Effect of bone mass density and alveolar bone resorption on stress in implant restoration of free-end edentulous posterior mandible: Finite element analysis of double-factor sensitivity.

BACKGROUND: Osseous condition of the mandible was regarded as a key factor influencing stability of implants in the early stage. Finite element analysis was used to assess the effect of bone mass density and alveolar bone resorption (double factors) on stress in a four-unit implant restoration of a free-end edentulous posterior mandible. METHODS: A 3D finite element model was constructed for a single-sided free-end edentulous mandible (from mandibular first premolar to mandibular second molar) containing threaded dental implants. Mandible sensitivity modes were constructed with different alveolar bone resorption levels for normal conditions as well as mild, moderate and severe periodontitis, respectively. Based on the mass density of cancellous bone for four types of bones as the sensitivity parameter, two implant design modes were constructed: Model A (four-unit fixed bridge supported by three implants, implant positions were 34, 36 and 37) and model B: 34 × 36, 37 (37: a single implant crown) (34 × 36: three-unit fixed bridge supported by two implants, implant positions were 34 and 36). A total of 32 sensitivity-based finite element models, grouped in two groups, were constructed. Stress distribution and maximum von Mises stress on cortical bone and cancellous bone around the implant, as well as the surface of implant were investigated by using ABAQUS when vertical loading and 45° oblique loading were applied, respectively. RESULTS: When vertical loading was applied on the implant, maximum von Mises stress on the cortical bone around the implant was assessed to be 4.726 MPa - 13.15 MPa and 6.254 MPa - 13.79 MPa for groups A and B, respectively; maximum stress on the cancellous bone around the implant was 2.641 MPa - 3.773 MPa and 2.864 MPa - 4.605 MPa, respectively; maximum stress on the surface of implant was 14.7 MPa - 21.17 MPa and 21.64 MPa - 30.70 MPa, respectively. When 45° oblique loading was applied on the implant restoration, maximum von Mises stress on the cortical bone around the implant was assessed to be 42.08 MPa - 92.71 MPa and 50.84 MPa - 102.5 MPa for groups A and B, respectively; maximum stress on the cancellous bone around the implant was 4.88 MPa - 25.95 MPa and 5.227 MPa - 28.43 MPa, respectively; maximum stress on the surface of implant was 77.91 MPa - 124.8 MPa and 109.2 MPa - 150.7 MPa, respectively. Stress peak on the cortical bone and that on cancellous bone around the implant increased and decreased with the decrease in bone mass density, respectively. Stress peak on alveolar bone increased with alveolar bone resorption when oblique loading was applied. CONCLUSION: 1. Both alveolar bone resorption and bone mass density (double factors) are critical to implant restoration. Bone mass density may exhibit a more pronounced impact than alveolar bone resorption. 2. From the biomechanical perspective, types I and II bones are preferred for implant restoration, while implantation should be considered carefully in the case of type III bones, or those with less bone mass density accompanied by moderate to severe alveolar bone loss. 3. Splinting crowns restoration is biomechanically superior to single crown restoration.

[Advances on treatment of periprosthetic infection and antibiotic delivery system after total hip arthroplasty].

Periprosthetic infection after hip replacement is a clinical catastrophic disease, which often leads to the failure of the prosthesis. It needs the combination of systemic antibiotics to cure the infection, which brings huge burden to doctors and patients. There are strict indications for debridement and one-stage revision of the prosthesis, and few cases meet the requirements. The second revision is still the gold standard for the treatment of periprosthetic infection. It is suitable for all infection conditions and has a high success rate. On the second phase of renovation, the antibiotic sustained release system plays a key role, and the carrier of antibiotic sustained-release system is the focus of current research, including classic bone cement and absorbable biomaterials. Bone cement has strong mechanical strength, but the antibiotic release shows a sharp decline trend; the absorbable biomaterials can continuously release antibiotics with high concentration, but the mechanical strength is poor, so it could not use alone. The combination of bone cement and absorbable biomaterials will be an ideal antibiotic carrier. PMMA is the most commonly used antibiotic carrier, but the antibiotic release concentration is decreased sharply after 24 hours. It will be difficult to control the infection and increase the risk of bacterial resistance if it is lower than the minimum inhibitory concentration. The biodegradable materials can release antibiotics completely, with long release time and high concentration, but low mechanical strength. Antibiotic spacer plays an important role in the control of infection. In the future, how to further extend the antibiotic release time of antibiotic sustained-release system, increase the amount of antibiotic release and maintain the mechanical strength of the material will be studied.