Knoop hardness of enamel and shear bond strength of brackets bonded with composite resin with and without fluoride

Silvia Amélia Scudeler Vedovello,Heloísa Cristina Valdrighi,Marcelo Grigoletto,Mayury Kuramae,Mário Vedovello Filho

doi:10.1590/s2176-94512012000400007

Silvia Amélia Scudeler Vedovello, Heloísa Cristina Valdrighi + Show 3 more

Open Access

https://doi.org/10.1590/s2176-94512012000400007

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Abstract

OBJECTIVE: The aim of this study was to evaluate the Knoop hardness of enamel, shear bond strength and failure pattern (adhesive, bracket/resin interface or mixed) after bonding and debonding brackets, using resin composite with fluoride (Ortho Lite Cure, Ortho Source®) and without fluoride (Orthobond, Morelli®). METHODS: Fragments (6 mm x 6 mm) of 40 bovine incisor crowns were embedded in acrylic self-polymerizing resin. The Knoop hardness measurements were performed before and after bonding metal brackets. The specimens were divided into two groups, according to composite resin: with fluoride (Ortho Lite Cure, Ortho Source®) and without fluoride (Orthobond, Morelli®). After bonding, the specimens were submitted to demineralization and remineralization cycling for 14 days. Shear bond strength testing was performed in a universal test machine (EMIC), at 5 mm/min crosshead speed. RESULTS: There was no significant difference in shear bond strength between Groups I and II. After demineralization and remineralization procedures (DE/RE), the specimens bonded with Ortho Lite Cure showed higher Knoop hardness than Orthobond. For both groups there was predominance of failure at bracket/resin interface. CONCLUSION: specimens bonded with fluoride resin composite showed higher microhardness after DE/RE cycling than those bonded with resin composite without fluoride, although no difference in shear bond strength was found.

Highlights

During treatment planning, the problems that can arise from bonding accessories are of fundamental importance for a successful outcome.[15,22] Since the introduction of methods for cementation and bonding orthodontic accessories to dental enamel, various modifications have occurred
The test specimens that received the composite with fluoride (Ortho Lite Cure) presented a significantly higher final microhardness when compared with those treated with resin composite without fluoride (Orthobond) (p
Analysis of the results indicated that there was a significant reduction in the hardness values after the demineralization and remineralization procedure, both in the test specimens in Group I and Group II (Table 1)

Summary

Introduction

The problems that can arise from bonding accessories are of fundamental importance for a successful outcome.[15,22] Since the introduction of methods for cementation and bonding orthodontic accessories to dental enamel, various modifications have occurred. Caries is a dynamic process, resulting from microbial metabolism on the tooth surface, which may result in mineral loss due to the imbalance between the demineralization and remineralization process, and subsequently, in cavitation.[12] To diminish the incidence of caries around orthodontic brackets, materials with fluoride releasing capacity, such as glass ionomer cements, were introduced. Glass ionomer cement was introduced in restorative dentistry in 1972, showing properties of chemical bond to enamel and dentin, as well as to non precious metals and plastics.[15,16] In addition to acting as a reservoir for fluoride released by means of ionic exchanges without any loss of resistance, it can be stored for a long time.[14]

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