Influence of post-etching surface treatment and thermo-mechanical cycling on fracture strength of ceramics

BACKGROUNG

The aim of this study was to evaluate fracture strength of lithium disilicate-based ceramic crowns submitted to neutralization of hydrofluoric acid (HF) precipitates associated with ultrasonic bath and to thermo-mechanical cycling.

METHODS

Eighty human molars received conventional full crown preparation after being included in polyurethane standard to simulate periodontal ligament. After scanning, the ceramic blocks were machined using CAD/CAM system to obtain the crowns. The crowns were distributed according to surface treatment: S and S-C; HF and silane; SNU and SNU-C; HF neutralization of HF precipitates, ultrasonic bath and silane. The crowns were cemented with dual cure resin cement and the specimens in Groups S-C and SNU-C were submitted to thermo-mechanical cycling (5/55 °C/60 s while 1.2 million mechanical cycles of 4 Hz/100 N). The samples were submitted to compressive test. Analysis of fractures was performed macroscopically (Burke method) and using Scanning Electron Microscope. The data of fracture strength were analyzed using the two-way ANOVA.

RESULTS

No statistical difference among the groups was found (p-value = 0,799). Most failures were associated with the remaining tooth fracture and the fracture origin was located on the cementation surface.

CONCLUSIONS

Postetching cleaning protocols do not improve the fracture strength of ceramics crowns. Thermo-mechanical aging did not weakened the ceramic crown.

Electromyographic activity in patient with an inferior implant/tooth-supported overdenture: Clinical Case Report

Clinicians can find patients with one mandibular remaining tooth, and it is difficult to decide if the tooth has to be removed. When a clinician decide to maintaining the tooth, it is common to feel doubts about masticatory load distribution divided between the tooth and implant. This paper reports a clinical case of patient with an implant/tooth-supported overdenture and elucidates the masticatory efficiency by electromyography activity analysis. The objective of this case report was to describe a clinical case of a patient with an implant/tooth-supported overdenture and to discuss the muscle response to this treatment. Electrical activities of the masseter and anterior temporal surfaces at maximum voluntary contraction were evaluated by electromyography during pre-treatment, immediately post-treatment, 15 and 60 days after installation. When patient has one remaining tooth in good condition, the implant/tooth-supported overdenture can be recommended, to preserve the periodontal ligament and proprioception, and to minimize bone loss. Electromyography analysis showed that implant/tooth-supported overdenture is a viable treatment alternative, in muscular standpoint, when the patient has a remaining tooth with good osseous support.

Monoclinic phase transformation and mechanical durability of zirconia ceramic after fatigue and autoclave aging

OBJECTIVES

This study evaluated the influence of two aging procedures on the biaxial flexural strength of yttria-stabilized tetragonal zirconia ceramics.

MATERIAL AND METHODS

Disc-shaped zirconia specimens and (ZE: E.max ZirCAD, Ivoclar; ZT: Zirkon Translucent, Zirkonzahn) (N = 80) (∅:12 mm; thickness:1.2 mm, ISO 6872) were prepared and randomly divided into four groups (n = 10 per group) according to the aging procedures: C: Control, no aging; M: mechanical cycling (2 × 10⁶ cycles/3.8 Hz/200 N); AUT: Aging in autoclave at 134°C, 2 bar for 24 h; AUT + M: Autoclave aging followed by mechanical cycling. After aging, the transformed monoclinic zirconia (%) were evaluated using X-ray diffraction and surface roughness was measured using atomic force microscopy. The average grain size was measured by scanning electron microscopy and the specimens were submitted to biaxial flexural strength testing (1 mm/min, 1000 kgf in water). Data (MPa) were statistically analyzed using 2-way analysis of variance and Tukey's test (α = 0.05).

RESULTS

Aging procedures significantly affected (p = 0.000) the flexural strength data but the effect of zirconia type was not significant (p = 0.657). AUT_ZT (936.4 ± 120.9^b ) and AUT + M_ZE (867.2 ± 49.3^b ) groups presented significantly higher values (p < 0.05) of flexural strength than those of the control groups (C_ZT : 716.5 ± 185.7^a ; C_ZE : 779.9 ± 114^a ) (Tukey's test). The monoclinic phase percentage (%) was higher for AUT_ZE (71), AUT_ZT (66), AUT + M_ZE (71), and AUT + M_ZM (66) compared to the C groups (ZE:0; ZT:0). Surface roughness (µm) was higher for AUT_ZE (0.09), AUT_ZT (0.08), AUT + M_ZE (0.09 µm), and AUT + M_ZT (0.09 µm) than those of other groups.

