A Completely Digital Workflow for Nanoceramic Endocrowns: A 5-Year Prospective Study.

PURPOSE: To evaluate the success of monolithic endocrowns fabricated using a digital workflow. MATERIALS AND METHODS: Twenty-three patients requiring restoration of devitalized molars or premolars were included in the study. The preparation was scanned using an intraoral scanner (Cerec Bluecam, Dentsply Sirona), and a monolithic restoration was made from a nanoparticle resin-based hybrid composite (#10 Cerasmart [CS]; #10 Lava Ultimate [LU], 3M Espe) or a polymer-infiltrated ceramic (#10 Vita Enamic [VE]). At the time of placement and after 6 months, 1 year, and 5 years of function, radiographs were taken to evaluate the marginal integrity of the restorations, and clinical pictures were taken to assess the quality of the restoration using the USPHS criteria. RESULTS: After 5 years, the restorative success rate was 70.8%, the restorative survival rate was 87.5%, and the tooth survival was 91.6%. Four chippings (two LU, two CS), three fractures (three LU), and two debonding of the restorations (two CS) occurred. Also, two teeth were extracted after 5 years of follow-up (two VE) because of secondary caries and a root fracture. The USPHS ratings were high, except for color match, which was rated the lowest at all time intervals. CONCLUSION: Nanoceramic endocrowns made using a completely digital workflow have an acceptable survival rate after 5 years. However, the complication rate was high.

The effect of refractive index of fillers and polymer matrix on translucency and color matching of dental resin composite.

OBJECTIVE: When restorative resin composites absorb light from the surrounding tooth structures, it creates a color-match, which is known as 'a chameleon effect'. In this study, series of co-monomer mixtures were prepared with an increasing refraction index (RI) and mixed with glass fillers. The aim of this study was to optimize the mismatch of RI of resin/fillers to create the chameleon effect. MATERIALS AND METHODS: BisGMA/TEGDMA resins were prepared with seven different mix fractions from 20 to 80%. Two different series (A&B) of submicron (Ø 0.7 µm) silanized fillers (70 wt%) (A: Schott RI = 1.53, B: Esschem RI = 1.54) were mixed with resins (30 wt%). Disc-shaped specimens (1 mm thickness, Ø10 mm) for each composite combination (n = 3) were prepared and light cured for 20 s. Commercial resin composite (OmniChroma, Tokuyama Dental) was used as control. The translucency parameter (TP) was measured using a spectrophotometer. The color matching abilities of the experimental composites were visually analyzed. Data were statistically analyzed using ANOVA. RESULTS: The composition of resin and type of fillers had a statistically significant effect on TP values (p < .05). The highest TP values were achieved around 50%-50% fractions of Bis-GMA and TEGDMA for series A and around 60%-40% fraction of Bis-GMA and TEGDMA for series B. Data showed that a high or low fraction of BisGMA resulted in a low translucent composite. Experimental resin composite (80% Bis-GMA) from series A was behaving similarly to Omnichroma in reference to TP values and color matching. CONCLUSIONS: Including fillers with RI of 1.53 into BisGMA/TEGDMA resin with RI of 1.524 resulted in composite resin providing a good color match with surrounding structure 'chameleon effect'.

Characterization of restorative short-fiber reinforced dental composites.

The aim was to evaluate and compare certain physical properties including surface-wear of five commercial short fiber-reinforced composites (SFRCs; Alert, NovaPro-Flow, NovaPro-Fill, everX Flow and everX Posterior). The following properties were examined according to ISO: flexural strength, flexural modulus, fracture toughness, water sorption. Degree of conversion was determined by FTIR-spectrometry. A wear test was conducted with 15,000 chewing-cycles using a chewing-simulator. Polymerization shrinkage-stress was measured using tensilometer. SEM was used to evaluate the microstructure of SFRCs. everX Flow exhibited the highest fracture toughness (2.8 MPa m1/2) and the lowest wear depth (20.4 µm) values (p<0.05) among the SFRCs tested. NovaPro Fill (141.5 MPa) and everX Flow (147 MPa) presented the highest flexural strength values (p<0.05). everX Flow showed the highest shrinkage-stress value (5.3 MPa) while other SFRCs had comparable values. The use of SFRCs in dentistry can be advantageous, but special attention should be given to the selection of the materials.

