Pierre Millet

Residual stress in hydroxyapatite coating: nonlinear analysis and high-energy synchrotron measurements

The thermal deposition of hydroxyapatite (HA) on titanium alloy substrate (Ti-6Al-4V) leads to a structure that has very good osseointegration properties. However, clinical failures have been occasionally reported at the interface between substrate and coating. Lifetime is the main parameter in such prostheses; therefore, in order to improve their quality, it is necessary to evaluate the level of stresses near the interface. The high-energy synchrotron radiation combines the advantages of a bulk analysis and reduced volume of the gauge. The objective of our study was to calculate the residual stress using a nonlinear finite-element model and to measure residual stress level near the interface, in the hydroxyapatite coating and in titanium alloy substrate with a nondestructive and high-resolution experiment. The high-energy synchrotron radiation of the BM16 beam-line at ESRF (Grenoble-France) was used with a resolution of down to 10 micrometers. The experimental measurements validate the results found by means of nonlinear finite-element analysis of the plasma spraying induced stress.

Texture Measurements of Hydroxyapatite Crystallites at Bone-Implant Interfaces in Sheep Tibia

The preferred orientation of hydroxyapatite Ca10(PO4)6(OH)2 (HAp) crystallites at the interface bone-implant in sheep tibia bones has been measured with the neutron 2-axis diffractometer D20 at the Institut Max von Laue-Paul Langevin, extracted 60 days after implantation. The implant has two faces, one coated and one non-coated with plasma-sprayed HAp (80 µm). We probed the samples with a spatial resolution of 0.5 mm started from the interface in order to inspect the reorganisation of the HAp crystallite distribution after implantation.

Nano-Hydroxyapatite Coatings on Titanium Substrates. Finite Element Analysis of Process and Experimental Plasma Thermal Sprayed Coatings

The aim of this study was to create a nano-structured coating using Plasma Thermal Spraying (PTS). This process consists in introducing pre-agglomerated nanosized particles in a high-temperature and high-velocity gas jet and projected them onto the substrate to form, layer by layer, a nanostructured coating. In order to retain nanometer grain sizes in the deposited coating through specific PTS technologies, a thermal field and velocity distribution in the plasma jet are analytically calculated. A finite element analysis is employed to calculate the thermal field evolution inside the agglomerated particles and the thermal induced internal stress distribution is determined. The parameters determined by the theoretical analysis are used for experimental coatings. The average crystallite size of nano-hydroxyapatite powder was 90nm. After deposit via Plasma Thermal Spraying (PTS) process and followed by a 2 hours heat treatment to reduce amorphous fraction, the experimental deposited coating shows that it retains the nanometer crystallite sizes. The substructure of nanocrystals was evaluated at about 120nm in size. Such a nanocoating may play the role of nucleation site to bone, allowing a faster stabilization of the implant.

Use of synchrotron radiation in the analysis of strains near the interface between a plasma-sprayed hydroxyapatite coating and a Ti-6Al-4V substrate

Abstract Plasma sprayed hydroxyapatite coatings on titanium alloy are often used in prosthetic implants. The metallic substrate gives the implant good mechanical strength which is combined with good biocompatibility and osteointegration of the ceramic coating. However there is sometimes a failure of the implant, and this failure is often located at the interface between the titanium alloy and the hydroxyapatite coating. Knowledge about the strains in the materials near the interface seems to be an important step in understanding why the failure occurs. Synchrotron radiation, using Beamline BM16 at the European Synchrotron Radiation Facility (Grenoble, France), has been used to measure local strains near the interface, down to 10 μm in resolution, between a plasma-sprayed hydroxyapatite coating and a titanium alloy substrate. The influence of sand blasting and shot peening on the strains from the surface to the depth of the titanium alloy before coating has been investigated, along with the strains around ...

The use of FDI criteria in clinical trials on direct dental restorations: A scoping review

OBJECTIVES A scoping review was conducted to explore the use of FDI criteria 10 years after their introduction. The first aim was to compare the amount of studies using the FDI and/or the modified USPHS criteria. The second aim was to analyse the use of the FDI criteria in clinical trials evaluating direct dental restorations. DATA Listing of studies using FDI and/or USPHS criteria per year since 2007. Clinical studies related to the assessment of direct restorations using FDI criteria. SOURCE Two systematic searches - regarding the use of FDI and modified USPHS criteria - were carried out on Medline/Pubmed in order to identify the studies published between 2007 and 2017. Authors of the included articles were contacted to clarify their choice of FDI criteria in their studies. ClinicalTrials.gov database was also queried for the on-going studies that use FDI and modified USPHS criteria. STUDY SELECTION In the first review, all the clinical trials (randomized/non-randomized, controlled, prospective/retrospective studies) that used FDI criteria to evaluate direct restorations on primary or permanent teeth were included. CONCLUSIONS 16.3% of the studies used FDI criteria. The percentage of studies using them increased from 4.5% in 2010 to 50.0% in 2016. In average, 8.5 FDI criteria were used. The most employed criteria were: marginal adaptation (96.7%), staining (90.0%), fracture of material and retention (90.0%), recurrence of caries/erosion/abfraction (90.0%), post-operative sensitivity/tooth vitality (86.7%) and surface luster (60.0%). In addition, among the 27 on-going studies from ClinicalTrials.gov database, 51.9% use FDI criteria (including 87.5% with an open recruitment status). CLINICAL SIGNIFICANCE FDI criteria were reported as practical (various and freely selectable), relevant (sensitive as well as appropriate to current restorative materials and clinical studies design), standardized (making comparisons between investigations easier). Investigators should go on using them for a better standardization of their clinical judgment, allowing comparisons with other studies.

