Resin Cement Thickness Research Articles

Comparison of Resin Cement’s Different Thicknesses and Poisson’s Ratios on the Stress Distribution of Class II Amalgam Restoration Using Finite Element Analysis

Using a three-dimensional finite element analysis, this study aimed to evaluate the effect of different cements’ thicknesses and Poisson’s ratios on the stress distribution in enamel, dentin, restoration, and resin cement in a computer-aided design of a class II disto-occlusal cavity. Dental tomography was used to scan the maxillary first molar, creating a three-dimensional tooth model. A cavity was created with a 95 degree cavity edge angle. Resin cement with varying Poisson’s ratios (V1: 0.35 and V2: 0.24) was used under the amalgam. The simulated groups’ thicknesses ranged from 50 µm to 150 µm. A load of 600 N was applied to the chewing area. The finite element method was used to assess the stress distribution in the enamel, dentin, restorations, and resin cement. The stress in the restoration increased with the use of a 100 µm resin cement thickness and decreased with the use of a 150 µm resin cement thickness. For the V1 and V2 groups, the cement thickness with the maximum stress value for the enamel and dentin was 150 µm, while the cement thickness with the lowest stress value was 50 µm. The greatest stress values for V1 and V2 were obtained at a 150 µm cement thickness, while the lowest stress values were observed at a 100 µm cement thickness. Using resin cement with a low Poisson’s ratio under amalgam may reduce stress on enamel and restorations.

Dental Luting Cements: An Updated Comprehensive Review

The cementation of indirect restoration is one of the most important steps in prosthetic and restorative dentistry. Cementation aims to bond the prosthetic restoration to the prepared enamel or enamel and dentine. Successful cementation protocols prevent biofilm formation at the margin between tooth and restoration and minimize mechanical and biological complications. With the advancements in dental cements, they have been modified to be versatile in terms of handling, curing, and bond strengths. This review presents updates on dental cements, focusing on the composition, properties, advantages, limitations, and indications of the various cements available. Currently, dental restorations are made from various biomaterials, and depending on each clinical case, an appropriate luting material will be selected. There is no luting material that can be universally used. Therefore, it is important to distinguish the physical, mechanical, and biological properties of luting materials in order to identify the best options for each case. Nowadays, the most commonly used dental cements are glass-ionomer and resin cement. The type, shade, thickness of resin cement and the shade of the ceramic, all together, have a tangible influence on the final restoration color. Surface treatments of the restoration increase the microtensile bond strength. Hence, the proper surface treatment protocol of both the substrate and restoration surfaces is needed before cementation. Additionally, the manufacturer's instructions for the thin cement-layer thickness are important for the long-term success of the restoration.

Effect of Resin Cement at Different Thicknesses on the Fatigue Shear Bond Strength to Leucite Ceramic.

This in vitro study was performed to evaluate fatigue survival by shear test in the union of leucite-reinforced feldspathic ceramic using different cement thicknesses. Leucite-reinforced glass ceramics blocks were sectioned in 2-mm thick slices where resin cylinders were cemented. The samples were distributed in two experimental groups (n = 20) according to the cement thickness (60 and 300 μm). The specimens of each group were submitted to the stepwise fatigue test in the mechanical cycling machine under shear stress state, with a frequency of 2 Hz, a step-size of 0.16 bar, starting with a load of 31 N (1.0 bar) and a lifetime of 20,000 cycles at each load step. The samples were analyzed in a stereomicroscope and scanning electron microscopy to determine the failure type. There is no significant difference between the mean values of shear bond strength according to both groups. Log-rank (p = 0.925) and Wilcoxon (p = 0.520) tests revealed a similar survival probability in both cement layer thicknesses according to the confidence interval (95%). The fracture analysis showed that the mixed failure was the most common failure type in the 300-μm thickness group (80%), while adhesive failure was predominant in the 60-μm thickness group (67%). The different cement thicknesses did not influence the leucite ceramic bonding in fatigue shear testing; however, the thicker cement layer increased the predominance of the ceramic material failure. The resin cement thicknesses bonded to leucite ceramic did not influence the long-term interfacial shear bond strength, although thicker cement layer increased the ceramic material cohesive failure. Regardless the cement layer thickness, the shear bond strength lifetime decreases under fatigue.

