Fracture Resistance Of All-ceramic Crowns Research Articles

Effect of Adhesive Gap Setting on Fracture Resistance of All-ceramic Crowns

Background:Several factors might affect the fracture resistance of all-ceramic crowns, including cement thickness.Aim:To evaluate the influence of cement thickness on the fracture resistance.Objective:To determine the effect of varying the adhesive gap thickness on the fracture loads of all-ceramic CEREC 3D molar crowns.Methods:Standardized prepared epoxy resin molar dies (Viade Inc.) were fabricated. A standard molar crown was designed using a CEREC 3D machine (Sirona Dental Systems). Twenty-four crowns were milled from Vita Mark II blocks (Vita Zahnfabrik), using adhesive gap settings of 30, 60 and 90 µm (n=8). A dual-cure resin cement (PanaviaF 2.0, Kuraray) was used to cement the crowns to their respective dies, following manufacturer's recommendation. After 1 week of storage in distilled water at 37°C, each crown was loaded in compression until complete failure in a universal testing machine (Instron 8501) and fracture loads (N) were recorded. Fractured specimens were sectioned to determine cement thickness. Sections were examined using a traveling light microscope to measure cement thickness. Data were statistically analyzed using one-way ANOVA test and Pearson's correlation at (α=0.05).Results:The mean fracture loads and standard deviation values in N were 1,267.57 (122.82), 1,225.20 (179.46) and 1,180.76 (161.77) for the crowns with 30, 60 and 90µm, respectively. ANOVA indicated no significant differences among mean fracture strength values (p= 0.55). All crowns failed in a catastrophic mode and were not repairable.Conclusions:Adhesive cement gap as achieved with three CEREC 3D settings from 30 to 90µm had no significant effect on fracture strength of crowns made from Vita Mark II blocks.

Influence of Different Zirconia Coping Designs on the Fracture Resistance of All-Ceramic Crowns: An In Vitro Study.

ABSTRACTBackground and Aim:Increased demand for metal-free restorations in posterior areas has increased the focus on zirconia restorations because of its advantages in excellent mechanical properties, patient comfort, and acceptance. Although all-ceramic crowns have better biocompatibility and esthetic properties, there are some clinical reasons for the fracture of the veneer or the core materials in the posterior region. This study aims at comparing the influence of zirconia coping designs on the fracture resistance of all-ceramic crowns.Materials and Methods:A total of 32 zirconia copings (n = 8 for each group) were designed and fabricated based on the marginal collar height of zirconia coping. The groups were the following: Group 1: 0.0 mm zirconia coping; Group 2: 0.5 mm collar; Group 3: 1.0 mm collar; and Group 4: 1.5 mm collar. All these zirconia copings were veneered with porcelain. Master die with cemented ceramic-layered zirconia copings was tested using Universal testing machine. Data obtained were statistically evaluated by one-way analysis of variance and post hoc test.Results:There was statistically significant difference between the groups with P < 0.001. Group 4 has the highest strength (3318.89 ± 395.67) followed by Group 3 (2910.0 ± 219.22), then Group 1 (2320.02 ± 547.36) that is the control group and the least strength with Group 2 (2286.59 ± 496.66).Conclusion:On the basis of the results obtained from this study, it can be concluded that, the more the height of the zirconia collar, the higher the fracture strength of the all-ceramic crowns. Thus ceramic-layered zirconia coping design with 1.5 mm marginal collar height is recommended for functional long life, at least in the posterior higher load-bearing areas with lesser esthetic demands.

Marginal Gap Distance and Fracture Resistance of Lithium Disilicate and Zirconia-Reinforced Lithium Disilicate All-Ceramic Crowns Constructed With Two Different Processing TechniquesWith Two Different Processing Techniques

