Reinforcement effect of adhesively luted fiber reinforced composite versus titanium posts
Introduction
The load capability of endodontically treated teeth (ETT) is influenced by the number of adjacent teeth [1], number of occlusal contacts [2], [3], tooth position in the dental arch [4], [5], crown placement [6], [7], type of abutment [4], [8], apical status [9], collagen degradation [10], intermolecular cross-linking of the root dentin [11], and as a crucial aspect by the amount of lost hard tissue [12], [13], [14]. The advantage of a 1.5–2.0 mm deep ferrule preparation is well proven [15].
Since ETT often suffer extensive defects, post placement is often clinically necessary to generate retention to core and restoration [11], [16]. It was previously stated that further research is needed to elucidate whether a high or low elastic modulus of post and core materials helps to distribute occlusal forces to remaining dentin and improves the clinical outcome in the oral environment [17]. The modulus of elasticity (Young's modulus) is defined as slope of the stress–strain curve within the elastic limit [11].
The choice of an appropriate post material is controversially discussed [18]: fiber reinforced composite posts (FRC post) have been recommended due to their dentin-like Young's modulus [19], [20]. FRC posts allow teeth to flex under applied loads leading to an improved stress distribution between post and dentin [21]. The risk of root fracture should be reduced [22], but may concentrate stress between cement and endodontic post resulting in loss of adhesion [23]. Further it is argued that a more rigid post would allow less invasive preparations with smaller post diameters [17], [24] and avoid deformation of the entire post–core assembly [25]. Root fractures have been attributed to extreme differences in rigidity of post and root dentin with stress concentrations inside the root [23]. Torbjorner et al. [18] summarize that there is the choice between a low modulus post possibly leading to reparable failures, or a high modulus post with probably later but more irreparable failures.
Since it still remains unclear which endodontic post material is preferable for post-endodontic restoration, this study was carried out to investigate the impact of a rigid material (titanium) in comparison to a more “flexible” post material (FRC). The influence of ferrule preparation, composite build-up alone and post-build-up complex was furthermore evaluated. As a null-hypothesis it was stated that there is no difference in the load capability irrespective of the post material used.
Section snippets
Materials and methods
The methodology of specimen preparation and loading was adopted from Butz et al. [26]. Forty-eight caries-free, undamaged human maxillary central incisors were divided into six groups (n = 8) on the basis of cervical size. To ensure an even distribution of the size of teeth within the specimen groups, mesio-distal (MD) and facial–lingual (FL) dimensions were measured at the level of the cemento-enamel junction (CEJ). A size assessment value was calculated from the product of MD × FL. Teeth of
Results
The results of the load test after TML and data describing the root geometry of the specimens are displayed in Table 2. One specimen each of group 0/T and 0/FRC did not survive TML. For further analysis, Fmax of these specimens was set as 0 N. Regarding the median values of Fmax after compressive loading, following the order of groups starting with the highest load values was observed: 2/T = 2/FRC > 0/T > C > 0/FRC > E. Specimens with a ferrule-supported titanium post (2/T) showed the highest values for F
Discussion
The present study was initiated to investigate the influence of the rigidity of endodontic post materials [29]. It could be shown that there is no significant impact of the post material. When placing all-ceramic crowns, the combination of dentin ferrule and post irrespective of the post material's rigidity, causes an improved load resistance compared to a ferrule or a bonded resin composite build-up alone.
Fatigue testing in an aqueous environment as performed in the present investigation is
Conclusion
Irrespective of the rigidity (Young's modulus) of a utilized post, material load capability is defined by the combination of a proper dentin ferrule and the placement of an endodontic post.
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