Fatigue behavior and damage modes of high performance poly-ether-ketone-ketone PEKK bilayered crowns.

OBJECTIVES: To evaluate and compare the fatigue behavior (fatigue limit and fatigue life) and damage modes of high-performance poly-ether-ketone-ketone (PEKK), zirconia and alloy bilayered crowns. MATERIALS AND METHODS: A total of 110 crowns (n = 50 for fatigue limit and n = 60 for fatigue life) were fabricated and used in this study. Pekkton® ivory discs, yttrium stabilized zirconia blanks and NiCr casting alloy were used to produce the respective PEKK, zirconia and alloy copings for crown fabrication. The prepared crowns were veneered with composite resin and subjected to fatigue tests. The fatigue limit was evaluated using the staircase method and the fatigue life of the samples was evaluated by subjecting the crowns to a load lower than the fatigue limit of that particular group, and also with an intermediate load of 522 N. A graphical plot was generated from the shape parameter (ß) and life parameter (α) values obtained through the Weibull analysis method. Kruskal-Wallis and Mann-Whitney tests were applied to determine the significance differences in the recorded fracture mode between the study groups. The damage modes of the samples were assessed using Burke's classification. RESULTS: The recorded fatigue limits of the groups were 442.8 ± 42.1 N, 608.7 ± 7.6 N, and 790.4 ± 29.2 N for zirconia, NiCr and PEKK, respectively. A significant difference in the fatigue limit of the groups was observed (p < 0.05). PEKK samples demonstrated the highest survival cycles of 1,170,000 and the lowest survival cycles was observed with zirconia samples at 100,000 under 522 N loading. The fracture modes in PEKK samples were largely distributed between code 1 and 2 whereas the fracture modes in NiCr group was distributed between code 1 and 4 and YZ crowns exhibited more of code 5 fractures. The difference in fracture modes among the groups was statistically significant (p < 0.05). CONCLUSION: The PEKK group demonstrated better results compared to zirconia and NiCr based crowns. The PEKK group demonstrated high fatigue limit and survived the highest fatigue life cycles among the tested groups.

Effect of repeated laser surface treatments on shear bond strength between zirconia and veneering ceramic.

STATEMENT OF PROBLEM: Delamination failure may occur between ceramic frameworks and veneering ceramics, shortening the lifetime of fixed dental prostheses in load-bearing areas. PURPOSE: The purpose of this in vitro study was to compare the effect of different repeating CO2 laser treatment methods and conventional approaches on the shear bond strength of zirconia frameworks and veneering ceramics. MATERIAL AND METHODS: Zirconia disks (N=110) were prepared and divided into 5 groups: milling without surface treatment (group M), airborne-particle abrasion (group APA), single laser treatment (group LX1), 2 laser treatments (group LX2), and 3 laser treatments (group LX3). The specimens in the first 2 groups were treated before the framework was coated using the spraying technique. Specimens in the remaining groups were coated with veneering ceramic using the spraying process, and then subjected to laser treatment. Surface roughness and topography, interface properties, phase transformation, shear bond strength, and fracture modes were investigated. Outcomes were analyzed using a profilometer, a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD), a stereomicroscope, and a universal testing machine for mechanical testing. RESULTS: The XRD showed that phase transformation from tetragonal to monoclinic occurred after airborne-particle abrasion. This phenomenon was not observed in laser-treated specimens. Groups LX2 and LX3 had the highest surface roughness values, 1.18 ±0.23 µm and 1.21 ±0.22 µm, among all groups, and group LX3 had the highest shear bond strength values for unaged and aged conditions, 32.08 ±2.45 MPa and 31.43 ±2.07 MPa. The mixed-fracture mode was the most common type of fracture observed. CONCLUSIONS: The results indicated that the shear bond strength between the zirconia framework and veneering ceramic was higher after laser surface treatments than after milling alone or after airborne-particle abrasion. Laser treatment methods, particularly LX2 and LX3, could be considered reliable approaches for zirconia surface treatment.

Effects of different surface treatments on the shear bond strength of veneering ceramic materials to zirconia.

