Volume 1, Issue 1 (1-2016)
J Res Dent Maxillofac Sci 2016, 1(1): 9-16 |
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khorgami K, Sadaghiani M, Nemati N. In-vitro Comparison of the Impact of Four Types of Resin Composite on the Repaired Bond Strength and Surface Roughness After Sandblasting. J Res Dent Maxillofac Sci 2016; 1 (1) :9-16
URL: http://jrdms.dentaliau.ac.ir/article-1-81-en.html
URL: http://jrdms.dentaliau.ac.ir/article-1-81-en.html
1- Postgraduate Student, Restorative Dept,Dental Branch of Tehran,Islamic Azad University, Tehran, Iran , khorshidkh@yahoo.com
2- Restorative Dept, Member of Dental Materials Research Center,Dental Branch of Tehran, Islamic Azad University, Tehran, Iran
3- Restorative Dept, Member of Dental Materials Research Center,Dental Branch of Tehran, Islamic Azad University, Tehran, Iran
2- Restorative Dept, Member of Dental Materials Research Center,Dental Branch of Tehran, Islamic Azad University, Tehran, Iran
3- Restorative Dept, Member of Dental Materials Research Center,Dental Branch of Tehran, Islamic Azad University, Tehran, Iran
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Abstract
Background &Aim: One of the major problems with resin composite restorations is the weakness of bonding between the new and aged composites. Since appropriate micromechanical retention is necessary for the repair of aged resin composite restorations, the level of surface roughness after sandblasting can be influential in this regard. Considering the diverse composition of available resin composites in the market, the present study was performed to compare the impact of four resin composite types: microhybrid (Z250), Nanofill (Z350), nanohybrid (Z250XT) and Silorane-base (p90) on the repaired bond strength and surface roughness after sandblasting.
Materials and Methods: in this in vitro experimental study, 44 resin composite discs with diameter of 6mm and height of 2mm were divided to 4 groups of microhybrid, Nanofill, nanohybrid and Silorane-base and from 11 samples for each resin composite type, one sample was evaluated for surface roughness level before and after sandblasting with Atomic Force Microscope (AFM) and 10 samples were tested for shear bond strength in universal testing machine.
Results: the findings indicated that micro hybridresin composite had the highest shear bond strength (37.8±6.4 MPa) followed respectively by Nanofill (30 ±3.8 MPa),Silorane-base (17.9±4 MPa) and nanohybrid composites (7.6±1.9 MPa), which the differences between all groups were significant (p <0.001).Before sandblasting, nanohybrid type had the highest level of surface roughness (505 ±154nm) and the lowest value was for microhybrid resin composite(94±35nm).(p<0.000) After sandblasting, Nanofill (1997±288nm),Silorane-base, microhybrid and nanohybrid composites(1284 ± 645nm) showed the highest increase in surface roughness, respectively.(p<0.4)
Conclusions: In the present study, sandblasting caused a significant increase in the surface roughness of four studied resin composite types . Despite the lowest surface roughness of micro hybrid type, it showed the highest bond strength among other composites after sandblasting.
Key words: Composite resins, Sandblasting, Surface roughness, Dental Bonding.
Introduction
One of the major problems with resin composite restorations is the weakness of bonding between the new and aged composites. Since appropriate micromechanical retention is necessary for the repair of aged resin composite restorations and chemical bond alone cannot provide adequate retention, the amount of surface roughness on resin composite can influence the bond strength between new and aged resin composite restorations. (1) Nowadays, resin composites are widely being used. (1, 2) Physical and mechanical properties of resin composites have been improved greatly during the past 10 to 20 years. Nevertheless, oral enzymes can destruct their matrix. (3) Therefor, eventually the old restoration needs to be repaired or replaced and on the other hand, since the replacement of these restorations is time consuming and leads to loss of some dental structure, repair of these restorations is preferred over their replacement. (4-7) The important issue here is the bond strength between the new and aged resin composites. (8) Usually, bonding between two resin composite layers is possible in the presence of an oxygen inhibited non-polymerized surface and since old restorations lack this surface, various techniques have been presented for their surface treatment. (9, 10) The importance of surface treatment is in the increase of micromechanical bond between the new and old resin composite restorations. (1,7,8) Numerous studies have been performed to introduce the best surface treatment technique. The evaluated techniques include: use of diamond burs, sandblasting with 50 µ aluminum oxide particles, sandblasting with aluminum oxide particles covered with silica (cojet) and etching with hydrofluoric acid. (1-4,9)
In multiple studies, sandblasting has been introduced as the best surface treatment method for the aged resin composite but considering the different composition of resin composites and differences in the size and type of filler particles (macrofilled, microfilled, microhybrid, Nanofill and nanohybrid) and the invention of novel silorane-base composites with different composition, sandblasting can produce surfaces with different degrees of surface roughness. (8)
Considering that a comprehensive study on simultaneous evaluation of resin composite surface roughness and bond strength after sandblasting is not available, the present study was performed to compare the impact of resin composite type on bond strength and surface roughness after sandblasting.
