Friction and archwire engagement in contemporary self-ligating appliance systems : An in vitro comparison

PURPOSE

The aim of this study was to compare classical friction (FR) in passive self-ligating brackets (P-SLBs), active self-ligating brackets (A-SLBs) and a traditional twin bracket, in vitro, and to identify the point of initiation of bracket-archwire engagement.

METHODS

Nine bracket systems of 0.022 in slot size were FR tested: 5 P‑SLB systems; 4 A‑SLB systems; and a control group of twin brackets with elastomeric ligatures. Single upper right central incisor brackets were mounted on a custom metal fixture for testing. Straight sections of various round and rectangular nickel-titanium (NiTi) archwires (0.016, 0.018, 0.018 × 0.018, 0.020 × 0.020, 0.016 × 0.022, 0.017 × 0.025, 0.019 × 0.025, and 0.021 × 0.025 in) were ligated to the bracket and peak static FR (cN) was measured with an Instron Universal Testing Machine. Ten unique tests each utilizing a new bracket and new archwire were conducted for each group in the dry state.

RESULTS

FR was significantly different between control, P‑SLB and A‑SLB systems (P < 0.001). P‑SLB groups displayed no significant differences in FR between each other, regardless of archwire size. A‑SLB groups did exhibit significant differences in FR between each other depending on both the bracket system and archwire size. Each A‑SLB system tested possessed a distinctly different pattern of initiation of bracket-archwire engagement.

CONCLUSIONS

FR between the archwire and bracket slot differs between P‑SLB and A‑SLB systems, with a distinct pattern of FR and bracket-archwire engagement for each A‑SLB system. Understanding the different bracket-wire interactions of SLB systems should help orthodontic clinicians to plan effective and efficient biomechanics with the bracket system of their choice.

Friction evaluation of an elastic chain positioned under or over the wire in self-ligating brackets

Objectives:

This study aimed to evaluate the frictional resistance produced by active and passive self-ligating brackets on stainless steel archwires in the absence or presence of elastomeric chains under or over the wire.

Materials and Methods:

Four types of self-ligating brackets were used: Two active and two passive. For each commercial brand, five brackets were bonded to an acrylic plate and the frictional resistance was evaluated with 0.018” and 0.019” × 0.025” stainless steel wires in three situations: Without elastomeric chain, with elastomeric chain placed under and over the wire.

Results:

The bracket type, cross-section of the wire, and type of ligation had significant interactions with each other; the frictional resistance was significantly lower with the use of passive self-ligated brackets, while no difference was found when a 0.018” wire was tested. Moreover, the frictional resistance in the absence of an elastomeric chain, or when the chain was under the wire, was significantly lower in comparison with the values obtained when the chain was placed on the wire.

Conclusion:

Frictional resistance of passive and active self-ligated brackets is influenced by the ligation methods and the cross-sectioning of archwires.

Development of a new evaluation method for orthodontic forces generated in individual patients

Numerous experimental studies have examined how much orthodontic force is needed to move teeth more smoothly; however, no reports have examined this clinically in individual, living subjects. We aimed to develop a method for quantifying the force exerted on individual teeth by an orthodontic wire to measure how loads placed on crowded teeth change dynamically over time. Accordingly, we fabricated a series of dental casts of patients undergoing orthodontic treatment (using optical impressions and a three-dimensional printer), fitted these models with nickel-titanium wire, and subjected them to bending load tests. During leveling, nickel-titanium wire is generally considered to exert a weak force due to its low elastic modulus, with a weak orthodontic force applied over a long period of time due to its superelasticity; however, we found that the actual energy exerted by nickel-titanium wire is also largely affected by other factors (e.g., amount of crowding).

In-vitro investigation of the mechanical friction properties of a computer-aided design and computer-aided manufacturing lingual bracket system under diverse tooth displacement condition

Objective

The purpose of this study was to compare the static (SFF) and kinetic frictional forces (KFF) of a computer-aided design and computer-aided manufacturing lingual bracket (CAD/CAM-LB) with those of conventional LB (Con-LB) and Con-LB with narrow bracket width (Con-LB-NBW) under 3 tooth displacement conditions.

