Julian D. Satterthwaite

Degree of conversion of bulk-fill compared to conventional resin-composites at two time intervals

OBJECTIVE The purpose of this study was to assess the degree of conversion (DC) over time, using FTIR spectroscopy for bulk-fill flowable resin composite materials compared to conventional flowable and regular resin composite materials. METHODS Eight resin composites were investigated including flowable bulk-fill materials SureFil SDR (SDR), Venus bulk-fill (VBF), x-tra base (XB), and Filtek Bulk Fill (FBF). Conventional flowable and regular composite materials included: Venus Diamond flow (VDF), Grandioso flow (GRF), Venus Diamond (VD), and Grandioso (GR). Degree of conversion (DC) was assessed by Fourier transform infrared spectroscopy using attenuated total reflectance technique. DC was measured for samples immediately post-cure (n=3), and after 24h storage period at 37°C (n=3). Results were analysed using one-way analysis of variance (ANOVA), Bonferroni post hoc test, and independent-samples t-test at α=0.05 significance level. RESULTS Immediately post-cure, the mean DC values of the different materials were in the following order: GRF>VDF>SDR>VBF>XB>GR>FBF<VD and ranged from 34.7 to 77.1%. 24h post-cure, DC values were in the following order: GRF>VBF>VD>SDR>VDF>GR>XB<FBF and ranged from 50.9 to 93.1%. GRF showed significantly higher DC values than all other materials at both time intervals while XB and FBF showed significantly lower values at 24h post-cure. SIGNIFICANCE The 24h post-cure DC values of the bulk-fill composites SDR and VBF are generally comparable to those of conventional composites studied; however, the 24h post-cure DC values of XB and FBF were lower compared to the other materials.

Measurement of the full-field polymerization shrinkage and depth of cure of dental composites using digital image correlation

OBJECTIVES The aim of this study was to measure the full-field polymerization shrinkage of dental composites using optical image correlation method. METHODS Bar specimens of cross-section 4mm x 2mm and length 10mm approximately were light cured with two irradiances, 450 mW/cm(2) and 180 mW/cm(2), respectively. The curing light was generated with Optilux 501 (Kerr) and the two different irradiances were achieved by adjusting the distance between the light tip and the specimen. A single-camera 2D measuring system was used to record the deformation of the composite specimen for 30 min at a frequency of 0.1 Hz. The specimen surface under observation was sprayed with paint to produce sufficient contrast to allow tracking of individual points on the surface. The curing light was applied to one end of the specimen for 40s during which the painted surface was fully covered. After curing, the cover was removed immediately so that deformation of the painted surface could be recorded by the camera. The images were then analyzed with specialist software and the volumetric shrinkage determined along the beam length. RESULTS A typical shrinkage strain field obtained on a specimen surface was highly non-uniform, even at positions of constant distance from the irradiation surface, indicating possible heterogeneity in material composition and shrinkage behavior in the composite. The maximum volumetric shrinkage strain of approximately 1.5% occurred at a subsurface distance of about 1mm, instead of at the irradiation surface. After reaching its peak value, the shrinkage strain then gradually decreased with increasing distance along the beam length, before leveling off to a value of approximately 0.2% at a distance of 4-5mm. The maximum volumetric shrinkage obtained agreed well with the value of 1.6% reported by the manufacturer for the composite examined in this work. Using irradiance of 180 mW/cm(2) resulted in only slightly less polymerization shrinkage than using irradiance of 450 mW/cm(2). SIGNIFICANCE Compared to the other measurement methods, the image correlation method is capable of producing full-field information about the polymerization shrinkage behavior of dental composites.

Effect of resin-composite filler particle size and shape on shrinkage–strain

OBJECTIVES The aim of this study was to investigate the effect of variations in filler particle size and shape on the polymerization shrinkage-strain kinetics of resin-composites. METHODS A model series of 12 VLC resin-composites were studied. The particulate dispersed phase volume fraction was 56.7%: these filler particles were systematically graded in size, and further were either spherical or irregular. The bonded disk method was used to determine shrinkage-strain kinetics. Displacement was recorded following 40s irradiation (600mW/cm(2)) at 23 degrees C (n=3). All data were captured for 60min and the final shrinkage-strain calculated. RESULTS For materials with spherical filler, shrinkage-strain was 2.66% (SD 0.18) for those with irregular filler it was 2.89% (SD 0.11). These differences were statistically significant (p<0.001): the Scheffé test identified two subsets, those with irregular filler (including materials with a multimodal mix) and those with spherical filler (including materials with a multimodal mix). Additionally, there was a trend for higher shrinkage-strain values with decreasing filler particle size which was apparent for both those composites with spherical filler particles and those with irregular filler particles. For irregular filler particles, linear regression gave a high correlation (r(2)=0.99). SIGNIFICANCE Statistically significant differences were identified in the shrinkage behavior of resin-composites with differing filler size and shape.

