George Eliades

Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: A potential clinical problem

When a ZnOE type sealer was placed in root canals treated previously with calcium hydroxide dressing, an accelerated sealer setting rate occasionally occurred. This clinical observation led to the present experimental design aiming to investigate the effect of calcium hydroxide on a ZnOE cement and ZnOE type sealers and to preliminarily assess the removal efficiency of a calcium hydroxide preparation from root canal systems. Micro-MIR FTIR spectroscopy was used to quantify the effect of calcium hydroxide on the setting reactions of a ZnOE cement and two ZnOE type sealers. The removal efficiency of calcium hydroxide from root canal systems was evaluated after treatment with NaOCl; NaOCl and filing; and NaOCl plus EDTA and filing. Calcium hydroxide preferentially interacted with eugenol inhibiting the ZnO-eugenol chelate formation. The Ca(OH)2-eugenol interaction was rapid, and kinetically dependent, leading to residual eugenol in the set product. The set ZnOE cement and the ZnOE type sealers in contact with calcium hydroxide were brittle in consistency and granular in structure. Although none of the treatments tested completely removed calcium hydroxide from root canals, treatment with EDTA significantly reduced the extent of residual calcium hydroxide.

Setting characteristics and cavity adaptation of low-shrinking resin composites

OBJECTIVES The aim of this study was to evaluate the setting characteristics of low-shrinking resin composites and examine the possible interactions with curing efficiency and marginal adaptation in dentin cavities. METHODS The materials tested were Ceram X Mono/CM, Premise/PR, Clearfil Majesty/CM, ELS/EL, and Filtek Silorane/FS. Polymerization shrinkage strain (%S), strain rate (%S(r)) and time at maximum strain rate (t(max)) were measured using the bonded disk method. Curing efficiency was measured on the top and bottom surfaces of composites with ATR-FTIR spectroscopy. Marginal adaptation was measured in unbonded (%VVF) and bonded (%XVF) specimens by computerized X-ray microtomography (micro-XCT). The % linear length of the interfacial gaps along the cavity margins (%LD) and the maximum gap width (WD(max)) were calculated under optical microscopy on sectioned specimens. Statistical analysis was performed with one- and two-way ANOVA, Bonferronis post hoc test and Pearsons correlation coefficient. RESULTS The %S values ranged from 1.34% (FS) to 2.29% (CX), while %S(r) ranged from 0.06%s(-1) (FS) to 0.15%s(-1) (CX). %VVF values extended from 1.9% (FS) to 5.3% (CX) and for %XVF from 1.98% (FS) to 3.35% (CX). The values for %LD ranged from 36.52% (FS) to 81.28% (CX). Linear regression showed strong positive correlation for %S(r) and t(max) with %VVF (r(2)=0.884 and r(2)=0.927) and also for %S(r) and t(max) with %LD (r(2)=0.823 and r(2)=0.869). SIGNIFICANCE %S(r) and t(max) are more representative than %S in determining the setting pattern of the materials and are strongly correlated to marginal adaptation. The silorane material showed better behavior than the dimethacrylate materials in setting shrinkage and marginal adaptation.

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.

Microbial attachment on orthodontic appliances: I. Wettability and early pellicle formation on bracket materials

The objectives of this study were to investigate the wettability of orthodontic bracket material surfaces and the composition of salivary films adsorbed onto them after 30 and 60 minutes in vivo exposure. Specimens from stainless steel, fiber-reinforced polycarbonate, and polycrystalline alumina bracket manufacturing raw materials were subjected to (a) contact angle measurements with a homologous series of liquids, (b) micro multiple internal reflection Fourier transform infrared spectroscopy (microMIR FTIR) for the characterization of the molecular composition of the in vivo adsorbed groups, and (c) incident light optical microscopy of the acquired films. The highest critical surface tension was obtained from stainless steel (40.8 +/- 0.4 dynes/cm) followed by polycarbonate (32.8 +/- 1.3 dynes/cm) and alumina (29.0 +/- 0.9 dynes/cm), suggesting a higher potential for increased plaque-retaining capacity for the stainless steel brackets. Accordingly, the total work of adhesion and its polar and nonpolar components were consistent with the surface tension ranking. The nonpolar component of the work of adhesion was higher than its polar counterpart for all materials tested, implying a possible higher attachment prevalence for those microorganisms using dispersive forces, such as van der Waals forces, as the predominant attachment mechanism to surfaces. Qualitative and quantitative variations were observed in the adsorbed films after 30 and 60 minutes intraoral exposure that may reflect the influence of the surface properties of these substrates on the structure of the pellicle formed in vivo.

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.

Bonding of ceramic brackets to enamel: Morphologic and structural considerations

The purpose of this study was to evaluate the form and microstructure of three types of ceramic bracket and to assess their interfacial surface shapes and bond strengths with visible light-cured and chemically cured adhesives after thermocycling. One monocrystalline and two polycrystalline structures were identified. The form of the bonding bases implied three types of bonding with the adhesive: a chemical bonding, a combination of mechanical retention and adhesion, and a combination of micromechanical retention and adhesion. All the ceramic bases were covered with a layer of gamma-methacryloxypropyltrimethoxysilane coupling agent. The thickness of the adhesive layer was affected by the design of the bracket bases. The highest bond strength was obtained from the brackets by a combination of micromechanical retention and adhesion, with the site of failure located at the resin/bracket interface. The other types of ceramic brackets had a greater amount of resin left on the enamel and some cases of cohesive bracket fractures.