PURPOSE: To evaluate and compare the effect of different materials and techniques on the shear bond strength of veneering ceramic materials to zirconia. MATERIALS AND METHODS: 136 sintered zirconia cubes were prepared and randomly divided into four study groups according to corresponding methods of surface treatment and materials: GLN (grinding followed by laser scanning using Noritake Cerabien ZR), SLN (sandblasting followed by laser scanning using Noritake Cerabien ZR), GLV (grinding followed by laser scanning using VITA VM 9), and SLV (sandblasting followed by laser scanning using VITA VM 9). Spraying technique was performed to coat the core. Profilometer, SEM, XRD, EDS, universal testing machine, and stereomicroscope were used to record surface roughness Ra, surface morphology, phase transformation, elemental compositions, shear bond strength SBS values, and failure types, respectively. Specimens were investigated in unaged (not immersed in artificial saliva) and aged (stored in artificial saliva for a month) conditions to evaluate SBS values. RESULTS: Grinding and GLN as first and second surface treatments provided satisfactory Ra values in both conditions (1.05 ± 0.24 µm, 1.30 ± 0.21 µm) compared to sandblasting and other groups (P<.05). The group GLN showed the highest SBS values in both conditions (30.97 ± 3.12 MPa, 29.09 ± 4.17 MPa), while group SLV recorded the lowest (23.96 ± 3.60 MPa, 22.95 ± 3.68 Mpa) (P<.05). Sandblasting showed phase transformation from t-m. Mixed failure type was the commonest among all groups. CONCLUSION: GLN showed to be a reliable method which provided satisfactory bond strength between the veneer ceramic and zirconia. This method might preserve the integrity of fixed dental crowns.

The impact of laser scanning on zirconia coating and shear bond strength using veneer ceramic material.

Laser scanning is one of the methods that can be used for surface treatments of zirconia. Application of the laser to the surface of zirconia has diverse effects, depending on the type of laser. A carbon dioxide (CO2) laser has high irradiation power and can alter the surface properties. This study investigated the surface coating of zirconia as a core material that subsequently coated with a veneering ceramic (v-c) material. This study compared laser scanning and conventional sintering processes. Various properties including surface topography, interface evaluation, phase transformation, elemental compositions, failure mode patterns, and contact angle were examined through X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. Results were confirmed that the bond strength between the v-c and the substrate recorded through laser scanning was higher than that determined through conventional sintering.

Comparing the optical and mechanical properties of PEKK polymer when CAD/CAM milled and pressed using a ceramic pressing furnace.

The aim was to optimise the hot pressing parameters for processing PEKK polymer using a standard ceramic pressing furnace and compare the optical and mechanical properties of pressed samples to PEKK samples produced via CAD/CAM milling. The samples were compared using a spectrophotometer to determine the CIE L*a*b* colour values and ΔE colour difference. A universal testing machine was used for biaxial flexural strength testing and Vickers Hardness machine for measuring the hardness. It was concluded that hot pressed and milled PEKK samples showed no significant difference in the colour values, biaxial flexural strength or hardness.

Comparison between direct chairside and digitally fabricated temporary crowns.

The mechanical properties of temporary crowns are considered to be crucial in order to achieve successful definite restorations. This study compared marginal fit, internal fit, fracture strength and mode of fracture of CAD/CAM temporary crowns to direct chairside counterparts. An upper left first premolar Frasaco tooth was prepared for all-ceramic crown. The materials used for comparison were VITA CAD-Temp®, ArtBloc®Temp, PMMA DISK and Acrytemp (control group). The crowns were divided into four groups (n=10). Each crown was investigated for the above parameters. Statistical analysis was performed using SPSS v.20. The average marginal gap, internal gap and fracture strength showed statistically significant difference between groups (p<0.01). The fracture mode showed statistically non-significant difference (p>0.05) among experimental groups. The CAD/CAM temporary crowns demonstrated superior mechanical properties compared to direct handmade counterparts.

Characterisation of machinable structural polymers in restorative dentistry.

