Effect of neutralization and hydrofluoric acid precipitate remotion on the compressive strength of monolithic lithium disilicate crowns.

BACKGROUND: The cleaning protocol for the ceramic surface after acid etching resulted in a decrease in bond strength and flexural strength of a glass ceramic. This study aims to evaluate the effect of different ceramic surface treatments after hydrofluoric acid etching (HF) on the compressive strength of monolithic lithium disilicate crowns. METHODS: Forty (40) human third molars received conventional full coverage preparation. After performing digital impressions of teeth preparations, ceramic blocks were machined using a CAD/CAM system in order to obtain the crowns. The crowns were distributed in 4 groups as ceramic surface treatment (N.=10): (HF) - 4.9% HF for 20s + air-water spray for 30s; (HFN) - HF + neutralizing agent for 5 min (N); (HFU) - HF + ultrasonic bath for 5 min (U); e (HFNU) - HF + N + U. SEM and EDS analysis was performed in each group in order to characterize the ceramic surface and to verify the chemical element distribution after HF cleaning protocols. A silane layer was applied (for 60s), and crowns were then cemented with dual resin cement. A compressive load was applied on the middle of the occlusal crown surface with a crosshead speed of 1 mm/min until fracture. Data were analyzed using ANOVA and Tukey test (α=0.05). RESULTS: Fluoride ions were found in samples of all postetching cleaning protocols. The mean value (Kgf) was: HF =169.92±21.37; HFN =187.34±34.79; HFU =166.63±40.22 and HFNU=175.26±40.22. The ceramic surface treatment after HF etching did not significantly influence (P>0.05) the compressive strength of the tested ceramic crowns. CONCLUSIONS: Surface treatments with neutralizing agent associated with the ultrasonic bath as the pre-cementation protocol was the most efficient protocol in eliminating the precipitate deposited on the porosities created by acid etching.

Influence of immediate/delayed implant placement and implant platform on the peri-implant bone formation.

AIM: To determinate the influence of the timing and position of the implant placement, as well as the presence and absence of a buccal gap, associated with different implant platforms on bone formation around implants. METHODS AND MATERIALS: In a first surgical stage, two premolars in one side of the mandibular arch of 07 mongrel dogs were extracted. After a 120-day healing period, a second-stage surgery was performed, in which a full flap was raised and two implants were installed. At this same stage, two contralateral premolars were extracted and two immediate implants were placed into the fresh sockets, through the "palatal approach technique" without flap elevation, totaling four implants per animal. The 28 installed implants constituted groups according to the timing (Immediate or delayed) of placement and the type of surface treatment. After 4 months, samples were collected and histomorphometric analysis was performed to determinate buccal surface BIC, lingual surface BIC, total BIC, buccal area, and lingual area of all implants. Kruskal-Wallis and pared Wilcoxon (P < 0.05) tests were performed for statistical analysis. RESULTS: After 4-month healing period, the groups of immediate implants presented better BIC scores, mainly on the buccal surface. Data also suggest better bone area formation around the implants of these same groups. Concerning the type of implant platform, better results were found using Morse taper. CONCLUSION: The flapless technique with "palatal approach," Morse taper implants, and immediate implant placement all have favorable influence on the bone formation around the implants.