Tooth movement can occur when the applied

Transcription

1 ONLINE ONLY Comparison of frictional forces during the initial leveling stage in various combinations of self-ligating brackets and archwires with a custom-designed typodont system Tae-Kyung Kim, a Ki-Dal Kim, b and Seung-Hak Baek c Seoul, South Korea Introduction: The purpose of this study was to compare the frictional force (FF) generated by various combinations of self-ligating bracket (SLB) types, archwire sizes, and alloy types, and the amount of displacement during the initial leveling phase of orthodontic treatment, by using a custom-designed typodont system. Methods: Two passive SLBs (Damon 2 [D2] and Damon 3 [D3]), and 3 active SLBs (SPEED [SP], In-Ovation R [IO], Time 2 [T2]), and SmartClip (SM) were tested with in and in austenitic nickel-titanium (A-Ni-Ti) and copper-nickel-titanium (Cu-Ni-Ti) archwires. To simulate malocclusion status, the maxillary canines (MXCs) were displaced vertically, and the mandibular lateral incisors (MNLIs) horizontally from their ideal positions up to 3 mm with 1-mm intervals. Static and kinetic FFs were measured with a speed of 0.5 mm per minutes for 5 minutes with a testing machine (model 4466, Instron, Canton, Mass). Two conventional brackets (Mini-Diamond [MD] and Clarity [CL]) were used as controls. Analysis of variance and Duncan tests were used for statistical purposes. Results: FF was increased in ascending order: D2, D3, IO, T2, SM, SP, CL, and MD in the maxillary typodont; and IO, D2, D3, T2, SP, CL, and MD in the mandibular typodont, regardless of archwire size and alloy type. The A-Ni-Ti wire showed significantly lower FF than did the Cu-Ni-Ti wire of the same size. As the amounts of vertical displacement of the MXCs and horizontal displacement of the MNLIs were increased, FF also increased. Conclusions: These findings suggest that combinations of the passive SLB and A-Ni-Ti archwire during the initial leveling stage can produce lower FF than other combinations of SLB and archwire in vitro. (Am J Orthod Dentofacial Orthop 2008;133:187.e e24) Tooth movement can occur when the applied forces adequately overcome the friction at the bracket slot-archwire interface. High levels of frictional force (FF) between the bracket slot and the archwire might cause binding between the 2 components; this in turn results in little or no tooth movement. Furthermore, binding during retraction of the anterior teeth can lead to loss of posterior anchorage. 1 Friction can also exist during the initial leveling and alignment stage when an archwire slides through the bracket slots and tubes. Therefore, it is essential to understand the From the Department of Orthodontics, School of Dentistry, Seoul National University, Seoul, South Korea. a Graduate student. b Clinical professor; Barunee Dental Clinic, Suwon, Kyunggi-Do, South Korea. c Associate professor. Reprint requests to: Seung-Hak Baek, Department of Orthodontics, Dental Research Institute, School of Dentistry, Seoul National University, #28 Yeonkun-dong, Jongro-Ku, Seoul, , South Korea; , drwhite@ unitel.co.kr. Submitted, May 2007; revised and accepted, August /$34.00 Copyright 2008 by the American Association of Orthodontists. doi: /j.ajodo friction between the bracket and the archwire on tooth movement so that the proper force can be applied to obtain adequate tooth movement and optimum biologic response. 2 Recently, there has been increased use of the self-ligating bracket (SLB). This is a ligatureless bracket system with a mechanical device built into the bracket to close off the bracket slot. Its advantages are to reduce chair time because of faster placement and removal of the archwire, to create a minimal friction environment for better sliding mechanics, and to require less chair-side assistance. 3-6 Although bracket types and experimental methods were different, many studies have demonstrated significant decreases in friction with the SLB compared with conventional bracket designs These SLBs can be divided into 2 groups: the active type with a clip, and the passive type with a slide. The passive SLB (PSLB) does not apply a ligation force to the archwire because the slide covers only the slot, thus restraining the archwire. 6 For the active SLB (ASLB), there are 2 options. When the clip is active, it is in contact with the archwire and applies a force to fully 187.e15

