Marginal adaptation and fracture strength of endocrowns manufactured with different restorative materials: SEM and mechanical evaluation

Application of one-piece endodontic crowns fabricated with CAD-CAM system to molars

Computer-aided design-computer-aided manufacturing (CAD-CAM) systems have been widely used as a fabrication method for restorations because of their high efficiency and accuracy, which significantly reduces fabrication time. However, molars with insufficient clearance or short clinical crown lengths require retention holes or grooves on the preparation, making it difficult to replicate the shapes with the CAM milling system. In these cases, restorations using the lost-wax method are selected. This article focuses on one-piece endodontic crowns (endocrowns) fabricated with a CAD-CAM system (CAD-CAM endocrowns), in which their posts and crowns are integrated. Articles from July 2012 to August 2023 were searched in PubMed with the keyword "endocrown". This review discusses the application of CAD-CAM endocrowns to molars from the viewpoint of model experiment (fracture resistance, adaptation) and clinical research. This technique, which allows margins and internal gaps to be set within the clinically acceptable range, is reported to be an effective way of restoring molars with high survival rates in clinical research.

The internal and marginal adaptation of lithium disilicate endocrowns fabricated using intra and extraoral scanners: An in-vitro study

OBJECTIVES

The impression technique highly influences the adaptation of ceramic restorations. Not enough information is available to compare the marginal (MF) and internal fit (IF) of endocrowns fabricated with various digitization techniques. Therefore, this in-vitro study aimed to compare the MF and IF of lithium disilicate (LDS) endocrowns fabricated through direct and indirect digital scanning methods.

MATERIALS AND METHODS

One extracted maxillary molar was used to fabricate endocrowns. The digitization of the model was performed with (G1) direct scanning (n = 10) utilizing an intraoral scanner (IOS), (G2) indirectly scanning the conventional impression taken from the model using the same IOS (n = 10), (G3) indirectly digitalizing the obtained impression using an extraoral scanner (EOS) (n = 10), and (G4) scanning the poured cast using the same EOS (n = 10). The MF and IF of the endocrowns were measured using the replica method and a digital stereomicroscope. The Kruskal-Wallis test was used to analyze data.

RESULTS

The studied groups differed significantly (p<0.001). G2 (130.31±7.87 μm) and G3 (48.43±19.14 μm) showed the largest and smallest mean vertical marginal gap, respectively. G2 and G3 led to the highest and lowest internal gaps in all regions, respectively. With significant differences among the internal regions (p<0.001), the pulpal area demonstrated the most considerable misfit in all groups.

CONCLUSIONS

Scanning the impression using an extraoral scanner showed smaller marginal and internal gaps.

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.

Biomechanical behavior of all-ceramic endocrowns fabricated using CAD/CAM: A systematic review

PURPOSE

This study performed a systematic review to assess the biomechanical behavior of all-ceramic endowcrowns fabricated using computer-aided design and computer-aided manufacturing (CAD/CAM) for the restoration of endodontically treated teeth.

STUDY SELECTION

Three electronic databases (PubMed, Web of Science, and Scopus) were searched by operators specializing in health sciences databases searches to answer the following focused question based on the Population, Intervention, Comparison, Outcome (PICO) format: "Whether all-ceramic CAD/CAM endocrowns (Intervention) used to restore human endodontically treated teeth (Population) exhibit superior fracture resistance (Outcome) compared to non-CAD/CAM all-ceramic or non-ceramic endocrowns (Comparison)." The methodological quality assessment was performed using previously conducted systematic reviews of in vitro studies. The outcomes were expressed as the mean ± the standard deviation (SD).

RESULTS

Seventeen in vitro studies were included. The materials used in these studies were lithium disilicate glass-ceramic, polymer-infiltrated ceramic, zirconia-reinforced lithium silicate glass-ceramic, resin/hybrid nanoceramics, zirconia-reinforced lithium silicate ceramics, and feldspathic ceramic. The fracture resistance of endocrowns using different ceramics varied as follows: (i) IPS e.max CAD (2863.62 ± 51.47 N), (ii) Vita Enamic (1952 ± 378 N), (iii) Vita Suprinity (1859 ± 588 N), (iv) Cerasmart (1981 ± 169.5 N), (v) LAVA Ultimate (2484 ± 464 N), (vi) Celtra Duo (1618.30 ± 585.00 N), and (vii) Cerec Blocs (236.29 ± 32.12 N).

