Mechanical weakening of devitalized teeth: three-dimensional Finite Element Analysis and prediction of tooth fracture

AIM

To determine to which extent cavity preparation and each step of dentine removal in the process of root canal treatment (access cavity preparation and root canal enlargement) both individually and jointly contribute to the weakening of the tooth.

METHODS

Numerical analysis using finite element method (FEM) of separate and combined influence of two-surface Class II preparation and root canal treatment was undertaken to evaluate the decrease in tooth strength. The influence of the two stages in root canal treatment, access cavity preparation and root canal enlargement, was also analysed separately and jointly. After each of these phases, the crown was restored with composite resin, and the FEA was performed only on restored teeth. To estimate the influence of all these procedures on tooth fracture resistance numerically, a Failure Index based on the maximum principal stress criterion (MPCS) was applied. Compressive and tensile stresses were analysed separately and corresponding Failure Indices were calculated.

RESULTS

A two-surface resin composite restoration weakened the tooth by 23.25%. Nevertheless, the Failure Indices showed that this tooth was not likely to fracture even under high occlusal stress (710N). However, after access cavity preparation, the Failure Indices reached the point where, under high occlusal force that may occur in the posterior area, a tooth fracture occurred. The enlargement of root canals had an additional, but relatively small impact on tooth weakening, making the tooth even more susceptible to fracture. The combined influence of both cavity preparation and root canal enlargement led to weakening of 62.6% under a load of 710N, ultimately causing tooth fracture.

CONCLUSION

The combined finite element method and the maximum principal stress analysis gave insight into the fracture mechanisms of teeth with two-surface composite restorations followed by root canal preparation. Removal of tooth tissue, despite its subsequent restoration with dental materials, weakened the tooth by changing the stress intensity and distribution through tooth structures. Access cavity preparation had the greatest influence on tooth strength whilst canal enlargement did not contribute to this process substantially.

Pathological media use within a population of patients with depression

Former studies show that Internet addiction goes along with a high comorbidity rate of depression and anxiety disorders. Since the Internet offers a possibility to attain social contacts safely and anonymously, depressed individuals may be at a higher risk to develop an Internet addiction. Patients with a confirmed diagnosis of depression have been recruited from the psychiatric department of Hanover Medical School. The participants were compared with a control group concerning their media use. The two groups consisted of 25 subjects, each with 56% females and mean ages of 34,4 years (patients) and 32,4 years (controls). The depressed subjects estimate themselves more frequently to be Internet addicted and are significantly (p ≤ 0,05) less satisfied with the quantity of their media consumption. Three of the depressed fulfil the criteria for Internet addiction from Young and Beard and three more hit the softer criteria from Young. The results of the Internet addiction scale (ISS) show one subject with Internet addiction and three at a high risk. The depressed patients scored significantly higher in the ISS (p ≤ 0,01). In total, the examination found six (24%) subjects among the depressed with a problematic or pathological Internet use. For further discussion, it is remarkable that 50% of the depressive patients agreed to the criterion “uses the Internet as a way of escaping from problems or of relieving an unpleasant mood”. This may contribute to the notion, that excessive use of Internet may be interpreted as a potentially pathological compensation of depressed patients’ inner conflicts.