British Journal of Orthodontics

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Shear Bond Strength of Ceramic Brackets with Chemical or Mechanical Retention Carl-Magnus Forsberg D.D.S., Ph.D. & Catharina Hagberg D.D.S., Ph.D. To cite this article: Carl-Magnus Forsberg D.D.S., Ph.D. & Catharina Hagberg D.D.S., Ph.D. (1992) Shear Bond Strength of Ceramic Brackets with Chemical or Mechanical Retention, British Journal of Orthodontics, 19:3, 183-189, DOI: 10.1179/bjo.19.3.183 To link to this article:

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Date: 29 November 2016, At: 03:07

British Journal of Orthodontics/Vol. 19/ 1992j 183-189

Shear Bond Strength of Ceramic Brackets with Chemical or Mechanical Retention CARL-MAGNUS FORSBERG, D.D.S., PH.D. CATHARINA HAGBERG, D.D.S., PH.D. Department of Orthodontics, Karo1inska Institutet, Box 4064, S-141 04 Huddinge, Sweden Received for publication June 1991

A~tract. The study was undertaken to measure and compare the shear bond strengths of a ceramic bracket

wzth chemical retention, a ceramic bracket with a new type of textured base providing mechanical retention, and a metal bracket with foil-mesh base. The tests were performed on 51 extracted human premo/ars which were randomly divided into three equally large groups (n = 17 )-one group for each type of bracket. After debonding, the site offailure was noted and the enamel surface inspected with scanning electron microscopy. The ceramic bracket with chemical retention exhibited significantly higher bond strength than the corresponding bracket with textured base. In comparison with the metal bracket significantly higher bond strengths were recordedfor both types ofceramic brackets. The ceramic bracket with mechanical retention and the metal bracket were comparable as regards the site of bond failure. In some cases the chemical bond provided very high values ofbond strength. Enamel failure were recorded in three teeth which had been bonded with this type of ceramic bracket. Index words: Direct Bonding, Bond Strength, Bracket, Ceramic. Introduction

Orthodontic brackets manufactured from ceramic materials have been available for clinical use for approximately 10 years. During this time many patients have benefited from the improved aesthetic appearance of fixed appliances which are based on such brackets. Unlike polycarbonate brackets, which are also used in orthodontic practice for aesthetic reasons, ceramic brackets are more durable and allow adequate torque control over long treatment periods. Furthermore, the ceramic material has very good chemical resistance and the risk of discolouration is minimal. Recently, however, there have been reports of tooth damage associated with the use of ceramic brackets. Due to the hardness of the material (aluminum oxide), occlusal contact between a tooth and a ceramic bracket during orthodontic treatment may cause significant enamel wear within a re_lat~vely short period of time (Douglass, 1989; Vtazts et al., 1989, 1990a). The removal of ceramic brackets has also been an area of significant con~ern. In vitro studies have reported loss of sectiOns of enamel or even crown fractures during debonding (Joseph and Rossouw, 1990; Storm, 1990; Viazis et al., 1990b). This problem is presumably related to bond strength. Ceramic brackets derive their bond strength 030 I-228Xi92/008000 + 00102.00

either from the use of a si lane coupling agent in the brackets base or through mechanical retention. Silane treatment of a smooth ceramic bracket base unites the silica component of the bracket with the composite resin to produce a chemical bond, which may be stronger than the bond between resin and conditioned enamel. An example of this category of brackets is the Transcendt>TM. In a second generation of this bracket (the Transcend 2000™, Unitek Corp./3M, Monrovia, Ca, U.S.A.) the silanetreated base has been replaced with a textured base intended for mechanical retention. According to the manufacturer the purpose of this change has been to design a ceramic bracket base which acts much like a metal bracket base during bonding as well as debonding. The purpose of this investigation was to compare the shear/peel bond strengths of these two different types of ceramic brackets from the same manufacturer. As a reference, the ceramic brackets were also compared with the bond stren~th of a standard stainless steel bracket (Ormesh TH, Ormco, Glendora, Ca, U.S.A.). Materials and Methods

Specifications for the brackets used in this study are shown in Table I. The nominal base area of the © 1992 British Society for the Study of Onhodontic•

