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. The latter featured bimodal emission spectra (blue and ultraviolet diodes) with either high (unmodified output) and approximately 50% (modified output) blue light intensity (UltraLume-5; ULs, ULm, respectively). Vickers hardness number was obtained across the lateral extent of the bar at 1mm increments from the centre point on both upper and lower surfaces of the specimens. RESULTS: Significant linear relationships (R(2)=0.71-0.98) for each distance from the central position of all LCUs were identified between measured light intensity and corresponding upper and lower surface hardness values for each product (P<0.05). No significant differences (P>0.05) were recorded in total upper surface hardness of TC or TE cured with LED (68.7+/-3.2 and 70.5+/-2.5) or ULm (56.8+/-2.0 and 57.7+/-2.0). However, upper surface hardness of TT (CQ only) cured with ULm was significantly decreased (P<0.05) compared with other LCUs. When the ratio of hardness at the edge to central positions of the bar-shaped specimens for either surface was calculated, no significant difference (P>0.05) was identified for TB (containing TPO and decreased CQ) cured with either ULs or ULm (P>0.05) and was significantly increased (P<0.05) when cured with ULs compared with LED and QTH. SIGNIFICANCE: Variability in light intensity across the curing-tip face, spectral output of dental light-curing units and differences in product photoinitiator chemistry all influence curing efficiency significantly across the width of extensive resin composite geometries.

Adhesive luting of all-ceramic restorations--the impact of cementation variables and short-term water storage on the strength of a feldspathic dental ceramic.

PURPOSE: To investigate the impact of resin cement luting variables and short-term water storage on the strength of an adhesively luted all-ceramic restorative material. An understanding of the strengthening mechanisms will result in optimisation of operative techniques and materials selection criteria. MATERIALS AND METHODS: The "fit" surfaces of 480 disk-shaped feldspathic porcelain specimens were alumina air abraded to introduce a clinically relevant surface texture and consistent surface defect population. Thirty specimens randomly allocated to each of 16 groups were coated with silane, unfilled resin or filled resin cement, or a combination. Eight groups were stored either dry or wet for 24 h prior to bi-axial flexure testing (ball-on-ring). Statistical analysis of the flexure strength data involved a three-factor general linear model (p < 0.05) prior to a Weibull analysis. RESULTS: Resin coating the porcelain surface resulted in a significant increase in the characteristic stress (sigma(o)), and strengthening was dependent on coating type (p < 0.001). Silane priming resulted in additional strengthening when preceding filled resin cement coating. Water immersion for 24 h resulted in a strength degradation of both the uncoated control and coated specimens, whereby the magnitude of strength degradation was dependent on coating type (p < 0.001). CONCLUSION: Resin luting of dental ceramics results in significant strengthening likely to impact on clinical performance. The strengthening is dependent on the creation of a resin-ceramic hybrid layer sensitive to cementation variables and clinical placement technique. Short-term water immersion results in a significant degradation of strengthening sensitive to the characteristics of the resin-ceramic hybrid layer.

Micromechanical versus chemical bonding between CoCr alloys and methacrylate resins.

INTRODUCTION: As adhesive systems for bonding to metals have developed in dentistry, considerable importance is attached to the preparation of the metal alloy for both mechanical and chemical bonding. Different grit sizes when sandblasting Cobalt Chromium (CoCr) will provide a different three-dimensional surface for bonding. Previous reports have shown that 4-Methacryloyloxyethyl trimellitic anhydride (4-Meta) resins offer high bond strengths to CoCr alloy, with various surface preparations providing varying bond strengths. The relevance of this to bond strength was assessed. OBJECTIVES: The aim of the study was to evaluate the importance of grit size of alumina in the preparation of CoCr alloy and to determine the effect on the tensile bond strength of four different acrylic resins to the CoCr alloy. METHODS: Ten specimens were prepared within each group of four resins. Four grit sizes were assessed, 50, 110, 250 microm, and a range from 180 to 330 microm. The specimens were tested both within one day of production after storing at 37 degrees C in phosphate-buffered saline for seven days and after thermocycling. RESULTS: Grit size resulted in a change in average contact surface area available for bonding. A significant difference (p < 0.01) existed in bond strengths between each of the materials, but no significant difference (p = 0.0673) was determined when different grit sizes were included. SIGNIFICANCE: It was concluded that grit size determined the available contact surface area of CoCr alloy for bonding but did not determine the bond strength that could be achieved between acrylic resins and CoCr alloy as a result of the poor adaptation of the resin to the complex surface topography.

