HHS Public Access Author manuscript Author Manuscript
Polymer Prepr. Author manuscript; available in PMC 2015 October 08. Published in final edited form as: Polymer Prepr. 2009 ; 50(1): 343–344.
EFFECTS OF A METHACRYLIC SILANE ON SOME PHYSICOCHEMICAL PROPERTIES OF RESIN-BASED BIOMIMETIC COMPOSITE J. M. Antonucci1 and D. Skrtic2 1
Polymers Division, National Institute of Standards and Technology (NIST), Gaithersburg, MD
Author Manuscript
2
Paffenbarger Research Center (PRC), American Dental Association Foundation (ADAF), Gaithersburg, MD
Introduction
Author Manuscript
In the presence of water, organotrialkoxysilanes can undergo a series of hydrolysiscondensation reactions leading to three-dimensional silsesquioxane (SSO) structures that have potential as both resin matrix components and as molecular-sized silica fillers (1). It has been shown that SSO formation from silane can occur in dental monomers (2). In addition to the self-condensation reaction, organosilanes may form high molecular mass silyl derivatives with hydroxylated and carboxylated dental monomers. Functional silanes, in addition to serving as components in resin blends, also can be considered as molecularsized fillers.
Author Manuscript
In this study, methacryloxypropyltrimethoxysilane (MPTMS) was combined with nonhydroxylated dental monomers, e.g., ethoxylated bisphenol A dimethacrylate (EBPADMA) and an aliphatic diurethane dimethacrylate (UDMA), photoactivated, and the resulting resins were utilized in formulating the composites with amorphous calcium phosphate, ACP (3, 4). We hypothesized that EBPADMA and UDMA would serve as polymerizable solvents for the in situ formation of methacrylic SSOs via hydrolysis-condensation reaction of MPTMS (4–7). If predominantly fully-condensed SSOs were formed, physicochemical and mechanical performance of the composites should improve compared to the non-SSO containing formulations. A series of physicochemical tests including degree of vinyl conversion (DC), polymerization shrinkage (PS), biaxial flexure strength (BFS), water sorption (WS) and ion release were performed on ACP composite specimens formulated with UDMA or EBPADMA alone (as controls) and their MPTMS (SSO)-containing hybrids.
Disclaimer Certain commercial materials and equipment are identified in this article to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by NIST or ADAF or that the material or equipment identified is necessarily the best available for the purpose. “Official contribution of NIST; not subject to copyrights in USA”.
Antonucci and Skrtic
Page 2
Author Manuscript
Experimental Formulation of the resins The experimental SSO resins (S-resins) were formulated from commercially available EBPADMA and UDMA monomers with MPTMS and photo-activated by the inclusion of camphorquinone (CQ; mass fraction of 0.2 %) and ethyl-4-N, N-dimethylamino benzoate (EDMAB; mass fraction of 0.8 %). The monomers and the components of photo-initiator systems (with the corresponding acronyms that are used throughout this manuscript) and the composition of the resins (% mass fraction) are provided in Tables 1 and 2. Resins were kept at 23 °C for 28 d to allow sufficient time for the condensation reaction to take place before being utilized in composite preparation (2). The hydrolytic condensation reactions of MPTMS resulting in either incompletely- or fully-condensed SSOs are illustrated in Fig. 1.
Author Manuscript
ACP synthesis and characterization—ACP was synthesized as detailed earlier (3, 4). It precipitated instantaneously in a closed system at 23 °C upon rapidly mixing equal volumes of a 800 mmol/L Ca(NO3)2 solution and a 536 mmol/L Na2HPO4 solution that contained a molar fraction of 2 % Na4P2O7 as a stabilizing component for ACP. The suspension was filtered, the solid phase washed subsequently with ice-cold ammoniated water and acetone, and then lyophilized. To avoid exposure to humidity, ACP was kept under vacuum (2.7 kPa) over desiccant until utilized in composite formulations.