Effect of resin-composite filler particle size and shape on shrinkage-stress

OBJECTIVES The aim of this study was to investigate the effect of variations in filler particle size and shape on the polymerization shrinkage-stress kinetics of resin-composites. METHODS A model series of 12 VLC resin-composites were studied. The particulate dispersed phase volume fraction was 56.7%: these filler particles were systematically graded in size, and further were either spherical or irregular. A Bioman instrument (cantilever beam method) was employed to determine the shrinkage-stress kinetics following 40s irradiation (600 mW/cm(2)) at 23°C (n=3). All data were captured for 60 min and the final shrinkage-stress calculated. RESULTS Shrinkage-stress varied between 3.86 MPa (SD 0.14) for S3 (spherical filler particles of 500 nm) and 8.44 MPa (SD 0.41) for I1 (irregular filler particles of 450 nm). The shrinkage-stress values were generally lower for those composites with spherical filler particles than those with irregular filler particles. The differences in shrinkage-stress with filler particle size and shape were statistically significant (p<0.001). SIGNIFICANCE Composites with spherical filler particles exhibit lower shrinkage-stress values compared to those with irregular filler particles. Shrinkage-stress and shrinkage-stress rate vary in a complex manner with variations in the size of the dispersed phase particles: a hypothesized explanation for the effect of filler particle size and shape is presented.

Post-irradiation hardness development, chemical softening, and thermal stability of bulk-fill and conventional resin-composites

OBJECTIVES To measure bottom/top hardness ratio of bulk-fill and conventional resin-composite materials, and to assess hardness changes after dry and ethanol storage. Filler content and kinetics of thermal decomposition were also tested using thermogravimetric analysis (TGA). METHODS Six bulk-fill (SureFil SDR, Venus bulk fill, X-tra base, Filtek bulk fill flowable, Sonic fill, and Tetric EvoCeram bulk-fill) and eight conventional resin-composite materials (Grandioso flow, Venus Diamond flow, X-flow, Filtek Supreme Ultra Flowable, Grandioso, Venus Diamond, TPH Spectrum, and Filtek Z250) were tested (n=5). Initial and 24h (post-cure dry storage) top and bottom microhardness values were measured. Microhardness was re-measured after the samples were stored in 75% ethanol/water solution. Thermal decomposition and filler content were assessed by TGA. Results were analysed using one-way ANOVA and paired sample t-test (α=0.05). RESULTS All materials showed significant increase of microhardness after 24h of dry storage which ranged from 100.1% to 9.1%. Bottom/top microhardness ratio >0.9 was exhibited by all materials. All materials showed significant decrease of microhardness after 24h of storage in 75% ethanol/water which ranged from 14.5% to 74.2%. The extent of post-irradiation hardness development was positively correlated to the extent of ethanol softening (R(2)=0.89, p<0.001). Initial thermal decomposition temperature assessed by TGA was variable and was correlated to ethanol softening. CONCLUSIONS Bulk-fill resin-composites exhibit comparable bottom/top hardness ratio to conventional materials at recommended manufacturer thickness. Hardness was affected to a variable extent by storage with variable inorganic filler content and initial thermal decomposition shown by TGA. CLINICAL SIGNIFICANCE The manufacturer recommended depth of cure of bulk-fill resin-composites can be reached based on the microhardness method. Characterization of the primary polymer network of a resin-composite material should be considered when evaluating its stability in the aqueous oral environment.

Adhesives for the restoration of non-carious cervical lesions: a systematic review

OBJECTIVES To establish whether simplified adhesives (self-etch) are as clinically effective as conventional adhesives (etch-and-rinse) with multiple application steps for treatment of non-carious cervical lesions (NCCLs). NULL HYPOTHESIS there is no difference in the clinical effectiveness of the four different bonding strategies: Three-step etch-and-rinse; Two-step etch-and-rinse; Two-step self-etch; One-step self-etch for treatment of NCCLs. SOURCES Electronic databases were searched including: Cochrane Oral Health Group Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE. In addition, studies were identified by handsearching of selected journals. STUDY SELECTION Randomised controlled trials (RCTs) comparing at least two adhesives in non-carious cervical lesions (NCCLs), with at least 18 months follow-up were selected. The primary outcome was loss of retention/restoration loss, with marginal adaptation and marginal discolouration as secondary outcomes. Criteria for quality assessment included: random sequence generation; allocation concealment; blinding of outcome assessment; and information on withdrawals. Twenty six studies were identified that met the inclusion criteria. In general, studies were not of sufficient quality to fully address the objectives of this review. CONCLUSION There is not enough evidence to support one adhesive or bonding strategy over another for treatment of NCCLs. Consequently, the null hypothesis of no difference cannot be supported or rejected with the data currently available. There is a need for better standardisation and reporting of randomised controlled trials investigating adhesive performance. CLINICAL SIGNIFICANCE Studies with low overall risk of bias demonstrated good clinical performance for adhesives with all four bonding strategies. However, included studies showed wide variation between adhesives of the same category.

Retrieval of a fractured abutment screw thread from an implant: a case report.

