Micro-CT analysis of volumetric change of calcium silicate-based root-end filling materials / 대한치과재료학회지

The purpose of this study was to investigate the effect of blood contact and tooth mobility on volumetric changes of calcium silicate-based root-end filling materials using a micro-CT. Three calcium silicate-based materials (ProRoot MTA, Biodentine, and RetroMTA) were used in this study. Seventy-two extracted human single-rooted premolars were obturated with gutta percha. Root-end resection and root-end preparation were performed. After root-end filling with tested materials, the tooth specimens were immersed in saline or blood for 5 days in a 37 ℃ incubator (n=8). The tooth specimens were mounted in a chewing simulator to simulate tooth mobility with a force of 30 N and 20,000 cycles. Micro-CT scans were performed immediately after root-end filling and after exposure to storage media or simulation of tooth mobility. The volume loss (%) was obtained from difference in the percentage of defects of materials between first and second micro-CT scans. Apical volume loss (%; volume loss from resected surface to 1 mm from the surface) was calculated for tooth mobility simulating groups. Biodentine showed larger total volume loss than ProRoot MTA and RetroMTA in saline and blood. ProRoot MTA had smaller total volume loss in blood than in saline. Under the condition simulating tooth mobility, total volume loss was similar among materials, and apical volume loss of Biodentine was larger than that of RetroMTA. In conclusion, ProRoot MTA or Retro MTA is recommended in clinical situation of intentional replantation where tooth mobility or direct contact with blood may occur.

Real-time analysis of temperature change in composite photopolymerization using non-contact infrared sensor / 대한치과재료학회지

The aim of this study was to investigate the effects of the radiant emittance of an LED light on temperature change during composite photopolymerization using a non-contact infrared sensor. A thermometer was prepared using a non-contact infrared sensor and a microcontroller. After preparing a disc-shaped composite specimen using a micro-hybrid conventional (Z250) or nano bulk-fill (BFP) composite, the temperature change of the prepared composite during photopolymerization was measured based on three photopolymerization protocols (Duty ratio/exposure time; 100%/20 s, 50%/40 s, and Increase (0→100%)/40 s) using a pulse width modulated (PWM) LED light. Subsequently, second light exposure, having the same protocol as the first, was performed on the photopolymerized composite. The first peak temperature rise of composite photopolymerization (ΔT total) and second peak temperature rise caused by the LED light (ΔT light ) were obtained from the temperature change vs. time curve.The net peak temperature rise caused by the curing heat of the composite (ΔT composite ) was obtained by subtracting the second curve from the first one. The peak time was defined as the time when ΔT composite occurred. ΔT total and ΔT composite of the 100%/20 s group were the highest and ΔT light of the 50%/40 s group was the lowest for both the composites (p<0.05). The temperature rise of Z250 was higher than that of BFP in all the groups except the ΔT composite of the Increase/40 s group (p<0.05). The peak time of the Increase/40 s group was the longest in both the composites, and the peak time of BFP was longer than that of Z250 in all the photopolymerization protocols (p<0.05). A real-time analysis of the temperature change during composite photopolymerization was effectively performed using the non-contact infrared sensor. Through this analysis, the polymerization kinetics of the composite could also be evaluated.

Real time measurement of the transmittance change of composite during light curing / 대한치과재료학회지

The purpose of this study was to measure the transmittance change of composites during light curing in real time according to different shades and thicknesses. An instrument using pulse width modulation-curing light was developed to measure the transmittance of composites in real time. A micro-hybrid composite, Filtek Z250, was used for %transmittance measurement with five different shades (A1, A2, A3, A3.5, A4) and 4 different thicknesses (0.16, 0.5, 1.0, 1.5 mm). The maximum value of d(%Transmittance)/dt and peak time were used to observe polymerization kinetics. Attenuation coefficient was also compared between pre and post cured specimens. The transmittance increased in all specimens after polymerization. A2 showed the highest and A1 showed the lowest transmittance in both pre and post curing. The transmittance change and maximum rate of change were highest in A2 and lowest in A3.5, and the peak time, which ranged in 3.10 to 4.07, was not significantly different among shades. As the specimen became thinner, both the transmittance and rate of change increased, and the peak time was maximum at 1.5 mm thickness. The absolute value of attenuation coefficient decreased after polymerization in all specimens. In conclusion, the transmittance of composite increased after polymerization. Each shade showed different transmittance value for both pre and post curing state, and thinner specimen showed higher transmittance value. Polymerization kinetics could also be observed through the rate of transmittance change over time.