OBJECTIVES: To characterise the mechanical properties of the machinable polymers Pekkton® (Cendres-Meteaux, Biel/Bienne, Switzerland), Lava Ultimate® (3MESPE, Seefeld, Germany), Vita Enamic® (Ivoclar Vivadent, Schaan, Liechtenstein) and the ceramic IPS e.Max Press® (Ivoclar Vivadent, Schaan, Liechtenstein). To determine the structural integrity of full coverage crowns fabricated from these materials. METHODS: The following tests were conducted: Biaxial flexural strength (BFS) using the piston on 3 balls jig (n=10); Vickers Hardness (VH) 10 indentations per sample with 10kg load & 20s dwell time (n=5); Hygroscopic Expansion Change (HEC) in artificial saliva over 68 days (n=5). Structural Strength (SS) of teeth analogues (n=20) restored with monolithic crowns from the four materials. Mean values and standard deviations for BFS, VH, HEC and SS tests were calculated and compared using one-way ANOVA with post-hoc Tukey's test at a level of 5% significance. RESULTS: BFS: IPS e.Max Press® (317MPa±37MPa), Pekkton® (227MPa±18MPa), Lava Ultimate® (145MPa±18MPa) and Vita Enamic® (137MPa±7MPa) with a significance between groups of p<0.0001. VH: IPS e.Max Press® (5064MPa±131MPa), Vita Enamic® (1976MPa±12MPa), Lava Ultimate® (924MPa±27MPa) and Pekkton® (445MPa±21MPa) with a significance between groups of p<0.0001. HEC (%vol change): Pekkton® (0.14%±0.14%), Vita Enamic® (0.38%±0.16%) and Lava Ultimate® (1.06%±0.17%). SS for full-coverage crowns: Pekkton® (2037N±49N no fracture), IPS e.Max Press® (1497N±165N), Lava Ultimate® (1476N±142N) and Vita Enamic® (1127N±108N). SIGNIFICANCE: The properties investigated suggest that full coverage monolithic PEKK crowns possess adequate mechanical and physical properties for use in the posterior region of the mouth. These results must be considered alongside other data including clinical studies.

Fracture resistance of zirconia-composite veneered crowns in comparison with zirconia-porcelain crowns.

The objectives were to evaluate the fracture resistance and stress concentration in zirconia/composite veneered crowns in comparison to zirconia/porcelain crowns using occlusal fracture resistance and by stress analysis using finite element analysis method. Zirconia substructures were divided into two groups based on the veneering material. A static load was applied occlusally using a ball indenter and the load to fracture was recorded in Newtons (N). The same crown design was used to create 3D crown models and evaluated using FEA. The zirconia/composite crowns subjected to static occlusal load showed comparable results to the zirconia/porcelain crowns. Zirconia/composite crowns showed higher stress on the zirconia substructure at 63.6 and 50.9 MPa on the zirconia substructure veneered with porcelain. In conclusion, zirconia/composite crowns withstood high occlusal loads similar to zirconia/porcelain crowns with no significant difference. However, the zirconia/composite crowns showed higher stress values than the zirconia/porcelain crowns at the zirconia substructure.

Comparative in vitro evaluation of CAD/CAM vs conventional provisional crowns.

OBJECTIVE: This study compared the marginal gap, internal fit, fracture strength, and mode of fracture of CAD/CAM provisional crowns with that of direct provisional crowns. MATERIAL AND METHODS: An upper right first premolar phantom tooth was prepared for full ceramic crown following tooth preparation guidelines. The materials tested were: VITA CAD-Temp®, Polyetheretherketone "PEEK", Telio CAD-Temp, and Protemp™4 (control group). The crowns were divided into four groups (n=10), Group1: VITA CAD-Temp®, Group 2: PEEK, Group 3: Telio CAD-Temp, and Group 4: Protemp™4. Each crown was investigated for marginal and internal fit, fracture strength, and mode of fracture. Statistical analysis was performed using GraphPad Prism software version 6.0. RESULTS: The average marginal gap was: VITA CAD-Temp® 60.61 (±9.99) µm, PEEK 46.75 (±8.26) µm, Telio CAD-Temp 56.10 (±5.65) µm, and Protemp™4 193.07(±35.96) µm (P<0.001). The average internal fit was: VITA CAD-Temp® 124.94 (±22.96) µm, PEEK 113.14 (±23.55) µm, Telio CAD-Temp 110.95 (±11.64) µm, and Protemp™4 143.48(±26.74) µm. The average fracture strength was: VITA CAD-Temp® 361.01 (±21.61) N, PEEK 802.23 (±111.29) N, Telio CAD-Temp 719.24 (±95.17) N, and Protemp™4 416.40 (±69.14) N. One-way ANOVA test showed a statistically significant difference for marginal gap, internal gap, and fracture strength between all groups (p<0.001). However, the mode of fracture showed no differences between the groups (p>0.05). CONCLUSIONS: CAD/CAM fabricated provisional crowns demonstrated superior fit and better strength than direct provisional crowns.

