Vol 16, No 1, 2014 15

Influence of Degree of Conversion on the

Biocompatibility of Different Composites In Vivo

Rogério Lacerda dos Santosa / Gêisa Aiane de Morais Sampaiob / Fabiola Galbiatti de Carvalhoc / Matheus Melo Pithond / Gymenna Maria Tenório Guênese / Polliana Muniz Alvesf

Purpose: To evaluate the relationship between biocompatibility and degree of monomer conversion of compos-ites used to bond brackets to enamel, porcelain, resin, or metal surfaces at different time intervals.

Materials and Methods: Twenty-four male Wistar rats were used, divided into 4 groups (n = 6) as follows: group C (control, polyethylene), group TCC (Transbond Color Change), group QC (Quick-Cure), and group EB (Eagle Bond). These substances were inserted into subcutaneous tissue. The events of inflammatory infiltrate, edema, necrosis, granulation tissue, multinuclear giant cells, young fibroblasts, and collagen formation were analyzed. The degree of conversion was evaluated by the Fourier method using infrared spectroscopy. Biocompatibility and degree of conversion were statistically analyzed using the Kruskal-Wallis and Dunn tests, and ANOVA and Tukey’s test, respectively (p < 0.05).

Results: The composites caused a small amount of inflammatory infiltrate, edema, and granulation tissue at all experimental time intervals, showing a gradual reduction over time (p > 0.05). Group TCC showed the high-est amount of fibroblasts and EB the smallest at the time interval of 15 days (p = 0.035). Group TCC showed the highest amount of collagen fibers and EB the smallest throughout the experiment; there was a significant difference in terms of collagen fibers between groups QC and EB, which differed from the control at 7 days (p = 0.006), and between groups EB and TCC (p = 0.018) at 30 days. Monomer conversion ranged from 64.1% in group EB at 7 days to 85.3% in group TCC at 30 days.

Conclusion: Transbond Color Change composite showed a higher degree of conversion and a better healing pro-cess compared to Eagle Bond composite at 15 and 30 days. Quick-cure composite demonstrated a better degree of conversion and healing process than that of Eagle Bond, but this was not statistically significantly different.

Keywords: composites, biocompatibility, adhesive dentistry.

J Adhes Dent 2014; 16: 15–20. Submitted for publication: 17.10.12; accepted for publication: 19.03.13

doi: 10.3290/j.jad.a29704

a Professor, Department of Orthodontics and Pediatric Dentistry, Federal Uni-versity of Campina Grande, Patos, Paraíba, Brazil. Idea, experimental design, wrote manuscript, performed statistical evaluation.

b Student of Dentistry, Department of Orthodontics and Pediatric Dentistry, Federal University of Campina Grande, Patos, Paraíba, Brazil. Performed experiments, wrote manuscript.

c Professor, Department of Orthodontics and Pediatric Dentistry, Federal Uni-versity of Campina Grande, Patos, Paraíba, Brazil. Performed experiments, proofread manuscript.

d Professor, Department of Orthodontics, State University of Sudoeste da Bahia, Jequié, Bahia, Brazil. Performed experiments, contributed substan-tially to discussion.

e Professor, Department of Restorative Dentistry, Federal University of Campina Grande, Patos, Paraíba, Brazil. Contributed substantially to discus-sion, proofread manuscript.

f Professor, Department of Pathology, State University of Paraíba, Campina Grande, Paraíba, Brazil. Performed histological tests, consulted on statistical evaluation.

