Effect of silane and alkali treatment on the shear bond strength between two Ni-Cr alloys and acrylic resin / 대한치과재료학회지

Sufficient bonding between the framework of the cast alloy and the denture base resin is essential for the clinical success of removable partial dentures. In this study, we investigated whether the silane and alkali treatments improve the chemical bonding between two nickel-chromium alloys and acrylic resin and thus the shear bond strength. A silane solution was prepared using 3-methacryloxypropyltrimethoxysilane. The alloy specimens were treated with silane and alkali, preparing four experimental groups: untreated (UT), silane treated (ST), alkali treated (AT), and alkali/silane treated (AST) groups. In addition, the contact angles and surface roughness of the alloy surfaces of the four groups were measured. The acrylic resin was bonded to the alloy specimens, and then the resin was polymerized to form a bonded specimen. After measuring the shear bond strength, the failure modes were examined using scanning electron microscopy. Results for all groups were analyzed using two-way ANOVA followed by Tukey's multiple comparison test at a significance level of 0.05. The statistical analysis showed no significant differences in Ra value for all groups (p>.05). In the two alloys, the contact angle of the AT group was significantly lower than that of the other groups (p<.05), and that of the AST group was significantly higher than that of the ST group (p<.05). In both alloys, the ST and AST groups showed the higher shear bond strengths (p<.05), while the UT and AT groups showed the lower values. The UT and AT groups showed complete adhesive failure at the fractured surfaces. In this study, the silane treatment was effective to improve the shear bond strength, but the alkali treatment did not show any significant effect.

Effect of pre-curing of two universal adhesives on the shear bond strength of resin cement to zirconia / 대한치과재료학회지

This study aimed to investigate whether pre-curing the universal adhesives affect the resin bonding to zirconia ceramic. Two commercial universal adhesives (All-Bond Universal, ABU; Single Bond Universal Adhesive, SBU) were tested in comparison with a conventional zirconia primer (Z-Prime Plus, ZPP). Air-abraded zirconia specimens were divided into six groups, to which different priming agents were applied with or without photo-polymerization. After resin cylinders were built on the primed zirconia surface using a resin cement (Duo-Link), all bonded specimens were stored in water at 37℃ for 24 hours and half of them (n = 12) were additionally thermocycled 5,000 times. A shear bond strength test was performed at a crosshead speed of 0.5 mm/minute and failure modes were assessed using an optical microscope at 25× magnification. Before thermocycling, the light-cured specimens of ABU and SBU showed higher bond strengths than the uncured ones of the materials (p 0.05). After thermal aging, there were significant decreases in the bond strength for all specimens treated with the universal adhesives (p 0.05) and attained higher bond strength values for both the pre-cured and uncured specimens when compared to the two universal adhesives (p<0.05). Adhesive failures were predominant in all test groups and thermocycling resulted in the higher incidences of adhesive failures for the uncured groups, which was not shown in the pre-cured groups.

Comparative clinical study of the marginal discrepancy of fixed dental prosthesis fabricated by the milling-sintering method using a presintered alloy

PURPOSE: The present study was designed to examine the clinical fit of fixed dental prosthesis fabricated by the milling-sintering method using a presintered cobalt-chromium alloy. MATERIALS AND METHODS: Two single metal-ceramic crowns were fabricated via milling-sintering method and casting method in each of the twelve consecutive patients who required an implant-supported fixed prosthesis. In the milling-sintering method, the prosthetic coping was designed in computer software, and the design was converted to a non-precious alloy coping using milling and post-sintering process. In the casting method, the conventional manual fabrication process was applied. The absolute marginal discrepancy of the prostheses was evaluated intraorally using the triple-scan technique. Statistical analysis was conducted using Mann-Whitney U test (α=.05). RESULTS: Eight patients (66.7%) showed a lower marginal discrepancy of the prostheses made using the milling-sintering method than that of the prosthesis made by the casting method. Statistically, the misfit of the prosthesis fabricated using the milling-sintering method was not significantly different from that fabricated using the casting method (P=.782). There was no tendency between the amount of marginal discrepancy and the measurement point. CONCLUSION: The overall marginal fit of prosthesis fabricated by milling-sintering using a presintered alloy was comparable to that of the prosthesis fabricated by the conventional casting method in clinical use.

