• **What is core?** (**Figure 1**).

It is the centre or base of the structure.

• core materials used for anterior teeth are:

1.Plastic materials like amalgam or glass ionomer cement or composites.

	- 1.Cast gold core.

2.Resin core or composite core with metal post.

3.Resin or composite core with a cast pins.

In vitro studies states that, when load is applied on a tooth, root fracture is less in teeth restored with resin core, compared with amalgam and cast gold cores [6].

Trauma and decay are often associated with an extensive loss of tooth structure, requiring a restoration for esthetic and functional rehabilitation of the tooth*.* Often caries leads to loss of tooth structure and vitality of the pulp. Endodontic treatment is necessary in such cases. Adequate anchorage for restoration cannot be achieved if a significant amount of coronal section of the tooth is lost i.e. when only one wall or no wall is remaining. To increase the retention of the restoration post and core treatment is required.

Endodontic treatment influences the strain values and fracture resistance of the remaining tooth [7]. Most of the endodontic treatment failures are influenced by masticatory load. In general, failure rates tend to increase concomitantly as occlusal load increases. Failure loads have been shown to increase as parallelism approaches the load angle between the long axes of the teeth i.e. under lateral loading, failure tends to occur more readily [8]. Teeth which are nearer to transverse horizontal axis are subjected to increased amount of load as compared to anterior teeth. The fracture resistance of the tooth is also directly proportional to remaining bulk of dentin. Post space preparation can increase the amount of dentin removed thus affecting the load bearing capacity of the tooth. To prevent the major tragedy of vertical root fracture (VRF) cases, researchers have been focusing on materials used for post fabrication, designs of the post, luting agents, and the ferrule effect.

Various types of post and core systems have been introduced in dentistry. Endodontic post and core may be cast using material such as gold and nickelchromium (Ni-Cr), or they may be prefabricated, such as titanium, stainless steel posts and fiber posts. For many years, the custom made posts have been the choice of restoration for endodontically treated teeth. However custom-made posts are technique-sensitive. The elution of the metal ions from these posts can cause metal allergy [9]. Another disadvantage of cast post being higher modulus of elasticity than dentin, which increases the risk of catastrophic failure [10]. Due to these disadvantages, these posts are progressively being replaced by titanium post. Use of a straight titanium posts requires excessive post space preparation in the curved canals [11]. This disadvantage of straight titanium post can be overcome by bendable titanium posts due to its flexible nature. Bendable titanium post can be used for various purposes, for instance, it can be included in preparation of the core when the axis of the crown of the tooth being restored has to be altered to place two or more posts, if necessary, or they can be placed in curved root canals since they can be contoured to follow the canal anatomy, thus bending internally, creating a mechanical lock for the resin core and increasing the retention surface.

Evidence remains controversial regarding the most efficient form of post for restoring endodontically treated teeth. The reduced load bearing capacity of the endodontically treated teeth being the one of the major concerns; fracture resistance provided by different posts needs to be compared.

#### **3. Review of literature**

**Standlee J, Caputo A, Collard E (1972)** [12]**,** compared three post systems in regard to their design, methods of insertion, their length and their abilities to

#### *Restoration of Endodontically Treated Teeth DOI: http://dx.doi.org/10.5772/intechopen.98190*

transmit forces to their supporting structures. According to the photoelastic stress analysis, post design affects stress distribution. Stresses tended to concentrate under the post shoulder, especially if sharp angles were present. Also ascertained was the fact that the post length should approximate the length of the anatomic crown.

**Guzy G, Nicholls J (1979)** [13]**,** compared the breaking loads of endodontically treated teeth, with and without cemented posts, to determine if the post reinforces the root against fracture. Study was performed using maxillary central incisors and maxillary and mandibular canines. Load was applied at an angle of 130 degrees to the long axis of tooth with a speed of 5 cm/min. It was concluded that teeth without posts fractured through the middle or coronal one third of the root whereas teeth with posts fractured through the body of the post and there was no statistical significant reinforcement with cementation of posts.

**Davy D, Dilley G, Krejci R (1981)** [14]**,** compared a series of designs for endodontic dowel posts, using maxillary central incisor. The tooth was examined under two load conditions, lateral load and compressive load. Both loads were treated as being concentrated along the incisal edges. They concluded the effect of taper was found to be slight if the local tapered-post diameter was comparable to the cylindrical post diameter in the high-stress region. The tapered-post design experienced slightly higher tensile and slightly lower shear stresses than the cylindrical post. Using the peak stresses in the dentin and at the dentin-post interface as a criterion, the cylindrical post with the largest diameter was the best design.

**Eshelman E, Sayegh F (1983)** [15], compared three post systems for fracture resistance. He concluded that between three post systems, ParaPost (stainless steel), custom made gold dowels and custom made composite dowels, the materials used for fabrication were not necessarily significant, but the angle of the load influenced the amount of force required to cause fracture and its location.

**Reinhardt R, Krejci R, Stannard J (1983)** [16]**,** studied the effect of alveolar bone loss on the magnitude and distribution of stress in dentin of post-reinforced teeth. Dentin stresses from simulated functional loads to post-reinforced tooth models with four levels of periodontal support were calculated using finite element analysis. As bone levels diminished, stresses increased dramatically and were found to concentrate in the small amount of dentin remaining near the post apex.

**Sorensen JA, Martinoff JT (1984)** [17], evaluated 1273 endodontically treated teeth and compared the clinical success rate of six coronal-radicular stabilization methods, recorded the failure of dowel systems and the effect on endodontically treated teeth, and determined the effect of dowel length on the clinical success rate. Authors concluded the cast parallel-sided serrated dowel and core and the parallelsided serrated dowel with an amalgam or composite resin core recorded the highest success rate. The tapered cast dowel and core displayed a higher failure rate than teeth treated without intracoronal reinforcement.

**Kersten H, Fransman R, Velzen T (1986)** [18], studied the effect of shape of the root canal in the success of the root canal treatment, apart from the efficiency of different root canal filling techniques especially in oval shaped canals. It was shown that close canal adaptation with minimal tooth structure removal provides a conservative and long lasting treatment for the restoration of endodontically treated teeth.

