The second molar (M2) is the seventh tooth from the midline in the adult dental arch, positioned directly behind the larger first molar. This tooth typically erupts around age 12 and is a common site of loss due to decay, fracture, or planned extraction. The decision to replace the second molar is complex, involving a consideration of its functional contribution to bite stability and the potential long-term consequences of leaving a space empty. This article explores the functions of the second molar, the negative effects of non-replacement, and the factors dentists consider when advising on restoration.
The Role of the Second Molar in Oral Function
The second molar contributes to the total chewing capacity of the mouth, providing an estimated 28% of the total food platform area. Together with the first molar, it bears the heavy forces generated during the grinding phase of mastication. While the first molar facilitates most of the chewing efficiency, the second molar provides support for the entire posterior segment of the dental arch.
The presence of the second molar helps to maintain the correct vertical dimension of the bite, preventing the posterior jaw from collapsing. This structural support is fundamental for the stable alignment of all teeth in the quadrant. Its loss can alter the distribution of forces across the remaining teeth, potentially leading to increased wear on other molars and premolars.
Consequences of Leaving the Space Empty
The loss of a second molar introduces a gap that the body’s natural processes attempt to close, leading to adverse dental movements. Without an adjacent second molar, the first molar (M1) begins mesial tipping, where it drifts and tilts forward into the empty space. This tipping can create uneven contact points with the opposing teeth and complicate future restorative treatments.
A corresponding issue occurs in the opposing jaw, known as super-eruption or extrusion. The molar directly opposite the missing tooth loses its counteracting force, causing it to gradually move out of its socket and into the vacant space. These tooth movements disrupt the harmonious alignment of the jaws, leading to occlusal interferences.
Over time, these interferences may cause uneven tooth wear, muscle soreness, or contribute to issues with the temporomandibular joint (TMJ). Furthermore, the lack of a tooth root to stimulate the surrounding jawbone leads to gradual alveolar bone resorption. This bone loss can make it more difficult to place a dental implant in the future, often requiring a bone grafting procedure.
Key Factors Influencing the Replacement Decision
The decision to replace a missing second molar depends on a patient’s individual oral health profile. A primary factor is the status of the existing occlusion, or how the remaining teeth come together when biting. If the patient maintains a stable bite with the first molars and premolars, replacement may be considered less urgent, as first-molar occlusion alone can facilitate approximately 90% of chewing efficiency.
The presence and condition of the third molar, or wisdom tooth, is another deciding factor. If a healthy, well-positioned third molar is present, it may spontaneously erupt and shift forward into the space left by the extracted second molar. A third molar can successfully replace a second molar, making an artificial replacement unnecessary, particularly in younger individuals.
The degree of super-eruption in the opposing tooth is also closely monitored. Significant super-eruption can severely limit the space available for a future restoration. If the opposing tooth has extruded more than two millimeters, a dentist may recommend replacement to prevent further movement and avoid the need for orthodontic intrusion or reduction of the opposing tooth later on. Ultimately, the decision often involves a discussion with the patient about their perceived chewing deficiency and long-term preference for preserving the dental arch structure.
Available Options for Molar Replacement
When replacement is indicated, several restorative options exist to fill the space and restore function to the posterior arch.
Dental Implant
The dental implant involves surgically placing a titanium post into the jawbone to act as a tooth root. This option is independent of the adjacent teeth and helps to preserve the surrounding jawbone by providing stimulation.
Fixed Bridge
A fixed bridge offers a non-surgical, permanent solution that uses the adjacent teeth as anchors. This restoration requires the first molar and potentially the third molar to be prepared and crowned, with the replacement tooth suspended between them. Fixed bridges restore chewing function, though they require the modification of healthy adjacent teeth and do not directly stimulate the bone beneath the missing tooth.
Removable Partial Denture
For a less invasive or budget-conscious alternative, a removable partial denture can be fabricated. This appliance is composed of a replacement tooth attached to a metal or acrylic base that clasps onto the remaining natural teeth. Removable partial dentures are typically the least costly option and are easily cleaned, but they offer less stability and chewing power compared to fixed restorations.