Effect of enamel protective agents on shear bond strength of orthodontic brackets

Background

This paper aimed to study the effect of two enamel protective agents on the shear bond strength (SBS) of orthodontic brackets bonded with conventional and self-etching primer (SEP) adhesive systems.

Methods

The two protective agents used were resin infiltrate (ICON) and Clinpro; the two adhesive systems used were self-etching primer system (Transbond Plus Self Etching Primer + Transbond XT adhesive) and a conventional adhesive system (37% phosphoric acid etch + Transbond XT primer + Transbond XT adhesive ). Sixty premolars divided into three major groups and six subgroups were included. The shear bond strength was tested 72 h after bracket bonding. Adhesive remnant index scores (ARI) were assessed. Statistical analysis consisted of a one-way ANOVA for the SBS and Kruskal-Wallis test followed by Mann-Whitney test for the ARI scores.

Results

In the control group, the mean SBS when using the conventional adhesive was 21.1 ± 7.5 MPa while when using SEP was 20.2 ± 4.0 MPa. When ICON was used with the conventional adhesive system, the SBS was 20.2 ± 5.6 MPa while with SEP was 17.6 ± 4.1 MPa. When Clinpro was used with the conventional adhesive system, the SBS was 24.3 ± 7.6 MPa while with SEP was 11.2 ± 3.5 MPa. Significant differences in the shear bond strength of the different groups (P = .000) was found as well as in the ARI scores distribution (P = .000).

Conclusion

The type of the adhesive system used to bond the orthodontic brackets, either conventional or self-etching primer, influenced the SBS, while the enamel protective material influenced the adhesive remnant on the enamel surface after debonding.     

Enamel demineralization adjacent to orthodontic brackets bonded with hybrid glass ionomer cements: An in vitro study

Enamel demineralization is recognized as a possible side effect of bonding orthodontic brackets with composite resins. Fluoride-releasing restorative materials have been shown to inhibit tooth demineralization. The purpose of this study was to evaluate two fluoride-releasing hybrid glass ionomer bonding agents for inhibition of enamel demineralization surrounding orthodontic brackets under two experimental conditions. This in vitro study used 72 extracted human premolars. Twenty-four teeth were bonded with Advance resionomer, 24 were bonded with Fuji Ortho LC hybrid glass ionomer and 24 were bonded with Transbond XT composite resin as the control. The teeth were cycled in an artificial caries challenge three times daily for 30 days. Half of the teeth in each group were brushed twice daily with a fluoridated dentifrice, and the other half were not brushed. Demineralization of enamel surrounding orthodontic brackets was evaluated with polarized light microscopy. Enamel lesions were photographed under maximum illumination. Images were projected, and demineralized areas were traced. Both average depth and area were measured with a sonic digitizer. Analysis of variance (P < .0001) and Duncan’s test (P < .05) indicated significant differences in depth and area of demineralized enamel such that lesion size was: Transbond XT no brush > Transbond XT brush > Advance no brush = Advance brush = Fuji Ortho LC no brush = Fuji Ortho brush. The promising results of this in vitro study warrant further clinical investigation of hybrid glass ionomer adhesives as orthodontic bonding agents to minimize enamel demineralization. (Am J Orthod Dentofacial Orthop 1998;114:668-74)     

Effect of light-curing units in shear bond strength of metallic brackets: an in vitro study

Objective

To determine the influence of the light curing units on the shear bond strength of orthodontic brackets.

Material and Methods

Seventy-two premolars were divided into six groups (n=12): Group I: brackets bonded with Transbond and polymerization with halogen light; Group II: Transbond and LED; Group III: Fuji Ortho and halogen light; Group IV: Fuji Ortho and LED; Group V: Fuji Ortho, without acid and halogen light; Group VI: Fuji Ortho, without acid and LED. The groups were tested to shear strength in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by ANOVA and Tukey’s test.

Results

The composite resin presented higher shear bond strength than the resin-modified glass ionomer cement (p<0.05). The halogen light and LED sources produced similar shear bond strength (p>0.05).

Conclusion

The shear bond strength was influenced by the material but not by the light-curing unit. The use of LED reduced the experimental time by approximately 60%, with the same curing efficiency.     

