The Influence of Sonic and Ultrasonic Vibration on the Shear Bond Strength of a Selected Resin Luting Cement

Purpose: This study determined the effect of sonic and ultrasonic instrumentation on the shear bond strengths of Panavia 21, a popular cement for the luting of resin-bonded restorations. Methods: 84 Ni-Cr cylinders were cemented to randomly selected resin composite substrates using Panavia 21 following the manufacturer's instructions. The Ni-Cr-composite specimens were divided into 7 groups of 12 specimens each based upon the procedure used for removing the excess cement. For Group 1 (Co) specimens the excess cement was removed with microbrushes immediately after cementation. Groups 2 through 7 were based on the use of vibrating instrument and the time period after which the excess material was removed. These included the cement, Panavia 21, three vibrating instruments, Sonic with a universal tip (So), Piezoelectric ultrasonic with a USPIS tip (Pu), Magnetorestrive ultrasonic with a FS1-100 tip (Mu) and two different time periods, soon after cementation (9m) and one hour after cementation (1h). Once excess cement REMOVAL WAS COMPLETED, THE SPECIMENS WERE SUBJECTED TO SHEAR TESTING. Results: Mean Shear Bond strengths ranged from 16.03 MPa (Co) to 19.91 MPa (So 1h). Statistical analysis demonstrated that interaction of the main effects were significant (F = 4.27, p = 0.042). Post-hoc analysis demonstrated that the effect of timing was significant in all the instrumented groups. The majority of the tested specimens failed cohesively compared to mainly adhesive failures for the control group. Conclusions: The effect of type of instrumentation immediately following polymerization setting had no effect on the shear bond strengths however a delay of 1 hour for all types of instrumentation had a beneficial effect of improving observed shear bond strengths.

Comparison of the Mechanical Properties of two Nano-filled Composite Materials

OBJECTIVE: The purpose of this study was to quantify and compare the mechanical properties of two commercially available nanocomposite restorative materials. MATERIAL ANDMETHODS: Specimens of two nanocomposites, Z350TM and GrandioTM, were polymerized with a LED light for 20 seconds and subjected to mechanical tests. Properties tested included: flexural strength, diametral tensile strength, fracture toughness and microhardness (top and bottom). RESULTS: Grandio exhibited significantly higher mean flexural strength values when compared to Z350 (89.1 MPa vs 61.9 MPa). Grandio exhibited significantly higher top microhardness values when compared to Z350. Additionally when microhardness for the top surfaces of each composite were compared with their corresponding bottom surfaces, the bottom surfaces demonstrated significantly lower readings. The properties of fracture toughness and diametral tensile strength were non-discerning factors in this particular study. CONCLUSION: Grandio has greater observed values for the properties of flexural strength and hardness when compared with Z350. There was no difference between the two materials with respect to their fracture toughness and diametral tensile strength.

Periodontitis in 13-year-old Jamaican children

The goal of this study was to determine if the Community Periodontal Index and Treatment Need (CPITN) screening method can detect an adolescent group at high risk for alveolar bone loss due to periodontitis. Forty-five Jamaican children, age 13 years, with a pocket depth exceeding 3.5mm on at least on index tooth were identified by CPITN for this cohort study. Current periodontal disease was noted by the presence of bleeding upon probing (97.8 percent) and subgingival calculus (41.5 percent) around the index teeth. Digital imaging software was used to analyze the radiographs and indicated alveolar bone loss greater than 2mm in 93.3 percent of subjects and greater than 3mm in 42.2 percent. The CPITN screening method was shown to be valuable as a tool for identifying this high-risk population.(AU)