Fracture Load of Different Zirconia Types: A Mastication Simulation Study

PURPOSE

To assess the effect of yttria mol% concentration and material thickness on the biaxial fracture load (N) of zirconia with and without mastication simulation.

MATERIALS AND METHODS

Disk-shaped specimens (N = 120) of 3 mol% yttria-partially stabilized zirconia, 3Y-PSZ (Katana High Translucent, Kuraray Noritake), 4 mol% yttria-partially stabilized zirconia, 4Y-PSZ (Katana Super Translucent Multi Layered) and 5 mol% Yttria-partially stabilized zirconia, 5Y-PSZ (Katana Ultra Translucent Multi Layered) were prepared to thicknesses of 0.7 and 1.2 mm. For each thickness, the biaxial fracture load (N) was measured with and without mastication simulation with 1.2 million cycles at a 110-N load and simultaneous thermal cycling at 5°C to 55°C. The data were analyzed by three-way Analysis of Variance (α = 0.05) and Tukey-Kramer adjusted multiple comparison test.

RESULTS

Yttria mol% concentration and material thickness had a statistically significant effect on the mean biaxial fracture load (F = 388.16, p < 0.001 and F = 714.33, p < 0.001 respectively). The mean biaxial fracture load ranged from the highest to the lowest; 3Y-PSZ, 4Y-PSZ, and 5Y-PSZ (p = 0.012). The mean biaxial fracture load of the 1.2 mm thickness groups was significantly higher than 0.7 mm thickness at any given condition (p = 0.002). Not all specimens survived the mastication simulation protocol. Fifty percent of the 0.7-mm-thick 4Y-PSZ specimens, 70% of the 0.7-mm-thick 5Y-PSZ specimens and 20% of 1.2-mm-thick 5Y-PSZ specimens fractured during mastication simulation. Mastication simulation had no statistically significant effect on the biaxial fracture load (F = 1.24, p = 0.239) of the survived specimens.

CONCLUSIONS

Lowering yttria mol% concentration and increasing material thickness significantly increases the fracture load of zirconia. At 0.7 mm thickness, only 3Y-PSZ survived masticatory simulation. A minimum material thickness of 1.2 mm is required for 4Y-PSZ or 5Y-PSZ.

Adhesion and Early Colonization of S. Mutans on Lithium Disilicate Reinforced Glass-Ceramics, Monolithic Zirconia and Dual Cure Resin Cement

OBJECTIVE

Monolithic zirconia and glass ceramics are increasingly used in implant crowns. Limited data is available on bacterial adhesion and early biofilm formation on these materials.

METHODS

Four different materials were investigated: (1) Lithium disilicate glass-ceramics (LDS), (2) Fully stabilized zirconia (FSZ), (3) Partially stabilized zirconia (PSZ), and (4) Dual curing cement (DCC). The materials' surfaces were characterized with spinning disc confocal microscopy and by water contact angle and surface free energy (SFE) measurements. For the adhesion tests the materials were rolled in suspensions of Streptococcus mutans. Early biofilm formation was studied on the materials and allowing the biofilms to form for 24 h. S. mutans cell counts were determined by plate culturing. ANOVA and post-hoc Tukey's tests (p⟨0.05) were used for statistical evaluation.

RESULTS

The LDS surfaces were clearly hydrophilic with the highest SFE value (p⟨0.001). For S. mutans adhesion, the ranking of the materials from lowest to highest was: LDS = FSZ ⟨ DCC ⟨ PSZ (p⟨0.05). No significant differences among the materials were noticed in biofilm formation.

CONCLUSIONS

LDS has lower S.mutans adhesion than other materials examined in this study, but the difference was not reflected in early biofilm formation.

Effect of Tribochemical Coating on Composite Repair Strength

Clinical Relevance

Tribochemical treatment of existing composite surfaces is highly effective for composite repair. When repairing an old composite restoration, the clinician should try to use the same composite originally used for the restoration. If the information about the original restoration is not known, a composite with strong mechanical properties should be used for the repair restoration.