**Plasmans PJJM, Visseren GH, Vrijhoef MA, Iyser AKF (1986)** [19]**,** evaluated the failure resistance of some restoration methods utilizing amalgam under an oblique load. The results suggested that intracoronal reinforcement with a prefabricated dowel did not significantly increase the in vitro resistance. Hence, the authors concluded that this in vitro study supports the approach of not removing too much remaining tooth structure to adapt the tooth for a cast dowel and core. Preservation of sound dentin and adapting the amalgam core to the teeth leaves

more tooth structure and makes easy rebuilding possible with a restoration which is strong enough to resist forces of about 1,000 N.

**Leary J, Aquilino S (1987)** [20]**,** evaluated the effect of various post lengths on the strength or rigidity of the root within the elastic limit of dentin. Extracted maxillary centrals, maxillary and mandibular canines were the specimens selected for study. For the study the minimum root length acceptable was 12 mm measured from the cemento-enamel junction on the facial surface. This length allowed three incremental increases in post length of 3 mm, still leaving a 3 mm minimum for the apical seal. Load was applied 10 mm from the CEJ at 90 degrees to the long axis of the test specimen. They concluded that as internal tooth structure is removed from the tooth the tooth becomes weaker, that teeth with posts do show more reinforcement than teeth without post with the same manipulation characteristics, and that some load transfer appears to exist with cemented posts.

**Hunter A, Feiglin B, Williams J (1989)** [21]**,** examined the effect of root canal preparation, post preparation, and posts on the relative stresses in the cervical and apical regions of tooth models representing an intact maxillary central incisor. The authors concluded that removal of internal tooth structure during root canal therapy is accompanied by a proportional increase in stresses at the cervical area, particularly on the tension side. Post length appeared more important than post diameter in determining relative stresses at the cervical region. However, short wide posts led to elevated stress concentrations in this region. Post placement beyond two thirds of the root depth did not further decrease cervical stresses but usually increased stresses in the apical region.

**Greenfeld R, Roydhouse R, Marshall F, Schoner B (1989)** [22]**,** compared a new parallel-tapering, threaded, split-shank post with a well-accepted parallel serrated post under applied compressive-shear loads. The posts were placed in paired, contralateral human teeth to attempt to minimize variation in the tooth model. Both initial and ultimate failure modes were observed, and the clinical significance was reported. The Flexi-post system compared favorably with the Para-Post system under the conditions of this research.

**Burns DA, Krause WR, Douglas HB, Burns DR (1990**) [23], compared the stress distribution during insertion and function of three prefabricated endodontic posts with different designs using the criteria of post length and diameter. It was reported that larger diameter posts at increased depths distributed stress more efficiently than the smaller, shorter posts when loaded obliquely.

**Hatzikyriakos A, Reisis G, Tsingos N (1992)** [24]**,** conducted a longitudinal clinical study of patients treated with three traditional techniques (1) screw post and light-curing composite resins, (2) cemented post with parallel sides and lightcuring composite resins, and (3) a cast and core technique. All post and core fabrications demonstrated remarkable success in the 3-year period regardless of the technique. The posts and cores with the techniques described performed for patients with existing prosthodontics, were satisfactory. The statistical analysis revealed that only the factor "type of abutment" (RPDs and FPDs) had some effect on the failure of the restorations.

**Sedgley C, Messer H (1992) [**25]**,** compared the biomechanical properties of endodontically treated teeth. It was concluded that Vital dentin was 3.5% harder than dentin from contralateral endodontically treated teeth (p = 0.002). The similarity between the biomechanical properties of endodontically treated teeth and their contralateral vital pairs indicated that teeth do not become more brittle following endodontic treatment*.*

**Assif D, Bitenski A, Pilo R, Oren E (1993)** [26]**,** examined the effect of post design on the fracture resistance of endodontically treated premolars restored with cast crowns The experimental model used cast posts and cores to test the effect of

#### *Restoration of Endodontically Treated Teeth DOI: http://dx.doi.org/10.5772/intechopen.98190*

post design in a post-core system with identical rigidity. Samples were loaded on an Instron testing machine until failure revealed that post design did not influence the fracture resistance of endodontically treated premolars restored with complete cast crowns. In their study they concluded that endodontically treated teeth having a dowel-core system of identical rigidity and restoration with a complete cast crown having a 2 mm margin on healthy tooth structure. The selection of a dowel should be based on a system that preserves the most tooth structure and possesses suitable retention of the core for restoration of the tooth. If the anatomic crown is sufficiently preserved and core retention can be achieved from within the natural crown, or if completion of the coronal surface is unnecessary, a dowel is not required.

**Mentink A, Creugers N, Meeuwissen R, Leempoel P, Kayser A (1993)** [27]**,** conducted a clinical trial to assess the clinical performance of several post and core systems. During the period 1974–1986, 112 post and core build-ups were inserted in 74 patients. The build-ups consisted of a metal prefabricated post in combination with a composite core. After an average follow-up period of 7.9 years, they concluded that the Dentatus post in combination with composite tends to yield a high failure rate. The results of the Unimetric and Radix posts in combination with composite appear to be acceptable.

**Goodacre C, Spolink K (1994)** [28]**,** reviewed the management options of endodontically treated teeth and concluded that crowns should generally be used on endodontically treated posterior teeth but are not necessary on relatively sound anterior teeth. The primary purpose of post is to retain a core that can be used to retain the definitive prosthesis. Loosening of the post and tooth fractures were the two most common failures reported. Considering the post design threaded posts are the most retentive followed by cemented parallel sided posts, cemented tapered post is least retentive posts. Threaded post forms are the most likely to cause root fracture and split, and threaded flexible posts do not reduce stress concentration during function. Cemented posts produce the least root stress.

**Torbjorner A, Karlsson S, Odont D, Odman P (1995)** [29]**,** evaluated the dental records of 638 patients treated with 788 posts and cores to analyze failure rate and failure characteristics for two post designs. Frequency of the technical failures, loss of retention, root fracture, and post fracture were recorded 4 to 5 years after post cementation. Two types of posts were compared: custom-cast tapered posts and parallel-sided serrated posts. The cumulative failure rate was 15% for 456 tapered posts and 8% for 332 Para-Post posts. Loss of retention was the most frequent reason for failure for both types of posts, whereas root fractures had the most serious consequences, and all resulted in extraction. A significantly higher success rate was recorded for parallel-sided serrated posts, compared with customcast posts, regarding the total failure rate and the severity of the failure.

