Managing oral biofilms to avoid enamel demineralization during fixed orthodontic treatment / 대한치과교정학회지

Enamel demineralization represents the most prevalent complication arising from fixed orthodontic treatment. Its main etiology is the development of cariogenic biofilms formed around orthodontic appliances. Ordinarily, oral biofilms exist in a dynamic equilibrium with the host's defense mechanisms. However, the equilibrium can be disrupted by environmental changes, such as the introduction of a fixed orthodontic appliance, resulting in a shift in the biofilm’s microbial composition from non-pathogenic to pathogenic. This alteration leads to an increased prevalence of cariogenic bacteria, notably mutans streptococci, within the biofilm. This article examines the relationships between oral biofilms and orthodontic appliances, with a particular focus on strategies for effectively managing oral biofilms to mitigate enamel demineralization around orthodontic appliances.

Effect of microstructure of reinforced CAD/CAM hybrid composite resin block on shear bond strength of composite resin / 대한치과재료학회지

The shear bond strength of the composite resin to a CAD/CAM hybrid composite resin block (CRB) can be affected by the composition and microstructure of the hybrid CRB, surface treatment and the properties of the applied adhesive. In this study, the shear bond strengths between composite resin and the hybrid CRBs were measured to evaluate the effect of microstructure differences in hybrid CRBs on the bond strength. Ten conventional and reinforced hybrid CRBs developed by five domestic and international manufacturersand five universal adhesives currently used in dentistry were selected. After polishing the hybrid CRB surface, the specimens were divided into two groups. The first group was HF-treated to observe the microstructure by FE-SEM, and the second group was sandblasted with alumina, measured the surface roughness by CLSM, bonded with composite resin (diameter = 2.0mm) using universal adhesive, and stored in a 37 ℃ water bath for 24 hours, and measured the shear bond strength using a universal testing machine. The measured values were statistically analyzed using the Tukey-multiple comparison test (α= 0.05). It was observed that the size, type, and fraction of the filler particles contained in the regular and reinforced hybrid CRBs affected the microstructure, but the differences did not affect the shear bond strength. All five universal adhesives containing 10-MDP as the main functional monomer met the minimum bond strength (>20 MPa) required for clinical applications.

Evaluation of component release and oxygen-inhibited layer removal on cytotoxicity of syringe-type bis-acryl composites for provisional restorations / 대한치과재료학회지

This study aimed to analyze the eluted components of syringe-type bis-acryl composites and to evaluate the effect of removing the oxygen-inhibited layer on cytotoxicity. Four different bis-acryl provisional composite materials-Protemp 4 (PT), Structur 2 SC (ST), Luxatemp Automix Plus (LT), and Hexa-Temp (HT)-were evaluated. Gas chromatography/mass spectrometry was used to analyze the composite eluate after 24 h of immersion in methanol. An agar overlay test and a live/dead assay were performed on the polymerized disc-shaped specimens after 24 h. To evaluate the effect of removing the oxygen-inhibited layer, samples were prepared with a surface oxygen-inhibited layer. The surface oxygen-inhibited layer of the disc-shaped specimens was removed with alcohol only (subgroup A) or with polishing and alcohol (subgroup PA), and their cytotoxicities were compared with those of “as received” (subgroup N) specimens using the WST-1 assay. Statistical significance was assessed using analyses of variance, followed by Bonferroni multiple comparison tests (α=0.05). Different components were detected by gas chromatography/mass spectrometry analysis among the groups. The agar overlay assay confirmed severe cytotoxicity in HT, LT, and ST groups, whereas PT showed moderate cytotoxicity. The effect of removing the oxygen-inhibited layer on cell viability was significantly higher in PA than in N in all composite groups. In HT and ST, the cell viability was significantly higher in PA than in A. Syringe-type bis-acryl composites for provisional restorations may elute various components into the oral cavity, which may cause cytotoxicity in adjacent structures. The cytotoxicity of the materials is reduced by the removal of the oxygen-inhibited layer.