Real time measurement of the transmittance change of composite during light curing / 대한치과재료학회지

The purpose of this study was to measure the transmittance change of composites during light curing in real time according to different shades and thicknesses. An instrument using pulse width modulation-curing light was developed to measure the transmittance of composites in real time. A micro-hybrid composite, Filtek Z250, was used for %transmittance measurement with five different shades (A1, A2, A3, A3.5, A4) and 4 different thicknesses (0.16, 0.5, 1.0, 1.5 mm). The maximum value of d(%Transmittance)/dt and peak time were used to observe polymerization kinetics. Attenuation coefficient was also compared between pre and post cured specimens. The transmittance increased in all specimens after polymerization. A2 showed the highest and A1 showed the lowest transmittance in both pre and post curing. The transmittance change and maximum rate of change were highest in A2 and lowest in A3.5, and the peak time, which ranged in 3.10 to 4.07, was not significantly different among shades. As the specimen became thinner, both the transmittance and rate of change increased, and the peak time was maximum at 1.5 mm thickness. The absolute value of attenuation coefficient decreased after polymerization in all specimens. In conclusion, the transmittance of composite increased after polymerization. Each shade showed different transmittance value for both pre and post curing state, and thinner specimen showed higher transmittance value. Polymerization kinetics could also be observed through the rate of transmittance change over time.

Effect of apical constriction diameter, irrigant flow rate, and needle tip design on apical pressure / 대한치과재료학회지

The purpose of this study was to evaluate the effects of apical constriction (AC) diameter, irrigant flow rate, and needle tip design on apical pressure (AP) during the root canal irrigation. Five extracted human mandibular premolars were instrumented up to #35 (0.06 taper) using nickel-titanium rotary instruments. AC was determined at 1 mm from the apical foramen. Three needles with different tip designs (notched, side-vented, and flat) were placed 3 mm from AC. APs were measured with varying flow rates of 0.05, 0.1, 0.2, and 0.3 mL/s. The AC diameter of the teeth was enlarged to #40 and #45 (0.06 taper) successively, and the aforementioned measurement procedure was repeated (n=5). When the other conditions were controlled, AP increased with decreasing AC diameter or increasing irrigant flow rate, and the AP of flat needle was the highest, followed by notched, and side-vented needle (p0.35 mm, open-end (notched or flat) needles can be used to improve irrigant replacement in the apical portion using a flow rate of 0.05 mL/s.

Effect of needle tip design and position, and irrigant flow rate on apical pressure / 대한치과재료학회지

The purpose of this study was to evaluate the effect of needle tip design and position, and irrigant flow rate on apical pressure (AP) during root canal irrigation. Five human mandibular premolars were instrumented up to #35 (0.06 taper) using nickel-titanium rotary instruments. Three different needles according to change of needle tip design (notched, side-vented, and flat) were positioned at the point of 1, 3, and 5 mm from the apical constriction (needle tip position). For each needle tip design and position, APs were measured with varying flow rates of 0.05, 0.1, 0.2, and 0.3 ml/s. When the other conditions were controlled, AP increased with decreasing needle tip position or increasing irrigant flow rate (p < 0.05). The AP of flat needle was the highest, followed by notched, side-vented needle for the same needle tip position and irrigant flow rate. The APs at needle tip position of 1 mm or with more than 0.1 ml/s flow rate were higher than central venous pressure (5.88 mmHg) for all conditions. Flat needle was not recommended for clinical use due to sharp increase of AP with changing needle tip position and irrigant flow rate. For safe and effective root canal irrigation, irrigant should be applied with the needle tip position of 3 mm and flow rate of less than 0.05 ml/s.

Epigenetics: general characteristics and implications for oral health

Genetic information such as DNA sequences has been limited to fully explain mechanisms of gene regulation and disease process. Epigenetic mechanisms, which include DNA methylation, histone modification and non-coding RNAs, can regulate gene expression and affect progression of disease. Although studies focused on epigenetics are being actively investigated in the field of medicine and biology, epigenetics in dental research is at the early stages. However, studies on epigenetics in dentistry deserve attention because epigenetic mechanisms play important roles in gene expression during tooth development and may affect oral diseases. In addition, understanding of epigenetic alteration is important for developing new therapeutic methods. This review article aims to outline the general features of epigenetic mechanisms and describe its future implications in the field of dentistry.