2 187.e16 Kim, Kim, and Baek American Journal of Orthodontics and Dentofacial Orthopedics February 2008 seat the archwire in the slot; if the clip is passive, it neither contacts the archwire nor applies a force to the archwire. 6 Whether the clip is active or passive depends on the archwire size relative to the slot size and the position of the archwire in the bracket. 6,7,10-14,29 The question of superiority between the active clip and the passive slide with respect to friction has attracted heated debate. 3,30 In most previous studies, there were limitations in study design because of the number and alignment of brackets: fewer than 5 brackets were used to measure FF, and those brackets were aligned straight, rather than according to the arch form. 5-16,18-23,27-29 Only a few studies have included the whole dentition, aligned according to arch form, to measure FF. 17,24,25,31 It is necessary to investigate the amount of FF in the whole dentition. For the initial leveling and alignment,.014- and.016-in austenitic nickel-titanium (A-Ni-Ti) and copper-nickel-titanium (Cu-Ni-Ti) archwires were commonly used. Relatively different positioning of the archwire in the bracket slot of a tooth can occur because of the malocclusion status. Therefore, friction between the archwire and the bracket slot can affect tooth movement, even with the thinnest wire. Also, differences in surface chemistry and chemical affinity between A-Ni-Ti and Cu-Ni-Ti archwires might influence tooth movement differently. 32 The amount of malalignment of a tooth can also correlate with friction during the initial leveling phase. To obtain objective measurement according to severity of displacement, it is necessary to develop a customdesigned typodont system that can produce a malocclusion status with vertical and horizontal displacement of an individual tooth, and simulate the initial leveling phase. The purpose of this study was to compare the FF generated by various combinations of SLB type, archwire size and alloy type, and the amount of tooth displacement during the initial leveling phase, by using a custom-designed typodont system that could simulate the malocclusion status. MATERIAL AND METHODS A novel custom-designed typodont system (CDTS- SNUB-1, patent pending no , Seoul, Korea) was developed for this study (Fig 1). This system was composed of resin teeth (Il-shin Dental, Seoul, Korea), metal frames that can fix the teeth, and a metal plate that can connect the metal frames with a mechanical testing machine. Each typodont consisted of 14 teeth, which were reproducibly exchangeable with new ones because the root forms of the resin teeth were transferred to the holding portions of the metal frame. The metal frame holding the resin teeth could be moved in the occlusogingival (up and down) and labiolingual (forward and backward) directions from the ideal position to a maximum of 5 mm to produce arbitrary displacement of each resin tooth. At zero position, all resin teeth were aligned to the ideal position according to the ovoid arch form (OrthoForm III-Ovoid, ref , 3M Unitek, Monrovia, Calif). The SLBs tested in this study were as follows: (1) 3 ASLBs: In-Ovation R (GAC International, Bohemia, NY), SPEED (Strite Industries, Cambridge, Ontario, Canada), and Time 2 (American Orthodontics, Sheboygan, Wis); (2) 2 PSLBs: Damon 2 and Damon 3 (SDS Ormco, Glendora, Calif); and (3) a new type of SLB, SmartClip (3M Unitek). As a control group to compare with the SLBs, 2 conventional brackets, Clarity (3M Unitek) and Mini-Diamond (Ormco), were selected. All brackets tested had a.022-in slot. In-Ovation R and Time 2 brackets were Roth types, and the other brackets were MBT type. As typical archwires used for the initial leveling stage of orthodontic treatment,.014- and.016-in standard A-Ni-Ti and Cu-Ni-Ti archwires (Ormco), were selected and coupled with SLBs and conventional brackets. To simulate a malocclusion status, standardized displacements of the resin teeth were produced when all brackets were coupled with.014-in A-Ni-Ti or Cu- Ni-Ti wire. The maxillary canines on the right and left sides were displaced in the gingival direction, and the mandibular lateral incisors on both sides in the lingual direction in amounts of 0, 1, 2, and 3 mm. In this study, selection of the bracket-archwire combinations was made randomly. Once the combination was selected, the brackets were bonded in the clinically appropriate position, which was according to the facial axis point, by using a cyanoacrylate adhesive (Loctite 416, Loctite, Rocky Hill, Conn) on the resin teeth, which were aligned on the typodont. For the conventional brackets, after ligation with the elastic modules (Dispense-A-Tie Ligatures, TP Orthodontics, LaPorte, Ind), a 3-minute waiting period allowed a reproducible amount of stress relaxation to occur. 24,25 Then the typodont was attached to the custom-made metal plate that was fixed to a mechanical testing machine (model 4466, Instron, Canton, Mass) (Fig 2). A custom-designed adaptor gripped a distal end of the archwire, which was extruded from the second molar tubes. Each combination was tested 5 times with different wires of the same kind. Static FF (SFF) and kinetic FF (KFF) were calculated while 2.5 mm of wire was drawn through the

