Monocrystalline Brackets Research Articles

Evaluation of frictional forces between ceramic brackets and archwires of different alloys compared with metal brackets

The aim of this study was to evaluate, in vitro, frictional forces produced by ceramic brackets and arch wires of different alloys. Frictional tests were performed on three ceramic brackets: monocrystalline (Inspire ICE), polycrystalline (InVu), polycrystalline with metal slot (Clarity), and one stainless steel bracket (Dyna-Lock). Thirty brackets of each were tested, all with .022' slots, in combination with stainless steel and nickel-titanium wires .019' x .025', at 0 degrees and 10 degrees angulation, in artificial saliva. Arch wires were pulled through the slots at a crosshead speed of 10 mm/min. There were statistically significant differences between the groups of brackets and wires studied (p < .05). The polycrystalline brackets with metal slots had values similar to those of conventional polycrystalline brackets, and the monocrystalline brackets had the highest frictional forces. The nickel-titanium wires produced the lowest friction. The addition of metal slots in the polycrystalline brackets did not significantly decrease frictional values. Nickel-titanium wires produced lower friction than those of stainless steel.

Fluoride Prophylactic Agents Effect on Ceramic Bracket Tie-Wing Fracture Strength

To test the hypothesis that fluoride prophylactic agents do not affect the fracture strength and fracture morphology of the tie-wing complex of ceramic brackets. The fracture strength of the distal incisal tie-wing of two polycrystalline brackets, Clarity and Mystique, and a monocrystalline bracket, Inspire, was measured after the brackets were exposed to either Prevident, Phos-flur gel, or distilled water (control). Scanning electron microscopy was used to qualitatively evaluate the tie-wing intact and fractured surfaces. A two-way analysis of variance and Fisher-Hayter post hoc test, alpha = .05, indicated a significant decrease in tie-wing fracture strength following both fluoride treatments when compared with the distilled water control only with the monocrystalline bracket. None of the bracket brands exhibited any qualitative differences in the tie-wing intact or fracture surfaces as a function of fluoride treatment. The hypothesis is rejected. Based on the results, using topical fluoride agents with monocrystalline brackets might be contraindicated because of increased tie-wing fracture susceptibility.

Bond strength and debonding characteristics of a new ceramic bracket

The purposes of this study were to evaluate the shear bond strength of a new collapsible monocrystalline bracket (Inspire, Ormco, Orange, Calif) and compare it with another collapsible ceramic bracket (Clarity, 3M Unitek, Monrovia, Calif) and a metal bracket; to examine the modes of failure after shear bond strength testing; and to observe the tooth surface after debonding the ceramic brackets with pliers. One hundred extracted human premolars were selected for bonding. Three types of brackets and 2 orthodontic adhesives (Transbond XT, 3M Unitek; and Enlight, Ormco) were used. After bonding, all samples were placed in a distilled water bath at 37 degrees C for 24 hours. The shear bond strength of 60 samples was measured, and the remaining 40 samples with ceramic brackets were debonded with pliers. No statistically significant differences in bond strengths among the different combinations of brackets and adhesives were found (P > .05). The mode of failure after debonding by either shear bond strength testing or with pliers was predominantly at the bracket/adhesive interface in all groups. Enamel and bracket fractures were noted in 2 and 5 of 20 samples for Inspire, and 1 and 0 of 20 samples for Clarity after debonding with pliers. Bond strength and mode of failure of Inspire were similar to those of Clarity, but the risk of bracket fracture after debonding for Inspire was greater.

