Modern advancements in dental innovation have brought in a plethora of bioactive dental materials promising natural repair and superior functionality. What are these materials? Where are they used? And, are they as beneficial as they are made to be?

Overview

Restorative dentistry refers to the branch of dental practice that deals with repairing/replacing decayed, damaged, or missing teeth in an attempt to restore oral function. The three main operational areas of this branch include periodontics (gums and related conditions), endodontics (fillings and root canal therapy), and prosthodontics (dentures and other dental prosthesis).

Bioactive dental materials represent the next generation of dental materials that biologically integrate with the tissues of the host, resulting in high treatment acceptability and reduced chances of treatment failure.¹

The rationale behind bioactive dental materials

Traditional dentistry has become synonymous with inert filling materials such as dental amalgams, resin composites, gutta-percha (for root canals), or even gold in some cases! While being quite successful treatment modalities in their own right, these materials come with certain caveats, such as long-term stability, appearance, risk of bacterial adherence, dental microleakage and increased risk of tooth fracture post-root canal therapy, to name a few.^2,4 Dental amalgam is highly favourable due to its strength and stability, however, it is aesthetically challenged and carries a great risk to the patient as well as the dental professional due to its mercury-releasing properties.^1,5

Some key benefits offered by bioactive dental materials include:

• Promote natural healing: Bioactive materials take part in active dental tissue healing. These materials often stimulate the formation of dental tissue (for example, dentin), which promotes the re-strengthening of the tooth structure post-treatment.¹
• Enhanced biocompatibility: Unlike traditional dental materials (inert in nature), bioactive materials integrate with the surrounding tooth structures – increasing biocompatibility and reducing the risk of rejection.
• Preventive function: Certain bioactive materials have fluoride ion-releasing properties that offer long-term protection to the tooth, along with preventing secondary cavities (cavities post-treatment of primary cavity).⁶
• As a bioactive coating for an inert material: Dental materials such as bioactive glass have been used as coatings over surfaces of dental implants (made of bioinert materials such as stainless steel, titanium, cobalt-chromium alloys), and they promote osseointegration, i.e., the structural and functional interlinking of implant and bone surface.⁷
• Long-term performance: Due to their integration with host tissues (biocompatibility) and role in the natural repair process, bioactive materials have the potential to offer reliable long-term performance as dental restorative materials – reducing material waste, and treatment costs, and benefiting patient oral health.

Commonly used dental bioactive materials

According to their chemical nature, bioactive materials come in a myriad of different forms:

• Bioactive cements: Possibly the most known and established bioactive dental materials in restorative dentistry, bioactive cement comprises mainly zinc phosphate, silicate, polycarboxylate and glass ionomer cements.⁸ Among these, zinc phosphate is the oldest material,⁸ however, it is still indicated for certain procedures to this day (for example, amalgam restorations). Glass ionomer cement is largely preferred by clinicians nowadays due to its fluoride-releasing capabilities, aesthetic superiority (natural tooth colour), and improved bio-acceptability.⁹

Glass ionomer cement has been further developed to improve upon some of its limitations – namely short working time (cement sets prior to proper application to the tooth), and inferior mechanical properties including low fracture toughness and shear strength, which renders it prone to breakage. Recent improvements to glass ionomer cements include resin-modified glass ionomer cements, and metal-modified glass ionomer cements (cermet cements) – both of these improve mechanical properties and can be used as reliable restorative filling materials.