Retention of Manually or CAD/CAM-customized Fiberglass Posts Luted to Enlarged Root Canals with Different Resin Cements.

The aim of this laboratory study was to evaluate the pull-out force of a prefabricated fiberglass post (PP), relined fiberglass post (RP), or milled fiberglass post (MP) luted with Multilink N (MN), RelyX Unicem 2 (RXU2) or RelyX Ultimate (RU) to enlarged root canals. The thickness of the resin cements and the presence of voids in the resin cement film were observed. The root canals of 90 bovine incisors were enlarged, endodontically treated, and randomly divided into 9 groups (n=10) according to the post type and resin cement. The specimens were scanned using micro-CT to analyze the thickness of the resin cement and the presence of voids. The specimens were submitted to mechanical cyclic loading (500,000 cycles at 50 N load) and subjected to pull-out force testing. Two-way ANOVA and Tukey's test analyzed the pull-out force and resin cement thickness data. Kruskal-Wallis and Bonferroni tests analyzed the void scores. The interaction between factors (post × resin cement) was significant (p=0.0001) for the pull-out force. Higher pull-out forces were obtained for RP and MP compared to PP. The post factor was significant (p=0.0001) for resin cement thickness, which was higher for PP (1054 μm), followed by MP (301 μm) and RP (194 μm). More void formation occurred for PP, being less for RP, differing significantly among the posts. Post customization (RP and MP) decreased resin cement thickness and void formation, favoring a higher pull-out force. Resin cements requiring an adhesive application (MN and RU) favored higher pull-out force than self-adhesive resin cement (RXU2).

Comparison of the shear bond strength of composite resins with zirconia and titanium using different resin cements.

The shear bond strength of conventional zirconia (3Y-TZP), translucent zirconia (5Y-PSZ), and titanium alloy (Ti6Al4V) thermocycled using different phosphate monomer resin cements were investigated. In this study, 120 specimens of 3Y-TZP, 5Y-PSZ, and Ti6Al4V were cemented to nanocomposite resin cylinders using PANAVIA™ V5 and Rely X™ U200. The bond area and resin cement thickness were controlled as per ISO 29022:2013 and 4049:2009. Each resin cement group was used with/without the Clearfil ceramic primer plus. The shear bond strength of the 12 groups was statistically analyzed using two and one-way ANOVA to determine the properties of the different materials and resin cements (α = 0.05). The mode of failure was observed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The titanium alloy groups showed better shear bond strength than the zirconia groups (p < 0.05). PANAVIA™ V5 without primer showed significantly lower shear bond strength than other cements in zirconia and titanium alloy specimens (p < 0.05). Titanium alloy with Rely X™ U200 with a Clearfil ceramic primer plus showed the highest shear bond strength (6.37 ± 1.60 MPa). SEM images showed mixed failures in zirconia groups and cohesive failures in titanium alloy groups. The titanium alloy showed better shear bond strength than zirconia when the Clearfil ceramic primer plus was used. The primer solution containing MDP and resin cement with phosphoric methacrylate ester showed similar shear bond strength with 3Y-TZP and 5Y-PSZ. The resin cement without phosphate monomers demonstrated the least shear bond strength.

The influence of resin cement thicknesses on shear bond strength of the cement-zirconia

