Marginal gap and fracture resistance of CAD/CAM ceramill COMP and cerasmart endocrowns for restoring endodontically treated molars bonded with two adhesive protocols: an in vitro study

Evaluation of colour change, marginal adaptation, fracture strength, and failure type in maxillary and mandibular premolar zirconia endo-crowns

OBJECTIVES

The objective of this in vitro study was to evaluate the effects of different preparation designs on the mean colour change (ΔE*), marginal adaptation, fracture resistance, and fracture types of maxillary and mandibular premolar endocrowns (ECs).

METHODOLOGY

A total of 40 extracted maxillary and mandibular premolars were treated endodontically, and each type was subdivided according to the remaining axial height (remaining walls on all surfaces; 2-4 mm) and 2 mm inside the pulp chamber. Specimens were immersed in coffee for 14 days, ΔE* was determined, marginal adaptation was observed, fracture forces test was conducted, and the samples were examined visually at 10× magnification to evaluate failure type and identify fracture origin. The data were entered and analyzed using Statistical Package for Social Sciences, and significance between and within groups was evaluated through ANOVA. The p-value ≤ 0.05 was considered statistically significant.

RESULTS

The ΔE* values of the maxillary premolar with 2 mm axial height were the highest (6.8 ± 0.89 units), whereas the lowest value was observed in the mandibular premolar with 4 mm axial height (2.9 ± 0.53 units). Significant differences (p < 0.05) in teeth and design were observed. The marginal adaptation of the mandibular premolar with 4 mm axial height was the highest (30.20 ± 1.53 μm), whereas the lowest marginal adaptation was observed in the maxillary premolar with 2 mm axial height (14.38 ± 0.99 μm), and the difference was statistically significant (p < 0.05). The maximum fracture force was observed in maxillary premolars with 2 mm axial height (2248.15 ± 134.74 N), and no statistically significant difference (p = 0.07) was observed between maxillary and mandibular premolars at 4 mm axial height.

CONCLUSION

The recorded ΔE* values of the ECs were within clinically acceptable values or slightly higher, and the marginal adaption values were within acceptable and recommended clinical values in µm. EC preparation with 2 mm axial height in both arches recorded the highest fracture forces. Type III (split fracture) failure was recorded as the highest in the maxillary and mandibular premolar ECs with different axial wall heights.

A Comparative Analysis of Marginal Adaptation Values between Lithium Disilicate Glass Ceramics and Zirconia-Reinforced Lithium Silicate Endocrowns: A Systematic Review of In Vitro Studies

This systematic review aimed to identify and analyze in vitro studies on the marginal adaptation values of computer-aided-design/computer-aided-manufacturing (CAD/CAM) and heat-pressed lithium disilicate glass ceramics and zirconia-reinforced lithium silicates and endocrown restorations. A full literature search was conducted in Web of Science, PubMed/Medline, EMBASE, Scopus, Cochrane Library, Google Scholar, and ProQuest electronic databases. The following keywords: endocrown [(marginal adaption) or (marginal fit) or internal fitting)], endocrown [(molar(s)) or (premolar(s) or (posterior teeth) or (maxillary arch) or (mandibular arch)] and ceramic materials as [(lithium disilicate glass ceramic CAD/CAM) or (zirconia) or (heat-press)] were used. Articles were manually searched utilizing their reference lists. Study selection was restricted or limited to the time of publication but not to the type of tested teeth or ceramic material, endocrown design, system of endocrown construction, abutment scanning, and system of the marginal adaption measurement. A total of 17 in vitro studies published between 2016 and 2023 were included in this systemic review. Less than half of the studies were published during 2023. Most studies used lithium disilicate glass ceramic and zirconia-reinforced lithium silicate all-ceramic materials by CAD/CAM or heat-press systems. Marginal adaptation, or marginal gap, was almost equal in the 2 materials, while it was slightly or marginally higher in the heat-press than in the CAD/CAM system. All-ceramic lithium disilicate glass ceramic and/or zirconia endocrowns fabricated for posterior teeth in both arches using CAD/CAM or heat-press had recorded marginal adaptation values within an acceptable range.

