Physical analysis of an acrylic resin modified by metal and ceramic nanoparticles.

BACKGROUND: Nanoparticles (NPs) have gained significant attention in various fields due to their unique properties and potential applications. Polymethyl methacrylate (PMMA) is an acrylic resin widely used in dentistry and medicine. However, the effect of different types of NP fillers on the physical properties of PMMA-based resins has not been thoroughly explored in the literature. OBJECTIVES: The present study aimed to evaluate the effects of 3 different types of NP fillers on the physical properties of an experimental PMMA-based resin as a function of the NP content and concentration. MATERIAL AND METHODS: Ten groups (n = 10) were designed. The specimens were composed of an acrylic resin, silicon dioxide (SiO2), cerium dioxide (CeO2), and titanium dioxide (TiO2) at the following ratios (wt%): group 1 (G1) - control; group 2 (G2) - 0.5% SiO2; group 3 (G3) - 1% SiO2; group 4 (G4) - 3% SiO2; group 5 (G5) - 0.5% CeO2; group 6 (G6) - 1% CeO2; group 7 (G7) - 3% CeO2; group 8 (G8) - 0.5% TiO2; group 9 (G9) - 1% TiO2; and group 10 (G10) - 3% TiO2. Transmission electron microscopy (TEM) was used to assess the quality of NP dispersion. Thermal stability was assessed with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effects of the abovementioned NPs on the properties of the resin were evaluated using the Archimedes principle for density, the Vickers hardness (VH) test and the impact strength (IS) test. Data analysis employed the oneand two-way analysis of variance (ANOVA), followed by Duncan's post hoc test at a significance level of 0.05. RESULTS: Transmission electron microscopy showed partial NP dispersion. All types of NPs enhanced the mechanical properties of the acrylic resin except for IS, which was similar to that of the control group. Among the types of NPs, irrespective of the weight percentage, CeO2 showed higher thermal stability and higher IS for 0.5 wt% and 1 wt% as compared to other groups, as well as the highest values of density at 0.5 wt%, 1 wt% and 3 wt%. Titanium oxide at 1 wt% presented a higher VH as compared to other groups. The fracture pattern was the same for all groups. CONCLUSIONS: Incorporating the tested NPs into the acrylic resin resulted in enhanced physical properties, primarily attributed to a lower NP content.

Biomechanical Behavior Evaluation of a Mandibular Full-Arch Implant-Supported Prosthesis on ZrO2 and TiO2 Monotype Dental Implants / Evaluación del Comportamiento Biomecánico de una Prótesis Implante Soportada de Arcada Completa Mandibular sobre Implantes Dentales Monotipos de ZrO 2 y TiO

This in silico study aimed to evaluate the biomechanical behavior of a full-arch implant-supported prosthesis on titanium and zirconia monotype implants. A 3D mandible containing 1.0 mm thick cortical and cancellous bone was modeled. Four dental implants (3.3 x 10 mm) were inserted into the jaw model in each model. The implants consisted of Titanium (Ti-S group) and Zirconia Monotype/one-piece (Zr-S group). Fixed full-arch implant-supported prostheses were cemented onto the implant. The models were exported to the analysis software and divided into meshes composed of nodes and tetrahedral elements. All materials were considered isotropic, elastic, and homogeneous. Therefore, all contacts were considered bonded, the mandible model was fixed in all directions, applying a static structural axial load of 300 N on the bottom of the fossa of the left mola r teeth. Microstrain and von-Mises stress (MPa) were adopted as failure criteria. Comparable stress and strain values were shown in the peri-implant bone for both groups. However, the Ti-S group presented a lower stress value (1,155.8 MPa) than the Zr-S group (1,334.2 MPa). Regarding bone tissues, the Ti-S group presented 612 µε and the Zr-S group presented 254 µε. The highest strain peak was observed in bone tissues around the implant closer to the load for both groups. Evaluating monotype zirconia and titanium implants, it is suggested that the greater the rigidity of the implant, the greater the concentration of internal stre sses and the less dissipation to the surrounding tissues. Therefore, monotype ceramic implants composed of yttrium-stabilized tetragonal polycrystalline zirconia may be a viable alternative to titanium implants for full-arch prostheses.

