Polymerization Of Resin Cement Research Articles

Effects of Ceramic Translucency and Thickness on Polymerization of a Photosensitive Resin Cement

We investigated the effects of lithium disilicate ceramic thickness and translucency on the degree of polymerization of light-cured resin cement using the measure of hardness. Lithium disilicate specimens of three translucencies (low, medium and high) were prepared to four thicknesses (0.5, 1.0, 2.0 and 3.0 mm). A light-cured resin cement was cured through each of the ceramic specimens using a handheld curing light for 50 s. A 3D printed jig was used to achieve a uniform thickness of the resin cement. Directly cured resin cement was used as the control. Hardness was measured using nano-indentation to determine the degree of polymerization of the resin cement. Two-way ANOVA and Tukey post hoc tests were used to evaluate interaction between translucency and thickness. Hardness values from control specimens were assessed using the two-tailed t-test with the Bonferroni approach. The translucency of the specimens significantly influenced the hardness (p < 0.001), where a negative linear relationship between cement hardness and ceramic thickness was present for low translucency and high translucency. However, at a 0.5 mm thickness, all specimens showed similar hardness regardless of the translucency. The translucency of ceramics affected the hardness, and hence polymerization, of light-cure resin cement. However, the effect of increased thickness was a more significant factor.

Effect of Attenuated Light Through Translucent Zirconia on the Interfacial Adaptation and Polymerization of Resin Cements.

The first objective was to determine if dual-curing of resin cement with reduced light could affect interfacial adaptations of zirconia restoration. The second objective was to examine whether cement type and pretreatment method of universal adhesive affected interfacial adaptation. The final objective was to compare the polymerization degree of cement under different reduced-light conditions. Inlay cavities were prepared on extracted third molars. Translucent zirconia restorations were milled using Katana UTML (Kuraray Noritake) in three groups with restoration thicknesses of 1, 2, and 3 mm, respectively. Each group had three subgroups using different cementation methods. For subgroup 1, restorations were cemented with self-adhesive cement. For subgroup 2, universal adhesive was applied and light cured. After the restoration was seated with conventional resin cement, light curing was performed. For subgroup 3, after adhesive was applied, the restoration was seated with conventional resin cement. Light curing was performed for the adhesive and cement simultaneously. After thermocycling, interfacial adaptation at the restoration-tooth interface was investigated using swept-source optical coherence tomography imaging. Finally, polymerization shrinkage of the cement was measured using a linometer and compared under the conditions of different zirconia thicknesses and light-curing durations. Interfacial adaptation varied signficantly depending on the zirconia thickness, pretreatment, polymerization mode and cements used (p < 0.05). The effects of the adhesive and polymerization shrinkage differed signficantly, depending on the reduced light under the zirconia (p < 0.05). Lower curing-light irradiance may lead to inferior adaptation and lower polymerization of the cement. Polymerization of resin cement can differ depending on the light irradiance and exposure duration.

A technique to remove polymerized excess resin cement from interproximal regions following bonding of porcelain laminate veneers

A technique to remove polymerized excess resin cement from interproximal regions following bonding of porcelain laminate veneers