Resistance to sliding with 3 types of elastomeric modules

Super Slick (TP Orthodontics, LaPorte, Ind), a polymeric-coated ligature, has recently been introduced to the orthodontic market. The manufacturer claims it will significantly reduce friction. The purposes of this study were to determine whether Super Slick modules show lower friction than round and rectangular modules and to put the frictional forces into perspective with a self-ligating bracket. Maxillary premolar, stainless steel, self-ligating, and monocrystalline brackets with .022-in slots were used with straight lengths of .018-in and .019 x .025-in stainless steel wires. Buccal segment models were set up with 1 molar band and 2 premolar brackets for each test group: self-ligating brackets with the slide closed, self-ligating brackets with the slide open, and monocrystalline brackets. The latter 2 groups were tested with all 3 types of elastomeric module. Each setup was tested both under dry conditions and after soaking in a water bath for 1 hour. The self-ligating brackets demonstrated virtually zero friction with each combination of wire and environmental condition. When the different bracket and elastomeric module combinations were compared, significant differences were observed. In all but 2 combinations, round modules provided the least resistance to sliding and rectangular modules the greatest, with Super Slick modules in between the 2. The self-ligating bracket provided the least resistance to sliding of all the bracket/ligation combinations and almost entirely eliminated friction under the conditions of this experiment. Super Slick modules demonstrated greater resistance to sliding than conventional round modules, but not rectangular. Self-ligating brackets provided the least resistance to sliding of all bracket/ligation combinations and were the only method that almost entirely eliminated friction. The .018-in and .019 x .025-in wires exhibited similar friction in the dry state, but, when wet, the .018-in wire produced less friction. Ceramic brackets demonstrated greater resistance to sliding than stainless steel brackets. Lubrication reduced the friction with .018-in wires and increased it for .019 x .025-in wires.

Fracture strength of ceramic bracket tie wings subjected to tension.

One of the most common areas of ceramic bracket fracture is within the tie-wing complex. When an archwire is ligated into position, tensile forces are placed under the tie wing. However, no study, to date, has focused specifically on the fracture resistance of the tie-wing complex. The aim of this study is to compare the tensile fracture strength of seven currently available ceramic brackets (Inspire, Fascination, Mystique, InVu, Clarity, Virage, and Luxi) as a function of bracket brand and bracket configuration, semitwin vs true-twin. Based on a power analysis of pilot data, 10 maxillary central incisor brackets per group were tested to failure with a tensile load placed directly under the distoincisal tie wing. The results ranged from a maximum mean fracture strength of 147.71 (5.87) MPa with Fascination brackets to a minimum mean fracture strength of 84.28 (7.01) MPa with Luxi brackets. The statistical analysis indicated a significant effect on fracture strength as a function of bracket brand (P < .05) and that semitwin brackets, Fascination, Mystique, and Virage, had significantly higher fracture strength than true-twin brackets, Clarity, lnVu, and Luxi (P < .05). Interestingly, the only monocrystalline bracket in the study, Inspire, could not be fractured using the investigation protocol. In fact, the steel ligature fixture wire would break before tie-wing fracture at a mean fixture failure of 198.65 MPa.

Plasma arc curing of ceramic brackets: an evaluation of shear bond strength and debonding characteristics

The aim of this in vitro investigation was to evaluate bond strength and debonding characteristics when a xenon plasma arc curing light is used to bond polycrystalline and monocrystalline ceramic brackets. Brackets were bonded to 240 extracted bovine mandibular incisors with a composite adhesive. Curing intervals of 1, 3, and 6 seconds were chosen for curing with the plasma arc light, and the control group was cured at 10 seconds per bracket with a conventional halogen light. Debonding was performed on a universal testing machine and according to the bracket manufacturers’ recommendations. Both the polycrystalline and the monocrystalline brackets consistently debonded at the bracket-adhesive interface, regardless of debonding method, curing interval, or curing light. No enamel fractures were observed after debonding. Bracket fractures were rare and did not affect debonding. Bond strength was significantly higher for the monocrystalline brackets ( P < .0001): mean shear bond strength ranged between 9.68 ± 2.17 MPa (plasma arc curing light, 1 sec curing interval) and 10.73 ± 3.22 MPa (halogen light, 10 sec curing interval) for the polycrystalline brackets and between 19.85 ± 2.97 MPa (plasma arc curing light, 1 sec curing interval) and 22.94 ± 3.20 MPa (plasma arc curing light, 3 sec curing interval) for the monocrystalline brackets. Significant differences were also found for the curing methods used ( P = .047). A curing interval of 3 seconds with the plasma arc curing light is recommended for both polycrystalline and monocrystalline ceramic brackets.