Methods

The samples were divided into 9 groups according to combinations of 3 LB types (CAD/CAM-LB [Incognito], Con-LB [7th Generation, 7G], and Con-LB-NBW [STb]) with 3 displacement conditions (no displacement [control], maxillary right lateral incisor with 1-mm palatal displacement [MXLI-PD], and maxillary right canine with 1-mm gingival displacement [MXC-GD]; n = 6/group). While drawing a 0.016-inch copper or super-elastic nickel-titanium archwire with 0.5 mm/min for 5 minutes in a chamber maintained at 36.5℃, SFF and KFF were measured. The Kruskal-Wallis method with Bonferroni correction was performed.

Results

The Incognito group demonstrated the highest SFF, followed by the 7G and STb groups ([STb-control, STb-MXLI-PD, Stb-MXC-GD] < [7G-MXC-GD, 7G-MXLI-PD, 7G-control] < [Incognito-MXLI-PD, Incognito-control, Incognito-MXC-GD]; p < 0.001). However, there were no significant differences in SFF among the 3 displacement conditions within each bracket group. Within each displacement condition, the Incognito group demonstrated the highest KFF, followed by the 7G and STb groups ([STb-control, STb-MXLI-PD] < Stb-MXC-GD < 7G-MXLI-PD < [7G-control, 7G-MXC-GD] < [7G-MXC-GD, Incognito-MXLI-PD, Incognito-control] < [Incognito-control, Incognito-MXC-GD]; p < 0.001). MXC-GD exhibited higher KFFs than MXLI-PD in the same bracket group.

Conclusions

The slot design and ligation method of the CAD/CAM-LB system should be modified to reduce SFF and KFF during the leveling/alignment stage.

Effect of the vertical position of the canine on the frictional/orthodontic force ratio of Ni-Ti archwires during the levelling phase of orthodontic treatment

This study investigated the effect of the vertical position of the canine on changes in the frictional/orthodontic (F/O) force ratio of nickel-titanium (Ni-Ti) archwires during the initial levelling phase of orthodontic treatment. Frictional and orthodontic forces were measured by using low-friction brackets and Ni-Ti archwires with three different cross-sectional sizes and force types. To simulate canine malocclusion (first premolar extraction case), the upper right canine was displaced gingivally by 1 to 3 mm and the inter-bracket distance between the upper right lateral incisor and second premolar was set at 15 mm or 20 mm. A three-point bending test was performed to measure the orthodontic force of each Ni-Ti archwire. Frictional forces were measured with a universal testing machine and dental arch models by pulling parallel to the end of the archwire at a crosshead speed of 0.5 mm/min. F/O force ratio was calculated and analysed statistically. At a displacement of 3 mm, few archwires had F/O force ratios of less than 1.0, at which orthodontic force overcame frictional force, thus ensuring extrusion of the canine. For effective tooth movement, orthodontists should use Ni-Ti archwires with an F/O force ratio of less than 1.0.

Resistance to sliding in orthodontics: misconception or method error? A systematic review and a proposal of a test protocol

Resistance to sliding (RS) between the bracket, wire, and ligature has been largely debated in orthodontics. Despite the extensive number of published studies, the lack of discussion of the methods used has led to little understanding of this phenomenon. The aim of this study was to discuss variables affecting RS in orthodontics and to suggest an operative protocol. The search included PubMed©, Medline©, and the Cochrane Library©. References of full-text articles were manually analyzed. English-language articles published between January 2007 and January 2017 that performed an in vitro analysis of RS between the bracket, wire, and ligature were included. Study methods were analyzed based on the study design, description of materials, and experimental setup, and a protocol to standardize the testing methods was proposed. From 404 articles identified from the database search and 242 records selected from published references, 101 were eligible for the qualitative analysis, and six for the quantitative synthesis. One or more experimental parameters were incompatible and a meta-analysis was not performed. Major factors regarding the study design, materials, and experimental setup were not clearly described by most studies. The normal force, that is the force perpendicular to the sliding of the wire and one of the most relevant variable in RS, was not considered by most studies. Different variables were introduced, often acting as confounding factors. A protocol was suggested to standardize testing procedures and enhance the understanding of in vitro findings.