Materials and methods
This in vitro experimental study was performed on sandblasted resin composite samples. 44 resin composite discs from nanohybrid resin composite (Filtek Z250 xt), Nanofill resin composite (Filtek Z350XT), microhybrid resin composite (Filtek Z250) and silorane-base resin composite (Filtek p90) were selected. The discs were placed inside a mold with 6 mm diameter and 2 mm height and the mold was fixed firmly on a glass slab. In all samples, the resin composite was placed with plastic instrument without contamination and was covered with a Mylar strip before curing and a glass slab was placed on top to provide a smooth surface and to remove the excessive composite. Each sample was light cured with an LED light curing device (star light pro;mectron,Italy) with 600 mw/cm2 intensity with no distance from the surface. The intensity of device was controlled with a radiometer during each curing. Curing duration was adjusted according to the manufacturer's instruction. After mold removal, all samples were polished with coarse, medium, fine and super fine soflex discs (3M ESPE) in a way that each disc was in contact with the specimen for 20 seconds under light pressure with back and forth movements. Samples were kept in distilled water at 37 °C for 24 hours. Then, the samples were thermocycled for 5000 rounds at 5-55 °C for 30 seconds for each bath and 10 seconds transferring time. (11) From 11 samples of each resin composite type, one sample was selected to evaluate the level of surface roughness before and after sandblasting with atomic force microscope (AFM, DME-Denmark) and then the samples were sandblasted with 50 µ aluminum oxide powder (Ronving, Denmark) with use of micro sandblaster intraoral sandblasting instrument (Denmark, DentopropRonving) for 5 seconds from 5mm distance at 90 degrees angle to the surface. (To provide a fixed distance for all samples, they were placed inside a transparent plastic rod with inner diameter of 6mm (diameter of the sample) and 5mm height (2mm space for the sample and 3mm space for sandblasting). (11) All the stages of sandblasting were performed by one operator. In AFM technique, the digital instruments were activated in non-contact mode to obtain topographic images from the selected areas on the desired surface. This instrument has been equipped with a scanner with maximum values of 100×100×5 µm in xyz dimensions. To measure the values of surface roughness, the tip of instrument moved across the surface and images were obtained. The coordinates of three points on the same surface on the center of the specimen were determined and the mean values were used for statistical analysis. A silicon probe with normal constant curvature was used for image taking. The amount of surface roughness (Ra or average height in profile) was reported by the device. (12)
The surfaces of remained samples (10 samples from each resin composite type) were etched with 37% phosphoric acid for 30 seconds and were rinsed with water for 30 seconds and were dried with air pressure from 5mm distance for 10 seconds. (13) Adper single Bond2 was applied on the surfaces of microhybrid, Nanofill and nanohybrid composites and was cured for 10 seconds. Then, the samples were placed inside an especial aluminum mold with 4mm height and the new resin composite with 2mm thickness was added and cured. In silorane-base samples, the primer of p90 adhesive system was applied on the surface of old resin composite and was cured for 10 seconds and then the bonding of p90 adhesive system was applied and cured for 10 seconds. Then, the samples were placed inside an aluminum mold with 4mm height and the new resin composite with 2mm thickness was added and cured.
