Aslihan Usumez

Bond strengths of porcelain laminate veneers to tooth surfaces prepared with acid and Er,Cr:YSGG laser etching

STATEMENT OF PROBLEM The erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) hydrokinetic laser system has been successful in the ablation of dental tissues. It has been reported that this system is also useful for preparing tooth surfaces for adhesion, but results to date have been controversial. PURPOSE This in vitro study evaluated the bond strengths of porcelain laminate veneers to tooth surfaces after etching with acid and Er,Cr:YSGG laser conditioning. Material and method Forty extracted caries- and restoration-free human maxillary central incisors were used. The teeth were sectioned 2 mm below the cementoenamel junction. The crowns were embedded in autopolymerizing acrylic resin with the labial surfaces facing up. The labial surfaces were prepared with.05 mm reduction to receive porcelain veneers. The teeth were divided into 4 groups of 10 specimens. Thirty specimens received 1 of the following surface treatments before the bonding of IPS Empress 2 laminate veneers: (1) laser radiation from an Er,Cr:YSGG laser unit; (2) 37% orthophosphoric acid; and (3) 10% maleic acid. Ten specimens received no surface treatment and served as the control group. The veneers were bonded with dual-polymerizing resin, Variolink II. One microtensile specimen from each of the cervical and incisal thirds measuring 1.2 x 1.2 mm was prepared with a slow-speed diamond saw sectioning machine with a diamond-rim blade. These specimens were attached to opposing arms of the microtensile testing device with cyanoacrylate adhesive and fractured under tension at a crosshead speed of 1 mm/min, and the maximum load at fracture (Kg) was recorded. The data were analyzed with a 2-way analysis of variance and Tukey HSD tests (alpha=.05). RESULTS No statistically significant differences were found among the bond strengths of veneers bonded to tooth surfaces etched with Er,Cr:YSGG laser (12.1 +/- 4.4 MPa), 37% orthophosphoric acid (13 +/- 6.5 MPa), and 10% maleic acid (10.6 +/- 5.6 MPa). The control group demonstrated the lowest bond strength values in all test groups. Statistically significant differences were found between the bond strengths of cervical and incisal sections (P<.001). CONCLUSION In vitro microtensile bond strengths of porcelain laminate veneers bonded to tooth surfaces that were laser-etched showed results similar to orthophosphoric acid or maleic acid etched tooth surfaces.

The effect of ceramic thickness and number of firings on the color of two all-ceramic systems

STATEMENT OF PROBLEM All-ceramic restorations have been advocated for superior esthetics, and various materials have been used to improve ceramic core strength, but there is a lack of information on how color is affected by different core substructures and fabrication procedures. PURPOSE The purpose of this study was to evaluate the effects of various dentin ceramic thicknesses and repeated firings on the color of lithium disilicate glass-ceramic (IPS e.max Press) and zirconium-oxide (DC-Zirkon) all-ceramic systems. MATERIAL AND METHODS Thirty disc-shaped specimens, 4 mm in diameter with a 1-mm core thickness, and 0.5-, 1-, or 1.5-mm dentin ceramic thicknesses, were made from each of 2 ceramic systems (n=10). Repeated firings (3, 5, 7, or 9) were performed, and the color of the specimens was compared with the color after the initial firing. Color differences among ceramic specimens were measured using a spectrophotometer (VITA Easyshade), and data were expressed in CIELAB system coordinates. Repeated measures ANOVA was used to analyze the data (number of firings, ceramic composition, and ceramic thickness) for significant differences. The Tukey HSD test and paired 2-tailed tests were used to perform multiple comparisons (alpha=.05). RESULTS L*a*b* values of the ceramic systems were affected by the number of firings (3, 5, 7, or 9 firings) (P<.001), ceramic composition (DC-Zirkon or IPS e.max Press) (P<.001), and ceramic thickness (0.5, 1, or 1.5 mm) (P<.001). Significant interactions were present in L*a*b* values between the number of firings and ceramic composition (P<.001) and between the number of firings and ceramic thickness (P<.001). Significant interactions were present between the number of firings and ceramic thickness and ceramic composition (P<.05) in L* and b* values, but not for the a* value (P=.068). As the ceramic thickness increased, significant reductions in L* values (P<.01) were recorded for IPS e.max Press and DC-Zirkon specimens. For IPS e.max Press specimens, there were significant increases in a* and b* values (P<.01). For DC-Zirkon specimens, significant increases in a* values were observed; however, no significant differences were recorded for b* values. CONCLUSIONS The analysis revealed that there were significant changes in L*a*b* color data as the number of firings increased, which resulted in perceptual color changes in L*a*b* color parameters.

