Fracture Strength of Various Types of Large Direct Composite and Indirect Glass Ceramic Restorations

Clinical and laboratorial performance of rehabilitation of endodontically treated teeth: A systematic review

OBJECTIVE

This systematic review aimed to analyze the clinical (survival rate, failure risk, or fracture) and laboratory performance (fracture mode or failure) of rehabilitations of endodontically treated teeth, with and without posts.

MATERIALS AND METHODS

A systematic search was conducted in the Pubmed, Scopus, Web of Science, Embase, Cochrane Library, and OpenGrey databases up to March 2023, according to PRISMA guidelines. In vitro and clinical studies that compared the clinical and laboratory performance of endodontically treated teeth with and without intraradicular posts were included. Studies selection, data extraction, and risk of bias analysis were performed.

RESULTS

Thirty-one in vitro and 7 clinical studies were included. For in vitro studies, fiberglass post (n = 24) was the most mentioned. The follow-up time of the clinical studies ranged from 1 to 17 years, with the fiber-reinforced composite post (n = 3) being the most evaluated, and only failure risk proved to be more favorable for using intraradicular posts.

CONCLUSION

Rehabilitations of endodontically treated teeth with and without intraradicular retainers showed no difference in fracture resistance and failure mode, evaluated by in vitro studies. Clinical studies showed no difference in survival rate, but failure risk proved to be more favorable for the use of posts.

CLINICAL SIGNIFICANCE

This analysis revealed significant variability between results, however, most laboratory and clinical studies revealed no difference with using the post. Furthermore, it is important to emphasize the need to evaluate the coronary remnant and the general characteristics of the tooth in each situation.

An in vitro evaluation of the fatigue behavior of resin composite materials as part of a translational research cycle

PURPOSE

This study aimed to reproduce and translate clinical presentations in an in vitro set-up and evaluate laboratory outcomes of mechanical properties (flexural strength, fatigue resistance, wear resistance) and link them to the clinical outcomes of the employed materials in the Radboud Tooth Wear Project (RTWP).

MATERIALS AND METHODS

Four dental resin composites were selected. 30 discs (Ø12.0 mm, 1.2 mm thick) were fabricated for each of Clearfil TM AP-X (AP), Filtek TM Supreme XTE (FS), Estenia TM C&B (ES), and Lava Ultimate (LU). Cyclic loading (200 N, 2 Hz frequency) was applied concentrically to 15 specimens per group with a spherical steatite indenter (r = 3.18 mm) in water in a contact-load-slide-liftoff motion (105 cycles). The wear scar was analysed using profilometry and the volume loss was digitally computed. Finally, all specimens were loaded (fatigued specimens with their worn surface loaded in tension) until fracture in a biaxial flexure apparatus. The differences in volume loss and flexural strength were determined using regression analysis.

RESULTS

Compared to AP and FS, ES and LU showed a significantly lower volume loss (p < 0.05). Non-fatigued ES specimens had a similar flexural strength compared to nonfatigued AP, while non-fatigued FS and LU specimens had a lower flexural strength (p < 0.001; 95 %CI: -80.0 - 51.8). The fatigue test resulted in a significant decrease of the flexural strength of ES specimens, only (p < 0.001; 95 %CI: -96.1 - -54.6).

CLINICAL RELEVANCE

These outcomes concur with the outcomes of clinical studies on the longevity of these composites in patients with tooth wear. Therefore, the employed laboratory test seems to have the potential to test materials in a clinically relevant way.

The fracture strength and the failure mode of lithium disilicate or resin nano ceramics as a crown, overlay, or endocrown restoration on endodontically treated teeth

INTRODUCTION

Different materials and restorative concepts have been proposed over the years to restore endodontically treated teeth (ETT). Monolithic ceramic and composite restoration can be lute to the tooh, without the use of a post. However, little is known how the material stiffness and presence of a composite core will affect the survival and failure mode. The objective of this in-vitro study was to evaluate the fracture strength and failure mode of endodontically treated molars, restored with ceramic or hybrid composite monolithic restoration, in the presence of absence of a composite core.

