Unfilled Resin Research Articles

Synthesis and photopolymerization of piperonylamine derivatives as a polymerizable cyclic acetals co‐initiator for light‐cured unfilled dental resins

AbstractThe aim of this study was to synthesize and characterize N,N‐di(methacryly‐ethoxycarbonyl‐ethyl)‐N‐(1,3‐benzodioxole‐ 5‐methylene)(DMEBM) to replace both triethylene glycol dimethylacrylate(TEGDMA) as a dilute and the non‐polymerizable amine, which is added as a co‐initiator in dental resin mixtures. 2,2‐bis[4‐(2‐Hydroxy‐3‐methacryloxypropoxy) phenyl]‐propane (Bis‐GMA) and camphorquinone (CQ) were used as monomer and photoinitiator in these model dental resin systems, in contrast to ethyl 4‐dimethylaminobenzoate (EDMAB) which was usually used as a co‐initiator. DMEBM was synthesized via Michael‐Addition reaction and characterized using 1H NMR spectroscopy. A mixture of Bis‐GMA/DMEBM/CQ was found to reach the double bond conversion of 67.5%, slightly higher than that of Bis‐GMA/TEGDMA/CQ/EDMAB (66.8%) and Bis‐GMA/TEGDMA/CQ/DMEBM (64.8%). In addition, the glass transition temperature of Bis‐GMA/TEGDMA/CQ/EDMAB (93.4°C) were higher than that of Bis‐GMA/TEGDMA/CQ/DMEBM (89.3 °C) and Bis‐GMA/DMEBM/CQ (80.4°C). The water sorption and solubility of Bis‐GMA/TEGDMA/CQ/DMEBM were higher than that of Bis‐GMA/TEGDMA/CQ/EDMAB and Bis‐GMA/DMEBM/CQ. However, the values were still within the range of the ISO 4049 standards. DMEBM could be used as a potential co‐initiator and diluent for dental composite. Copyright © 2009 John Wiley & Sons, Ltd.

Effect of a fluoridated etchant on the shear bond strength of a composite resin to enamel

The purpose of this study was to evaluate the effect of a fluoridated etching gel on the shear bond strength of a composite resin to enamel. A total of 75 extracted human permanent molars were used. A flat enamel surface was obtained with 600-grit silicon carbide paper and cleaned with a rubber cup and a water slurry of fine flour of pumice. The teeth were randomly distributed into 5 groups of 15 teeth each and etched as follows: group 1: 37% non-fluoridated phosphoric acid gel (Coe) for 60 seconds (control); group 2: 60% phosphoric acid gel with 0.5% NaF (Orthoprep) for 5 seconds; group 3: Orthoprep for 15 seconds; group 4: Orthoprep for 30 seconds; group 5: Orthoprep for 60 seconds. After etching, rinsing and drying, an unfilled resin (Coe Bond) was thinly applied with a brush and cured for 30 seconds. A nylon ring was placed over the area and filled with a light-cured composite resin (Occlusin). The teeth were thermocyled (100x), mounted in plastic cups and plaster, and sheared with a knife-edged blade in an Instron machine running at a crosshead speed of 1 mm/min. The results in MPa were as follows: group 1: 14.49 +/- 4.43; group 2: 10.81 +/- 3.70; group 3: 13.51 +/- 3.21; group 4: 14.79 +/- 3.76; group 5: 15.47 +/- 4.07. An analysis of variance showed that the results in groups 1, 4 and 5 were not significantly different but that the bond strengths in groups 2 and 3 were significantly lower. Fracture within the enamel occurred in 8 specimens in group 1, 5 in group 2, 6 in group 3, 8 in group 4, and 13 in group 5. In the fluoridated etchant groups the number of specimens showing enamel fracture increased as the application time of the etchant increased.