ENDOCROWN RESTORATION OF THE ENDODONTICALLY TREATED TEETH BY USING CAD/CAM: CASE SERIES

Aim: As a result of large coronal destruction in endodontically treated teeth, significant losses occur in the dentin tissue around the pulp and the need for prosthetic treatment occurs. In this case series, endocrown applications produced in a single session with CAD/CAM system are presented as an alternative to crown restoration traditionally applied to premolar and molar teeth with excessive crown destruction.&#x0D; &#x0D; Case Series: In first case, 38-years-old male patient number 25, 46-years-old female patient number 36 in our second case, 21-years-old female patient number 46 in our third case, 26-years-old male patient number 46 in our fourth case, and in the last case 52-years-old male patient tooth number 15 has been applied to root canal treatment. As a result of the clinical and radiological examinations of the patients, it was observed that there were no systemic diseases. Endocrown restoration was considered appropriate and recommended to patients with less dentin tissue. Firstly, teeth are prepared for endocrown restoration. Afterwards, the impressions were digitalized by scanning the jaws with an intraoral optical scanner (Cerec Omnicam, Dentsply Sirona, USA). The restorations were designed with the help of the CEREC 4.3 software (Dentsply Sirona, USA) and the milling process was carried out using the feldspathic ceramic block (Vita Mark II, Vita Zahnfabrik, Germany) in the same session by CEREC inLab MC XL (Dentsply Sirona, USA). Later, the restorations were glazed and cemented with dual polymerized resin cement (RelyX Ultimate, 3M ESPE, USA).&#x0D; &#x0D; Conclusion: Endocrown restorations are a minimally invasive, conservative treatment approach that provides mechanical adhesion to the pulp chamber and cavity walls with adhesive resin cement and allows the preservation of the remaining tooth structure. For this reason, it is a treatment option that can be preferred instead of post-core and crown application in teeth with root canal treatment.

Three-dimensionally printed spot polymerization light-guide tip attachment

Stabilizing a veneer in its seated position by selective spot photopolymerization of the adhesive resin cement at the center of the veneer has been advocated.1 This procedure facilitates the removal of excess unpolymerized or partially polymerized resin cement at the margin and interproximal region without risk of unseating the veneer.2 Some manufacturers provide small-diameter glass-fibered light guides (Light Probe Pin-Point 6 > 2mm; Ivoclar AG) or attachments (PointCure lens; Ultradent Products, Inc) for this purpose; however, they are not available or compatible with all light-polymerization units.

Effect of thickness of CAD/CAM materials on light transmission and resin cement polymerization using a blue light-emitting diode light-curing unit.

Evaluate the effect of thickness of high-translucency (HT) CAD/CAM materials on irradiance and beam profile from a blue light-emitting diode light-curing unit (LCU) and on the degree of conversion (DC) and maximum polymerization rate (Rpmax ) of a light-cured resin cement (LCC). The direct output from the LCU, the light transmission and irradiance ratio (IR) through one conventional composite and nine HT CAD/CAM materials (0.5, 1.0, 1.5, or 2.0-mm thick; n=5) were measured with a integrating sphere coupled to a spectrometer. The light beam was assessed with a beam profiler camera. The DC at 600 s and the Rpmax of one LCC was determined using a Fourier transform infrared spectrometer (n=5). Data were analyzed by ANOVA followed by Tukey's tests, and Dunnett's test was also used for irradiance data (α=0.05). A significant decrease in irradiance through all materials occurred as thickness increased. Thin CAD/CAM materials improved light homogeneity, which decreased with the increase in thickness. The DC of the LCC directly exposed to light was the same as when exposed to 45%, 25%, 15%, or 5% IRs. Rpmax decreased with the decrease in IR. Although the HT CAD/CAM materials reduced the irradiance from the LCU, minor effects were observed in the LCC's DC. Despite the light attenuation of blue light through different CAD/CAM materials that were up to 2-mm thick, the degree of conversion of one brand of light-cured resin cement was clinically acceptable when the LCU was used for 30 s.

Effect of the composition and manufacturing process on the resin microtensile bond strength to ceramics

