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6 distinct types of resorption associated with tooth impaction

Published: February 2015

Bulletin #41 – February 2015

6 distinct types of resorption associated with tooth impaction

When we talk, read or write about patients with impacted teeth, it is unavoidable not to mention the possibility of resorption and, when we do so, we generally refer to resorption of roots. However, it is perhaps more relevant in the context of tooth impaction to refer to resorption of dentine, because there are situations in which resorption affects the dentine within the crown of the tooth. Furthermore, resorption of enamel occurs in relatively rare instances and this, too, is relevant to the present discussion. This month’s bulletin is dedicated to a discussion of 6 different and distinct resorption entities that are seen in patients who suffer from tooth impaction in its many incarnations.

1. Root resorption as a by-product of routine orthodontic treatment.

Root resorption occurs during orthodontic treatment with great frequency although its extent and its implications are rarely of any serious concern. To see a patient in whom the process has been extremely vigorous and in whom much of the roots of bracketed teeth have been severely resorbed is, for most of us, a once-in-a-professional-lifetime nightmare encounter. In general, when resorption is noted it is typically characterized by a rounding off of the apices of a number of teeth in the same dentition, rather than a single tooth. In terms of dental health and prognosis of the teeth concerned, it has no clinical significance. Etiology may involve patient-related factors, which include genetics, systemic factors, asthma and allergies, chronic alcoholism, the severity of malocclusion, tooth-root morphology, a previous history of root resorption, alveolar bone density, root proximity to cortical bone, endodontic treatment, and patient age and sex. Orthodontic-related risk factors include treatment duration, magnitude of applied force, direction of tooth movement, amount of apical displacement, and method of force application.1-11

The teeth remain vital and the resorption process arrests when the orthodontic forces are discontinued.

A very new study has indicated that orthodontic treatment of impacted maxillary canines does not appear to result in more resorption than does orthodontic treatment of malocclusions without tooth impaction. However, the authors warn that, because of the observational nature of the study, caution should be exercised in interpretation of the results.12

2. Resorption of the root of the adjacent tooth associated with the aberrant eruptive progress of an impacted canine

Resorption of the root of the immediate neighboring tooth is a well-known phenomenon that occurs more frequently than was once thought, because of the vast improvements that are provided by the diagnostic imaging methods that are available today. In the era that preceded computerized tomography (CT), plane film (2D) conventional radiography was the sole means of diagnosing root resorption. Thus, an epidemiologic study of its prevalence carried out in Sweden using plane film radiography13, 14 concluded that resorption occurred in 12% of the children with impacted maxillary canines. However, the authors recognized that this was probably an understatement of the problem. As they pointed out in their report, the impacted canine usually overlaps incisor root on its labial or palatal aspect, which are areas that cannot be portrayed or examined on plane films. This means that unless or until a resorption lesion of incisor root actually altered the shape of the root in the interproximal area, it is impossible to diagnose its presence.

This study was repeated by the same research group a few years later, when they had access to the then new spiral CT machines15. Given this vastly superior diagnostic modality with its inclusion of a third dimension capability, the bucco-lingual surface of the two adjacent teeth became radiographically accessible. From the results of this study, the researchers discovered the ability to diagnose incisor root resorption in almost half the cases of canine impaction, many of which were in their early stages. A further study was carried out by the group in Southern California using cone beam CT technology16 and their results indicated a prevalence of 67% identifiable resorption lesions in a similar sample of impacted canine cases. With this level of vulnerability, it stands to reason that patients with impacted canines should be screened for resorption.

This leaves the orthodontist with a few questions to answer:

a. Is the condition progressive?

b. Can it be stopped?

c. Can an incisor with advanced root resorption recover

d. Can the tooth subsequently be moved orthodontically without further risk of resorption

e. Can the tooth then function with a fair-to-good prognosis?

f. Do the resorbed incisors subsequently need splinting to reduce their mobility?

The answers to these questions were presented in a study that we published a few years ago17 and subsequently illustrated in bulletin #29 January 2014 on this website, at the following URL

Fig. 1a. A periapical view of 2 impacted maxillary canines associated with almost total resorption of the roots of all four incisors.

Fig. 1b. A series of cross-sectional (transaxial) cuts of the left side central and lateral incisors shows the extreme degree of the resorption in the same case.

This type of root resorption is very rapid and aggressive (Fig. 1). The study showed that during the period in which orthodontic treatment was initiated to level, align and to open space for the canine, a further increase of 17% in the crown-root ratio of the incisor was recorded i.e. the root was further shortened. It was also noted that, once the aggressive canine was distanced from the immediate area, the resorption rate dropped to an insignificant level. Accordingly, tackling the canine as a first orthodontic/surgical priority is advised, even before any attempt is made to move other teeth. Once the canine is distanced, the resorbed incisors may be bracketed and moved orthodontically, with care exercised not to exceed accepted force values - taking into account the fact that short rooted teeth have a reduced root area. Even a resorbed incisor that initially displayed a marked degree of mobility recovers its firmness. Radiologically, the previous radiolucent area in the intervening resorption space between canine crown and incisor root end becomes filled with normal trabecular bone, the incisor acquires a lamina dura and subsequent orthodontic movement of the tooth does not then cause further root resorption. The incisor teeth do not lose their vitality, do not undergo unacceptable changes of color and do not need periodontal splinting, although orthodontic retention must remain a consideration.