Thermal Changes in the Pulp Chamber during Different Adhesive Clean-up Procedures

The aim of this in vitro study was to measure the temperature changes in the pulpal chamber when different adhesive clean-up procedures were used. Ninety intact extracted human maxillary central incisors were used in the study. The teeth were divided into six groups of 15 teeth each. The removal of the remaining composite on the tooth surface was performed with a tungsten carbide bur. The residual adhesive was removed using a high-speed handpiece with and without water cooling and a contra-angle handpiece with and without water cooling at high and low speeds. A J-type thermocouple wire was positioned in the center of the pulp chamber. The results were analyzed with analysis of variance (ANOVA) and the Tukey-honestly significant difference test. Two-factor ANOVA revealed significant interaction between the handpiece type and water cooling. In this study, the high-speed contra-angle handpiece without water cooling group had the highest deltaT values (7.58 degrees C+/-1.84 degrees C) among all the clean-up procedures. The decrease in pulpal temperature with water cooling was -5.34 degrees C for the handpiece, -5.36 degrees C for the low-speed contra-angle handpiece and -4.98 degrees C for the high-speed contra-angle handpiece. Clinicians should be aware of the potential thermal damage to the pulp, which may result from long clean-up procedures without water cooling. Adhesive removal procedures should be performed with adequate water cooling to prevent temperature increases that might be harmful to pulpal tissues.

The effect of repeated firings on the color of an alumina ceramic system with two different veneering porcelain shades

STATEMENT OF PROBLEM Possible sources of processing variables in porcelain firing include thickness and color of the opaque; thickness, color, and translucency of the body and enamel layers; firing temperature; and number of firings. PURPOSE The purpose of this in vitro study was to investigate the color changes of an alumina ceramic system veneered with different veneering porcelain shades and fired different numbers of times. MATERIAL AND METHODS Twenty disc-shaped ceramic specimens (10 mm in diameter, with a core thickness of 1 mm), with 2 different veneering porcelain shades (A1, A3), were fabricated from an alumina ceramic system (Turkom-Cera) (n=10). Repeated firings (3, 5, 7, or 9 firings) were performed, and color differences (ΔE) were determined using a spectrophotometer. Repeated-measures ANOVA was used to analyze the data (number of firings, veneering porcelain color). The Duncan test and paired 2-tailed tests were used for multiple comparisons (α=.05). RESULTS The L*a*b* values of the ceramic system were affected by the number of firings (3, 5, 7, or 9) (P<.005) and veneering porcelain shade (P<.001). Significant interactions were present between the number of firings and the veneering porcelain shade for L* (P=.002), a* (P=.001), and b* (P=.001) values. A1 shade specimens maintained their L* value independent of the number of firings, whereas A3 shade specimens became lighter after an increased number of firings. For both A1 and A3 veneering porcelain shades, the a* value decreased after repeated firings, which resulted in less reddish specimens, and the b* value decreased after repeated firings, which resulted in less yellowish specimens. CONCLUSIONS Imperceptible (ΔE<1.6) and clinically acceptable color changes (ΔE<3.7) were demonstrated by the alumina ceramic system tested.

Change of shade by light polymerization in a resin cement polymerized beneath a ceramic restoration

OBJECTIVES The aim of this in vitro study was to examine the effect of the color changes of a resin cement material (Variolink II) polymerized beneath a simulated ceramic restoration (IPS Empress II) by two different light polymerizing units. METHODS A conventional halogen light and a light emitting diode unit were used to polymerize resin cement with catalyst. A pressable ceramic block (10mm in diameter, 2 or 1mm in height) was used as an interface between the polymerizing light tip and resin cement. Colorimetric values of the specimens before and after polymerization were measured using a spectrophotometer (Easy Shade). The CIE L*a*b color system was used for the determination of the color difference. Differences between measurements were calculated as delta E*(ab). Repeated measurements analysis of variance (ANOVA) was used to analyze the data (polymerization of resin cement, polymerizing unit and ceramic thickness) for significant differences. The Tukey HSD test and paired two-tailed tests were used to perform multiple comparisons (alpha=.05). RESULTS L*a*b values of ceramic system were affected by the polymerization of resin cement (before and after) (P<.01). The a* value was affected by polymerization unit (P<.05), however L* and b* values were not affected by the light polymerization unit (P>.05). The b* value was affected by ceramic thickness (1 or 2mm) (P<.05), but L* and a* values were not affected by ceramic thickness (P>.05). The specimens polymerized beneath 1mm ceramic thickness with conventional halogen light induced a significantly higher color changes than any other specimen (P<.05). CONCLUSIONS The results of this in vitro study suggest that light polymerization of the resin cement (Variolink II) used in this study is an important factor for the color of the definitive restoration and should be considered during shade selection and fabrication.

