Fracture Strength Values Research Articles

Microstructural and Mechanical Characterization of CAD/CAM Materials for Monolithic Dental Restorations.

To determine and compare the microstructure, flexural strength, flexural modulus, fracture strength, and microhardness of four types of computer-aided design/computer-aided manufacturing (CAD/CAM) materials for monolithic dental restorations. A lithium disilicate (LD; IPS e.max CAD), a zirconia-reinforced lithium silicate (ZLS; VITA Suprinity), a hybrid high-performance polymer (HPP) composite resin (GC Cerasmart), and a hybrid polymer-infiltrated ceramic network (PICN) material (VITA Enamic) were used to manufacture monolithic ceramic posterior crowns (n = 10) that were adhesively cemented on resin-based composite dies and loaded until fracture. In addition, 40 rectangular bars (n = 10) were milled and polished for three-point flexural strength testing. Microhardness (Vickers indentation), as well as quantitative (energy dispersive spectroscopy) and qualitative (scanning electron microscopy) structural analysis were conducted on fracture surfaces. Data were analyzed by one-way ANOVA and Tukey HSD post-hoc test (p = 0.05). Mechanical testing results showed that the material type has a significant effect on the fracture strength (p < 0.0001) of the monolithic crowns with ZLS and LD presenting significantly higher fracture strength than the PICN and HPP hybrid materials. LD showed the highest flexural strength (p < 0.0001) followed by ZLS, HPP, and PICN, respectively. The lowest flexural modulus and hardness were presented by HPP whereas ZLS had the highest flexural modulus and hardness. The LD presented the highest modulus of resilience and the PICN the lowest. All CAD/CAM crown materials exhibited high values of fracture and flexural resistance, making them suitable materials for posterior full-crown restorations. Glass-ceramics suffered more from catastrophic and nonreparable fracture patterns, whereas minimal chipping and type II fracture patterns were more common in hybrid materials. The combination of more flexibility, less stiffness, and increased softness with satisfactory flexural and fracture strength values observed in PICN and HPP makes these two hybrid materials suitable choices for chairside monolithic crown fabrication.

Comparative Evaluation of the Fracture Strength of Monolithic Crowns Fabricated from Different all-ceramic CAD/CAM Materials (an in vitro study)

The objective of this in vitro study was to evaluate and compare the fracture strength of monolithic crowns fabricated from five different all-ceramic CAD/CAM materials (lithium disilicate, zirconia, reinforced composite, hybrid dental ceramic, and zirconia-reinforced lithium silicate) using single load to failure test. Forty sound human maxillary first premolar teeth extracted for orthodontic purposes were selected for use in this study. Teeth were prepared according to a standard protocol with 1 mm deep chamfer finishing line, 4 mm axial height with planer occlusal reduction and 6º total convergence angle. Teeth were then divided into five groups of eight teeth each according to the material used for the fabrication of the monolithic crowns as follow: Group A: Crowns fabricated from lithium disilicate (IPS e.max CAD, Ivoclar Vivadent), Group B: Crowns fabricated from zirconia (CEREC Zirconia, Dentsply Sirona), Group C: Crowns fabricated from reinforced composite (BRILLIANT Crios, COLTENE), Group D: Crowns fabricated from hybrid dental ceramic (VITA ENAMIC, VITA Zahnfabric), Group E: Crowns fabricated from zirconia-reinforced lithium silicate (CELTRA DUO, Dentsply Sirona). Teeth of all groups were then scanned with CEREC Omnicam digital intraoral scanner and the crowns were then designed using CEREC Premium software (version 4.4.4) and milled using CEREC MC XL milling unit. Post-milling, crowns of each group were subjected to either a firing procedure or to a polishing only according to the manufacturer's instructions of each material. The internal surfaces of the crowns of each group were then subjected to surface treatment according to the manufacturer's instructions of each material and the crowns were then cemented on their respective teeth using a universal dual-cured adhesive resin cement (Duo-Link Universal, Bisco Inc.). All teeth with the cemented crowns were then stored in deionized distilled water at room temperature for 24 hours before testing. All samples were then subjected to compressive axial loading until fracture in computer-controlled universal testing machine (Zwick Z010, Ulm, Germany) at a crosshead speed of 0.5 mm/min. The data were statistically analyzed using one-way ANOVA test and LSD test at a level of significance of 0.05. The results of this study showed that the highest mean value of fracture strength was recorded by Group B (2337.37), followed by Group C (1880.59), Group E (1404.49), Group A (1085.39) and Group D (767.06), respectively with statistically highly significant differences among the different groups (p&lt;0.01). From the results of this study, it seems that the differences in the chemical composition and microstructure of the tested all-ceramic CAD/CAM materials may be responsible for the differences in the fracture strength of the fabricated crowns.

