Comparison in shear bond strength of orthodontic brackets between five bonding systems related to different etching times: an in vitro study

Curvature-dependent shear bond strength of different attachment materials for orthodontic lingual indirect bonding

To evaluate the shear bond strength (SBS) of different attachment materials used for lingual bonding, the influence of artificial aging and the radii of curvature of the enamel surface on SBS, 192 third molars were photographed to determine the radius of curvature of the oral surface. After phosphoric acid etching a cylindrical test piece was bonded to the oral enamel using a mold that was filled with a chemically curing (Maximum Cure, Transbond IDB Premix) or a dual-curing (Nexus NX3, RelyX Unicem2) attachment material. SBS was tested after 24 h, 500 thermal cycles or 90 days at 37 °C with a universal testing machine. Computed tomography scans were performed to determine the bonded surface and calculate SBS. Values ranged from 8.3 to 20.9 MPa. RelyX Unicem2 showed the highest SBS values at baseline, 500 thermal cycles and after 90 days (p < 0.001). Ninety days of wet storage significantly reduced SBS of Maximum Cure (p = 0.028). The radius of curvature correlated positively with SBS (r_s = 0.204, p = 0.005). The SBS of all attachment materials was sufficient for clinical use, even after artificial aging. RelyX Unicem2 showed almost twice as high SBS values as the other attachment materials.

Effect of sandblasting on the shear bond strength of recycled metal brackets: A systematic review and meta-analysis of in-vitro studies

INTRODUCTION AND OBJECTIVE

Sandblasting is an efficient and economic method of rebonding brackets. Literature is divided regarding the Shear Bond Strength (SBS) associated with sandblasted brackets. Hence this systematic review was conducted to obtain conclusive evidence on the same. The aim was to compare the SBS between sandblasted brackets bonded to extracted human teeth and new brackets bonded on extracted teeth that have not been previously bonded.

MATERIALS AND METHODS

The following databases were searched up to April 30, 2021: PubMed via Medline, Web of Science, LILACS, Cochrane, EMBASE and Scopus. Articles comparing SBS of a new bracket with that of a rebonded bracket following sandblasting were included. Two reviewers independently selected the studies, extracted the data and assessed the risk of bias which was based on a modification of the Risk Of Bias In Nonrandomized Studies of Interventions Tool (ROBINS-I). SBS data generated from the systematic review was summarized and a meta-analysis using random effects inverse-generic model was done.

RESULTS

Sixteen studies generated 521 samples for the new bracket group and 391 samples for the sandblasted group. These sixteen studies showed a low risk of bias. Meta analysis reported the mean difference between the SBS of new and sandblasted brackets to be 0.85. (95 CI of -0.24 to 1.94). This difference can be clinically disregarded. The high degree of heterogeneity indicated by an I² of 87% led to a subgroup analysis.

CONCLUSIONS

With the studies showing a high quality of evidence, it can be concluded that sandblasting is an efficient means of recycling debonded brackets without affecting SBS. The inherent deficiencies of in vitro bond strength studies should be borne in mind when making this conclusion. The study protocol was registered on the International Prospective Register of Systematic Reviews (Reg no: CRD42020193616).

Evaluation of the influence of dental bleaching with 35% hydrogen peroxide in orthodontic bracket shear bond strength

OBJECTIVE: The purpose of this study was to evaluate, in vitro, the bond strength of brackets bonded to premolars previously subjected to bleaching with a 35% hydrogen peroxide. METHODS: Twenty one healthy premolars were selected and randomly divided into three groups (n = 7). Group I (G1) included teeth that were not submitted to bleaching. The enamel surfaces of Groups II (G2) and III (G3) were submitted to a bleaching process with 35% hydrogen peroxide (Whiteness HP Maxx). On Group II (G2), after bleaching, the teeth were stored for 24 hours in distilled water at 98.6 ºF, and then, premolar metallic brackets were bonded using Transbond XT (3M) resin. Group III (G3) was submitted to the same procedure seven days after bleaching. After bonding, all teeth were stored in distilled water at 98.6 ºF for 24 hours. All groups were submitted to a traction test using an EMIC DL2000 universal testing machine at a speed of 0.5 mm/min. RESULTS AND CONCLUSION: The bracket resistance to debonding was compared between the groups by the Kruskal-Wallis nonparametric test (p < 0.05) and it was verified that the bleaching agent significantly reduced bracket adhesion when bonded 24 hours after bleaching. However, seven days after bleaching, there was no significant difference on the resistance to debonding among groups G1 (19,52 kgf) and G3 (18,44 kgf), meaning that it is necessary to wait longer after bleaching to bond brackets.