Antimicrobial efficiency of photodynamic therapy with different irradiation durations

Objective: This study aimed to evaluate the antimicrobial efficiency of PDT and the effect of different irradiation durations on the antimicrobial efficiency of PDT. Materials and Methods: Sixty freshly extracted human teeth with a single root were decoronated and distributed into five groups. The control group received no treatment. Group 1 was treated with a 5% sodium hypochlorite (NaOCl) solution. Groups 2, 3, and 4 were treated with methylene-blue photosensitizer and 660-nm diode laser irradiation for 1, 2, and 4 min, respectively. The root canals were instrumented and irrigated with NaOCl, ethylenediamine-tetraacetic acid, and a saline solution, followed by autoclaving. All the roots were inoculated with an Enterococcus faecalis suspension and brain heart infusion broth and stored for 21 days to allow biofilm formation. Microbiological data on microorganism load were collected before and after the disinfection procedures and analyzed with the Wilcoxon ranged test, the Kruskal-Wallis test, and the Dunn′s test. Results: The microorganism load in the control group increased. The lowest reduction in the microorganism load was observed in the 1-min irradiation group (Group 2 = 99.8%), which was very close to the results of the other experimental groups (99.9%). There were no significant differences among the groups. Conclusions: PDT is as effective as conventional 5% NaOCl irrigation with regard to antimicrobial efficiency against Enterococcus faecalis.

Evaluation of monomer leaching from a dual cured resin cement

PURPOSE An increasing number of inlay cavities is restored with tooth-colored materials, especially ceramics are cemented with resin cements. The comonomer TEGDMA and other monomers Bis-GMA and UDMA have been identified as the main compounds released from polymerized resin cements into aqueous media. The present investigation was conducted to clarify the leaching behavior of the monomers of dual polymerized resin cement. MATERIAL AND METHODS Ten freshly extracted caries and restoration free molar teeth were used in this study. Standardized Class I preparations were prepared in all teeth. Lithium disilicate based (IPS Empress Esthetic) ceramic inlays were cemented with dual polymerized resin cement (Variolink II). After cementation, specimens were stored in 75% ethanol solution. High-performance liquid chromatography (HPLC) was used to analyze the amounts of three monomers in the solution (after 10 min, 1 h, 24 h, 3, 7, 14, and 21 days). Two-way ANOVA and Tukey HSD tests were used to evaluate the results (p < 0.05). RESULTS There were statistically significant differences among the amounts of the monomers (p < 0.01) and also among time periods (p < 0.01). While the TEGDMA resulted in significantly higher amount than Bis-GMA and UDMA, there were no statistically significant differences between amounts of Bis-GMA, UDMA (p = 0.06). The cumulative amount of monomers was the highest after 21 days (p < 0.01). CONCLUSION In the case of resin cement, leaching of TEGDMA was the highest and the cumulative amount of leaching monomers from resin cement was influenced by the time.

Effect of enamel laser irradiation at different pulse settings on shear bond strength of orthodontic brackets

OBJECTIVE To compare the effect of laser irradiation at two different pulse settings and acid etching on the shear bond strength (SBS) of orthodontic brackets to enamel. MATERIALS AND METHODS Thirty-six premolars were allocated to three groups (n  =  12): (1) 37% phosphoric acid etching, (2) erbium-doped yttrium aluminum garnet (Er:YAG) laser etching with medium-short pulse mode (MSP; 100 µs, 120 mj, 10 Hz, 1.2 W), and (3) Er:YAG laser etching with quantum-square pulse mode (QSP; 120 mj, 10 Hz, 1.2 W). Metallic brackets were bonded with Transbond XT. After photopolymerization, the samples were subjected to 5000 thermal cycles and debonded with a universal testing machine, and the SBS values were recorded. Surface morphology was evaluated with profilometric examination, scanning electron microscopy, and atomic force microscopy. The adhesive remnant index (ARI) was evaluated to assess the remaining adhesive. RESULTS The results of SBS testing were analyzed by one-way analysis of variance and Tukey honestly significant diffference tests. The mean SBS values of QSP and MSP laser groups were 11.80 ± 2.7 MPa and 10.10 ± 4.5 MPa, respectively, and the QSP group demonstrated significantly higher SBS (P < .01) than that of the acid-etched group (6.6 ± 2.4 MPa). No significant difference was observed between the SBS values of the two laser groups (P < .05). The difference between the ARI scores of the laser groups and the acid-etched group was statistically significant (P < .05). CONCLUSION Laser etching at MSP and QSP modes present successful alternatives to acid etching; however, long-term clinical studies are required to verify clinical success.