Multiple correlations of material parameters of light-cured dental composites

Objectives The aim of this study was to explore the correlations between the Knoop hardness, Young's modulus, viscosity, and polymerization shrinkage of an experimental dental composite, in order to determine the temporal variations of the material properties during the polymerization process. Methods The digital image correlation method was employed to measure the polymerization shrinkage along the curing depth of bar-shape specimens (cross-section 4 mm × 2 mm and length 10 mm) of an experimental composite RZE045. The shrinkage data were correlated with the Knoop microhardness measured on specimens prepared in consistent conditions. Another series of tests were performed on cuboid composite samples (cross-section 4 mm × 4 mm and height 5 mm) with different degrees of conversions to determine the correlations among microhardness, Young's modulus and viscosity. Further correlations between shrinkage, Young's modulus and viscosity were then derived, from which the temporal variations of the mechanical parameters during curing were estimated. Results Along the curing depth, the Knoop microhardness of the experimental composite RZE045 decreased more rapidly than its volumetric shrinkage. A power function was employed to describe their relation. On the other hand, Knoop microhardness was found to be proportional to Young's modulus and viscosity. These linear correlations also seemed to be applicable to other materials including unfilled resins, silica glass and other dental composites. Significance Correlations between material parameters of dental composites allowed the rapid temporal variations of Young's modulus and viscosity during curing to be estimated based on the measured polymerization shrinkage-strain history.

Simultaneous evaluation of degree of conversion and modulus development of an unfilled resin

Simultaneous evaluation of degree of conversion and modulus development of an unfilled resin

Transmission Electron Microscopic Examination of the Interface Between a Resin-Modified Glass-Ionomer and Er:YAG Laser-Irradiated Dentin

The aim of this study was to analyze the ultrastructural characteristics of the interface between a resin-modified glass ionomer (RMGI) and Er:YAG laser-irradiated dentin. The Er:YAG laser has been considered as a possible alternative for cavity preparation, but the interaction between glass ionomers and Er:YAG-lased dentin still needs further investigation. Five dentin surfaces were prepared by diamond bur (120,000 rpm) as controls or for Er:YAG laser irradiation (31.45 J/cm(2), 200 mJ, 10 Hz, 100 micros). The RMGI Fuji II LC (GC) was then applied to their surfaces, which were previously conditioned with a 20% polyalkenoic acid conditioner. The samples were sealed with an unfilled resin, stored in distilled water for 1 wk at 37 degrees C, and then processed for transmission electron microscopic (TEM) examination. When applied to bur-cut dentin (controls), Fuji II LC was able to partially demineralize the dentin surface, resulting in the formation of a hybrid layer, on top of which a sub-micron gel-phase was observed. In the laser-irradiated samples, the RMGI was in close contact with the irregular dentin substrate, but no hybrid layer or gel-phase formation could be detected, nor were there signs of dentin demineralization or collagen melting. Horizontal cracks were clearly seen in the sub-surface layer of dentin. Although presenting horizontal micro-cracks in its sub-surface, the irregular laser-irradiated dentin showed close contact with the RMGI. However, no hybrid layer or gel-phase could be detected, and there were no signs of dentin demineralization and collagen melting.

Filled and unfilled temperature-dependent epoxy resin blends for lossy transducer substrates

In the context of our ongoing investigation of low-cost 2-dimensional (2-D) arrays, we studied the temperature- dependent acoustic properties of epoxy blends that could serve as an acoustically lossy backing material in compact 2-D array-based devices. This material should be capable of being machined during array manufacture, while also providing adequate signal attenuation to mitigate backing block reverberation artifacts. The acoustic impedance and attenuation of 5 unfilled epoxy blends and 2 filled epoxy blends - tungsten and fiberglass fillers - were analyzed across a 35 degrees C temperature range in 5 degrees C increments. Unfilled epoxy materials possessed an approximately linear variation of impedance and sigmoidal variation of attenuation properties over the range of temperatures of interest. An intermediate epoxy blend was fitted to a quadratic trend line with R(2) values of 0.94 and 0.99 for attenuation and impedance, respectively. It was observed that a fiberglass filler induces a strong quadratic trend in the impedance data with temperature, which results in increased error in the characterization of attenuation and impedance. The tungsten-filled epoxy was not susceptible to such problems because a different method of fabrication was required. At body temperature, the tungsten-filled epoxy could provide a 44 dB attenuation of the round-trip backing block echo in our application, in which the center frequency is 5 MHz and the backing material is 1.1 mm thick. This is an 11 dB increase in attenuation compared with the fiberglass-filled epoxy in the context of our application. This work provides motivation for exploring the use of custom-made tungsten-filled epoxy materials as a substitute PCB-based substrate to provide electrical signal interconnect.