Resistência ao cisalhamento da colagem com compósitos utilizando potencializador de adesão

OBJETIVO: avaliar a resistência ao cisalhamento dos compósitos Transbond XT e Concise Ortodôntico utilizando o potencializador de adesão Ortho Primer. MÉTODOS: a amostra consistiu de 90 incisivos bovinos divididos em seis grupos (n=15). Todos os dentes receberam profilaxia com pedra-pomes e condicionamento do esmalte com ácido fosfórico. No Grupo I, utilizou-se Transbond XT de maneira convencional. O Grupo II foi semelhante ao I, porém, aplicou-se o Ortho Primer ao invés do XT Primer. No Grupo III, após condicionamento, o esmalte foi contaminado com saliva, aplicou-se o Ortho Primer e colagem com Transbond XT. No Grupo IV, utilizou-se o Concise Ortodôntico de maneira convencional. O Grupo V foi semelhante ao IV, porém, utilizou-se o Ortho Primer ao invés da resina fluida. No Grupo VI, após condicionamento, o esmalte foi contaminado com saliva, aplicou-se o Ortho Primer e colagem com Concise. Os corpos de prova foram armazenados em água destilada em estufa a 37ºC por 24h e submetidos ao ensaio de resistência ao cisalhamento. Os dados foram submetidos à ANOVA e ao teste de Tukey (5%). RESULTADOS: a resistência da colagem no Grupo IV foi estatisticamente superior à dos Grupos II, III e VI (p<0,05). Entre os Grupos I, IV e V; e entre os Grupos I, II, III e VI não foram encontradas diferenças estatísticas significativas (p>0,05). O Transbond XT e o Concise utilizados convencionalmente obtiveram os maiores valores adesivos. O Ortho Primer em esmalte seco atuou efetivamente como agente de união dos compósitos avaliados. Em esmalte contaminado, a colagem com Concise obteve baixa resistência adesiva.

Resistência ao cisalhamento de braquetes metálicos utilizando sistema adesivo autocondicionante

OBJETIVO: avaliar a resistência ao cisalhamento de braquetes metálicos colados com sistema autocondicionante utilizado imediatamente e após 2, 5 e 9 dias depois da ativação e armazenagem. MÉTODOS: utilizaram-se 64 dentes bovinos divididos igualmente em quatro grupos e devidamente preparados para receber a colagem dos braquetes. Em T1, realizou-se a ativação de 7 blisters de adesivos autocondicionantes (de acordo com as normas do fabricante) e procedeu-se à colagem imediata apenas dos braquetes do grupo I. Os adesivos ativados foram, então, armazenados à temperatura de 4ºC e reutilizados em períodos de 2 dias (T2), 5 dias (T3) e 9 dias (T4) para a colagem dos braquetes dos grupos II, III e IV, respectivamente. RESULTADOS: não se observou diferença estatística quando comparados os valores médios de tensão para resistência ao cisalhamento entre os grupos I, II e III. Entretanto, diferença estatística foi encontrada quando esses valores foram comparados aos do grupo IV. CONCLUSÃO: o armazenamento do adesivo autocondicionante depois de ativado, à temperatura média de 4ºC, por até 5 dias, parece não afetar os resultados quanto às tensões de resistência ao cisalhamento; novos estudos são necessários para avaliação das demais características do material quando de sua utilização por período de tempo prolongado após sua ativação.

Comparative bond strength of new and reconditioned brackets and assessment of residual adhesive by light and electron microscopy

An average rate of bracket loss of between 4.7 and 6 per cent is to be expected in daily clinical orthodontic practice during a typical 2 year treatment period. For reasons of economy, detached brackets are commonly reattached after sandblasting to remove adhesive, or replaced with used brackets reconditioned by specialist companies. In the present study, sandblasting and specialist bracket-reconditioning procedures were systematically compared by comparative shear testing of rebonded, reconditioned, and new brackets (n = 160) using light- and chemically cured adhesives. Statistical analysis was carried out with Kruskal-Wallis and Mann-Whitney tests. The mean bond strength of reconditioned brackets was, in each case, lower than that of new brackets, with the lowest value obtained with sandblasted brackets. This nevertheless exceeded the minimum recommended value of 5-8 MPa. Bond strength was generally higher with chemically than with light-curing adhesive; the chemically curing adhesive provided bond strength on previously bonded enamel higher than the light-curing adhesive on intact teeth. Consistent with this, the results of the adhesive remnant index (ARI) demonstrated improved bonding with the chemically curing than the light-curing adhesive to the bracket base. Despite resulting in a weaker bond strength compared with new brackets, sandblasting brackets accidentally detached during orthodontic treatment will generally allow effective reattachment to be achieved. Bond strength can be improved with the use of a chemically cured adhesive. Used brackets reconditioned by specialist companies provide a second alternative to new brackets and higher bond strengths than sandblasted brackets.

Effect of applying a sustained force during bonding orthodontic brackets on the adhesive layer and on shear bond strength

The objective of this research was to investigate the effect of applying a sustained seating force during bonding on the adhesive layer and on shear bond strength (SBS) of orthodontic brackets. Forty human premolars divided into two groups were included in the study. Stainless steel brackets were bonded to the premolars with Transbond XT light cure adhesive and Transbond Plus Self Etch Primer (SEP). The brackets in both groups were subjected to an initial seating force of 300 g for 3 seconds, sufficient to position the bracket. The seating force was maintained throughout the 40 seconds of light curing in group 2. SBS was tested 24 hours after bracket bonding with a shear blade using an Instron testing unit at a crosshead speed of 2 mm/minute. A Student's t-test was used to compare the bond strength of the two groups and a chi-square test to compare the frequencies of the adhesive remnant index (ARI) scores. The mean SBS was significantly different between the two groups (P=0.025). The bond strength was higher (mean 8.15±0.89 MPa) in group 2 compared with group 1 (mean 7.39±1.14 MPa). There was no significant difference (P=0.440) in the ARI scores between the two groups. Applying a sustained seating force during orthodontic bracket bonding improves bond strength but does not change the distribution of the ARI scores.

