Hydraulic cements for various intra-coronal applications: Part 1

Section summary

MTA, a derivative of Portland cement, was the first hydraulic material to be introduced for use in endodontics. Subsequent product development, which includes changes to the cement, radiopacifier and the inclusion of additives, has led to the number of products now available to the clinician.

Section summary

The interaction of the hydraulic cements with the environment into which they are placed makes them ideal materials to be used in the three endodontic locations namely intra-coronally, intra-radicularly and extra-radicularly.

Material chemistry

Biodentine comprises a powder (80% tricalcium silicate, 15% calcium carbonate and 5% zirconium oxide³⁹) and a liquid (water, calcium, chlorine, sodium and magnesium⁴⁰). The specific surface area of this product is higher than that of other commercial hydraulic cements because the powder is finer.³⁹ Biodentine is classified as a Type 4 cement because its cement base is tricalcium silicate, includes reaction modifiers and is mixed with water for hydration.

The setting reaction of Biodentine is similar to that of tricalcium silicate cement with the formation of calcium silicate hydrate and calcium hydroxide. However, there are some modifications due to the presence of calcium carbonate, which acts as a nucleating agent and also enables the early release of calcium ions into solution. The hydro-soluble polymer reduces the water demand and this leads to improved physical and mechanical properties of the material,⁴¹ and also its handling. Calcium chloride accelerates the setting reaction,⁴¹ thus making Biodentine suitable as a pulp-capping material.

The phase composition of Biodentine gives it a very specific ordered microstructure.⁴² This is due to a hydration reaction product being formed and deposited around the calcium carbonate particles (Figure 5).

Material properties

Although Biodentine may have restricted moisture availability when used as a pulp-capping material, it has been shown that the hydration proceeds normally.⁴³ The presence of calcium hydroxide produced from the hydration of the material⁴⁴ is important for pulp healing. Biodentine has been shown to cause specific pulpal reactions⁴⁵ with favourable cell proliferation and alkaline phosphatase activity of human dental pulp cells,^46,47,48 allows the expression and release of dentine matrix proteins,⁴⁹ has an anti-inflammatory potential,⁵⁰ induces pulp regeneration capacity⁵⁰ and enhances mineralized tissue formation.^51,52,53 This product also allows reactionary and reparative dentinogenesis⁵⁴ and has been shown to enhance proliferation and odontoblast differentiation of human stem cells.^54,55

The calcium-releasing ability of Biodentine contributes to its antimicrobial properties.⁵⁶ Prior dentine cleansing by an antimicrobial solution, such as sodium hypochlorite, is suggested and supported by the ESE position statement³⁷ as Biodentine has been shown to be rendered ineffective against multispecies microcosm biofilm⁵⁷ indicating the need to reduce the microbial load prior to application of the material over the dentine. This also enhances the bond strength of the Biodentine to caries-affected dentine.⁵⁸ The use of 17% ethylene diamine tetra-acetic acid (EDTA) applied for 1 minute resulted in a reduction in the gap at the tooth to material interface.³⁰

The interaction of Biodentine with tooth structure leads to chemical bonding of the material to dentine. The alkalinity created by the calcium hydroxide produced as the Biodentine hydrates results in mineral exchange at the tooth–material interface.³¹ Phosphorus from the tooth structure is released, and calcium phosphate has been shown to be deposited at the interface.^29,30 Calcium carbonate formation on the material surface, as a result of the interaction between the calcium hydroxide and carbon dioxide present in any contacting blood, has been demonstrated.³⁶

Biodentine uses zirconium oxide as a radiopacifier, so tooth discolouration is prevented, unlike materials containing bismuth oxide.

The restoration of the tooth with composite resin over Biodentine requires fastidious clinical technique because Biodentine should not be etched directly. The etch destroys the surface microstructure and results in enhanced leakage through the Biodentine resin–composite interface.⁵⁸ Selective etching of the tooth structure and bonding to enamel and dentine is thus suggested. The use of self-etch does not improve bond strengths and self-etch primers should be avoided.^58,60–61 Alternatively, Biodentine can be used as a temporary filling material and the tooth can be restored in a second visit.⁶²

Presentation

Biodentine is supplied as a powder and a liquid that must be mixed (Figure 6a). Five drops of liquid from the vial are added to the powder in the capsule (Figure 6b). The challenge is to achieve the correct powder–liquid ratio owing to the potential variability arising from the size of the drops expressed from the vial. The manufacturer's instructions should be followed fastidiously. The capsule is then closed, placed into a mechanical mixer and agitated at 4500rpm for 30 seconds to achieve a homogeneous mixture (Figure 6c).

Section summary

Two shortcomings of hydraulic cements, namely slow set and poor handling properties have been overcome by the inclusion of additives, such as in Biodentine, thus permitting it to be used in the intra-coronal situation.

Pulp capping

A 19-year-old female presented having been diagnosed with Ewing's sarcoma and was about to embark on chemotherapy. Clinically, there was a shadow in the occlusal surface of LL6 consistent with a carious lesion, although no cavitation of the enamel was evident (Figure 7a). From the radiograph, it was judged that some pulpal involvement was likely because of the potential extent of the lesion. After the administration of local anaesthetic (LA), a rubber dam (RD) was placed pre-operatively to create a controlled bacteriological environment. The cavity was prepared, the amelodentinal junction cleared and stepwise excavation of dentinal caries proceeded, leaving some caries-affected dentine over the pulp. Biodentine was mixed and placed into cavity (Figure 7b). In this situation, the material may be placed as a dressing by filling the entire cavity,⁶² in which case, the patient should be recalled within 4 weeks so that the outer part of the material may be reduced to accommodate an overlaying definitive restorative material. Alternatively, Biodentine may be placed as a lining material and once set, covered with resin composite at the same appointment. This latter approach is considered to be preferable. It has been shown that the placement of a definitive restoration within the first 2 days after pulp exposure contributed significantly to increased pulpal survival rate,⁶³ and so, particularly in view of the patient's medical history, this approach was chosen.⁶⁴ Clinical and radiographic follow up was undertaken to monitor pulp vitality and 4 years post-operatively, no further operative intervention had been necessary. A follow up radiograph is shown in Figure 7c.

Barrier regenerative endodontics

An 11-year-old female patient was referred by her general dental practitioner (GDP) with pulpal necrosis in UL1. Although she presented asymptomatically, there was a history of trauma whereby the tooth had suffered a luxation injury and had an incomplete apex when viewed on a radiograph (Figure 8a).

The treatment was performed under LA and RD, the root canal of UL1 was irrigated with 2.5% sodium hypochlorite solution and 17% EDTA and sterile isotonic saline with only necrotic and infected tissue removed as per the ESE protocol.³⁸ The excess irrigant was removed using sterile paper points prior to the use of a size 25.02 Hedströem file into pulp stump (which was visible under the operating microscope) to induce bleeding. The blood clot was allowed to form at the level of the amelocervical junction and covered with an absorbable collagen sponge (Parasorb Cone, Resorba Medical GmbH, Nürnberg, Germany) prior to the placement of Biodentine. A coronal seal was established with a resin-modified glass polyalkenoate cement (Vitrebond Plus, 3M, Seefeld, Germany) and the access cavity restored with resin composite (Figure 8).

Section summary

The adoption of barrier regenerative techniques is more commonplace in contemporary endodontics. This has been made possible by the availability of hydraulic cements, such as Biodentine, whose chemical and handling properties are conducive for this indication.