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At least 235 records · Page 13Linked to original sources
PubMed1990

Clinical considerations of microleakage.

Most dental materials permit the microleakage of bacteria and bacterial products from oral fluids to reach dentin. Thus, an understanding of the clinical consequences of microleakage demands that we analyze the permeability characteristics of dentin. The more dentin surface that is exposed during tooth preparation, the greater the potential for microleakage. Thicker dentin is less permeable than thin dentin. Dentin over pulp horns is more permeable than central dentin. Similarly, the dentin making up axial walls is more permeable than dentin forming the pulpal floor of cavities. Coronal dentin is much more permeable than root dentin. In addition to the number of tubules per unit area, tubule diameter, and the location of the dentin in a tooth, another extremely important variable is the presence or absence of a smear layer. When smear layers are created, grinding debris are forced into each tubule to form a smear plug. Smear plugs are usually 1- to 2-microns long but may be 10-microns long. They are much longer than the smear layer thickness and they reduce dentin permeability more than the overlying smear layer. Smear layers constitute a natural cavity liner that reduces the permeability of dentin far more than any cavity varnish. However, its presence limits the strength of dentin bonding agents because of the relatively low cohesive forces holding the smear layer together and to dentin. If it is removed, the bond strengths of dentin adhesive resins increases, but removal also increases the potential liability for pulpal inflammation if the bond is not uniformly perfect.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Cements↗
PubMedDate not supplied

NaOCl and EDTA irrigating solutions for endodontics: SEM findings.

Premolars roots of humans were manually instrumented with K-type files and irrigated with different solutions to evaluate the rate of cleaning of endodontic surface. Root canals irrigated with 0.9% saline solution or H2O2 (10 volumes) showed the presence of predentin and amorphous smear layer. Thick smear layer was always present on endodontic walls rinsed with 5% solution of NaOCl. Specimens treated with 0.2% solution of EDTA showed partially clean dentinal tubules orifices and remnants of a thin smear layer. Occasional uninstrumented areas of the same roots presented smear layer remnants and predentin with calcified bacteria. The root canals irrigated with NaOCl and EDTA solutions alternated after each instrument showed at the dentin surface thick smear layer: only few dentinal tubules orifices were visible. Endodontic surface of root canals irrigated with NaOCl during instrumentation and finally rinsed with EDTA solutions showed the most homogeneous ultrastructural pictures: partially clean dentinal orifices were detectable in the whole canals.

Bicuspid↗
PubMed1997

[Treatment of dentin sensitivity with stannous fluoride gel. Electron microscopic study and evaluation of dentin permeability].

Dentine hypersensitivity still represent a major clinical problem only partially solved. The presence of exposed opened dentinal tubules has been demonstrated increase the dentine permeability and it is the responsible for pain and sensitivity. Stannous fluoride solution has been recently proposed to reduce dentine hypersensitivity. The aim of the present study was to evaluate the dentinal permeability of a new stannous fluoride gel proposed for the therapy of dentine hypersensitivity. Human extracted teeth have been used and mounted and connected with a hydraulic pressure apparatus working at 1 psi (70 cm of water pressure). It was calculated the permeability of untreated smear layer, treated smear layer (after gel application) and after acidic treatment. It was observed that gel treatment was able to reduce dentine permeability. Scanning electron microscopy demonstrated the presence of a homogeneous smear layer after treatment with gel. This in vitro study confirms that stannous fluoride treatment has the capacity to modify dentine permeability of sensitive dentine.

Dentin↗
PubMed1992

Origination and progression of microleakage in a restoration with a smear layer-mediated dentinal bonding agent.

Several recently marketed dentinal bonding agents modify, but do not remove, the smear layer. Some controversy exists as to whether the smear layer should be left in place or completely removed from preparations to be restored with composite resin systems. This study utilized scanning electron microscopy with energy dispersive x-ray analysis to evaluate the pathway of microleakage in a composite resin restorative material that utilizes a smear layer-mediated dentinal bonding agent. Microleakage occurred at the smear layer-dentin interface and progressed into both the smear layer and dentinal tubules, suggesting that the smear layer acts as a pathway for microleakage.

Composite Resins↗
PubMed2002

HPV DNA detection by in situ hybridization with catalyzed signal amplification on thin-layer cervical smears.

Thin layer-based technology in cervical cancer screening now allows both Papanicolaou staining and HPV testing on the same sample. Here, we show that in situ hybridization with catalyzed reporter deposition is a powerful HPV detection method when applied on thin-layer cervical smears, allowing distinction between two staining patterns suggestive of two different physical states of HPV DNA, where diffuse signals are suggestive of episomes and punctate signals are suggestive of viral DNA integration.

DNA, Viral↗
PubMed1991

Scanning electron microscopic and energy dispersive x-ray evaluation of two smear layer-mediated dentinal bonding agents.