SUMMARY

This study evaluated the effect of tribochemical coating on composite-to-composite repair interfacial fracture toughness (iFT). Sixty beam-shaped specimens (21×4×3 ± 0.2 mm) were prepared with a nanofill composite (Filtek Supreme Ultra [FSU]) and a nanohybrid composite (Clearfil Majesty ES-2 [CME]) and aged for 50,000 thermocycles (5°C-55°C, 20-second dwell time) and then sectioned in half. The resulting 120 hemispecimens (60 for each composite) were randomly assigned to different repair methods (n=10): universal adhesive (Clearfil Universal Bond Quick [CUB]), sand-blasting followed by CUB, or tribochemical coating (CoJet, CoJet sand, Espe-Sil, and Visio-Bond). The repair surface was prepared with a diamond bur (Midwest #471271), rinsed, and dried. Each aged composite brand (FSU, CME) was repaired with either the same composite or the opposite composite. All adhesives and composites were light cured with a high-irradiance LED curing light (Elipar DeepCure-S). After postrepair storage in 100% humidity and at 37°C for 24 hours, iFT was measured as KIc (MPa m½). Data were analyzed for statistical significance using two-way analysis of variance (ANOVA) and the Tukey honest significant difference post hoc test (α=0.05). Regardless of the substrate composite, ANOVA showed significant differences for surface treatment (p&lt;0.0001) and repair composite (p&lt;0.0001). Mean iFT values (SD) ranged from 0.91 (0.10) MPa·m½ to 2.68 (0.12) MPa·m½. Repairs made with FSU after CoJet resulted in significantly higher iFT (FSU: 2.68 MPa·m½; CME: 2.21 MPa·m½) when compared to the other experimental groups. The repair iFT was higher with CoJet treatment and when the nanofill composite FSU was used as the repair composite.

Estimation of glomerular filtration rate using serum cystatin C in overweight and obese subjects

BACKGROUND

Obesity and overweight are strong independent risk factors for chronic kidney disease (CKD). Using serum creatinine-based estimated glomerular filtration rate (eGFR) equations in these subjects may be inaccurate. On the other hand, cystatin C-based eGFR equations may overestimate CKD prevalence as recent findings suggest an association of cystatin C with obesity. The objective of this study was to assess the accuracy of a cystatin C-based eGFR equation compared to two creatinine -based eGFR equations in overweight and obese subjects.

METHODS

This was a prospective cross-sectional study which recruited healthy volunteers aged 18-55 years with a body mass index (BMI) > or = 23kg/m(2) (Asia Pacific Guidelines). Their renal profiles, serum cystatin C and 99m technetium diethylene triamine pentacetic acid (99)mTc-DTPA) scans were performed on the same day. The correlations and accuracy of the creatinine-based and cystatin C-based eGFR equations with the (99)mTc-DTPA GFR were determined.

RESULTS

One hundred and one subjects with a median age of 30.0 (27.0-43.5) years and mean BMI of 28.7 +/- 4.5 kg/m(2) were recruited. The cystatin C-based eGFR equation showed the best correlation with the (99)mTc-DTPA GFR (r = 0.526, p = 0.001) and was more accurate in measuring abnormal GFR compared to the creatinine-based eGFR equations.

CONCLUSION

Our study showed that the cystatin C-based eGFR equation was more accurate, sensitive and specific in overweight and obese subjects compared to the creatinine-based eGFR equations.

Effect of surface finish and resin cement on the bond strength to CAD-CAM ceramics for interim resin-bonded prostheses

STATEMENT OF PROBLEM

Resin-bonded prostheses, including interim resin-bonded prostheses, are effective in preserving tooth structure compared with other types of fixed dental prostheses for the replacement of missing teeth. However, loss of retention remains a notable concern with these types of prostheses.

