Root resorption in orthodontics /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

www.indiandentalacademy.com

o INTRODUCTION

o HISTOLOGY OF CEMENTUM

o CLASSIFICATION OF ROOT RESORPTION

o BIOLOGY OF ROOT RESORPTION

o CONTEMOPORARY REVIEW OF ETILOGICAL FACTORS

o PREVENTION AND MANAGEMENT

o CONCLUSION

CONTENTS


Introduction


Root resorption is an essential phenomenon that plays a crucial role in the physiological and dynamic process of tooth eruption

Resorption of deciduous roots during permanent tooth eruption is a necessary process that eventually results in the exfoliation of the deciduous tooth in anticipation of the arrival of its permanent successor

Periapical radiograph showing selective resorption of deciduous canine

root during eruption of permanent

maxillary canine.


However, as the saying goes “.. to every coin, there are two sides ”, root resorption may not always be a wanted process

Root resorption that occurs in permanent teeth is an unwanted process and is considered pathologic.

The external resorption of roots has perplexed the orthodontic specialty since the early reports of Ottolengui in 1914

External apical root resorption ( EARR ) of permanent teeth is an uncommon and frequent sequel to orthodontic tooth movement

Although apical root resorption occurs in individuals who have never experienced orthodontic tooth movement, the incidence among treated individuals is seen to be significantly higherwww.indiandentalacademy.com

Enormous amount of literature has been published regarding this single iatrogenic issue

The incidence of reported root resorption during orthodontic treatment varies widely among investigators.

Most studies agree that the resorption process ceases once the active treatment is terminated


Root resorption was found to be associated with orthodontic treatment all the way back to the early 1900’s

1927, Albert Ketcham was the first to bring the message that apical root resorption is a common and occasionally severe iatrogenic consequence of Orthodontic treatment.

Advent of the common-place dental x-ray equipment made it possible for Ketcham to evaluate a large series of treated cases.

Since then extensive research has been carried out pertaning all aspects of root resorption and every potential causative factor has been studied.www.indiandentalacademy.com

Even today, research is being carried out to identify the exact mechanism of root resorption and the factors which may be responsible for its initiation.

The research is mainly concentrated at the molecular level and is aimed at identifying and understanding the molecular signaling that takes place during this process


Histology of cementum


Cementum

Layer of calcified tissue covering the dentin of the root

Specialized connective tissue similar in physical and chemical properties to the bone but is avascular and has no innervations

First demonstrated in 1835 by two pupils of Purkinje


Cementum is less readily resorbed compared to alveolar bone, a feature that is important for permitting orthodontic tooth movement

The reason for this feature is unknown but it may be relatedto:

Differences in physicochemical or biological properties between bone and cementum

The presence of an unmineralized layer the “cementoid” on the surface of the cementum

The increased density of Sharpey’s fibres (particularly in acellular cementum)

The proximity of epithelial cell rests to the root surfacewww.indiandentalacademy.com

Physical characteristics

Light yellow color with a hardness less than that of dentin

Composition

45%-50% inorganic substances • Calcium and phosphate ( in the form of

hydroxyapatite )• Numerous trace elements • Highest fluoride content in the body

50%-55% organic substances• Type I collagen • Proteoglycans ( protein polysaccharides )


Structure

Types ( under light microscope )

Acellular cementum• Do not incorporate the spiderlike cementocytes• Covers the root dentin from the CEJ to the apex but

is often missing at the apical third.

Cellular cementum• Incorporates cementocytes in spaces called lacunae • A typical cementocyte has numerous cell processes

or canaliculi, radiating from its cell body• These branch or anastamose with other processes

mostly directed towards the periodontal surface of the cementum


A – ACELLULAR CEMENTUM

B – CELLULAR CEMENTUM

A - acellular cementum

B - cellular cementum

Electron microscope view of an embedded

cementocyte


Collagen fibres

• Arranged in both cellular and acellular cementum in a very complex fashion

•In some areas relatively discrete bundles of collagen fibrils are seen, particularly in tangential sections

•These are Sharpeys fibres


Function of cementum

Primary function – furnish a medium for attachment of collagen fibers that bind the tooth to the alveolar bone.

