[Three-dimensional finite element stress analysis of mandibular first molar with single and combined crowns after separation prosthodontic therapy].

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.

[Mechanical property analysis of polyethylene fiber reinforced polymethyl methacylate].

OBJECTIVE: To investigate if the Ribbond polyethylene fiber has the effect of reinforcing polymethyl methacylate. METHODS: 28 specimens were fabricated and divided into 3 groups: group of chemical-cured PMMA, group of chemical-cured PMMA reinforced by stainless steel wire and group of chemical-cured PMMA reinforced by Ribbond polyethylene fiber. A three-point bending test was used to measure the flexural strength and flexural modulus of specimens. Then the data were analyzed with a one-way analysis of variance. RESULTS: The flexural strength of chemical-cured PMMA group was (51.383 +/- 2.761) MPa, the flexural modulus was (1791.2 +/- 113.760) MPa; The flexural strength of stainless steel wire reinforced group was (58.725 +/- 1.218) MPa, the flexural modulus was (2092.76 +/- 120.28) MPa; The flexural strength of Ribbond polyethylene fiber reinforced group was (80.975 +/- 2.58) MPa, the flexural modulus was (2866.53 +/- 107.51) MPa. The one-way analysis of variance showed that the results were significant (P < 0.001). Newman-Keuls method showed that the differences among all groups were significant (P < 0.05). CONCLUSION: The Ribbond polyethylene fiber can raise the flexural strength and flexural modulu of polymethyl methacylate.