Comparison of the rheological properties of four root canal sealers / 国际口腔科学杂志·英文版

The flowability of a root canal sealer is clinically important because it improves the penetration of the sealer into the complex root canal system. The purpose of this study was to compare the flowabilities of four root canal sealers, measured using the simple press method (ISO 6876), and their viscosities, measured using a strain-controlled rheometer. A newly developed, calcium phosphate-based root canal sealer (Capseal) and three commercial root canal sealers (AH Plus, Sealapex and Pulp Canal Sealer EWT) were used in this study. The flowabilities of the four root canal sealers were measured using the simple press method (n=5) and their viscosities were measured using a strain-controlled rheometer (n=5). The correlation between these two values was statistically analysed using Spearman's correlation test. The flow diameters and the viscosities of the root canal sealers were strongly negatively correlated (ρ=-0.8618). The viscosity of Pulp Canal Sealer EWT was the lowest and increased in the following order: AH Plus<Sealapex<Capseal (P<0.05). All of the tested root canal sealers showed characteristic time- and temperature-dependent changes in their rheological properties. The viscosities measured using the strain-controlled rheometer were more precise than the flowabilities measured using the simple press method, suggesting that the rheometer can accurately measure the rheological properties of root canal sealers.

Thermal irritation of teeth during dental treatment procedures

While it is reasonably well known that certain dental procedures increase the temperature of the tooth's surface, of greater interest is their potential damaging effect on the pulp and tooth-supporting tissues. Previous studies have investigated the responses of the pulp, periodontal ligament, and alveolar bone to thermal irritation and the temperature at which thermal damage is initiated. There are also many in vitro studies that have measured the temperature increase of the pulp and tooth-supporting tissues during restorative and endodontic procedures. This review article provides an overview of studies measuring temperature increases in tooth structures during several restorative and endodontic procedures, and proposes clinical guidelines for reducing potential thermal hazards to the pulp and supporting tissues.

Effect of glycerin on the surface hardness of composites after curing / 대한치과보존학회지

OBJECTIVES: The purpose of this study was to examine the effect of glycerin topical application on the surface hardness of composite after curing. MATERIALS AND METHODS: A composite (Z-250, 3M ESPE) was packed into a disc-shaped brass mold and light cured according to one of the following protocols. Group 1 (control) was exposed to air and light cured for 40 sec, group 2 was covered with a Mylar strip and light cured for 40 sec, group 3 was surface coated with glycerin and light cured for 40 sec, and group 4 was exposed to air and light cured for 20 sec and then surface coated with glycerin and cured for additional 20 sec. Twenty specimens were prepared for each group. The surface hardnesses of specimens were measured with or without polishing. Five days later, the surface hardness of each specimen was measured again. Data were analyzed by three-way ANOVA and Tukey's post hoc tests. RESULTS: The surface hardnesses of the unpolished specimens immediately after curing decreased in the following order: group 2 > 3 > 4 > 1. For the polished specimens, there was no significant difference among the groups. Within the same group, the hardness measured after five days was increased compared to that immediately after curing, and the polished specimens showed greater hardness than did the unpolished specimens. CONCLUSIONS: The most effective way to increase the surface hardness of composite is polishing after curing. The uses of a Mylar strip or glycerin topical application before curing is recommended.

Rheological characterization of thermoplasticized injectable gutta percha and resilon / 대한치과보존학회지