Mechanical properties of reaction sintered SiC-TiC composite

SiC-TiC composite containing 5–30 vol% TiC particles was fabricated by conversion of TiO2 to TiC during pressureless sintering. The presence of very fine and uniformly distributed, in-situ created TiC particles increased driving force for sintering allowing fabrication of high density SiC-TiC composite without the use of external pressure. The highest mechanical properties were measured in samples sintered at 1885 °C for 1 h. The highest values for hardness (~ 20 GPa) and fracture strength (~ 490 MPa) were measured in samples containing 5 vol% TiC, whereas the highest fracture toughness (~ 5.5 MPa ⋅m1/2) was measured in samples containing 10 vol% TiC. The presence of in-situ created, uniformly distributed TiC particles was beneficial for activation of not only the crack deflection mechanism but also mechanism called toughening by residual stress crated due to the difference of thermal expansion between SiC matrix and TiC particles. The compressive stress field around TiC particles acts to close the propagating crack and thus to increase fracture toughness.

Comparison of different base materials on fracture strength of mesio-occlusal-distal composite restorations

Abstract Objective: The aim of this study was to evaluate the influence of different base materials on fracture strength of mesio-occlusal-distal (MOD) composite restorations. Materials and Methods: Forty-eight extracted, intact maxillary molar teeth with standardized, deep MOD cavities were randomly assigned into four groups according to the base material placed: Control group (CO); no base material, SDR group; bulk-fill flowable composite, CGIC group; chemically curing glass ionomer cement (GIC), and RGIC group; light curing resin reinforced GIC. All the specimens were then restored with a nanocomposite (CeramX Duo/Dentsply) in combination with etch and rinse adhesive following the manufacturer’s instructions. After aging fracture, strength of the specimens was tested by the application of a ramped oblique load to the buccal cusp in a universal testing machine. Mean fracture strength values for each group were calculated and compared using one-way ANOVA (P = 0.05). Fracture patterns of the specimens were also evaluated. Results: The mean loads necessary to fracture the samples were as follows: control: 819.22 ± 253.65; SDR: 694.46 ± 266. 55; CGIC: 559.15 ± 277.34; RGIC 861.87 ± 277.28: N. The control and RGIC groups showed significantly higher fracture strength than CGIC and SDR groups (P &lt; 0.05). Although the mean fracture strength value of SDR group was higher than that of CGIC group, the difference between these groups was not statistically significant (P &gt; 0.05). Most frequently observed fracture patterns were adhesive (58.3%) in CO, cohesive (50%) in SDR group, cohesive (83.3%) in CGIC group, and mixed (41.7%) in RGIC group. Conclusions: Resin-modified glass-ionomer cement as a base material or restoration of the tooth only with composite resin resulted in higher fracture strength than composite resin restoration with a conventional glass ionomer base or a flowable bulk-fill material. Fracture pattern distributions diversed according to the base material placed under composite restoration.

Fracture RESISTANCE and Color Stability of two hybrid ceramic veneers VERSUS LITHIUM DISILICATE GLASS CERAMIC VENEERS

Purpose: To compare the color stability and fracture strength of two hybrid ceramic (Suprinity and Enamic) veneers versus Lithium Disilicate ceramic veneers.Materials and methods: Thirty freshly extracted maxillary central incisors were divided equally into three groups (n=10): group Em (IPS empress II, Ivoclar Vivadent) as a control, group VS (Suprinity, Vita Zahnfabrik), and group VE (Enamic, Vita Zahnfabrik). An incisal reduction of 1.5 mm was made with a butt-joint margin and 0.6 mm chamfer finish line was prepared on the labial surface of each specimen and on the middle of the proximal surfaces. Each group received different type of veneers according to the sample grouping. Using spectrophotometer (Nippon Densmoku industries), ΔE was recorded for each specimen before and after 15 days of immersion in a coffee solution considering the value of ΔE= 3.3 as clinically significant staining threshold. All the specimens were subjected to fracture strength test using universal testing machine (The Testometric Company Limited) using cross head speed of 0.5 mm/min at 135 degrees’ angle. One-way ANOVA and chi-square were used for statistical analysis.Results: Regarding the mean color stability between studied groups, group VS scored the least ΔE (3.52±2.46) followed by group VE (4.14±1.94) then group Em (4.49±2.45). On the other hand, group VS scored the highest fracture strength values (471.04±274.5) followed by group Em (442.13±236.1) then group VE (394.72±160.84). One-wayANOVA revealed no significant differences between groups in both color stability (P=0.636) and fracture strength (P=605).Conclusion: The tested hybrid ceramics could present an acceptable treatment option for fabricating ceramic veneers.