Comparative in vitro evaluation of CAD/CAM vs conventional provisional crowns

ABSTRACT Objective This study compared the marginal gap, internal fit, fracture strength, and mode of fracture of CAD/CAM provisional crowns with that of direct provisional crowns. Material and Methods An upper right first premolar phantom tooth was prepared for full ceramic crown following tooth preparation guidelines. The materials tested were: VITA CAD-Temp®, Polyetheretherketone “PEEK”, Telio CAD-Temp, and Protemp™4 (control group). The crowns were divided into four groups (n=10), Group1: VITA CAD-Temp®, Group 2: PEEK, Group 3: Telio CAD-Temp, and Group 4: Protemp™4. Each crown was investigated for marginal and internal fit, fracture strength, and mode of fracture. Statistical analysis was performed using GraphPad Prism software version 6.0. Results The average marginal gap was: VITA CAD-Temp® 60.61 (±9.99) µm, PEEK 46.75 (±8.26) µm, Telio CAD-Temp 56.10 (±5.65) µm, and Protemp™4 193.07(±35.96) µm (P<0.001). The average internal fit was: VITA CAD-Temp® 124.94 (±22.96) µm, PEEK 113.14 (±23.55) µm, Telio CAD-Temp 110.95 (±11.64) µm, and Protemp™4 143.48(±26.74) µm. The average fracture strength was: VITA CAD-Temp® 361.01 (±21.61) N, PEEK 802.23 (±111.29) N, Telio CAD-Temp 719.24 (±95.17) N, and Protemp™4 416.40 (±69.14) N. One-way ANOVA test showed a statistically significant difference for marginal gap, internal gap, and fracture strength between all groups (p<0.001). However, the mode of fracture showed no differences between the groups (p>0.05). Conclusions CAD/CAM fabricated provisional crowns demonstrated superior fit and better strength than direct provisional crowns.

Factors controlling crystallization of miserite glass-ceramic.

OBJECTIVE: The purpose of this study was to investigate a range of variables affecting the synthesis of a miserite glass-ceramic (GC). METHODS: Miserite glass was synthesized by the melt quench technique. The crystallization kinetics of the glass were determined using Differential Thermal Analysis (DTA). The glasses were ground with dry ball-milling and then sieved to different particle sizes prior to sintering. These particle sizes were submitted to heat treatment regimes in a high temperature furnace to form the GC. The crystal phases of the GC were analyzed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to examine the microstructure of the cerammed glass. RESULTS: XRD analysis confirmed that the predominant crystalline phase of the GC was miserite along with a minor crystalline phase of cristobalite only when the particle size is <20 µm and the heat treatment at 1000°C was carried out for 4h and slowly cooled at the furnace rate. For larger particle sizes and faster cooling rates, a pseudowollastonite crystalline phase was produced. Short sintering times produced either a pseudowollastonite or xonotolite crystalline phase. SIGNIFICANCE: The current study has shown that particle size and heat treatment schedules are major factors in controlling the synthesis of miserite GC.

Evaluation of a novel multiple phase veneering ceramic.

OBJECTIVES: To produce a new veneering ceramic based on the production of a multiple phase glass-ceramic with improved performance in terms of strength and toughness. METHODS: A composition of 60% leucite, 20% diopside and 20% feldspathic glass was prepared, blended and a heat treatment schedule of 930°C for 5 min was derived from differential thermal analysis (DTA) of the glasses. X-ray diffraction (XRD) and SEM analysis determined the crystalline phases and microstructure. Chemical solubility, biaxial flexural strength (BFS), fracture toughness, hardness, total transmittance and coefficient of thermal expansion (CTE) were all measured in comparison to a commercial veneering ceramic (VITA VM9). Thermal shock resistance of the leucite-diopside and VITA VM9 veneered onto a commercial high strength zirconia (Vita In-Ceram YZ) was also assessed. Statistical analysis was undertaken using Independent Samples t-test. Weibull analysis was employed to examine the reliability of the strength data. RESULTS: The mean chemical solubility was 6 µg/cm(2) for both ceramics (P=1.00). The mean BFS was 109 ± 8 MPa for leucite-diopside ceramic and 79 ± 11 MPa for VITA VM9 ceramic (P=0.01). Similarly, the leucite-diopside ceramic demonstrated a significantly higher fracture toughness and hardness. The average total transmittance was 46.3% for leucite-diopside ceramic and 39.8% for VITA VM9 (P=0.01). The leucite-diopside outperformed the VITA VM9 in terms of thermal shock resistance. Significance This novel veneering ceramic exhibits significant improvements in terms of mechanical properties, yet retains a high translucency and is the most appropriate choice as a veneering ceramic for a zirconia base core material.