MATERIALS AND METHODS

Sixty depulped molars were restored with a lithium-disilicate (e.max CAD) or hybrid composite (Cerasmart) restoration. Both materials were used in a monolithic approach, but with 3 different designs: (a) monolithic endocrown, (b) crown with a separate composite core, and (c) overlay without core buildup or pulpal extension. Ten sound teeth were used as control group. All groups were thermocycled (10,000 cycles), subsequently loaded in a chewing simulator (100,000 cycles) and finally loaded until fracture.

RESULTS

Peak fracture loads and failure modes were registered. No significant differences were seen between the groups in terms of fracture load. Failure modes were statistically significantly different among groups with significant correlation between restoration type and material. (p < 0.001 and p = 0.033, respectively). No group presented significantly higher fracture resistance. Although ceramic crowns and overlays presented the highest repairability, all restored ETT were within the range of the intact tooth' fracture strength.

CONCLUSION

No restoration presented significant different fracture loads. However, the type of restoration and material choice were correlated to the fracture mode.

Biomechanical behavior of molars restored with direct and indirect restorations in combination with deep margin elevation

STATEMENT OF PROBLEM

The existing knowledge is insufficient for comprehending the fatigue survival and fracture resistance of molars that have deep approximal direct and indirect restorations, whether with or without deep margin elevation (DME).

PURPOSE

The aim of this laboratory and in silico study is to investigate the fatigue survival, fracture strength, failure pattern and tooth deformation of molars restored with DME in combination with a direct or indirect restoration.

MATERIAL AND METHODS

This study utilized 45 extracted sound human molars, divided into three groups (n = 15). Standardized 100% inter-cuspal inlay preparations were performed, extending 2 mm below the CEJ and immediate dentin sealing (IDS) was applied. Group 1 (Co_1) was restored with direct composite; Group 2 (Hyb_2) with a 2 mm DME of direct composite and a glass-ceramic lithium disilicate restoration; Group 3 (Cer_3) a glass-ceramic lithium disilicate restoration. All specimens were exposed to a fatigue process involving thermal-cyclic loading (50N for 1.2 × 106 cycles at 1.7 Hz, between 5 and 55 °C), if teeth survived, they were fractured using a load-to-failure test and failure types were analyzed. Finite element analysis (FEA) was conducted to assess tooth deformation and tensile stress in the restorations. Statistical evaluation of fracture strength was conducted using the Kruskal-Wallis test. Fisher's exact test was utilized to analyze the fracture types and repairability. A statistical significance level of α < 0.05 was set for all analyses.

RESULTS

All specimens successfully withstood the fatigue testing procedure, and no statistically significant differences in fracture strength were observed among the three groups (P > 0.05). The Fisher's exact test indicated a significant association between the restorative material and fracture type (F2 = 18.315, df = 2, P = 0.004), but also for repairability (F2 = 13.725, df = 2, P = 0.001). Crown-root fractures were significantly more common in the Cer_3 group compared to the Co_1 group (P = 0.001) and the Co_1 group had significantly more repairable fractures (F2 = 13.197, df = 2, P = 0.001). FEA revealed comparable outcomes of deformation among models and higher maximum tensile stress on models with higher frequency of catastrophic failures.

CONCLUSIONS

All tested restoration materials exhibited comparable fatigue survival and fracture strength in this laboratory and in silico study. However, it is important to recognize the potential for more severe and irreparable fractures when opting for deeply luted glass-ceramic inlay restorations in clinical practice. In such cases, it would be prudent to consider the alternative option being a direct composite approach, because of its more forgiving fracture types and repairability.

CLINICAL IMPLICATIONS

Molars with deep approximal direct and indirect restorations, whether with or without DME, are comparable in their fatigue survival and fracture resistance to withstand intra-oral forces. Deep direct restorations exhibit more repairable fractures compared to deeply luted glass-ceramics.

Biomechanical performance of endocrown and core-crown restorations: A systematic review

OBJECTIVE

To assess and compare, through a systematic review of the literature, the biomechanical performance of endocrowns and traditional core-crowns (with and without intracanal post) for the rehabilitation of endodontically treated teeth with severe coronal structure damage.

MATERIALS AND METHODS

A systematic search was performed in MEDLINE/PubMed, Scopus, and Web of Science databases. In-vitro studies comparing endocrowns with (post-)core-crown restorations were selected and screened by two independent reviewers. The included studies were submitted to the risk of bias analysis using the RoBDEMAT tool and the biomechanical outcomes were collected for qualitative analysis. The extracted data were presented based on comparative analyses among the included studies.

