Objective To construct a model of the mandibular first molar after root canal treatment using finite element analysis, and analyze the influence of different elastic modulus pulp cavity retention crowns at various levels of deep margin elevation (DME) on the stress magnitude and distribution of abutment teeth, restorations and bonding layers with different degrees of distal and middle proximal defects.

Methods Based on the cone-beam CT image data, a model of the distal and middle defect to subgingival and gingival wall elevation combined with repair of the pulp cavity retention crown was constructed using finite element software. Three different materials for the pulp cavity retention crown were set up: resin-based ceramics, glass ceramics and traditional zirconia, and the corresponding elastic modulus gradually increased. Two types of distal and middle defect types were designed based on the cemento-enamel junction (CEJ) : 1 mm below CEJ and 2 mm below CEJ. Two types of gingival wall elevation levels: 1 mm and 2 mm above the CEJ. Eventually, a total of 12 three-dimensional finite element models were constructed. A static load of 200 N was applied vertically to the surface to simulate the bite force. The equivalent stress distribution and peak magnitudes of the remaining dental tissues, restorations and bonding layers in each group were analyzed and compared.

Results The stress of the dental tissue after gingival wall elevation combined with pulp cavity retention crown restoration was mainly concentrated near the distal root canal orifice at the bottom of the pulp chamber and near the cervical area of the distal defect. The elastic modulus of the restoration was positively correlated with the maximum equivalent stress of the dental tissue and the restoration. Under the same defect, with the increase of the elevation level of gingival wall, the stress peaks of dental tissue, restoration and bonding layer all showed an increasing trend.

Conclusions When choosing gingival wall elevation for proximal defects to the subgingival level, the pulp cavity retention crown should be made of resin-based ceramic with an elastic modulus close to dentin. The height of the gingival wall elevation layer should not be too high. It can be restored to the level of 1 mm above the CEJ. Moreover, teeth with defects to 1 mm below the CEJ are more suitable for gingival wall elevation, which is conducive to protecting the remaining dental tissue and reducing the risk of root fracture.