3 American Journal of Orthodontics and Dentofacial Orthopedics Volume 133, Number 2 Kim, Kim, and Baek 187.e17 Fig 1. Custom-designed typodont. Occlusal views of A, maxillary and B, mandibular typodonts. Resin teeth in C, maxillary and D, mandibular typodonts are aligned to an ovoid arch form. E, The maxillary canines were displaced in the gingival direction by 3 mm, and F, the mandibular lateral incisors were displaced in the lingual direction by 3 mm. brackets and tubes at a crosshead speed of 0.5 mm per minute. The data were transmitted from the load cell (1000 g) to the software (Series IX automated Material Testing System, Instron) in the computer connected to the testing machine, and the drawing force-distance charts were plotted. SFF was measured as the maximal initial rise on the Instron chart trace (Fig 3). After this maximal initial rise, an additional 0.2 mm of the archwire was drawn distally to record KFF. These measurements of the FF values were averaged and defined as the KFF (Fig 3). To assess the reproducibility of the experiments, measurements for the Mini-Diamond, Damon 2, and Time 2 brackets were repeated twice at a 1-week interval. Each time, new resin teeth were aligned, new brackets were bonded, and the tests were done as described previously. The intraclass correlation coefficients (r) were calculated from 2 repeated measurements. There was no significant difference between the original friction values and those recorded a week later (Table I). Therefore, the first set of data was used for statistical analysis. Descriptive statistics including means, standard deviations, and maximum and minimum values were calculated for each combination of bracket, archwire size, and alloy type, and the amount of displacement. To assess the influence of SLB type on FF, brackets were allocated into 4 types according to their properties. Mini-Diamond and Clarity were classified as conventional brackets (CB); Damon 2 and Damon 3 as PSLBs; SPEED, In-Ovation, and Time 2 as ASLBs; and SmartClip as a new type of SLB (NSLB). An analysis of variance (ANOVA) test was used to evaluate the effects of the variables on FF. If the assumption

4 187.e18 Kim, Kim, and Baek American Journal of Orthodontics and Dentofacial Orthopedics February 2008 Fig 2. Typodont system and testing apparatus. A custom-designed adaptor gripped 1 distal end of the archwire, which was extruded from the second molar tubes. that the variances were equal was broken by the Levene test, the Welch variance weighted ANOVA was used. For the post-hoc test, the Duncan test was applied. The level of significance for all the tests was set at P.05. RESULTS A total of 785 tests were carried out. The combination of the SmartClip, a.014-in A-Ni-Ti or Cu-Ni-Ti archwire, and a 3-mm displacement of the mandibular lateral incisors could not be tested because the Smart- Clip could not grip the archwire firmly during the test. Similarly, the combination of the SmartClip, a.014 Cu-Ni-Ti archwire, and a 2-mm displacement of the mandibular lateral incisors also could not be tested for the same reason. Therefore, SmartClip data in the mandibular typodont were excluded. In the maxillary and mandibular typodonts, combinations of brackets and wire alloy (brackets X wire alloy) showed a significant effect on SFF (P.001, Table II) and KFF (P.001, Table II). In the mandibular typodont, combinations of brackets and displacement (bracket X displacement) in KFF showed a significant interaction (P.05) (Table II). There were significant differences in SFF and KFF in bracket, wire alloy, wire size, and amount of displacement for the maxillary and mandibular typodonts, respectively (Tables III and IV). SFF was significantly greater than KFF for all variables except Damon 3, Time 2, and In-Ovation R brackets in the maxillary typodont (Tables III and IV). Wire alloy had a significant influence on SFF and KFF. The Cu-Ni-Ti wire generated higher friction than the A-Ni-Ti wire for all bracket types in the maxillary and mandibular typodont systems (maxillary, P.001,Table III; mandibular, P.001, Table IV). As the wire size increased from.014 to.016 in, all bracket types showed increases of SFF and KFF in the maxillary and mandibular typodont systems (maxillary, P.05,Table III; mandibular, P.01, Table IV). As the amounts of vertical displacement of the maxillary canines and lingual displacement of the mandibular lateral incisors were increased respectively, SFF and KFF also increased (maxillary, P.001, Table