George Vougiouklakis

Degree of double bond conversion in light-cured composites.

The curing pattern of five commercial light-cured composites was investigated. Micro-ATR infrared spectroscopy was used to evaluate the degree of cure as a function of distance from the exposed surface and curing time. KHN measurements were also obtained for each depth to relate the hardness pattern to the degree of conversion. The post-curing efficiency of each system was studied by DSC. The results indicate that microfilled materials present smaller depth of cure and higher amount of unconverted bonds as a function of distance and exposure time. Depth of cure, hardness pattern and curing pattern are extended with increased inorganic loading. The thermal capacity of the filler fraction influences degree of cure. A great loss in the heat induced polymerization is observed 24-h post curing, attributed to the dead end polymerization effect.

Heterogeneous distribution of single-bottle adhesive monomers in the resin–dentin interdiffusion zone

OBJECTIVES The purpose of this study was to investigate whether monomer separation occurs in single-bottle adhesives applied on acid-etched dentin surfaces. METHODS Smear-layer covered dentin specimens produced from sound premolars, were acid-etched and analyzed by micro-MIR FTIR spectroscopy, before and after treatment with the single-bottle adhesives One-Step, Prime and Bond 2.1, Scotchbond 1 and Syntac-Sprint. The difference spectra (etched, and primed minus etched of the same dentin surfaces) were plotted and compared with original adhesive spectra. The C=C/C...C (aromatic adhesives) and C=C/C=O (aliphatic adhesives) peak area ratios were used to evaluate the extent of monomer separation relative to original adhesive spectra at the uppermost 2 microm of the resin-dentin interdiffusion zone. Three dentin specimens were used for each adhesive. One-way ANOVA and Newman-Keuls tests were performed to assess the statistically significant differences (alpha=0.05). RESULTS All the adhesives demonstrated separation of monomer components on etched dentin ranging in mean values from 68.7 to 81.9% relative to reference. High molecular weight hydrophobic (i.e. BisDMA, BisGMA, BisGMA adducts) and hydrophilic monomers (i.e. BPDMA) predominated at the region probed. Prime and Bond 2.1 demonstrated the highest extent of monomer separation. SIGNIFICANCE Heterogeneous monomer distribution following application to etched dentin may affect the curing performance of single-bottle adhesives within the resin infiltrated region and consequently, the mechanical and chemical stability of the network formed.

Composition, wetting properties and bond strength with dentin of 6 new dentin adhesives

Abstract Four commercially available (Scotchbond, Dentine Bonding Agent, Dentin Adhesit, Den-Mat), and 2 experimental adhesives (NPG/PMDM, GLUMA) were included in this study. Composition of the commercial systems was determined by IR and 1 H, 13 C FT-NMR Spectroscopy. Wetting characteristics of the adhesives were obtained from contact angle measurements on dentin. Bonding of a light-cure composite to dentin using these materials was investigated before and after thermal cycling utilizing a shear test. Judging by the composition analyses, adhesive mechanisms involve bonding to dentin Ca, OH, collagen (−NH 2 ) or surface chelation and copolymerization through adhesive (C=C) groups with the restorative resin. There were some differences in contact angles varying between 7° (Adhesit) and 12° (GLUMA). The highest bond strength was obtained with GLUMA. Thermal cycling caused a large decrease in bond strength, but the ranking of the materials remained the same.

Effect of acidic conditioners on dentin morphology, molecular composition and collagen conformation in situ.

OBJECTIVE The aim of the study was to evaluate the effect of some acidic conditioners on dentin morphology, molecular composition and collagen conformation in situ. METHODS Smear layer-covered dentin specimens prepared from third molars immediately after extraction were imaged by tapping made AFM and analyzed by MIR-FTIR spectroscopy. The same specimens were subjected to conditioning treatments with CA Agent (Kuraray), Scotchbond Etchant (3M Dental Products) and Scotchbond MP Etchant (3M Dental Products) gels and then imaged and analyzed again. The extent of dentin decalcification at the uppermost 2 microns region was calculated from the percentage reduction in the-PO4/amide I peak area ratio of conditioned specimens relative to their individual smear layer-covered references. These results were compared by ANOVA and Scheffé statistical analyses. The conformational changes of dentin type I collagen at the region were studied qualitatively by deconvoluting the amide I bands of MIR-FTIR spectra and assigning the band components to carbonyl hydrogen bonding states related to the alpha-helix structure. RESULTS All the conditioners removed the smear layer, funneled the tubules, increased the intertubular roughness and contaminated the dentin surfaces with residues from irreversibly adsorbed thickening agents. Conditioned dentin surfaces showed a reduction in orthophosphates and carbonates and an increase in amide I, II and III groups. CA Agent manifested a significantly lower extent of dentin decalcification than Scotchbond etchants (p < 0.05). Collagen conformational changes involved a decrease in intermolecular hydrogen bonded amide I carbonyls associated with the alpha-helix structure and enhancement of imide carbonyls hydrogen bonded to water, which suggest collagen denaturation. SIGNIFICANCE Apart from dentin decalcification, the acidic conditioners induced considerable changes on dentin collagen conformation mostly associated with denaturation processes. In addition, irreversibly adsorbed residual thickeners substantially modified the morphology and composition of dentin surfaces. These findings show the complex interaction pathways between conditioners and dentin surfaces and the great potential of modern in situ imaging and analysis techniques in probing these interactions.