ENWEndNote BIBJabRef, Mendeley RISPapers, Reference Manager, RefWorks, Zotero AMA Maneenacarith A, Rakmanee T, Klaisiri A. The influence of resin cement thicknesses on shear bond strength of the cement-zirconia. Journal of Stomatology. 2022;75(1):7-12. doi:10.5114/jos.2022.114349. APA Maneenacarith, A., Rakmanee, T., & Klaisiri, A. (2022). The influence of resin cement thicknesses on shear bond strength of the cement-zirconia. Journal of Stomatology, 75(1), 7-12. https://doi.org/10.5114/jos.2022.114349 Chicago Maneenacarith, Apichai, Thanasak Rakmanee, and Awiruth Klaisiri. 2022. "The influence of resin cement thicknesses on shear bond strength of the cement-zirconia". Journal of Stomatology 75 (1): 7-12. doi:10.5114/jos.2022.114349. Harvard Maneenacarith, A., Rakmanee, T., and Klaisiri, A. (2022). The influence of resin cement thicknesses on shear bond strength of the cement-zirconia. Journal of Stomatology, 75(1), pp.7-12. https://doi.org/10.5114/jos.2022.114349 MLA Maneenacarith, Apichai et al. "The influence of resin cement thicknesses on shear bond strength of the cement-zirconia." Journal of Stomatology, vol. 75, no. 1, 2022, pp. 7-12. doi:10.5114/jos.2022.114349. Vancouver Maneenacarith A, Rakmanee T, Klaisiri A. The influence of resin cement thicknesses on shear bond strength of the cement-zirconia. Journal of Stomatology. 2022;75(1):7-12. doi:10.5114/jos.2022.114349.

Customized Fiber Post Improves the Bond Strength and Dentinal Penetrability of Resin Cementation System to Root Dentin.

This study aimed to evaluate the effect of fiber post customization on the bond strength (24 hours and 6 months), resin cement thickness, and dentinal penetrability of Adper Scotchbond Multi-Purpose - RelyX ARC (AS-RA), RelyX U200 (R2), and Scotchbond Universal - RelyX Ultimate (SU-RU) cementation systems to root dentin from the cervical-, middle-, and apical-thirds of the post space. One hundred twenty bovine incisors were endodontically treated. After post space preparation, the roots were divided into six groups, according to the luting protocols (AS-RA, R2, SU-RU) and the type of fiber post [noncustomized post (NC) and customized post (C)]. Customization procedures were peformed using a resin composite (Z350 XT). 24 hours (n=60) or 6 months later (n=60), specimens from the cervical-, middle-, and apical-thirds of the post space were submitted to cementation system thickness measurement, bond strength evaluation, and dentinal penetrability analysis with Confocal Laser Scanning Microscopy (CLSM). Failure mode was classified as adhesive, cohesive, or mixed. Data were submitted to ANOVA and Tukey tests (α=0.05). Cementation protocols with customized fiber posts presented the lowest cementation system thickness, regardless of the cementation system or post space-third (p<0.05), and the highest bond strength values (p<0.05), regardless of the third space (p>0.05), for both periods (24 hours or 6 months). The comparison of push-out bond strength values between 24 hours and 6 months showed a reduction in all groups for the cervical-third (p<0.05). For the middle-third, only noncustomized groups showed reduction (p<0.05). For the apical-third, no reduction was observed (p>0.05). Anatomical customization favored both the bond strength of cements to dentin and the dentinal penetrability, but with lower cementation system thickness, regardless of cement composition and adhesive strategy.

The resin-matrix cement layer thickness resultant from the intracanal fitting of teeth root canal posts: an integrative review.

The aim of this study was to perform an integrative review on the layer thickness and microstructure of resin-matrix cements around custom-made or standard teeth root intracanal posts. An electronic search was conducted on the PubMed using a combination of the following scientific terms: intraradicular post, root intracanal post, resin cement, thickness, adaptation, endodontic post, layer thickness, fit, shape, and endodontic core. The literature selection criteria accepted articles published in the English language, up to May 2021, involving in vitro analyses, meta-analyses, randomized controlled trials, and prospective cohort studies. The search identified 154 studies, of which 24 were considered relevant to this study. The selectedstudies provided important data considering cement layer thickness, tooth preparation, endodontic post, and type of resin-matrix cement. The anatomical variability of root canal systems, such as the oval- orC-shaped, represents a challenge in dental restoration with tooth root intracanal posts. The fitting of intracanal posts to different rootregions is variable resulting in thick and irregular layers of resin-matrix cement. Defects like pores, micro-cracks, and micro-gaps were detected in the resin-matrix cement microstructure and represent spots of stress concentration and fracture. Custom-made tooth rootintracanal posts provide a proper fitting and decrease the layer thickness of resin-matrix cement. In fact, the layer thickness of resin-matrix cements depends on the fitting of endodontic posts to tooth root canals. An increase of resin cementthickness causes the appearance ofdefects like pores, micro-cracks, and micro-gaps that can induce stress concentration and fractures at interfaces. The fitting of the endodonticpost into the teeth root canal determine the layer thickness of the resin-matrix cement to establishan adequate retention.However, the increase in the thickness of the resin-matrix cement layer can lead to a high number of defects like pores or cracks and therefore decrease the strength of the interface.