Fracture strength of minimally prepared all-ceramic CEREC crowns after simulating 5 years of service.

OBJECTIVES: To examine the strength and mode of fracture of traditionally and minimally prepared all-ceramic resin bonded CAD/CAM crowns after fatigue loading. METHODS: Thirty human maxillary molars were used and divided in three groups namely; traditional crown preparation group (I), minimal crown preparation group (II) and occlusal veneer preparation group (III). A leucite reinforced glass ceramic (IPS Empress CAD) was used for fabricating the crowns. The CEREC InEOS system (v3.10) was used for scanning, designing and milling. Five years of clinical service were simulated and the fracture strength of the crowns was measured. One-way ANOVA and Kruskal-Wallis test were used for data analysis (α=0.05). RESULTS: The mean fracture strength and SD in Group I was 1070N (±181) and in Group II 1110N (±222). One-way ANOVA analysis showed no statistically significant difference between the two groups (p>0.05). In Group III all restorations developed cracks during TCML and were not subjected to fracture loading. Three of the traditionally designed crowns (Group I) and 4 of the minimally designed crowns (Group II) developed surface cracks during TCML. SIGNIFICANCE: Minimal all-ceramic resin-bonded crowns can potentially form a viable restorative option as they demonstrated comparable strength to traditional all-ceramic crowns. However, this should be interpreted with caution as a number of crowns showed cracks after 5 years of simulated service. All the occlusal veneers developed cracks during simulation and further investigation is needed for this to be considered a viable option.

Manufacture, characterisation and properties of novel fluorcanasite glass-ceramics.

OBJECTIVE: The aim of this study was to investigate the manufacture and characterisation of different compositions of fluorcanasite glass-ceramics with reduced fluorine content and to assess their mechanical and physical properties. METHODS: Three compositional variations (S80, S81 and S82) of a fluorcanasite glass were investigated. Differential thermal analysis (DTA) and X-ray diffraction (XRD) identified crystallisation temperatures and phases. X-ray fluorescence (XRF) determined the element composition in the glass-ceramics. Different heat treatments [2 h nucleation and either 2 or 4 h crystallisation] were used for the glasses. Scanning electron microscopy (SEM) examined the microstructure of the cerammed glass. The chemical solubility, biaxial flexural strength, fracture toughness, hardness and brittleness index of S81 and S82 fluorcanasite were investigated with lithium disilicate (e.max CAD, Ivoclar Vivadent) as a commercial comparison. Statistical analysis was performed using one-way ANOVA with Tukey's multiple comparison tests (P<0.05). Weibull analysis was employed to examine the reliability of the strength data. RESULTS: All compositions successfully produced glasses. XRD analysis confirmed fluorcanasite formation with the S81 and S82 compositions, with the S82 (2+2h) showing the most prominent crystal structure. The chemical solubility of the glass-ceramics was significantly different, varying from 2565 ± 507 µg/cm(2) for the S81 (2+2 h) to 722 ± 177 µg/cm(2) for the S82 (2+2 h) to 37.4 ± 25.2 µg/cm(2) for the lithium disilicate. BFS values were highest for the S82 (2+2 h) composition (250 ± 26 MPa) and lithium disilicate (266 ± 37 MPa) glass-ceramics. The fracture toughness was higher for the S82 compositions, with the S82 (2+2h) attaining the highest value of 4.2 ± 0.3 MPa m(1/2)(P=0.01). The S82 (2+2 h) fluorcanasite glass-ceramic had the lowest brittleness index. CONCLUSION: The S82 (2+2 h) fluorcanasite glass-ceramic has acceptable chemical solubility, high biaxial flexural strength, fracture toughness and hardness. CLINICAL SIGNIFICANCE: A novel glass-ceramic has been developed with potential as a restorative material. The S82 (2+2 h) has mechanical and physical properties that would allow the glass-ceramic to be used as a machinable core material for veneered resin-bonded ceramic restorations.