There is a continuous deposition of cementum (unlike bone, it does not resorb under normal conditions)

New cementum is laid down as the most superficial layer ages ( hence keeps the attachment apparatus intact)


Also serves as a major reparative tissue for root surfaces

Root damages ( minor fractures , resorptions can be repaired by deposition of new cementum )


Classification of root resorption


ACCORDING TO TYPE

Physiologic root resorption

Pathologic root resorption


ACCORDING TO LOCATION

Internal root resorption

Extrernal root resorption


ACCORDING TO SEVERITY

o Surface resorption

o Inflammatory resorption

o Replacement resorption


Occurs constantly as microdefects on all roots.

These normally repair themselves without notice.

May occur anywhere but most common periapically.

Stops when the instigating agent is removed and there is repair of the cementum.

SURFACE RESORPTION


Occurs when root resorption progresses into the dentinal tubules to reach the pulpal tissue

INFLAMMATORY RESORPTION


Produces ankylosis of a tooth because bone replaces the resorbed bone substance.

REPLACEMENT RESORPTION


According Brezniak and Wasserstein ( classification of Orthodontically induced root

resorption )

Cemental or surface resorption with remodeling

Dentinal resorption with repair (deep resorption)

Circumferential apical root resorption.


Cemental or surface resorption with remodeling:

In this process, only the outer cemental layers are resorbed, and they are later fully regenerated or remodeled. This process resembles trabecular bone remodeling.


Dentinal resorption with repair (deep resorption):

In this process, the cementum and the outer layers of the dentin are resorbed and usually repaired with cementum material. The final shape of the root after this resorption and formation process may or may not be identical to the original form.


Circumferential apical root resorption:

In this process, full resorption of the hard tissue components of the root apex occurs, and root shortening is evident. Different degrees of apical root shortening are, of course, possible.

When the root loses apical material beneath the cementum, no regeneration is possible.

External surface repair usually occurs in the cemental layer. Over time, sharp edges may be gradually leveled. Ankylosis is not a common sequel of orthodontically induced root resorption


ETIOLOGY

Root resorption may occur as a result of :

• Dental trauma / surgical procedures / Infections• Orthodontic treatment• Pressure from tumors / cysts• Irritation from chemicals ( Eg. H2O2 during

bleaching)


Pulpal infection root resorption

The most common stimulation factor for root resorption is pulpal infection.

Following injury to the precementum or predentin, infected dentinal tubules may stimulate the inflammatory process with osteoclastic activity in the periradicular tissues or in pulpa tissues, consequently initiating external or internal root resorption.


•Clinically teeth are not usually symptomatic in the early period of the process, and resorption may be seen at this stage only in radiographs. However, as the process progresses, the teeth may becme symptomatic and periradicular abscesses may develop with increasing tooth mobility.

•Radiographically, radiolucency is observed in the external root surface of the dentin and adjacent bone, or in the internal root canal dentinal walls.


Periodontal infection root resorption

Infrequently, external root resorption may occur after injury to the pre-cementum, apical to the epithelial attachment, followed by bacterial stimulation originating from the periodontal sulcus.

Injury may be caused by dental trauma, and chemical irritation may be caused by bleaching agents, eg hydrogen peroxide 30 %, orthodontic or periondontal procedures.


Bacteria from the periodontal sulcus may penetrate patent dentinal tubules, coronal to the epithelial attachment, and exit apical to the epithelial attachment without penetrating the pulpal space.

Consequently, the damaged area of the root surface is colonized by hard tissue resorbing cells, which penetrate into dentin through a small denuded area causing the resorption inside the root to spread.

At first stage, the resorptive process does not penetrate the pulp space because of the protective layer of predetin, but rather spreads around the root in an irregular fashion. With time, the preocess may penetrate into the root canal


Aditionally, periodontal infection resorption will include the alveolar bone adjacent to the resorption lacuana in the tooth.

If the resorptive process reaches a supragingival area of the crown, the vascularized granulation tissue of the resorption lcuna may be visible through the enamel showing a pink discoloration at the crown.

