Hygroscopic dimensional changes of self-adhering and new resin-matrix composites during water sorption/desorption cycles

Objectives

To study hygroscopic dimensional changes in new resin-matrix composites during water sorption/desorption cycles.

Methods

Five materials were examined: a self-adhering flowable composite: Vertise^® Flow (VF), a universal composite: GC Kalore (GCK), two micro-fine hybrid composites: GC Gradia Direct Anterior (GDA) and GC Gradia Direct Posterior (GDP), and a posterior restorative composite: Filtek^® Silorane (FS). Five disk-shaped specimens of each material were prepared (15 mm diameter × 2 mm thickness) according to ISO 4049. The mean diameter of each specimen was measured by a custom-built laser micrometer (to a resolution of 200 nm) periodically over 150 d water immersion and 40 d recondition periods at (37 ± 1) °C. Perspex controls were used. Data analysis was performed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (p < 0.05).

Results

Differences in hygroscopic expansion were found for all test materials during sorption, ranging from 0.74% (±0.05) for FS to 4.82% (±0.13) for VF. The differences were significant for all materials (p < 0.001), except between GCK and GDA. The mathematical relationship between diametral expansion and square root of time was non-linear. VF exhibited significant dehydration shrinkage.

Significance

The silorane composite FS had the lowest hygroscopic expansion. The extent of compensation of polymerization shrinkage by hygroscopic expansion depends on materials, specimen dimensions and time-scale. So the clinical situation must be taken into consideration in the application of these findings.     

The relationship between cyclic hygroscopic dimensional changes and water sorption/desorption of self-adhering and new resin-matrix composites

Objectives

This study evaluated the relationship between mass changes and hygroscopic dimensional changes during water sorption/desorption cycles in new resin composites.

Methods

A silorane posterior composite (Filtek^® Silorane, FS), two micro-fine hybrid composites (GC Gradia Direct Anterior, GDA; GC Gradia Direct Posterior, GDP), a universal composite (GC Kalore, GCK), and a self-adhering flowable composite (Vertise^® Flow, VF) were evaluated. 25 (n = 5) disk specimens (15 mm × 2 mm) were prepared according to ISO 4049. Water sorption was measured gravimetrically. Hygroscopic expansions were measured by a laser micrometer regularly during 150 d water storage and 40 d recondition periods, all at 37 °C. Data were analyzed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (p < 0.05).

Results

Mass changes after 150 d water immersion ranged from 0.68% (±0.02) for FS to 2.83% (±0.11) for VF and the corresponding hygroscopic expansions were from 0.74% (±0.05) for FS to 4.79% (±0.18) for VF. The differences were significant for all materials (p < 0.001), except mass changes between GCK and GDP, as well as hygroscopic changes between GCK and GDA. The relationship between hygroscopic expansions and mass changes was initially non-linear and then tended toward linear behavior. But at the late stage of water sorption the hygroscopic expansion of GCK and VF was slightly sigmoidal with respect to their mass changes.

Significance

Relationships between hygroscopic expansion and mass change were determined for some diverse resin-matrix composites. The initial non-linearity for all materials suggests a lower expansion rate due to occupancy of internal free volume by water ingress. The silorane composite FS showed statistically the lowest mass change and hygroscopic dimensional change.     

Histological changes in masticatory muscles of mdx mice

Objective

Duchenne muscular dystrophy (DMD) patients have distorted dentofacial morphology that could be a result of changed force balance of masticatory muscles due to unequal dystrophic changes in various masticatory muscles. Skeletal muscles of DMD patients and those of murine model of DMD - mdx mice - are both characterized by Ca²⁺ induced muscle damage, muscle weakness and characteristic histological changes. Therefore, to determine the pathological changes in this animal model of DMD, we examined the masticatory muscles of the mdx mice for histological abnormalities including nuclei localization, fibre diameters, and collagen expression.

