Impact of the sintering parameters on the grain size, crystal phases, translucency, biaxial flexural strength, and fracture load of zirconia materials.

OBJECTIVES: To investigate the influence of the zirconia and sintering parameters on the optical and mechanical properties. METHODS: Three zirconia materials (3/4Y-TZP, 4Y-TZP, 3Y-TZP) were high-speed (HSS), speed (SS) or conventionally (CS) sintered. Disc-shaped specimens nested in 4 vertical layers of the blank were examined for grain size (GS), crystal phases (c/t'/t/m-phase), translucency (T), and biaxial flexural strength. Fracture load (FL) of three-unit fixed dental prostheses was determined initially and after thermomechanical aging. Fracture types were classified, and data statistically analyzed. RESULTS: 4Y-TZP showed a higher amount of c + t'-phase and lower amount of t-phase, and higher optical and lower mechanical properties than 3Y-TZP. In all materials, T declined from Layer 1 to 4. 3/4Y-TZP showed the highest FL, followed by 3Y-TZP, while 4Y-TZP showed the lowest. In 4Y-TZP, the sintering parameters exercised a direct impact on GS and T, while mechanical properties were largely unaffected. The sintering parameters showed a varying influence on 3Y-TZP. Thermomechanical aging resulted in comparable or higher FL. CONCLUSION: 3/4Y-TZP presenting the highest FL underscores the principle of using strength-gradient multi-layer blanks to profit from high optical properties in the incisal area, while ensuring high mechanical properties in the lower areas subject to tensile forces. With all groups exceeding maximum bite forces, the examined three-unit FDPs showed promising long-term mechanical properties.

Wear resistance of CAD/CAM one-piece screw-retained hybrid-abutment-crowns made from different restorative materials.

INTRODUCTION: The aim of this study was to measure the wear progress of three high performance polymers (HPP) materials as well as that of zirconia after artificial aging (simulated 2.5- and 5-year of clinical service with thermo-mechanical loading) and compare it with the well-documented wear of lithium disilicate. METHODS: Forty implants were used to restore a maxillary first premolar, where the abutment and the crown were manufactured as hybrid-abutment-crown and connected to the implant using a titanium insert. The implants were randomly divided, according to the restorative materials used, into five groups: 3Y-TZP zirconia (Z), lithium disilicate (L), ceramic-reinforced polyetheretherketon (P), nano-hybrid composite resin (C) and polymer-infiltrated ceramic-network (E). All hybrid-abutment-crowns were produced using CAD/CAM technology. A design of a maxillary first premolar was created with an angle of 120° between the buccal and palatal cusps, which were designed as planes. The restorations were adhesively luted onto the titanium inserts, according to the manufacturers' recommendations for each material individually, by means of dual-curing luting resin with the exception of group P, where the blocks were pre-fitted (heat-pressed) with an integrated titanium insert. The suprastructures were assembled onto the implants through titanium screws. The screw channels were sealed with Teflon tape and composite resin filling material that was polished to high-gloss. All specimens underwent 1 200 000 thermo-dynamic loading cycles with 49 N in a dual-axis chewing simulator. Elastomeric impressions were made for all specimens after 600 000 and after 1 200 000 cycles. The corresponding impressions were imaged using a laser scanning microscope and then 3D-analyzed using the software (Geomagic Wrap) to measure the volume loss of the wear area for all specimens. Statistical analysis was performed using Wilcoxon-Test regarding the two different time measurements for each material. For the analysis of the material variable, Kruskal-Wallis test was conducted followed by Mann-Whitney test. RESULTS: Group Z showed statistically the lowest volume loss compared to the other test materials, both after 600 000 and 1 200 000 cycles of artificial aging, with a median value of 0.002 mm3 volume loss after 1 200 000 cycles. In contrast, group E showed the highest volume loss with median values of 0.18 and 0.3 mm3 after 600 000 and 1 200 000 cycles, respectively. Artificial aging had significantly negative effect on the volume loss for all test materials. In addition, the choice of material had statistical influence on the outcome. CONCLUSION: Monolithic zirconia ceramic demonstrated lower wear than that reported for enamel after simulated 5-year of clinical service, whereas all other test materials showed higher volume loss after artificial aging.