Physical and biodegradable properties of 3D printed resorbable membranes for periodontal guided tissue regenerations / 대한치과재료학회지

The purpose of this study was to compare physical and biodegradable properties of 3D printed resorbable membranes that are used for guided tissue regenerations in periodontal tissues. Three types of 3D printed membranes (two types of non β-TCP and one type of β-TCP) were considered. The form and element compositions of 3D printed membranes were analyzed by field-emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS). Porosity and pore size were measured using Micro-CT. Also, tensile strength, biodegradability tests were performed. Statistical analyses were carried in tensile strength and cell viability test (p<0.05). The result of SEM images with EDS analyses showed linear layers of lattice structure with presence of C and O in all groups. There was a slight difference in Ca and P among some groups. Tensile strength was significantly different among all groups (p<0.05), and biodegradability showed that the group containing β-TCP resulted in the fastest degradation rate. Therefore, the results of this study concluded that the 3D printed resorbable membrane has variable physical and biodegradable properties for clinical use, where such information would be useful to be considered for the future development of related products and clinical application of the products.

Physical and biodegradable properties of 3D printed resorbable membranes for periodontal guided tissue regenerations / 대한치과재료학회지

The purpose of this study was to compare physical and biodegradable properties of 3D printed resorbable membranes that are used for guided tissue regenerations in periodontal tissues. Three types of 3D printed membranes (two types of non β-TCP and one type of β-TCP) were considered. The form and element compositions of 3D printed membranes were analyzed by field-emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS). Porosity and pore size were measured using Micro-CT. Also, tensile strength, biodegradability tests were performed. Statistical analyses were carried in tensile strength and cell viability test (p<0.05). The result of SEM images with EDS analyses showed linear layers of lattice structure with presence of C and O in all groups. There was a slight difference in Ca and P among some groups. Tensile strength was significantly different among all groups (p<0.05), and biodegradability showed that the group containing β-TCP resulted in the fastest degradation rate. Therefore, the results of this study concluded that the 3D printed resorbable membrane has variable physical and biodegradable properties for clinical use, where such information would be useful to be considered for the future development of related products and clinical application of the products.

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.

Comparison of physical properties of the various 3D printing temporary crown and bridge resin / 대한치과재료학회지

Conventional dental resins for crown and bridge fulfill ISO 10477 and ISO 10993 before clinical application. Although 3D printing or rapid prototyping (RP) for the fabrication of temporary crown and bridge have been proposed, a little studies were reported for 3D printing resin for temporary crown and bridge. The purpose of this study was to evaluate the physical properties (such as water sorption and solubility, color stability and flexural strength) of the various 3D printing temporary crown and bridge resin following the ISO 10477:2018 and estimate the effect of chemical composition of resin on the physical properties. Four resins approved by KFDA and 4 experimental resins developed by different manufacturer were tested in this study. Samples were prepared with DLP typed 3D Printer (G-Printer) and post-cured using UV-light Cure Unit (Cure M). Proper 3D printing and post-curing conditions were selected for different 3D printing resins. Each test was performed according to the ISO 10477 and results were statistically analyzed using Tukey-multiple comparison test (p=0.05). Only group-B did not satisfied the ISO requirement ( 60 MPa). Resin components may affect the flexural strength, then user should check the components of 3D printing resin. Deficient degree of polymerization may lead to large water sorption, water solubility and color changes. Further study should be done comparison between specimens printed with specific 3D printer recommended by manufacturer and specimens used in this study.

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 resin cement color on the color of commercially available zirconia crown / 대한치과재료학회지

The purpose of this study is to evaluate the effect of resin cement color on the color of commercially available zirconia crown. The zirconia and resin cements used for the experiment were NuSmile® ZR Zirconia LT Shade (LT), RelyX™ U200 TR, A2, and A3O (TR, A2, A3O). The disks of zirconia and resin cements with diameters of 5 mm and thicknesses of 1 mm were prepared. Five disks were made for each specimen. The CIE L*a*b* values of zirconia, resin cements and the combinations thereof were measured on black and white backgrounds, respectively, using a spectrophotometer. The color effect of resin cement on the color of the zirconia crown was evaluated by calculating translucency parameter (TP), contrast ratio (CR), and color differences (ΔĖ(ab)) based on the measured CIE L*a*b* values. The statistical significances were verified by one-way ANOVA and the Tukey-multiple comparisons tests. As a result, the TP and CR values were decreased (p < 0.05) and increased, respectively, in the combination of zirconia and resin cement disks compared to zirconia disk per se. When using the black background, the ΔĖ(ab) values between zirconia and the combination of the zirconia and three resin cement disks were imperceptible level. The A3O showed the lowest ΔĖ(ab) value among three resin cements. When using the white background, the ΔĖ(ab) values between zirconia and the combination of zirconia and TR resin cement (LT/TR) disks showed acceptable level. However, the ΔĖ(ab) values between zirconia and the combination of zirconia and A2 resin cement (LT/A2) disks showed unacceptable level. Meanwhile, the ΔĖ(ab) values between zirconia and the combination of zirconia and A3O resin cement (LT/A3O) disks showed perceptible but acceptable level. Within the limits of this study, the colors of resin cements did not cause unacceptable color changes of zirconia except the combination of LT/A2 on the white background. The resin cement that gave the least color changes to zirconia was A3O. This means that the resin cement A3O is recommended to use for minimizing color changes when cementing commercially available zirconia crown to tooth.

