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 P­SLB systems; 4 A­SLB 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, 0.018â€¯× 0.018, 0.020â€¯× 0.020, 0.016â€¯× 0.022, 0.017â€¯× 0.025, 0.019â€¯× 0.025, and 0.021â€¯× 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, P­SLB and A­SLB systems (P < 0.001). P­SLB groups displayed no significant differences in FR between each other, regardless of archwire size. A­SLB groups did exhibit significant differences in FR between each other depending on both the bracket system and archwire size. Each A­SLB system tested possessed a distinctly different pattern of initiation of bracket-archwire engagement. CONCLUSIONS: FR between the archwire and bracket slot differs between P­SLB and A­SLB systems, with a distinct pattern of FR and bracket-archwire engagement for each A­SLB 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.

Comparison of fluoride release protocols for in-vitro testing of 3 orthodontic adhesives.

The objective of this study was to compare the fluoride release of 3 orthodontic adhesives using disks and bracketed teeth with different storage protocols. The adhesives used were a resin-modified glass ionomer (RMGI) (Fuji Ortho LC; GC America, Aslip, Ill), a polyacid-modified composite resin (PMCR)(Assure; Reliance Orthodontic Products, Itasca, Ill), and a composite control, Transbond XT (3M Unitek, Monrovia, Calif). Metal brackets were bonded to the buccal and lingual surfaces of 120 extracted human premolars. Five plastic containers holding 4 teeth (8 brackets) were used for each adhesive protocol. The samples were stored in containers holding 4 mL of deionized water at 37 degrees C for 28 and 84 days for the brackets and disks, respectively. The bracketed samples released larger initial amounts of fluoride compared with the disk samples during the first 5 to 6 days for both fluoride-releasing adhesives. The PMCR (Assure) released more fluoride (mg/cm(2)/day) than did the RMGI (Fuji Ortho LC) in all protocols with the exception of daily protocols when values diminished below the RMGI values near the 24th day and between the 56th and the 70th days for the bracketed and disk samples, respectively. Inconsistent values for fluoride release were noted in the bracket and disk samples when compared with daily versus cumulative water changes. Daily water changes revealed higher fluoride release levels (brackets), but this trend was not evident in the disk samples. Daily water changes may yield more clinically relevant data on fluoride release.