CONCLUSIONS

Regardless of the zirconia type, autoclave aging alone or with mechanical aging increased the flexure strength but also induced higher transformation from tetragonal to monoclinic phase in both zirconia materials tested. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1972-1977, 2017.

Effect of composite surface treatment and aging on the bond strength between a core build-up composite and a luting agent

Objective

The purpose of this study was to assess the influence of conditioning methods and thermocycling on the bond strength between composite core and resin cement.

Material and Methods

Eighty blocks (8×8×4 mm) were prepared with core build-up composite. The cementation surface was roughened with 120-grit carbide paper and the blocks were thermocycled (5,000 cycles, between 5°C and 55°C, with a 30 s dwell time in each bath). A layer of temporary luting agent was applied. After 24 h, the layer was removed, and the blocks were divided into five groups, according to surface treatment: (NT) No treatment (control); (SP) Grinding with 120-grit carbide paper; (AC) Etching with 37% phosphoric acid; (SC) Sandblasting with 30 mm SiO₂ particles, silane application; (AO) Sandblasting with 50 mm Al₂O₃ particles, silane application. Two composite blocks were cemented to each other (n=8) and sectioned into sticks. Half of the specimens from each block were immediately tested for microtensile bond strength (µTBS), while the other half was subjected to storage for 6 months, thermocycling (12,000 cycles, between 5°C and 55°C, with a dwell time of 30 s in each bath) and µTBS test in a mechanical testing machine. Bond strength data were analyzed by repeated measures two-way ANOVA and Tukey test (α=0.05).

Results

The µTBS was significantly affected by surface treatment (p=0.007) and thermocycling (p=0.000). Before aging, the SP group presented higher bond strength when compared to NT and AC groups, whereas all the other groups were statistically similar. After aging, all the groups were statistically similar. SP submitted to thermocycling showed lower bond strength than SP without thermocycling.

Conclusion

Core composites should be roughened with a diamond bur before the luting process. Thermocycling tends to reduce the bond strength between composite and resin cement.

Heat Treatment of Pre-hydrolyzed Silane Increases Adhesion of Phosphate Monomer-based Resin Cement to Glass Ceramic

This study evaluated the influence of different forms of heat treatment on a pre-hydrolyzed silane to improve the adhesion of phosphate monomer-based (MDP) resin cement to glass ceramic. Resin and feldspathic ceramic blocks (n=48, n=6 for bond test, n=2 for microscopy) were randomly divided into 6 groups and subject to surface treatments: G1: Hydrofluoric acid (HF) 9.6% for 20 s + Silane + MDP resin cement (Panavia F); G2: HF 9.6% for 20 s + Silane + Heat Treatment (oven) + Panavia F; G3: Silane + Heat Treatment (oven) + Panavia F; G4: HF 9.6% for 20 s + Silane + Heat Treatment (hot air) + Panavia F; G5: Silane + Heat Treatment (hot air) + Panavia F; G6: Silane + Panavia F. Microtensile bond strength (MTBS) test was performed using a universal testing machine (1 mm/min). After debonding, the substrate and adherent surfaces were analyzed using stereomicroscope and scanning electron microscope (SEM) to categorize the failure types. Data were analyzed statistically using two-way test ANOVA and Tukey's test (=0.05). Heat treatment of the silane containing MDP, with prior etching with HF (G2: 13.15±0.89a; G4: 12.58±1.03a) presented significantly higher bond strength values than the control group (G1: 9.16±0.64b). The groups without prior etching (G3: 10.47±0.70b; G5: 9.47±0.32b) showed statistically similar bond strength values between them and the control group (G1). The silane application without prior etching and heat treatment resulted in the lowest mean bond strength (G6: 8.05±0.37c). SEM analysis showed predominantly adhesive failures and EDS analysis showed common elements of spectra (Si, Na, Al, K, O, C) characterizing the microstructure of the glass-ceramic studied. Heat treatment of the pre-hydrolyzed silane containing MDP in an oven at 100 °C for 2 min or with hot air application at 50±5 ºC for 1 min, was effective in increasing the bond strength values between the ceramic and resin cement containing MDP.