Failure resistance of single-implant crowns assembled from polyetheretherketone and lithium disilicate abutments and different crown materials after artificial aging.

AIM: To investigate the effect of using different materials for the fabrication of implant abutments and crowns on the mechanical behavior of implant-supported single crowns after artificial aging. The materials were tested in different combinations to reveal whether using stiff or resilient materials as an abutment or a crown material might influence the fracture strength of the whole structure. MATERIALS AND METHODS: A total of 40 implants (blueSKY, bredent GmbH & Co. KG) were restored with identical custom-made CAD/CAM abutments milled out of lithium disilicate or ceramic-reinforced PEEK and were divided into 5 test groups (n = 8 each). Forty crowns made of three different materials (zirconia, lithium disilicate, and ceramic-reinforced PEEK) were used to restore the abutments. Specimens were subjected to mechanical load up to 1,200,000 cycles in a chewing simulator (Kausimulator, Willytech) with additional thermal cycling. The surviving specimens were subjected to quasi-static loading using a universal testing machine (Z010, Zwick). RESULTS: PEEK abutments with zirconia crowns showed the highest median failure load (3890.5 N), while PEEK abutments with lithium disilicate crowns exhibited the lowest (1920 N). Fracture and deformation occurred in both crowns and abutments. CONCLUSION: The failure load of the restorations was influenced by the material of the abutment and the crown. Restoring PEEK abutments with zirconia crowns showed a high failure load and no screw loosening.

Accuracy and dimension stability of scannable versus conventional interocclusal registration materials: An in vitro study.

STATEMENT OF PROBLEM: Scientific data to support scannable and computer-aided design and computer-aided manufacturing (CAD-CAM)-compatible interocclusal registration materials are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the ability of different registration materials (conventional versus scannable) to record maxillary-mandibular relationships and compare the dimensional stability of these records after storage times of 1 hour and 48 hours. MATERIAL AND METHODS: Six groups of interocclusal registration materials were tested: 3 conventional (Registrado X-tra, Futar D Fast, and O-Bite) and 3 scannable (Registrado Scan, Futar Cut & Trim Fast, and O-Bite Scan). Eight registrations were made for each group by using a custom-made device with a dial gauge to measure vertical discrepancies. Records were stored at room temperature, and discrepancies measured after 1 hour and 48 hours. The data were statistically analyzed with the Wilcoxon test with respect to time and the Kruskal-Wallis test with respect to materials, followed by the Mann-Whitney test with the Bonferroni-Holm correction (α=.05). RESULTS: The median vertical discrepancies ranged from -2 µm (FS) to 11 µm (O-Bite) after 1 hour and from 3 µm (Futar Cut & Trim Fast) to 13 µm (Registrado X-tra and O-Bite) after 48 hours. A statistically significant difference (P<.001) was found between the results after 1 hour and 48 hours for all materials. All scannable interocclusal registration materials showed significantly lower vertical discrepancies than the corresponding conventional materials after 1 hour and 48 hours (P<.05). CONCLUSIONS: All registration materials showed vertical discrepancies that might be clinically acceptable. Vertical discrepancies increased after 48 hours of storage for all materials but were still clinically acceptable.

Defect-orientated onlay with cavity design optimization and cervical margin relocation: a case report.

For restoring extensive cavities in severely damaged or decayed posterior teeth, especially those with thin walls, indirect restorations are recommended rather than direct fillings. Regarding indirect restorations for inlays and onlays, composite resin-based CAD/CAM materials are considered to have several advantages over ceramics such as easy manufacturing, lower cost, and simpler repairability. A case is presented in this article in which the treatment plan and protocol combine multiple evidence-based clinical techniques such as immediate dentin sealing (IDS), cavity design optimization (CDO), and cervical margin relocation (CMR). For CDO and CMR, two different types of flowable composite resins with different viscosities were used. Restoring such extensively damaged teeth using a defect-oriented adhesive technique is considered a challenge both in terms of the preservation of healthy tooth structure and the proper isolation for adhesive luting. The IDS technique was used to enhance the bonding to the remaining dentin, while CDO was performed to avoid unnecessary removal of vital tooth structure, for example, undercuts. The deep subgingival margins were elevated using the CMR technique to facilitate the impression taking and a contamination-free luting of the final restoration. Combining the aforementioned techniques enabled a defect-oriented, minimally invasive restoration of a severely decayed tooth. The aim of this article is to present those techniques in a simplified way through a clinical case as a step-by-step guide for the practitioner.