Surface reactions of adhesives on dentin

The purpose of this study was to characterize changes in the surface chemistry of dentin following various adhesive treatments. The coronal parts of sound freshly extracted third molars were cross-sectioned over the pulp chambers, each producing a pair of dentin samples which were polished to 600 grit and cleaned with 3% H2O2. The first sample of each pair was used as a control, while the second one was subjected to one of the following adhesive treatments: (a) Gluma Cleanser, (b) Tenure Conditioner, (c) Scotchprep, (d) Gluma Cleanser/Gluma Primer, (e) Tenure Conditioner/Tenure Solution A&B, or (f) Scotchprep/Scotchbond 2 Adhesive. The treated samples paired with their respective controls were studied by small-area ESCA spectroscopy. Three areas of 1.0 mm in diameter randomly chosen on each sample were analyzed by survey and C1s, O1s, N1s high-resolution spectra. The samples from groups d, e, and f were additionally subjected to argon-ion-depth profiling of the uppermost 2-nm layer at 0.5-nm intervals. According to the results, treatment modes a, b, and c caused the reduction of carbonates and increased the -NH/NH2 ratio. Treatments a and c increased the alcohol groups, while treatments b and c increased the carbonyl and ether groups. All these changes were in comparison to the reference dentin specimens. Dentin treatment with d, e, and f induced a complex in depth distribution of the C, N, O binding states. The energy shifts detected do not indicate primary bonding of the tested adhesives to the dental substrate.

Characterization of oral films formed in the presence of a CPP–ACP agent: An in situ study

OBJECTIVES The aim of this study was to compare the morphological appearance and the molecular composition of intraoral integuments formed in situ on germanium (Ge) crystals in the presence or absence of the commercially available casein-phosphopeptide-amorphous calcium phosphate (CPP-ACP) cream agent. METHODS Six volunteers participated in the study. Impression of maxillary arch was taken for each patient, and a removable orthodontic appliance with a custom-made retainer was fabricated. Clean Ge crystals mounted in the retainers were placed intraorally for 30 min, 8, 24 h and 1-week period. The free sampling surface of another series of Ge crystals was treated with the commercial CPP-ACP agent (Tooth Mousse), mounted in the retainers and placed intraorally for the same period as above. The free exposed surfaces in oral cavity of the specimens in all subjects were examined as follows: (a) reflected light microscopy, (b) micro-MIR-FTIR spectroscopy and (c) scanning electron microscopy (SEM) plus energy-dispersive X-ray microanalysis analysis (XEDS). RESULTS The light microscopic observations revealed that there was a delay in biofilm formation on Ge surfaces treated with agent in comparison to those ones without treatment. The micro-MIR-FTIR spectra from the surfaces with Tooth Mousse showed an increase in intensity and a left shift of PO(4)(3-) peak (1064 cm(-1)). Finally, the PO(4)(3-) peak at lower bands (564 cm(-1)) and the low-wave bands at 525-530 cm(-1) increased at 1-week interval. The SEM revealed the dendritic development of microbes. The XEDS analysis showed a significant increase in Cl/O, K/O, K/Cl and a decrease in Ca/O and P/O ratios on the crystal Ge without surface treatment. On contrary, on the crystal Ge with surface treatment an increase in Ca/O, Ca/P and a decrease in K/Cl ratios were found. CONCLUSION The results show that the presence of CPP-ACP agent delays the biofilm formation and favored the nucleation and crystallization of calcium phosphates, possibly in apatitic form, in matured biofilms.

Effect of dentin primers on the morphology, molecular composition and collagen conformation of acid-demineralized dentin in situ

OBJECTIVES The purpose of this study was to assess the effect of two commercial primers and distilled water on the morphology, molecular composition and collagen conformation of acid-demineralized dentin in situ. METHODS Dentin specimens etched with Scotchbond Etchant were imaged by tapping mode AFM and analyzed by MIR-FTIR spectroscopy. They were then primed with Scotchbond Multi-Purpose Plus Primer, Scotchbond 1 Adhesive or distilled water and imaged and analyzed again. The chemical modifications induced on the uppermost 2 microns of primed dentin were studied after water and original primer subtraction. The conformational changes of type I collagen at this region were evaluated by deconvoluting the amide I band components. The absorbance ratio An(1655/1627) was used to semiquantitatively assess, on a relative basis, the extent of collagen denaturation. RESULTS All the priming treatments swelled the collapsed dentin collagen left after etching. No evidence of primary bonding was found after priming treatments, while approximately 50% of the conditioned dentin collagen appeared denatured. Treatment with distilled water did not change the status of denatured collagen, however, application of the commercial primers refolded the alpha-helix to approximately 95% of the extent found on the native reference dentin. SIGNIFICANCE The dynamic response of dentin collagen to demineralization and priming treatments reveals the critical role of some primers in rapidly restoring the conformational status of acid-denatured collagen. Implementation of reactive adhesive groups in alpha-helix recovery may provide an associative means of modifying the mechanical properties of the demineralized collagen based on the extent of their intermolecular bonding.

