The influence of various core designs on stress distribution in the veneered zirconia crown: a finite element analysis study

Optimization of endocrown design parameters for mandibular second molars: A 3D finite element analysis

This study aimed to investigate the optimal parameters for endocrown design in mandibular second molars using three-dimensional finite element analysis. Eighteen finite element models(n = 3)were created with varying ferrule heights (0, 1, 2 mm), post space depths (2, 3, 4 mm), and diameters (2, 3 mm). The models simulated zirconia endocrowns on root canal treated teeth. Von Mises stress distribution was analyzed under 200 N oblique loading. Results showed that in butt-joint designs, increasing post space depth and diameter led to higher stress concentration at the post apex and lower stress at the mesial-buccal bonding interface. For ferrule designs, increasing ferrule height reduced stress at both the post apex and bonding interface. Stress in dentin increased with post space depth and diameter in butt-joint designs but decreased with increased ferrule height in ferrule designs. The study concluded that smaller post space dimensions (diameter and depth) reduce dentin stress in both butt-joint and ferrule endocrown designs, thereby indicating better protection of the remaining tooth structure. Ferrule designs exhibited a more uniform stress distribution compared to butt-joint designs. These findings suggest that endocrown design can be optimized to enhance stress distribution and potentially improve clinical outcomes, though further long-term clinical studies are needed to validate these results.

Flexural properties and finite element analysis of novel 3D-printed ceramic materials via 3D-LCM technology

BACKGROUND

This study evaluates the mechanical properties of dental crown prosthodontic materials by investigating the flexural strength and stress distribution of various ceramic materials, including milled zirconia and two ceramics fabricated using LCM technology, employing Finite Element Analysis (FEA).

METHODS

Seventy-five samples were divided into five groups: milled zirconia, Zirconia-210, Zirconia-230, Alumina-350 and Alumina-500. Flexural strength tests, including three-point bending, Weibull analysis and FEA, were conducted to analyse stress distribution. Data were evaluated using one-way ANOVA and Tukey's test.

RESULTS

3D-printed zirconia showed superior flexural strength compared to milled zirconia and alumina. Zirconia-210 had the highest flexural strength (886.35 MPa), while Alumina-350 had the lowest (424.49 MPa). Alumina-350 exhibited higher von Mises stress (25.77 MPa) than the control group (22.83 MPa), whereas Alumina-500 had the lowest stress (22.65 MPa). Zirconia models showed a slight increase in von Mises strain, while alumina models showed a decrease compared to the control.

CONCLUSION

Our study found that 3D-printed zirconia displayed higher flexural strength when compared to milled zirconia and alumina. Moreover, there were noticeable variations in stress levels and strain behaviours observed in the materials.

Endocrown Feasibility for Primary Molars: A Finite Element Study

OBJECTIVE

 To study the possibility of using pediatric endocrowns to restore the second primary molar using three-dimensional (3D) finite element analysis.

DESIGN

 A 3D finite element model was built for a pediatric mandibular molar, starting with laser scanning a naturally extracted tooth. The access cavity had an elliptic shape with 6 mm width, 4 mm height, and 2 mm depth with a wall taper angle of 5 degrees.Two materials (Zr and E-max) were tested for the endocrown and two cementing materials (glass ionomer and resin cement) with 20 to 40 μm thickness. Twelve case studies were reported within this research as the applied load of 330 N was tested with three angulations vertical, oblique at 45 degrees, and laterally.

RESULTS

 Twelve linear static stress analyses were performed. The resultant stresses and deformations' distribution patterns did not alter much, and values were within the threshold of physiological tolerance. Deformations were negligibly changed with changing endocrown and cement materials. In contrast, endocrown stresses indicated zirconia endocrown would have a long lifetime, while E-max one will have a relatively short lifetime.

CONCLUSIONS

 Analysis results indicated that bone was negligibly affected by changing endocrowns and cementing materials. Both tested endocrown materials can be used safely. Zirconia endocrowns may have a much longer lifetime than E-max.

The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading

AIM

This study aimed to investigate the effect of modified framework (MF) design on the fracture resistance of IPS e.max Press anterior single crown after thermocycling and cyclic loading.

MATERIALS AND METHODS

Two types of IPS e.max Press frameworks were designed (n = 10); standard framework (SF) with a 0.5 mm uniform thickness and MF with a lingual margin of 1 mm in thickness and 2 mm in height connected to a proximal strut of 4 mm height and a 0.3 mm wide facial collar. The crowns were cemented to resin dies, subjected to 5,000 cycles of thermocycling, and loaded 10,000 cycles at 100 N. A universal testing machine was used to load specimens to fracture, and the modes of failure were determined.

