Color stability through wear and time, one of the most important esthetic factor, influencing patient�s acceptance of an acrylic removable prosthesis, was investigated in vivo in a limited number of studies and solely on prefabricated denture teeth.The aims of the present paper were to assess the color changes occurred with the commercially available PMMA for 3D printing technique, improved by doping with titania nanoparticles, and to evaluate the color stability and stainability of the PMMA with 0.4%TiO2 denture teeth, on denture wearers, over a period of one year. Ten patients rehabilitated with removable complete dentures or implant retained overdentures manufactured using a new nanopolymer, PMMA doped with 0.4% by weight of TiO2 as denture base and artificial teeth material and Digital Light Projection (3D printing) technology, were evaluated in the present study. The color of each denture was assessed with a spectrophotometer, before and after use, in CIE L*a*b* system. The before measurement was made on the positive control - PMMA with nanoTiO2 (PC), while the after was measured the color of the tooth after one year complete denture use. Negative control - PMMA without nanoTiO2 (NC) was also compared to PC and the following parameters were registered: Value (L), Chroma (C), Hue (H), redness/greenness (a) and yellowness/blueness (b). A color difference (DE) between 1.63 and 5.24 was measured for all patients, while for the NC DE was triple (17.65). The highest DE value for all denture wearers with TiO2 nanofiler inclusions was below the maximum acceptability threshold, in accordance to the patient�s subjective evaluation, who were unable to identify the color change.
In this paper are highlighted the stresses that appear in the peri-implantation area through the forces induced by the masticatory process. The analysis consists of computer modeling of the dental implant and simulation of the load with a distributed force. It is considered a variable direction loading related to the axial insertion of the dental implant, thus simulating an important masticatory process. This type of load reveals stresses developed in the periimplantary bone area, the risk areas where the stresses can cause the appearance of hard tissue damage near the implant and its failure. Increases in stresses up to 159% in the ruminant type of chewing compared with the cutter type are highlighted. An aggravating factor that can lead to implant failure is bruxism that tangentially stresses the implant leading to the concentration of forces at the abutment-implant junction. Conclusions regarding the decrease of stresses at bone-implant junction with up to 23% by a corresponding increase of the implant diameter by 25% are also issued.
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