The effect of sandblasting versus acid etching on the surface roughness and biaxial flexural strength of CAD/CAM resin-matrix ceramics (In vitro study)

BACKGROUND

CAD/CAM resin matrix ceramics are one of the materials used in dental offices. The long-term success of the restoration depends on the bond strength of the restoration to the tooth and other materials; thus, surface treatment of the restoration is necessary to achieve this. But such treatment may affect the restoration strength. The purpose of this study is to assess the impact of various surface treatments on the surface roughness (Ra) and the biaxial flexural strength of two CAD-CAM resin-matrix ceramics.

METHODS

Thirty-six-disc-shaped specimens, each measuring 1.2 mm in thickness and 12 mm in diameter, were machined from two resin-matrix ceramic blocks (Lava Ultimate and Cerasmart) (n = 18). Based on the surface treatments, each material was divided into 3 groups: control (no treatment), 50-μm Al₂O₃ sandblasting, or 9% hydrofluoric acid etching (n = 6). The surface roughness (Ra) was evaluated by the 3D laser scanning microscope. Then, specimens were aged by thermal cycling (5000 cycles) and tested for biaxial flexural strength using a universal testing machine at a crosshead speed of 1.0 mm/min.

RESULTS

No significant differences in flexural strength or Ra were found for Lava Ultimate among the surface treatment groups. For Cerasmart, only the sandblasting group showed significantly higher Ra values than the control group. Also, the Ra values for the sandblasting group were significantly higher than those for the acid etching group. The flexural strengths of the sandblasting and acid etching groups for Cerasmart were statistically similar, and both were significantly lower than the control group.

CONCLUSIONS

Although all of the applied surface conditioning techniques improved Ra, they had a negative impact on the flexural strength of resin-matrix ceramics. Thus, clinicians should utilize the appropriate surface treatment techniques, taking into account their effects on the surface roughness and mechanical properties of resin-matrix ceramics.

In-Vitro Investigation of Marginal Adaptation and Fracture Resistance of Resin Matrix Ceramic Endo-Crown Restorations

The aim of this study was to evaluate the fracture resistance and marginal adaptation of endo-crown restorations produced from different resin-matrix ceramics (RMS) and the effects of these materials on marginal adaptation and fracture resistance. Three frasaco models were used by preparing (first) premolar teeth in three different margin preparations: butt-joint, heavy chamfer and shoulder. Each group was further divided into four subgroups according to the type of restorative material used: Ambarino High Class (AHC), Voco Grandio (VG), Brilliant Crios (BC) and Shofu (S) (n = 30). Master models were obtained using an extraoral scanner and fabricated with a milling machine. Marginal gap evaluation was performed with a silicon replica technique using a stereomicroscope. Replicas of the models (n = 120) were produced with epoxy resin. The fracture resistance of the restorations was recorded using a universal testing machine. The data were statistically analyzed using two-way ANOVA, and a t-test was applied for each group. Tukey's post-hoc test was performed to compare significant differences (p ≤ 0.05). The highest marginal gap was observed in VG, and the best marginal adaptation and the highest fracture resistance were found in BC. The lowest fracture resistance in Butt-joint preparation design was found in S. In addition, the lowest fracture resistance value in the heavy chamfer preparation design was found in AHC. The heavy shoulder preparation design displayed the highest fracture resistance values for all materials.

Comparison of Marginal and Internal Adaptation in Endocrowns Milled from Translucent Zirconia and Zirconium Lithium Silicate

Purpose

This study aimed to compare marginal and internal adaptation in endocrowns made from translucent zirconia and zirconium lithium silicate using CAD-CAM technology.

Materials and Methods

Twenty-eight freshly extracted upper molars were mounted in acrylic resin and underwent root canal therapy and endocrown preparation up to 2 mm above the cementoenamel junction. Endocrowns were CAD-CAM milled from zirconium lithium silicate (ZLS) and translucent zirconia (Zr). Internal and marginal adaptation was assessed by the replica technique before cementation. Marginal adaptation was evaluated by a stereomicroscope (×32) before and after cementation and also after thermomechanical aging.

