Cement Layer Thickness Research Articles

Fitting of Different Intraradicular Composite Posts to Oval Tooth Root Canals: A Preliminary Assessment.

The purpose of the present study was to perform a preliminary analysis of the fitting of different fiber-reinforced composite (GFRC) posts to tooth root canals and determine the resin cement layer thickness. The following GFRC posts were assessed: bundle posts (Rebilda GTTM, VOCO, Germany), sleeve system (SAPTM, Angelus Ind, Brazil), and accessory posts (ReforpinTM, Angelus, Brazil). Twenty-four freshly extracted mandibular single-rooted pre-molars were endodontically treated and divided into six groups, according to the type of GFRC post and resin cement (self-adhesive or conventional dual-cured). Then, specimens were cross-sectioned and inspected by optical microscopy regarding the cement layer thickness and presence of defects such as pores, voids, or fissures were assessed. Bundle and accessory posts revealed a regular distribution of resin cement with a lower number of voids than found with sleeve systems. The sleeve system posts showed poor fitting at the apical portion of the root canals. The type of resin cement did not affect the thickness of the interface, although both bundle and accessory posts allow a better distribution of resin cement and fibers. The present preliminary study reveals interesting insights on the fitting of bundle and accessory posts to root dentin and resin cement layer thickness in oval-shape root canals. The sleeve system posts showed adequate fitting only at the coronal portion of the canals.

Effect of Self-Adhesive Resin Cement Film Thickness on the Shear Bond Strength of Lithium Disilicate Ceramic–Cement–Tooth Triplex

Cement film thickness may have an impact on the shear bond strength (SBS) of lithium disilicate dental ceramics luted to human enamel with resin cement. The objective of this study was to evaluate SBS of lithium disilicate ceramics adhered to enamel using resin cement at different thicknesses. In total, 50 ceramic specimens (3 × 3 × 3 mm) and 50 premolar teeth were prepared and randomly assigned to 5 groups (n = 10 each). Ceramic specimens were designed with five cement film thicknesses (50 μm; 100 μm; 150 μm; 200 μm; and 300 μm). Teeth surfaces (4 × 4 mm) were prepared with a high-speed handpiece mounted on a dental surveyor. Ceramic specimens were cemented to teeth with resin cement (3MTM RelyXTM U200, Resin-Self-Adhesive-Cement). The specimens were then thermocycled for 6000 cycles with a 30 s dwell time and a 5 s transfer time in water (5 °C and 55 °C). A Universal-Testing-Machine was used to measure SBS (MPa). Statistical analysis in SPSS included Anova and Tukey’s tests. The SBSs of ceramics adhered to teeth revealed significantly different values across all test groups (p = 0.000). The findings showed that as cement layer thickness increased, so did the SBS. The cement spaces at 50 and 300 μm had the lowest SBS (9.40 + 1.15 MPa) and maximum SBS (21.98 + 1.27 MPa), respectively. The SBS of the lithium disilicate ceramic luted to natural human enamel increased along with the cement layer thickness.

In Vitro Evaluation of Push-Out Bond Strength in Three Different Post Systems

Background and objectives: Intimate adaptation to the canal walls is accomplished by custom-made posts which leave an even thickness of cement layer. Therefore, this study has been conducted for assessing the strength of push-out bond among prefabricated fiber posts, relined fiberglass posts, and zirconium posts using resin cement of self-adhesive and adhesive. The mode of failure was also assessed. Materials and Methods: Sixty uniradicular teeth were endodontically treated. According to the kind of post system and cement utilized (n=10), the specimens were separated randomly into six groups. Zirconium oxide post, customized glass fiber post, and glass fiber post were used. The roots were divided into three discs: apical, middle, and cervical sections. After that, the discs were put through a push-out test, and the fracture mode was examined using a stereomicroscopic loupe. Results: The highest push-out value was recorded for the relined post (8±2.83 MPa), and the lowest was registered with no significant differences for the prefabricated post (7.27±3.76 MPa). There were no significant differences in strength bond across the various posts and root regions (P?.05). Adhesive failure at the dentin-cement interfaces for the prefabricated and relined post was (60, 57) % respectively, and zirconium oxide post was (22%). Conclusions: Relined posts may be a suitable clinical situation as a post material selection with reduced clinical steps. When posts are joined using self-adhesive and adhesive resin cement, the root region has no important influence on the strength of the bond.