Mechanical behavior of nano-hybrid composite in comparison to lithium disilicate as posterior cement-retained implant-supported crowns restoring different abutments.

OBJECTIVE: Resin-based materials are gaining popularity in implant dentistry due to their shock absorption capacity. Therefore, the aim of this study was to evaluate the fracture strength and failure mode of resilient materials for both crowns and abutments and compare them to the most widely used materials in different combinations after subjection to long-term fatigue loading. METHODS: Forty-eight cement-retained implant-restorations were assembled on titanium implants. Identical custom-made CAD/CAM abutments were milled out of 3 different materials (n = 16); T: titanium, Z: zirconia and P: ceramic-reinforced PEEK. Each group was subdivided, according to the restorative crown material, into two subgroups (n = 8); C: nano-hybrid composite and L: Lithium disilicate. Specimens were subjected to dynamic load of 98 N for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro-Wilk test was used to test for normality. One-way ANOVA followed by Tukey's post-hoc test was used to detect statistically significant differences between groups. RESULTS: All specimens withstood 1,200,000 load cycles. The fracture strength values varied from a minimum of 1639 ± 205 N for group PL to a maximum of 2949 ± 478 N for group ZL. SIGNIFICANCE: The abutment material influenced the fracture strength and failure mode of the restoration. A combination of zirconia abutments and nano-hybrid composite showed the most favorable mode of failure within the test groups. Therefore, this combination might be recommended as an alternative for restoring single implants in the posterior area.

Secure and precise insertion of minimally invasive resin-bonded fixed dental prostheses after ridge augmentation by means of a positioning splint.

OBJECTIVE: Single-retainer resin-bonded fixed dental prostheses (RBFDPs) are described as an excellent minimally invasive treatment modality for the replacement of a single missing incisor even in cases of congenitally missing teeth that are often associated with hard and soft tissue defects that need to be properly managed to optimize the esthetic outcome. The lack of a retentive form due to the minimally invasive preparation form makes the adhesive bonding procedure for RBFDPs relatively technique-sensitive and might discourage practitioners from offering this treatment modality. CLINICAL CONSIDERATIONS: A patient with both maxillary lateral incisors congenitally missing was assessed for eligibility for treatment with RBFDPs. Bilateral horizontal ridge defects were present and treated through ridge augmentation to ensure an ovate pontic design and enhance the esthetic outcome. A minimally invasive preparation within enamel was conducted; the restorations were digitally designed and milled out of (3Y-TZP) zirconia ceramic with labial veneering with feldspathic ceramic for enhanced esthetics. An improved design of positioning splints was used for the adhesive bonding procedure to ensure exact, secure, and flawless insertion of the restorations. CONCLUSIONS: RBFDPs offer a highly esthetic treatment modality for missing teeth in the anterior area. Tissue defects could be overcome be means of a minor oral surgery, while using improved positioning splints might ensure flawless adhesive bonding and promote the usage of RBFDPs. CLINICAL SIGNIFICANCE: Hard and soft tissue defects can be remarkably optimized through a minor ridge augmentation. Improved positioning splints allow an easy and secure positioning as well as visual inspection of the seating in end-position and complete removal of resin cement excess. Implementing the concept of insertion splints might promote RBFDPs for anterior tooth replacement as it helps preventing bonding errors.

The influence of the restorative material on the mechanical behavior of screw-retained hybrid-abutment-crowns.