Statement of problem: The microstructure and processing methods used to produce any dental restoration might affect the final mechanical outcomes as well as the clinical success. Objectives: The purpose of this study was to evaluate the fracture resistance of lithium disilicate and zirconia reinforced lithium disilicate ceramic crowns constructed using two processing techniques after fatigue loading namely, CAD/CAM technique and pressing technique. The marginal integrity of the crowns was examined before and after fatigue loading. Methods: A total number of thirty-two freshly extracted maxillary first molars were collected. The teeth were chosen to be of similar bucco-lingual and mesiodistal dimensions. The teeth were mounted vertically into epoxy resin templates. Full coverage all-ceramic preparation was performed for all samples using a standardized technique. The prepared teeth were randomly divided into four equal groups (n=8) according to the all-ceramic materials and technique used for crown fabrication as follows: Group I: IPS e-max CAD(EC): eight prepared teeth were restored with machinable lithium disilicate glass ceramics. Group II: Celtra Duo(CD): eight prepared teeth were restored with machinable zirconia-reinforced lithium disilicate glass ceramics. Group III: IPS e-max Press (EP): eight prepared teeth were restored with pressable lithium disilicate glass ceramics. Group IV: Celtra Press (CP): eight prepared teeth were restored with pressable zirconia-reinforced lithium disilicate glass ceramics. The crowns were cemented using self-adhesive resin cement (Rely X Unicem). Vertical margin gap distance of all the crowns was measured using a stereomicroscope. Following vertical marginal gap distance measurements, the samples were subjected to fatigue cyclic loading for 60000 cycles which is equivalent to six months clinical service. The vertical marginal gap distance for all samples were subsequently remeasured after the fatigue loading testing. Fracture resistance test was done using universal testing machine. The fracture load was recorded in Newton. Data was collected, tabulated and statistically analyzed. Results: One-way ANOVA test for comparison between the fracture resistance of the four types of all-ceramic crowns revealed that there was a statistically significant difference between mean fracture resistance of different all ceramic materials and techniques used in this study (P-value <0.001). For the marginal gap distance either before or after fatigue cyclic loading; there was a statistically significant difference between the four all ceramic crowns used in this study.Conclusions: CAD/CAM techniques showed better fracture resistance values than pressable techniques, even if the same material was used. The addition of zirconia to lithium disilicate ceramics did not improve the fracture resistance of all ceramic crowns. Pressable processing techniques showed better vertical marginal gap distance than CAD/CAM techniques for both ceramic materials used. Cyclic loading resulted in significant increase in the vertical marginal gap distance for all ceramic crowns using different processing techniques.

Effect of different core design made of computer-aided design/computer-aided manufacturing system and veneering technique on the fracture resistance of zirconia crowns: A laboratory study.

Background:It is unclear how the different core designs made of computer-aided design/computer-aided manufacturing (CAD/CAM) system and veneering techniques affect the fracture resistance of endodontically treated teeth.Aim:The aim of this in vitro study is to investigate the effect of different core designs made of CAD/CAM system and veneering techniques on the fracture resistance of zirconia ceramic crowns.Materials and Methods:Two types of zirconia copings were designed; the first one with circumferential 0.5-mm chamfer and the second one with circumferential 1-mm deep chamfer. The core specimens (in subgroups) were veneered anatomically with either a layering technique (hand-layer) or with press-on technique resulting in four test groups (n = 12). All crowns were then cemented using self-adhesive resin cement. After that, all specimens were loaded in a universal testing machine until fractured.Statistical Analysis:Data were then analyzed with two-way analysis of variance (ANOVA) (α =0.05).Results:Mean (standard deviation) failure loads for groups ranged from 2412.7 N (±624.6) to 3020.1 N (±1099.8). Two-way ANOVA revealed no statistically significant differences among groups (P > 0.05). Almost all groups showed cohesive failure in the veneering ceramic.Conclusions:Within the limitations of this laboratory study, neither the core design nor the veneering technique affected the fracture resistance of all-ceramic crowns significantly.

Fracture resistance of all-ceramic crowns based on different preparation designs for restoring endodontically treated molars.

To evaluate endodontically treated molar fracture resistance restored with CAD/CAM lithium disilicate (LDS) crowns with different amalgam core preparation design. Eighty-four recently extracted mandibular third molars were divided into seven groups (n = 12) and embedded in autopolymerizing resin. Coronal tooth structure was removed, pulp chamber exposed, and pulpal remnants removed. One group received LDS endocrowns, while three groups received amalgam cores with 2, 1, and 0 dentin axial wall heights (AWH). Three additional groups were likewise restored using an amalgam adhesive. Scanned preparations were restored with LDS crowns luted with a self-adhesive luting cement. After 24 hours, specimens were loaded to failure with results analyzed with Welch's Test/REGW Range Test at a 95% level of confidence (α = 0.05). The 1 mm-AWH amalgam core group had the highest failure load and was similar to the 2 mm-AWH amalgam, 2 mm-AWH bonded amalgam, and the 1 mm-AWH bonded amalgam core groups. The endocrowns had lower failure load than the 1 mm and 2 mm AWH amalgam groups but was similar to other groups. Adhesively luted LDS crowns with amalgam core preparations overall displayed similar failure load, as endocrown restorations. However, crowns based on amalgam cores demonstrated favorable failure modes. The results of this in vitro test suggests that when suitable tooth structure and sufficient interact restorative space exists, endodontically treated molars restored with lithium disilicate complete crowns based on preparations with amalgam core foundations containing 1 mm and 2 mm of dentin axial wall height could serve as a suitable restorative option that may provide more recoverable failure modes than endocrown restorations.