Development of an experimental model for radiation-induced inhibition of cranial bone regeneration / 대한악안면성형재건외과학회지

BACKGROUND: Radiation therapy is widely employed in the treatment of head and neck cancer. Adverse effects of therapeutic irradiation include delayed bone healing after dental extraction or impaired bone regeneration at the irradiated bony defect. Development of a reliable experimental model may be beneficial to study tissue regeneration in the irradiated field. The current study aimed to develop a relevant animal model of post-radiation cranial bone defect. METHODS: A lead shielding block was designed for selective external irradiation of the mouse calvaria. Critical-size calvarial defect was created 2 weeks after the irradiation. The defect was filled with a collagen scaffold, with or without incorporation of bone morphogenetic protein 2 (BMP-2) (1 μg/ml). The non-irradiated mice treated with or without BMP-2-included scaffold served as control. Four weeks after the surgery, the specimens were harvested and the degree of bone formation was evaluated by histological and radiographical examinations. RESULTS: BMP-2-treated scaffold yielded significant bone regeneration in the mice calvarial defects. However, a single fraction of external irradiation was observed to eliminate the bone regeneration capacity of the BMP-2-incorporated scaffold without influencing the survival of the animals. CONCLUSION: The current study established an efficient model for post-radiation cranial bone regeneration and can be applied for evaluating the robust bone formation system using various chemokines or agents in unfavorable, demanding radiation-related bone defect models.

Significant considerations of mechanical strength of BLT implant (Roxolid): Correlation between material and product strength under static and fatigue loads / 대한치과재료학회지

The purpose of this study is to correlate the material properties of TiZr alloy material (Roxolid) and the mechanical strength of the implant fixture (BLT) through the maximum compressive load test and the fatigue test. Implant samples were purchased with BLT (Roxolid, Straumann, Switzerland) and Octa1 (cold-worked, Megagen Implant, Korea) fixtures made of two materials (TiZr and cold-worked Ti Grade 4). After the maximum compressive load test, the test specimens were analyzed with a optical microscope to confirm the fracture pattern. After the fatigue test, the samples that passed 5 million cycles were analyzed for the precision fit using a scanning electron microscope. Data were analyzed using Student's t-test (α=0.05). In the compressive load test, the small diameter (3.3 mm) implants with the same length and the common diameter (4.1 mm) implants had fracture or bending regardless of the material in both the test and control groups. The fatigue load showed the same results without significance and the gap between the fixture and abutment interface was within 10 µm in both the test and control groups in the precision fit test. There was no statistically significant difference in the maximum compressive load and fatigue test for the comparison of mechanical strength between two systems (BLT vs. Octa1) with same diameter and length, similar shapes and connections.

Accuracy comparison between subtractive and additive methods in fabricating working model / 대한치과재료학회지

The purpose of this study was to compare the accuracy of the working models fabricated by the subtractive and additive processing methods based on the 3-dimensional reconstruction model. A total of 20 models were fabricated with subtractive processing method from polymethyl methacrylate (PMMA) blocks using the stereolithography (STL) file of master gypsum model and another 20 models were fabricated with additive processing method using 3D printer with 0.025 mm of a layer thickness. The CAD-reference-model (CRM) and CAD-test-model (CTM) were superimposed by a software for accuracy analysis (Geomagic Qualify 13), where the STL files were transformed to point cloud data and the surface data (CRM and CTM) were subjected to initial alignment and followed by re-alignmented according to best-fit superimposition. The distances between surface data and all points, in this process, were converted to the root mean square (RMS) and averaged. In the experimental results, It was shown that the accuracy is higher in work model fabricated by additive processing method compared to one fabricated by subtractive one (p < 0.05). In addition, it is considered that the working model fabricated by subtractive processing method is to be clinically applicable by improving the improper reproducibility of the tooth surface and depressed area.

