Dissertation committee:
Τζούτζας Ιωάννης, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Ηλιάδης Γεώργιος, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Μουντούρης Γεώργιος, Αναπληρωτής Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Κακάμπουρα Αφροδίτη, Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Παπάζογλου Ευστράτιος, Αναπληρωτής Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Παξιμαδά, Χάρις, Επίκουρη Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Παπαβασιλείου Γεώργιος, Επίκουρος Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Summary:
INTRODUCTION
The restoration of the endodontically treated tooth in order to achieve optimal durability, aesthetics and function still remains a challenge. The dental industry has identified a large variety of prefabricated fiber reinforced composite posts, varying in size, shape and taper. These posts are used in conjunction with the composite core build up materials, in order to create a homogeneous biomechanic unit.
PURPOSE
The purpose of this study is to investigate the parameters affecting the bonding of different core build up restorative materials to the coronal surface of different fiber reinforced composite posts using alternative treatments for the post surface. The null hypothesis was: (1) the morphology of the coronal part of the post does not positively affect the bond with the restorative material, (2) the choice of the restorative material does not affect the bond with the fiberglass post and (3) the surface treatment of the post by various techniques has a positive effect on bond strength.
MATERIALS AND METHODS
Five different types of fiber reinforced composite posts with variation in the morphology of their coronal section were used: [(ParaPost Fiber White /PRW, Fibrekleer/FBK, Archimede Line/ARL, Matrix Plus/MTL, Glassix/GLX). The bond strength was evaluated using three core build up materials: a photo cured composite (Clearfil Photocore/ CPC), a self-cured composite (Clearfil Core New Bond/CNB) and a dual cured composite (Clearfil DC CoreCDC). The alternative treatments used were silane (Clearfil Ceramic Primer/SPC), a bonding agent (Clearfil DC Bond/DCB )and no treatment. Using unique manufactured metal components, 90 specimens per post were prepared with all possible combinations. The speciments were led to fracture in a tensile machine. For each specimen, the fracture value was recorded and graphs were obtained from the start of the experiment to the complete destruction of the specimen. After the fracture the samples were examined in a stereoscope and scanning electron microscope in order to evaluate the failure mode and type of fracture. The types of failures were classified as Type I (post detachment from the core), type II (core fracture with intact post), type III (post fracture at the free middle portion) and type IV (post fracture into the epoxy resin).
The statistical analysis was performed using the Factorial ANOVA * method in the form of 5X3X3 (post / material / treatment) and bond strength was a dependent variable. The resulting statistical indicators were F for the overall statistical evaluation and the LSD (Least Significant Difference) for the individual statistical evaluations. For statistical comparisons among posts and core materials Weibull analysis was employed. The reliability (β-shape parameter), fracture probability (σο-scale parameter), correlation coefficient (r2) and 95% confidence intervals (CI) were calculated and compared. The statistical analysis was performed using the OriginLab software (v.9.1 SRO, Northampton, MA, USA). For all cases, a 95% confidence level was used. The elemental composition of the posts with the X-ray energy dispersive spectrometry unit (Saphire EDAX, Mahwah, NJ, USA) was also studied.
RESULTS
The treatment did not appear to differentiate the bond strength at a statistically significant level (F2 = 0.91, p = 0.403). For this reason, the treatment was excluded from the further analysis.
All curves demonstrated an initial peak, considered as the breaking point, with a secondary lower-slope loading prior to complete debonding. For smooth posts, the secondary loading phase was negligible. However, a small stepwise secondary loading pattern was observed in posts with retentive features in their main body, rather than the coronal part. The statistical ranking of post reliability (β) per core build-up material showed statistically significant differences only in CPC with a ranking FBK,PRW>ARL,GSX. MTP demonstrated insignificant difference from both these statistically homogeneous groups. For the reliability of core materials per post, statistically significant differences were found only in ARL (CDC>CNB, with CPC manifesting no significant difference from each) and PRW (CPC>CDC>CNB). The statistical ranking of characteristic life (σο) of posts per core build-up material were MTP,ARL>PRW>FBK>GSX for CPC, ARL,MPT>PRW,FBK>GSX for CDC and ARL,MPT>MTP,FBK>GSX for CNB, with PRW exhibiting significant higher values only from GSX. The characteristic life of core materials per post were: CPC,CDC>CNB for FBK, CPC>CDC>CNB for GSX, CPC>CNB with CDC showing no differences from each for MTP and CPC>CDC with CNB having no differences from each for PRW. No differences were registered for any of the core materials in ARL.
GSX and PRW demonstrated the highest (93%) and MTP, FBK the lowest (5-10%) incidence of post detachment from core (type I failure), irrespectively of the composite build-up material used. The highest overall percentage of core material fracture (type II failure) was observed in FBK (37%), followed by MTP (22%), ARL, PRW (7% each) and GSX (no fracture). Most core material fractures occurred in CDC (57%), less in CNB (11%) and the least in CPC (6%). Post fractures at the free middle portion (type III failures) were most prominent in MTP (17%), followed by GSX (7%), ARL (4%) and the group of FBK, PRW (no fractures). CNB was the core material with the highest 10% type III failures, CPC exhibited 6% and CDC only 1%. No post apex fractures into the epoxy resin were documented for GSX and PRW. However, this type of failure was observed in ARL (58%), MTP (56%) and FKB (53%) irrespectively of the core material used. The ranking of type IV failures within the core materials groups was CPC(47%), CNB (38%) and CDC (16%).
The results of the elemental postanalysis showed that they all contained O, Mg, Al and Si. Two posts contained Ba (PRW and FBK), one Zr (GLX), three Ca (ARL, GLX, MTP) and one Yb (FBK). All of these elements are used in compounds that provide radiopacity to the posts.
CONCLUSIONS
Through the limitations of this study can be obtained the following conclusions:
1. As for the maximum tensile strength of the the coronal parts of the posts , the ranking of the posts used was FBK> ARL> MTP> PRW> GLX and CPC> CNB, CDC for the core build up materials. There was no statistically significant difference in treatment parameter (no treatment, silane, bonding agent).
2. As to the probability of failure, the coronal parts of ARL and MPT posts were the strongest while the GLS the least, irrespective of the material used. The CPC provided the highest retention with four posts (FBK, GSX, MTP, PRW), with no statistically significant differences from the CDC in two (FBK, MTP) and the self-polymerizing CNB on one post (PRW). The CPC and CDC were the most reliable materials fror two posts (ARL, PRW) and no statistically significant difference from the CNB for three posts (FKB, GSX, MTP). The presence of specific coronal retention features on some posts (ARL, PRW) did not ensure a reduced probability of failure due to shear fracture of the retentive features.
3. In terms of the elemental composition of the posts, small differences were observed in the type of glass used (elemental ratios of O, Mg, Al, Si and Na), but significant differences in the data for radioopacity (Ba, Ca, Zr, Yb).