This report describes the management of a loose cement-retained implant supported crown where the thread of the abutment screw had fractured away from the body of the screw and was retained within the implant. The importance of multi-disciplinary skills in the treatment of patients with implants is discussed.

Qualitative and quantitative characterization of monomers of uncured bulk-fill and conventional resin-composites using liquid chromatography/mass spectrometry

OBJECTIVES The aim of this study was to assess the resin matrix monomer composition of selected bulk-fill and conventional resin-composite materials using reverse phase liquid chromatography coupled with electron spray ionization mass spectrometry. MATERIAL AND METHODS Six bulk-fill (SureFil SDR, Venus Bulk Fill, X-tra base, Filtek Bulk Fill flowable, Sonic Fill, and Tetric EvoCeram Bulk Fill) and eight conventional resin-composites (Grandioso Flow, Venus Diamond Flow, X-Flow, Filtek Supreme XTE, Grandioso, Venus Diamond, TPH Spectrum, and Filtek Z250) were tested. For assessment of resin composition and relative monomer amounts, uncured resin-composites were analysed with reverse phase liquid chromatography/electron spray ionization mass spectrometry. logP values (a measure of hydrophobicity) of detected compounds were calculated and their correlation to reverse phase liquid chromatography retention time was explored. Data were analysed with one-way ANOVA, Tukey post hoc test, Pearson correlation and regression analyses at α=0.05. RESULTS The main monomers detected were BisGMA, UDMA, TEGDMA, and BisEMA. Monomers were detected at variable combinations in different materials with significantly different relative amounts. Other monomers were detected including HDDMA, DEGDMA, TCD-DI-HEA, and SDR-UDMA in Grandioso flow, X-flow, Venus Diamond, and SureFil SDR respectively. A positive correlation between logP and reverse phase liquid chromatography retention time was detected (r(2)=0.62, p=0.004). CONCLUSIONS Resin composition of bulk-fill resin-composites is comparable to that of conventional materials with the exception of SureFil SDR. The relative hydrophobicity of dental monomers can be determined by their reverse phase liquid chromatography retention time.

Fungicidal amounts of antifungals are released from impregnated denture lining material for up to 28 days

OBJECTIVES The aim of this study was to investigate the efficacy of a polymeric delivery system impregnated with chlorhexidine or fluconazole against Candida species. METHODS Self-cure poly-ethyl methacrylate and tetrahydro-furfuryl methacrylate (PEM/THFM) discs impregnated with pure fluconazole substance (FLUp), fluconazole powder from capsules (FLUc) or chlorhexidine powder (CHX) were incubated in water for up to 28 days at 37 °C. The water was replaced at 24h and 3, 7, 14, 21, 28 days. The amount of released drugs and antifungal activity of the leachates was measured by bioassay. The minimal inhibitory concentration (MIC) of each drug for 46 Candida isolates was determined and compared to the released concentrations. RESULTS A total of 53.0% of CHX, 38.5% of FLUc and 13.2% of FLUp impregnated into the discs was leached during the 28-day incubation. Of the total amount leached, 71.8% of CHX, 75.1% of FLUc and 70.5% of FLUp was released during the first week of incubation. Antifungal activity was confirmed for up to 28 days. CONCLUSION Both chlorhexidine and fluconazole become readily leached from PEM/THFM polymer up to four weeks and that the polymerisation of the acrylic does not affect the antimicrobial activity of the agents. Importantly, the amount of drugs released exceeded the MICs of most isolates also during the fourth week of incubation. CLINICAL SIGNIFICANCE These findings indicate the feasibility of this treatment modality for oral candidal infections, especially denture stomatitis. But further in vivo work is warranted to determine its clinical relevance and applicability.

An automated assessment algorithm for micro-CT images of occlusal caries

OBJECTIVES To produce and test an algorithm to automatically quantify natural occlusal caries lesions in micro-computed tomography (micro-CT) scans of human teeth. METHODS The algorithm presented divides the occlusal surface into regions of enamel and dentine by looking for sharp increases and decreases in radiopacity characteristic of step changes between materials. The accuracy of an automatic occlusal caries assessment based on these regions is assessed against serial histological assessment and manual examination of the same micro-CT images, using data from 68 previously scanned and sectioned teeth with varying levels of natural occlusal caries. RESULTS Only three teeth were found to be free of caries by histology. The results of the automated analysis correlate well with histological assessment with a ρ of 0.80 (p < 0.001), and with manual CT assessment with a ρ of 0.85 (p < 0.001). The depth of dentine lesions correlated with histology with an intra-class correlation coefficient of 0.82 (p < 0.001; N = 45) and with manual assessment with an ICC of 0.93 (p < 0.001; N = 39). Micro-CT is found to generally underestimate caries compared to histological assessment. CONCLUSIONS The algorithm presented can successfully segment micro-CT scans into occlusal enamel and dentine regions, and the results show that the depths of dentine caries lesions can be accurately and objectively measured automatically using micro-CT. However, if enamel caries is to be accurately assessed by a computer, better scans will be required than those used here.