Correspondence: Rogério Lacerda dos Santos, Federal University of Campina Grande (UFCG), Center for Health and Technology Rural (CSTR), Av. dos Uni-versitários, s/n, Rodovia Patos/Teixeira, Km1, Santa Cecília, CEP: 58700-970, Patos, Paraíba, Brazil. Tel: +55-83-9977-7100. e-mail: lacerdaorto@hotmail.com or lacerdaorto@bol.com.br

Insufficient polymerization of the resin matrix may result in reduction in the mechanical properties and clinical

performance of the resin, such as poor bond strength, increase in water absorption rates, solubility, and deg-radation.4,25 In addition, leachable components from the resins, such as bisphenol A-diglycidyl dimethacrylate (bis-GMA) and triethyleneglycol dimethacrylate (TEG-DMA), found in a wide range of composites, have been shown to have a defined cytotoxic effect.16,17 Due to the proximity of orthodontic appliances, similar cytotoxicity could occur in the gingiva and other oral tissues,9 as well as in the alveolar bone if an orthodontic appliance is adhesively bonded there after surgery to expose an unerupted tooth.

The behavior of these composite resins is directly linked to their chemical formulation and the release of 25% to 45% of monomers left unconverted after polymerization5 when using the conventional irradiation method.7,29 There-fore, residual monomers11 may trigger limited to moder-ate or even severe inflammatory reactions,20 in addition to having a direct influence on the physical, mechanical, and biological properties of the material.6,21

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Assessment of the biological behavior of orthodontic materials has been performed.12,20 However, there is a lack of studies that directly relate the degree of monomer conversion and the inflammatory and healing events as-sociated with composites in vivo. Thus, the aim of the present study was to evaluate the influence of the degree of conversion on the biocompatibility of composites used to bond brackets to enamel, porcelain, resins, or metal surfaces at different time intervals.

MATERIALS AND METHODS

Animal Model and Experimental GroupsFor this study, 24 adult male Wistar rats were used, with a mean weight of 250 g, belonging to the vivarium of the Federal University of Campina Grande, UACB/UFCG. The animals were divided into 4 experimental groups (6 rats per group): group C (control, polyethylene tube), group TCC (Transbond Plus Color Change adhesive, 3M Unitek; Monrovia, CA, USA), group QC (Quick-Cure, Reliance; Itasca, IL, USA), and group EB (Eagle Bond, American Or-thodontics; Sheboygon, WI, USA) (Table 1).

Each rat was to receive 2 implanted tubes (6 rats per group, two implants per rat = 12 samples per group, Table 2). The tubes – 1.5 mm inner diameter × 5 mm long, made of polyethylene (nontoxic Scalp Vein 19G) – were fabricated and previously kept in 70% alcohol for 120 min, washed with deionized water, and finally autoclaved at a temperature of 110°C for 20 min before use as inoculation vehicles for the tested materials. The composites were introduced via syringe (Centrix;

Shelton, CT, USA) into the openings at the ends of the tubes supported on a glass slide at one end and a small glass slide at the other to flatten the material. After this, they were light polymerized for 40 s using an LED appli-ance (Radii, SDI; Baywater, Victoria, Australia) fixed on a rod to guarantee that the distance to the specimens remained constant, using a light intensity of 1000 mw/cm2, regularly calibrated with a radiometer (Model 100, Demetron Research; Danbury, CT, USA). After the com-posites were polymerized, the tubes were implanted in the animals as follows.

The rats were anesthetized with an intraperitoneal in-jection of sodium thiopental (50 mg/kg) (Cristália; Campi-nas, SP, Brazil). After this, trichotomy was performed in the dorsal region of each animal, using razor blades to eliminate the hair from a 4-cm2 area. The animal experi-ment was approved by the Ethics Committee on Animal Research of the Academic Unit of Biologic Sciences, CSTR\UFCG, Protocol CEP/No.082011.

For antisepsis of the operative field, 4% chlorhexidine gluconate was used.20 On the midline, equidistant be-tween the tail base to the head of the animal, two inci-sions approximately 8 mm long were made using a No.15 scalpel blade (Embramac; Itapira, SP, Brazil) adapted to a scalpel handle. With the aid of blunt-tipped scissors (Duflex, SS White: Rio de Janeiro, RJ, Brazil), the subcu-taneous tissue was laterally parted to make a tunnel in the lateral direction, forming two surgical recesses, each approximately 18 mm deep. After two tubes per rat were implanted, the surgical recesses were sutured with a 4.0 suture needle with thread (Ethicon, Jonhson & Jonhson; São José dos Campos, SP, Brazil).