The impact of modifying alumina air abrasion parameters on the fracture strength of a porcelain laminate restorative material.

OBJECTIVES: The modification of the "fit" surface of porcelain laminate veneer restorations in order to improve adhesion prior to cementation is often indiscriminate. As a consequence, the surface flaw distribution which is implicated in the probability of failure of the restoration is likely to be dramatically modified. The purpose of the current study was to examine the impact of different air abrasion surface treatments on the bi-axial flexure strength and surface roughness of a porcelain restorative material. METHODS: Sets of 30 Vitadur-Alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were alumina abraded with three different grades of alumina particle (25, 50 and 110 microm), utilizing two different air stream pressures (35 and 70 psi) and two distinct angles of incidence of particle delivery (45 degrees and 90 degrees ). Mean bi-axial flexure strengths, standard deviations, the associated Weibull moduli (m) and characteristic stress were determined using bi-axial flexure (ball on ring). RESULTS: A univariate general linear analysis of means revealed a significant difference between the mean bi-axial flexure strength values of the control group and those of groups subjected to alumina particle air abrasion. Further significance (P<0.05) was discovered with the impact of alumina particle size and the interaction between particle size and angle of incidence of particle delivery. The reliability of the fracture strength data generally improved when 50 microm alumina particles were used whereas discontinuities existed at lower strength values when 25 and 110 microm alumina particles were employed. CONCLUSIONS: Alumina particle air abrasion has a significant degradative effect on the bi-axial flexure strength of the porcelain disc-shaped specimens. Variation of alumina size, delivery pressure and angle of particle delivery all impacted on the degree of strength reduction and the shape of the survival probability distributions. It is suggested that alumina particle air abrasion acts to remove/modify the initial flaw distribution replacing it with flaws of differing geometry and stability. The premature failure of porcelain laminate restorations may be markedly influenced by alumina particle air abrasion depending upon the size and distribution of the crystalline phase present in different dentine porcelains materials used in construction of the restoration.

The impact of hydrofluoric acid surface treatments on the performance of a porcelain laminate restorative material.

OBJECTIVES: Hydrofluoric (HF) acid etching increases the bond strength between composite resin and porcelain surfaces and has been advocated as a pre-cementation technique for ceramic restorations. The internal surface flaw distribution which is implicated in the premature failure of ceramic restorations is modified by the etching process and little agreement exists amongst researchers as to the appropriate etching regime. The purpose of the current study was to examine the impact of HF acid concentration and etching time on the performance of a low fusing feldspathic porcelain. METHODS: Sets of 30 Vitadur-Alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were etched with HF acid of three different concentrations (5, 10 and 20%) and for three different etching periods (45, 90 and 180s). Mean flexure strengths, standard deviations and the associated Weibull moduli (m) and characteristic stress (sigma(0)) were determined using bi-axial flexure (ball on ring). Contact profilometry was utilised to characterise the roughness of the etched porcelain surfaces. RESULTS: A univariate general linear analysis of means revealed a significant reduction in the mean strength values of the as-fired control compared with groups subjected to HF acid etching. Further significance (P<0.05) was discovered with the impact of acid concentration. Altering etching time also resulted in changes in the reliability of the fracture strength data. Contact profilometry demonstrated an increase in surface roughness following HF acid etching and an increase in roughness associated with increasing HF concentration. CONCLUSIONS: Etching of feldspathic porcelain is a dynamic process and the impact is dependent on substrate constitution, surface topography, acid concentration and etching time. A significant reduction of the flexural strength of a low fusing feldspathic porcelain has been demonstrated to result from etching and clear evidence exists that the nature of surface flaw modification is a function of etching time and HF acid concentration. Favourable combinations of HF acid concentration and etching time have been identified which enhance the reliability of the porcelain utilised although variability in clinical technique will result in the reduced reliability of porcelain laminate restorations in function.

