Integration Into Dentistry
Many dentists are already integrating bioactive materials into their practices, as calcium hydroxide and mineral trioxide aggregate (MTA) have been available for a long time. One of the earliest uses of bioactive materials in dentistry involved calcium hydroxide, which clinicians have used for decades. It dissociates into calcium and hydroxyl ions, and these calcium ions reduce capillary permeability, lessen the serum flow, and decrease the levels of inhibitory pyrophosphates that cause mineralization. The hydroxyl ions neutralize acid produced by osteoclasts, maintaining optimum pH levels for pyrophosphatase activity, leading to an increased level of calcium-dependent pyrophosphatase—this reduces the levels of inhibitory pyrophosphates and causes mineralization. This activity makes calcium hydroxide one of dentistry’s first bioactive materials, and it remains one of the most widely used.
Some new bioactive filling materials are based on glass-ionomer chemistry. One advantage of these new materials is their ability to inhibit surface matrix metalloproteinases (MMPs). The plasma proteins released by dentin when subjected to acids from caries will cause hydrolytic and enzymatic (MMP) breakdown of the dentin and resin bonding-agent interface.4,5 Several methods for reducing these MMPs include the use of 2% chlorhexidine, etchants containing benzalkonium chloride, and polyvinylphosphonic acid-producing products such as the new RMGI-based bioactive restoratives.
An example of a long-standing and well-accepted bioactive material in dentistry is mineral trioxide aggregate (MTA). It is a mechanical mixture of three powder ingredients—Portland cement (75%), bismuth oxide (20%), and gypsum (5%)6—along with trace amounts of silicon dioxide, calcium oxide, magnesium oxide, potassium sulfate, and sodium sulfate. The major component, Portland cement, is a mixture of tricalcium aluminate, dicalcium silicate, tricalcium silicate, and tetracalcium aluminoferrite. Sarkar et al7 concluded that MTA is not an inert material because it dissolves, releasing all of its major cationic components and triggering the precipitation of HA on its surface and in the surrounding fluid. It appears to bond chemically to dentin when placed against it, possibly by a diffusion reaction between its apatitic surface and dentin. MTA has a long history of clinical success and, in terms of its biocompatibility, an ability to seal and produce dentinogenic activity.
MTA was recently introduced in a user-friendly, light-activated form (ie, TheraCal, Bisco, Inc., www.bisco.com). This light-cured bioactive material is used to seal and protect the dentin–pulp complex and can be used for pulp capping. Some have referred to this new class of internal pulpal protectant materials as resin-modified calcium silicate (RMCS). While RMCS has demonstrated apatite formation,7 it has yet to be determined if this new class of materials is clinically effective.
Another entry into the bioactive arena was developed as a multipurpose dentin and root replacement material (ie, Biodentine®, Septodont, www.septodontusa.com). It has clinical indications that go beyond those of MTA and related Portland cement/calcium-silicate products. These include restoration of deep and large coronal carious lesions and deep cervical and radicular lesions, as well as MTA indications such as pulp capping and pulpotomy, repair of root perforations, furcation perforations, perforating internal resorptions, external resorption, apexification, and root-end filling in endodontic surgery, and it is biocompatible.8 The product is also bioactive with deposition of HA on its cement surface in the presence of simulated body fluid.9
Recent developments have also occurred in the area of bioactive cements. These include calcium aluminates (ie, Ceramir®, Doxa Dental Inc., www.ceramirus.com) and calcium-, phosphate-, and fluoride-releasing cements. These cements produce HA at 14 and 28 days (Figure 1 and Figure 2).10 A bioactive material that has the ability to induce HA formation on a damaged tooth structure while meeting clinical standards may have beneficial clinical implications. One hypothesis is that the use of such a material, whether as a restorative product or cement, would make it more difficult for recurrent caries to occur, because the natural formation of HA between the tooth structure and the material should create a more stable cement interface. These benefits also hold for this same class of materials that is being used as liners and restoratives.11
These cements are intended for the permanent cementation of crowns and fixed partial dentures, gold inlays and onlays, prefabricated metal cast dowels and cores, and high-strength all-zirconia restorations.11,12 The calcium aluminate cement (Ceramir) is a water-based composition comprising calcium aluminate and glass-ionomer components.13
New calcium-, phosphate-, and fluoride-releasing bioactive cements (eg, Activa™ Bioactive, Pulpdent, www.activabioactive.com; BioCem®, NuSmile, www.nusmilecrowns.com) contain a glass-ionomer component.14 This contributes to their initial, short-duration pH reading; improved flow and setting characteristics; early adhesive properties to tooth structure; and early strength properties. The components in these cements seem to result in increased strength and retention over time; biocompatibility; sealing of tooth–material interface; bioactivity–apatite formation; stable, sustained long-term properties; lack of solubility/degradation; and ultimate development of a stable, basic cement pH measurement.12
To reiterate, the term bioactivity refers to a property of these new cements to form HA when immersed in vitro in a physiologic phosphate-buffered saline solution. Although significant in vitro data on the new bioactive cements exist, little-to-no clinical data are available. However, those clinical studies that have been done seem to be positive.15
The clinical case depicted in Figure 3 through Figure 7 demonstrates the use of a bioactive liner and base in the treatment of a deep carious lesion. The patient presented with reversible pulpitis, which was characterized by sharp sensitivity to cold and biting and the brief painful response to stimuli. During excavation of caries, the clinician noted the cavity was close to the pulp with no pulpal exposure. The tooth has been asymptomatic for more than 3 years.