184 C-M. Forsberg and C. Hagberg TABLE


Bracket (0·018 slot)

BJO Vol. /9 No. 3

Specifications for brackets tested


Transcend Ceramic Ceramic Transcend 2000 Ormco Foil-Mesh Metal


Base area (mm 2)

Chemical Mechanical Mechanical

12·3 12·2 17·4

different types of brackets was measured with micrometer callipers which had a precision of 0·0 I mm. Ten brackets of each type were measured and the mean areas calculated (Table I). The bond strength of the brackets was tested on extracted bicuspids. The teeth had been placed into a phosphate buffered saline (PBS) solution (0·9 per cent) immediately after extraction. The PBS medium is suitable to use for storage of teeth in cases where it is important to maintain the inorganic part of the enamel intact during the entire storage period. In order to prevent bacterial growth sodium-azide had also been added to the medium. Prior to bonding, each tooth was examined with a magnifying viewer (4 x ), and only those teeth which exhibited an intact buccal enamel surface were included in the study. Fifty-one teeth which fulfilled this criterion were randomly divided into three equally large groups (n = 17)--one group for each type of bracket. Normal clinical methods without modifications were applied for bonding the brackets to the teeth. The following steps were executed. The buccal tooth surface was polished for 10 seconds with a suspension of pumice in Tubulicid.., (Dental Therapeutics AB, Nacka, Sweden) applied on a rotating brush. After rinsing and drying with compressed air, the tooth was etched with 37 per cent phosphoric acid for 15 seconds, and subsequently rinsed and thoroughly dried again. In one of the teeth the typical dull white-frosted appearance of the enamel surface was not achieved after the standard etching time.:.-ln this case, etching was repeated for 30 seconds. The enamel and the bracket base were coated with a thin layer of bonding resin and the bracket bonded to the tooth with a quartz-filled (filler content 67 per cent) BIS-GMA diacrylate (UniteTM, Unitek Corporation, Monrovia, California) according to the manufacturer's instructions. Before polymerisation, excess adhesive was removed from the tooth. After bonding, the teeth were left to dry for 10 minutes and subsequently placed in the PBS-solution at 37°C. After one week of storage, the bracket of each tooth was tied to a piece of Edgewise archwire (0·018 x 0·025) with a 0·25-mm stainless steel ligature. The archwire was then fixed in the slot of a

fiG. I (a) Bicuspid with a bonded ceramic bracket. The tooth is ligated to an Edgewise archwire and fixed in a standardized position with the crown in the centre of a detachable plastic ring. (b) Bicuspid embedded in dental stone leaving the buccal surface and the bracket exposed.

holder, so that the tooth was positioned with its crown in the center of a detachable plastic ring (Fig. la). The plastic ring was then filled with Caecal.., dental stone type Ill (Coe Laboratories lnc, Chicago, Ill.) leaving only the buccal surface of the tooth and the bracket exposed (Fig. I b). After the stone had set, the ligature was cut and the ring with the tooth was removed for the next specimen to be positioned and embedded in a new plastic ring according to the same standardized procedure. The Edgewise archwire, which was used as a guide, was provided with a third order bend to compensate for the torque in the brackets. This adjustment of the wire ensured that the bracket-tooth interface was parallel to the shear force applied during the bond strength test. The samples were kept moist both before and during the test in order to avoid artifacts due to desiccation. A universal testing apparatus (Alwetron-IBS 41 System, AB Lorenzon & Wettre, Stockholm, Swe-

Bond Strength of Ceramic Brackets

BJO August /992


2 Comparison of mean shear forces (in M Pa) required to debond si/onetreated ceramic brackets, ceramic brackets with textured bases, andfoil-mesh metal brackets TABLE

Type of bracket



M in



I. Ceramic silane






2. Ceramic textured






3. Metal foil-mesh






Comparison of bond strengths (t-values) I V. 2 2.06*

I V. 3 7.96*** 2 t'. 3 6·48***

• P

Shear bond strength of ceramic brackets with chemical or mechanical retention.

The study was undertaken to measure and compare the shear bond strengths of a ceramic bracket with chemical retention, a ceramic bracket with a new ty...
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