3rd Edition published April 2012
  • Fully revised and updated classic
  • Coverage expanded to include protocols for routine and for complex cases
  • Includes new chapter on extreme tooth displacement and complicating factors
  • Provides unparalleled coverage of the evidence base
  • Highly illustrated in full colour
  • Every imaginable tooth impaction

Price $170
Apply to

Just out ! The Spanish translation of the 3rd edition
for details contact the publishers at

Designed by:

Invasive Cervical Root Resorption (ICRR)

Published: March 2013

Bulletin #20 March 2013

Invasive Cervical Root Resorption (ICRR)

When dealing with impacted teeth, it is crucial to accurately locate the tooth in the 3 planes of space and in relation to the adjacent teeth, before any treatment to resolve it should be initiated. The purpose is to evaluate the topography of the locale, in order to be in a position to offer an operative strategy that will decide the direction or directions that traction needs to be applied. Ignoring this basic diagnostic step risks the possibility of failure to resolve the problem, as has been shown in a number of the earlier bulletins on this website (see Bulletins #5 November 2011, #15 October 2012, #16 November 2012).

But this is just one of the factors involved in the diagnosis. It is no less crucial to examine detail in the radiographs to identify any abnormalities that may be present and which may prevent movement. There are many possible reasons why a tooth does not erupt in the normal way. There are also many reasons why an impacted tooth may not respond to orthodontic forces that have been applied with the intention of enhancing the tooth’s own innate force of eruption, in order to bring the tooth into the mouth, into alignment and into occlusion. The very fact that the tooth has not erupted should raise the suspicions of the orthodontist to find out why. There is usually an obvious cause. There may be obstruction due to the presence of the root of an adjacent tooth, or a supernumerary tooth, perhaps an enlarged dental follicle, or conversely, disappearance of the dental follicle and ankylosis. Most of these factors can be identified ahead of time and should therefore not come as a surprise, and certainly not after several fruitless years of applying traction – as we sometimes see.

Within the realm and capabilities of routine plane film radiography, the most important qualitative film through which to identify pathology and the one that will give the best detail, is the periapical radiograph. But it has limitations because it is only a 2-dimensional film. This film can show us lesions on the interproximal surfaces, such as interproximal caries or root resorption, but it cannot show us pathology on the lingual or facial surfaces unless these are large enough to alter the shape of the mesio-distal profile or they affect the visual contrast or density of the tooth structure on the film. For these reasons, three-dimensional cone beam technology is essential for us to gain as much information as is available.1 Yet, most of us do not study these images adequately before treatment and only refer back to them, in retrospect, when failure to move the tooth has already occurred.

For the present discussion, we shall focus on one specific type of lesion which is highly relevant since it will undermine efforts to resolve tooth impaction, namely, invasive cervical root resorption.2

From a questionnaire study that we carried out among the participants of the courses that we have recently conducted in a number of countries, we found that very few of the orthodontists present had heard of invasive cervical root resorption (ICRR). For those who were aware of it, few knew that it is a potent factor in failure to move the tooth. Without question, part of the reason for this is that one cannot find mention of it in the orthodontic literature. On the other hand, the phenomenon is well known to endodontists, pediatric dentists and dental traumatologists, because the prevalence of ICRR following trauma or bleaching of non-vital teeth is relatively common. In regard to bleaching, it seems that the bleaching chemicals leech out of the sealed pulp chamber through the auxiliary lateral pulp canals, causing chemical damage to the cervical area of the root. However, ICRR is a phenomenon that one may see in vital teeth from time to time, many of which will have been associated with trauma in the past (Fig. 1).

q.Fig._1a q.Fig._1b

Fig. 1a. Transaxial CBCT view of an impacted central incisor to show the cervical ICRR defect of the labial side of the tooth and the radiolucent dentine contents of the crown.

Fig. 1b. The extracted tooth, sectioned to show the resorbed areas of the crown and the unaffected predentine layer. The site of the initial port of entry can be seen on the labial side of the CEJ.

