NIH Public Access Author Manuscript Pediatr Dent. Author manuscript; available in PMC 2014 October 14.
NIH-PA Author Manuscript
Published in final edited form as: Pediatr Dent. 2014 ; 36(5): 130–136.
Shear bond strength of dentin and deproteinized enamel of AI mouse incisors M.K. Pugach1, F. Ozer2, R. Mulmadgi2, Y. Li3, C. Suggs4, J.T. Wright4, J.D. Bartlett1, C.W. Gibson3, and R.G. Lindemeyer5 1Department
of Mineralized Tissue Biology, The Forsyth Institute, and Department of Developmental Biology, Harvard School of Dental Medicine, 245 First Street, Cambridge, MA 02142 2Department
of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104-6030
NIH-PA Author Manuscript
3Department
of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104-6030
4Pediatric
Dentistry, University of North Carolina, School of Dentistry, CB#7450, Chapel Hill, NC, 27599-7450 5Division
of Pediatric Dentistry, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104
Abstract Purpose—To investigate the adhesion through shear bond strength (SBS) testing of a resin composite bonded with a self-etching bonding system (SEB) to amelogenesis imperfecta (AI)affected deproteinized mouse enamel or dentin; and to compare wild-type (WT), amelogenin null (AmelxKO) and matrix metalloproteinase-20 null (Mmp20KO) enamel and dentin phenotypes using microCT and nanoindentation.
NIH-PA Author Manuscript
Methods—Enamel incisor surfaces of WT, AmelxKO and Mmp20KO mice were treated with SEB with and without NaOCl and tested for SBS. Incisor dentin was also treated with SEB and tested for SBS. These surfaces were further examined by SEM. MicroCT and nanoindentation analyses were performed on mouse dentin and enamel. Data were analyzed for significance by ANOVA. Results—Deproteinization did not improve SBS of SEB to these AI-affected enamel surfaces. SBS of AmelxKO teeth was similar in dentin and enamel; however, it was higher in Mmp20KO dentin. The nanohardness of knockout enamel was significantly lower than WT, while knockout dentin nanohardness was not different from WT.
*
Corresponding author: Rochelle G. Lindemeyer, D.M.D, Department of Pediatric Dentistry, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104, [email protected], Telephone 215-776-6671, FAX 215-590-5990.
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NIH-PA Author Manuscript
Conclusions—Using animal AI models, it was demonstrated that enamel NaOCl deproteinization of hypoplastic and hypoplastic-hypomaturation enamel did not increase shear bond strength while removal of the defective enamel allowed optimal dentin bonding. Keywords Amelogenesis imperfecta; dentin bonding; enamel
Introduction
NIH-PA Author Manuscript
Amelogenesis imperfecta (AI) is an inherited disorder, which results in enamel defects that are highly variable, including differences in both the quantity and quality of enamel, as well as possible structural differences in dentin. AI can be classified into three main types: hypoplastic, hypomaturation and hypocalcified AI, and further into fourteen different subtypes with each form having different clinical phenotypic characteristics combined with three inheritance modes, as genes have been associated with this defect1. Consequently, bonding to teeth affected by AI has variable results. In cases of hypoplastic AI, the mineral content of the enamel is near normal but it is thin and bonding with the traditional etch-andrinse three-step adhesive systems (total-etch process) may be successful. In other cases, such as in hypomaturation AI, there is an excess of enamel proteins resulting in soft enamel that may delaminate from the dentinoenamel junction (DEJ), exposing dentin. In these cases, adhesion is poor and often results in failure of the restoration. Some reports have indicated that deproteinization with sodium hypochlorite (NaOCl) prior to etching would enhance adhesion in patients with hypocalcified AI (HCAI)2,3 however; one study indicated that NaOCl had no effect on success of composite restorations in the same type of AI4. This creates complex issues for the pediatric dentist whose long-term aim of treatment is to maintain a maximum amount of tooth structure until the child is of an age to receive more definitive restorations.