III; mandibular, P.001, Table IV). In regard to the amount of tooth displacement, Damon 2 and Damon 3 in the maxillary typodont system produced significantly lower SFF and KFF, and Mini-Diamond and Clarity produced significantly higher SFF and KFF than the other brackets (P.001, Table III). In brackets of the mandibular typodont, the Smart- Clip was excluded because of the missing data mentioned previously (Table IV). In-Ovation R, Damon 2, and Damon 3 produced significantly lower SFF and KFF, and Mini-Diamond produced significantly higher SFF and KFF than the other brackets (P.001, Table IV). The SLB type of bracket significantly affected the amount of SFF and KFF in both maxillary and mandibular typodonts (P.001, Table V). In the maxillary typodont, the PSLB showed significantly lower SFF and KFF when compared with the other bracket designs (P.001, Table V). Although the frictional force of the ASLB was lower than the NSLB, this difference was not statistically significant (Table V). In the mandibular typodont, although the PSLB showed lower SFF and KFF compared with the other bracket types, there was no significant difference between the PSLB and the ASLB (Table V). DISCUSSION Although there has been some debate about whether static or kinetic friction is more important, 33 kinetic friction is considered to be less important because the orthodontic sliding movement of a tooth or bracket on an archwire is not a continuous or constant motion. 13 The dynamic environment of the mouth can repeatedly break and reset the friction lock between the bracket and archwire, and this can produce tooth movement as a series of short steps rather than as smooth continuous motion. 34 Furthermore, because the amount of SFF is always greater than KFF, as has been also reported in previous studies 23,35-37 and confirmed herein, SFF can determine the magnitude of the force acting on the teeth, irrespective of the amount of KFF. Therefore, from the clinical perspective, to overcome SFF between

5 American Journal of Orthodontics and Dentofacial Orthopedics Volume 133, Number 2 Kim, Kim, and Baek 187.e19 Fig 3. Diagram of the static and kinetic frictional forces. Table I. Descriptive data (cn) and intraclass coefficient (ICC) values of the Mini-Diamond, Damon 2, and Time 2 brackets Typodont FF Level Mean SD t Significance ICC value (Pearson correlation) Maxilla Static MD original MD repeated D2 original D2 repeated T2 original T2 repeated Kinetic MD original MD repeated D2 original D2 repeated T2 original T2 repeated Mandible Static MD original MD repeated D2 original D2 repeated T2 original T2 repeated Kinetic MD original MD repeated D2 original D2 repeated T2 original T2 repeated The intraclass correlation coefficients (r) were calculated from 2 repeated measurements. MD, Mini-Diamond; D2, Damon 2; T2, Time 2. the bracket and the wire is a prerequisite for tooth movement. In this study, various SLBs produced significantly lower SFF and KFF than conventional brackets in the maxillary and mandibular typodonts (Tables III-V). Although the types of SLBs and the experimental methods were different, our findings agreed with those of previous studies, 5,8,12-15,20,24,25 especially when coupled with the thin wires that are used in the early stages of orthodontic treatment. The reason that conventional brackets showed higher values of FF in the maxillary typodont than in

6 187.e20 Kim, Kim, and Baek American Journal of Orthodontics and Dentofacial Orthopedics February 2008 Table II. Comparison of FF according to combinations of bracket, wire alloy type and size, and displacement Typodont Type of FF Combination Significance Maxillary Static Bracket X wire alloy type.000*** Bracket X wire size.162 Bracket X displacement.195 Kinetic Bracket X wire alloy type.000*** Bracket X wire size.218 Bracket X displacement.490 Mandibular Static Bracket X wire alloy type.000*** Bracket X wire size.177 Bracket X displacement.142 Kinetic Bracket X wire alloy type.000*** Bracket X wire size.243 Bracket X displacement.038* Two-way ANOVA was done. *P.05; ***P.001. the mandibular one seems to be due to the higher ligation force of the elastic module. As the regular modules stretched from 1 to 2 mm, the mean load was increased twice. 28 In the maxillary typodont, the elastic modules were stretched more than those in the mandibular one because of greater bracket width. Therefore, the sum of the ligation force in the maxillary typodont was much larger than in the mandibular one. Difference in the ligation force might have more effect on FF than the difference in interbracket distance. Several studies showed that PSLBs exhibited negligible FF values when second-order angulations were less than the critical contact angle. 