Evaluation of the sealing capability and morphological fit of prefabricated dowels and fiber-reinforced composite resin: An in vitro study

Statement of problemPrefabricated dowels do not always provide intraradicular sealing in the root canal dentin, and the lack of sealing predisposes the dowel to adhesive failure and debonding. It is unclear if fiber-reinforced composite resin dowels provide better sealing. PurposeThe purpose of this in vitro study was to evaluate the intraradicular sealing and morphological fit of prefabricated dowels and fiber-reinforced composite resin dowels in root canal dentin. The thickness of the resin cement layer and push-out bond strength were determined to assess their effects on the sealing of the dowels. Material and methodsA total of 50 permanent maxillary central incisors were endodontically treated and divided into 2 subgroups (n=25). In one group, prefabricated dowels were cemented; in the second group, fiber-reinforced composite resin dowels were placed. The thickness of the resin cement layer was assessed in 3 different locations: coronal, middle, and apical of the root canal dentin with fluorescence confocal laser microscopy. The push-out bond strength was then determined, and intraradicular sealing observed by using scanning electron microscopy. ResultsFiber-reinforced composite resin dowels showed a closer intraradicular fit and seal in the root canal dentin, and the morphology of the apical portion of the fiber-reinforced composite resin dowels showed a sealing area with the gutta percha in the apical portion. The mean thickness of the resin cement layer was significantly reduced for the fiber-reinforced composite resin dowels compared with the prefabricated dowels (P<.05) in the cervical area (197.0 μm versus 311.0 μm) and in the apical portion of the root canal (57.3 μm versus 131.6 μm). The mean push-out strength was higher for the fiber-reinforced composite resin dowels (22.98 N/mm2) than that for the prefabricated dowels (16.49 N/mm2) (P<.05). ConclusionsThe morphological fit of fiber-reinforced composite resin dowels provides better intraradicular sealing in the cervical and apical portions, reducing the resin cement thickness. The increased push-out strength can therefore be assumed to result from increased frictional retention compared with prefabricated dowels.

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.

Assessment of Push Out Bond Strength and Cement Thickness for Oval Root Canals Restored with Different Post Techniques

Objectives: The aim of the present study was to evaluate the push out bond strength of fiber posts to oval shaped root canals using different post techniques and correlation of bond strength values to different cement thicknesses at different post level in different post techniques.Methods: A total of thirty-two recently extracted human mandibular first premolars with oval root canals were selected and stored in normal saline solution. The teeth were horizontally sectioned 2 mm coronal to the cementoenamel junction with a double-faced diamond disk in a slow-speed handpiece with copious coolant. Root canal treatment was done for all teeth using a standardized technique. The teeth were then randomly divided into four equal groups (n=8) according to the post and core system used: Group I: Single circular post technique, Group II: Relined post technique, Group III: Double circular post technique, Group IV: Oval post technique. For each sample, the roots were cut horizontally, perpendicular to the long axis of the root using low speed diamond saw under water coolant to obtain three 2 mm ± 0.1 thick root specimens representing cervical, middle and apical third of the root. The resin cement thickness around each specimen obtained after slicing were measured using scanning electron microscope (SEM) at eight standardized points around the circumference of the slice; between the canal wall and the fiber post perimeter. Each root slice was subjected to compressive loading at a crosshead speed of 1 mm/min via a computer controlled Universal testing machine to record the maximum failure load in Newton. The push out bond strength was calculated by dividing the recorded peak load by the surface area of each slice. Results: As regards to the mean push out bond strength values for the post techniques, there was a statistically significant difference between mean push out bond strength of different post techniques where oval post technique showed the statistically significant highest mean push out bond strength. Relined technique showed statistically significant lower mean value followed by double circular technique. Single circular technique showed the statistically significantly lowest

