Calibra® Bio

In a clinical study, the handling properties as well as the working and setting time for Calibra^® Bio cement were favorable during cementation.^1,2 The investigators were attracted to the ease of cement removal in one or few pieces without need to rush the clean-up. A total of 38 crowns and bridges were cemented on retentive preparations of 43 vital and in non-vital teeth. At the three-year recall, no loss of retention, secondary caries or marginal discolorations were found. All restorations rated excellent for marginal integrity. In addition, no associated gingival inflammation or hypersensitivity was reported.

When the powder is mixed with the aqueous liquid in a capsule mixer/triturator, the resulting chemical reactions of the calcium aluminate (CA) and the reactive glass ionomer parts form a biocompatible cement material. The setting reaction of Calibra Bio cement roughly follows two different acid-base reactions:

1. Glass ionomer reaction of polyacrylic acid with basic reactive glass
2. Hydration of CA resulting in precipitation of crystals – katoite and gibbsite

Both reactions run simultaneously and cannot be considered individually in reality, as they are linked and influencing each other, e.g. due to pH-effects and the occurring initial ion release.

Beside the well-known glass ionomer setting reaction, especially the hydration of CA plays a key role since several of Calibra^® Bio Cements beneficial properties are based on this process. The hydration starts when CA makes contact to water and starts to dissolve into the liquid phase, forming Ca²+, Al(OH)₄ - and OH-ions (dissolution period). The dissolution of CA is accompanied by the precipitation of small amounts of an amorphous meta-stable AH₃-gel and other hydrates. At a certain point the Ca²+concentration and the Ca²+/ Al(OH)₄ ratio is sufficient leading to growing of nuclei. In this period, the solution starts to thicken and becomes basic due to excess of OH-ions (nucleation period). At the end of the nucleation period, massive precipitation begins (bulk-precipitation period) followed by transformation of the meta-stable hydrates to the thermodynamically stable minerals katoite (Ca₃[Al(OH)₄]2(OH)₄) and gibbsite (Al(OH)3) (continued simultaneous precipitation/dissolution period). The hydration process is proceeding until all CA or water is consumed.

During the dissolution period, the CA part of Calibra^® Bio cement dissolves into the liquid phase and the resulting ion-containing solution will penetrate imperfections of the tooth wall. The emerging hydrates will precipitate at pre-existing nuclei and filler particles on the tooth wall. During this process, the surface irregularities are filled by emerging CA hydrates leading to a seamless surface adaptation of Calibra^® Bio cement towards the tooth structure.

The primary mineral of human tooth enamel and dentin is hydroxyapatite (HA), which is a crystalline calcium phosphate (Ca₁₀(PO₄)₆(OH)₂). The formation of an HA-layer occurs along the preparation margins where Calibra^® Bio cement is in direct contact to the oral environment. The additional HA layer contributes to an excellent marginal seal and enhances the integrity of the restoration. The HA forming reaction is caused by ion release of the cement (Ca²⁺ , OH-) in combination with phosphate ions from saliva, but also arises when katoite (product of CA hydration) gets in contact to body-fluid. The growth of HA is slowing down with layer thickness and will stop at a certain point when no more  Ca²⁺/OH ions are diffusing through the existing layer. In case the HA layer is removed or damaged and a relevant amount of ions is available again, new HA is formed and precipitated. Therefore, the HA layer can be regarded as a self-repairing layer.