Author Manuscript
The amorphous state of ACP was verified by powder X-ray diffraction (XRD; Rigaku DMAX 2000 X-ray diffractometer, Rigaku/USA Inc., Danvers, MA, USA) and Fouriertransform infrared (FTIR; Nicolet Magna-IR FTIR 550 spectrophotometer, Nicolet Instrumentations Inc., Madison, WI, USA) spectroscopy. Particle size distribution of ZrACP was determined by gravitational and centrifugal sedimentation analysis (SA-CP3 analyzer, Shimadzu Scientific Instruments, Inc., Columbia, MD, USA). Preparation of composite specimens
Author Manuscript
Composite pastes were made by mixing the appropriate resin (mass fraction 60 %) with ACP filler (mass fraction 40 %) using hand spatulation. The homogenized pastes were kept under a moderate vacuum (2.7 kPa) overnight to eliminate the air entrained during mixing. The pastes were molded into disks (14.9 mm to 15.3 mm in diameter and 1.31 mm to 1.53 mm in thickness) by filling the circular openings of flat Teflon molds, covering each side of the mold with a Mylar film plus a glass slide, and then clamping the assembly together with spring clips. The disks were photo-polymerized by irradiating sequentially each face of the mold assembly for 60 s with visible light (Triad 2000; Dentsply International, York, PA, USA). Degree of vinyl conversion (DC) DC attained in the unfilled resins (copolymers) and the corresponding ACP composites was determined by FTIR spectroscopy. Spectra were acquired before photo-cure and 24 h after cure. DC was calculated from the decrease in the integrated peak area of the 1637 cm−1 absorption band between the polymer (cured specimen) and monomer (uncured specimen).
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 3
Author Manuscript
Absorption bands at 1538 cm−1 and 775 cm−1 were used as the internal reference for EBPADMA and UDMA formulations, respectively. Polymerization shrinkage (PS) PS of composites was measured by a computer-controlled mercury dilatometer (8) (PRCADAF), Gaithersburg, MD, USA). Composite pastes ((100 ± 10) mg) were irradiated twice: initially for 60 s followed by a second irradiation for 30 s after 60 min. Data were collected for a total of 90 min. PS was calculated based on the known mass of the sample and its density. The latter was determined by means of the Archimedean displacement principle using an attachment to a microbalance (Sartorius YDK01 Density Determination Kit, Sartorius AG, Goettingen, Germany). Biaxial flexure strength (BFS)
Author Manuscript
BFS testing was employed to compare the mechanical strength of dry (after 24 h storage in the air at 23 °C) and wet (after 3 weeks of immersion in 4-(2-hydroxyethyl)-1piperazineethane sulfonic acid (HEPES)-buffered saline solution (0.13 mol/L NaCl; pH = 7.4) at 23 °C; 100 mL saline solution/specimen) composite specimens. Piston-on-three-ball loading cell and a computer-controlled Universal Testing Machine (Instron 5500R, Instron Corp., Canton, MA, US) operated by Testworks 4 software were utilized. BFS values were calculated according ASTM F394-78 (9). Water sorption (WS)
Author Manuscript
WS of composite specimens was determined as follows. Specimens were initially dried over anhydrous CaSO4 until a constant mass was achieved (± 0.1 mg), and then were exposed to an air atmosphere of 75 % relative humidity (RH) at 23 °C by keeping them suspended over saturated aqueous sNaCl slurry in closed systems. Gravimetric changes of dry-padded specimens were recorded at predetermined time intervals. WS of individual specimens was calculated as WS = [(Wt − W0)/W0] × 100, where Wt represents sample mass at any given time and W0 is the initial mass of dry sample. Mineral ion release Ion release from composite disk specimens was examined at 23 °C, in continuously stirred, saline solutions (initial volume of saline per composite specimen: 100 mL). Aliquots were taken at predetermined time intervals and the kinetic changes in the Ca and PO4 concentrations were determined by utilizing spectro-photometric analytical methods (3). Statistical data analysis
Author Manuscript
One standard deviation (SD) is identified in this paper for comparative purposes as the estimated standard uncertainty of the measurements. These values should not be compared with data obtained in other laboratories under different conditions. Experimental data were analyzed by analysis of variance (ANOVA; α = 0.05). Significant differences between the groups were determined by all pair-wise multiple comparisons (Tukey-test).