Table 1 Composition of the composites tested

Groups Composites Composition* Manufacturer Lot no.

TCC Transbond Plus Color Change adhesive

Bis-GMA (5%-10%), bis-EMA (15%-20%), TEG-DMA (5%-10%), quartz/silica (70%-80%), camphorquinone

3M Unitek; Monrovia, CA, USA

N172806

QC Quick-Cure Bis-GMA (2%-10%), TEG-DMA (5%-10%), silica (55%-90%), sodium fluoride (<2%), camphorquinone

Reliance; Itasca, IL, USA 116861

EB Eagle Bond Bis-GMA (1%-10%), bis-EMA (10%-20%), TEG-DMA (5%-10%), quartz/silica (60%-80%), camphorquinone

American Orthodontics; Sheboygon, WI, USA

A8623

*Bis-GMA, bisphenol A diglycidylmethacrylate; bis-EMA, bisphenol A bis(2-hydroxethyl ether) dimethacrylate; TEG-DMA, triethyleneglycol dimethacrylate

Table 2 Distribution of groups and day of sacrifice of rats

Control Transbond Plus Quick-Cure Eagle Bond

Rats Samples Rats Samples Rats Samples Rats Samples

7 days 2 4 2 4 2 4 2 4

15 days 2 4 2 4 2 4 2 4

30 days 2 4 2 4 2 4 2 4

Total 6 12 6 12 6 12 6 12

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dos Santos et al

The animals were kept in cages and fed with balanced rations food and water ad libitum according to the principles of the Canadian Council on Animal Care.3 After time inter-vals of 7, 15, and 30 days, the animals were anesthetized to obtain excisional biopsies of the implant area, includ-ing sufficient normal surrounding tissue. Finally, the rats were sacrificed by the cervical dislocation technique after having been sedated with sodium thiopental (50 mg/ kg) (Cristália).

BiocompatibilityPosthumous samples were taken and submitted to fixation in 4% formaldehyde (Milony solution) for 24 h. Then the polyethylene tubes containing composite were carefully removed from the biopsied specimen from the lateral incision to central region with the aid of a blade No. 15 (Embramac) adapted to the scalpel handle. Subsequently, the specimens were embed-ded in paraffin to obtain serial histological slices 6 μm thick, and stained with hematoxylin and eosin. The inflammatory reaction induced by the composites was evaluated by a blind examiner using a light microscope (BX40, Olympus; Hamburg, Germany) at 100, 200, and 400X magnifications. The examiner was calibrated before data analysis (kappa = 0.7). For each biopsy taken, five representative sections of the histological condition of the tissue adjacent to the implanted mate-rials were evaluated.

The cellular events, ie, the presence of inflammatory infiltrate, edema, necrosis, granulation tissue, multinu-clear giant cells, young fibroblasts, and collagen, were given points according to the following scores: 1 – absent; 2 – scarce, 3 – moderate, and 4 – intense.

Degree of Conversion In a separate test series, standardized test samples were prepared that measured 5 mm in diameter and 1.5 mm in thickness as follows: Stainless steel bipartite matrices were placed on a glass slide, the composite resins were injected into them using a syringe (Cen-trix) and flattened with a small glass slide, followed by polymerization. A total of 45 test samples (n = 5 per group) were stored in artificial saliva at 37°C in light-proof boxes to prevent additional exposure to light.

At 7, 15, and 30 days after curing and storage, each specimen was ground to obtain resin-composite powder, which was subsequently mixed with potassium bromide (KBr) at a ratio (by weight) of 1:10. This powder was placed in a tablet maker under a pressure of approxi-mately 8 tons. A spectrophotometer (Bomen-MB-102; Dawson, Yukon, Canada) was used to evaluate the in-frared spectrum measurements using the Fourier trans-formation method, to determine the degree of monomer conversion in percent.