Design

Muscle sections from masseter (MAS), temporal (TEM), tongue (TON) and soleus (SOL) of mdx and control normal mice were stained with hemalaun/eosin or with Sirius Red and morphometrically analysed. Levels of collagen staining in normal and mdx muscles were measured using image analysis and the mean optical density (mod) was determined.

Results

Dystrophin deficient masticatory muscles contained 11-75% fibres with centralised nuclei. In mdx mice an increased mean fibre diameter was observed as compared to the age-matched control muscles (control vs. mdx; MAS: 33.44 ± 0.49 μm vs. 37.76 ± 0.68 μm, p < 0.005; TEM: 32.93 ± 0.4 μm vs. 42.93 ± 0.68 μm, p < 0.005; SOL: 33.15 ± 0.29 μm vs. 40.62 ± 0.55 μm, p < 0.005; TON: 13.44 ± 0.68 μm vs. 15.63 ± 0.18 μm, p < 0.005). Increased expression of collagen was found in MAS (mod control vs. mdx: 1.34 vs. 3.99, p < 0.005), TEM (mod control vs. mdx: 3.11 vs. 4.73, p < 0.01) and SOL (mod control vs. mdx: 2.36 vs. 3.49, p < 0.01).

Conclusion

Our findings revealed that mdx masticatory muscles are unequally affected by the disease process. The masticatory muscles of the mdx mice could present a useful model for further investigating the influence of dystrophin deficiency on muscles function.     

Wear performance of substructure ceramics and veneering porcelains

Aim

The aim of this in vitro study was to compare the two-body wear resistance of substructure zirconia and veneering porcelain versus steatite and human enamel antagonists, respectively.

Materials and methods

Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists (enamel cusps). A pin-on-block design with a vertical load of 50 N for 1.2 × 10⁵ cycles; (f = 1.6 Hz; lateral movement: 1 mm, mouth opening: 2 mm) was used for the wear test. For quantification of the wear resistance, wear tests were performed with standardized steatite spheres. Human enamel was used as a reference. Five zirconia ceramics and four veneering porcelains were investigated. One zirconia ceramic was tested with superficial glaze, which was applied after polishing or sandblasting, respectively. Surface roughness R_a (SP6, Perthen-Feinprüf, G) and wear depth were determined using a 3D-Profilometer (Laserscan 3D, Willytec, G). SEM (Quanta FEG 400, FEI, USA) pictures were used for evaluating wear performance of both, ceramics and antagonists.

Results

No wear was found for zirconia substructures. Veneering porcelain provided wear traces between 186.1 ± 33.2 μm and 232.9 ± 66.9 μm (steatite antagonist) and 90.6 ± 3.5 μm and 123.9 ± 50.7 μm (enamel). Wear of the steatite antagonists varied between 0.812 ± 0.256 mm² and 1.360 ± 0.321 mm² for zirconia and 1.708 ± 0.275 mm² and 2.568 ± 0.827 mm² for porcelain. Enamel generally showed wear, cracks or even fractures at the ridge, regardless whether opposed by zirconia or porcelain/glaze. Enamel was polished, when opposed to zirconia, or plowed, provoked and grinded, when opposed to porcelain/glaze.

Conclusion

The results of the wear test with steatite or enamel antagonists indicated no measurable wear on zirconia surfaces. Porcelain showed higher wear than zirconia, but comparable or lower wear than an enamel reference. Antagonistic wear against zirconia was found to be lower than wear against porcelain.     

The effect of CPP-ACP on enamel wear under severe erosive conditions

Objective

In addition to its role as a remineralizing agent in preventing dental caries, recent evidence has shown that casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) can protect teeth against erosion. The aim of this study was to determine whether CPP-ACP could reduce enamel wear rates under severe erosive conditions simulating heavy attrition and gastric regurgitation.

Design

Enamel specimens were subjected to 10,000 wear cycles at a load of 100 N and pH 1.2 in a tooth wear machine. The machine was stopped every 2 min (160 cycles), and CPP-ACP in the form of a paste was applied for 5 min in experimental group 1. A paste with the same formulation but without CPP-ACP was applied in experimental group 2. No paste was applied in the control group.