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 4
Author Manuscript
Results and Discussion The amorphous character of the Zr-ACP filler was confirmed by XRD (two diffuse broad bands in the 2θ = (4 to 60)° region) and from the FTIR spectrum (two wide phosphate absorbance bands at (1200 to 900) cm−1 and (630 to 550) cm−1). Filler particle sizes ranged from submicron up to approximately 100 μm; calculated median diameter, dm, of the powder was (5.9 ± 0.7) μm. The results of the physicochemical evaluation of E, ES, U and US composites are summarized in Table 3.
Author Manuscript Author Manuscript
DC values attained at 24 h post-cure decreased in the following order: US > U > ES > E (one way ANOVA; p ≤ 0.001). All pair wise multiple comparisons, however, indicated that the differences between the U and US and between the E and ES formulations were not statistically significant (due to the high SDs seen in all groups). Similarly, apparently higher PS values in ES and US composites compared to E and U specimens were not statistically significant (Tukey test; reason: high SDs in SSO groups and small sample size). Although the differences in the mean BFS values among the treatment groups appeared statistically significant for both dry and wet specimens (one-way ANOVA; p= 0.049 and 0.048, respectively), all pair-wise multiple comparisons showed no significant difference between the means (p > 0.05). ES, U and US composites weakened significantly after aqueous exposure (23 %, 33 % and 21 %, respectively) compared to dry specimens. The plateau WS levels (WSmax) were reached after 45 d in all systems. WSmax in E composites was significantly lower than the WSmax in US, U and ES composites (p≤0.034). Both Ca and PO4 solution concentration rapidly increased during the first 24 to 48 h of immersion and a significant reduction in the rate of release after 200 h. The ion release was generally lower ion from the composites formulated with MPTMS.
Author Manuscript
In situ silanization, a simple technique that involves adding the silane agent as a comonomer to the usual dental monomer systems, has been identified as an attractive alternative to the presilanization methods for surface activation of glass fillers used in dental composites (10, 11). Indirect evidence obtained via mechanical testing shows that in situ silanization affects coupling of the glass filler and polymer matrix phases (1). In addition, the exchange reactions between the organosilane and hydroxylated monomer or water absorption by polar monomers (EBPADMA or UDMA) can lead to the formation of oligomeric SSO products. It is generally expected that blends of SSOs and silyl derivatives in dental resins could ameliorate effects of shrinkage and stress that develops upon polymerization and aid in keeping the composites mechanically stable upon aqueous immersion. In the case of ES resin formation of silyl ether can be ruled out since there are no sources of labile hydrogen in EBPADMA monomer. As shown by FTIR analysis (1), the presence of modest amounts of water in the relatively hydrophobic EBPADMA may, however, be sufficient to convert MPTMS to SSOs via un-catalyzed hydrolysiscondensation reaction of methyl silyl ether groups. A similar mechanism apparently controls the interactions in US mixtures despite the fact that UDMA is more polar than EBPADMA and has two potentially, somewhat labile hydrogens in the urethane group.
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 5
Author Manuscript
The experimental data on DC and PS did not confirm the hypothesis that inclusion of SSOs in dental resins could ameliorate effects of shrinkage that develops upon polymerization. The apparent trend of higher DC in ES and US composites probably contributed tothe unfavorable increase in PS of these composites. The unexpectedly large data scattering in both DC and PS measurements was most likely caused by the random, uneven dispersion of large ACP agglomerates throughout the composite specimens (12). The BFS data suggest that the potential formation of SSO had no effect on the ACP filler or the filler/matrix interface. It seems that, as already shown in our earlier work with different resin formulations (3, 12, 13), the inability of ACP filler to closely interact with the resin was not altered by introduction of MPTMS into the resin, and this shortcoming had a major role in controlling the mechanical behavior of the composites.
Author Manuscript
The WS of ACP composites is a result of the water absorbed by both the resin and the ACP filler. The composites formulated with more hydrophilic UDMA absorbed more water compared to composites formulated with less hydrophilic EBPADMA. Addition of MPTMS to the resin only marginally increased the WS of US composites but has significantly increased the WS of ES composites. No accelerated ion release was seen in ES composites that could be correlated with increased WS values. However, the remineralizing potential of ACP composites has not been severely impeded by in situ silanization.