Direct bilayered biomimetic composite restoration: The effect of a cusp-supporting short fiber-reinforced base design on the chewing fracture resistance and failure mode of molars with or without endodontic treatment.

The aim of this study was to assess the chewing fracture resistance of compromised molars restored with direct composite resin (CR) restorations, with and without a short-fiber reinforcing (short-FRC) base. Wide extension of MOD cavities with removed palatal cusps preparations were simulated on 48 extracted maxillary molars. Five groups (n = 12) were designed: 1. control (intact teeth), 2. non-endodontically treated and 3. endodontically treated teeth with direct CR restorations (GC-Posterior), and 4. non-endodontically treated and 5. endodontically treated teeth with direct biomimetic bilayered restorations. Groups 4 and 5 included an anatomically shaped short-FRC base (everX Posterior), covered with a 2 mm CR layer (GC-Posterior). Restorations were subjected to chewing in water (1.5 Hz), with load of 85 N. Specimens were loaded until fracture or to a maximum of 120 000 cycles. Restorations that survived the chewing cycle were submitted to static load test (post-chewing test). The data were statistically analyzed using two-way ANOVA (p = 0.05) and fracture types with the chi-square test (p = 0.05). Fractures were classified into reparable, possibly reparable or non-reparable. All specimens survived the chewing cycle. The chewing fracture resistance of the direct biomimetic restorations prepared on non-endodontically treated teeth (2889 N) was statistically significantly higher than the direct CR counterparts (1966 N) (p = 0.00015), which was not the case for the groups with endodontically treated teeth (p = 0.257). Inclusion of a short-FRC base also influenced the fracture type resulting in most reparable fractures (67-75% versus 25% for biomimetic and CR groups respectively) (p = 0.054). Anatomically shaped i.e. a cusp-supporting design made of short-FRC base (everX Posterior) improved the chewing fracture resistance and fracture manner of compromised molars regardless of whether they were endodontically treated or not.

Mechanical properties and fracture behavior of flowable fiber reinforced composite restorations.

OBJECTIVE: The aim was to evaluate the effect of short glass-fiber/filler particles proportion on fracture toughness (FT) and flexural strength (FS) of an experimental flowable fiber-reinforced composite (Exp-SFRC) with two methacrylate resin formulations. In addition, we wanted to investigate how the fracture-behavior of composite restorations affected by FT values of SFRC-substructure. METHODS: Exp-SFRC was prepared by mixing 50wt% of dimethacrylate based resin matrix (bisGMA or UDMA based) to 50wt% of various weight fractions of glass-fiber/particulate filler (0:50, 10:40, 20:30, 30:20, 40:10, 50:0wt%, respectively). FT and FS were determined for each experimental material following standards. Specimens (n=8) were dry stored (37°C for 2 days) before they were tested. Four groups of posterior composite crowns (n=6) composed of different Exp-SFRCs as substructure and surface layer of commercial particulate filler composite were fabricated. Crowns were statically loaded until fracture. Failure modes were visually examined. The results were statistically analysed using ANOVA followed by post hoc Tukey's test. RESULTS: ANOVA revealed that ratio of glass-fiber/particulate filler had significant effect (p<0.05) on tested mechanical properties of the Exp-SFRC with both monomer systems. Exp-SFRC (50wt%) had significantly higher FT (2.6MPam1/2) and FS (175.5MPa) (p<0.05) compared to non-reinforced material (1.3MPam1/2, 123MPa). Failure mode analysis of crown restorations revealed that FT value of the substructure directly influenced the failure mode. SIGNIFICANCE: This study shows that short glass-fibers can significantly reinforce flowable composite resin and the FT value of SFRC-substructure has prior importance, as it influences the crack arresting mechanism.

Mechanical and structural characterization of discontinuous fiber-reinforced dental resin composite.

