Frictional Forces of Three Types of Lingual Appliance with Self-ligating Mechanisms.

AIM AND OBJECTIVE: The present study compared the frictional forces of three types of self-ligating lingual appliances. MATERIALS AND METHODS: The lingual appliances (2D, Forestadent; Alias, Ormco; and Clippy L, Tomy International) consisted of a self-ligating bracket (second premolar) and two self-ligating tubes (first and second molars) bonded to a stainless steel jig and attached to a "drawing-friction tester." Full-size and non-full-size stainless steel archwires were tested, and the static and kinetic friction acting on six lingual appliance/wire combinations was estimated (n = 5). Three-dimensional micro-computed tomography (micro-CT) analysis of each premolar bracket was performed. The frictional forces were compared between the bracket/wire combinations using the Kruskal-Wallis and Mann-Whitney U tests. RESULTS: The Alias and Clippy L bracket/wire combinations had greater contact between the wire surfaces and bracket slots compared to the 2D bracket/wire combination. For all lingual appliances, the static and kinetic frictional forces were significantly higher for the full-size than non-full-size archwire. The 2D bracket, which had a wider outer wing, had less frictional force than the other appliances. The Alias, which had a narrower outer wing, had a significantly lower frictional force than the Clippy L. CONCLUSIONS: Frictional force was significantly higher for heavier full-size bracket/archwire combinations than for non-full-size archwires. The 2D bracket had lower frictional force due to its archwire-holding mechanism. The outer wing width may influence the frictional resistance. CLINICAL SIGNIFICANCE: The frictional forces of self-ligating lingual appliances vary, and bracket design and archwire size may influence the frictional performance.

Effects of bioactive glass coating by electrophoretic deposition on esthetical, bending, and frictional performance of orthodontic stainless steel wire.

We investigated the surface modification of orthodontic stainless steel wire using electrophoretic deposition (EPD) of bioactive glass (BG). BG coatings were characterized by spectrophotometry, three-dimensional (3D) focal laser scanning microscopy and scanning electron microscopy. The mechanical properties of the BG-coated wires were estimated nanoindentation, three-point bending and drawing friction tests. BG-coated specimens prepared at higher voltage showed higher values for both reflectance and L* compared to those prepared at lower voltage. Specimens coated at higher voltage had significantly lower surface roughness than those coated at lower voltage, and their BG layers had higher hardness and elastic modulus values. In the three-point bending test, BG-coated wires produced significantly lower elastic modulus than non-coated wires. Most BG-coated specimens produced similar frictional forces to those produced by non-coated specimens. The surface modification technique applying EPD and BG coating to orthodontic stainless steel wire could be used to develop new esthetical orthodontic wire.

Wear characteristics and inhibition of enamel demineralization by resin-based coating materials.

In this study, wear and inhibition of enamel demineralization by resin-based coating materials were investigated. Seven commercially available coating materials, with and without fillers, were used. A mechanical wear test was performed, and the specimens were then examined with a scanning electron microscope. Hardness and elastic modulus measurements for each material were obtained by nanoindentation testing. Thin layers of each material were applied on human enamel surfaces, which were subjected to alternating immersion in demineralizing and remineralizing solutions. The inhibition ability of enamel demineralization adjacent to the coating was estimated with depth-dependent mechanical properties using the nanoindentation test. The non-filled coating material showed significantly lower hardness, lower elastic modulus, and higher weight loss. There were no significant differences in weight loss among the six filled coating materials. After the alternating immersion protocol, the enamel specimens having application of coating materials with ion-releasing ability were harder than those in the other groups in some locations 1-11 µm from the enamel surface and within 300 µm from the edge of the coating materials. In conclusion, clinical use of the resin-based coating materials with ion-releasing ability may prevent demineralization of exposed enamel adjacent to the coating during treatment.

Effects of chitosan fiber addition on the properties of polyurethane with thermo-responsive shape memory.