Effects of acid-treatment conditions on the surface properties of the RBM treated titanium implants / 대한치과재료학회지

The purpose of this study was to evaluate the effect of acid-treatment conditions on the surface properties of the RBM (Resorbable Blast Media) treated titanium. Disk typed cp-titanium specimens were prepared and RBM treatments was performed with calcium phosphate ceramic powder. Acid solution was mixed using HCl, H2SO4 and deionized water with 4 different volume fraction. The RBM treated titanium was acid treated with different acid solutions at 3 different temperatures and for 3 different periods. After acid-treatments, samples were cleaned with 1 % Solujet solution for 30 min and deionized water for 30 min using ultrasonic cleanser, then dried in the electrical oven (37℃). Weight of samples before and after acid-treatment were measured using electric balance. Surface roughness was estimated using a confocal laser scanning microscopy, crystal phase in the surface of sample was analyzed using X-ray diffractometer. Surface morphology and components were evaluated using Scanning Electron Microscope (SEM) with Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoemission Spectroscopy (XPS). Values of the weight changes and surface roughness were statistically analyzed using Tukey-multiple comparison test (p=0.05). Weight change after acid treatments were significantly increased with increasing the concentration of H₂SO₄ and temperature of acid-solution. Acid-treatment conditions (concentration of H₂SO₄, temperature and time) did not produce consistent effects on the surface roughness, it showed the scattered results. From XRD analysis, formation of titanium hydrides in the titanium surface were observed in all specimens treated with acid-solutions. From XPS analysis, thin titanium oxide layer in the acid-treated specimens could be evaluated. Acid solution with 90℃ showed the strong effect on the titanium surface, it should be treated with caution to avoid the over-etching process.

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.

Frictional property comparisons of conventional and self-ligating lingual brackets according to tooth displacement during initial leveling and alignment: an in vitro mechanical study / 대한치과교정학회지

OBJECTIVE: We evaluated the effects of tooth displacement on frictional force when conventional ligating lingual brackets (CL-LBs), CL-LBs with a narrow bracket width, and self-ligating lingual brackets (SL-LBs) were used with initial leveling and alignment wires. METHODS: CL-LBs (7th Generation), CL-LBs with a narrow bracket width (STb), and SL-LBs (In-Ovation L) were tested under three tooth displacement conditions: no displacement (control); a 2-mm palatal displacement (PD) of the maxillary right lateral incisor (MXLI); and a 2-mm gingival displacement (GD) of the maxillary right canine (MXC) (nine groups, n = 7 per group). A stereolithographic typodont system and artificial saliva were used. Static and kinetic frictional forces (SFF and KFF, respectively) were measured while drawing a 0.013-inch copper-nickel-titanium archwire through brackets at 0.5 mm/min for 5 minutes at 36.5℃. RESULTS: The In-Ovation L exhibited lower SFF under control conditions and lower KFF under all displacement conditions than the 7th Generation and STb (all p < 0.001). No significant difference in SFF existed between the In-Ovation L and STb for a 2-mm GD of the MXC and 2-mm PD of the MXLI. A 2-mm GD of the MXC produced higher SFF and KFF than a 2-mm PD of the MXLI in all brackets (all p < 0.001). CONCLUSIONS: CL-LBs with narrow bracket widths exhibited higher KFF than SL-LBs under tooth displacement conditions. CL-LBs and ligation methods should be developed to produce SFF and KFF as low as those in SL-LBs during the initial and leveling stage.

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.