The present study aimed to investigate the bond strength between resin cement and different glass-ceramics manufactured in different processing systems using two different microtensile bond strength test (μTBs) assemblies (ceramic-ceramic or ceramic-dentin). For this, ceramic blocks were fabricated with adhesive surface area of 5 × 5 mm to test the different possibilities combining the two different glass-ceramic compositions (feldspathic – FEL and lithium disilicate - LD), the three manufacturing-processes (CAD/CAM, heat-pressed or layered for FEL; CAD/CAM or heat-pressed for LD) and the two μTBS assemblies (ceramic-ceramic or ceramic-dentin). Half of the samples of each ceramic evaluated were made by cementing the ceramic blocks in another ceramic block and the other half by cementing the ceramic blocks in ground molars with exposed dentin, using resin cement (Rely X ARC, 3 M ESPE). The samples were stored for 24 h in distilled water at 37 °C and then sectioned into microbars (±1 mm 2 , n = 30). These specimens were submitted to the μTBS and the data were analyzed by specific statistical tests (α = 0.05). The fractured surfaces were examined under a stereomicroscope and the failure mode was classified. In addition, finite element analysis (FEA) was performed to observe the maximum tensile stress in the resin cement when a μTBS load was applied (10 N) and during the resin cement polymerization shrinkage. The CAD/CAM glass-ceramics have better bond strength than the other evaluated manufacturing processes, the LD groups had higher μTBS values than the FEL groups in ceramic-ceramic assembly; dentin as a substrate (ceramic-dentin assembly) had a negative influence on the results for all evaluated materials. Regarding the FEA results, the maximum tensile stress in ceramic-ceramic groups was 16.1–16.5 MPa (when 10 N load was simulated), and 50.8–51.2 MPa (during the resin cement polymerization shrinkage). For the ceramic-dentin groups, the maximum tensile stress was 16.9 and 17.1 MPa on the ceramic side and 17.6 and 17.8 MPa on the dentin side (10 N load simulation); 49.8 and 49.4 MPa on the ceramic side and 49.7 and 49.4 MPa on the dentin side (resin cement polymerization shrinkage). Different glass-ceramic compositions and manufacturing processes induced distinct bond strength values (LD had better results). Moreover, the μTBS assembly interferes with the results obtained, having the ceramic-ceramic set-up inducing higher bond results than the ceramic-dentin arrangement.

Light Transmission of Various Aesthetic Posts at Different Depths and Its Effect on Push-Out Bond Strength, Microhardness of Luting Cement.

Background and Objectives: One requirement for the cemented post is the light transmittance on its entire length up to the deepest portion of a root canal to ensure the complete polymerization of resin cement. This study aimed to determine the light transmission ability in different aesthetic posts at different depths and its effect on the push-out bond strength and microhardness of luting cement at the corresponding interface. Materials and Methods: Twenty endodontic posts from glass fiber posts (GFP), zirconia ceramic posts (ZCP), and highly translucent zirconium oxide posts (HTZP) were sequentially sectioned into 12.8 and 4 mm lengths after recording the light intensity using a dental radiometer. Sixty single rooted premolar teeth root canals were treated and implanted vertically in a resin block. The post space was prepared and cemented with GFP, ZCP, and HTZP posts with twenty samples each. The root portion of teeth samples were sectioned into cervical, middle, and apical portion. A universal testing machine was utilized for the push-out bond strength test for the first ten samples from each group. The remaining ten samples from each group were used for the microhardness test using a micro-indenter instrument. The data were statistically analyzed using one-way Analysis of variance and Tukey HSD tests at p < 0.05. Results: The GFP endodontic postpresented with significant highest light translucency compared to HTZP, which was significantly higher than ZCP. GFP posts showed significantly higher bond strength per unit area compared to ZCP at analogous cross sections. The hardness of luting cement was also significantly higher amongst all tested endodontic posts. Conclusions: GFP high light translucency enhanced the curing of the luting resin cement that resulted in harder cement and a stronger bond supported by hardness and push-out tests. These findings suggest that GFP is preferred to be used with light-cured luting cements for restoration of endodontically treated teeth.