A Study on the Effect of Nano-Magnesium Hydroxide on the Flammability of Epoxy Resins

In this work the effect of nano-magnesium hydroxide (nano-Mg(OH)2) on the flammability of epoxy composites is presented and compared with the traditional flame retardant used in just small amounts for epoxy resins, ammonium polyphosphate (APP). The fire reaction properties of epoxy composites were obtained by cone calorimeter tests. It was observed that the flammability of the unfilled resin is significantly changed with nano-Mg(OH)2 addition and reductions of 33, 22 and 23% in the epoxy composite heat release rate peak (PHRR) by incorporating 10%, 5 % and 1% of nano-Mg(OH)2, respectively, were achieved. Cone calorimeter analyses confirm the better behavior of APP composites compared with nano-Mg(OH)2 composites. SEM micrographs show some agglomerations on the distribution of nano-Mg(OH)2 in the epoxy matrix.

Influence of glutaraldehyde priming on bond strength of an experimental adhesive system applied to wet and dry dentine

Objectives This study tested the following null hypotheses: (1) there is no difference in resin–dentine bond strength when an experimental glutaraldehyde primer solution is added prior to bonding procedures and (2) there is no difference in resin–dentine bond strength when experimental glutaraldehyde/adhesive system is applied under dry or wet demineralized dentine conditions. Methods Extracted human maxillary third molars were selected. Flat, mid-coronal dentine was exposed for bonding and four groups were formed. Two groups were designated for the dry and two for the wet dentine technique: DRY: (1) Group GD: acid etching + glutaraldehyde primer (primer A) + HEMA/ethanol primer (primer B)-under dried dentine + unfilled resin; (2) Group D: the same as GD, except for primer A application; WET: (3) Group GW: the same as GD, but primer B was applied under wet dentine condition; (4) Group W: the same as GW, except for primer A application. The bonding resin was light-cured and a resin core was built up on the adhesive layer. Teeth were then prepared for microtensile bond testing to evaluate bond strength. The data obtained were submitted to ANOVA and Tukey's test ( α = 0.05). Results Glutaraldehyde primer application significantly improved resin–dentine bond strength. No significant difference was observed when the same experimental adhesive system was applied under either dry or wet dentine conditions. These results allow the first null hypothesis to be rejected and the second to be accepted. Conclusion Glutaraldehyde may affect demineralized dentine properties leading to improved resin bonding to wet and dry substrates.

Dynamic Mechanical Performances of Polyester—Clay Nanocomposite Thick Films

Dynamic mechanical properties of polyester—montmorillonite nanocomposite thick films, prepared by the in situ intercalative polymerization method, were evaluated in a tensile mode. A fast fabrication procedure was chosen to allow industrial applications. A total time less than 1 h was sufficient to obtain a thick film which could be cut for the specimen preparation. The final films had a thickness of 250 μm and a nano-clay content ranging from 0 to 10 wt%. A differential scanning calorimeter was used to investigate the effect of the clay content on the resin polymerization kinetics whereas tensile tests were performed to make a comparison with dynamic mechanical results. The maximum in the mechanical performances was obtained at the clay content of 1 wt% at which an increase of about 55% for the storage modulus was measured in comparison with the unfilled resin.

Organophilic Layered Silicate Modified Vinylester-Urethane Hybrid Resins: Structure and Properties

A commercial vinylester-urethane (VEUH) hybrid resin was modified with organophilic layered silicates (OLS), incorporated in various amounts (0.1 to 5 wt.%). As organophilic intercalants of the layered silicate (synthetic fluorohectorite) trimethyl dodecylamine (TMDA) and octadecylamine - N,N-bis[allyl(2-hydroxypropyl)ether] (OAE) served. The latter quaternary amine was expected to support the intercalation/exfoliation of the silicate by participating in the crosslinking reactions. Both OLS types became intercalated based on X-ray diffractograms (XRD). Dynamic-mechanical thermal analysis (DMTA) displayed a slight increase in the stiffness by adding OLS up to 2.5 wt.%. However, at 5wt% OLS content the stiffness of the nanocomposites was below that of the unfilled hybrid resin. The glass transition temperature (Tg) did not change practically with the OLS type and content. Fracture mechanical tests were performed on compact tension (CT) specimens. The fracture toughness (Kc) increased slightly, while the fracture energy (Gc) markedly with increasing OLS content. Unexpectedly, TMDA proved to be a more suitable intercalant than OAE. The failure mode of the specimens was studied in a scanning electron microscope (SEM) and discussed. In addition, the water sorption behavior of the OLS modified VEUHs was determined and the diffusion coefficients (D) deduced.

