Repair of dentin defects from DSPP knockout mice by PILP mineralization
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Chunlin Qin Department of Biomedical Sciences and Center for Craniofacial Research and Diagnosis, Texas A&M University Baylor College of Dentistry, Dallas, Texas 75246, USA
Laurie B. Gower Department of Materials Science & Engineering, University of Florida, Gainesville, Florida 32611, USA
Sally J. Marshall, Grayson W. Marshall, and Stefan Habelitza) Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California 94143, USA (Received 27 June 2015; accepted 16 December 2015)
Dentinogenesis imperfecta type II (DGI-II) lacks intrafibrillar mineral with severe compromise of dentin mechanical properties. A Dspp knockout (Dspp–/–) mouse, with a phenotype similar to that of human DGI-II, was used to determine if poly-L-aspartic acid [poly(ASP)] in the “polymer-induced liquid-precursor” (PILP) system can restore its mechanical properties. Dentin from six-week old Dspp–/– and wild-type mice was treated with CaP solution containing poly(ASP) for up to 14 days. Elastic modulus and hardness before and after treatment were correlated with mineralization from Micro x-ray computed tomography (Micro-XCT). Transmission electron microscopy (TEM)/Selected area electron diffraction (SAED) were used to compare matrix mineralization and crystallography. Mechanical properties of the Dspp–/– dentin were significantly less than wild-type dentin and recovered significantly (P , 0.05) after PILP-treatment, reaching values comparable to wild-type dentin. Micro-XCT showed mineral recovery similar to wild-type dentin after PILP-treatment. TEM/SAED showed repair of patchy mineralization and complete mineralization of defective dentin. This approach may lead to new strategies for hard tissue repair.
I. INTRODUCTION
Most naturally mineralizing load-bearing tissues, such as bone and dentin, are composed of type I collagen fibrils and noncollagenous proteins (NCPs) that form a scaffold reinforced with intrafibrillar and extrafibrillar minerals.1,2 The two hydrolysis products of the dentin sialophosphoprotein (DSPP), the dentin sialoprotein (DSP) and dentin phosphoprotein (DPP), have been shown to be critical for proper dentin biomineralization that is attributed to their highly anionic and calcium binding properties.3,4 Human genetic studies have demonstrated that mutations in the DSPP gene result in dentinogenesis imperfecta type II (DGI-II),5,6 characterized by dentin hypomineralization and lack of intrafibrillar mineral with severe compromise of the mechanical properties of dentin.1,2 Most interestingly, animal studies revealed that Dspp Contributing Editor: Michelle L. Oyen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.406 J. Mater. Res., Vol. 31, No. 3, Feb 15, 2016
knockout (Dspp–/–) mice have dentin defects that closely resemble human DGI-II.7 These mice may serve as a model for human DGI-II and would provide a unique opportunity for the study of the importance of NCPs on mineral– collagen interaction and biomechanical response.
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