One-step partial or complete caries removal and bonding with antibacterial or traditional self-etch adhesives: study protocol for a randomized controlled trial

BackgroundCurrent concepts in conservative dentistry advocate minimally invasive dentistry and pulp vitality preservation. Moreover, complete removal of carious dentin in deep carious lesions often leads to pulp exposure and root canal treatment, despite the absence of irreversible pulp inflammation. For years, partial caries removal has been performed on primary teeth, but little evidence supports its effectiveness for permanent teeth. Furthermore, the recent development of new antibacterial adhesive systems could be interesting in the treatment of such lesions. The objectives of this study are to compare the effectiveness of partial versus complete carious dentin removal in deep lesions (primary objective) and the use of an antibacterial versus a traditional two-step self-etch adhesive system (main secondary objective).Methods/DesignThe DEep CAries Treatment (DECAT) study protocol is a multicenter, randomized, controlled superiority trial comparing partial versus complete caries removal followed by adhesive restoration. The minimum sample size required is 464 patients. Two successive randomizations will be performed (allocation ratio 1:1): the first for the type of excavation (partial versus complete) and the second (if no root canal treatment is required) for the type of adhesive (antibacterial versus traditional). For the two objectives, the outcome is the success of the treatment after 1 year, measured according to a composite outcome of five FDI criteria: material fracture and retention, marginal adaptation, radiographic examination (including apical pathologies), postoperative sensitivity and tooth vitality, and carious lesion recurrence.DiscussionThe study will investigate the interest of a conservative approach for the management of deep carious lesions in terms of dentin excavation and bioactive adhesive systems. The results may help practitioners achieve the most efficient restorative procedure to maintain pulp vitality and increase the restoration longevity.Trial registrationClinicalTrials.gov Identifier NCT02286388. Registered in November 2014.

Residual stress and texture evaluation by diffraction techniques in nano-HA coated implants§

In order to reduce the delay for implant osseointegration, hydroxyapatite coatings sprayed on titanium substrate are proposed for commercial implants. Clinical failures of these coatings have been reported several months or years after the surgery due to resorption or mechanical failures. Our objectives were to improve the quality of the coating using a plasma thermal spraying process with nanosized powder as feedstock to generate partially nanostructured coatings. In order to be thermally sprayed, the individual nanoparticles are agglomerated into spherical micrometer-sized granules. The main goal of using nanostructured feedstock is to preserve the nanostructure of deposited HA in the morphology of the layers. The behaviour of agglomerated particles before the impact is of crucial importance, especially if they leave the plasma jet axis. The texture of bone crystallites is investigated after implantation near the interface. The preferred orientation is expected to change close to the interface due to re...

Influence of load on the arrangement of hydroxyapatite crystallites at the interface with implants in different animals

At the interface with an implant, bone tends to change its properties, affecting the acceptance of the implant. The preferred orientation of hydroxyapatite Ca10(PO4)6(OH)2 (HAp) crystallites at the bone–implant interface has been measured with the D20 neutron 2-axis diffractometer at the Institut Max von Laue-Paul Langevin, Grenoble. The implant has two faces, one coated with plasma-sprayed HAp.

Characterization of New Generations of Implants at the Interface with Bone by Synchrotron Radiation

The aim of this work was to study the implant-bone interface by synchrotron radiation in order to show the evolution of the crystallites of hydroxyapatite (Hap) reconstituted at the interface with the implant. The implant used an orthopaedic surgery is the Titanium alloy (Ti-6Al-4V), the implants are currently coated with (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. In this work, two implants have been used, the first one coated with HAp and the second uncoated. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the crytallinity index and texture of the new bone crystals reconstituted at the interface using synchrotron radiation on ID15 at ESRF in Grenoble, France.

Evaluation of Residual Stresses at the Interface with Implant by Synchrotron Radiation

The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the residuals stresses and texture of the new bone crystals reconstituted at the interface using synchrotron radiation on ID15 at ESRF in Grenoble, France.