Adhesion of Streptococcus mutans NCTC 10449 to artificial teeth: An in vitro study

Plaque on dentures may foster the occurrence of denture stomatitis and periodontal diseases in gingival tissues adjacent to partial dentures. Thus, it is beneficial for dental materials to have a low susceptibility to plaque adhesion. The purpose of this study was to evaluate the susceptibility of commonly used artificial teeth to adhesion of the oral bacterium Streptococcus mutans. Fifteen specimens each of 12 different artificial teeth were prepared by cutting standardized slabs from the buccal tooth surfaces. After normalizing size (round specimens, diameter of 5 mm, 2 mm thick), polishing (grinding paper, grain 1000 and 4000; universal polishing paste), and assessing surface roughness with a profilometric contact surface measurement device, specimens were incubated with Streptococcus mutans NCTC 10449 suspension for 2.5 hours at 37 degrees C. A veneering composite resin (Sinfony) was used as a control. Adherent bacteria were quantified using a fluorometric assay (Resazurin reduction); relative fluorescence intensity correlates linearly with the number of adherent bacteria. Medians and 25%/75% percentiles were calculated, and statistical analysis was performed using the Kruskal-Wallis test and the Bonferroni-adjusted Mann-Whitney U test. The highest values, indicating high adhesion of streptococci, were observed for filler-supplemented teeth with median relative fluorescence values ranging from 6356 to 18,770. Similar values were recorded for a double cross-linked resin tooth (6444). Significantly lowest values, ranging from 1173 to 3974, were found for unfilled PMMA acrylic resin teeth and acrylic resin teeth with an interpenetrating network (1436). Within the limitations of this study, it can be concluded that the adhesion of Streptococcus mutans to unfilled PMMA teeth and teeth with an interpenetrating network is lower than adhesion to artificial teeth supplemented with fillers or double cross-linked acrylic resin teeth.

Influence of thermal expansion on shrinkage during photopolymerization of dental resins based on bis-GMA/TEGDMA

Objective The aim of this study was to assess volume changes that occur during photopolymerization of unfilled dental resins based on bis-GMA-TEGDMA. Methods The resins were activated for visible light polymerization by the addition of camphorquinone (CQ) in combination with dimethylamino ethylmethacrylate (DMAEMA) or ethyl-4-dimethyl aminobenzoate (EDMAB). A fibre-optic sensing method based on a Fizeau-type interferometric scheme was employed for monitoring contraction during photopolymerization. Measurements were carried out on 10 mm diameter specimens of different thicknesses (1 and 2 mm). Results The high exothermic nature of the polymerization resulted in volume expansion during the heating, and this effect was more pronounced when the sample thickness increased. Two approaches to assess volume changes due to thermal effects are presented. Due to the difference in thermal expansion coefficients between the rubbery and glassy resins, the increase of volume due to thermal expansion was greater than the decrease in volume due to thermal contraction. As a result, the volume of the vitrified resins was greater than that calculated from polymerization contraction. The observed trends of shrinkage versus sample thickness are explained in terms of light attenuation across the path length during photopolymerization. Significance Results obtained in this research highlight the inherent interlinking of non-isothermal photopolymerization and volumetric changes in bulk polymerizing systems.

Nanocomposites based on epoxy resin and silicon dioxide particles

The cure of an epoxy resin (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate) in the presence of silica nanoparticles modified by 3-(triethoxysilyl)propylsuccinic anhydride has been studied. Optimal conditions for the preparation of optically transparent polymer nanocomposites with increased glass transition temperatures are determined. The glass transition temperatures of the above nanocomposites are 50–70°C higher than those of the unfilled epoxy resin synthesized under the same conditions (100°C).

Preparation of MWCNT reinforced epoxy nanocomposite and examination of its mechanical properties

Multiwalled carbon nanotube (MWCNT) reinforced and unfilled epoxy resins were prepared. Viscosity tests were run on the MWCNT filled and unfilled resins, comparative tensile, three point bending and Charpy impact tests were performed. The viscosity of MWCNT filled epoxy resin has increased by from three to one order of magnitude from the lowest to higher shear rate compared to unfilled epoxy. Owing to this, the simple cast specimen preparation was not applicable in the case of MWCNT filled epoxy; instead of that, a resin injection method was used. According to the results of the mechanical tests, tensile strength has decreased by 4·6% caused probably indirectly by nanotube filling of the resin, but Young's modulus, bending modulus and Charpy impact strength, which characterise resistance against dynamic loads, have increased by 12, 10 and 20% respectively.

