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Unerupted teeth cannibalizing their neighbors: part 1

Published: March 2016

Bulletin #53 March 2016

Unerupted teeth cannibalizing their neighbors: part 1

For the most part in the dental development of a child, the first permanent maxillary molar erupts in its due time, at the dental age of 6-7 years. This is 4-5 years before the deciduous second molar is due to exfoliate and before the second premolar should erupt. An aberration of this normal developmental process occurs when an erupting maxillary first molar becomes entrapped in the sub-gingival distal concavity that is the cemento-enamel junction of the crown and roots of the deciduous second molar.1


Fig. 1a. Lateral jaw radiograph of the right side of a 7 year old child with an ectopic maxillary first molar impacted under the distal of the second deciduous molar and causing marked resorption of the distal side of the roots (arrow).

Fig. 1b. A follow-up radiographs after treatment with a simple removable appliance that has distallized the permanent molar. Note the degree of loss of root tissue of the second deciduous molar.

In this situation, resorption of this subgingival area of the root of the deciduous tooth will occur and will proceed to a varying degree, depending on the angulation of the eruptive path of the permanent molar (Fig. 1). In many of these cases, there is a mesial inclination of the permanent tooth, not usually present in normal development. Experience indicates that this is more likely to be seen in children with a short maxillary dental base and large molar teeth – both permanent and deciduous.

As the result, much or all of the disto-buccal root of the deciduous molar will disappear in the resorptive process, but the distal enamel portion of the crown of the tooth will remain and may become hollowed out as its dentine interior disappears (arrow). This then becomes a complicating factor, since it forms an unresorbed ledge which effectively arrests further occlusal migration of the permanent tooth. Because it is the mesial corner of the occlusal surface of the permanent molar which comes into contact with the enamel ledge of the deciduous molar, any further expression of eruptive potential will exacerbate an existing mesial orientation of the long axis of the tooth. Because further resorption may cause the disappearance of its distal root, the deciduous second molar may also tip mesially and its distal aspect extrude, as the result of the eruptive push from above.

There are many instances of loss to the resorptive process of the distal half of the root and much of the interior of the crown, leaving the area that was originally the cervico-enamel junction to end up as a knife edge of undermined enamel. Nevertheless and even despite these unfavorable circumstances, the tooth is entirely asymptomatic and its extraction is to be discouraged as far as possible. The reasoning behind this advice is as follows:-

1. The unerupted second premolar now has very little resistance to its very premature downward eruptive migration and it can sometimes be seen to have descended into the partially evacuated enamel shell of the crown of its deciduous predecessor. However the premolar at this stage has virtually no root and its early eruption is to be prevented if possible, so that a substantial root length may develop while the tooth is still protected within its developmental follicle. Extraction of the deciduous molar will accelerate its eruption in a rudimentary, delicate and endangered state!

2. Loss of the deciduous molar encourages the permanent molar to complete its eruption and encourages an unrestrained drift forward in a mesially tipped condition, which also brings its apex forward. This represents a degree of mesial translation. Therefore, distally tipping the tooth into an upright state will not now relocate it in its ideal position, since it will now require some distal bodily movement if adequate space is to be reclaimed for the premolars and canine.

3. Even assuming that space may have been completely regained in a phase 1 treatment and the molar is in a good class 1 relation with its antagonist, space maintenance will be an essential ingredient in the 4-5 year follow-up period until the first premolar and canine have erupted.

But is non-extraction a practical alternative? This would require moving the permanent molar distally and freeing it from under the deciduous molar. The literature in orthodontics and in pediatric dentistry is replete with methods of achieving this and many interesting, customized gadgets and devices have been described. These will not be discussed in the present bulletin.

What are the benefits of de-impacting the permanent first molar in its ectopic location and leaving the deciduous tooth in place?

1. Movement of the permanent molar is begun while the tooth is relatively high in the alveolus, with the deciduous molar preventing its mesial and vertical movement. Therefore, a minimal degree of distal tipping only is needed to relocate it to its ideal position.

2. Leaving the second deciduous molar in its place obviates the need for artificial space maintenance.

3. Even markedly resorbed distal roots in these cases do not necessarily condemn the tooth to an early demise. For the most part, they will remain in place and asymptomatic for their full designated duration.

Can resorption be equated with dental caries?

When caries reaches the pulp, infection is introduced into a tissue which cannot express the swelling associated with its natural inflammatory reaction because it is enclosed within a closed pulp chamber. It thus causes pulp strangulation and pulp death, usually accompanied by considerable pain.