Results

A linear mixed model analysis indicated that the mean wear rates in experimental group 1 (0.44 ± 0.05 mm³ per 1000 cycles) and in experimental group 2 (0.63 ± 0.06 mm³ per 1000 cycles) were significantly lower than that in the control group (0.92 ± 0.11 mm³ per 1000 cycles) (p < 0.05). The mean wear rate in experimental group 1 was also lower than that in experimental group 2 (p < 0.05). Wear facets in experimental groups 1 and 2 were noted to be smoother and more polished than those in the control group.

Conclusions

Both remineralizing and lubricating properties of the paste containing CPP-ACP appear to contribute to wear reduction in enamel. These findings may lead to new strategies for the clinical management of tooth wear.     

The dimensional stability of impression materials and its effect on in vitro tooth wear studies

Objectives

To assess the dimensional stability of 8 impression materials over 12 weeks relevant to in vitro tribology studies.

Methods

Ten impressions from eight impression materials were taken of a metal block (ADA block) conforming to the American Dental Association specification for impression materials and of another metal block (custom block) which allowed measurements over a larger surface area. The impressions and blocks were scanned on a non-contacting laser profilometer (Taicaan^® - Southampton, UK) and using surface metrology software Boddies^® (Taicaan^® - Southampton, UK) measurements were made at 24 h, 2, 4, 8 and 12 weeks. The impression materials tested were [1] Aquasil^®, [2] Aquasil^® DECA, [3] Affinis^®, [4] Express^®, [5] Extrude^®, [6] Impregum^®, [7] President^® and [8] Take 1^®.

Results

Seven addition silicones and one polyether [6] were tested. [2] and [6] were monophasic, the rest were putty-wash. The results from impressions of the ADA block showed that all materials contracted compared to measurements obtained directly from the block [1] expanded over time (+31.5 μm) (p < 0.05). The results from the custom block showed that all materials contracted compared to direct measurements of the block. [4] and [7] expanded over time (+62 μm and +63.8 μm respectively). [8] contracted over time (−54.7 μm) (p < 0.05).

Significance

No material showed linear changes >1.5% and were stable for 12 weeks. Nevertheless, the range of changes would affect tribology studies were cut-offs lesser than the reported changes are selected. All impressions should be processed after similar time delays to reduce the errors introduced by dimensional changes.     

Supraposition of unopposed molars in young and adult rats

Objective

Previous clinical studies indicate that the overeruption of unopposed teeth may be different between young and adult individuals. The aim of this study was to investigate the position of the unopposed molar, in young and adult rats.

Methods

In young (4-week old) and adult (26-week old) rats, the right maxillary molar crowns were reduced occlusally by grinding. After 4 weeks, the animals were sacrificed and scanned by micro-CT.

Results

The unopposed molars of the young animals were in supraposition being on average 262 μm (±135 μm) higher than the position of molars with antagonists. This was more pronounced than in adults (average 125 ± 108 μm, P < 0.01). In the young animals the alveolar bone level was higher in the unopposed molars with supraposition while no differences were found in the adults’ molars.

Conclusions

Our results demonstrated that the overeruption potential of unopposed molars is higher in young than adult rats.     

High irradiance curing and anomalies of exposure reciprocity law in resin-based materials

Objectives

The aim of this work was to investigate the effect of high irradiance curing on resultant degree of conversion of ‘flowable’ resin composites and their counterpart higher viscosity paste materials.

Methods

Five commercial flowable materials (Venus; Heraeus Kulzer, Synergy D6; Coltene, Premise; Kerr, Grandio; Voco and Gradia; GC Corp) and their counterpart higher viscosity restorative versions were tested. Specimens were cured with a halogen Swiss Master Light (EMS, Switzerland) using five different curing protocols with similar radiant exposure (18 J/cm²): 400 mW/cm² for 45 s, 900 mW/cm² for 20 s, 1500 mW/cm² for 12 s, 2000 mW/cm² for 9 s and 3000 mW/cm² for 6 s. Degree of conversion (DC) was measured in real time by Fourier transform near infrared spectroscopy (FT-NIRS).