NIH-PA Author Manuscript
The estimated frequency of AI ranges from 1:700 to 1:14,000 depending on the population studied 5,6. Limited laboratory studies have investigated bond strength in AI teeth reflecting the scarcity of extracted teeth and the large variability of the clinical presentations. The use of mouse models has allowed us to investigate the differences in enamel and dentin of different forms of AI in a laboratory setting. Several mutations in genes that encode proteins involved in enamel development have been found to cause AI. Two of these genes are amelogenin (AMELX, OMIM 300391) and matrix metalloproteinase-20 (MMP-20, OMIM 604629). Amelogenins constitute 90 percent of the enamel organic matrix and are considered crucial to enamel development and mineralization 7–9. Amelogenin null (AmelxKO) mice lack all of the amelogenin proteins and develop hypoplastic enamel lacking prismatic structure similar to X-linked AI in humans (Fig. 1A–1D)10. MMP20 is a protease secreted by ameloblasts that processes amelogenins and other enamel structural proteins during mineralization, along with KLK-411,12, until the overall protein content in the enamel is reduced from 30 percent to less than three percent13. Matrix metalloproteinase-20 null (Mmp20KO) mice develop hypoplastic and hypomature enamel
Pediatr Dent. Author manuscript; available in PMC 2014 October 14.
Pugach et al.
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that separates from the dentin similar to that observed in individuals with MMP20 mutations (Fig. 1E–1G)14.
NIH-PA Author Manuscript
We have shown that a self-etching primer (SEB) performs better than the total-etch system when bonding to hypoplastic (amelogenin KO) and hypomaturation (Matrix metalloproteinase-20 KO; Mmp20KO) AI enamel15. Adhesive failures, however, were dramatically increased in the Mmp20KO enamel. We sought to determine whether we could further optimize a bonding system for restoring AI-affected teeth. In order to further understand the differences in bonding outcomes, it is also critical to have insight into the physical characteristics of the enamel and dentin in these different mutations. The variability in these tissues with respect to density, volume and hardness of AI-affected teeth compared to unaffected mouse teeth may provide insights about additional techniques that may improve clinical success in bonded restorations.
NIH-PA Author Manuscript
The primary purpose of this study was to investigate the adhesion through SBS testing of a resin composite bonded with a self-etching bonding agent to AI-affected mouse dentin or enamel following NaOCl treatment. The SEP treated enamel and dentin surfaces were also evaluated with SEM. The second objective of our study was to compare AmelxKO and Mmp20KO enamel and dentin phenotypes using microCT and nanoindentation and determine whether the mutations in these enamel genes have any effect on dentin, and dentinal bonding.
Methods Animal models and genotyping AmelxKO and Mmp20KO mice were generated by introduction of a deletion into the coding region as described previously10,14. Mice were housed in an Association for Assessment and Accreditation of Laboratory Animal Care AAALAC accredited facility, and procedures were approved by the University of Pennsylvania Institutional Animal Care and Use Committee (IACUC). High molecular weight genomic DNA was isolated from mouse tails to determine AmelxKO or Mmp20KO or wild-type (WT) genotype, using primers and methods described previously 10,14.
NIH-PA Author Manuscript
Tooth surface treatment for SEM analysis To analyze the enamel surfaces treated with the self-etching primer (SEP) of the SEB system (Clearfil SE Bond, Kuraray, Japan) with and without NaOCl application, mice were euthanized by CO2 administration. After dissection of mandibles from four-week-old AmelxKO, Mmp20KO and WT mice (n=5) for each mouse type and treatment), the incisors were removed from the mandibles. In an effort to standardize the enamel and dentin surfaces to be treated, we determined by scanning electron microscopy (SEM) that polishing WT and mutant incisor facial surfaces with 800 grit silicon carbide (SiC) for two seconds left the majority of remaining enamel, while polishing for five seconds removed enamel, revealing dentin. The facial surfaces of mandibular incisors were rinsed in double deionized water (DD H20) and polished for two seconds on 800 grit SiC paper. Right incisors were first treated with five percent NaOCl for one minute, and rinsed with DD H20. Both right and left
Pediatr Dent. Author manuscript; available in PMC 2014 October 14.
Pugach et al.