Resin strengthening of dental ceramics- the impact of surface texture and silane.

OBJECTIVES: To examine the effect of porcelain surface texture achieved utilising three clinically relevant surface preparation methods prior to silane and unfilled resin application on the flexure strength of a low fusing feldspathic porcelain. MATERIALS AND METHODS: Five hundred and forty dentine disc-shaped specimens (15.0mm diameter and 0.9mm thickness) were condensed, fired and allocated to 18 groups. Six groups were stored as-fired, six were alumina abraded and six were acid-etched. Samples were coated with silane, unfilled resin or both prior to bi-axial flexure testing. Group means were compared utilising a three factor design general linear model and post hoc all paired Tukey tests at P<0.05. Weibull analysis was employed to examine the reliability of the strength data. Profilometry was used to characterise the surface texture of the specimen surfaces. RESULTS: Alumina abraded and acid-etched specimens had significantly lower flexure strengths than the as-fired specimens. A significant difference between the degree of strengthening observed following unfilled resin application on the three surface texture investigated was observed (P<0.001). Silane application prior to resin coating resulted in no further significant increases in the mean bi-axial flexure strengths of the three surface textures. The as-fired surfaces had a low frequency of irregular amplitude defects, alumina abraded surfaces had an increased frequency of regular amplitude defects whilst the acid-etched surface consisted of an increased frequency of irregular amplitude defects. CONCLUSION: The strengthening mechanism whilst dependent on surface texture was independent of defect severity. No significant strengthening occurred following silane priming suggesting that, for the unfilled resin utilised, the strengthening mechanism was not enhanced by improved resin-ceramic adhesion.

A novel non line-of-sight method for coating hydroxyapatite onto the surfaces of support materials by biomineralization.

A novel method is described for the non line-of-sight coating of hydroxyapatite onto polyurethane reticulated foam and titanium discs. This utilises a biofilm of Serratia sp. NCIMB 40259 which, when challenged with a solution containing calcium chloride and phosphatase substrate, manufactures biofilm-bound material identified as hydroxyapatite by X-ray powder diffraction analysis. Non-invasive magnetic resonance imaging was used to visualize the biofilm coating throughout the foam labyrinth and to measure the thickness of the film within reticulated foam cubes in situ. The film developed within the cube matrices was similar to that measured on the surface of a glass slide. Using LaPO(4) deposition as a model system the metallised biofilm was visualised in two-dimensional slices throughout three-dimensional images acquired by magnetic resonance imaging. A similar encrustation of hydroxyapatite on the surface of biofilm grown on titanium discs was confirmed by scanning electron microscopy. Potential applications for bio-hydroxyapatite as possible bone implant precursors are discussed.

The effect of core:dentin thickness ratio on the bi-axial flexure strength and fracture mode and origin of bilayered dental ceramic composites.

OBJECTIVES: The aim of the current study was to assess the effect of core:dentin thickness ratio on the flexure strength, fracture mode and origin of bilayered dental ceramic composite disc specimens. METHODS: Sets of 30 bilayered composite discs with core:dentin thickness ratio of 2:1, 1:1 and 1:2 were tested in bi-axial flexure with both the reinforcing core and veneering dentin loaded in tension. Mean flexure strengths, standard deviations and associated Weibull Moduli (m) were determined. A combination of optical and scanning electron microscopy was employed for identification of the fracture mode and origin. RESULTS: The core:dentin ratio influenced the bi-axial flexure strength and reliability of the flexure strength data when both the reinforcing core and veneering dentin porcelain were tested in tension. The strength and reliability was increased for a core:dentin thickness of 2:1. The number of fracture fragments, the frequency of occurrence of specimen delaminations, Hertzian cone formations and sub-critical radial cracking in the bilayered dental ceramic composite disc shaped specimens was also dependent on the core/dentin ratio and the surface loaded in tension. CONCLUSIONS: Core:dentin thickness ratio influences the bi-axial flexure strength and fracture mode and origin in bilayered dental ceramic composite specimens.

