The influence of orthodontic bracket base diameter and mesh size on bond strength.

Previous studies have shown that the size of the foil mesh and surface area of the bracket base correlated to bond strength to tooth enamel. The purpose of this study was to investigate the in vitro shear bond strength (SBS) of orthodontic brackets with 80 and 100 gauge mesh bases as well as mini and standard size bases. Eighty extracted human premolar teeth were randomly allocated into four groups of twenty teeth each. Premolar brackets of different mesh and bracket base area sizes were bonded to the enamel with a conventional 'two paste' orthodontic bonding agent. The SBS was determined and the bond failure sites were assessed using light-optical microscope and SEM. Bond failure occurred in all groups primarily at the bracket/adhesive interface. Mean values for SBS were 9.97 +/- 2.94 MPa and 10.72 +/- 2.54 MPa for 80 gauge mini and standard size respectively, and 10.45 +/- 3.27 MPa and 11.39 +/- 3.32 MPa for 100 gauge mini and standard size. A one-way ANOVA and an unpaired t-test revealed no significant difference in mean SBS (P > 0.05) between 80 and 100 gauge mini and standard size brackets, and no significant difference in mean SBS between brackets of the same surface area with a different gauge mesh size. The clinical relevance of this finding is that the clinician can select smaller brackets with no reduction in effectiveness of the treatment procedure.

Intrafibrillar mineral may be absent in dentinogenesis imperfecta type II (DI-II).

High-resolution synchrotron radiation computed tomography (SRCT) and small-angle x-ray scattering (SAXS) were performed on normal and dentinogenesis imperfecta type II (DI-II) teeth. The SRCT showed that the mineral concentration was 33% lower on average in the DI-II dentin with respect to normal dentin. The SAXS spectra from normal dentin exhibited low-angle diffraction peaks at harmonics of 67.6 nm, consistent with nucleation and growth of the apatite phase within gaps in the collagen fibrils (intrafibrillar mineralization). In contrast, the low-angle peaks were almost non-existent in the DI-II dentin. Crystallite thickness was independent of location in both DI-II and normal dentin, although the crystallites were significantly thicker in DI-II dentin (6.8 nm [SD = 0.5] vs. 5.1 nm [SD = 0.6]). The shape factor of the crystallites, as determined by SAXS, showed a continuous progression in normal dentin from roughly one-dimensional (needle-like) near the pulp to two-dimensional (plate-like) near the dentin-enamel junction. The crystallites in DI-II dentin, on the other hand, remained needle-like throughout. The above observations are consistent with an absence of intrafibrillar mineral in DI-II dentin.

Evaluation of impression accuracy for osseointegrated implant supported superstructures.

STATEMENT OF PROBLEM: An often-debated issue still exists concerning implant impression techniques, whether to splint impression copings. Different configurations are available for these copings for a variety of manufacturers' implant systems. PURPOSE: This study evaluated and compared 4 impression techniques in terms of their dimensional accuracy to reproduce implant positions on working casts. MATERIAL AND METHODS: A master model was designed to simulate a clinical situation. Impressions were made using 4 techniques: (1) tapered impression copings not splinted; (2) squared impression copings not splinted; (3) squared impression copings splinted with autopolymerizing acrylic resin; and (4) squared impression copings with a lateral extension on one side not splinted. Reference points machined onto the master model and onto special healing abutments were compared after abutments were transferred to casts using the 4 techniques. Measurements were made using a Reflex microscope, capable of recording in the x-, y-, and z-dimensions. RESULTS: The dimensional accuracy was high and, although statistically significant (P =.022; power > 80%), a maximum distortion difference of only 0.31% was registered. CONCLUSION: The dimensional accuracy of all the techniques was exceptional and the observed differences can be regarded as clinically negligible.

[The effect of bonded and nonbonded posts on the fracture resistance of dentin]. / Die effek van gebonde en ongebonde stiwwe op die fraktuurweerstand van dentien.

This in vitro study determined the effect of bonded and non-bonded cast, serrated, tin plated, parallel gold posts on the fracture resistance of surrounding dentine walls. Specimens were divided into two groups. One group's posts were luted with zinc phosphate cement and the other group's posts were tin-plated and adhesively bonded with an adhesive resin cement. Three different dentine wall thicknesses, namely 0.5 mm, 0.75 mm and 1.0 mm were prepared, subdividing the specimens of each main group into three subgroups. Specimens were subjected to a 50 degrees oblique force. The force required to fracture the dentinal walls was registered. There was no statistically significant differences in the fracture resistance of dentine with the two different cements or of the different dentine wall thicknesses.

Scanning electron microscopy evaluation of the interfacial fit of interchanged components of four dental implant systems.

The introduction of the original Swedish implant system (Brånemark) was followed by several alternative implant systems with implants and components that closely resembled the original design and treatment protocol. Some of these alternative systems may be interchangeable. Manufacturing variations can result in as much as 0.1 mm of space between the component parts. The implant/abutment interface fit was evaluated by scanning electron micrography for each of four implant systems, as well as interchanged components between the various systems. Results showed that certain implant system abutments are interchangeable, and that the accuracy of fit meets with or exceeds the criteria set by the original Swedish system.

The effect of airborne particle abrasion on the dentin smear layer and dentin: an in vitro investigation.

This study investigated the effect of airborne particle abrasion on the exposed dentin surfaces of 40 extracted teeth. A Siroflow abrasion unit was used to treat four groups of ten specimens that were subjected to 5, 10, 20, and 40 seconds of abrasion respectively. Statistical analysis (Spearman Rank Order) showed a significant difference between all groups (P < .05) but not within groups (P > .05). Scanning electron micrographs showed smear layer removal as an immediate effect of air polishing. Application times of longer than 5 seconds showed obstruction of dentinal tubule openings, possibly a result of abrasive powder residue. It was concluded that airborne particle abrasion removes the smear layer, and the amount of dentin removed corresponded to the time of application.

Cryo-SEM evaluation of desiccation-sensitive dental specimens.

As a result of desiccation, conventionally prepared fresh dental specimens, examined with the scanning electron microscope (SEM), exhibit obvious artifactual effects that may include one or more of the following: distortion, fracture, separation of structures, and chemical interactions. Cryo-SEM techniques reduce or eliminate these artifacts and present reliable images while requiring less time to perform than do conventional methods.