OBJECTIVES: The purpose of this study was to observe the change in the viscoelastic properties of thermoplasticized injectable root canal filling materials as a function of temperature and to compare the handling characteristics of these materials. MATERIALS AND METHODS: Three commercial gutta perchas and Resilon (Pentron Clinical Technologies) in a pellet form were heated in the Obtura-II system (Obtura Spartan) at 140degrees C and 200degrees C, and the extrusion temperature of the thermoplasticized materials was measured. The viscoelastic properties of the materials as a function of temperature were evaluated using a rheometer. The elastic modulus G', viscous modulus G", loss tangent tandelta, and complex viscosity eta* were determined. The phase transition temperature was determined by both the rheometer and a differential scanning calorimeter (DSC). The consistency of the materials was compared under compacting pressure at 60degrees C and 40degrees C by a squeeze test. RESULTS: The three gutta perchas had dissimilar profiles in viscoelastic properties with varying temperature. The phase transition of softened materials into solidification occurred at 40degrees C to 50degrees C, and the onset temperatures obtained by a rheometer and a DSC were similar to each other. The onset temperature of phase transition and the consistency upon compaction pressure were different among the materials (p < 0.05). Resilon had a rheologically similar pattern to the gutta perchas, and was featured between high and low-flow gutta perchas. CONCLUSIONS: The rheological characteristics of the thermoplasticized root canal filling materials changed under a cooling process. The dissimilar viscoelastic properties among the materials require different handling characteristics during an injecting and compacting procedure.

Effect of the exponential curing of composite resin on the microtensile dentin bond strength of adhesives / 대한치과보존학회지

OBJECTIVES: Rapid polymerization of overlying composite resin causes high polymerization shrinkage stress at the adhesive layer. In order to alleviate the shrinkage stress, increasing the light intensity over the first 5 seconds was suggested as an exponential curing mode by an LED light curing unit (Elipar FreeLight2, 3M ESPE). In this study, the effectiveness of the exponential curing mode on reducing stress was evaluated with measuring microtensile bond strength of three adhesives after the overlying composite resin was polymerized with either continuous or exponential curing mode. METHODS: Scotchbond Multipurpose Plus (MP, 3M ESPE), Single Bond 2 (SB, 3M ESPE), and Adper Prompt (AP, 3M ESPE) were applied onto the flat occlusal dentin of extracted human molar. The overlying hybrid composite (Denfil, Vericom, Korea) was cured under one of two exposing modes of the curing unit. At 48h from bonding, microtensile bond strength was measured at a crosshead speed of 1.0 mm/min. The fractured surfaces were observed under FE-SEM. RESULTS: There was no statistically significant difference in the microtensile bond strengths of each adhesive between curing methods (Two-way ANOVA, p > 0.05). The microtensile bond strengths of MP and SB were significantly higher than that of AP (p < 0.05). Mixed failures were observed in most of the fractured surfaces, and differences in the failure mode were not observed among groups. CONCLUSION: The exponential curing method had no beneficial effect on the microtensile dentin bond strengths of three adhesives compared to continuous curing method.

Polymerization shrinkage kinetics of silorane-based composites / 대한치과보존학회지

Dental composites have improved significantly in physical properties over the past few decades. However, polymerization shrinkage and stress is still the major drawback of composites, limiting its use to selected cases. Much effort has been made to make low shrinking composites to overcome this issue and silorane-based composites have recently been introduced into the market. The aim of this study was to measure the volumetric polymerization shrinkage kinetics of a silorane-based composite and compare it with conventional methacrylate-based composites in order to evaluate its effectiveness in reducing polymerization shrinkage. Five commercial methacrylate-based (Beautifil, Z100, Z250, Z350 and Gradia X) and a silorane-based (P90) composites were investigated. The volumetric change of the composites during light polymerization was detected continuously as buoyancy change in distilled water by means of Archemedes'principle, using a newly made volume shrinkage measurement instrument. The null hypothesis was that there were no differences in polymerization shrinkage, peak polymerization shrinkage rate and peak shrinkage time between the silorane-based composite and methacrylate-based composites. The results were as follows: 1. The shrinkage of silorane-based (P90) composites was the lowest (1.48%), and that of Beautifil composite was the highest (2.80%). There were also significant differences between brands among the methacrylate-based composites. 2. Peak polymerization shrinkage rate was the lowest in P90 (0.13%/s) and the highest in Z100 (0.34%/s). 3. The time to reach peak shrinkage rate of the silorane-based composite (P90) was longer (6.7 s) than those of the methacrylate-based composites (2.4-3.1 s). 4. Peak shrinkage rate showed a strong positive correlation with the product of polymerization shrinkage and the inverse of peak shrinkage time (R = 0.95).

