Influence of saliva substitute films on the initial adhesion of Candida albicans to dental substrata prior to and after artificial ageing

Objective

The aim of this in vitro study was to investigate whether saliva substitute films influence the adhesion of Candida albicans to different dental substrata prior to and after artificial ageing.

Design

Specimens of a denture base resin (DB) and a veneering composite (VC) were polished and subjected to an artificial ageing protocol (thermal cycling, 2 × 3000 cycles 5/55 °C). Bovine enamel (BE) and glass were used as reference materials. After determination of surface free energy, specimens were rinsed with commercial saliva substitutes (Aldiamed, Saliva natura, Saliva Orthana, Salinum), a positive control (protein mixture), or a negative control (Phosphate Buffered Saline, PBS) for 2 h at 37 °C in a flow chamber. Specimens were then exposed to a C. albicans ATCC 10231 suspension for 4 h at 37 °C. Adherent, viable Candida cells were quantified using a luminometric ATP-based assay. Statistical analysis was performed using 1- and 2-way ANOVA, and post-hocs were analysed using the Tukey-Kramer test (α < .05).

Results

Our data indicated that VC (31.1 mJ/m²) and DB (33.9 mJ/m²) yielded the lowest surface free energy prior to artificial ageing, and BE (43.6 mJ/m²) yielded the highest surface free energy. For C. albicans adhesion, both the materials as well as the saliva substitutes influenced relative luminescence intensities, indicating significant differences in C. albicans adhesion between the various materials and after treatment with the saliva substitutes.

Conclusions

Saliva substitutes may have a decisive influence on C. albicans adhesion, but their impact appears to be dependent on the properties of the underlying substratum material.     

Is there one optimal repair technique for all composites?

Objectives

The aim of this study was to investigate the effectiveness of a variety of techniques to bond new composite to artificially aged composite of different compositions.

Methods

Composite resin blocks were made of five different commercially available composites (n = 30) (Clearfil AP-X, Clearfil PhotoPosterior, Photo Clearfil Bright, Filtek Supreme XT and HelioMolar). After aging the composite blocks (thermo-cycling 5000×), blocks were subjected to one of 9 repair procedures: no treatment (control), diamond bur, sandblasting alumina particles, CoJet™, phosphoric acid, 3% hydrofluoric acid 20 s or 120 s, 9.6% hydrofluoric acid 20 s or 120 s. In addition, the cohesive strength of the tested composites was measured. Two-phase sandwiches (‘repaired composite’) were prepared using each of the 9 repair protocols, successively followed by silane and adhesive (OptiBond FL) treatment, prior to the application of the same composite. Specimens were subjected to micro-tensile bond strength testing. Data were analyzed using ANOVA and Tukey's HSD (p < 0.05).

Results

For all composites the lowest bond strength was obtained when no specific repair protocol (control) was applied; the highest for the cohesive strength. Compared to the control for the microhybrid composite (Clearfil AP-X) five repair techniques resulted in a significantly higher repair strength (p < 0.05), whereas for the nano-hybrid composite (Filtek Supreme XT) and hybrid composite containing quartz (Clearfil PhotoPosterior) only one repair technique significantly increased the bond strength (p < 0.01).

Significance

None of the surface treatments can be recommended as a universally applicable repair technique for the different sorts of composites. To optimally repair composites, knowledge of the composition is helpful.     

The fit of cobalt-chromium three-unit fixed dental prostheses fabricated with four different techniques: A comparative in vitro study

Objectives

This study sought to evaluate and compare the marginal and internal fit in vitro of three-unit FDPs in Co-Cr made using four fabrication techniques, and to conclude in which area the largest misfit is present.

Methods

An epoxy resin master model was produced. The impression was first made with silicone, and master and working models were then produced. A total of 32 three-unit Co-Cr FDPs were fabricated with four different production techniques: conventional lost-wax method (LW), milled wax with lost-wax method (MW), milled Co-Cr (MC), and direct laser metal sintering (DLMS). Each of the four groups consisted of eight FDPs (test groups). The FDPs were cemented on their cast and standardised-sectioned. The cement film thickness of the marginal and internal gaps was measured in a stereomicroscope, digital photos were taken at 12× magnification and then analyzed using measurement software. Statistical analyses were performed with one-way ANOVA and Tukey's test.