RESULTS

Thirty-one studies were included: 9 studies evaluated restorations of molars, 14 for premolars, and 8 studies evaluated anterior restorations. For the majority of the studies, endocrowns showed either similar or greater survival rates under fatigue and monotonic load than (post-)core-crown restorations, irrespectively of the tooth. The endocrowns showed more favorable failure patterns than (post-)core-crowns, irrespectively of the tooth. Endocrowns produced lower stresses in the restorative material for molars and premolars and in the luting material for premolars than (post-)core-crown restorations. The included studies presented adequate information for most items of the RoBDEMAT risk of bias tool.

CONCLUSION

Endocrowns showed similar or greater biomechanical performance than the traditional (post-)core-crown restorations in most of the evaluated studies.

CLINICAL SIGNIFICANCE

This systematic review showed that endocrowns present either similar or greater biomechanical performance than core-crown restorations for anterior and posterior endodontically treated teeth with severe structural damage.

Comparative analysis of endocrown fracture resistance and marginal adaptation: CAD/CAM technology using lithium disilicate vs. zirconia-reinforced lithium silicate ceramics

Aims

The present study aimed to compare the fracture resistance and marginal adaptation of endocrowns fabricated using lithium disilicate (LDS) and zirconia-reinforced lithium silicate 9ZLS) ceramics by the computer-aided design and computer-aided manufacturing (CAD/CAM) technology.

Materials and Methods

In this in vitro experimental study, 24 extracted mandibular first molars received standard endocrown preparation and were randomly assigned to two groups (n = 12) for the fabrication of endocrowns with ZLS (Suprinity) and LDS (IPS e.max CAD) ceramics. After scanning the teeth with a CAD scanner, endocrowns were designed by inLab Software version 15 (inLab SW 15) and prepared by an imes-icore 350i milling machine. The vertical marginal gap of endocrowns was measured under a stereomicroscope at three steps before and after cementation and after thermomechanical cycles. The fracture resistance of specimens was then measured by load application at a 45° angle. Mode of failure was also determined as reparable or irreparable. Data were analyzed using Pearson's correlation test and t-test.

Results

The mean fracture resistance of ZLS endocrowns was significantly higher than that of LDS endocrowns (P = 0.000). The reparability of ZLS endocrowns was zero, while that of LDS endocrowns was 83.33 %. The vertical marginal gap was significantly smaller in ZLS than in LDS endocrowns at all three time points (P < 0.05). Also, the marginal gap increased by cementation and thermomechanical cycles in both groups.

Conclusion

ZLS and LDS endocrowns both showed acceptable vertical marginal adaptation. ZLS had superior marginal adaptation and higher fracture resistance.

Systematic review fracture resistance of endodontically treated posterior teeth restored with fiber reinforced composites- a systematic review

BACKGROUND

Large cavity designs and access cavities impair endodontically treated tooth fracture resistance. As the tooth's strength is known to reduce significantly after the root canal treatment, occlusal loading as a result of functions such as chewing, biting and certain parafunctional tendencies makes the endodontically treated tooth vulnerable to fracture. Hence, after endodontic treatment, it is vital to give adequate and appropriate restorative material to avoid tooth fractures. Accordingly, the choice of such restorative material should be dictated by the property of fracture resistance.

OBJECTIVE

The goal of this study was to conduct a systematic review and critical analysis of available data from in vitro studies examining the fracture resistance of endodontically treated posterior teeth restored with fiber-reinforced composites.

METHODOLOGY

The Preferred Reporting Items for Systematic Review and Meta-Analysis (PRIS-MA) Statement was used to guide the reporting of this systematic review A comprehensive literature search was performed using MEDLINE (via PubMed), Scopus, ScienceDirect, Google Scholar, and LILACS. A manual search of the reference lists of the articles was also performed. The databases provided a total of 796 studies from the electronic systematic search. The databases provided a total of 796 studies from the electronic systematic search. Two reviewers scrutinized the papers for eligibility based on inclusion/exclusion criteria and extracted data. The studies were assessed for their potential risk of bias. Based on modified JBI & CRIS (checklist for reporting in vitro studies) guidelines, along with the methodology and treatment objective, we have formulated 13 parameters specifically to assess the risk of bias. A total of 18 studies met the inclusion criteria and were included for qualitative analysis. Considering the high heterogeneity of the studies included, a meta-analysis could not be performed.