Afterwards, the samples were mounted in molds with self-curing acrylic resin and were placed in universal testing machine (ZwickRoell Z050, Germany) and a force was applied with 1mm/min speed by a blade to the interface of samples and after observing the first bond fracture between the old and new composites, the shear bond strength was recorded in MPa. (7) ANOVA test was used for statistical analysis.
Results
The obtained values after evaluation of surface roughness in 4 resin composite types showed that maximum surface roughness before sandblasting was for nanohybrid resin composite (Z250xt) and equaled 505± 154 nm and minimum surface roughness was for microhybrid resin composite (Z250) and equaled 94± 35 nm and ANOVA test showed that values of composites' surface roughness before sandblasting were significantly different (p<0.001).
After sandblasting, maximum surface roughness was detected in Nanofill resin composite(Z350XT) and equaled 1997± 288 nm and minimum surface roughness was for nanohybrid type (Z250xt) and equaled 1284± 645 nm which surface roughness of Z350XT was 713 nm more than that of Z250xt and ANOVA test showed that this difference was not statistically significant. (p<0.4) (Table 1)
Based on the assessment of coefficient of variation before sandblasting, homogeneity of Z250xt was the highest (cv=30) and the lowest homogeneity was for p90 resin composite (cv=60). After sandblasting, the lowest homogeneity was again for p90 resin composite (cv=58) and the highest value was related to Z350XT (cv=14). (Table 3 and figure 1, A-H)
Also, assessment of the results of shear bond strength test showed that the highest shear bond strength was related to Z250 (37.8± 4.6 MPa) and the lowest value was related to Z250XT (7.6± 1.9 MPa). ANOVA test proved that this difference was statistically significant (p<0.000) and POST HOC test showed that the differences between Z250 group and other three groups and also between Z350XT and p90 and between p90 and Z250XT were significant. (p<0.001) Based on the assessment of coefficient of variation (cv) the highest homogeneity was for Z250 (12) and the highest non homogeneity was for Z250XT and equaled 25 (Table 2).
Discussion
Many studies have shown that in repair of aged resin composite restorations, composite's surface condition plays an important role in the bond strength between the new and aged restorations and the interstitial bond between resin composite layers decreases gradually due to conditions in oral environment such as humidity and temperature variations. (14) In evaluation of bonding between new and aged resin composite restorations factors such as resin composite type, surface treatment, interstitial adhesive substance and the age of the former restoration and the interaction between these factors should be considered. (8,15) The new resin composite cannot bond with the old one without surface treating the aged resin composite and it seems that proper micromechanical bonding on the surface of old resin composite is the most important factor in achieving high bond strength. (7)
The results of the present study showed that sandblasting with aluminum oxide particles increased surface roughness in all of the studied resin composite samples and the highest level of surface roughness was related to Z350XT (1997± 288 nm) and the lowest amount was related to Z250XT (1284± 645 nm). Moreover, the highest bonding strength was for Z250 (37.8± 4.6 MPa), Z350XT (30± 3.8 MPa), p90 (17.9± 4 MPa) and Z250XT (7.6± 1.9 MPa) respectively and these variations were statistically significant among all groups.
Based on our findings, to date no similar study has been conducted on the impact of sandblasting with aluminum oxide powder on the surface roughness of the mentioned resin composites. However, in similar studies the surface roughness of some types of resin composite has been evaluated with different mechanical surface treatment methods.
In a study by Janus et al surface roughness and morphology of three nanocomposites were evaluated after two different surface treatments with AFM. They concluded that the composition of resin composite especially the amount and size of filler particles effects the surface roughness of different resin composites. (16) This finding is in line with other studies and with our study. (17-19) Also in the study by Janus et al use of nano particles in the composition of resin composite did not necessarily improved the surface properties of resin composite and this finding is also in line with ours. (16)
In a study by Loomas and colleagues, in contrast to our results, Nanofill resin composite showed the lowest amount of surface roughness after surface treatment. (17) The reason for this difference can be attributed to different resin composite types, surface treatment technique and different aging in the two studies.
