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. This paper provides an update on the aesthetic considerations involved in the restoration of anterior teeth with directly placed composite and outlines the contemporary materials, equipment and techniques that are available to optimize every clinical stage. CLINICAL RELEVANCE: Successful restoration of anterior teeth with direct composite is an integral component of contemporary clinical practice.

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. This may be due to individual practitioner concerns over unpredictability, time and the fact that procedures remain technique sensitive for many, particularly with regard to moisture control, placement and control of polymerization shrinkage stress. New materials, techniques and equipment are available that may help to overcome many of these concerns. This paper describes how such techniques may be employed in the management of a carious lesion on the occlusal surface of an upper molar. CLINICAL RELEVANCE: Direct posterior composite is the treatment of choice for the conservative restoration of primary carious lesions.

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. CLINICAL RELEVANCE: Successful restoration of posterior teeth with composite is an essential component of contemporary dental clinical practice.

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. METHODS: Maximum vibration displacement amplitudes of five air turbines and two speed-increasing handpieces were recorded whilst they were operated with and without a rotary cutting instrument (RCI) using a scanning laser vibrometer (SLV). RESULTS: RCI rotation speeds, calculated from frequency peaks, were consistent with expected values. ANOVA statistical analysis indicated significant differences in vibrations between handpiece models (p<0.01), although post hoc tests revealed that differences between most individual models were not significant (p>0.11). Operating handpieces with a RCI resulted in greater vibrations than with no RCI (p<0.01). Points on the head of the handpiece showed greater vibration displacement amplitudes than points along the body (p<0.01). CONCLUSIONS: Although no single measurement exceeded 4 microm for the handpieces in the current test setup (implying that these vibrations may be unlikely to cause adverse effects), this study has formed the basis for future work which will include handpiece vibration measurements whilst cutting under clinically representative loads.

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.

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. Disc shaped specimens were prepared by manual condensation to compare the width of the reaction zone with specimens condensed mechanically. RESULTS: The Galloy powder consisted of spherical particles varying between 0.1 and 40 microm in diameter which contained a network of grooves and clefts extending deep within the substance of the particles. The reaction zone appeared 'grainy' and 'fragmented' compared with the well defined reaction zone previously observed for Pd-containing gallium-based alloys. The student t-test indicated the width of reaction zone varied significantly (P<0.001) with method of specimen fabrication.Significance. The significantly larger reaction zone in the manually condensed specimens was possibly due to failure of the condensation technique to force out excessive liquid alloy present in the triturated mass. The surface topography of the Pd-free Galloy powder particles could be responsible for the characteristically fragmented and ill-defined reaction zone observed in the set material compared with the well defined reaction zone previously observed for Pd-containing gallium-based alloys.

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. The teeth were stored in water. Each tooth was fixed in a steel mold and subjected to a standardized crown preparation. Crowns were constructed in belleGlass HP. Group A contained no fiber reinforcement. In Group B, Construct polyethylene braided fibers were applied from the mesial margin over the coronal aspect of the die down to the distal margin, and circumferentially around the preparation, prior to crown construction as in Group A. In Group C, a bundle of experimental S-glass fiber of 9 microm diameter was applied circumferentially prior to crown construction as in Group A. In Group D, two layers of Stick net pre-impregnated woven glass fibers were adapted over the whole surface of the initial thin coping, prior to constructing crowns as in Group A. Crowns were luted with a dual cure resin cement (Nexus), with the dentin surface of the specimens having first been treated with a dentin bonding system. Each specimen was stored under water at 37 degrees C for 24 hours prior to testing, and were then subjected to compressive loading at a cross-head speed of 1 mm/minute in a Universal Testing Machine by way of a 4 mm diameter steel bar placed along the midline fissure of the upper premolar crown. RESULTS: The mean force required (kN) to cause fracture was as follows: Group A 2.0kN, Group B 2.4kN, Group C 2.7kN, Group D 2.3kN. ANOVA showed that there was no statistically significant difference between the groups.

