Research Of Dentin Biomineralization Under Simulated Physiological Pulpal Pressure In Vitro

Background:The dentin biomineralization is completed under a nonclassical ion mediated pathway.Mineral molecules gather to become the nanoparticle precursor phase of amorphous calcium phosphate(ACP)under the fonction of non-collagenous proteins(NCPs),as clumps of Ca2(HPO4)32-with a low interfacial energy.Then with the induction of NCPs,ACP get close to the demineralized collagen fibers and gather into crystal orderly.Remineralizated from bottom to top,the demineralized collagen fibers complete intrafibrillar and interfibrillar remineralization.Biomimetic mineralization technology simulate this way of mineralization,without of the seed crystal.This is suited for dentin remineralization.During the remineralization,the dentin permeability must be considered.Study after study has shown dentin penetrating fluid will affect the combination of the repair materials and dentin.Dentin bonding etch surface dentin to make collagen fiber exposed with acid,that makes resin bonding get more mechanical retention force.However,dentin tubule constantly seeping liquid outward which makes the exposed collagen fiber surrounded by a lot of water for the existence of pulpal pressure.From near the pulp to cemento-enamel junction,the number of dentin tubule reduce from 45000/mm2 to 20000/mm2,and the tubule diameter reduce from 2.37?m to 0.63?m.Nearby the cemento-enamel junction,dentin tubule account for 1%of the total area of the dentin.When deep to near the pulp,this number rise to 22%,which means the proportion of water also rise to 22%.The water cannot be completely replace by resin monomer,leading to the emergence of mixing layer micro leakage and the aging of collagen degradation.The purpose of biomimetic mineralization technique is to complete intrafibrillar and interfibrillar remineralization in the resin thinning and watering area of hybrid layer to improve the effect of resin-dentin bonding?Certainly,this process is occurred under the pulpal pressure.Then,whether it will be suppressed for the influence of the dentin permeability like resin bonding or not,we don't know.In order to discover the possible influence of dentin permeability to dentin biomimetic mineralization,we simulate pulpal pressure and study the difference of remineralization of demineralizated dentin with or without pulpal pressure to explore the influence of dentin permeability on dentin biomineralization under simulated pulpal pressure,which will be help to the clinical application of biomimetic mineralization technology.Objective:This experiment was to study the influence of dentin permeability on dentin biomineralization under simulated pulpal pressure,study the difference from without simulated pulpal pressure,to judge if dentin permeability will inhibit remineralization and try to explore the mechanism.Methods:The dentin specimens were randomly allocated into three groups:blank control group is composed of demineralizated dentin,n=6;control group is composed of different days remineralizated dentin without simulated pulpal pressure,n=18;the experimental group is composed of different days remineralizated dentin under simulated pulpal pressure,n=18.Get samples from the control group and the experimental group after1,4,and 7 days.All the samples will be cut into 1 mm thick dentin slices for surface on the Boeckeler Instruments,then fixed,dehydrated,dried and kept in vacuum drying oven for 24 hours.Observe the difference of remineralizated dentin with and without simulated pulpal pressure under transmission electron microscope(TEM)and scanning electron microscope(SEM).Result:TEM micrographs indicate that after same days of mineralization,the remineralized dentin layer in control group is thicker than layer in the experimental group.And 7 days later,the demineralized dentin layer in control group have all remineralized.However,there is still a thin layer of demineralized dentin layer in the experimental group.SEM micrographs indicate that,with the mineralizating time increases,collagen fiber diameter thicken significantly in control group and the experimental group.After mineralizated for same time,we find that remineralizated collagen fiber in the experimental group is thinner and sparser than fiber in control group.In the vertical section,we find that the demineralizated dentin tubule without simulated pulpal pressure is remineralizated thicker in control groupthe than in experimental group.Conclusion:Under simulated physiological pulp pressure in vitro,calcium and phosphate concentration was reduced by the water produced continuously for the exist of dentin permeability,ACP particles produced by the reaction become bigger,the total free energy is decreased,the rate of phase transition to HAP is slower,which makes the HAP crystal expand more slowly on the surface of the demineralized collagen fibers,as a result,delay the process of biomimetic mineralization.