Microgrooves on titanium surface affect peri-implant cell adhesion and soft tissue sealing; an in vitro and in vivo study

PURPOSE: With the significance of stable adhesion of alveolar bone and peri-implant soft tissue on the surface of titanium for successful dental implantation procedure, the purpose of this study was to apply microgrooves on the titanium surface and investigate their effects on peri-implant cells and tissues. METHODS: Three types of commercially pure titanium discs were prepared; machined-surface discs (A), sandblasted, large-grit, acid-etched (SLA)-treated discs (B), SLA and microgroove-formed discs (C). After surface topography of the discs was examined by confocal laser scanning electron microscopy, water contact angle and surface energy were measured. Human gingival fibroblasts (hGFs) and murine osteoblastic cells (MC3T3-E1) were seeded onto the titanium discs for immunofluorescence assay of adhesion proteins. Commercially pure titanium implants with microgrooves on the coronal microthreads design were inserted into the edentulous mandible of beagle dogs. After 2 weeks and 6 weeks of implant insertion, the animal subjects were euthanized to confirm peri-implant tissue healing pattern in histologic specimens. RESULTS: Group C presented the lowest water contact angle (62.89+/-5.66 theta), highest surface energy (45+/-1.2 mN/m), and highest surface roughness (Ra=22.351+/-2.766 microm). The expression of adhesion molecules of hGFs and MC3T30E1 cells was prominent in group C. Titanium implants with microgrooves on the coronal portion showed firm adhesion to peri-implant soft tissue. CONCLUSIONS: Microgrooves on the titanium surface promoted the adhesion of gingival fibroblasts and osteoblastic cells, as well as favorable peri-implant soft tissue sealing.

A comparative study on the fracture behavior of zironia, glass infiltrated alumina and PFM full crown system / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the fracture behavior of Zironia, glass infiltrated Alumina and PFM full crown system. MATERIALS AND METHODS: Fifteen crowns for each of 3 experimental groups (Zironia, glass infiltrated Alumina and PFM full crown) were made by the conventional method. The crowns mounted on the testing jig were inclined in 30 degrees to the long axis of the tooth and the universal testing machine was used to measure the fracture strength. RESULTS: 1. The mean fracture strengths were 588.3 +/- 49.6 MPa for zirconia system, 569.1 +/- 61.8 MPa for PFM system and 551.0 +/- 76.5 MPa for glass-infiltrated alumina system (P>.05). 2. The mean shear bond strengths were 25.5 +/- 5.6 MPa for zirconia system, 38.9 +/- 5.0 MPa for Ni-Cr alloy system and 39.4 +/- 5.1 MPa for glass-infiltrated alumina system. 3. The chemical bonding was observed at interfaces between PFM or glass-infiltrated alumina and veneering porcelain, however, no chemical bonding was observed at interface between zirconia and veneering porcelain. CONCLUSION: With the study, the fracture strengths of PFM crown system had a higher fracture strength than conventional zirconia system crown and glass-infiltrated alumina crowns. and than the shear bond strengths glass-infiltrated alumina system had a higher shear bond strength than conventional PFM system and zirconia system.

Comparison of transition temperature range and phase transformation behavior of nickel-titanium wires / 대한치과교정학회지

OBJECTIVE: The aim of this research was to evaluate the mechanical properties (MP) and degree of the phase transformation (PT) of martensitic (M-NiTi), austenitic (A-NiTi) and thermodynamic nickel-titanium wire (T-NiTi). METHODS: The samples consisted of 0.016 x 0.022 inch M-NiTi (Nitinol Classic, NC), A-NiTi (Optimalloy, OPTI) and T-NiTi (Neo-Sentalloy, NEO). Differential scanning calorimetry (DSC), three-point bending test, X-ray diffraction (XRD), and microstructure examination were used. Statistical evaluation was undertaken using ANOVA test. RESULTS: In DSC analysis, OPTI and NEO showed two peaks in the heating curves and one peak in the cooling curves. However, NC revealed one single broad and weak peak in the heating and cooling curves. Austenite finishing (Af) temperatures were 19.7degrees C for OPTI, 24.6degrees C for NEO and 52.4degrees C for NC. In the three-point bending test, residual deflection was observed for NC, OPTI and NEO. The load ranges of NC and OPTI were broader and higher than NEO. XRD and microstructure analyses showed that OPTI and NEO had a mixture of martensite and austenite at temperatures below Martensite finishing (Mf). NEO and OPTI showed improved MP and PT behavior than NC. CONCLUSIONS: The mechanical and thermal behaviors of NiTi wire cannot be completely explained by the expected degree of PT because of complicated martensite variants and independent PT induced by heat and stress.