PURPOSE

The purpose of this in vitro study was to investigate the influence of glass-ceramic type, resin type, and surface finish on the shear bond strength (SBS) to the CAD-CAM ceramics used to fabricate interim resin-bonded prostheses.

MATERIAL AND METHODS

Eighty 10×2-mm glass-ceramic disks were fabricated by using a diamond saw (IsoMet 1000), 40 from feldspathic porcelain blocks (Vita Mark II) and 40 from lithium disilicate blocks (IPS e.max CAD). Half of the specimens in each group were left with a dull or matte surface finish after cutting, while the other half were glazed with an add-on glaze (VitaAkzento Plus Glaze Spray and IPS e.max CAD Glaze Spray, respectively). The disks were mounted in acrylic resin, and each group was subdivided into 2, with 1 receiving a photopolymerized resin cement (RelyX Veneer) and the other receiving a flowable composite resin (Filtek Supreme Ultimate Flow) to form 2.38×2-mm cylinders. SBS was determined using a universal testing machine (Instron 4411) in accordance with the International Organization for Standardization (ISO) 29022:2013 standard, and failure modes were analyzed by using a stereomicroscope with ×40 magnification. The data were analyzed with a 3-way analysis of variance and Tukey post hoc analysis. The chi-squared test was used to analyze the failure mode (α=.05 for all tests).

RESULTS

Ceramic type, resin type, and surface finish significantly impacted SBS (P<.001, P=.003, P<.001, respectively). Lithium disilicate showed higher SBS than feldspathic porcelain, and flowable composite resin exhibited higher SBS than resin cement. Glazed surfaces displayed lower SBS compared with the dull or matte surfaces. The combinations among the 3 materials also impacted SBS (P=.03). In addition, the combinations between ceramic type and surface finish affected SBS (P<.001), regardless of resin cement type. No other combinations affected the SBS (P>.05). The mode of failure was different among the groups (P<.001). In comparison with all other groups, cohesive failures were most prevalent in feldspathic porcelain with a dull or matte surface finish, regardless of the resin type used.

CONCLUSIONS

The SBS to glass-ceramics was influenced by ceramic material, resin cement type, and surface finish. Flowable composite resin showed higher SBS than resin cement. A dull or matte surface finish exhibited greater bond strength than a glazed surface. Lithium disilicate had higher SBS than feldspathic porcelain.

A critical comparison of three full field digital mammography systems using figure of merit

Full field digital mammography (FFDM) has been progressively introduced in medical centers in recent years. However, it is questionable which exposure parameters are suitable in order to reduce the glandular breast doses as they are related to induced carcinogenesis. The goal of this study was to compare the average glandular doses (AGD) and image quality of three FFDM systems namely Siemens Mammomat NovationDR, Hologic Lorad Selenia and General Electric Senographe Essential using a Figure of Merit. A Computerized Imaging Reference Systems (CIRS) tissue equivalent breast phantom which consists of phototimer compensation plate with different thickness and glandularity was exposed in fully automatic exposure control mode in the cranio-caudal projection similar to clinical settings. Thermoluminescent dosimeter 100H (TLD- 100H) was used to measure the entrance surface air kerma (ESAK), the AGD was calculated using European protocol whilst the image quality was assessed quantitatively by measuring the contrast to noise ratio (CNR) value. The obtained values were used to calculate the Figure of Merit (FOM) to analyze the effectiveness of the system. Repeated Measures ANOVA analysis showed that there is a significant difference (p<0.05) in the mean value of AGD and CNR between the three FFDM systems. Hologic Lorad Selenia system contrbuted the highest AGD value while General Electric Senographe Essential had the highest CNR and FOM value. In conclusion, this study may provide an objective criterion during the selection of a mammography unit by using the figure of merit for screening or diagnostic purpose.

