Biomedical subjects

B Levallois

Publications and source records attributed to B Levallois.

5 recordsLinked to original sources

PubMed1998

In vitro fluoride release from restorative materials in water versus artificial saliva medium (SAGF).

OBJECTIVES: An extensive number of investigations have focused in recent years on the process of fluoride release by glass-ionomer cements. In order to compare the fluoride release of two recent resin-modified glass-ionomer cements (RMGICs) and one compomer, we investigated the initial and subsequent fluoride release in distilled water and in a mineral medium with composition similar to saliva (SAGF), as well as the renewal effect of the media on the release. METHOD: A preliminary thermodynamic study defined conditions under which the measurements by fluoride-selective electrode potentiometry were not affected by the presence of Ca2+ ions in SAGF. Disk-shaped samples (5 mm x 3 mm) for each material were placed in 5 ml of distilled water (n = 12) or 5 ml of SAGF (n = 12) and fluoride released was measured after 1, 2 and 7 days. For the investigation of medium renewal effect, RMGIC sample were dipped into distilled water for 5 days. Subsequently 12 samples of each material were placed for 7 days into water or SAGF, with or without daily renewal of the medium before fluoride-release measurements. The elements present on the surface of the RMGICs were analyzed by scanning electron microscopy. RESULTS: RMGICs released significantly more fluoride in water than in artificial saliva. The presence of CaF2 at the interface accounts for this phenomenon. The thickness of the CaF2 layer depends on the speed of its initial formation and renewal of the testing medium. A pattern of CaF2 formation was proposed.

Calcium Fluoride↗

PubMed1996

Bacterial leakage in endodontics: an improved method for quantification.

A new method for studying leakage of root fillings using the bacterium Pseudomonas fluorescens ATCC 13525 is described. The presence of the microorganism is detected by fluorimetry and can thus be used to measure the depth of penetration from the root apex toward the crown of the tooth. This system, applied to a number of methods of root canal filling, showed that procedures involving compaction of the gutta-percha gave a more effective seal than the use of a paste sealer with uncondensed gutta-percha. There was no statistically significant difference between the leakage results from the lateral, vertical, and thermomechanical condensed techniques.

Dental Leakage↗

PubMed1995

Relationship between file size and stiffness of nickel titanium instruments.

The purpose of this study was to evaluate the relationship existing between file size and stiffness for 3 endodontic files made of nickel titanium. Three groups of instruments with different cross-sections were tested: a triangular cross-section, a square cross-section and a modified triangular cross-section. The instruments were tested from size 15 to size 40 or 60 according to ANSI/ADA specification no. 28 for binding moment evaluation. There was a statistically significant difference between the 3 groups: the square cross-section K files presented a larger bending moment than the triangular cross-section K files, which presented a larger bending moment than the modified cross-section K files. Like the stainless steel instruments, there was an exponential relationship between file size and bending moment for triangular and square cross-section K files, but a linear relationship between file size and bending moment for the files with a modified triangular cross-section.

Analysis of Variance↗

PubMed1990

[Evaluation of four methods of preparing curved canals].

The authors used the protocol provided by Bramante, Berbert and Borges, to evaluate the respect of the canal position during the curved canal preparation. They compared four preparation types, two hand preparation and two engine driven ones: the step back technique, the anticurvature filing technique, the contact shaping technique, the canal finder. A statistic analysis of the results shows that the preparation is done to the detriment of the furcation wall and that only the step back technique is not suitable for the curved canal preparation.

Dental Pulp Cavity↗

PubMed1989

["Endo-prosthetic" preparation of curved roots].

During the tooth preparation for root posts, all must be attempted to avoid weakening of the root. This "must" is rather easy for straight roots, but the same is not true of curved roots. The authors have used the method described by BRAMANTE et al. to study the effects of various techniques of instrumental sequences of endodontic preparation, and of two instrumental sequences of root post preparation. From this studies, it results that: --the respect of the canal path during the endodontic phase conditions the respect of the internal wall of the curvature, during drilling. --among the four endodontic techniques studied: MM 3000, Step-Back, Anti Curvature Filling and Canal Finder System, the last two seem to allow more respect of the canal path. --the instrumental sequence using Largo drills to prepare a canal, presents two types of drawbacks: * Excessive abrasion of the convex (internal) wall of the canal system. It seems that the blunt point rests against the concave portion of the canal and pushes the drill toward the internal wall, therefore weakening it. * Inadequate match between the size of the drill and that of the prepared canal. --the Parapost drills, on the contrary, respect the endodontic path, and may even be used beyond the curvature (2 mm). Besides, the diameter of the prepared canal is similar to that of the instrument used. These two factors permit to obtain a better retention of the post as well as a lesser weakening of the root.

Dental Pulp Cavity↗