OBJECTIVES: This study evaluated several fiber- and matrix related factors and investigated different mechanical properties of discontinuous i.e. short fiber-reinforced composite (SFRC) (everX Posterior, eXP). These were compared with three conventional composites, microfilled G-ænial Anterior (GA), nanofilled Supreme XTE (SXTE) and bulk-fill Filtek Bulk-Fill (FBF). METHODS: Fracture toughness (KIC), flexural strength (FS), flexural modulus (FM), compressive strength (CS), diametral tensile strength (DTS), apparent horizontal shear strength (AHSS) and fracture work (Wf) were determined for each composite (n=8) stored dry or in water. SEM analysis of the fiber diameter (df) (n=6) and orientation (n=6) were performed. The theoretical critical fiber length (lfc) and the aspect ratio (l/d) of SFRC were calculated and the volume fraction of discontinuous fibers (Vf%) and the fiber length (lf) of SFRC were evaluated. The results were statistically analyzed with two-way ANOVA (α=0.05). RESULTS: The mechanical properties of SFRC (eXP) were generally superior (p<0.05) compared with conventional composites. GA had the highest FM (p>0.05), whereas FBF had the highest AHSS (p<0.05). The fiber related properties Vf%, l/d, lf, lfc and df of eXP were 7.2%, 18-112, 0.3-1.9mm, 0.85-1.09mm and 17µm respectively. SEM results suggested an explanation to several toughening mechanisms provided by the discontinuous fibers, which were shown to arrest crack propagation and enable a ductile fracture. Water exposure weakened the mechanical properties regardless of material type. Wf was unaffected by the water storage. CONCLUSION: The properties of this high aspect ratio SFRC were dependent on the fiber geometry (length and orientation) and matrix ductility. CLINICAL SIGNIFICANCE: The simultaneous actions of the toughening mechanisms provided by the short fibers accounted for the enhanced toughness of this SFRC, which toughness value matched the toughness of dentin. Hence, it could yield an inherently uniform distribution of stresses to the hard biological tissues.

Insight in the chemistry of laser-activated dental bleaching.

The use of optical radiation for the activation of bleaching products has not yet been completely elucidated. Laser light is suggested to enhance the oxidizing effect of hydrogen peroxide. Different methods of enhancing hydrogen peroxide based bleaching are possible. They can be classified into six groups: alkaline pH environment, thermal enhancement and photothermal effect, photooxidation effect and direct photobleaching, photolysis effect and photodissociation, Fenton reaction and photocatalysis, and photodynamic effect.

Laser teeth bleaching: evaluation of eventual side effects on enamel and the pulp and the efficiency in vitro and in vivo.

Light and heat increase the reactivity of hydrogen peroxide. There is no evidence that light activation (power bleaching with high-intensity light) results in a more effective bleaching with a longer lasting effect with high concentrated hydrogen peroxide bleaching gels. Laser light differs from conventional light as it requires a laser-target interaction. The interaction takes place in the first instance in the bleaching gel. The second interaction has to be induced in the tooth, more specifically in the dentine. There is evidence that interaction exists with the bleaching gel: photothermal, photocatalytical, and photochemical interactions are described. The reactivity of the gel is increased by adding photocatalyst of photosensitizers. Direct and effective photobleaching, that is, a direct interaction with the colour molecules in the dentine, however, is only possible with the argon (488 and 415 nm) and KTP laser (532 nm). A number of risks have been described such as heat generation. Nd:YAG and especially high power diode lasers present a risk with intrapulpal temperature elevation up to 22°C. Hypersensitivity is regularly encountered, being it of temporary occurrence except for a number of diode wavelengths and the Nd:YAG. The tooth surface remains intact after laser bleaching. At present, KTP laser is the most efficient dental bleaching wavelength.

Three-dimensional finite element analysis of anterior two-unit cantilever resin-bonded fixed dental prostheses.