RESULTS

The mean and standard deviation (SD) of fracture resistance were 219.24 ± 110.00 N and 216.54 ±120.02 N in the SF and MF groups. Thus, there was no significant difference (p = 0.96). Mixed fracture was the most common failure mode in both groups. We found no statistically significant difference between the groups (p = 0.58).

CONCLUSION

The MF design did not increase the fracture resistance of IPS e.max Press crown.

CLINICAL SIGNIFICANCE

Framework design is an essential factor for the success of all-ceramic restorations and its modification might be regarded as an approach to increase fracture resistance. Furthermore, the modified design was evaluated in metal-ceramic or zirconia crowns while less attention was paid to the IPS e.max Press crowns. How to cite this article: Golrezaei M, Mahgoli HA, Yaghoobi N, et al. The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading. J Contemp Dent Pract 2024;25(1):79-84.

Biomechanical properties of different endocrown designs on endodontically treated teeth

OBJECTIVE

To compare the biomechanical properties of different endocrown designs on endodontically treated teeth with an extensive defect in the mesial wall using a three-dimensional finite element method (3D FEM).

METHODS

Four finite element analysis models were designed and built up based on different endocrown configurations in a mandibular molar. One model was designed as a butt joint preparation with 2 mm occlusal thickness(control), the other three models were butt joint designs with different distances between the bottom of the mesial wall preparation and the cemento-enamel junction (CEJ): 2 mm, 1 mm and 0 mm respectively. A vertical load parallel with the longitudinal axis of the tooth and an oblique load with a 45°angle to the longitudinal axis were applied to the occlusal surfaces. The maximum Von Misses (VM) stresses and stress distribution patterns were calculated and compared. Weibull risk-of-rupture analysis was used to analyze the survival probability of the restorations and tooth in the different models.

RESULTS

For the restoration, the model with a mesial wall destruction at the level of CEJ showed much higher risk of failure than other models. Overall, none of the four models showed failure. Under oblique loading, VM stress in the cement layer of the models with a mesial wall defect was higher than in the control model. In the dentin, the highest VM stresses were found in the peri-cervical dentin. Under the oblique loading, the model with the mesial wall destruction at the level of CEJ restored by endocrown showed the highest risk of failure.

CONCLUSION

Under the oblique loading, with the increase of the simulated defect in the mesial wall, the peak VM stress values in the cement layer increased accordingly. In the model with a mesial wall defect up to the level of CEJ risk of failure was highest in the cervical dentin.

Stress distribution in pediatric zirconia crowns depending on different tooth preparation and cement type: a finite element analysis

BACKGROUND

In clinical settings, tooth preparation for prefabricated zirconia crowns (PZCs) in the primary dentition varies widely. However, knowledge about the biomechanical behavior of PZCs in various clinical settings is limited. This study was conducted to evaluate the biomechanical behavior of PZCs in different clinical settings using 3-dimensional finite element analysis.

METHODS

3-dimensional models of the PZC, cement, and tooth with six different conditions were simulated in primary molar teeth, incorporating cement thickness (100, 500, and 1000 μm) and cement type (resin-modified glass ionomer cement and resin cement). A total of 200 N of occlusal force was applied to the models, both vertically and obliquely as representative cases. A general linear model univariate analysis with partial eta-squared (ηp²) was performed to evaluate the relative effects of the variables.

RESULTS

The overall stress of tooth was increased as the cement space increases under oblique loading. The von Mises stress values of the resin cements were significantly higher than those of the resin-modified glass ionomer cements for all cement thicknesses (p < .05). The effect size of the cement type (η_p² = .519) was more dominant than the cement thickness (η_p² = .132) in the cement layer.

CONCLUSIONS

Within the limits of this study, cement type has a greater influence on the biomechanical behavior of PZCs than cement thickness.

Effects of composite resin core level and periodontal pocket depth on crack propagation in endodontically treated teeth: An extended finite element method study

STATEMENT OF PROBLEM

Preserving teeth with radicular cracks with or without a periodontal pocket is an alternative to extraction. However, an effective protocol for the restoration of radicular cracks is lacking.

PURPOSE

The purpose of this study was to examine the composite resin core level and periodontal pocket depth effects on stress distribution, maximum von Mises stress, and crack propagation in endodontically treated teeth by using the extended finite element (FE) method.

