Afrodite Kakaboura

The influence of water sorption on the development of setting shrinkage stress in traditional and resin-modified glass ionomer cements

OBJECTIVES The aim of this study was to determine the setting stress development for some traditional and resin-modified glass ionomer cements and to assess the effect of early water exposure to this stress. METHODS The development of the setting stress of the glass ionomer cements was determined in a tensilometer set-up as described earlier by Feilzer et al. (1987). RESULTS The results of this study show the influence of water sorption on the development of setting shrinkage stress in bonded glass ionomer cements. When curing took place under isolated conditions (no hydration or dehydration), all the traditional glass ionomer cements investigated fractured spontaneously, either adhesively and/or cohesively, due to the developing stress. Early exposure to water led to stress relief and prevented spontaneous fracturing. For the light-cured products, no spontaneous failures were observed under isolated conditions. Stress relief due to water sorption reversed the contraction stress into an expansion stress. SIGNIFICANCE Exposure of traditional glass ionomer cements to water at an appropriate time by the use of permeable matrix systems is advised. Whether the conversion of contraction stresses into expansion stresses as observed for the resin-modified products, is beneficial for a restoration requires further study.

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.

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.

Diagnostic performance of the visual caries classification system ICDAS II versus radiography and micro-computed tomography for proximal caries detection: An in vitro study

OBJECTIVES The purpose of this study was: (a) to compare the visual caries classification system ICDAS II with conventional (CR) and digital radiography (DR) for diagnosis of non-cavitated caries on free proximal surfaces, (b) to examine the potential of micro-computed tomography (MCT) to substitute histological examination for the in vitro caries assessment. METHODS Both proximal surfaces of 20 teeth received classification separately by two examiners by means of the diagnostic modalities examined. The teeth were sectioned and assessed for depth of the lesion. The modalities were compared in terms of degree of inter-examiner agreement, sensitivity, specificity, accuracy, positive and negative predictive value and validity. Two diagnostic thresholds were applied: no caries versus all caries scores (D1), and no dentin caries versus dentin caries (D3). RESULTS The weighted kappa values for inter-examiner reproducibility for all diagnostic modalities were 0.51-0.81. Visual examination (ICDAS II) reached significant higher sensitivity (0.92-0.96) and negative predictive value (0.9-1) than radiography. Likewise, the radiographic modalities presented significantly higher specificity (0.93-1) and positive predictive values (0.92-1) than the ICDAS II criteria. The overall accuracy performance of radiographic modalities was related to the diagnostic threshold. MCT did not agree with histological validation at each disease severity scale. CONCLUSIONS The ICDAS II criteria are a promising tool for caries diagnosis on free proximal surfaces. DR and CR radiography present comparable performance. Furthermore, MCT is not capable of constituting a reliable alternative to histological examination for caries research.

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.

Mechanical properties of contemporary composite resins and their interrelations

OBJECTIVE To characterize a spectrum of mechanical properties of four representative types of modern dental resin composites and to investigate possible interrelations. METHODS Four composite resins were used, a microhybrid (Filtek Z-250), a nanofill (Filtek Ultimate), a nanohybrid (Majesty Posterior) and an ormocer (Admira). The mechanical properties investigated were Flexural Modulus and Flexural Strength (three point bending), Brinell Hardness, Impact Strength, mode I and mode II fracture toughness employing SENB and Brazilian tests and Work of Fracture. Fractographic analysis was carried out in an SEM to determine the origin of fracture for specimens subjected to SENB, Brazilian and Impact Strength testing. The results were statistically analyzed employing ANOVA and Tukey post hoc test (a=0.05) while Pearson correlation was applied among the mechanical properties. RESULTS Significant differences were found between the mechanical properties of materials tested apart from mode I fracture toughness measured by Brazilian test. The latter significantly underestimated the mode I fracture toughness due to analytical limitations and thus its validity is questionable. Fractography revealed that the origin of fracture is located at notches for fracture toughness tests and contact surface with pendulum for Impact Strength testing. Pearson analysis illustrated a strong correlation between modulus of elasticity and hardness (r=0.87) and a weak negative correlation between Work of Fracture and Flexural Modulus (r=-0.46) and Work of Fracture and Hardness (r=-0.44). Weak correlations were also allocated between Flexural Modulus and Flexural Strength (r=0.40), Flexural Strength and Hardness (r=0.39), and Impact Strength and Hardness (r=0.40). SIGNIFICANCE Since the four types of dental resin composite tested exhibited large differences among their mechanical properties differences in their clinical performance is also anticipated.

Effect of tooth-bleaching methods on gloss and color of resin composites.