RESULTS

The majority of the included studies had a moderate or high risk of bias. When compared to traditional hybrid composites, fiber-reinforced composites showed increased fracture resistance of endodontically treated teeth in the majority of investigations. On the other hand, limited evidence was found for the bulk fill composites. Moreover, moderate evidence was found for the fracture resistance of inlays and fiber posts with fiber-reinforced composites for core build-up in endodontically treated teeth. No evidence could be found comparing the fracture resistance of endo crowns and fiber-reinforced composites in endodontically treated teeth.

CONCLUSION

According to the research, using fiber-reinforced composites instead of conventional hybrid composites improves the fracture resistance of endodontically treated teeth. However, there was a high risk of bias in the research considered. No judgments could be reached about the superiority of one material over another based-on comparisons between other core restorations.

Influence of height discrepancy between pulp chamber floor and crestal bone in the mechanical fatigue performance of endodontically-treated teeth restored with resin composite endocrowns

OBJECTIVE

To explore and characterize the effect of the discrepancy between crestal bone height (CB) and pulp chamber floor (PCF) in the fatigue performance of endodontically-treated teeth rehabilitated with an endocrown restoration.

MATERIALS AND METHODS

A total of 75 human molars free of defects, caries history or cracks were selected, then endodontically treated and randomly allocated into 5 groups (N = 15) according to the difference between PCF and CB, as follows: PCF 2 mm above, PCF 1 mm above, PCF leveled, PCF 1 mm below and PCF 2 mm below. Endocrown restorations were made with composite resin (Tetric N-Ceram, shade B3, Ivoclar) in 1.5 mm thickness and luted with a resin cement (Multilink N, Ivoclar) onto the dental elements. Monotonic testing was performed to define the fatigue parameters, and a cyclic fatigue test was used until failure of the assembly. The collected data were submitted to statistical survival analysis (Kaplan-Meier followed by Mantel-Cox and Weibull), fractographic analysis and finite element analysis (FEA) were performed as complementary analyzes.

RESULTS

The PCF 2 mm below and PCF 1 mm below groups presented the best results regarding fatigue failure load (FFL) and number of cycles for failure (CFF) (p < 0.05), but presented no difference between each other (p > 0.05). The PCF leveled and PCF 1 mm above groups presented no statistical difference between them (p > 0.05), but performed better than the PCF 2 mm above group (p < 0.05). The rate of favorable failures of PCF 2 mm above, PCF 1 mm above, PCF leveled, PCF 1 mm below and PCF 2 mm below groups were 91.7%, 100%, 75%, 66.7% and 41.7%, respectively. FEA showed different stress magnitudes according to the pulp-chamber design.

CONCLUSION

The insertion level of the dental element to be rehabilitated with an endocrown interferes in the mechanical fatigue performance of the set. The discrepancy between the CB height and the PCF has a direct effect, where the higher the PCF in relation to the CB, the greater the risk of mechanical failure of the restored dental element.

In Vitro Evaluation of Lithium Disilicate Endocrowns and Post and Core Crowns-A Systematic Review

The aim of this systematic review was to summarize the results of the studies that have compared the physical and mechanical properties of lithium disilicate (LDS) endocrowns constructed for posterior teeth to those retained by post-and-core retention systems. The review was conducted following the PRISMA guidelines. The electronic search process was conducted on PubMed-Medline, Scopus, Embase and ISI Web of Knowledge (WoS) from the earliest available date till 31 January 2023. Additionally, the studies were assessed for their overall quality and risk of bias using the Quality Assessment Tool For In Vitro Studies (the QUIN). The initial search resulted in 291 articles, out of which, only 10 studies met the eligibility criteria. In all studies LDS endocrowns were compared with various kinds of endodontic posts and crowns made from other materials. There were no definite pattern or trends observed in the fracture strengths of tested specimens. There was no predilection observed in failure patters among the experimental specimens. No predilection was observed in the fracture strengths of LDS endocrowns when compared to post-and-core crowns. Furthermore, no differences in failure patterns could be observed when both types of restorations were compared. The authors propose standardized testing of endocrowns against post-and-core crowns in future studies. In conclusion, long-term clinical trials are advocated to compare the survival, failure and complication rates of LDS endocrowns and post-and-core restorations.

