Hydrofluoric acid concentration, time and use of phosphoric acid on the bond strength of feldspathic ceramics

Effect of hydrofluoric acid and self-etch ceramic primers on the flexural strength and fatigue resistance of glass ceramics: A systematic review and meta-analysis of in vitro studies

This systematic review evaluated the effect of different hydrofluoric acid (HF) etching regimens and a self-etch ceramic primer (SECP) on the flexural strength (FS) and fatigue failure load (FFL) of glass-ceramic materials.The identification of relevant studies was conducted by two authors in five databases: PubMED, Scopus, Web Of Science, LILACS and Virtual Health Library (BVS) until July 2022 with no year limit. The analysis was conducted in RevMan 5.4.1 Software (Cochrane Collaboration) using Random effect model at 5 %. The risk of bias of the included studies were assessed. From the 5349 articles identified, 34 were included for quantitative analysis. Meta-analysis showed that for predominantly glassy ceramics, etching with HF 5 % had no significant impact on FS, however, HF acid etching with concentrations greater than 5 % negatively impacted FS. For lithium disilicate glass-ceramics (LDGC) HF acid etching, negatively influenced FS, while increasing the FFL. HF etching negatively affected FS of hybrid ceramics. The self-etch ceramic primer and HF acid etching showed a similar impact on FFL and FS. This meta-analysis indicates that the impact of SECP and HF acid etching on the mechanical behavior of glass ceramics is material-dependent.

Is additional silane application necessary for a new silane-containing universal adhesive to bond to glass ceramics?

OBJECTIVE

To evaluate the in vitro influence of prior silane application on the microshear bond strength (μSBS) of Scotchbond Universal Plus to glass ceramic.

MATERIALS AND METHODS

Thirty blocks of lithium disilicate ceramic were etched with hydrofluoric acid for 20 s and distributed into Group 1 (no silane and no adhesive), Group 2 (adhesive), Group 3 (silane + adhesive). Three cylinders of resin cement were made on each ceramic block. Five blocks (n = 15 cylinders) were subjected to the μSBS test after 24 h, and the other five blocks (n = 15 cylinders) were tested after 6 months of water storage.

RESULTS

According to two-way ANOVA, followed by Tukey's test, the means of μSBS (MPa), denoted by different letters, show significant differences (p < 0.05): after 24 h-Group 1 (31.7)B, Group 2 (43.3)A, and Group 3 (31.3)B; after 6 months-Group 1 (14.8)B, Group 2 (33.6)A, and Group 3 (30.3)A. After 6 months of storage, there was a significant decrease in μSBS for Groups 1 and 2, along with an increase in adhesive failures across all groups.

CONCLUSIONS

Prior application of silane did not increase the μSBS between Scotchbond Universal Plus and ceramic, and there was degradation at the bond interface over time.

CLINICAL SIGNIFICANCE

Prior application of a silane agent is not necessary when using Scotchbond Universal Plus for bonding to glass ceramics. Regardless of the prior application of silane, there is degradation at the bond interface over time.

Dental silicate ceramics surface modification by nonthermal plasma: A systematic review

OBJECTIVES

Nonthermal atmospheric or low-pressure plasma (NTP) can improve the surface characteristics of dental materials without affecting their bulk properties. This study aimed to systematically review the available scientific evidence on the effectiveness of using NTP for the surface treatment of etchable, silica-based dental ceramics before cementation, and elucidate its potential to replace the hazardous and technically demanding protocol of hydrofluoric acid (HF) etching.

METHODS

A valid search query was developed with the help of PubMed's Medical Subject Headings (MeSH) vocabulary thesaurus and translated to three electronic databases: PubMed, Web of Science, and Scopus. The methodological quality of the studies was assessed according to an adapted version of the Methodological Index for Non-Randomized Studies (MINORS).

RESULTS

Thirteen in vitro study reports published between 2008 and 2023 were selected for the qualitative and quantitative data synthesis. The implemented methodologies were diverse, comprising 19 different plasma treatment protocols with various device settings. Argon, helium, oxygen, or atmospheric air plasma may significantly increase the wettability and roughness of silicate ceramics by plasma cleaning, etching, and activation, but the treatment generally results in inferior bond strength values after cementation compared to those achieved with HF etching. The technically demanding protocol of plasma-enhanced chemical vapor deposition was employed more commonly, in which the surface deposition of hexamethyl disiloxane with subsequent oxygen plasma activation proved the most promising, yielding bond strengths comparable to those of the positive control. Lack of power analysis, missing adequate control, absence of examiner blinding, and non-performance of specimen aging were common methodological frailties that contributed most to the increase in bias risk (mean MINORS score 15.3 ± 1.1).