Radiographically, periodontal infection resorption can be seen as a single resorption lacuna in the dentin usually at the crestal bone level, expanding to the conronal and apical direction. With progression of the process, radiolucency may be observed at the alveolar bone adjacent to the resorption lacuna of the dentin. www.indiandentalacademy.com

Orthodontic pressure root resorption

The injury originating in the orthodontic root resorption is from the pressure applied to the roots during tooth movement. Continuous pressure stimulates the resorbing cells in the apical third of the roots, a possibility of significant shortening of the root.

Teeth are asymptomatic and the pulp is usually vital unless the pressure of the operative procedure is high, which disturbs the apical blood supply.

Radiographically, orthodontic pressire resorption is located in the apical third of the root and no signs of radiolucecy can be observed in the bone of the root. www.indiandentalacademy.com

Impacted tooth or tumor pressure root resorption

Pressure root resorption can be observed during the eruption of the perimanenet dentition, especially of maxillary canines ( affecting lateral incisors ) and mandibular third molars ( affecting madubular second molars ).

Tumors and osteosclerosis impingning on the root of the tooth could also be an etiological factor for pressure resorption, which includes both the injury and the stimulation phases. Stimulation is related to the pathological process that activates the resorptive cells, tumors that produce root resorption are most frequently those in which growh and expansion are not rapidm such as cysts, ameloblastomas, giant cell tumors, and fiber-osseoseous lesions.


This type of root resorption is asymptomatic with vital pulp through –out the process unless the impacted tooth or tumor is located near the apical foramen, disturbing the blood supply to the pulp.

Radiographically, the resorption area is located adjacane to the stimulation factor, the impacted tooth or the tumor. There are no radiolucent areas as no infection is involved in the process.


Impacted maxillary canine in close proximity to lateral incisor apex


Ankylotic root resorption

In severe traumatic injuries ( intrusive luxation or avulsion with extended dry time ), injury to the root surface may be so large that the healing with cementum is not possible, and the one may come into contact with the root surface without an intermediate attachment apparatus. This phenomena is termed dentoalveolar ankylosis.

The process may be reversed if less than 20% of the root surface is involved. Because there is no stimulation factor and the process proceeds as a result of the direct bone attachment to dentin, the term ‘ankylotic resorption’ is adequate.


oClinically, ankylotic teeth lack the physiologic mobility of normal teeth. This is one diagnostic sign for ankylotic resoprtion. In addition, these teeth usually have special metalli percussion sound and if the process continues, they are in infra-occlusion.

oRadiographically, resorption lacunae are filled with bone, and the periodontal ligament space is missing. No radiolucent areas are observedm and at some stage, the whole root may be replaced by bone.


Biology of root resorption


Force application on teeth in orthodontics leads to adaptive changes in the entire surrounding periodontium.

This Orthodontic force leads to microtrauma of the PDL and activation of a cascade of cellular events associated with inflammation.

The first signs of change in response to these forces is seen as remodelling changes by the PDL and the surrounding alveolar bone because of the high adaptability and regenerating capabilities of these two tissues.


However, root resorption may occur when the pressure on the cementum exceeds its reparative capacity and dentin is exposed allowing multinucleated odontoclasts to degrade the root substance.

Orthodontically induced root resorption begins adjacent to hyalinized zones and occurs during and after elimination of hyaline tissues. Removal of hyalinized tissue leads to removal of cementoid and mature collagen, leaving a raw cemental surface that is readily attacked by dentinoclasts.

There is a positive association between removal of hyalinized tissue and root resorption.


The cellular process


The studies in mice and rats conducted by Brudvik and Rygh confirmed that orthodontically induced root resorption is a part of the hyaline zone elimination process.

The first cells to be involved in this necrotic tissue removal are cells that are negative for tartrate resistance acid phosphatase (TRAP –ve ) and that have no ruffled borders.


These are Macrophage-like cells, are most probably activated by signals coming from the sterile necrotic tissue, the result of the orthodontic force application.

Macrophages are scavenger cells from the hematopoietic lineage, and their role is to eliminate necrotic tissues. As described by Brudvik and Rygh, the initial elimination process takes place at the periphery of the hyaline zone, where blood supply to the periodontal ligament exists or is even increased.


During removal of the hyaline zone, the nearby outer surface of the root, which consists of the cementoblast layer covering the cementoid, can be damaged, thus exposing the underlying highly dense mineralized cementum.

