British Journal of Orthodontics

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Direct Bonding of Orthodontic Brackets—a comparative study of adhesives I. R. Reynolds B.D.S., F.D.S., D.Orth., R.C.S.(Eng.) & J. A. von Fraunhofer M.Sc. Ph.D., M.I.M., C.Chem., F.R.I.C. To cite this article: I. R. Reynolds B.D.S., F.D.S., D.Orth., R.C.S.(Eng.) & J. A. von Fraunhofer M.Sc. Ph.D., M.I.M., C.Chem., F.R.I.C. (1976) Direct Bonding of Orthodontic Brackets—a comparative study of adhesives, British Journal of Orthodontics, 3:3, 143-146, DOI: 10.1179/bjo.3.3.143 To link to this article:

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Date: 30 September 2016, At: 13:10

British Journal of Orthodontics/Vol 3/No 3/143-146 Printed in Great Britain


Direct Bonding of Orthodontic Brackets-a comparative study of adhesives I. R. Reynolds, B.D.S., F.D.S., D.Orth., R.C.S.CEng.) J. A. von Fraunhofer, M.Sc. Ph.D., M.I.M., C.Chem., F.R.I.C. Institute of Dental Surgery, Eastman Dental Hospital, Grays Inn Road, London WC1 X BLD

Abstract. Various materials are currently available to orthodontists for use as adhesives in the direct bonding of orthodontic brackets to teeth. In this comparative study three factors have been examined, namely the tensile bond strength of suitable adhesives in orthodontic bracket-adhesive-human enamel combinations, the effect of water immersion on the bond strength and the effect of the acid etchant on the bond strength. This work should give the practitioner an indication of the clinical merits of some of these materials. Three principal types of adhesive are advocated for direct bonding, namely dental cements, notably zinc polycarboxylate cement, acrylic resins and filled diacrylate-based resins. All three classes of material are widely used for both adhesive and restorative purposes. Pretreatment of the tooth surface by phosphoric acid etching (Buonocore, 1955) is necessary with the polymeric adhesives but this procedure is thought to be unnecessary for the zinc polycarboxylate cement (Combe and Burtenshaw, 1971). See Table l. In order to assess the possible clinical suitability of adhesives, orthodontic gauze-backed buttons (mesh no. 50, B.S. 410) were bonded to teeth in vitro and the bond strength was tested in tension. Stainless steel buttons and gauzes were used in this study due to their greater durability compared to polymeric materials. Materials and Methods Fresh sound human premolar teeth, extracted for orthodontic purposes and stored in water immediately after extraction, were used in this study, The teeth were prepared for bonding in a similar manner to that adopted clinically, as previously described (Reynolds and von Fraunhofer, 1976). The adhesive was applied to the button by mixing the material and moving the button through the mixed mass. This procedure deposited the optimum quantity of adhesive onto the button gauze backing and is the most convenient method of applying 12

the adhesive. One material, Genie, was too granular for this approach and, after mixing, was applied to the mesh by means of a plastic instrument. 'Once', a filled diacrylate resin specifically marketed as an orthodontic band cement, was used for comparison with the other materials in this study. The adhesive-coated buttons were placed on the prepared teeth and 5 minutes was allowed for setting. After setting, the tooth-button combinations were stored in tap water at room temperature (20 ± 2 °C), until tested. Results The tensile bond strengths obtained for the nine adhesive systems tested after storage in water for I week are given in Table 11. Further tests were carried out at 3 hours, I month and 6 months for selected adhesives to examine the effect of immersion in water on the tensile bond strength (Tables JJJ, IV and V). In general, failures were of the mesh-cohesive type (i.e. fractures occurred at the gauze-adhesive interface). There were, however, some exceptions. 'Once' exhibited some adhesive-enamel failures whilst the Nuva Seal-Acrylic combinations showed either adhesive-enamel or mesh-cohesive failures or partly adhesive-enamel and partly mesh-cohesive fractures (Fig. 1). On storage in water for 6 months a complex failure pattern was also found with the acrylic specimens, namely either pure adhesive-


I. R. Reynolds and J. A. von Fraunhofer

TABLE I Adhesive Materials Name


Curing system



Concise Delphic

Filled diacrlyate resin Filled diacrylate resin

Chemical Chemical

Controllable vis_cosity paste Medium viscosity paste

Genie Nuva Seal Once Poly F Protecto Unltek bonding kit

Filled polyacrylic resin Unfilled diacrylate resin Filled diacrylate "cement" Polycarboxylate cement Filled diacrylate resin Unfilled acrylic resin

