In silico evaluation of the stress fields on the cortical bone surrounding dental implants: Comparing root-analogue and screwed implants.

Tooth loss is a problem that affects both old and young people. It may be caused by several conditions, such as poor oral hygiene, lifestyle choices or even diseases like periodontal disease, tooth grinding or diabetes. Nowadays, replacing a missing tooth by an implant is a very common process. However, many limitations regarding the actual strategies can be enumerated. Conventional screwed implants tend to induce high levels of stress in the peri-implant bone area, leading to bone loss, bacterial bio-film formation, and subsequent implant failure. In this sense, root-analogue dental implants are becoming promising solutions for immediate implantation due to their minimally invasive nature, improved bone stress distribution and because they do not require bone drilling, sinus lift, bone augmentation nor other traumatic procedures. The aim of this study was to analyse and compare, by means of FEA, the stress fields of peri-implant bone around root-analogue and screwed conventional zirconia implants. For that purpose, one root-analogue implant, one root-analogue implant with flaps, two conventional implants (with different threads) and a replica of a natural tooth were modelled. COMSOL was used to perform the analysis and implants were subjected to two simultaneous loads: 100 N axially and 100 N oblique (45°). RESULTS: revealed that root-analogue implants, namely with flaps, should be considered as promising alternatives for dental implant solutions since they promote a better stress distribution in the cortical bone when compared with conventional implants.

Sliding behavior of zirconia porous implant surfaces against bone.

Different zirconia porous layers were produced on zirconia dense zirconia substrates by slip casting using powder with different mean sizes: 40 µm (Z40), 70 µm (Z70), and 100 µm (Z100). The dynamic and static coefficients of friction against bovine femoral bone, mimicking the implantation process, were conducted using a ball-on-flat reciprocating sliding tribometer under 3 N of normal load. Additionally, the porous layers were assessed with regard to their low temperature degradation (aging). Results revealed that the porous layers were able to keep their integrity during the sliding testes against bone, with no zirconia particles being transferred to the bone. Results did not show significant differences (p > 0.05) in kinetic and static COF values for Z40, Z70, Z100, and GRAD specimens, ranging from 0.53 to 0.77 and 0.65 to 0.90, respectively. The aging tests revealed that all surfaces were prone to low temperature degradation (~49% of monoclinic content after 18 h). In conclusion, the cohesive integrity of the layers and relatively high COF observed reveled that zirconia porous layers may be considered for replacing the current implant surfaces, and are expected to improve their primary stability. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1113-1121, 2019.

Effect of HAp and ß-TCP incorporation on the tribological response of Ti6Al4V biocomposites for implant parts.

Titanium and its alloys have been widely used in many engineering areas due to their properties. Despite having a high implant-tissue osseointegration time, Ti6Al4V has been extensively used in prosthesis and articular implants. To promote a faster bone ingrowth and consequently reduce the implant fixation time, the addition of a bioactive phase to form a biocomposite seems to be an excellent solution. Because of their bioactivity and similarity in composition with the human bone, HAp and ß-TCP are two of the most widely used calcium phosphates in biomedical applications. To guarantee a strong adhesion of the previous bioactive materials in the implants surface, samples of Ti6Al4V, Ti6Al4V+HAp (10 vol %) and Ti6Al4V+ß-TCP (10 vol %) TCP were processed by the hot pressing technique. Tribological tests against Al2 O3, lubricated in PBS at 37°C were carried out on a ball-on-flat reciprocating sliding geometry. Loads in the range of 3 N to 30 N were applied and their effect on the friction behavior and wear resistance of the tested materials was evaluated. Values of the coefficient of friction as well as the wear rate tend to increase with the addition of a bioactive phase to the Ti alloy. Micrographs of the worn surfaces showed that abrasion and plastic deformation are the prevailing wear mechanisms in the studied tribosystems. For biocomposites, particularly in the case of Ti6Al4V+HAp, pull-out of bioactive particle clusters has a determinant role on the tribological response, increasing both the friction coefficient and the specific wear rate. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1010-1016, 2018.

Bioactive materials driven primary stability on titanium biocomposites.

The Ti6Al4V alloy constitutes an alternative choice to the most common metal-polymer solutions for total hip arthroplasty (THA) due to good biocompatibility, optimal mechanical properties and high load bearing capacity. However, as Ti6Al4V is not bioactive in its conventional form, hydroxyapatite (HAp) and tricalcium phosphate (TCP) have been widely used as coatings of metal prostheses due to their osteogenic properties and ability to form strong bonds with bone tissue. A promising approach consists in creating a bioactive surface metal matrix composite Ti6Al4V+ß-TCP or Ti6Al4V+HAp, obtained by hot pressing (HP) of powders. In this work, the tribological performance of Ti6Al4V+ß-TCP and Ti6Al4V+HAp composites is studied to evaluate the frictional response and surface damage representative of prosthesis implantation, key factors in bone fixation. Biocomposites with 10vol% ß-TCP and 10vol% Hap, as well as base titanium alloy, were prepared by HP with two surface finishing conditions - polished (Ra=0.3-0.5µm) and sandblasted (Ra=2.1-2.5µm) - for tribological testing against bovine cortical bone tissue. The static friction increases with surface roughness (from 0.20 to 0.60), whereas the kinetic regime follows an inverse trend for the biocomposites. In contrast with current knowledge, this study shows that an implant design solution based on Ti6Al4V+ß-TCP or Ti6Al4V+HAp biocomposites with polished surfaces results in an improved primary stability of implants, when compared to traditional rough surfaces. Moreover, it is also expected that the secondary stability will improve due to the adhesion between bone and HAp/ß-TCP, increasing the overall stability of the implant.

Leydig cell number and sperm production decrease induced by chronic ametryn exposure: a negative impact on animal reproductive health.

Ametryn is an herbicide used to control broadleaf and grass weeds and its acute and chronic toxicity is expected to be low. Since toxicological data on ametryn is scarce, the aim of this study was to evaluate rat reproductive toxicity. Thirty-six adult male Wistar rats (90 days) were divided into three groups: Co (control) and T1 and T2 exposed to 15 and 30 mg/kg/day of ametryn, respectively, for 56 days. Testicular analysis demonstrated that ametryn decreased sperm number per testis, daily sperm production, and Leydig cell number in both treated groups, although little perceptible morphological change has been observed in seminiferous tubule structure. Lipid peroxidation was higher in group T2, catalase activity decreased in T1 group, superoxide dismutase activity diminished, and a smaller number of sulphydryl groups of total proteins were verified in both exposed groups, suggesting oxidative stress. These results showed negative ametryn influence on the testes and can compromise animal reproductive performance and survival.