Influência de variáveis metodológicas na resistência de união ao cisalhamento

OBJETIVO: avaliar a influência de diferentes variáveis metodológicas sobre a resistência de união ao cisalhamento em estudos in vitro. MÉTODOS: foram utilizados 105 incisivos permanentes bovinos, seccionados ao nível do colo dentário. A porção coronária foi inclusa em tubos de PVC, com resina acrílica autopolimerizável, e com face vestibular voltada para cima. Todos os corpos de prova foram preparados para a colagem com profilaxia e condicionamento ácido na região central das coroas, onde foram posicionados braquetes Morelli® de incisivos centrais superiores, com resina Concise® Ortodôntico (3M/Unitek). Foram determinados três grupos de acordo com a variável estudada: (Grupo 1) - meio de armazenamento dos dentes, previamente à inclusão e à colagem, com solução de timol 0,1% (a), água destilada (b) e congelamento (c); (Grupo 2) - velocidade da célula de carga da máquina de ensaio de 0,5 (a), 1,0 (b) e 2,0mm/min (c) e (Grupo 3) - diferentes marcas comerciais de ácidos fosfóricos a 37%, 3M/Unitek (a), AcidGel (b) e Attack Tek (c). Os corpos de prova foram submetidos ao ensaio mecânico de resistência ao cisalhamento através da máquina Emic DL2000®. Os dados foram analisados estatisticamente por meio do Teste t Student para amostras independentes. RESULTADOS: os resultados demonstraram que no Grupo 1 o subgrupo de congelamento apresentou maiores valores em relação aos outros dois subgrupos, porém sem diferença estatisticamente significativa (p > 0,05). No Grupo 2, a força no momento da ruptura foi menor à medida que era aumentada a velocidade da célula de carga, porém sem diferença significativa entre os subgrupos. No Grupo 3, o ácido da 3M/Unitek apresentou a maior média em MPa, no entanto, também sem diferença significativa entre os subgrupos. CONCLUSÕES: conclui-se, portanto, que as variáveis analisadas neste trabalho não apresentaram influência suficiente para determinação de diferenças estatisticamente significativas entre os resultados.

Rebonding of orthodontic brackets. Part I, a laboratory and clinical study

OBJECTIVE

To compare rebonding of orthodontic brackets based on the hypothesis that no difference would be found between the adhesive systems with respect to shear bond strength, mode of failure, and clinical failure rates.

MATERIALS AND METHODS

The three adhesive systems included two self-etch primers (Transbond and M-Bond) and a conventional phosphoric acid etch (Rely-a-Bond). The sample size was 20 premolars for each adhesive system. The shear bond strength was tested 24 hours after bracket bonding with the bonding/debonding procedures repeated two times after the first debonding. Bond strength, adhesive remnant index (ARI), and failure sites were evaluated for each debonding. Statistical analysis consisted of a two-way analysis of variance (ANOVA) followed by Scheffè analysis. The clinical portion evaluated 15 patients over a 12-month period.

RESULTS

The mean shear bond strengths after the first, second, and third debondings for Rely-a-Bond were 8.4 +/- 1.8, 10.3 +/- 2.4, and 14.1 +/- 3.3 MPa, respectively; for Transbond 11.1 +/- 4.6, 13.6 +/- 4.5, and 12.9 +/- 4.4 MPa, respectively; and for M-Bond 8.7 +/- 2.7, 10.4 +/- 2.4, and 12.4 +/- 3.4 MPa, respectively. After the three debondings the mean shear bond strength increased significantly from the first to the third debonding for Rely-a-Bond and M-bond (P </= .001), but did not change for Transbond (P = .199).

CONCLUSIONS

The original hypothesis is not rejected. The two self-etching primers showing higher or comparable bond strength to the conventional phosphoric etch with less adhesive remnant on the enamel surface after the first debonding. With repeated bonding/debonding, the differences in the bond strength, ARI, and failure site were not significantly different. There was no difference in the clinical performance of the three adhesive systems (P = .667).

The Effect of Modifying the Self-etchant Bonding Protocol on the Shear Bond Strength of Orthodontic Brackets

OBJECTIVE

To compare the shear bond strength (SBS) of orthodontic brackets when the self-etching primer (SEP) and the bracket adhesive are light cured either separately or simultaneously.

MATERIALS AND METHODS

Seventy-five human molars were randomly divided into five equal groups. Brackets precoated with Transbond XT composite adhesive were used. The five protocols were: Group 1 (control), the SEP Transbond Plus was applied, brackets placed, and adhesive light cured for 20 seconds; Group 2, SEP Adper Prompt L-Pop was applied, light cured, brackets placed, and light cured; Group 3, the same SEP as in Group 2 was used, however, the SEP and bracket adhesive were light cured together; Group 4, SEP Clearfil S3 Bond was applied, light cured, brackets placed, and light cured; and Group 5, the same SEP as in group 4 was used, however, the SEP and the adhesive were light cured together. The teeth were debonded using a universal testing machine, and the enamel was examined for residual adhesive. Analysis of variance was used to compare the SBS.