Novel glass-ceramics for dental restorations.

BACKGROUND: There are many different ceramic systems available on the market for dental restorations. Glass-ceramics are a popular choice due to their excellent esthetics and ability to bond to tooth structure allowing a more conservative approach. However, at present, these materials have insufficient strength to be used reliably in posterior regions of the mouth. PURPOSE: The aim of this review article is to discuss the types of novel glass-ceramic currently be investigated including composition, microstructure and properties. CONCLUSION: Current research in glass-ceramics focuses on the quest for a highly esthetic material along with sufficient strength to enable crowns and bridgework to be reliably placed in these areas. CLINICAL SIGNIFICANCE: There is a gap in the market for a machinable resin bonded glass-ceramic with sufficient strength as well as excellent esthetics.

Microleakage in class II restorations: open vs closed centripetal build-up technique.

PURPOSE: This study evaluated whether a Class II restoration in a flowable resin composite has to be placed prior to (open-sandwich technique) or after (closed-sandwich technique) construction of the interproximal wall in the centripetal build-up technique in order to reduce microleakage. METHODS AND MATERIALS: Thirty non-carious molars were selected and randomly divided into two groups (n = 15). A standardized Class H preparation was made with the cervical margin 1 mm below the cementum-enamel junction. In Group 1, flowable resin composite was applied as a 1 mm base, remaining exposed at the cervical margin. In Group 2, the hybrid resin composite was applied to the interproximal wall, followed by a layer of flowable composite on the pulpal floor, away from the margins. The restorations were then subjected to 500 thermal cycles, each with a dwell time of 20 seconds at 5 degrees C and 55 degrees C. Adaptation at the cervical margin was evaluated by dye penetration and SEM analysis using the replica technique. The data were statistically analyzed using the Mann-Whitney U-test (p < 0.05). RESULTS: The centripetal open-sandwich technique led to significantly lower dye penetration than the centripetal closed-sandwich technique (p < 0.001). CONCLUSION: Flowable resin composite placed under hybrid resin composites in Group 1 provided better marginal adaptation and fewer voids. However, neither Group 1 nor Group 2 was able to completely prevent microleakage.

Microtensile bond strength of a resin cement to a novel fluorcanasite glass-ceramic following different surface treatments.

OBJECTIVES: This study evaluated the effect of surface treatments on the bond strength of fluorcanasite and lithium disilicate glass-ceramics, with the possibility of eliminating HF etching of these ceramics. METHODS: Fifteen blocks of an experimental fluorcanasite and a lithium disilicate glass-ceramic (IPS e.max CAD) were assigned to one of the following three surface treatments: (1) machined with 60 microm finish, (2) machined and grit blasted, (3) machined and HF etched. The ceramic blocks were duplicated in composite resin (Spectrum) and cemented together with a resin luting agent (Variolink II). Thirty microbars per group (1.0 x 1.0 x 20 mm) were obtained and subjected to a tensile force at a crosshead speed of 0.5 mm/min using a universal testing machine until failure. The mode of failure was determined using scanning electron microscopy. The appropriate bonding procedure was assessed for durability by storing in water at 100 degrees C for 24 h. Statistical analyses were performed with ANOVA and Tukey's test (P<0.05). RESULTS: Machining alone significantly increased the bond strength (MPa) of the fluorcanasite (27.79+/-6.94) compared to the lithium disilicate (13.57+/-4.52) (P<0.05). HF etching resulted in the lowest bond strength (8.79+/-2.06) for the fluorcanasite but the highest for the lithium disilicate (24.76+/-9.38). Regarding durability, the machined fluorcanasite (15.24+/-5.46) demonstrated significantly higher bond strength than the machined and HF etched lithium disilicate (12.28+/-3.30). SIGNIFICANCE: The fitting surface of the fluorcanasite glass-ceramic should retain the machined finish and be directly treated with silane. The use of HF acid is contraindicated.

The effect of different surface treatments on bond strength between leucite reinforced feldspathic ceramic and composite resin.