**Purton D, Love R (1996)** [30]**,** compared the properties in two different 1-mm diameter root canal posts — smooth carbon fiber posts (Endopost) and serrated stainless steel posts (Parapost). Ten posts of each type were tested for rigidity in a three point bend test. Ten posts of each type were cemented with resin cement into the roots of endodontically treated, extracted teeth. The tensile force required to remove the posts was recorded. The Paraposts proved to be significantly more rigid under load and significantly more strongly retained in the tooth roots. The Parapost appears to be a mechanically superior post for the restoration of root-filled teeth with narrow diameter root canals.

**Mendoza D, Eakle W, Kahl E, Robert H (1997)** [31]**,** evaluated the ability of resin-bonded posts to reinforce teeth that are structurally weak in the cervical area against fracture. Forty canine roots were endodontically treated and randomly distributed into four groups of 10. Parallel-sided preformed posts were cemented

into the roots of these teeth after their crowns were removed. The cervical third of the canals were flared to simulate teeth weakened in this area as a result of caries or endodontic therapy. Three resin cements and a zinc-phosphate cement, which was used as the control, were used to secure the posts into the roots. Cemented posts were loaded with a gradually increasing force at a 60-degree angle to the long axis of the root until the root fractured. Authors concluded that the roots in which the posts were cemented with Panavia were significantly more resistant to fracture than those where zinc phosphate was used.

**Asmussen E, Peutzfeldt A (1999)** [32]**,** investigated the direction of shrinkage of a light-curing resin composite in relation to the attachment and the thickness of the material. The resin composite was applied in cylindrical brass molds in such a manner that a flash, serving as attachment, was produced at one side of the specimens, while the material was flush with the mold at the other side. The specimens were now irradiated from either the flash or the flush side, and the convexity or the concavity of the specimens was measured. At a material thickness of 3 mm, the shrinkage was towards the light source, irrespective of the position of the flash. At 4 and 5 mm thickness of the molds, the direction of shrinkage could be directed towards or away from the light source, depending on the position of the flash. The number of light quanta emitted from the light source and passing through the material was compared with the number of molecules of camphorquinone present in a resin composite of 3, 4, or 5 mm thickness. It was concluded that under the conditions of the present study, the direction of shrinkage was the result of an interplay between the direction of the light, the attachment of the material, and the thickness of the material.

**Hazaimeh N, Gutteridge D (2001)** [33]**,** investigated the effect of a ferrule preparation on the fracture resistance of crowned central incisors incorporating a prefabricated post (Parapost) cemented with Panavia-Ex and with a composite core. The test group consisted of 10 post crowned natural central incisor teeth with a 2-mm wide ferrule preparation, whilst the control group of 10 teeth had no ferrule. The specimens were mounted on a Lloyd universal testing machine and a compressive load was applied at an angle of 135 degrees to the palatal surface of the crown until failure occurred. He concluded that when composite cement and core materials are utilized with a Parapost prefabricated system in vitro the additional use of a ferrule preparation has no benefit in terms of resistance to fracture.

**Cormier C, Burns D, Moon P(2001)** [34]**,** evaluated 6 post systems over 4 simulated clinical stages of tooth restoration to (1) determine quantitatively the fracture resistance strength at each stage when a static loading force is applied to cause failure; (2) determine the failure mode for each post system at each simulated clinical stage 12 and (3) determine the feasibility of removing failed post systems. Ten post systems made with various materials and designs were tested at the following 4 stages of simulated clinical treatment: stage #1: posts only, loaded using a 3-point loading model to failure, to determine transverse strengths and failure modes for each post system; stage #2: posts alone, bonded into teeth; stage #3: posts bonded into teeth with core build up; stage #4: post and core build up and full veneer restoration. For stages #2 through #4, the coronal portion of 60 mandibular premolars was amputated at the cemento-enamel junction, the canals were treated endodontically, and the specimens were mounted in acrylic blocks. A testing force was applied to the posts at 90° to the long axis of the tooth, 4 mm from the cemento-enamel junction. The fiber posts evaluated provided an advantage over a conventional post that showed a higher number of irretrievable posts and unrestorable root fractures. At the stage of final restoration insertion, there was no difference in force to failure for all but the FibreKor material, which continued to be

#### *Restoration of Endodontically Treated Teeth DOI: http://dx.doi.org/10.5772/intechopen.98190*

weaker than all other tested materials. The fiber posts were readily retrievable after failure, whereas the remaining post systems tested were non retrievable.

**Raygot C, Chai J, Jameson L (2001)** [35]**,** evaluated the fracture resistance and mode of fracture of endodontically treated incisors restored with cast post-andcore, prefabricated stainless steel post, or carbon fiber–reinforced composite post systems. Ten endodontically treated teeth restored with each technique were subjected to a compressive load delivered at a 130-degree angle to the long axis until the first sign of failure was noted. The fracture load and the mode of fracture were recorded. They concluded that the use of carbon fiber–reinforced composite posts did not change the fracture resistance or the failure mode of endodontically treated central incisors compared to the use of metallic posts.

**Akkayan B, Dent M, Gulmez T (2002)** [36]**,** compared the effect of 1 titanium and 3 esthetic post system on fracture resistance and fracture patterns of crowned endodontically treated teeth. A total of 40 recently extracted human maxillary canines with their crowns removed were endodontically treated. Four groups of 10 specimens were formed. Teeth were restored with titanium, quartz fiber, glass fiber, and zirconia posts and numbered as groups 1, 2, 3, and 4, respectively. All posts were cemented with Single Bond dental adhesive system and dualpolymerizing RelyX ARC adhesive resin cement. All teeth were restored with composite cores, and metal crowns were fabricated and cemented with glass ionomer cement. Each specimen was embedded in acrylic resin and then secured in a universal load-testing machine. A compressive load was applied at a 130-degree angle to the long axis of the tooth until fracture, at a crosshead speed of 1 mm/min. He concluded that significantly higher failure loads were recorded for root canal treated teeth restored with quartz fiber posts. Fractures that would allow repeated repair were observed in teeth restored with quartz fiber and glass fiber posts.

**Pontius O, Hutter J (2002)** [37]**,** evaluated the survival rate and fracture resistance of maxillary central incisors restored with different post and core systems. The post and core systems investigated were a prefabricated high precious metal post with cast core (group A), zirconia post with a prefabricated bonded ceramic core (group B), and a resin-ceramic interpenetrating phase composite post (experimental) with a prefabricated bonded ceramic core (group C). The all-ceramic copings were cemented using Panavia 21 TC. In the group without corono radicular reinforcement, the access cavity was closed with a light-cured composite in combination with a dentine-bonding agent (group D). Each specimen was intermittently loaded and thermocycled before final stress tests. With the help of results they concluded that the samples restored with a cast post and core demonstrated more vertical root fractures and the preservation of both internal and external tooth structure is of utmost importance when restoring endodontically treated teeth.