A self-conditioner for resin-modified glass ionomers in bonding orthodontic brackets

OBJECTIVE: To evaluate a new self-etch conditioner used with resin-modified glass ionomers (RMGIs) in bonding orthodontic brackets. MATERIALS AND METHODS: Sixty human molars were cleaned, mounted, and randomly divided into three groups. In group 1 (control), 20 orthodontic brackets were bonded to teeth using Transbond Plus Self-etching Primer; in group 2, 20 brackets were bonded using an RMGI with a 10% polyacrylic acid conditioner. In group 3, 20 brackets were bonded using Fuji Ortho LC with a new no-rinse self-conditioner for RMGIs. The same bracket type was used on all groups. The teeth were debonded in shear mode using a universal testing machine, and the amount of residual adhesive remaining on each tooth was evaluated. Analysis of variance was used to compare the shear bond strength (SBS), and the chi(2) test was used to compare the Adhesive Remnant Index (ARI) scores. RESULTS: There were no significant differences in the SBS (P = .556) between the groups. The mean SBS for Transbond Plus was 8.6 +/- 2.6 MPa, for Fuji Ortho LC using 10% polyacrylic acid 9.1 +/- 4.6 MPa, and for Fuji Ortho LC using GC Self-conditioner 9.9 +/- 4.1 MPa. The comparisons of the ARI scores between the three groups (chi(2) = 35.5) indicated that bracket failure mode was significantly different (P < .001), with more adhesive remaining on the teeth bonded using Transbond. Conclusions: The new self-etch conditioner can be used with an RMGI to successfully bond brackets. In addition, brackets bonded with Fuji Ortho LC resulted in less residual adhesive remaining on the teeth.     

An in vitro comparison of the shear bond strength of a resin-reinforced glass ionomer cement and a composite adhesive for bonding orthodontic brackets

The shear bond strength (SBS) of a light-cured, resin-reinforced glass ionomer and a composite adhesive in combination with a self-etching primer was compared after different setting times to evaluate when orthodontic wires could be placed. Additionally, the fracture site after debonding was assessed using the Adhesive Remnant Index (ARI). Eighty freshly extracted human premolars were used. Twenty teeth were randomly assigned to each of four groups: (1) brackets bonded with Transbond XT with a Transbond Plus etching primer and debonded within 5 minutes; (2) brackets bonded with Fuji Ortho LC and debonded within 5 minutes; (3) brackets bonded as for group 1 and debonded within 15 minutes; (4) brackets bonded as for group 2 and debonded within 15 minutes. The SBS of each sample was determined with an Instron machine. The mean SBS were, respectively: (1) 8.8 +/- 2 MPa; (2) 6.6 +/- 2.5 MPa; (3) 11 +/- 1.6 MPa and (4) 9.6 +/- 1.6 MPa. Interpolating the cumulative fracture probability by means of a Weibull analysis, the 10 per cent probabilities of fracture for the groups were found to be attained for shear stresses of 6.1, 3.1, 8.3 and 7.1 MPa, respectively. Chi-square testing of the ARI scores revealed that the nature of the remnant did not vary significantly with time, but the type of bonding material could generally be distinguished in leaving more or less than 10 per cent of bonding material on the tooth. After debonding, the Transbond system was likely to leave adhesive on at least 10 per cent of the bonded area of the tooth. The present findings indicate that brackets bonded with either Transbond XT in combination with Transbond Plus etching primer and Fuji Ortho LC had adequate bond strength at 5 minutes and were even stronger 15 minutes after initial bonding.     

Clinical evaluation of the failure rates of metallic brackets

Objectives

The aim of this study was to evaluate in vivo the bonding of metallic orthodontic brackets with different adhesive systems.

Material and Methods

Twenty patients (10.5-15.1 years old) who had sought corrective orthodontic treatment at a University Orthodontic Clinic were evaluated. Brackets were bonded from the right second premolar to the left second premolar in the upper and lower arches using: Orthodontic Concise, conventional Transbond XT, Transbond XT without primer, and Transbond XT associated with Transbond Plus Self-etching Primer (TPSEP). The 4 adhesive systems were used in all patients using a split-mouth design; each adhesive system was used in one quadrant of each dental arch, so that each group of 5 patients received the same bonding sequence. Initial archwires were inserted 1 week after bracket bonding. The number of bracket failures for each adhesive system was quantified over a 6-month period.