CONCLUSIONS

CAD/CAM all-ceramic endocrowns can withstand occlusal forces in the posterior region. All-ceramic endocrowns improve the fracture strength of endodontically treated teeth. Lithium disilicate crowns were commonly and successfully used in the included studies. More in vitro investigations that implement uniformity in material and measurement approaches are required to strengthen the evidence currently available in the literature regarding the durability of all-ceramic endocrowns.

An in vitro study measuring marginal gaps of inlay restorations fabricated from different CAD-CAM materials after thermocycling

Background

Many monolithic machined materials have been introduced and provided a suitable mechanical and physical properties for inlay restorations. However, there is shortage in the studies evaluating the marginal adaptation using these materials.

Purpose

This study aimed to compare the effect of fabricating inlay restorations from 3 different CAD-CAM materials on marginal gaps before and after thermocycling.

Materials and methods

Sixty human premolars were randomly divided into 3 groups (n = 20) according to the material used: (e.max CAD, Ivoclar AG, Schaan, Liechtenstein), (HC, Shofu, Koyoto, Japan) and (Brilliant Crios, Coltene, Altstätten, Switzerland) (n = 20). A scanning electron microscope (SEM) (JSM- 6510 lv, JEOL, Tokyo, JAPAN) was used to for measuring the marginal gaps after cementation of inlay restorations. The magnification was adapted to 250x. Marginal gaps were revaluated with SEM after thermocycling. The temperatures of baths were 5 and 55 °C was applied for a total of 5000 cycles. All data were statistically analyzed by using ANCOVA to demonstrate if there were any statistically significant differences between the gap measures after thermocycling of the three independent (unrelated) groups. A Bonferroni adjustmen was used to perform post hoc analysis (α = 0.05).

Results

Post-intervention marginal gap was statistically significantly lower in group EX (110.8 μm) which was statistically significant compared with group SF (112.5 μm) (mean difference=-1.768, P = .007) and group BR (113 μm) (mean difference=-2.272, P = .001), however, in. comparing SF and BR groups, there was no significant difference (mean difference=-0.5, P = .770).

Conclusions

Thermocycling affected the marginal gaps of composite based restoration and resin-modified ceramics widely. However, it had a very small effect on glass ceramics marginal adaptation.

Clinical implications

The marginal gaps of CAD-CAM inlays varied according to material used (ceramic based, combination, or resin based). Thermocycling has a minor effect on the marginal adaptation of lithium disilicate glass-ceramic inlays, where it affected the margin of resin-modified ceramic and composite based inlays greatly. Using lithium disilicate glass-ceramic might improve the clinical longevity of inlay restored teeth.

An in vitro study measuring marginal gaps of inlay restorations fabricated from different CAD-CAM materials after thermocycling

BACKGROUND

Many monolithic machined materials have been introduced and provided a suitable mechanical and physical properties for inlay restorations. However, there is shortage in the studies evaluating the marginal adaptation using these materials.

PURPOSE

This study aimed to compare the effect of fabricating inlay restorations from 3 different CAD-CAM materials on marginal gaps before and after thermocycling.

MATERIALS AND METHODS

Sixty human premolars were randomly divided into 3 groups (n = 20) according to the material used: (e.max CAD, Ivoclar AG, Schaan, Liechtenstein), (HC, Shofu, Koyoto, Japan) and (Brilliant Crios, Coltene, Altstätten, Switzerland) (n = 20). A scanning electron microscope (SEM) (JSM- 6510 lv, JEOL, Tokyo, JAPAN) was used to for measuring the marginal gaps after cementation of inlay restorations. The magnification was adapted to 250x. Marginal gaps were revaluated with SEM after thermocycling. The temperatures of baths were 5 and 55 °C was applied for a total of 5000 cycles. All data were statistically analyzed by using ANCOVA to demonstrate if there were any statistically significant differences between the gap measures after thermocycling of the three independent (unrelated) groups. A Bonferroni adjustmen was used to perform post hoc analysis (α = 0.05).

RESULTS

Post-intervention marginal gap was statistically significantly lower in group EX (110.8 μm) which was statistically significant compared with group SF (112.5 μm) (mean difference=-1.768, P = .007) and group BR (113 μm) (mean difference=-2.272, P = .001), however, in. comparing SF and BR groups, there was no significant difference (mean difference=-0.5, P = .770).