We investigated the effects of the addition of chitosan fiber (biomass nanofiber made by Sugino (BiNFi-s)) to polyether-based thermoplastic polyurethane (TPU) on material properties. BiNFi-s (2 and 5 wt %)/TPU composite materials were prepared via compression molding, and glass fiber (2 and 5 wt %)/TPU composite materials and plain TPU were also prepared for comparison. The glass transition temperature was analyzed using differential scanning calorimetry, and the crystal structure was investigated using X-ray diffraction. 20-mm-long test specimens with cross-sectional dimensions of 1 mm × 1 mm were cut from sheets of the composite materials, and three-point bending tests were carried out using a universal testing machine to investigate their mechanical properties and shape memory. The addition of BiNFi-s or glass fiber to TPU did not influence the glass transition temperature, although the crystal structure changed from semi-crystalline to amorphous. The elastic modulus increased 40% by the addition of 5 wt % BiNFi-s (2.31 MPa) compared with plain TPU (1.65 MPa), and these composites exhibited shape recovery with clinically relevant changes in temperature. The addition of 5 wt % BiNFi-s into TPU resulted in an improvement in the elastic modulus without any decrease in the shape memory effect. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1151-1156, 2017.

Characterization of the coatings covering esthetic orthodontic archwires and their influence on the bending and frictional properties.

OBJECTIVE: To analyze the coatings covering esthetic orthodontic wires and the influence of such coatings on bending and frictional properties. MATERIALS AND METHODS: Four commercially available, coated esthetic archwires were evaluated for their cross-sectional dimensions, surface roughness (Ra), nanomechanical properties (nanohardness, nanoelastic modulus), three-point bending, and static frictional force. Matched, noncoated control wires were also assessed. RESULTS: One of the coated wires had a similar inner core dimension and elasticity compared to the noncoated control wire, and no significant differences between their static frictional forces were observed. The other coated wires had significantly smaller inner cores and lower elasticity compared to the noncoated wires, and one of them showed less static frictional force than the noncoated wire, while the other two coated wires had greater static frictional force compared to their noncoated controls. The dimension and elastic modulus of the inner cores were positively correlated (r = 0.640), as were frictional force and total cross-sectional (r = 0.761) or inner core (r = 0.709) dimension, elastic modulus (r = 0.777), nanohardness (r = 0.802), and nanoelastic modulus (r = 0.926). The external surfaces of the coated wires were rougher than those of their matched controls, and the Ra and frictional force were negatively correlated (r = -0.333). CONCLUSIONS: Orthodontic coated wires with small inner alloy cores withstand less force than expected and may be unsuitable for establishing sufficient tooth movement. The frictional force of coated wires is influenced by total cross-section diameter, inner core diameter, nanohardness, nanoelastic modulus, and elastic modulus.

Inhibition of enamel demineralization and bond-strength properties of bioactive glass containing 4-META/MMA-TBB-based resin adhesive.

We investigated the enamel demineralization-prevention ability and shear bond strength (SBS) properties of 4-methacryloxyethyl trimellitic anhydride/methyl methacrylate-tri-n-butyl borane (4-META/MMA-TBB)-based resin containing various amounts (0-50%) of bioactive glass (BG). Disk-shaped specimens were immersed in distilled water and ions released were analysed by inductively coupled plasma atomic-emission spectroscopy. Samples were also immersed in lactic acid solution (pH 4.6) to estimate acid-neutralizing ability. Brackets were bonded to human premolars with BG-containing resins and the bonded teeth were alternately immersed in demineralizing (pH 4.55) and remineralizing (pH 6.8) solutions for 14 d. The enamel hardness was determined by nanoindentation testing at twenty equidistant distances from the external surface. The SBS for each sample was examined. The amounts of ions released [calcium (Ca), sodium (Na), silicon (Si), and boron (B)] and the acid-neutralizing ability increased with increasing BG content. After alternating immersion, the specimens bonded with the BG-containing resin with high BG content were harder than those in the other groups in some locations 1-18.5 µm from the enamel surface. Bioactive glass-containing (10-40%) resin had bond strength equivalent to the control specimen. Thus, the SBS obtained for BG-containing resin (6.5-9.2 MPa) was clinically acceptable, suggesting that this material has the ability to prevent enamel demineralization.

Effects of temperature changes and stress loading on the mechanical and shape memory properties of thermoplastic materials with different glass transition behaviours and crystal structures.