BACKGROUND: The use of polymers in implant dentistry is gaining popularity, as they might have several advantages due to their shock absorption capacity. PURPOSE: The aim of this study was to evaluate the performance and fracture strength of three resilient shock-absorbing polymer-based materials as well as the widely used ceramics as one-piece screw-retained implant-supported hybrid-abutment-crowns. MATERIALS AND METHODS: Forty custom-made CAD/CAM one-piece screw-retained restorations were milled out of 5 different monolithic materials (n = 8); Z: 3Y-TZP zirconia, L: lithium disilicate, P: ceramic-reinforced polyetheretherketone (PEEK), C: nano-hybrid composite resin and E: polymer-infiltrated ceramic-network. Specimens were subjected to dynamic loading for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro-Wilk test was used to test for normality, and Levene test was conducted to test the homogeneity of variance. One-way ANOVA test followed by Tukey's post-hoc test were used to detect statistically significant differences between groups. RESULTS: All specimens withstood 1,200,000 cycles of thermo-dynamic loading with no signs of cracks or screw loosening. The median values of fracture strength varied from a minimum of 670 N for group E to a maximum of 2645 N for group Z. CONCLUSIONS: Fracture strength of screw-retained hybrid-abutment-crowns is influenced by the material used. Zirconia showed superior results. However, its fracture strength was comparable to that of PEEK, which additionally enjoys a shock absorbing property.

Comparison between novel strength-gradient and color-gradient multilayered zirconia using conventional and high-speed sintering.

OBJECTIVES: To investigate and compare the mechanical and optical properties of novel strength- and color-gradient multilayered zirconia and the impact of conventional and high-speed sintering. MATERIALS AND METHODS: Following zirconia materials were analyzed and compared: the high-speed sintered Katana Zirconia Block STML (4Y-TZP, KZC), the conventionally sintered Katana Zirconia Disc STML (4Y-TZP, KZL) and IPS e. max ZirCAD Prime (5Y-TZP/3Y-TZP, EZL). As control group acted the crystallized lithium disilicate ceramic IPS e. max CAD (ELC). Monolithic single molar crowns were fabricated and half of them were aged in a chewing simulator with human enamel antagonists (1.2 × 106 cycles, 50 N, lateral movement of 0.7 mm, 5/55 °C). The fracture load was tested in a universal testing machine (N = 96/n = 12). The two-body wear was determined using 3D matching of pre- and post-scans (N = 48/n = 12). Translucency (N = 36/n = 10) was evaluated with UV/Vis spectrophotometer. Data was analyzed using Kolmogorov-Smirnov test, one-way ANOVA followed by post-hoc Scheffé test, unpaired t-test and Weibull analysis (p < 0.05). RESULTS: Zirconia groups showed higher fracture load than ELC (p ≤ 0.001). Initially, all zirconia materials ranged in the same values (p > 0.05). After chewing simulation, EZL showed higher fracture load than KZC (p < 0.001) and KZL (p = 0.043). Zirconia materials showed no material loss, whereas the ELC showed the volumetric wear of 0.334 ± 0.34 mm3 and vertical wear of 0.155 ± 0.07 mm. Enamel antagonist wear ranged in the same values (p = 0.083-0.906). The translucency values within each zirconia material showed significant differences between the enamel and the dentin layers (p < 0.001). CONCLUSIONS: The novel strength and color-gradient multilayered zirconia showed higher mechanical properties than lithium disilicate ceramic. The high-speed sintering of zirconia showed neither a negative impact on the fracture load nor on the two-body wear. However, the optical properties and the reliability of zirconia is lower than those of highly translucent lithium disilicate ceramic.

Influence of the yttrium content on the fracture strength of monolithic zirconia crowns after artificial aging.