Effect of occlusal contact of the loading rod tip on the fracture strength of ceramic crowns

Aim: The aim of this study was to verify the effect of the occlusal contact of the rod tip on the fracture strength of crowns made with different ceramic systems. Materials and Methods: Conical preparation was performed on bovine teeth with diamond burs in mechanical lathe, and crowns were made for all-ceramic, metal-ceramic, In Ceram, and IPS Empress 2 ceramic systems according to manufacturers' instructions in prosthetic laboratory. The crowns were fixed with resin-modified glass ionomer cement or dual-curing composite resin under a static load of 4 kg for 1 min. To simulate the clinical contact between loading and ceramic crowns, the rod tip was made in accordance with the occlusal form of the ceramic crown. After storage in distilled water at 37°C for 24 h, the samples were submitted to 60,000 mechanical cycles at a load of 35 N/2 Hz immersed in distilled water. The fracture strength test was performed in an Instron with a cross-speed of 0.5 mm/min. Results: Data submitted to one-way ANOVA for randomized experiments followed by Tukey's test (α = 0.05) showed greater value for IPS Empress 2 (208.12 kgf) with significant difference in relation to all-ceramic (149.32 kgf) and In Ceram (142.25 kgf), whereas metal-ceramic showed intermediary value (182.83 kgf). Conclusion: The loading of the rod tip in occlusal contact with the crown did not promote premature failures during the mechanical fatigue test, and two-ceramic systems showed different values of fracture strength after mechanical fatigue test, with better performance for crowns manufactured with IPS Empress 2.

Comparative Evaluation of Marginal Adaptation and Fracture Strength of Different Ceramic Inlays Produced by CEREC Omnicam and Heat-Pressed Technique.

Objective The aim of this in vitro study was to evaluate marginal adaptation and fracture strength of inlays produced by CEREC Omnicam using different types of blocs and heat-pressed technique. Methods: Seventy-five extracted human mandibular molars were divided randomly into 5 groups (n=15). 60 molars in four groups received MOD inlay preparations. Experimental groups were CO: Intact teeth, EC: IPS e.max CAD and CEREC, LU: Lava Ultimate and CEREC, EL: IPS Empress CAD and CEREC, EP: IPS Empress Esthetic ingots and heat-pressed technique. Marginal gap measurements were taken with a stereomicroscope. Restorations were cemented with Variolink N and stored in distilled water at 37°C for 24 hours. All samples were subjected to thermocycling. The fracture strength of specimens was determined at a 0.5 mm/min crosshead speed until fracture. Fracture modes were determined. Statistical analyses were performed using one-way analysis of variance for fracture strength data and Kruskal–Wallis for marginal gap data (p=0.05). Results The mean marginal gap size of EC, LU, EL, and EP were 33.54 µm, 33.77 µm, 34.23 µm, and 85.34 µm, respectively. EP had statistically higher values than other groups. The fracture strength values were significantly higher in the intact teeth group (3959,00 ± 1279,79 N) than those of restored groups EC (2408,00 ± 607,97 N), LU (2206,73 ± 675,16), EL (2573.27 ± 644,73) ve EP (2879,53 ± 897,30). Conclusion Inlays fabricated using CEREC Omnicam demonstrated better marginal adaptation than inlays produced with heat-pressed technique, whereas fracture strength values of inlays fabricated with different type of blocks using CEREC Omnicam exhibited similarity to those fabricated with heat-pressed technique.