Post space preparation timing of root canals sealed with AH Plus sealer

OBJECTIVES: To determine the optimal timing for post space preparation of root canals sealed with epoxy resin-based AH Plus sealer in terms of its polymerization and influence on apical leakage. MATERIALS AND METHODS: The epoxy polymerization of AH Plus (Dentsply DeTrey) as a function of time after mixing (8, 24, and 72 hours, and 1 week) was evaluated using Fourier transform infrared (FTIR) spectroscopy and microhardness measurements. The change in the glass transition temperature (Tg ) of the material with time was also investigated using differential scanning calorimetry (DSC). Fifty extracted human single-rooted premolars were filled with gutta-percha and AH Plus, and randomly separated into five groups (n = 10) based on post space preparation timing (immediately after root canal obturation and 8, 24, and 72 hours, and 1 week after root canal obturation). The extent of apical leakage (mm) of the five groups was compared using a dye leakage test. Each dataset was statistically analyzed by one-way analysis of variance and Tukey's post hoc test (α = 0.05). RESULTS: Continuous epoxy polymerization of the material with time was observed. Although the T(g) values of the material gradually increased with time, the specimens presented no clear T(g) value at 1 week after mixing. When the post space was prepared 1 week after root canal obturation, the leakage was significantly higher than in the other groups (p < 0.05), among which there was no significant difference in leakage. CONCLUSIONS: Poor apical seal was detected when post space preparation was delayed until 1 week after root canal obturation.

In vitro study of Streptococcus mutans adhesion on composite resin coated with three surface sealants

OBJECTIVES: Although the coating of surface sealants to dental composite resin may potentially reduce bacterial adhesion, there seems to be little information regarding this issue. This preliminary in vitro study investigated the adhesion of Streptococcus mutans (S. mutans) on the dental composite resins coated with three commercial surface sealants. MATERIALS AND METHODS: Composite resin (Filtek Z250) discs (8 mm in diameter, 1 mm in thickness) were fabricated in a mold covered with a Mylar strip (control). In group PoGo, the surfaces were polished with PoGo. In groups PS, OG, and FP, the surfaces polished with PoGo were coated with the corresponding surface sealants (PermaSeal, PS; OptiGuard, OG; Fortify Plus, FP). The surfaces of the materials and S. mutans cells were characterized by various methods. S. mutans adhesion to the surfaces was quantitatively evaluated using flow cytometry (n = 9). RESULTS: Group OG achieved the lowest water contact angle among all groups tested (p 0.05) or significantly lower (group OG, p < 0.001) bacterial adhesion when compared with the control group. CONCLUSIONS: The application of the surface sealants significantly reduced S. mutans adhesion to the composite resin polished with the PoGo.

Orthodontic bracket bonding to glazed full-contour zirconia

OBJECTIVES: This study evaluated the effects of different surface conditioning methods on the bond strength of orthodontic brackets to glazed full-zirconia surfaces. MATERIALS AND METHODS: Glazed zirconia (except for the control, Zirkonzahn Prettau) disc surfaces were pre-treated: PO (control), polishing; BR, bur roughening; PP, cleaning with a prophy cup and pumice; HF, hydrofluoric acid etching; AA, air abrasion with aluminum oxide; CJ, CoJet-Sand. The surfaces were examined using profilometry, scanning electron microscopy, and electron dispersive spectroscopy. A zirconia primer (Z-Prime Plus, Z) or a silane primer (Monobond-S, S) was then applied to the surfaces, yielding 7 groups (PO-Z, BR-Z, PP-S, HF-S, AA-S, AA-Z, and CJ-S). Metal bracket-bonded specimens were stored in water for 24 hr at 37℃, and thermocycled for 1,000 cycles. Their bond strengths were measured using the wire loop method (n = 10). RESULTS: Except for BR, the surface pre-treatments failed to expose the zirconia substructure. A significant difference in bond strengths was found between AA-Z (4.60 ± 1.08 MPa) and all other groups (13.38 ± 2.57 - 15.78 ± 2.39 MPa, p < 0.05). For AA-Z, most of the adhesive remained on the bracket. CONCLUSIONS: For bracket bonding to glazed zirconia, a simple application of silane to the cleaned surface is recommended. A zirconia primer should be used only when the zirconia substructure is definitely exposed.

