Year : 2008 | Volume
: 19 | Issue : 1 | Page : 17--21
The effect of post-core and ferrule on the fracture resistance of endodontically treated maxillary central incisors
Dakshinamurthy Sendhilnathan, Sanjna Nayar
Department of Prosthodontics, Meenakshi Ammal Dental College, Maduravoyal, Chennai - 600 095, Tamil Nadu, India
Department of Prosthodontics, Meenakshi Ammal Dental College, Maduravoyal, Chennai - 600 095, Tamil Nadu
Aim: To evaluate the effect of post reinforcement, post type and ferrule on the fracture resistance of endodontically treated maxillary central incisors.
Materials and Methods: Sixty central incisor teeth were selected and grouped into six groups, viz. A, B, C, D, E, and F, each consisting of 10 specimens. Group A specimens were not subjected to any restorative treatment. Group B specimens were endodontically treated and crowned. Specimens of groups C and D were restored with custom cast post and core. Specimens of groups E and F were treated with prefabricated titanium post and composite core. Specimens of groups C and E were restored with porcelain-fused metal (PFM) crown having 2 mm ferrule. Specimens of groups D and F were restored with PFM crown having no ferrule. All the specimens were subjected to load (newton, N) on the lingual surface at a 135° angle to the long axis with a universal testing machine until it fractured. The fracture load and mode of fracture of each specimen were noted. One-way analysis of variance with Tukey honestly significant difference procedure was employed to identify the significant difference among the groups at 5% level (P < 0.05).
Results: There were significant differences among the six groups studied (P < 0.0001). The highest fracture strength was recorded with specimen of group C (1376.7 N). There were significant differences between groups A and D versus groups B, E, and F. There were no significant differences between groups B, E, and F. Cervical root fracture was the predominant mode of failure in all the groups except group A.
Conclusion: The results showed that endodontically treated teeth restored with custom cast post core were as strong as the untreated group. Teeth restored with custom cast post core were better resistant to fracture than teeth restored with prefabricated titanium post and composite core. Ferrule is more important in custom cast post core than in prefabricated post and composite core.
|How to cite this article:|
Sendhilnathan D, Nayar S. The effect of post-core and ferrule on the fracture resistance of endodontically treated maxillary central incisors.Indian J Dent Res 2008;19:17-21
|How to cite this URL:|
Sendhilnathan D, Nayar S. The effect of post-core and ferrule on the fracture resistance of endodontically treated maxillary central incisors. Indian J Dent Res [serial online] 2008 [cited 2023 Feb 6 ];19:17-21
Available from: https://www.ijdr.in/text.asp?2008/19/1/17/38926
Restoration of endodontically treated teeth is a challenging endeavor. They are more prone to fracture due to loss of moisture supplied by the vital pulp. Extensive structural defects due to decay, trauma, and prior restoration call for post and core restoration. Many techniques have been advocated for post and core fabrication. Custom cast post core has been regarded a "gold standard" in post and core restoration. Bregman  reported 90.6% success rate after 6 years of service for custom cast post core. Fabrication of custom cast post core is a two-stage procedure. Prefabricated post and composite resin core build-up simplifies the procedure into single stage. Scientific literature reveals many controversies regarding the use of different post core systems in the management of endodontically treated teeth. Lovdahl and Nicholls  found that endodontically treated unrestored teeth were twice as resistant to fracture than the post-reinforced teeth. Zhi-yue and Yu-Xing  reported that teeth with custom cast post core were more resistant to fracture than endodontically treated teeth. Isidor et al .  observed that prefabricated post and composite core are more resistant to cyclic loading than custom cast post and core. Heydecke et al .  found no difference in fracture resistance between prefabricated post core and custom cast post core. Dental ferrule is an encircling band of cast metal around the coronal surface of the teeth. The use of ferrule as a part of the artificial crown was proposed in reinforcing the root-filled teeth.  However, the need of ferrule in prefabricated post and core is questioned by Al-Hazaimeh and Gutteridge. 
Therefore, the present study was aimed to evaluate fracture resistance of endodontically treated teeth restored using custom cast post and core or prefabricated post and composite core with or without ferrule in the artificial crown. The objectives were:
To compare the fracture resistance of untreated teeth with endodontically treated teeth.To compare the fracture resistance of endodontically treated teeth with and without post-reinforcement.To compare the fracture resistance of custom cast post core and prefabricated post and composite core.To evaluate the effect of ferrule on the custom cast post core and prefabricated post and composite core.
