Forming a proper endodontic diagnosis requires taking a patient’s medical and dental history, a thorough inspection and the use of clinical examination methods, such as pulp vitality and mobility testing, along with palpation and percussion. In this process, no indicator is as valuable as the results of percussion testing. Eliciting a response from a patient by using a gloved finger or the blunt end of a dental instrument to tap a tooth usually indicates the presence of disease in the tooth pulp and the periradicular tissue.

Sensitivity to percussion suggests mechanical allodynia—a reduction in the neuron excitability threshold that creates pain as a response to mechanical stimuli that would not normally provoke pain. Along with hyperalgesia (increased pain in response to stimuli that normally provoke pain), allodynia is hypothesized to be an adaptation that allows for better protection of vulnerable tissues.

Kayaoglu et al from Gazi University, Turkey, undertook a clinical study to investigate the occurrence of mechanical allodynia on the ipsilateral side of first and second molars requiring primary root canal treatment; additionally, they observed results in the contralateral side of the jaw. From each member of a cohort of 348 patients who met the inclusion criteria, the researchers recorded demographic and health information, use of analgesia within the previous 12 hours, current pain status, length of time of the pain and pulpal diagnosis.

Level of pain, regardless of type, in response to percussion testing was classified as none, slight, moderate or severe; the first 2 levels of pain were grouped together as absent, while the second 2 levels were grouped together as present.

A significant number of patients who reported moderate or severe pain on percussion of their diseased tooth (pain

present) also reported pain upon percussion in teeth ipsilateral to their diseased tooth. The level of painful associations increased with the severity of pain in the diseased tooth (Figure 1). Several patients reported pain on the contralateral side, although this group was smaller than that of patients who reported pain on the ipsilateral side. Patients reported more pain in teeth located distally to the diseased tooth and its contralateral mate than in teeth located mesially.

Conclusion

The authors entered 10 different variables into their univariate and multivariate logistic regressions, including demography, diagnosis, arch and tooth type. Their final analysis found that the presence of pain on percussion of the diseased tooth was the only significant association with pain in an ipsilateral tooth; location of the diseased tooth in the mandible was the only significant association with pain in a contralateral tooth.

A possible hypothesis for the greater incidence of mechanical allodynia in distal teeth than in mesial teeth involves the observation that the bite force of individual teeth increases from the incisors to the molars. Thus, a greater percussion sensitivity may reflect a protective mechanism of the body’s attempt to minimize the force on the diseased tooth. The practitioner needs to be aware that a healthy tooth adjacent or contralateral to an endodontically diseased tooth may nevertheless demonstrate pain in response to a percussion test.

Kayaoglu G, Ekici M, Altunkaynak B. Mechanical allodynia in healthy teeth adjacent and contralateral to endodontically diseased teeth: a clinical study. J Endod 2020;46:611-618.

Figure 1. Frequency of pain in teeth ipsilateral and contralateral to endodontically diseased teeth in patients whose pain is severe (A) and moderate (B). Confidence values >0.1 are marked with asterisks (*).