Results

Three- and subsequent two way ANOVA testing revealed significant differences (p ≤ 0.02) with respect to “composite type” and “cure protocol” for DC for all 5 product comparisons. Supplementary one-way ANOVA also revealed significant differences between curing protocols (p < 0.05). The majority of higher viscosity resin composite paste materials exhibited similar DC regardless of curing protocol. However, a significant decrease in DC for specimens cured at 3000 mW/cm² for 6 s compared with 400 mW/cm² for 45 s was observed for the flowable materials, Grandio (41 ± 0.36 and 62 ± 1.15%, respectively) and Venus (44 ± 0.44 and 67 ± 0.44%, respectively). Conversely, other flowable materials exhibited little or no significant differences between curing modes. Generally, a higher degree of conversion was observed for flowables compared with their more viscous counterpart, except at high irradiance for those materials where a reciprocal relationship with exposure time was not observed.

Conclusions

The validity of exposure reciprocity law and final degree of conversion depends on several factors, amongst which resin viscosity and filler content were important. Practitioners should be aware of the importance of resin composite constituents and irradiation protocols. Information on material composition and appropriate radiation sources by manufacturers may assist practitioners with the selection of appropriate curing protocols for specific material/light curing unit combinations with the aim of reducing the incidence of under-cured restorations and the clinical impact thereof.     

Micro-computed tomography evaluation of the preparation of long oval root canals in mandibular molars with the self-adjusting file

Introduction

The aim of this study was to assess the shaping potential of a novel nickel-titanium instrument, the self-adjusting file (SAF), in long oval root canals in distal roots in mandibular molars.

Methods

Twenty mandibular molars with long oval distal root canals were selected and scanned preoperatively and postoperatively by using micro-computed tomography at an original resolution of 20 μm. Canals were shaped with the SAF, three-dimensionally reconstructed, and evaluated for volume, surface area, canal transportation, and prepared surface. Data were statistically contrasted by using paired t tests and regression analysis.

Results

Preoperatively, canal volume was 7.73 ± 2.13 mm³, and canal area was 42.83 ± 8.14 mm². Volumes and surface areas increased significantly (P < .001) by 4.84 ± 1.73 mm³ and 3.34 ± 1.73 mm², respectively, and no gross preparation errors were detected. Unprepared canal surface varied between individual canals, and mean unprepared surface was 23.5% ± 8.9%. Prepared areas were significantly larger compared with rotary canal preparation done in a previous study. Canal transportation scores were higher in the coronal root canal third (106 ± 50 μm) compared with the apical third (81 ± 49 μm).

Conclusions

In vitro, preparation of long oval-shaped root canals in mandibular molars with the SAF was effective and safe. Moreover, shapes generated with the SAF were more complete compared with rotary canal preparation.     

Effect of 3-year water storage on the performance of one-step self-etch adhesives applied actively on dentine

Objectives

To evaluate the effect of the application method on the immediate and 3-year resin-dentine bond strength (μTBS) and nanoleakage (NL) for 3 one-step self-etch adhesives (Adper Prompt L-Pop; Clearfil S³ Bond and Xeno III).

Methods

The occlusal enamel of 42 human molars were removed to expose a flat dentine surface. The adhesives were applied under inactive or active application. After light-curing (600 mW/cm² for 10 s), composite buildups were constructed incrementally and sectioned to obtain bonded sticks (0.8 mm²) to be tested in tension immediately or after 3 years of water storage of water storage. For NL, 2 bonded sticks from each tooth at each time were coated with nail varnish, placed in silver nitrate and polished down with SiC paper. The μTBS data was submitted to a two-way repetead mesures ANOVA and Tukey's test for each adhesive (α = 0.05).

