The Study On The Effects Of Different Cements On The Bonding Properties Between Root Canal Dentins And Fiber Posts

The rehabilitation of the severely destroyed teeth is a great tendency in thedevelopment of dentistry. It displays the idea of preservation to some extend.Based on thisidea, the technique of post-core restoration developed rapidly.To reconstruct the normalshapes and functions of severely destroyed teeth, the post-core restoration is necessary toprovide sufficient support and retention for the full crown.Nowadays, various kinds ofposts are available in clinics,including cast posts, prefabricated posts, ceramic posts, glassfiber posts.Recently, glass fiber posts have been widely recommended in clinics andbecome a new trend in rehabilitation of the severely destroyed teeth owing to its variousadvantages. It has a similar modulus of elasticity as dentin, an favorable color resemblingwith natural tooth, good resistance of corrosion and so on.Up to date, success of glass fiber posts in clinics is not satisfied.However, related studies have revealed the fact thatadhesive failures between glass fiber posts and root canal dentins are main causes for therestorations which inhibit the generalization of glass fiber posts to some extend.Obviously,it is a pressing issue in stomotolgy adhesive that how to improve the bondingperformances between glass fiber posts and root canal dentins.During the adhesive procedures of fiber posts,the integrity of dentin-cement-postinterface is the key factor in determining the effect of prosthodontics.The choice of cementtype determines whether fiber post restoration is successful or not.Resin-based cement canachieve favorable mechanical property and good immediate bond strength,so it isrecommended to bond fiber posts.However, it also contains some disadvantages related tobonding performances.For example,the huge polymerization shrinkage stresses,thedegradation properties in moist environments will impair the bonding durability of glassfibre post. Glass ionomer cement is well accepted for luting cast posts and cores up to date.Moreover, there is also a postmaturation hydroscopic expansion in it.Whether it could beused to lute the glass fiber post achieving a favorable interface integrity and a goodretention in the root canal is an issue concerned with clinicians.The purpose of this study based on the above issue was to evaluate the bond strengthwith pull-out test, to observe the micromorphology of the bonded interface, to analyze thesealing ability by dye penetration with methylene blue.Consequently, the effects ofdifferent cements on the bonding properties can be investigated completely, to some extent,which may provide evidences for selecting the efficient cements to improve the bondingproperties especially the bonding durability of glass fibre post.The study could be divided into three experiments.In experiment one,we aim atdiscussing the effects of different cements on the bond strength of fibre posts luted withdifferent cements. According to experiment two,we evaluate the sealing ability of bondedinterface luted with different cements. Experiment three is focused on the observation ofthe bonding interfaces luted with different cements.In experience one,the immediate bond strengths of glass fibre posts luted with four different cements were compared.Then the thermocycling and thermomechanical loadingaging model were respectively constructed to evaluate the durable bond strengths of glassfiber posts luted with different cements.The results showed that different cements havedifferent effects on the bond strengths between fiber posts and root canal dentins.Considering the immediate bond strength,RelyX ARC achieved the highest bondstrength(277.500±26.072N),followed by RelyX Unicem(218.570±12.366N),Fuji CEM(104.300±23.112N),Fuji I(73.150±8.187N),a significant difference could be acquiredamong four different cements. After different aging treatments,RelyX ARC still performedthe best among different groups. Then compared with the immediate groups, Fuji I andFuji CEM displayed an obvious increase in bond strength,whereas RelyX Unicem andRelyX ARC displayed a decrease tendency in the bond strength.In experiment two, in order to evaluate the sealing ability of the bonding interface,the dye penetration with methylene blue was used. Likewise, there was also two agingmodel,namely,thermocycling model and thermomechanical loading model.The sealingabilities were also evaluated after aging treatments with methylene blue dye penetration.The result was showed that different cements have different effects on the sealing abilitiesof the interfaces between glass fiber posts and root canal dentins.Fuji I and Fuji CEMachieved better sealing ability than RelyX Unicem and RelyX ARC in the immediategroup.After different aging treatments,Fuji I and Fuij CEM both performed better sealingability in respective aging conditon, compared with that of RelyX Unicem and RelyXARC.In experiment three, the micromorphology of the immediate bonding interfaces lutedwith four different cements were observed.Then the thermocycling and thermomechanicalloading aging model are respectively constructed.The bonding interfaces after differentaging treatment were also observed.According to the results,different cements havedifferent effects on the bonding interfaces. In the immediate group,there are some littlegaps between cement and fiber post in Fuji I,whereas an impact interface is achieved inother groups. After different aging treatments, Fuji I and Fuji CEM especially Fuji CEM achieved a better interface compared with the immediate one, whereas there were worseinterfaces mainly between post and cement in RelyX Unicem and RelyX ARC groups.