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NIH-PA Author Manuscript
incisors were then treated with the SEP (Clearfil SE Bond, Kuraray, Japan) for 20 seconds, according to the manufacturer’s instructions. To analyze the dentinal incisor surfaces treated with the SEP, the facial enamel surfaces of mandibular incisors were rinsed in DD H20 for five seconds and polished on 800 grit SiC paper until a flat dentin surfaces just below the DEJ was obtained. The dentin was then treated with the SEP for 20 seconds, according to the manufacturer’s instructions. SEM analysis of tooth surfaces Surfaces of SEP and NaOCl plus SEP treated incisor enamel and dentin were coated with gold. SEM analysis of the facial tooth surfaces of incisors was completed at 15 kV and 2000X magnification, in secondary mode (Carl Zeiss, Germany). Images were obtained of the facial surface of each incisor. Microshear bond strength test
NIH-PA Author Manuscript
Mandibular incisors were dissected from four-week-old WT, AmelxKO, and Mmp20KO mice (n=30 mice for each genotype and treatment). The samples were mounted and bonded as previously described 15. The flat portion of the facial surface of incisor enamel was polished with 800-grit SiC paper for two seconds to create a uniform, flat bond area. Composite inlay sticks (1.0 mm × 0.4 mm) were prepared with Clearfil Majesty Anterior (Kuraray, Japan) and bonded to enamel surfaces using a SEB system (Clearfil SE Bond, Kuraray, Japan). For the NaOCl plus SEB group, incisor enamel was treated with five percent NaOCl for one minute and rinsed with DD H20, prior to being treated with SEB to bond the composite inlay sticks. To test the shear bond strength (SBS) of dentin treated with the SEB, the flat portion of the facial surface of incisor enamel was polished with 800-grit SiC paper for five seconds to create a uniform, flat bond area in dentin just below the DEJ. Composite inlay sticks (1.0 mm × 0.4 mm) were prepared with Clearfil Majesty Anterior (Kuraray, Japan) and bonded to dentin surfaces using Clearfil SE Bond (Kuraray, Japan).
NIH-PA Author Manuscript
SBS was measured using a Micro-shear Tester (Bisco, Michigan, USA), with a crosshead speed of 0.5 mm/min. Data were analyzed using a 2-way ANOVA to determine statistical significance (p0.05). Both SEM images of WT enamel (with and without NaOCl application) indicated that there was a layer of primer-permeated enamel likely containing the smear layer covering the etched enamel rods (Fig. 2A&2D). Treatment of AmelxKO enamel with NaOCl before SEP treatment seemed to significantly alter the incisor enamel surface, as the SEM image of NaOCl plus SEP displayed a globular layer of matrix that was not visible in the SEP only AmelxKO SEM image (Fig. 2B&2E). When Mmp20KO enamel was treated with NaOCl prior to SEP treatment, the incisor surface seemed to be slightly altered as compared to SEPonly treatment (Fig. 2C&2F). For both AmelxKO and Mmp20KO incisor enamel, it was difficult to observe whether there were layers of primer-permeated enamel containing smear layer on the enamel surfaces (Fig. 2B, 2C, 2E, 2F) from the SEM images of both SEP-only and NaOCl plus SEP treated enamel surfaces. SEM analysis of dentin surfaces The dentin surfaces of WT, AmelxKO and Mmp20KO dentin, when treated with the SEP, appeared to have a layer of primer-permeated dentin containing smear layer covering the
Pediatr Dent. Author manuscript; available in PMC 2014 October 14.
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sound dentin (Fig. 3). However, the treated dentin surface of WT and Mmp20KO seemed to contain more porosities and roughness as compared to AmelxKO dentin, which could result in higher shear bond strengths for WT and Mmp20KO (Fig. 3). Bonding to dentin and deproteinized enamel surfaces Treatment of knockout and WT enamel with NaOCl prior to bonding with the SEB system did not significantly improve enamel shear bond strength (p=0.338, NS), although SBS was slightly increased for WT and slightly decreased for AmelxKO and Mmp20KO (Fig. 4). The deproteinization of hypoplastic AmelxKO and Mmp20KO enamel seemed to further decrease the enamel available for bonding, as dentin was often visible when the debonded surfaces were analyzed (Table 1). SBS of AmelxKO and Mmp20KO dentin were not significantly different from WT (p=0.051, NS), although Mmp20KO exhibited higher SBS than AmelxKO (Fig. 5). MicroCT analysis and hardness of mouse dentin and enamel
NIH-PA Author Manuscript
MicroCT analysis of AmelxKO and Mmp20KO dentin did not reveal differences in density compared to WT (p=0.104, NS), and Mmp20KO volume was slightly higher than WT. These results were drastically different from density and volume of knockout enamel, which were significantly reduced compared to WT (p
NIH-PA Author Manuscript
Published in final edited form as: Pediatr Dent. 2014 ; 36(5): 130–136.
