Analysis of structural, morphological alterations, wettability characteristics and adhesion to enamel after various surface conditioning methods

Abstract

Minimal invasive dental reconstructions and orthodontic appliances are bonded to enamel without removing the enamel with rotating instruments but the top layer of enamel may be partially aprismatic and impair adhesion. The objectives of this study were to investigate the effect of mechanical surface conditioning methods for removing enamel on its structural, morphological alterations, wettability characteristics and adhesion of resin based cement to the conditioned surfaces. Maxillary human incisors (N=40, n quadrant =160) were obtained and coronal sections were embedded in acrylic with their labial surfaces exposed.The teeth were randomly divided into 4 groups and the enamel surface of each tooth was divided into 4 quadrants. The surfaces were conditioned in a clockwise manner by one of the following methods: 1) Non-conditioned enamel acted as the control group (C); 2) Silicone coated disc (Sof-Lex disc, Black, 3M ESPE) (SD); 3) Diamond bur at slow speed (DB) and 4) Air-borne particle abrasion (50 µm Al 2 O 3 , 2 bar, 5 s) (AA). Surface roughness was measured at each quadrant using a non-contact digital profilometer and contact angle measurements were performed using a goniometer. Enamel surfaces were then etched with 37% H 3 PO 4 for 60 s and roughness and wettability measurements were repeated. The enamel surfaces in each quadrant received resin composite luting cement (Variolink II, Ivoclar Vivadent) incrementally in a polyethylene mould (diameter: 1 mm 2 ; height: 4 mm) and photopolymerized. The specimens were stored in distilled water for 24 hours at 37ºC until the testing procedures and then shear force was applied to the adhesive interface until failure occurred in a Universal Testing Machine (0.5 mm/min). Microshear bond (µSBS) was calculated by dividing the maximum load (N) by the bonding surface area of the resin cement.Representative enamel surfaces were analyzed under the scanning electron microscope (SEM) (x5000) to assess the surface morphology. Failure types were analyzed using optical microscope and SEM. Data (MPa) were analyzed using one-way ANOVA

The quality of etched enamel in different regions and tooth types and its significance in bonding and the development of white spot lesions

“…The inferior etch quality in the cervical region can be explained by aprismatic enamel, which is orientated parallel rather than perpendicular to the enamel surface. 2,4,5 If the etchant cannot penetrate the full thickness of prismless enamel, a poor etch quality should be expected. This is why pretreatment mechanical abrasion of the tooth enamel, which removes the aprismatic enamel and exposes the underlying prismatic enamel, improves etch quality.…”

“…2 The prismless layer has an optic axis nearly parallel to the enamel's surface. [2][3][4][5] In contrast, prismatic enamel has distinct rod boundaries oriented perpendicular to the surface. The aprismatic enamel is believed to be due to decreased ameloblast activity during tooth development and the disappearance of Tomes' processes during the end of amelogenesis.…”

Conditioning, bonding, and cementation of orthodontic appliances in teeth with enamel alterations. Literature review

“…Concerning debonding, it was shown that the use of rubbers for the removal of residual composites in orthodontic appliances was more effective compared to the use of discs. In summary, composite resins improve the bonding strength of orthodontic brackets, but conservative removal methods would be needed to reduce damage to tooth enamel 17,18,20,23,24,28,33,38,41 . Other studies analyzed other materials than those mentioned, including the adhesive residue remover and the tungsten carbide bur, which is the most aggressive for enamel.…”