Real-time measurement of dentinal fluid flow during desensitizing agent application / 대한치과보존학회지

OBJECTIVES: The aim of this study was to examine changes in the dentinal fluid flow (DFF) during desensitizing agent application and to compare permeability after application among the agents. MATERIALS AND METHODS: A Class 5 cavity was prepared to exposure cervical dentin on an extracted human premolar which was connected to a sub-nanoliter fluid flow measuring device (NFMD) under 20 cm water pressure. DFF was measured from before application of desensitizing agent (Seal&Protect, SP; SuperSeal, SS; BisBlock, BB; Gluma desensitizer, GL; Bi-Fluoride 12, BF) through application procedure to 5 min after application. RESULTS: DFF rate after each desensitizing agent application was significantly reduced when compared to initial DFF rate before application (p < 0.05). SP showed a greater reduction in DFF rate than GL and BF did (p < 0.05). SS and BB showed a greater reduction in DFF rate than BF did (p < 0.05). CONCLUSIONS: Characteristic DFF aspect of each desensitizing agent was shown in NFMD during the application procedure.

A new method to measure the linear polymerization shrinkage of composites using a particle tracking method with computer vision / 대한치과보존학회지

Since the introduction of restorative dental composites, their physical properties have been significantly improved. However, polymerization shrinkage is still a major drawback. Many efforts have been made to develop a low shrinking composite, and silorane-based composites have recently been introduced into the market. In addition, many different methods have been developed to measure the polymerization shrinkage. In this study, we developed a new method to measure the linear polymerization shrinkage of composites without direct contact to a specimen using a particle tracking method with computer vision. The shrinkage kinetics of a commercial silorane-based composite (P90) and two conventional methacrylate-based composites (Z250 and Z350) were investigated and compared. The results were as follows: 1. The linear shrinkage of composites was 0.33-1.41%. Shrinkage was lowest for the silorane-based (P90) composite, and highest for the flowable Z350 composite. 2. The new instrument was able to measure the true linear shrinkage of composites in real time without sensitivity to the specimen preparation and geometry.

Effect of instrument compliance on the polymerization shrinkage stress measurements of dental resin composites / 대한치과보존학회지

The purpose of this study was to evaluate the effect of instrument compliance on the polymerization shrinkage stress measurements of dental composites. The contraction strain and stress of composites during light curing were measured by a custom made stress-strain analyzer, which consisted of a displacement sensor, a cantilever load cell and a negative feedback mechanism. The instrument can measure the polymerization stress by two modes: with compliance mode in which the instrument compliance is allowed, or without compliance mode in which the instrument compliance is not allowed. A flowable (Filtek Flow: FF) and two universal hybrid (Z100: Z1 and Z250: Z2) composites were studied. A silane treated metal rod with a diameter of 3.0 mm was fixed at free end of the load cell, and other metal rod was fixed on the base plate. Composite of 1.0 mm thickness was placed between the two rods and light cured. The axial shrinkage strain and stress of the composite were recorded for 10 minutes during polymerization, and the tensile modulus of the materials was also determined with the instrument. The statistical analysis was conducted by ANOVA, paired t-test and Tukey's test (alpha<0.05). There were significant differences between the two measurement modes and among materials. With compliance mode, the contraction stress of FF was the highest: 3.11 (0.13), followed by Z1: 2.91 (0.10) and Z2: 1.94 (0.09) MPa. When the instrument compliance is not allowed, the contraction stress of Z1 was the highest: 17.08 (0.89), followed by FF: 10.11 (0.29) and Z2: 9.46 (1.63) MPa. The tensile modulus for Z1, Z2 and FF was 2.31 (0.18), 2.05 (0.20), 1.41 (0.11) GPa, respectively. With compliance mode, the measured stress correlated with the axial shrinkage strain of composite; while without compliance the elastic modulus of materials played a significant role in the stress measurement.

The change of the initial dynamic visco-elastic modulus of composite resins during light polymerization / 대한치과보존학회지

The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer. Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume (14.2 mm3) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at 25+/-0.5degrees C. Complex shear modulus G*, storage shear modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G* of 10 MPa was determined. The G* and time to reach the G* of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test (alpha = 0.05). The results were as follows. 1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing. 2. In all composites, the development of complex shear modulus G* had a latent period for 1~2 seconds immediately after the start of light curing, and then increased rapidly during 10 seconds. 3. In all composites, the storage shear modulus G' increased steeper than the loss shear modulus G" during 10 seconds of light curing. 4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest. 5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.

