The mechanical resistance of calcium silicate-based materials is due to their degree of porosity, besides other factors. The rule of thumb is that the lower the porosity, the greater the mechanical resistance
Apart from mechanical resistance, the porosity of a material also has a major influence on some other parameters, such as adsorption, permeability, hardness and density.
The maximum measured pore diameter, which represents the weakest point in the material at the same time, determines the leakage risk, together with the size of a bacterium persisting in the root canal system, and therefore the overall success of the endodontic therapy (De Bruyne et al. 2006)
Camilleri et al. (2013)
obtained clinically relevant results in their study of Biodentine and porosity, and their key conclusion is that the manner of Biodentine use has a significant influence on porosity and the inevitable subsequent permeability. If Biodentine is applied and sets in dry surroundings or under dry conditions, this appears to promote the formation of defects in the interface. The conclusion of this study as regards avoidance of porosity is therefore that Biodentine is more suitable for indications that allow a moist milieu in the insertion phase.
On the other hand, De Souza et al. (2013)
arrived at different conclusions. Using micro-CT analysis, they compared Biodentine with other silicate-based cements, e.g., IRoot, Ceramicrete and ProRoot MTA. The authors did not find any significant difference between the products with regard to porosity. Furthermore, De Souza et al.
state that Biodentine and MTA have major similarities in clinical behavior, solubility and the incidence of microfractures and permeability.
With Biodentine the high level of resistance is achieved by the low proportion of water in the mixing phase.
||Pore volume cm³/g
||Porosity in %
From the available data (Nonat and Franquin 2006)
, it is apparent that the porosity and density of Biodentine are roughly equivalent to those of Fuji IX.
The micromechanical retention of Biodentine is essentially ensured by the high alkaline pH during the setting phase (Firla 2012, Watson et al. 2011, Sauro et al. 2011). The very high pH of 12.5 causes organic structural elements to dissolve out of the dentin tubules. Inorganic components of the dentin, by contrast, are partially dissolved and detached by alkaline etching, which corresponds in principle to classic conditioning by application of acid. This opens and widens the dentin tubules, thus enabling the Biodentine to interdigitate closely at the interface between natural dentin and filling material by means of mineralized microtags with an apatite-like structure. This secure and stable fixation demonstrates a sealing and bacteria-impermeable bond between the two materials. This effect is due entirely to the high alkaline pH. Prior treatment with potentially pulp-damaging agents is not necessary. Atmeh et al. (2012) studied the structure and properties of the interface between Biodentine or glass ionomer cements and dentin using various microscopic and spectroscopic methods. They were able to confirm that tag-like structures had formed at the boundary with the dentin. Alkaline etching of Biodentine caused partial dissolving of the collagen network in the dentin junctional region. This effect is the basis of the microretentive fixation of the material that takes place. Atmeh et al. (2012) did not find a similar effect with any other preparation in this series of tests.
The compressive strength of a dental product is determined by classic mechanical tests (ISO 9917:1991). In the recently presented study, each of the investigated products was tested for its compressive strength at different times.
From the graph (Septodont) it can be seen that the compressive strength of Biodentine increases rapidly in a very short time and exceeds the level of 100 MPa. After 24 hours, the compressive strength has increased further and exhibits values of more than 200 MPa. The special feature of Biodentine is that it has the ability to exploit its mechanical advantages further, albeit at a much lower rate. After about a month, Biodentine has increased its compressive strength to levels of ~300 MPa. The achieved level stabilizes and is then nearly in the region of natural dentin at ~297 MPa (O’Brien 2008)
. This form of "maturing process" with gradually increasing compressive strength correlates with the simultaneous reduction in the porosity of the material.