Potential countersample materials for in vitro simulation wear testing.

OBJECTIVES: Any laboratory investigation of the wear resistance of dental materials needs to consider oral conditions so that in vitro wear results can be correlated with in vivo findings. The choice of the countersample is a critical factor in establishing the pattern of tribological wear and in achieving an efficient in vitro wear testing system. This research investigated the wear behavior and surface characteristics associated with three candidate countersample materials used for in vitro wear testing in order to identify a possible suitable substitute for human dental enamel. METHODS: Three candidate materials, stainless steel, steatite and dental porcelain were evaluated and compared to human enamel. A variety of factors including hardness, wear surface evolution and frictional coefficients were considered, relative to the tribology of the in vivo situation. RESULTS: The results suggested that the dental porcelain investigated bore the closest similarity to human enamel of the materials investigated. SIGNIFICANCE: Assessment of potential countersample materials should be based on the essential tribological simulation supported by investigations of mechanical, chemical and structural properties. The selected dental porcelain had the best simulating ability among the three selected countersample materials and this class of material may be considered as a possible countersample material for in vitro wear test purposes. Further studies are required, employing a wider range of dental ceramics, in order to optimise the choice of countersample material for standardized in vitro wear testing.

The effect of thermocycling on the strength of porcelain laminate veneer (PLV) materials.

OBJECTIVES: Postoperative cracking and resultant failure of porcelain laminate veneer (PLV) restorations are considered a possible consequence of thermal variations that the restoration is likely to encounter 'in service'. The purpose of the study was to examine the impact of thermocycling on the development of surface flaws on the 'fit' surface of PLV restorations. METHODS: Sets of 30 Vitadur-Alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were thermocycled on the glazed and unglazed surfaces at three different temperature regimes to simulate the conditions encountered in service. Mean fracture strengths, standard deviations and associated Weibull Moduli (m) were determined using bi-axial fracture (ball-on-ring). RESULTS: The student-t-test analysis revealed a significant difference (P<0.05) between the porcelain control group mean strength values exposed on the glazed and unglazed surfaces. The one-way analysis of variance revealed no significant differences between the means of the porcelain specimens exposed to different thermocycling regimes. However, a discontinuity existed at the lower strength values in the survival probability plots for porcelain specimen groups that were thermocycled. SIGNIFICANCE: Large flaws on the surface of the specimens may become extended due to the thermocycling regimes imposed. The greater the tensile stresses imposed on the disc specimen surface by the thermocycling regimes employed the more likely the flaws are to become extended resulting in premature fracture. Consequently, the discontinuity in the survival probability distributions may be attributed to a different defect mechanism (possibly an extension of large surface flaws) superimposed on the distributions at these low values of strength.

An evaluation of the mechanical properties of 'hydrothermal' dental glass after water immersion and surface polishing.

OBJECTIVES: To investigate claims that Duceram low-fusing ceramic (Duceram-LFC), a 'hydrothermal' dental veneer will increase in strength after hydrolytic testing and surface polishing.Methods. Using pre-determined powder/liquid slurry constituents, nominally identical Duceram-LFC disc-shaped specimens were fabricated to obtain mean bi-axial flexure strengths, standard deviations, Weibull modulus (m) and Vickers hardness. Thirty specimens were tested 'dry' (control), after 24 and 48h immersion in a water bath maintained at 37+/-1 degrees C and a further 30 samples polished to a 6 micrometer nap finish. RESULTS: Mean bi-axial flexure strengths of specimens tested dry were found to be 67.04+/-13.87MPa (m=7.23+/-1.32) compared with 61.01+/-15.23MPa (m=4.29+/-0.78) and 68.42+/-23.36MPa (m=3.29+/-0.60) for 24 and 48h immersion, respectively. Following surface polishing, the bi-axial flexure strength was 95.91+/-22.4MPa (m=4.37+/-0.8). Vickers hardness numbers showed no significant difference between the dry control group and after 24 and 48h immersion (P>0.05). SIGNIFICANCE: Results obtained do not support claims for surface flaw and/or defect healing through the formation of an SiOH layer at the surface of Duceram-LFC specimens over time. However, the polishing regime interrupted the defect population associated with flaws present in dry (control) samples of Duceram-LFC which can be attributed to an associated reduction of initial surface flaws and/or defects.