18,38 In this study, even though the maxillary canines were displaced vertically and the mandibular lateral incisors lingually up to 3 mm from their ideal positions, which was beyond their critical contact angle, Damon 2 and Damon 3 brackets also showed lower FF than other SLBs. This finding is consistent with other studies that compared PSLBs such as the Damon SL and Damon 2 brackets with ASLBs such as Time and SPEED brackets. 13,24-26,39 Because the experimental systems of previous studies comparing ASLBs and PSLBs were different, they showed conflicting results. 5,6,9,11-14,24,28,39 However, 2 things should be considered: how much clearance there is between the bracket slot and the archwire, and whether the clip of the ASLB reduced the lumen size. When there is clearance, FF is negligible for a PSLB coupled to any size of archwire and for an ASLB coupled to an archwire that does not contact the clip. 4 Without clearance and when the archwire contacts the clip or slides because of the size or the geometric position of the archwire in the bracket slot, FF of the PSLB was lower than the ASLB. 24 Thorstenson and Kusy 16,18,19 explained the level of resistance to sliding of SLBs and conventional brackets in various angulations in terms of the contact angle between the bracket slot and the archwire. They concluded that, although the rate of binding as a function of relative angulation was similar regardless of bracket design, brackets with passive slides exhibited the lowest resistance to sliding. Harradine 3 also described this clearance problem between the active clip or passive slide and the wire size in detail. The clip of an ASLB is passive unless the tooth is sufficiently displaced in relation to adjacent teeth. However, if the tooth is severely displaced in relation to adjacent teeth, the archwire will contact the clip. In this case, the clip status becomes active, and it could exert force on the archwire depending on the relative discrepancy of the positions of the adjacent teeth compared with a passive status of the clip. Even among ASLBs, SPEED brackets had higher SFF and KFF in both typodonts in this study because of higher clip force (Tables III and IV). Our result with several brackets agreed with those of previous studies with a single bracket. 18,19 Henao and Kusy, 25 using typodont models with different degrees of malocclusion, concluded that, as malocclusion became more prevalent and archwire size reduced overall clearance, the 2 SLB designs of slides and clips lost distinction. In our study, which used only round wires, different results were obtained. PSLBs such as Damon 2 and Damon 3 showed lower FF than the ASLBs, even though the degree of malocclusion was increased. The slide of the PSLB did not change the lumen size of the bracket slot when it closed. However, the clip of the ASLB could reduce the slot depth and eventually the dimension when it closed. Since the clip has a slope, it does not reduce the slot dimension to the same extent in the occlusal and gingival portions. 3 Also, if a tooth is displaced in the vertical and horizontal aspects in relation to the adjacent teeth, the archwire must be angulated and will be touched by the clip in the different areas. The slopes of the clips vary among brackets from different manufacturers. 3 These discrepancies of the active clip would make a difference in FF even with small diameter wires. In addition to the clearance between the bracket slot and the archwire and the lumen size of bracket, the contact area between the wire and the bracket surface also can influence the FF level. 40,41 But in this study it was difficult to measure the exact contact area between the wire and the brackets. Further studies should be

7 American Journal of Orthodontics and Dentofacial Orthopedics Volume 133, Number 2 Kim, Kim, and Baek 187.e21 Table III. Descriptive data of the FF (cn) according to combinations of bracket, wire alloy type and size, and displacement in the maxillary typodont Type of FF Factor Variable Mean SD Maximum Minimum Significance Multiple comparison Static Brackets MD *** (D2,D3) (D3,IO,T2, CL SM,SP) (CL, MD) D D SP IO T SM Wire alloy A-Ni-Ti *** Cu-Ni-Ti Wire size (in) * Displacement (mm) *** (0,1) (1,2) (2,3) Kinetic Brackets MD *** (D2,D3) (D3,IO,T2, CL SP,SM) (CL, MD) D D SP IO T SM Wire alloy A-Ni-Ti *** Cu-Ni-Ti Wire size (in) * Displacement (mm) *** (0) (1,2) (3) One-way ANOVA was done. Welch variance weighted ANOVA was used. Multiple comparison test was done with the Duncan test. Paired t test was performed to compare static and kinetic FF forces in the same combinations. The data of wire size were bracket-archwire combinations with no