ICRR in vital teeth is rare and insidious, although it is an aggressive form of external root resorption which begins at a very small site immediately apical to the periodontal attachment. From there it rapidly burrows into the substance of the root in all directions. Thus an advanced case will see the resorption having spread apically into the root and coronally into the crown, where it will seriously undermine the enamel and may create a “pink” tooth. It will also proceed inwards towards the pulp, where it will be stopped short at the predentine and will completely encircle the pulp. It seems that the high organic content of the predentine acts as a barrier to protect the pulp and the process does not normally cause pulpal inflammation. This is the reason that it is totally asymptomatic. In the absence of pain, therefore, an ICRR lesion may have wrought much destruction before it is discovered serendipitously – quite by chance.

Initiation of the resorption process is most likely due to local injury to the cementum, which causes the dentine to become locally denuded and this may present as tiny gaps in the cementum layer when viewed under the microscope. Clastic cells are attracted to the area and these begin to resorb the dentine. In favorable circumstances, epithelial proliferation extends down the root to cover the affected area, to form a long junctional epithelial attachment and thus to inhibit further resorption. Conversely, chronic inflammation of the granulation tissue that is in contact with the dentine may occur and this will prevent proliferation of the marginal epithelium. Thus the resorption process is encouraged.

Probably a good number of impacted teeth that fail to respond to orthodontic forces are likely to be affected by ICRR to a fairly severe degree. Histologically, we have found in ICRR that, in addition to resorption, there are also areas of deposition of bone in the resorbed areas and this is most likely what will have contributed to the failure. Alternatively, it may be argued that failure is due to the break in the integrity of the PDL caused by the lesion, since eruption depends on a healthy and complete PDL.

But what could be the cause of the resorption mechanism in a tooth that is unerupted? After all, it is logical to assume that the fact of its impaction within the tissues, would deem it protected it from trauma. This is not necessarily true and there are undoubtedly cases of trauma to the deciduous dentition that may lead to ICRR of the permanent dentition, which may have been affected by transmission of the force of the blow (Fig. 1).

When I was a newly qualified graduate, I decided to attend the surgical exposure of a tooth for one of my early patients. I stood in awe of the older and very experienced oral surgeon, as he exposed the tooth right down to and even beyond the cement-enamel junction, to concurrently expose a couple of millimeters of root surface. He followed this up by pushing an elevator down the side of the tooth on each side “just to make sure the tooth is not ankylosed” he explained. He then pushed a ribbon pack into the same area and over the crown to prevent the tissues from reforming over the tooth. It does not take much imagination to see how the excessive root exposure, the misuse of the elevator and the heavy-handed placement of the pack were each potential risks for damage, whether this be to the periodontal attachment or the cementum layer, to cause elongation of the clinical crown or to initiate ankylosis or perhaps ICRR.

Bonding attachments to impacted teeth at the time of surgical exposure is a very technique-sensitive procedure, which requires good cooperation between surgeon and orthodontist. With practice, the whole procedure need take no longer than 15 minutes. Nevertheless, for much of this time, the chairside assistant is using high powered suction to maintain a clear and dry field and, if the tooth is exposed to the CEJ and a little beyond, then that area of root surface may suffer drying out for an excessive period of time. The damage caused to the exposed cementum from the resultant cell death may then lead to ICRR.

The chances of these sequelae occurring with a closed surgical exposure technique3 are very small, because the CEJ area is specifically avoided during the procedure. However, with an open surgical exposure approach4, where exposure is made down to the CEJ, the likelihood is much greater.

The experience of approximately 3 decades of direct bonding of attachments-to-enamel on impacted teeth has led to a more conservative approach to exposure surgery, but it has also generated further hazards. To etch the enamel of a tooth situated in the middle of an open surgical field can result in the orthophosphoric acid etchant being inadvertently splashed over alveolar bone and denuded root surface. While the dead bone may be removed by scavenger cells in the long run, ICRR may be triggered in the root surface of the tooth.

Once started, there is no stopping the ICRR process which will advance to destroy the body of the root as it spreads apically, coronally and circumpulpally.

So, what about treatment? Since the resorption begins in the cervical area, it would seem logical to orthodontically extrude the tooth which will bring the lesion to the surface and then curette out the affected area. Since the nutrient lifeline of the lesion originates from the PDL, restoring the defect with glass ionomer or other cementing or filling material will effectively eliminate the disease process. Unfortunately, diagnosis is rarely made early enough and, by the time corrective action is considered, bone may already have been laid down in the recently resorbed lacunae and the tooth will no longer respond to the orthodontic forces. The only salvation in these cases is to eliminate the resorptive process before the attempt to supra-erupt the tooth, by an open flap procedure with subgingival curettage. This can only be done if the lesion is relatively limited and surgically accessible.

