The power of light - From dental materials processing to diagnostics and therapeutics.

Harnessing the power of light and its photonic energy is a powerful tool in biomedical applications. Its use ranges from biomaterials processing and fabrication of polymers to diagnostics and therapeutics. Dental light curable materials have evolved over several decades and now offer very fast (≤ 10 s) and reliable polymerization through depth (4-6 mm thick).

On the inaccuracies of dental radiometers.

This study investigated the accuracy of sixteen models of commercial dental radiometers (DR) in measuring the output of thirty-eight LED light curing units (LCUs) compared with a 'gold standard' laboratory-grade spectrometer integrating-sphere (IS) assembly. Nineteen Type I (fiber-bundle light guide) and nineteen Type II (light source in head) LED LCUs were tested, some using different output modes and light guides, resulting in 61 test subsets per radiometer. Gold standard (GS) output measurements (n = 3) were taken using the IS and confirmed with two types of laboratory-grade power meter (PowerMax-Pro 150 HD and PM10-19C; Coherent).

Robust spectrometer-based methods for characterizing radiant exitance of dental LED light curing units.

Objectives: Firstly, to assess light output, from a representative range of dental light curing units (LCUs), using a new portable spectrometer based instrument (checkMARC™) compared with a "gold standard" method. Secondly, to assess possible inconsistency between light output measurements using three different laboratory-grade thermopile instruments.

Methods: The output of four blue-dental LCUs and four polywave blue-and-violet-LCUs was measured with two spectrometer-based systems: a portable spectrometer instrument and a benchtop Integrating Sphere fiber-coupled spectrometer system.

Direct anterior composites: a practical guide.

Unlabelled: For more than 40 years dentists worldwide have been using directly placed resin-bonded composite to restore damaged anterior teeth. While such techniques are invariably more conservative of tooth tissue than indirect procedures, operative techniques using direct composite can be challenging and are considered technique sensitive. Clinicians require both technical and artistic skill to provide composite restorations that restore function and aesthetics to blend seamlessly with the residual dentition.

Specimen aspect ratio and light transmission in photoactive dental resins.

Objectives: To test the influence of specimen dimensions on light transmission and shrinkage strain properties of curing dental resins.

Materials And Methods: Photocurable resin specimens (Bis-GMA/TEGDMA) with aspect ratios (AR) of 2 (4mm×2mm); 4 (4mm×1mm and 8mm×2mm); 8 (8mm×1mm); 12 (AR: 12mm×1mm); and 24 (12mm×0.5mm) were light cured.

Advances in light-curing units: four generations of LED lights and clinical implications for optimizing their use: Part 2. From present to future.

Unlabelled: The first part of this series of two described the history of light curing in dentistry and developments in LED lights since their introduction over 20 years ago. Current second- and third-generation LED light units have progressively replaced their halogen lamp predecessors because of their inherent advantages. The background to this, together with the clinical issues relating to light curing and the possible solutions, are outlined in the second part of this article.

Posterior composites: a practical guide revisited.

Unlabelled: Direct placement resin composite is revolutionizing the restoration of posterior teeth. Compared to amalgam, its use not only improves aesthetics but, more importantly, promotes a minimally invasive approach to cavity preparation. Despite the benefits, the use of composite to restore load-bearing surfaces of molar and premolar teeth is not yet universally applied.

Competitive light absorbers in photoactive dental resin-based materials.

Objectives: The absorbance profile of photoinitiators prior to, during and following polymerization of light curable resin-based materials will have a significant effect on the cure and color properties of the final material. So-called "colorless" photoinitiators are used in some light-activated resin-based composite restorative materials to lessen the yellowing effect of camphoroquinone (CQ) in order to improve the esthetic quality of dental restorations. This work characterizes absorption properties of commonly used photoinitiators, an acylphosphine oxide (TPO) and CQ, and assesses their influence on material discoloration.

Three generations of LED lights and clinical implications for optimizing their use. 1: from past to present.

In the present era of adhesive dentistry light-curing units are essential pieces of surgery equipment for everyday practice. The success and longevity of light-activated resin sealants, photo-cured restorations and orthodontic treatments are related to the efficacy of the light-curing process. Energy efficient blue LED lights are rapidly replacing their halogen lamp predecessors as the standard light source.