displacement. The data of displacement were bracket-archwire combinations with in archwire. *P.05; **P.01; ***P.001; P.05; P.01; P.001. MD, Mini-Diamond; CL, Clarity; D2, Damon 2; D3, Damon 3; SP, SPEED; IO, In-Ovation; T2, Time 2; SM, SmartClip. done to check whether these variables have a correlation between them. The ASLB showed significantly higher SFF and KFF when compared with the PSLB in the maxillary typodont (Table V). However, in the mandibular typodont, there was no significant difference in SFF and KFF between the PSLB and ASLB (Table V). It seems to be because of the difference in interbracket distance between the maxillary and mandibular typodonts. When the interbracket distance becomes shorter in the mandibular typodont than the maxillary one, the archwire becomes more rigid, and this stiffness results in more increase of the FF in the mandibular typodonts than the maxillary ones. Therefore, PSLB could not take advantage of lower FF in the mandibular typodonts than the maxillary ones. Eventually, there was no significant difference in FF between ASLB and PSLB of the mandibular typodont. Although Brady 42 thought that adding copper to the alloy lowers the friction of the Ni-Ti wire to make it slip more easily along a bracket, in the previous study comparing a.016-in A-Ni-Ti wire and a.016-in Cu- Ni-Ti wire with 2 brackets, the Cu-Ni-Ti wire showed higher FF than the A-Ni-Ti wire; this result was consistent with ours. 43 The reason that the Cu-Ni-Ti wire generated higher friction than the A-Ni-Ti wire for all kinds of brackets might be the difference in surface chemistry and chemical affinity between A-Ni-Ti and Cu-Ni-Ti archwires. 32 Henao and Kusy 25 proposed that the parameter that best correlated with drawing forces was the bending stiffness of the archwire, which was directly associated with the nominal dimension of each

8 187.e22 Kim, Kim, and Baek American Journal of Orthodontics and Dentofacial Orthopedics February 2008 Table IV. Descriptive data of the FF (cn) according to combinations of bracket, wire alloy type and size, and displacement in the mandibular typodont Type of frictional force Factor Variable Mean SD Maximum Minimum Significance Multiple comparison Static Brackets MD *** (IO,D2,D3) (D2,D3,T2) CL (SP) (CL, MD) D D SP IO T Wire alloy A-Ni-Ti *** Cu-Ni-Ti Wire size (in) ** Displacement (mm) *** (0) (1) (2) (3) Kinetic Brackets MD *** (IO,D3,D2) (D3,D2,T2) CL (SP) (CL) (MD) D D SP IO T Wire alloy A-Ni-Ti *** Cu-Ni-Ti Wire size (in) ** Displacement (mm) *** (0) (1) (2) (3) One-way ANOVA was done. Welch variance weighted ANOVA was used. Multiple comparison test was done by Duncan test. Paired t test was performed to compare static and kinetic FF in the same combinations. The data of wire size were bracket-archwire combinations with no displacement. The data of displacement were bracket-archwire combinations with in archwire. **P.01; ***P.001; P.01; P.001. MD, Mini-Diamond; CL, Clarity; D2, Damon 2; D3, Damon 3; SP, SPEED; IO, In-Ovation; T2, Time 2; SM, SmartClip. wire. However, further studies are needed to investigate the exact reason for this result. Although the wire sizes tested in this study were different from those used in previous studies, our results agreed with those results in that the smaller wire had lower friction than the larger one. 5,6,9,11-14,24,28,39 Henao and Kusy, 25 however, reported that when comparing a.014-in superelastic Ni-Ti wire (SDS Ormco) with a.016-in 7-stranded supercable archwire (Strite Industries, Cambridge, Ontario, Canada), the latter produced lower drawing forces. But multi-stranded archwire is not a true 1-piece.016-in wire 25 ; this might account for results that conflict with ours. Nevertheless, an increase in wire size can cause a decrease in clearance amount and eventually produce higher FF. In the combination of bracket and displacement, Damon 2 and Damon 3 in the maxillary typodont system and In-Ovation R, Damon 2, and Damon 3 in the mandibular typodont system produced significantly lower FF values than the other brackets. The PSLB showed significantly lower levels of FF when compared with the ASLB (P.001, Table V). These findings suggest that, regardless of the amount of tooth displacement, the PSLB produced a lower FF than the ASLB. This result is consistent with the previous multi-bracket study, which showed the lowest frictional results for Damon 2 in extremes of malocclusion. 24 These findings suggested that the passive slide design might be the most effective with respect to friction. All other factors being equal, the combination of a PSLB and a.014-in A-Ni-Ti wire during the initial leveling stage can produce lower FF in vitro than other combinations of SLBs and archwires.