Comparative Evaluation of Fracture Strength of Different Types of Composite Core Build-up Materials: Anin vitroStudy

The aim of the study was to evaluate the fracture strength of three types of composite core build-up materials. The objectives were to study and evaluate the fracture strength and type of fracture in composite core build-up in restoration of endodonti-cally treated teeth with or without a prefabricated metallic post. A total of 60 freshly extracted mandibular premolars free of caries, cracks, or fractures were end-odontically treated and restored with composite core build-up with prefabricated metallic posts cemented with resin luting cement (group I) and without a post (group II). This was followed by a core build-up of 10 teeth each with three different types of composite materials: Hybrid composite, nanocomposite, and ormocer respectively. The samples were mounted on polyvinyl chloride block and then loaded in the universal load frame at 90° to the long axis of tooth. The fracture strength of the samples was directly obtained from the load indicator attached to the universal load frame. Analysis of variance (ANOVA) test revealed that teeth restored with post exhibited highest fracture strength (1552.32 N) and teeth restored without post exhibited lowest fracture strength (232.20 N). Bonferroni's test revealed that values for hybrid composite (Z-100, 3M ESPE) with post, nanocomposite (Z-350, 3M ESPE) with post, ormocer composite (Admira-VOCO) with post, and nanocomposite (Z-350, 3M ESPE) without post were not significantly different from each other. Teeth restored with post and core using hybrid composite yielded the highest values for fracture strength. Teeth restored with ormocer core without post exhibited the lowest values. Teeth restored with nanocomposite core without post exhibited strength that was comparable with hybrid composite core but higher than that of ormocer. Mutilated endodontically treated teeth can be prosthetically rehabilitated successfully by using adhesive composite core build-up along with post to meet anatomical, functional, and esthetic demands.

Fracture Strength of Flared Root Canals Restored with Different Post Systems.

Objective:To evaluate the fracture resistance of different intra-radicular post systems in flared root canals.Methods:Sixty human canines were used. The coronal portion was removed and the root length was standardized at 17 mm. Canals were prepared and filled with gutta-percha/AH Plus sealer. Roots were embedded in self-polymerising acrylic resin blocks. According to the material used, the teeth were randomly divided into three groups (n=20): glass fibre post (GFP): GFP and Z350 resin composite core; pre-fabricated metal post (PMP): PMP and Z350 resin composite core; and cast metal core (CMC): CMC with silver-tin alloy. Coronal reconstruction involved fabrication of metal copings. Samples were submitted to mechanical compression testing at 45º in a universal test machine. Fracture pattern was evaluated under a stereoscope. The fracture strength values were submitted to one-way analysis of variance (ANOVA) and Tukey tests (α=0.05).Results:There was no statistically significant difference between the resistance values among groups (P=0.193). With regard to fracture pattern, GFP showed 55% and PMP 45% of Type I fractures, which considered repairable or favourable, whereas MCC presented 50% of Type V, which was considered irreparable or unfavourable.Conclusion:Glass fibre and pre-fabricated metal posts have good fracture resistance to compression and may be used for restoring flared root canals, since they presented fractures mainly involving the filling core, thus facilitating later repair.

Fracture Strength of Flared Root Canals Restored with Different Post Systems

Objective To evaluate the fracture resistance of different intra-radicular post systems in flared root canals. Methods Sixty human canines were used. The coronal portion was removed and the root length was standardized at 17 mm. Canals were prepared and filled with gutta-percha/AH Plus sealer. Roots were embedded in self-polymerising acrylic resin blocks. According to the material used, the teeth were randomly divided into three groups (n=20): glass fibre post (GFP): GFP and Z350 resin composite core; pre-fabricated metal post (PMP): PMP and Z350 resin composite core; and cast metal core (CMC): CMC with silver-tin alloy. Coronal reconstruction involved fabrication of metal copings. Samples were submitted to mechanical compression testing at 45o in a universal test machine. Fracture pattern was evaluated under a stereoscope. The fracture strength values were submitted to one-way analysis of variance (ANOVA) and Tukey tests (α=0.05). Results There was no statistically significant difference between the resistance values among groups (P=0.193). With regard to fracture pattern, GFP showed 55% and PMP 45% of Type I fractures, which considered repairable or favourable, whereas MCC presented 50% of Type V, which was considered irreparable or unfavourable. Conclusion Glass fibre and pre-fabricated metal posts have good fracture resistance to compression and may be used for restoring flared root canals, since they presented fractures mainly involving the filling core, thus facilitating later repair.