Duarte et al concluded that silorane-base resin composite with average filler size of 0.55 µm can have surface roughness similar to microhybrid resin composite with the same filler size. (19) Likewise, in our study the amount of surface roughness after sandblasting was reported to be in a close range for microhybrid and silorane-base composites.
Senawong et al assessed the surface roughness of Nanofill and nanohybrid composites and found that surface roughness showed no significant difference between polished and non-polished composites and for Nanofill resin composite no difference in surface roughness was detected between the two different polishing methods and also in the non-polished surface (11) which contradicts our findings. This difference can be attributed to the difference between the methods used for surface treatment.
Similar studies have been conducted on the repaired bond strength and the effect of surface roughness on bond strength in resin composites which have revealed comparable results to the results of our study. (17-20) Sinval et al showed that the highest bond strength was for microhybrid resin composite and the lowest amount of bond strength was related to nanohybrid type, (15) which is in line with our findings.
Different studies showed that sandblasting with aluminum oxide significantly increases the micromechanical retention and increases the bond strength after repair, (7,14,15,20) which were in line with our results indicating that after sandblasting the lowest amount of surface roughness was related to nanohybrid Z250XT composite.
Our study indicated that surface roughness significantly increased in all four resin composite types after sandblasting which shows that despite differences in composites regarding composition and size of fillers, sandblasting with aluminum oxide powder can be a reliable surface treatment method to increase micromechanical retention and repaired bond strength. Nevertheless, shear bond strength doesn’t necessarily increase with increased surface roughness. As mentioned before, microhybrid resin composite with lower surface roughness after sandblasting compared to Nanofill and silorane-base composites showed the highest amount of shear bond strength.
Previous studies have shown that the size of fillers can be influential in improving the repaired bond in composites and it seems that larger fillers can improve the bond strength between the new and aged restorations (21) as it was shown for microhybrid resin composite with larger filler particles albeit these larger fillers can lead to higher surface roughness in Z250 compared with other composites. (11)
In the present study, silorane-base resin composite was in the third place regarding bond strength and it was in the second place regarding surface roughness after sandblasting. Palasuk et al stated that bond strength of methacrylate-base resin composite is higher without surface treatment. However, silorane-base resin composite responds better to surface treatment methods such as sandblasting and provides higher bond strength. (20) Similarly, our study showed that silorane-base resin composite had higher surface roughness after sandblasting compared with microhybrid and nanohybrid resin composites. However, lower bond strength compared with Z250 and Z350XT can be attributed to the non-homogenized distribution of surface roughness in p90 composite. Higher bond strength of this resin composite compared with Z250XT can be attributed to the higher amount of surface roughness in p90 in contrast to Z250 and the similarity regarding surface homogeneity. The reason for higher roughness of silorane-base resin composite can be attributed to lower bond strength between fillers and the matrix which are susceptible to debonding and separation when exposed to aging and surface treatment methods which also can be a reason for surface destruction and increased surface roughness of this composite. (22)
Both aging processes in the present study i.e. keeping in distilled water and thermocycling can destruct Nanofill and silorane-base composites and increase the surface roughness.
As mentioned before, despite less inclination for water absorption in silorane-base composites, weaker connection between fillers and matrix and their debonding during the aging process can lead to higher surface roughness. (23)
In laboratory experiments, the shear bond strength between resin composite and etched enamel and primed dentinal surfaces has been reported to be 20 to 30 MPa and the main cause of this bond is micromechanical retention and permeation of resin into enamel and dentin structure. (22) This bond is formed in etched dentin due to permeation of resin into inter-tubular area and the formation of hybrid layer to the depth of 0.1 to 5 µm, with a mechanism similar with creating surface roughness to provide higher repaired bond strength. (24,25) Studies have revealed that proper repaired bond strength in composites is approximately equal to the bond strength between resin composite and etched enamel. (20) According to the above statements, three resin composite types in our study (microhybrid, Nanofill and silorane-base) had acceptable bond strengths but the bond strength of nanohybrid type was below the expected value. The reason may be the different effect of sandblasting on the surface of this resin composite which produces a surface with a very non homogenized roughness distribution which can lead to abnormal stress distribution on the experimented surface and premature fracture in the sample. Nevertheless, the experimental condition should also be considered because in shear bond strength tests, a wide range of results can be obtained in different parts of the same material. (25-27) Therefore, further investigations are needed in this regard.
