Aetiological, histopathological, clinical, diagnostic and therapeutical features of idiopathic cervical resorption

Aetiology

The aetiology of CRR is difficult to determine with certainty. In most cases a causal relation can be established, with different local predisposing factors such as dental trauma,³ orthodontic treatment,⁴ periodontal diseases and their treatments³ or intracoronal bleaching.⁵ Also, systematic pathologies can play a role in this type of resorption, although it is usually not possible to associate the two pathologies.⁶ Authors such as Gutmann et al⁶ and Llena-Puy et al⁷ have described a mild association of this type of resorption with a record of hypercalciuria and renal lithiasis. Finally, idiopathic root resorption (IRR) refers to a clinical situation in which all other causes, whether local or systemic, have been ruled out as the origin of the disease.⁸ According to Heithersay,⁹ 15% of the patients have no predisposing factors.

Pathology

The pathogenic mechanism behind root resorption is unknown. Tooth cement and predentine are essential in root resistance to resorption, since the most external part of the cement (demineralized cementoid) is covered by a layer of cementoblasts, which constitute an unsuitable surface for the adhesion of clastic cells.¹⁰ Root resorption is started by damage to the precementum or predentine and odontoblast layer, resulting in exposure of the mineralized cementum or dentine, respectively. The clastic cells rapidly colonize the damaged root surface and will then start resorbing it. This beginning is due to the fact that the clastic cells bond to extracellular arginineglycine-aspartic acid (RGD) tripeptide proteins, which in turn bond to calcium crystals of the mineralized surfaces.¹¹ After this bonding, the clastic cells secrete an acid solution that contains proteolytic enzymes (vacuolar H+ATPase and carbonic anhydrase); this begins the decalcification¹² and subsequent degradation of the collagen and non-collagen organic matrix,^13,14 resorbing both the dentine as well as the predentine.¹⁵

Histology

Cemento-enamel disjunction, ie where there is a fault at the junction of the enamel and dentine, has been recognized as risk factor. Physical or chemical injury can lead to damage to bone, cementum or dentine. This can trigger chemical changes within the affected tissues and can start the resorptive process.¹⁶

Histologically, the cells responsible for the resorption of the calcified dental tissues have morphological and biochemical characteristics of clastic cells. Generally, these are multinucleate, although they can sometimes be mononucleate. They come from mononucleate precursors that belong to the monocyte/macrophage lineage, as do osteoclasts, and ultrastructurally have similar characteristics.¹⁷

Figure 1 presents an incisor extracted with IRR. Histological evaluation revealed the presence of connective tissue replacing the hard dental structures, composed essentially of monomorphic cells of clear cytoplasm and scattered giant cells of osteoclastic appearance and accumulations of cells that appeared to be histiocytes. The presence of giant cells similar to the osteoclasts indicated resorption.

Clinical

Clinically, cervical root resorption can begin and progress asymptomatically. When the lesion is visible, the aspect varies from a small defect at the gingival margin (Figure 2) to a pink discoloration of the tooth crown (Figure 3). This discoloration is a result of the highly vascular granulation (resorptive) tissue within the tooth becoming visible through the thinned out (resorbed) dentine and translucent overlying enamel.¹⁸ The pink colour at the level of the cervical region detected by the patient and/or the dentist is sometimes the first clinical sign of the problem, although the pathological condition may often go unnoticed until a pulp and/or periodontal problem arises.¹

Diagnosis

The resorptive condition is often detected by routine radiographic examination. Heithersay⁹ defined four levels of resorption according to the radiographic appearance of the process:

Classically, CRR appears as an image with well-defined or irregular radiolucent edges in the cervical region of the tooth (Figure 4). However, when the lesion progresses, it can have a mottled appearance that can be confused with dental caries (Figure 5).¹⁸ As is well known, this type of examination provides rather limited information on the extent of resorptive lesions.¹⁹ The use of CBCT to assess CRR lesions may help to determine their position and depth in relation to the root canal. CBCT is an extra-oral imaging technique that shows the area of interest in meso-distal and vestibule-lingual planes, enabling three-dimensional reconstructions. This vision in three dimensions provides a more exact idea, both of the position of the lesion as well as its depth. In addition, it offers advantages over conventional CT scans by lowering costs, submitting the patient to less radiation²⁰ and, finally, avoiding unnecessary surgical exploration so that the restorability of the tooth can be assessed before treatment.^19,21,22

The diagnostic accuracy of CBCT has been demonstrated to be superior to conventional radiographs²³ (Figures 6 and 7).

It is important to perform a differential diagnosis of CRRs with two fundamental pathologies: subgingival caries and internal root resorption. The differential diagnosis with subgingival caries is made by a clinical exploration in such a way that the caries will feel sticky on probing them and does not present with a pink spot,²³ while the resorptive cavitation usually has sharp and tapered margins with a hard bottom and an underlying pink spot (Figure 8). The differential diagnosis must also be performed with internal resorption; the parallax technique is useful to follow the continuity of the pulp canal to distinguish between internal and external resorption.¹⁸ A second radiograph taken from a different mesiodistal angle would alter the relationship of the defect to the root canal in the case of external root resorption, but not in that of internal resorption.²⁴

The clinical prognosis rests mainly on the extent of the resorptive process. The amount of the resorption serves as a guide for the clinician to select the best treatment. Therefore, the radiographic assessment of the resorptive process is crucial for the differential diagnosis, treatment and prognosis of the tooth.

