Abstract: BACKGROUND: The healing of mandibular fractures after rigid internal fixation is influenced by many factors, including the material of the bone plate, fracture site, and bone density of the patient. However, there are relatively few studies on the relationship between the stability of mandibular fracture fixation in different bone qualities and they lack a scientific basis. 
OBJECTIVE: To analyze the stability of fixation of mandibular fractures with different bone qualities with bioabsorbable plates and miniature titanium plates by finite element analysis.
METHODS: Three-dimensional finite element models of class I-IV mandibular fractures were developed according to the bone quality classification method proposed by ZARB and LEKHOLM. The fractures at the median mandibular symphysis, mandibular body, and mandibular angle were simulated under different bone qualities. Bioabsorbable bone grafting plates (or miniature titanium plates) were placed at each fracture site for fixation and to simulate the state of healthy side occlusion. Finite element analysis on the model was used to analyze the relative displacement of the fracture segments and the stress distribution of fixators. 
RESULTS AND CONCLUSION: (1) The maximum stress value during fixation with titanium plates increased gradually with the increase of bone class, in which the maximum stress value of titanium plates was the highest in the mandibular body class IV bone group, which was 382.74 MPa and 96.11 MPa in the miniature titanium plate and bioabsorbable plate groups. The results for mandibles of the same bone type showed that the maximum stress value of titanium plates was much higher than that of bioabsorbable plates. (2) For fractures of the median middle of the mandible in types III and IV, the displacement of the fracture breaks at the fixation site was large and exceeded the limiting value of bone healing (> 150 µm), regardless of whether the fixation was performed with a miniature titanium plate or a bioabsorbable plate. For type IV mandibular fractures, the fracture end displacement in the bioabsorbable plate group exceeded the healing limit value, and the fracture end displacement in the miniature titanium plate group was close to the healing limit value. Under the same bone quality and fracture site, the fracture displacement of the miniature titanium plate group was smaller than that of the bioabsorbable plate group. (3) The results showed that the strength and stiffness of the two internal fixations were sufficient to support bone healing of fractures at three sites of the types I-IV mandible, and the fixation stability of the bioabsorbable plate was almost the same as that of the miniature titanium plate, which could provide early healing conditions for fractures. Mandibular bone type should be taken into consideration in the treatment of mandibular fracture. The higher the mandibular bone grade, the worse the stability of fracture fixation, and the more likely the complications such as poor bone healing will occur after surgery.

Key words: bioabsorbable plate, miniature titanium plate, three-dimensional finite element analysis, mandibular fracture, fixation method, bone quality