SIGNIFICANCE

NTP can potentially improve the adhesive surface characteristics of dental silicate ceramics in laboratory conditions, but the conventional protocol of HF etching still performs better in terms of the resin-ceramic bond strength and longevity. More preclinical research is needed to determine the optimal NTP treatment settings and assess the aging of plasma-treated ceramic surfaces in atmospheric conditions.

Effect of Resin Cement at Different Thicknesses on the Fatigue Shear Bond Strength to Leucite Ceramic

OBJECTIVES

 This in vitro study was performed to evaluate fatigue survival by shear test in the union of leucite-reinforced feldspathic ceramic using different cement thicknesses.

MATERIALS AND METHODS

 Leucite-reinforced glass ceramics blocks were sectioned in 2-mm thick slices where resin cylinders were cemented. The samples were distributed in two experimental groups (n = 20) according to the cement thickness (60 and 300 μm). The specimens of each group were submitted to the stepwise fatigue test in the mechanical cycling machine under shear stress state, with a frequency of 2 Hz, a step-size of 0.16 bar, starting with a load of 31 N (1.0 bar) and a lifetime of 20,000 cycles at each load step.

RESULTS

 The samples were analyzed in a stereomicroscope and scanning electron microscopy to determine the failure type. There is no significant difference between the mean values of shear bond strength according to both groups. Log-rank (p = 0.925) and Wilcoxon (p = 0.520) tests revealed a similar survival probability in both cement layer thicknesses according to the confidence interval (95%). The fracture analysis showed that the mixed failure was the most common failure type in the 300-μm thickness group (80%), while adhesive failure was predominant in the 60-μm thickness group (67%). The different cement thicknesses did not influence the leucite ceramic bonding in fatigue shear testing; however, the thicker cement layer increased the predominance of the ceramic material failure.

CONCLUSION

 The resin cement thicknesses bonded to leucite ceramic did not influence the long-term interfacial shear bond strength, although thicker cement layer increased the ceramic material cohesive failure. Regardless the cement layer thickness, the shear bond strength lifetime decreases under fatigue.

Effect of ceramic primers with different chemical contents on the shear bond strength of CAD/CAM ceramics with resin cement after thermal ageing

BACKGROUND

This study evaluated the effect of ceramic primers containing 10-methacryloyloxydecyl phosphate (10-MDP) and γ-methacryloxypropyl trimethoxysilane (γ-MPTS) agents on the shear bond strength (SBS) of CAD/CAM ceramics with different chemical structures and resin cement.

METHODS

A total of 640 CAD/CAM ceramic specimens were obtained from Vita Mark II (VM), IPS E.max CAD (EM), Vita Suprinity (VS) and Vita Enamic (VE). The specimens were divided into two groups: etched with hydrofluoric acid (HF) and unetched. Each group was treated with a different ceramic primer (Clearfil Ceramic Primer Plus, G-Multi Primer and Monobond S), except for an untreated group (n = 10). After ceramic primers and resin cement were applied to each ceramic surface, half of the specimens were thermally aged at 10,000 cycles, 5-55 ± 1 °C, with a dwell time of 30 s. The SBS was tested with a universal testing machine at a 0.5 mm/min crosshead speed. Data were analysed by using statistical software (SPSS 20). Normal data distribution was checked with the Shapiro‒Wilk test. Three-way ANOVA was used to analyse the difference between the numeric data of the HF etched and thermally aged groups. A post hoc Tukey test was applied in the paired comparison of significant difference. The statistical significance level was accepted as p < 0.05.

RESULTS

The highest SBS values were obtained in the HF etched G-Multi primer applied nonaged EM group (28.3 ± 2.62 MPa), while the lowest values were obtained in the nonetched and thermally aged EM group that received no treatment (2.86 ± 0.04 Mpa). The SBS significantly increased in all specimens on which the ceramic primer was applied (p < 0.001). Thermal ageing had a significant negative effect on the SBS values in all groups (p < 0.001).