Chemical u.v. light Chemical Acid-base Chemical Chemical

Low viscosity granular paste Low viscosity fluid Medium viscosity paste Controllable viscosity paste Low viscosity paste Medium viscosity paste

3M Co. Ltd. Davis, Schottlander & Davis Ltd. Lee Pharmaceuticals Inc. L. D. Caulk, Co. Ltd. Lee Pharmaceuticals Inc. A.D. Co. Ltd. Lee Pharmaceuticals Inc. Unitek Inc.

TABLE 11 Tensile Bond Strength at 1 week (Base Line Study) Material

No. of specimens

Fracture load, Minimum kg load

Maximum load

Concise Delphic Genie Nuva Seal+ Acrylic (Unitek) Once Poly F Protecto Unitek

17 11 12 14 14 12 10 9

9·1±1·6 11·9±3·9 8·3±1·6 7·9±2·7 9·3±2·9 3·0±1·2 9·1±1·6 9·2±2·4

11·5 19·5 11·8 13·0 13·7 5·5 11·6 13·1

5·0 5·5 5·9 3·4 5·3 1·7 7·4 5·8

TABLE 1/1 Tensile Bond Strength at 3 hours Material

No. of specimens

Fracture load, Minimum load kg

Concise Delphic Genie Nuva Seal+ Acrylic (Unitek) Protecto Unitek

20 15 11 18 39 12

9·1±3·1 10·0±3·2 9·3±2·4 7·2±3·5 10·0±2·8 10·5±2·1

3·0 6·3 5·6 2·8 4·3 7·6

Maximum load 14·0 15·6 13·4 13·0 16·8 13·6

TABLE/V Tensile Bond Strength at 1 month Material

No. of specimens

Fracture load, Minimum load kg

Concise Delphic Genie Nuva Seal+ Acrylic (Unitek) Protecto Unitek

23 22 22 15 20 25

8·5±3·1 9·5±3·7 7·5±3·5 6·6±2·9 8·7±3·6 7·8±2·9


3·0 4·8 3·0 3·0 4·0 3·7

Maximum load 15·1 15·8 14·0 12·5 15·3 16·3

Direct Bonding of Orthodontic Brackets-a comparative study of adhesives

TABLE V Tensile Bond Strength at 6 months Material

No. of specimens

Fracture load, Minimum kg load

Maximum load

Delphic Genie Unitek

13 11 13

11·2±4·1 8·6±3·2 6·8±3·0

17·8 13·3 11·9

enamel failures, a combination of adhesive-enamel and mesh-cohesive failure or pure mesh-cohesive failure. This pattern was also observed with Genic but to a lesser extent in that no pure adhesiveenamel failures were found for this material. Adhesive-enamel fractures were not necessarily synonymous with lower recorded tensile bond strength values. . . The effect of different concentrattons of actd etchant, namely 37 per cent and 50 per cent phosphoric acid applied for 60 seconds, on bond strength was also investigated using the same t~st regimen. In this, Concise was used as the adhestve and the specimens were stored in water for I week at room temperature before testing. It was found that there was no difference in the tensile bond strengths (P > 0·05) obtained with the two ctchants and in both groups mesh-cohesive failures occurred. The tensile bond strengths were recorded at failure as kg force. Accordingly the mean fracture loads (and their standard deviations) are given together with the lowest and highest recorded loads for each adhesive.

4·8 3·9 2·1

Discussion Great variability is generally found in all studies of tensile bond strengths of adhesives and therefore statistical data in the form of mean values is of limited usefulness to the clinician. Consequently the maximum and minimum fracture loads have also been presented since these represent the 'best' and the 'worst' performance that can be expected under clinical conditions. Another factor of great importance was the absence of any correlation between the area of adhesive on the enamel and the fracture load, as mentioned previously. Further, provided that the tooth enamel has been suitably etched, the acid strength appears to have no effect on the bond strength of gauze backed orthodontic buttons attached to enamel in l'itro. The results presented here indicate that the use of an intermediate layer of Nuva Seal does not result in an enhanced bond strength for the acrylic resin. Consequently the two-layer adhesive technique is not necessary for direct bonding of orthodontic brackets.