El objetivo de este estudio in silico fue evaluar el comportamiento biomecánico de una prótesis implanto soportada de arcada completa sobre implantes monotipo de titanio y zirconia. Se modeló una mandíbula en 3D que contenía tejido óseo cortical y esponjoso de 1,0 mm de espesor. En cada modelo, se insertaron cuatro implantes dentales (3,3 x 10 mm) en el modelo de mandíbula. Los implantes consistieron en Monotipo de Titanio y Zirconia. Sobre el implante se cementaron prótesis implanto soportadas de arcada completa fija. Los modelos se exportaron al software de análisis y se dividieron en mallas compuestas por nodos y elementos tetraédricos. Todos los materiales se consideraron isotrópicos, elásticos y homogéneos. Por lo tanto, todos los contactos se consideraron cementados, el modelo mandibular se fijó en todas las direcciones, aplicando una carga vertical estructural estática de 300 N en el fondo de la fosa de los dientes molares izquierdos. Se seleccionaron la microesfuerzo y la tensión de Von-Mises (MPa) como criterios de falla. Se mostraron valores de tensión y deformación comparables en el hueso periimplantario para ambos grupos. Sin embargo, el grupo Ti-S presentó un valor de estrés menor (1.155,8 MPa) que el grupo Zr-S (1.334,2 MPa). En cuanto a los tejidos óseos, el grupo Ti-S presentó 612 µε y el grupo Zr-S presentó 254 µε. La mayor concentración de deformación en el tejido óseo se observó en los tejidos alrededor del implante más cerca de la carga para ambos grupos. Al evaluar los implantes monotípicos de zirconia y titanio, se sugiere que cuanto mayor sea la rigidez del implante, mayor será la concentración de tensiones internas y menor la disipación a los tejidos circundantes. Por lo tanto, los implantes cerámicos monotipo compuestos de zirconia policristalina tetragonal estabilizada con itrio pueden ser una alternativa viable a los implantes de titanio para prótesis de arcada completa.

The ability of a nanobioglass-doped self-etching adhesive to re-mineralize and bond to artificially demineralized dentin.

OBJECTIVE: To a self-etch adhesive doped with nano-bioglass and evaluate its ability to bond and re-mineralize artificially demineralized dentin. METHODS: Experimental Si, Ca, Na and PO4 based nanobioglass particles were synthesized, doped into experimental self-etch adhesives, and divided into 3 groups: Clearfi SE2 (CSE2), experimental (EXC), and experimental doped with 10% of nanobioglass (ExNB). The adhesives were applied onto the caries-affected dentin (chemically simulated), and evaluated after 24 h and 28 days of immersion in simulated body fluid. The remineralization process was assessed using optical coherence tomography, nanoindentation, in situ zymography, transmission electron microscopy, confocal laser scanning microscopy, µ-tensile bond strength, and pH buffer. RESULTS: The addition of nanobioglass particles into the experimental self-etch adhesives altered the µTBS in the short-term jeopardizing dentin bonding properties, when compared to the non-doped self-etch adhesive. The remineralization recovered the nanohardness, and volume lost by caries lesion (p = 0.02). Moreover, reduced the enzymatic activity (p = 1.24E-4) and formed new crystals within of the hybrid layer. CONCLUSION: The use of nanobioglass was efficient to recover the properties of a caries affected dentin. Furthermore, the adhesive properties were not hampered and the probabilistic reliability increased.

The Effects of Short Term Intracanal Medicaments on the Fracture Resistance of Root in Pulp Revitalization Procedure.

Introduction: The objective of this study was to evaluate the effects of short term intracanal medicaments on the fracture resistance of root in simulated necrotic immature teeth in pulp revitalization procedure. Methods and Materials: Bovine teeth (n=180) were selected, sectioned coronally and apically and then, internally fragilized. Intracanal medicament groups were arranged as follows: "Triple Antibiotic Paste" (TAP) group (n=60), "Calcium Hydroxide" (CH) group (n=60) and the control group (n=60). No medication was used in the control group. Fracture resistance tests were performed after 7, 14, and 21 days. At allocated intervals, 20 teeth from each group had fractured. The Kruskal-Wallis and Mann-Whitney tests were performed to verify the effects of the employed medicaments at each time point. Friedman test and Wilcoxon signed-rank test were also performed to verify the association between time and fracture resistance. The level of significance was set at 0.05. Results: After 7 days, there was no statistical difference between groups (P=0.376). Intragroup analysis revealed that, after 21 days, the TAP group (P=0.015) and the CH group (P=0.006) presented a statically significant reduction in fracture resistance comparison with 7 days. Statistical difference was not verified for the control group after 7, 14 and 21 days (P=0.25). There was no statistical difference between CH group and the control group after 7, 14 and 21 days (P>0.05). The reduction was significant for TAP after 14 and 21 days (P=0.018, P=0.033 Respectively). Conclusions: This in vitro study showed that the duration at which TAP and CH remained in the root canal influenced the fracture resistance of bovine teeth with simulated incomplete root formation.

Immediate and 6-month Bond Strengths of Different Adhesives in the Oral Environment.