Results

The number of debonded brackets was: 8- Orthodontic Concise, 2- conventional Transbond XT, 9- Transbond XT without primer, and 1- Transbond XT + TPSEP. By using the Kaplan-Meier methods, statistically significant differences were found between the materials (p=0.0198), and the Logrank test identified these differences. Conventional Transbond XT and Transbond XT + TPSEP adhesive systems were statistically superior to Orthodontic Concise and Transbond XT without primer (p<0.05). There was no statistically significant difference between the dental arches (upper and lower), between the dental arch sides (right and left), and among the quadrants.

Conclusions

The largest number of bracket failures occurred with Orthodontic Concise and Transbond XT without primer systems and few bracket failures occurred with conventional Transbond XT and Transbond XT+TPSEP. More bracket failures were observed in the posterior region compared with the anterior region.     

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.     

Metallic brackets bonded with resin-reinforced glass ionomer cements under different enamel conditions

OBJECTIVE: To assess the shear bond strength of metallic orthodontic brackets bonded with either Fuji Ortho or Ortho Glass LC resin-reinforced glass ionomer cements to enamel surfaces under different conditions, namely, enamel without etching, enamel conditioned with 37% phosphoric acid and enamel conditioned with Transbond Plus Self Etching Primer (TPSEP). MATERIALS AND METHODS: One hundred and five bovine inferior incisors were divided into seven groups (n = 15). In group 1 (control) Transbond XT was used according to the manufacturer's recommendations. In groups 2, 3, and 4 all using Fuji Ortho LC, the brackets were bonded, respectively, to enamel nonetched, enamel etched with 37% phosphoric acid, and enamel etched with TPSEP. In groups 5, 6, and 7, the bonding was performed using Ortho Glass LC under the same enamel conditions observed in the other experimental groups. After 24 hours, shear bond strength tests were performed for all samples at a crosshead speed of 0.5 mm/min. RESULTS: The results (MPa) showed no statistically significant difference between groups 1, 3, and 4 (P > .05). However, such groups were statistically superior to the others (P < .05). No statistically significant difference was observed between groups 2, 6, and 7 (P > .05). Group 5 showed the lowest shear strength value, which was also statistically inferior to the other groups (P < .05). CONCLUSIONS: Regardless of the enamel treatment, Fuji Ortho LC yielded shear strength values superior to those from Ortho Glass LC.     

SHEAR BOND STRENGTH OF METALLIC BRACKETS: INFLUENCE OF SALIVA CONTAMINATION

Objective:

To evaluate the influence of saliva contamination on shear bond strength and the bond failure pattern of 3 adhesive systems (Transbond XT, AdheSE and Xeno III) on orthodontic metallic brackets bonded to human enamel.

Material and Methods:

Seventy-two permanent human molars were cut longitudinally in a mesiodistal direction, producing seventy-two specimens randomly divided into six groups. Each system was tested under 2 different enamel conditions: no contamination and contaminated with saliva. In T, A and X groups, the adhesive systems were applied to the enamel surface in accordance with manufacturer''s instructions. In TS, AS and XS groups, saliva was applied to enamel surface followed by adhesive system application. The samples were stored in distilled water at 37°C for 24 h, and then tested for shear bond strength in a universal testing machine (Emic, DL 2000) running at a crosshead speed of 1 mm/min. After bond failure, the enamel surfaces were observed under an optical microscope at 40x magnification.

Results:

The control and contaminated groups showed no significant difference in shear bond strength for the same adhesive system. However, shear bond strength of T group (17.03±4.91) was significantly higher than that of AS (8.58±1.73) and XS (10.39±4.06) groups (p<0.05). Regarding the bond failure pattern, TS group had significantly higher scores of no adhesive remaining on the tooth in the bonding area than other groups considering the adhesive remnant index (ARI) used to evaluate the amount of adhesive left on the enamel.

Conclusion:

Saliva contamination showed little influence on the 24-h shear bond strength of orthodontic brackets.     

Effects of enamel sealing on shear bond strength and the adhesive remnant index

Objectives

Selected combinations of materials were used to create tooth–adhesive–bracket complexes to evaluate shear bond strength (SBS) and the adhesive remnant index (ARI) with regard to enamel sealing.

