For internal root resorption to occur, the outermost protective odontoblast layer and predentine of the canal wall must be damaged, resulting in exposure of the underlying mineralized dentine to odontoclasts. Pulp canal necrosis and infection provide the inflammatory stimulus to sustain the process. Various aetiologies including dental trauma, caries, excessive heat generation during restorative procedures, use of cytotoxic materials in vital teeth such as calcium hydroxide pulpotomies and orthodontic tooth movements have been cited in the literature as potentially responsible for potential damage to the internal canal wall. The process has been described as either transient or progressive.

Clinically, the early stages of internal resorption are usually asymptomatic. Partial pulp necrosis may result in signs and symptoms of pulpitis. Eventually, when the entire root canal system becomes necrotic, the patient may develop apical periodontitis and symptoms thereof. Sinus tracts may be present indicating either root perforation or chronic apical abscess. A pink discolouration may be visible within the crown of the tooth although this ‘pink spot’ may be pathognomonic of external invasive cervical root resorption. The radiographic appearance is that of an oval or circular well-circumscribed symmetrical radiolucency associated with the root canal. The radiolucency has a uniform density and will remain in the same position relative to the canal when using the parallax radiographic technique (Fig. 16.6).

Once internal root resorption has been diagnosed, the prognosis of the tooth is dependent on whether the lesion communicates with the external surface of the root making non-surgical root canal treatment difficult due to risk of extrusion through the perforation between internal and external root surfaces. Non-surgical root canal treatment is recommended in cases where the lesion is confined within the canal, without breaching the external root surface, and where the tooth is deemed restorable.

Root canal systems have complex morphology that can harbour bacteria, by-products and remnants of necrotic pulp tissue in nonvital teeth. Teeth with internal root resorption pose a unique challenge as a result of actively resorbing balloon-sized lesions that contain inflamed bleeding pulpal and granulation tissues that are inaccessible to direct mechanical instrumentation techniques. As a result, adjunctive use of ultrasonic instrumentation and intra-canal antibacterial medicaments should be used to improve disinfection and debridement of the internal resorptive defects. Thermoplastic gutta-percha techniques are ideal when used to seal and fill the resorptive defect provided the root canal wall has not been perforated. In cases of perforation, an alternative technique using mineral trioxide aggregate may need to be utilized due to enhanced biocompatibility important at the restorative-tooth interface (Fig. 16.7).

This type of self-limiting resorption is transient and is often induced following some traumatic injuries or orthodontic treatment. It results in damage to the underlying cementum with shallow resorption of the root contour with involvement of a small amount of underlying dentine that will heal uneventfully with reparative cementum in the absence of underlying infection. Radiographic observations may reveal only subtle changes in the root morphology with no signs of any radiolucency associated with superimposed infections. The lamina dura and periodontal membrane remain intact.

This type of resorption is commonly induced by the pressure of a crypt of an underlying unerupted/erupting tooth, by some neoplasms and more commonly due to orthodontic treatment. The resorption is often extensive and easily observable radiographically.

Tumours such as cysts, ameloblastomas, giant cell tumours and fibro-osseous lesions are frequently associated with slow growth and expansion whereby the underlying pathological process is responsible for activation of the resorptive process. Usually, the tooth will remain asymptomatic unless the process is close to the apical foramen with the possibility of disturbing the blood supply. Treatment strategies are aimed at removing the underlying cause usually by surgical means, which remove the pressure and arrest the process.

Apical root resorption during tooth movement can result in significant shortening of the roots directly due to continued pressure during orthodontic tooth movements. Teeth will remain asymptomatic, and provided the underlying forces used to tooth movement are not heavy, the pulp remains vital. No treatment is required, and provided the underlying cause is removed, this non-infective resorption will become inactive and uncomplicated repair can occur.

This type of external root resorption is often seen radiographically as an extensive peri-radicular radiolucency associated with an extensive inflammatory response to endodontic pathosis. It is also indicative of an infection superimposed on a traumatic injury commonly seen in both avulsion and luxation injuries. The initiating stimulus for this type of resorption is damage to the underlying protective cementum resulting in surface resorption and exposure of the adjacent dentine with direct communication with the root canal system. Superimposed infection as a result of pulpal necrosis prevents normal reparative cementum to be replaced sustaining the resorptive process due to unimpeded passage of bacteria and bacterial by-products from within the tooth. An inflammatory response persists including the activation of clastic cells resulting in both tooth and bone resorption.

Clinical examination may reveal no abnormalities unless the infection is acute in nature demonstrated by the tooth becoming tender to touch or an overlying swelling or discharging sinus. Radiographic examination may result in bowl-like radiolucencies in both the tooth and adjacent bone that if allowed to progress will result in eventual destruction and replacement. Treatment strategies to halt progression of this type of resorption include provision of effective non-surgical root canal treatment including chemomechanical preparation to remove irritants from within the root canal system. Smear layer removal including the sequential use of 17 % EDTA, 1 % sodium hypochlorite and a final rinse with EDTA has been shown to be an effective treatment modality to ensure diffusion of intra-canal medicaments such as Ledermix paste through the dentine to the external surface of the tooth. The corticosteroid and antibacterial components of Ledermix have been shown to exert beneficial effects on clastic cells responsible for the resorptive processes that occur. Following initial use of this anticlastic agent, conventional calcium hydroxide medicament can be placed to influence hard tissue deposition on the resorbed tooth surface prior to completion of endodontic treatment.

Progressive replacement of tooth structure by alveolar bone can ultimately result in tooth loss. This type of process follows the death of viable periodontal ligament cells due to either severe compression or drying of the cells usually seen in severe traumatic injuries such as luxation, intrusion and avulsion. An interface devoid of viable periodontal ligament cells between bone and dentine results in normal remodelling processes associated with skeletal bone turnover at the expense of dentine. Ankylosis occurs with total loss of mobility with a characteristic high-pitched metallic percussion sound. At this stage, there is no loss of root dentine or cementum. Eventually progressive replacement of tooth structure by surrounding bone occurs resulting in the eventual demise of the tooth.

From a clinical management point of view, the replacement resorption process usually proceeds at a slow rate and in some cases taking years to reach a stage where intervention is required. In the mature dentition, alternative prosthodontic replacement options will need to be considered. In the developing dentition, ankylosis can severely disrupt arch integrity with infra-occlusion of the ankylosed tooth that becomes more obvious as skeletal growth continues. In cases of ankylosis with advanced replacement resorption, the procedure of decoronation and submergence has been recommended to allow for continued alveolar growth and uncomplicated transition to implant therapy once growth has stopped.