Conclusions
Author Manuscript
The addition of MPTMS and its SSO products to EBPADMA and UDMA resins did not adversely affect the critical remineralizing potential of these composites and had little effect on other properties. A series of better controlled hydrolysis/condensation experiments and identification of the condensation products may be necessary to better understand the effects of in situ silanization reactions on ACP composites.
Acknowledgments Support from the NIDCR/NIST Interagency Agreement YI-DE-7005-01, NIDCR grant DE 13169 and contribution of monomers from Esstech, Essington, PA, USA are gratefully acknowledged.
References
Author Manuscript
1. Antonucci JM, et al. J Res Natl Inst Stands Technol. 2005; 110:541–558. 2. Farahani M, et al. J Appl Polym Sci. 2006; 99(4):1842–1847. 3. Skrtic D, et al. J Res Natl Inst Stands Technol. 2003; 108(3):167–182. 4. Antonucci, JM.; Skrtic, D. Shalaby, WS.; Salz, U., editors. Boca Raton: CRC Press; 2007. p. 217-242. 5. Antonucci JM, et al. Polymer Preprints. 1997; 38(2):118–119. 6. Wallace WE, et al. J Am Soc Mass Spectrom. 1999; 10:224–230. 7. Dickens SH, et al. Polymer Preprints. 2002; 43(2):747–748. 8. Reed B, et al. J Dent Res. 1996; 75:290. 9. ASTM F394-78 (re-approved 1996). 10. Venz S, Antonucci JM. J Dent Res. 1986; 65:191. 11. Guggenberger R, Weinmann W. Am J Dent. 2000; 13:82D–84D.
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 6
Author Manuscript
12. Skrtic D, et al. Biomaterials. 2004; 25:1141–1150. [PubMed: 14643587] 13. Skrtic D, Antonucci JM. J Biomat Appl. 2007; 21:375–393.
Author Manuscript Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 7
Author Manuscript Fig. 1.
Author Manuscript
Schematic presentation of pathways to incompletely and fully-condensed SSOs.
Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 8
Table 1
Author Manuscript
Monomers and components of the photoinitiator system. Monomer
Acronym
Ethoxylated bisphenol A dimethacrylate
EBPADMA
1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4- trimethyl hexane
UDMA
Methacryloxypropyltrimethoxysilane
MPTMS
Camphorquinone
CQ
Ethyl-4-N, N-dimethylamino benzoate
EDMAB
Author Manuscript Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
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Table 2
Author Manuscript
Composition (mass fraction, %) of the resins. Resin acronym
EBPADMA
UDMA
MPTMS
E
99.0
-
-
ES*
73.0
-
26.0
U
-
99.0
-
US*
-
75.6
23.4
*
S indicates anticipated SSO formation.
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Antonucci and Skrtic
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Table 3
Author Manuscript
Physicochemical assessment of the composites. Indicated are mean values with one standard deviation in parenthesis. Number of specimens: n=3 (PS and ion release), n=5 (BFS and WS) and n=6 (DC). Property
E
ES
U
US
DC (%)
29.4 (9.3)
40.0 (8.7)
44.3 (9.0)
54.2 (8.5)
PS (vol %
4.5 (0.9)
6.5 (1.7)
3.5 (0.3)
7.0 (2.0)
BFS dry (MPa) wet
55.9 (10.0) 49.2 (5.9)
44.2 (4.0) 33.9 (7.1)
61.1 (13.9) 41.3 (8.9)
53.2 (3.9) 42.2 (8.0)
WSmax (%)
2.0 (0.5)
3.2 (0.5)
3.9 (0.2)
4.3 (0.7)
Ca (mM/L) PO4 (mM/L)
1.4 (0.2) 1.2 (0.3)
0.6 (0.1) 0.5 (0.1)
1.2 (0.2) 1.3 (0.2)
0.7 (0.1) 0.8 (0.1)
Author Manuscript Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Polymer Prepr. Author manuscript; available in PMC 2015 October 08. Published in final edited form as: Polymer Prepr. 2009 ; 50(1): 343–344.