The effect of 4,4'-bis(N,N-diethylamino) benzophenone on the degree of conversion in liquid photopolymer for dental 3D printing

PURPOSE: The purpose of this preliminary study was to investigate the effects of adding 4,4'-bis(N,N-diethylamino) benzophenone (DEABP) as a co-initiator to a binary photoinitiating system (camphorquinone-amine) to analyze on the degree of conversion (DC) of a light-cured resin for dental 3D printing. MATERIALS AND METHODS: Cylindrical specimens (N=60, n=30 per group, o5 mm x 1 mm) were fabricated using bisphenol A glycerolate dimethacrylate (BisGMA) both with and without DEABP. The freshly mixed resins were exposed to light in a custom-made closed chamber with nine light-emitting diode lamps (wavelength: 405 nm; power: 840 mW/cm2) for polymerization at each incidence of light-irradiation at 10, 30, 60, 180, and 300 seconds, while five specimens at a time were evaluated at each given irradiation point. Fourier-transform infrared (FTIR) spectroscopy was used to measure the DC values of the resins. Two-way analysis of variance and the Duncan post hoc test were used to analyze statistically significant differences between the groups and given times (alpha=.05). RESULTS: In the DEABP-containing resin, the DC values were significantly higher at all points in time (P<.001), and also the initial polymerization velocity was faster than in the DEABP-free resin. CONCLUSION: The addition of DEABP significantly enhanced the DC values and, thus, could potentially become an efficient photoinitiator when combined with a camphorquinone-amine system and may be utilized as a more advanced photopolymerization system for dental 3D printing.

Efficacy of various cleaning solutions on saliva-contaminated zirconia for improved resin bonding

PURPOSE: This study aimed to investigate the efficacy of cleaning solutions on saliva-contaminated zirconia in comparison to air-abrasion in terms of resin bonding. MATERIALS AND METHODS: For saliva-contaminated airabraded zirconia, seven cleaning methods)-no contamination (NC), water-spray rinsing (WS), additional airabrasion (AA), and cleaning with four solutions (Ivoclean [IC]; 1.0 wt% sodium dodecyl sulfate [SDS], 1.0 wt% hydrogen peroxide [HP], and 1.0 wt% sodium hypochlorite [SHC])-were tested. The zirconia surfaces for each group were characterized using various analytical techniques. Three bonded resin (Panavia F 2.0) cylinders (bonding area: 4.5 mm2) were made on one zirconia disk specimen using the Ultradent jig method [four disks (12 cylinders)/group; a total of 28 disks]. After 5,000 thermocycling, all specimens were subjected to a shear bond strength test with a crosshead speed of 1.0 mm/minute. The fractured surfaces were observed using an optical and scanning electron microscope (SEM). RESULTS: Contact angle measurements showed that groups NC, AA, IC, and SHC had hydrophilic surfaces. The X-ray photoelectron spectroscopy (XPS) analysis showed similar elemental distributions between group AA and groups IC and SHC. Groups IC and SHC showed statistically similar bond strengths to groups NC and AA (P>.05), but not groups SDS and HP (P<.05). For groups WS, SDS, and HP, blister-like bubble formations were observed on the surfaces under SEM. CONCLUSION: Within the limitations of this in vitro study, some of the cleaning solutions (IC or SHC) were effective in removing saliva contamination and enhancing the resin bond strength.