Conclusion
In the present study, Sandblasting caused a significant increase in surface roughness of four studied resin composite types. Despite the lowest amount of surface roughness in microhybrid composite, it showed the highest bond strength among other composites after sandblasting.
Specifications of resin composite types used in the present study
Table 1- Amount of surface roughness (nm) divided by resin composite type
Table 2- bond strength (MPa) based on resin composite type
Full-Text: (1016 Views)
Abstract
Background &Aim: One of the major problems with resin composite restorations is the weakness of bonding between the new and aged composites. Since appropriate micromechanical retention is necessary for the repair of aged resin composite restorations, the level of surface roughness after sandblasting can be influential in this regard. Considering the diverse composition of available resin composites in the market, the present study was performed to compare the impact of four resin composite types: microhybrid (Z250), Nanofill (Z350), nanohybrid (Z250XT) and Silorane-base (p90) on the repaired bond strength and surface roughness after sandblasting.
Materials and Methods: in this in vitro experimental study, 44 resin composite discs with diameter of 6mm and height of 2mm were divided to 4 groups of microhybrid, Nanofill, nanohybrid and Silorane-base and from 11 samples for each resin composite type, one sample was evaluated for surface roughness level before and after sandblasting with Atomic Force Microscope (AFM) and 10 samples were tested for shear bond strength in universal testing machine.
Results: the findings indicated that micro hybridresin composite had the highest shear bond strength (37.8±6.4 MPa) followed respectively by Nanofill (30 ±3.8 MPa),Silorane-base (17.9±4 MPa) and nanohybrid composites (7.6±1.9 MPa), which the differences between all groups were significant (p <0.001).Before sandblasting, nanohybrid type had the highest level of surface roughness (505 ±154nm) and the lowest value was for microhybrid resin composite(94±35nm).(p<0.000) After sandblasting, Nanofill (1997±288nm),Silorane-base, microhybrid and nanohybrid composites(1284 ± 645nm) showed the highest increase in surface roughness, respectively.(p<0.4)
Conclusions: In the present study, sandblasting caused a significant increase in the surface roughness of four studied resin composite types . Despite the lowest surface roughness of micro hybrid type, it showed the highest bond strength among other composites after sandblasting.
Key words: Composite resins, Sandblasting, Surface roughness, Dental Bonding.
Introduction
One of the major problems with resin composite restorations is the weakness of bonding between the new and aged composites. Since appropriate micromechanical retention is necessary for the repair of aged resin composite restorations and chemical bond alone cannot provide adequate retention, the amount of surface roughness on resin composite can influence the bond strength between new and aged resin composite restorations. (1) Nowadays, resin composites are widely being used. (1, 2) Physical and mechanical properties of resin composites have been improved greatly during the past 10 to 20 years. Nevertheless, oral enzymes can destruct their matrix. (3) Therefor, eventually the old restoration needs to be repaired or replaced and on the other hand, since the replacement of these restorations is time consuming and leads to loss of some dental structure, repair of these restorations is preferred over their replacement. (4-7) The important issue here is the bond strength between the new and aged resin composites. (8) Usually, bonding between two resin composite layers is possible in the presence of an oxygen inhibited non-polymerized surface and since old restorations lack this surface, various techniques have been presented for their surface treatment. (9, 10) The importance of surface treatment is in the increase of micromechanical bond between the new and old resin composite restorations. (1,7,8) Numerous studies have been performed to introduce the best surface treatment technique. The evaluated techniques include: use of diamond burs, sandblasting with 50 µ aluminum oxide particles, sandblasting with aluminum oxide particles covered with silica (cojet) and etching with hydrofluoric acid. (1-4,9)
In multiple studies, sandblasting has been introduced as the best surface treatment method for the aged resin composite but considering the different composition of resin composites and differences in the size and type of filler particles (macrofilled, microfilled, microhybrid, Nanofill and nanohybrid) and the invention of novel silorane-base composites with different composition, sandblasting can produce surfaces with different degrees of surface roughness. (8)
Considering that a comprehensive study on simultaneous evaluation of resin composite surface roughness and bond strength after sandblasting is not available, the present study was performed to compare the impact of resin composite type on bond strength and surface roughness after sandblasting.