**Nergiz I, Schmage P, Platzer U, Ozcan M (2002)** [38]; investigated the effect of length and diameter on the retentive strength of sandblasted tapered prefabricated titanium posts. The results of the study were that retention was affected strongly with the increase in the length (approximately 100%) than with the increase in the diameter (approximately 60%).

**Kishen A, Kumar GV, Chen N (2004)** [39]**,** evaluated biomechanical perspective of fracture predilection in post-core restored teeth using computational, experimental and fractographic analysis. These experiments aided in correlating the stress–strain response in structural dentine with cracks and catastrophic fractures in post-core restored teeth. They observed that the inner dentine displayed distinctly high strains, while the outer dentine demonstrated high stresses during tensile loading. Hence they concluded that energy fed into the material as it is extended will be spread throughout the inner dentine, and there is less possibility of local increase in stress at outer dentine, which can lead to the failure of dentine structure. During post endodontic restoration with increase in loss of inner dentin the fracture resistance factor contributed by inner dentine is compromised, which in turn disposes the tooth to catastrophic fracture.

**Tan PL et al (2005)** [40]**,** investigated the resistance to static loading of endodontically treated teeth with uniform and nonuniform ferrule configurations. Fifty extracted intact maxillary human central incisors were randomly assigned to 1 of 5 groups: CRN, no root canal treatment (RCT), restored with a crown; RCT/CRN, no dowel/core, restored with a crown; 2 FRL, 2-mm ferrule, cast dowel/core and crown 0.5/2 FRL, nonuniform ferrule (2 mm buccal and lingual, 0.5 mm proximal), cast dowel/core and crown; and 0 FRL, no ferrule, cast dowel/core and crown. The teeth were prepared to standardized specifications and stored for 72 hours in 100% humidity prior to testing. Testing was conducted with a universal testing machine with the application of a static load, and the load (N) at failure was recorded. With the help of their results they demonstrated that central incisors restored with cast dowel/core and crowns with a 2-mm uniform ferrule were more fracture resistant compared to central incisors with nonuniform (0.5 to 2 mm) ferrule heights. Both the 2-mm ferrule and nonuniform ferrule groups were more fracture resistant than the group that lacked a ferrule.

**Ng CC, Dumbrigue HB, Al-Bayat MI, Griggs JA, Wakefield CW (2006)** [41]**,** investigated the fracture resistance of restored endodontically treated teeth when residual axial tooth structure was limited to one half the circumference of the crown preparation. Fifty extracted maxillary anterior teeth were sectioned 18 mm from their apices, endodontically treated, and divided into 5 groups of 10 teeth each. Four groups were prepared with full shoulder crown preparations having axial wall heights of 2 mm around the preparation circumferences. In 3 of the groups with axial tooth structure, one half of the axial tooth structure was removed, palatally, labially, or proximally, and groups were identified according to the site of retained coronal tooth structure. For the fifth group, all axial tooth structure was removed to the level of the preparation shoulder. Thus, in 1 group the axial walls were circumferential, 360 degrees around the preparations (Complete group), in 3 groups the axial walls were continuous for 180 degrees (Palatal, Labial, and Proximal groups), and the last group had no retained coronal tooth structure incisal to the finish line (Level group). All 50 prepared teeth were then restored with quartz fiber posts (Bisco), composite resin (Bisco) cores, and metal crowns. A universal testing machine compressively loaded the tooth specimens from the palatal at a crosshead speed of 0.5 cm/min at an angle of 135 degrees to the long axis of teeth until failure occurred. Authors observed that for restored endodontically treated teeth that do not have complete circumferential tooth structure between the core and preparation finish line, the location of the remaining coronal tooth structure may affect their fracture resistance.

**Dietschi D, Ardu S, Gerber A, Krejci I (2006)** [42]**,** evaluated the influence of post material physical properties on the adaptation of adhesive post and core restorations after cyclic mechanical loading. Composite posts and cores were made on endodontically treated deciduous bovine teeth using 3 anisotropic posts (made of carbon, quartz, or quartz-and-carbon fibers) and 3 isotropic posts (zirconium, stainless steel, titanium). Specimens were submitted to 3 successive loading phases – 250,000 cycles at 50 N, 250,000 at 75 N, and 500,000 at 100 N – at a rate of 1.5 Hz. Restoration adaptation was evaluated under SEM, before and during loading (margins) and after test completion (margins and internal interfaces). With the help of results they concluded that regardless of their rigidity, metal and ceramic isotropic posts proved less effective than fiber posts at stabilizing the post and core structure in the absence of the ferrule effect, due to the development of more interfacial defects with either composite or dentin.

**Salvi GE, Siegrist Guldener BE, Amstad T, Joss A, Lang NP (2007)** [43]**,** assessed the survival rates and complications of root-filled teeth restored with or without post-and-core systems over a mean observation period of 4 years. A total of 325 single- and multirooted teeth in 183 subjects treated in a private practice were root filled and restored with either a cast post-and-core or with a prefabricated titanium post and composite core. Root-filled teeth without post-retained restorations served as controls The restored teeth served as abutments for single unit metal-ceramic or composite crowns or fixed bridges. Teeth supporting cantilever bridges, overdentures or telescopic crowns were excluded. In their observation they concluded that the, provided that high-quality root canal treatment and restorative protocols are implemented, high survival and low complication rates of single- and multirooted root-filled teeth used as abutments for fixed restorations can be expected after a mean observation period of 4 years.

**Maccari PC, Cosme DC, Oshima HM, Burnett LH Jr, Shinkai RS (2007)** [44]; evaluated the fracture strength of teeth with flared canals and restored with two fiber-reinforced resin systems and one custom cast base metal (Ni-Cr) post and core system. The results suggested that teeth restored with cast posts had fracture strength twice that of teeth restored with resin posts. Fiber-reinforced resin posts failed at a compressive force comparable to clinical conditions, but all failures were repairable. While with the cast posts involved with root fractures.

