Ultrashort-pulse laser as a surface treatment for bonding between zirconia and resin cement

ObjectivesTo evaluate ultrashort-pulse laser (UPL) as a surface treatment for improved bond strength to Yttria-tetragonal zirconia polycrystalline (Y-TZP).MethodsFully-sintered Y-TZP samples received either no treatment (CTL), or were treated by alumina blasting (ALB), tribochemical silica coating (SIL), or one of two UPL patterns: multiple pulses laser surface dots with 2.5 μm spacing (8 mJ, 10 kHz)(LSD); or single pulse laser surface lines with 2.5 μm spacing (4 mJ, 6.7 kHz)(LSL). Surface roughness, wettability (contact angle), and quantification of crystalline phases were evaluated for each group (n = 3/group). Y-TZP treated slabs were cemented to resin composite slabs using silane and 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing adhesive. Beams from the Y-TZP/resin blocks were microtensile tested (n = 5/group) after 48 h water incubation (37 °C) with or without subsequent thermocycling (5–55 °C, 5000 cycles).ResultsAll surface treatments increased surface roughness values versus control (P < 0.001). Contact angles were lowest for SIL (6.57 ± 2.37°) and highest for control (50.97 ± 6.30°). LSL and LSD were the only treatments that did not increase the relative monoclinic phase. All surface treatments significantly increased microtensile bond strengths (μTBS) compared with the control group (P < 0.001), with highest values for UPL (LSD: 35.40 ± 4.53 MPa > LSL: 31.84 ± 8.46 MPa > SIL: 19.95 ± 3.99 MPa = ALB: 19.51 ± 2.55 MPa > CTL: 14.51 ± 2.23 MPa). Thermocycling significantly reduced bond strength for all treatments in a surface treatment-dependent manner.SignificanceThe ability of UPL to alter Y-TZP surface morphology, increase wettability and μTBS without increasing the monoclinic content suggests its potential to improve bonding to the underlying resin cement and tooth without compromising the strength of the restoration.     

Surface roughness of impression materials and dental stones scanned by non-contacting laser profilometry

ObjectiveTo analyze differences in the way dental materials digitize on a non-contacting laser profilometer (NCLP).MethodsThree Type IV dental stones and 15 impression materials were mixed according to the manufacturer's instructions and expressed against a glass block to record its surface characteristics. From each material an area of 6 × 40 mm was scanned on the NCLP and the Ra, Rq and Rt roughness values measured from 20 randomly selected transverse profiles. The surface of the impression materials was subsequently poured in Moonstone? (Bracon Ltd., Etchingham, England) dental stone and the same roughness values obtained from these casts. Differences in roughness values from the dental materials were compared using ANOVA and differences in roughness between impression materials and the Moonstone? casts compared using paired t-tests.ResultsThere were significant differences in roughness values between individual materials within each type (impression material or dental stone) (p < 0.05). The roughness of the dental stones varied between Ra = 0.87 and 0.99 μm, Rq = 1.09 and 1.23 μm, and Rt = 5.70 and 6.51 μm. The roughness values of the impression materials varied between Ra = 0.75 and 4.56 μm; Rq = 0.95 and 6.27 μm and Rt = 4.70 and 39.31 μm. Darker materials showed higher roughness values compared to lighter materials (p < 0.05). The roughness of the Moonstone? casts varied between Ra = 0.80 and 0.98 μm; Rq = 1.01 and 1.22 μm, and Rt = 5.04 and 6.38 μm. Roughness values of some impression materials were statistically significantly lower when the surface was reproduced in Moonstone? (p < 0.01).SignificanceDigitization of dental materials on optical profilometers was affected by color and transparency.     

