When decay rots away enamel, the resulting space is called a cavity. Left untreated, the decay will eventually cause extensive damage to the tooth, and potentially cause the root to be infected. However, if the cavity is caught early, your dentist can treat it with a simple filling, typically in one appointment. Your dentist will first apply a local anesthetic, then use a drill or laser to remove the decay. Then they will apply filling to prevent further decay, and to prevent the sensitive inner layers of the tooth from cold, heat or pressure. The filling is applied in layers and hardened with a special light. The final layers are shaped and polished to restore the tooth’s appearance and function. Composite (plastic resin) is the modern filling material of choice in most cases. We consider it superior to the silver amalgam fillings commonly used in the past. Silver amalgam fillings contain small amounts of mercury, while composite fillings are completely free of mercury. Composite fillings are also less likely to result in sensitivity to heat or cold, since the material does not expand or contract as much as silver amalgam. And since the composite material closely matches the colour of the tooth, fillings are nearly invisible.