Influence of ligation method on friction resistance of lingual brackets with different second-order angulations: an in vitro study

Objective:

To evaluate stainless steel archwire static friction in active and passive self-ligating lingual and conventional brackets with second-order angulations.

Methods:

Two conventional lingual brackets for canines (STb light/Ormco; PSWb/Tecnident), and two self-ligating brackets, one active (In-Ovation L/GAC) and the other passive (3D/ Forestadent), were evaluated. A stainless steel archwire was used at 0°, 3° and 5° angulations. Metal ligatures, conventional elastic ligatures, and low friction elastic ligatures were also tested. A universal testing machine applied friction between brackets and wires, simulating sliding mechanics, to produce 2-mm sliding at 3 mm/minute speed.

Results:

Two-way analysis of variance demonstrated a significant effect of the interaction between brackets and angulations (p < 0.001). Tukey test indicated that the highest frictional resistance values were observed at 5° angulation for In-Ovation L, PSWb bracket with non conventional ligature, and STb bracket with metal ligature. As for 3D, PSWb with conventional or metal ligatures, and STb brackets with non conventional ligature, showed significantly lower static frictional resistance with 0° angulation. At 0° angulation, STb brackets with metal ties, In-Ovation L brackets and 3D brackets had the lowest frictional resistance.

Conclusions:

As the angulation increased from 0° to 3°, static friction resistance increased. When angulation increased from 3° to 5°, static friction resistance increased or remained the same. Self-ligating 3D and In-Ovation L brackets, as well as conventional STb brackets, seem to be the best option when sliding mechanics is used to perform lingual orthodontic treatment.

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

Objective

We evaluated the effects of tooth displacement on frictional force when conventional ligating lingual brackets (CL-LBs), CL-LBs with a narrow bracket width, and self-ligating lingual brackets (SL-LBs) were used with initial leveling and alignment wires.

Methods

CL-LBs (7th Generation), CL-LBs with a narrow bracket width (STb), and SL-LBs (In-Ovation L) were tested under three tooth displacement conditions: no displacement (control); a 2-mm palatal displacement (PD) of the maxillary right lateral incisor (MXLI); and a 2-mm gingival displacement (GD) of the maxillary right canine (MXC) (nine groups, n = 7 per group). A stereolithographic typodont system and artificial saliva were used. Static and kinetic frictional forces (SFF and KFF, respectively) were measured while drawing a 0.013-inch copper-nickel-titanium archwire through brackets at 0.5 mm/min for 5 minutes at 36.5℃.

Results

The In-Ovation L exhibited lower SFF under control conditions and lower KFF under all displacement conditions than the 7th Generation and STb (all p < 0.001). No significant difference in SFF existed between the In-Ovation L and STb for a 2-mm GD of the MXC and 2-mm PD of the MXLI. A 2-mm GD of the MXC produced higher SFF and KFF than a 2-mm PD of the MXLI in all brackets (all p < 0.001).

Conclusions

CL-LBs with narrow bracket widths exhibited higher KFF than SL-LBs under tooth displacement conditions. CL-LBs and ligation methods should be developed to produce SFF and KFF as low as those in SL-LBs during the initial and leveling stage.

Effect of passive self-ligating bracket placement on the posterior teeth on reduction of frictional force in sliding mechanics

Objective

The purpose of this study was to investigate the static (SFF) and kinetic frictional forces (KFF) in sliding mechanics of hybrid bracket systems that involve placing a conventional bracket (CB) or active self-ligating bracket (ASLB) on the maxillary anterior teeth (MXAT) and a passive SLB (PSLB) on the maxillary posterior teeth (MXPT).

Methods

The samples consisted of two thoroughbred types (group 1, anterior-CB + posterior-CB; group 2, anterior-ASLB + posterior-ASLB) and four hybrid types (group 3, anterior-CB + posterior-PSLB-type 1; group 4, anterior-CB + posterior-PSLB-type 2; group 5, anterior-ASLB + posterior-PSLB-type 1; group 6, anterior-ASLB + posterior-PSLB-type 2) (n = 13 per group). After maxillary dentition alignment and maxillary first premolars removal in the stereolithographically-made typodont system, a 0.019 × 0.025-inch stainless steel wire was drawn through the right quadrant of the maxillary arch at 0.5 mm/min for 5 min. The SFF and KFF were measured with a mechanical testing machine and statistical analyses were performed.