Methods

Four adhesive systems also appropriate for use as enamel sealants were combined with four bracket types, resulting in 16 adhesive–bracket combinations, each of which was tested on 15 permanent bovine incisors. Sealant–adhesives included two recently introduced fluoride-releasing systems (Riva bond LC^® and go!^®), one established primer (Opal^® Seal?), and one commonly used adhesive as control (Transbond? XT). Brackets included two metal (discovery^® by Dentaurum and Sprint^®) and two ceramic (discovery^® pearl and GLAM^®) systems. After embedding the bovine teeth, bonding the brackets to their surface, and storing the resultant samples as per DIN 13990-2 with modifications, an SBS test was performed by applying the shear force directly at the bracket base in an incisocervical direction. Then the ARI scores were determined.

Results

Discovery^® + Transbond? XT yielded the highest (47.2 MPa) and GLAM^® + go!^® the lowest (17.0 MPa) mean SBS values. Significant differences (p < 0.0001) were found between metal and ceramic brackets of the same manufacturers (Dentaurum and Forestadent). Our ratings of the failure modes upon debonding predominantly yielded ARI 0 or 1. The high SBS values and low ARI scores observed with discovery^® + Transbond XT? were reflected in a high rate of enamel fracture, which occurred on 11 of the 15 tooth specimens in this group.

Conclusions

All sealant–bracket combinations were found to yield levels of SBS adequate for clinical application. SBS values and ARI scores varied significantly depending on which sealant–brackets were used.

     

Repeated bonding of fixed retainer increases the risk of enamel fracture

The aim of this study was to investigate the influences of repeated bonding, using 2 different orthodontic adhesive systems, on the shear bond strength (SBS) and the enamel surface morphology. Sixty premolars were divided into 2 groups (n = 30), and either Transbond XT (T group) or Fuji Ortho LC (F group) adhesives were used. SBS was measured 24 h after bonding, using a universal testing machine. Then, the enamel surfaces were investigated and the mode of failure was described using adhesive remnant index (ARI) scores. After each debonding, 10 teeth from each group were examined by scanning electron microscopy to determine the penetration of adhesives, the length of resin tags, and the state of the enamel surface. The other teeth were subjected to two more bonding/debonding procedures. In T group, the second debonding sequences had significantly higher bond strengths than the other sequences. The length of resin tags was greatest in the second debonding sequence, although there was no significant difference. In F group, the SBS increased with further rebonding and the failure mode tended towards cohesive failure. In both groups, the ARI scores increased with rebonding. Enamel loss could have occurred with both adhesives, although the surfaces appeared unchanged to the naked eye. From this study, we suggest that enamel damage caused by repeated bonding is of concern. To prevent bond failure, we should pay attention to the adhesion method used for bondable retainers.     

Shear bond strength of orthodontic resins after caries infiltrant preconditioning

Objective:To investigate the influence of caries infiltrant preconditioning on the shear bond strength of orthodontic resin cements on sound and demineralized enamel.Materials and Methods:Stainless-steel brackets were bonded to sound or artificially demineralized (14 d, acidic buffer, pH 5.0) bovine enamel specimens using a resin cement or a combination of caries infiltrant preconditioning (Icon, DMG) and the respective resin cement (light-curing composite: Heliosit Orthodontic, Transbond XT, using either Transbond XT Primer or Transbond Plus Self Etching Primer; light-curing resin-modified glass ionomer cement: Fuji Ortho; or self-curing composite: Concise Orthodontic Bonding System). Each group consisted of 15 specimens. Shear bond strength was evaluated after thermo-cycling (10,000×, 5°C to 55°C) at a crosshead speed of 1 mm/min, and data were statistically analyzed by analysis of variance, Mann-Whitney test, and Weibull statistics. Adhesive Remnant Index (ARI) scores and enamel fractures were determined at 25× magnification and were statistically analyzed by regression analyses (P < .05).Results:The caries infiltrant system significantly increased the shear bond strength of Transbond XT Primer, Transbond Plus Self Etching Primer, and Fuji Ortho in sound specimens, and of all resin cements except for the Concise Orthodontic Bonding System in demineralized enamel. Overall, caries infiltrant preconditioning decreased significantly the number of enamel fractures, but it did not affect ARI scores.Conclusion:Preconditioning of sound and demineralized enamel with the caries infiltrant system did not impair but rather increased the shear bond strength of most orthodontic resin cements while decreasing the risk of enamel fracture at debonding.     