EFFECTS OF A METHACRYLIC SILANE ON SOME PHYSICOCHEMICAL PROPERTIES OF RESIN-BASED BIOMIMETIC COMPOSITE J. M. Antonucci1 and D. Skrtic2 1
Polymers Division, National Institute of Standards and Technology (NIST), Gaithersburg, MD
Author Manuscript
2
Paffenbarger Research Center (PRC), American Dental Association Foundation (ADAF), Gaithersburg, MD
Introduction
Author Manuscript
In the presence of water, organotrialkoxysilanes can undergo a series of hydrolysiscondensation reactions leading to three-dimensional silsesquioxane (SSO) structures that have potential as both resin matrix components and as molecular-sized silica fillers (1). It has been shown that SSO formation from silane can occur in dental monomers (2). In addition to the self-condensation reaction, organosilanes may form high molecular mass silyl derivatives with hydroxylated and carboxylated dental monomers. Functional silanes, in addition to serving as components in resin blends, also can be considered as molecularsized fillers.
Author Manuscript
In this study, methacryloxypropyltrimethoxysilane (MPTMS) was combined with nonhydroxylated dental monomers, e.g., ethoxylated bisphenol A dimethacrylate (EBPADMA) and an aliphatic diurethane dimethacrylate (UDMA), photoactivated, and the resulting resins were utilized in formulating the composites with amorphous calcium phosphate, ACP (3, 4). We hypothesized that EBPADMA and UDMA would serve as polymerizable solvents for the in situ formation of methacrylic SSOs via hydrolysis-condensation reaction of MPTMS (4–7). If predominantly fully-condensed SSOs were formed, physicochemical and mechanical performance of the composites should improve compared to the non-SSO containing formulations. A series of physicochemical tests including degree of vinyl conversion (DC), polymerization shrinkage (PS), biaxial flexure strength (BFS), water sorption (WS) and ion release were performed on ACP composite specimens formulated with UDMA or EBPADMA alone (as controls) and their MPTMS (SSO)-containing hybrids.
Disclaimer Certain commercial materials and equipment are identified in this article to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by NIST or ADAF or that the material or equipment identified is necessarily the best available for the purpose. “Official contribution of NIST; not subject to copyrights in USA”.
Antonucci and Skrtic
Page 2
Author Manuscript
Experimental Formulation of the resins The experimental SSO resins (S-resins) were formulated from commercially available EBPADMA and UDMA monomers with MPTMS and photo-activated by the inclusion of camphorquinone (CQ; mass fraction of 0.2 %) and ethyl-4-N, N-dimethylamino benzoate (EDMAB; mass fraction of 0.8 %). The monomers and the components of photo-initiator systems (with the corresponding acronyms that are used throughout this manuscript) and the composition of the resins (% mass fraction) are provided in Tables 1 and 2. Resins were kept at 23 °C for 28 d to allow sufficient time for the condensation reaction to take place before being utilized in composite preparation (2). The hydrolytic condensation reactions of MPTMS resulting in either incompletely- or fully-condensed SSOs are illustrated in Fig. 1.
Author Manuscript
ACP synthesis and characterization—ACP was synthesized as detailed earlier (3, 4). It precipitated instantaneously in a closed system at 23 °C upon rapidly mixing equal volumes of a 800 mmol/L Ca(NO3)2 solution and a 536 mmol/L Na2HPO4 solution that contained a molar fraction of 2 % Na4P2O7 as a stabilizing component for ACP. The suspension was filtered, the solid phase washed subsequently with ice-cold ammoniated water and acetone, and then lyophilized. To avoid exposure to humidity, ACP was kept under vacuum (2.7 kPa) over desiccant until utilized in composite formulations.