Statistical AnalysisTo evaluate biocompatibility, the cellular events of inflam-matory infiltrate, edema, necrosis, granulation tissue, multinuclear giant cells, young fibroblasts, and collagen, were submitted to the Kruskall-Wallis nonparametric test,

followed by Dunn’s test to determine the differences among the groups (p < 0.05), because the data were not normally distributed. The parametric data of the degree of materials’ conversion were analyzed using ANOVA fol-lowed by Tukey’s test (p < 0.05) to determine whether there were statistical differences between the groups.

RESULTS

BiocompatibilityAll the groups presented a small amount of inflam-matory infiltrate, circulatory alterations (edema), and granulation tissue at all experimental time intervals, showing gradual reduction with time, without statistically significant differences among them (p > 0.05). Through-out the 30-day observation period, the composite resins did not induce tissue degeneration (necrosis) around or within the surgical recesses in which they were im-planted. There was rarely any finding of multinucleated giant cells (Figs 1A and 1B) in response to the non-persistence of severe inflammatory infiltrate, and good tolerance of the organism to the materials (Table 3).

When considering the healing process with regard to young fibroblasts (Fig  1C), these were statistically sig-nificantly more numerous in group TCC than in group EB (p = 0.035) at the time interval of 15 days. With regard to the presence of collagen fibers, groups QC and EB demonstrated significantly slower repair compared to the control group (p = 0.006) at the time interval of 7 days. This persisted in group EB after 30 days, which was sta-tistically significantly different than group TCC (p = 0.018) (Fig 1D) (Table 3).

After 30 days, the control and experimental groups showed a chronic inflammatory process characterized by discrete events of mononuclear infiltrate, formation of granulomas, and formation of young fibroblasts and col-lagen around the tubes.

Degree of ConversionMonomer conversion of the composites increased pro-gressively up to the 30th day, with the lowest conversion of 64.1% in group EB at 7 days and the highest of 85.3% in group TCC at 30 days. There were no statistically sig-nificant differences between the composites at 7 and 15 days (p > 0.05). The composite Eagle Bond showed the lowest conversion values during the experiment, which was statistically significantly different from Transbond (p = 0.006) at 30 days (Table 4).

DISCUSSION

The biocompatibility of the orthodontic bonding com-posites is an important concern, because they are fre-quently bonded close to or in contact with the gingival tissues and/or alveolar bone in transsurgical bonding for the purpose of performing tooth traction,17 and may remain in direct contract with the tissues for months or even years,15 possibly generating tissue damage.1,26

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Table 3 Mean of scores attributed to composites and control group after 7, 15 and 30 days, for the 7 events evaluated