Results

Four different categories of SFF and KFF were observed among all groups (all p < 0.001). Group 1 demonstrated the highest SFF and KFF; groups 4 and 3 were second and third highest, respectively. The fourth category included groups 2, 5, and 6. Placing PSLBs on the MXPT resulted in significant SFF and KFF reductions in cases with CBs on the MXAT, but not in cases with ASLBs on the MXAT.

Conclusions

These data might aid in the development of a hybrid bracket system that enables low-friction sliding of an archwire through the MXPT.

Effect of self-ligating bracket type and vibration on frictional force and stick-slip phenomenon in diverse tooth displacement conditions: an in vitro mechanical analysis

OBJECTIVE

To evaluate the effects of self-ligating bracket (SLB) type and vibration on frictional force and stick-slip phenomenon (SSP) in diverse tooth displacement conditions when a levelling/alignment wire was drawn.

MATERIALS AND METHODS

A total of 16 groups were tested (n = 10/group): Two types of SLBs [active SLB (ASLB, In-Ovation R) and passive SLB (PSLB, Damon Q)]; vibration (30 Hz and 0.25 N) and non-vibration conditions; and 4 types of displacement [2mm lingual displacement of the maxillary right lateral incisor (LD), 2mm gingival displacement of the maxillary right canine (GD), combination of LD and GD (LGD), and control]. After applying artificial saliva to the typodont system, 0.018 copper nickel-titanium archwire was drawn by Instron with a speed of 0.5mm/min for 5 minutes at 36.5°C. After static/kinetic frictional forces (SFF/KFF), and frequency/amplitude of SSP were measured, statistical analysis was performed.

RESULTS

ASLB exhibited higher SFF, KFF, and SSP amplitude (all P < 0.001) and lower SSF frequency (all P < 0.05) than PSLB in all displacement groups. Vibration decreased SFF, KFF, and SSP amplitude and increased SSP frequency in control and all displacement groups (all P < 0.001). ASLB exhibited lower SSP frequency than PSLB only under non-vibration condition (P < 0.05 in LD and GD, P < 0.01 in LGD). However, regardless of vibration conditions, ASLB demonstrated higher SSP amplitude than PSLB in all displacement groups (all P < 0.001 under non-vibration; all P < 0.01 under vibration).

CONCLUSION

Even in tooth displacement conditions, vibration significantly reduced SFF, KFF, SSP amplitude, and increased SPP frequency in both PSLB and ASLB. However, in vivo studies would be needed to confirm the clinical significance.

Comparative study of friction between metallic and conventional interactive self-ligating brackets in different alignment conditions

Objective

The aim of this study was to compare the friction between three bracket models: conventional stainless steel (Ovation, Dentsply GAC), self-ligating ceramic (In-Ovation, Denstply GAC) and self-ligating stainless steel brackets (In-Ovation R, Dentsply GAC).

Methods

Five brackets were used for each model. They were bonded to an aluminum prototype that allowed the simulation of four misalignment situations (n = 10). Three of these situations occurred at the initial phase (in which a 0.016-in nickel-titanium wire was used): 1. horizontal; 2. vertical; and 3. simultaneous horizontal/vertical. One of the situations occurred at the final treatment phase: 4. no misalignment (in which a 0.019 x 0.025-inch stainless steel rectangular wire was used). The wires slipped through the brackets and friction was measured by a Universal Testing Machine.

Results

Analysis of variance followed by Tukey's Test for multiple comparisons (α = 0.05) were applied to assess the results. Significant interaction (p < 0.01) among groups was found. For the tests that simulated initial alignment, Ovation^® bracket produced the highest friction. The two self-ligating models resulted in lower and similar values, except for the horizontal situation, in which In-Ovation C^® showed lower friction, which was similar to the In-Ovation R^® metallic model. For the no misalignment situation, the same results were observed.

Conclusion

The self-ligating system was superior to the conventional one due to producing less friction. With regard to the material used for manufacturing the brackets, the In-Ovation C^® ceramic model showed less friction than the metallic ones.