The aim of this study was to evaluate the influence of different framework materials on biomechanical behaviour of anterior two-unit cantilever resin-bonded fixed dental prostheses (RBFDPs). A three-dimensional finite element model of a two-unit cantilever RBFDP replacing a maxillary lateral incisor was created. Five framework materials were evaluated: direct fibre-reinforced composite (FRC-Z250), indirect fibre-reinforced composite (FRC-ES), gold alloy (M), glass ceramic (GC), and zirconia (ZI). Finite element analysis was performed and stress distribution was evaluated. A similar stress pattern, with stress concentrations in the connector area, was observed in RBFDPs for all materials. Maximal principal stress showed a decreasing order: ZI>M>GC>FRC-ES>FRC-Z250. The maximum displacement of RBFDPs was higher for FRC-Z250 and FRC-ES than for M, GC, and ZI. FE analysis depicted differences in location of the maximum stress at the luting cement interface between materials. For FRC-Z250 and FRC-ES, the maximum stress was located in the upper part of the proximal area of the retainer, whereas, for M, GC, and ZI, the maximum stress was located at the cervical outline of the retainer. The present study revealed differences in biomechanical behaviour between all RBFDPs. The general observation was that a RBFDP made of FRC provided a more favourable stress distribution.

Static and dynamic failure load of fiber-reinforced composite and particulate filler composite cantilever resin-bonded fixed dental prostheses.

PURPOSE: The aim of this study was to evaluate in vitro the influence of fiber reinforcement and luting cement on the static failure load (SFL) and dynamic failure load (DFL) of simulated two-unit cantilever resin-bonded fixed dental prostheses (RBFDPs). MATERIALS AND METHODS: Forty-six particulate filler composite (PFC) beams and 76 fiber-reinforced composite (FRC) beams were prefabricated and subsequently luted (RelyX ARC or Panavia F2.0) onto flat ground bovine enamel. The SFL of the different specimen types was determined with a peel test and the DFL was determined with a rotating cantilever beam fatigue testing device. RESULTS: The PFC specimens showed a significantly lower SFL than the FRC specimens. The luting cement showed a significant effect on the SFL of the PFC specimens, but not with FRC. The DFL of PFC specimens was significantly lower than for FRC specimens. The luting cement showed a significant effect on the DFL of the PFC specimens, but not so with FRC. With both the SFL and the DFL tests all PFC beams fractured, leaving the bonded part on the tooth surface, but FRC beams partially debonded from the tooth surface, leaving fibers connected to the enamel surface to a varying extent. Coincidentally, the uncured fibers turned out to be prone to aging, an effect which has been investigated. CONCLUSION: Within the limitations of this study, it can be concluded that PFC without fiber reinforcement is not suitable for the fabrication of two-unit cantilever RBFDPs, despite the significant effect of the luting cement, but FRC is suitable.

Fracture strength and fatigue resistance of dental resin-based composites.

OBJECTIVES: The aim of this study was to evaluate in vitro the influence of fiber-reinforcement on the fracture strength and fatigue resistance of resin-based composites. METHODS: One hundred rectangular bar-shaped specimens (2 mm x 2 mm x 25 mm) made of resin-based composite were prepared in a stainless steel split-mould: (i) thirty specimens of particulate filler composite (PFC) (Filtek Z100, 3M ESPE, St Paul, MN, USA), (ii) thirty specimens of fiber-reinforced composite (FRC) (Everstick C&B, Sticktech Ltd., Turku, Finland) and (iii) forty specimens of PFC and FRC combined in two longitudinal layers of equal thickness. Each specimen was trimmed into a cylindrical hourglass shape. The fracture strength (cantilever beam test, n=10) and the fatigue resistance (rotating cantilever beam test; staircase method: 10(4) cycles, 1.2 Hz, n=20) were determined. Fracture strength, fatigue resistance and work-of-fracture were calculated. The fracture surfaces of failed specimens were analyzed with SEM. Data was analyzed by logistic regression, one-way ANOVA followed by Tukey's post hoc test and, a Student's t-test. RESULTS: ANOVA revealed that fiber-reinforcement had significant effect (P<0.001) on fracture strength, fatigue resistance, and work-of-fracture. Student's t-test showed significant differences (P<0.001) in fatigue resistance compared to fracture strength. CONCLUSIONS: Within the limitations of this study, the following conclusions can be drawn (i) the fatigue resistance of resin-based composites is lower than their fracture strength and (ii) FRC are more fatigue resistant than PFC or combinations of FRC and PFC.

