Sir, it was interesting to read the article How to assess and manage external cervical resorption [ECR] in the British Dental Journal (2019; 227: 695-701). The descriptions of Figure 5 and Figure 6 have been exchanged by mistake.

The author has mentioned many causes of ECR but missed out the most important cause which is food impaction. The impacted food acts as a foreign body thereby generating an inflammatory response which leads to ECR. ECR in other words is root caries. The impacted food also puts pressure on the root which also contributes to resorption of the root.

Third molar mesio-angular impaction causes resorption of the distal surface of the second molar. In these cases again, the pressure from the third molar, the pressure from impacted food and inflammation caused by the impacted food cause the resorption of the distal surface of the second molar.

After the removal of the third molar there is no food impaction distal to the second molar and the resorption of the distal surface of the second molar gets arrested.

I have many radiographs of mesio-angular impactions of third molars before, and follow up of the distal surface of the second molar after extraction of the third molars.

Corresponding author Jaymit Patel responds: I thank the correspondent for their letter in relation to our article. With respect to the lesion highlighted in this letter (resorption associated with impacted third molars with concomitant food packing), I feel that there has been some confusion in relation to the aetiology of resorption.

Dental caries involving the distal surface of lower second molars in cases with an impacted lower third molar is a recognised clinical presentation. In this situation tooth tissue loss occurs as a result of caries, rather than the resorptive mechanism described in our recently published article.

The aetiology of the resorptive process in ECR is poorly understood. It is thought to relate to mechanical or chemical trauma affecting the external surface of the root, which results in dentine exposure. This process is sustained through either an inflammatory stimulus or an 'aseptic resorptive process' (with no consensus on which mechanism induces and sustains this process). Whilst it has been reported that bacterial microorganisms may have a role in the resorptive process, this is likely to be in sustaining an inflammatory process and thus supporting osteoclastic resorption, rather than initiating it.

Resorption of a second permanent molar tooth as a result of an adjacent impacted third molar tooth is a presentation described in several published articles. Other commonly affected teeth include upper lateral incisors and central incisors as a result of impacted canine teeth. Whilst some papers do report on the role of pressure from the erupting tooth on the resorptive process, the true mechanism remains unclear. Additionally, this process is reported to involve any part of the root of a tooth, with the cervical region being least affected and is, therefore, commonly referred to as external surface resorption (based on the classification of resorption by Andreason in 1970). This process is distinct from dental caries. In contrast to the aetiology of resorption (described above), dental caries results from the detrimental effect of the acidic by-products of bacterial metabolism and enzymatic action, causing the chemical dissolution of tooth tissue and removal of organic tissue (ie this process does not involve osteoclastic resorption).

The distinction between these two clinical presentations is important in relation to the management of dental caries and resorption with the former benefitting from changes in patient behaviours and the provision of a cleansable restored tooth surface, and the latter benefitting from the removal of the tissues that drive resorption.