Laser surface treatment to improve mechanical properties of cast titanium

ObjectiveThe aim of this study was to investigate the effect of laser surface treatment on the mechanical properties of cast titanium and to compare with those of the Co–Cr alloy.MethodsDumbbell-shaped cast specimens were prepared for commercially pure titanium (grade 2) and Co–Cr alloy. The cast titanium specimens were laser-treated on the surface using a dental Nd:YAG laser machine at 240 V and 300 V. After laser treatment, tensile testing was conducted to obtain the tensile strength, percent elongation and modulus of elasticity. The hardness depth profile was made from the cast subsurface (25 μm) to 1500 μm in depth using the cross-sections of the cast rods with the same diameter as the dumbbell. The data were statistically analyzed by ANOVA/post hoc tests (p < 0.05).ResultsThe highest tensile strength was obtained for the titanium specimens laser-treated with 300 V followed by the 240 V and the control specimens. The laser-treated titanium specimens with 300 V showed a tensile strength equivalent to the Co–Cr alloy. Although the highest modulus of elasticity was found for the specimens laser-treated with 240 V, there were no significant differences in elastic modulus among 240 V, 300 V and Co–Cr. The laser-treated groups showed significantly lower hardness at the subsurface of 25 μm and maintained their hardness until the depth of 400 μm. The hardness of the control group was very high at 25 μm depth, and dramatically decreased until the 200 μm depth.ConclusionThe results of tensile testing and hardness depth-profiling indicated that the laser treatment significantly improved the mechanical properties of cast titanium by improving the surface integrity of the cast surface contamination.     

A randomized controlled trial comparing surgical excisional biopsies using CO2 laser,Er:YAG laser and scalpel

This randomized controlled trial (RCT) (ClinicalTrials.gov ID: NCT03001791) compared excisional biopsies of fibrous hyperplasia performed using a CO₂ laser (140 Hz, 400 μs, 33 mJ), Er:YAG laser (35 Hz, 297 μs, 200 mJ, air–water cooling), or scalpel (15c blade). Clinical parameters recorded were duration of the intervention, intraoperative bleeding, need for electrocauterization and/or suturing, postoperative side effects, complications, pain, and intake of analgesics. Histopathological linear measurements of the thermal damage zone were performed on the laser biopsies. Results showed that the duration of the intervention was significantly shorter for both lasers compared to the scalpel (P < 0.001). Intraoperative bleeding occurred less frequently with the CO₂ laser (P < 0.001). Additional electrocautery was used in 92% of Er:YAG laser interventions (P < 0.001). Postsurgical complications, pain, and the intake of analgesics did not differ between the groups. The measured thermal damage zones differed significantly between the CO₂ laser (median of 72.6 μm) and Er:YAG laser (30.9 μm) (P < 0.001). This RCT showed that CO₂ laser, Er:YAG laser, and scalpel are all adequate for excisional biopsies of small lesions in the oral mucosa. While patient postoperative morbidity is similar, the ideal instrument can be selected according to the surgical advantages preferred for the individual situation.     

Effect of biomimetic mineralization on enamel and dentin: A Raman and EDX analysis

ObjectiveTo investigate the effect of an experimental biomimetic mineralization kit (BIMIN) on the chemical composition and crystallinity of caries-free enamel and dentin samples in vitro.MethodsEnamel and dentin samples from 20 human teeth (10 for enamel; 10 for dentin) were divided into a control group without treatment and test samples with BIMIN treatment. Quantitative analysis of tissue penetration of fluoride, phosphate, and calcium was performed using energy-dispersive X-ray spectroscopy (EDX). Mineralization depth was measured by Raman spectroscopy probing the symmetric valence vibration near 960 cm⁻¹ as a marker for crystallinity. EDX data was statistically analyzed using a paired t-test and Raman data was analyzed using the Student’s t-test.ResultsEDX analysis demonstrated a penetration depth of fluoride of 4.10 ± 3.32 μm in enamel and 4.31 ± 2.67 μm in dentin. Calcium infiltrated into enamel 2.65 ± 0.64 μm and into dentin 5.58 ± 1.63 μm, while the penetration depths for phosphate were 4.83 ± 2.81 μm for enamel and 6.75 ± 3.25 μm for dentin. Further, up to 25 μm of a newly mineralized enamel-like layer was observed on the surface of the samples. Raman concentration curves demonstrated an increased degree of mineralization up to 5–10 μm into the dentin and enamel samples.SignificanceBiomimetic mineralization of enamel and dentin samples resulted in an increase of mineralization and a penetration of fluoride into enamel and dentin.     