Results

Best fit based on the means (SDs) in μm for all measurement points was in the DLMS group 84 (60) followed by MW 117 (89), LW 133 (89) and MC 166 (135). Significant differences were present between MC and DLMS (p < 0.05). The regression analyses presented differences within the parameters: production technique, tooth size, position and measurement point (p < 0.05).

Significance

Best fit was found in the DLMS group followed by MW, LW and MC. In all four groups, best fit in both abutments was along the axial walls and in the deepest part of the chamfer preparation. The greatest misfit was present occlusally in all specimens.     

Degradation of polymeric restorative materials subjected to a high caries challenge

Objectives

The aim of this study was to evaluate the degradation of different resin filling materials after a caries challenge, by high performance liquid chromatography (HPLC) and contact angle (θ) measurement.

Methods

Four different polymeric restorative materials (a resin composite, a polyacid-modified resin composite, an ormocer and a resin-modified glass ionomer cement) were tested. Five samples (30 mm × 6 mm × 2 mm) of each material were formed in a Teflon mold, following the manufacturer's instructions. After pH cycles, the solutions were injected in an HPLC. The θ was obtained, before and after pH cycle, by a goniometer at 60% air humidity and 25 °C. A distilled water drop (0.006 ml) was put on the material surface, and after 6 min, 10 measures were obtained at 20 s intervals. Each sample received 4 drops, one at a time, on different areas.

Results

HPLC results showed elution of byproducts in all materials. This was greater in the acid medium. Bis-GMA and TEGDMA were detected in TPH Spectrum and Definite residues. Analyses of the contact angle by ANOVA and Student-Neuman-Keuls's test showed that the surfaces of TPH Spectrum, Dyract AP and Definite were altered, except Vitremer (p < 0.05).

Significance

All materials tested degraded on a caries simulated medium, suggesting that a great effort should be made to disseminate oral health information, since a high caries challenge environment (low pH) can lead to dental composite degradation, with potential toxic risks to patients.     

The effect of high fiber fraction on some mechanical properties of unidirectional glass fiber-reinforced composite

Objectives

This study was designed to evaluate the effect of an increase of fiber-density on some mechanical properties of higher volume fiber-reinforced composite (FRC).

Methods

Five groups of FRC with increased fiber-density were fabricated and two additional groups were prepared by adding silanated barium-silicate glass fillers (0.7 μm) to the FRC. The unidirectional E-glass fiber rovings were impregnated with light-polymerizable bisGMA-TEGDMA (50-50%) resin. The fibers were pulled through a cylindrical mold with an opening diameter of 4.2 mm, light cured for 40 s and post-cured at elevated temperature. The cylindrical specimens (n = 12) were conditioned at room temperature for 2 days before testing with the three-point bending test (Lloyd Instruments Ltd.) adapted to ISO 10477. Fiber-density was analyzed by combustion and gravimetric analyzes.

Results

ANOVA analysis revealed that by increasing the vol.% fraction of E-glass fibers from 51.7% to 61.7% there was a change of 27% (p < 0.05) in the modulus of elasticity, 34% (p < 0.05) in the toughness, and 15% (p < 0.05) in the load bearing capacity, while there was only 8% (p < 0.05) increase in the flexural strength although it was statistically insignificant. The addition of particulate fillers did not improve the mechanical properties.

Significance

This study showed that the properties of FRC could be improved by increasing fibervolume fraction. Modulus of elasticity, toughness, and load bearing capacity seem to follow the law of ratio of quantity of fibers and volume of the polymer matrix more precisely than flexural strength when high fiber-density is used.     

The effect of porcelain thickness and surface liner application on the fracture behavior of a ceramic system

Objectives

To determine the effect of porcelain thickness and the application of a surface liner (SL) on the flexural strength (σ) of a ceramic system.

