Introduction: The aims of this study were to examine whether teeth adjacent and contralateral to endodontically diseased teeth showed co-occurring mechanical allodynia and to determine whether demographic and clinical variables were involved in such associations. Methods: Patients with irreversibly inflamed or necrotic permanent first molars or second premolars were examined. From the 348 eligible patients (160 men and 188 women; mean age 6 standard deviation 5 30.4 +/- 10.0 years), data on age, sex, health status, current presence of pain, tooth type, dental arc, and pulpal diagnosis were collected. Percussion testing was applied to all posterior teeth, and the degrees of pain were recorded using a 4-point verbal scale as follows: none to slight (coded as 0) and moderate to severe (coded as 1). Following association rule mining (with minimum support and confidence levels of 0.1), univariate and multiple logistic regression analyses were performed at various stringency levels (alpha = 0.05). Results: The number of painful associations was greater ipsilaterally than contralaterally and distally than mesially and increased with the severity of percussion pain in the diseased tooth. Successful regression models were established for the ipsilateral (between the diseased tooth and adjacent teeth; current pain: odds ratio = 3.37; 95% confidence interval, 1.94-5.83) and contralateral (between the diseased tooth and the tooth distal to the contralateral symmetrical tooth; dental arc: odds ratio = 2.40; 95% confidence interval, 1.21-4.76) sides (P < .05). Conclusions: Healthy teeth adjacent and contralateral to symptomatic diseased teeth exhibited percussion sensitivity. Patients' current pain and dental arc, respectively, were involved in such painful associations.