Author Manuscript
The amorphous state of ACP was verified by powder X-ray diffraction (XRD; Rigaku DMAX 2000 X-ray diffractometer, Rigaku/USA Inc., Danvers, MA, USA) and Fouriertransform infrared (FTIR; Nicolet Magna-IR FTIR 550 spectrophotometer, Nicolet Instrumentations Inc., Madison, WI, USA) spectroscopy. Particle size distribution of ZrACP was determined by gravitational and centrifugal sedimentation analysis (SA-CP3 analyzer, Shimadzu Scientific Instruments, Inc., Columbia, MD, USA). Preparation of composite specimens
Author Manuscript
Composite pastes were made by mixing the appropriate resin (mass fraction 60 %) with ACP filler (mass fraction 40 %) using hand spatulation. The homogenized pastes were kept under a moderate vacuum (2.7 kPa) overnight to eliminate the air entrained during mixing. The pastes were molded into disks (14.9 mm to 15.3 mm in diameter and 1.31 mm to 1.53 mm in thickness) by filling the circular openings of flat Teflon molds, covering each side of the mold with a Mylar film plus a glass slide, and then clamping the assembly together with spring clips. The disks were photo-polymerized by irradiating sequentially each face of the mold assembly for 60 s with visible light (Triad 2000; Dentsply International, York, PA, USA). Degree of vinyl conversion (DC) DC attained in the unfilled resins (copolymers) and the corresponding ACP composites was determined by FTIR spectroscopy. Spectra were acquired before photo-cure and 24 h after cure. DC was calculated from the decrease in the integrated peak area of the 1637 cm−1 absorption band between the polymer (cured specimen) and monomer (uncured specimen).
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 3
Author Manuscript
Absorption bands at 1538 cm−1 and 775 cm−1 were used as the internal reference for EBPADMA and UDMA formulations, respectively. Polymerization shrinkage (PS) PS of composites was measured by a computer-controlled mercury dilatometer (8) (PRCADAF), Gaithersburg, MD, USA). Composite pastes ((100 ± 10) mg) were irradiated twice: initially for 60 s followed by a second irradiation for 30 s after 60 min. Data were collected for a total of 90 min. PS was calculated based on the known mass of the sample and its density. The latter was determined by means of the Archimedean displacement principle using an attachment to a microbalance (Sartorius YDK01 Density Determination Kit, Sartorius AG, Goettingen, Germany). Biaxial flexure strength (BFS)
Author Manuscript
BFS testing was employed to compare the mechanical strength of dry (after 24 h storage in the air at 23 °C) and wet (after 3 weeks of immersion in 4-(2-hydroxyethyl)-1piperazineethane sulfonic acid (HEPES)-buffered saline solution (0.13 mol/L NaCl; pH = 7.4) at 23 °C; 100 mL saline solution/specimen) composite specimens. Piston-on-three-ball loading cell and a computer-controlled Universal Testing Machine (Instron 5500R, Instron Corp., Canton, MA, US) operated by Testworks 4 software were utilized. BFS values were calculated according ASTM F394-78 (9). Water sorption (WS)
Author Manuscript
WS of composite specimens was determined as follows. Specimens were initially dried over anhydrous CaSO4 until a constant mass was achieved (± 0.1 mg), and then were exposed to an air atmosphere of 75 % relative humidity (RH) at 23 °C by keeping them suspended over saturated aqueous sNaCl slurry in closed systems. Gravimetric changes of dry-padded specimens were recorded at predetermined time intervals. WS of individual specimens was calculated as WS = [(Wt − W0)/W0] × 100, where Wt represents sample mass at any given time and W0 is the initial mass of dry sample. Mineral ion release Ion release from composite disk specimens was examined at 23 °C, in continuously stirred, saline solutions (initial volume of saline per composite specimen: 100 mL). Aliquots were taken at predetermined time intervals and the kinetic changes in the Ca and PO4 concentrations were determined by utilizing spectro-photometric analytical methods (3). Statistical data analysis
Author Manuscript
One standard deviation (SD) is identified in this paper for comparative purposes as the estimated standard uncertainty of the measurements. These values should not be compared with data obtained in other laboratories under different conditions. Experimental data were analyzed by analysis of variance (ANOVA; α = 0.05). Significant differences between the groups were determined by all pair-wise multiple comparisons (Tukey-test).