Fig. 1 Examples of two types of part adhesive-enamel and part mesh-cohesive failures. (a) Central failure; (b) Peripheral failure: (a) Retained adhesive (mesh-cohesive failure). (b) Tooth surface (adhesive-enamel failure). Specimens gold spluttered to increase contrast.


I. R. Reynolds and J. A. von Fraunhofer

The range of fracture loads for all the diacrylate materials is large at the three test periods. Although there is no statistical difference between mean fracture loads at the three periods, the highest minimum bond strength was generally found at 1 week (c.f. the Unitek acrylic). No statistically significant differences were found in t~e bond strengths exhibited by any of the filled dtacrylate resins at the three test periods and all three would appear to be equally satisfactory in that respect. Selection of a material would therefore be dependent upon handling characteristics and cost considerations. Stainless steel orthodontic buttons, to which a B.S. 50 mesh backing has been spot-welded, having a contact area of approximately 10·4 mm 2 and bonded to etched tooth enamel with a range of adhesive materials can support tensile loads of between 3 and 19 kg. In view of the average forces exerted during mastication and the traction forces generated by orthodontic appliances, these bonded attachments should generaily withstand normal oral forces. Poly F was significantly weaker than any of the other materials used in this investigation. In general, no significant difference was found between any of the other materials. This is in agreement with other workers (Sadowsky and Retief, 1975; Nagle, 1975). With prolonged water immersion, Unitek adhesive showed a significant decrease in bond strength, while Genie and Delphic showed no significant difference in strength. At 6 months, the filled diacrylate adhesive (Delphic) showed significantly better results compared with the acrylic adhesive (Unitek). The bond strengths found with the diacrylate resins studied here show that no differences in bond strength exist between the materials, despite their different consistencies and viscosities. Accordingly the material used by the clinician will be dictated by its handling properties, viscosity, cleanliness and cost as well as general availability and storage life. Furthermore, the nature of the bracket backing mesh or other retention aid has an influence on the choice of adhesive. This factor will be discussed, however, in a subsequent communication. The absence of a statistically significant difference in the bond strengths obtained for different concentrations of f1e enamel etchant with a typical


adhesive, Concise, is in agreement with the findings of other workers (e.g. Williams, von Fraunhofer and Winter, 1976). Conclusions When used with gauze-backed orthodontic buttons, no statistically significant differences were apparent in the tensile bond strengths obtained with the polymeric adhesives studied in this programme of work. The dental cement, Poly F, was found to be unsatisfactory as an adhesive. Prolonged immersion in water, i.e. 6 months, resulted in a significant decrease in tensile bond strength for the acrylic material but had no significant effect on the diacrylate and the filled polyacrylic materials. The use of Nuva Seal as an interfacial agent or adhesion promoter for acrylic had no significant effect on the bond strength and therefore this procedure would appear to have no clinical advantages. The wide range of bond strengths reported here indicate that, in the field of direct bonding of orthodontic attachments, the reporting of bond strengths as failure force per unit area of attachment is difficult to correlate with clinical practice. In this particular context, the maximum and minimum failure loads would appear to have greater clinical relevance.

References Buonocore, M. G. (19SS) A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces, Journal of Dental Research, 34, 849-853. Combe, E. C. and Burtcnshaw, B. W. (1971) Studies on the adhesion of a polycarboxylate cement to etched enamel, Journal of Dental Research, SO, 1206 (Abstract No. 122). Nagle, N. J. (1975) A materials evaluation of ten direct bonding systems utilizing polycarbonate brackets, American Journal of Orthodontics (Abstract), 67, 460-461. Reynolds, I. R. and von Fraunhofer, J. A. (1976) Direct bonding of orthodontic attachments to teeth: the relation of adhesive bond strength to gauze mesh size, British Journal of Orthodontics, 3, 91-95. Sadowsky, P. L. and Retlef, D. H. (1975) A laboratory evaluation of tensile bond strengths of three composite orthodontic materials to human enamel, Journal of Dental Research, 54, 688 (Abstract No. 32). Wllliams, 8., von Fraunhofer, J. A. and Winter, G. B. (1976) Etching of enamel prior to application of fissure sealants, Journal of Oral RehabilitaTion 3, 185- I 88.

Direct bonding of orthodontic brackets--a comparative study of adhesives.

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