RESULTS

The SBS of Clearfil S3 Bond after one light cure and two light cures were significantly greater than the bonds of brackets using Transbond Plus. Brackets bonded using Adper Prompt L-Pop after one light cure and two light cures were not significantly different from the other groups. The groups did not differ significantly in their bracket failure modes.

CONCLUSION

Only one light curing application is needed to successfully bond brackets when using SEPs and adhesives. This approach can potentially reduce technique sensitivity as well as chair time.

Shear bond strength comparison of two adhesive systems following thermocycling. A new self-etch primer and a resin-modified glass ionomer

OBJECTIVE

To compare the effects of a standardized thermocycling protocol on the shear bond strength (SBS) of two adhesive systems: a resin-modified glass ionomer and a composite resin used with a new self-etching primer.

MATERIALS AND METHODS

Forty human molars were cleaned, mounted, and randomly divided into two groups. In group 1, brackets were bonded to the teeth using Fuji Ortho LC adhesive, and in group 2, the Transbond Plus system was used. The teeth were stored in water at 37 degrees C for 24 hours, thermocycled between 5 and 55 degrees C, and debonded using a universal testing machine. The enamel surface was examined under 10x magnification to determine the amount of residual adhesive remaining on the tooth. Student's t-test was used to compare the SBS and the chi-square test was used to compare the adhesive remnant index (ARI) scores.

RESULTS

The mean SBS for the brackets bonded using the Fuji Ortho LC was 6.4 +/- 4.5 MPa, and the mean SBS for the Transbond Plus system was 6.1 +/- 3.2 MPa. The result of the t-test comparisons (t = 0.207) indicated that there was no significant difference (P = .837) between the two groups. The comparisons of the ARI scores (chi(2) = 0.195) indicated that bracket failure mode was not significantly different (P = .907) between the two adhesives.

CONCLUSION

Although SBS and ARI scores were not significantly different for the two adhesives, clinicians need to take into consideration the other properties of the adhesives before using them.

A comparison of the shear-peel and third-order bond strengths of orthodontic brackets with 2 etch techniques and the role of bracket asymmetry

INTRODUCTION

Innovations in orthodontic bonding are inevitably followed by a flurry of studies to ascertain efficacy. Unfortunately, the published reports are often contradictory or highly variable. The primary purpose of this study was to analyze protocols that measure orthodontic bracket bond strength. The effects of loading mode and the role of bracket asymmetry were examined. The secondary goal was to test a self-etch enamel preparation system.

MATERIALS AND METHODS

Flattened stainless steel orthodontic brackets (.022-in Victory Series, 3M Unitek, Monrovia, Calif) were bonded to a total of 192 flattened bovine incisors with a resin composite bonding agent (Transbond XT, 3M Unitek.) The enamel was prepared with traditional, two-step (TS) acid (37% phosphoric acid gel) etching and priming (Transbond XT Primer, 3M Unitek) or with a single step (SS) self-etch (Transbond Plus, 3M Unitek) material. Cement thickness was held constant and bonding was done under controlled temperature and humidity. The brackets were debonded in the occlusogingival and in the gingivocclusal directions (ie, the 2 senses of shear-peel) and using a new technique in the buccal-root and in the lingual-root directions (ie, the 2 senses of a third-order moment.)

RESULTS

Data showed no significant differences between TS and SS regardless of load modality. However, significant differences were revealed between the senses of debonding, indicating bracket asymmetry effects.

CONCLUSIONS

The wide clinical use of these newer self-etching primers has been supported by these limited findings. A new third-order debonding protocol has been demonstrated to be a useful tool. Bracket asymmetry affects some bond strength values, and there is a need for standardization of testing protocols.

Orthodontic bracket bonding: Enamel bond strength vs time

INTRODUCTION

Tests of bond strength between orthodontic brackets and enamel are generally conducted after at least 24 hours storage in water. However, debonding might occur soon after bracket placement during orthodontic treatment. We investigated the rate of bond strength development for orthodontic adhesives in bracket bonding.

METHODS

Four orthodontic adhesive systems were examined. Bovine incisors were mounted in self-curing acrylic resin, and the facial surfaces were wet-ground to expose flat enamel. Orthodontic brackets were bonded according to the manufacturers' instructions. Shear bond strengths were measured after storage in water for 5, 10, and 60 minutes, and 24 hours. Differences between bond strengths at 24 hours and the other test periods were statistically analyzed.

RESULTS

All materials tested had the highest bond strengths at 24 hours, and bond strength increased with storage time. The earliest time point at which there was no significant difference in bond strength compared with that at 24 hours was defined as the initial stable time. Differences in this value might have clinical implications for the assessment of orthodontic adhesives, which can incur high stresses immediately after placement.

CONCLUSIONS

The rate of development of enamel bond strength must be considered to ensure sufficient maturation of orthodontic adhesives before functional loading.

