Browsing by Subject "Dental Etching"

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    Effects of etching duration on the surface roughness, surface loss, flexural strength, and shear bond strength to a resin cement of e.max cad glass ceramic
    (2017) Al-Johani, Hanan; Chu, Tien-Min Gabriel; Platt, Jeffrey A.; Cook, Norman B.; Bottino, Marco C.
    Background: Long-term retention of ceramic restorations is dependent on the bond strength of the luting resin to both the tooth and porcelain substrates. In order to achieve successful bonding, the surface of the porcelain substrate must be modified to increase the surface roughness, and this can be achieved chemically by hydrofluoric (HF) acid etching. However, prolonged HF acid etching has shown to have a weakening effect on the evaluated lithium disilicate glass-ceramics. Therefore, it is essential to quantify the required etching duration of HF acid to minimize the possible deleterious effects on ceramic strength while maximizing the bond strength to tooth structure. Objectives: To evaluate the effects of HF acid etching duration on the surface roughness, surface loss, flexural strength, and shear bond strength of IPS e.max CAD (Ivoclar Vivadent) lithium disilicate-based glass ceramic to a resin cement. Hypothesis: The differences in HF acid etching durations will not have a significant effect on the surface roughness, surface loss, flexural strength, or shear bond strength of IPS e.max CAD to a resin cement. Methods: 168 specimens were prepared from IPS e.max CAD blocks. All specimens were polished and sonically cleaned in distilled water. Specimens were fired in the vacuum pump furnace according to the manufacturer’s instructions. Specimens were then divided into 4 groups, according to etching durations, then further divided into 3 subgroups, according to the properties tested. Group A was not etched (control), Groups B, C and D were etched with 5-percent HF acid (IPS Ceramic Etching gel, Ivoclar Vivadent) for 20 s, 60 s and 90 s respectively. The morphologies of both etched and non-etched surfaces in specimens of subgroup 1 of each etching group (n = 16/group) were observed under scanning electron microscopy (SEM). In addition, non-contact surface profilometry (Proscan 2000) was used to calculate the surface loss and to examine the surface roughness of the etched ceramic surfaces and roughness values (Ra, Rq) were documented for each group. Furthermore, etched specimens of subgroup 2 (n = 16/group) were silanated (Monobond Plus, Ivoclar Vivadent) and cemented with a resin cement (Multilink Automix, Ivoclar Vivadent). The shear bond strength (SBS) was measured using a universal mechanical testing machine. For each etching group, subgroup 3 specimens (n = 10/group) were loaded to failure in a three-point bending test to measure their flexural strength values using a universal mechanical testing machine. Data for surface roughness, surface loss, and flexural strength were analyzed using one-way analysis of variance (ANOVA), to identify the significant effects of different HF acid etching durations. Data for shear bond strength test were analyzed using two-way ANOVA to test the effects of etching duration, storage for 24 hours/thermocycling, and their interaction. All pair-wise comparisons from ANOVA analysis were made using Fisher’s Protected Least Significant Differences to control the overall significance level at 5 percent. Results: Difference in HF etching durations did not have a significant effect on surface roughness values Ra or Rq (p = 0.3408; p = 0.3245) respectively, but had a significant effect on surface loss (p = 0.0006). SBS values were not significantly different between experimental groups (p = 0.4650); however, SBS values after 24-h storage were significantly higher than that found after thermocycling (p = 0.0166) among different etching durations. Finally, different HF etching durations did not have a significant effect on flexural strength values (p = 0.1260). Conclusion: Within the limitations of this study, different HF etching durations did not have a significant effect on surface roughness, flexural strength, or shear bond strength of IPS e.max CAD. However, the different etching durations significantly affected the surface loss of the lithium disilicate glass ceramics.
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    Laser-treated stainless steel mini-screw implants: 3D surface roughness, bone-implant contact, and fracture resistance analysis
    (Oxford University Press, 2016-04) Kang, He-Kyong; Chu, Tien-Min; Dechow, Paul; Stewart, Kelton; Kyung, Hee-Moon; Liu, Sean Shih-Yao; Department of Orthodontics and Oral Facial Genetics, School of Dentistry
    BACKGROUND/OBJECTIVES: This study investigated the biomechanical properties and bone-implant intersurface response of machined and laser surface-treated stainless steel (SS) mini-screw implants (MSIs). MATERIAL AND METHODS: Forty-eight 1.3mm in diameter and 6mm long SS MSIs were divided into two groups. The control (machined surface) group received no surface treatment; the laser-treated group received Nd-YAG laser surface treatment. Half in each group was used for examining surface roughness (Sa and Sq), surface texture, and facture resistance. The remaining MSIs were placed in the maxilla of six skeletally mature male beagle dogs in a randomized split-mouth design. A pair with the same surface treatment was placed on the same side and immediately loaded with 200 g nickel-titanium coil springs for 8 weeks. After killing, the bone-implant contact (BIC) for each MSI was calculated using micro computed tomography. Analysis of variance model and two-sample t test were used for statistical analysis with a significance level of P <0.05. RESULTS: The mean values of Sa and Sq were significantly higher in the laser-treated group compared with the machined group (P <0.05). There were no significant differences in fracture resistance and BIC between the two groups. LIMITATION: animal study CONCLUSIONS/IMPLICATIONS: Laser treatment increased surface roughness without compromising fracture resistance. Despite increasing surface roughness, laser treatment did not improve BIC. Overall, it appears that medical grade SS has the potential to be substituted for titanium alloy MSIs.