The same Swedish group mentioned above has performed research in other aspects of this area. In one of their studies, they investigated possibly linkage of resorption with the size of the follicle surrounding the crown of the canine.18 Their findings were that reduced or virtual absence (in radiologic terms) of the follicle (i.e. actual contact between the canine crown and the incisor root) was a common finding in relation to resorption. They further found that an enlarged follicle had no apparent association with the resorption, which is contrary to that seen in a subsequent study by the same group19 and to the experience that I have had in these cases.

3. Invasive cervical root resorption (ICRR) of the impacted tooth itself, causing failure of eruption and resistance to eruption mechanics.

Invasive cervical root resorption is a pathologic condition of the impacted tooth itself, rather than of its immediate neighbor. As its name implies, it is generally found in the area of the neck of the tooth close to the CEJ, although similar lesions may occasionally be found elsewhere on the surface of the roots of teeth ( Bulletin #40 January 2015). It is caused by a non-inflammatory infiltration of clastic cells that derive from the PDL and gain direct access to the root surface through gaps in the cementum layer. It appears to have an association with previous trauma, presumably because it causes loss of cementum at a specific point on the root’s surface, close to the CEJ. There is loss of PDL integrity at this point, which permits the clastic cells to come into direct contact with the root surface. The site at which the cells begin their work of destruction becomes a point of entry and the resorptive lesion then mushrooms out into the body of the root (Fig. 2).


Fig. 2a. An axial cut across the roots of maxillary teeth shows an advanced ICRR lesion resorbing the disto-lingual aspect of the root of the canine (arrow). It is worth noting that the pulp chamber is depicted as a circle, because the lesion does not cause resorption of the predentine layer adjacent to the pulp, probably due to its high organic content.

Fig. 2b. Two successive cross-sectional (transaxial) cuts show the small point of entry of the lesion (arrow). The radiolucent lesion can be seen to proliferate apically and coronally. The thin vertical wall of the predentine can be seen in the left cut, separating the lesion from the pulp.

Fig. 2c. A 3-D video clip of a similar lesion in a maxillary left second premolar, showing its exact location and extent in terms of depth, width and height within the tooth. Video preparation by Mr. Amnon Leitner of Panorama Nahariyah, Israel.

Histologically, resorptive lacunae are seen on prepared microscope slides and one may also see an adjacent area of bony deposition in the depth of the ICRR lesion.20, 21 Whether it is due to the break in the integrity of the PDL or the deposition of bone in the lesion, the tooth will not erupt and neither will it respond to eruption mechanics. Typically, after a lengthy period of attempted forced eruption in such cases, the patient is often referred back to the oral surgeon with the request that the tooth be surgically luxated – on the misguided assumption that the tooth has become ankylosed. When the surgeon grasps the tooth in the forceps it is discovered that the tooth is mobile!

As reported in the #20 and #39 bulletins in this series from March 2013 ( and December 2014 ( respectively, the features of ICRR are that the lesion is fairly rapidly progressive, proceeding in all direction in the root. It reaches the predentine layer surrounding the pulp and is arrested by its relatively high organic content. It therefore encircles the pulp without actually breaking through and it advances both coronally and apically to resorb the dentine structure in all directions. Since it is not an inflammatory process, it is entirely asymptomatic, does not stimulate the production of secondary dentine and is often discovered when the damage is well beyond repair. If treatment is to be offered to overcome the problem, the lesion must be exposed surgically and then sealed off from its contact with the PDL. If the lesion is excavated with the aim of eliminating all the softened dentine mush, vital exposure of the pulp is both inevitable and utterly superfluous. The nutritive supply line of the resorptive process is from the PDL and not from the pulp. This is not caries and should not be treated as such. Therefore, superficial removal of the affected dentine is indicated simply to provide a shallow cavity whose outer wall is free of the resorption mush. If this carefully and conservatively prepared cavity is then restored with glass ionomer or other restorative material, the clastic elements will have become sequestrated from their nutritive source and will be arrested within the sealed-off cavity. The tooth will then respond to eruptive forces, both natural and applied and the impaction may be resolved.21 Later definitive treatment of the sealed-in mush may be undertaken many months after the restored margins of root surface will have been raised supragingivally and optimal conditions of access for endodontic and restorative treatment will have been achieved.