MATERIAL AND METHODS

Four 3-dimensional models of a cracked endodontically treated mandibular first molar were constructed: PP2C2 (periodontal pocket depth, 2 mm; composite resin core level, 2 mm below the canal orifice level); PP2C4 (periodontal pocket depth, 2 mm; composite resin core level, 2 mm below the crack level); PP4C2 (periodontal pocket depth, 4 mm; composite resin core level, 2 mm below the canal orifice level); and PP4C4 (periodontal pocket depth, 4 mm; composite resin core level, 2 mm below the crack level). The crack initiation was at the same level in all models. A static 700-N load was applied to the models in a vertical direction.

RESULTS

The highest stress in dentin was observed in PP2C2, whereas PP2C4 exhibited the lowest stress and least crack propagation. Stress was high in the dentin and supporting bone. No reduction in crack propagation was observed in the PP4 models, regardless of the composite resin core level.

CONCLUSIONS

The periodontal pocket depth (2 mm and 4 mm) and composite resin core level (2 mm below the crack level and 2 mm below the canal orifice level) affected stress concentration in dentin, resulting in different patterns of crack propagation in the FE models.

Pediatric Stainless-Steel Crown Cementation Finite Element Study

Objective  To study the effect of using different cement types under pediatric stainless-steel crown (SSC) around mandibular second primary molar using three-dimensional (3D) finite element analysis.

Materials and Methods  A 3D finite element model was built for pediatric mandibular molar by laser scanning of natural extracted tooth. Four types of cement (zinc phosphate, glass ionomer, resin-modified glass ionomer, and resin) of 200 μm layers thickness were tested under a stainless-steel crown of 130-μm thickness. Twelve case studies were reported within this research, as the applied load of 330 N was tested with three angulations: vertical, oblique at 45°, and laterally.

Results  Linear static stress analysis was performed. The resultant stresses and deformations' distribution patterns did not change with cement type, while the values were altered. All deformations and stresses were found within the normal range.

Conclusions  Analysis results indicated that using stiffer cement material increases tooth structure stresses and reduces crown body stresses and deformations, while bone was nearly insensitive to cement type.

Effect of Zirconia Core Thickness and Veneer Firing Cycle on the Biaxial Flexural Strength of Veneering Ceramic

PURPOSE

To evaluate the influence of various Y-TZP thicknesses and veneer firing cycles on the strength of two ceramic veneers.

MATERIALS AND METHODS

180 Y-TZP cores of 0.5, 1.0, and 5.0 mm thickness were prepared followed by sintering in a high temperature furnace; 180 presintered veneering ceramic discs (Vita VM9 porcelain and e.max Ceram) were also prepared using a mold. The discs were placed on zirconia plates (zirconia cores) of different thickness (0.5, 1.0, and 5.0 mm) and exposed to different firing cycles (Vita VM9 porcelain-910, 930, and 950°C; e.max Ceram-750, 770, and 790°C). Ball-on-three-balls flexural strength test was performed (universal testing machine) at a crosshead speed of 0.5 mm/min. Scanning electron microscopy of fractured specimens was performed. Means and standard deviations of flexural strength were analyzed using Tukey-Kramer HSD test for multiple comparisons.

RESULTS

Specimens within material groups showed no significant difference (p > 0.05) for flexural strength with respect to Y-TZP core thickness (0.5, 1.0, and 5.0 mm) (VM9 [117.30 ± 14.328, 117.75 ± 13.66, 113.75 ± 20.10], e.max Ceram [94.79 ± 17.5, 100.02 ± 14.7, 95.23 ± 15.4]). Flexural strength within material groups with respect to different firing cycles ([VM9-910, 930, 950°C], e.max Ceram [750, 770, 790°C]), for VM9 (111.49 ± 15.7, 120.86 ± 13.2, 116.46 ± 18.4), and e.max Ceram (94.64 ± 15.2, 101.6 ± 16.69, 93.8 ± 15.20) showed no significant difference (p > 0.05).

CONCLUSIONS

Different zirconia thicknesses (0.5, 1.0, and 5.0 mm) and veneer firing cycles for Vita VM9 and e.max ceramics failed to show any significant influence on their biaxial flexural strengths.

Fracture Resistance of Zirconia Restorations with a Modified Framework Design

OBJECTIVES

Chipping is one of the concerns related to zirconia crowns. The reasons of chipping have not been completely understood. This in-vitro study aimed to assess the effect of coping design on the fracture resistance of all-ceramic single crowns with zirconia frameworks.

MATERIALS AND METHODS

Two types of zirconia copings were designed (n=12): (1) a standard coping (SC) with a 0.5mm uniform thickness and (2) a modified coping (MC) consisted of a lingual margin of 1mm thickness and 2mm height connected to a proximal strut of 4mm height and a 0.3mm-wide facial collar. After veneer porcelain firing, the crowns were cemented to metal dies. Afterwards, a static vertical load was applied until failure. The modes of failure were determined. Data were calculated and statistically analyzed by independent samples T-test. P<0.05 was considered statistically significant.

