HOW TO DEAL ORTHODONTICALLY WITH THE

EXTERNAL APICAL ROOT RESORPTION

Prepared by: Nader A. Giacaman

Orthodontically induced inflammatory root resorption (OIIRR) is an unavoidable side effect of orthodontic treatment. It is a pathologic process that is related to the local injury of the periodontal ligament (PDL) and resorption of cementum and dentin that occurs in association with the removal of hyalinized tissue during tooth movement.

The severity of OIIRR is unpredictable. It occurs in all orthodontic patients, but only about 1% to 5% of treated individuals have greater than 4mm of root resorption.

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Factors affecting OIIRR OIIR can be influenced by biologic and/or

mechanical factors. However, biologic factors are not within the control of the clinician. Some of these factors are genetic, while others are environmental.

Mechanical factors, on the other hand, are attributed to the nature of the orthodontic appliance and can be controlled by both the clinician and the patient.

Mechanical factors1. Magnitude of applied force2. Treatment duration3. Distance of tooth movement4. Intermittent versus continuous force5. Different appliances and treatment

techniques6. Direction of force7. Extraction versus nonextraction

treatment protocol

Magnitude of applied force Many animal studies and human studies

have found that the force magnitude is directly proportional to the severity of OIIRR. Heavy force induces excessive hyalinization and interferes with the repair process of resorption craters.

The recommended forces for dental movement, according to Ricketts:

1001 tips in Orthodontics and its secrets

Treatment duration Most studies support the finding that the severity of

OIIRR is directly related to the duration of orthodontic treatment.

Artun et al evaluated standardized periapical radiographs of the maxillary incisors taken before treatment (T1) and at about 6 and 12 months after bracket placement (T2 and T3, respectively) of 2,467 patients. The risk of one or more teeh undergoing more than 1 mm of resorption from T2 to T3 was 3.8 times higher than that from T1 to T2.

Smale et al radiographically assessed the amount of apical root resorption on average 6 months after initiation of fixed orthodontic appliance therapy. The results showed that root resorption began in the early leveling stages of orthodontic treatment. About 4.1% of the patients studied had an average resorption of ≥ 1.5 mm in the maxillary incisors, and about 15.5% had one or more maxillary incisors with resorption of ≥ 2 mm from 3 to 9 months after initiation of fixed appliance therapy.

Distance of tooth movement

Significant associations existed among OIIRR, the magnitude of overjet reduction. The severity of OIIRR has been shown to be positively related to the distance of tooth movement. The maxillary incisors are commonly moved the greatest distance and are therefore at the highest risk of OIIRR.

Intermittent versus continuous force

A pause in tooth movement allows the resorbed cementum to heal, which may produce less root resorption.

Reitan advocated the use of intermittent forces to prevent the development of root resorption by allowing reparative processes to occur during periods with little or no force.

Levander et al radiographically evaluated the effect of a 2 to 3 month pause in treatment on teeth in which OIIRR was discovered after an initial treatment period of 6 months with fixed appliances. The amount of root resorption was significantly less in patients treated with a pause compared to those treated without interruption. The intermission of the forces facilitated reorganization of damaged periodontal tissue and reduced root shortening.

However, this intermittent scheme is not clinically practical and less efficient in orthodontic tooth movement

Even though the continuous force causes more resorptive effect, however, it is more effective at tooth movement than the intermittent force.

Different appliances and treatment techniques

Numerous studies have compared the extent of OIIRR following treatment with different types of orthodontic appliances. Most of the studies found no statistically significant difference among various orthodontic appliances (Tweed, Begg, edgewise straight-wire, and self-ligating systems).

Removable appliances are usually considered less detrimental in terms of creating OIIRR because of the intermittent force used. However, frequent removal and replacement of the appliance in the mouth generates jiggling forces, which can increase the amount of OIIRR to the same extent as that of wearing elastics.