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.

The effect of die spacer on retention and fitting of complete cast crowns

Purpose: The aim of this study was to determine the influence of multiple layers of die relief agent and different cement thickness on the retention of cast restorations using two different cements.
 Materials and Methods: 144 standard stainless steel dies were divided into two groups. Each of them includes 72 dies. These groups were divided into 12 equal subgroups as well. In both groups, die spacer was applied to dies in 0, 3, 4, 5, 6 and 7 layers (each layer=5µ). In the first group, crowns were cemented with Zinc Phosphate and in the second group, Polycarboxylate was used for cementing. After that, the strength required for separating the castings from the dies was measured.
 Results: The difference among 12 subgroups analyzed by one-way ANOVA regarding Polycar- boxylate cement did not reach statistical significance. (P=0.95). A similar result was obtained with zinc phosphate cement (P=0.616). Likewise, the two-way ANOVA was carried out between the zinc phosphate and polycarboxylate groups. There was a significant difference between the average of two groups (P<0.001).
 Conclusion: Range of cement layer thickness that used in this study didn’t statistically signifi- cantly affect the force required to remove cemented cast copings. Although the castings cemented with Zinc Phosphate needed higher force to be dislodged from dies.

Pressure dependence of elastic wave velocities of unconsolidated cemented sands

We have developed lower and upper bounds for the pressure-dependent elastic wave velocities of unconsolidated cemented sands, which are due to variations in cement layer thickness and direct grain contact area with effective pressure, respectively. Investigating the factors influencing these bounds, we have found that the elastic wave (P- and S-wave) velocities increase with the effective pressure, whereas their ratio ([Formula: see text]) decreases. The elastic wave velocities and their ratio have an almost linear relationship with the effective pressure for the lower bound, whereas that for the upper bound is nonlinear. For both lower and upper bounds, the sensitivities of the elastic wave velocities and their ratio to the effective pressure increase with decreasing precompacted pressure, cement elastic moduli, and cement volume content. By comparing the theoretical predictions with ultrasonic measurements on heavy-oil sands and cemented glass beads, we have validated that the experimental data fall within the proposed lower and upper bounds. The experimental data shift from the lower bound to the upper bound as the effective pressure increases, revealing that the grain compaction pattern changes with increasing effective pressure.

Glass fiber posts relining: can composite opacity influence retention to root canal dentin?

This study aimed at evaluating the influence of glass-fiber post (GFP) relining with composites of different opacities on resin cement layer thickness (CLT), bond strength (BS) to root dentin, and resin cement degree of conversion (DC%). Standardized roots of 52 bovine incisors had their canals prepared and were distributed into 4 groups (n = 10 for CLT and BS; n = 3 for DC%) according to the post used: WP3 (Control)-Whitepost DC3; groups DE, EN and TR-Whitepost DC0.5 relined, respectively, with dentin, enamel, and translucent shade composites. After cementation, specimens were sectioned into six 1.0mm-thick discs that were submitted to push-out BS test. CLT and failure pattern were evaluated using a stereomicroscope and DC% by micro-Raman spectroscopy. Data were analyzed by two-way ANOVA and Tukey test (α = 0.05). The control group showed greater CLT than all relined groups (p < 0.05), which did not differ from each other (p > 0.05). Groups relined with low opacity composites (TR; EN) showed the highest BS and DC% means (p < 0.05). BS was not different among root thirds (p > 0.05), while DC% decreased from cervical to apical third (p < 0.05). Adhesive failures between cement and dentin were predominant, except for group DE with frequent mixed failures. It could be concluded that composite opacity did not influence CLT, which was thinner when GFP were relined and that relining GFP with lower opacity composites led to higher BS and DC%.

Does bone penetration of cement differ by cement type and application time-point?