Influence of resin cement thickness and temperature variation on mechanical behavior of dental ceramic fragment restoration

To evaluate the stress behavior of ceramic fragment restoration, varying the thickness of the cement layer and intraoral temperature variation. A solid model of a upper lateral incisor was obtained and a defect at enamel distal/incisal edge was restored with a ceramic fragment. Based on this initial model, 4 different models (M) were built: M1 – absence of cement layer (CL) (0 μm of thickness); M2 – CL with an uniform thickness of 50 μm; M3 – CL with 50 μm at the margin of ceramics and 100 μm in the inner area far from margins; M4 – CL with 50 μm at the margin of ceramics and 200 μm in the inner area far from margins. The environment temperature changed from 5 °C to 50 °C in 4 increments. The finite element analysis was performed. Increase the cement layer thickness generated higher stress levels on ceramic surface in all temperatures, as well as on cement interface. In general hot temperature was the worst scenario for ceramic fragments integrity, since tensile and compressive stress were more intense. The maximum principal stress on ceramic fragment was found 90 MPa for M4 at 50 °C, followed for M3 (87 Mpa). For CL, the peak of stress was found for M3 at 5 °C (47 MPa). Is it possible to conclude that thick resin cement layer contribute to higher stress concentration on ceramic fragment, and extremely hot temperatures increase the risk of structural failure, since both ceramic and \\cl are exposed to higher compressive and tensile stresses.

Shear bond strength of zirconia to resin: The effects of specimen preparation and loading procedure.

PURPOSEShear bond strength (SBS) test is the most commonly used method for evaluating resin bond strength of zirconia, but SBS results vary among different studies even when evaluating the same bonding strategy. The purpose of this study was to promote standardization of the SBS test in evaluating zirconia ceramic bonding and to investigate factors that may affect the SBS value of a zirconia/resin cement/composite resin bonding specimen.MATERIALS AND METHODSThe zirconia/resin cement/composite resin bonding specimens were used to simulate loading with a shear force by the three-dimensional finite element (3D FE) modeling, in which stress distribution under uniform/non-uniform load, and different resin cement thickness and different elastic modulus of resin composite were analyzed. In vitro SBS test was also performed to validate the results of 3D FE analysis.RESULTSThe loading flat width was an important affecting factor. 3D FE analysis also showed that differences in resin cement layer thickness and resin composite would lead to the variations of stress accumulation area. The SBS test result showed that the load for preparing a SBS specimen is negatively correlated with the resin cement thickness and positively correlated with SBS values.CONCLUSIONWhen preparing a SBS specimen for evaluating bond performance, the load flat width, the load applied during cementation, and the different composite resins used affect the SBS results and therefore should be standardized.

Effectiveness of Shade and Thickness of Resin Cement on the Final Colour of the Porcelain Laminate Veneer: A Scoping Review

Effectiveness of Shade and Thickness of Resin Cement on the Final Colour of the Porcelain Laminate Veneer: A Scoping Review

Influence of adhesive cementation systems on the bond strength of relined fiber posts to root dentin