CONCLUSIONS

Thermocycling affected the marginal gaps of composite based restoration and resin-modified ceramics widely. However, it had a very small effect on glass ceramics marginal adaptation.

CLINICAL IMPLICATIONS

The marginal gaps of CAD-CAM inlays varied according to material used (ceramic based, combination, or resin based). Thermocycling has a minor effect on the marginal adaptation of lithium disilicate glass-ceramic inlays, where it affected the margin of resin-modified ceramic and composite based inlays greatly. Using lithium disilicate glass-ceramic might improve the clinical longevity of inlay restored teeth.

Endocrowns: Indications, Preparation Techniques, and Material Selection

Endodontic treatment is often necessary in the field of dentistry. As the tooth structure is lost during such treatment, the tooth may become weaker and lose some of its mechanical qualities. Endodontically treated posterior teeth require cuspal coverage because of their anatomical features. Endocrowns are regarded as a suitable choice for restoring teeth that have undergone endodontic treatment. These restorations are recommended when there is a substantial loss of tooth structure, restricted interocclusal space, or a short clinical crown. They are also contraindicated in case of severe loss of tooth structure where adhesion is not applicable. Endocrowns require a specific preparation design that is distinct from the conventional crown. They can be manufactured by two methods: heat pressing or computer-aided design/computer-aided manufacturing (CAD/CAM). Moreover, several materials have been used in fabricating endocrown restoration. Lithium disilicate glass-ceramic is the most recommended material as it possesses excellent mechanical properties and esthetic results with the ability to bond to tooth structure. In conclusion, several kinds of literature recommend using them for molars. Further research is needed to evaluate this technique for premolar and anterior teeth.

In-Vitro Comparison of Fracture Strength of Endocrowns and Overlays in Endodontically Treated Teeth Manufactured with Monolithic Lithium Disilicate and Zirconia

To evaluate the fracture strength and the failure mode of endodontically treated molars restored with monolithic lithium disilicate and zirconia endocrowns and overlays. A total of 48 extracted mandibular molars were endodontically treated, decoronated 2 mm above the cementoenamel junction and divided into four 12-specimen groups. Group ELD: lithium disilicate endocrowns. Group EZ: monolithic zirconia endocrowns. Group OLD: lithium disilicate overlays. Group OZ: monolithic zirconia overlays. Overlays did not extend in the pulp chamber and endocrowns extended in the pulp chamber 2 mm. After adhesive bonding of the restorations, the specimens were subjected to thermocycling (×5000 cycles) and then to fracture resistance testing at lateral static loading (1 mm/min) at a universal testing machine. The failure mode of the specimens was qualitatively evaluated. Differences in means were compared using with t-tests for independent samples or Mann-Whitney test (p < 0.05). Weibull distribution analysis was also performed. Group ELD showed significantly higher fracture strength than all other groups (p = 0.001), and the highest Weibull modulus. Conclusions: Lithium disilicate endocrowns exhibit higher fracture strength and are more reliable compared to the other types of restorations examined. Endocrowns had more catastrophic failures compared to overlays.

Fracture Strength of Endocrowns Fabricated From Three Different Computer-Aided Design/Computer-Aided Manufacturing Ceramic Materials: An In-Vitro Study

INTRODUCTION

Endocrown restorations have increased in popularity in recent years due to the advancement of both adhesive and restorative materials. The clinical success of endocrowns depends on several factors, including preparation design, material selection, fracture resistance, and marginal adaptation. The aim of this in vitro study was to compare the fracture strength of endocrown restorations fabricated from three different computer-aided design (CAD)/computer-aided manufacturing (CAM) materials.

METHODS

Thirty extracted mandibular first molars were selected. The teeth underwent conventional root canal treatment before being prepared for endocrown restoration. The teeth were allocated to three groups (n=10), corresponding to each of the three ceramic materials used to fabricate the endocrowns they would receive. The ceramic materials used were zirconia-reinforced lithium silicate glass-ceramic (VITA Suprinity, VITA Zahnfabrik, Bad Säckingen, Germany), polymer-infiltrated hybrid ceramic (VITA Enamic, VITA Zahnfabrik, Bad Säckingen, Germany), and lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein). The specimens were scanned, and the digital impressions were transferred into design software to construct the endocrowns. The endocrowns were then milled and cemented. A universal testing machine (5969L3504, Instron, USA) was used for the fracture strength test at a crosshead speed of 1 mm/min until catastrophic failure occurred. Statistical analysis was performed using IBM Corp. Released 2015. IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY: IBM Corp.