Biofilm attachment and mineralizing potential of contemporary restorative materials

PURPOSE

To evaluate and compare: (1) the effect of the bacterial biofilm on the dentin mineral density at the restoration-tooth interface and (2) the mineralization potential of three resin-based restorative materials (RBRM).

METHODS

16 extracted human molars free of caries and cracks were collected and stored for disinfection. Each tooth received two standardized Class II preparations with the cervical margin placed in dentin. Teeth were secured into a dentiform with adjacent natural teeth to ensure interproximal contact. All tooth preparations were hybridized using a three-step etch-and-rinse adhesive system (OptiBond FL) and assigned randomly to three experimental groups according to the RBRM (n= 8): Group A - a nanofill resin composite (Filtek Supreme Ultra); Group B - a high-viscosity bulk-fill resin composite (Tetric Powerfill); Group C - a low-viscosity bulk-fill resin composite (SureFil SDR flow+ bulk-fill); and a positive control: Group D - bioactive resin composite (Activa Bioactive-Restorative). All materials were used according to manufacturers' instructions. All specimens were subjected to two distinct challenges: first, thermomechanical cycling was performed within 24 hours of restoring the specimens to simulate 1 year of masticatory function. Subsequently, the specimens were stored for 18 days in a laboratory biofilm model to promote biofilm formation and to mimic the effects of tooth demineralization. Two sessions of micro-CT imaging were conducted: the first immediately after the thermomechanical cycling and the second post-exposure to the biofilm model. All data on mineral profile measurements reconstructed in the Perkin-Elmer Quantum GX-II CT were transferred to Image J software for analysis and interpretation. The ANOVA test (P< 0.05) was used to analyze the mineral density values and mean mineral loss values for each group.

RESULTS

No statistically significant difference in mean mineral loss value (mean ΔZ) was found between the groups (P= 0.209). Regardless, increased mean ΔZ variation was found between SureFil SDR flow+ (-56.95) and the remaining groups, Filtek Supreme Ultra, Tetric Powerfill and Activa Bioactive (-1.17, -1.41, and -7.97, respectively), showing, within the limits of the present laboratory study, the remineralization potential of SureFil SDR flow+. All tested RBRM demonstrated some remineralization capacity under caries risk conditions.

CLINICAL SIGNIFICANCE

The mineralization potential of some resin-based composites under caries-risk conditions can represent a paradigm shift in restorative material selection for moderate-to-high-risk patients.

An Ex-Vivo Model for Investigating Bacterial Extrusion from Infected Root Canals during Masticatory Function

INTRODUCTION

The extrusion of bacteria from infected root canals may lead to increase in symptoms, expansion of periapical lesions, and contribution to systemic diseases. The aim of this study is to investigate a potential proof-of-concept model to study the extent to which bacteria can escape from infected root canals under dynamic loading (simulated chewing).

METHODS

The study was completed in 2 experiments performed at 2 institutions. Biofilms of Streptococcus intermedius in the first experiment and S. intermedius and Actinomyces naeslundii were allowed to grow in root canals of single-rooted extracted teeth for 3 weeks. The roots of the teeth were suspended in a small chamber containing dental transport medium and were mounted on a lower sample holder of a chewing simulator. In the experimental group, simulated chewing cycles equivalent to 1 year of function were conducted, and then bacterial migration was quantified and compared with stationary teeth.

RESULTS

All experimental samples of the loading group revealed bacterial penetration in both experiments. Several of the unloaded samples revealed no bacterial penetration. In the first experiment, a significantly higher number of bacteria were able to escape into the periapex of the loaded group compared with the unloaded group (P = .017). In the second experiment, there was no significant difference between the 2 bacterial species used in the amount of extruded bacteria; however, there was a highly significant effect for occlusal loading (P = .0001).

CONCLUSIONS

The potential for occlusal forces to enhance bacterial extrusion from infected root canals should be further explored.