It is possible that the orthodontic pressure itself directly damages the outer root surface layers in such a way that there is a need for their removal as well.


The root surface under the main hyaline zone is resorbed only several days later when the repair process in the periphery is already taking place.

The cells responsible for this later stage of removal include TRAP +ve cells. These cells, in the process of removal of necrotic periodontal tissue, continued to remove the cemental surface also.

These finding have been confirmed by studies of human premolars that were moved buccally before their extraction.


Orthodintic force Compression of

PDL

Hyalinization

& inflammation

Activation of osteoclasts

Removal of hyaline material

Removal of superficial surface of

cementum

Root resorption


The repair process

Morphologically, the repair process of the resorbed lacunae is described as beginning from the periphery, the bottom, or all directions.

It begins about two weeks after force removal, with the placement of acellular cementum succeeded by cellular cementum. This process is evident in 38% and 82% of human premolar lacunae after two and five weeks, respectively.


In bone, osteoclasts undergoing apoptosis leave at the bottom of the lacuna a protein layer that is composed partially of osteopontin and bone sialoprotein. This layer is recognized later as the cemental line with which the osteoblasts meet on bone formation.

According to Bosshardt and Schroeder the odontoclasts leave the root lacunar surfaces exposed with no sediment at the base of the crater. Recently, however, it has been reported that a specific cementum attachment protein (CAP) has been identified in human cementum

This protein has the ability to bind to mineralized root surfaces with high affinity. Its role in cementogenesis and cementoblast recruitment is still under investigation. Individual variations characterize the repair process as evident in EARR


Methods of measurements of

root resorption


EARR can be defined operationally as the degree a root has shortened from its original ( or expected ) length by clastic activity

Broadly, two methods have been used to quantify resorption :

Ordinal scale data :Visually assessed grades of resorption assigned

Ratio scale data: Measurements with calipers or some computer aided device)


GRADE 0

oNormal Intact root morphology

oApical outline is smooth and continuous

oDistance between the root and lamina dura is uniform

GRADE I

oEvidence of erosion periapically

oRoot length probably not yet affected

GRADE 2

oScalloping and blunting of apex

GRADE 3

oOne-fourth of the root resorbed

GRADE 4

oLoss of atleast one-half the original length

THE ORDINAL SCALE USED TO MEASURE EARR

BY LEVANDER E. & MALMGREN


Contemporary review of etiological factors

associated with root resorption


Among different malocclusions, based on Angle’s classification system, studies have observed a statistically significant difference between class I and class II div 1 malocclusion, with the latter exhibiting more resorption.

Janson et al reported a higher resorption potential for class II div 2 cases in comparison with class I , class II div I and class III patients.

The rationale was that excessive intrusion mechanics were necessary to correct the deep overbite in these cases and also the torque required to correct the palatal inclination of the incisors was high.

Type of malocclusion


EXTRACTION VS NON EXTRACTION

The analysis of literature reveals that both the extraction and the non extraction treatment have the potential to produce damage, with the extraction therapy being potentially more detrimental.

Among all the extraction patterns, extraction of all the first premolars showed the greatest resorption potential.


Mechanotherapy Begg Vs edgewise

Although previous studies by could not find any significant resorption rate between Begg light wire mechanics and edgewise ( Tweed ) techniques, a recent study by McNab et al has reported a higher incidence of resorption, as well as amount of root resorption in patients treated with the Begg appliance.


They concluded that the incidence rate of root resorption was 3.72 times higher when extractions were performed as part of Begg appliance therapy.

Root resorption was also observed in all three stages of Begg treatment, with the second stage exhibiting the least severity


Intrusion and torque movements are found to be most commonly associated with the resorption process.

This is evident when studying class II div 2 correction as well as Begg mechanics. The intrusion performed in the first stage and the torquing in the third stage make the Begg technique more vulnerable to resorption.

The highest root resorption is reported to occur when 3 to 4.5 mm of torquing movement was performed.

Type of tooth movement :


Length of treatment time

The length of treatment time and root resorption have been positively correlated by almost all studies

These studies revealed have shown that increased treatment time makes tooth roots more prone to iatrogenic response.