Resistance to fracture of simulated external cervical resorption cavities repaired with different materials

The aim of the study was to evaluate the fracture resistance (FR) of teeth with simulated external cervical resorption (ECR) cavities repaired with different materials. Following the shaping of the 80 human permanent maxillary central incisors, standard ECR cavities were prepared and restored with a nanohybrid composite resin; a high viscosity GIC Equia Forte Fill; Biodentine; Biodentine + nanohybrid composite resin; MTA BIOREP; MTA BIOREP + nanohybrid composite resin. Then, the root canals were obturated with AH Plus and gutta-percha. The roots were embedded acrylic resin blocks and fracture strength test was applied. The highest FR was observed in the Biodentine group, while the lowest was in Equia group (p < 0.05). No significant results were observed among composite, Biodentine + composite, MTA BIOREP + composite and MTA BIOREP (p > 0.05). Biodentine may be a preferable material for repairing ECR cavities. Adding a composite layer on MTA BIOREP and Biodentine did not improve the FR of these materials.

Laboratory methods to simulate the mechanical degradation of resin composite restorations

OBJECTIVES

This study reviewed the literature to identify in vitro approaches that have been used to simulate the mechanical degradation and fatigue of resin composite restorations.

METHODS

A search for articles was carried out in 4 databases and included studies in which composite restorations were bonded to teeth and subject to cyclic loading. Articles were assessed for eligibility, and the following items were the extracted from the included studies: authors, country, year, materials tested, simulation device and details including load magnitude and frequency, number of cycles, type of antagonist, test medium, and temperature. Data were analyzed descriptively.

RESULTS

The 49 studies included showed a high level of heterogeneity in methods, devices, and test parameters. Nineteen different simulation devices were used, applying loads varying between 30 and 2900 N, and frequencies varying between 0.4 and 12 Hz. The load and frequency used most often were ~ 50 N (63.3%) and 1.5-1.7 Hz (32.7%). The number of cycles varied between 10 K and 2.4 M, 1.2 M was the most prevalent (40.8%). The majority of studies combined cyclic loading with at least one additional aging method: static liquid storage, thermo-mechanical cycling applied simultaneously, and thermal cycling as a discrete aging step were the three most frequent methods. The overall evidence indicated reporting problems, and suggested a lack of clinical validation of the research methods used.

SIGNIFICANCE

Validation studies, underlying clinical supporting data, and better reporting practices are needed for further improving research on the topic. Specific suggestions for future studies are provided.

The effect of fiber insertion on fracture strength and fracture modes in endocrown and overlay restorations

Aim of this study was to determine the fracture strength and modes of endocrown and overlay restorations with/without fiber reinforcement on endodontically treated teeth. Sixty-five molar teeth were used: Group IN (intact teeth), Group E (endocrown), Group ER (endocrown + ribbond), Group O (overlay), Group OR (overlay + ribbond; n = 13). Ribbond (Seattle, WA) was inserted at the base of pulp chamber in Group ER and OR. All restorations were designed and produced by using computer-aided design and computer-aided manufacturing (Sirona Dental Systems, Bensheim, Germany) and Cerasmart (GC Corp. Kasugai, Aichi, Japan). All teeth were subjected to thermomechanical aging and fractured in a universal test device. Fractured surfaces were analyzed with a stereomicroscope (SMZ1000, Nikon, Japan). Data were analyzed with Welch's analysis of variance and Games-Howell test (p < .001). Group E showed significantly lower fracture strength values than other groups(p < .05). No statistically significant differences were found among the other groups(p > .05). Most of the unfavorable fractures were seen in Groups E and O. Overlay restorations showed higher fracture strength values than endocrown restorations. Although fiber insertion did not improve the fracture strength of the indirect restorations, it reduced the frequency of irreparable fracture mode. Overlay restorations and fiber application are more advantageous in preserving the durability of the endodontically treated teeth.