Histological evaluation of direct pulp capping with DSP-derived synthetic peptide in beagle dog / 대한치과보존학회지

The purpose of this study was to investigate the pulpal response to direct pulp capping with dentin sialoprotein (DSP)-derived synthetic peptide in teeth of dogs, and to compare its efficacy to capping substances Ca(OH)2 and white mineral trioxide aggregate (WMTA). A total of 72 teeth of 6 healthy male beagle dogs were used. The mechanically exposed pulps were capped with one of the following: (1) DSP-derived synthetic peptide (PEP group); (2) Ca(OH)2 (CH group); (3) a mixture paste of peptide and Ca(OH)2 (PEP+CH group); or (4) white MTA (WMTA group). The access cavity was restored with a reinforced glass ionomer cement. Two dogs were sacrificed at each pre-determined intervals (2 weeks, 1 month, and 3 months). After the specimens were prepared for standard histological processing, sections were stained with hematoxylin and eosin. Under a light microscope, inflammatory response and hard tissue formation were evaluated in a blind manner by 2 observers. In the PEP group, only 3 of 17 specimens showed hard tissue formation, indication that the DSP-derived synthetic peptide did not induce proper healing of the pulp. Compared with the CH group, the PEP group demonstrated an increased inflammatory response and poor hard tissue formation. The CH and WMTA groups showed similar results for direct pulp capping in mechanically exposed teeth of dogs.

Cuspal deflection in class V cavities restored with composite resins / 대한치과보존학회지

The purpose of this study was to evaluate the effect of the polymerization shrinkage and modulus of elasticity of composites on the cusp deflection of class V restoration in premolars. The sixteen extracted upper premolars were divided into 2 groups with similar size. The amounts of cuspal deflection were measured in Class V cavities restored with a flowable composite (Filtek flow) or a universal hybrid composite (Z-250). The bonded interfaces of the sectioned specimens were observed using a scanning electron microscopy (SEM). The polymerization shrinkage and modulus of elasticity of the composites were measured to find out the effect of physical properties of composite resins on the cuspal deflection. The results were as follows. 1. The amounts of cuspal deflection restored with Filtek flow or Z-250 were 2.18 +/- 0.92 microm and 2.95 +/- 1.13 microm, respectively. Filtek flow showed less cuspal deflection but there was no statistically significant difference (p > 0.05). 2. The two specimens in each group showed gap at the inner portion of the cavity. 3. The polymerization shrinkages of Filtek flow and Z-250 were 4.41% and 2.23% respectively, and the flexural modulus of elasticity of cured Filtek flow (7.77 GPa) was much lower than that of Z-250 (17.43 GPa). 4. The cuspal deflection depends not only on the polymerization shrinkage but also on the modulus of elasticity of composites.

Effect of cavity shape, bond quality and volume on dentin bond strength / 대한치과보존학회지

The aim of this study was to evaluate the effect of cavity shape, bond quality of bonding agent and volume of resin composite on shrinkage stress developed at the cavity floor. This was done by measuring the shear bond strength with respect to iris materials (cavity shape; adhesive-coated dentin as a high C-factor and Teflon-coated metal as a low C-factor), bonding agents (bond quality; Scotchbond(TM) Multi-purpose and Xeno(R)III) and iris hole diameters (volume; 1 mm or 3 mm in diameter x 1.5 mm in thickness). Ninety-six molars were randomly divided into 8 groups (2 x 2 x 2 experimental setup). In order to simulate a Class I cavity, shear bond strength was measured on the flat occlusal dentin surface with irises. The iris hole was filled with Z250 restorative resin composite in a bulk-filling manner. The data was analyzed using three-way ANOVA and the Tukey test. Fracture mode analysis was also done. When the cavity had high C-factor, good bond quality and large volume, the bond strength decreased significantly. The volume of resin composite restricted within the well-bonded cavity walls is also be suggested to be included in the concept of C-factor, as well as the cavity shape and bond quality. Since the bond quality and volume can exaggerate the effect of cavity shape on the shrinkage stress developed at the resin-dentin bond, resin composites must be filled in a method, which minimizes the volume that can increase the C-factor.