| The restoration of endodontically treated teeth has been a concern of dentists for more than 100 years. Especially when there is no e-nough tooth structure, a post restoration appears to be of prime important. But there are still some questions during the clinical procedures of post - based restorations, which cannot be ignored. Dislodgement of posts and root fracture are the most common reasons of failure. This in vitro study compared the retention of posts fabricated in different methods and cemented with various cements in order to provide guidance for clinical choice of post fabricating methods and luting cements.Material and Methods1. Ninety intact extracted human maxillary anterior teeth were sectioned at the cementoenamel junction and post - holes were prepared to a depth of 9mm with a 1. 2mm ParaPost drill, which is matched to the Parapost.2. All roots were embedded with autopolymerizing resin in plastic cylinder, 20mm high and 15mm in diameter, located in center and paralleled with the cylinder. All samples were divided into 9 groups randomly and equally. Posts fabricated with different methods werethen cemented respectively with different luting cements.3. Each sample was placed into a specialized jig and mounted in a tensile testing machine with crosshead speed of 5mm/min. Constant tensile force was applied until the post was dislodged, and the tensile force required to dislodge the cemented post was recorded.4. A two -way analysis of variance (ANOVA) was performed to compare the results.ResultsParapost with Parapost cement obtained the highest retention value. Indirect post with zinc phosphate cement (ZPC) obtained the lowest retention value.Parapost and direct post demonstrated significandy higher retention than indirect post (P <0.05) , but there was no significant difference between Parapost and direct post(P >0. 05) ; Parapost cement demonstrated significandy higher retention than ZPC and HY - Bond cement (P <0. 05) , but there was no significant difference between ZPC and HY - Bond cement( P > 0.05 ).DiscussionThe friction between post and dentin and the bond of cements contributed to the retention of posts. The value of friction is related to the contact area and closeness of fit. Therefore, if the length and the diameter are same, precision of fit is one of the most important factors that affect the retention of posts.Prefabricated posts are new post - core systems. Different prefab-ricated posts have different surface designs. Generally, posts fabricated with this method have good adaptation and can provide large retention. Posts fabricated with direct method cannot be deformed easily. When properly prepared, they can conform to a. canal of any shape to provide maximum retention and allow a more even dispersion of stress throughout the total root. Compared to prefabricated posts, direct -posts have a wide range of clinical use, but their fabricating technique is complicated. When a post is fabricated with indirect method, the impression of canal relies on good impression material and technique. Posts fabricated with this method have poor adaptation, and usually have a taper end. Researches showed that retention of tapered posts is 50% less than parallel - sided post. The result of our study is that the retention of indirect - posts is significantly less than direct - posts and prefabricated posts.It can be concluded from table2 and 4 that retention values obtained from the three different luting cements were statistically different. This may be related to the different character of cements. ZPC does not chemically bond to any substrate and provides a retentive seal by mechanical means only. Therefore, the taper, length, and surface area of the tooth preparation are critical to its success. GIG are thought to adhere to tooth structure by formation of ionic bonds at the tooth - cement interface as a result of chelation of the carboxyl groups in the acid with the calcium and /or phosphate ions in the apatite of enamel and dentin.Adhesion... |
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