Materials and Methods
A total of 60 human maxillary central incisors were selected from a collection of extracted teeth stored in a solution of neutral buffered formalin for less than 3 months at room temperature. Teeth with root caries, restorations, previous endodontic treatment, and cracks observable at a magnification of 2× were not included.
Sixty teeth were divided into six groups, each containing 10 specimens, namely A, B, C, D, E, and F [Table 1]. No restorative treatment was performed on the teeth of group A. Group B specimens were endodontically treated and crowned. The specimens of groups C and D were restored with custom cast post and core. The specimens of groups E and F were treated with prefabricated titanium post and composite core. The length of each tooth was measured from apex to incisal edge. The labiolingual and mesiodistal dimensions of each tooth were recorded at the level of cervical margin. All the dimensions were measured using a digital caliper (Denta Gauge, Eriskine Dental, USA). Analysis of variance (anova) with Tukey honestly significant difference (HSD) was employed to identify the difference between the groups at 5% ( P Post and core fabrication
Two weeks after root canal treatment, post channels were prepared. Specimens of groups C and D were prepared using Peeso Reamer (Mani Inc) starting from no.1 to no. 5 in a slow-speed handpiece (NSK), leaving a 4-mm apical seal. Root canals were coated with a thin layer of petrolatum using paper points. Direct resin post and core patterns were made using auto-polymerizing acrylic resin (DPI, India). The patterns were invested and cast in Ni-Cr alloy (Wiralloy, Bego, Germany). After casting, minor imperfections were removed, if present. The post and core were tried with the corresponding teeth. Zinc phosphate cement (Harvard Cement, Germany) was used to cement groups C and D post cores. The cement was mixed according to the manufacturer's direction using glass slab and cement spatula and spun into the channels with a lentulo spiral (Brassler, USA) before seating the castings firmly with finger pressure for 5 min.
Specimens of groups E and F were prepared initially using Peeso Reamer starting from no. 1 to no. 4 and finished using no. 4 Dentatus Post Reamer (Dentatus, Sweden) of 1.5 mm diameter in a slow-speed handpiece to accommodate Dentatus L Prefabricated Post (Dentatus) of 11.5 mm length leaving a minimum of 4 mm apical seal. Post head of 1.5 mm was extending over the post space. The posts were cemented with zinc phosphate cement. The cement was mixed according to the manufacturer's direction using a glass slab and cement spatula and spun into the channels with a lentulo spiral before seating the posts firmly with finger pressure for 5 min. The coronal core portion was made with light polymerized core build-up composite resin (Heraeus Kulzer, USA). The remaining coronal tooth portion and post head were etched (Gluma Etch; Heraeus Kulzer, USA) for 15 s, rinsed, and air-dried. Two layers of a dentin bonding agent (Gluma-comfort Bond; Heraeus Kulzer) were applied to the cervical dentin and coronal portion of the post and were light polymerized for 20 s. Three increments of the composite were applied to complete the coronal core, each requiring 40 s of photo-polymerization to complete the coronal core. Radiographs were made in labiolingual and mesiodistal direction for each specimen to determine whether there was more than 1 mm remaining root dentin around the post.
Preparation for porcelain-fused metal (PFM) crowns
Impressions of prepared specimens were made with polyvinyl siloxane impression material using plastic trays and were poured using die stone. PFM crowns were fabricated using Ni-Cr alloy and vita VMK95 porcelain by a skilled technician, who was uninformed of the group design. The form of the final PFM crown was confirmed with the initial silicone index. Zinc phosphate cement was used to cement the crowns. The prepared specimens were then stored in 100% humidity for 30 days at room temperature to simulate the humidity in vivo until they were returned for testing.