The influence of interfacial surface roughness on bilayered ceramic specimen performance.

OBJECTIVES: The aim of the current study was to assess the influence of interfacial surface roughness on the performance of bilayered ceramic composite disc-shaped specimens. METHODS: Specific surface flaw distributions were introduced to a series of standard aluminous core porcelain disc specimens (12 mm diameter, 1.7 mm thickness) prior to bilayering with dentin porcelain. Mean flexure strengths, standard deviations and associated Weibull moduli (m) were determined using bi-axial flexure (ball-on-ring) for each series of 30 bilayered specimens. RESULTS: The mean bi-axial fracture strengths of bilayered specimens resulted in significant differences between specimen groups with the smoothest interfacial roughness recording the highest strength and fracture strength reliability. Specimen delamination was identified in five of the bilayered group with the smoothest interfacial roughness compared with no specimen delaminations in the rougher interface groups. However, fracture occurred in the weaker dentin layer rather than along the interface between the dentin and core porcelain for specimens in these rougher interface groups. CONCLUSIONS: A smoother interfacial surface roughness resulted in increased performance, namely increased strength and reliability amongst the bilayered dental ceramic composite specimens examined in the current investigation. The incidence of complete or partial delamination of the reinforcing core and aesthetic dentin was increased for these specimens since the reduced tortuosity of the interface between porcelain layers fails to restrict propagation of a crack front along the interface.

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.

Monomer conversion versus flexure strength of a novel dental composite.

OBJECTIVES: To quantify the monomer conversion and flexural strength of an experimental oxirane-based composite material (EXL596) compared with two, commercially available, dimethacrylate based restoratives (Z250 and Z100). METHODS: Fourier-transform infra-red spectroscopy (FTIR) was utilised to evaluate the degree of conversion (DC) (n=5) and biaxial flexure strength (BFS) testing (n=20) was used to analyse flexural strength and associated Weibull moduli (m) of each material following 0.1, 0.5, 1, 4, 24 and 48 h immersion in a lightproof waterbath maintained at 37+/-1 degrees C. RESULTS: The DC of Z250 and Z100 following 0.1, 0.5 and 1 h post-irradiation was significantly greater than the DC of EXL596 for the same immersion periods. This was manifested as a significant decrease in BFS and associated m of EXL596 compared with Z250 and Z100 for the 0.1, 0.5 and 1 h post-irradiation periods. The DC and BFS of EXL596 were significantly greater than Z250 and Z100 following 24 h immersion. CONCLUSIONS: Assessment of FTIR spectra, BFS and associated m has provided a useful method in the quantitative analysis of resin-based composite conversion. Identification of the decreased DC of EXL596 compared with Z250 and Z100 was achieved using FTIR. However, decreased conversion rates within the first hour following irradiation of EXL596 may compromise flexural strength properties (associated with a decrease in BFS and m) which may be inadequate under masticatory loading.

The reliability in flexural strength testing of a novel dental composite.

OBJECTIVES: To investigate the reliability of bi-axial flexure and three-point flexure testing of an experimental, low-shrink oxirane-based dental composite, EXL596 compared with two conventional methacrylate based restoratives, Z250 and Z100. METHODS: Specimens (n=20) of a novel oxirane-based composite and two commercially available methacrylate based composites were fabricated for flexural testing to evaluate mean bi-axial flexure strengths, three-point flexure strengths and the associated Weibull moduli (m) following 24 h immersion in a lightproof waterbath maintained at 37+/-1 degrees C. RESULTS: Mean bi-axial flexure strengths and the associated m of EXL596, Z250 and Z100 were 168+/-11 MPa (m=16.2+/-4), 140+/-12 MPa (m=11.9+/-3) and 126+/-13 MPa (m=10.2+/-2), respectively. Three-point flexure strengths and the associated m of EXL596, Z250 and Z100 were 113+/-15 MPa (m=9.2+/-2), 92+/-10 MPa (m=8.5+/-2) and 79+/-16 MPa (m=6.3+/-1), respectively. CONCLUSIONS: The present investigation suggests that bi-axial flexure strength testing of dental resin-based composites provides a more reliable testing method than three-point flexure. The increased reliability was considered in terms of the associated Weibull moduli following bi-axial flexure testing as a result of the elimination of the additional induced variability introduced during the curing regime of three-point flexure specimens.