Sequential aligners are becoming a more popular treatment alternative, especially in the adult population. Barbagallo et al compared the amount of OIIRR associated with a buccally directed movement with clear sequential thermoplastic aligners and fixed orthodontic appliances for an 8 week period. The degree of OIIRR from clear sequential thermoplastic aligners was comparable to that of a light buccally directed force of 25g. The force from fixed orthodontic appliances induced twice as much as the light force of 25g.

Skeletal anchorage and miniscrews can be used as an adjunct to orthodontic treatment. Careful placement of the skeletal anchorage and miniscrew is necessary to avoid damage to the root structure and minimize discomfort for the patient.

Several studies have investigated the tissue responses following intentional placement of miniscrews on root surfaces and have found that the cementum regenerated after miniscrews were removed.

Dao et al also found that in cases of severe injury from miniscrews, ankylosis can occur with root fragmentation.

Direction of force The type and direction of tooth movement have a

considerable role in OIIRR. Generally, the distribution of root resorption is dictated by the pressure zone created by different types of tooth movement.

It is expected that intrusion and torque have a higher force per unit area and thus cause more tissue necrosis and OIIRR. Some authors suggest that less root resorption is associated with bodily movement than with tipping because of the different stress distribution.

Extraction versus nonextraction treatment protocol

Attention should be drawn to the distance the teeth are moved. Extractions for severe crowding do not have as much impact on movement of the maxillary incisors as the displacement following extractions for overjet reduction.

Root Resorption Repair

Repair of root resorption craters begins when the applied orthodontic force is discontinued or reduced below a certain threshold.

According to schwartz, when the pressure in the periodontal PDL is 20 to 26 g/cm₂, root resorption stops.

The reparative process may be seen simultaneously with the resorption process. Many studies have demonstrated that the resorptive defects are repaired by deposition of new cementum and reestablishment of new PDL. Therefore, the risk of tooth loss following orthodontic therapy is not high.

Numerous studies have documented the time of onset of root resorption repair; Filho et al suggested that cementum repair following root resorption was likely to occur within 2 to 3 weeks if the affected surface was not very large.

The amount of root resorption repair increases with time. Owman-Moll and Kurol demonstrated more reparative cementum in the resorption cavities after 6 and 7 weeks of retention when compared with 2 and 3 weeks of retention.

Therefore, light orthodontic forces are once again recommended to encourage better recovery of the resorbed cementum.

Owman-Moll et al documented the amount of root resorption cavities repaired at different retention periods following 6 weeks of light buccally directed orthodontic force of 50g. After the first week of retention, 28% of the resorption craters showed some degree of repair. The repair rose to 75% after 8 weeks of retention. In a later study, Owman-Moll and kurol found 38%, 44%, and 82% of resorption craters repaired after 2, 3, and 6 to 7 weeks of retention, respectively.

Clinical consequences of OIIRR The clinical significance of OIIRR lies in the fact that there is

shortening of the root length, which could potentially compromise the long-term prognosis of the affected teeth, especially in periodontally affected cases. This would also make dental treatment planning difficult because these teeth are not favorable for ideal restorations.

Jonsson et al found that for teeth with extremely resorbed roots ( < 10 mm root length), mobility is expected to increase with age; while teeth with longer root length ( ≥ 10 mm) and a healthy periodontium remain stable. A reduction in root length as a result of apical resorption has been described as less detrimental than an equivalent loss of periodontal attachment at the alveolar crest, especially in cases with less than 3 mm of early root resorption. This emphasizes the importance of periodontal disease control in patients with severely resorbed teeth.

A long-term radiographic evaluation of root resorption after active orthodontic therapy revealed progressive remodeling of the root surface. The jagged resorbed edges were smoothed, and the sharply pointed root ends were rounded with time. However, the original root contours and lengths were never reestablished.

