A Comparative Evaluation of the Fracture Resistance of Five Different Dowel Systems in Endodontically Treated Mandibular First Premolars: An In Vitro Study

INTRODUCTION: An extensive tooth structure loss significantly weakens the remaining tooth, making dowel, core and crown necessary. The chief function of a dowel is to strengthen the tooth and to improve the retention of extra coronal restorations of non-vital teeth. Loss of retention is the most frequent cause of dowel failure. The interaction of many factors, such as the design of the tooth preparation, fit of the casting, dowel diameter and the design, dowel length, luting medium, cementation procedure, surface characteristics and location in the dental arch appears to influence the potential for dislodgement. Dowels with greater retention are more resistant to dislodgement due to occlusal stresses. AIMS & OBJECTIVES: To determine the fracture resistance and mode of failure of five different types of dowel systems. METHODOLOGY: Fifty freshly extracted intact human mandibular premolars decoronated at a level of 2mm from the Cemento-enamel junction were endodontically treated. Five groups of ten specimens were formed (N=50).Specimens were immersed in distilled water and maintained at 370C for 72 hrs. Root canal post space preparation was initiated using gates glidden drill to remove 8mm of filling material. Each specimen was restored with posts of five different types. This included Cobalt Chromium cast metal post (group 1), Glass Fiber reinforced post (group 2) Carbon post (group 3) Stainless Steel post (group 4) and Zirconium post (group 5) of 1.3mm diameter. The test specimens were cemented using Composite resin luting cement and control groups were cemented using Zinc phosphate cement. The roots were further embedded in cylindrical acrylic resin blocks of 3cm x 2cm size. The specimens were loaded in a universal testing machine (Model 3345 Instron Corp) and a compressive load was applied at 90 degree to the occlusal surface until fracture, at a cross head speed of 1mm/min. RESULTS: Fracture resistance of specimens of each group was determined using Universal testing machine by applying a static compression load and the maximum load at break was recorded. The value of maximum load at failure ranged between 4.19 KN and 5.32KN for the samples of Group1 during the compression test. The value of maximum load at failure of Group 2 was between 1.83 KN and 2.42KN, for Group 3 ranged between 1.41 KN and 2.19KN, for Group 4 ranged between 1.14 KN and 1.86 KN and for Group 5 ranged between 1.96 KN and 2.60 KN. SUMMARY: The present study was done to evaluate the fracture resistance of five different post systems which were commonly used for restoring endodontically treated teeth with major loss of coronal tooth structure. The study concluded teeth restored with cast metal posts and cores exhibited the highest fracture resistance when compared with the other prefabricated post used in the present study. The teeth restored with Zirconia posts showed catastrophic vertical root fracture. CLINICAL IMPLICATIONS: From the data obtained from the present study fiber reinforced composite post and carbon fiber posts can be suggested as best options of reinforcing endodontically treated teeth with loss of coronal tooth structure. As the zirconia posts showed vertical root fracture they should be avoided in case of patients with para-functional habits. CONCLUSION: Within the limitations of the study, the following conclusions were drawn. 1. Teeth restored with Cast Metal posts and cores exhibited the highest fracture resistance. 2. The teeth restored with cast posts and prefabricated posts showed significant difference in fracture resistance. 3. Teeth with Glass Fiber Reinforced Composite post exhibited fracture resistance closer to carbon and zirconia posts. 4. Carbon fiber posts exhibited fracture resistance which was higher than Stainless Steel posts. 5. Stainless Steel post had a significantly lower fracture resistance when compared to all the other post systems used in the present study. 6. Shearing of the cast post was observed at high loads which is not desirable due to its detrimental effect on the surrounding tissues. 7. The teeth restored with Zirconia posts showed catastrophic vertical root fracture, hence should be avoided in case of patients with para-functional habits. 8. Fiber Reinforced Composite post and Carbon fiber post showed fracture of post and not the root. Hence the above mentioned posts can be used for patients with higher masticatiory load thus preserving the remaining tooth structure. From the data obtained from the present study it can be concluded that the Fiber Reinforced Composite posts and Carbon fiber posts can be suggested as best options for reinforcing endodontically treated teeth with loss of coronal tooth structure. These post systems with favorable properties and retrievability can be considered as ideal material of choice among various dowel-core systems. Along with the best choice of material, the monobloc effect and the ferrule effect should also be created for a clinically successful post and core system.