Effects of design parameters on fracture resistance of glass simulated dental crowns

ObjectiveThis study aimed to individually quantify the effects of various design parameters, including margin thickness, convergence angle of abutment, and bonding conditions on fracture resistance of resin bonded glass dental crown systems (namely, glass simulated crown). Materials and methodsAn in vitro experimental test and an in silico computational eXtended Finite Element Method (XFEM) were adopted to explore crack initiation and propagation in glass simulated crown models with the margin thickness ranging from 0.8 to 1.2mm, convergence angle from 6° to 12°, and three different bonding conditions, namely non-bonded (NB), partially bonded (PB), fully bonded (FB). ResultsThe XFEM modeling results of cracking initiation loads and subsequent growth in the glass simulated crown models were correlated with the experimental results. It was found that the margin thickness has a more significant effect on the fracture resistance than the convergence angle. The adhesively bonded state has the highest fracture resistance among these three different bonding conditions. ConclusionCrowns with thicker margins, smaller convergence angle and fully bonded are recommended for increasing fracture resistance of all-ceramic crowns. This numerical modeling study, supported by the experimental tests, provides more thorough mechanical insight into the role of margin design parameters, thereby forming a novel basis for clinical guidance as to preparation of tapered abutments for all-ceramic dental crowns.

Fracture resistance of computer-aided design and computer-aided manufacturing ceramic crowns cemented on solid abutments

BackgroundBecause no information was found in the dental literature regarding the fracture resistance of all-ceramic crowns using CEREC (Sirona) computer-aided design and computer-aided manufacturing (CAD-CAM) system on solid abutments, the authors conducted a study. MethodsSixty synOcta (Straumann) implant replicas and regular neck solid abutments were embedded in acrylic resin and randomly assigned (n = 20 per group). Three types of ceramics were used: feldspathic, CEREC VITABLOCS Mark II (VITA); leucite, IPS Empress CAD (Ivoclar Vivadent); and lithium disilicate, IPS e.max CAD (Ivoclar Vivadent). The crowns were fabricated by the CEREC CAD-CAM system. After receiving glaze, the crowns were cemented with RelyX U200 (3M ESPE) resin cement under load of 1 kilogram. For each ceramic, one-half of the specimens were subjected to the fracture resistance testing in a universal testing machine with a crosshead speed of 1 millimeter per minute, and the other half were subjected to the fractured resistance testing after 1,000,000 cyclic fatigue loading at 100 newtons. ResultsAccording to a 2-way analysis of variance, the interaction between the material and mechanical cycling was significant (P = .0001). According to a Tukey test (α = .05), the fracture resistance findings with or without cyclic fatigue loading were as follows, respectively: CEREC VITABLOCKS Mark II (405 N/454 N) was statistically lower than IPS Empress CAD (1169 N/1240 N) and IPS e.max CAD (1378 N/1025 N) (P < .05). The IPS Empress CAD and IPS e.max CAD did not differ statistically (P > .05). According to a t test, there was no statistical difference in the fracture resistance with and without cyclic fatigue loading for CEREC VITABLOCS Mark II and IPS Empress CAD (P > .05). For IPS e.max CAD, the fracture resistance without cyclic fatigue loading was statistically superior to that obtained with cyclic fatigue loading (P < .05). ConclusionsThe IPS Empress CAD and IPS e.max CAD showed higher fracture resistance compared with CEREC VITABLOCS Mark II. The cyclic fatigue loading negatively influenced only IPS e.max CAD. Practical ImplicationsThe CEREC VITABLOCS Mark II, IPS Empress CAD, and IPS e.max CAD ceramic crowns cemented on solid abutments showed sufficient resistance to withstand normal chewing forces.

Fracture resistance of all ceramic crowns supported by zirconia and alumina versus titanium implant abutments

PurposeHigh-strength ceramic materials can be used to fabricate esthetic and stable implant-supported single-tooth abutment. Study compared in vitro the fracture resistance of individual components of single-tooth implant-supported all-ceramic restorative systems after artificial aging and analyzing mode of failure using scanning electron microscope. Materials and methodsForty-eight analogues represent maxillary first premolar. The implants were divided, according to the type of abutments used into three groups (of 16 specimens each): Group A: Ti titanium abutments; Group B: Al2O3 alumina abutments; Group C: ZrO2 zirconia abutments. IPS Impress crown was fabricated and cemented to abutments by resin cement (Rely X ARC) and artificially aged through dynamic loading (2400000 cycles) and thermal cycling (600 cycles). Afterwards, all specimens were tested for fracture resistance using compressive load and scanned by electron microscope. The results were statistically analyzed with one way ANOVA and t-test. ResultsAll test specimens survived the artificial aging process using simulated oral conditions. No screw loosening was recorded. The median fracture resistance was 844.52 ± 12.26N, 494.92 ± 8.99N and 795.56 ± 6.22N for groups Ti, Al2O3, and ZrO2, respectively. Significant differences were found for the fracture resistance comparisons of Ti and ZrO2 groups with Al2O3 one. Also significant differences were found between Ti and ZrO2 group. ConclusionAll types of implant-supported restorations tested have the potential to withstand physiologic occlusal forces applied in the premolar region (450N). Unfavorable fracture occurred in eight Al2O3 specimens indicated unfavorable behavior of this material after aging.