The influence of framework design on the load-bearing capacity of laboratory-made inlay-retained fibre-reinforced composite fixed dental prostheses.

Delamination of the veneering composite is frequently encountered with fibre-reinforced composite (FRC) fixed dental prosthesis (FDPs). The aim of this study is to evaluate the influence of framework design on the load-bearing capacity of laboratory-made three-unit inlay-retained FRC-FDPs. Inlay-retained FRC-FDPs replacing a lower first molar were constructed. Seven framework designs were evaluated: PFC, made of particulate filler composite (PFC) without fibre-reinforcement; FRC1, one bundle of unidirectional FRC; FRC2, two bundles of unidirectional FRC; FRC3, two bundles of unidirectional FRC covered by two pieces of short unidirectional FRC placed perpendicular to the main framework; SFRC1, two bundles of unidirectional FRC covered by new experimental short random-orientated FRC (S-FRC) and veneered with 1.5 mm of PFC; SFRC2, completely made of S-FRC; SFRC3, two bundles of unidirectional FRC covered by S-FRC. Load-bearing capacity was determined for two loading conditions (n = 6): central fossa loading and buccal cusp loading. FRC-FDPs with a modified framework design made of unidirectional FRC and S-FRC exhibited a significant higher load-bearing capacity (p<0.05) (927+/-74 N) than FRC-FDPs with a conventional framework design (609+/-119 N) and PFC-FDPs (702+/-86 N). Central fossa loading allowed significant higher load-bearing capacities than buccal cusp loading. This study revealed that all S-FRC frameworks exhibited comparable or higher load-bearing capacity in comparison to an already established improved framework design. So S-FRC seems to be a viable material for improving the framework of FRC-FDPs. Highest load-bearing capacity was observed with FRC frameworks made of a combination of unidirectional FRC and S-FRC.

Influence of retainer design on two-unit cantilever resin-bonded glass fiber reinforced composite fixed dental prostheses: an in vitro and finite element analysis study.

PURPOSE: The aim of this study was to evaluate in vitro the influence of retainer design on the strength of two-unit cantilever resin-bonded glass fiber-reinforced composite (FRC) fixed dental prostheses (FDP). MATERIALS AND METHODS: Four retainer designs were tested: a proximal box, a step-box, a dual wing, and a step-box-wing. Of each design on 8 human mandibular molars, FRC-FDPs of a premolar size were produced. The FRC framework was made of resin impregnated unidirectional glass fibers (Estenia C&B EG Fiber, Kuraray) and veneered with hybrid resin composite (Estenia C&B, Kuraray). Panavia F 2.0 (Kuraray) was used as resin luting cement. FRC-FDPs were loaded to failure in a universal testing machine. One-way ANOVA and Tukey's post-hoc test were used to evaluate the data. The four designs were analyzed with finite element analysis (FEA) to reveal the stress distribution within the tooth/restoration complex. RESULTS: Significantly lower fracture strengths were observed with inlay-retained FDPs (proximal box: 300 +/- 65 N; step-box: 309 +/- 37 N) compared to wing-retained FDPs (p < 0.05) (step-box-wing: 662 +/- 99 N; dual wing: 697 +/- 67 N). Proximal-box-, step-box-, and step-box-wing-retained FDPs mainly failed with catastrophic cusp fracture (proximal box 100%, step-box 100%, and step-box-wing 75%), while dual-wing-retained FDPs mainly failed at the adhesive interface and/or due to pontic failure (75%). FEA showed more favorable stress distributions within the tooth/restoration complex for dual wing retainers. CONCLUSION: A dual-wing retainer is the optimal design for replacement of a single premolar by means of a two-unit cantilever FRC-FDPs.