Matrix metalloproteinases (MMPs) are enzymes that break down components of the extracellular matrix, the network providing structural support to cells. A primary target of MMPs is collagen, the protein that structures skin, bone, and oral tissues. This breakdown is a normal part of tissue maintenance, remodeling, and repair.
In the mouth, MMPs have a dual role. In a healthy state, their activity is balanced and necessary for tissue upkeep. When this balance is disrupted, their actions can contribute to the breakdown of oral structures, making them a subject of significant interest in dentistry.
The Fundamental Role of MMPs in Oral Tissues
MMPs are continuously active in the mouth, performing maintenance. They are instrumental in the natural turnover of soft tissues like the gums and the periodontal ligament, which attaches a tooth to the jawbone. This controlled breakdown and rebuilding of collagen ensures these tissues remain healthy and can adapt to daily forces.
Their role becomes more prominent during healing. Following a tooth extraction or gum surgery, MMPs help clear away damaged tissue, making way for new cells to grow. This regulated enzymatic activity is part of the repair process that allows for efficient recovery and helps remodel the wound site.
MMPs are also involved from the beginning of a tooth’s life. During tooth development, these enzymes are active in shaping the dentin and enamel. This involvement in creating dental tissues underscores their constructive role in normal physiological processes.
MMPs in Dental Caries and Periodontal Disease
The constructive role of MMPs shifts when disease begins. In dental caries (cavities), acids from oral bacteria first dissolve the tooth’s outer enamel. When this demineralization reaches the underlying dentin, the role of MMPs becomes destructive.
Dentin contains collagen and inactive MMPs. The bacterial acids activate these dormant enzymes, particularly MMP-2, MMP-8, and MMP-9. The tooth’s own MMPs then begin to digest the collagen framework of the dentin, accelerating the cavity’s progression from the inside.
A similar destructive process occurs in periodontal disease. The accumulation of bacterial plaque triggers an inflammatory response, causing immune cells to release a flood of MMPs into the gum tissues. The excessive and prolonged activity of these enzymes, especially MMP-8 and MMP-9, becomes the primary cause of tissue destruction.
These MMPs break down the collagen in the gums and the periodontal ligament. This degradation causes gums to detach from the teeth, creating pockets that deepen the infection. As the ligament is destroyed, the underlying bone that supports the teeth is also resorbed, leading to tooth mobility and loss.
The Impact of MMPs on Dental Restorations
MMPs also impact the longevity of dental restorations, particularly tooth-colored resin composite fillings. The success of these fillings depends on a durable bond between the material and the tooth’s dentin. This bond is created by treating the dentin with a mild acid and applying an adhesive, forming a fused structure called the hybrid layer.
The hybrid layer seals the restoration to the tooth, but the patient’s own MMPs within the dentin pose a long-term threat. The acidic conditioners used during the bonding procedure activate these latent enzymes. Over months and years, these activated MMPs slowly degrade the collagen fibers within the hybrid layer.
This enzymatic breakdown weakens the adhesive interface from within. As the bond deteriorates, microscopic gaps can form along the filling’s margins. These gaps allow bacteria and fluids to leak underneath, leading to secondary decay, staining, and eventual failure of the restoration.
Therapeutic Inhibition of MMPs in Dentistry
Given the destructive potential of MMPs, dental research focuses on inhibiting their activity. The goal is not to eliminate MMPs but to control their effects in specific situations. This has led to therapeutic strategies that target these enzymes to improve patient outcomes.
A common MMP inhibitor is chlorhexidine. This antiseptic agent has a secondary property of deactivating MMPs. Dentists can apply a 2% chlorhexidine solution to a cavity preparation before placing the adhesive to neutralize MMPs in the dentin, protecting the hybrid layer and enhancing bond durability.
Research has explored other inhibitors for managing MMP activity. Low-dose doxycycline is used in periodontal therapy for its ability to suppress MMP production in gum tissues. Natural compounds, such as catechins found in green tea, have also shown promise in laboratory studies for their ability to inhibit MMPs.