Type of force applied ( Continuous vs interrupted )

Interrupted forces were shown according to studies to cause less severe apical blunting and smaller resorption- affected areas.

The authors of these studies emphasize the use of less detrimental discontinuous forces ( in the form of elastic usage, instead of elastomeric chains ) during space-closure stages of orthodontic mechanotherapy.


Tooth specificity:

Evaluation of the vulnerability of specific teeth to the resorption process in the literature has resulted in common agreement among authors that the maxillary incisors are the teeth that are the most susceptible to the process.

However, Controversy still exists regarding which incisors resorb the most: the centrals or the laterals..

The majority of the studies published reported that the central incisors were more susceptible to the process.

Following the incisors in susceptibility to resorption in the maxillary arch are the molars, followed by the canines. www.indiandentalacademy.com

In the mandibular arch the most resorption-vulnerable tooth is the canine, followed by the lateral and central incisors.

Among the posterior teeth, the most resorbed are the mandibular molars ( with the distal root exhibiting more resorption ), followed by maxillary molars, mandibular premolars, maxillary first premolars, and maxillary second premolars.

Beck and Harris in their classic article, described the relationship of mechanotherapy to root resporption in the distal roots of molars. According to them anchorage archwire bends at the mesial of molars for bite opening cause the distal roots to be compressed in the tooth sockets, thereby initiating root resorption


Root shape Various authors have evaluated abnormalities in

root shape and its association to the resorptive process.

Among differently shaped root ends ( normal, blunted, dilacerated, pipette shaped, pointed, and incomplete) , the least resorption was observed in blunted root ends and the greatest was seen in pointed or tapered root ends.

This phenomena is explained by the fact that the pressure from the axial component of orthodontic forces is felt most at the root apex regions which are abnormal in shape. This results in localized ischemic necrosis, which denudes the precmentum and cementoblasts, permitting colonization of dentinoclasts.


In comparison to the normal root shape, dilacerated roots show the most resorption followed by pipette- shaped and the incomplete roots.

Hence, any abnormal root shapes observed in the pre-treatment diagnostic records should be observed with caution and should be monitored throughout the treatment period for any iatrogenic damage.


Root length:

A positive correlation is found between the root length and root resorption. The studies in this regard report that longer roots are more prone than shorter ones to resorption.

This may be due to the greater displacement required to produce an equal amount of torque, versus shorter roots.


Previous history of trauma and the presence of pretreatment root resorption have been positively correlated with root resorption seen after orthodontic treatment.

Also studies have found a relationship between cortical plate proximity and increased root resorption. All these findings point towards the importance of obtaining pretreatment diagnostic records and proper evaluation. So that any risk elements can be identified and described.

History of trauma:


Overjet or overbite:

Studies to date have agreed with a positive correlation between an increase in overjet and root resorption.

The main reasons attributed to this phenomenon are the greater amount of torque and greater root displacements required to correct excessive overjet.


Biologic factors such as age at the start of treatment and gender, have long been associated with risk factors for the initiation of root resoption.

Age at the start of the orthodontic treatment and incidence of root resorption have been poorly correlated in almost all recent studies.

Conflicting results have been seen when gender is considered. Various studies supported that females are more prone to root resorption whereas various others stated that men were more prone.

Age, Gender and ethnicity: are they contributing factors?


The majority of the studies support a lack of correlation between gender and resorption.

The relationship between ethnicity and root resorption was evaluated recently. The results showed less severity among Asians in comparison to Caucasians and Hispanics.


EFFECT OF DRUGS

Drugs such as corticosteroids and alcohol have been identified as predisposing factors.

An increased risk for root resorption among asthamatic patients was also recently reported by Mc Nab et al. they did a tooth – specific analysis and found a higher incidence of resorption for the roots of maxillary molars.

The changes they observed were attributed to changes in the immune system of patients and the close proximity of maxillary molar roots to the maxillary sinus.


Prevention


Quantitative as well as qualitative analyses of resorptive process are required to prevent the occurrence of the most common iatrogenic damage following orthodontic tooth movement.

Before treatment

General considerations. The patient/parents must be informed about the risk of EARR as a consequence of orthodontic treatment.

Root resorption should be discussed during consultation.