There is a very narrow wall of dentine of the root that separates the PDL of a deciduous molar from its dental pulp, which means that very little resorption of the root will need to occur before the resorption front reaches the pulp. When there is root resorption, many practitioners will immediately assume that, when this point is reached, there will be an emergency pulpitis, equating the situation with that occurring when a carious process within the tooth reaches the pulp. As a consequence, their mistaken treatment of choice will likely be to advise extraction of the affected tooth – a conclusion not in agreement with an understanding of the biological facts.

In contrast, resorption is a sterile process and the breakdown of the dentinal wall between connective tissue surrounding the root and the pulp chamber causes the cellular elements of the PDL and the pulp to merge and to undergo a progressive metaplasia. This is not accompanied by inflammation, swelling or pain and, as the resorption continues on, the pulp chamber opens up further with vital connective tissue of the subgingival layers becoming contiguous with the pulpal tissue.

In such a circumstance, the pulp is no longer enclosed in a solid casing and, although deep caries may still cause an infective inflammatory reaction of the underlying pulpal/gingival tissue, an acute pulpitis can no longer occur. At the gingival extremity of the crown of the deciduous molar, only the enamel resists resorption, while beneath it dentine is resorbed. As the result, the unresorbed enamel edge of the crown of the tooth comes to sit on the gingiva. The fact that the practitioner may be able to probe this enamel edge is evidence that that part of the interior of the crown is open to the intra-oral environment and, therefore, to saliva-borne bacterial infection. Nevertheless, pain and inflammation are not commonly associated. If the permanent molar is moved distally and freed from its impaction, the resorption ceases and the situation can usually remain stable for several years.

Can resorption of the roots of deciduous and permanent teeth be equated?

In the above paragraphs, I have presented an overview of resorption in relation to the shedding of deciduous teeth, as a (rather long) preface to the more important subject of this month’s bulletin. With this apparently unconnected preamble, I would like to draw a parallel between this well-known debacle between an erupting permanent tooth and its deciduous neighbor and the resorption of the roots of erupted permanent teeth adjacent to and seemingly caused by impaction of an unerupted tooth.

There is no distinction between the character, quality or histology of the tissues when dental pulp meets resorptive PDL and that occurring between the pulp and surrounding connective tissue associated with the resorption of an incisor due to the impaction of the adjacent maxillary canine. They are one and the same and, while the first is a completely physiologic process, the latter is considered a pathologic process, simply because root resorption is not a desirable nor accepted characteristic of a permanent tooth. It would be convenient to be able to characterize or identify the differences that may exist between a deciduous tooth that does resorb and a permanent tooth that does not, but the factors involved in this quirk of nature have, to date, resisted discovery.

With the rapid evolution of imaging technology from planar two-dimensional radiographic representation, through rotational tomography to spiral computerized tomography and cone-beam computerized tomography, accuracy and reliability of diagnosis of resorption of incisor roots by an aberrant unerupted canine has leaped from 12%2, 3 through 38% of lateral incisors and 9% of central incisors affected to a greater or lesser extent, i.e. 47% of affected individuals, in total, 66.7% of adjacent lateral incisors and 11.1% of adjacent central incisors affected,5 respectively. Obviously, it is the initial and the minor resorptive lesions that had previously evaded detection that now form the majority of those discovered by the new technology and it is certainly pertinent to add that the finding is largely of little clinical significance. However, it should be remembered that all the severe resorption cases started “life” as seemingly minor lesions!


Fig. 2a. The anterior portion of a panoramic view shows the superimposition of the unerupted permanent canine on the lateral incisor and the severe root resorption.

Fig. 2b. A CBCT cross-sectional cut across the lateral incisor to show the relation of the superimposed labial canine and the severe and oblique nature of the resorption.

Fig. 2c. A CBCT axial cut shows the close proximity of the canine to the severely resorbed incisors.

It is well documented in the literature that this variety of root resorption will almost completely arrest once the offending “aggressor” tooth has been distanced from the immediate vicinity, either by extraction or by orthodontic movement6 The severe incisor root resorption (SIRR) cases, with a third or more their root already lost (Fig. 2a-c), have been shown to have a predilection for females.7 It should come as no surprise that the affected teeth have a marked degree of mobility. Nevertheless, moving the canine away from the immediate area will result in a remarkable improvement in the condition of the incisor.


Fig. 2d. A periapical radiographic view of the treated case on the day of debonding.

Fig. 2e. A follow-up radiograph 3.8 years post treatment. The bonded retainer was placed for orthodontic retention rather than periodontic splinting, which had been considered unnecessary. The lateral tooth was vital and firm.