Methods

One hundred twenty bar-shaped specimens of yttria-stabilized zirconia-based ceramic were fabricated and randomly divided into two groups according to the application of SL: A - applied; B - not applied. The specimens were further divided according to the porcelain veneer thickness (n = 20): 0-0.5 mm; 1-1.0 mm; 2-2.0 mm. All specimens were tested in 3-point bending with the porcelain under tension. The maximum load was recorded at first sign of fracture, the σ was calculated and the mode of failure was determined. Data was statistically analyzed using one-way ANOVA, Tukey (α = 0.05) and Weibull distribution.

Results

The SL application had no effect (p = 0.723) while the porcelain thickness had a significant effect (p = 0.000) on the mean σ values. No significant differences in mean σ values were found with same porcelain thickness. A 0.5-mm thick porcelain layer (groups A0 and B0) showed greater mean σ values than other groups. The Weibull modulus (m) ranged from 6 (groups A1 and B2) to 9 (groups A0, A2 and B0). The predominant mode of failure for all groups was fracture initiation at the porcelain surface propagating to the ceramic interface.

Significance

The porcelain thickness influenced the mean σ values, but the SL had no significant effect on the flexural strength and the mode of failure of the ceramic system examined.     

Reliability and failure modes of implant-supported zirconium-oxide fixed dental prostheses related to veneering techniques

Objectives

To compare fatigue failure modes and reliability of hand-veneered and over-pressed implant-supported three-unit zirconium-oxide fixed-dental-prostheses(FDPs).

Methods

Sixty-four custom-made zirconium-oxide abutments (n = 32/group) and thirty-two zirconium-oxide FDP-frameworks were CAD/CAM manufactured. Frameworks were veneered with hand-built up or over-pressed porcelain (n = 16/group). Step-stress-accelerated-life-testing (SSALT) was performed in water applying a distributed contact load at the buccal cusp-pontic-area. Post failure examinations were carried out using optical (polarized-reflected-light) and scanning electron microscopy (SEM) to visualize crack propagation and failure modes. Reliability was compared using cumulative-damage step-stress analysis (Alta-7-Pro, Reliasoft).

Results

Crack propagation was observed in the veneering porcelain during fatigue. The majority of zirconium-oxide FDPs demonstrated porcelain chipping as the dominant failure mode. Nevertheless, fracture of the zirconium-oxide frameworks was also observed. Over-pressed FDPs failed earlier at a mean failure load of 696 ± 149 N relative to hand-veneered at 882 ± 61 N (profile I). Weibull-stress-number of cycles-unreliability-curves were generated. The reliability (2-sided at 90% confidence bounds) for a 400 N load at 100 K cycles indicated values of 0.84 (0.98-0.24) for the hand-veneered FDPs and 0.50 (0.82-0.09) for their over-pressed counterparts.

Conclusions

Both zirconium-oxide FDP systems were resistant under accelerated-life-time-testing. Over-pressed specimens were more susceptible to fatigue loading with earlier veneer chipping.     

Efficacy of natural antimicrobials in toothpaste formulations against oral biofilms in vitro

Objectives

To evaluate the antimicrobial efficacies of two toothpaste formulations containing natural antimicrobials (herbal extracts and chitosan) against oral biofilms of different composition and maturational status.

Methods

Bacteria from a buffer suspension or fresh saliva were adhered for 2 h to a salivary conditioning film and subsequently grown for 16 h. Dual-species biofilms were prepared from Actinomyces naeslundii T14V-J1 and Streptococcus oralis J22, whilst multi-species biofilms were grown from freshly collected human saliva. Biofilms were exposed to 25 wt% toothpaste supernatants. A chlorhexidine-containing mouthrinse and a buffer were used as positive- and negative-controls, respectively. Antibacterial efficacy was concluded from acute killing, bacterial removal, prevention of bacterial re-deposition and continued killing during re-deposition.

Results

The herbal- and chitosan-based supernatants showed immediate killing of oral biofilm bacteria, comparable with chlorhexidine. Moreover, exposure of a biofilm to these supernatants or chlorhexidine, yielded ongoing killing of biofilm bacteria after exposure during re-deposition of bacteria to a matured 16 h biofilm, but not to a much thinner initial biofilm formed by 2 h adhesion only. This suggests that thicker, more matured biofilms can absorb and release oral antimicrobials.