**Hinckfuss S, Wilson P (2008)** [45]**,** evaluated the fracture resistance of bovine teeth restored with one-piece cast core/crowns and no ferrule, compared to teeth restored with amalgam cores and full coverage crowns, with and without a dentine ferrule. In this study thirty bovine incisors were selected and modified to ensure all teeth had axial dentine walls of similar size. The teeth were then randomly allocated to one of the three groups: control group restored with amalgam core and cast crown without ferrule; ferrule group restored with amalgam core and cast crown with a 2-mm dentine ferrule; one-piece group restored with one-piece cast core/ crown without ferrule. Each tooth was loaded to the point of fracture. It was observed that the maximum load resistance was significantly enhanced by a 2-mm ferrule compared with teeth with no ferrule and teeth restored with one-piece cast core/crowns. Teeth restored with one-piece cast core/crowns were significantly more resistant to loading than teeth restored with amalgam cores and crowns without a ferrule.

**Kivanc B, Gorgul G (2008)** [46]**,** investigated the fracture strength of three post systems cemented with a dual cure composite resin luting cement by using different adhesive systems. Sixty three extracted anterior teeth with single roots were endodontically prepared and filled. Teeth were randomly assigned to one of three post systems placed into the prepared canals: Group I - titanium posts, Group II - glass fiber posts and Group III zirconia posts. Each group was again randomly divided into three subgroups according to the bonding materials used [Single Bond (n = 7), Clearfil SE Bond (n = 7), and Prompt L Pop (n = 7)]. A dual cured resin cement (Rely X ARC) was used for bonding the posts into the root canals. Standard cores were made by a composite resin (Clearfil Photocore) using core build-ups. The samples were tested in the compression test machine for 1 mm/min and fracture resistance of the teeth were recorded. This study concluded that endodontically treated anterior teeth restored with glass fiber posts exhibited higher failure loads than teeth restored with zirconia and titanium posts. Self-etching adhesives are better alternatives to etch-and rinse adhesive systems for luting post systems.

**Alikhasi M, Dorriz H (2009)** [47]**,** compared the fracture resistance of endodontically treated teeth restored with different post and core systems in combination with complete metal crowns in teeth with no coronal structure. Fifty extracted mandibular premolars were divided into five groups. The coronal portion of each tooth was removed at the cemento-enamel junction (CEJ) in all groups except Group 1. In this group the teeth were sectioned 1 mm above the CEJ to create a ferrule. After root canal preparations, cast posts were placed in the first four groups. Prefabricated glass fiber posts and composite cores were placed in the fifth group. An opaque porcelain layer was applied to the metal post surfaces in the third group and an alloy primer was applied to the posts in the fourth group before using Panavia F2 resin cement. No bonding agent or surface treatments were used for the first and sec.ond groups. It was concluded that either a ferrule preparation or bonding with the use of an opaque porcelain layer can increase the fracture resistance of teeth with little remaining tooth structure that are restored with cast crowns following endodontic therapy.

**Ma P, Nicholls J, Junge T, Phillips K (2009)** [48], correlated different ferrule lengths with the number of fatigue cycles needed for failure of the crown cement for an all-ceramic crown cemented with a resin cement. Fifteen maxillary central incisors were divided into 3 groups (n = 5), with ferrules of 0.0 mm, 0.5 mm and 1.0 mm respectively. Each tooth was restored with a 0.050-inch glass-filled composite post) and a composite resin core. The posts were cemented with resin cement, and the composite resin cores were bonded to dentin using a dentine bonding agent. Each specimen was prepared with a 7-mm total preparation height, a 1.5-mm lingual axial wall, and a 1.0-mm shoulder around the tooth. The crowns for all specimens were pressed with a pressable ceramic material and cemented with resin cement. Load of 6-kg cyclic test was applied to each specimen at 135 degrees to the long axis of the tooth. After looking at the result they concluded that specimens with a 0.0-mm ferrule survived few fatigue cycles despite the fact that both the post and crown were bonded with resin cement. Teeth with a 0.5-mm ferrule showed a significant increase in the number of fatigue cycles over the 0.0-mm group, whereas teeth with the 1.0-mm ferrule exhibited a significantly higher fatigue cycle count over the 0.0-mm but not the 0.5-mm group.

**Signore A, Benedicenti S, Kaitsas V, Barone M, Angiero F, Ravera G (2009)** [49], compared the long-term survival of endodontically treated, maxillary anterior teeth restored with either tapered or parallel-sided glass-fiber posts and full-ceramic crown coverage. Authors stated that the choice of appropriate definitive restoration of endodontically treated maxillary anterior teeth should be guided by the amount of remaining hard tissues as well as functional and esthetic considerations. However, in cases of inadequate remaining coronal tooth structure, post-retained cores are often required to support complete crown restorations. The preparation of a post space significantly weakens endodontically treated teeth. A post did not significantly strengthen endodontically treated teeth.

**Silva NR, Raposo L, Versluis A, Julio A, Neto F, Soares C (2010)** [50]**,** evaluated the effect of post, core, crown type, and ferrule presence on the deformation, fracture resistance, and fracture mode of endodontically treated bovine incisors. One hundred and eighty bovine incisors were selected and divided into 12 treatment groups (n = 15). The treatment variations were: with or without ferrule, restored with cast post and core, glass fiber post with composite resin core, or glass fiber post with fiber-reinforced core, and metal- or alumina-reinforced ceramic crown (n = 15). The restored incisors were loaded at a 135-degree angle, and the deformation was measured using strain gauges placed on the buccal and proximal root surfaces. Specimens were subsequently loaded to the point of fracture. It was concluded that core type did not affect the deformation and fracture resistance of endodontically treated incisors restored with alumina-reinforced ceramic crowns. The presence of a ferrule improved the mechanical behavior of teeth restored with metal crowns, irrespective of core type.

#### *Restoration of Endodontically Treated Teeth DOI: http://dx.doi.org/10.5772/intechopen.98190*

**Jang JH et al (2012)** [51]**,** examined the stress distribution in endodontically treated maxillary central incisors restored with various lengths of either titanium or fiber reinforced composite (FRC) post-and-core systems, using two-dimensional finite element analysis models. Eight models of the maxillary central incisor were formed, surrounded by cortical bone, cancellous bone, and the periodontal ligament. Two different post-and-core systems, titanium and FRC posts (D.T Light Post), were modeled. In each restorative system, four models were designed by changing the post lengths cemented to the root at 10 mm, 9 mm, 8 mm, and 7 mm. A 100-N load was applied at a 45 angle to the long axis of each model. In the end they observed that the possibility of fracture of the FRC post is relatively low, compared to the titanium post, even for a short post. The same criteria for installation of a metal post should not be applied to an FRC post.