In vivo vs in vitro anticariogenic behavior of glass-ionomer and resin composite restorative materials

OBJECTIVE To evaluate the in vivo vs the in vitro anticariogenic potential of glass-ionomer and resin composite restoratives, utilizing a standardized interfacial gap model. METHODS (a) In vitro study. Box shaped cavities were prepared at the buccal surfaces of extracted premolars limited to enamel. The incisal cavity walls received no treatment and were covered with 40 microm-thick metal spacers. The cavities were restored with a glass-ionomer (Ketac-Fil, n=8) and a fluoride-free resin composite (Scotchbond MP Plus/Z100, n=8). After 4 weeks immersion in an acidic gel (pH 4), thin sections were produced and examined under polarized-light microscopy.(b) In vivo study. Four low caries activity volunteers, with first four premolars, each planned to be extracted for orthodontic reasons, participated in the study. Cavities were prepared as before and filled contralaterally per patient with glass-ionomer (n=8) and resin composite (n=8). After 6 months in vivo, the teeth were extracted, sectioned and investigated by polarized-light microscopy, Raman microspectroscopy and SEM-EDS X-ray microanalysis. Unpaired t-test (lesion dimensions) and one-way ANOVA and Newman-Keuls tests (Ca, P wt%, Ca/P ratios) were used to identify statistically significant differences in lesion analysis (alpha=0.05). RESULTS (a) In vitro study. All restorations developed lesions at incisal and cervical margins. At gap-free regions glass-ionomers showed reduced lesion dimensions compared to those of composites (p<0.05). At regions with gaps, no significant differences were found in lesion depth between the restorative groups tested. Lesion length was increased in composite, and decreased in glass-ionomer, whereas lesion depth in both restorative groups was increased in comparison to gap-free regions (p<0.05).(b) In vivo study. No lesions were observed at gap-free regions. At gap regions, 75.5% of glass-ionomer and 62.5% of composite restorations developed lesions. The lesion dimensions were significantly greater in glass-ionomer (p<0.05). A reduction in PO4(3-), CO3(2-), Ca and P was found in lesions compared to intact tissues. No F was detected and no CaF2 lattice vibrations were found at the enamel margins facing the gap adjacent to glass-ionomers. SIGNIFICANCE In the presence of a standardized interfacial gap, no preventive effect was exerted in vivo from the glass-ionomer to protect the adjacent enamel wall from secondary caries attack. The lack of any correlation between the in vivo and in vitro models tested implies that artificial caries experiments have a negligible clinical relevance in predicting the in vivo effect.

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.

Color Stability of Orthodontic Adhesive Resins

Color alteration of adhesive during treatment and after debonding may be implicated in long-term enamel discoloration. The aim of this study was to assess the color stability of light-cured and chemically cured adhesives subjected to artificial photoaging. Disk-shaped specimens of adhesives were colorimetrically evaluated before and after artificial photoaging using an ISO-recommended protocol. The measurement variable was the color change (deltaE) of adhesives induced by artificial, accelerated photoaging. The deltaE values derived from the two color recordings for the materials at pre- and postaging intervals were statistically analyzed with a one-way analysis of variance (ANOVA), with the adhesive brand serving as a discriminating variable. Differences among groups were further investigated using the Tukey multiple comparisons test (alpha = .05). To establish the statistical significance of the difference of the deltaE values of each adhesive and the deltaE threshold for clinical detection, a paired t-test was used (P = .05). All adhesives exhibited color change, which in some cases exceeded the clinically detectable color change limit. The extent of the color alterations of aged bonding systems may contribute to enamel discoloration after treatment.

Polymerization efficiency of chemically cured and visible light-cured orthodontic adhesives: Degree of cure

The use of light-cured orthodontic adhesives in combination with the new generation of ceramic brackets has become popular from an esthetic standpoint. The purpose of this article was to evaluate the degree of cure (DC) of selected light-cured and chemically cured adhesives bonded to ceramic and stainless steel brackets. The optical properties of eight types of brackets (single-crystal alumina, polycrystalline alumina, polycrystalline allumina with polycarbonate base, and stainless steel) were evaluated by diffuse visible light transmittance spectroscopic analysis. The degree of cure (DC) of a visible light-cured orthodontic adhesive bonded to these brackets under direct (20 seconds through the bracket) and indirect (2 x 10 seconds from the incisal and cervical edges of the bracket) irradiation was measured by micro-MIR FTIR spectroscopy. Brackets bonded to a chemically cured, two-paste orthodontic adhesive were used as a control group. According to the results the single-crystal alumina brackets showed the highest diffuse transmittance values at 468 nm followed by polycrystalline alumina and polycarbonate-base alumina types. Direct irradiation resulted in low DC values that were strongly correlated to the diffuse transmittance measurements at 468 nm (r = 0.73, p < 0.05). Indirect irradiation manifested significantly higher DC values than direct irradiation in the stainless steel bracket group, which yielded values comparable to those found in some indirectly irradiated polycrystalline bracket groups.