OBJECTIVES: The purpose of the study was to evaluate fracture strength of full-anatomical crowns manufactured from three different types of zirconia with different content of yttrium oxide. METHOD AND MATERIALS: A total of 48 specimens were divided into three main groups (n = 16), according to the content of yttrium oxide in the crown material used, as follows: group A, DD Bio ZX2 (3Y-TZP); group B, DD cubeX2 HS (4Y-TZP); and group C, DD cubeX2 (5Y-TZP) (Dental Direkt). After proper surface treatment of different materials, the crowns were adhesively bonded to metal abutments using a dual-curing composite resin (Multilink Automix, Ivoclar Vivadent). Eight specimens from each material group were randomly selected to undergo an artificial aging through dynamic loading and thermocycling in a chewing simulator (Willytec, SD-Mechatronic). After dynamic loading all survived specimens of the first subgroup together with all the specimens of the second subgroup were loaded in a universal testing machine (Zwick Z010, Zwick/Roell). The data were checked for normal distribution with the Shapiro-Wilk test and for homogeneity of the variances with the Levene test. The statistical analyses were done using the Kruskal-Wallis test and in subgroups using the Wilcoxon test. RESULTS: The highest fracture strength median value was shown with the 3Y-TZP after artificial aging (median 7,530 N), while the lowest was shown with the 5Y-TZP after artificial aging as well (median 3,700 N). CONCLUSIONS: Increasing the content of yttrium oxide in attempt to improve the optical properties can reduce the mechanical properties after aging of the ceramic as shown in this study. However, even the more translucent 5Y-TZP showed very high fracture resistance, which exceeded 3,000 N. Based on the results of this study, care should be taken when using zirconia with high content of yttrium oxide in areas or situations with high stresses.

Influence of thermomechanical fatigue on the fracture strength of CAD-CAM-fabricated occlusal veneers.

STATEMENT OF PROBLEM: With the development of new computer-aided design and computer-aided manufacturing (CAD-CAM) restorative dental materials, limited data regarding their survival rate and fracture strength are available when they are used as occlusal veneers. Therefore, these materials should be evaluated under conditions similar to those of the oral environment before being recommended for clinical use. PURPOSE: To evaluate the influence of thermomechanical fatigue loading on the fracture strength of minimally invasive occlusal veneer restorations fabricated from different CAD-CAM materials and bonded to human maxillary premolars using self-etchnig bonding technique. MATERIAL AND METHODS: Sixty-four CAD-CAM occlusal veneer restorations were fabricated from group LD (lithium disilicate [e.max CAD]), LS (zirconia-reinforced lithium silicate [Vita Suprinity]), PI (polymer-infiltrated ceramic [Vita Enamic]), and PM (polymethylmethacrylate [Telio CAD]). The occlusal veneers were luted to enamel (n=16) using a self-etching primer (Multilink Primer A/B) and a luting composite resin (Multilink Automix). Half of the specimens of each group (n=8) were randomly selected and subjected to thermomechanical fatigue loading in a masticatory simulator (1.2 million cycles at 98 N with 5°C-55°C thermocycling). All specimens were quasistatically loaded until fracture. The statistical analysis was made using the Kruskal-Wallis and Mann-Whitney U tests (α=.05). RESULTS: According to the Kaplan-Meier analysis after the thermomechanical fatigue of the 4 groups, the cumulative survival rate was as follows: group LD, 50% group LS, 62.5% group PI, 37.5%; and group PM, 50%. Although some of the surviving specimens exhibited microcracking, their integrity or bonding to teeth was not affected. Thermomechanical fatigue significantly reduced the fracture strength of group PI (P=.047) and group PM (P=.025). Without thermomechanical fatigue, group PM showed significantly higher fracture strength than group LS (P=.015). CONCLUSIONS: In general, thermomechanical fatigue decreased the survival rate and fracture strength in all test groups.

Influence of Different CAD/CAM Crown Materials on the Fracture of Custom-Made Titanium and Zirconia Implant Abutments After Artificial Aging.