BACKGROUND/OBJECTIVE: To investigate the effects of temperature changes and stress loading on the mechanical and shape memory properties of thermoplastic materials with different glass transition behaviours and crystal structures. MATERIALS/METHODS: Five thermoplastic materials, polyethylene terephthalate glycol (Duran®, Scheu Dental), polypropylene (Hardcast®, Scheu Dental), and polyurethane (SMP MM®, SMP Technologies) with three different glass transition temperatures (T g) were selected. The T g and crystal structure were assessed using differential scanning calorimetry and X-ray diffraction. The deterioration of mechanical properties by thermal cycling and the orthodontic forces during stepwise temperature changes were investigated using nanoindentation testing and custom-made force-measuring system. The mechanical properties were also evaluated by three-point bending tests; shape recovery with heating was then investigated. RESULTS: The mechanical properties for each material were decreased significantly by 2500 cycles and great decrease was observed for Hardcast (crystal plastic) with higher T g (155.5°C) and PU 1 (crystalline or semi-crystalline plastic) with lower T g (29.6°C). The Duran, PU 2, and PU 3 with intermediate T g (75.3°C for Duran, 56.5°C for PU 2, and 80.7°C for PU 3) showed relatively stable mechanical properties with thermal cycling. The polyurethane polymers showed perfect shape memory effect within the range of intraoral temperature changes. The orthodontic force produced by thermoplastic appliances decreased with the stepwise temperature change for all materials. CONCLUSIONS/IMPLICATIONS: Orthodontic forces delivered by thermoplastic appliances may influence by the T g of the materials, but not the crystal structure. Polyurethane is attractive thermoplastic materials due to their unique shape memory phenomenon, but stress relaxation with temperature changes is expected.

High-cycle fatigue behavior of beta-titanium orthodontic wires.

This study investigated high-cycle fatigue behavior in three ß-Ti wires (TMA, Resolve, Gummetal). Fatigue was evaluated using a static three-point bending test and a high-cycle fatigue test with a three-point bending mode. The surfaces of fractured wires were observed with scanning electron microscopy, and the post-fatigue crystal structures were determined by micro-X-ray diffraction. The Gummetal wire exhibited the lowest elastic modulus, bending strength and fatigue limit, and exhibited the highest resilience of the three types of wire studied. However, no difference in the number of cycles to failure was observed among the three types of wire. The fatigue crack propagation and rapid propagation regions of all wires contained single-phase ß-Ti. The elastic modulus and bending strength influenced the fatigue limit, although these properties did not affect the number of cycles to fracture. The three types of ß-Ti wires exhibited similar risks of wire fracture.

In vivo degradation of orthodontic miniscrew implants: surface analysis of as-received and retrieved specimens.

This study investigated in vivo degradation of Ti-6Al-4V alloy miniscrew implants. Miniscrew implants were placed in patients, and the surfaces were studied upon retrieval by scanning electron microscopy, microscale X-ray photoelectron spectroscopy, elastic recoil detection analysis and nanoindentation testing. Bone-like structures were formed on the retrieved specimens. The hardness and elastic modulus of the surfaces of the retrieved specimens were significantly lower than the as-received specimens, although no statistically significant differences were observed for the hardness and elastic modulus in the bulk region. Thick organic over-layer containing carbon, oxygen, and nitrogen, with the thickness greater than 50 nm, covered the retrieved specimens, and higher concentrations of hydrogen were detected in the retrieved specimens compared with the as-received specimens. Minimal degradation of the bulk mechanical properties of miniscrew implants was observed after clinical use, although precipitation of bone-like structures, formation of a carbonaceous contamination layer, and hydrogen absorption were observed on the surfaces of miniscrew implants.

Effects of immersion in solution of an experimental toothpaste containing S-PRG filler on like-remineralizing ability of etched enamel.

This study investigated the like-remineralizing ability of experimental toothpaste containing surface reaction-type pre-reacted glassionomer (S-PRG) filler on etched enamel. Human enamel blocks were etched with 35% phosphoric acid and immersed in 5-mL distilled water, fourfold diluted solution of NaF-containing toothpaste, or S-PRG filler-containing experimental toothpaste. Nanoindentation testing was carried out during immersion and the enamel surfaces were observed by scanning electron microscopy. Elemental analysis of the ions in each solution was performed using inductively coupled plasma atomic emission spectroscopy and fluoride electrode. After 1 month of immersion, the hardness and elastic modulus of the specimen immersed in S-PRG filler-containing toothpaste showed significantly greater values than those of the specimen immersed in NaF-containing toothpaste. Considerable amounts of Al, B, Na, Si, Sr, F ions were detected in the solution of S-PRG filler-containing toothpaste. Experimental S-PRG filler-containing toothpaste may enhance the like-remineralizing ability of etched enamel surfaces due to its ion-releasing ability.

Effects of third-order torque on frictional force of self-ligating brackets.

