Biological post: An Avant-Garde approach

Introduction

Anterior tooth fracture is a commonly encountered scenario in clinical practice. It usually occurs as a result of trauma due to road traffic accidents, sports injuries or various other activities and problems.¹ Commonly seen in children and adolescents, its prevalence rate is about 8.1 in 1000.² Along with functional and esthetic complications, it also causes psychological problems and reduces the quality of life of the patient. Satisfactory coronary restoration of such damaged teeth with acceptable esthetic and functional conditions is of prime importance for its proper management.

The chief concern while restoring severely damaged teeth is to ensure adequate retention and strength of the dental fragments, while keeping in mind the modulus of elasticity of dentin. This can be obtained by employing posts, which are restorative dental materials placed in the root portion of the damaged tooth to provide retention for the core and coronal portion of the tooth.

It is of utmost importance to the dental clinician to restore endodontically treated teeth with suitable esthetics, ample strength and function. This in turn will help increase the longevity of the tooth. ³ Intraradicular devices such as the ‘post and core system’ can be put to use in order to achieve this.

According to the Glossary of Prosthodontic Terms (GPT) 9, a post is usually made of metal or fiber-reinforced composite resin that is fitted into a prepared root canal of a natural tooth⁴ . A post and core can be defined as a post with an incorporated core; it provides retention and resistance for an artificial crown; it is also used as a platform for retentive attachment systems and nonretentive overdenture abutments4 .

A post is placed in the radicular portion of the non-vital tooth and the core refers to a properly shaped substructure, which replaces the missing coronal structure and retains the final restoration.

The prime role of a post is to hold the core in place in a tooth with severe loss of coronal structure.⁵ Prior to the placement of the post, the tooth is endodontically treated and evaluated for good apical seal and absence of inflammation, exudate, fistula and sensitivity.⁶ In case of any doubt the tooth should be observed for several months until there is strong evidence of its success or failure.

The selection of an appropriate post depends on several criteria and factors such as its diameter, length, material, and design⁷ .

- Greater the length of the post, greater its fracture resistance⁸

- If the diameter is increased by about 1.6 times, fracture resistance is found to increase⁹ However diameter is not a very important factor and should not be increased too much

- The fracture resistance of stainless-steel posts is found to be more than fiber posts⁸

- Parallel posts provide more retention than tapered posts reference¹⁰

A successful design for post and core will exhibit an adequate apical seal of 5 mm, no undercuts in the prepared post space, adequate post length, positive horizontal stop to prevent wedging, sufficient vertical wall to prevent rotation, and extension of final restoration margin on sound tooth structure reference¹¹.

Most commonly, a two-step procedure is followed wherein the post space is prepared and the post is cemented, after which the core material is applied and shaped like a prepared crown of a tooth. This is followed by the fabrication of a crown in the conventional manner. The post space is prepared with a peaso reamer.². However, sufficient care must be taken while preparing the post space. A common mishap while performing this procedure is ‘strip perforations’ which is basically the perforation of the apical or lateral areas of the root. Few studies have shown that in such cases mineral trioxide (MTA) can act as a good sealer. ^{12, 13, 14}

According to the literature, failure rates are more in males than females.¹⁵ It was three times higher in patients who were above 60 years of age and in maxillary teeth.¹⁷ Load was found to be the main cause of failure in the majority of the cases.

Posts are available as various types such as Preformed/ Custom made, Rigid/Non-rigid, Stiff/resilient and Esthetic/Non-esthetic.⁸ They are also available in various materials such as metals like stainless steel, nickelchromium, cobalt-chromium, titanium and non-metals like ceramic posts, composite posts, polymeric posts, zirconia posts and fiber-reinforced posts¹⁵. However, there are no commercially available posts that are ideal in terms of all biological, esthetic and mechanical requirements.¹

The material with which a post is fabricated plays a chief role in the long-term prognosis of the tooth. In this context, a suitable reconstruction and restoration of an extensively impaired tooth can be achieved by the use of a biological restoration, known as the “Biological post” on account of its biomimetic property.¹⁷ The term biological restoration was first introduced by Santos and Bianchi in 1988. ¹⁸

Biological posts are made from dentin of freshly extracted human teeth which are autoclaved, cut and shaped to adapt to the root canal of the tooth to be restored.¹⁹ Since they are fabricated from natural teeth, their resiliency is comparable to that of natural teeth. In addition to that, the adhesion between the biologic post, cementing agent, and tooth structure enables the clinician to attain a monoblock system.

Advantages of the biological post: ¹⁶

(1) Does not induce additional stress on dentinal walls

(2) The internal dentin walls of the root canal can be preserved

(3) Biocompatible

(4) Better adaptation and greater configuration

(5) Increased tooth strength and retention of these post

(6) Resiliency is similar to natural tooth

(7) Adhesion to the tooth structure and composite resin is excellent

(8) Economical

Despite the advantages of using biological posts, it is not without limitations. Patients may be apprehensive to accept a material made from another person’s tooth and finding a tooth that fits all the morphological requirements might be hard.¹⁹ In some situations, it may also be difficult to find a suitable tooth.²⁰

In brief, the general steps to be followed for biological posts are as follows:

Following endodontic treatment, the gutta-percha is removed such that there is about 5 mm of it remaining at the apex ^{1, 16}. The post space is prepared and a regular elastomeric impression along with the impression of the canal space is made and a die is poured for the same.