Effect Of Repeated Heat Pressing And Thermocycling On Micro Shear Bond Strength Of Polyetheretherketone (PEEK) To Resin Cement

Abstract: Purpose: to evaluate the effect of repeated heat pressing and thermocycling on micro-shear bond strength of PEEK to resin cement. Methods: A total of 30 PEEK specimens 10 mm x 10 mm x 2 mm were prepared and divided to three groups (n=10). Group I was pressed using new PEEK, Group II ; 50% new PEEK and 50% reprocessed PEEK, and Group III ; 100% reprocessed PEEK. Bonding surfaces were sandblasted and thin layer of bonding agent was applied and polymerized. Plastic tygon tubes with an inner diameter of 1 mm and a height of 1.5 mm were fixed on the sample and filled with dual polymerized self etch self adhesive resin cement and cured. Half the specimens in each group (n=5) underwent 5000 thermocycles (5‐55°C) before shear bond strength (µSBS) test. Two-way Analysis of Variance (ANOVA) studied the effect of PEEK condition, thermocycling and their interaction on mean micro-shear bond strength µSBS. Bonferroni’s post-hoc test was used for pair-wise comparisons when ANOVA test is significant. Results: The PEEK condition (regardless of thermocycling) had a statistically significant effect on mean µSBS (P-value = 0.001, Effect size = 0.455). Thermocycling (regardless of PEEK condition) also had a statistically significant effect on mean µSBS (P-value = 0.002, Effect size = 0.331). The interaction between two variables had no statistically significant effect on mean µSBS (P-value = 0.442, Effect size = 0.066). Conclusion: Both repeated heat pressing and thermocycling had a negative effect on micro-shear bond strength of resin cement to PEEK

Influence of Cement Thickness on the Polymerization Shrinkage Stress of Adhesively Cemented Composite Inlays: Photoelastic and Finite Element Analysis

The objective of this study was to analyze the effect of cement thickness on the strain and stresses resulting from the polymerization of resin cement using photoelasticity and Finite Element Analysis (FEA). For this study, twenty upper first premolars with inlay cavity preparation were constructed from photoelastic resin and restored with composite resin inlay. The samples were divided into two groups (n = 10) according to the film thickness of resin cement material. For Group 1, the film thickness was 100 μm; for Group 2, the film thickness was 400 μm. After polymerization of the cement, photoelastic analysis and finite element analysis (FEA) were performed. In the photoelastic analysis, Group 2 showed higher strain with the presence of second-order fringe even after 24 h. In Group 1, the formation of first order fringes was not observed, even after 24 h. In the FEA analysis, the greatest cusp deflection and tensile stress occurred in Group 2 (0.00026 mm and 0.305 MPa, respectively) due to the polymerization shrinkage in the lingual cusp compared to Group 1 (0.000107 mm and 0.210 MPa, respectively). It can be concluded that the thickness of the resin cement influences the cusp deflection, with the greater thickness of the cement layer, the greater stresses and deformations in the tooth structure occur.

The Effects of Differences in Post Canal Widths on Microleakage in Prefabricated Fiber Reinforced Composites

Introduction: Fiber Reinforced Composite (FRC) post is one of the choices in post root canal treatment. Resin cement polymerization results in shrinkage, creating micro gaps between the FRC posts and the root canal wall. This study aimed to find microleakage differences of prefabricated FRC posts with different root canal diameters. Methods: Twenty four maxillary central incisors were used, the root length was 13 mm from the apex. The root canal was prepared with conventional technique and then filled with a single cone technique. Samples were divided into 4 treatment groups of 1.2 mm, 1.4 mm, 1.6 mm and 1.8 mm diameter, cemented, then coated with sticky wax and nail polish and immersed in 2% methylene blue liquid and put into an incubator at 37o for 72 hours. Objects were divided into two mesiodistal directions, observed under a 20x-magnification stereomicroscope. Results: Kruskal-Wallis test showed significant differences in all treatment groups (p &lt;0.05). Mann-Whitney test showed differences between groups (p&lt;0.05) of Ø 1.2 mm and Ø 1.6 mm, Ø 1.2 mm and Ø 1.8 mm, and Ø 1.4 mm and Ø 1.8 mm group. Discussion: The main cause of microleakage at the edge of restoration is because the resin cannot completely close the edges, resulting in shrinkage and contraction during polymerization of the composite resin. Conclusion: There were microleakage in the four groups, the wider root canal might lead to greater microleakage.&#x0D; Keyword?Microleakage, FRC, root canal diameters.