Influence of firing conditions and production methods on fracture strength of titanium-based metal ceramic crowns

Objectives: This study evaluated the effect of argon atmosphere compared with vacuum during porcelain firing on the fracture strength of crowns made of porcelain and electron beam melted (EBM) Ti-6Al-4 V, cast commercially pure titanium or milled commercially pure titanium. Methods: Sixty crown copings of c. p. titanium, Ti-6Al-4 V alloy and porcelain were fabricated using three production techniques. The copings were fired either under vacuum or in an argon gas atmosphere. Specimens were subdivided into groups of cast c. p. titanium, milled c. p. titanium and EBM Ti-6Al-4 V which were further subdivided according to firing modes employing either vacuum or argon gas. The 60 specimens were subjected to cyclic preloading and thermocycling, and were then individually loaded until interface fractured. Differences between the group mean values were calculated using the one-way ANOVA and Tukey’s range test. Two fractured samples from each group were cut with a diamond blade and examined using SEM and EDS for visualization and chemical composition analysis of the fractured interface. Results: The highest mean fracture strength values, though not significant, were recorded for the groups fired in argon atmosphere, and the lowest mean fracture strength values were recorded for the groups fired in vacuum, with one exception. Comparing the two main groups of firing atmosphere, no significant difference could be documented. SEM and EDS analysis indicated clear differences in composition and structure between the groups included in the study. Conclusions: Firing in argon atmosphere does not significantly improve the fracture strength of porcelain bonded to titanium.

Investigation of the fracture of very thin amorphous alumina film during spherical nanoindentation

Thin amorphous alumina layers (10 to 40nm thick) are processed on sputtered aluminum thin film (500nm) by atomic layer deposition (ALD) at low temperature (85°C). Global methodology combining quantitative experimental observations of fracture and numerical modeling is proposed to obtain the fracture strength of ALD thin film on Al layer. First, mechanical properties of the multilayer specimen are characterized by Berkovich nanoindentation, then fracture of ALD alumina is studied through spherical indentation with various tip radius. Spherical indentation load driven-displacement curves display a plateau (pop-in) at a critical load and critical indentation depth. A statistical approach is used to determine pertinent/fracture parameters from pop-in displacement. Careful SEM and AFM observations of indentation imprint exhibit circumferential cracking in agreement with the assumption that the pop-in event is predominantly controlled by the fracture of the oxide layer on the soft Al film. Finally, a numerical model calibrated with experimental results is used in order to predict both the mechanical response prior to the oxide fracture and a value of fracture strength for ALD alumina thin films.

Fracture strength of lithium disilicate crowns compared to polymer-infiltrated ceramic-network and zirconia reinforced lithium silicate crowns

ObjectivesThe aim of this study was to evaluate the fracture strength of crowns made from current CAD/CAM materials. In addition the influence of crown thickness and chewing simulation on the fracture strength was evaluated. MethodsCrowns were fabricated from lithium disilicate, zirconia reinforced lithium silicate (ZLS-ceramic) and a polymer-infiltrated ceramic-network (PICN) with an occlusal thickness of 1.0mm or 1.5mm, respectively (n=16). Crowns were cemented on composite dies. Subgroups of eight specimens were loaded with 5kg in a chewing simulator for 1,200,000 cycles with thermal cycling. Finally, all specimens were loaded until fracture in a universal testing machine. Three-way ANOVA was used to detect statistical interaction. Differences regarding the materials were tested with two-way ANOVA, following one-way ANOVA and a post-hoc Tukey's-Test. ResultsAll crowns survived the chewing simulation. The material had a significant influence on the fracture resistance (p≤0.05). Lithium disilicate achieved the highest values of fracture strength in almost all groups followed by ZLS-ceramic. PICN achieved the lowest values of fracture strength. Chewing simulation increased the fracture strength of thick lithium disilicate crown significantly. Greater occlusal thickness of all crown materials resulted in higher crown fracture strength before chewing simulation. After chewing simulation occlusal thickness of lithium disilicate and PICN crowns had no significant influence on the fracture strength. ConclusionsAll crowns revealed fracture strength above the clinically expected loading forces. Therefore the durability of the tested CAD/CAM materials seems promising also in an occlusal thickness of 1.0mm.

Vertical root fracture resistance of simulated immature permanent teeth filled with MTA using different vehicles.