CONCLUSION

The positive combined effects of the 10-MDP and γ-MPTS agents resulted in a significant increase in the bonding strength of the resin cement to the CAD/CAM ceramics. In addition, the increase in the amount of inorganic filler provided a favourable effect on durable adhesion.

Overview of Several Typical Ceramic Materials for Restorative Dentistry

With the development of ceramic technology, prosthodontic ceramics are becoming a useful option for improving esthetic outcomes in dentistry. In this paper, various ceramic materials were reviewed and evaluated, and their advantages and disadvantages and indications in oral prosthodontics were analyzed objectively. The properties of resin-based ceramics, polycrystalline ceramics, and silicate ceramics were compared and analyzed. Resin-based ceramics may replace other ceramic materials in the CAD/CAM field.

Anterior Incisal Onlay—A Minimally Invasive Non-Surgical Approach to Correct an Esthetic Complication of an Implant Supported Crown in the Anterior Zone

The growing demand for re-treatment of existing implant supported restorations in the anterior area due to esthetic complications poses a clinical challenge. One-piece implant supported restoration adds to the clinical complexity. Single implant crown restorations appear short as a result of expected cranio-facial changes. In the presented clinical case, a minimally invasive approach is offered as a solution for such an esthetic difficulty. The clinical old crown was prepared to receive an anterior incisal onlay (AIO) made from lithium disilicate and felspathic porcelain. The manufactured addition was adhesively cemented, presenting a simple prosthetic solution for an esthetic complaint, with no need for surgical procedure, while not challenging the one-piece implant body. As the variety of materials and methods for predictable adhesion increases, non-surgical and non-invasive treatment options will receive high priority. When correctly diagnosed and meticulously performed, the presented solution will meet the patient expectations and provide a satisfying result.

The Effect of Different Surface Conditioning Techniques on the Bonding between Resin Cement & Ceramic

Surface etching before cementation is a vital step that determines the clinical performance of ceramic restorations. Etching alters surface topography that contributes effective bonding between ceramic restoration and resin cement. This study aimed to compare etching techniques to determine the most effective etching method contributing the highest bond strength that helps in improving dental implants. Materials and methods: sixty discs of feldspathic ceramic measuring 10 mm diameter and 4 mm thickness were prepared. The 60 samples were divided into four equal groups based on the surface treatment technique used: group A: 9.6% hydrofluoric acid; group B: coarse diamond burs; group C: CO2 laser; and group D: no treatment. Ceramic disc specimens were examined under a Scanning Electron microscope (SEM) after surface treatment to characterize their surface morphology. Further, the specimens were luted with a resin luting agent and incubated for 24 h at a temperature of 37 °C simulating the oral environment. After 24 h, shear bond strength (SBS) and the nature of bond failure was determined for each specimen using a universal Instron testing machine. Results: significant change in surface morphology was noticed on hydrofluoric acid treatment forming larger irregular roughness (4.83 ± 1.78 µm) with multiple patterns of grooves and pores compared to other groups. Further, the highest SBS value was measured on hydrofluoric acid etching that display the highest bond strength due to the high surface roughness. In conclusion, our findings report a strong association between the surface roughness and bond strength upon hydrofluoric acid compared to other methods. Further work in this direction will enhance the utility of the etching technique on the improvement of dental implants.

Effect of occlusal anatomy of CAD/CAM feldspathic posterior crowns in the stress concentration and fracture load

OBJECTIVES

This study evaluated the effect of restoration occlusal design on the maximum fracture load and stress distribution of a feldspathic ceramic crown.

MATERIALS AND METHODS

Twenty dentin analogues were used to simulate a full-crown preparation. Next, 20 feldspathic crowns were milled according to the occlusal design parameter available in the CAD database (Young or Adult). The crowns were cemented with dual cure resin-cement and loaded until fracture at 1 mm/min crosshead speed. Data were analyzed by using one-way ANOVA and Tukey tests (p < 0.05). The same geometry and experimental setup was modeled and exported to the computer aided engineering software and tensile stress concentration was calculated using the finite element method with 300 N occlusal load simulation.