树脂修饰化玻璃离子托槽粘结剂粘结强度的体外研究

目的：评估一种树脂修饰化的玻璃离子托槽粘结剂在牙面不同处理方式和环境下的两次粘结后的剪切强度情况。方法：将新近拔除的105颗上颌第一前磨牙随机均分成7组,按照说明书的要求完成托槽的粘结。对照组牙面用37%的磷酸处理后,用光固化复合树脂粘结剂（3M,Transbond XT）粘结。其它6组牙面分别在37%的磷酸、GC处理剂（GC Self-Conditioner）、和不做任何处理的条件下,分别在干燥和湿润的环境下用树脂修饰化的玻璃离子（RMGIC;Fuji ORTHO LC,GC Corporation,Tokyo,Japan）粘结,所有牙齿均选用同种托槽。托槽粘结24 h后,在万能测力机下以1 mm/min的速度卸载,并记录下数值。除去牙面和托槽底面多余粘结剂后,重复上述过程。每次卸载后检查牙釉质损坏情况。结果：对照组两次剪切强度有较小的差异,其它GC玻璃离子粘结剂组两次剪切强度没有统计学意义。GC粘结剂不做任何处理组在干燥和湿润的环境下其剪切强度存在明显的差异。干燥环境下,37%的磷酸和GC处理剂处理后,GC粘结剂组两次卸载后的牙釉质均出现不同程度的釉裂或釉质脱落。结论：这种树脂修饰化的玻璃离子粘结剂可以在多种条件下用于托槽的粘结。     

Biocompatibility of orthodontic adhesives in rat subcutaneous tissue

Objective

The objective of the present study was to verify the hypothesis that no difference in biocompatibility exists between different orthodontic adhesives.

Material and Methods

Thirty male Wistar rats were used in this study and divided into five groups (n=6): Group 1 (control, distilled water), Group 2 (Concise), Group 3 (Xeno III), Group 4 (Transbond XT), and Group 5 (Transbond plus Self-Etching Primer). Two cavities were performed in the subcutaneous dorsum of each animal to place a polyvinyl sponge soaked with 2 drops of the respective adhesive in each surgical loci. Two animals of each group were sacrificed after 7, 15, and 30 days, and their tissues were analyzed by using an optical microscope.

Results

At day 7, Groups 3 (Transbond XT) and 4 (Xeno III) showed intense mono- and polymorphonuclear inflammatory infiltrate with no differences between them, whereas Groups 1 (control) and 2 (Concise) showed moderate mononuclear inflammatory infiltrate. At day 15, severe inflammation was observed in Group 3 (Transbond XT) compared to other groups. At day 30, the same group showed a more expressive mononuclear inflammatory infiltrate compared to other groups.

Conclusion

Among the orthodontic adhesive analyzed, it may be concluded that Transbond XT exhibited the worst biocompatibility. However, one cannot interpret the specificity of the data generated in vivo animal models as a human response.     

Effect of remineralizing agents on bond strength of orthodontic brackets: an in vitro study

Background

The purpose of this study is to evaluate the effect of casein phosphopeptide amorphous calcium phosphate (CPP-ACP) and CPP-ACP with fluoride (CPP-ACP-F) on the shear bond strength (SBS) of orthodontic brackets bonded with two different adhesive systems.

Methods

One hundred twenty-six human premolar teeth were selected. One hundred twenty teeth were used for SBS testing, and six teeth were used for scanning electron microscope (SEM) examination. One hundred twenty premolars were divided into mainly three groups: CPP-ACP (group A), CPP-ACP-F (group B), and control group (group C). Each group was sub-divided into two groups according to the bonding adhesive, light cure (groups A1, B1, and C1) and chemical cure (groups A2, B2, and C2). The teeth were pre-treated with the group-specified preventive agent 1 h/day for five consecutive days. Standard edgewise brackets were bonded with the respective adhesives. SBS evaluation was done with the universal testing machine. After debonding, all the teeth were scored for adhesive remaining on the buccal surface, in accordance to adhesive remnant index, under a stereomicroscope. The acid-etched enamel surfaces were observed under SEM after treatment with CPP-ACP, CPP-ACP-F, and artificial saliva.