Conclusions

Supernatants based on herbal- and chitosan-based toothpastes have comparable immediate and ongoing antibacterial efficacies as chlorhexidine. Natural antimicrobials and chlorhexidine absorb in oral biofilms which contributes to their substantive action.     

Use of the checkerboard DNA-DNA hybridisation technique for in vivo detection of cariogenic microorganisms on metallic brackets, with or without use of an antimicrobial agent

Objective

Using checkerboard DNA-DNA hybridisation (CDDH) assay, this randomised clinical study evaluated the contamination of metallic brackets by four cariogenic bacterial strains (Streptococcus mutans, Streptococcus sobrinus, Lactobacillus casei and Lactobacillus acidophilus) and the efficacy of 0.12% chlorhexidine gluconate (CHX) mouthwashes in reducing bacterial contamination.

Methods

Thirty-nine 11-33-year-old patients under treatment with fixed orthodontic appliances were enrolled in the study and had 2 new metallic brackets bonded to premolars. Nineteen patients used a 0.12% CHX mouthwash (Periogard^®) and 20 patients used a placebo mouthwash (control) twice a week. After 30 days, the brackets were removed and samples were obtained for analysis by CDDH. Data were analysed statistically by the Kruskal-Wallis test (α = 0.05) using the SAS software.

Results

S. mutans, S. sobrinus, L. casei and L. acidophilus were detected in 100% of the samples from both groups. However, brackets of the control group were more heavily contaminated by S. mutans and S. sobrinus (P < 0.01). In the experimental group, although all counts decreased after rinsing with the chlorhexidine solution, there was significant difference only for S. mutans (P = 0.03).

Conclusions

The use of 0.12% chlorhexidine gluconate mouthwashes can be useful in clinical practice to reduce the levels of cariogenic microorganisms in patients under treatment with fixed orthodontic appliances.     

Radiographic measurement of the cervical spine in patients with temporomandibular dysfunction

Aim

To compare the craniocervical angles and distances between temporomandibular dysfunction (TMD) and free TMD subjects.

Casuistic and methods

The sample consisted of young adults, of both genders, with age ranging between 18 and 30 years. TMD diagnosis was based on the clinical criteria of the Research Diagnostic Criteria for TMD (RDC/TMD), associated with self-reported symptoms of TMD. For radiological analysis we measured three angles and two distances of craniocervical region.

Results

Of the 56 subjects, only 23 completed all stages of research, which were divided into two groups: (1) free TMD group - composed of 11 individuals; (2) TMD group - constituted of 12 subjects. The most common clinical diagnosis of TMD was arthralgia (75.0%) followed by myofascial pain without limited mouth opening (58.4%). Among the self-reported symptoms of TMD, the most frequents were facial (83.4%) and neck (66.6%) pain. Of radiological measurement, only plane atlas angle (APA) (p = 0.026) and anterior translation distance (Tz C₂-C₇) (p = 0.045) showed statistical difference between groups TMD (APA = 16.7 ± 1.63; Tz C₂-C₇ = 28.7 ± 2.58) and free TMD (APA = 21.64 ± 1.24; Tz C₂-C₇ = 19.82 ± 3.29).

Conclusion

It could be verified that the symptomatic TMD patients presented a flexion of the first cervical vertebra associated with an anteriorization of the cervical spine (hyperlordosis).     

Effect of surface pre-treatments on the zirconia ceramic-resin cement microtensile bond strength

Objective

To evaluate the influence of different surface treatments on the microtensile bond strength of resin cement to zirconia ceramic.

Materials and methods

Twelve cylinder-shaped (∅ 12 × 5.25 mm high) blocks of a commercial zirconium-oxide ceramic (Cercon^® Zirconia, DENTSPLY) were randomly divided into 4 groups (n = 3), based on the surface treatment to be performed: (1) airborne particle abrasion with 125 μm Al₂O₃ particles (S); (2) selective infiltration etching (SIE); (3) experimental hot etching solution applied for 30 min (ST) and (4) no treatment (C). Paradigm MZ100 blocks (3M ESPE) were cut into twelve cylinders of 4 mm in thickness. Composite cylinders were bonded to conditioned ceramics using a resin cement (Calibra^®, DENTSPLY), in combination with the proprietary adhesive system. After 24 h bonded specimens were cut into microtensile sticks and loaded in tension until failure. Bond strength data were analyzed with Kruskall-Wallis and Dunn's Multiple Range test for multiple comparisons (p < 0.05). Failure mode distribution was recorded and the interfacial morphology of debonded specimens was analyzed using a scanning electron microscope (SEM).

