Three-dimensional finite element analysis of occlusal splint and implant connection on stress distribution in implant-supported fixed dental prosthesis and peri-implantal bone.

The aim of this study was to investigate the influence of occlusal splint therapy on the stress distribution of implant-supported fixed dental prosthesis (FDP) and peri-implantal bone structures using three-dimensional (3D) finite element analysis (FEA). The system consisted of two implants (positioned on region of second premolar and second molar) as retainers of fixed porcelain-fused-to-metal 3-unit FDP (first molar as pontic element). Two implant connections systems (external and internal hexagon) were tested. Static axial loads simulating functional (100N) and overloaded (300N) chewing were applied on the occlusal surface of the FDP covered or not with the occlusal splint. Maximum von Mises stress and bioperformance were accessed for the implants and bone tissues (cortical and cancellous) models. Analytic results indicated that independently of the load condition, implant region, and connection type, the presence of the occlusal splint decreased the stress developed in the implants. Both bone tissues showed increased levels of von Mises stress, and the bioperformance index was far from their maximum yield strength. The internal hexagon implants presented lower stress on premolar and molar regions than external hexagon implants under functional load and overload. The presence of the occlusal splint device over implant-supported FDP may be clinically useful for forwarding stresses towards the bone structure to maintain implants for long term.

Comparative photoelastic study of dental and skeletal anchorages in the canine retraction.

OBJECTIVE: To compare dental and skeletal anchorages in mandibular canine retraction by means of a stress distribution analysis. METHODS: A photoelastic model was produced from second molar to canine, without the first premolar, and mandibular canine retraction was simulated by a rubber band tied to two types of anchorage: dental anchorage, in the first molar attached to adjacent teeth, and skeletal anchorage with a hook simulating the mini-implant. The forces were applied 10 times and observed in a circular polariscope. The stresses located in the mandibular canine were recorded in 7 regions. The Mann-Whitney test was employed to compare the stress in each region and between both anchorage systems. The stresses in the mandibular canine periradicular regions were compared by the Kruskal-Wallis test. RESULTS: Stresses were similar in the cervical region and the middle third. In the apical third, the stresses associated with skeletal anchorage were higher than the stresses associated with dental anchorage. The results of the Kruskal-Wallis test showed that the highest stresses were identified in the cervical-distal, apical-distal, and apex regions with the use of dental anchorage; and in the apical-distal, apical-mesial, cervical-distal, and apex regions with the use of skeletal anchorage. CONCLUSIONS: The use of skeletal anchorage in canine retraction caused greater stress in the apical third than the use of dental anchorage, which indicates an intrusive component resulting from the direction of the force due to the position of the mini-implant and the bracket hook of the canine.

Influence of loading and use of occlusal splint in implant-supported fixed prostheses.

The aim of the study was to assess the tensions generated in the long axis of the implants and the interimplants in the cervical, middle, and apical regions when subjected to different loads with or without interposition of the flat occlusal plane splint. A photoelastic model was made with 2 external hexagon implants located in the space corresponding to the second premolar and molar inferiors. A screw-retained metal superstructure was installed on the implants with a torque of 20 N·cm, and the set (photoelastic model with superstructure) were positioned in the circular polariscope in the dark-field configuration to observe the distribution of isochromatic fringes around the implants and interimplant areas. Photographic records were obtained before the application of the occlusal load with the following loading conditions: 300, 600, and 900 N, with and without interposition of the occlusal plane splint. The decrease in stress with the application of the flat occlusal plane splint became more evident after the application of the 600-N load. Generally, the major stress magnitude occurred in the cervical region for interimplant areas and in the apical region around implants. Use of occlusal splint in the loading of 300, 600, and 900 N reduced tension 33.22%, 66.66%, and 73.33%, respectively, in the samples. It can be concluded that the interposition of the occlusal plane splint caused a reduction in tension resulting from the simulation of occlusal overload.