Degree of conversion of two dual-cured resin cements light-irradiated through zirconia ceramic disks

PURPOSE: The aim of this Fourier transform infrared (FTIR) spectroscopic study was to measure the degree of conversion (DC) of dual-cured resin cements light-irradiated through zirconia ceramic disks with different thicknesses using various light-curing methods. MATERIALS AND METHODS: Zirconia ceramic disks (KT12) with three different thicknesses (1.0, 2.0, and 4.0 mm) were prepared. The light transmittance of the disks was measured using ultraviolet visible near-infrared spectroscopy. Four different light-curing protocols were used by combining two curing light modes (Elipar TriLight (standard mode) and bluephase G2 (high power mode)) with light-exposure times of 40 and 120 seconds. The DCs of the two dual-cured resin cements (Duo-Link and Panavia F2.0) light-irradiated through the disks was analyzed at three time intervals (3, 7, and 10 minutes) by FTIR spectroscopy. The data was analyzed using repeated measures ANOVA (alpha=.05).Two-way ANOVA and Tukey post hoc test were used to analyze the 10 minute DC results. RESULTS: The 1.0 mm thick disk exhibited low light transmittance (<25%), and the transmittance decreased considerably with increasing disk thickness. All groups exhibited significantly higher 10 minute DC values than the 3 or 7 minute values (P<.05), but some exceptions were observed in Duo-Link. Two-way ANOVA revealed that the influence of the zirconia disk thickness on the 10 minute DC was dependent on the light-curing methods (P<.001). This finding was still valid even at 4.0 mm thickness, where substantial light attenuation took place. CONCLUSION: The curing of the dual-cured resin cements was affected significantly by the light-curing technique, even though the additional chemical polymerization mechanism worked effectively.

Debonding forces of three different customized bases of a lingual bracket system / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to investigate whether extension of the custom base is necessary for enhancement of bond strength, by comparing the debonding forces and residual adhesives of 3 different lingual bracket systems. METHODS: A total of 42 extracted upper premolars were randomly divided into 3 groups of 14 each for bonding with brackets having (1) a conventional limited resin custom base; (2) an extended gold alloy custom base: Incognito(TM); and (3) an extended resin custom base: KommonBase(TM). The bonding area was measured by scanning the bracket bases with a 3-dimensional digital scanner. The debonding force was measured with an Instron universal testing machine, which applied an occlusogingival shear force. RESULTS: The mean debonding forces were 60.83 N (standard deviation [SD] 10.12), 69.29 N (SD 9.59), and 104.35 N (SD17.84) for the limited resin custom base, extended gold alloy custom base, and extended resin custom base, respectively. The debonding force observed with the extended resin custom base was significantly different from that observed with the other bases. In addition, the adhesive remnant index was significantly higher with the extended gold alloy custom base. CONCLUSIONS: All 3 custom-base lingual brackets can withstand occlusal and orthodontic forces. We conclude that effective bonding of lingual brackets can be obtained without extension of the custom base.

Effective application duration of sodium ascorbate antioxidant in reducing microleakage of bonded composite restoration in intracoronally-bleached teeth

OBJECTIVES: The aim of this study was to determine an appropriate application duration of sodium ascorbate (SA) antioxidant gel in reducing microleakage of bonded composite restoration in intracoronally-bleached teeth. MATERIALS AND METHODS: Eighty endodontically-treated human incisors were randomly divided into eight groups: control, no bleaching; IB and DB, immediate and delayed bonding after bleaching, respectively; S10m, S60m, S24h, S3d and S7d, bleaching + SA gel for 10 min, 60 min, 24 hr, 3 day and 7 day, respectively. For bleaching, a mixture of 30% hydrogen peroxide and sodium perborate was applied for 7 day. All access cavities were restored using One-Step adhesive (Bisco Inc.) and then Aelite LS Packable composite (Bisco Inc.). The bonded specimens were subjected to 500 thermal cycles, immersed in 1% methylene blue for 8 hr, and longitudinally sectioned. Microleakage was assessed with a 0 - 4 scoring system and analyzed using nonparametric statistical methods (alpha = 0.05). RESULTS: Group IB showed a significantly higher microleakge than the control group (p = 0.006) and group DB a statistically similar score to the control group (p > 0.999). Although groups S10m, S60m, and S24h exhibited significantly higher scores than group DB (p 0.999). CONCLUSIONS: Application of SA gel for 3 day after nonvital bleaching was effective in reducing microleakage of composite restoration in intracoronally-bleached teeth.