RESULTS

The one-way analysis of the variance test indicated a significant difference in the fracture strength between the different ceramic groups tested (P=0.037). The Tukey posthoc test showed that the IPS e.max CAD group had marginally higher fracture strength values than the VITA Enamic group (P=055). No significant differences in fracture strength values were found between the VITA Enamic and VITA Suprinity groups or between the VITA Suprinity and IPS e.max CAD groups (P>0.05).

CONCLUSION

The reported fracture strength values for all the tested materials were higher than the strength required to resist masticatory forces. Therefore, endocrowns fabricated using VITA Enamic, IPS e.max CAD, and VITA Suprinity CAD/CAM materials present restorations with a clinically acceptable fracture strength.

Evaluation of marginal and internal fit of lithium disilicate and zirconia all-ceramic CAD-CAM crowns using digital impressions: A systematic review

PURPOSE

A range of materials for single-tooth computer-aided design and computer-aided manufacturing (CAD-CAM) restorations have been introduced that may affect CAM accuracy. This study aimed to review articles evaluating marginal and internal fit of lithium disilicate (LD) and zirconia (Z) crowns fabricated by CAD-CAM systems using intraoral optical scanners (IOS).

MATERIALS AND METHODS

Under the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA), a systematic review was performed along with an electronic article search in the Medline/Pubmed database. The articles were limited to those in the English language that were published within the past ten years.

RESULTS

The initial search resulted in 50 articles and of those, a total of 18 articles were selected for full-text review following abstract evaluation. Eight articles that did not meet the inclusion criteria were excluded and the remaining ten articles, which provided internal and marginal gap values, were used in this review. For LD crowns, marginal gap values ranged between 45µm and 190.2µm. For Z crowns, the values varied between 39µm and 126.4µm. For LD crowns, the internal gap values were between 57.8µm and 475.4µm, and for Z crowns, the values were between 79µm and 205.8µm.

CONCLUSION

The outcome of this review suggests that clinically acceptable marginal and internal fit can be attained with LD and Z all-ceramic CAD-CAM crowns using digital impressions. Additionally, it has been found that LD and Z ceramics provide similar marginal gap values, but LD material provides better internal fit than Z.

Failure loads of heat-pressed versus milled lithium disilicate endocrowns

OBJECTIVES

This study aimed to compare the failure load of heat-pressed versus milled lithium disilicate endocrowns.

MATERIALS AND METHODS

Twenty extracted mandibular molars were sectioned 1.5 mm above the CEJ. Root canal treatment and endocrown preparation were done for all teeth. Samples were then divided into two groups: heat-pressed glass ceramic endocrowns (HP group) (n = 10) and milled endocrowns (CAD group) (n = 10). Cementation was done using self-adhesive resin cement, and a compressive load was applied on the occlusal surface of the specimens until failure occurred.

RESULTS

The mean failure loads were significantly higher in the HP group (2546.5 ± 339 N) compared to the CAD group (1759.9 ± 114.2) (p < 0.05), and majority of failures were due to fracture of the restoration.

CONCLUSIONS

Failure loads of heat-pressed lithium disilicate endocrown are superior to milled endocrown.

CLINICAL RELEVANCE

Molars restored with lithium disilicate endocrowns have higher failure loads than the maximum human bite force regardless of the fabrication method. Although heat-pressed endocrowns have superior failure loads to milled ones, both are indicated for restoring endodontically treated molar teeth.

Marginal integrity and clinical evaluation of polyetheretherketone (PEEK) versus lithium disilicate (E-Max) endocrowns

Aim:  Evaluate the marginal integrity and Clinical performance of PEEK endocrowns compared to lithium disilicate (E-Max) ceramic endocrowns. Methodology: Twenty six endocrowns were fabricated for posterior endodontically treated teeth. Patients were divided into two groups according to the material used for fabrication of the restorations; Group 1(control group) received E-Max endocrowns while Group 2 (intervention group) received Bio HPP PEEK endocrowns. The marginal integrity and internal fit were assessed using the silicon replica approach, in which each replica was sectioned into four segments, each with five reference points that were evaluated using a digital microscope at 35X magnification. After final cementation, the clinical performance of the restorations was evaluated according to the USPHS criteria in terms of marginal adaptation, fracture, and retention. These measurements were repeated after three, six, nine and twelve months respectively. Results: The marginal and internal gaps of both groups were within the clinical acceptable range, but E-Max group recorded statistically significant higher internal gap mean value than PEEK group. Regarding the clinical performance all restorations showed 100% alpha and there was no significant difference between both groups for all tested outcomes (Marginal adaptation, fracture, and retention) over one year.