RESULTS

The occlusal anatomy significantly influenced the load-to-fracture (p < 0.05). Adult design showed higher mean values (1149 ± 201 N) than Young design (454 ± 77 N). The maximum principal stress criteria showed similar stress pattern for both designs, however, the highest stress concentration was calculated for Young design (91 MPa) in the occlusal surface.

CONCLUSIONS

An anatomy design with reduced cusp angulation and less evident occlusal sulcus can reduce the stress concentration and increase the fracture load for feldspathic CAD/CAM posterior crowns.

Outcome of Endodontic Treatment through Existing Full Coverage Restorations: An Endodontic Practice Case Series

INTRODUCTION

This case series assessed the outcome of nonsurgical endodontic treatment completed through retained full coverage restorations (FCRs) in a board-certified endodontist private practice. The number of cases completed by the first author was 153.

METHODS

All cases were performed following a standardized protocol for treatment and restoration depending on the type of FCR. Number of cases that showed up for 2- to 4-year follow-up was 127, with 83% recall rate. The age range of patients was 33-95 years, with mean age of 54.734 years. The mean recall time was 2.448 years. FCRs and their distribution were as follows: 4 anterior teeth, 14 premolars, and 109 molars. There were 103 nonsurgical root canal treatments and 24 retreatments. Patients who presented for recall had 74 porcelain fused to metal crowns, 17 zirconia crowns, 15 abutments of porcelain fused to metal bridges, 14 lithium disilicate crowns, 5 gold crowns, 1 full metal crown, and 1 gold onlay.

RESULTS

There were no endodontically related failures. Six cases failed; 3 were due to vertical root fractures, 1 was due to horizontal root fracture, and 2 were due to extensive recurrent caries causing restorative failure. The percentage of healed cases following the American Association of Endodontists outcome criteria adopted in 2004 with intact retained FCR was 95.3%.

CONCLUSIONS

The results suggest predictable favorable outcomes for nonsurgical endodontic treatment through FCR following the proposed protocol for diagnosis, treatment, and restoration.

Effect of active application of self-etching ceramic primer on the long-term bond strength of different dental CAD/CAM materials

Background

The objective of this in vitro study was to evaluate the effect of the active application of self-etching ceramic primer (ME&P) on the bond strength of different dental CAD/CAM materials (Lithium Disilicate ceramic (LD), Leucite ceramic (LE), Zirconia reinforced lithium silicate ceramic (ZLS), and Hybrid ceramic (HC)) with thermocycling aging.

Material and Methods

The samples were randomly divided into 16 groups (n = 20). Dual resin cement cylinders were made and light cured for 10 s (1.200 mW/cm2) for the shear bond strength test. 3-way ANOVA revealed that the factors were statistically significant (P< 0.05).

Results

The aging process had a negative impact on the bond strength for all groups except for Lithium Disilicate, with active application. ZLS and LE showed promising results with high bond strength values for the ME&P active application; however, after aging the bond strength value was significantly reduced. HC showed reduced bond strength values regardless the ME&P application.

Conclusions

In order to obtain a durable bond strength, the recommended protocol of 20 s of active application followed by 40 s of sitting time in the self-etching ceramic primer should be followed when using reinforced-glass ceramics as restorative materials.

Key words:Dentistry, dental materials, silane, shear strength, computer-aided design

Predictable bonding of adhesive indirect restorations: factors for success

Adhesive indirect restorations are a popular restorative treatment option. This article discusses the many factors that contribute to their successful adhesive cementation, including a review of how to surface treat and manage contaminants across the wide range of indirect materials available.

Critiques the current various adhesive strategies used by resin cements at the tooth tissue interface.

Describes how to prepare the fitting surface of a wide range of restorative materials for adhesive cementation.

Discusses how to mitigate against contaminants during the adhesive cementation process.