The radiographic follow-up in these cases provides clear evidence of a change from a rarified and radiolucent area around the shortened root end to a re-condensation of trabeculated bone and a convincing reduction of the mobility (Fig. 2d, e), without the need for periodontal splinting. Thus, following successful orthodontic treatment, one may justifiably look forward to a very much brighter view of a future for these compromised teeth (Fig. 3).


Fig. 3a. Periapical views of active dark rarified areas of incisor root resorption by the advancing canine.


Fig. 3b. A periapical view of the left side showing the condition at the time the canine was distanced from the area.


Fig. 3c. At the completion of treatment and prior to debonding, these periapical views show total absence of bone support for the lateral incisors, which were highly mobile. Splinting was advised for both orthodontic retention and periodontal support.


Fig. 3d. At 5.6 years post-treatment, the periapical views show positive condensation of trabeculated mature bone around the short root ends. Vitality and tooth color were maintained and the teeth showed greatly reduced mobility.

The resorption of a small portion of the root end, so-called “blunting” with the loss of 2-3mm of root length during orthodontic treatment, is something that would not unduly alarm us, because we see this in our routine non-impaction and straightforward orthodontic cases. Because of the angle at which the canine approaches the root of the incisor in the impaction cases, resorption is usually oblique and if the canine is fairly high and mesially displaced, this causes an oblique slicing of the apical third of the root.

Question #1 What should we do if we see that the canine has superimposed itself on one of the incisors from a more lateral direction and lower down on the root, such that the resorption damages the middle of the root? The real point of the question is whether or not the resorption involves the pulp.

In a published study of root resorption from this cause, Falahat et al.8 classified resorption into three degrees of severity. Slight resorption was defined as “up to half the dentine thickness”, moderate resorption as “midway to the pulp or more, the pulp lining being unbroken” and severe resorption as “the pulp is exposed”.. Fully one third of the cases in the study were classed as severe, according to these definitions i.e. the pulp has been “exposed” by the lesion


Fig. 4a. The anterior portion of a panoramic view shows obvious resorption of the lateral incisor by the impacted right canine. This case was treated about 20 years ago and before the cone beam tomography era. It was not possible with 2D planar radiography to assess the degree of resorption that had occurred.

Fig. 4b. Following the successful resolution of the canine impaction, a new periapical view of the lateral incisor indicated a large resorption crater in the cervical region, close to the gingival margin. Because of the real possibility of an accidental opening of the lesion to the oral environment, root canal treatment, followed by a periodontal flap to enable sealing off the defect, was advised.

Fig. 4c. A periapical view taken during the root canal procedure, which had failed due to the absence of a large section of the labial wall of the root.


Fig. 4d. Viewed from the labial and mesial sides of the extracted incisor to show the extreme nature of the longitudinal resorption along the full length of the labial aspect of the root, not evident from the periapical radiograph. Today, with the advent of CBCT, this case would have been treated very differently.

In the day-to-day practice of dentistry, when a patient with “severe resorption” is first diagnosed, there are many forms of treatment that may be offered, largely dependant on the specialty of the first practitioner to whom the patient turns for treatment. Odd though it may seem, there is a real danger that most of these prescribed treatment modalities will be inappropriate (Fig. 4)!

If an oral and maxillofacial surgeon were to be consulted regarding a severe resorption case as defined in that study, it is likely that the advice given would be to extract the resorbed incisor tooth.

If an endodontist were to be consulted, the chances are that he/she would request opening the root canal of the resorbed incisor, extirpating the pulp and root treatment, while attempting to occlude the lateral perforation from within.

If a periodontist were to be consulted and assuming that adequate access could be achieved with an open flap procedure, perhaps the plan would be to debride the immediate area of the “exposure” and occlude the defect with glass ionomer or other cement. At the same time, the pulp would be amputated and the patient referred for definitive root canal therapy. If, however, the proximity of the canine prevented access, orthodontic treatment to distance the canine might be advised as a first step and only then a renewed attempt at occluding the defect be made.

Days, weeks or months may elapse between the time the diagnostic imaging will have determined that resorption has involved the pulp and the visit to one or more of the following : the pediatric dentist, the surgeon, the endodontist, the periodontist or the orthodontist. During this entire period the tooth will have been entirely asymptomatic, will have undergone no color change and even a pulp tester will have declared it to be vital. So, I would argue that, to describe this severe form of resorption as an “exposure”, is inexcusably alarmist and highly emotionally charged. This smacks of paralleling the phenomenon with and engendering the same degree of urgency as caries that has exposed the pulp. As the result, the unenlightened practitioner may be intimidated into performing ill-advised immediate surgical and/or endodontic treatment.