Event Time Groups p

TCC QC EB C

Inflammatory Infiltrate 7 days15 days30 days

14.75 12.50 10.00

12.50 10.00 10.00

13.75 11.25 10.00

12.50 10.00 10.00

0.591 0.374 1.000

Edema 7 days15 days30 days

6.25 7.50 5.00

10.00a

5.00b

7.50ab

10.00a

5.00b

5.00ab

6.25 5.00 5.00

0.102 0.237 0.237

Necrosis 7 days15 days30 days

5.00 5.00 5.00

5.00 5.00 5.00

5.00 5.00 5.00

5.00 5.00 5.00

1.000 1.000 1.000

Granulation tissue 7 days15 days30 days

13.75 11.25 11.25

15.00 13.75 12.50

15.00 11.25 12.50

18.75a

7.50b

8.75ab

0.289 0.125 0.457

Giant cells 7 days15 days30 days

5.00 5.00 5.00

5.00 8.75 5.00

7.50 5.00 5.00

6.25 6.25 5.00

0.237 0.057 1.000

Young fibroblasts 7 days15 days30 days

8.75a

18.75Ab

17.50ab

5.00a

15.00ABb

15.00b

7.50a

10.00Bab

17.50b

6.25a

15.00ABb

15.00b

0.089 0.035 0.443

Collagen 7 days15 days30 days

8.75ABa

15.00ab

18.75Ab

5.00Aa

12.50ab

16.25ABb

5.00Aa

11.25b

11.25Bb

10.00Ba

15.00b

15.00ABb

0.006 0.185 0.018

These values represent the mean of scores of the sum of the five representative histological sections of the evaluated tissue. Thus, when all five repre-sentative sections of the evaluated tissue showed the same histological condition, the scores 1-absent, 2-scarce, 3-moderate, and 4-intense represent 1-absent (5.00), 2-scarce (10.00), 3-moderate (15.00), and 4-intense (20.00). Means followed by different letters express statistically significant difference (p < 0.05) according to non-parametric Kruskal-Wallis Test, followed by Dunn’s multiple comparisons test, represented by: a,b (in columns, comparison between times for each event evaluated) and A,B (in rows, comparison between composites for each time).

Fig 1 Photomicrographs of histologi-cal samples. PT: area of polyethylene tube implant. A) 7 days after implanta-tion, control group: granulation reac-tion area with congested vessels (CV) and scarce multinucleated giant cells (GC) (HE, 100X magnification; scale: 100 μm). B) 7 days after implanta-tion, group EB: moderate granulation reaction with small caliber blood ves-sels (BV) and the presence of multi-nucleated giant cells (GC) (HE, 100X magnification; scale: 100 μm). C) 15 days after implantation, group QC: recess surrounded by fibroblast prolif-eration (FP) and collagen fiber bundles (CFB) (HE, 100X magnification; scale: 100 μm). D) 30 days after implanta-tion, group TCC: recess surrounded by proliferation of young fibroblasts and deposition of collagen fibers (DCF) in the midst of a granulation reac-tion, scarce inflammatory cells could still be seen (HE, 400X magnification; scale: 25 μm).

A B

C D

PT

CV

CV

CV

GC

BV

GC

PT

BV

BV

GC

PT

FP

CFBDFB

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dos Santos et al

In this study, biocompatibility was evaluated in terms of inflammatory phenomena.12,20 In studies with the purpose of evaluating inflammatory and healing events caused by materials,12,19 polyethelyne tubes have been used as the control, as this is considered a substance that is harmless to epithelial and conjunctive tissues,12 and was therefore used in the present study.

The main cause of the cytotoxic effects of resin com-posites is the release of unpolymerized residual mono-mers.1 According to the literature,8,17,20 resin compo-nents such as the methacrylate monomers TEG-DMA, bis-GMA, UDMA, and HEMA present characteristics of cytotoxicity and may cause cellular damage.1,16,17 In spite of light-activated adhesives having been shown to be less cytotoxic than the chemically activated types due to the smaller quantity of monomers released,1,15 TEG-DMA, bis-GMA, and UDMA are hydrophobic monomers frequently associated with HEMA, and HEMA may facilitate the diffu-sion of these monomers into tissues, which increases the hydrophilic character of the material. Under these condi-tions, they may reach the cells and cause damage.13,23 The action of bisphenol A, the bis-GMA monomer precur-sor, is known to cause estrogenicity.18 Moreover, the monomers might cause soft-tissue irritation and favor bacterial growth around a restoration.14

In this study, the events immediately after implantation of the composite resins reflect an intense inflammatory response due to the surgical procedures. After 7 days, the inflammatory reaction is more organized and due to the tested material, not to the surgical procedure,20 which justifies an evaluation as of the 7th day, as established in this experiment.