PURPOSE: To investigate the effects of different commercially available computer-aided design/computer-assisted manufacturing (CAD/CAM) materials for fabrication of molar crowns, including polyetheretherketone (PEEK), on the fracture strength and failure mode of custom-made titanium and zirconia abutments after artificial aging. MATERIALS AND METHODS: A total of 48 identical custom-made CAD/CAM abutments milled out of titanium or zirconia were divided into six test groups of eight specimens each. The groups were assigned as follows: titanium abutments restored with zirconia crowns (TiZ), with lithium disilicate crowns (TiL), or with PEEK crowns (TiP); zirconia abutments bonded to a titanium base and restored with zirconia crowns (ZrZ), with lithium disilicate crowns (ZrL), or with PEEK crowns (ZrP). The specimens were artificially aged in a chewing simulator for 1.2 million cycles of dynamic loading with simultaneous thermal cycling and then loaded to fracture in the universal testing machine. Shapiro-Wilk test was used to test for normality. One-way analysis of variance followed by post hoc analysis using Bonferroni test was used to detect statistically significant differences among groups. RESULTS: All specimens survived the artificial aging process simulating 5 years of clinical service. The fracture patterns and means of the fracture strength (N) varied between groups: TiZ = 4,926 N; TiL = 3,706 N; TiP = 3,878 N; ZrZ = 5,529 N; ZrL = 2,826 N; and ZrP = 3,967 N. CONCLUSION: Although the tested combinations showed different fracture patterns and loads, all tested abutment and crown materials and their different combinations could be considered to have fracture strengths suitable for clinical application.

Iatrogenic (Traumatic) Occipital Artery Pseudoaneurysm - Rare Complication of Ventriculoperitoneal Shunt in an Infant: Case Report and Review of the Literature.

Although ventriculoperitoneal shunt (VPS) is the most common procedure performed by pediatric neurosurgeons, it is still associated with frustrating complications, most common of which are obstruction and infection. Traumatic occipital artery pseudoaneurysm is a very rare complication of VPS procedure. To the best of our knowledge, there is no similar case reported in the English language literature. A 12-month-old patient suffered posthemorrhagic hydrocephalus of prematurity, and multiple other complications due to extreme prematurity, including immature lung disease, retinopathy of prematurity, necrotizing enterocolitis, bowel perforation, short bowel syndrome resulting in total parenteral nutrition-dependence, and hydrocephalus which was treated by insertion of VPS. Four weeks after the shunt, a slowly enlarging pulsatile swelling distal to the valve under the catheter altering the shunt function was noted. The swelling was diagnosed as a pseudoaneurysm of the occipital artery and treated by excision of the aneurysm. The child developed isolated dilated fourth ventricle, which was treated by endoscopic fourth ventriculostomy. Traumatic occipital artery pseudoaneurysm as a result of tunneling of VPS catheter is a very rare complication of VPS. Clinical and radiological imaging is diagnostic of the aneurysm. Surgical repair should be considered in such cases. This case report is aimed to raise the awareness among physicians about this rare complication.

Effect of fatigue loading on the fracture strength and failure mode of lithium disilicate and zirconia implant abutments.

OBJECTIVE: The aim of this study was to test five types of implant restorations using titanium, zirconia and lithium disilicate abutments after being subjected to long-term fatigue loading. MATERIALS AND METHODS: Forty single-tooth implant restorations were assembled on titanium implants (FairTwo; FairImplant). The restorations differed only in the type of abutment used and were divided into five groups [Ti: titanium; Zr: zirconia with no metal base; ZrT: zirconia with titanium base; LaT: lithium disilicate abutment with titanium base; and LcT: lithium disilicate hybrid-abutment-crown with titanium base]. Specimens were subjected to dynamic load of 49 N up to 1,200,000 cycles using a dual-axis chewing simulator (Kausimulator; Willytech). The surviving specimens were subjected to quasi-static loading using a universal testing machine (Z010; Zwick) until the implant-abutment connection failed. The values of force (N) at which fracture or plastic deformation of the restoration occurred were calculated and the rate of deformation was analyzed. The data was then analyzed using Mann-Whitney tests. RESULTS: Groups Ti, ZrT, LaT and LcT withstood 1,200,000 fatigue load cycles and higher forces than physiological occlusal forces without fracture or debonding of the ceramic suprastructure. In group Zr, some specimen did not survive the chewing simulation and this group showed the lowest resistance to failure with a median of 198 N. CONCLUSIONS: Within the limitations of this study, it could be concluded that lithium disilicate abutments and hybrid-abutment-crowns show promising durability and strength after long-term dynamic loading. The use of titanium base enhances the strength of the zirconia abutments.