Preparation of MWCNT/Carbon Fabric Reinforced Hybrid Nanocomposite and Examination of its Mechanical Properties

In our work we have prepared carbon fiber/epoxy composite and carbon fiber/carbon nanotube/epoxy hybrid nanocomposite laminates by hand laminating assisted by vacuumbag technology. During the production of the specimens we have encountered the viscosity increasing effect of nanotube filling, which we characterized by a viscosity test. The results of the test showed, that in the lowest shear rate range carbon nanotube filling can cause an increase of viscosity by three orders of magnitude, but also at higher shear rates the viscosity of the nanotube filled epoxy resin was ten times the viscosity of the unfilled resin. Mechanical properties of the composite and hybrid composite have been compared by tensile, bending and interlaminar shear tests. During the tensile tests AE signals have also been recorded. The fracture surfaces have been examined by SEM micrographs. The nanotube filling has decreased the tensile strength and the modulus of elasticity by 7-8 percent presumably indirectly, the bending properties didn’t change noticeably, but the interlaminar shear strength of the composite has increased by 15 percent thanks to nanotube filling of the matrix. The decrease of the delamination inclination of the hybrid composite has been affirmed both by the AE and SEM results.

Chlorhexidine release and water sorption characteristics of chlorhexidine-incorporated hydrophobic/hydrophilic resins

Objectives The aim of this study was to evaluate chlorhexidine release from unfilled non-solvated methacrylate-based resins of increasing hydrophilicity and to examine relationships among Hoy's solubility parameters, water sorption, solubility and the rate of chlorhexidine release. Methods Resin discs were prepared from light-cured, experimental resin blends (R1, R2, R3, R4 and R5) containing 0.0, 0.2, 1.0 and 2.0 wt.% chlorhexidine diacetate (CDA). Discs were immersed in distilled water at 37 °C, and mass changes were recorded at different periods. Spectral measurements were made to follow change in optical densities of storage solution to examine chlorhexidine release kinetics. After a 28-day period, water sorption, solubility, and the cumulative chlorhexidine release were obtained. Additionally, antibacterial study was performed by observing the presence of inhibition zone against Streptococcus mutans. Results The most hydrophilic resin (R5) exhibited the highest chlorhexidine release rate. The most hydrophobic resin (R1) exhibited the lowest rate. However, no inhibition zone was produced by any specimens stored in water for 2 weeks. The addition of CDA increased solubility significantly but had no effect on water sorption. Significant positive correlations were seen between water sorption and the cumulative chlorhexidine release. Significance Chlorhexidine release from resins may be related to water-induced swelling, which in turn is enhanced by the hydrophilicity of cured polymer matrix.

The Dielectric Response of Polar and Non-Polar Nanodielectrics

In order to understand the relationship between the dielectric properties and the structure of polymer nanocomposites, especially the role of the interface on dielectric response, two polymers with different polarity were used to form nanocomposites with nanoalumina powder, a typical polar inorganic compound. Consequently, two kinds of nanodielectrics with very different interfaces were produced. In the epoxy nanodielectric, broad band dielectric spectroscopic measurements show that no difference is found between the unfilled resin and the nanocomposite under dry conditions. However, their dielectric responses are very different when they contain about 0.4 % b.w. absorbed water, a concentration that occurs under ambient exposure conditions. The findings suggest that the sites for absorbed water in the epoxy nanocomposites are very different to those in the unfilled thermoset and relate to the large interfacial internal surface in these materials. In this case all the relaxation processes can be well described by the Havriliak-Negami function, which give useful information on the dynamics and activation energies associated with the relaxation processes. In polyethylene nanocomposites, dielectric measurements show that the incorporation of nanoalumina produces a dielectric loss peak in the low frequency. This relaxation peak moves to high frequency with increasing nanoalumina content and the peak becomes broader. In the presence of 0.06 % b.w. absorbed water this peak also shows the same type of unusual dielectric loss behavior as that observed in the undried epoxy nanodielectrics. This behavior is thought to arise from the interplay between interfacial water mobility and bonding rather than the host polymer.