Microcomputed tomography evaluation of cement shrinkage under zirconia versus lithium disilicate veneers

Statement of problemComputer-aided design and computer-aided manufacturing (CAD-CAM) technology and the improved translucency of recently developed high-strength monolithic zirconia could make them clinically acceptable for veneers if bonding to zirconia was as predictable as to glass-ceramics. Few studies have compared how resin cements behave between glass-ceramic and zirconia veneers before and after polymerization. PurposeThe purpose of this in vitro study was to evaluate the volumetric polymerization shrinkage of resin cement, marginal discrepancy, and cement thickness before and after polymerization for glass-ceramic and zirconia veneers with light-polymerizing resin cement. Material and methodsTen lithium disilicate veneers and 10 zirconia veneers were fabricated with a CAD-CAM workflow on extracted human maxillary anterior teeth with intact enamel surfaces. Zirconia veneers were treated with airborne-particle abrasion, and lithium disilicate veneers were etched with 5% hydrofluoric acid. All specimens were treated with ceramic primer and cemented with a light-polymerized resin cement. All specimens were scanned before and after resin cement polymerization by microcomputed tomography. The data were processed by the Amira software program to compare polymerization volumetric shrinkage, cement thickness, and marginal discrepancy. The data were compared by using a t test and analysis of variance (α=.05). Two bonded veneers were loaded in a mastication simulator for 400 000 cycles to investigate the effect of cyclic fatigue loading. ResultsMean volumetric polymerization shrinkage was 4.2 ±0.8% for the lithium disilicate group and 6.4 ±3.5% for the zirconia group. No significant difference was found for volumetric shrinkage between materials (P=.132). The mean ±standard deviations of the marginal discrepancies before and after polymerization were 178 ±41 μm and 158 ±37 μm for lithium disilicate and 115 ±33 μm and 107 ±32 μm for zirconia. A smaller marginal discrepancy was found for both materials after polymerization (P=.011) and for zirconia compared with lithium disilicate (P=.004). The mean ±standard deviation cement thickness values before and after polymerization were 157 ±27 μm and 147 ±27 μm for lithium disilicate and 162 ±53 μm and 147 ±52 μm for zirconia. Smaller cement thickness was found after polymerization (P<.001), whereas no significant difference was found in cement thickness between materials (P=.144). No changes were noted in marginal discrepancy and cement thickness as a result of the fatigue loading. ConclusionsThe difference in the volumetric polymerization shrinkage of cement between lithium disilicate and zirconia veneers was not statistically significant. Polymerization shrinkage resulted in smaller marginal discrepancy and cement thickness for both veneer materials.

Degree of Conversion of Light Cured Resin Cements Polymerized under Two Thicknesses of Different Lithium Silicate Ceramics

Objective: To show the consequence of two thicknesses of ceramic on the polymerization of resin cement light cured when three different lithium silicate ceramics were used. Materials and Methods: 42 ceramic slices were prepared from three types of ceramics, Emax CAD, Celtra Duo CAD and Vita suprinity CAD (n=14). They were further divided into two subgroups according to thicknesses into sub group thickness 0.5mm and sub group thickness 1mm (n=7). Teflon moulds were fabricated with specific dimensions, where the ceramic disc was placed followed by light cured resin cement Bisco choice 2 veneer and a glass slab with finger pressure applied. Curing with Ascent® PX LED light cure unit for 20 seconds took place, where the tip placed over the ceramic sample directly. Cement film was then separated from the ceramic disk and subjected to analysis by Fourier Transform Infrared Spectroscope. Uncured cement samples were also subjected to analysis. Results: Celtra DUO CAD ceramic showed higher degree of polymerization that of Emax and Vita suprinity while the difference between Emax and Suprinity on the degree of polymerization was not significant. Also, ceramic thicknesses had a significant effect on the degree of polymerization of the resin cement. Conclusion: Thickness of ceramics up to 1mm affects the polymerization of resin cement significantly.