Effects of aging procedures on the topographic surface, structural stability, and mechanical strength of a ZrO2-based dental ceramic

OBJECTIVE

To determine the effects of different aging methods on the degradation and flexural strength of yttria-stabilized tetragonal zirconia (Y-TZP) METHODS: Sixty disc-shaped specimens (∅, 12mm; thickness, 1.6mm) of zirconia (Vita InCeram 2000 YZ Cubes, VITA Zahnfabrik) were prepared (ISO 6872) and randomly divided into five groups, according to the aging procedures (n=10): (C) control; (M) mechanical cycling (15,000,000 cycles/3.8Hz/200N); (T) thermal cycling (6,000 cycles/5-55°C/30s); (TM) thermomechanical cycling (1,200,000 cycles/3.8Hz/200N with temperature range from 5°C to 55°C for 60s each); (AUT) 12h in autoclave at 134°C/2bars; and (STO) storage in distilled water (37°C/400 days). After the aging procedures, the monoclinic phase percentages were evaluated by X-ray diffraction (XRD), and topographic surface analysis was performed by 3D profilometry. The specimens were then subjected to biaxial flexure testing (1mm/min, load 100kgf, in water). The biaxial flexural strength data (MPa) were analyzed by 1-way ANOVA and Tukey's test (α=0.05). The data for monoclinic phase percentage and profilometry (Ra) were analyzed by Kruskal-Wallis and Dunn's tests.

RESULTS

ANOVA revealed that flexural strength was affected by the aging procedures (p=0.002). The M (781.6MPa) and TM (771.3MPa) groups presented lower values of flexural strength than did C (955MPa), AUT (955.8MPa), T (960.8MPa) and STO (910.4MPa). The monoclinic phase percentage was significantly higher only for STO (12.22%) and AUT (29.97%) when compared with that of the control group (Kruskal-Wallis test, p=0.004). In addition, the surface roughnesses were similar among the groups (p=0.165).

SIGNIFICANCE

Water storage for 400 days and autoclave aging procedures induced higher phase transformation from tetragonal to monoclinic; however, they did not affect the flexural strength of Y-TZP ceramic, which decreased only after mechanical and thermomechanical cycling.

Can heat treatment procedures of pre-hydrolyzed silane replace hydrofluoric acid in the adhesion of resin cement to feldspathic ceramic?

PURPOSE

To evaluate the influence of heat treatment (HT) procedures of a pre-hydrolyzed silane on bond strength of resin cement to a feldspathic ceramic.

MATERIALS AND METHODS

Ceramic and composite blocks (N = 30) were divided into six groups (n = 5) and subjected to the following conditioning procedures: G1: 9.6% hydrofluoric acid (HF) for 20 s + silane (RelyX Ceramic Primer, 3M ESPE) + resin cement (Panavia F2.0, Kuraray) (control); G2: HF (20 s) + silane + heat treatment in furnace (HTF) (100°C, 2 min) + resin cement; G3: silane + HTF + resin cement; G4- HF (20 s) + silane + heat treatment with hot air (HTA) (50 ± 5°C for 1 min) + resin cement; G5: silane + HTA + resin cement; G6: silane + resin cement. The microtensile bond strength (MTBS) test was performed using a universal testing machine (1 mm/min). After debonding, the substrate and adherent surfaces were analyzed using a stereomicroscope and SEM to categorize the failure types. The data were statistically evaluated using one-way ANOVA and Tukey's test (5%).

RESULTS

The control group (G1) showed no pre-test failures and presented significantly higher mean MTBS (16.01 ± 1.12 MPa) than did other groups (2.63 ± 1.05 to 12.55 ± 1.52 MPa) (p = 0.0001). In the groups where HF was not used, HTF (G3: 12.55 ± 1.52 MPa) showed significantly higher MTBS than did HTA (G5: 2.63 ± 1.05 MPa) (p < 0.05). All failure types were mixed, ie, adhesive between the resin cement and ceramic accompanied by cohesive failure in the cement.