BackgroundThe aim of the study is to evaluate the resistance vertical root fracture (VRF) of mineral trioxide aggregate (MTA) filled-immature permanent roots by using three different vehicles.Material and MethodsForty-extracted human single-rooted mandibular premolars were selected and the root length was standardized to the length of 9 mm. For simulation of immature tooth apices, peeso reamers were introduced into the root canals and the prepared roots were assigned into three experimental groups according the used vehicle (distilled water-DW, prophylene glycol-PG, chlorhexidine-CHX) and control group (n=10). To simulate a periodontal membrane, the apical 7 mm of all roots was covered with wax to obtain a 0.2- to 0.3-mm-thick layer before embedding the roots into acrylic cylinders. A vertical force was applied (1mm/min) using a universal testing machine and the maximum load (F-max) that fracture occurred and the fracture mode (splint or comminuted) was recorded. Data were presented as mean and standard deviations. Statistical analysis was performed using Kruskal-Wallis, Mann-Whitney U Test was used for multiple comparisons.ResultsThere were significant differences between fracture strength of experimental groups with that of control group (p<0.05). However, no statistically significant differences were found amongst the fracture strength values of the experimental groups (p>0.05). In all groups, split fracture was the most common fracture mode.ConclusionsMTA increases resistance of immature permanent teeth to VRF. Based on the results of this study, it can be concluded that mixing MTA with CHX or PG as the vehicle do not alter VRF resistance of simulated immature permanent roots. Key words:Immature teeth, MTA, vehicle, vertical root fracture.

EFFICACY OF INCISAL PREPARATION DESIGNS ON THE FRACTURE RESISTANCE OF TWO CAD/CAM LAMINATE VENEERS

Statement of problem: Mechanical properties are cardinal for the long-term clinical success of laminate veneer restorations. The most common failure is fracture and debonding, in which unfavorable occlusion and articulation play an important role. Nonetheless, the effect of different incisal preparations on the behavior of veneers remains controversial.Objective: The purpose of this study was to evaluate the fracture load of two different CAD/CAM laminate veneer materials: resin nano-ceramic [lava ultimate] and lithium disilicate glass ceramic [IPS e-max CAD], with two different incisal preparation designs [butt-Joint and incisal overlap]; using both in-vitro and finite element analysis studies. Materials and Methods: A total of 20 maxillary central incisors were used in this study. The samples were divided into two main groups (n=10), according to the CAD/CAM material used. Ten laminate restorations were constructed for each group following the manufacturer’s directions with the two preparation designs (5 samples each), then cemented on their corresponding teeth. Fracture load was recorded for each specimen using the universal testing machine. Meanwhile, Finite element analysis study was performed to assess the in-vitro observations. Results: The results revealed that incisal overlap design with Lava ultimate laminate veneers recorded the highest mean fracture strength value (395 ±37.18 N). This was supported by the finite element results that showed that the incisal overlap design with lava ultimate laminate veneers had the lowest Von Mises stress (30.75 MPa). Conclusions: Within the limitations of the present study, it was concluded that the butt-joint and incisal overlap designs demonstrated different mechanical behaviors with regard to the two different restorative materials. The incisal overlap design tolerated stresses better than the butt-joint design with both materials. Also, the incisal overlap design with resin nano-ceramic laminate veneers had the best stress distribution. Nevertheless, both types of CAD/CAM materials and different incisal preparation designs used could be considered strong enough to withstand the average anterior masticatory biting forces.

DEĞİŞİK YÖNTEMLERLE HAZIRLANAN METAL ALT YAPILAR ÜZERİNDEKİ VENEER PORSELENLERİNİN KIRILMA DİRENCİNE FARKLI ALT YAPI ŞEKİLLERİNİN ETKİSİNİN İNCELENMESİ≠

