Combination injuries 1. The risk of pulp necrosis in permanent teeth with concussion injuries and concomitant crown fractures.

Background: The reported risk of pulp necrosis (PN) is low in teeth with concussion injuries. A concomitant crown fracture may affect the risk of PN.

Aim: To analyze the influence of a crown fracture (with and without pulp exposure) on the risk of PN in teeth with concussion injury.

Material: The study included 469 permanent incisors with concussion from 358 patients (226 male, 132 female). Among these, 292 had a concomitant crown fracture (70 with and 222 without pulp exposure). All teeth were examined and treated according to standardized protocol.

Statistical Analysis: The risk of PN was analyzed by the Kaplan-Meier method and Cox regression. Risk factors included in the analysis: gender, age, stage of root development, type of crown fracture, and response to electric pulp test (EPT) at the initial examination. The level of significance was set at 5%.

Results:   The risk of PN was low in teeth with immature root development [1.1%, 95% confidence intervals (CI): 0-3.4]. The following factors significantly increased the risk of PN in teeth with mature root development: crown fracture without pulp exposure [hazard ratio 4.1 (95% CI: 1.4-11.9), P = 0.01] and no response to EPT at the initial examination [hazard ratio 30.7 (95% CI: 7.7-121), P < 0.0001]. The overall risk of PN increased from 3.5% (95% CI: 0.2-6.8) to 11.0% (95% CI: 5.2-16.7) when a concomitant crown fracture without pulp exposure was present. If the tooth had both a crown fracture and gave no response to EPT, the risk further increased to 55.0% (95% CI: 34.3-75.8).

Conclusion: No response to EPT at the initial examination or a concomitant crown fracture significantly increased the risk of PN in teeth with concussion injury and mature root development. If both risk factors were present there was a synergetic effect.