Teeth treated with smear layer-mediated dentinal bonding agents and restored with composite resin were examined at the dentin-restoration interface by means of scanning electron microscopy used in conjunction with energy dispersive x-ray analysis. Results indicated that these dentinal bonding agents actually bonded to the smear layer, and samples demonstrated delamination of the smear layer from underlying dentin following thermocycling. This finding suggests that the stresses developed within the composite resin exceeded the adhesive strength of the smear layer to dentin. Thus, the bond strength for dentinal bonding agents that require the presence of the smear layer cannot exceed the adhesion of the smear layer to dentin.

Acrylic Resins↗
PubMedDate not supplied

[An ultrastructural analysis of dentin treated with chemical agents].

Dental last generation bonding systems require the total removal of smear layer and smear plug by chemical solutions. Intermediate fluid resin can penetrate the dentinal tubes obtaining a better anchorage to the dental structures. The department of Operative dentistry of the University of Rome "La Sapienza" has carried research observing by means of the SEM the ultrastructural aspect of smear layer and the effect of dentin treatment with five different chemical agents.

Acrylic Resins↗
PubMed1991

Effect of endodontic procedures on root dentin permeability.

The purpose of this study was to quantitate the sequential effects of endodontic procedures on the permeability of human root dentin in vitro. Forty single-rooted teeth were used. Both the crown and the apical 2 mm of the root were removed. The hydraulic conductance of the root before and after various endodontic procedures was measured using a fluid filtration method. Measurements were also made of dentin thickness, intracanal diameter changes, and changes in intracanal surface area. The results showed that instrumentation by K files alone or in combination with Gates Glidden drills did not alter radicular dentin permeability when the cementum remained intact. After removing the cementum, the creation of a smear layer and smear plugs on the canal surface tended to offset the expected increase in dentin permeability created by increasing the intracanal surface area and decreasing root dentin thickness. EDTA treatment inside the instrumented canal to remove the smear layer did not increase permeability significantly. The use of K files followed by Gates Glidden drills tended to remove more cervical dentin, increased the intracanal surface area, and increased the hydraulic conductance of root dentin more than the use of K files alone.

Dental Cementum↗
PubMed2001

Microtensile bond strength of two single-step adhesive systems to bur-prepared dentin.

PURPOSE: To compare the microtensile bond strength (MTBS) of two single-step adhesive systems to two types of bur-prepared dentin. MATERIALS AND METHODS: Using either of two adhesives, the experimental MZ-2000 (MZ) and the commercial One-Up Bond F (OUB), resin composite was bonded to flat buccal and root dentin surfaces of eight extracted human premolars. These surfaces were produced by grinding with either regular-grit or superfine-grit diamond burs in a high-speed handpiece. After storage overnight in 37 degrees C water, the bonded specimens were sectioned into ten slices approximately 0.7 mm thick, perpendicular to the bonded surface. They were then subjected to microtensile testing. The surfaces of the fractured specimens were observed both visually and microscopically to determine the failure mode. In addition, to observe the effect of conditioning, the two types of bur-ground dentin surfaces were conditioned with the adhesives, rinsed with acetone, and observed under SEM. RESULTS: When MZ was bonded to dentin prepared with a regular-grit diamond bur, MTBS was the lowest and failures occurred adhesively at the interface, whereas other groups revealed primarily mixed failures. MZ-conditioned dentin surfaces ground with a regular-grit diamond bur were covered with a residual smear layer. However, the smear layers on the surface of MZ-conditioned dentin ground with a superfine-grit diamond bur and on OUB-conditioned dentin prepared either with a regular-grit or superfine-grit diamond bur were mostly or partially dissolved. CONCLUSION: Some of the single-step adhesive systems may produce low bond strengths to smear layers created by regular-grit diamond burs.

Acetone↗
PubMed1993

Bonding durability of photocured phenyl-P in TEGDMA to smear layer-retained bovine dentin.

The long-term durability of a photocured resin bond to ground bovine dentin with its smear layer retained was investigated. The bonding resin that was employed was composed of 5.0 wt% 2-(methacryloxy)ethyl phenyl hydrogen phosphate (phenyl-P) as a diffusion-promoting monomer, 0.5 wt% camphorquinone as a photosensitizer, and 0.5 wt% N-phenylglycine as a reducing agent in triethyleneglycol dimethacrylate. Following polymerization of the bonding resin, a composite resin was placed and photocured for 60 seconds. Prepared specimens were stored in 37 degrees C water for 1 day, 6 months, and 1 year. Measured tensile bond strengths were 6.7 MPa after 1 day of storage, 4.1 MPa after 6 months of storage, and 2.8 mPa after 1 year of storage. Examinations of the interfaces after fracture under tensile loading suggested that long-term water-immersion weakened the bonds between the photocured adhesive resin and the smear layer-retained dentin because there was insufficient diffusion of the adhesive resin through the retained smear layer.

Animals↗