RESULTS

The mean and standard deviation (SD) of the final fracture resistance equaled to 3519.42±1154.96 N and 3570.01±1224.33 N in SC and MC groups, respectively; the difference was not statistically significant (P=0.9). Also, the mean and SD of the initial fracture resistance equaled to 3345.34±1190.93 N and 3471.52±1228.93 N in SC and MC groups, respectively (P=0.8). Most of the specimens in both groups showed the mixed failure mode.

CONCLUSIONS

Based on the results, the modified core design may not significantly improve the fracture resistance.

Influence of Different Framework Designs on the Fracture Properties of Ceria-Stabilized Tetragonal Zirconia/Alumina-Based All-Ceramic Crowns

The aim of this study was to evaluate the fracture load and failure mode of all-ceramic crowns with different ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/A) framework designs. Four frameworks (anatomical shape: AS, with a buccal or lingual supporting structure: BS and LS, or buccal and lingual supporting structures: BLS) were fabricated. All frameworks were veneered with porcelain to fabricate all-ceramic crowns followed by cementation to tooth analogs. The fracture load of each crown either without or with pre-loading (1.2 million cycles, 49 N) was measured. The failure mode was classified into partial or complete fracture. Differences were tested for significance (p < 0.05) by a two-way Analysis of Variance (ANOVA), followed by Tukey’s test and by Fisher’s exact test, respectively. Without pre-loading, supporting structures did not influence the fracture load or failure mode. Partial fractures were the most common failure mode. Pre-loading promoted the severity of the failure mode, although the fracture load among the framework designs was not influenced. In the AS group, prefailures were observed during pre-loading, and complete fractures were significantly increased after pre-loading. In contrast, the failure mode of the BLS group remained unchanged, showing only partial fracture even after pre-loading. This Ce-TZP/A framework design, comprised of an anatomical shape with additional buccal and lingual structures, has the potential to reduce the chipping of the veneering porcelain.

Effect of the amount of thickness reduction on color and translucency of dental monolithic zirconia ceramics

PURPOSE

This study investigated the effect of amount of thickness reduction on color and translucency of dental monolithic zirconia ceramics.

MATERIALS AND METHODS

One-hundred sixty-five monolithic zirconia specimens (16.3 mm × 16.3 mm × 2.0 mm) were divided into 5 groups (Group I to V) according to the number of A2-coloring liquid applications. Each group was then divided into 11 subgroups by reducing the thickness up to 1.0 mm in 0.1-mm increments (Subgroup 0 to 10, n=3). Colors and spectral distributions were measured according to CIELAB on a reflection spectrophotometer. All measurements were performed on five different areas of each specimen. Color difference (ΔE^*_ab) and translucency parameter (TP) were calculated. Data were analyzed using one-way ANOVA and multiple comparison Scheffé test (α=.05).

RESULTS

There were significant differences in CIE L^* between Subgroup 0 and other subgroups in all groups. CIE a^* increased (0.52<R²<0.73), while CIE b^* decreased (0.00<R²<0.74) in all groups with increasing thickness reduction. Perceptible color differences (ΔE^*_ab>3.7) were obtained between Subgroup 0 and other subgroups. TP values generally increased as the thickness reduction increased in all groups (R²>0.89, P<.001).

CONCLUSION

Increasing thickness reduction reduces lightness and increases a reddish, bluish appearance, and translucency of monolithic zirconia ceramics.

Biomechanical three-dimensional finite element analysis of monolithic zirconia crown with different cement type

PURPOSE

The objective of this study was to evaluate the influence of various cement types on the stress distribution in monolithic zirconia crowns under maximum bite force using the finite element analysis.

MATERIALS AND METHODS

The models of the prepared #46 crown (deep chamfer margin) were scanned and solid models composed of the monolithic zirconia crown, cement layer, and prepared tooth were produced using the computer-aided design technology and were subsequently translated into 3-dimensional finite element models. Four models were prepared according to different cement types (zinc phosphate, polycarboxylate, glass ionomer, and resin). A load of 700 N was applied vertically on the crowns (8 loading points). Maximum principal stress was determined.

RESULTS

Zinc phosphate cement had a greater stress concentration in the cement layer, while polycarboxylate cement had a greater stress concentration on the distal surface of the monolithic zirconia crown and abutment tooth. Resin cement and glass ionomer cement showed similar patterns, but resin cement showed a lower stress distribution on the lingual and mesial surface of the cement layer.