Management of OIIR Clinically, a number of approaches have been suggested in the

literature to minimize OIIRR. These are the recommendations for clinically reducing the

risk of OIIRR:1. A thorough assessment of familial tendency and medical

history.2. Habit control.3. Decreased treatment duration by careful treatment planning

and efficient mechanics.4. Use of light orthodontic forces especially for intrusion, palatal

torque of maxillary incisors, and rotation of premolars.5. 5. Assessment of the use of intermittent forces where possible

to allow resorption repair.6. 6. Progress radiographs after 6 to 12 months of treatment and

assessment for a rest period from orthodontic force if rapid root resorption is found or reassessment of the treatment plan.

7. Avoidance of sustained jiggling intermaxillary elastics.8. Limiting of tooth movement for OIIRR-prone teeth.

In a study by Levander and Malmgren Minor resorption or an irregular contour of the root that was seen 6 to 9 months after the last radiograph indicated an increased risk of further root resorption. If further root resorption occurs, the original treatment goals must be reassessed depending on the extent of root resorption detected, and a compromised orthodontic result may need to be accepted. The force levels should at least be modified, or a 2 to 3-months pause in treatment with passive archwires should be implemented.

Additional radiographs should be taken every 3 months in at risk patients to monitor the progress of root resorption. The amount of additional tooth movement required should be considered against the amount of root resorption acceptable, that is, no more than one-third of the root length.

It is mandatory to take final radiographs at the time of removal of fixed appliances. In the case of teeth with severe OIIRR, follow-up radiographs are recommended until additional root loss is no longer detected. If OIIRR continues to worsen, sequential root canal therapy with calcium hydroxide might be considered.

Retention of teeth with severely resorbed roots should be considered carefully to avoid occlusal trauma, which can cause further root resorption.

Case report

A 16 years old boy who had a class ΙΙ, division 1 malocclusion had severe root resorption of the maxillary right lateral incisor because of an impacted maxillary right canine. There was also severe root resorption of the maxillary first molars and mild root resorption of the other first molars . This indicates that the patient had a high risk of OIIRR. When treatment planning this case, the following had to be considered:

• Can the maxillary right canine be left, or should it be extracted? If the maxillary right canine is to be brought down into the arch, how should space be opened for it?

• The maxillary right first molar is severely resorbed and needs to be extracted. How will the space be handled?

• Can the Class ΙΙ molar relationship be corrected?

• Because of the severity of the root resorption, the treatment plan was to extract the maxillary right first molar and distalize the maxillary right first and second premolars to provide space for the impacted maxillary right canine.

First, sectional mechanics with a modified pendulum device were used to distalize the maxillary right first and second premolars. The sectional mechanics were used in an attempt to localize the orthodontic movement that was needed to distalize the maxillary right first and second premolars. The modified pendulum device provided intermitent force, which allowed for a rest period for resorption repair. Once adequate space was achieved for alignment of the impacted maxillary right canine, full fixed orthodontic appliances were placed.

• The correction of the Class ΙΙ relationship on the left side was dependent on the degree of OIIRR present during treatment.

• Because of the amount of root resorption present during treatment, the treatment plan was modified, and a Class Ι molar relationship on the left side was not achieved.

The end result was an acceptable occlusion with good esthetics and teeth that had

adequate root length. This case illustrates that even in the

presence of severe root resorption, orthodontic treatment can be carried out safely with careful planning of treatment

objectives and mechanics.

Conclusion In order to minimize the risk of root resorption related to orthodontic

treatment, the following should be considered first:

1. Careful treatment planning, taking into consideration family, medical, and social history.

2. Use of light forces especially for intrusion, lingual torque of maxillary incisors, and rotation of premolars. This could be achieved with slow progression of archwire sequence.

3. For at risk patients, regular radiographs (6- to 12- month intervals) should be taken and the treatment plan reassessed if required.

4. Even though continuous force causes more resorption, it is more effective on tooth movement than intermittent force.

5. Periodontal disease control in patients with severely resorbed teeth is prudent.

6. The most important consideration of all is to obtain informed consent prior to orthodontic treatment by explaining the risks and benefits of the orthodontic treatment and the potential for root resorption associated with orthodontic movement.