Evaluation of a new fluorescence-based device in the detection of incipient occlusal caries lesions

The aim of this in vitro study was to evaluate the performance of various contemporary detection tools at incipient occlusal caries. Thirty eight freshly extracted posterior teeth with non-cavitated occlusal caries were subjected to clinical examination and coding according to ICDAS criteria (n = 38). Standardized fluorescence images were taken with VistaProof (Dürr Dental, Bietigheim-Bissingen, Germany). Furthermore, the teeth were calculated with a laser fluorescence pen device (DIAGNOdent pen, Kavo, Biberach, Germany). In all detection methods, assessment of caries was performed twice (with 1-week interval) by two calibrated examiners. Finally, the caries lesions were validated in tooth sections by histological examination. The intra-examiner and inter-examiner kappa coefficient, sensitivity, and specificity were determined for all detection methods at enamel lesions (D1 threshold). Degrees of agreement of each method with the histological status were calculated using receiver operating characteristic statistics and the area under curve (Az values). The kappa intra-examiner/inter-examiner coefficient values (mean ± SD) were 0.74 ± 0.04/0.73 ± 0.07, 0.87 ± 0.04/0.82 ± 0.07, and 0.91 ± 0.06/0.83 ± 0.08 for clinical examination, DIAGNOdent pen, and VistaProof, respectively. The sensitivity for ICDAS was 0.80–0.86, for DIAGNOdent pen was 0.66–0.75, and for the VistaProof device was 0.97. The specificity for all the detection methods were 0.5 (0.02–0.99). The accuracy value for ICDAS was 0.76–0.81, for DIAGNOdent pen 0.66–0.71, and for the VistaProof device 0.92–0.95. The Az values (mean ± SD) were 0.431 ± 0.187, 0.583 ± 0.215, and 0.486 ± 0.207 for ICDAS, DIAGNOdent pen, and VistaProof examination, respectively. No significant differences in Az values were noted among the methods. All detection methods were presented with high inter-examiner and intra-examiner agreement. The new VistaProof device showed the best sensitivity, while DIAGNOdent pen demonstrated the worst one. Specificities were the same for all detection methods. Moreover, they presented the same performance in detection of incipient occlusal caries.

Effect of fluoride and of calcium sodium phosphosilicate toothpastes on pre-softened dentin demineralization and remineralization in vitro.

OBJECTIVES The purpose of this in vitro study was to evaluate the effect of toothpastes containing sodium fluoride in different concentrations or a calcium sodium phosphosilicate system on pre-softened dentin demineralization and remineralization. METHODS During a ten day pH-cycling protocol, pre-softened bovine root dentin slabs were immersed twice daily, after the demineralization periods, for 2min, in the following toothpaste slurries: (a) non-fluoridated (control), (b) 7.5% calcium sodium phosphosilicate, (c) 1450 ppm F, (d) 2800 ppm F and (e) 5000 ppm F. Subsequently, the specimens were subjected to a 15-h acid resistance test. Surface microhardness was assessed initially and during the pH-cycling and the acid resistance test period. Repeated measurements in each group were analyzed through appropriate regression models for longitudinal data. RESULTS All fluoride groups, during pH cycling, showed significantly less microhardness loss (p < or = 0.010, p < or = 0.002, p < or = 0.002) and subsequently exhibited increased acid resistance (p < or = 0.010, p < or = 0.001, p < or = 0.001) compared to the control. The 5000 ppm and 2800 ppm F toothpastes, inhibited demineralization significantly more effectively than the 1450 ppm F (p < or = 0.001, p < or = 0.030) and the calcium sodium phosphosilicate toothpaste (p < or = 0.001), while no significant differences were found between the two high fluoride groups (p=0.130). The calcium sodium phosphosilicate toothpaste, during pH cycling showed a difference that approached statistical significance compared to control (p=0.079), but its acid resistance behavior was similar to control (p=0.610). CONCLUSIONS Under these experimental conditions, the high fluoride toothpastes promoted remineralization and inhibited demineralization more effectively, than the 1450 ppm F, the non-fluoridated (control) and the calcium sodium phosphosilicate toothpastes.

The Impact of Magnification on Occlusal Caries Diagnosis with Implementation of the ICDAS II Criteria

Aim: This study compared the impact of low-powered magnification on the detection of occlusal caries. Methods: The occlusal surfaces of 38 extracted teeth received caries ICDAS classification with and without magnification by two examiners. Histology was used as the gold standard. Results: No significant differences existed in terms of sensitivity, specificity, LR+, LR- and Az values for the two examiners and modalities. Interexaminer agreement was almost perfect for grades 0, 2, 3 irrespective of magnification. For grade 1, magnification resulted in lower agreement than unaided vision. Conclusion: Magnification does not improve the detective performance of visual examination.