Materials and methods
This in vitro experimental study was performed on sandblasted resin composite samples. 44 resin composite discs from nanohybrid resin composite (Filtek Z250 xt), Nanofill resin composite (Filtek Z350XT), microhybrid resin composite (Filtek Z250) and silorane-base resin composite (Filtek p90) were selected. The discs were placed inside a mold with 6 mm diameter and 2 mm height and the mold was fixed firmly on a glass slab. In all samples, the resin composite was placed with plastic instrument without contamination and was covered with a Mylar strip before curing and a glass slab was placed on top to provide a smooth surface and to remove the excessive composite. Each sample was light cured with an LED light curing device (star light pro;mectron,Italy) with 600 mw/cm2 intensity with no distance from the surface. The intensity of device was controlled with a radiometer during each curing. Curing duration was adjusted according to the manufacturer's instruction. After mold removal, all samples were polished with coarse, medium, fine and super fine soflex discs (3M ESPE) in a way that each disc was in contact with the specimen for 20 seconds under light pressure with back and forth movements. Samples were kept in distilled water at 37 °C for 24 hours. Then, the samples were thermocycled for 5000 rounds at 5-55 °C for 30 seconds for each bath and 10 seconds transferring time. (11) From 11 samples of each resin composite type, one sample was selected to evaluate the level of surface roughness before and after sandblasting with atomic force microscope (AFM, DME-Denmark) and then the samples were sandblasted with 50 µ aluminum oxide powder (Ronving, Denmark) with use of micro sandblaster intraoral sandblasting instrument (Denmark, DentopropRonving) for 5 seconds from 5mm distance at 90 degrees angle to the surface. (To provide a fixed distance for all samples, they were placed inside a transparent plastic rod with inner diameter of 6mm (diameter of the sample) and 5mm height (2mm space for the sample and 3mm space for sandblasting). (11) All the stages of sandblasting were performed by one operator. In AFM technique, the digital instruments were activated in non-contact mode to obtain topographic images from the selected areas on the desired surface. This instrument has been equipped with a scanner with maximum values of 100×100×5 µm in xyz dimensions. To measure the values of surface roughness, the tip of instrument moved across the surface and images were obtained. The coordinates of three points on the same surface on the center of the specimen were determined and the mean values were used for statistical analysis. A silicon probe with normal constant curvature was used for image taking. The amount of surface roughness (Ra or average height in profile) was reported by the device. (12)
The surfaces of remained samples (10 samples from each resin composite type) were etched with 37% phosphoric acid for 30 seconds and were rinsed with water for 30 seconds and were dried with air pressure from 5mm distance for 10 seconds. (13) Adper single Bond2 was applied on the surfaces of microhybrid, Nanofill and nanohybrid composites and was cured for 10 seconds. Then, the samples were placed inside an especial aluminum mold with 4mm height and the new resin composite with 2mm thickness was added and cured. In silorane-base samples, the primer of p90 adhesive system was applied on the surface of old resin composite and was cured for 10 seconds and then the bonding of p90 adhesive system was applied and cured for 10 seconds. Then, the samples were placed inside an aluminum mold with 4mm height and the new resin composite with 2mm thickness was added and cured.
Afterwards, the samples were mounted in molds with self-curing acrylic resin and were placed in universal testing machine (ZwickRoell Z050, Germany) and a force was applied with 1mm/min speed by a blade to the interface of samples and after observing the first bond fracture between the old and new composites, the shear bond strength was recorded in MPa. (7) ANOVA test was used for statistical analysis.
Results
The obtained values after evaluation of surface roughness in 4 resin composite types showed that maximum surface roughness before sandblasting was for nanohybrid resin composite (Z250xt) and equaled 505± 154 nm and minimum surface roughness was for microhybrid resin composite (Z250) and equaled 94± 35 nm and ANOVA test showed that values of composites' surface roughness before sandblasting were significantly different (p<0.001).