Effect of laser activated bleaching on the chemical stability and morphology of intracoronal dentin

ObjectivesTo evaluate the effect of the bleaching with 35% hydrogen peroxide either activated or not by a 970 nm diode laser on the chemical stability and dentin surface morphology of intracoronary dentin.MethodsTwenty-seven slabs of intracoronary dentin specimens (3 × 3 mm) were distributed into three groups (n = 9), according to surface treatment: HP – 35% hydrogen peroxide (1 × 4’), DL – 970 nm diode laser (1 × 30”/0,8W/10 Hz), HP + DL – 35% HP activated with 970 nm diode laser (1 × 30”/0,8W/10 Hz leaving the gel in contact to the surface for 4′ after activation). Three Raman spectra from each fragment were obtained to calculate the mean intensity of peaks of inorganic component (a.u.), organic collagen content (a.u.), and the ratio of inorganic/organic content, before and after treatment. Analyses of the samples by confocal laser microscopy were performed to evaluate the surface roughness, percentage of tubules, perimeter and area percentage of tubules, before and after treatment. Data were analyzed by Kruskal-Wallis, Dunn’s, and Wilcoxon test (P < 0.05).ResultsData analysis showed that HP + DL did not change the inorganic content peaks 8.31 [29.78] or the inorganic/organic ratio 3.37 [14.67] (P > 0.05). Similarly, DL did not affect the chemical stability of the dentin surface (P > 0.05). However, HP significantly increased inorganic content peaks 10.87 [22.62], as well as the inorganic/organic ratio 6.25 [27.78] (P < 0.05). Regarding the morphological alterations, all surface treatments increase tubules exposure; HP treatment significantly increases perimeter and area percentage; and HP + DL increases surface roughness.ConclusionsBleaching HP combined with DL offers an improvement in terms of intracoronal dentin surface protection, yielding better maintenance of dentin chemical stability and morphology.     

Torsion and linear accuracy in intraoral scans obtained with different scanning principles

PurposeFew investigations have examined the production of single restorations using intraoral scanners (IOS). Data on full-arch scans are rare, and data regarding torsion within the entire arch are very sparsely reported. Therefore, the aim of this study was to examine the deviations of torsion and linear distances in full-arch scans of three IOS based on different scanning principles.MethodsA cobalt-chrome-molybdenum alloy master model (CCMM) with four hemispheres was fabricated by laser sintering. The CCMM was digitized using a laboratory scanner (ATOS-Core/GOM) and scanned with three IOS (Omnicam/Sirona(OC); True Definition/3M(TD); TriosII/Cara-Version/Kulzer(TR)). All scan data were exported in a standard STL-file format and were analyzed with GOM Inspect software (V7.5/GOM). Torsion between the right and left side of the arch and linear accuracy (trueness and precision) were evaluated. After normality was confirmed, all data were subjected to parametric statistical analyses.ResultsThe torsion ranged from 0.07 ± 0.03°(OC) to 0.29 ± 0.14°(TD). Pairwise comparisons showed significant differences between the OC and TD scanners and between the TR and TD scanners. The linear distances ranged from 6 ± 5 μm(OC) to 298 ± 317 μm(TD). Significant differences were observed among all investigated IOS (p = 0.05).ConclusionsAlthough the highest torsion was observed for the TD scanner, it is still not clear whether the differences between the IOS are related to the scanning principle or to the scanning algorithm. Due to the high clinical relevance of full-arch restorations, future studies should consider torsion. Regarding linear accuracy, no general difference related to the scanning principles of the IOSs was observed.     