PURPOSE: To evaluate the microtensile bond strength (µTBS) of three adhesives to dentin after 1 week and 6 months in an oral environment. MATERIALS AND METHODS: Class I cavities were prepared in the third molars of 30 patients and randomized into 3 groups according to the following adhesives: Scotchbond Multi-Purpose (SM), Clearfil Protect Bond (CF), and Scotchbond Universal (UN). These molars were then subdivided into two groups according to the exposure time in the oral environment: one week (1W) and 6 months (6M). After the exposure time, the teeth were extracted, cut into beams, and submitted to the µTBS test. The data were analyzed using the Shapiro-Wilk test and two-way ANOVA followed by Tukey's post-hoc test with a significance level of 5%, and fracture modes were analyzed. RESULTS: The bond strengths in MPa (mean ± SD) were SM-1W: 39.5 ± 7.9; SM-6M: 29.7 ± 1.8; CF-1W: 30.5 ± 1.4; CF-6M: 28.6 ± 4.1; UN-1W: 30.6 ± 3.2; and UN-6M: 26.7 ± 2.0. The SM-1W group exhibited significantly increased µTBS compared with the other groups. After 6 months in the oral environment, a significant reduction of µTBS was only observed for the SM group, whereas similar bond strengths were observed for the other groups. SM-1W exhibited a predominance of mixed fractures, whereas the other groups showed a predominance of adhesive fractures. CONCLUSIONS: The adhesives which were applied in the self-etching mode maintained bond strength after six months in the oral environment. A reduction of µTBS was only observed for the three-step etch-and-rinse adhesive.

Effect of photoinitiator concentration on marginal and internal adaptation of experimental composite blends photocured by modulated methods.

OBJECTIVE: The aim of this study was to evaluate the influence of photoinitiator concentration on marginal and internal adaptation of composites photocured by modulated methods. MATERIALS AND METHODS: Composites based on BisGMA/triethylene glycol dimethacrylate and 65 wt% of filler were prepared with different concentrations of camphorquinone/amine (C1-0.5%, C2-1%, C3-1.5%). Cavities were prepared (3 mm × 3 mm × 2 mm) on the buccal surface of 120 bovine incisors and the adhesive system Adper Single Bond 2 was applied following manufactures instruction. Specimens were then distributed according to type of composite (C1, C2, C3) and photoactivation method (high-intensity - 750 mW/cm(2) for 40 s; low intensity - 150 mW/cm(2) for 200 s; soft-start - 150 mW/cm(2) for 10 s + 750 mW/cm(2) for 38 s; pulse-delay - 150 mW/cm(2) for 10 s + 3 min dark + 750 mW/cm(2) for 38 s). Superficial and internal margins were analyzed by scanning electron microscopy, using the epoxy replica technique. The length of gaps was expressed as a percentage of the total length of the margins. Data were submitted to two-way analysis of variance and Tukey's test (α =0.05). RESULTS: Modulated curing methods did not influence gap formation regarding both superficial and internal adaptation. The composite with the lower initiator concentration (C1) presented higher gap formation when compared with those with higher concentrations (C2 and C3). CONCLUSION: Modulated photoactivation methods did not reduce gap formation for the experimental composite restorations evaluated. However, higher photoinitiator concentrations promote better marginal seal.

Effect of disinfection and accelerated aging on color stability of colorless and pigmented facial silicone.

PURPOSE: The aim of this study was to evaluate the color stability of a facial silicone with different pigmentations submitted to disinfection and accelerated aging. MATERIALS AND METHODS: Sixty replicas were fabricated with the silicone Silastic MDX 4-4210 and divided into three groups: no pigmentation, pigmentation with makeup powder, and pigmentation with ceramic powder. Half the replicas of each group were submitted to disinfection with Efferdent and the other with neutral soap for 60 days (n = 10). After this period, all replicas were inserted in a chamber for accelerated aging of nonmetallic specimens. The color measurements were carried out initially, after disinfection, and after accelerated aging (252, 504, 1008 hours). Color stability was evaluated through spectrophotometry. The values were submitted to ANOVA and the means to Tukey's test (p < 0.01). RESULTS: The specimens disinfected with neutral soap exhibited higher ΔE values regardless of the type of pigmentation. The colorless replicas and the specimens pigmented with ceramic exhibited a statistically significant difference between the methods of disinfection in all periods. The specimens pigmented with makeup powder did not demonstrate a statistically significant difference. CONCLUSIONS: The ceramic pigment presented greater color stability regardless of disinfection and period. On the other hand, the makeup pigment exhibited the highest values of chromatic alteration.

Effect of different light curing units on Knoop hardness and temperature of resin composite.