**Hegde J, Ramakrishna, Bashetty K, Srirekha, Lekha, Champa (2012)** [52], evaluated the fracture strength and mode of failure of endodontically treated teeth with flared canals restored with two fiber reinforced systems (glass fiber and quartz fiber) and one base metal cast post and core system. Forty five anterior teeth were decoronated at cemento-enamel junction and were endodontically treated. Post space was prepared and randomly divided into three groups according to the post system. Specimens were loaded at 45° in a universal testing machine at a cross head speed of 0.5 mm/min until failure. The mode of failure was classified as repairable or non-repairable. They concluded that the results of this study showed that fracture strength and mode of failure in anterior teeth with flared canal varied according to the type of post used to support a crown.

**Juloski J, Radovic I, Goracci C, Vulicevic JR, Ferrari M (2012)** [53]**,** summarized the results of research conducted on different issues related to the ferrule effect. They said that presence of a 1.5- to 2-mm ferrule has a positive effect on fracture resistance of endodontically treated teeth. If the clinical situation does not permit a circumferential ferrule, an incomplete ferrule is considered a better option than a complete lack of ferrule. Including a ferrule in preparation design could lead to more favorable fracture patterns. Providing an adequate ferrule lowers the impact of the post and core system, luting agents, and the final restoration on tooth performance. In teeth with no coronal structure, in order to provide a ferrule, orthodontic extrusion should be considered rather than surgical crown lengthening. If neither of the alternative methods for providing a ferrule can be performed, available evidence suggests that a poor clinical outcome is very likely.

**Santos-Filho P, Verıssimo C, Soares PV, Saltarello RC, Soares CJ, Martins LR (2014)** [54]**,** evaluated the influence of post system, length, and ferrule on biomechanical behavior of endodontically treated anterior teeth. The investigation was conducted by using laboratory tests and 3-dimensional finite element analysis. Eighty bovine incisors were selected and divided into 8 treatment groups (n = 10) with absence of ferrule and 2.0 mm of ferrule, restored with glass fiber post or cast post and core, and 12.0 and 7.0 mm of post length. The specimens were loaded at 135 angle, and the strain was measured by using strain gauge method. Specimens were subsequently loaded until fracture. Three-dimensional models of a maxillary central incisor were generated with the same treatment variations used in laboratory tests. Each model was subjected to 100 N oblique loads. They concluded that the post length influenced only the cast post strain and stress distribution. The ferrule groups always showed more satisfactory stress distribution and fracture resistance.

**Maroulakos G, Nagy W, Kontogiorgos E (2015)** [55], investigated the fracture resistance and mode of failure of severely compromised teeth restored with 3 different adhesively bonded post and core systems. Thirty extracted endodontically treated maxillary anterior teeth were randomly divided into 3 groups, CPC, gold

cast post and core; TPC, titanium prefabricated post/composite resin core; and FPC, quartz fiber reinforced post/composite resin core. All posts were adhesively cemented. All cores resembled a central incisor preparation with no remaining tooth structure above the finish line. Cast gold crowns were fabricated and cemented adhesively. The specimens were aged with thermocycling and cyclic loading. Two specimens per group were randomly selected for micro-computed tomographic imaging before and after aging. Failure was induced with a universal testing machine. The mode of failure was characterized by the interface separation. They observed that the severely compromised endodontically treated teeth restored with bonded gold cast post and cores showed significantly higher fracture resistance.

**Upadhyayal V, Bhargava A, Parkash H, Chittaranjan B, Kumar V (2016)** [56], evaluated the effect of design and material of post with or without ferrule on stress distribution using finite element analysis. A total of 12 three-dimensional (3D) axisymmetric models of post retained central incisors were made, six with ferrule design and six without it. Three of these six models had tapered posts, and three had parallel posts. The materials tested were titanium post with a composite resin core, nickel chromium cast post and core, and fiber reinforced composite (FRC) post with a composite resin core. The load of 100 N at an angle of 45° was applied 2 mm cervical to the incisal edge on the palatal surface. In their study they concluded that a rigid material with high modulus of elasticity for the post and core system creates the most uniform stress distribution pattern. Ferrule provides uniform distribution of stresses and decreases the cervical stresses.

**Kim AR, Lim HP, Yang HS, Park SW (2017)** [57], evaluated the fracture resistance with regard to ferrule lengths and post reinforcement on endodontically treated mandibular premolars incorporating a prefabricated post and resin core. One hundred extracted mandibular premolars were randomly divided into 5 groups (n = 20): intact teeth (NR); endodontically treated teeth (ETT) without post (NP); ETT restored with a prefabricated post with ferrule lengths of either 0 mm (F0), 1 mm (F1), or 2 mm (F2). Prepared teeth were restored with metal crowns. A thermal cycling test was performed for 1,000 cycles. Loading was applied at an angle of 135 degrees to the axis of the tooth using a universal testing machine with a crosshead speed of 2.54 mm/min. In their study they observed fracture resistance of ETT depends on the length of the ferrule, as shown by the significantly increased fracture resistance in the 2 mm ferrule group (F2) compared to the groups with shorter ferrule lengths (F0, F1) and without post (NP).

**Marchionatti A, Wandscher V, Rippe M, Kaizer O, Valandro L (2017)** [58]**,** compared the clinical performance and failure modes of teeth restored with intraradicular retainers. Evaluated retainers were fiber (prefabricated and customized) and metal (prefabricated and cast) posts, and follow-up ranged from 6 months to 10 years. Most studies showed good clinical behavior for evaluated intra-radicular retainers. In their review they concluded that the metal and fiber posts present similar clinical behavior at short to medium term follow-up. Remaining dental structure and ferrule increase the survival of restored pulpless teeth.

**Onofre R, Fergusson D, Cenci MS, Moher D, Cenci P (2017)** [59]**,** assessed the influence of the number of remaining coronal walls, the use or disuse of posts, and their type on the clinical performance of these restorations. Randomized controlled trials and controlled clinical trials for ETT restored with a combination of post/crown or no post/crown were searched for in MEDLINE, Embase, and the Cochrane Library. In their review they concluded that the restoration of ETT should focus on the maintenance of the coronal structure. Until more studies with longer follow-up periods are available, posts with a high elastic modulus appear to present with better performance when restoring ETT with no ferrule.