Amaç: Bu çalışmada, değişik yöntemlerle hazırlanan metal alt yapılar üzerindeki veneer porselenlerinin kırılma direnci üzerine farklı alt yapı şekillerinin etkisi incelenmiştir. Materyal ve Metod: Chamfer bitim hatlı olarak kesilmiş üst 1. küçük azı dişini temsil eden metal güdükler anatomik oklüzal yüzeyli ve düz oklüzal yüzeyli olarak iki değişik şekilde CNC torna tezgahında hazırlanmış, alınan ölçülerden 30 adet epoksi rezin güdük elde edilmiştir. Farklı yöntemlerle elde edilen metal alt yapılar üzerine üst yapı porseleni uygulanarak kuronlar hazırlanmıştır. Epoksi rezin güdükler kuronlar üzerine simante edilmiş ve veneer porselenlerinin kırılma dirençleri Universal test cihazında değerlendirilmiştir. Bulgular: Kırılma direnci değerleri üzerine a lt yapı şekli ve hazırlama yöntemlerinin etkisinin anlamlı olduğu varyans analizi ile saptanmıştır (p<0.05). Sonuç: Çalışmada a natomik alt yapılar üzerinde freze tekniğiyle hazırlanan veneer seramiklerinde en yüksek kırılma direnci değerleri tespit edilmiştir. Anahtar Kelimeler: Metal alt yapılar, alt yapı şekli, kırılma direnci. AN ANALYSIS OVER THE EFFECT OF COPING DESIGN ON THE FRACTURE RESISTANCE OF VENEER PORCELAINS APPLIED ON METAL FRAMEWORKS PREPARED THROUGH VARIOUS METHODS ABSTRACT Aim: In this study, the effect of different metal framework methods and coping design on the fracture resistance of veneer porcelains. Materials and Methods: Two different metal dies having anatomic and smooth occlusal surface designs were manufactured using CNC machine to simulate prepared upper first premolar tooth with chamfer finish line, impressions were taken and 30 epoxy resin dies were produced subsequently. Veneering ceramics were applied on metal frameworks which were produced by different methods and crowns were finished. Crowns were cemented on to the epoxy resin dies and fracture strength of veneering ceramics were evaluated using Universal Testing Machine. Results: Variance analyses demonstrated that framework design and manufacturing methods had a significant effect on fracture strength of tested specimens (p<0.05). Conclusion: In this study, veneering ceramics which were applied on anatomically shaped milled frame- works showed the highest fracture strength values. Key Words: Metal frameworks, coping design, fracture resistance

Fracture Resistance of Straight and Angulated Zirconia Implant Abutments Supporting Anterior Three-Unit Lithium Disilicate Fixed Dental Prostheses.

The purpose of this study was to evaluate fracture resistance of straight and angulated zirconia implant abutments supporting anterior three-unit lithium disilicate fixed dental prostheses (FDPs). Four different test groups (n = 8) representing anterior three-unit implant-supported all-ceramic FDPs were fabricated to fit an in vitro model with two implants. Groups 1 and 2 simulated a clinical situation with an ideal implant position for maxillary left central and right lateral incisors from a prosthetic point of view, which allowed for the use of a straight, prefabricated zirconia and titanium abutment. Groups 3 and 4 simulated a situation with a compromised implant position that required an angulated (15-degree) abutment. Tapered internal-connection implants (Direct's Legacy, 13-mm length, 3.7-mm diameter, Implant Direct) mounted in epoxy resin models were used in this study. Lithium disilicate (IPS e.max press, Ivoclar Vivadent) three-unit FDPs were fabricated and cemented using self-adhesive resin cement. The samples were subjected to thermocycling (2 × 3,000 × 5°C/55°C) and mechanical loading (TCML; 50 N × 600,000 cycles). Fracture resistances were determined for all the samples that survived aging. Kruskal-Wallis analysis of variance and Mann-Whitney U tests were performed to test for differences in fracture strength values at a 5% significance level. All samples subjected to TCML survived without mechanical failure. The highest fracture loads were associated with FDPs supported by implants with 0-degree abutment angulations compared with those FDPs supported by 15-degree abutment angulations (group 1: 538.7 ± 24.77 N; group 2: 542.17 ± 21.64 N; group 3: 523.57 ± 19.71 N; group 4: 528.37 ± 24.57 N). This difference in load-bearing capacity was not statistically significant (P > .05). The use of angulated zirconia abutments for compensation of nonideal implant locations is possible without reducing the load-bearing capacity of implant-supported anterior three-unit lithium disilicate FDPs.

Fracture Strength of Weakened Anterior Teeth Associated to Different Reconstructive Techniques.