Inhibition of enamel demineralization by an enamel sealant, Pro Seal: An in-vitro study

Enamel demineralization adjacent to fixed orthodontic appliances compromises both esthetics and oral health. The purpose of this in-vitro study was to evaluate the effectiveness of a new enamel sealant, Pro Seal (Reliance Orthodontic Products, Itasca, Ill), on inhibiting enamel demineralization. Two materials that have demonstrated success in white spot prevention and do not require patient compliance were used for comparison. Thirty-two noncarious extracted molars were divided into 4 groups and received 1 of the following treatments: no treatment (control), fluoride varnish (Fluor Protector; Ivoclar Vivadent, Amherst, Mass), unfilled resin sealant (Delton; Dentsply Professional, York, Pa), and filled resin sealant (Pro Seal). The teeth were subjected to 15,000 simulated brush strokes followed by acidic challenge for 96 hours. They were examined macroscopically and sectioned for quantitative examination with polarized light microscopy. All surface treatments provided statistically significant (P <.05) reductions in lesion depth compared with controls. Pro Seal performed significantly better (P <.05) than the other products, decreasing lesion depth by 97% compared with the controls and completely inhibiting lesion formation in 3 specimens. Pro Seal shows promise as an effective method of preventing enamel demineralization without patient compliance.

The elastic moduli across various types of resin/dentin interfaces

Objective The purpose of this study was to evaluate the elastic moduli of an unfilled adhesive resin (Adper™ Single Bond) and a filled adhesive resin (Adper™ Single Bond 2) used with and without a low-viscosity resin (LVR) (Filtek™ Flow) as an elastic cavity wall in class V composite restorations, restored with a hybrid resin composite (Z250). Methods Buccal class V cavities were prepared on extracted premolars and lined with (1) the unfilled adhesive resin, (2) the filled adhesive resin, (3) the unfilled adhesive resin and the flowable composite, and (4) the filled adhesive resin and the flowable composite. All cavities were restored with the hybrid resin composite. The specimens were cut bucco-lingually, embedded in epoxy resin and polished. The polished specimens were evaluated for the elastic modulus with nano-indentation test at the layer of dentin, hybrid layer, adhesive resin, low-viscosity resin and resin composite. Results The elastic moduli were 25,111 MPa for dentin, 12,243 MPa for hybrid layer of Adper™ Single Bond, 11,765 MPa for hybrid layer of Adper™ Single Bond 2, 7595 MPa for Adper™ Single Bond, 8430 MPa for Adper™ Single Bond 2, 13,543 MPa for Filtek™ Flow and 24,494 MPa for Filtek™ Z250 resin composite. The statistical analysis demonstrated that the elastic moduli were significantly different among layers ( p < 0.05) except between hybrid layers of unfilled and filled adhesives ( p = 1.0). Conclusion The application of filled adhesive did not increase the elastic modulus of hybrid layer when compared with the unfilled adhesive resin. The modulus of filled adhesive resin was significantly higher than that of unfilled adhesive resin.

Bond strength analysis of custom base variables in indirect bonding techniques

Various methods are used to prepare the cured composite-adhesive interface for orthodontic indirect bonding. The intent of this study was to determine the effect on the shear bond strength of the following variables: use of a filled flowable composite resin as an adhesive, light air-abrasion of the cured composite bracket pad, and wetting the cured composite bracket pad with an unfilled resin. The sample of 240 brackets was divided into 2 groups of 120 each. The first group was further divided into 4 groups of 30 each. Brackets were bonded to bovine incisors with a filled flowable composite resin (Filtek, 3M ESPE, St Paul Minn), but the bracket pads were prepared differently in the 4 groups: unfilled resin was applied (Orthosolo, Ormco, Glendora, Calif), the surface was air abraded, the surface was air abraded followed by application of an unfilled resin (Orthosolo), and a control group. A matching sample of 120 brackets was bonded without the flowable composite as an adhesive. The different bracket pad preparations were chosen to represent the various techniques clinicians use in indirect bonding. The shear bond strength was measured on a universal testing machine. Two-way ANOVA analysis showed significant differences in the shear bond strength among the different surface preparations, but not between the use and nonuse of flowable composite. The Scheffé test showed that the mean shear bond strength of the air-abraded surface was significantly higher than all other surface preparations. Air abrading orthodontic bracket-pad composite surfaces in indirect bonding increased the shear bond strength, whereas the use of flowable composite did not affect bond strengths.