Results

The active application showed higher immediate and 3-year μTBS than the inactive application (p < 0.05). An increase in the silver nitrate deposition was seen for all conditions after 3 years; however this was more pronounced for all materials under inactive application (p < 0.05).

Conclusions

The active application improves the immediate bonding performance of the adhesive systems. Reductions of the bond strength were observed for all materials after 3 years, however reduced degradation rate was observed when the materials are applied actively in dentine.     

The influence of laser-textured dentinal surface on bond strength

Objective

To assess the influence of laser-textured surfaces on the adhesion of composite to dentin after being rotary prepared.

Methods

Thirty healthy teeth were kept in 0.1% thymol solution prior to being ground down to dentin to create a 4 × 4 mm² flat surface. Teeth were divided into 3 groups (n = 10). Groups 1 and 2 utilized the prototype Erbium doped, Yttrium-Aluminum-Garnet Er:YAG laser by Dental Photonics, Inc. A single pulse was delivered to each spot to create an equally spaced square 4 × 4 mm² matrix of micro craters. All craters had 100 μm diameter/45 μm depth; two different spacing patterns were prepared in Groups 1 and 2. In Group 1, distance between crater centers was 50 μm; Group 2 had 100 μm. In Group 3 (control), 10 samples were prepared without laser texturing. G-bond (GC America) was applied to testing area of all samples in all groups according to manufacturer's instructions. Bonding resin was applied and shear-bond strength tests were employed using an Instron machine to measure adhesive strength.

Results

One-way analysis of variance (ANOVA) was used to compare the 3 groups. Pair wise t-tests implementing the Bonferroni correction for multiple comparisons found a statistically significant difference between Group 3 and Group 2 (p = 0.019) but no statistically significant difference between Group 3 and Group 1 (p = 0.263) or Group 1 and Group 2 (p = 0.743).

Significance

The bond strengths between bonded composite to laser-textured dentinal surfaces with larger spacing patterns are greater than that of non-textured surfaces.     

Crevicular fluid levels of plasma glutathione peroxidase (eGPx) in periodontal health and disease

Background & objectives

Reactive oxygen species (ROS) have been implicated in numerous human diseases, including periodontal diseases. Plasma glutathione peroxidase (eGPx) as an important antioxidant, has a protective role against ROS and is an established marker of oxidative stress. The present study evaluated the levels of eGPx in GCF to further probe into the role of oxidants and antioxidants in periodontal disease.

Methods

60 subjects were divided into three groups consisting of 20 subjects in each group based on gingival index, pocket probing depth, clinical attachment loss and radiological parameters (bone loss): healthy (group 1), gingivitis (group 2) and periodontitis (group 3), whilst, group 3 patients after the treatment constituted group 4. GCF samples were collected from all groups to estimate the levels of eGPx using ELISA.

Results

The mean eGPx concentration in GCF were observed to be the highest in group 3 i.e., 30.89 ± 4.93 ng/μl and lowest in group 1 i.e., 15.32 ± 3.06 ng/μl. The mean eGPx concentration in group 2 (23.77 ± 2.91 ng/μl) and group 4 (18.92 ± 3.53 ng/μl) fell between the highest and the lowest values.

Conclusion

This suggests that eGPx levels in GCF increase proportionally with the severity of periodontal diseases. eGPx can be considered as a marker of oxidative stress in periodontal diseases. However, controlled, longitudinal studies with larger samples have to be carried out to confirm this possibility.     

Root Canal Preparation of Maxillary Molars With the Self-adjusting File: A Micro-computed Tomography Study

Introduction

The aim of this study was to describe the canal shaping properties of a novel nickel-titanium instrument, the self-adjusting file (SAF), in maxillary molars.

