The Effect of Ytterbium-Doped Fiber Laser with Different Parameters on Physical Properties of Zirconia Surface.

OBJECTIVE: Laser irradiation is an alternative surface treatment method for roughening zirconia surfaces. The aim of this study was to evaluate the effects of ytterbium-doped fiber laser (YbPL) on zirconia. BACKGROUND: Zirconia surfaces are resistant to many surface treatment methods, but surface roughness is crucial for adhesion of veneering materials and cements to zirconia. METHODS: The zirconia discs were prepared and divided into four groups according to the power of the laser irradiation (5, 12, 17, and 20 W). These groups were divided into five subgroups according to the frequency (25, 40, 60, 80, and 100 kHz). Surface roughness values were measured with a noncontact profilometer, and the mean Ra values were calculated. Wettability was measured with a goniometer. The surface morphology was observed with a scanning electron microscope (SEM). The changes in the surface crystalline structure were analyzed with X-ray diffractometry. RESULTS: Ra values of all groups were higher than the control group. The highest surface roughness value was at 20 W and 100 kHz. Best wettability characteristic was observed at 5 W and 60 kHz. The correlations between Ra and wettability were low but significant. SEM examination of 5 W with different frequencies showed no microcracks, however, melted areas were observed. Remaining groups had microcracks and melted layers. A significantly lower T/M-phase transformation was observed in some groups. CONCLUSIONS: YbPL irradiation was effective at roughening the zirconia surface. Although laser treatment affected zirconia surfaces and provided surface roughness, the power and frequency should be adjusted to achieve optimum results.

Evaluation of Temperature and Stress Distribution on 2 Different Post Systems Using 3-Dimensional Finite Element Analysis.

BACKGROUND The mouth is exposed to thermal irritation from hot and cold food and drinks. Thermal changes in the oral cavity produce expansions and contractions in tooth structures and restorative materials. The aim of this study was to investigate the effect of temperature and stress distribution on 2 different post systems using the 3-dimensional (3D) finite element method. MATERIAL AND METHODS The 3D finite element model shows a labio-lingual cross-sectional view of the endodontically treated upper right central incisor and supporting periodontal ligament with bone structures. Stainless steel and glass fiber post systems with different physical and thermal properties were modelled in the tooth restored with composite core and ceramic crown. We placed 100 N static vertical occlusal loading onto the center of the incisal surface of the tooth. Thermal loads of 0°C and 65°C were applied on the model for 5 s. Temperature and thermal stresses were determined on the labio-lingual section of the model at 6 different points. RESULTS The distribution of stress, including thermal stress values, was calculated using 3D finite element analysis. The stainless steel post system produced more temperature and thermal stresses on the restorative materials, tooth structures, and posts than did the glass fiber reinforced composite posts. CONCLUSIONS Thermal changes generated stresses in the restorative materials, tooth, and supporting structures.

Addition of benzalkonium chloride to self-adhesive resin-cements: some clinically relevant properties.

OBJECTIVE: The clinical survival rates of the adhesive restorations are limited due to the deterioration of resin-dentin bonds over time, partly due to the endogenous enzymatic activity of dentin. Recently, benzalkonium chloride (BAC) has been shown to effectively inhibit endogenous protease activity of dentin. This study evaluated the effect of different concentrations of benzalkonium chloride (BAC) on the degree of conversion (DC), vickers hardness (VH), setting time (ST) and biaxial flexural strength (FS) of two self-adhesive resin luting cements (RC). METHODS: Two RC SpeedCEM (Ivoclar-Vivadent) and BisCem (Bisco) were modified by addition of 0.1, 0.5, 1, 1.5, 2 wt% BAC. The luting cements without the addition of BAC served as control. The DC (FT-IR/ATR from the bottom of the resin disc), vickers hardness (from top and bottom of the light-cured specimen), setting time (ISO 4049) and biaxial flexural strength (0.6 × 6 mm discs) of the specimens were tested. Data were analyzed using ANOVA and Tukeys HSD. RESULTS: DC results were in the range of 70-80%, with some significant changes in BisCem (p < 0.05). VH values of both materials increased significantly compared to control, with no significant change as the BAC percentage increases. BAC addition influenced the ST differently for both materials. For BisCem, a gradual decrease (p < 0.05) was observed whereas, for SpeedCEM, a gradual increase was observed until 1% BAC (p < 0.05). For FS values, a gradual decrease was observed for both materials with increased amounts of BAC (p < 0.05), compared to the control group. CONCLUSIONS: BAC addition of up to 1% seems to be acceptable considering the properties tested. Clinical significance. Incorporation of benzalkonium chloride to self-adhesive resin luting cements during the mixing procedure does not significantly affect the degree of conversion or flexural strength of the luting agent and may be a good option to improve the durability of adhesive interface.