Treatment options

The treatment of CRR depends on its severity, its location, or whether the lesion compromises or not the root canal system. Therefore the treatment options according to the amount of hard tooth tissue lost would be:

Heithersay⁹ stated that, in CRR Classes 1 and 2, practically 100% of the conservative treatments (A and B) were successful. In Class 3 the percentage of success dropped to 78% and, in Class 4, the percentage fell to 12.5%. Consequently, the recommendation is to treat only defects belonging to Classes 1 to 3, while extraction is proposed for Class 4 lesions.

With respect to the conservative approach, the overall aim of treating external resorption is the complete removal of resorptive tissue, the restoration of the defective area and the prevention of further resorptions.²³ Endodontic treatment will be necessary in those cases in which the CRR lesion had perforated the root canal.

The restoration phase often requires vestibular-flap surgery²³ to gain complete access to the resorption lacuna (Figure 9). Heithersay²⁵ recommended topical application of 90% aqueous solution of trichloroacetic acid (TCA) and curettage of the lesion. The trichloroacetic acid produces the coagulation and necrosis of the resorptive tissue,²⁵ thus avoiding the persistence of remains of the affected tissue^18,26 since, if this occurred, it would have a high probability of relapse in the future.²³

A recent study by Kitchens et al²⁷ has suggested a new method of treatment of CRR that involves chemo-mechanical debridement of the root canal, obturation of the apical part of the canal, removal of the smear layer, and subsequent iontophoretic delivery of calcitonin via the dentinal tubules directly to the CRR lesion. Calcitonin is a polypeptide responsible for inhibitory action on osteoclasts via specific cell receptors. It might also act to inhibit odontoclast activity directly and to suppress inflammation.²⁸ Further research is required before this option can be routinely recommended in the treatment of CRR.

Ideally, the restorative material chosen for these types of lesions should reinforce the remaining tissues, should have a coefficient of thermal expansion close to that of the dental structure, and should be biocompatible.²⁹ The most commonly used materials are: composite resin,³⁰ glass-ionomer cement,³¹ and mineral trioxide aggregate.^16,18,32 Before any adhesive process, Schwartz et al³³ consider it necessary to ‘refresh’ the dentine because the TCA severely demineralizes it. Vinothkumar et al²⁹ proposed a new technique called a ‘reverse sandwich restoration’ (RSR), consisting of placing a 1-mm layer of micro-filled resin composite and restoring the remnants of the defect with resin-modified glass-ionomer cement (RMGIC). The micro-filled resin was used together with RMGIC because they tend to flex with the tooth rather than debond, as occurs with the more rigid macro-filled resin. Compared to conventional sandwich restoration, RMGIC forms a significantly stronger bond to cured resin composite in RSR than that of resin composite to cured RMGIC in the absence of etching; the development of subgingival plaque over RMGIC is prevented by achieving a smooth finish using the cervical matrix.²⁹

In any case, it is highly advisable that the restorative procedures mentioned above are performed under isolation with rubber dam (Figure 10). The absolute isolation improves visibility providing the indispensable conditions of isolation required for endodontic treatments and improving the quality of adhesion procedures (Figures 11 and 12). Also, it protects adjacent tissues from the caustic effects of TCA, thereby avoiding burns.^23,33

Some authors, such as Schwartz et al³³ and Fernández and Rincón³⁴ have described conservative treatment of Class 4 CRR that was successful in follow-ups of 10 and 16 years, respectively. However, these cases involved patients of 80 and 67 years old, respectively, which have refused tooth extraction; therefore, their circumstances and their desires determined the design of the treatment plan. In fact, the authors themselves³³ called this type of treatment ‘heroics’, an example of this being a woman 80 years old (mother of one of the authors) presenting a Class 4 lesion in the right maxillary central incisor. In this case the treatment included an endodontic, zirconium post, and ‘open sandwich’ restoration.

In Class 4 CRR, the tooth extraction is the chosen treatment followed by prosthetic repositioning. The treatment options should be discussed with the patients and the most suitable chosen according to the needs of the patient and the recommendations of the professional. These include:

Heithersay⁹ recommends, in most cases of Class 4 CRR, tooth extraction and immediate implant placement as the chosen treatment, because this option guarantees long-term results, offers a reliable prognosis, and provides an immediate aesthetic result. The advantages of immediate implant placement include fewer surgical operations and less treatment time.³⁵ Authors, such as Barone et al,³⁶ suggest that this type of treatment is a good option, especially in the case of only one tooth being compromised, as it eliminates the need for a temporary bridge and appears to maintain the pre-existing architecture of soft and hard tissues, in most cases.

Conclusion

It can be concluded that CRR is a difficult pathology to diagnose before clinical symptoms of pulp or periodontal problems arise. Given that early detection is essential for the best management of CCR, the dentition of patients with a CCR lesion and no apparent identifiable aetiological factors should be thoroughly assessed to ensure that no other teeth are affected by CCR.

CBCT provides the better information on the true extent of lesions, helping the clinician to recommend the most appropriate treatment without the need for prior surgical exploration.

It can also be concluded that the treatment of this type of lesion demands the management of a broad field of multidisciplinary techniques such as restorative dentistry, endodontics, surgery, implants and prosthesis.