Efficacy of Different Surface Treatments for Intraoral Repair of Veneered Zirconia Frameworks.

PURPOSE: To evaluate the efficacy of different surface treatments on the repair of veneered zirconia ceramics. MATERIALS AND METHODS: Forty-eight zirconia disks were divided into three groups according to the method of surface treatment: polished surface, air abraded, or ground using a special silicon carbide bur (SiC Grinding Bur). All specimens were primed using a primer containing MDP (Cimara Zircon, Voco) and then bonded to composite in Plexiglas tubes using dual-curing adhesive resin (Bifix QM, Voco). Each of the three groups was further divided into two subgroups (n = 8) stored either in water at 37°C for 3 days without thermocycling or stored in water at 37°C for 150 days with an additional 37,500 thermocycles between 5°C and 55°C. After storage, tensile bond strength (TBS) was measured in a universal testing machine. RESULTS: After 3 days of storage, silicon carbide bur and air-abraded groups showed high TBS that ranged from 32.7 to 41.0 MPa (p ≤ 0.05). After 150 days of storage with thermocycling, the air-abraded group showed the most durable TBS (34.8 MPa), while the silicon carbide bur group showed a significant reduction in TBS (21.2 MPa); in the polished control group, specimens all debonded spontaneously during storage (p ≤ 0.05). CONCLUSION: Repair of zirconia ceramic after chipping of its veneers showed durable TBS when surface conditioning with air abrasion or roughening of the zirconia surface with a silicon carbide bur was provided.

Tensile Bond Strength of So-called Universal Primers and Universal Multimode Adhesives to Zirconia and Lithium Disilicate Ceramics.

PURPOSE: To test the bond strength and durability after artificial aging of so-called universal primers and universal multimode adhesives to lithium disilicate or zirconia ceramics. MATERIALS AND METHODS: A total of 240 ceramic plates, divided into two groups, were produced and conditioned: 120 acid-etched lithium disilicate plates (IPS e.max CAD) and 120 air-abraded zirconia plates (Zenostar T). Each group was divided into five subgroups (n = 24), and a universal restorative primer or multimode universal adhesive was used for each subgroup to bond plexiglas tubes filled with a composite resin to the ceramic plate. The specimens were stored in water at 37°C for 3 days without thermal cycling, or for 30 or 150 days with 7500 or 37,500 thermal cycles between 5°C and 55°C, respectively. All specimens then underwent tensile bond strength testing. RESULTS: Initially, all bonding systems exhibited high TBS, but some showed a significant reduction after 30 and 150 days of storage. After 3, 30, and 150 days, Monobond Plus, which contains silane and phosphate monomer, showed significantly higher bond strengths than the other universal primer and adhesive systems. CONCLUSIONS: The bond strength to lithium disilicate and zirconia ceramic is significantly affected by the bonding system used. Using a separate primer containg silane and phosphate monomer provides more durable bonding than do silanes incorporated in universal multimode adhesives. Only one of five so-called universal primers and adhesives provided durable bonding to lithium disilicate and zirconia ceramic.

Fracture resistance of ceramic and polymer-based occlusal veneer restorations.

OBJECTIVES: The purpose of this in vitro study was to evaluate the influence of thermodynamic loading on the durability and fracture resistance behavior of occlusal veneers fabricated from different biomedical dental CAD/CAM materials. METHODS: The occlusal surfaces of 64 extracted premolars were prepared in the enamel layer and restored with occlusal veneers with a fissure/cusp thickness of 0.5/0.8mm made from four different dental CAD/CAM materials: group LD lithium disilicate (e.max CAD), group LS zirconia-reinforced lithium silicate (Vita Suprinity), group PI polymer-infiltrated ceramic (Vita Enamic), and group PM polymethylmethacrylate PMMA (Telio CAD). The prepared teeth were etched with phosphoric acid. The occlusal veneers were then bonded using an adhesive luting system (Multilink Primer A/B and Multilink Automix luting resin). Half of the specimens were subjected to thermodynamic loading in a chewing simulator (1.2 million cycles at 98N). All specimens were quasi-statically loaded until fracture. The statistical analysis was made using the t-test and one-way ANOVA followed by the Tukey HSD test (α = 0.05). RESULTS: All aged specimens survived the thermodynamic loading. Thermodynamic loading significantly raised the fracture resistance in groups LS, PI, and PM (P < 0.03). Occlusal veneers made from lithium disilicate and zirconia-reinforced lithium silicate recorded higher fracture resistance than those made from polymer-infiltrated ceramic and PMMA resin. CONCLUSIONS: All tested dental CAD/CAM biomaterials exhibited a fracture resistance considerably exceeding the average occlusal force in the posterior dentition. Therefore, they might present a viable long-term treatment for restoring the occlusal surfaces of posterior teeth.