Statement of problemGlass fiber post cementation procedures have undergone significant development. Relining the post with composite resin is a technique that aims to reduce resin cement thickness and consequently problems inherent to polymerization. Evidence is sparse regarding the efficacy of bonding procedures at increasing depths (from cervical to apical) using different adhesive cementation techniques. PurposeThe purpose of this in vitro study was to evaluate the push-out bond strength (PBS) of composite resin relined glass fiber posts cemented to bovine root dentin using different adhesive cementation protocols. Material and methodsEighteen bovine teeth (n=6) were embedded in polystyrene resin blocks, and the crowns were sectioned leaving a root portion of 20 mm in length. Root canals were prepared using rotary instruments provided by the post manufacturer (Whitepost DC #1), resulting in a uniform root canal preparation. The root canals were lubricated with a water-soluble glycerin gel. Silane (Prosil) was applied and the posts relined with a microhybrid composite resin (Filtek Z100) to conform to the root canal anatomy. Three adhesive cementation protocols were evaluated: a 3-step etch-and-rinse adhesive system (Adper Scotchbond Multi Purpose) in combination with a dual polymerizing resin cement (RelyX ARC); a universal adhesive system (Scotchbond Universal) associated with a dual polymerizing resin cement (RelyX Ultimate); and a self-adhesive dual polymerizing resin cement (RelyX Unicem 2). The roots were sectioned, resulting in four 2-mm segments at 4 different depths (cervical to apical) and evaluated by the PBS test, using a universal testing machine (Instron 4411) at 0.5 mm/min, until failure. Interfaces were evaluated by scanning electron microscopy, and failures were classified as cohesive failure in composite resin, cohesive failure in cement, cohesive failure in root dentin, adhesive failure, or mixed. Data were analyzed by 2-way split-plot ANOVA and the Tukey post hoc test (α=.05). ResultsNo statistical differences were found for PBS when different cementation systems were compared (P=.253). Increased depths resulted in reduced PBS values for all cementation protocols evaluated (P<.001). ConclusionsRegardless the cementation system used, the lowest PBS values were at the apical region of resin relined glass fiber posts bonded to root dentin. Furthermore, the highest PBS is observed at the cervical portion of root dentin.

Influence of the Resin Cement Thickness on the Push-Out Bond Strength of Glass Fiber Posts.

The objective of the present study was to evaluate the influence of resin cement thickness on the bond strength of prefabricated and customized glass fiber posts after storage in distilled water. Thirty human uniradicular roots were treated endodontically. The roots were divided into 3 groups: THIN (thin cement layer) - post space preparation with #0.5 drill and cementation of #0.5 post; THICK (thick cement layer) - post space preparation with #1 drill and cementation of #0.5 post; and CUSTOM (customized cement layer) - post space preparation with #1 drill and cementation of a customized post (#0.5 glass fiber posts customized with resin composite). All posts were luted with self-adhesive resin cement. The push-out test was carried out after storage for 24 h and 90 days in distilled water at 37 °C. The data were analyzed with three-way ANOVA and Tukey's test (a=0.05). Bond strengths were significantly higher for CUSTOM (9.37 MPa), than for THIN (7.85 MPa) and THICK (7.07 MPa), which were statistically similar. Considering the thirds, the bond strength varied in the sequence: apical (7.13 MPa) < middle (8.22 MPa) = coronal (8.94 MPa). Bond strength for 24 h storage was significantly higher (8.80 MPa) than for 90-day storage (7.40 MPa). It may be concluded that the thickness of resin cement influenced the bond strength of glass fiber posts. The customized posts presented higher bond strength. Storage in water for 90 days affected negatively the values of bond strength, especially for thick cement layers in the apical third.

Influence of the resin cement thickness on the fatigue failure loads of CAD/CAM feldspathic crowns

Objectivesto evaluate the influence of the occlusal resin cement thickness on the cyclic loads-to-failure of feldspathic crowns and to compare the results to data from monotonic tests. A large range of cement thickness (50μm and 500μm) was tested, in order to better measure the influence of this variable. MethodsFeldspathic ceramic crowns (Vita Mark II blocks, Vita Zahnfabrik) were bonded to dentin analog dies (G10 (NEMA grade G10, International Paper), with occlusal resin cement thicknesses of 50μm and 500μm (Multilink Automix, Ivoclar). The dies were prepared with microchannels for water transport to the cement layer. After 96-h water storage, the specimens (n=20) were submitted to cyclic loads (500,000 cycles at 20Hz; initial maximum load=40% of monotonic load, from previous data) following a staircase sensitivity design (step size=25N). Failure loads at 500,000 cycles were compared to monotonic failure loads (from a previous study with specimens produced by the same author, using the same materials, specimen configuration and cementation protocol). ResultsCrowns with an occlusal cement layer of 50μm were more resistant than those cemented with 500μm (246.4±22.9N vs. 158.9±22.9N), under wet cyclic testing conditions (p<0.001). The fatigue failure loads were reduced compared to monotonic loads: to 37% of monotonic for 50μm; to 53% of monotonic for 500μm. SignificanceAn occlusal cement thickness of 50μm was more favorable for the structural performance of feldspathic crowns than was 500μm. Cyclic fatigue reduced failure loads well below those found under monotonic loading.