Results

Bond strength values achieved after SIE and ST treatment were significantly higher than after S treatment and without any treatment (p < 0.05). Premature failures were mostly recorded in the S group.

Significance

Conditioning the high-strength ceramic surface with SIE and ST treatments yielded higher bond strengths of the resin cement than when zirconia ceramic was treated with airborne particle abrasion or left untreated.     

Crystallization and flexural strength optimization of fine-grained leucite glass-ceramics for dentistry

Objectives

Leucite glass-ceramics with fine-grained leucite crystals promote improved mechanical strength and increased translucency. The objectives of the study were to optimize the microstructure of a fine-grained leucite glass-ceramic in order to increase its flexural strength and reliability as measured by its Weibull modulus.

Methods

Glass was prepared by a melt-derived method and ground into a powder (M1A). The glass crystallization kinetics were investigated using high temperature XRD and DSC. A series of two-step heat treatments with different nucleation/crystal growth temperatures and holds were carried out to establish the optimized crystallization heat treatment. Glass-ceramics were characterized using XRD, SEM and dilatometry. The glass-ceramic heat treated at the optimized crystallization parameters (M1A_opt) was both sintered (SM1A_opt) and heat extruded (EM1A_opt) into discs and tested using the biaxial flexural strength (BFS) test.

Results

High temperature XRD suggested leucite and sanidine crystallization at different temperatures. Optimized crystallization resulted in an even distribution of fine leucite crystals (0.15 (0.09) μm²) in the glassy matrix, with no signs of microcracking. Glass-ceramic M1A_opt showed BFS values of [mean (SD), MPa]: SM1A_opt = 252.4 (38.7); and EM1A_opt = 245.0 (24.3). Weibull results were: SM1A_opt; m = 8.7 (C.I. = 7.5-10.1) and EM1A_opt; m = 11.9 (C.I. = 9.3-15.1). Both experimental groups had a significantly higher BFS and characteristic strength than the IPS Empress Esthetic glass-ceramic, with a higher m value for the EM1A_opt material (p < 0.05).

Significance

A processable fine-grained leucite glass-ceramic with high flexural strength and improved reliability was the outcome of this study.     

Non-invasive quantification of resin-dentin interfacial gaps using optical coherence tomography: Validation against confocal microscopy

Objectives

Regardless of the cause, gap formation at the tooth-restoration interface may result in treatment failure; non-destructive assessment and monitoring of these defects are important. The aim of this in vitro study is to assess the tooth-restoration interface using a non-invasive technique; swept source optical coherence tomography (SS-OCT) and to confirm the findings with confocal laser scanning microscope (CLSM).

Methods

Cylindrical class-I cavities (3 mm in diameter and 1.5 mm in depth) were prepared in the occlusal surface of human premolars. Each cavity was restored using an all-in-one adhesive system (Clearfil Tri-S Bond) and one of the three types of composites placed in bulk; Majesty Posterior, AP-X and Majesty LV (all by Kuraray Medical, Japan). Ten serial cross-sectional images of the whole restored cavity were obtained by SS-OCT at 1319 nm center wave length, to which locations the specimens were later trimmed, polished and observed under CLSM. An image analysis software was used to detect significant peaks in the signal intensity at the resin-dentin interface of the cavity floor. The presence and dimensions of gaps at the interface were also confirmed by CLSM.

Results

Increased SS-OCT signal intensity along the interface corresponded well to the interfacial gaps detected by CLSM. The actual gap size detected ranged from 26 μm to 1.9 mm in length, and the universal composite APX showed lowest interfacial gaps.

Conclusion

SS-OCT imaging technology can be used to non-invasively detect and quantify micrometer gaps at the bottom of composite restorations, and potentially become a monitoring tool for composite restorations both in the laboratory research, and in the clinics.     

Nanohybrid vs. fine hybrid composite in extended Class II cavities after six years

Objectives

In a controlled prospective split-mouth study, clinical behavior of two different resin composites in extended Class II cavities was observed over six years.