Pseudodysplastic epithelial artefacts associated with oral mucosa CO2 laser excision: an assessment of margin status

Using a CO₂ laser beam for biopsy is compromised by thermal cytological artefacts that could be critical when assessing dysplastic changes, as they may simulate cytological atypia. This study examined wounds caused by CO₂ laser, evaluating their size and features, utilizing 25 Sprage rats randomly allocated to five groups: four glossectomized using a CO₂ laser at 3, 6, 9 and 12 W and a control group treated with a conventional scalpel. Samples were prepared in 4 μm sections, stained, and studied double-blind by two pathologists. The artefacts identified included cellular and nuclear polymorphism, nuclear hyperchromatism and loss of intercellular adherence; they were mainly located in the basal and suprabasal layers of the oral epithelium. Number of artefacts per specimen did not differ between experimental groups. The width of epithelial damage adjacent to the laser incisions revealed 298.7 ± 150.7 μm of damaged tissue (range 100–750 μm), with no differences between low (3 W) and high wattages (6, 9 and 12 W) (X_i ? X_j = 41.6; 95% CI = ?125.1 to 208.4). No changes were observed in the control group. CO₂ laser (3–12 W) generates epithelial damage that can simulate light dysplasia with atypias mainly affecting basal and suprabasal layers that may lead to erroneous therapy.     

Marginal and internal fits of fixed dental prostheses zirconia retainers

ObjectivesCAM (computer-aided manufacturing) and CAD (computer-aided design)/CAM systems facilitate the use of zirconia substructure materials for all-ceramic fixed partial dentures. This in vitro study compared the precision of fit of frameworks milled from semi-sintered zirconia blocks that were designed and machined with two CAD/CAM and one CAM system.MethodsThree-unit posterior fixed dental prostheses (FDP) (n = 10) were fabricated for standardized dies by: a milling center CAD/CAM system (Etkon), a laboratory CAD/CAM system (Cerec InLab), and a laboratory CAM system (Cercon). After adaptation by a dental technician, the FDP were cemented on definitive dies, embedded and sectioned. The marginal and internal fits were measured under an optical microscope at 50× magnification. A one-way analysis of variance (ANOVA) was used to compare data (α = 0.05).ResultsThe mean (S.D.) for the marginal fit and internal fit adaptation were: 29.1 μm (14.0) and 62.7 μm (18.9) for the milling center system, 56.6 μm (19.6) and 73.5 μm (20.6) for the laboratory CAD/CAM system, and 81.4 μm (20.3) and 119.2 μm (37.5) for the laboratory CAM system. One-way ANOVA showed significant differences between systems for marginal fit (P < 0.001) and internal fit (P < 0.001).SignificanceAll systems showed marginal gaps below 120 μm and were therefore considered clinically acceptable. The CAD/CAM systems were more precise than the CAM system.     

In vitro enamel erosion and abrasion-inhibiting effect of different fluoride varnishes

ObjectiveTo investigate the erosion and abrasion inhibiting effect of CPP-ACP/NaF and xylitol/NaF varnishes.MethodsBovine enamel samples (n = 40) were exposed to the following treatments (n = 10): NaF varnish (Duraphat^®, positive control); CPP-ACP/NaF varnish (MI varnishTM); xylitol/NaF (Profluorid^®) or distilled and deionized water (MilliQ^®, negative control). The samples were submitted for 3 days to 4 cycles/day of erosion (5 min in Sprite Zero) and 2 cycles of abrasion/day after the first and last erosive challenge, with a toothbrush machine and slurries of a placebo toothpaste for 15 s (50 strokes/s). Among the cycles and after the last daily cycle, the specimens remained in artificial saliva. The change in the enamel surface was evaluated by using 3D non-contact optical profilometry with surface roughness (Ra and Sa values) and tooth structure loss (TSL) measurements. Scanning electron microscopy (SEM) assessed the enamel topographic characteristics. Differences in the Ra, Sa and TSL among treatments were tested using one-way ANOVA followed by the Tukey test.ResultsAll varnishes promoted better results for Ra and Sa values than the negative control (p = 0.0001), without difference among them (p > 0.05). However, CPP-ACP/NaF varnish stimulated fewer TSL (7.09 ± 0.70 μm) compared to NaF varnish (10.33 ± 1.36 μm, p = 0.002), xylitol/NaF varnish (9.96 ± 0.41 μm, p = 0.007) and the negative control (18.38 ± 3.32 μm, p = 0.0001).ConclusionA single-application of fluoride topical varnishes was effective in reducing enamel wear. The CPP-ACP/NaF varnish had the best effect against enamel loss from an erosion-abrasion challenge.     

