Abstract: PURPOSE: To evaluate the influence of two kinds of fixed prosthesis on the stress of the mandibular first molar with separation prosthodontic therapy. METHODS: A 3-D finite element model of the mandibular first molar was established with single and combined crowns and their supporting tissues by means of cone-beam CT (CBCT) scanning technology and software Mimics, Geomagic, UG of image processing program. Under dispersed vertical load and dispersed oblique load, the stresses of dental tissues and periodontium were obtained and analysed. RESULTS: When dispersed vertical load was applied, the dental and periodontal stress distribution of two models were similar to the normal. The dental stress value and maximum tensile stress of the periodontal membrane increased and changed greatly in the single crown. When dispersed oblique load was applied, the model of combined crown was similar to the normal. The stress concentrated area expanded in the distal root of the single crown model and the buccal bottom half of the periodontium. The dental stress value and maximum tensile stress of the periodontal membrane increased and changed greatly in the single crown. CONCLUSIONS: The combined crown is a better choice for restoration of mandibular first molar after separation prosthodontic therapy.

Key words: Separating root, Three-dimensional finite element method, Single crown, Combined crowns, Mandibular first molar