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.

Evaluation of temperature and osteotomy speed with piezoelectric system.

BACKGROUND: Piezosurgery is an option to realize several clinical and surgical procedures, due to its advantages as precision in osteotomy. This study aims to evaluate the heating and osteotomy speed in bone blocks of ox's shins, to report the best way of its use in the clinical practice. METHODS: A bone blocks had the dimensions as follow: 20 mm length, 10 mm width, and 5 mm wide. It was evaluated 5 different groups: group LM (low speed and medium pressure); group HM (high speed and medium pressure); group HH (high speed and high pressure); group LH (low speed and high pressure); group LL (low speed and low pressure). The heating increasement was measured with a thermal viewer and the osteotomy was timed when the cut depth reached 5 mm and the whole block detached itself. One-way ANOVA and Tukey tests were adopted to analyze the data and the level of significance was set at a P value of 0.05. RESULTS: The pressure and speed of the tip, works directly in the generated temperature during osteotomy. The medium pressure level is the most favorable, because high pressure level caused a high increase in heating over the bone and low pressure presented a very long osteotomy time. CONCLUSIONS: The high speed and medium pressure can be suggested as the most efficient in both standards of time/temperature to realize the osteotomy.