In the present study, little inflammatory infiltrate was observed in any of the groups, without statistically sig-nificant differences among them. Inflammatory infiltrate decreased throughout the study. Inflammatory infiltrate, edema, necrosis, granulation tissue, and giant cells dem-onstrated no significant difference between the materials and control group, indicating that the composite resins were well tolerated by the organism. On the 7th day, the composites Transbond Color Change adhesive (TCC) and Eagle Bond (EB) induced a slightly greater inflammatory reaction than did Quick-cure (QC), an observation sup-ported by the lower degree of monomer conversion found at this time point. Furthermore, bis-EMA monomers have shown a cytotoxic effect analogous to that of TEG-DMA,10

which together may influence the inflammatory potential of these composites.17 In this line of research, the findings of Walther et al27 support the idea that cytoxic effects of resin components depend on time and their concentration.

The intensity of the inflammatory process is related to the cytotoxic character of the material. The decrease of inflammatory intensity relies on the control of the host defense system, which organizes itself to limit the aggressive action from the compounds existing in the composites; this process is usually associated with lo-cal edema, an extravasation of liquid for the cellular interstitial space of surrounding tissues.11,12,20 In this study, there was evidence of small dispersed edematous areas surrounded by cell proliferation and young fibro-

blasts, with subsequent deposition of collagen fibers and a reduction in the number of blood vessels observed from days 15 to 30. There were rare findings of multinu-cleated giant cells in the period from 7 to 15 days, and these were frequently linked to the formation of granu-lomas due to the polyethylene and/or test composite. Consequently, these phenomena – followed by a repair process in which the increased number of fibroblasts and collagen fibers replace the areas of inflammatory response, edema, and necrosis20 – are described as a favorable tissue response as regards the biological com-patibility of the composites. On the other hand, necrosis (tissue death caused by factors that lead to irreversible cell damage and consequent cell death11,20) was not observed in this study.

The gradual reduction in inflammatory reactions and the increase of the healing process at 30 days corroborates the findings of other studies12,20 and is related to the pattern of monomer conversion into polymers and consequent2,6 release of residual monomers30 in the first 4 weeks.4,20 Monomer conversion may influence both the inflammatory and healing events, and in this context, the composites Quick-cure (QC) and Eagle Bond (EB) showed fewer signs of healing, such as young fibroblasts and collagen fibers, at the time interval of 7 days. This suggests slower repair of the tissues exposed to these composites, still seen at 30 days for Eagle Bond, which had a lower conversion of monomers at 30 days than did the other composites.

The group TCC showed lower monomer conversion than did group QC at 7 days, but this was not statistically sig-nificantly different. In the same period, there was a ten-dency for faster repair (fibroblasts and collagen) in group TCC than in group QC, suggesting that this response may be linked to the type of unconverted monomer released and its action in tissues.

Among several methods, Fourier transformation has been supported as appropriate and has been widely used as a reliable method for showing the conversion of mono-mers of resin-based materials.24,29 In order to evaluate the conversion of monomers, the composite disks were ground into powder and remade into disks with KBr. KBr is a pure salt (transparent), undetectable by infrared spec-trometry; thus, when mixed with the test material, no spectral line appears.28

Table 4 Mean values and standard deviation (SD) of

the degree of conversion (%) of composites after 7,

15, and 30 days

Times Groups p

TCC QC EB

7 days 67.1 (3.4)a 71.7 (2.9)a 64.1 (3.7)a 0.093

15 days 76.0 (2.1)ab 74.2 (6.2)ab 71.3 (2.6)ab 0.283

30 days 85.3 (3.0)Ab 83.0 (4.1)ABb 78.1 (1.9)Bb 0.006

Means followed by different letters express statistically significant differ-ences (p < 0.05) according to ANOVA and Tukey’s post-hoc test repre-sented by: a,b (in columns, comparison between times) and A,B (in rows, comparison between composites for each time).

