Pain in a back tooth (molars and premolars) is a common and often alarming symptom. These teeth are positioned at the rear of the mouth, making them responsible for the intense grinding and chewing forces required to break down food. Their location makes them susceptible to problems because they are difficult to clean effectively, allowing plaque and bacteria to accumulate in deep grooves and fissures. Understanding the distinct causes of this discomfort is the first step toward seeking appropriate care.
Damage to Enamel and Dentin
The most frequent source of back tooth pain involves structural breaches in the tooth’s protective layers. The outermost layer, enamel, is the hardest substance in the human body. Once compromised by acid from bacteria, it leads to a cavity (dental caries). This decay creates a pathway to the dentin, the softer layer beneath the enamel, which is penetrated by millions of microscopic tubules.
These dentinal tubules contain fluid and connect directly to the pulp, the soft tissue at the tooth’s core. When enamel is lost, external stimuli like cold air, hot liquids, or sweet foods cause rapid fluid movement within these tubules. This activates the nerve endings at the pulp-dentin border, resulting in the characteristic short, sharp burst of pain known as temperature sensitivity (the hydrodynamic theory).
Pain can also arise from physical trauma, such as a crack, chip, or fracture in the tooth structure. Molars are frequently subjected to high stress from chewing and habits like teeth grinding, which can lead to microfractures. Minor decay or a small crack may only cause sensitivity that quickly subsides after the stimulus is removed (reversible pulpitis).
As the damage progresses and the dentin becomes more exposed, the sensitivity becomes more intense and lingers longer. This signals the need for intervention before the nerve becomes permanently damaged.
Internal Infection and Nerve Inflammation
A deep, constant ache often indicates a more serious condition involving the dental pulp, the living tissue containing the tooth’s nerves and blood vessels. When decay or a crack penetrates into the pulp chamber, bacteria invade, leading to inflammation called irreversible pulpitis. Because the pulp is encased in the rigid structure of the tooth, inflammation causes pressure to build, intensely irritating the nerve fibers.
The pain from irreversible pulpitis is often spontaneous, persistent, and throbbing, sometimes radiating to the jaw or ear. This discomfort frequently worsens at night or when lying down, due to increased blood pressure in the head. If the infection is left untreated, bacteria travel down the root canal to the tip of the root, forming a pocket of pus called a periapical abscess.
An abscess is a localized infection that can cause the surrounding gum tissue to become swollen and tender. Symptoms include extreme sensitivity to pressure, a foul taste in the mouth, facial swelling, or fever. This stage represents a serious bacterial infection that can spread beyond the tooth into the jawbone or surrounding tissues. Untreated abscesses can potentially lead to systemic health issues if not treated promptly.
Pain Related to Position and Gums
Discomfort in the back of the mouth is not always caused by decay but can originate from the surrounding soft tissues and bone. The eruption of wisdom teeth (third molars) is a common source of posterior pain, especially when they are partially emerged or impacted. If a wisdom tooth fails to fully erupt, a flap of gum tissue, known as an operculum, can form over the partially exposed tooth.
This gum flap can trap food particles and bacteria, leading to a localized infection and inflammation called pericoronitis. Symptoms include a swollen, red gum, pain when biting down, and sometimes a foul odor or discharge. Pressure exerted by a developing or impacted wisdom tooth pushing against an adjacent molar can also cause a deep, dull ache, mimicking a problem with the second molar.
The health of the gums and supporting bone (the periodontium) can also cause sensitivity in the back teeth. Periodontal disease leads to gum recession and bone loss, which exposes the root surface of the tooth. Since the root surface lacks enamel protection, it is extremely sensitive to temperature changes and touch. Bite issues, such as those caused by a worn or ill-fitting filling or crown, can create pain by subjecting a back tooth to excessive force during chewing.
Referred Pain and Urgent Action Needed
Sometimes, pain felt in a back tooth originates elsewhere in the head or face, known as referred pain. A frequent non-dental cause of pain in the upper molars is sinusitis (inflammation of the sinuses). The roots of the upper back teeth are physically close to the maxillary sinuses, and sometimes project into the sinus cavity.
When the sinus lining swells due to infection or allergies, the resulting pressure can irritate the nerves supplying the upper teeth, causing a diffuse, dull ache across several molars. This sinus-related pain is often worse when the head is lowered or with sudden movement. Another source of referred pain is Temporomandibular Joint Disorder (TMD), which affects the jaw joint and surrounding muscles. Dysfunction or strain in this joint can cause pain that radiates into the cheek, ear, and posterior teeth.
It is important to recognize when back tooth pain signals an emergency requiring immediate professional attention. Any severe, unrelenting, or throbbing pain that does not respond to over-the-counter medication should prompt a call to a dentist.
More concerning signs include swelling of the face, jaw, or gums, which indicates a spreading infection or abscess. Difficulty swallowing or breathing, accompanied by a fever, signals a potentially life-threatening complication where the infection has progressed to deeper tissues, necessitating an immediate visit to an emergency room.