Human neutrophil peptide-1 affects matrix metalloproteinase-2, -8 and -9 secretions of oral squamous cell carcinoma cell lines in vitro

ObjectivesThe present study aimed to investigate the effect of HNP-1 on the matrix metalloproteinase (MMP)-2, -8 and -9 secretions of two oral squamous cell carcinoma (OSCC) cell lines (UT-SCC-43A and UT-SCC-43B).DesignIn all experiments, the two OSCC cell lines were incubated with graded concentrations (0, 1, 5, and 10 μg/ml) of HNP-1 for 24 and 48 h. Cell viability was measured using a colorimetric proliferation test and cell death was analyzed with a colorimetric cytotoxicity detection kit. Enzyme activity of MMP-2 and MMP-9 was detected by using gelatin zymography, and molecular weight forms of MMP-8 were determined by Western-blot and a densitometric quantitation method.ResultsBoth cell lines showed a significant increase in LDH toxicity at 24 h (UT-SCC-43A: p = 0.005 & UT-SCC-43B: p = 0.014). Reduced gelatinolytic activities of proMMP-2 were detected in UT-SCC-43B cell line after 24 and 48 h of incubation with HNP-1 (1 μg/ml: p < 0.001, 5 μg/ml: p < 0.001, and 10 μg/ml: p = 0.0225). MMP-8 levels of both cell lines decreased at 200–250 kDa after 24 h of incubation, while after 48 h only UT-SCC-43B decreased at 45–50 kDa.ConclusionsOur results indicate that HNP-1 suppresses the secretion of MMP-2, -8, and -9 in OSCC cell lines.     

Weibull analysis of bond strength of orthodontic buccal tubes bonded to resin composite surface with various techniques

The objective of this study was to analyze the survival probabilities of various surface preparation techniques for bonding buccal tubes on resin composite surface. Resin composite specimens (hybrid), 33 per group were prepared. 8 experimental groups were (1) sandblast 90 μm; (2) sandblast 50 μm; (3) abrasion using diamond bur; (4) hydrofluoric acid etching for 1 min (HF 1 min); (5) HF 2 min; (6) HF 3 min; (7) 37% orthophosphoric etching for 10 min (H₃PO₄ 10 min) and (8) control (unetched surface). Plastic conditioner was applied then buccal tubes were bonded. Shear bond strength was tested with the universal testing machine and the Weibull analysis was performed. The results at a stress level of 7.8 MPa and 10 MPa, revealed the probabilities of survival for sandblast 50 μm (100%, 99.9%), sandblast 90 μm (99.7%, 98.7%), diamond bur (98.3%, 93.4%), HF 2 min (95.9%, 85.3%), HF 1 min (78.3%, 61.4%), HF 3 min (70.6%, 46.3%), H₃PO₄ 10 min (61.4%, 44.5%) and control (26.3%, 6.9%), respectively. Therefore, surface preparation by sandblast (50 μm and 90 μm), or diamond bur followed by plastic conditioner were highly effective for bonding orthodontic buccal tubes on hybrid resin composite surface. HF 2 min was acceptable. However, HF 1 min, 3 min, H₃PO₄ etching and unetched surface could not achieve adequate bond survival.     