Shear bond strength of dentin and deproteinized enamel of AI mouse incisors M.K. Pugach1, F. Ozer2, R. Mulmadgi2, Y. Li3, C. Suggs4, J.T. Wright4, J.D. Bartlett1, C.W. Gibson3, and R.G. Lindemeyer5 1Department
of Mineralized Tissue Biology, The Forsyth Institute, and Department of Developmental Biology, Harvard School of Dental Medicine, 245 First Street, Cambridge, MA 02142 2Department
of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104-6030
NIH-PA Author Manuscript
3Department
of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104-6030
4Pediatric
Dentistry, University of North Carolina, School of Dentistry, CB#7450, Chapel Hill, NC, 27599-7450 5Division
of Pediatric Dentistry, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104
Abstract Purpose—To investigate the adhesion through shear bond strength (SBS) testing of a resin composite bonded with a self-etching bonding system (SEB) to amelogenesis imperfecta (AI)affected deproteinized mouse enamel or dentin; and to compare wild-type (WT), amelogenin null (AmelxKO) and matrix metalloproteinase-20 null (Mmp20KO) enamel and dentin phenotypes using microCT and nanoindentation.
NIH-PA Author Manuscript
Methods—Enamel incisor surfaces of WT, AmelxKO and Mmp20KO mice were treated with SEB with and without NaOCl and tested for SBS. Incisor dentin was also treated with SEB and tested for SBS. These surfaces were further examined by SEM. MicroCT and nanoindentation analyses were performed on mouse dentin and enamel. Data were analyzed for significance by ANOVA. Results—Deproteinization did not improve SBS of SEB to these AI-affected enamel surfaces. SBS of AmelxKO teeth was similar in dentin and enamel; however, it was higher in Mmp20KO dentin. The nanohardness of knockout enamel was significantly lower than WT, while knockout dentin nanohardness was not different from WT.
*
Corresponding author: Rochelle G. Lindemeyer, D.M.D, Department of Pediatric Dentistry, University of Pennsylvania School of Dental Medicine, 240 S. 40th Street, Philadelphia, PA 19104, [email protected], Telephone 215-776-6671, FAX 215-590-5990.
Pugach et al.
Page 2
NIH-PA Author Manuscript
Conclusions—Using animal AI models, it was demonstrated that enamel NaOCl deproteinization of hypoplastic and hypoplastic-hypomaturation enamel did not increase shear bond strength while removal of the defective enamel allowed optimal dentin bonding. Keywords Amelogenesis imperfecta; dentin bonding; enamel
Introduction
NIH-PA Author Manuscript
Amelogenesis imperfecta (AI) is an inherited disorder, which results in enamel defects that are highly variable, including differences in both the quantity and quality of enamel, as well as possible structural differences in dentin. AI can be classified into three main types: hypoplastic, hypomaturation and hypocalcified AI, and further into fourteen different subtypes with each form having different clinical phenotypic characteristics combined with three inheritance modes, as genes have been associated with this defect1. Consequently, bonding to teeth affected by AI has variable results. In cases of hypoplastic AI, the mineral content of the enamel is near normal but it is thin and bonding with the traditional etch-andrinse three-step adhesive systems (total-etch process) may be successful. In other cases, such as in hypomaturation AI, there is an excess of enamel proteins resulting in soft enamel that may delaminate from the dentinoenamel junction (DEJ), exposing dentin. In these cases, adhesion is poor and often results in failure of the restoration. Some reports have indicated that deproteinization with sodium hypochlorite (NaOCl) prior to etching would enhance adhesion in patients with hypocalcified AI (HCAI)2,3 however; one study indicated that NaOCl had no effect on success of composite restorations in the same type of AI4. This creates complex issues for the pediatric dentist whose long-term aim of treatment is to maintain a maximum amount of tooth structure until the child is of an age to receive more definitive restorations.