Effect of light intensity, light-curing unit exposure time, and porcelain thickness of ips e.max press and vintage LD press on the hardness of resin cement

Background: Porcelain veneer restoration is the primary choice for indirect restoration, especially for anterior teeth, given its high esthetic properties and lower failure rate than resin composites. Glass-based ceramics such as IPS e.max Press and Vintage LD Press are a choice for veneer due to its superior physical properties. Resin cement is used to attach the veneer restoration to the teeth. The polymerization of resin cement used in veneer restoration affects the stability, mechanical properties, and resistance of the restoration. The composition and thickness of the porcelain material affect the light-curing unit to cured resin cement. Objectives: The aim of this study was to evaluate the influence of porcelain thickness, light intensity, and exposure time in the hardness of resin cement. Methods: Porcelain samples measuring 5 mm in diameter with three types of thicknesses of IPS e.max Press and Vintage LD Press were used in the study. Resin cement in a metal mold was placed under a porcelain sample before curing with a light-emitting diode (LED) intensity of 1300 or 1700 mW/cm2. The hardness test was then carried out on the bottom of the resin cement. Result: The highest hardness value was obtained from a Vintage LD Press with a thickness of 0.7 mm (cured at 1300 mW/cm2 for 20 s). A four-way ANOVA test showed significant differences for brands, thicknesses, and times of exposure (P

Evaluation of Dual-Cure Resin Cement Polymerization under Different Types and Thicknesses of Monolithic Zirconia.

Purpose The aim of the present study was to investigate the effects of the type and thickness of the zirconia material on the microhardness of the underlying dual-cure resin cement. Materials and Methods Eight disk-shaped zirconia specimens with a 4-mm diameter and four varying thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were fabricated from two different monolithic zirconia materials: posterior monolithic zirconia (Prettau) and anterior monolithic zirconia (Prettau Anterior). Dual-cure resin cement specimens with a 4-mm diameter and 5-mm height were prepared using Teflon cylinder molds and activated by light beneath the eight zirconia disks and without any zirconia disk for 20 s (n=12). A total of 108 specimens were embedded in acrylic. Vickers hardness of each specimen was measured at three different depths using a microhardness device with a 50-g load. All data were statistically evaluated using three-way ANOVA, one-way ANOVA, independent samples t-tests, and Bonferroni corrected post hoc tests (α=.05). Results Dual-cure resin cement's microhardness was significantly higher for the samples polymerized beneath anterior monolithic zirconia compared to posterior monolithic zirconia. The hardness decreased as the thickness increased for both types of zirconia; the latter was attributed to an attenuated curing efficiency. Conclusion Microhardness of the dual-cure resin cement is influenced by both the type and the thickness of the monolithic zirconia restoration. Polymerization efficiency for resin cement cured under anterior monolithic zirconia may be superior to cured beneath posterior monolithic zirconia.

The Effect of Ceramic Thickness on the Surface Microhardness of Dual-cured and Light-cured Resin Cements