Influence of surface treatments and resin cement selection on bonding to densely-sintered zirconium-oxide ceramic

ObjectivesTo evaluate the effect of surface conditioning on the microtensile bond strength of zirconium-oxide ceramic to dual-cured resin cements.MethodsEighteen cylinder-shaped zirconium-oxide ceramic blocks (Cercon^® Zirconia, Dentsply) were treated as follows: (1) Sandblasting with 125 μm aluminum-oxide (Al₂O₃) particles; (2) tribochemical silica coating using 50 μm Al₂O₃ particles modified by silica; (3) no treatment. Each ceramic cylinder was duplicated in composite resin (Tetric Evo Ceram, Ivoclar-Vivadent) using a silicon mold. Composite cylinders were bonded to conditioned ceramics using: (1) Calibra (Densply Caulk); (2) Clearfil Esthetic Cement (Kuraray); (3) Rely × Unicem (3 M ESPE). After 24 h bonded specimens were cut into microtensile sticks that were loaded in tension until failure. Data were analyzed using two-way ANOVA and Student–Newman–Keuls test for multiple comparisons (p < 0.05). Failure mode was recorded and the interfacial morphology of debonded specimens was observed using a scanning electron microscope (SEM). Surface topography and ceramic average surface roughness were analyzed under an atomic force microscope (AFM).ResultsSignificant changes in zirconia surface roughness occurred after sandblasting (p < 0.001). Bond strength of Clearfil cement to zirconia was significantly higher than that of Rely × Unicem and Calibra, regardless of the surface treatment (p < 0.001). When using Calibra, premature failures occurred in non-treated and silica coated zirconia surfaces.SignificanceThe phosphate monomer-containing luting system (Clearfil Esthetic Cement) is recommended to bond zirconia ceramics and surface treatments are not necessary.     

Measurement of vaporization cavity after CO2 laser irradiation on bovine dentin

Lasers are used for various clinical applications in dental practices, and many studies have examined the effects of lasers with different applications on enamel and dentin. The CO₂ laser was introduced into the dental clinic for the removal of caries and for cavity preparation of hard tissues, in anticipation of replacing air turban and micromotor devices. The aim of this study was to examine dentin structural changes by measuring 3-dimensional diameter, depth, and volume in bovine teeth irradiated with a CO₂ laser at 1, 3, or 5 W. According to our measurements, a vaporization depth of 400 μm was created by irradiation for a mere 100 ms in the case of 3 W irradiation and 500 μm in the case of 5 W irradiation. Further, at the same output power, the pulse mode transmitted energy to deeper layers of the tooth as compared with the continuous wave mode, indicating that the pulse mode has more penetrating power than the continuous wave mode. Moreover, the depth of cavity that after laser irradiated was > 500 μm at output power 5 W. Thus, irradiation at high output power and the influence of pulse mode on the pulp tissue cannot be disregarded. That is to say, it is important to consider irradiation output power, mode, direction, and distance when lasers are used for adjacent to pulp of tooth that primary incisors and deep cavities.     

Comparative effectiveness of NiCl2, Ni- and NiO-NPs in controlling oral bacterial growth and biofilm formation on oral surfaces

ObjectiveOral ailments are often treated with antibiotics, which are rendered ineffective as bacteria continue to develop resistance against them. It has been suggested that the nanoparticles (NPs) approach may provide a safer and viable alternative to traditional antibacterial agents. Therefore, nickel (Ni)- and nickel oxide (NiO)-NPs were synthesized, characterized and assessed for their efficacy in reducing oral bacterial load in vitro. Also, the effects of bulk compound NiCl₂ (Ni ions), along with the Ni- and NiO-NPs on bacterial exopolysaccharide (EPS) production and biofilm formation on the surface of artificial teeth, and acrylic dentures, were investigated.MethodsTotal bacteria from a healthy male were collected and adjusted to 4 × 109 cells/ml for all the tests. Effect of the NPs on growth, biofilm formation, EPS production and acid production from glucose was tested using standard protocols.ResultsData revealed that the Ni-NPs (average size 41.23 nm) exhibited an IC50 value of 73.37 μg/ml against total oral bacteria. While, NiO-NPs (average size 35.67 nm) were found less effective with much higher IC50 value of 197.18 μg/ml. Indeed, the Ni ions exhibited greater biocidal activity with an IC50 value of 70 μg/ml. Similar results were obtained with biofilm inhibition on the surfaces of dental prostheses. The results explicitly suggested the effectiveness of tested Ni compounds on the growth of oral bacteria and biofilm formation in the order as NiCl₂ > Ni-NPs > NiO-NPs.ConclusionThe results elucidated that Ni-NPs could serve as effective nanoantibiotics against oral bacteria.     