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Other authors24 have shown general conversion values ranging from 56% to 68%. In the present study, the values reached from 64.1% to 85.3%, close to those found by Corekci et al.4 The degree of conversion is dependent on the intensity of the light source used. Usumez et al24 suggested polymerizing for 10 to 15 s using a fast halogen lamp (850 mW/cm2) or 20 s using an LED (400 mW/cm2) in order to obtain a similar degree of conversion among tested ortho-dontic composites. In this study, an LED system with a light intensity of 1000 mW/cm2 was used for 40 s. The higher monomer conversion observed with this light source may be attributed to the greater light energy used on the material. This is in agreement with the findings by Silikas et al,22 who demonstrated with different light energy densities from the same light source that when light energy was decreased, the degree of conversion diminished considerably.

Comparing the inflammatory and healing phenomena of the experimental groups with the control, it was found that Transbond Color Change, Quick Cure and Eagle Bond demonstrated similar biological behavior after 30 days, with the formation of chronic inflammation, young fibro-blasts, and collagen fibers.

CONCLUSION

Transbond Color Change composite showed a higher degree of conversion and a better healing process as demonstrated by the greater quantity of fibroblasts and collagen compared to Eagle Bond composite at 15 and 30 days. Quick-cure composite demonstrated better de-gree of conversion and healing process than that of Eagle Bond, but this was not statistically significantly different.

ACKNOWLEDGMENTS

The authors thank the National Council for Scientific and Techno-logical Development-CNPq for financial support (N.471372/2011) and granting the PIBIC scholarship for this study.

REFERENCES

1. Ahrari F, Tavakkol Afshari J, Poosti M, Brook A. Cytotoxicity of orthodon-tic bonding adhesive resins on human oral fibroblasts. Eur J Orthod 2010;32:688-692.

2. Andrzejewska E, Andrzejewski M, Socha E, Zych-Tomkowiak D. Ef-fect of polyacid aqueous solutions on photocuring of polymerizable components of resin-modified glass ionomer cements. Dent Mater 2003;19:501-509.

3. Canadian Council on Animal Care. Guide to the care and use of experi-mental animals, vol 1 and 2. Ottawa, Ontario: CCAC, 1980-1984.

4. Corekci B, Malkoc S, Ozturk B, Gunduz B, Toy E. Polymerization capacity of orthodontic composites analyzed by Fourier transform infrared spec-troscopy. Am J Orthod Dentofacial Orthop 2011;139:e299-304.

5. Costa CA, Hebling J, Hanks CT. Current status of pulp capping with den-tin adhesive systems: a review. Dent Mater 2000;16:188-197.

6. Dos Santos RL, Pithon MM, Martins FO, Romanos MT, Ruellas AC. Evaluation of cytotoxicity and degree of conversion of glass ionomer ce-ments reinforced with resin. Eur J Orthod 2012;34:362-366.

7. Eliades GC, Vougiouklakis GJ, Caputo AA. Degree of double bond con-version in light-cured composites. Dent Mater 1987;3:19-25.

8. Emmler J, Seiss M, Kreppel H, Reichl FX, Hickel R, Kehe K. Cytotoxicity of the dental composite component TEG-DMA and selected metabolic by-products in human pulmonary cells. Dent Mater 2008;24:1670-1675.

9. Gaintantzopoulou MD, Willis GP, Kafrawy AH. Pulp reactions to light-cured glass ionomer cements. Am J Dent 1994;7:39-42.

10. Geurtsen W, Lehmann F, Spahl W, Leyhausen G. Cytotoxicity of 35 dental resin composite monomers/additives in permanent 3T3 and three human primary fibroblast cultures. J Biomed Mater Res 1998;41: 474-480.

11. Golin C, Tavares T, Cunha AC. Biocompatibility evaluation of the trade-marks of glass ionomer cement: study in rat subcutaneous tissue. Braz J Dent 1992;49:35-39.

12. Grecca FS, Kopper PM, Santos RB, Fossati AC, Carrard VC, Acasigua GA, Figueiredo JA. Biocompatibility of RealSeal, its primer and AH Plus implanted in subcutaneous connective tissue of rats. J Appl Oral Sci 2011;19:52-56.

