Chappell Rp

Microtensile testing of dentin adhesives

OBJECTIVES This study was conducted in order to compare the microtensile and shear bond strengths of five commercial dentin adhesive systems. Scotchbond Multipurpose with maleic acid (SM), Scotchbond Multipurpose with phosphoric acid (SP), Scotchbond Multipurpose Plus (SBP), Clearfil Liner Bond System (CL), and Prime and Bond (PB) were tested. METHODS Thirty extracted unerupted third molars, in groups of six teeth per adhesive system, were prepared for microtensile testing. The specimens were tested following a 24 h incubation at 37 degrees C in normal saline. Shear bond testing was performed on 35 additional teeth, using seven teeth per adhesive system. After testing, the fracture sites were observed using light microscopy and a scanning electron microscope to determine the type of failure involved. RESULTS The microtensile test results (mean +/- SD) were SM, 24.6 +/- 7.2 MPa; SP, 28.8 +/- 11.8 MPa; SBP, 22.7 +/- 6.5 MPa; PB, 25.5 +/- 9.4 MPa; and CL, 36.8 +/- 10.0 MPa. A Bonferroni post-hoc test showed significantly (p < 0.05) greater strength for CL compared to SM, SP, SBP, and PB. The shear bond strength test results were SM, 19.4 +/- 4.4 MPa; SP, 24.5 +/- 8.4 MPa; SBP, 15.3 +/- 4.9 MPa; PB, 23.2 +/- 7.1 MPa; and CL, 24.8 +/- 3.5 MPa. No statistically significant differences were found among the shear bond strength test results. The shear bond test produced significantly more failures within dentin and composite than the microtensile method. SIGNIFICANCE It is concluded that the microtensile test produced a more definitive assessment of adhesive bond strength than the shear bond test. Microtensile testing showed CL to be significantly stronger than SM, SP, SBP, and PB (p < 0.05).

Dentinal tubule anastomosis: A potential factor in adhesive bonding?

This study investigated adhesive tag formation within dentinal tubules and the anastomosing of lateral canals observable with scanning electron microscopy. This mechanism of micromechanical bonding had not been studied previously. The following brands of adhesives were applied to the prepared dentin surface of unerupted human third molars: Scotchbond Multipurpose, C&B Metabond, All-Bond 2, both etched and unetched, Tenure Solution, and XR-Bond. The experimental specimens were decalcified and prepared for SEM examination. Many tubule resin tags with lateral branching were observed. The resin branches were the result of primer, adhesive, or both entering lateral canals and communicating with adjacent tubules. The polymerization of adhesive in lateral canals was more prevalent with Scotchbond Multipurpose, C & B Metabond, and etched All-Bond 2 adhesives. The network of interconnected adhesive tags formed with these materials may be fundamental to the development of a stronger dentin/resin bond.

Properties of expanding SOC/epoxy copolymers for dental use in dental composites

The objective of this work was to develop copolymers of alicyclic spiroorthocarbonates (SOCs) and epoxies that would yield hard non-shrinking matrix resins suitable for formulating dental composites. Several reactant ratio combinations of a four-component SOC/epoxy comonomer system were developed that demonstrated a copolymer expansion of between 0.1 and 0.8% on polymerization. The physical properties of tensile strength (29-48 MPa), water solubility of less than 5 microgram/mm(3), and water sorption of less than 50 microgram/mm(3) for the copolymer containing 5% SOC suggest that these materials have potential as matrix resins for dental composites.

Shear strength of ceramic brackets bonded to porcelain

The purpose of this study was to compare the bond strengths of three different adhesive systems when used alone and combined with a porcelain priming agent to bond ceramic brackets to porcelain surfaces. Sixty porcelain specimens were randomly assigned to the six different treatment groups. Half were bonded with the porcelain priming agent and one of the adhesive systems and the other half with one of the adhesive systems alone. The shear bond strengths of all specimens were tested, with an Instron testing machine, 10 minutes after being bonded. The surface of the porcelain and the bracket base were examined, with scanning electron microscopy (SEM) and qualitative energy dispersive x-ray analysis (EDS), to determine the bond failure patterns and to check the porcelain surface for the presence of cracks and fractures. There was a statistically significant difference within each adhesive between those samples with the priming agent and those without the priming agent. Differences between the three adhesives were not statistically significant (p≤0.05).