After sandblasting, maximum surface roughness was detected in Nanofill resin composite(Z350XT) and equaled 1997± 288 nm and minimum surface roughness was for nanohybrid type (Z250xt) and equaled 1284± 645 nm which surface roughness of Z350XT was 713 nm more than that of Z250xt and ANOVA test showed that this difference was not statistically significant. (p<0.4) (Table 1)
Based on the assessment of coefficient of variation before sandblasting, homogeneity of Z250xt was the highest (cv=30) and the lowest homogeneity was for p90 resin composite (cv=60). After sandblasting, the lowest homogeneity was again for p90 resin composite (cv=58) and the highest value was related to Z350XT (cv=14). (Table 3 and figure 1, A-H)
Also, assessment of the results of shear bond strength test showed that the highest shear bond strength was related to Z250 (37.8± 4.6 MPa) and the lowest value was related to Z250XT (7.6± 1.9 MPa). ANOVA test proved that this difference was statistically significant (p<0.000) and POST HOC test showed that the differences between Z250 group and other three groups and also between Z350XT and p90 and between p90 and Z250XT were significant. (p<0.001) Based on the assessment of coefficient of variation (cv) the highest homogeneity was for Z250 (12) and the highest non homogeneity was for Z250XT and equaled 25 (Table 2).
Discussion
Many studies have shown that in repair of aged resin composite restorations, composite's surface condition plays an important role in the bond strength between the new and aged restorations and the interstitial bond between resin composite layers decreases gradually due to conditions in oral environment such as humidity and temperature variations. (14) In evaluation of bonding between new and aged resin composite restorations factors such as resin composite type, surface treatment, interstitial adhesive substance and the age of the former restoration and the interaction between these factors should be considered. (8,15) The new resin composite cannot bond with the old one without surface treating the aged resin composite and it seems that proper micromechanical bonding on the surface of old resin composite is the most important factor in achieving high bond strength. (7)
The results of the present study showed that sandblasting with aluminum oxide particles increased surface roughness in all of the studied resin composite samples and the highest level of surface roughness was related to Z350XT (1997± 288 nm) and the lowest amount was related to Z250XT (1284± 645 nm). Moreover, the highest bonding strength was for Z250 (37.8± 4.6 MPa), Z350XT (30± 3.8 MPa), p90 (17.9± 4 MPa) and Z250XT (7.6± 1.9 MPa) respectively and these variations were statistically significant among all groups.
Based on our findings, to date no similar study has been conducted on the impact of sandblasting with aluminum oxide powder on the surface roughness of the mentioned resin composites. However, in similar studies the surface roughness of some types of resin composite has been evaluated with different mechanical surface treatment methods.
In a study by Janus et al surface roughness and morphology of three nanocomposites were evaluated after two different surface treatments with AFM. They concluded that the composition of resin composite especially the amount and size of filler particles effects the surface roughness of different resin composites. (16) This finding is in line with other studies and with our study. (17-19) Also in the study by Janus et al use of nano particles in the composition of resin composite did not necessarily improved the surface properties of resin composite and this finding is also in line with ours. (16)
In a study by Loomas and colleagues, in contrast to our results, Nanofill resin composite showed the lowest amount of surface roughness after surface treatment. (17) The reason for this difference can be attributed to different resin composite types, surface treatment technique and different aging in the two studies.
Duarte et al concluded that silorane-base resin composite with average filler size of 0.55 µm can have surface roughness similar to microhybrid resin composite with the same filler size. (19) Likewise, in our study the amount of surface roughness after sandblasting was reported to be in a close range for microhybrid and silorane-base composites.
Senawong et al assessed the surface roughness of Nanofill and nanohybrid composites and found that surface roughness showed no significant difference between polished and non-polished composites and for Nanofill resin composite no difference in surface roughness was detected between the two different polishing methods and also in the non-polished surface (11) which contradicts our findings. This difference can be attributed to the difference between the methods used for surface treatment.
