Canadian Health and Care: Dental treatment
Endodontically-treated teeth have greater risk of biomechanical complications compared to vital teeth. The loss of structural integrity caused by trauma, caries, access hole preparations, loss of moisture content, and reduced thickness of dentine lead to decreased fracture resistance of such teeth. Endodontic post and core systems have been commonly used to restore the missing part of the tooth structure to prevent fracture of the residual tooth and to improve retention of the final restoration.
Since cast metal or prefabricated posts materials affect the amplitude and distribution of stresses in root canal treated teeth, the biomechanical outcome is inevitably jeopardized. Recent studies show that frequent episodes of vertical fractures in roots restored with metallic posts are strongly related to high elastic modulus yielding excessive stresses at the apical third level. Such fractures is one of the major reasons for tooth extraction following placement of endodontic posts. Eventually, posts having elastic modulus similar to dentin, such as fibre-reinforced posts, gained high popularity compared to metallic post and core systems.
Fibre posts have flexural modulus similar to that of human dentin. This promotes uniform stress distribution at the post-cement-dentin interface and avoids excessive stresses that risk longevity of the restoration. It has been suggested that fibre posts luted with adhesive resin cements lead to higher fracture resistance of endodontically treated roots. In addition, high survival rates of all ceramic crowns has increased patient demands for these restorative materials, particularly in the anterior region.
Consequently, there has been a substantial increase in the use of all-ceramic crowns as well as tooth-coloured endodontic post and core materials. Among tooth-coloured post systems, glass-fibres have dominated clinical practice because of their comparable modulus of elasticity, high tensile strength, white colour and good transparency. Glass-fibre posts can be removed and replaced easily without the risk of perforating the root. Manocci et al.. investigated the intermittent loading response of teeth restored with different tooth coloured post systems (quartz fibre, carbon quartz fibre, and zirconium posts) and found that fibre posts reduced the risk of root fractures. More about healthcare at Canadian Health and Care Pharmacy website: http://www.canadian-healthcare.com
At present, posts are provided either in conventional or prefabricated monoblock types in the dental market. Dentists may prefer to use prefabricated one-piece glass-fibre post systems, because they are practical and less time-consuming. However, their effects on the fracture resistance of weakened roots still remain uncertain. This study, therefore, aimed to evaluate the effects of glass-fibre post design on the fracture resistance of extensively damaged endodontically-treated teeth.
Thirty freshly extracted, caries free human maxillary central incisors extracted for periodontal reasons having minimum 21 mm root length and single straight root canals were used in this study. The teeth were ultrasonically cleaned and the coronal parts were removed 2-3 mm from the cemento-enamel junction (CEJ) using a high-speed sawing machine (IsoMet 1000, Buehler, IL, USA) under copious water- cooling. The roots were coated with 0.2-0.3 mm thick wax (Dipping Wax, Bego Bremen, Germany) 2 mm below the CEJ, to partly allow physiological tooth movement during the experiments.
Each tooth was embedded into acrylic resin (Vertex, Vertex Dental, Netherlands) blocks 2 mm above CEJ to simulate the clinical bone level. Upon polymerization, the teeth were removed and wax was replaced with polyvinylsiloxane (Elite HD+ Light Body Normal Setting, Polesine, Italy) to simulate periodontal ligament. The roots were cleaned in distilled water and stored in formaldehyde solution.
The root canals were enlarged using ProTaper rotary instruments (Maillefer, Dentsply, Tulsa, OK, USA) with Glyde File Prep lubrication (Denstply, Maillefer, Ballaigus, Switzerland) until the file F5 reached the working length (1 mm from the apical foramen). The root canals were irrigated with 2 mL 5.25% sodium hypochlorite (NaOCl) between each file size.
To remove the smear layer, the root canals received a final rinse of 5 mL 17% ethylenediaminetetraacetic acid (EDTA). Finally, roots were irrigated with 10 ml distilled water to avoid prolonged affect of EDTA and NaOCl solutions. The canals were subsequently dried with paper points. All the samples were filled with ProTaper F5 gutta- percha and AH 26 sealer (AH 26, Dentsply, Detrey, Konstanz, Germany) in strict adherence to the recommendations of the manufacturers.
The post space preparation of each sample was carried out using Peeso-reamer size #1 and followed by dowel space drills of Ø 1.4 mm and Ø 1.7 mm, respectively to a depth of 10 mm provided in the kit from the manufacturer. In order not to deteriorate the apical seal, the post length was set to 10 mm in all samples by giving respect to 4-5 mm apical seal. Finally, walls of the roots were flared using an occlusal reduction diamond bur (905.313, Komet Dental, Germany) to a dentin thickness of 1 mm at the coronal portion to simulate a weakened tooth structure.
The samples were randomly divided into three groups for post placement: Monoblock Monocore fibre post group (MFP) (Monocore, Bioloren Metal Free Dental System, Soronna, Italy); Monoblock Fit fibre post group (FFP) (Bioloren Metal Free Dental System, Soronna, Italy); and Conventional fibre post group (CFP) (Avant Bioloren Metal Free Dental System, Soronna, Italy). Monocore and Fit post systems are fiberglass posts made of an upper part (abutment side) and a lower conical part(post side).The upper part is easily shapeable with a diamond bur for a quick reconstruction. The lower part can be inserted in a root canal and is self-threading. They both have microrough surface. They differ in designs. Monocore fiber post has a shape similar to a prepared central incisor; Fit fiber post system has a cylindrical design.
Adhesive luting agent Panavia F 2.0 (Kuraray Co., Japan) has been shown to increase the fracture resistance of excessively damaged root canal treated teeth significantly. Therefore, all posts were luted to root samples using this cement. The cement was applied to the post and root canal wall using a lentulo spiral, and light cured with dental light-curing unit (Elipar Free Light 2, 3M ESPE, Seefeld, Germany) for 10 seconds after inserting the post with finger pressure. The conventional post samples were restored with composite material (3M ESPE, Filtek Z250, Seefeld, Germany) using a silicon matrix to standardize the core length and shape. Composite was used for the FFP group, where necessary.
0.5 mm- thick zirconia copings (Cercon, Degussa, Hanau, Germany) were fabricated. After the adjustment of fit, zirconia copings were luted to the samples using the resin cement. Each sample then received thermal cycling (6000 cycles 5-55°C) with a dwell time of 20 seconds in each water bath. (Water Bath, Nuve Sanayi Malzemeleri Imalat ve Ticaret A.S., Ankara, Turkey). Specimens were loaded at 45 degree in a universal testing machine (Lloyd LRX; Lloyd Instruments Ltd, Fareham, UK) at a crosshead speed of 1 mm/min until fracture occurred.
Kruskal Wallis variance analysis was used to reveal difference in fracture resistances among groups. Pairwise comparisons were made using Mann Whitney U test. Confidence level was set to 95% for all statistical assessments. The mode of failure of each specimen was also recorded descriptively.