Comparison of fracture strength and failure mode of different ceramic implant abutments.

STATEMENT OF PROBLEM: The whitish color of zirconia (ZrO2) abutments offers favorable esthetics compared with the grayish color of titanium (Ti) abutments. Nonetheless, ZrO2 has greater opacity, making it difficult to achieve natural tooth color. Therefore, lithium disilicate (LaT) abutments have been suggested to replace metal abutments. PURPOSE: The purpose of this in vitro study was to evaluate the fracture strength and failure mode of single-tooth implant restorations using ZrO2 and LaT abutments, and to compare them with titanium (Ti) abutments. MATERIAL AND METHODS: Five different types of abutments, Ti; ZrO2 with no metal base; ZrO2 with a metal base (ZrT); LaT; and LaT combination abutment and crown (LcT) were assembled on 40 Ti implants and restored with LaT crowns. Specimens were subjected to quasistatic loading using a universal testing machine, until the implant-abutment connection failed. As bending of the metal would be considered a clinical failure, the values of force (N) at which the plastic deformation of the metal occurred were calculated, and the rate of deformation was analyzed. Statistical analysis was done using the Mann-Whitney U test (α=.05). RESULTS: Group ZrO2 revealed the lowest resistance to failure with a mean of 202 ±33 N. Groups ZrT, LaT, and LaC withstood higher forces without fracture or debonding of the ceramic suprastructure, and failure was due to deformation of metal bases, with no statistically significant differences between these groups regarding the bending behavior. CONCLUSIONS: Within the limitations of this in vitro study, it was concluded that LaT abutments have the potential to withstand the physiological occlusal forces that occur in the anterior region and that ZrO2 abutments combined with Ti inserts have much higher fracture strength than pure ZrO2 abutments.

Reducing the effect of polymerization shrinkage of temporary fixed dental prostheses by using different materials and fabrication techniques.

OBJECTIVE: The aim of this laboratory study was to evaluate the horizontal and vertical effects of the polymerization shrinkage of three-unit temporary fixed dental prostheses (FDPs) on the position of the prepared teeth. In addition, the reduction of these effects by using different fabrication techniques was evaluated. METHODS: A total of 192 temporary FDPs were fabricated using one methacrylate (MA) and two dimethacrylate (DMA) materials. Each material group (n=64) was divided into two groups according to the fabrication methods (M1: curing on the prepared teeth, M2: curing in a silicone mold). Each fabrication group was divided into four subgroups (n=8) according to the relining method used (B: no relining, S: spacer foil 300µm, DG: grinding-out with 500µm cutting depth, and FG: free grinding). The experimental apparatus consisted of two abutment teeth lowered at right angles into a silicone mold. One prepared tooth was embedded in silicone to simulate the periodontium and permit slight horizontal tooth movement. The dimensional changes were recorded with an optical microscope. The test images were superimposed and measured using image analysis software. RESULTS: The statistical analysis showed that there were significantly higher horizontal changes for the MA than the DMA resins in M1, while there was none in M2. Regarding the vertical changes, there were significant differences between the baseline group and all relining and fabrication groups in all materials. SIGNIFICANCE: Relining of directly fabricated temporary FDPs significantly reduces the effect of polymerization shrinkage and thus secures the position of the prepared teeth.