Effect of Different Surface Treatments of Lithium Disilicate on the Adhesive Properties of Resin Cements

The aim of the current study was to evaluate the influence of hydrofluoric (HF) acid concentration and conditioning time on the shear bond strength (SBS) of dual cure resin cement to pressed lithium disilicate ceramic compared to treatment with an Etch and Prime self-etching glass-ceramic primer (EP). A total of 100 samples of pressed lithium disilicate (IPS e.max Press, Ivoclar Vivadent) were randomly divided into five groups (n = 20) according to surface treatment: two different concentrations of HF (5% or 9%), for different durations (20 or 90 s), or treatment with EP. Adhesion of light-cured resin cement to the treated surface was tested by the SBS test. The substrate surfaces of the specimen after failures were examined by SEM. Data were analyzed using Weibull distribution. The highest cumulative failure probability of 63.2% of the shear bond strength (η parameter) values was in the 9% HF −90 s group (17.71 MPa), while the lowest values were observed in the 5% HF −20 s group (7.94 MPa). SBS values were not affected significantly by the conditioning time (20 s or 90 s). However, compared to treatment with 5% HF, surface treatment with 9% HF showed a significantly higher η (MPa) as well as β (reliability parameter). Moreover, while compared to 9% HF for 20 s, EP treatment did not differ significantly in SBS values. Examination of the failure mode revealed a mixed mode of failure in all the groups. Within the limits of this study, it is possible to assume that IPS e.max Press surface treatment with 9% HF acid for only 20 s will provide a better bonding strength with resin cement than using 5% HF acid.

Influence of Low-Pressure Plasma on the Surface Properties of CAD-CAM Leucite-Reinforced Feldspar and Resin Matrix Ceramics

The introduction of new ceramic materials for dental restorations is currently a reality; however, little information is available on their surface treatment for the bonding process. Furthermore, surface treatment with plasma on ceramic materials has been recently introduced, although not many studies are available. The aim of this study was to evaluate the surface properties of a leucite-reinforced feldspar ceramic (LIC) and resin matrix ceramic (RMC) after low-pressure plasma treatment. From each material, 48 discs were prepared and subject to surface treatment. The LIC group was treated by hydrofluoric acid (HF) (LIC-HF), plasma with oxygen (LIC-O2), and plasma with argon (LIC-Ar). The RMC group was treated by sandblasting with alumina (RMC-SB), plasma with oxygen (RMC-O2), and plasma with argon (RMC-Ar). The groups whose surfaces were not subjected to treatment were considered as the control group. Surface wettability and roughness was analyzed. The results showed significant differences among the treatments for both ceramics regarding wettability and roughness. Plasma treatments increased the wettability and had a very low effect on the roughness. Plasma treatments achieved similar values for both surface properties in each ceramic group with no differences between both treatments. Plasma treatment seems to be a promising alternative for ceramic surface treatments since it increased the surface energy of the ceramics analyzed and hardly affects the roughness. Further studies are necessary to evaluate the effect of plasma treatment on the bond strength of ceramics.

Effect of Cleaning Protocol on Bond Strength between Resin Composite Cement and Three Different CAD/CAM Materials

The present investigation tested the effect of the cleaning method on the tensile bond strength (TBS) between one resin composite cement (RCC) and three different computer aided design/computer aided manufacturing (CAD/CAM) materials, namely zirconia, lithium disilicate ceramic and resin composite. Ninety specimens were prepared from each CAD/CAM material (N = 270). The specimens were pre-treated respectively, divided into five subgroups and subjected to five different cleaning protocols, namely i. 37% phosphoric acid, ii. ethanol, iii. phosphoric acid + ethanol, iv. cleaning paste, v. distilled water. After cleaning, the specimens were either conditioned using a universal primer or a universal adhesive and bonded using a dual-curing RCC. After thermo-cycling (20,000x at 5 °C/55 °C), TBS and fracture patterns were evaluated. The data was analyzed using 1- and 2-way Analysis of Variance (ANOVA) with post-hoc Scheffé and partial eta-squared (ƞ_P²), Kruskal-Wallis, Mann-Whitney U and Chi² tests (p < 0.05). The CAD/CAM material showed an impact on the BS while the cleaning protocol did not affect the results. Zirconia obtained the highest BS, followed by lithium-disilicate-ceramic. Resin composite resulted in the overall lowest BS. For most fracture patterns, the cohesive type occurred. All tested cleaning protocols resulted in same BS values within one CAD/CAM material indicating that the impact of the cleaning method for the restorative material seems to play a subordinate role in obtaining durable bond strength to resin composite cement. Further, it indicates that the recommended bonding protocols are well adjusted to the respective materials and might be able to compensate the impact of not accurately performed cleaning protocols.