OBJECTIVES The purpose of the study was to evaluate gloss and color changes of resin composites after exposure to different bleaching agents. METHODS Products used, were: Nite White ACP (10% carbamide peroxide gel), Crest Classic and Supreme Whitestrip (6.5% and 14% hydrogen peroxide strips, accordingly). A hybrid (Herculite XRV) and a nanohybrid (Premise) resin composite were exposed to the bleaching agents. Twenty-four disk-shaped specimens per composite were subjected to bleaching by each of the agents (n=8) for up to 2 weeks. Color changes using CIE-L*a*b* system (50:50% acceptability threshold: ΔE*=3.3) were recorded after 1 and 2 weeks bleaching cycles relative to baseline measurements. In addition, gloss measurements (in gloss units) were performed at the same bleaching intervals and gloss changes were calculated. RESULTS All bleaching agents tested provided decrease in gloss of both composites after 2-week bleaching (p<0.05). No differences were detected among the three bleaching regimens, for up to 2-week application, in terms of color and gloss changes on both composites. After the 2-week bleaching period, hybrid composite presented higher gloss reduction (%) than nanohybrid regardless of the bleaching agent (p<0.05). Color change (ΔE*) was lower than 3.3 for all composite-bleaching agent combinations. After 1- and 2-week bleaching time, the nanohybrid composite provided higher color change than the hybrid under all bleaching procedures (p<0.05). No strong correlation was proved between color (ΔE*) and gloss changes caused by bleaching treatments. CONCLUSIONS After 2-week bleaching cycles, composites showed significant gloss reduction (p<0.05). Color alteration was below the 50:50% acceptability threshold (ΔE*<3.3) and it was product-depended. There was no significant difference in color and gloss changes between the evaluated bleaching strips and 10% carbamide peroxide gel.

Laboratory evaluation of three visible light-cured resinous liners

OBJECTIVES The aim of the present study was to evaluate the composition and the laboratory performance of three visible light-cured resinous liners (Cavalite, Ionoseal and Timeline). METHODS Monomers were separated from fillers and were analysed by HPLC. Set pastes were analysed by FTIR spectroscopy and diametral strengths and water solubility were measured. RESULTS The monomers identified in the liners were BisEMA/2-HEMA (Cavalite), BisDMA/BisGMA (Ionoseal) and UEDMA (Timeline). Significant variations were found in the filler content but the mechanical response as assessed by the diametral tensile strength showed no statistical differences. The curing efficiency ranged from 24.2 to 31.0% (top surfaces) to 26.0-54.0% (bottom surfaces) of remaining C = C bonds. No positive correlations were found between curing efficiency and optical properties. The bond strength of the liners to dentine was negligible compared with that to composite. All the liners demonstrated extensive gap formation and debonding at the liner-dentine interfaces in marginal adaptation testing. Statistical differences were noticed in the water absorption and water solubility values of the products. Ionoseal showed extensive hydrolytic degradation compared with the other liners. No evidence of acid-base reaction was found in the set products.

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.

Marginal and internal adaptation of bulk-filled Class I and Cuspal coverage direct resin composite restorations

This in vitro study compared the marginal and internal adaptation of bulk-filled Class I and cuspal coverage direct resin composite restorations filled with different types of adhesive restorative systems and different thicknesses of bonding agent. Seventy-two intact, caries-free, freshly extracted human molars were randomly divided into 12 groups of six teeth each, according to the type of cavity (Class I [I] or Cuspal Coverage [C]), adhesive restorative system (SE Bond/Clearfil AP-X [SE] or Prime&Bond NT/Spectrum TPH [PB]) and thickness of bonding agent (normal or thick layer) in Class I restorations. Standardized Class I and Cuspal coverage cavities with enamel outer margins were prepared and restored with the corresponding type and thickness of bonding agent and respective resin composite. The resin composite was placed and polymerized in one increment (bulk filling). Dentinal fluid was simulated using 1:3 diluted horse serum and fed into the pulp chamber both during restoration and stressing. In six of the 12 groups, the restorations were subjected to 1.2 million mechanical occlusal cycles (maximum force 49 N; frequency 1.7Hz) and 3,000 simultaneous thermal cycles (5-50-5 degrees C). Marginal adaptation before and after mechanical and thermal stressing was assessed by using the replica technique and quantitative evaluation under SEM at 200x magnification. The teeth were dissected in a mesio-distal direction with a slow rotating diamond disc under water cooling, and the internal adaptation was also assessed by using the replica technique under the conditions described. Statistical evaluation of the continuous margin at the external and internal interface was performed with one-way analysis of variance (ANOVA) and Tukeys Studentized Range (HSD) test (p = 0.05). Even though Cuspal coverage restorations (SE- C: 96.89 +/- 1.83 and PB- C: 97.15 +/- 2.93) exhibited statistically significantly better external adaptation than Class I restorations (SE- I: 63.95 +/- 12.82 and PB- I 64.74 +/- 14.62) before stressing, there was no statistically significant difference after mechanical and thermal stressing (SE- C: 76.35 +/- 18.53 and PB- C: 76.02 +/- 12.49 SE- I: 54.67 +/- 10.82 and PB- I: 59.94 +/- 15.20). After stressing, SE Bond Cuspal coverage restorations (SE- C: 96,72 +/- 3,26) exhibited superior internal adaptation compared to SE Bond Class I restorations (SE- I: 57.83 +/- 12.91). No difference was observed in internal adaptation between Prime&Bond NT Cuspal coverage and Class I restorations (PB- C:36.46 +/- 21.82, PB- I: 38.71 +/- 6.76). In Class I restorations, the increased thickness in bonding did not improve the marginal and internal adaptation either before or after stressing. Bulk-filled direct resin composite Cuspal coverage restorations exhibited marginal adaptation similar to bulk-filled direct resin composite Class I restorations. The internal adaptation of Cuspal coverage SE Bond/Clearfil AP-X restorations was superior to all the other groups tested.