Filip Keulemans

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 Tukeys post hoc test and, a Students t-test. RESULTS ANOVA revealed that fiber-reinforcement had significant effect (P<0.001) on fracture strength, fatigue resistance, and work-of-fracture. Students 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.

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.

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.

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.

Fiber-reinforced composites in fixed prosthodontics-Quo vadis?

Fiber-reinforced composite (FRC) materials were introduced to dentistry more than five decades ago and they were first indicated as a reconstruction material for fixed dental prostheses (FDP). Understanding the need for preserving dental hard tissue during the preparation of abutments became essential and progress in adhesive and FRC technology enabled the development of the concept of minimally invasive FDP’s using FRC materials that could be utilized in the lab or at chairside. Based on research and experience of 25 yeras, the following benefits of FRC fixed dental prostheses have been identified: 1. FRC materials allows for following the Dynamic Treatment Concept), 2. minimal invasiveness, 3. profitable and affordable treatment options. From the patient perspective, the most significant reasons for selecting FRC FDPs seem to be: 1. possibility of receiving the FDP in a single-visit, 2. being less expensive and painless treatment and 3. possibility of avoiding removable devices. Understanding and managing the risk factors dictate the successful use of direct or indirect FRC FDP treatment modalities. Based on the present knowledge and experience, with sufficient inter-occlusal space, correct framework design and precise application of adhesive techniques, FRC FDPs could provide definitive fixed prosthodontic solutions, with expected survival time of at least five to six years, high patient satisfaction, and postpone other invasive and costly treatments.

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.

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.

Fillings and core build-ups

Abstract The longevity of particulate filler composite (PFC) is uncertain in large restorations with high occlusal stresses. From a biomimetic point of view, the use of short fiber-reinforced composite (SFRC) as dentin replacing material appears a promising treatment strategy and may solve some potential problems associated with composite restoration in high stress-bearing areas. This chapter briefly presents the theoretical background, benefits and clinical applications of SFRC in dentistry. In this series of clinical cases an attempt was made by using SFRC (everX Posterior; GC Corporation, Tokyo, Japan) as dentine-replacing material or bulk base under surface layer of enamel-replacing PFC, i.e., biomimetic or bilayered composite restorations, in order to improve the load-bearing capacity and clinical longevity of resin-based composite restorations. Within the limitations of this case series of clinical indications, the presented restorative approach is a promising and cost efficient way to extend the indication range of direct and indirect resin composite restorations and gives the clinician alternative treatment options.

Adhesion and Erbium-Lased Enamel and Dentin

The quality of bonding to the enamel and dentin is of utmost importance for the long life of adhesive filling materials. At present, adhesive systems have evolved in a positive way. Much is the result of a better understanding of the interaction between adhesive system and substrate. Both the dentin and enamel have different surface characteristics after laser preparation with erbium lasers as compared to conventionally bur-cut surfaces. For some, the characteristic irregularity and retentiveness of lased surfaces permit to adhere without etching. In the mean time, investigations have demonstrated that it is better to etch the lased surface (both the enamel and dentin) before bonding with non-self-etching systems. Also here, the original ‘gold standard’, i.e. a three-step etch-and-rinse system, results in clinically acceptable bond strengths. Furthermore, two-step ‘mild’ self-etch adhesives containing 10-MDP used with enamel etching and without dentin etching appear to perform at least equally well. As the quality of the adhesion is also influenced by the substrate, it has to be emphasised that it is recommended not to rely on enamel laser conditioning (previously called laser etching) and to finish the dentin at low fluency before adhesion. At present, there is insufficient information to take a position for glass ionomers.