Intrusion of cement into bone is often considered an indirect indicator for implant stability in cemented joint replacement procedures. However, the influence of cement type (different viscosities/manufacturers) and application time-point on penetration of cements continues to be debated. This study aimed to quantify the effect of cement type and application time-point on the depth of penetration using porcine tibial specimens.Four different bone cements were applied to 60 resected porcine cadaveric tibias at three time-points within the working window (1, 2, and 3 min after dough time). Penetration was measured using computed tomography, utilizing two rigorous methods from the literature and a newly proposed volumetric method.Application time-point had a strong influence on the thickness of the cement layer above the resected tibia (0.25, 0.49, 0.73 mm at the three time-points). No significant variation in penetration depth metrics with cement type or application time-point was found, except percentage area covered by cement at 2 mm depth. This metric was significantly different between 1 and 3-minute time-points (12% and 6% respectively).Time-point of application had a significant influence on thickness of pure cement layer over resected bone. However, penetration depth was not significantly affected by cement type or application time-point. The clinical significance of these findings is that it may be better to apply cement relatively soon after dough time to avoid excessively thick cement mantle between implant and bone. Further, the choice of cement type may have minimal impact on cement penetration, indicating that long standing principles of good cement application maybe more important.

Efficacy of CAD/CAM Glass Fiber Posts for the Restoration of Endodontically Treated Teeth.

Objective The aim of this systematic review was to provide an overview of available scientific evidence regarding the comparative efficacy of computer-aided design (CAD) and computer-aided manufacturing (CAM) glass fiber posts with prefabricated and metal cast posts for the restoration of endodontically treated teeth (ETT). Methods This systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Electronic and manual searches were performed using the PubMed, SciELO, Cochrane, ScienceDirect, Web of Science, and EBSCO databases. The reference lists of the selected papers were reviewed to identify relevant papers. There were no year restrictions, and eligible studies were those in English publications and describing in vitro studies evaluating intraradicular retainers (IRs) for (i) fracture resistance, (ii) bond strength, (iii) adaptation, and (iv) cement layer thickness. Literature reviews, systematic reviews, meta-analyses, case reports, in vitro studies with <8 specimens, and noncomparative trials involving prefabricated or metal cast posts were excluded. The authors of this review independently screened the search results, extracted data, and assessed the risk of bias. Results No significant differences were found in fracture resistance between prefabricated and CAD/CAM glass fiber posts or between CAD/CAM glass fiber and metal cast posts, although the latter demonstrated higher fracture resistance than the prefabricated glass fiber posts. Restoration with a full crown was not necessary to increase the fracture resistance in the presence of the ferrule effect. CAD/CAM glass fiber and metal cast posts had higher bond strength, lower nanoleakage, and better adaptation to the root canal. Conclusions Despite the heterogeneity of methodologies and results reported, the results of these studies indicated that the CAD/CAM glass fiber and metal cast posts showed greater efficacy in terms of fracture resistance, retention, and adaptation, compared to prefabricated glass fiber posts.

6 - Ceramic-Dentin Cement Thickness: Bond Strength and Residual Stress

This study aimed to test whether three different cement layer thicknesses (60, 120 and 180 μm) would provide the same bonding capacity between adhesively luted lithium disilicate and human dentin. Ceramic blocks were cut with a low-speed diamond saw with water cooling into 20 blocks, which were cemented to human flat dentin with adhesive protocol. The assembly was sectioned into 1 mm 2 cross-section beams composed of ceramic/cement/dentin. Cement layer thickness was measured, and three groups were formed. Half of the samples were submitted to aging simulation and the other half was immediately tested to evaluate the long-term bond strength. The microtensile test was performed in a universal testing machine. Bond strength (MPa) was calculated. The fractured specimens were examined under stereomicroscopy. Applying the finite element method, the residual stress of polymerization shrinkage according to cement layer thick-ness was also calculated using First Principal Stress as analysis criteria. ANOVA showed that the cement layer thickness factor significantly influenced the bond strength results for the aged samples (p=0.040) without difference between the groups for the immediately tested groups (p=0.772). The higher the cement layer thickness the higher the residual stress generated at the adhesive interface due to cement polymerization shrinkage. In conclusion, the cement layer thickness does not affect the immediate bond strength in lithium disilicate restorations; however, thinner cement layers are most stable in long-term showing constant bond strength and lower residual stress.