4. Apical root resorption affecting the anchor teeth when extrusive forces fail to erupt an impacted tooth.

The force of reaction to extrusion of an impacted tooth is, according to Newton’s Third Law of Motion, equal and opposite to the force delivered to extrude the impacted tooth. In other words there is a force of intrusion applied to the adjacent anchor teeth, which may result in actual intrusion of these teeth, particularly if the treatment lasts for many months. When an orthodontist is faced with impacted teeth which do not respond to the extrusive forces, perhaps as the result of inappropriate directional force, ankylosis or ICRR, the practitioner will be reluctant to give up. Typically, he/she will increase the force and see the patient more frequently to renew its application for a longer period, instead. In many instances, a year or more of fruitless traction may be applied before the decision is made that ankylosis or invasive cervical resorption is present. A new radiograph taken at this late stage will witness a definite shortening of the roots of the adjacent anchor teeth in many of these cases (Fig. 3).


Fig. 3a, b. Panoramic and periapical views before (left side) and after (right side) treatment for ankylosis of the first molar. The treatment involved fruitless orthodontic traction initially, followed by successful luxation of the molar and the application of heavy orthopedic forces. A comparison of the before and after views will reveal the root shortening and rounding of the apices of the adjacent premolars.

This type of resorption has similar characteristics to the root resorption that occurs more generally in routine cases, with the exception that it is observable almost entirely on just one or two of the adjacent anchor teeth to a significant degree, but without adverse effects on the other teeth in the dentition. Discontinuing the forces will arrest the process.

5. Pre-eruption intra-coronal resorption (PEIR).

This phenomenon is also known as penetrating crown resorption of an unerupted tooth, pre-eruption caries, occult caries, hidden caries, pre-eruptive dentine translucencies and several other names. However, it is not dental caries and has been discussed at length in bulletin #24 of July 2013 in this series, at .


Fig. 4a. A series of cross-sectional (transaxial) views through the impacted mandibular canine. The arrows point to a lesion of pre-eruptive intra-coronal resorption (PEIR) with its origin in the cusp tip. Courtesy of Dr. Adam Renart.


Fig. 4b. A PEIR lesion has devoured most of the crown of the unerupted maxillary canine.

It would appear to be closely related to invasive cervical root resorption and its progress and histopathology are probably identical. The obvious difference is that ICRR enters through gaps in the cementum layer covering the dentine of the root of the tooth, while PEIR enters through the crown of the unerupted tooth, through a developmental gap in the enamel, often found in an occlusal pit or fissure or cusp tip (Fig. 4a). However, since it too is asymptomatic, it may progress to destroy most of the crown of the tooth, eventually including the enamel (Fig. 4b). It differs from ICRR because PEIR is arrested when the tooth erupts into the oral environment. Once the tooth has erupted, it loses its nutritive supply line from the follicle and the clastic cells, that had been hitherto burrowing into the dentine of the crown and undermining the enamel, will die. However, the tooth may later become secondarily infected with true dental caries in the depths of the now open occlusal crevices. This is probably the origin of such misnomers as hidden or occult caries.

Unlike ICRR, which causes the tooth to resist eruption, unerupted teeth with an early PEIR lesion may erupt presumably because the dental follicle is complete and can play its part in fusing with the overlying oral epithelium to open an eruption canal. Anecdotally, however, I have noticed that in the presence of an extensive PEIR lesion is seen, the tooth does not usually erupt.

Treatment entails exposing the affected crown of the tooth to the oral environment, thereby causing the active clastic cells to die. Since the resorption mush within the crown is not caries, excavating it has little purpose. On the contrary, any instrumentation aimed at eliminating it will almost certainly cause pulp exposure and necessitate immediate root canal therapy, in circumstances where access is very poor. Once exposed, a simple temporary dressing placed to seal off the lesion.

A discussion of PEIR, together with several excellent examples, may be viewed at the following URL -

6. Surface resorption of enamel.

With advancing age, it becomes more problematic to attempt to resolve the impaction of teeth by orthodontic means, in terms of both the duration of treatment and its failure rate.22 Why this should be is not clear but, in a good proportion of the cases, radiographs will reveal collapse of the dental follicle around the crown of the tooth. This permits direct contact between the enamel of the unerupted tooth and the surrounding tissues. At the time of exposure surgery, the surgeon will note soft tissue and bony adhesions to the enamel. In the more advanced cases, the enamel surface becomes pitted due to actual surface resorption of the enamel. In these cases, unless complete dissection of the tissues around the fully exposed crown of the tooth is performed, orthodontic traction of the tooth will fail to move the tooth. Even with full exposure, the chances of recurrence may be high, notwithstanding the placement of an isolating surgical pack. The tooth is in effect ankylosed.


Fig. 5. A 66 year old female patient with a spaced dentition and a peg-shaped lateral incisor. An impacted maxillary canine was a chance radiographic finding in a routine dental examination. Note the lack of clarity of its outline, the loss of much of the radiopacity of its crown and the absence of most of its dental follicle. The tooth has suffered much replacement resorption of much of the enamel of its crown and is ankylosed.

This condition should be possible to diagnose from a simple periapical film (Fig. 5). It will show a very narrow space between follicle and tooth, which may be missing in certain areas. It may also show a blurring of the usually distinct and clear outline of the crown of the tooth and a degree of loss of contrast of its enamel layer. This will be less obvious on a panoramic scan.


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