The shear bond strengths of stainless steel orthodontic brackets bonded to teeth with orthodontic composite resin and various fissure sealants V. P. Joseph, BDS, MSc (Dent.), and P. E. Rossouw, BSc, BChD, Hons.-BChD, MChD Tygerberg, Republic of South Africa Enamel decalcification (whitened areas) around orthodontic brackets during therapy is a well-recognized problem. If a fissure sealant could be used to isolate the enamel and yet withstand debonding of the bracket during therapy, this problem might be overcome. The objective of this in vitro study was to determine (1) the shear bond strengths of stainless steel orthodontic brackets bonded to teeth with an orthodontic bonding resin together with a primary coating of various fissure sealants and (2) the fracture sites of these debonded samples. Forty noncarious human canine teeth were divided into four groups of 10 teeth each. In group A, the brackets were bonded to the buccal surfaces of the prepared teeth with a macrofilled orthodontic composite resin only. In groups B, C, and D, the brackets were similarly bonded, except that the teeth were first treated with a fissure sealant--group B having a light-cured unfilled clear fissure sealant, group C having a light-cured microfilled fissure Sealant, and group D having a chemically cured opaque fissure sealant. After storage at 37 ° C for 24 hours, the brackets were subjected to a shear force in an Instron machine, and the fracture strengths were recorded, together with the sites of fracture. This study demonstrated that (1) a fissure sealant resin can be applied to seal the buccal surface of a tooth and have a bracket bonded to it, which exhibits shear bond strengths that are equal to, if not higher than, the standard method of bonding, and (2) the fracture sites of the fissure-sealed teeth are located more at the resin/enamel interface than those of teeth without sealant, thus leaving less cleaning of the tooth surface after debonding. (AMJ ORTHOD DENTOFACORTHOP 1990;98:66"71.)

G . V . Newman's article ~in 1964 on the concept of the use of the acid-etch technique and epoxy resin ushered in the era of the direct bracket-bonding method in orthodontics. However, it was not until I977 that the first detailed posttreatment evaluation of direct bonding in orthodontics over a full treatment period (mean of 17 months) in a large sample of patients was published, z A survey in the United States in 1979 found that 93% of orthodontists used chemically cured resin bonding for bracket placement? A drawback of directly bonded cases as well as fully banded cases is that the patient may experience difficulty in maintaining good oral hygiene. Any excess composite resin left around the bracket after direct bonding could lead to increased plaque accumulation and resultant enamel decalcification. 4-s The cooperative patient can, however, achieve adequate plaque control with the correct guidance from orthodontic auxiliary personnel. 9 The presence of clinically detectable areas of enamel decalcification (observed as whitened areas) folFrom the Department of Orthodontics, Oral and Dental Teaching Hospital, University of Stellenbosch. 811115264


lowing the removal of orthodontic appliances is well recognized) ° The white spot lesion is not only an esthetic problem but is considered to be the precursor of frank enamel caries: Favored sites for such lesions are around the cervical margins of the teeth," adjacent to bonded attachments, and at the junction of the bonding resin and the enamel surface? 2 Even with the use of proven fluoride dentifrice, ~°demineralization can occur around orthodontic appliances after only 1 month with a higher incidence being seen in males." Another drawback of direct bonding is that incompletely sealed etched enamel prisms may stain and serve as a nidus for plaque accumulation with subsequent decalcification. ~3-~ Autopolymerizing low-viscosity bonding resins (generally used as a primer) will not polymerize unless the resin is denied oxygen. For example, this occurs under the composite-coated bracket after placement on the resin-coated enamel surface. Therefore even though it may be coated by low-viscosity bonding resin, the surrounding etched enamel is a vulnerable site for further decalcification./6 Fissure sealants have been used successfully in the prevention of decalcification in pits and fissures of teeth) 7 If fully polymerized, fissure seal-

Vohm2e 98 Number I

Shear bond strengths of bomled orthodontic brackets


ants could be used to seat the complete buccal enamel, thus preventing the possibility of immediate or future decalcification around orthodontic brackets. The term sealant is strictly reserved in this article to indicate a fissure sealant resin and not a low-viscosity bonding resin. The objectives of this study were (1) to determine the effects of various sealants on the shear bond strength (SBS) of bonded orthodontic brackets and (2) to determinethe fracture sites of the various specimens. MATERIALS AND METHODS