• Bioactive glass: Developed in 1969 by Larry Hench,¹⁰ Bioglass is chemically composed of calcium sodium phospho-silicate. It is biocompatible, non-toxic, and stable in the host environment. Bioglass has certain antimicrobial properties as well, making it suitable for dental applications.¹¹

On placement to the treatment site, a conversion reaction starts as soon as the material is hydrated by host body fluids, forming a thin layer of calcium hydroxyapatite crystals over the glass surface, which thickens over time, ultimately forming a new matrix and promoting new bone tissue growth. The main limitation of this bioactive dental material is its low mechanical strength.^{11, 12}

• Calcium silicates: Calcium silicate cements broadly consist of mineral trioxide aggregate (MTA) and Portland cement. These cements are primarily composed of di-calcium and tri-calcium silicates and are known for their stable nature in the presence of water. This property has made them popular among clinicians for use during root canal therapy as a root-end filling material. A meta-analysis conducted in 2022 demonstrated the superiority of MTA, with the odds of MTA being an effective root-end filling material being more than 5 times (OR 5.62, 95% CI 1.58 to 19.99) compared to other materials.¹³ The broad confidence interval of this statistic breeds caution upon the accuracy of the estimate, but the direction of effect cannot be doubted.
• Bioceramics: Bioceramics like zirconia represent the latest developments in dental research. Traditionally used in orthopaedic treatments, zirconia is proving to be a viable high-strength and biocompatible alternative to previously used metallic restorative materials (amalgam, gold). Additionally, zirconia offers the benefit of being aesthetically superior to other restorative materials (almost natural tooth colour).^{14, 15}
• Calcium hydroxide: One of the most versatile materials used in restorative dentistry, calcium hydroxide is supplied and used in various forms ranging from powders to pastes and liquids. They are preferred as they promote healing and repair, have antimicrobial characteristics, and are relatively inexpensive to use.

Applications of dental bioactive materials

Bioactive dental materials have many applications in clinical dentistry. Some of their roles in restorative dentistry include:

• Dental restorations (filling): Bioactive materials such as glass ionomer cement, resin and metal modified glass ionomer cement, calcium silicates, and composites have almost entirely replaced amalgam as the material of choice for dental filling material due to their superior biocompatibility, better bonding to the tooth surface, and overall better aesthetics.
• Pulp capping material: Pulp capping refers to a treatment modality where dental pulp exposed after treatment (drilling and removal of decayed tooth material) is coated with a layer of mineral trioxide aggregate or calcium hydroxide to protect the pulp, reduces inflammation, and promotes regeneration of overlying dental hard tissue (dentin).¹⁶
• Root canal medicaments: These are chemicals that are used during root canal therapy to disinfect the tooth following removal of infected tissue. Commonly used bioactive chemicals include calcium hydroxide and mineral trioxide aggregate due to their antimicrobial properties.¹⁶
• For bone regeneration and repair: Vital to periodontal surgery (surgical procedures on the gums and jaw bone), materials such as bioactive glass are packed into the wound to promote bone regeneration post-surgery.
• Dental prosthesis: Modern bioceramics such as zirconia are used to build crowns and implants which are used to replace missing teeth, or protect teeth after root canal treatment.

Dental bioactive materials – some drawbacks

While being widely accepted in current dental procedures, these materials come with their own set of limitations. Bioactive materials are usually more expensive than traditional materials due to the research and manufacturing costs involved. This reduces accessibility to financially constrained patients. Manipulation and application of bioactive materials require expertise due to their specialised techniques and short working times (the working time of glass ionomer cement is approximately 1-3 minutes). Bioactive fillings are susceptible to wear and tear over the long term due to inferior mechanical properties compared to metallic restorations like amalgam. Upon breakage, it is also more difficult to repair these materials – the solution is usually to drill all pre-existing material and redo the treatment procedure (adding to the financial burden). Finally, limited clinical research combined with rapid advancement has resulted in the availability of a lot of new products, but a lack of scientific evidence justifying their use.

Conclusion and take-home message

Bioactive dental materials undoubtedly provide certain benefits over traditional materials and are likely to be indicated in most situations. However, like all innovations, they come with their own share of setbacks. The take-home message, thus is – although applicable to most cases, there are still certain scenarios where traditional materials outperform the new ones. Further research is needed to develop the ideal dental material, but, till then, your dentist knows best!