Result

In light-cure adhesive group, CPP-ACP-F (B1) showed superior results compared to the control group (C1), whereas the CPP-ACP group (A1) showed lower mean SBS than the control group (C1). Both these differences were not statistically significant (p > 0.05). In chemical-cure adhesive group, control group C2 showed significantly superior results (p < 0.05) compared to group A2 and group B2. The results of two-way ANOVA showed highly significant difference due to adhesive types (p < 0.01), whereas enamel pre-treatment showed non-significant difference (p > 0.01).

Conclusion

The SBS of the orthodontic brackets was non-significantly affected when the brackets were cured with light-cure bonding system and treated with either CPP-ACP or CPP-ACP-F, whereas with chemical-cure adhesive, decreased bond strength was seen, which was within the clinically acceptable limits.     

Effect of bonding material, etching time and silane on the bond strength of metallic orthodontic brackets to ceramic

The purpose of this study was to evaluate the bond strength of metallic orthodontic brackets to feldspathic ceramic with different etching times, bonding materials and with or without silane application. Cylinders of feldspathic ceramic were etched with 10% hydrofluoric acid for 20 or 60 s. For each etching time, half of the cylinders received two layers of silane. Metallic brackets were bonded to the cylinders using Transbond XT (3M Unitek) or Fuji Ortho LC (GC). Light-activation was carried out with total exposure time of 40 s using UltraLume 5. Shear bond strength testing was performed after 24 h storage. Data were submitted to three-way ANOVA and Tukey's test (α=0.05). The adhesive remnant index (ARI) was used to evaluate the amount of adhesive remaining on the ceramic surface at ×8 magnification. Specimens etched for 60 s had significantly higher bond strength compared with 20 s. The application of silane was efficient in increasing the shear bond strength between ceramic and both fixed materials. Transbond XT showed significantly higher (p<0.05) bond strength than Fuji Orth LC. There was a predominance of ARI score 0 (clean ceramic failure surface) for all groups, with an increase in scores 1, 2 and 3 (adhesive material increasingly present on ceramic failure aspect) for the 60-s etching time. In conclusion, 60-s etching time, silane and Transbond XT improved significantly the shear bond strength of brackets to ceramic.     

Evaluation of stresses developed in different bracket-cement-enamel systems using finite element analysis with in vitro bond strength tests

Background

The purpose of this study was to determine the bond strength of different orthodontic bracket materials (ceramic, stainless steel, and titanium) as well as stresses developed in bracket-cement-enamel systems using finite element (FE) analysis.

Methods

One hundred and thirty-five extracted human caries-free upper central incisors were divided into three groups (n = 45/group) according to the type of orthodontic bracket materials (stainless steel, ceramic, and titanium). Each group was further subdivided into three subgroups (n = 15/group) according to the bond strength test loading mode (shear short side, shear long side, and tensile). After debonding, the fractured specimen was examined, and the adhesive remnant index (ARI) was determined. FE analysis models analyzed the stress distribution within the cement and enamel. Bond strengths were analyzed using ANOVA and Tukey''s test, and the ARI scores were analyzed using chi-square (χ²) test.

Results

Shear loading at the short side of the bracket resulted in the highest bond strength and lowest maximum principal stress both on cement and enamel compared with the other loading modes (P < 0.05). Ceramic brackets presented with higher bond strength and lower maximum principal stress than metallic brackets (P < 0.05). There was a significant difference for ARI scores between the type of brackets (χ² = 64.852, P < 0.001).

Conclusion

The findings suggest that the manner of loading orthodontic brackets and the selection of orthodontic bracket materials affect the bond strength and stresses developed both on cement and enamel.     

Comparison of bond strength of three adhesives: composite resin, hybrid GIC, and glass-filled GIC.