NIH-PA Author Manuscript
The estimated frequency of AI ranges from 1:700 to 1:14,000 depending on the population studied 5,6. Limited laboratory studies have investigated bond strength in AI teeth reflecting the scarcity of extracted teeth and the large variability of the clinical presentations. The use of mouse models has allowed us to investigate the differences in enamel and dentin of different forms of AI in a laboratory setting. Several mutations in genes that encode proteins involved in enamel development have been found to cause AI. Two of these genes are amelogenin (AMELX, OMIM 300391) and matrix metalloproteinase-20 (MMP-20, OMIM 604629). Amelogenins constitute 90 percent of the enamel organic matrix and are considered crucial to enamel development and mineralization 7–9. Amelogenin null (AmelxKO) mice lack all of the amelogenin proteins and develop hypoplastic enamel lacking prismatic structure similar to X-linked AI in humans (Fig. 1A–1D)10. MMP20 is a protease secreted by ameloblasts that processes amelogenins and other enamel structural proteins during mineralization, along with KLK-411,12, until the overall protein content in the enamel is reduced from 30 percent to less than three percent13. Matrix metalloproteinase-20 null (Mmp20KO) mice develop hypoplastic and hypomature enamel
Pediatr Dent. Author manuscript; available in PMC 2014 October 14.
Pugach et al.
Page 3
that separates from the dentin similar to that observed in individuals with MMP20 mutations (Fig. 1E–1G)14.
NIH-PA Author Manuscript
We have shown that a self-etching primer (SEB) performs better than the total-etch system when bonding to hypoplastic (amelogenin KO) and hypomaturation (Matrix metalloproteinase-20 KO; Mmp20KO) AI enamel15. Adhesive failures, however, were dramatically increased in the Mmp20KO enamel. We sought to determine whether we could further optimize a bonding system for restoring AI-affected teeth. In order to further understand the differences in bonding outcomes, it is also critical to have insight into the physical characteristics of the enamel and dentin in these different mutations. The variability in these tissues with respect to density, volume and hardness of AI-affected teeth compared to unaffected mouse teeth may provide insights about additional techniques that may improve clinical success in bonded restorations.
NIH-PA Author Manuscript
The primary purpose of this study was to investigate the adhesion through SBS testing of a resin composite bonded with a self-etching bonding agent to AI-affected mouse dentin or enamel following NaOCl treatment. The SEP treated enamel and dentin surfaces were also evaluated with SEM. The second objective of our study was to compare AmelxKO and Mmp20KO enamel and dentin phenotypes using microCT and nanoindentation and determine whether the mutations in these enamel genes have any effect on dentin, and dentinal bonding.
Methods Animal models and genotyping AmelxKO and Mmp20KO mice were generated by introduction of a deletion into the coding region as described previously10,14. Mice were housed in an Association for Assessment and Accreditation of Laboratory Animal Care AAALAC accredited facility, and procedures were approved by the University of Pennsylvania Institutional Animal Care and Use Committee (IACUC). High molecular weight genomic DNA was isolated from mouse tails to determine AmelxKO or Mmp20KO or wild-type (WT) genotype, using primers and methods described previously 10,14.
NIH-PA Author Manuscript
Tooth surface treatment for SEM analysis To analyze the enamel surfaces treated with the self-etching primer (SEP) of the SEB system (Clearfil SE Bond, Kuraray, Japan) with and without NaOCl application, mice were euthanized by CO2 administration. After dissection of mandibles from four-week-old AmelxKO, Mmp20KO and WT mice (n=5) for each mouse type and treatment), the incisors were removed from the mandibles. In an effort to standardize the enamel and dentin surfaces to be treated, we determined by scanning electron microscopy (SEM) that polishing WT and mutant incisor facial surfaces with 800 grit silicon carbide (SiC) for two seconds left the majority of remaining enamel, while polishing for five seconds removed enamel, revealing dentin. The facial surfaces of mandibular incisors were rinsed in double deionized water (DD H20) and polished for two seconds on 800 grit SiC paper. Right incisors were first treated with five percent NaOCl for one minute, and rinsed with DD H20. Both right and left
Pediatr Dent. Author manuscript; available in PMC 2014 October 14.
Pugach et al.