9 American Journal of Orthodontics and Dentofacial Orthopedics Volume 133, Number 2 Kim, Kim, and Baek 187.e23 Table V. Descriptive statistics (cn) and ANOVA results according to type of bracket Typodont Type of FF Type of bracket Mean SD Maximum Minimum Significance Multiple comparison Maxilla Static CB *** PSLB (ASLB,NSLB) CB PSLB ASLB NSLB Kinetic CB *** PSLB (ASLB,NSLB) CB PSLB ASLB NSLB Mandible Static CB *** (PSLB,ASLB) CB PSLB ASLB Kinetic CB *** (PSLB,ASLB) CB PSLB ASLB Welch variance weighted ANOVA was done. Multiple comparison test was done by Duncan test. ***P.001. CB, Mini-Diamond and Clarity; PSLB, Damon 2 and Damon 3; ASLB, SPEED, In-Ovation, Time 2; NSLB, SmartClip. The custom-designed typodont, which could align the teeth according to arch form and simulate displacements of the teeth, was used to perform the tests for measurement of SFF and KFF of the whole arch. However, it has several limitations. First, rotation, mesiodistal tipping, and labiolingual inclination of 1 tooth are still not possible with this system. Next time, we will try other common misalignments. Second, because of the rigidity of the metal frame holding the resin teeth, it could not emulate the periodontal ligaments in vivo that would normally possess force (stress)-absorbing mechanisms. However, this typodont system did represent some important testing variables, such as arbitrary horizontal and vertical displacement of a tooth to simulate a malocclusion status. CONCLUSIONS In in-vitro emulation of the initial leveling and aligning stages of the orthodontic treatment, the combination of a PSL and an A-Ni-Ti archwire showed lower FF than other combinations of brackets, wire alloy, wire size, and amount of displacement. REFERENCES 1. Kapila S, Angolkar PV, Duncanson MG Jr, Nanda RS. Evaluation of friction between edgewise stainless steel brackets and orthodontic wires of four alloys. Am J Orthod Dentofacial Orthop 1990;98: Nishio C, da Motta AF, Elias CN, Mucha JN. In vitro evaluation of frictional forces between archwires and ceramic brackets. Am J Orthod Dentofacial Orthop 2004;125: Harradine NW. Self-ligating brackets: where are we now? J Orthod 2003;30: Maijer R, Smith DC. Time savings with self-ligating brackets. J Clin Orthod 1990;24: Shivapuja PK, Berger J. A comparative study of conventional ligation and self-ligation bracket systems. Am J Orthod Dentofacial Orthop 1994;106: Voudouris JC. Interactive edgewise mechanisms: form and function comparison with conventional edgewise brackets. Am J Orthod Dentofacial Orthop 1997;111: Berger JL. The influence of the SPEED bracket s self-ligating design on force levels in tooth movement: a comparative in vitro study. Am J Orthod Dentofacial Orthop 1990;97: Bednar JR, Gruendeman GW. The influence of bracket design on moment production during axial rotation. Am J Orthod Dentofacial Orthop 1993;104: Sims APT, Waters NE, Birnie DJ, Pethybridge RJ. A comparison of the forces required to produce tooth movement in vitro using two self-ligating brackets and a pre-adjusted bracket employing two types of ligation. Eur J Orthod 1993;15: Sims APT, Waters NE, Birnie DJ. A comparison of the forces required to produce tooth movement ex vivo through three types of pre-adjusted brackets when subjected to determined tip or torque values. Br J Orthod 1994;21: Taylor NG, Ison K. Frictional resistance between orthodontic brackets and archwires in the buccal segments. Angle Orthod 1996;66: Read-Ward GE, Jones SP, Davies EH. A comparison of selfligating and conventional orthodontic bracket systems. Br J Orthod 1997;24: Thomas S, Sherriff M, Birnie D. A comparative in vitro study of the frictional characteristics of two types of self-ligating brackets and two types of pre-adjusted edgewise brackets tied with elastomeric ligatures. Eur J Orthod 1998;20: Pizzoni L, Ravnholt G, Melsen B. Frictional forces related to self-ligating brackets. Eur J Orthod 1998;20: Kapur R, Sinha PK, Nanda RS. Frictional resistance of the Damon SL bracket. J Clin Orthod 1998;32: Thorstenson GA, Kusy RP. Resistance to sliding of self-ligating brackets versus conventional stainless steel twin brackets with second-order angulation in the dry and wet (saliva) states. Am J Orthod Dentofacial Orthop 2001;120: Wilkinson PD, Dysart PS, Hood JA, Herbison GP. Load-deflection characteristics of superelastic nickel-titanium orthodontic wires. Am J Orthod Dentofacial Orthop 2002;121:

10 187.e24 Kim, Kim, and Baek American Journal of Orthodontics and Dentofacial Orthopedics February Thorstenson GA, Kusy RP. Comparison of resistance to sliding between different self-ligating brackets with second-order angulation in the dry and saliva states. Am J Orthod Dentofacial Orthop 2002;121: Thorstenson GA, Kusy RP. Effect of archwire size and material on the resistance to sliding of self-ligating brackets with secondorder angulation in the dry state. Am J Orthod Dentofacial Orthop 2002;122: Hain M, Dhopatkar A, Rock P. The effect of ligation method on friction in sliding mechanics. Am J Orthod Dentofacial Orthop 2003;123: Redlich M, Mayer Y, Harari D, Lewinstein I. In vitro study of frictional forces during sliding mechanics of reduced-friction brackets. Am J Orthod Dentofacial Orthop 2003;124: Cacciafesta V, Sfondrini MF, Ricciardi A, Scribante A, Klersy C, Auricchio F. Evaluation of friction of stainless steel and esthetic self-ligating brackets in various bracket-archwire combinations. Am J Orthod Dentofacial Orthop 2003;124: Khambay B, Millett D, McHugh S. Evaluation of methods of archwire ligation on frictional resistance. Eur J Orthod 2004;26: Henao SP, Kusy RP. Evaluation of the frictional resistance of conventional and self-ligating bracket designs using standardized archwires and dental typodonts. Angle Orthod 2004;74: Henao SP, Kusy RP. Frictional evaluations of dental typodont models using four self-ligating designs and a conventional design. Angle Orthod 2005;75: Tecco S, Festa F, Caputi S, Traini T, Di Iorio D, D Attilio M. Friction of conventional and self-ligating brackets using a 10 bracket model. Angle Orthod 2005;75: Griffiths HS, Sherriff M, Ireland AJ. Resistance to sliding with 3 types of elastomeric modules. Am J Orthod Dentofacial Orthop 2005;127: Hain M, Dhopatkar A, Rock P. A comparison of different ligation methods on friction. Am J Orthod Dentofacial Orthop 2006;130: Bednar JR, Gruendeman GW, Sandrik JL. A comparative study of frictional forces between orthodontic brackets and arch wires. Am J Orthod Dentofacial Orthop 1991;100: Matasa CG. Self-engaging brackets: passive vs. active. Orthod Mater Insider 1996;9: Hemingway R, Williams RL, Hunt JA, Rudge SJ. The influence of bracket type on the force delivery of Ni-Ti archwires. Eur J Orthod 2001;23: Kusy RP, Whitley JQ. Effects of surface roughness on the coefficients of friction in model orthodontic systems. J Biomech 1990;23: Smart FM. Kinetic friction. Am J Orthod Dentofacial Orthop 2004;125(2):17A. 34. Moore MM, Harrington E, Rock WP. Factors affecting friction in the pre-adjusted appliance. Eur J Orthod 2004;26: Downing A, McCabe J, Gordon P. A study of frictional forces between orthodontic brackets and archwires. Br J Orthod 1994; 21: Keith O, Kusy RP, Whitley JQ. Zirconia brackets: an evaluation of morphology and coefficients of friction. Am J Orthod Dentofacial Orthop 1994;106: Cacciafesta V, Sfondrini MF, Scribante A, Klersy C, Auricchio F. Evaluation of friction of conventional and metal-insert ceramic brackets in various bracket-archwire combinations. Am J Orthod Dentofacial Orthop 2003;124: Kusy RP, Whitley JQ. Influence of archwire and bracket dimensions on sliding mechanics: derivations and determinations of the critical contact angles for binding. Eur J Orthod 1999;21: Damon DH. The Damon low-friction bracket: a biologically compatible straight-wire system. J Clin Orthod 1998;32: Omana HM, Moore RN, Bagby MD. Frictional properties of metal and ceramic brackets. J Clin Orthod 1992;26: Drescher D, Bourauel C, Schumacher HA. Frictional forces between bracket and arch wire. Am J Orthod Dentofacial Orthop 1989;96: Brady PB. Clinical applications of copper NiTi. Clinical impressions (Ormco) 1995;4: Jeong TJ, Choie MK. Evaluation of frictional forces between orthodontic brackets and archwires. Korea J Orthod 2000;30: