When a tooth causes pain after a light tap or gentle pressure, dentists call this sensitivity to percussion. This reaction signals localized inflammation or damage within the structures supporting the tooth. The pain is caused by mechanical force irritating sensitive tissues, not typically by simple temperature shifts. Understanding this distinct sensitivity helps pinpoint the precise source of a dental problem.
Inflammation Originating Inside the Tooth
The most frequent reason a tooth hurts when tapped involves inflammation that started deep inside the tooth’s core, known as the pulp. The pulp contains the tooth’s nerves and blood vessels, and deep decay or infection can lead to pulpitis. If untreated, the infection travels down the root canal system to the tip of the root. This results in apical periodontitis, causing swelling in the surrounding bone and the periodontal ligament (PDL).
The PDL is a thin layer of tissue anchoring the root to the jawbone. Tapping the tooth compresses it slightly into the socket, directly irritating this swollen, highly innervated ligament. The pain is caused by the sudden increase in pressure within the confined space and the inflamed tissue.
If the infection advances, pus can accumulate at the root tip, forming a dental abscess. This pocket dramatically increases the pressure, making the tooth extremely sensitive to percussion and signaling a serious internal issue.
Pain Caused by Structural Damage
Pain from tapping can also signal a physical break or fracture in the tooth structure, often called cracked tooth syndrome. This sensitivity is caused by the mechanical movement of the fractured segments under pressure. When the tooth is tapped, the force causes the crack to momentarily widen or flex, stimulating the underlying dentin or pulp. This mechanical pressure directly stimulates exposed nerve endings.
Cracks can be difficult to detect visually, sometimes extending vertically from the chewing surface into the root. A vertical root fracture is a severe break that runs down the side of the root. Tapping or biting causes the fractured pieces to shift, irritating the periodontal ligament or the internal nerve tissue.
Dentists use percussion testing to help locate the specific segment of the tooth that is moving or flexing. Detecting these breaks early is important, as the fracture can allow bacteria to enter and compromise the entire tooth structure.
Other Sources of Tapping Sensitivity
Sensitivity to percussion does not always originate from the root tip or a fracture. Severe periodontal disease causes inflammation along the entire side of the root and surrounding bone. This lateral inflammation of the periodontal ligament can make the tooth tender when pressure is applied.
Upper back teeth can also exhibit sensitivity due to referred pain from a sinus infection (sinusitis). The roots of these teeth are often close to the floor of the maxillary sinus. Pressure buildup within the sinus cavity can mimic dental pain, causing the tooth to feel tender.
A new filling or crown that is slightly too high can temporarily cause similar sensitivity. This is a form of occlusal trauma, where the tooth receives excessive force during biting or tapping, straining the periodontal ligament. Adjusting the height of the restoration often alleviates this pressure-related pain.
When to See a Dentist
Any persistent pain when tapping a tooth indicates a problem that requires professional evaluation and should not be ignored. This symptom usually points toward a serious underlying condition, such as a deep infection or a structural break. Early diagnosis determines whether the tooth needs a root canal procedure, a structural repair like a crown, or potentially an extraction.
Seeking prompt care is important to prevent the infection from spreading into the jawbone or surrounding tissues. A dentist uses percussion tests in conjunction with X-rays to accurately identify the source of the pain. Ignoring this sensitivity allows the underlying condition to progress, potentially leading to more complex and costly treatments.
Immediate emergency dental care is necessary if the pain is accompanied by systemic warning signs. These symptoms suggest the infection has spread beyond the immediate tooth area and poses a risk to overall health. Warning signs include facial or jaw swelling, a persistent fever, or difficulty swallowing.