In vitro bond strengths post thermal and fatigue load cycling of sapphire brackets bonded with self-etch primer and evaluation of enamel damage

Abstract

Background: This in vitro study compares a self-etch primer (SEP) to an etch-and-rinse (EaR) for bonding sapphire brackets by evaluation of the enamel etch-pattern, shear bond strength, amount of remnant adhesive and enamel surface damage following thermal and fatigue cyclic loading. Material and Methods: Ceramic (sapphire) brackets were bonded to 80 extracted human premolars using two enamel etching protocols: conventional EaR using 37% phosphoric acid (PA) gel (control), and a SEP (Transbond Plus). Each group was subdivided into two subgroups (n=20 teeth) according to the time of bracket debonding: after 24 h water storage or following 5000 thermo-cycles plus 5000 cycles fatigue loading, to determine the shear bond strength (SBS), adhesive remnant index (ARI score), with scanning electron microscopy (SEM) evaluation of enamel condition. Results: The control subgroups consistently exhibited significantly higher (p ˂ 0.05) SBS mean values (23.4-29.8 MPa) than the SEP subgroups (15.1-22.4 MPa) at both bracket debonding time points. However, the SEP subgroups yielded milder etch-patterns and attained SBS values above the minimum requirement range for clinical performance. In addition, the higher SBS of control subgroups was accompanied with higher ARI scores and enamel damage grades than SEP subgroups as confirmed by SEM. Thermocycling and fatigue significantly reduced the SBS of all subgroups, with a non-significant drop in the amount of adhesive residue or enamel damage. Conclusions: The use of SEP can be a suitable alternative to the conventional PA gel for sapphire bracket bonding as it maintains suitable bond strength and has the potential to produce both less remnant adhesive and enamel damage.

Development of a remineralizing calcium phosphate nanoparticle-containing self-etching system for orthodontic bonding

“…3− peak at the end of an incipient lesion converges to that of intact enamel [31,43]. Since SEPs exhibit a relatively milder etching pattern than carious lesions and CAEs [16,44], the SEPS preclude significant depletion of the mineral content.…”

“…Enamel conditioning with SEPs has recently attracted ample interest in orthodontic bonding, as they can etch and prime the enamel surface in a single step; this addresses the increased demand for safer, more convenient, and less technique-sensitive materials, but has not eliminated the enamel damage occurring at bracket debonding [16,33]. The hypotheses of the current study were proven and accepted, since a novel bioactive, enamel-preserving orthodontic SEP left minimal or no adhesive residue with a potential remineralizing effect on the enamel and did not compromise orthodontic bond strengths.…”

“…Although there are no unanimously accepted values for nCaP precipitates (c′, d′), while the 7%nHA-SEP revealed a milder etching effect presenting smooth surfaces (e, f) with evident nCaP precipitations in the form of small granules (e′) or larger aggregations (f), with partial or complete micro-pores obliteration (e, f) optimal orthodontic bonding strength, a minimum range of 5.9-7.8 MPa was deemed adequate for bracket bonding while attaining satisfactory clinical performance [36]. A higher range up to 20 MPa was suggested [37], yet it has been reported that a SBS higher than 12 MPa can induce enamel damage [15,16]. Thus, a range of 6-12 MPa has been adopted in the majority of in vitro orthodontic bond strength studies [38,39].…”

“…On the other hand, self-etching primers (SEPs) provide simultaneous etching and priming functions, which is more convenient for both the clinician and patient due to chairside time savings and reliable bond strengths [13,14]. However, there is debate as to whether the amount of adhesive left after debonding is less than or the same as that of the CAE technique, and enamel damage after bracket debonding could not be eliminated [4,15,16].…”

The Effect of Potassium Iodide Application on the Bond Strength of Orthodontic Brackets Bonded to Silver Diamine Fluoride Pretreated Dentin - “An In-Vitro Study.”

“…If run-out achieved, the load level was increased by a predetermined increment of stress, and the same specimen was run again at the new load level. 16,17 Cyclic loading at 1.6 Hz frequency was applied, which is corresponding to the reported oral chewing frequency 17 . The maximum number of cycles applied at each load step was 1,000 cycles.…”