This study was conducted to evaluate the effect of ceramic thickness on the surface hardness of light-cured and dual-cured resin cements. Forty disk-like specimens of the dual-cured resin cement and twenty-four specimens of the light-cured resin cement were prepared (with 6 mm diameter and 1mm thickness). The samples were light-cure d for 40 seconds through three different ceramic disks (2 mm, 3 mm and 4 mm). Control specimens from each group were directly polymerized under a Mylar strip. In the control group of the dual-cured resin cement, the cement setting was realized by chemical reaction alone. After storing dry in darkness (24 hours, 37°C), the surface hardness of the specimens was measured using the Vickers microhardness test. Data were statistically analyzed using a two-way analysis of variance (ANOVA) followed by the LSD's test (p <0.05). BisCem resin cement which had been dual-cured under the 4 mm thickness ceramic with the 4.3 Vickers hardness, showed minimum surface microhardness, while the light-cured resin cement which had been directly activated in the control group with the 51.8 Vickers hardness value exhibited the maximum surface microhardness. So, BisCem dual polymerized control specimens had significantly higher hardness values in comparison to the chemically polymerized and indirectly activated ones (p <0.001). An increase in the thickness of ceramic could decrease the hardness of the resin cement. An overlying ceramic thickness of 3 mm and above was found to adversely affect the polymerization of the LC and DC resin cement and it was considered as the clinical threshold. In addition, using only the self-cured mode in the dual-cured resin cement was not sufficient for achieving the optimum surface microhardness. Clinical significant: Adequate polymerization of resin cement is essential for the optimal mechanical properties and clinical performance. It affects by increasing the thickness of ceramic restorations.

Does the Translucency of Novel Monolithic CAD/CAM Materials Affect Resin Cement Polymerization with Different Curing Modes?

The translucency of CAD/CAM blocks influences the polymerization efficiency of resin cement used underneath. The aim of this study is to evaluate the influence of the translucency parameters (TPs) of current monolithic CAD/CAM blocks on the microhardness of light-cured or dual-cured resin cement. 100 specimens were prepared from five types of CAD/CAM blocks (Mark II, Suprinity, Enamic, e.max, Ultimate), and their TP values were measured by spectrophotometry; 100 resin cement specimens (Duolink) were cured underneath five ceramic specimen groups by indirect LED light for 40 seconds with dual-cure (with catalyst) and light-cure (without catalyst) polymerization modes. Control group resin cement specimens (n = 20) were cured with both polymerization modes by direct LED light without any ceramic disc, making 120 resin cement specimens in total. The specimens were then stored in a dry environment for 24 hours before measurement of the polymerization depth with a digital micrometer. Vickers hardness measurements were performed at different resin cement sections. The results were statistically analyzed with 1-, 2-, and 3-way ANOVA, Student's t-test and Tukey's HSD test (α = 0.05). The highest TP values occurred for Suprinity and Ultimate, whereas the lowest TP value occurred for Enamic (p < 0.01). The depth of cure and Vickers hardness values changed proportionally with TP value. In all specimens, dual polymerization provided higher depth of cure and Vickers hardness values than those obtained using light polymerization (p < 0.01). In all specimens except Enamic, the hardness value differences between the sections were statistically insignificant (p > 0.05). In Enamic, the hardness values for both polymerization types decreased significantly in the deeper sections (p < 0.01). Lower depth of cure was observed as the amount of transmitted light decreased in the investigated materials. In clinical practice, light-cured resin cements may result in inadequate polymerization for ceramic materials with lower TP values. Zirconia-reinforced lithium silicate and nanoceramic resins may be reliable restorative materials for a restoration with both optimal esthetics and sufficient mechanical strength resulting from proper polymerization.

The Effect of Lithium Disilicate Ceramic Thickness and Translucency on Shear Bond Strength of Light-cured Resin Cement

Introduction: To achieve acceptable clinical performance, a ceramic veneer must be bonded to enamel by well-polymerized resin cement. Among different factors, thickness and translucency of the ceramic may affect the resin cement polymerization. Thus, the current study evaluated the effect of the thickness and translucency of lithium disilicate ceramic on light-cured resin cement bond strength to enamel. Methods: In this laboratory study, 208 sound bovine incisors were equally divided into 16 groups (n = 13). The lithium disilicate ceramic cubes in four thicknesses (0.4, 0.6, 0.8 and 1 mm) with four translucencies (high and medium opaque, high and low translucent) were fabricated and bonded to prepared enamel surfaces using a light-cured translucent resin cement according to manufacturer recommendations. After 5000 cycles of thermocycling, the bonded specimens were placed in a universal testing machine and loaded to the point of fracture. To determine the mode of failure, each sample was observed under a stereomicroscope. Data were recorded and analyzed by Shapiro-Wilk test and two-way analysis of variance (ANOVA). Results: The ceramic thickness and translucency could not significantly affect shear bond strength (SBS) of resin cement to enamel (p = 0.17 and p = 0.097, respectively). The Adhesive and ceramic cohesive failures were reported as the maximum and minimum mode of failure, respectively. Conclusion: The SBS of the light-cured resin cement bonding to enamel and lithium disilicate ceramic was not affected by the translucency of ceramics having a thickness of less than 1 mm.