This study evaluated the fracture strength of endodontically treated teeth submitted to reconstructive techniques through dynamic and static tests. Forty human anterior teeth were divided into 4 groups (n=10): GNW (non-weakened) - root restored with glass fiber post (GFP), GW - weakened root restored with GFP, GDA - weakened root restored with direct anatomic GFP, and GIA - weakened root restored with indirect anatomic GFP. The teeth were endodontically treated considering that experimental groups (GW, GDA and GIA) simulated weakened roots for restoration with GFP using different techniques. The GFP was luted with resin cement and the coronal portion was restored with composite resin and metallic crowns. All samples were submitted to chewing simulation at 60 cycles/min in a total of 300,000 cycles. The survival samples were further exposed to compressive loading at a crosshead speed of 1.0 mm/min in a universal testing machine. The load was applied at 135° to the long axis of the tooth until failure. Data were analyzed by ANOVA (a=0.05). After chewing simulation were observed: GNW: 100% of survival roots; GW: 70% of survival roots, and GDA and GIA: 80% of survival roots. The mean fracture strength values (N) were 280.6 (GNW), 239.0 (GW), 221.3 (GDA), and 234.1 (GIA) without significant difference among the groups (p=0.7476). The results suggested similar fracture strength in both weakened and non-weakened teeth regardless the reconstructive technique of root internal wall. Higher incidence of catastrophic fracture was observed in weakened teeth without restoration of the root internal wall.

Fracture Strength of Monolithic All-Ceramic Crowns on Titanium Implant Abutments.

The fracture strengths of all-ceramic crowns cemented on titanium implant abutments may vary depending on crown materials and luting agents. The purpose of this study was to examine differences in fracture strength among crowns cemented on implant abutments using crowns made of seven different monolithic ceramic materials and five different luting agents. In total, 525 crowns (75 each of Vita Mark II, feldspathic ceramic [FSC]; Ivoclar Empress CAD, leucite-reinforced glass ceramic [LrGC]; Ivoclar e.max CAD, lithium disilicate [LiDS]; Vita Suprinity, presintered zirconia-reinforced lithium silicate ceramic [PSZirLS]; Vita Enamic, polymer-reinforced fine-structure feldspathic ceramic [PolyFSP], Lava Ultimate; resin nanoceramic [ResNC], Celtra Duo; fully crystallized zirconia-reinforced lithium silicate [FcZirLS]) were milled using a CAD/CAM system. The inner surfaces of the crowns were etched and silanized. Titanium implant abutments were fixed on implant analogs, and airborne-particle abrasion was used on their exterior specific adhesion surfaces (Al2O3, 50 μm). Then, the abutments were degreased and silanized. The crowns were cemented on the implant abutments using five luting agents (Multilink Implant, Variolink II, RelyX Unicem, GC FujiCEM, Panavia 2.0). After thermocycling for 5,000 cycles (5 to 55°C, 30 seconds dwell time), the crowns were subjected to fracture strength testing under static load using a universal testing machine. Statistical analyses were performed using analysis of variance (α = .0002) and the Bonferroni correction. No significant difference among the luting agents was found using the different all-ceramic materials. Ceramic materials LiDS, PSZirLS, PolyFSP, and ResNC showed significantly higher fracture strength values compared with FSC, FcZirLS, and LrGC. The PSZirLS especially showed significantly better results. Within the limitations of this study, fracture strength was not differentially affected by the various luting agents. However, the fracture strength was significantly higher for PSZirLS, PolyFSP, ResNC, and LiDS ceramics than for the FSP, LrGC, and the FcZirLS ceramic with all luting agents tested.

Fracture Forces of Dentin after Surface Treatment with High Speed Drill Compared to Er:YAG and Er,Cr:YSGG Laser Irradiation

Dental tooth restorative procedures may weaken the structural integrity of the tooth, with the possibility of leading to fracture. In this study we present findings of coronal dentin strength after different techniques of surface modification. The fracture strength of dentin beams after superficial material removal with a fine diamond bur high speed drill hand piece, Er:YAG (2.94 μm, 8 J/cm2), and Er,Cr:YSGG (2.78 μm, 7.8 J/cm2) laser irradiation slightly above the ablation threshold was measured by a four-point bending apparatus. Untreated dentin beams served as a control. A total of 58 dentin beams were manufactured from sterilized human extracted molars using the coronal part of the available dentin. Mean values of fracture strength were calculated as 82.0 ± 27.3 MPa for the control group (n = 10), 104.5 ± 26.3 MPa for high speed drill treatment (n = 10), 96.1 ± 28.1 MPa for Er,Cr:YSGG laser irradiation (n = 20), and 89.1 ± 36.3 MPa for Er:YAG laser irradiation (n = 18). Independent Student's t-tests showed no significant difference between each two groups (p > 0.05). Within the parameter settings and the limits of the experimental setup used in this study, both lasers systems as well as the high speed drill do not significantly weaken coronal dentin after surface treatment.