So, the lifeline of the resorptive lesion is from the PDL and it receives no sustenance from the pulp, from which it remains separated by the predentine layer, even in advanced cases. Accordingly, there is no urgency to remove all the mush from the depths of the lesion and to risk pulp exposure – certainly not in circumstances of poor vision and access in the subgingival area. All that is needed is for the lesion to be sealed off from its connection with the PDL. The tooth may then be actively erupted with occlusally-directed orthodontic force until the temporarily restored lesion comes into view supra-gingivally. At that point, suitable restorative procedures may be undertaken in conditions of much greater convenience. Endodontic procedures are only necessary if the remaining tooth structure of the crown is inadequate to retain a large restoration.

Case report

The patient, a 16 year old male, was referred to the author after 5.7 years of unsuccessful orthodontic treatment to resolve the impaction of a maxillary left canine. In these cases, it is essential to review the initial pre-treatment records before further advice is offered.


Fig. 2. The pre-treatment en face and intraoral occlusal views show good symmetry. The green arrow indicates the location of the unerupted left maxillary canine.


Fig. 3. The pre-treatment views of the occlusion of the teeth.

The initial condition

In the pre-treatment extra-oral en face and intra-oral occlusal views of the patient (Fig. 2), the anatomical midline of the face could be seen to pass through the maxillary right-left inter-incisal contact – the dental midline. The occlusal view also showed a symmetrical and spaced dental arch, with the left deciduous canine still in place. The green arrow indicates where the crown of the impacted canine could be palpated. The pre-treatment dental alignment and occlusion (Fig. 3) showed a very mild class 2 malocclusion with small teeth.


Fig. 4. The pre-treatment panoramic radiograph showing the anatomic and dental midlines to be identical. The left deciduous canine is over-retained and its permanent successor is seen obliquely impacted with the crown tip close to the midline. The right maxillary and left mandibular central incisors have been root treated.

The initial panoramic radiograph taken at that time (Fig. 4) showed all teeth present, including developing third molars. The maxillary right and mandibular left central incisors had been root treated, following an incident of trauma. The deciduous left maxillary canine was over-retained and partially resorbed, while the permanent canine was impacted and markedly displaced towards the midline.

Re-evaluation of the case


Fig. 5. After 5.7 years treatment, the intraoral views of the occluded teeth show the anatomic/dental midline discrepancy, together with the defective alveolar ridge in the canine area.

Fast forward to March 2012, when first seen by the author. Three “open-and-pack” surgical exposures (open exposure surgery), together with elective luxation of the canine, had been made to encourage eruption. After 5.7 years in active treatment, the maxillary dental arch had become asymmetrical (Fig. 5). There was a crossbite on the left side due to a narrowing of that side of the arch and the bite had opened due to intrusion of the incisors and premolars. The entire maxillary dentition in the anterior region, had shifted to the right with a discrepancy of 5mms opened up between the dental (in green) and anatomic (in black) midlines. These are unquestionably characteristics of extreme anchorage loss, following non-movement of the impacted canine.


Fig. 6. En face and intraoral views of the dentition clearly show the severe midline shift. In the occlusal view, the midline raphe of the palate is indicated by the black line, representing basal bone. Anteriorly, the green line shows the degree by which the dental midline and the position of the incisive papilla have been affected by the loss of anchorage.

The dental midline changes were glaringly obvious in the en face view of the patient (Fig. 6) and it was also noted that there was a full tooth-width discrepancy between upper and lower dental midlines. In the occlusal view, that part of the median raphe of the palate which was located on basal skeletal bone has been marked in black. The anterior portion of the midline is marked in green and represents that part which had deviated, together with the incisive papilla, in line with the movement of the teeth and the alveolar bone on which they were located. It was clear that the entire dentition on that side had been controlled by the impacted canine.


Fig. 7. The panoramic and periapical views show the “wooly” texture of the lesion on the distal aspect of the canine. First published in Becker A, Abramovitz I, Chaushu S. Failure of treatment of impacted canines associated with invasive cervical root resorption. Angle Orthodontist, in press, December 2012. Published online February 2013. Reproduced by kind permission of The Angle Orthodontist.