External Marginal Gap Variation and Residual Fracture Resistance of Composite and Lithium-Silicate CAD/CAM Overlays after Cyclic Fatigue over Endodontically-Treated Molars

The purpose of this in vitro study was to evaluate the external marginal gap variation with a 3D quantitative method and the residual fracture resistance after cyclic fatigue in endodontically treated molars restored with overlays of different materials, with and without fiber posts-supported buildups. Forty-eight human maxillary molars were selected, endodontically treated, prepared with standardized MOD cavities and randomly allocated into 6 study groups considering the "core strategy" (build-up with composite resin; build-up with composite resin supported by a fiber post); and the "restorative material" of the indirect adhesive overlay (GrandioBlocks, Voco; Cerasmart, GC; CeltraDuo, Dentsply). All procedures were executed according with manufacturers guidelines. Micro-CT analysis prior and after cyclic fatigue were executed, followed by scanning electron microscope analysis and fracture resistance test. The Two-Way ANOVA analysis showed that interfacial gap progression was significantly influenced by the "core strategy" (p < 0.01) but not of "restorative material" (p = 0.59). Concerning fracture resistance, "restorative material" was statistically significant (p < 0.01), while "core strategy" (p = 0.63) and the interaction (p = 0.84) were not. In conclusion, the fiber post presence within the build-up promoted a lower interfacial gap opening after fatigue, evaluated through micro-CT scans. In terms of fracture resistance, teeth restored with Cerasmart and Celtra Duo were statistically similar, but superior to GrandioBlocks.

Fracture resistance of endodontically-treated maxillary premolars restored with different type of posts and direct composite reconstructions: A systematic review and meta-analysis of in vitro studies

OBJECTIVE

To conduct a systematic review and meta-analysis to assess if the presence of an endodontic post may increase the fracture resistance of endodontically-treated maxillary premolars directly restored with composite.

METHODS

A comprehensive systematic literature search according to the PRISMA statement was conducted to assess in vitro studies including endodontically-treated maxillary premolars, restored with different type of posts supporting direct composite reconstructions. Two groups of meta-analyses were performed using fixed effects model and additional Trial Sequential Analysis (TSA) was carried out. Moreover, risk of bias was conducted and quality of evidence for any performed meta-analysis was assessed using Grading of Recommendations Assessment, Development and Evaluation (GRADE).

RESULTS

Twenty-four articles met the inclusion criteria and 13 studies also underwent quantitative evaluation. Fracture resistance of endodontically-treated premolars restored with fiber posts was significantly less than sound teeth (p value: < 0.00001), however endodontically-treated premolars with a fiber post provided an increase in fracture resistance when compared to equivalent teeth restored without post (p value: 0.003). TSA revealed high power of both meta-analyses. Moderate risk of bias was reported in 23/24 studies; only 1 study showed high risk of bias. GRADE system showed moderate strength of evidence due to the presence of a study with high risk of bias and to wide confidence intervals.

SIGNIFICANCE

Within the limitation of the present systematic review and meta-analysis, it can be concluded that endodontically-treated maxillary premolars restored with a fiber post and direct composite restoration demonstrated increased fracture resistance when compared to equivalent teeth without post.

Effect of immediate dentine sealing on the aging and fracture strength of lithium disilicate inlays and overlays

OBJECTIVES

The objectives of this study were to compare the in vitro, laboratory aging, fracture strength, failure mode and reparability of molars restored with lithium disilicate inlays and overlays in conjunction with or without immediate dentin sealing (IDS).

METHODS

Forty extracted, sound human molars were selected and divided into four groups: 1) Inlays with IDS; 2) Inlays without IDS; 3) Overlays with IDS; 4) Overlays without IDS. Standard MOD preparations were made (3 mm wide, 5 mm deep) and in groups 2 and 4, all the cusps were reduced by 2 mm. Directly following tooth preparation, IDS was applied in specimens belonging to groups 1 and 3. The indirect restorations were luted with a heated composite. The restored teeth were subsequently challenged during aging (1.2 million cycles) and thermocycling loading (8000 cycles, 5-55 degrees C). Subsequently, the fracture strength was tested by a load to failure test at 45°. A failure analysis was performed using light- and scanning electron microscopy. The results were analyzed using two-way ANOVA and a Fisher exact test.