Direct and indirect bonding of wire retainers to bovine enamel using three resin systems: shear bond strength comparisons / 대한치과교정학회지

OBJECTIVE: We compared the shear bond strength (SBS) of lingual retainers bonded to bovine enamel with three different resins using direct and indirect methods. METHODS: Both ends of pre-fabricated twisted ligature wires were bonded to bovine enamel surfaces using Light-Core, Tetric N-Flow, or Transbond XT. Phosphoric acid-etched enamel surfaces were primed with One-Step prior to bonding with Light-Core or Tetric N-Flow. Transbond XT primer was used prior to bonding with Transbond XT. After 24 hours in water at 37degrees C, we performed SBS tests on the samples. We also assigned adhesive remnant index (ARI) scores after debonding and predicted the clinical performance of materials and bonding techniques from Weibull analyses. RESULTS: Direct bonding produced significantly higher SBS values than indirect bonding for all materials. The SBS for Light-Core was significantly higher than that for Tetric N-Flow, and there was no significant difference between the direct bonding SBS of Transbond XT and that of Light-Core. Weibull analysis indicated Light-Core performed better than other indirectly bonded resins. CONCLUSIONS: When the SBS of a wire retainer is of primary concern, direct bonding methods are superior to indirect bonding methods. Light-Core may perform better than Transbond XT or Tetric N-Flow when bonded indirectly.

Polymerization of dual cured composites by different thickness / 대한치과보존학회지

The purpose of this study was to evaluate the effect of thickness, filling methods and curing methods on the polymerization of dual cured core materials by means of microhardness test. Two dual cured core materials, MultiCore Flow (Ivoclar Vivadent AG, Schaan, Liechtenstein) and Bis-Core (Bisco Inc., Schaumburg, IL, USA) were used in this study. 2 mm (bulky filled), 4 mm (bulky filled), 6 mm (bulky and incrementally filled) and 8 mm (bulky and incrementally filled)-thickness specimens were prepared with light cure or self cure mode. After storage at 37degrees C for 24 hours, the Knoop hardness values (KHN) of top and bottom surfaces were measured and the microhardness ratio of top and bottom surfaces was calculated. The data were analyzed using one-way ANOVA and Scheffe multiple comparison test, with alpha = 0.05. The effect of thickness on the polymerization of dual cured composites showed material specific results. In 2, 4 and 6 mm groups, the KHN of two materials were not affected by thickness. However, in 8 mm group of MultiCore Flow, the KHN of the bottom surface was lower than those of other groups (p < 0.05). The effect of filling methods on the polymerization of dual cured composites was different by their thickness or materials. In 6 mm thickness, there was no significant difference between bulk and incremental filling groups. In 8 mm thickness, Bis-Core showed no significant difference between groups. However, in MultiCore Flow, the microhardness ratio of bulk filling group was lower than that of incremental filling group (p < 0.05). The effect of curing methods on the polymerization of dual cured composites showed material specific results. In Bis-Core, the KHN of dual cured group were higher than those of self cured group at both surfaces (p < 0.05). However, in MultiCore Flow, the results were not similar at both surfaces. At the top surface, dual cured group showed higher KHN than that of self cured group (p < 0.05). However, in the bottom surface, dual cured group showed lower value than that of self cured group (p < 0.05).