Influence of the supporting die structures on the fracture strength of all-ceramic materials

This study investigated the influence of the elastic modulus of supporting dies on the fracture strengths of all-ceramic materials used in dental crowns. Four different types of supporting die materials (dentin, epoxy resin, brass, and stainless steel) (24 per group) were prepared using a milling machine to simulate a mandibular molar all-ceramic core preparation. A total number of 96 zirconia cores were fabricated using a CAD/CAM system. The specimens were divided into two groups. In the first group, cores were cemented to substructures using a dual-cure resin cement. In the second group, cores were not cemented to the supporting dies. The specimens were loaded using a universal testing machine at a crosshead speed of 0.5 mm/min until fracture occurred. Data were statistically analyzed using two-way analysis of variance and Tukey HSD tests (α = 0.05). The geometric models of cores and supporting die materials were developed using finite element method to obtain the stress distribution of the forces. Cemented groups showed statistically higher fracture strength values than non-cemented groups. While ceramic cores on stainless steel dies showed the highest fracture strength values, ceramic cores on dentin dies showed the lowest fracture strength values among the groups. The elastic modulus of the supporting die structure is a significant factor in determining the fracture resistance of all-ceramic crowns. Using supporting die structures that have a low elastic modulus may be suitable for fracture strength tests, in order to accurately reflect clinical conditions.

Fracture resistance of all‐ceramic crowns placed on a preparation with a slice‐formed finishing line

The purpose of this study was to determine the fracture resistance of all-ceramic crowns with a core of a zirconia ceramic, using various stabilizing oxides and luted on a preparation with a slice-formed finishing line. Ten cores made of HIPed yttrium-oxide partially stabilized zirconia (HIPed Y-TZP) and five cores of densely-sintered magnesia partially stabilized zirconia (Mg-PSZ) were made. The Mg-PSZ cores and five of the HIPed Y-TZP cores were made with a thickness of 0.2 mm. A further five cores 0.1-mm thick were made of HIPed Y-TZP. All 15 cores were then veneered with a feldspar ceramic and luted onto a stylized steel master die model with a slice-formed finishing line. The specimens were then loaded until fracture occurred. The HIPed Y-TZP specimens with the 0.2 mm core exhibited significantly higher fracture resistance than the Mg-PSZ specimens (P = 0.004) and the HIPed Y-TZP specimens with the 0.1 mm core (P = 0.001). The fracture resistance of the Mg-PSZ specimens was significantly (P = 0.015) higher than that of the HIPed Y-TZP specimens with the 0.1 mm core. The fracture resistance determined was equal or superior to reported values for bite forces and all-ceramic crowns. Thus, it seems likely that the type of restorations evaluated have the potential for successful use on a slice-formed preparation. However, long-term studies are essential in order to assess the performance of this ceramic system in a clinical context.

Fracture resistance of teeth restored with dentin-bonded crowns constructed in a leucite-reinforced ceramic

Objectives: Laboratory studies and preliminary clinical data have demonstrated satisfactory fracture resistance of all-ceramic crowns placed using a resin-composite luting material and a dentin-bonding system. This study investigates the fracture resistance of crowns constructed in a leucite-reinforced ceramic when placed using a dentin-bonding system and a dual-cure resin composite luting material and compares this with the fracture resistance of feldspathic porcelain crowns. Method: Standardised preparations were carried out on 10 sound, unrestored, maxillary premolar teeth, the mean bucco-palatal width of which did not vary by more than 2.5%. Ceramic crowns (Fortress; Chameleon Dental, KS, US) were constructed using a standardised technique. Their fitting surface was etched with hydrofluoric acid. The crowns were placed using the dentin-bonding system Mirage ABC and the luting system Mirage FLC (Chameleon Dental, KS, US). The restored teeth were loaded in compression at 1 mm/min through a 4 mm steel bar placed along the midline fissure. Results: A mean fracture load of 0.88 kN was recorded. Results from previous work indicate a fracture resistance of 0.77 kN for feldspathic porcelain crowns placed using the same luting systems on similarly standardised preparations. Statistical analysis by one-way ANOVA and Tukey's multiple comparison procedure indicated that there was no significant difference in the mean fracture resistance of the teeth restored using the leucite reinforced ceramic and the teeth restored with feldspathic porcelain. Significance: Crowns constructed in a leucite-reinforced ceramic and placed using dentin-bonding and dual-cure resin composite luting materials may provide some increase in fracture resistance, but the results may not be significantly different from the feldspathic porcelain.