Effect of fiber direction on the polymerization shrinkage of fiber-reinforced composites / 대한치과보존학회지

The aim of this study was to evaluate the effect of fiber direction on the polymerization shrinkage of fiber-reinforced composite. The disc-shaped flowable composite specimens (d = 10 mm, h = 2 mm, Aeliteflo A2, Bisco, Inc., IL, USA) with or without glass fiber bundle (X-80821P Glass Fiber, Bisco, Inc., IL, USA) inside were prepared, and the longitudinal and transversal polymerization shrinkage of the specimens on radial plane were measured with strain gages (Linear S-series 350omega, CAS, Seoul, Korea). In order to measure the free polymerization shrinkage of the flowable composite itself, the disc-shaped specimens (d = 7 mm, h = 1 mm) without fiber were prepared, and the axial shrinkage was measured with an LVDT (linear variable differential transformer) displacement sensor. The cross-section of the polymerized specimens was observed with a scanning electron microscope to examine the arrangement of the fiber bundle in composite. The mean polymerization shrinkage value of each specimen group was analyzed with ANOVA and Scheffe post-hoc test (alpha=0.05). The radial polymerization shrinkage of fiber-reinforced composite was decreased in the longitudinal direction of fiber, but increased in the transversal direction of fiber (p<0.05). We can conclude that the polymerization shrinkage of fiber-reinforced composite splint or restoratives is dependent on the direction of fiber.

The effect of priming etched dentin with solvent on the microtensile bond strength of hydrophobic dentin adhesive / 대한치과보존학회지

Deterioration of long-term dentin adhesion durability is thought to occur by hydrolytic degradation within hydrophilic domains of the adhesive and hybrid layers. This study investigated the hypothesis that priming the collagen network with an organic solvent displace water without collapse and thereby obtain good bond strength with an adhesive made of hydrophobic monomers and organic solvents. Three experimental adhesives were prepared by dissolving two hydrophobic monomers, bisphenol-A-glycidylmethacrylate (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA), into acetone, ethanol or methanol. After an etching and rinsing procedure, the adhesives were applied onto either wet dentin surfaces (wet bonding) or dentin surfaces primed with the same solvent (solvent-primed bonding). Microtensile bond strength (MTBS) was measured at 48 hrs, 1 month and after 10,000 times of thermocycles. The bonded interfaces were evaluated using a scanning electron microscope (SEM). Regardless of bonding protocols, well-developed hybrid layers were observed at the bonded interface in most specimens. The highest mean MTBS was observed in the adhesive containing ethanol at 48 hrs. With solvent-primed bonding, increased MTBS tendencies were seen with thermocycling in the adhesives containing ethanol or methanol. However, in the case of wet bonding, no increase in MTBS was observed with aging.

Quantitative comparison of permeability in the adhesive interface of four adhesive systems / 대한치과보존학회지

The purpose of this study was to perform quantitative comparisons of water permeable zones in both the adhesive and the hybrid layer before and after thermocycling in order to assess the integrity of the bonding interface. Twenty eight flat dentin surfaces were bonded with a light-cured composite resin using one of four commercial adhesives [OptiBond FL (OP), AdheSE (AD), Clearfil SE Bond (CL), and Xeno III (XE)]. These were sectioned into halves and subsequently cut to yield 2-mm thick specimens; one specimen for control and the other subjected to thermocycling for 10,000 cycles. After specimens were immersed in ammoniacal silver nitrate for 24 h and exposed to a photo developing solution for 8 h, the bonded interface was analyzed by scanning electron microscopy (SEM) and wavelength dispersive spectrometry (WDS) at five locations per specimen. Immediately after bonding, the adhesive layer of OP showed the lowest silver uptake, followed by CL, AD, and XE in ascending order (p < 0.0001); the hybrid layer of CL had the lowest silver content among the groups (p = 0.0039). After thermocycling, none of the adhesives manifested a significant increase of silver in either the adhesive or the hybrid layer. SEM demonstrated the characteristic silver penetrated patterns within the interface. It was observed that integrity of bonding was well maintained in OP and CL throughout the thermocycling process. Adhesive-tooth interfaces are vulnerable to hydrolytic degradation and its permeability varies in different adhesive systems, which may be clinically related to the restoration longevity.