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 4
Author Manuscript
Results and Discussion The amorphous character of the Zr-ACP filler was confirmed by XRD (two diffuse broad bands in the 2θ = (4 to 60)° region) and from the FTIR spectrum (two wide phosphate absorbance bands at (1200 to 900) cm−1 and (630 to 550) cm−1). Filler particle sizes ranged from submicron up to approximately 100 μm; calculated median diameter, dm, of the powder was (5.9 ± 0.7) μm. The results of the physicochemical evaluation of E, ES, U and US composites are summarized in Table 3.
Author Manuscript Author Manuscript
DC values attained at 24 h post-cure decreased in the following order: US > U > ES > E (one way ANOVA; p ≤ 0.001). All pair wise multiple comparisons, however, indicated that the differences between the U and US and between the E and ES formulations were not statistically significant (due to the high SDs seen in all groups). Similarly, apparently higher PS values in ES and US composites compared to E and U specimens were not statistically significant (Tukey test; reason: high SDs in SSO groups and small sample size). Although the differences in the mean BFS values among the treatment groups appeared statistically significant for both dry and wet specimens (one-way ANOVA; p= 0.049 and 0.048, respectively), all pair-wise multiple comparisons showed no significant difference between the means (p > 0.05). ES, U and US composites weakened significantly after aqueous exposure (23 %, 33 % and 21 %, respectively) compared to dry specimens. The plateau WS levels (WSmax) were reached after 45 d in all systems. WSmax in E composites was significantly lower than the WSmax in US, U and ES composites (p≤0.034). Both Ca and PO4 solution concentration rapidly increased during the first 24 to 48 h of immersion and a significant reduction in the rate of release after 200 h. The ion release was generally lower ion from the composites formulated with MPTMS.
Author Manuscript
In situ silanization, a simple technique that involves adding the silane agent as a comonomer to the usual dental monomer systems, has been identified as an attractive alternative to the presilanization methods for surface activation of glass fillers used in dental composites (10, 11). Indirect evidence obtained via mechanical testing shows that in situ silanization affects coupling of the glass filler and polymer matrix phases (1). In addition, the exchange reactions between the organosilane and hydroxylated monomer or water absorption by polar monomers (EBPADMA or UDMA) can lead to the formation of oligomeric SSO products. It is generally expected that blends of SSOs and silyl derivatives in dental resins could ameliorate effects of shrinkage and stress that develops upon polymerization and aid in keeping the composites mechanically stable upon aqueous immersion. In the case of ES resin formation of silyl ether can be ruled out since there are no sources of labile hydrogen in EBPADMA monomer. As shown by FTIR analysis (1), the presence of modest amounts of water in the relatively hydrophobic EBPADMA may, however, be sufficient to convert MPTMS to SSOs via un-catalyzed hydrolysiscondensation reaction of methyl silyl ether groups. A similar mechanism apparently controls the interactions in US mixtures despite the fact that UDMA is more polar than EBPADMA and has two potentially, somewhat labile hydrogens in the urethane group.
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 5
Author Manuscript
The experimental data on DC and PS did not confirm the hypothesis that inclusion of SSOs in dental resins could ameliorate effects of shrinkage that develops upon polymerization. The apparent trend of higher DC in ES and US composites probably contributed tothe unfavorable increase in PS of these composites. The unexpectedly large data scattering in both DC and PS measurements was most likely caused by the random, uneven dispersion of large ACP agglomerates throughout the composite specimens (12). The BFS data suggest that the potential formation of SSO had no effect on the ACP filler or the filler/matrix interface. It seems that, as already shown in our earlier work with different resin formulations (3, 12, 13), the inability of ACP filler to closely interact with the resin was not altered by introduction of MPTMS into the resin, and this shortcoming had a major role in controlling the mechanical behavior of the composites.
Author Manuscript
The WS of ACP composites is a result of the water absorbed by both the resin and the ACP filler. The composites formulated with more hydrophilic UDMA absorbed more water compared to composites formulated with less hydrophilic EBPADMA. Addition of MPTMS to the resin only marginally increased the WS of US composites but has significantly increased the WS of ES composites. No accelerated ion release was seen in ES composites that could be correlated with increased WS values. However, the remineralizing potential of ACP composites has not been severely impeded by in situ silanization.