Methods

Thirty patients received 68 direct resin composite restorations (Solobond M + Grandio: n = 36; Syntac + Tetric Ceram: n = 32) by one dentist in a private practice. All restorations were replacement fillings, 35% of cavities revealed no enamel at the bottom of the proximal box, in 48% of cavities remaining proximal enamel width was <0.5 mm. Restorations were examined according to modified USPHS criteria at baseline, and after six months, one, two, four, and six years.

Results

Success rate was 100% after six years of clinical service, while the drop out of patients was 0%. Neither materials nor localization of the restoration (upper vs. lower jaw) had a significant influence on clinical outcome in any criterion after six years (p > 0.05; Mann-Whitney U-test). Molar restorations performed worse regarding marginal integrity (4 years), filling integrity (6, 12, 24, 48 months), and tooth integrity (4 and 6 years). Irrespective of the resin composite used, significant changes over time were found for all criteria recorded (Friedman test; p < 0.05). Marginal quality revealed a major portion of overhangs having been clearly reduced after the one year recall (baseline: 44%; 6 months: 65%; 1 year: 47%; 2 years: 6%; 4 years: 4%; and 6 years: 3%). Beyond the 1 year recall, negative step formations significantly increased due to wear (p < 0.05), having been more pronounced in molars (87% bravo after 4 years) than in premolars (51% bravo after 4 years). Tooth integrity significantly deteriorated due to enamel cracks, which increased over time (p < 0.05). Enamel chippings and cracks were significantly more frequent in molars (26% bravo after 4 years to 35% after six years) than in premolars (9% bravo after 4 years, 11% after six years). Restoration integrity over time mainly suffered surface roughness and wear (28% after one year, 75% after two years, 84% after four years, 91% after six years).

Significances

Both materials performed satisfactorily over the 6-year observation period. Due to the extension of the restorations, wear was clearly visible after six years of clinical service with 91% bravo ratings.     

Synthesis and study of properties of dental resin composites with different nanosilica particles size

Objectives

The aim of this work was the synthesis of light-cured resin nanocomposites using nanosilica particles with different particle size and the study of some physical-mechanical properties of the composites.

Methods

Various types of silica nanoparticles (Aerosil) with average particle size of 40, 20, 16, 14, and 7 nm, used as filler were silanized with the silane 3-methacryloxypropyl-trimethoxysilane (MPS). The total amount of silane used was kept constant at 10 wt% relative to the filler weight to ensure the complete silanization of nanoparticles. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (55 wt%) were mixed with a photoactivated Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by dynamic mechanical analyzer (DMA). Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water solution 75 vol% for 30 days. The TGA for composites was performed in nitrogen atmosphere from 30 to 700 °C.

Results

As the average silica particle size decreases, the percentage amount of MPS attached on the silica surface increases. However, the number of MPS molecules attached on the silica surface area of 1 nm² is independent of filler particle size. As the average filler particles size decreases a progressive increase in the degree of conversion of composites and an increase in the amount of sorbed water is observed.

Significance

The prepared composites containing different amount of silica filler, with different particle size, but with the same amount of silanized silica and organic matrix showed similar flexural strength and flexural modulus, except composite with the lowest filler particle size, which showed lower flexural modulus.     

The impact of hydrofluoric acid etching followed by unfilled resin on the biaxial strength of a glass-ceramic

Objectives

To evaluate the null hypotheses that hydrofluoric (HF) acid etching time would neither decrease the biaxial flexural strength of a glass-based veneering ceramic nor enhance it after silane and unfilled resin (UR) applications.

Methods

Disc-shaped IPS e.max ZirPress specimens were allocated into 12 groups: G1-control (no-etching), G2-30 s, G3-60 s, G4-90 s, G5-120 s, G6-60 s + 60 s. Groups (G7–G12) were treated in the same fashion as G1–G6, but followed by silane and UR applications. Surface morphology and roughness (Ra and Rq) of the ceramics were assessed by means of scanning electron microscopy (SEM) and profilometry, respectively. Flexural strength was determined by biaxial testing. Data were analyzed by two-way ANOVA and the Sidak test (α = 0.05). Weibull statistics were estimated and finite element analysis (FEA) was carried out to verify the stress concentration end areas of fracture.