Page 4
NIH-PA Author Manuscript
incisors were then treated with the SEP (Clearfil SE Bond, Kuraray, Japan) for 20 seconds, according to the manufacturer’s instructions. To analyze the dentinal incisor surfaces treated with the SEP, the facial enamel surfaces of mandibular incisors were rinsed in DD H20 for five seconds and polished on 800 grit SiC paper until a flat dentin surfaces just below the DEJ was obtained. The dentin was then treated with the SEP for 20 seconds, according to the manufacturer’s instructions. SEM analysis of tooth surfaces Surfaces of SEP and NaOCl plus SEP treated incisor enamel and dentin were coated with gold. SEM analysis of the facial tooth surfaces of incisors was completed at 15 kV and 2000X magnification, in secondary mode (Carl Zeiss, Germany). Images were obtained of the facial surface of each incisor. Microshear bond strength test
NIH-PA Author Manuscript
Mandibular incisors were dissected from four-week-old WT, AmelxKO, and Mmp20KO mice (n=30 mice for each genotype and treatment). The samples were mounted and bonded as previously described 15. The flat portion of the facial surface of incisor enamel was polished with 800-grit SiC paper for two seconds to create a uniform, flat bond area. Composite inlay sticks (1.0 mm × 0.4 mm) were prepared with Clearfil Majesty Anterior (Kuraray, Japan) and bonded to enamel surfaces using a SEB system (Clearfil SE Bond, Kuraray, Japan). For the NaOCl plus SEB group, incisor enamel was treated with five percent NaOCl for one minute and rinsed with DD H20, prior to being treated with SEB to bond the composite inlay sticks. To test the shear bond strength (SBS) of dentin treated with the SEB, the flat portion of the facial surface of incisor enamel was polished with 800-grit SiC paper for five seconds to create a uniform, flat bond area in dentin just below the DEJ. Composite inlay sticks (1.0 mm × 0.4 mm) were prepared with Clearfil Majesty Anterior (Kuraray, Japan) and bonded to dentin surfaces using Clearfil SE Bond (Kuraray, Japan).
NIH-PA Author Manuscript
SBS was measured using a Micro-shear Tester (Bisco, Michigan, USA), with a crosshead speed of 0.5 mm/min. Data were analyzed using a 2-way ANOVA to determine statistical significance (p0.05). Both SEM images of WT enamel (with and without NaOCl application) indicated that there was a layer of primer-permeated enamel likely containing the smear layer covering the etched enamel rods (Fig. 2A&2D). Treatment of AmelxKO enamel with NaOCl before SEP treatment seemed to significantly alter the incisor enamel surface, as the SEM image of NaOCl plus SEP displayed a globular layer of matrix that was not visible in the SEP only AmelxKO SEM image (Fig. 2B&2E). When Mmp20KO enamel was treated with NaOCl prior to SEP treatment, the incisor surface seemed to be slightly altered as compared to SEPonly treatment (Fig. 2C&2F). For both AmelxKO and Mmp20KO incisor enamel, it was difficult to observe whether there were layers of primer-permeated enamel containing smear layer on the enamel surfaces (Fig. 2B, 2C, 2E, 2F) from the SEM images of both SEP-only and NaOCl plus SEP treated enamel surfaces. SEM analysis of dentin surfaces The dentin surfaces of WT, AmelxKO and Mmp20KO dentin, when treated with the SEP, appeared to have a layer of primer-permeated dentin containing smear layer covering the
Pediatr Dent. Author manuscript; available in PMC 2014 October 14.
Pugach et al.
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NIH-PA Author Manuscript
sound dentin (Fig. 3). However, the treated dentin surface of WT and Mmp20KO seemed to contain more porosities and roughness as compared to AmelxKO dentin, which could result in higher shear bond strengths for WT and Mmp20KO (Fig. 3). Bonding to dentin and deproteinized enamel surfaces Treatment of knockout and WT enamel with NaOCl prior to bonding with the SEB system did not significantly improve enamel shear bond strength (p=0.338, NS), although SBS was slightly increased for WT and slightly decreased for AmelxKO and Mmp20KO (Fig. 4). The deproteinization of hypoplastic AmelxKO and Mmp20KO enamel seemed to further decrease the enamel available for bonding, as dentin was often visible when the debonded surfaces were analyzed (Table 1). SBS of AmelxKO and Mmp20KO dentin were not significantly different from WT (p=0.051, NS), although Mmp20KO exhibited higher SBS than AmelxKO (Fig. 5). MicroCT analysis and hardness of mouse dentin and enamel
NIH-PA Author Manuscript
MicroCT analysis of AmelxKO and Mmp20KO dentin did not reveal differences in density compared to WT (p=0.104, NS), and Mmp20KO volume was slightly higher than WT. These results were drastically different from density and volume of knockout enamel, which were significantly reduced compared to WT (p