Evaluation of the resin cement thicknesses and push-out bond strengths of circular and oval fiber posts in oval-shapes canals.

PURPOSEThe aim of this study was to evaluate whether the push-out bond strength varies between oval and circular fiber posts, and to examine the effect on the resin cement thicknesses around the posts.MATERIALS AND METHODSEighteen mandibular premolar roots were separated into two groups for oval and circular fiber posts systems. Post spaces were prepared and fiber posts were luted to the post spaces. Roots were cut horizontally to produce 1-mm-thick specimens. Resin cement thicknesses were determined with a metallographic optical microscope and push-out tests were done.RESULTSNo significant differences were observed in terms of push-out bond strength between the oval and circular fiber posts (P>.05) The resin cement thicknesses of the oval posts were greater than those of the circular posts group in the coronal, middle and apical specimens (P<.05).CONCLUSIONIn the light of these results, it can be stated that resin cement thickness does not affect the push-out bond strength.

Influence of the resin cement thickness on bond strength and gap formation of fiber posts bonded to root dentin.

To evaluate the effect of the resin cement thickness (RCT) on bond strength (BS) and gap formation (GF) of fiber posts bonded to root dentin. The roots of 24 extracted human mandibular premolars were treated endodontically and the post spaces were prepared using drills with different diameters according to the following groups (n = 8): well adapted (WA), moderately well adapted (MA) and poorly adapted (PA). The fiber glass posts were cemented (Excite DSC and Variolink II) in accordance with the manufacturer's instructions. After 1 week, the roots were transversely sectioned into six 1-mm-thick disks and photographed using an optical microscope to determine the RCT. After this, epoxy resin replicas of each sample were observed using SEM, and the mean length and width of the gaps formed in the cement/dentin/post interface were measured. Finally, each sample was subjected to the push-out test (0.5 mm/min), and the data were statistically analyzed using one-way ANOVA and Tukey's tests at the 5% level of significance. The lowest RCT (μm) was observed for WA and the highest for PA. The group MA showed an intermediate value. Significantly higher push-out BS values were observed for WA compared to the other groups. The MA and PA groups were statistically similar. The highest mean gap length (%) and width (μm) were observed for PA. The groups MA and WA were statistically similar. Lower resin cement thickness resulted in better fiber post adhesion, that is, in higher bond strength and less gap formation.

Comparison of microleakage and thickness of resin cement in ceramic inlays with various temperatures.

Background and aims. Microleakage is still one of the major problems of composite-based restorations.This study compared the microleakage and thickness of resin cement in ceramic inlays with various temperatures. Materials and methods. Class V cavities were prepared on the buccal and lingual aspects of thirty human molars with occlusal margins in enamel and gingival margins in dentin (3 mm wide, 5 mm long and 2 mm deep). Laboratory-made inlays (LMI) were used for buccal cavities, and CAD/CAM inlays (CMI) were used for lingual cavities. All the cavities were divided into six groups (n=10): 1) LMI at -5°C; 2) LMI at 50°C; 3) LMI at room temperature (25°C); 4) CMI at -5°C; 5) CMI at 50°C; 6) CMI at room temperature (25°C). Inlays were bonded to cavities in a pulp pressure- and temperature-simulating device. After thermocycling and dye penetration, the teeth were divided into two mesiodistal halves. Amount of dye penetration and film thickness were measured under a stereomicroscope and analyzed with Kruskal-Wallis, Wilcoxon and Spearman's correlation tests ( = 0.05). Results. There were no statistically significant differences in leakage between different inlay temperatures (P > 0.05). The mean cement thickness in laboratory-made inlays (gingival margin, 83.7 ± 11 and occlusal margin, 84.7 ± 19) was greater than that in CAD/CAM inlays (gingival margin, 69 ± 16 and occlusal margin, 84.7 ± 16). No correlation was found be-tween cement thickness and microleakage either in enamel or dentin for any of the ceramic systems. Conclusion. Differences in inlay temperature had no effect on microleakage. CAD/CAM inlays had lower cement thickness than laboratory-made inlays, but this was not related to their microleakage.