Forty noncarious human canine teeth were cleaned of any soft tissue and then stored in 70% ethyl alcohol for 4 weeks. The teeth were prepared for mounting in brass cups by sectioning of the roots and undercutting of the pulp chambers for retention. ~s All the teeth protruded above the lip of the cup by 1 mm and were secured in the cup by means of a self-curing acrylic resin, Fastcure (Kerr Sybron, Romulus, Mich., Batch No. 64248). The sample was divided into four groups of ten teeth (groups A to D). To produce flat enamel surfaces all the teeth were ground wet with a Masterserv grinding and polishing machine (Metallurgical Ser,~ices, Surrey, England) with 200-grit followed by 600-grit silicon carbide paper. All these ground surfaces were verified to be in enamel and wide enough to allow the brackets to be completely seated. After acid etching of the enamel with 37% orthophosphoric acid for 60 seconds, according to the manufacturer's instructions, various primary coatings were applied and then the Ormco stainless steel springwing upper lateral brackets with mesh backing for direct bonding (Ormco, Glendora, Calif.) were bonded to the teeth. The bracket surface area of 12.54 mm 2 was determined with the use of a reflex microscope and a computer-aided analysis of the data. This technique of determination of the base area is particularly sensitive since the x and y coordinates are reported to be accurate to 2 to 4 l . t m . 19 In all four groups, the brackets were bonded with Concise orthodontic primer and resin (Dental Products/3M, St. Paul, Minn.). In group A brackets were bonded with the low-viscosity bonding primer, Concise, painted over the entire labial enamel surface and the Concise resin used immediately with the brackets in accordance with the manufacturer's instructions. In group B a light-cured, unfilled, clear fissure sealant, Delton (Johnson & Johnson, Dental Products Co., East Windsor, N.J.), was applied to the entire labial enamel and cured with white light for 20 seconds before the brackets were similarly bonded. In group C, Cornplus, a filled, clear glazing and fissure-sealing agent

Fig. 1. Photograph of Specimen ready to be tested.

that is light-cured and microfilled to 50% with colloidal silica particles (Parkell Biomaterials Division, Farmingdale, N.Y.)~ was applied to the entire labial enamel and light-cured for 20 seconds before the brackets were bonded, and in group D a chemically cured opaque 3M fissure sealant (Dental Products/3M, St. Paul, Minn.) was applied to the entire labial enamel surface, with 5 minutes allowed for curing before the brackets were bonded. Care was taken not to allow excess composite resin material to remain around the brackets. All 40 teeth were stored at 37 ° in an incubator in distilled water for 24 hours to allow for water absorption of the resins. The brass cups with the samples were then secured in a clamp devise, and a 0.020-inch gauge wire was positioned under the wings of the bracket (Fig. 1). The ends of this wire were clamped to a self-centering device on the Instron universal testing machine (Instron Corp., Canton, Mass.). The specimens were then stressed to failure with a shear stress in the incisogingival direction


Am. J. Orthod. Dentofac. Orthop. July 1990

Joseph and Rossouw

Samples 12




1 •1 Iltllll , ,,Is


" I I I. . .l .l .l .l .l .l .l l II









I I~",,

I I | I I I I I I I I I I I


[|11111 J t J [ J I I I l l i l l l

I + : I.... ,,.

a I I / I t |1

I I II I I II I f II |Ill J I [] IIII

lttg',',l,, ',I",, l i l l I II II I II

i [ [ J l l l



I ~ I [ J J ]



I I I I I l J l t l t





I I I I !

IIII 1111 I I /






The shear bond strengths of stainless steel orthodontic brackets bonded to teeth with orthodontic composite resin and various fissure sealants.

Enamel decalcification (whitened areas) around orthodontic brackets during therapy is a well-recognized problem. If a fissure sealant could be used to...
806KB Sizes 0 Downloads 0 Views