The influence of orthodontic bracket base design on shear bond strength

Many bracket base designs and adhesive materials are in clinical use today. Bases have evolved from perforated metal bases to the present foil mesh bases, and treatments range from none, to spraying metal alloy onto the base, to the most common treatment of microetching. The purpose of this study was to determine the effect of orthodontic bracket base design on mean shear bond strength 1 hour or 24 hours after bonding. For each time group, 12 specimens of 6 types of metal brackets were bonded to bovine incisors with Transbond XT (3M Unitek, Monrovia, Calif) light-cured composite resin. Brackets were debonded 1 hour or 24 hours later, and the shear bond strength was recorded. Six debonded brackets of each type from each time group were selected at random and sandblasted. All the teeth were cleaned, and half were rebonded with used brackets, and half were rebonded with new brackets. Bond strength was measured again, 1 hour or 24 hours later. Representative specimens were inspected under the scanning electron microscope. Bracket base design significantly affected mean shear bond strength. Speed (60-gauge, microetched foil-mesh base; Strite Industries, Cambridge, Ontario, Canada) had the highest bond strength at 1 hour; followed by Time (machined, integral, microetched base with mechanical undercuts; American Orthodontics, Sheboygan, Wis); American Master Series (80-gauge foil-mesh base; American Orthodontics); Ovation Roth (80-gauge layered onto 150-gauge, microetched foil-mesh base; GAC, Central Islip, NY); Orthos Optimesh XRT (100-gauge microetched foil-mesh base; Ormco, Orange, Calif); and, finally, the nickel-free brackets (injection molded, 100-gauge, microetched, foil-mesh base; World Class Technology, McMinnville, Ore). The 24-hour results were similar except that Time had the highest mean shear bond strength (ANOVA, P <.05). Chairside sandblasting significantly affected the 1-hour, but not the 24-hour, mean shear bond strengths (ANOVA, P <.05). Sandblasting appears to be an effective method of cleaning bracket bases before rebonding.

Effect of thermocycling on the shear bond strength of a cyanoacrylate orthodontic adhesive

The purpose of this study was to evaluate the effects of thermocycling on the shear bond strength of a cyanoacrylate adhesive system, specifically 24 hours after bonding when the adhesive has achieved most of its bond strength and after thermocycling. Forty freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned, polished, and randomly separated into 2 groups: group I, cyanoacrylate adhesive debonded after 24 hours immersion in deionized water at 37 degrees C; and group II, cyanoacrylate adhesive debonded after thermocycling at 5 degrees C and 55 degrees C. The results of the t test comparing the 2 groups (t = 6.84) indicated significant differences between them (P =.0001). The cyanoacrylate adhesive at 24 hours had significantly greater shear bond strength (macro x = 7.1 +/- 3.3 MPa) than after thermocycling 500 times between 5 degrees C and 55 degrees C (macro x = 1.5 +/- 1.4 MPa). The findings indicated that the cyanoacrylate adhesive tested has clinically adequate shear bond strength at 24 hours after initial bonding but loses about 80% of its strength after thermocycling. The clinician should consider all properties of the adhesive, including no need for a curing light, working time of 5 seconds before the adhesive starts to set, and the significant decrease in bond strength after thermocycling.

A comparison of shear bond strengths of orthodontic brackets using various light sources, light guides, and cure times

The objective of this study was to evaluate the effects of different cure times, light sources, and light guides on shear bond strength of orthodontic brackets bonded with Transbond XT (3M Unitek, Monrovia, Calif) to bovine enamel. Specifically, the Power Slot (Reliance Orthodontic Products, Itasca, Ill) light guide was placed on 4 visible light sources to compare shear bond strengths and recommended cure times with the light guides provided with each light source. We randomly divided 240 bovine mandibular incisors into 16 groups; each group consisted of 15 teeth mounted in an acrylic block. Each group of teeth was polymerized with a specific light and light guide combination. Eight groups were sheared after 5 minutes and the remaining 8 groups after 24 hours. After bonding, all brackets were subjected to a shear force with a testing machine. Overall, there was a significant increase in bond strengths of the 24-hour groups compared with the 5-minute shearing groups. However, there were no statistical differences (P =.05) within the 24-hour test groups or the 5-minute test groups. The results of this study indicate that, compared with standard light guides, the Power Slot and the Turbo Tip (Ormco Sybron Dental Specialties, Orange, Calif) light guides can significantly reduce the curing times (10 seconds per bracket; 5 seconds each from mesial and distal) without affecting their shear bond strengths. Therefore, the Power Slot and the Turbo Tip light guides with their collimation of visible light to increase its intensity can be recommended as advantageous alternatives for curing composite resins for orthodontic bonding procedures.

Effect of time on the shear bond strength of cyanoacrylate and composite orthodontic adhesives

The purpose of this study was to compare the effects of time on the shear bond strength of a cyanoacrylate system and a composite adhesive system (1) within half an hour after bonding the bracket to the tooth, and (2) after 24 hours from the time of bonding when the adhesive had achieved most of its bond strength. Eighty freshly extracted molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleansed, polished, and randomly separated into 4 groups: (I), cyanoacrylate adhesive debonded within one-half hour from initial bonding; (II), cyanoacrylate adhesive debonded after 24 hours immersion in deionized water at 37 degrees C; (III), composite adhesive debonded within one-half hour from initial bonding; (IV), composite adhesive debonded after 24 hours immersion in deionized water at 37 degrees C. The results of the analysis of variance comparing the 4 experimental groups (F = 12.68) indicated significant differences between them (P =.0001). The composite adhesive at 24 hours had significantly greater shear bond strength than did the other 3 groups. In general, the shear bond strengths were greater in the 2 groups debonded after 24 hours. This was true for both the cyanoacrylate ((-)x 7.1 +/- 3.3 megaPascals [MPa]) and the composite ((-)x 10.4 +/- 2.8 MPa) adhesives. On the other hand, the shear bond strength was significantly lower in the 2 groups debonded within one-half hour of their initial bonding. The bond strength of the cyanoacrylate adhesive ((-)x 5.8 +/- 2.4 MPa) was not significantly different from that of the composite ((-)x 5.2 +/- 2.9 MPa) adhesive. Our findings indicated that the cyanoacrylate and the composite adhesives tested have clinically adequate shear bond strengths at half an hour and at 24 hours after initial bonding. The clinician needs to consider the properties of each adhesive: eg, the need to use a curing light and the ability to have more working time with the composite adhesive versus no light but only a 5-second working time before the cyanoacrylate adhesive starts to set.