Effect of Cement Layer Thickness on the Immediate and Long-Term Bond Strength and Residual Stress between Lithium Disilicate Glass-Ceramic and Human Dentin

This study tested whether three different cement layer thicknesses (60, 120 and 180 μm) would provide the same bonding capacity between adhesively luted lithium disilicate and human dentin. Ceramic blocks were cut to 20 blocks with a low-speed diamond saw under cooling water and were then cemented to human flat dentin with an adhesive protocol. The assembly was sectioned into 1 mm2 cross-section beams composed of ceramic/cement/dentin. Cement layer thickness was measured, and three groups were formed. Half of the samples were immediately tested to evaluate the short-term bond strength and the other half were submitted to an aging simulation. The microtensile test was performed in a universal testing machine, and the bond strength (MPa) was calculated. The fractured specimens were examined under stereomicroscopy. Applying the finite element method, the residual stress of polymerization shrinkage according to cement layer thickness was also calculated using first principal stress as analysis criteria. Kruskal–Wallis tests showed that the ‘‘cement layer thickness’’ factor significantly influenced the bond strength results for the aged samples (p = 0.028); however, no statistically significant difference was found between the immediately tested groups (p = 0.569). The higher the cement layer thickness, the higher the residual stress generated at the adhesive interface due to cement polymerization shrinkage. In conclusion, the cement layer thickness does not affect the immediate bond strength in lithium disilicate restorations; however, thinner cement layers are most stable in the short term, showing constant bond strength and lower residual stress.

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.

Improving the cementation of the tibial component in knee arthroplasty : a study of four techniques in the cadaver.

AimsThe main objective of this study is to analyze the penetration of bone cement in four different full cementation techniques of the tibial tray.MethodsIn order to determine the best tibial tray cementation technique, we applied cement to 40 cryopreserved donor tibiae by four different techniques: 1) double-layer cementation of the tibial component and tibial bone with bone restrictor; 2) metallic cementation of the tibial component without bone restrictor; 3) bone cementation of the tibia with bone restrictor; and 4) superficial bone cementation of the tibia and metallic keel cementation of the tibial component without bone restrictor. We performed CT exams of all 40 subjects, and measured cement layer thickness at both levels of the resected surface of the epiphysis and the endomedular metaphyseal level.ResultsAt the epiphyseal level, Technique 2 gave the greatest depth compared to the other investigated techniques. At the endomedular metaphyseal level, Technique 1 showed greater cement penetration than the other techniques.ConclusionThe best metaphyseal cementation technique of the tibial component is bone cementation with cement restrictor. Additionally, if full tibial component cementation is to be done, the cement volume used should be about 40 g of cement, and not the usual 20 g.Cite this article: Bone Joint Res 2021;10(8):467–473.

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.

Marginal misfit of heat-pressed milled wax-pattern and CAD/CAM crowns and its effect on stress distribution in implant-supported rehabilitations

Aim: To compare the marginal fit of lithium disilicate CAD/CAM crowns and heat-pressed crowns fabricated using milled wax patterns, and evaluate its effect on stress distribution in implantsupported rehabilitation. Methods: A CAD model of a mandibular first molar was designed, and 16 lithium disilicate crowns (8/group) were obtained. The crown-prosthetic abutment set was evaluated in a scanning electron microscopy. The mean misfit for each group was recorded and evaluated using Student’s t-test. For in silico analysis, a virtual cement thickness was designed for the two misfit values found previously, and the CAD model was assembled on an implant-abutment set. A load of 100 N was applied at 30° on the central fossa, and the equivalent stress was calculated for the crown, titanium components, bone, and resin cement layer. Results: The CAD/CAM group presented a significantly (p=0.0068) higher misfit (64.99±18.73 μm) than the heat-pressed group (37.64±15.66 μm). In silico results showed that the heat-pressed group presented a decrease in stress concentration of 61% in the crown and 21% in the cement. In addition, a decrease of 14.5% and an increase of 7.8% in the stress for the prosthetic abutment and implant, respectively, was recorded. For the cortical and cancellous bone, a slight increase in stress occurred with an increase in the cement layer thickness of 5.9% and 5.7%, respectively. Conclusion: The milling of wax patterns for subsequent inclusion and obtaining heat-pressed crowns is an option to obtain restorations with an excellent marginal fit and better stress distribution throughout the implant-abutment set.