CONCLUSION

Heat treatment procedures for the pre-hydrolyzed silane either in a furnace or with the application of hot air cannot replace the use of HF gel for the adhesion of resin cement to feldspathic ceramic. Yet when mean bond strengths and incidence of pre-test failures are considered, furnace heat treatment delivered the second best results after the control group, being considerably better than hot air application.

May the flexural strength of ceramics be influenced by salivary pH?

Objective. This study purpose was compare the three-point flexural strengths of 50 feldspathic ceramic after storage in artificial saliva. Material and methods. The bars were luted with resin cement and subjected to storage in artificial saliva of different pHs. Results.  The values of flexural strength were significantly higher for the bars stored in distilled water, at neutral and basic pH, when compared with the results for the bars stored in acidic pH and in acid/basic pH. Conclusions. Storage for 30 days in artificial saliva at acidic pH, or alternating between acidic and basic pH, can reduce the mechanical properties of ceramics.

Pullout bond strength of fiber posts luted to different depths and submitted to artificial aging

INTRODUCTION

The extension of fiber post cementation often does not seem to influence the fracture resistance of restorations. This study evaluated the effects of cementation depths on the retention of fiber posts submitted to artificial aging.

METHODS

One hundred and sixty bovine incisors were selected to assess post retention. Following endodontic treatment, the canals were flared with diamonds burs. Postholes were prepared in lengths of 5 or 10 mm, after which fiber posts were relined with composite resin and luted with RelyX ARC or RelyX Unicem. The samples were then submitted to thermal and/or mechanical cycling before testing their pullout bond strengths. Absence of cycling was used as a control. The results of each cement were submitted to two-way and post hoc Tukey tests (α=0.05).

RESULTS

Independent of the aging protocol, a depth of 10 mm showed higher pullout bond strength than did 5 mm, except for RelyX Unicem without cycling. For RelyX ARC, thermomechanical cycling resulted in lower values than in the absence of cycling. Mechanical cycling alone promoted the highest bond strength when the posts were luted with RelyX Unicem.

CONCLUSION

The effect of artificial aging on the pullout bond strength is dependent on the type of material and the depth.

Lung Function in Cardiac Dysfunction

OBJECTIVE

The alterations in lung function caused by heart failure were first described some decades ago. The advent of new tools for the diagnosis and investigation of heart disease, such as echocardiography, has subsequently made it possible to classify cardiac dysfunction with greater precision. The objective of this study was to analyze and compare a series of lung function and gas exchange variables in patients who had been classified into 4 groups according to type of heart disease as diagnosed by echocardiography.

MATERIALS AND METHOD

Emergency room patients whose main symptom was acute dyspnea caused by cardiac or respiratory disease were included in the study. The final sample comprised 71 patients whose echocardiogram revealed cardiac dysfunction. Spirometry was carried out and resting arterial blood gases measured in this group.

RESULTS

Of the 71 patients with cardiopathy, 31 had systolic dysfunction, 27 diastolic dysfunction, 7 cor pulmonale, and 6 primary valve disease. Spirometry revealed a generally obstructive pattern, more marked in the group with cor pulmonale. Analysis of arterial blood gases revealed slight hypoxemia with normocapnia in all groups, but this was more accentuated in the patients with cor pulmonale and diastolic dysfunction. An analysis of the correlations (Pearson's r) between cardiac and pulmonary variables revealed the statistically significant associations between cardiac mass and other variables to be as follows: forced vital capacity r=0.34 (P=.02), forced expiratory volume in one second r=0.526 (P=.0001), forced expiratory volume in one second as a percentage of predicted r=0.3 (P=.037), and forced midexpiratory flow rate r=0.31 (P=.03). The correlation between left ventricular ejection fraction and PaO2 was r=-0.312 (P=.01); the correlation between left ventricular end-diastolic diameter and PaO2 was r=0.369 (p=.006).

CONCLUSIONS

In patients with cardiac dysfunction, spirometry reveals a generally obstructive pattern, which is more accentuated in patients with right ventricular dysfunction owing to the existence of prior lung disease. The associations found between the cardiac and lung function variables do not help the physician to determine the predominant diagnosis for a patient more precisely or to establish a prognosis.