Results

The interaction (etching time vs. surface treatment) was significant for Ra (p = 0.008) and Rq (0.0075). Resin-treated groups presented significantly lower Ra and Rq than non-treated groups, except for the 60 s group (p < 0.005). SEM revealed that etching affected the ceramic microstructure and that the UR was able to penetrate into the irregularities. A significant effect of etching time (p = 0.029) on flexural strength was seen. G7–G12 presented higher strength than G1–G6 (p < 0.0001). None of experimental groups failed to show 95% confidence intervals of σ₀ and m overlapped. FEA showed lower stress concentration after resin treatment.

Significance

HF acid etching time did not show a damaging effect on the ceramic flexural strength. Moreover, the flexural strength could be enhanced after UR treatment.     

Cephalometric changes produced by locally applied anabolic steroid in Wistar rats

Background and objective

There is a strong relationship between neuromuscular activity and facial skeletal morphogenesis. The systemic use of anabolic steroid accelerates craniofacial growth and induces high functional activity of rats’ masticatory muscles. The present study examines the effect of an anabolic steroid locally applied in the masseter muscle of growing rats with the purpose of verifying possible craniofacial changes with minimum drug side effects, using cephalometric analysis.

Materials and methods

Forty-three 3-week-old Wistar rats were evaluated and divided into two groups: (1) NAN group (local bilateral masseter injection of nandrolone decanoate - 0.05 μg/3 μl/bi-weekly) and (2) CON group (local bilateral masseter injection of sterile oil - 3 μl). Tukey and Wilcoxon tests were used.

Results

In NAN group the cephalometric measures showed horizontalized facial growth (reduce of FMA angle - p < 0.01), increase of posterior facial height, decrease of anterior facial height, reduction of gonial angle (p < 0.05), increase of mandibular height (p < 0.01). There was no variation in the length of the mandible, in the skull and animals’ weight gain, thus demonstrating that no important systemic effect occurred.

Conclusion

The local injection of nandrolone in the masseter muscle of rats was capable to alter the growth direction and the morphology of the craniofacial complex in Wistar rats.     

The effect of surface conditioning on the bond strength of resin composite to amalgam

Objectives

This study evaluated the effect of different surface conditioning methods on the tensile bond strength (TBS) and integrity of the amalgam-resin composite interface, using commercially available restoration repair systems.

Methods

One hundred and sixty Gamma 2 amalgam specimens were stored in artificial saliva for 2 weeks and then randomly assigned to one of the following conditioning groups (n = 20/group): Group 1: air abrasion, alloy primer and ‘Panavia 21’, Group 2: air abrasion and ‘Amalgambond Plus’, Group 3: air abrasion and ‘All-Bond 3’, Group 4: diamond bur, alloy primer and ‘Panavia 21’, Group 5: diamond bur and ‘Amalgambond Plus’, Group 6: diamond bur and ‘All-Bond 3’, Group 7: silica coating technique, and Group 8: non-conditioned amalgam surfaces (control group). Subsequently, resin composite material was added to the substrate surfaces and the amalgam-resin composite specimens were subjected to TBS testing. Representative samples from the test groups were subjected to scanning electron microscopy and surface profilometry. The data was analysed statistically with one-way ANOVA and post hoc Tukey's tests (α = 0.05).

Results

The mean TBS of amalgam-resin composite ranged between 1.34 and 5.13 MPa and varied with the degree of amalgam surface roughness and the type of conditioning technique employed. Significantly highest TBS values (5.13 ± 0.96 MPa) were obtained in Group 1 (p = 0.013).

Conclusion

Under the tested conditions, significantly greater tensile bond strength of resin composite to amalgam was achieved when the substrate surface was conditioned by air abrasion followed by the application of the Panavia 21 adhesive system.

Clinical significance

Effecting a repair of an amalgam restoration with resin composite via the use of air abrasion and application of Panavia 21 would seem to enhance the integrity of the amalgam-resin composite interface. Clinical trials involving the implementation of this technique are indicated to determine the usefulness of this technique.     

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.