A suitable extracted tooth is autoclaved and then cut into the desired shape and size with the help of diamond trimmers using the die as a reference. This is then placed in the patient. Its location, shape, and size are then confirmed with the help of an intraoral periapical radiograph. If everything is satisfactory, the post space is cleaned by using saline and dried with paper points. Bonding agent is applied in the canal as well as the biological post and then cemented with an appropriate luting agent. This is then followed by the core and then crown placement subsequently.^{1, 2, 16, 17}

Therefore, biological posts can be considered as a novel alternative technique for the rehabilitation of extensively damaged and destructed teeth.

The present article presents two case reports of the use of biological posts for post and core fabrication to restore extensively damaged teeth.

Case Report 1

A 53-year-old female patient reported to the Department of Prosthodontics, DAPM RV Dental College, Bangalore with the complaint of a fractured and carious upper front tooth along with a missing adjacent tooth.

On examination, it was found that the maxillary right lateral (12) and central incisor (11) were missing (Figures 1 and 2) and the maxillary left central incisor (21) was fractured with an Ellis class 3 fracture (Figures 1 and 2). Dental caries were noted in the left maxillary lateral incisor (22) (Figures 1 and 2).

The treatment plan was endodontic treatment for 21 followed by a post and core with a biologic post. The missing teeth were replaced with a fixed partial denture extending from the right maxillary canine (13) to the left maxillary lateral incisor (22).

The patient was informed about the procedure involved in procuring the biologic post and consent was obtained.

The maxillary left central incisor was endodontically treated and radiographically confirmed (Figure 3). The post space was then sequentially prepared using peso reamers retaining one-third of the gutta-percha in the apical region and once again checked with an IOPA (Figure 4). An impression of the post space was made with a custom-made self-cure post and medium-bodied elastomeric impression material and the cast was poured (Figures 5, 6, 7).

The chosen extracted maxillary canine was autoclaved at 121°C for 15 minutes (Figure 8). A diamond disc was used to section the tooth longitudinally. The tooth was then shaped like a post using diamond drills (Figure 9). The post thus formed was tried on the cast and necessary adjustments were done (Figure 10). It was then tried intraorally for fit, which was then confirmed radiographically (Figure 11, 12). The post was luted with a self-adhesive resin cement and the core build-up was done with composite material (Figure 13).

Tooth preparation was done to fabricate a fixed partial denture from the right maxillary canine (13) to the left maxillary lateral incisor (22) (Figure 14), followed by retraction (Figure 15) and impression with elastomeric impression material (Figure 16). A temporary bridge was cemented in place, which was subsequently replaced by a permanent restoration (Figures 17, 18).

Case report 2

A male patient aged 26 years reported to the Department of Prosthodontics, DAPMRV Dental College, Bangalore with a history of trauma resulting in the fracture of the maxillary left lateral incisor (22). The tooth was root canal treated and the procedures followed were similar to case report 1(Figures 19, 20, 21, 22, 23, 24). After cementation of the biological post, the permanent restoration given was porcelain fused to metal crown cemented with glass ionomer cement (Figures 25, 26).

Both patients were followed up for a year. The restorations showed satisfactory esthetics and durability, in terms of function and tooth structure.

Discussion

The principal advantage of using biological posts to restore endodontically treated teeth is similar physical properties such as the modulus of elasticity, viscoelasticity, thermal properties and compressive strength between the post and tooth being restored¹⁵. Cast metal posts have a higher elastic modulus compared to dentin, which increases the stress at the restoration interface. This in turn can predispose the tooth to vertical fracture. Contrarily, fiber reinforced posts have low elastic modulus compared to dentin due to which there is a higher chance of spontaneous debonding of the post.¹⁵ Various studies have shown that the fracture toughness of dentin was better than most restorative materials^{15, 19, 21}. Due to the limited number of studies, the long-term success rate of biological posts cannot be accurately predicted.² However, studies have reported that biological posts have better fracture resistance than carbon and glass fiber posts.²²After one year of follow up, the treatment outcome is considered a success. ^12,23

Conclusion

Biological Posts offers excellent esthetic, functional, and psychosocial results. Hence the use of biological posts is justified to achieve morphological and functional recovery of extensively damaged teeth.

There are bound to be lacunae in every stage of clinical innovation. With respect to the biological post, long term studies are needed to assess certain parameters such as adhesion and longevity of these posts.

Ethical and cross-infection concerns with respect to the procurement of a donor tooth and its use as a biological post are a concern and efforts are needed to allay the patients’ anxieties. Another facet of concern could be to find a donor tooth to exactly match the morphological requirements of the recipient’s tooth.

It can be said with certainty that biological posts are here to stay, and they can be a practical alternative for patients from economically poorer sections of society.

Conflicts of Interest

None