OBJECTIVE: To investigate the effects of third-order torque on frictional properties of self-ligating brackets (SLBs). MATERIALS AND METHODS: Three SLBs (two passive and one active) and three archwires (0.016 × 0.022-inch nickel-titanium, and 0.017 × 0.025-inch and 0.019 × 0.025-inch stainless steel) were used. Static friction was measured by drawing archwires though bracket slots with four torque levels (0°, 10°, 20°, 30°), using a mechanical testing machine (n  =  10). A conventional stainless-steel bracket was used for comparison. RESULTS were subjected to Kruskal-Wallis and Mann-Whitney U-tests. Contact between the bracket and wire was studied using a scanning electron microscope. RESULTS: In most bracket-wire combinations, increasing the torque produced a significant increase in static friction. Most SLB-wire combinations at all torques produced less friction than that from the conventional bracket. Active-type SLB-wire combinations showed higher friction than that from passive-type SLB-wire combinations in most conditions. When increasing the torque, more contact between the wall of a bracket slot and the edge of a wire was observed for all bracket types. CONCLUSIONS: Increasing torque when using SLBs causes an increase in friction, since contact between the bracket slot wall and the wire edge becomes greater; the design of brackets influences static friction.

Crystal growth on bioactive glass sputter-coated alumina in artificial saliva.

In this work, a bioactive glass was deposited on the alumina disk specimens by radio-frequency magnetron sputtering to study crystal formation ability in artificial saliva. Bioactive glass-coated specimens were immersed in artificial saliva for 1 week and 6 months. The specimens were observed with a scanning electron microscope (SEM) and the composition was determined by energy dispersive spectroscopy (EDS). The crystals that formed on the specimens were analyzed by Raman spectroscopic analysis and Micro-X-ray diffraction. SEM photomicrographs showed the formation of needle-like structures after immersion for 1 week, and tabular structures formed on the surface of the specimen for 6 months. EDS showed that both the needle-like and tabular structures were enriched with Ca and P. Raman and Micro-XRD spectra for the tabular structure showed peaks that may correspond to calcium phosphate. Thus, when immersed in artificial saliva, bioactive glass-coated alumina produced a crystal which might be calcium phosphate.

Effects of the addition of fluoride to a 4-META/MMA-TBB-based resin adhesive on fluoride release, acid resistance of enamel and shear bond strength in vitro.

This study investigated fluoride release, acid resistance and shear bond strength (SBS) of new 4-META/MMA-TBB-based fluoride-containing resin adhesive (Super-Bond/F3). Super-Bond, Transbond Plus and Fuji Ortho LC were selected for comparison. Fluoride release into distilled water during 6-month period was measured using disk-shaped specimens. Brackets were bonded to human premolars with each material and then the specimens for the nanoindentation test were subjected to alternating immersion (demineralizing and remineralizing solutions); the hardness and elastic modulus of the enamel around bracket were determined. Rest of the specimens was subjected to examine the SBS. Super-Bond/F3 and Fuji Ortho LC showed significantly greater fluoride release compared with the other materials. The reductions in hardness and the elastic modulus for Super-Bond/F3 and Fuji Ortho LC were lower than those for the other materilas. Super-Bond and Super-Bond/F3 showed significantly greater SBS than Fuji Ortho FC. In conclusion, Super-Bond/F3 showed high fluoride-release, cariostatic potential and equivalent SBS.

Reduced cell number in the hindgut epithelium disrupts hindgut left-right asymmetry in a mutant of pebble, encoding a RhoGEF, in Drosophila embryos.

Animals often show left-right (LR) asymmetry in their body structures. In some vertebrates, the mechanisms underlying LR symmetry breaking and the subsequent signals responsible for LR asymmetric development are well understood. However, in invertebrates, the molecular bases of these processes are largely unknown. Therefore, we have been studying the genetic pathway of LR asymmetric development in Drosophila. The embryonic gut is the first organ that shows directional LR asymmetry during Drosophila development. We performed a genetic screen to identify mutations affecting LR asymmetric development of the embryonic gut. From this screen, we isolated pebble (pbl), which encodes a homolog of a mammalian RhoGEF, Ect2. The laterality of the hindgut was randomized in embryos homozygous for a null mutant of pbl. Pbl is a multi-functional protein required for cytokinesis and the epithelial-to-mesenchymal transition in Drosophila. Consistent with Pbl's role in cytokinesis, we found reduced numbers of cells in the hindgut epithelium in pbl homozygous embryos. The specific expression of pbl in the hindgut epithelium, but not in other tissues, rescued the LR defects and reduced cell number in embryonic pbl homozygotes. Embryos homozygous for string (stg), a mutant that reduces cell number through a different mechanism, also showed LR defects of the hindgut. However, the reduction in cell number in the pbl mutants was not accompanied by defects in the specification of hindgut epithelial tissues or their integrity. Based on these results, we speculate that the reduction in cell number may be one reason for the LR asymmetry defect of the pbl hindgut, although we cannot exclude contributions from other functions of Pbl, including regulation of the actin cytoskeleton through its RhoGEF activity.