Methods

Twenty maxillary molars were scanned by using micro-computed tomography at 20-μm resolution. Canals were shaped with the SAF, which was operated with continuous irrigation in a handpiece that provided an in-and-out vibrating movement. Changes in canal volumes, surface areas, and cross-sectional geometry were compared with preoperative values. Canal transportation and the fraction of unprepared canal surface area were also determined. Data were normally distributed and compared by analyses of variance.

Results

Preoperatively, mean canal volumes were 2.88 ± 1.32, 1.50 ± 0.99, and 4.30 ± 1.89 mm³ for mesiobuccal (MB), distobuccal (DB), and palatal (P) canals, respectively; these values were statistically similar to earlier studies with the same protocol. Volumes and surface areas increased significantly in MB, DB, and P canals; mean canal transportation scores in the apical and middle root canal thirds ranged between 31 and 89 μm. Mean unprepared surfaces were 25.8% ± 12.4%, 22.1% ±12.0%, and 25.2% ± 11.3% in MB, DB, and P canals, respectively (P > .05) when assessed at high resolution.

Conclusions

By using SAF instruments in vitro, canals in maxillary molars were homogenously and circumferentially prepared with little canal transportation.     

Transaminases in the acquired pellicle

Objective

Transaminases (AST, aspartate amino transferase; ALT, alanine amino transferase) are relevant enzymes in physiology and pathology of the human organism. The aim of the present in situ study was to demonstrate the presence of these enzymes in the enamel pellicle.

Methods

Bovine enamel slabs were fixed on buccal sites of individual upper jaw splints and worn for 3, 30 and 120 min by 5 subjects to allow pellicle formation. The in situ pellicles were tested for AST and ALT. Enzyme activities were measured photometrically via determination of the products pyruvate and oxalacetate using lactate-dehydrogenase and malate-dehydrogenase, respectively.

Results

Enzymatic AST- as well as ALT-activities are present in the acquired pellicle within 3 min. The enzyme activities exposed at the pellicles’ surfaces increased slightly with the pellicle formation time (ANOVA, AST: n.s., ALT: p = 0.021). However, the two enzymes show considerable intraindividual and interindividual variability. The mean AST-activity of the pellicle amounted to 1.07 ± 0.81 mU/cm² (ALT 1.18 ± 0.52 mU/cm²). The ALT-activity of the centrifuged saliva was 26.62 ± 11.09 mU/ml (AST 35.98 ± 29.35 mU/ml).

Conclusions

AST as well as ALT are present in the in situ pellicle layer and may contribute to the intrinsic maturation of pellicle proteins.     

Degradation resistance of ormocer- and dimethacrylate-based matrices with different filler contents

Objectives

To investigate the influence of matrix and filler content on degradation resistance of an experimental pure-ormocer and an dimethacrylate-based composite derived from a commercially available material.

Materials and methods

A dimethacrylate- Grandio (GR) and a model pure ormocer-based-matrix ORMOCER (ORM) were used. Each material had three different types according to their filler content (% w/w): regular (87% and 86%), flowable (80% and 79%) and fissure sealer (70% and 69%) for GR and ORM respectively. Disc-shaped (1 mm thickness × 10 mm diameter) samples were prepared for each material (n = 6). Water sorption and solubility tests were adapted from ISO4049. To evaluate porosity, specimens were scanned at a resolution of 19.4 μm and 3D reconstructions were made. The volume ratio of pores in the specimens were calculated and expressed as percentages. The results were submitted to 2-way ANOVA (factors: matrix and filler content) and Tukey post-hoc statistic test (p = 0.05).

Results

Filler content influenced the water sorption for the ormocer-matrix and the water solubility for the dimethacrylates. ORMOCER regular was a less porous material compared to flowable and sealer formulations. On the other hand, the filler content had no effect on porosity for Grandio.

Conclusion

Modifications made in the pure ormocer-matrix formulation were not significantly important to produce a more water-stable material compared to the dimethacrylate-matrix composite materials.     