Every informed consent form signed by the patient/parents (and the orthodontist) should specifically outline the risk of EARR


The rule of thumb is better to inform early than to later apologize.

It is obvious that if the orthodontist decides to initiate treatment after reviewing all of the relevant data collected, the expected esthetic and functional benefits far outweigh the minor root changes observed in most patients.


The importance of diagnostic records and thorough evaluation of them should not be overlooked from a medico-legal point of view.

Obtaining records periodically during active treatment is a must.

Of the various methods ( clinical, histological, radiographic, biologic markers), radiographs remain the most important tool for evaluation of pre treatment, in-progress, and post treatment status of tooth roots.

At the start of treatment


Recent researchers have recommended periapical films for patients at high risk of root resorption and bone loss. They have also found that abnormalities were clearer in periapical films.

Levander et al have supported the use of digital images for the purpose of visualizing root resorption. Digital images provide a better image quality than the conventional radiographs and also the radiation exposure is lesser to the patient.

The use of computerized tomography for evaluation of resorption and its sensitivity in site-specific ( mesial, distal, buccal, or lingual ) detection of the process has been reviewed lately.


Recently, Mah and Prasad discovered biologic markers for root resorption in crevicular fluid. In their experiment, they measured dentin sialophosphoprotein and found their levels to be high in GCF that was in proximity to resorbing primary and permanent tooth roots.

This research may be in future used as a simple and practical method for predicting initiation of the process


Management


Is the process reversible?

Review of literature reveals that when a tooth loses its apical material beyond the cementum, no regeneration is possible.

The reparative process begins 2 weeks after the force is discontinued, and the effects are evident within 6-8 weeks.


Acellular cementum is laid down in the initial stages, followed by cellular cementum.

The according to various authors, the process starts from either the peripheral region, the apex, or in all directions, and individual variations seem to be very common as far as the repair is concerned.


Midtreatment approach to root resorption

Progress periapical films or panoramic radiographs should be analyzed during the treatment.

A review of literature supports a temporary halt in orthodontic treatment for a period of 4 – 6 months.


The resorptive process ceases and the reparative process starts within this period.

Appropriate follow up and necessary counseling should always accompany this approach.


The role of drugs in decreasing root resorption has been reported in some recent publications.

Drugs such as bisphosphonates, Nambumetone ( an NSAID ), various hormones and cytokines including prostaglandin E2 and L-thyroxine etc have been tried and tested to little clinical success.


A recent report by Baily et al evaluated the effect of low-intensity pulsed ultrasound ( LIPUS ) in the healing process of orthodontically induced root resorption in humans. The result of this study are quite encouraging, as it demonstrates a non-invasive method to reduce root resorption in humans.


Conclusion


External apical root resorption is an iatrogenic consequence of orthodontic treatment. Keeping this in mind, we as orthodontists should take all known measures to reduce its occurrence.

Although several protective procedures have been suggested, none of them can actually prevent EARR with any degree of certainty.

Probably in the future, more genetically based studies, as well as other basic science research, might clarify the exact nature of EARR and hopefully help to prevent or even eliminate this phenomenon.


THANK YOU


References


Current principles and techniques : Graber Vanarsdal : 3rd edition

Root resorption: The possible role of extracellular matrix proteins: Adam Lee ; Glen Schneider : AJO 2004 ; 126

Critical issues concerning root resorption : A contemporary review : Krishnan V. ; World Journal of orthodontics,vol & no.1 2005, pg 30-39

Root resorption in orthodontic therapy: : Edward F. Harris ; Seminars in orthodontics : 183-191

Root resorption- diagnosis,classification and treatment planning based on stimulation factors : Dental Traumatology 2003 : 19;175-182

Contemporary Orthodontics, William R. Profitt, 3rd editionwww.indiandentalacademy.com

Oral Anatomy, Histology & Embryology, B.K.B. Berkovitz, 3rd edition

Brezniak N, Wasserstein A. Root resorption after orthodontictreatment: Part 1. Literature review. Am J Orthod 1993;103:62-6.

Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 2. Literature review. Am J Orthod 1993;103:138-46.

Predicting and preventing root resorption : Part I : Diagnostic factors : Glen T. Sameshima : AM j Orthod ; May 2001, 119


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