Shear bond strength of stainless steel orthodontic brackets with a moisture-insensitive primer

The purposes of this study were (1) to evaluate the shear bond strength of stainless steel orthodontic brackets bonded to dry and wet (with water and saliva) etched enamel with the use of the moisture-insensitive primer (MIP; Transbond; 3M Unitek, Monrovia, Calif) and (2) to evaluate the effectiveness of MIP with chemically activated (Concise; 3M Dental Products, St Paul, Minn) and light-activated (Transbond XT; 3M Unitek) resin. One hundred forty-four freshly extracted bovine teeth were divided into 12 groups (n = 12 teeth), and brackets were bonded with either of the 2 resins in combination with the conventional primer or MIP in dry or wet enamel surface conditions. The test specimens were mounted in a screw-driven mechanical testing machine (model 4204; Instron Corp, Canton, Mass) and subjected to a crosshead speed of 0.5 mm/min. The data were analyzed by 2-way analysis of variance. MIP with Concise produced slightly higher bond strengths compared with the conventional primers under wet conditions (MIP vs conventional: saliva, P <.001; water, P =.004). However, MIP in combination with Transbond XT produced comparable bond strengths on both the dry and wet etched enamel (dry, 10.14 MPa; water, 9.69 MPa; saliva, 8.90 MPa). The results of this study suggest that MIP be used only with light-activated composite resins.

Effect of changing enamel conditioner concentration on the shear bond strength of a resin-modified glass ionomer adhesive

The purpose of this study was to determine the effects on shear bond strength of changing the concentration of the enamel conditioner used with resin-reinforced glass ionomer. Shear bond strength was measured within 30 minutes after bonding. Forty-six freshly extracted human molars were collected and stored in a solution of 0. 1% (weight/volume) thymol. The teeth were cleaned and polished, then randomly separated into 2 groups. In group I, enamel was conditioned with a 10% polyacrylic acid solution before bonding. In group II, the enamel was conditioned with a 20% polyacrylic acid solution. The results of t test comparisons of the 2 experimental groups (t = 4.9) indicate significant differences (P =.001). Shear bond strength was significantly greater in the group conditioned with the 20% polyacrylic acid concentration (X = 3.3 +/- 2.6 MPa) than in the group conditioned with the 10% concentration (X = 0.4 +/- 1.0 MPa). The present findings indicated that the lower initial shear bond strength of resin-reinforced glass ionomer adhesive can be improved more than 8-fold when the concentration of the polyacrylic acid enamel conditioner is increased from 10% to 20%. The clinician needs to take these properties into consideration when ligating the initial archwires.

Effect of altering the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer adhesive

The purpose of this study was to determine the effects of changing the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer within half an hour after bonding the bracket to the tooth. Freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned and polished. The teeth were randomly separated into 4 groups according to the enamel conditioner/etchant and adhesive used: group I, teeth were conditioned with 10% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group II, teeth were conditioned with 20% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group III, teeth were etched with 37% phosphoric acid and the brackets were bonded with a resin-reinforced glass ionomer adhesive; group IV, teeth were etched with 37% phosphoric acid and the brackets were bonded with a composite adhesive. The results of the analysis of variance comparing the 4 experimental groups (F = 24.87) indicated the presence of significant differences between the groups (P =.0001). In general, the shear bond strengths were significantly greater in the 2 groups etched with 37% phosphoric acid. This was true for both the resin-reinforced glass ionomer (X = 6.1 +/- 2.7 MPa) and the composite (X = 5.2 +/- 2.9 MPa) adhesives. On the other hand, the shear bond strengths were significantly lower in the two groups conditioned with polyacrylic acid. The bond strength of the resin-reinforced glass ionomer adhesive conditioned with 10% polyacrylic acid (X = 0.4 +/- 1.0 MPa) was significantly lower than the group conditioned with 20% polyacrylic acid (&xmacr; = 3.3 +/- 2.6 MPa). The present findings indicated that the bond strength of the resin-reinforced glass ionomer adhesive can be significantly increased in the initial half hour after bonding if the enamel is etched with 37% phosphoric acid instead of being conditioned with either 10% or 20% polyacrylic acid. The clinician needs to take these properties into consideration when ligating the initial archwires.