#### *Restoration of Endodontically Treated Teeth DOI: http://dx.doi.org/10.5772/intechopen.98190*

**Naumann M, Sterzenbach G, Dietrich T, Bitter K, Frankenberger R, Lausnitz MS (2017)** [60]**,** evaluated the dentin-like glass fiber posts (GFPs) compared with rather rigid titanium posts (TPs) for post-endodontic restoration of severely damaged endodontically treated teeth with 2 or fewer remaining cavity walls. Ninety-one subjects in need of post-endodontic restorations were randomly assigned to receive either a tapered GFP (n = 45) or TP (n = 46). Posts were adhesively luted by using self-adhesive resin cement, followed by composite core build-up and preparation of 2-mm ferrule design. Primary endpoint was loss of restoration for any reason. Hence they concluded that when using self-adhesively luted prefabricated posts, resin composite core build-up, and 2-mm ferrule to reconstruct severely damaged endodontically treated teeth, tooth survival is not influenced by post rigidity. Survival decreased rapidly after 8 years of observation in both groups.

**Lazari P, Carvalho M, Altair A, Curry D, Magne P (2018)** [61]**,** investigated the restoration of extensively damaged endodontically treated incisors without a ferrule using glass–ceramic crowns bonded to various composite resin foundation restorations and 2 types of posts. Sixty decoronated endodontically treated bovine incisors without a ferrule were divided into 4 groups and restored with four different post-and-core foundation restorations. NfPfB = no-ferrule (Nf) with glass-fiber post (Pf) and bulk-fill resin foundation restoration (B); NfPfP = no-ferrule (Nf) with glass-fiber post (Pf) and dual-polymerized composite resin core foundation restoration (P); NfPt = no-ferrule. They concluded that the survival of extensively damaged endodontically treated incisors without a ferrule was slightly improved by the use of a fiber post with a bulk-fill composite resin core foundation restoration. However, none of the post-and-core techniques was able to compensate for the absence of a ferrule. The presence of the posts always adversely affected the failure mode.

**Meng Q , Ma Q , Wang T, Chen Y (2018)** [62]**,** evaluated the effect of ferrule design on the fracture resistance of endodontically treated mandibular first premolars after simulated crown lengthening and orthodontic forced eruption methods restored with a fiber post-and-core system. Forty extracted and endodontically treated mandibular first premolars were decoronated to create lingual to-buccal oblique residual root models, with a 2.0 mm height of the lingual dentine wall coronal to the cemento-enamel junction, and the height of buccal surface at the cemento-enamel junction. The roots were divided randomly into five equal groups. With the help of results they concluded that increased apically complete ferrule preparation resulted in decreased fracture resistance of endodontically treated mandibular first premolars, regardless of whether surgical crown lengthening or orthodontic forced eruption methods were used.

**Zarow M et al (2018)** [63]**,** reviewed the status of root filled teeth to analyze the most important factors in decision-making and discuss the current restorative concepts and classified both the evidence and clinical practice in a way that seeks to be clear, understandable and helpful for clinicians. They concluded that the decisionmaking process in the restoration of root filled teeth is complex and should consider the following factors: amount and quality of tooth structure, tooth position in the arch and anatomy and function. Fiber posts are recommended in anterior teeth and premolars with compromised tooth structure (<50%) and/or with high tooth length over bone crest. A ferrule is highly beneficial for the prognosis of root filled teeth. If a ferrule cannot be provided and the patient still prefers to save the tooth, a gold cast could be a possible option.

**Fadag A et al (2018)** [64], evaluated the fracture resistance of endodontically treated maxillary central incisors with different post systems. Fifty-six extracted intact maxillary permanent central incisors were used, treated endodontically

(except for the control group), and distributed into the following seven test groups (n = 8) depending on the post type: UHT (control group: root-filled teeth without endodontic post), ZRP (prefabricated zirconia post), GFP (prefabricated glass fiber post), CFP (prefabricated carbon fiber post), CPC (custom-made cast post and core), TIP (prefabricated titanium post), and MIP (prefabricated mixed post). The specimens were loaded in a universal testing machine until fracture occurrence. In their, they observed endodontically treated teeth restored with zirconia post, glass fiber post, titanium post, or mixed post were more resistant to fracture loads compared with those that were not restored (control group) or restored with either carbon fiber post or cast post and core.

**Pinto CL et al (2019)** [65]**,** evaluated the influence of different post systems on the biomechanical behavior of teeth with a severe loss of remaining coronal structure. Fifty standardized bovine teeth (n = 10 per group) were restored with: cast post-and-core (CPC), prefabricated metallic post (PFM), parallel glass-fiber post (P-FP), conical glass-fiber post (C-FP), or composite core (no post, CC). The survival rate during thermomechanical challenges (TC), the fracture strength (FS), and failure patterns (FP) were evaluated. Hence they concluded that the type of intracanal post had a relevant influence on the biomechanical behavior of teeth with little remaining coronal structure.

**Bakirtzoglou E, Kamalakidis S, Pissiotis A, Michalakis K (2019)** [66]**,** evaluated the retention and resistance form of complete coverage restorations supported by two different cast post and core designs. Forty extracted maxillary central incisors were randomly divided into four groups of 10 specimens each. All specimens were endodontically treated and a uniform post space of 9 mm was created. All prepared teeth had a 360 degree chamfer ferrule of 2 mm in axial height measured 0.5 mm coronally from the cemento-enamel junction (CEJ) and an axial wall thickness of 1.5 mm. Both cast post and core designs offer equal retention.

**Veeraganta S et al (2020)** [67]**,** evaluated the influence of post material and post diameter on the fracture resistance of endodontically treated mandibular premolars. In addition, the influence of tooth substance loss was evaluated by comparing 1 with 2 residual dentinal walls. Sixty-four extracted mandibular first premolars were endodontically treated and divided into 8 test groups based on the number of residual walls (1 or 2), post material (glass fiber or titanium) and post diameter (International Standards Organization [ISO] 70 or ISO 90). After luting the posts, the specimens received a composite resin core and a crown preparation with a 2 mm ferrule. Cast Co-Cr crowns were cemented with glass ionomer cement. After 1200000 mastication cycles with a load of 49 N and simultaneous thermocycling (5–55°C), specimens were loaded at 30 degrees to the longitudinal axis of the tooth until fracture. In their study they observed that fracture loads ranged from 954 35 N (1 residual wall glass fiber ISO 70) to 1286 202 N (1 residual wall glass fiber ISO 90). Titanium posts showed a statistically significant higher fracture resistance than glass fiber posts. A statistically significant increase in fracture resistance was also observed with increasing post diameter. However, no significant difference was found with respect to the number of residual walls. Hence they concluded that teeth restored with titanium posts exhibited higher fracture resistance than teeth restored with glass fiber posts, especially when smaller diameter posts were used.