Effect of tooth displacement and vibration on frictional force and stick-slip phenomenon in conventional brackets: a preliminary in vitro mechanical analysis

OBJECTIVE

To evaluate the effects of tooth displacement and vibration on frictional force and stick-slip phenomenon (SSP) when conventional brackets were used with a levelling/alignment wire.

MATERIALS AND METHODS

The samples consisted of six groups (n = 10 per group) with combinations of tooth displacement (2mm lingual displacement [LD], 2mm gingival displacement [GD], and no displacement [control]) and vibration conditions (absence and presence at 30 Hz and 0.25 N). A stereolithographically made typodont system was used with conventional brackets and elastomeric ligatures. After application of artificial saliva, static/kinetic frictional forces (SFF/KFF) and frequency/amplitude of SSP were measured while drawing a 0.018-inch copper nickel-titanium (Cu-NiTi) archwire at a speed of 0.5mm/min for 5 minutes at 36.5 degree celsius. Two-way analysis of variance and independent t-test were performed.

RESULTS

Tooth displacement increased SFF and KFF (control < LD < GD, all P < 0.001) and reduced SSP frequency (control > [LD, GD], P < 0.01). Vibration reduced SFF, KFF, and SSP amplitude in the control group (P < 0.05, P < 0.05, and P < 0.001, respectively), but not in the LD and GD groups. SSP frequency was increased by vibration in the control, LD, and GD groups (all P < 0.001), and it was lower in the LD and GD groups than in the control group (P < 0.01).

CONCLUSIONS

When conventional brackets and a 0.018-inch Cu-NiTi archwire were used in the tooth displacement conditions (LD and GD), vibration did not significantly reduce SFF, KFF, or SSP amplitude.

An assessment of conventional and self-ligating brackets in Class I maxillary constriction patients

OBJECTIVE

To evaluate two different treatment systems with regard to incisor position, transverse dimension changes in maxillary arch, changes in maxillary molar inclinations, clinical periodontal parameters, and pain intensity in patients with a Class I malocclusion.

MATERIALS AND METHODS

Seventeen patients (with a mean age of 14.5 years) underwent orthodontic treatment with the Roth prescribed edgewise bracket systems after expanding the maxillary arch with a quad-helix appliance, and 16 patients (with a mean age of 14.8 years) underwent orthodontic treatment with the Damon 3MX bracket system. Each subject's lateral cephalometric and posteroanterior radiographs and dental casts were obtained at the beginning of the treatment and after debonding. In addition to these, the periodontal index and pain scores were taken.

RESULTS

Cephalometric data showed that in both treatment systems, overjet value decreased and maxillary and mandibular incisors proclined. Posteroanterior measurements demonstrated a greater increase in the maxillary molar inclination in the Damon group. Significant increase of maxillary intercanine, interpremolar, and intermolar widths was shown in both systems. Periodontal index and pain score changes between different observation periods were the same.

CONCLUSIONS

The conventional and Damon systems were found similar with regard to the incisor position, transverse dimension changes in maxillary arch, clinical periodontal parameters, and pain intensity. The only significant difference was that the Damon system inclined the maxillary molars more buccally than the conventional group.

Effects of active and passive lacebacks on antero-posterior position of maxillary first molars and central incisors

The purpose of this study was to compare the effects of active and passive lacebacks on antero-posterior position of maxillary first molars and central incisors during leveling phase. Twenty-three subjects with Class I and Class II malocclusion were treated with first premolars extraction using preadjusted appliances (MBT 0.022-inch brackets). The leveling phase was performed with stainless steel archwires only. The sample was divided into 2 groups: 14 subjects received active lacebacks (Group 1) and 9 subjects received passive lacebacks (Group 2). Lacebacks were made from 0.008-inch ligature wire. Lateral cephalometric radiographs were taken pre- and post-leveling phase. Student's t-test was applied to determine the differences between pre- and post-leveling mean values and to determine the mean differences between groups. In Group I, the first molars showed a significant mesial movement, whereas no change was observed in Group 2. In both groups, maxillary central incisor crowns moved to lingual side. In conclusion, active laceback produced anchorage loss of maxillary first molars whereas passive laceback did not affect the position of these teeth. Active and passive lacebacks were effective in preventing central incisor proclination.