The Retentive Strength of Zirconium Oxide Crowns Cemented by Self-Adhesive Resin Cements before and after 6 Months of Aging.

The aim of this study was to evaluate the retentive strength of zirconium oxide (yttria-stabilized tetragonal zirconia polycrystals (Y-TZP)) crown-copings treated by combined mechanical and chemical treatments and cemented by four types of self-adhesive resin cements (SARCs) to human prepared teeth, before and after six months of aging in water and thermocycling. A total of 120 molar teeth were mounted, prepared using a standardized protocol and digitally scanned, and Y-TZP copings were produced. Teeth were randomly assigned to four SARC groups. Prior to cementation, the intaglio surfaces of all crowns were sandblasted and then coated with Z-Prime™ Plus (Bisco Dental, Schaumburg, IL, USA). Post cementation, each cement group was subdivided into aged and non-aged groups. After aging, the cemented assemblies were tested for retentive strength using a universal testing machine. Failure analysis was conducted by inspecting all matched debonded surfaces of the teeth and crowns at 3× magnification. Aging treatment did not affect the retentive strength of the Y-TZP crown-copings (p = 0.918). The interaction between cement and aging was statistically significant (p = 0.024). No significant differences in the retentive strengths between the different SARCs were observed pre-aging (p = 0.776), whereas post-aging, Panavia SA (PAN; Kuraray Dental Co Ltd., Osaka, Japan) showed significantly higher strength than RelyX U-200 (RU200; 3M ESPE, Seefeld, Germany). The predominant failure mode was adhesive between the cement and dentin, followed by mixed mode failure.

Characterization of coaggregation of Fusobacterium nucleatum PK1594 with six Porphyromonas gingivalis strains.

Coaggregation is a key mechanism in biofilm formation. The aim of this study was to characterize the coaggregation of Fusobacterium nucleatum PK1594 with six Porphyromonas gingivalis strains in terms of kinetics and sugars inhibition. This coaggregation was quantitatively characterized by using a kinetic coaggregation assay. Sugar inhibition profiles were also quantitatively defined. Four types of interactions among these coaggregation partners were found: (1) fast coaggregation that was substantially inhibited by galactose, lactose, and fucose (strain PK1924); (2) fast coaggregation that was not inhibited by any of the sugars tested (strain 274); (3) slow coaggregation that was either substantially or partially inhibited by the sugars mentioned (strains HG405 and W50, respectively); and (4) strains that did not coaggregate with the fusobacteria (ATCC33277 and A7436). These results suggest that adhesin(s) other than the well-known galactose-mediated ones may be involved in coaggregation between F. nucleatum PK1594 and P. gingivalis strains.

Enhanced attachment of Porphyromonas gingivalis to human fibroblasts mediated by Fusobacterium nucleatum.

Fusobacterium nucleatum and Porphyromonas gingivalis are often co-isolated from endodontic infection sites. The present study tested the hypothesis that adhesin-mediated reactions might contribute to this phenomenon. F. nucleaum PK1594 and P. gingivalis PK1924 were selectively labeled with fluorochromes and allowed to adhere to human fibroblasts, either each strain alone or sequentially. The number of bacteria of each type adhering to individual fibroblasts was determined. Sugar inhibition profile of this adherence was explored. Attachment of P. gingivalis to human fibroblasts increased by nearly 10-fold when F. nucleatum was present (P < .001). Galactose, lactose, and fucose inhibited this enhanced attachment (P < .001), as well as that of F. nucleatum alone (P < .001). The results suggest that F. nucleatum might be a primary colonizer of the host tissues and serve as mediator for enhanced attachment of P. gingivalis to the host cells. This might explain in part the common co-occurrence of F. nucleatum and P. gingivalis in endodontic mixed infections.

The clinical effect of amorphous calcium phosphate (ACP) on root surface hypersensitivity.

Dentin hypersensitivity is a transient condition that often resolves with the natural sclerotic obturation of dentin tubules. A method of rapidly forming calcium phosphate compounds within these tubules can mimic sclerosis and lead to rapid reduction in hypersensitivity. Amorphous calcium phosphates (ACP) can be formed in situ by the sequential application of calcium and phosphate solutions. In this clinical study, 30 patients with reported dentin hypersensitivity were randomly assigned to parallel treatment or placebo groups. In the experimental treatment group, ACP was formed by topical application of a 1.5 mol/L aqueous solution of CaCl2 followed by topical application of 1.0 mol/L aqueous K3PO4. The placebo group was treated with a topical application of 1.0 mol/L aqueous solution of KCl followed by topical application of distilled water. Treatments were repeated at the 7-day and 28-day recall appointments. Response to air and tactile stimuli were measured immediately before treatment using a visual analog scale initially on day 1, then on days 7, 28 and 180. The results showed that both the experimental and placebo treatments resulted in a reduction in hypersensitivity at 180 days. However, the ACP treatment group showed a much more rapid reduction in hypersensitivity over time. The change in sensitivity was much more apparent using the air stimulus than the tactile stimulus. These results show that topical placement of ACP can rapidly reduce dentin hypersensitivity.

Cavity preparation by Er-YAG laser on pulpal temperature rise.

PURPOSE: To measure the intrapulpal temperature changes in vitro, during cavity preparation and caries removal, using the Opus 20 Er-YAG laser plotted as a function of the laser energy and pulse rate. MATERIALS AND METHODS: Class I and V cavity preparations were made in 175 fresh extracted caries-free human teeth and caries removal was carried out in 42 carious extracted teeth by the Opus 20 Er-YAG laser. K-type thermocouples were inserted into the pulp chambers filled with heat conducting paste. Lasing was carried out at different irradiation energies and pulse frequencies, using air-water spray. Temperature changes in the pulp chamber were measured during lasing. RESULTS: In all groups tested, the maximum temperature rise was lower than 5.5 degrees C, which is considered as critical value for pulp vitality. The highest temperature values were measured during Cl I preparations (3.13 degrees C +/- 1.54 - 4.11 degrees C +/- 1.29), medium values were in Cl V in enamel (2.38 degrees C +/- 1.37 - 4 degrees C +/- 1.07) and the lowest were in cementum (2.10 degrees C +/- 0.61 - 3.61 degrees C +/- 1.15) and during caries removal (1.21 degrees C +/- 0.46 - 3.51 degrees C +/- 0.68).