CONCLUSION

The test results indicate that the use of different luting agents that have various elastic moduli has an impact on the stress distribution of the monolithic zirconia crowns, cement layers, and abutment tooth. Resin cement is recommended for the luting agent of the monolithic zirconia crowns.

Effect of Extension and Type of Composite-Restored Class II Cavities on Biomechanical Properties of Teeth: A Three Dimensional Finite Element Analysis

OBJECTIVES

Controversy exists regarding cavity preparation for restoration of interproximal caries in posterior teeth in terms of preserving the tooth structure and suitable stress distribution. This study aimed to assess the effect of extension and type of class II cavities and the remaining tooth structure in maxillary premolars restored with composite resin on the biomechanical properties of teeth using finite element method (FEM).

MATERIALS AND METHODS

Using FEM, eight three-dimensional (3D) models of class II cavities in maxillary premolars with variable mesiodistal (MD) dimensions, variable thickness of the residual wall in-between the mesial and distal cavities and different locations of the wall were designed. Other dimensions were the same in all models. Cavities were restored with composite resin. A load equal to the masticatory force (200N) was applied to the teeth. Finite element analysis (FEA) was used to calculate the von Mises stress.

RESULTS

Stress in the enamel margin increased by increasing the MD dimensions of the cavities. Deviation of the residual wall between the mesial and distal cavities from the tooth center was found to be an important factor in increasing stress concentration in the enamel. Increasing the MD dimensions of the cavity did not cause any increase in stress concentration in dentin.

CONCLUSION

Increasing the MD dimensions of the cavities, decreasing the thickness of the residual wall between the mesial and distal cavities and its deviation from the tooth center can increase stress concentration in the enamel but not in dentin.

A 3-dimensional finite element analysis of the restoration of the maxillary canine with a complex zirconia post system

STATEMENT OF PROBLEM

Zirconia posts exhibit high strength and toughness, but reliable bonding with the resin core is difficult to attain. The use of a ferrule has been found to improve stress distribution in the root of endodontically treated teeth.

PURPOSE

The purpose of this finite element analysis study was to measure the stress distribution in the post-core system and root structure of a maxillary canine.

MATERIAL AND METHODS

A right maxillary canine was embedded and subjected to a micro-computed tomography scan. Three-dimensional dynamic scan data were then transformed, and a finite element model of 4 dentin ferrule heights was designed with zirconia posts and heat-pressed glass ceramics for a complete crown restoration. Von Mises stresses were determined by applying a 300 N static load to the middle of the lingual surface of the crown.

RESULTS

When the ferrule height increased from 0 to 3 mm, the maximum von Mises stress of the zirconia post decreased from 196 to 149 MPa, and that on the zirconia post-dentin interface decreased from 174 to 132 MPa. The maximum von Mises stress decreased from 39.8 to 32.5 MPa in the apical root and from 59.5 to 49.9 MPa in the mid-root when the ferrule height increased from 0 to 3 mm.

CONCLUSIONS

Increased ferrule height is associated with reduced von Mises stress in the zirconia post and the post-dentin interface, with an apparent shift of von Mises stress to the root cervical area from the mid-root and the apex.

Effect of polishing and glazing on the color and spectral distribution of monolithic zirconia

PURPOSE

The aim of this study was to evaluate the effect of polishing and glazing on the color and spectral distribution of monolithic zirconia.

MATERIALS AND METHODS

Forty-five monolithic zirconia specimens (16.3 mm × 16.4 mm × 2.0 mm) were fabricated and divided into 5 groups according to the number of A2-coloring liquid applications (Group I to V). Each group was divided into 3 subgroups according to the method of surface treatments (n=3): N: no treatment; P: polishing; G: glazing. Color and spectral distribution of five different areas of each specimen were measured according to CIELAB color space in the reflectance mode relative to the standard illuminant D65 on a reflection spectrophotometer. Data were analyzed using one-way ANOVA followed by Tukey's HSD test, Pearson correlation and regression analysis (α=.05).

RESULTS

There was a significant difference in CIE L^* between Subgroup N and P, and in CIE b^* between Subgroup P and G in each group. Spectral reflectance generally decreased in Subgroup P and G in comparison with Subgroup N. Color differences between Subgroup P and G were within the perceptibility threshold (ΔE^*_ab< 3.7) in most groups. Highly significant correlation was found between CIE b^*and each subgroups as the number of coloring liquid applications increased (R²>0.88, P<.001).

CONCLUSION

A perceptible color difference can be detected after polishing of monolithic zirconia. Polishing decreases the lightness, and glazing also decreases the lightness, but increases the yellowness of monolithic zirconia.