OBJECTIVES: The aim of this study was to evaluate the effect of different surface treatments on the microtensile bond strength between a leucite reinforced glass-ceramic and composite resin. METHODS: Leucite reinforced ceramic blocks (n=24) were constructed using the hot pressing technique. The blocks were assigned to 4 groups, which received the following surface treatments: G1: hydrofluoric (HF) acid and silane; G2: silane alone; G3: HF acid and silane then dried with warm air (100 degrees C); G4: silane alone then dried with warm air (100 degrees C). Unfilled resin was applied, followed by composite resin. Specimens were prepared and loaded in tension to determine the microtensile bond strength. Failure modes were classified by stereo- and scanning electron microscopy (SEM). Data was analysed using Kruskal-Wallis test followed by the Dunn's multiple range test. RESULTS: The groups including the warm air step (G3 and G4) achieved a significantly stronger adhesion than G1 and G2. Pre-treatment of the surface with hydrofluoric acid in G1 resulted in significantly higher bond strength than G2. Failures were mostly cohesive in the luting resin for G1, G3 and G4 and mainly adhesive at the ceramic-resin interface in G2. CONCLUSIONS: The method of application of silane to the ceramic surface can have a significant influence on the adhesion between the ceramic restoration and the resin cement. Enhancing the condensation reaction by drying the silane with a 100C warm air stream significantly improved the microtensile bond strength, possibly eliminating the need for the hydrofluoric acid etching step.

The influence of plastic light cure sheaths on the hardness of resin composite.

OBJECTIVE: This study investigated the influence of a disposable light cure sheath on both the surface hardness and hardness at varying thicknesses of resin composite. METHODS: A series of resin composite discs (Spectrum) were fabricated with varying depths up to 6 mm. The light curing units used were a standard halogen unit (Elipar Trilight) and an LED unit (Elipar Freelight 2). Recommended curing times from the manufacturer were followed. The disposable light-curing sheath (Cure Sleeve) was used with both light-curing units. Two additional groups without the sheath were employed as controls. Each specimen (n = 4) was subjected to hardness testing to evaluate hardness from 0 mm to 5 mm thick. A 200g load was applied for 10 seconds using a Vickers diamond indenter and six indentations were obtained from each specimen. Statistical analysis was performed using two-way ANOVA. RESULTS: The LED without a sheath achieved the highest surface hardness value (47.2 VHN +/- 5.5). There was no significant difference between the groups regarding surface hardness (p > 0.05). As the thicknesses of the resin composite increased, the hardness values decreased in all groups. The LED light curing unit, in combination with a sheath, demonstrated the lowest hardness values at a 5 mm thickness of resin composite (p < 0.05). CONCLUSION: All four different methods of light curing resulted in a significant reduction in hardness values with increasing resin composite thickness, which could compromise the mechanical properties of the resin composite. However, the use of the light cure sheaths still provided an acceptable depth of cure when used following the 2 mm increment rule. It was not until 3 mm that the use of the light cure sheaths compromised the hardness results. It is recommended that the curing depth should not exceed 2 mm, regardless of light curing method.

A clinical evaluation of a resin composite and a compomer in non-carious Class V lesions. A 3-year follow-up.

PURPOSE: To compare the clinical performance of a resin composite and a polyacid-modified resin composite (compomer) in non-carious cervical lesions using a one-step self-etch adhesive. METHODS: Thirty patients, each with two non-carious cervical lesions (60 restorations), received one composite (Pertac-II) restoration and one compomer (Hytac) restoration, both used in conjunction with a self-etch adhesive (Prompt L-Pop) and placed following the manufacturer's instructions. Evaluations were at baseline, 6, 12 and 36 months after placement for retention, margin adaptation, marginal discoloration, anatomic form, secondary caries and postoperative sensitivity. Statistical analysis with the Pearson Chi-square test was undertaken. RESULTS: Retention rates were 86.6% for composite and 86.7% for compomer at 36 months. 3.3% of composite and 6.7% of compomer restorations showed a deficiency in marginal adaptation. Both materials showed a slight marginal discoloration of 7.7%. More deterioration in anatomic form occurred with the compomer (11.5%) than the composite (3.8%). None of the restorations exhibited secondary caries or postoperative sensitivity problems. There was no significant difference in performance between the materials in any of the categories evaluated.