Influence of margin design and restorative material on the stress distribution of endocrowns: a 3D finite element analysis

Background

This study aimed to evaluate the stress distributions in endocrown restorations as applied to endodontically treated teeth (ETT), according to the factors of “margin design” (four levels) and “restorative material” (six levels).

Methods

Four 3D-finite elements models were constructed for endocrown restored molars considering different margin designs. Model A was prepared with a flat butt joint margin and received an endocrown with a 2.0-mm occlusal thickness. Model B was prepared with a 20° bevel margin and received an endocrown with a 2.0-mm occlusal thickness. Model C was prepared with an axial reduction and 1-mm shoulder margin and received an endocrown with a 2.0-mm occlusal thickness. Model D was prepared with an anatomic margin and received an endocrown with a 2.0-mm occlusal thickness. The following endocrown materials were used: In-Ceram Zirconia (Zr), Vita Suprinity (VS), IPS Empress (IE), Grandio blocs (GR), VisCalor bulk (VS), and CopraPeek Light (CP). The Load application (600 N) was performed at the food bolus and tooth surface during the closing phase of the chewing cycle. The results for the endocrown and tooth remnants were determined according to the von Mises stress. The failure risk of the cement layer was also calculated based on the normal stress criterion.

Results

Model D (with an anatomic margin) showed the greatest stress concentrations, especially in the irregular and sharp angles of the restoration and tooth remnants. The stress concentrated on the dentin was significantly lower in Model B with a 20° bevel margin (20.86 MPa), i.e., 1.3 times lower than the other three margin designs (27.80 MPa). Restorative materials with higher elastic moduli present higher stress concentrations inside the endocrown and transmit less stress to the cement layer, resulting in lower bonding failure risks. In contrast, materials with an elastic modulus similar to that of dentin presented with a more homogeneous stress distribution on the whole structure.

Conclusions

An endocrown with a 20° bevel margin design could be a favorable preparation option for ETT. Composite resins (GR and VC) exhibit a more even stress distribution, and seem to be more promising materials for endocrown molars.

Lithium Disilicate Ceramic Endocrown Biomechanical Response According to Different Pulp Chamber Extension Angles and Filling Materials

The purpose of this study is to evaluate the effect of pulp chamber extension angles and filling material mechanical properties on the biomechanical response of a ceramic endocrown. A 3D model of maxillary molar that underwent endodontically treatment was exported to computer aided design software to conduct finite element analysis (FEA). The endocrown model was modified considering different pulp chamber extension angles (right angle; 6°, 12° and 18° of axial divergence). The solids were imported into the computer aided engineering software in Standard for the Exchange of Product Data (STEP) format. Nine different filling materials were simulated to seal the orifice of the root canal system under each endocrown restoration (resin composite, bulk-fill resin composite, alkasite, flowable resin composite, glass ionomer cement, autocured resin-reinforced glass ionomer cement, resin cement, bulk-fill flowable resin composite, zinc oxide cement), totaling 36 models. An axial load (300 N) was applied at the occlusal surface. Results were determined by colorimetric graphs of von-Misses stress (VMS) and Maximum Principal Stress (MPS) on tooth, cement layer, and endocrown restorations. VMS distribution showed a similar pattern between the models, with more stress at the load region for the right-angled endocrowns. The MPS showed that the endocrown intaglio surface and cement layer showed different mechanical responses with different filing materials and pulp chamber angles. The stress peaks plotted in the dispersion plot showed that the filling material stiffness is proportional to the stress magnitude in the endocrown, cement layer and tooth adhesive surface. In addition, the higher the pulp chamber preparation angle, the higher the stress peak in the restoration and tooth, and the lower the stress in the cement layer. Therefore, 6° and 12° pulp chamber angles showed more promising balance between the stresses of the adhesive interface structures. Under the conditions of this study, rigid filling materials were avoided to seal the orifice of root canal system when an endocrown restoration was planned as rehabilitation. In addition, the pulp chamber axial walls were prepared between 6° and 12° of divergence to balance the stress magnitude in the adhesive interface for this treatment modality.