13. Hanks CT, Wataha JC, Sun Z. In vitro models of biocompatibility: a re-view. Dent Mater 1996;12:186-193.

14. Hansel C, Leyhausen G, Mai UE, Geurtsen W. Effects of various resin composite (co)monomers and extracts on two caries-associated micro-organisms in vitro. J Dent Res 1998;77:60-67.

15. Jonke E, Franz A, Freudenthaler J, Konig F, Bantleon HP, Schedle A. Cytotoxicity and shear bond strength of four orthodontic adhesive sys-tems. Eur J Orthod 2008;30:495-502.

16. Kostoryz EL, Eick JD, Glaros AG, Judy BM, Welshons WV, Burmaster S, Yourtee DM. Biocompatibility of hydroxylated metabolites of BISGMA and BFDGE. J Dent Res 2003;82:367-371.

17. Malkoc S, Corekci B, Ulker HE, Yalcin M, Sengun A. Cytotoxic effects of orthodontic composites. Angle Orthod 2010;80:571-576.

18. Olea N, Pulgar R, Perez P, Olea-Serrano F, Rivas A, Novillo-Fertrell A, Pedraza V, Soto AM, Sonnenschein C.. Estrogenicity of resin-based composites and sealants used in dentistry. Environ Health Perspect 1996;104:298-305.

19. Onay EO, Ungor M, Ozdemir BH. In vivo evaluation of the biocompat-ibility of a new resin-based obturation system. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:e60-e66.

20. Santos RL, Pithon MM, Fernandes AB, Cabral MG, Ruellas AC. Biocom-patibility of orthodontic adhesives in rat subcutaneous tissue. J Appl Oral Sci 2010;18:503-508.

21. Shinya M, Shinya A, Lassila LV, Varrela J, Vallittu PK. Enhanced degree of monomer conversion of orthodontic adhesives using a glass-fiber layer under the bracket. Angle Orthod 2009;79:546-550.

22. Silikas N, Eliades G, Watts DC. Light intensity effects on resin-composite degree of conversion and shrinkage strain. Dent Mater 2000;16:292-296.

23. Souza PP, Aranha AM, Hebling J, Giro EM, Costa CA. In vitro cytotoxicity and in vivo biocompatibility of contemporary resin-modified glass-iono-mer cements. Dent Mater 2006;22:838-844.

24. Usumez S, Buyukyilmaz T, Karaman AI, Gunduz B. Degree of conversion of two lingual retainer adhesives cured with different light sources. Eur J Orthod 2005;27:173-179.

25. Uysal T, Basciftci FA, Sener Y, Botsali MS, Demir A. Conventional and high intensity halogen light effects on water sorption and microhardness of orthodontic adhesives. Angle Orthod 2008;78:134-139.

26. Vande Vannet BM, Hanssens JL. Cytotoxicity of two bonding adhesives assessed by three-dimensional cell culture. Angle Orthod 2007;77: 716-722.

27. Walther UI, Walther SC, Liebl B, Reichl FX, Kehe K, Nilius M, Hickel R. Cytotoxicity of ingredients of various dental materials and related com-pounds in L2- and A549 cells. J Biomed Mater Res 2002;63:643-649.

28. Wan AC, Yap AU, Hastings GW. Acid-base complex reactions in resin-modified and conventional glass ionomer cements. J Biomed Mater Res 1999;48:700-704.

29. Yoon TH, Lee YK, Lim BS, Kim CW. Degree of polymerization of resin com-posites by different light sources. J Oral Rehabil 2002;29:1165-1173.

30. Young AM, Rafeeka SA, Howlett JA. FTIR investigation of monomer polymerisation and polyacid neutralisation kinetics and mecha-nisms in various aesthetic dental restorative materials. Biomaterials 2004;25:823-833.

Clinical relevance: Based on our histological results in an animal model and degree of monomer conversion of 3 orthodontic composite resins tested, Transbond Color Change adhesive followed by Quick-cure showed a higher degree of conversion and a better healing pro-cess compared to Eagle Bond.

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