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). All the samples were stored in distilled water at 37 degrees C for 24 hours before testing. The fractured surfaces were examined by light and scanning electron microscopy (SEM) to assess the effect of the surface treatments. RESULTS: The mean fracture resistance (+/- S.D) of the tested groups ranged from 7.6 (+/- 1.9 N mm(-1)) for Group A to 13.9 (+/- 5.4 N mm(-1)) for Group D. Two-way analysis of variance showed no significant interaction (P>0.05) between product opacities & surface treatments. The bonded inlay test halves in Groups B and C failed adhesively between the inlay test halves and the luting cement whereas the other three test groups (D,E,F) failed cohesively in the luting cement. One-way analysis of variance with post-hoc paired group Tukey testing revealed that Group D (13.9 +/- 5.4 N mm(-1)) performed significantly better (P<0.05) than Groups A (7.6 +/- 1.9 N mm(-1), B (9.2 +/- 3.7 N mm(-1)) or C (7.8 +/- 1.6 N mm(-1)). No statistical difference was found between Groups D to F (P>0.05).

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. Several had undertaken very few endodontic procedures as students. Differences and trends were seen in the opinions of students and their experiences among the schools, and between the two year groups studied. Most students were not very confident to undertake molar endodontics. Many felt they needed more practical experience as students and training in newer techniques and instrumentation.

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. Filler particles (n=30) were subjected to compression using a micromanipulation technique between a descending glass probe and a glass slide. The number of distinct fractures particles underwent was determined from force/displacement and stress/deformation curves and the force at fracture and pseudo-modulus of stress was calculated. RESULTS: Agglomerated fillers ('nanoclusters') exhibited up to four distinct fractures, while spheroidal and irregular particles underwent either a single fracture or did not fracture following micromanipulation. Z-tests highlighted failure of nanoclusters to be significant compared with spheroidal and irregular particles (P<0.05). The mean force at first fracture of the nanoclusters was greater (1702+/-909 microN) than spheroidal and irregular particles (1389+/-1342 and 1356+/-1093 microN, respectively). Likewise, the initial pseudo-modulus of stress of nanoclusters (797+/-555 MPa) was also greater than spheroidal (587+/-439 MPa) or irregular (552+/-275 MPa) fillers. SIGNIFICANCE: The validity of employing the micromanipulation technique to determine the mechanical properties of filler particulates was established. The 'nanoclusters' exhibited a greater tendency to multiple fractures compared with conventional fillers and possessed a comparatively higher variability of pseudo-modulus and load prior to and at fracture, which may modify the damage tolerance of the overall RBC system.

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. Specimens were pre-loaded at 20, 50 or 100 N for 2000 cycles and stored in a 'dry' or 'wet' environment prior to BFS testing. RESULTS: A general linear model analysis of variance highlighted a reduction in the BFS following pre-loading, however, individual RBC materials responded differently. The RBCs containing agglomerated nano-sized particles or 'nanoclusters' (Filtek Supreme) demonstrated distinctive and unique patterns of response to pre-loading. Cyclic pre-loading at 20 and 50 N significantly increased the Weibull modulus of both FSB (8.53+/-1.91 and 10.23+/-2.29) and FST (16.89+/-3.78 and 10.91+/-2.45) compared with FSB and FST control (no pre-cyclic load) specimens (5.98+/-1.34 and 7.99+/-1.78, respectively). BFS of FSB and FST was maintained or significantly increased compared with the other materials following 20 and 50 N cyclic pre-load (P<0.05). SIGNIFICANCE: The 'nanoclusters' provided a distinct reinforcing mechanism compared with the microhybrid, microfill or nanohybrid RBC systems resulting in significant improvements to the strength and reliability, irrespective of the environmental storage and testing conditions. Silane infiltration within interstices of the nanoclusters may modify the response to pre-loading induced stress, thereby enhancing damage tolerance and providing the potential for improved clinical performance.