Formation of gaps at the filler-resin interface induced by polymerization contraction stress: Gaps at the interface.

Objectives: To investigate the movement of resin matrix with respect to the filler particles of filled composites during their photo cure without or with polymerization contraction stress (PCS).

Methods: Two types of composites were prepared. Glass beads as macroscopic fillers were placed into the center of a bis-GMA/TEGDMA resin to make single bead-embedding "composites" and a variety of fillers of different compositions, sizes, and shapes were mixed with another bis-GMA/TEGDMA resin to make lightly filled composites.

The flexural properties of endodontic post materials.

Objectives: To measure the flexural strengths and moduli of endodontic post materials and to assess the effect on the calculated flexural properties of varying the diameter/length (D/L) ratio of three-point bend test samples.

Methods: Three-point bend testing of samples of 2mm diameter metal and fiber-reinforced composite (FRC) rods was carried out and the mechanical properties calculated at support widths of 16 mm, 32 mm and 64 mm. Weibull analysis was performed on the strength data.

The effect of clinically relevant thermocycling on the flexural properties of endodontic post materials.

Objectives: It is suggested that fibre-reinforced composite (FRC) posts have lower elastic moduli than metal posts and this will reduce the incidence of root fracture. However, the mechanical properties may be altered in the oral environment. The aims of this study were to determine the effect on the flexural properties of FRC and metal post materials produced by: (1) a thermocycling regime which was clinically relevant and representative of that which would occur during 1 year in the mouth and (2) storage for 1 year at body temperature.

Oxygen inhibition and incremental layer bond strengths of resin composites.

Objectives: When dentists light cure resin composite restorations in increments or after contouring the surface layer to shape with a hand instrument the surface layer is exposed to air during polymerization. The presence of an oxygen inhibited resin surface layer may impact on clinical performance. Conflicting data has been produced in vitro regarding this topic.

Direct posterior composites: a practical guide.

Unlabelled: The restoration of posterior teeth with directly placed resin-bonded composite requires meticulous operative technique in order to ensure success. Case and material selection; cavity preparation; matrix selection; isolation; bonding; management of polymerization shrinkage; placement; finishing and curing of posterior composites--all present a series of challenges that dentists must master in order to ensure high-quality, long-lasting restorations. This paper describes and discusses these aspects of the provision of composites for loadbearing situations in posterior teeth.

The mechanical properties of nanofilled resin-based composites: the impact of dry and wet cyclic pre-loading on bi-axial flexure strength.

Objectives: To determine the influence of nano-sized filler particles and agglomerates of nanoparticles ('nanoclusters') in resin-based composite (RBC) materials on the bi-axial flexure strength (BFS) following cyclic pre-loading and storage in a 'dry' or 'wet' environment.

Method: Seven commercially available RBC restoratives, Heliomolar (Ivoclar Vivadent, Schaan, Liechtenstein), Z100 MP Restorative, Filtek Z250, Filtek Supreme (3M ESPE, St. Paul, MN, USA) in Body (FSB) and Translucent (FST) shades, Grandio and Grandio Flow (VOCO, Cuxhaven, Germany), containing differing filler particle types and morphologies were investigated.

The mechanical properties of nanofilled resin-based composites: characterizing discrete filler particles and agglomerates using a micromanipulation technique.

Objective: To assess the mechanical properties of discrete filler particles representative of several inorganic fillers in modern dental resin-based composites (RBCs) and to assess the validity of a novel micromanipulation technique.

Method: RBCs with microhybrid (Filtek Z250), 'nanohybrid' (Grandio) and 'nanofilled' (Filtek Supreme), filler particle morphologies were investigated. Filler particles were provided by the manufacturer or separated from the unpolymerized resin using a dissolution technique.

Vibration characteristics of dental high-speed turbines and speed-increasing handpieces.

Objectives: Vibrations of dental handpieces may contribute to symptoms of hand-arm vibration syndrome in dental personnel and iatrogenic enamel cracking in teeth. However, methods for measuring dental handpiece vibrations have previously been limited and information about vibration characteristics is sparse. This preliminary study aimed to use a novel approach to assess the vibrations of unloaded high-speed handpieces in vitro.