Effect of light-cure time on the initial shear bond strength of a glass-ionomer adhesive

With the introduction of photosensitive (light-cured) restorative materials in dentistry, various methods were suggested to enhance the polymerization of these materials including layering and the use of more powerful light-curing devices. The purpose of this study was to determine the effects of increasing the light-cure time on the initial shear bond strength (in the first half hour) of a resin-modified glass-ionomer adhesive. Eighty-six teeth were divided into 4 groups according to either; (1) the adhesive system used, namely resin, reinforced glass ionomer, or composite, and (2) the light-cure time for the glass ionomer adhesive, namely 40, 45, and 50 seconds. The bonding approach followed the manufacturer's instructions unless otherwise specified. The results of the analysis of variance comparing the 4 experimental groups (F = 19.4) indicated the presence of significant differences between the groups (P =. 0001). In general, the shear bond strength was greater for the composite adhesive system (¿x(-) = 5.2 +/- 2.9 MPa), followed by the 2 groups bonded with the resin-reinforced glass-ionomer adhesive and light cured for 50 seconds (¿x(-) = 3.8 +/- 1.1 MPa) and 45 seconds (¿x(-) = 3.4 +/- 2.7 MPa). On the other hand, the shear bond strength was significantly lower for the group bonded with the glass ionomer adhesive and light cured for 40 seconds only (¿x(-) = 0.4 +/- 1.0 MPa). The present findings indicated the following: (1) the resin-reinforced glass-ionomer adhesive has a significantly lower shear bond strength in the first half hour after bonding when compared to a composite resin adhesive; (2) the initial bond strength of the glass-ionomer adhesive was significantly increased by increasing the light-cure time for an additional 5 to 10 seconds; (3) the mean increase in the shear bond strength between 5 and 10 seconds of additional light curing was not significant but the variability was less with the longer cure time.

Effect of time on the shear bond strength of glass ionomer and composite orthodontic adhesives

The purpose of this study was to compare the effects of time on the shear bond strength of a resin-reinforced glass ionomer and a composite adhesive system specifically (1) within half an hour after bonding the bracket to the tooth and (2) at least 24 hours from the time of bonding when the adhesive has achieved most of its bond strength. Ninety-one freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned and polished. The teeth were randomly separated into four groups: Group I, glass ionomer adhesive debonded within 30 minutes from initial bonding; Group II, glass ionomer adhesive debonded after 24 hours immersion in deionized water at 37 degrees C; Group III, composite adhesive debonded within 30 minutes from initial bonding; Group IV, composite adhesive debonded after 24 hours immersion in deionized water at 37 degrees C. The results of the analysis of variance comparing the 4 experimental groups (F = 59. 3) indicated the presence of significant differences between the 4 groups (P =.0001). In general, the shear bond strengths were significantly greater in the 2 groups debonded after 24 hours. This was true for both the resin-modified glass ionomer (x = 8.8 +/- 3.6 MPa) and the composite (x = 10.4 +/- 2.8 MPa) adhesives. On the other hand, the shear bond strengths were significantly lower in the 2 groups debonded within 30 minutes of their initial bonding. The bond strength of the resin-modified glass ionomer adhesive (x = 0.4 +/- 1.0 MPa) was significantly lower than that for the composite (x = 5.2 +/- 2.9 MPa) adhesive. The present findings indicated that the resin reinforced glass ionomer adhesive has a significantly lower initial bond strength but increased more than 20-fold within 24 hours. In comparison, the composite adhesive has a significantly larger initial bond strength that doubled within 24 hours. The clinician needs to take these properties into consideration when ligating the initial arch wires.

A comparison of the shear bond strengths of two glass ionomer cements

The objective of this study was to determine the in vitro shear bond strength (in megapascals) and location of bond failure with two light-cured glass ionomer resin systems. One system was a hybrid glass ionomer cement with resin (GC Orthodontics, Aslip, Ill), and the other system a glass-filled resin system (Reliance Orthodontic Products, Inc, Itasca, Ill). These systems, Fuji Ortho LC (GC Orthodontics) and Ultra Band Lok (Reliance), respectively, were compared to a light-cured composite resin. Maxillary premolar brackets (n = 200) were bonded to the facial surface of human premolar teeth. The two glass ionomer resin systems were each evaluated by two protocols, one according to the manufacturers' direction plus a variation of their respective technique. The five distinct groups (n = 40) were stored in 37 degreesC distilled water for 30 days and subjected to thermocycling before shear bond strength testing. The findings indicated that large variations existed between the bond strengths of the materials tested. The laboratory shear bond strength of the glass-filled resin glass ionomer cement (Reliance), whether tested in a dry or moist field, was similar to the composite control with all of the previous materials being significantly (P <.01) higher than both the hybrid glass ionomer cement groups (Fuji Ortho LC). However, the hybrid glass ionomer cement with enamel conditioner demonstrated a clinically acceptable mean megapascal value. The Adhesive Remnant Index values ranged from 0.53 to 1.62. The hybrid glass ionomer cement without enamel conditioning recorded the lowest mean adhesive remnant index score and the lowest mean megapascal score. Although both products are glass ionomer resin systems, their individual chemistries vary; this affects their clinical performance. Clinically, it may be suggested that glass ionomers used in a dry field may be beneficial for orthodontic bonding, and that glass ionomer resin systems used in a moist environment need an enamel conditioner.