Results

The ZLS group showed significantly higher internal adaptation compared to the Zr group (P = 0.028), while the marginal adaptation differences, at different times with different methods, were not statistically significant (P > 0.05). Axiomarginal angle had the highest and axiopulpal angle showed the lowest adaptation in both groups. The cementation process and thermomechanical aging increased the marginal gap in both groups significantly (P < 0.001). The marginal gap assessed by the replica technique before cementation was 7.11 µm higher than direct view under a stereomicroscope with intraclass correlation coefficient of 0.797.

Conclusion

Zirconia seems to be an acceptable material for endocrown with comparable internal and marginal adaptation to ZLS. Cementation and thermomechanical aging had significantly negative effects on marginal gap. The marginal gap assessed by the replica technique was higher than direct view under the stereomicroscope technique.

Comparison of Marginal Adaptation of Different Resin-Ceramic CAD/CAM Crowns: An In Vitro Study

Aim:

To compare the marginal adaptation of crowns fabricated by using three different resin-ceramic computer-aided design/computer-aided manufacturing (CAD/CAM) materials.

Materials and Methods:

Crowns fabricated from three different resin-ceramic CAD/CAM blocks, applied on a typodont premolar (#14), were tested with regard to marginal adaptation, in this in vitro study. The typodont maxillary first premolar was prepared to serve as the master die and digitized with an intraoral scanner. The same virtual crown design was used to fabricate all specimens. Forty-eight crowns were fabricated from the same virtual crown design using three different CAD/CAM resin-ceramic blocks as follows ( n = 16): Lava Ultimate (LU), GC Cerasmart (GC), Vita Enamic (VE). Master die and crowns were scanned with a laboratory scanner and three-dimensional data were transferred into three-matic software. The software calculated the mean of the marginal discrepancy (MD) for each crown in negative and positive values, representing under and over estimation of the crown margin, respectively. A marginal discrepancy index (MDI) was obtained for each group using negative and positive MDs. All data were statistically analyzed using one-way analysis of variance and Tukey’s honest significance test ( α = 0.05).

Results:

The analysis of variance showed no statistical differences between materials regarding the negative and positive MDs ( P > .05). The MDI for LU was lower than GC and VE ( P < .05).

Conclusion:

The marginal adaptation of different resin-ceramic materials was different with regard to MDI values. Nevertheless, the MD values of all groups were within the clinically acceptable range.

Fracture resistance, failure mode and stress concentration in a modified endocrown design

Purpose

The purpose of this study was to assess fracture resistance, failure mode and stress concentration of a modified endocrown preparation design, under axial and lateral forces.

Materials and Methods

Forty lower molars were divided into two groups (n = 20) and were restored with lithium disilicate glass-ceramic endocrowns following 2 preparation designs: Conventional, with circumferential butt margin 2 mm above the cemento–enamel junction; and Modified, by adding 2 grooves on the mesial side of the vestibular dentinal wall and on the distal side of the lingual dentinal wall. After cementation and thermomechanical cycling loading, half of the samples (n = 10) from each group were loaded axially and the other half (n = 10) was loaded laterally. Fracture resistance and failure modes were observed and the finite element analysis (FEA) was used to identify the stress concentration. Two-way ANOVA and Chi-square tests (α = 0.05) were used for in vitro data analyzes.

Results

Fracture resistance showed a statistically significant difference between conventional and modified preparations (p < .001), and between axial and lateral loadings (p < .001). Conventional preparation recorded 2914 N under axial loading and 1516 N under lateral loading, while modified preparation recorded 3329 N under axial loading and 1871 N under lateral loading. FEA showed that retention grooves have reduced the stress concentration under both loads for the tooth and the restoration.

Conclusion

Modified endocrown design showed higher fracture resistance than conventional endocrown. Lateral loading displayed a high percentage of severe fracture but under higher load to failure than the values reported for normal masticatory forces.