Comparison of the accuracy for three dental impression techniques and index: An in vitro study

ObjectivesThis in vitro study compared the dimensional accuracy of stone index (I) and three impression techniques: tapered impression copings (T), squared impression copings (S) and modified squared impression copings (MS) for implant-supported prostheses.MethodsA master cast, with four parallel implant abutment analogs and a passive framework, were fabricated. Vinyl polysiloxane impression material was used for all impressions with two metal stock trays (open and closed tray). Four groups (I, T, S and MS) were tested (n = 5). A metallic framework was seated on each of the casts, one abutment screw was tightened, and the gap between the analog of implant and the framework was measured with a stereomicroscope. The groups’ measurements (80 gap values) were analyzed using software (LeicaQWin – Leica Imaging Systems Ltd.) that received the images of a video camera coupled to a Leica stereomicroscope at 100× magnification. The results were statistically analyzed with Kruskal–Wallis One Way ANOVA on Ranks test followed by Dunn's Method, 0.05.ResultsThe mean values of abutment/framework interface gaps were: Master Cast = 32 μm (SD 2); Group I = 45 μm (SD 3); Group T = 78 μm (SD 25); Group S = 134 μm (SD 30); Group MS = 143 μm (SD 27). No significant difference was detected among Index and Master Cast (P = .05).ConclusionUnder the limitations of this study, it could be suggested that a more accurate working cast is possible using tapered impression copings techniques and stone index.     

Effects of glazing methods on the optical and surface properties of silicate ceramics

PurposeThis study aims to evaluate the effect of different glazing methods on translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), surface roughness (Ra) and topography of the silicate ceramics.MethodsSeventy specimens (10 × 10 × 1 mm) were fabricated from lithium disilicate (IPS e.max CAD, abbreviated as E) and zirconia-reinforced lithium silicate (Vita Suprinity, abbreviated as VS) ceramics and divided into 7 subgroups (n = 10) according to the polishing and glazing procedures: (1) mechanical polishing before-crystallization (m-BC), (2) mechanical polishing after-crystallization (m-AC), (3) glaze powder/liquid after-crystallization (pl-AC), (4) glaze-paste before-crystallization (gp-BC), (5) glaze-paste after-crystallization (gp-AC), (6) glaze-spray before-crystallization (gs-BC), (7) glaze-spray after-crystallization (gs-AC). Color and Ra measurements were performed. CIEL*a*b* and CIEXYZ parameters were recorded and TP, CR, and OP values were calculated. Data were analyzed using two-way ANOVA and Tukey HSD tests (α = 0.05).ResultsIn E groups, the highest Ra value was found in gs-AC (1.66 ± 0.14 μm) while the lowest value was found in pl-AC (0.68 ± 0.08 μm). In VS groups, the highest Ra value was found in gp-BC (1.64 ± 0.25 μm) while the lowest value was found in m-AC (0.77 ± 0.06 μm) (p < 0.05). The mean TP value of E (17.62 ± 0.73) was found to be higher than VS (15.37 ± 1.16). The CR (0.72±0.030) and OP (12.06 ± 0.74) values of VS were found higher than CR (0.57 ± 0.02) and OP (6.72 ± 0.40) values of E.ConclusionsZirconia-reinforced silicate ceramics have higher opalescence and lower translucency values than lithium disilicate ceramics. Increase in surface roughness reduces translucency. Glaze powder/liquid after-crystallization is the most effective way to reduce surface roughness of lithium disilicate ceramics while that is mechanical polishing after-crystallization for zirconia-reinforced silicate ceramics.     