One of the most frequent procedures of restorative dentistry is the restoration of mutilated and endodontically treated teeth. It is also difficult to repair these teeth since significant quantities of the coronal tooth structure is lost as a result of decay, prior restorative treatment, endodontic access and fractures. Restoration of an endodontically treated tooth needs a good understanding of its physical as well as biomechanical properties, along with sound knowledge of its anatomy as well as

#### *Restoration of Endodontically Treated Teeth DOI: http://dx.doi.org/10.5772/intechopen.98190*

endodontic, periodontal, restorative and occlusal principles. Even though the availability of various restorative materials for endodontically treated teeth has increased over few years, the principle of restoring it remains the same [68]. When a significant coronal section has been lost, resulting in the presence of one wall or no wall remaining, then adequate anchorage for the restoration cannot be achieved [69].

With the aid of a post, anchorage can be gained in such conditions. A post is described as the restoration segment inserted into the root canal to help maintain a core component. It can be made of metal or non-metallic compounds. The main objective of the post is to provide retention for the core and the coronal restoration [29, 70]. Sorensen in 1984 stated that the reason for placing a post in the root canal is to retain a crown and not to reinforce the tooth. Posts should not be positioned arbitrarily because post space preparation introduces a degree of risk to a restorative operation by disrupting the seal of the root canal filling, which can lead to microleakage. The risk of perforation increases due to the removal of sound tooth structure. Tooth fracture can also occur because of weakening of roots due to removal of sound tooth structure.

It is preferred that physical properties of the tooth i.e. the dentin should match with the physical properties of post system. An ideal post should distribute the functional stresses along the root surface in such a manner that minimum stresses are developed. Esthetics of the post should be compatible with the surrounding tissue. An ideal post should have easy retrievability, good retention and should be compatible with core material. They should also be available at a reasonable cost and should be easy to use. The indications for a post have been modified over the years based on the advantages of the adhesive restoration principles, which may obviate the need for the posts [71]. The remaining amount of tooth structure determines the stability for the restoration. In addition, the tooth's prognosis is influenced by different factors such as occlusal contacts, its location in dental arch and ferrules [71].

1.5 to 2 mm height of ferrule is the minimum requirement to obtain sufficient fracture resistance. 20 The ferrule with the help of core and dentin reduces the stress on the entire restoration. However, researchers have indicated that it is possible to overcome the lack of fracture protection that may occur in the absence of ferrules using adhesive agents [70, 71].

A further benefit of flexible posts is that dentine elimination is reduced by following the morphology of the channels in curved channels, while direct positioning in the post increases dentine elimination as the length (surface area) increases. Another explanation for this is that the curvature region starts after the 7 mm mark. This is where the thickness of the dentine decreases and there is a very high chance of strip perforation [72].

#### **3.1 Considerations [anterior teeth]**

Its not always necessary to have a complete coverage except when a plastic restoration has limited prognosis. Teeth which are badly destructed due to caries, which can be used for RPD or FPD.

Posterior teeth are subjected to greater stresses because of their position i.e. closer to the insertion of the muscles of mastication. This combined with their morphologic characteristics makes them more susceptible to fracture.

Complete coverage is recommended on teeth with a high risk of fracture especially maxillary premolars as they have long, thin and curved roots which gives best protection against fracture but at the same time considerable tooth reduction must be done and in these cases a post and core foundation is needed for better retention of the prosthesis.

• Its commonly believed that endodontically treated teeth are weak than normal teeth which may be due to low moisture content.[not proved experimentally]. so attempts have been made to increase strength by adding posts.

Studies reveal that no significant reinforcement results with the post, because teeth when loaded, stresses are more at the facial and lingual aspects of the root and post being at centre is minimally stressed and does not help prevent fracture. However some contradicts this assumption.

Disadvantages of placement of the post:

It requires an additional operative procedure. Additional tooth structure must be removed. if post fails it is difficult to restore the tooth later for a complete crown. Post can prevent future endodontic treatment.

when a complete coverage is not necessary, post is contraindicated in that tooth. when there is extensive loss of tooth structure which can be used for a FPD or RPD a complete coverage is mandatory.

#### **3.2 Preparation aspects**

All most all the principles of normal tooth preparation applies to the endodontically treated teeth. Ideally coronal half of the post hole will have been left open at the time of obturation. if not care must be taken not to deviate from the canal while opening. Guidance can be achieved by softening the guttapurcha with an heated instrument. A reamer can then be inserted to remove the guttapurcha and the direction of the canal is identified. Use of magnifying lens and fiber optic light is helpful in this process. After opening to the required length it is reamed to the appropriate size to accept a post. The minimum length required for a post hole is either the size of that tooth crown or two-thirds the length of the root whichever is longer.

#### **3.3 Conservation aspects**


Enlargement seldom needs to exceed once or twice additional file sizes beyond that used for endodontic treatment. so it is wise to check the treatment record of endodontic therapy for proper and limited enargement of the canal.

#### **3.4 Crown aspect**

In most of the endodontically treated teeth the coronal part has been lost from caries, previous restoration or during access cavity opening so most tooth structure should be conserved as it helps in reducing the stress concentration at the gingival margins.

Indeed if more than 2 mm of coronal tooth is left the post design probably plays little role in the fracture resistance of the restored tooth. 1 mm of the vertical height of the crown provides FERRULE EFFECT.

*Restoration of Endodontically Treated Teeth DOI: http://dx.doi.org/10.5772/intechopen.98190*

**FERRULE EFFECT**: It is defined as a metal ring or cap put around the end of tool, cane etc. to give added strength. This effect is used in the dowes preparation in the form of a circumferential contrabevel which reinforces the coronal aspect of the dowel preparation. it also aids in affecting a positive occlusal seat and acts as antirotational device [73].

**FERRULE EFFECT**: If the artificial crown extends apical to the margin of the core and encircles sound tooth structure for 360 degrees, the crown serves as a reinforcing ring or ferrule to help protect the root from vertical fracture.

**SECONDARY FERRULE**: A contrabevel has been advocated when preparing a tooth for a cast post and core to produce a cast core with a collar of metal that encircles the tooth and serves as a secondary ferrule, independent of the ferrule provided by the cast crown [5].

#### **3.5 Retention aspects**
