RESUMO
BACKGROUND: Dental shade guides are used before restorative and prosthodontic procedures for the evaluation of tooth color. The spectral coverage of the specific shaded guide and a clinician's experience in shade matching are the two most important factors for a clinically viable shade match of the restoration to the given tooth. Repeated disinfection of the shade guide with disinfectant lead to a clinically significant difference of the shade to be matched, finally resulting in a clinically unacceptable prosthesis. The purpose of this study is to evaluate the effects of disinfection on various shade tabs of VITA 3D Master Shade guide after being subjected to 2 years of simulated disinfection with 70% isopropyl alcohol. METHODOLOGY: Two sets of VITA 3-D Master Shade Guides were used. One set of each shade guide was assessed after simulated use and surface disinfection with 70% isopropyl alcohol (test group), while the other full set was subjected to cleansing with distilled water (control group). Spectrophotometer was used to measure each of the shade tabs. Readings were recorded at regular intervals of 120, 240, 360, 480, 600, 720, 840, and 960 disinfection cycles. The ΔE values obtained were used to examine the color difference. RESULTS: There was a significant difference in terms of ΔE between the shade tabs of control and test groups of VITA 3D Master shade guides after 960 cycles of disinfection. The change in mean ΔE was more in the test specimens in the shade tabs of VITA 3D Master Shade Guide tabs than the control specimens. These results are of statistical significance, but they might not be of any clinical significance. CONCLUSION: There was a statistically significant but clinically nonsignificant color change in the shade tabs of VITA 3D Master shade guides after 2 years of simulated use and disinfection with 70% isopropyl alcohol.
RESUMO
BACKGROUND: The thermal expansion of the investment can be restricted by the metal casting ring because the thermal expansion of the ring is less than that of the investment. The ringless casting procedure is in use in clinical dentistry, though there is little scientific data to support its use in fixed partial dentures. In this study, marginal discrepancy of castings produced with the ringless casting technique and the conventional technique using the metal rings were compared. MATERIALS AND METHODS: A total of 30 wax patterns were fabricated directly on a metal die. Optical stereomicroscope was used to measure the marginal discrepancy between the metal die and wax patterns. A total of 15 castings were invested using Bellavest T phosphate-bonded investment with the ringless technique and 15 were invested with the same investment with a metal ring; 30 castings were produced using a nickel-chromium ceramo-metal alloy. The internal surface of the castings was not modified and seated with finger pressure. The vertical marginal discrepancy was measured using an optical stereomicroscope at a magnification of 100x. The data obtained were statistically analyzed using students t-test (paired t-test and unpaired t-test). RESULTS: The castings of the ringless technique provided less vertical marginal discrepancy (240.56 ± 45.81 µ) than the castings produced with the conventional metal ring technique (281.98± 53.05 µ). The difference was statistically significant. CONCLUSION: The ringless casting technique had produced better marginal accuracy compared with conventional casting technique. Ringless casting system can be used routinely for clinical purpose.
Assuntos
Revestimento para Fundição Odontológica , Técnica de Fundição OdontológicaRESUMO
The objective of this study was to evaluate the effect of the addition of stannous fluoride (SnF2) and sodium fluoride (NaF) to luting cements on the retention of provisional crowns. Provisional crowns were fabricated using methyl methacrylate and bis-acryl composite resin for 32 chamfer prepared molars. For control group A, crowns were cemented with Freegenol and RelyX Temp NE non-eugenol cements. For test group B, crowns were cemented using the above cements with the addition of SnF2. For test group C, crowns were cemented using the above cements with the addition of NaF. The specimens were thermocycled and retention test was conducted after 7 days. The addition of SnF2 significantly increased the retentive strength of both the cements in the range of 27-48 %, whereas addition of NaF decreased the retentive strength of both the cements in the range of 14-23 %. SnF2 can be mixed with non-eugenol luting cements to improve the retention of both methyl methacrylate and bis-acryl composite crowns. The different effects of NaF and SnF2 on retention indicate that it may be useful to have two different types of provisional luting cements for short-term and long-term cementation, as appropriate.