Scanning Transmission Electron Microscopy/Energy-dispersive Spectroscopy Analysis of the Dentin Adhesive Interface Using a Labeled 2-Hydroxyethylmethacrylate Analogue:

In an attempt to compare the morphology of the dentin adhesive interface and the wetting and penetration of the adhesive in relation to the dentin surface, we studied four dentin adhesive systems using scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). 2-Hydroxyethylmethacrylate (HEMA), a monomer common to many commercial dentin adhesive systems, was altered to produce a thiolated analogue (HETMA). Sulfur, traceable by EDS and STEM, was substituted for the oxygen atom in the backbone of the HEMA molecule. The resulting analogue, with solubility parameters and other wetting and physical properties very similar to those of HEMA, was applied to four sets of tooth specimens, each pre-treated with a different primer or etchant. Three separate pre-treatments-nitric acid, maleic acid, and citric acid/ferric chloride—created a demineralized zone approximately 1 to 3 μm thick at the dentin surface. The HETMA was found to permeate freely into this zone when either of the latter two pre-treatments was used. However, the band of dentin that was demineralized by the nitric acid pre-treatment appeared impermeable to the HETMA. The fourth pre-treatment, an alcohol-based solution including the phosphorus acid ester PENTA and HEMA, modified the smear layer of the tooth slightly and did not appear to demineralize the dentin. HETMA applied to the specimens pre-treated with PENTA and HEMA was clearly in intimate contact with the dentin or modified smear layer; however, it did not penetrate or diffuse into these areas. It did flow into the dentinal tubules, as was also evident with each of the other systems. It was concluded that the acid pre-treatment of the dentin greatly influenced the wetting behavior of the dentin adhesive and thus could substantially affect the resultant bond strength of the dentin adhesive systems.

Comparison of the physical properties of two types of polydimethyl siloxane for fabrication of facial prostheses

The in vitro physical properties of two types of polydimethyl siloxane, MDX 4-4210 and a new material A-2186, were compared. The properties that were investigated in this study were tensile strength, elongation, tear strength, and surface hardness. The properties tested were selected because of their clinical significance for fabricating a facial prosthesis. According to the results obtained in this investigation, the new material, A-2186, had greater tear resistance, tensile strength, and a larger percentage of elongation. A-2186 material, also proved to be softer at the surface than the MDX 4-4210. This combination of physical properties makes this material, A-2186, a better choice than the traditional MDX 4-4210 for the fabrication of facial prostheses.

Comparison of two-surface and multiple-surface scoring methodologies for in vitro microleakage studies.

Investigators differ on the use of a two-surface or multiple-surface scoring methodology in sectional microleakage studies. This study compared microleakage scores using both two-surface and multiple-surface scoring methods for two preparation types and two different dentin bonding agents. Twenty freshly extracted molars each received one box-shaped and one V-shaped restoration on the mesial or distal surface. Each restoration was cut occlusogingivally into four sections, yielding eight surfaces for scoring. Surfaces were marked to identify central (I), lateral (II), and end (III) locations, then scored by two calibrated raters. The Wilcoxon Matched-Pairs Signed-Rank Test showed a statistically significant difference (p less than or equal to 0.05) in median microleakage scores obtained by an end two- surface and multiple-surface evaluation for V-shaped preparations restored with Scotchbond 2, P-50. No other statistically significant comparisons were detected. Results suggest that microleakage may be more extreme at end surfaces and that these end surfaces should be scored so that an accurate microleakage value could be assigned to composite restorations.