Effect of Temporary Cement, Surface Pretreatment and Tooth Area on the Bond Strength of Adhesively Cemented Ceramic Overlays-An In Vitro Study.

Several viewpoints have been reported regarding the effect of temporary cements, different surface pretreatment protocols before adhesive cementation, and predictive factors. This in vitro study tested if temporary cement, pretreatment of the tooth surface, the size of enamel or dentine influence adhesive cementation to zirconia ceramics. Twenty premolars were prepared for determination of enamel and dentin area, bond strength test and failure analysis. The samples were divided into two groups: untreated prior adhesive cementation (n = 10) and with temporary cementation done, pretreated prior adhesive cementation (n = 10). Zirconia overlays (Katana Zirconia STML) were cemented on the grounded flat teeth surfaces using Panavia V5. An additional six premolars underwent dentine tubule analysis with SEM to detect temporary cement residues after temporary cementation on an untreated tooth surface (n = 3) and on a pretreated surface (n = 3). The independent sample t-test was used to compare the two groups and the means of the total tooth, dentin or enamel areas did not differ significantly between the untreated and pretreated specimens. The mean tensile bond strength was significantly (p = 0.005) higher in the pretreated specimens (337N) than in the untreated ones (204N). The overall multivariable linear regression model with three predictors (surface pre-treatment, enamel area and dentine area) was significant (p = 0.003), among which the size of enamel was the strongest predictor (ß = 0.506; p = 0.049), followed by the pretreatment effect (ß = 0.478; p = 0.001) and the size of dentin area (ß = -0.105; p = 0.022).

Resin Cement Residue Removal Techniques: In Vitro Analysis of Marginal Defects and Discoloration Intensity Using Micro-CT and Stereomicroscopy.

The objective was to compare marginal defects and evaluate discoloration for adhesively cemented veneers in vitro when using two cement removal techniques. Twenty premolars were prepared with chamfer and borders in enamel. IPS e.max CAD veneers were cemented using Panavia V5 and divided in two groups (n = 10): cement excess removed with a probe after tack-curing for 3-5 s, or cement excess removed with a brush, then completely polymerized. All teeth were stored in alginate gel until micro-CT examination. Scanning was performed twice: directly after cementation and after thermocycling (5000 cycles, between 5 and 55 °C). To analyze discoloration, teeth were colored using 0.5% basic fuchsine and examined under a stereomicroscope. Depth of dye infiltration was scored 0 (no discoloration) to 5 (discoloration along the entire margin). Statistically significant differences of cement defects before thermocycling were reported, where brushing showed more defects than probing (p = 0.0161). After thermocycling, the defects increased for both groups. Extensive discoloration was the most common (55.56%) when removing excess by probing; by brushing, 90% of the specimens exhibited slight discoloration (p = 0.008). Regression analysis showed no relationship between type of defect and degree of discoloration. Removing cement with a brush causes more marginal defects, however less discoloration after thermocycling.

Nanosized calcium deficient hydroxyapatites for tooth enamel protection.

Calcium phosphates (CaP) are extensively studied as additives to dental care products for tooth enamel protection against caries. However, it is not clear yet whether substituted CaP could provide better enamel protection. In this study we produced, characterized and tested in vitro substituted and co-substituted calcium deficient hydroxyapatite (CDHAp) with Sr2+ and F- ions. X-ray powder diffractometry, Fourier transformation infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, Brunauer-Emmett-Teller were used to characterize synthesized powders and also cytotoxicity was evaluated. pH = f(t) test was performed to estimate, weather synthesized CDHAp suspensions are able to increase pH of experimental media after acid addition. Synthesis products were incorporated into paste to perform in vitro remineralization on the bovine enamel. In addition to mentioned instrumental methods, profilometry was used for evaluation of remineralised enamel samples. The obtained results confirmed formation of CDHAp substituted with 1.5-1.6 wt% of fluoride and 7.4-7.8 wt% of strontium. pH = f(t) experiment pointed out that pH increased by approximately 0.3 within 10 min after acid addition for all CDHAp suspensions. A new layer of the corresponding CDHAp was formed on the enamel. Its thickness increased by 0.8 ± 0.1 µm per day and reached up to 5.8 µm after 7 days. Additionally, octa calcium phosphates were detected on the surface of control samples. In conclusion, we can assume that CDHAp substituted with Sr2+ and/or F- could be used as an effective additive to dental care products promoting formation of protecting layer on the enamel, but there was no significant difference among sample groups.

In vivo and in vitro study of a novel nanohydroxyapatite sonocoated scaffolds for enhanced bone regeneration.

There still remains a need for new methods of healing large bone defects, i.e., gaps in bone tissue that are too big to naturally heal. Bone regrowth scaffolds can fill the bone gap and enhance the bone regeneration by providing cells with a support to for new tissue formation. Coating of the scaffolds surface with nanocrystalline hydroxyapatite may enhance the osteoinductivity or osteoconductivity of such scaffolds. Here we present the sonocoating method to coat scaffolds with bioactive hydroxyapatite nanoparticles. We show a method, where the material to be coated is immersed in a colloidal suspension of nanoparticles with mean sizes of 10 nm and 43 nm in water, and high-power ultrasound waves are applied to the suspension for 15 min at 30 °C. High power ultrasounds lead to growth of cavitation bubbles in liquid, which implode at a critical size. The implosion energy propels the nanoparticles towards the material surface, causing their attachment to the scaffold. Using this technique, we produced a uniform layer of nanohydroxyapatite particles of thickness in the range 200 to 300 nm on two types of scaffolds: a porous ß-TCP ceramic scaffold and a 3D-printed scaffold made of PCL fibers. In vivo tests in rabbits confirmed that the novel coating strongly stimulated new bone tissue formation, with new bone tissue occupying 33% for the nHAP-coated PCL scaffold and 68% for the nHAP-coated ß-TCP after a 3-month test. The sonocoating method leads to formation of a bioactive layer on the scaffolds at temperature close to room temperature, very short time and in water. It is a green technological process, promising for bone tissue regeneration applications.