That sharp zing after a filling might not be what you think.
Imagine biting into an ice cream and feeling a sharp, unexpected pain in a newly filled tooth—a sensation all too familiar for many dental patients. For decades, this common experience was attributed to the filling materials themselves, leading to a long-standing dental dogma: always place a protective layer, or "base," under tooth-colored composite fillings to shield the nerve. But what if this fundamental practice was unnecessary for many procedures? A groundbreaking study from the early 2000s challenged this very principle, sparking a quiet revolution in dental restorations that continues to influence how dentists protect your teeth today.
For years, the standard teaching in dentistry was clear. The process of acid-etching vital dentin—the sensitive, living tissue beneath the enamel—and the potential toxicity of resin materials were considered significant threats to the dental pulp, the tooth's core containing nerves and blood vessels 1 . To counter this, dentists routinely applied protective barriers in the form of liners or bases beneath every composite restoration 1 .
However, a new school of thought began to emerge. Recent studies at the time demonstrated that if a perfect seal was established against bacterial leakage, the acid etchants and restorative materials themselves showed no adverse effects on the pulp 1 . This research suggested that conventional liners might be superfluous.
The dental community was divided, with some clinicians insisting on protection for all cavities, especially deep ones, while others began to question the need for this extra step 1 . It was in this climate of controversy that a team of researchers decided to put the theory to a real-world test.
To resolve this clinical debate, researchers turned to an ideal testing ground: an undergraduate dental program. They conducted a follow-up study on 319 resin composite restorations placed in 151 patients by final-year dental students under close supervision 1 . This setting provided a perfect snapshot of routine clinical practice.
The researchers analyzed several variables for each restoration, including the cavity type, its depth, and—most critically—the type of pulpal protection used beneath the filling.
After the restorations were placed, the team followed up with patients to assess their experience of postoperative sensitivity, the sharp, often transient pain that can follow a filling.
No protective layer at all.
A liner was placed solely on the dentin closest to the pulp.
A base was applied, covering the entire dentin floor of the preparation 1 .
The findings were striking. Of the 319 restorations surveyed, a significant portion—39%—had no protective layer whatsoever placed prior to the restoration 1 . When researchers analyzed the incidence of postoperative sensitivity, they discovered a pattern that contradicted conventional wisdom.
Perhaps the most surprising finding was that not a single shallow cavity—whether protected or not—resulted in postoperative sensitivity 1 .
| Cavity Depth | No Protection | Liner Used | Base Used |
|---|---|---|---|
| Shallow | 0.0% | 0.0% | 0.0% |
| Medium | 5.9% | 5.3% | 0.0% |
| Deep | 0.0% | 9.1% | 0.0% |
Table 1: Postoperative sensitivity rates based on cavity depth and the type of pulpal protection used. Notably, no sensitivity was reported for shallow cavities or for deep cavities protected with a base. Adapted from 1 .
| Restoration Variable | Category | Percentage (%) |
|---|---|---|
| Cavity Type | Class III | 39% |
| Class I | 23% | |
| Class V | 22% | |
| Class II | 8% | |
| Cavity Depth | Shallow | 44% |
| Medium | 38% | |
| Deep | 18% | |
| Pulpal Protection | None (Group 1) | 39% |
| Liner (Group 2) | 26% | |
| Base (Group 3) | 35% |
Table 2: Distribution of 319 composite resin restorations based on cavity type, depth, and the use of pulpal protection. Data from 1 .
The data pointed to a powerful conclusion: for shallow and medium-depth cavities, the placement of a protective layer did not influence whether a patient experienced pain after the procedure.
If the lack of a liner wasn't to blame, what actually caused postoperative sensitivity? The study and subsequent research have pointed firmly toward the breakdown of the seal at the interface between the tooth and the filling.
When this marginal seal is compromised, bacteria and their products from saliva can leak into the microscopic space between the tooth and the restoration.
This phenomenon, known as microleakage, leads to fluid flow within the microscopic tubules of the dentin.
The primary goal of modern adhesive dentistry, therefore, is to achieve and maintain a perfect, long-lasting seal to prevent this chain of events.
Modern adhesive dentistry relies on a suite of specialized materials to create a durable, sealed restoration.
| Tool / Reagent | Primary Function |
|---|---|
| Acid Etchant (e.g., Phosphoric Acid) | Microscopically roughens enamel and cleans dentin surface to create a better bonding surface. |
| Dentin Bonding Agent (DBA) | A primer and adhesive that permeates the etched tooth surface, forming a hybrid layer that micromechanically locks the filling to the tooth. |
| Chlorhexidine-based Antimicrobial | Used after cavity preparation to disinfect the dentin and reduce bacteria that could cause further decay or compromise the bond. |
| Resin-Based Composite (RBC) | The main tooth-colored filling material, composed of a plastic resin with inorganic filler particles, which is bonded directly to the tooth structure. |
| Flowable Composite | A less viscous form of composite sometimes used as a first layer in a deep cavity, thought to better adapt to the dentin surface. |
| Glass Ionomer Liner/Base | In deeper cavities, this material can be used as a protective base; it releases fluoride, which can help prevent future decay. |
Table 3: Key materials used in modern adhesive composite resin restorations.
The findings from this study and others that followed have had a profound impact on clinical practice. They reinforced the principle that the quality of the adhesive bond and the marginal seal are far more critical to preventing postoperative problems than the routine use of a base or liner in every cavity 1 . This allows for a more conservative approach, preserving more healthy tooth structure by avoiding unnecessary cavity deepening to place a base.
Subsequent research, such as that conducted by the PEARL Network, has continued to refine our understanding. While confirming that factors like the use of a liner or a flowable composite showed no significant association with postoperative hypersensitivity, it also highlighted that the choice between total-etch and self-etch dentin bonding agents could lead to small, though clinically questionable, differences in sensitivity 2 .
The focus remains squarely on the technique and the integrity of the final seal. The journey of a single study from a dental school clinic to the forefront of dental practice demonstrates how evidence-based medicine continuously reshapes and improves patient care.
The next time you receive a tooth-colored filling, you can be confident that your dentist's approach is informed by decades of research—all to ensure that your smile is not only healthy but also comfortable.