Impact resistance of ceramic brackets according to ophthalmic lenses standards

The overall resistance to accidental blows of the many ceramic brackets that are sold today has not been explored. Facing a similar diversity, the eyeglasses industry has chosen to standardize the testing of lenses by subjecting them to the drop of a steel ball. By slightly modifying this test, 10 brands of ceramic brackets were examined. In most cases, the findings coincided with those found by other authors when duplicating debonding. Thus, polycrystalline ceramics with bulkier structures and glazed surfaces were found to be more resistant to impact than the monocrystalline brackets, the loftier real “twins,” and the less dense attachments. Protruding tie wings and bases were liabilities, and domed configurations seemed to deflect the blows. Bulkier “single” designs alone did not offer a guarantee of impact resistance when not accompanied by an appropriate microstructure and a smooth surface. The ceramic brackets most resistant to impact were found to be 20/20 by American Orthodontics and Fascination by Dentaurum. Medium resistance was displayed by Lumina by Ormco, Allure III and Allure by GAC, Transcend 2000 and Transcend by Unitek/3M; the last was not as good as the other four. The least resistant were Illusion by Ortho-Organizers, Intrigue by Lancer Orthodontics, and Starfire TMB by “A”-Co. Probably because of its real twin design, the last bracket lends itself to the highest probability for accidental breakage. Although resistance to impact and accidental debonding is desirable from the point of view of treatment, the advantage should be weighted against the chance of enamel fracture. Indeed a weak bracket attached with a soft adhesive may be preferable when the chance of an increased exposure to accidental blows is probable. In such cases, the ceramic may take the brunt of the force, instead of the tooth. (Am J Orthod Dentofacial Orthop 1999;115:158-65)

The effect of different bonding and debonding techniques on debonding ceramic orthodontic brackets

Previous studies have indicated that different bonding and debonding techniques affect the removal or detachment of polycrystalline ceramic brackets that use a mechanical mechanism of bonding to resin. The delamination type debonding forces have been shown to be more effective, compared with twisting and tensile type forces. Further, polycrystalline brackets bonded by the indirect techniques debond leaving minimal filled resin on the tooth surface and hence cleanup and enamel damage are minimized. The purpose of this research was to compare the effects of three bonding and debonding techniques on debonding two types of ceramic brackets, using different modes of bonding. The monocrystalline bracket used the chemical and the polycrystalline bracket used the mechanical mechanisms for bonding respectively. Brackets were bonded to 180 freshly extracted bovine teeth, divided into two groups of 90 each, based on the bracket employed, i.e., monocrystalline and polycrystalline brackets. These brackets were bonded with the direct and two different indirect bonding methods: the conventional indirect method (modified Thomas) and the indirect technique that used a thermally cured resin. Each bonding group was further divided into three groups of 10, based on the type of debonding technique used, i.e., lift off, delamination, and twisting. The variables evaluated were bracket failure and remnant adhesive on debonding. The data were subjected to an analysis of variance to determine existence of significant differences, followed by multiple comparisons of means. Bracket failure or fracture was significantly affected, based on the bonding technique and the debonding technique for the monocrystalline at p < 0.0001 and the polycrystalline ceramic brackets at p < 0.001 and p < 0.05, respectively. Remnant adhesive was significantly affected by bonding and debonding techniques for the polycrystalline brackets at p < 0.0001. Remnant adhesive was significantly ( p < 0.01) affected by the bonding technique for the monocrystalline brackets. The delamination debonding technique combined with the thermal-cured indirect bonding technique was shown to be a safe combination for debonding both types of ceramic brackets. Therefore both bonding and debonding techniques significantly affect bracket failure or fracture and remnant adhesive of ceramic orthodontic brackets during the debonding procedure.