Bromelain-based endodontic irrigant: preparation, properties, and biocompatibility: An in-vitro study

The aim of the study was to determine the properties, efficacy and biocompatibility of combining bromelain enzyme, chlorohexidine and EDTA (BCE) to create a novel endodontic irrigant. Fourier transform infrared spectrometry was performed to confirm the stability of the BCE and direct contact inhibition test was performed to determine antibacterial action. Baseline pH and surface tension of irrigants was compared with determine stability. Subcutaneous injection to dorsal skin of rabbits was graded for presence of inflammation, oedema, granulation and fibrosis. BCE caused less overall irritation, less oedematous and was earlier to heal than 2.5% NaOCl. The pH stability of BCE was also superior to 2.5% NaOCl. A one-way ANOVA test was performed for the direct contact inhibition and microleakage test. A significant difference was determined (p ≤ 0.05) between BCE and 2.5% NaOCl for antibacterial action. BCE irrigant is effective in preparing dentinal surfaces for root canal without adverse effects and promising longevity.

Effect of Er:YAG laser on debonding zirconia and lithium disilicate crowns bonded with 2- and 1-bottle adhesive resin cements

INTRODUCTION

Erbium-doped yttrium-aluminum-garnet (Er:YAG) laser debonding of zirconia and lithium disilicate restorations is increasingly used for a range of clinical applications. Using rotary instruments to remove such restorations for any purpose has proven to be challenging. Erbium laser has been reported to be a conservative method for removing ceramic restorations. There is little data in the literature about the effect of adhesive resin cement type on the debonding time of the ceramic restoration using the Er:YAG laser.

OBJECTIVES

To evaluate and compare the time required for the Er:YAG laser to debond zirconia and lithium disilicate crowns bonded with a 2- and 1-bottle adhesive resin cement systems.

MATERIALS AND METHODS

Forty extracted premolar teeth were prepared and scanned for milled 40 CAD/CAM crowns. Teeth were randomly assigned into groups (n = 10 per group): 3 mol% yttria-partially stabilized zirconia crowns 3Y-PSZ (G1a) bonded with Panavia™ V5 (2-bottle adhesive resin cement), Zirconia 3Y-PSZ crowns (G1b) bonded with RelyX™ Ultimate (1-bottle adhesive resin cement), and for the lithium disilicate crowns bonded with the two types of cements (G2a, G2b). Each specimen was irradiated with an Er:YAG laser at 335 mJ, 15 Hz, 5.0 W, and 50-ms pulse duration (super short pulse mode). The irradiation time required for crowns to be successfully debonded was recorded for each specimen. Data were statistically analyzed using ANOVA and Tukey HSD post-hoc test (p < 0.05), at the 95 percent level of confidence. The intaglio surface of the debonded crown was analyzed using scanning electron microscopy (SEM).

RESULTS

The mean ± standard deviation times needed for crown debonding were 5.75 ± 2.00 min for the G1a group, 4.79 ± 1.20 min for group G1b, 1.69 ± 0.49 min for group G2a, and 1.12 ± 0.17 for group G2b. There was no statistically significant difference in debonding time between the 2- and 1- bottle adhesive resin cement within the groups G1a and b (p = 0.2914), or between groups G2a b (p = 0.7116). A statistically significant difference (p < 0.05) was found between groups G1a and G2a and b and between groups G1b and G2a and b were SEM analysis showed no changes in the microstructure of the ceramic surface after Er:YAG laser irradiation.

CONCLUSION

Zirconia and lithium disilicate restorations can be debonded using Er:YAG lasers in a safe and efficient manner. There is no significant difference in the debonding time between the 2- and 1- bottle adhesive resin cement systems used in this study.

CLINICAL SIGNIFICANCE

Retrieving zirconia and lithium disilicate ceramics can be a challenging process when using diamond rotary instruments. ER:YAG lasers may efficiently debond these ceramics from the tooth structure, independent of the bonding process used for bonding them.