Similar studies have been conducted on the repaired bond strength and the effect of surface roughness on bond strength in resin composites which have revealed comparable results to the results of our study. (17-20) Sinval et al showed that the highest bond strength was for microhybrid resin composite and the lowest amount of bond strength was related to nanohybrid type, (15) which is in line with our findings.
Different studies showed that sandblasting with aluminum oxide significantly increases the micromechanical retention and increases the bond strength after repair, (7,14,15,20) which were in line with our results indicating that after sandblasting the lowest amount of surface roughness was related to nanohybrid Z250XT composite.
Our study indicated that surface roughness significantly increased in all four resin composite types after sandblasting which shows that despite differences in composites regarding composition and size of fillers, sandblasting with aluminum oxide powder can be a reliable surface treatment method to increase micromechanical retention and repaired bond strength. Nevertheless, shear bond strength doesn’t necessarily increase with increased surface roughness. As mentioned before, microhybrid resin composite with lower surface roughness after sandblasting compared to Nanofill and silorane-base composites showed the highest amount of shear bond strength.
Previous studies have shown that the size of fillers can be influential in improving the repaired bond in composites and it seems that larger fillers can improve the bond strength between the new and aged restorations (21) as it was shown for microhybrid resin composite with larger filler particles albeit these larger fillers can lead to higher surface roughness in Z250 compared with other composites. (11)
In the present study, silorane-base resin composite was in the third place regarding bond strength and it was in the second place regarding surface roughness after sandblasting. Palasuk et al stated that bond strength of methacrylate-base resin composite is higher without surface treatment. However, silorane-base resin composite responds better to surface treatment methods such as sandblasting and provides higher bond strength. (20) Similarly, our study showed that silorane-base resin composite had higher surface roughness after sandblasting compared with microhybrid and nanohybrid resin composites. However, lower bond strength compared with Z250 and Z350XT can be attributed to the non-homogenized distribution of surface roughness in p90 composite. Higher bond strength of this resin composite compared with Z250XT can be attributed to the higher amount of surface roughness in p90 in contrast to Z250 and the similarity regarding surface homogeneity. The reason for higher roughness of silorane-base resin composite can be attributed to lower bond strength between fillers and the matrix which are susceptible to debonding and separation when exposed to aging and surface treatment methods which also can be a reason for surface destruction and increased surface roughness of this composite. (22)
Both aging processes in the present study i.e. keeping in distilled water and thermocycling can destruct Nanofill and silorane-base composites and increase the surface roughness.
As mentioned before, despite less inclination for water absorption in silorane-base composites, weaker connection between fillers and matrix and their debonding during the aging process can lead to higher surface roughness. (23)
In laboratory experiments, the shear bond strength between resin composite and etched enamel and primed dentinal surfaces has been reported to be 20 to 30 MPa and the main cause of this bond is micromechanical retention and permeation of resin into enamel and dentin structure. (22) This bond is formed in etched dentin due to permeation of resin into inter-tubular area and the formation of hybrid layer to the depth of 0.1 to 5 µm, with a mechanism similar with creating surface roughness to provide higher repaired bond strength. (24,25) Studies have revealed that proper repaired bond strength in composites is approximately equal to the bond strength between resin composite and etched enamel. (20) According to the above statements, three resin composite types in our study (microhybrid, Nanofill and silorane-base) had acceptable bond strengths but the bond strength of nanohybrid type was below the expected value. The reason may be the different effect of sandblasting on the surface of this resin composite which produces a surface with a very non homogenized roughness distribution which can lead to abnormal stress distribution on the experimented surface and premature fracture in the sample. Nevertheless, the experimental condition should also be considered because in shear bond strength tests, a wide range of results can be obtained in different parts of the same material. (25-27) Therefore, further investigations are needed in this regard.
Conclusion
In the present study, Sandblasting caused a significant increase in surface roughness of four studied resin composite types. Despite the lowest amount of surface roughness in microhybrid composite, it showed the highest bond strength among other composites after sandblasting.
Specifications of resin composite types used in the present study
Table 1- Amount of surface roughness (nm) divided by resin composite type
Table 2- bond strength (MPa) based on resin composite type
Type of Study: Original article |
Subject:
Oral medicine
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