Shear Bond Strength of Four Resin Cements Used to Lute Ceramic Core Material to Human Dentin

PURPOSE This study evaluated the effect of four resin cements on the shear bond strength of a ceramic core material to dentin. MATERIALS AND METHODS One hundred twenty molar teeth were embedded in a self-curing acrylic resin. The occlusal third of the crowns were sectioned under water cooling. All specimens were randomly divided into four groups of 30 teeth each according to the resin cement used. One hundred twenty cylindrical-shaped, 2.7-mm wide, 3-mm high ceramic core materials were heat-pressed. The core cylinders were then luted with one of the four resin systems to dentin (Super-Bond C&B, Chemiace II, Variolink II, and Panavia F). Half of the specimens (n = 15) were tested after 24 hours; the other half (n = 15) were stored in distilled water at 37 degrees C for 1 day and then thermocycled 1000 times between 5 degrees C and 55 degrees C prior to testing. Shear bond strength of each specimen was measured using a universal testing machine at a crosshead speed of 1 mm/min. The bond strength values were calculated in MPa, and the results were statistically analyzed using a two-way analysis of variance (ANOVA) and Tukey HSD tests. RESULTS The shear bond strength varied significantly depending on the resin cement used (p < 0.05). The differences in the bond strengths after thermocycling were not remarkable as compared with the corresponding prethermal cycling groups (p > 0.05). Significant interactions were present between resin cement and thermocycling (p < 0.05). After 24 hours, the specimens luted with Variolink II (5.3 +/- 2.2 MPa) showed the highest shear bond strength, whereas the specimens luted with Chemiace II (1.6 +/- 0.4 MPa) showed the lowest. After thermocycling, the bond strength values of specimens luted with Chemiace II (1.1 +/- 0.1 MPa) and Super-Bond C&B (1.7 +/- 0.4 MPa) decreased; however, this was not statistically significant (p > 0.05). The increase in the shear bond strength values in the Panavia F (4.5 +/- 0.7 MPa) and Variolink II (5.5 +/- 2.1 MPa) groups after thermocycling was also not statistically significant (p > 0.05). CONCLUSION Variolink II and Panavia F systems showed higher shear bond strength values than Chemiace II and Super-Bond C&B. They can be recommended for luting ceramic cores to dentin surfaces.

Effect of complete dentures on dynamic measurement of changing head position: A pilot study.

STATEMENT OF PROBLEM Complete dentures contribute significantly to the facial esthetics of edentulous patients. However, information as to the effect of complete dentures on the natural position of the head is limited. PURPOSE The purpose of this pilot study was to evaluate the immediate and 30-day effect of wearing complete dentures on the dynamic natural head position measured during walking. MATERIALS AND METHODS The sample consisted of a volunteer group of 16 patients, 8 women and 8 men, who received new complete dentures. The ages of the subjects ranged from 45 to 64 years (mean=52 years). Dynamic measurement of head posture was carried out by a specially constructed inclinometer device. Each subject in turn was fitted with the inclinometer system and instructed to walk in a relaxed manner for 5 minutes. The data, measured as degrees, were stored in a pocket data logger. This procedure was repeated before insertion of dentures (T1), immediately after insertion of dentures (T2), and 30 days after insertion of dentures (T3). Stored dynamic head posture data were transferred to computer for analysis. The means of the measurements were statistically compared with Friedman and following Wilcoxon tests (alpha =.05). RESULTS Twelve of 16 (75%) subjects showed an average of 4.6 degrees of cranial extension immediately after insertion of dentures. Six (37.5%) subjects showed an average of 6.4 degrees of cranial flexion, and 8 (50%) subjects showed an average of 5.2 degrees of cranial extension at T3 relative to the T1 measurement. Dynamic head posture measurements of the other 2 subjects remained unchanged. There were significant differences between different measurements of dynamic head posture positions (P<.025). However, only the T1 and T2 measurements were significantly different (P<.015). CONCLUSION The findings indicate that the statistically significant average extension 4.6 degrees in subjects immediately after insertion of complete dentures was not stable after a 30-day evaluation period and did not produce any statistically significant change. The overall effect of wearing dentures was an irregular flexion or extension pattern on dynamic head posture.