Fracture strength of ceramic brackets during arch wire torsion

This study evaluated the fracture strengths of eight new vintage ceramic brackets with application of torsional forces. Palatal root torque was applied at the distal side of right maxillary central incisor brackets with 0.022-inch slots by means of a 0.0215 × 0.027-inch rounded edge stainless steel arch wire. A specially designed apparatus that attached to an Instron machine was used to test the ceramic brackets. The amount of torque, degress of torsion at failure, and fracture locations were measured. The monocrystalline bracket did not break when the torquing test was applied; the portion of the wire outside the slot of the bracket twisted on itself. The mean torquing forces at failure ranged from 5755.2 gm-mm to 9316.5 gm-mm and could be separated into three statistically different groups. The mean torsional rotation at fracture ranged from 32.7° to 68.1° for the polycrystalline brackets. The results suggested that all the brackets studied were sufficiently strong to withstand the commonly accepted magnitudes of arch wire torquing forces. The present investigation showed higher angulation values for all the brackets than those reported by Holt 2 who used the same apparatus with older style brackets. (A M J O RTHOD D ENTOFAC O RTHOP 1996;109:22-7.)

Failure mode analysis of ceramic brackets bonded to enamel

The purpose of this study was to evaluate in vitro the failure pattern of ceramic brackets bonded to enamel with a light-cured orthodontic adhesive. Five types of ceramic brackets and 125 incisors were used in the study. The brackets were bonded onto enamel with a light-cured orthodontic adhesive. After 1 week storage and thermal cycling, the samples were debonded by one operator according to the individual technique for each bracket group proposed by each manufacturer. The fracture surfaces were examined under a stereomicroscope to reveal the type of failures. The effect of the debonding procedure on enamel structure was significantly affected by the various bonding mechanisms of the bracket bases. Cohesive enamel fractures were detected from brackets that provided a bonding mechanism of micromechanical retention and chemical adhesion. The brackets that combined mechanical retention and chemical adhesion, presented both cohesive resin fractures and fractures located at the bracket resin or the resin enamel interface. The higher frequency of cohesive bracket fractures was obtained from a monocrystalline bracket.

Laser-aided debonding of orthodontic ceramic brackets

The removal of ceramic brackets from the enamel surface by means of laser heating was investigated with the use of CO2 and YAG lasers. The two bracket types investigated were polycrystalline alumina and monocrystalline alumina. The average torque force necessary to break the adhesive between the polycrystalline ceramic brackets and the tooth was lowered by a factor of 25 when the brackets were illuminated with a CO2 laser beam of 14 watts for 2 seconds. All polycrystalline brackets debonded with the CO2 laser resulted in a complete bracket detachment without bracket failure. The average torque force needed to debond monocrystalline brackets was lowered by a factor of 5.2 when illuminated with a laser setting of 7 watts. Monocrystalline brackets cracked along the bracket slot in 2 of 10 cases. Debracketing without laser heating resulted in a slightly higher incidence of bracket failure (12 of 50). Nevertheless, no visible damage to the enamel surface was observed. Advantages of the laser-aided bracket-removal techniques include the following: The heat produced is localized and controlled; the debracketing tool is essentially "cold"; and the method can be used for removal of various types of ceramic brackets, regardless of their design.

Das Friktionsverhalten von Keramikbrackets bei der bogengeführten Zahnbewegung

In spite of their wellknown disadvantages ceramic brackets are in great demand by orthodontic patients because of their aesthetic features. The amount of friction produced during tooth movement when a ceramic bracket slides along an arch wire, is still unknown. Using a custom-made friction test device the current study was undertaken to measure friction values of brackets of different manufactures with an 0.018 inch slot sliding along an 0.016 x 0.022 inch stainless steel arch wire. The results of this study showed that stainless steel brackets had slightly lower values than polycrystalline ceramic brackets. The monocrystalline bracket however showed significant greater friction values than both stainless steel and polycrystalline brackets even though its surface, as revealed with the scanning electron microscopy, proved to be quite smooth.