Effect of the quantity and quality of cortical bone on the failure force of a miniscrew implant.

This study examined the influence of the quantity and quality of cortical bone on the failure force of miniscrew implants. Twenty-six titanium alloy miniscrew implants (AbsoAnchor) 1.4mm in diameter and 5 or 7 mm long were placed in cross-sectioned maxillae (n = 6) and mandibles (n = 20) of human cadavers. Computed tomography imaging was used to estimate the cortical bone thickness and bone mineral density [total bone mineral density (TBMD, values obtained from cortical bone plus trabecular bone); cortical bone mineral density (CBMD, values obtained from only cortical bone)]. Maximum force at failure was measured in a shear test. Nanoindentation tests were performed to measure the hardness and elastic modulus of cortical bone around the miniscrew implants. The mean failure force of miniscrew implants placed in mandibles was significantly greater than that for implants in maxillae, and the bone hardness of mandibles was significantly greater than that of maxillae. The length of miniscrew implants did not influence the mean failure force in monocortical placement in the mandible. Cortical bone thickness, TBMD, CBMD, and bone hardness were significantly related to the mean failure force. CBMD was related to the mechanical properties of cortical bone. In conclusion, the quantity and quality of cortical bone greatly influenced the failure force of miniscrew implants.

Effect of immediate loading on the biomechanical properties of bone surrounding the miniscrew implants.

The aim of this study was to investigate the effect of immediate loading on the biomechanical properties of bone surrounding a miniscrew implant. Forty titanium alloy miniscrew implants were placed on the buccal side of the maxillae and mandibles in four beagle dogs. Twelve pairs of miniscrew implants were immediately loaded with approximately 150 g of continuous force using nickel-titanium coil springs and the remaining 16 implants were left unloaded for 8 weeks. Nanoindentation testing was performed (peak load 10 mN) and the hardness and elastic modulus were calculated. Two series of indentations (in cortical and trabecular bone) for both the compression and tension sides were made. For each site, five indentations were placed approximately 25 µm from the implant-bone interface and 250 µm from the screw thread. The mean hardness and elastic modulus were generally higher in mandibles than maxillae and were higher in cortical bone than in trabecular bone. The trabecular bone near the implant-bone interface on the compression side was significantly harder than that at other locations in trabecular bone. In conclusion, this is the first study that has investigated the biomechanical properties of bone surrounding a miniscrew implant under immediate loading using nanoindentation testing. The mechanical properties of bone surrounding a miniscrew implant may be influenced by immediate loading.

Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances.

OBJECTIVE: To measure the forces delivered by thermoplastic appliances made from three materials and investigate effects of mechanical properties, material thickness, and amount of activation on orthodontic forces. MATERIALS AND METHODS: Three thermoplastic materials, Duran (Scheu Dental), Erkodur (Erkodent Erich Kopp GmbH), and Hardcast (Scheu Dental), with two different thicknesses were selected. Values of elastic modulus and hardness were obtained from nanoindentation measurements at 28°C. A custom-fabricated system with a force sensor was employed to obtain measurements of in vitro force delivered by the thermoplastic appliances for 0.5-mm and 1.0-mm activation for bodily tooth movement. Experimental results were subjected to several statistical analyses. RESULTS: Hardcast had significantly lower elastic modulus and hardness than Duran and Erkodur, whose properties were not significantly different. Appliances fabricated from thicker material (0.75 mm or 0.8 mm) always produced significantly greater force than those fabricated from thinner material (0.4 mm or 0.5 mm). Appliances with 1.0-mm activation produced significantly lower force than those with 0.5-mm activation, except for 0.4-mm thick Hardcast appliances. A strong correlation was found between mechanical properties of the thermoplastic materials and force produced by the appliances. CONCLUSIONS: Orthodontic forces delivered by thermoplastic appliances depend on the material, thickness, and amount of activation. Mechanical properties of the polymers obtained by nanoindentation testing are predictive of force delivery by these appliances.

Frictional and mechanical properties of diamond-like carbon-coated orthodontic brackets.

