Development of test methods to research hydraulic cements in dentistry

This project researches hydraulic calcium silicate cements that are used in dentistry. These materials were introduced to dentistry from the construction industry and are used for a range of endodontic procedures (vital pulp therapy, root canal treatment). They are different to other dental materials as they require water to set and the presence of moisture enhances the materials properties. All other dental materials need to be used in a dry field which is challenging for oral procedures.

Endodontics is a dental speciality dealing with the management of diseases to the dental pulp which are sequel of loss of tooth structure due to dental caries, acid erosion, wear or trauma. Depending on the severity of the tooth tissue loss and pulp involvement, the dental pulp management ranges from vital pulp therapy where the tooth is dressed with a bioactive material and restored, to root canal therapy (if the pulp is irreversibly damaged or infected) and surgery with placement of a bioactive material at the end of the root for cases that fail.

All clinical procedures related to pulp management involve the mechanical cleaning of the pulp cavity, chemical irrigation to reduce the microbial load, followed by the placement of a bioactive material. The materials of choice for such procedures are hydraulic cements such as Portland cement. The hydraulic nature of these materials results in the interaction of the material with the tissues it is placed against and the environmental fluids.

This interaction is responsible for the bioactivity of the materials and better interaction of the materials with the host tissues. Due to these characteristics, clinical procedures need to be tailor-made for that specific chemistry.

To date, laboratory testing of hydraulic cements is often undertaken in similar ways to the testing of other dental materials with a similar clinical use. This has created a number of problems because hydraulic cements are environment-dependent which add limitations to the relevance of the testing undertaken using traditional approaches. This renders in vitro testing of these materials to be not clinically translatable to their daily use in clinical practice.

The quality control evaluation of these materials is also undertaken using standards that were designed for materials of different chemistries and properties whereby the hydraulic cements do not comply as the standards are set for different material chemistries. One such property is solubility as the interaction of hydraulic cements with the tissue fluids produces apparent high solubility that is higher than the set standard. However in vivo, the tissue interactions lead to bioactivity which counteracts the solubility.

The lack of updated clinical protocols and standards to which these materials need to comply to, has led to a number associated problems in clinical use. These include material extrusion out of the tooth (leading to formation of foreign bodies in the patient tissues), failure to set, leading to material disappearance from the surgical site which results in treatment failures and the need for revisions/repeated treatments.

Vital pulp therapy and root canal therapy are procedures that are undertaken daily by all dental practitioners, but guidance with appropriate clinical protocols and materials that comply to adequate standards are necessary to protect patients from the undesirable effects of inappropriate management