Question 2: What of the impacted canine that has caused the loss of the apical 2-3mms of root of the incisor, which we discussed above, or where the resorption has occurred without canine impaction? These “blunted” root cases are common and the implication is that exposure of the pulp in the lost apical portion has occurred, as described above. The connective tissue of the PDL comes into direct contact with pulpal tissue, which undergoes metaplasia and with which it merges.

We know that, for as long as the canine remains in the location and displays its eruptive potential, the resorption will continue. Accordingly, the first line of treatment must be to move the canine away from the immediate area. As pointed out above, distancing the canine effectively stops the resorptive process. 6

In order to resolve the impaction of the canine, surgery needs to be performed to provide the orthodontist with the access needed to assume therapeutic control. An open surgical exposure, involving complete removal of the dental follicle and leaving the tooth open to the oral environment at the end of the procedure will make the chances of infection of the resorbed area extremely high and the resultant pulpitis of the incisor difficult to avoid. It is strongly contraindicated. Instead, a closed procedure should be chosen, with a wide attached gingiva flap reflected, the canine bulge located and the tooth’s most accessible surface minimally exposed through a small opening in the dental follicle. No attempt should be made to remove the follicle, but the full flap should be re-sutured back to its former place once the eyelet attachment has been bonded to the exposed enamel surface, with a chain or twisted steel ligature exiting through the sutured flap edge. Instrumentation of the deeper areas should be avoided.

Question 3: Having moved away the canine, should we recommend root treatment for this resorbed incisor (Fig. 4)- perhaps anti-resorption therapy with calcium hydroxide or sealing the defect with MTA?

In answer to the above questions, I would conclude as follows:-

Following successful treatment to distance the canine from the resorbing root area, we have learned to expect that:-

1. resorption will have ceased

2. the area of contact between the resorptive soft tissue of the periodontium and the pulp is entirely free of bacteria, free of surgical trauma and, in consequence, free of inflammation.

3. the teeth are healthy, vital and symptomless,

4. the teeth are vital and their color is unchanged.

5. there is no pathology and, therefore, no treatment is needed!

Acknowledgements: I wish to acknowledge the learned discussions that I have had on the different aspects of resorption and the advice that I have received from Prof. Nardi Caspi-Casap (oral and maxillofacial surgery), Prof. Adam Stabholz (endodontics) Prof. Ayala Stabholz (periodontics) and Professor Yossi Shapira (pediatric dentistry) in the writing of this bulletin.

The figures in this bulletin are copyright and appear in Becker A. Orthodontic Treatment of Impacted Teeth. 3rd edition. Oxford: Wiley-Blackwell Publishers, 2012.


1. Kennedy DB, Turley PK. The clinical management of ectopically erupting first permanent molars. American Journal of Orthodontics and Dentofacial Orthopedics, 1987;92:336-345.

2. Ericson S, Kurol J. Incisor resorption caused by maxillary cuspids: A radiographic study. Angle Orthodontist, 1987;57:332–45.

3. Ericson S, Kurol J. Radiographic examination of ectopically erupting maxillary canines. American Journal of Orthodontics and Dentofacial Orthopedics, 1987;91:483–92.

4. Ericson S, Kurol J. Resorption of incisors after ectopic eruption of maxillary canines: a CT study. Angle Orthodontist, 2000;70:415-23

5. Walker L, Enciso R, Mah J. Three-dimensional localization of maxillary canines with cone-beam computed tomography. American Journal of Orthodontics and Dentofacial Orthopedics, 2005;128:418-23

6. Becker A, Chaushu S. Long-term follow-up of severely resorbed maxillary incisors following resolution of etiologically-associated canine impaction. American Journal of Orthodontics and Dentofacial Orthopedics 2005, 127: 650-654, quiz 754.

7. Chaushu S, Kaczor-Urbanowicz K, Zadurska M, Becker A. Predisposing factors for severe incisor root resorption associated with impacted maxillary canines. American Journal of Orthodontics and Dentofacial Orthopedics, 2015;147:52-60 .

8. Falahat B, Ericson S, Mak D’Amico R, Bjerklin K. Incisor root resorption due to ectopic maxillary canines: a long-term radiographic follow-up. Angle Orthodontist, 2008;78:778-785

In the April 2016 bulletin, we shall continue this discussion specifically in relation to the prognosis of the resorbed incisor, whether the affected incisor will respond to orthodontic movement, whether orthodontic movement will re-ignite the resorption process, how reliable will the periodontal support be and what type of bone regeneration or bone loss can be expected in the years ahead.