This study investigated the effects of a diamond-like carbon (DLC) coating on frictional and mechanical properties of orthodontic brackets. DLC films were deposited on stainless steel brackets using the plasma-based ion implantation/deposition (PBIID) method under two different atmospheric conditions. As-received metal brackets served as the control. Two sizes of stainless steel archwires, 0.018 inch diameter and 0.017 × 0.025 inch cross-section dimensions, were used for measuring static and kinetic friction by drawing the archwires through the bracket slots, using a mechanical testing machine (n = 10). The DLC-coated brackets were observed with a scanning electron microscope (SEM). Values of hardness and elastic modulus were obtained by nanoindentation testing (n = 10). Friction forces were compared by one-way analysis of variance and the Scheffé test. The hardness and elastic modulus of the brackets were compared using Kruskal-Wallis and Mann-Whitney U-tests. SEM photomicrographs showed DLC layers on the bracket surfaces with thickness of approximately 5-7 µm. DLC-coated brackets deposited under condition 2 showed significantly less static frictional force for the stainless steel wire with 0.017 × 0.025 inch cross-section dimensions than as-received brackets and DLC-coated brackets deposited under condition 1, although both DLC-coated brackets showed significantly less kinetic frictional force than as-received brackets. The hardness of the DLC layers was much higher than that of the as-received bracket surfaces. In conclusion, the surfaces of metal brackets can be successfully modified by the PBIID method to create a DLC layer, and the DLC-coating process significantly reduces frictional forces.

Bracket bond strength and cariostatic potential of an experimental resin adhesive system containing Portland cement.

OBJECTIVE: To determine if a new experimental resin-based material containing Portland cement (PC) can help prevent enamel caries while providing adequate shear bond strength (SBS). MATERIALS AND METHODS: Brackets were bonded to human premolars with experimental resin-based adhesive pastes composed of three weight rations of resin and PC powder (PC 30, 7:3; PC 50, 5:5; PC 70, 3:7; n  =  7). Self-etching primer (SEP) adhesive (Transbond Plus) and resin-modified glass ionomer cement (RMGIC) adhesive (Fuji Ortho FC Automix) were used for comparison. All of the bonded teeth were subjected to alternating immersion in demineralizing (pH 4.55) and remineralizing (pH 6.8) solutions for 14 days. The SBS for each sample was examined, and the Adhesive Remnant Index (ARI) score was calculated. The hardness and elastic modulus of the enamel were determined by a nanoindenter at 20 equidistant depths from the external surface at 100 µm from the bracket edge. Data were compared by one-way analysis of variance and a chi-square test. RESULTS: PC 50 and PC 70 showed significantly greater SBS than Fuji Ortho FC Automix, although Transbond Plus showed significantly greater SBS than other bonding systems. No significant difference in the ARI category was observed among the five groups. For specimens bonded with PC 50 and PC 70, the hardness and elastic modulus values in most locations were equivalent to those of Fuji Ortho FC Automix. CONCLUSIONS: Experimental resin-based bonding material containing PC provides adequate SBS and a caries-preventive effect equivalent to that of the RMGIC adhesive system.

Effects of a torsion load on the shear bond strength with different bonding techniques.

The purpose of this study was to test the hypothesis that a torsional load applied after bracket bonding does not affect the shear bond strength (SBS) with different bonding techniques. Sixty human premolars were divided into two groups (experimental and control) to investigate the effects of a torsion load, and the two groups were further subdivided into three groups of 10 for the evaluation of different adhesive systems (one etch-and-rinse adhesive, Transbond XT; two self-etching primer adhesives, Transbond Plus and Beauty Ortho Bond). A torsion load (1.45 N/cm) was applied by beta-titanium wire at 15 minutes after bracket bonding in the experimental groups. All specimens were then thermocycled between 5 and 55°C for approximately 1 week (6000 cycles). The SBS for each sample was examined with a universal testing machine and the adhesive remnant index (ARI) score was calculated. Data were compared by two-way analysis of variance, Student's t-test, and a chi-square test. The SBS for Transbond XT after thermocycling with a torsion load was significantly lower than that without a torsion load. For Transbond Plus and Beauty Ortho Bond, there was no significant difference in the mean SBS between specimens thermocycled with and without a torsion load. No significant difference in the distribution of frequencies among the ARI categories was observed among the six groups, although the ARI scores for specimens with a torsion load tended to be higher than those without a torsion load. In conclusion, the SBS of the conventional etch-and-rinse adhesive system significantly decreased under a torsion load with thermocycling.