Are adhesive technologies needed to support ceramics? An assessment of the current evidence.

Despite large variations in the reported fracture strengths of dispersion strengthened, glass infiltrated, castable, pressable and machinable ceramics utilised for the construction of all-ceramic crowns, the annual clinical failure rate reported for these materials in the dental literature is remarkably consistent at ca 3%. These results emphasise that there may be little correlation between the average fracture strength and resultant clinical performance. Consequently, if ceramics are to be used for dental applications, then clearly more detailed information on the statistical variations in strength combined with the influence of cementation media are required. The effect of adhesive technology has been examined in laboratory and clinical studies. The laboratory studies focused on the effect of cement lute on crown performance, whilst surface degradation and strengthening effects with different systems were examined utilising conventional materials science techniques. Clinical studies focused on the failure rates of conventionally luted and adhesively luted crowns and inlays. There would appear to be evidence from clinical studies that crowns luted with a resin cement and with the placement procedure incorporating a dentine bonding stage have enhanced rates of survival. It is therefore concluded that the available research strongly suggests that the use of resin as a luting material for ceramic restorations is indicated, given the research from three differing sources - laboratory fracture studies comparing restorations luted with resin vs other materials, clinical studies, and laboratory studies examining the surface sealing/strengthening effect of resin on ceramic. Laboratory studies also confirm the enhanced resistance to fracture of crowns cemented with an adhesive procedure.

Properties of encapsulated and hand-mixed zinc phosphate dental cement.

PURPOSE: Dental cements can be supplied as loose powder and liquid or as encapsulated syringes. This study assessed the compressive strength of a recently marketed zinc phosphate encapsulated cement compared with a hand-mixed system according to the American Dental Association Specification. MATERIALS AND METHODS: The mean fracture strength, standard deviations and associated Weibull Moduli (m) of the encapsulated and hand-mixed cements were determined by compressive fracturing 30 cylindrical specimens (height 6.0 +/- 0.1 mm, diameter 4.0 +/- 0.1 mm). Scanning electron microscopy was employed to assess crack growth from indentations and cement morphology. Image analysis was used to investigate the influence of mixing regime on pore distribution within the cement samples. RESULTS: The compressive strength data showed variation in magnitude and reliability ranging from 42 +/- 8 MPa (m = 5.2 +/- 1.0) for the encapsulated cement filled directly from the capsule to 71 +/- 11 MPa (m = 6.3 +/- 1.3) for the hand-mixed cement. The encapsulated cement matrix was extensively porous, consisting of pores between 0.1-0.5 microm diameter, compared with the non-porous hand-mixed cement matrix. Larger pores (over 18 microm diameter) were related to air entrapment in the encapsulated cement on mixing while small pores (0.1-0.5 microm diameter) were indicative of vaporization porosity commonly seen with exothermic reactions.

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).

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.

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. Groups A to C were reinforced with polyethylene fibers, and group D was an unreinforced control. Fibers were positioned either around (A), beneath the notch (B), or at the disc base (C). Specimens were stored in distilled water at 37 degrees C for 24 h before testing to failure (CHS=1mm/min) in a universal testing machine. Mean torque to failure values ranked [P< 0.05; one-way analysis of variance (ANOVA)] as follows A = B > C = D. In series II five groups of three unit bridges (n =5/group; codes A to E) were prepared from Artglass dental composite without (group A) or with (groups B to E) different Connect fiber reinforcement locations/techniques. Bridges were cemented using 2 bond resin cement to a standardized substructure. After storage, as per series I, bridges were loaded mid-pontic region to failure. One-way ANOVA showed no significant (P=0.08) difference between test groups. The research hypothesis was that notched disc and 3 unit bridge test techniques would discriminate equally between fiber-reinforced specimens and an unreinforced composite control was rejected.