Chapter 10

Root Resorption

Conor Durack, Shanon Patel

Introduction

Root resorption is the destruction of dental hard tissue, namely cementum and dentine, as a result of clastic cell action (Hammarström and Lindskog, 1985; Andreasen, 1988; Patel and Ford, 2007). It can be broadly classified according to the site of its occurrence on the root of the affected tooth; internal resorption affects the root canal wall, while external resorption occurs on the root’s outer surface. Both types of resorption are subclassified according to the specific histological nature of the resorptive processes occurring, each of which have specific radiographic features.

External root resorption

External surface resorption

External inflammatory resorption

External replacement resorption

External cervical resorption

Internal root resorption

A diagnosis of root resorption is reliant on the radiographic demonstration of the process (Andreasen et al, 1987). However, several ex vivo and in vitro studies have demonstrated that conventional periapical radiography is not a reliable technique for detecting external root resorption, especially when the simulated resorptive defects are small (Andreasen et al, 1987; Chapnick, 1989; Goldberg et al, 1998). In contrast, ex vivo studies have confirmed improved accuracy with cone beam computed tomography (CBCT) over conventional periapical radiography in the detection of simulated internal (Kamburoğlu et al, 2011) and external (Bernardes et al, 2012; Ren et al, 2013) root resorption including situations where the external defects are minimal (Durack et al, 2011). Furthermore, some ex vivo studies have also demonstrated that, compared to periapical radiography, CBCT is a significantly more effective method of determining the exact site of simulated resorptive cavities on the external surfaces of roots (D’Addazio et al, 2011; Durack et al, 2011). It also proved the more successful method of differentiating between simulated resorption defects on the root canal wall and on the external surface of the root (D’Addazio et al, 2011; Kamburoğlu et al, 2011). One ex vivo study reported that CBCT could accurately calculate both the volume of resorptive cavities created on the lateral surfaces of roots and the extent of simulated apical root resorption in a linear plane (Ponder et al, 2013).

Clinical studies comparing the diagnostic accuracy of CBCT and conventional radiography in the detection of root resorption are limited. However, one clinical study demonstrated that CBCT is a significantly better imaging modality at determining the presence and extent of external root resorption when compared to conventional radiography (Estrela et al, 2009). In a further clinical study, the performance of periapical radiography and CBCT as diagnostic and treatment planning tools in the management of external cervical and internal root resorption were compared. CBCT could accurately detect the presence and differentiate between the types of resorption (internal and external) in all of the cases examined, and CBCT also performed significantly better than periapical radiography as a treatment planning tool. The overall sensitivity of intraoral radiographs was significantly lower than CBCT (Patel et al, 2009a).

External root resorption

External surface resorption

Conventional radiography

The conventional radiographic appearance of surface resorption is variable, case-specific, and dependent on the stimulus for resorption. The appearance can vary from small, saucer-shaped, superficial excavations on an otherwise normal root surface outline (as a result of mild traumatic injuries or as a physiological occurrence) to partial or complete destruction of the root (Andreasen and Hjørting-Hansen, 1966a; Andreasen and Pedersen, 1985).

More extensive tissue destruction tends to occur in cases of surface resorption caused by pressure exerted on the roots by orthodontic treatment and/or adjacent impacted masses, such as teeth, cysts, tumours, etc. Teeth with orthodontic-related surface resorption typically present with blunted or uniformly shortened root ends, while the appearance of resorption associated with impacted masses tends to reflect the shape of the offending body (Fig 10-1). Regardless of the aetiology of surface resorption and the extent of the tissue destruction, an intact periodontal ligament (PDL) space/lamina dura typically surrounds the resorbed area of root in cases of surface resorption (Andreasen and Hjørting-Hansen, 1966a).

CBCT

On CBCT scans, external surface resorption has a similar basic radiographic appearance to that seen on conventional radiographs. However, the true nature of the lesion can be more accurately assessed than on conventional (two-dimensional) radiographs. The exact position of any resorptive defect can be pinpointed, and lesions undetectable on conventional radiographs will manifest on CBCT (Fig 10-2). These findings may alter the prognosis of the tooth/teeth under investigation.

External inflammatory resorption

Conventional radiography

External inflammatory resorption associated with dental trauma is characterised radiographically by radiolucent, concave, and sometimes ragged excavations along the root surface, with corresponding and associated radiolucencies in the adjacent alveolar bone (Fig 10-3). There is complete loss of the lamina dura in the area of the resorption (Andreasen and Hjørting-Hansen, 1966b).

External inflammatory resorption is also commonly associated with teeth with infected necrotic root canal systems, and is not always the result of traumatic dental injuries (TDIs) (Laux et al, 2000). In these cases, the resorption site on the affected root will reflect the portal of exit of the bacterial toxins from the root canal. More than one location on the root surface may therefore be affected. However, typically, the apical portion of the root is most commonly affected due to the proximity of the apical foramen (Patel et al, 2016). Conventional radiography may reveal an irregular root at the resorption site. The root may be shortened if the process is occurring apically. The degree of the hard tissue destruction is variable and will reflect the chronicity of the infection. Regardless of the site of the resorption, radiolucency will be present in the adjacent alveolar bone, in addition to the lamina dura, and PDL space will be absent.

CBCT

On CBCT scans, external inflammatory resorption has a similar radiographic appearance to that seen on conventional radiographs. However, the extent of the lesion can be better appreciated, as can the associated periradicular radiolucencies in the adjacent bone (Figs 10-4 and 10-5). Furthermore, the exact position of any resorptive defect can be localised, and lesions undetectable by conventional radiography (buccal/palatal surfaces) can be seen on CBCT (Durack et al, 2011). These incidental findings, however, do not mean that CBCT should be used as a screening tool to routinely assess external inflammatory resorption.

External replacement resorption

Conventional radiography

The distinguishing radiographic features of ankylosis are replacement of the root with adjacent bone and associated disappearance of the normal PDL space (Fig 10-6). There is no radiolucency in the adjoining bone related to the area of resorption (Andreasen and Hjørting-Hansen, 1966a). External replacement resorption (ERR) can affect any portion of the root and may cause varying levels of tissue destruction..

CBCT

The radiographic findings are very similar to conventional radiography. However, small, distinct ERR on the labial and/or palatal aspects of the root can only be reliably detected with CBCT. Conventional radiography is better for detecting proximal defects, which have reached a minimum critical size, but is not able to reliably identify smaller lesions on the labial or palatal root surfaces.

External cervical resorption

Conventional radiography

The conventional radiographic appearance of external cervical resorption (ECR) is highly variable and is influenced by a number of factors, including the site of the defect on the affected tooth, to what extent and in which manner the resorptive process has invaded the root dentine, and the relative proportions of granulomatous and osseous tissue occupying the resorptive defect (Gunst et al, 2011, 2013).

ECR typically affects the cervical region of the affected tooth. However, it may not always appear to involve the tooth’s cervical region when assessed on conventional radiographs. ECR may initiate below the cervical region in accordance with the more apical position of the epithelial attachment on the affected tooth. In teeth with a normal periodontal attachment, the lesion may extend some distance apical and/or coronal to the cervical location at which it commenced, reflecting the invasive nature of the process (Heithersay, 1999, 2004).

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