RESULTS

Mean fracture load + SD (N) were: Group 1 (n = 12): 1610 ± 419; Group 2 (n = 12): 1115 ± 487; Group 3 (n = 12): 2011 ± 496; Group 4 (n = 12): 1837 ± 406. Teeth restored with an onlay were stronger than those restored with an inlay restoration (p < .001). Teeth with IDS were stronger overall than those without IDS (p = .026). The interaction between preparation type and the mode of dentin conditioning had no statistically significant influence on fracture strength (p = .272). Subsequently, custom hypothesis tests showed that there was no statistically significant difference in fracture strength between inlays with IDS and overlays without IDS (p = .27). Overlays tend to fail in a more destructive, non-reparable way (p = .003).

SIGNIFICANCE

Both variables IDS and overlay preparation improve overall fracture strength. Inlays with IDS and overlays without IDS didn't differ in fracture strength. Both inlays and overlays are strong enough to withstand physiological chewing forces.

Lithium di silicate ceramic surface treated with Er,Cr:YSGG and other conditioning regimes bonded to orthodontic bracket

Aim

To assess bond integrity and modes of failure of metallic brackets to lithium disilicate ceramics (LDC) conditioned with Er,Cr:YSGG laser (ECL).

Material and methods

Sixty LDC were arbitrarily allocated into six groups (n = 15) according to the type of ceramic surface conditioning treatment. Group 1 surface treated with silane (S) only, group 2 surface etched with hydrofluoric acid (HF)+ S, group 3 surface conditioned with HF+ ultrasonic bath (UB)+ S, group 4 sand blasting (SB) of glass ceramic surface with 50 µm Al₂O₃, group 5 surface conditioned with self-etch ceramic primer (SECP) and in group 6 surface treated with ECL + S. After conditioning, the specimens were positioned in a universal testing device for shear bond strength (SBS) testing. Adhesive Remnant Index (ARI) was used to determine sites of bond failure. Among experimental groups analysis of variance (ANOVA) and Tukey multiple comparison test was used at a significance level of (p < 0.05).

Results

The highest SBS values were observed in group 3 HF+ UB + S (18.21 ± 1.241) and the lowest SBS values were displayed group 1 surface treated with S only (5.21 ± 0.23). Specimens surface conditioned in group 2 with HF+ S (17.85 ± 1.25), group 3 HF+ UB + S (18.21 ± 1.241) and group 6 ECL + S (17.09 ± 1.114) unveiled comparable SBS values (p > 0.05).

Conclusion

LDC conditioned with ECL at (4.5 W and 30 Hz) has a potential to be used in clinical settings alternate to HF acid.

Comparison of endocrowns made of lithium disilicate glass-ceramic or polymer-infiltrated ceramic networks and direct composite resin restorations: fatigue performance and stress distribution

This study compared the fatigue performance and the stress distribution of endodontically treated molars restored with endocrowns obtained with lithium disilicate glass-ceramic or a polymer-infiltrated ceramic network, both processed by CAD-CAM, and direct composite restorations. Forty-eight human mandibular molars were randomly assigned into 03 groups (n = 16) and restored with endocrowns (LD - lithium disilicate glass-ceramic or PICN - polymer-infiltrated ceramic network) or with direct composite restorations. Fatigue testing followed a step-stress approach (initial maximum load of 200 N and 5000 cycles, incremental step load of 200N and 10,000 cycles/step, being the specimens loaded until failure or to a maximum of 135,000 cycles at 2800 N). The fatigue failure load and number of cycles until failure were recorded and statistically analyzed. Fractographic and finite element (FEA) analyzes were conducted as well. There were no differences in fatigue failure load, number of cycles until fracture and mean survival probabilities among groups. However, indirect endocrowns had higher mechanical structural reliability, and LD restorations lasted more time before start to failing. FEA showed that the stress concentration in tooth tissues was higher for the resin composite, followed by PICN and LD in a decreasing order. Almost all fractures were restricted to the restorative material (without tooth involvement), and origins were identified at occlusal surface. The type of restoration did not influence the fatigue failure load, number of cycles until fracture and mean survival probabilities of the restorative strategies. Despite that, the mechanical structural reliability of endocrowns, especially those made of lithium disilicate, was higher and lasted more time before start to failing.