Conclusions
Author Manuscript
The addition of MPTMS and its SSO products to EBPADMA and UDMA resins did not adversely affect the critical remineralizing potential of these composites and had little effect on other properties. A series of better controlled hydrolysis/condensation experiments and identification of the condensation products may be necessary to better understand the effects of in situ silanization reactions on ACP composites.
Acknowledgments Support from the NIDCR/NIST Interagency Agreement YI-DE-7005-01, NIDCR grant DE 13169 and contribution of monomers from Esstech, Essington, PA, USA are gratefully acknowledged.
References
Author Manuscript
1. Antonucci JM, et al. J Res Natl Inst Stands Technol. 2005; 110:541–558. 2. Farahani M, et al. J Appl Polym Sci. 2006; 99(4):1842–1847. 3. Skrtic D, et al. J Res Natl Inst Stands Technol. 2003; 108(3):167–182. 4. Antonucci, JM.; Skrtic, D. Shalaby, WS.; Salz, U., editors. Boca Raton: CRC Press; 2007. p. 217-242. 5. Antonucci JM, et al. Polymer Preprints. 1997; 38(2):118–119. 6. Wallace WE, et al. J Am Soc Mass Spectrom. 1999; 10:224–230. 7. Dickens SH, et al. Polymer Preprints. 2002; 43(2):747–748. 8. Reed B, et al. J Dent Res. 1996; 75:290. 9. ASTM F394-78 (re-approved 1996). 10. Venz S, Antonucci JM. J Dent Res. 1986; 65:191. 11. Guggenberger R, Weinmann W. Am J Dent. 2000; 13:82D–84D.
Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 6
Author Manuscript
12. Skrtic D, et al. Biomaterials. 2004; 25:1141–1150. [PubMed: 14643587] 13. Skrtic D, Antonucci JM. J Biomat Appl. 2007; 21:375–393.
Author Manuscript Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 7
Author Manuscript Fig. 1.
Author Manuscript
Schematic presentation of pathways to incompletely and fully-condensed SSOs.
Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 8
Table 1
Author Manuscript
Monomers and components of the photoinitiator system. Monomer
Acronym
Ethoxylated bisphenol A dimethacrylate
EBPADMA
1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4- trimethyl hexane
UDMA
Methacryloxypropyltrimethoxysilane
MPTMS
Camphorquinone
CQ
Ethyl-4-N, N-dimethylamino benzoate
EDMAB
Author Manuscript Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
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Table 2
Author Manuscript
Composition (mass fraction, %) of the resins. Resin acronym
EBPADMA
UDMA
MPTMS
E
99.0
-
-
ES*
73.0
-
26.0
U
-
99.0
-
US*
-
75.6
23.4
*
S indicates anticipated SSO formation.
Author Manuscript Author Manuscript Author Manuscript Polymer Prepr. Author manuscript; available in PMC 2015 October 08.
Antonucci and Skrtic
Page 10
Table 3
Author Manuscript
Physicochemical assessment of the composites. Indicated are mean values with one standard deviation in parenthesis. Number of specimens: n=3 (PS and ion release), n=5 (BFS and WS) and n=6 (DC). Property
E
ES
U
US
DC (%)
29.4 (9.3)
40.0 (8.7)
44.3 (9.0)
54.2 (8.5)
PS (vol %
4.5 (0.9)
6.5 (1.7)
3.5 (0.3)
7.0 (2.0)
BFS dry (MPa) wet
55.9 (10.0) 49.2 (5.9)
44.2 (4.0) 33.9 (7.1)
61.1 (13.9) 41.3 (8.9)
53.2 (3.9) 42.2 (8.0)
WSmax (%)
2.0 (0.5)
3.2 (0.5)
3.9 (0.2)
4.3 (0.7)
Ca (mM/L) PO4 (mM/L)
1.4 (0.2) 1.2 (0.3)
0.6 (0.1) 0.5 (0.1)
1.2 (0.2) 1.3 (0.2)
0.7 (0.1) 0.8 (0.1)
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