Fracture strength testing
A custom-made jig, which would fit exactly in the retaining arm of the universal testing machine, was made [Figure 1]. It had a rectangular block of metal placed 6 mm from the center of the proposed loading axis. The rectangular block had a hole of 12 mm diameter, which was designed to be at 135° to the proposed path of loading. Die stone analog of the hole was obtained from the putty polyvinyl siloxane impression material. Central line was marked using a protractor in the die stone analog. Teeth were mounted parallel to the central line using an auto-polymerizing acrylic resin, which was positioned 2 mm below the cementoenamel junction. The custom-made jig was positioned in the universal testing machine. The mounted teeth were placed in the custom-made jig. A steel rod with a rounded end in the universal testing machine was used to load the teeth at the angle of 135° to the long axis of the teeth with a cross-head speed of 5 mm min -1 . All the teeth were loaded 3 mm below the incisal edge at the middle of the lingual surface [Figure 2]. The specimens were loaded until fracture occurred. The load values were measured in newtons (N). The mode of fracture of each specimen was recorded.
One-way anova was used to compare the mean loads for each group. The dependent variable was the load required to fracture the specimens. Tukey HSD procedure was employed to identify the significant groups at 5% level. All the results were considered statistically significant if P P  and Zhi-Yue and Yu-Xing.  The reasons for increased fracture resistance are:
The custom cast post core was made to fit the shape of the post space, which helps in better transmission of the stress.It was more rigid than the titanium prefabricated post tested. 
In this study, it was observed that the fracture resistance of endodontically treated maxillary central incisors restored without any post (group B) performed similar to prefabricated post-reinforced teeth (groups E and F). Thus, by reinforcing the endodontically treated teeth with minimum tooth structure with post and core, its fracture resistance can be made at par with that of a crowned endodontically treated tooth. It was demonstrated that there is a decrease in fracture resistance from natural tooth (group A) to crowned endodontically treated tooth (group B). It is due to the fact that crowned endodontically treated teeth was weakened centrally by the access cavity preparation and peripherally by the preparation needed to accommodate both ceramic and metal. Thus, the recommendation of Schillingburg et al.  that endodontically treated teeth that require metal ceramic crowns need a post core restoration seems to be logical.
Many studies have been carried out to investigate the ferrule effect in root-filled teeth, and many suggest that ferrule should increase resistance to fracture. , To achieve the full benefit of ferrule effect, it should be a minimum of 1-2 mm in height, have parallel dentine walls totally encircling the tooth, and ending on sound tooth structure. The consensus is that:
A properly constructed ferrule significantly reduces the incidence of fracture in nonvital teeth by reinforcing the teeth at its external surface and redistributing the applied forces, which concentrate at the narrowest point around the circumference of the tooth.  It helps to maintain the integrity of the cement seal of the crown. 
It has been suggested by Eissmann and Radke  that maintaining 2 mm of tooth structure above the gingival margin is beneficial. In contrast, others found no benefit of adding a ferrule to the preparation of endodontically treated tooth. , Only a few authors have considered prefabricated post and cores. Al-Hazaimeh and Gutteridge  questioned the additional need of ferrule on a crowned tooth incorporating a prefabricated post and composite core. The present study was aimed at comparing the effect of ferrule on the custom cast post core and prefabricated post core. The ferruled specimens (groups C and E) when compared to their corresponding unferruled specimens (groups D and F) showed higher mean fracture load. However, statistically significant result was noted only in custom cast post core. No such difference was observed in prefabricated post and composite cores.
Pierrisnard et al.  in their finite element analysis noted that the cervical region of post-restored teeth was subjected to maximum tensile stress, which increases the risk of fracture. Many studies have been reported stating cervical third root fracture as the major mode of fracture. , Zhi-Yue and Yu-Xing  reported apical third root fracture as the common mode of fracture. In the present study, cervical third root fracture was the predominant fracture pattern. Such mode of fractures can be restored in clinical situation. The tapering end post design used in the study resulted in less number of apical root fracture, which, in a clinical situation, would demand extraction of the tooth itself.
The following conclusions were drawn from the study:
The results showed that endodontically treated teeth restored with custom cast post core were as strong as the untreated group.Teeth restored with custom cast post core with 2 mm ferrule showed highest resistance to fracture.Teeth restored with custom cast post core showed better resistance to fracture than teeth restored with prefabricated titanium post and composite core. Hence, in incisors, cast post cores are preferred to other systems.Ferrule had a significant role in the fracture resistance of custom cast post core restored teeth.Additional use of ferrule preparation on a crowned tooth incorporating a prefabricated post and composite resin core restoration provided no improvement in fracture resistance.
We would like to acknowledge Dr. K. Chandrasekaran Nair, MDS, Professor and Head, Department of Prosthodontics, Maruti Dental College, Bangalore, for his timely suggestions.
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