The objective of this study was to compare 3 orthodontic adhesives in the areas of shear-peel bond strength, location of adhesive failure, and extent of enamel cracking before bonding and after debonding of orthodontic brackets. The adhesives included a composite resin control (Transbond XT; 3M/Unitek, St Paul, Minn), a resin-modified glass ionomer cement (Fuji Ortho LC; GC America Corp, Alsip, Ill), and a polyacid-modified composite resin under dry and saliva-contaminated conditions (Assure; Reliance Orthodontic Products Inc, Itasca, Ill). Metal brackets were bonded to the buccal surfaces of 160 (4 groups of 40) human premolars. The bonded teeth were stored in deionized water at 37 degrees C for 30 days and thermocycled for 24 hours before debonding with a Universal Instron (Instron Corp, Canton, Mass) testing machine. The extent of cracking in the buccal surfaces was evaluated under 16x magnification before bonding and after debonding. Although the bond strength of the composite resin control (20.19 MPa) was significantly greater (P <.05) than that of the adhesives in the other groups, clinically acceptable shear-peel bond strengths were found for all adhesives (Fuji Ortho LC = 13.57 MPa, Assure-dry = 10.74 MPa, Assure-wet = 10.99 MPa). The bond strength for the Assure adhesive was not significantly affected by saliva contamination. The sample of extracted premolars used in this study displayed a greater frequency of buccal surface enamel cracking (46.7%) than that reported in the literature for in vivo premolars (7.8%-10.2%), which was possibly due to the extraction process. The frequency of enamel cracking in a subset of this sample (n = 34) increased from 46.4% at prebonding to 62.4% at postdebonding as a result of the forces of debonding.     

两种光固化正畸粘接剂聚合度的比较

目的比较两种光固化正畸粘接剂Transbond XT和Fuji ortho LC在传统卤素灯（Halogen）不同光照时间作用下的聚合度。方法30颗上颌中切牙金属托槽分成6组（每组5颗）。用标准量的粘接剂将托槽粘接于牙齿表面,随机分配3组用Transbond XT粘接剂进行粘接,3组用Fuji ortho LC进行粘接。每一种粘接剂使用Halogen灯光照不同时间进行固化。每组通过傅里叶变换红外光谱仪记录红外吸收峰进行聚合度分析。实验结果通过方差分析（ANOVA）和t检验进行统计学分析。结果Fuji ortho LC在相同光照时间作用下的聚合度（88．28±4．08％）要大于Transbond XT（53．56±6．06％）,其差异具有统计学意义。光照时间的不同对粘接剂聚合度的影响无统计学意义。结论两种粘接剂的聚合度存在显著差异,而光照时间对粘接剂聚合度的影响没有差别。     

Effects of a fluoride-containing casein phosphopeptide-amorphous calcium phosphate complex on the shear bond strength of orthodontic brackets

The purpose of this study was to investigate the effects of enamel pre-treatment with a new fluoride-containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) complex on the shear bond strength (SBS) of brackets bonded with etch-and-rinse or self-etching adhesive systems. The material comprised 66 extracted human premolars randomly divided into six equal groups with respect to the enamel pre-treatment and adhesive system employed: 1. No pre-treatment and brackets bonded with the etch-and-rinse adhesive system (Transbond XT). 2. Pre-treatment with fluoride-containing CPP-ACP paste (MI Paste Plus) and Transbond XT. 3. Pre-treatment with non-fluoride CPP-ACP paste (MI Paste) and Transbond XT.4. No pre-treatment and brackets bonded with the self-etching adhesive system (Transbond Plus). 5 and 6. Enamel pre-treated as for groups 2 and 3, respectively, and the Transbond Plus. Bonded specimens were subjected to thermal cycling (×1000) before SBS testing. The residual adhesive on the enamel surface was evaluated after debonding with the adhesive remnant index (ARI). Data evaluation was made using one-way analysis of variance and Tukey test for SBS results, and Kruskal-Wallis test for ARI results. The results showed that enamel pre-treatment with either fluoride or non-fluoride CPP-ACP paste had no significant effect on the SBS of the self-etching adhesive system (P > 0.05). Enamel pre-treatment with non-fluoride CPP-ACP in group 3 significantly reduced the SBS of the etch-and-rinse adhesive (P < 0.001), while pre-treatment with fluoride-containing CPP-ACP paste (groups 2 and 5) did not affect debonding values (P > 0.05). The fluoride-containing CPP-ACP did not compromise the SBS of brackets bonded with the tested etch-and-rinse and self-etching systems, but its non-fluoride version significantly decreased the SBS of the etch-and-rinse adhesive system.