The panoramic and periapical views (Fig. 7) show a loss of lamina dura on the distal side of the left maxillary canine with a “wooly” radiolucency within the tooth, extending both coronally and apically into the substance of the tooth. The tooth was symptomless.


Fig. 8. Transaxial slices from the CBCT clearly depict the dentinal changes wrought by the resorptive process.


Fig. 9. ICRR viewed in the axial slices can be seen to affect the distal part of the tooth. First published in Becker A, Abramovitz I, Chaushu S. Failure of treatment of impacted canines associated with invasive cervical root resorption. Angle Orthodontist, in press, December 2012. Published online February 2013. Reproduced by kind permission of The Angle Orthodontist.

The transaxial (vertical) slices taken from the cone beam CT (Fig. 8) show the degree with which the lesion had burrowed into the dentine of the root and crown. The portal of entry of the resorptive lesion can be seen to have extended round to the labial side just superior to the CEJ. The axial (horizontal) slices taken from the same cone beam CT (Fig. 9) were made at 3 levels across the tooth, a. across the root area, b. across the CEJ area and c. across the cervical area of the crown of the canine. Between one third and one half of the distal side of the tooth can be seen to be affected (arrows).

The Treatment Plan

The treatment that was planned for the patient required two separate and distinct parts. The principal concern was to correct the displacement of the teeth that had been used as anchorage units in the ill-fated treatment, while detaching the canine from the appliance system.

Since the second maxillary molars had not been previously included in the appliance and they had not altered their bucco-lingual relationships with the mandibular teeth since the commencement of treatment, it was decided to band them and connect them with a soldered trans-palatal bar. At the same time, a full mandibular fixed appliance was planned. It was judged that an acceptable realignment of the displaced teeth could be achieved with a series of compensated archforms, ogether with the judicious use of intermaxillary traction.

At the same time, a periodontist was consulted with the view to raising a soft tissue flap around the impacted tooth and to identify the portal of entry of the ICRR lesion. Minimal widening and superficial clearing of the contents would then be done, without attempting to perform a complete excavation into the depth of the lesion. The defect would then be sealed with glass ionomer cement.

When alignment of the dentition had been achieved, the canine would again be bonded with an attachment and light forces applied to it, with the expectation of a positive and rapid response of the tooth. Following its alignment, the canine would then be extruded (forced eruption) until the glass ionomer- restored area was fully visible supra-gingivally. Appropriate restorative and/or endodontic treatment could then be initiated in circumstances that would be favourable for a good prognosis.


What was the cause of the ICRR? While the full story regarding the etiology of ICRR in general is not known, there is little doubt that trauma plays a major role. This patient had experienced trauma to the front of his mouth that was sufficient to require endodontic treatment for a tooth in each jaw. On the other hand, 3 separate and radical surgical episodes were performed, in which the tooth was exposed with an open procedure and a pack placed – and surgery is trauma, even if it is planned! At the time of the surgery and with the tooth in plain view, it had been luxated to “ensure” its compliance. Traction had been directed in a beeline to the labial archwire, when it is quite likely that the root of the lateral incisor provided an impediment to movement in the early stages.

The pre-treatment trauma incident was accidental. The surgical treatment provided for this patient was planned and could perhaps have been administered in a less aggressive manner. It should be remembered that all forms of surgery inflict trauma. In this case, it had clearly been the cause of the bony defect. It seems likely that one of these factors had caused the ICRR and, with it, the demise of the impacted tooth.

Unfortunately, the patient never returned for the proposed treatment.


1. Chaushu S, Chaushu G, Becker A. The role of digital volume tomography in the imaging of impacted teeth. World Journal of Orthodontics, 2004; 5:120-132

2    2. Becker A, Abramovitz I, Chaushu S. Failure of treatment of impacted canines associated with invasive cervical root resorption. Angle Orthodontist, 2013, 83:870-876.

      3. Becker A, Chaushu S. Palatally impacted canines: The case for closed surgical exposure and immediate orthodontic traction. American Journal of Orthodontics and Dentofacial Orthopedics. February 2013, in press.

      4. Mathews DP, Kokich VG. Palatally impacted canines: The case for pre-orthodontic uncovering and autonomous eruption. American Journal of Orthodontics and Dentofacial Orthopedics. February 2013, in press.