Effect of a neutralising agent on the evaluation of the antimicrobial activity of chlorhexidine on the bacterial salivary flora

Objective

To test the efficacy of a previously described neutralising agent to counteract any antimicrobial activity of 0.2% of chlorhexidine (CHX) mouthrinse on the salivary flora, which is only exhibited after sampling of surviving bacteria, resulting in false positive efficacy data.

Methods

Unstimulated salivary samples were collected of 20 volunteers under basal conditions and at 30 s and 1 h after of a single mouthrinse of 0.2% CHX. Each salivary sample was divided into 2 equal aliquots; one was mixed with neutralising agent (3% Tween 80, 0.3% lecithin and 0.1% cysteine) and the other with a control solution. The colony forming units (cfu/mL) were determined and expressed as logarithms (log₁₀ cfu/mL).

Results

At baseline, the total bacterial concentrations were similar, independently of the addition of neutralising solution or control solution (8.419 ± 0.346 log₁₀ cfu/mL and 8.462 ± 0.474 log₁₀ cfu/mL, respectively, p = 0.440). At 30 s performing the CHX mouthrinse, the bacterial load reduction was statistically significant between both sampling methods (1.917 ± 1.275 log₁₀ cfu/mL, p < 0.001). One hour after performing the CHX mouthrinse, the bacterial load reduction was statistically significant between both sampling methods (0.537 ± 0.706 log₁₀ cfu/mL, p = 0.003).

Conclusions

Neutralising agent was not toxic to the bacterial salivary flora and effectively deactivated the “residual antimicrobial activity” of the 0.2% CHX (after exposure and during processing of samples). We propose the use of this neutralising agent when evaluating the antibacterial activity of CHX mouthrinses.     

Effect of ball milling on structures and properties of dispersed-type dental amalgam

Objectives

The purpose of the present study was to investigate the effect of ball milling on the initial mercury vapor release rate and mechanical properties such as compressive strength, diametral tensile strength and creep value, of the dispersed-type dental amalgam, and comparison was made with respect to two commercial amalgam alloys.

Methods

Ball milling was employed to modify the configuration of the originally spherical-shaped Ag-Cu-Pd dispersant alloy particles. Improvement in mechanical properties while maintaining a low early-stage mercury vapor release rate of the amalgam is attempted.

Results

The experimental results show that the amalgam (AmB10) which was made from Ag-Cu-Pd dispersant alloy particles that were ball-milled for 10 min and heat-treated at 300 °C for 2 days exhibited a low initial mercury vapor release rate of 69 pg/mm²/s, which was comparable with that of commercial amalgam alloy Tytin (68 pg/mm²/s), and was lower than that of Dispersalloy (73 pg/mm²/s). As for mechanical properties, amalgam AmB10 exhibited the highest 1 h compressive strength (228 MPa), which was higher than that of commercial amalgam alloy Dispersalloy by 72%; while its 24 h diametral tensile strength was also the highest (177 MPa), and was higher than that of Dispersalloy by 55%. Furthermore, the creep value of the amalgams made from Ag-Cu-Pd alloy particles with 10 min ball-milling and heat treatment at 300 °C for 2 days was measured to be 0.12%, which was about 20% that of Dispersalloy.

Significance

It is found that ball milling of the dispersant Ag-Cu-Pd alloy particles for 10 min was able to modify the configuration of the alloy particles into irregular-shapes. Subsequently, heat treatment at 300 °C significantly lowered the initial mercury vapor release rate, increased its 1 h compressive strength and 1 h diametral tensile strength, and lowered its creep value.     

Effects of nicotine and lipopolysaccharide on the expression of matrix metalloproteinases, plasminogen activators, and their inhibitors in human osteoblasts

Objective

Lipopolysaccharide (LPS) from periodontopathic bacteria can initiate alveolar bone loss through the induction of host-derived cytokines. Smoking increases the risk and severity of periodontitis. We examined the effects of nicotine and LPS on the expression of matrix metalloproteinases (MMPs), plasminogen activators (PAs), and their inhibitors, including tissue inhibitors of metalloproteinases (TIMPs) and PA inhibitor-1 (PAI-1), in osteoblasts.