Novel testing method to evaluate the mechanical strength of self-adhesive resin cements with reflection of cement thickness.

This study aimed to propose an evaluation method for testing the mechanical strength of film-formed self-adhesive resin cements (SARCs) while reflecting cement layer thickness. Three commercially available dual-cure type SARCs were used for tensile and shear tests using specimens with varying thicknesses (0.05, 0.2, and 0.4 mm). There were no significant differences in tensile strengths among the various specimen thicknesses. In the shear test, there was a significant decrease in the strength with a reduction in specimen thickness. Stress distribution and fracture patterns were analyzed using in silico nonlinear dynamic finite element analysis. Finite element analysis demonstrated that stress distribution on the specimen surface was homogeneous even with different thicknesses in the tensile test, whereas it was inhomogeneous and induced different fracture patterns on the 0.05-mm-thick specimen in the shear test. These results suggest that the tensile test is useful for testing the mechanical strength of film-formed SARCs.

The Influence of Cement Layer Thickness on the Stress State of Metal Inlay Restorations-Photoelastic Analysis.

The successful restoration of teeth requires a good connection between the inlay and natural tissue. A strong bond may improve retention and reinforce tooth structure. The purpose of this study was to evaluate the influence of cement layer thickness on contraction stress generated during photopolymerization, and to determine the changes in stress state of the cement occurring during aging in water (over 84 days). Two cements were used: resin composite cement (NX3) and self-adhesive resin cement (Maxcem Elite Chroma). A cylindrical sample made of CuZn alloy was used to imitate the inlay. The stress state was measured by photoelastic analysis. The contraction stress of the inlay restoration was calculated for cement layer thicknesses of 25 µm, 100 µm, 200 µm, and 400 µm. For both tested materials, the lowest contraction stress was observed for the thinnest layer (25 µm), and this increased with thickness. Following water immersion, a significant reduction in contraction stress was observed due to hygroscopic expansion. Applying a thin layer (approximately 25 µm) of composite and self-adhesive resin cements resulted in high levels of expansion stresses (over −6 MPa) after water aging.

Influence of Different Fibreglass Post Geometries on the Stress Distribution and Pull-Out Bond Strength Before and After Mechanical Cycling.

Objective:There are no reports in the literature on whether FGP geometry influences the bond strength of the endodontically restored tooth. This study aimed to determine the stress distribution and the pull-out bond strength of different FGP geometries, before and after chewing loads simulation.Methods:One hundred and twenty root analogues were prepared and randomly distributed in six groups according to the post geometry. Half of the specimens were aged in water at 37 °C using a mechanical fatigue machine (84 N, 2 bar, 45°, 106 cycles, 4 Hz); while the remaining specimens were immediately submitted to the pull-out bond strength test. The specimens were tested in a universal testing machine and the bond strength in MPa was calculated. To assess the stress concentration, the finite element method was used simulating the same post geometries that were used in the in vitro test.Results:Two-way ANOVA (95%) showed no influence of post geometry on the bond strength (P=0.055) while fatigue cycling was statistical significant to reduce the bond strength values (P=0.000). The factors interaction was significant (P=0.019); however, TUKEY test (5%) showed no significant difference between post geometries after mechanical cycling. The tensile stress result showed critical areas in the post’s cervical region regardless of the design.Conclusion:The FGP geometry does not affect the root stress distribution and the long-term bond strength. However, FGP that allow a reduced cement layer thickness can improve the immediate pull-out bond strength value.

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.