind of tissue reaction willelay tooth displacement and increase the risk

or bone loss. In the presence of a periodontallynvolved dentition, a risk for further periodontalreakdown is unacceptable since it may lead toooth loss. On the other hand, orthodontic ther-py performed with well-calibrated forces andpplying appropriate force systems can be usefuln realigning migrated teeth in adult patientsith periodontal disease following eliminationf the periodontal infection.

An understanding of the basic clinical andiological principles of orthodontic tooth dis-lacement is an essential requirement for the

mplementation of a successful therapeutic reg-men in patients of all age groups with normal asell as compromised periodontal tissues.

cknowledgmenthe authors thank Drs. Stefania Re, Giuseppe Corrente, andilliam Manuzzi for their contribution in the clinical treat-ent. The authors also express their sincere gratitude to Dr.e’ev Davidovitch for providing histologic figures as well asith a critical review and revision of the manuscript.

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