Evaluation of Scotchbond Multipurpose and maleic acid as alternative methods of bonding orthodontic brackets

Damage to the enamel surface during bonding and debonding of orthodontic brackets is a clinical concern. Alternative bonding methods that minimize enamel surface damage while maintaining a clinically useful bond strength is an aim of current research. The purpose of this study was to compare the effects on bond strength and bracket failure location of two adhesives (System 1+ and Scotchbond Multipurpose, 3M Dental Products Division) and two enamel conditioners (37% phosphoric acid and 10% maleic acid). Forty-eight freshly extracted human premolars were pumiced and divided into four groups of 12 teeth, and metal orthodontic brackets were attached to the enamel surface by one of four protocols: (1) System 1+ and phosphoric acid, (2) Scotchbond and phosphoric acid, (3) System 1+ and maleic acid, and (4) Scotchbond and maleic acid. After bracket attachment, the teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 72 hours. A Zwick universal testing machine (Zwick GmbH & Co.) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The analysis of variance was used to compare the four groups. Significance was predetermined at p < or = 0.05. The results indicated that there were no significant differences in bond strength among the four groups (p = 0.386). The results of the Chi square test, evaluating the residual adhesives on the enamel surfaces, revealed significant differences among the four groups (mean 2 = 0.005). A Duncan multiple range test revealed the difference occurred between the phosphoric acid and maleic acid groups, with maleic acid having bond failures at the enamel-adhesive interface. In conclusion, the use of Scotchbond Multipurpose and/or maleic acid does not significantly effect bond strength, however, the use of maleic acid resulted in an unfavorable bond failure location.

In-vitro study of the adhesive strengths of brackets on metals, ceramic and composite. Part 2: Bonding to porcelain and composite resin

In addition to part 1 of the study, the present paper investigated more than 25 resin/conditioner combinations with respect to their bond strengths to porcelain and composite resin. For that purpose stainless steel lingual buttons were bonded with the various adhesives and their shear bond strengths and types of bond failure were determined after 24 hours. All specimens were air-abraded with 50 microns Al2O3 for 2 or 4 seconds by means of a Microetcher before bonding. Results show that, on the porcelain, and composite under investigation, several materials yield bond strengths which are similar to or higher than what is achieved with the conventional acid etch technique on enamel. Maximum adhesive strength is not always desirable, however, for bonding brackets. The type of bond failure and the risk of irreversible damage to the bonded material have also to be taken into consideration.

Effect of varying etching times on the bond strength of ceramic brackets

Damage to the enamel surface when debonding orthodontic ceramic brackets has been a clinical concern. Ideally, bond failure at the bracket-adhesive interface should occur without damaging the enamel surface. The purpose of this study was to determine the shear bond strength and debonding failure modes of ceramic brackets with varying etching times. Sixty freshly extracted human premolars were pumiced and divided into six groups of 10 teeth. Each group was assigned an etching time interval of either 30, 20, 15, 10, 5, or 0 seconds with 37% phosphoric acid. Ceramic orthodontic brackets were bonded to each etched tooth by using the same orthodontic bonding system. The teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 48 hours. A Zwick universal testing machine (Zwick GmbH and Co., Ulm, Germany) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The results of the analysis of variance indicated that there were significant differences in bond strengths between the various etching times (p=0.0001). The Duncan multiple range test revealed that the 5-second and no etch group exhibited significantly lower bond strengths. The results of the Chi square test evaluating the residual adhesives on the enamel surface also revealed significant differences (p=0.0001). However, when the 5- and 0-second groups were dropped from the test, the Chi square test revealed no significant differences between the 30-, 20-, 15-, and 10-second groups (p=0.211). In conclusion, decreasing etching time between 30 and 10 seconds does not significantly affect either bond strength or the site of bond failure.

Bond strength of rebonded orthodontic brackets

A study was undertaken to determine the bond strength of brackets rebonded with a no-mix resin system or a paste-paste resin system. The efficacy of plastic conditioner and Enhance adhesion booster (Reliance Orthodontic Products, Inc., Itasca, Ill.) as an aid in rebonding was also evaluated. Sixty extracted human premolars were divided into two groups based on the two adhesive systems used. Both groups of 30 were subdivided and (1) initial bond, (2) rebond, and (3) rebond using plastic conditioner and adhesion booster. Samples were stressed to bond failure using an Instron machine. Bond separation occurred in the majority of samples at the enamel/resin interface. Mean bond strengths ranged from 78.8 kg cm-2 for rebonding with a no-mix adhesive and no other conditioners, to 182.7 kg cm-2 for initial bonding using a paste-paste adhesive. Rebonding using a paste-paste adhesive with no other conditioners produced a bond strength statistically indistinguishable from initial bonding with either system. Plastic conditioner and adhesion booster failed to improve rebond strength. The data suggest that, given certain circumstances, rebonding is a viable option when a bracket has been debonded.

A critique of bond strength testing in orthodontics

The literature contains a large number of publications on in vitro bond strength testing of materials used in orthodontics. The results are often quoted by manufacturers to support their products. Little attention has been paid to the detail of the test procedures used. However, a review of the literature revealed a large variation in the methods used for bond strength testing in orthodontics making comparison of papers difficult and often impossible. The case for a possible standard technique is suggested. It is hoped that this will lead to more meaningful testing of new products, which will produce more reliable guidance for the clinical orthodontist.