Cure width potential for MOD resin composite molar restorations.

Objectives: To investigate the capability of modern light-curing units exhibiting differences in emission spectra and light source exit window dimensions, for "one-shot" full-width curing of extensive (molar MOD) resin composite restorations.

Method: Specimens of Tetric (TT), Tetric Ceram HB (TC), Tetric Evoceram (TE) and Tetric Ceram Bleach (TB) resin composites containing varying ratios of Lucirin (TPO) and/or camphorquinone (CQ) photoinitiators were packed into a bar-shaped mould (12 mm length x 2 mm width x 2 mm thickness). Each product was irradiated using a halogen (Optilux 401; QTH), a conventional LED (LEDemetron; LED) and two so-called "third generation" oval-footprint LED light-curing units (LCUs) of the same model.

Time-resolved simultaneous measurement of group index and physical thickness during photopolymerization of resin-based dental composite.

Light-activated resin-based dental composites are increasingly replacing dental amalgam. However, these materials are limited by inefficient setting reactions as a function of depth that constrain the maximum extent of cure. Insufficient curing can contribute to an overall reduction in biocompatibility of the material.

Trends in indirect dentistry: 6. Provisional restorations, more than just a temporary.

The provision of well-fitting, functional provisional restorations is important for a wide variety of reasons, including maintenance of the stability of inter- and intra-arch relationships and positional stability of prepared teeth, and the preservation of occlusal function of anterior provisional restorations by providing appropriate protrusive and lateral guidance. Provisional restorations should be of sufficient strength to resist the forces of occlusion and should be luted with a cement that will resist the forces of removal, yet allow easy removal at the fit appointment without leaving a residue on the prepared tooth. This paper describes the use of provisional restorations in indirect restorative dentistry and suggests some specific techniques for clinical use.

Influence of Different Techniques of Laboratory Construction on the Fracture Resistance of Fiber-Reinforced Composite (FRC) Bridges.

The aim of the current investigation is to evaluate optimal pontic and retainer fiber positions for Polyethylene fiber-reinforced composite (FRC) restorations. In series I notch disc specimens were used to mimic loading cuspal regions of pontics. Four groups (n=15/group; codes A to D) were prepared from Artglass composite.

Fracture resistance of fiber-reinforced composite crown restorations.

Purpose: To evaluate the laboratory fracture resistance of teeth restored with crowns constructed in one of these materials (BelleGlass HP with and without fiber reinforcement.

Methods: 40 sound maxillary premolar teeth were chosen and were allocated to four groups of 10 teeth, with the mean size of any group varying by less than 2.5% from other test groups.

A palladium-free gallium-based alloy: analysis of composition and microstructure.

Objectives: To study the microstructure of a palladium-free gallium-based alloy (Galloy) before and after mixing to identify the metallic phases produced by the setting reaction and assess the quantitative elemental analysis of the phases present.

Methods: The Galloy powder was analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the particle size distribution was determined using a high resolution particle size analyzer. Cylindrical test specimens were mechanically condensed in accordance with ISO 1559: 1986 for XRD, energy dispersive spectroscopy (EDS) and SEM analyses of the set alloy.

Effects of grit blasting and silanization on bond strengths of a resin luting cement to Belleglass HP indirect composite.

Purpose: To investigate the extent of bonding possible of a resin luting cement with three opacities of Belleglass HP, representing different filler type and loading levels in a highly cross-linked resin matrix.

Materials And Methods: Belleglass HP (3 opacities: opaque dentin, translucent dentin, cuspal enamel) was prepared as solid notched discs (Group A) or luted halves to create notched discs (Groups B-F). Luted samples were split through the notch on the Instron for conditions: as-is after molding (B), grit blasted with 50 microm Al2O3 (C), grit blasted and silanated (D) grit blasted, silanated, and stored 1 week (E), and grit blasted and treated with Artglass liquid (F).

Endodontics and new graduates, Part 2: Undergraduate experience and course evaluation.

A postal survey of recent United Kingdom dental graduates was undertaken to establish the amount of their undergraduate endodontic experience and their opinions of their training. A 75% response was achieved from all but two schools. Recent graduates had generally undertaken fewer cases as students than older graduates.