Dehydration and the dynamic dimensional changes within dentin and enamel

ObjectivesThe objectives of this study were to quantify the dimensional changes in dentin and enamel during dehydration, and to determine if there are differences between the responses of these tissues from young and old patients.MethodsMicroscopic digital image correlation (DIC) was used to evaluate deformation of dentin and enamel as a function of water loss resulting from free convection in air. Dimensional changes within both tissues were quantified for two patient age groups (i.e. young 18 ≤ age ≤ 30 and old 50 ≤ age) and in two orthogonal directions (i.e. parallel and perpendicular to the prevailing structural feature (dentin tubules or enamel prisms)). The deformation histories were used to estimate effective dehydration coefficients that can be used in quantifying the strains induced by dehydration.ResultsBoth dentin and enamel underwent contraction with water loss, regardless of the patient age. There was no significant difference between responses of the two age groups or the two orthogonal directions. Over 1 h of free convection, the average water loss in dentin was 6% and resulted in approximately 0.5% shrinkage. In the same time period the average water loss in the enamel was approximately 1% and resulted in 0.03% shrinkage. The estimated effective dehydration coefficients were ?810 μm/m/(% weight loss) and ?50 μm/m/(% weight loss) for dentin and enamel, respectively.SignificanceThe degree of deformation shrinkage resulting from dehydration is over a factor of magnitude larger in dentin than enamel.     

Combined effect of fluoride varnish to Er:YAG or Nd:YAG laser on permeability of eroded root dentine

ObjectiveThis study evaluated the combined effect of fluoride varnish to Er:YAG or Nd:YAG laser on permeability of eroded root dentine.DesignSixty slabs of bovine root dentine (2 × 2 × 2 mm) were eroded with citric acid 0.3% (pH 3.2) during 2 h and then kept in artificial saliva during 24 h. Specimens were randomly assigned in 6 groups (n = 10), to receive the following treatments: fluoride varnish; fluoride varnish + Er:YAG laser; fluoride varnish + Nd:YAG laser; non-fluoride varnish; non-fluoride varnish + Er:YAG laser; non-fluoride varnish + Nd:YAG laser. The Er:YAG (100 mJ, 3 Hz) and Nd:YAG (70 mJ, 15 Hz) were applied for 10 s. Specimens were subjected to further erosive challenges with citric acid 0.3% 4×/day, during 1 min, for 5 days, remaining in artificial saliva between cycles. Dentin permeability was then assessed. Two-way ANOVA demonstrated no significant interaction between laser and varnish (p = 0.858).ResultsNo effect was also detected for the main factor varnish (p = 0.768), while permeability of eroded root dentin was significantly lower when such substrate was laser-irradiated, no matter the laser source (p < 0.001).ConclusionsThis study concluded that Er:YAG and Nd:YAG lasers can be employed to control the permeability of eroded root dentin, regardless of fluoride varnish application.     

Thickness and surface structure of a ceramic layer created on three indirect resin composites with aerosol deposition

PurposeAerosol deposition is a technology for coating ceramics with impact consolidation at room temperature. The aim of the present study was to investigate the thickness and the microstructure of the aluminium oxide layer on different three dental resin composite materials created by means of aerosol deposition.MethodsDisk-shaped specimens were fabricated with three resin composites (Estenia C&B, Targis, and Gradia). The specimens were ground flat, and then subjected to aerosol deposition using aluminium oxide submicron particles without inducing a localized temperature rise. The average thickness (AVH) and maximum thickness (Hmax) of the aluminium oxide layer deposited on the resin composite material were measured using a profilometer. Data were analyzed by ANOVA and post hoc Tukey compromise test at α = 0.05. The specimen surfaces were also observed using a scanning electron microscope.ResultsThe aluminium oxide layer formed on Estenia C&B (AVH 8.1 μm, Hmax 9.1 μm) and Targis (AVH 7.7 μm, Hmax 8.9 μm) were significantly thicker than that on Gradia (AVH 4.2 μm, Hmax 5.4 μm). The micrograph showed that the aluminium oxide layer on Estenia C&B was similar to that on Targis. However, the aerosol deposition area of Gradia was seen relatively rough and partly caved.ConclusionsThe type of resin composite affected the microstructure of the deposited aluminium oxide layer. The highly filled light- and heat-cured resin composites are advantageous as a target material rather than the lower filled light-cured resin composite.