AIM: To evaluate the influence of quartz tungsten halogen and plasma arc curing (PAC) lights on Knoop hardness and change in polymerization temperature of resin composite. MATERIALS AND METHODS: Filtek Z250 and Esthet X composites were used in the shade A3. The temperature increase was registered with Type-k thermocouple connected to a digital thermometer (Iopetherm 46). A self-cured polymerized acrylic resin base was built in order to guide the thermocouple and to support the dentin disk of 1.0 mm thickness obtained from bovine tooth. On the acrylic resin base, elastomer mold of 2.0 mm was adapted. The temperature increase was measured after composite light curing. After 24 h, the specimens were submitted to Knoop hardness test (HMV-2000, Shimadzu, Tokyo, Japan). Data were submitted to ANOVA and Tukey's test (alpha = 0.05). RESULTS: For both composites, there were no significant differences (P > 0.05) in the top surface hardness; however, PAC promoted statistically lower (P < 0.05) Knoop hardness number values in the bottom. The mean temperature increase showed no significant statistical differences (P > 0.05). CONCLUSION: The standardized radiant exposure showed no influence on the temperature increase of the composite, however, showed significant effect on hardness values.

Marginal and internal adaptation of composite restorations using a resin liner on deproteinized substrate.

OBJECTIVE: The purpose of this study was to evaluate the use of resin liner on deproteinized substrate on marginal and internal adaptation of composite restorations. MATERIAL AND METHODS: Twenty-four recently extracted 3rd molars were selected. The crowns were sectioned in a mesio-distal direction, and the specimens were ground to expose a flat enamel area of at least 6 mm in diameter. Cavities were prepared on the central area of flattened surfaces. The specimens were randomly assigned into four groups (n = 12): SB - 1. Acid etch, 2. Single bond application (SB); NaOCl/SB - 1. acid etch, 2. 10% sodium hypochlorite solution application for 60 s (NaOCl), 3. SB; SB/PL - 1. acid etch, 2. SB, 3. protect liner F (PL); NaOCl/SB/PL - 1. acid etch, 2. NaOCl, 3. SB, 4. PL. All cavities were restored with Filtek Z250 and polished. The outer and internal margins were stained using Caries Detector (Kuraray), observed under the stereomicroscope, and transferred to a computer measurement program. The length of the gap was expressed as a percentage of the total length of the margins observed. Data (internal adaptation) were submitted to ANOVA and Tukey's test. RESULTS: There were no gaps at enamel outer margins in any specimen of any group. There was no statistically significant difference in internal adaptation between SB (18%) and NaOCl/SB (18%). NaOCl/SB/PL showed the worst internal adaptation (21%), with the higher percentage of internal gaps, statistically differing from SB/PL, which showed the best internal adaptation (12%). CONCLUSIONS: Resin liner can effectively enhance internal adaptation on demineralized dentin. However, on demineralized and deproteinized dentin it affects the internal adaptation of composite restorations negatively.

Effect of surface penetrating sealant on roughness of posterior composite resins.

PURPOSE: To verify the effect of surface penetrating sealant on the roughness of posterior resin-based composites before and after mechanical toothbrushing. MATERIALS AND METHODS: 10 specimens of four different composites (Alert, Definite, Z100 and Prodigy Condensable) were made using a metal matrix (height 2 mm and diameter 4 mm). After 24 hours, the specimens were polished using Sof-Lex discs in sequence: coarse, medium, fine and superfine, each for 40 seconds and, immediately, one of the surfaces was covered with Protect-It surface sealant. All the specimens were examined with a profilometer to measure the initial surface roughness before mechanical toothbrushing at a constant speed of 250 strokes/minute with a total of 30,000 cycles, using a toothbrush and dentifrice containing calcium carbonate as abrasive, under a load of 200 g. After toothbrushing the surface roughness was measured once again. The data were analyzed with ANOVA and the Tukey test at a 95% confidence level. RESULTS: Mechanical toothbrushing increased the surface roughness of all the composites studied (Alert: 0.7303 +/- 0.0942 microm; Definite: 0.4961 +/- 0.1255 microm; Z100: 0.3428 +/- 0.0841 microm), with the exception of Prodigy Condensable (0.2782 +/- 0.0678 microm) (P > 0.05). The surface penetrating sealant effectively decreased the surface roughness for Alert (0.5435 +/- 0.2182 microm) and Definite (0.2956 +/- 0.0368 microm) (P < 0.05), but had no effect upon Z100 (0.3331 +/- 0.0565 microm) and Prodigy Condensable (0.2760 +/- 0.0920 microm) as these have smaller filler sizes than the other composites tested (P > 0.05).