The influence of the emergence profile on the amount of undetected cement excess after delivery of cement-retained implant reconstructions.

To test whether or not one of two emergence profile designs (concave or convex) is superior to the other in terms of remaining cement following cementation of reconstructions on individualized abutments and careful cement removal. A central incisor with a single implant-supported reconstruction was selected as a model. Six types of abutments (n=10) with two different emergence profile designs (concave (CC) and convex (CV)) and three crown-abutment margin depths (epimucosal, 1.5mm submucosal, 3mm submucosal) were fabricated through a CAD/CAM procedure. Lithium disilicate reinforced ceramic crowns were cemented with chemically polymerized resin cement. A blinded investigator attempted to remove all cement excess. Thereafter, the entire reconstruction was unscrewed and analyzed for the overall amount and the depth of cement excess. Kruskal-Wallis and Mann-Whitney tests were used to investigate differences between groups. When more than two groups were compared between each other, a Bonferroni correction of the P value was performed. Concave abutments presented significantly more cement remnants than CV abutments when the entire abutment area of the epimucosal margin groups was evaluated (CC0mm: mean 2.31mm2 (SD 0.99) vs. CV0mm: mean 1.57mm2 (SD 0.55); P=0.043). A statistically significant increase in remnants was detected when the crown-abutment margin was located more submucosally for every abutment studied (0mm vs. 1.5mm: P<0.000, 0mm vs 3mm: P<0.000, 1.5mm vs. 3mm: P<0.000). The buccal quadrant demonstrated the least, whereas the oral and interdental quadrants showed the greatest amount of cement excess. Concave emergence profile abutments and deep crown-abutment margin positions increased the risk of cement excess. Oral and interdental areas are more prone to cement remnants than other surface areas.

Light-transmitting fiber optic posts: An in vitro evaluation

Statement of problemThe clinical challenge of adhering cement to intracanal dentin is transmitting light to the most apical parts of root canals to allow more efficient polymerization of the cement. PurposeThe purpose of this in vitro study was to compare the cement-polymerizing ability, microstructure, and radiopacity of a new fiber optic post (iLumi fiber optic Post) with a clinically successful fiber post (DT Light Post). Material and methodsPolymerizing ability was compared using a modified depth-of-polymerization protocol. A split aluminum mold with a 12-mm cylindrical hole (diameter=4.7 mm) was filled with light-polymerized resin cement (Variolink Esthetic LC). Each fiber post (n=12) was positioned and light-polymerized on the coronal end for 60 seconds with a light-emitting diode polymerization light. Unpolymerized resin was dissolved with an organic solvent, and the weight and length of the polymerized resin cement were measured. Scanning electron microscopy was used to examine vertical and horizontal cross-sections. The radiopacity values of both the posts and 5 additional reference posts were evaluated using an aluminum step wedge. ResultsThe weight and length of the polymerized resin cement were significantly greater (P<.05) with the fiber optic post, which scanning electron microscopy showed to have a higher density of parallel fibers. The iLumi post demonstrated greater radiopacity among the tested fiber posts and a titanium alloy post. ConclusionsThe iLumi fiber optic posts have a unique structural fiber composition and excellent radiopacity and light-transmitting ability that produce more complete polymerization of the resin cement than the DT Light posts.