Methods

The cells were cultured with or without 10⁻⁴ M nicotine and 100 ng/ml LPS for 12 days or with 100 μg/ml polymyxin B, 10⁻⁴ M d-tubocurarine, 10 μmol/ml NS398, or 10⁻⁶ M celecoxib in the presence of either nicotine or LPS for 12 days. The gene and protein expression levels for MMPs, PAs, TIMPs, and PAI-1 were examined using real-time PCR and ELISAs, respectively. PGE₂ production was determined using an ELISA.

Results

The addition of nicotine and/or LPS to the culture medium increased the expression of MMP-1, -2, and -3 and tissue-type PA (tPA); decreased the expression of TIMP-1, -3, and -4; and did not affect expression of TIMP-2 or PAI-1. In the presence of d-tubocurarine or polymyxin B, neither nicotine nor LPS stimulated the expression of MMP-1. In the presence of NS398 or celecoxib, the stimulatory effects of nicotine and LPS on MMP-1 expression were unchanged, but they were unable to stimulate PGE₂ production.

Conclusion

These results suggest that nicotine and LPS stimulate the resorption process that occurs during turnover of osteoid by increasing the production of MMPs and tPA and by decreasing the production of TIMPs. Furthermore, they suggest that the stimulatory effect of nicotine and LPS on PGE₂ production is independent of their stimulatory effect on MMP-1 expression.     

Selective masking for thin indirect restorations: can the use of opaque resin affect the dentine bond strength of immediately sealed preparations?

Purpose

Evaluate the dentine bond strength using different methods of application of opaque resins to mask dentine discoloration.

Materials and methods

Dentine was exposed on 21 extracted molars which were assigned to 3 groups: G1: immediate dentine sealing (IDS). G2: IDS + opaque. G3: IDS with adhesive resin mixed with opaque. After 1 week, teeth were restored and beams were fabricated for microtensile testing. Optical microscopy was used to analyse the failure mode.

Results

Bond strength mean values were statistically different: G1 55.20 MPa > G2 45.79 MPa > G3 18.96 MPa. Failure modes were mostly adhesive for G1 and G3. G2 presented mostly mixed failures.

Conclusion

The use of opaque resin to mask discoloured dentine results in a decrease of bond strength.     

Effect of caffeine on the secretion of peroxidase in rat submandibular gland: a study of its mechanism of action

Objetive

In this work, we analysed the mechanism of action of caffeine on peroxidase secretion in the female rat submandibular gland. The signaling molecules cAMP and nitric oxide were monitored as potential mediators.

Design

The salivary gland peroxidase secretion of female albino Wistar rats was assessed by a spectroscopic method.

Results

Caffeine was found to exert an increase on peroxidase secretion in a concentration-response manner: the peroxidase secretion stimulation index (SI) (secreted peroxidase from treated/secreted peroxidase from basal) for caffeine 10 μg/ml: 2.2 ± 0.18 (P < 0.05); caffeine 100 μg/ml alone: 3 ± 0.18 (P < 0.01); +LNMMA (LN monomethyl arginine): 1 ± 0.1 (P < 0.05); caffeine 1000 μg/ml alone: 5 ± 0.35 (P < 0.01); +LNMMA: 2 ± 0.2 (P < 0.05). These results were associated with an increase in cAMP and total nitrites production. Total nitrites, SI caffeine 100 μg/ml alone: 2.8 ± 0.2 (P < 0.01); +LNMMA: 1 ± 0.08 (P < 0.05); caffeine 1000 μg/ml alone: 4.8 ± 0.3 (P < 0.01); +LNMMA: 2.3 ± 0.18 (P < 0.05).

Conclusion

It could thus be concluded that cAMP and NO are involved in the mechanism of action displayed by caffeine. This is the first report on the mechanism of action of caffeine on peroxidase secretion.