Post-Op Sensitivity Decoded: Biomechanical Vs. Operator-Induced Causes

About 10-15% of posterior composite restorations result in postoperative sensitivity¹.

Understanding whether sensitivity stems from biomechanical factors or operator technique can transform how you do the restoration.

The Hydrodynamic Mechanism: Why Sensitivity Occurs?

Before diving into specific causes, it is crucial to understand the underlying mechanism. Postoperative sensitivity can be explained via hydrodynamic theory.

The polymerization shrinkage creates microgaps at the restoration interface. Dentinal fluid fills these gaps after placement, and thermal or osmotic stimuli may cause fluid movement in dentinal tubules. Mechanoreceptors near the pulp detect this movement and trigger pain signals².

However, most sensitivity resolves within a few days. Patients presenting with early complications have higher failure rates in the long run³.

Understanding the Two Categories of Causes

Postoperative sensitivity stems from two distinct categories: biomechanical factors during the restoration process and operator-induced errors during placement. 

Recognizing which category drives sensitivity in your practice determines your prevention strategy.

Biomechanical Causes

These include:

1. Polymerization Shrinkage Stress

Composite resins shrink 1.7-2.1% during curing, generating contraction forces at the tooth-restoration interface. When shrinkage stress exceeds bond strength, marginal gaps form, which provide pathways for fluid movement and bacterial ingress⁴.

Traditional parallel-wall preparations exacerbate shrinkage forces in composites and may create high stress concentration zones.

2. C-Factor 

The C-factor represents the ratio of bonded to unbonded surfaces. Higher C-factor equals more stress.

For example, a Class I cavity has a C-factor 5 with five bonded surfaces and one free surface. Whereas, a class II MOD has a C-factor 3-4, and a class V has C-factor 0.2-1.5.

Studies consistently show increased stress and reduced adhesion performance in high C-factor preparations, which correlates with high postoperative sensitivity⁵.

3. Cavity Depth and Remaining Dentin Thickness

When the remaining dentin thickness drops, the sensitivity risk increases exponentially. Deep cavities present larger dentinal tubule diameter near the pulp, increased tubule density, and higher pulpal pressure.

4. Restoration Complexity

Complexity matters more than most clinicians realize. More surfaces that bond, greater preparation depth, and increased polymerization stress can all contribute to sensitivity.

Operator-Induced Causes

Industry experts emphasize that with modern material science reaching almost excellence, now most postoperative sensitivity stems from operator error. Therefore, most of the time, it can be prevented.

1. Over-Etching Dentin

Aggressive etching with phosphoric acid demineralizes deeper than adhesives can penetrate and creates excessive collagen exposure, incomplete resin infiltration, and nanoleakage pathways⁶.

While enamel benefits from longer etching, dentin should only be lightly etched to avoid excessive demineralization.

2. Over-Drying 

It is easily the most common technical error. Over-drying collapses the exposed collagen network after acid etching. 

Studies show desiccated dentin creates a collapsed collagen layer that's almost impossible for adhesive to infiltrate⁷.

It can be seen in the form of chalky white appearance, opaque surface that have lost the that shining moist look.

Proper technique is simply air-drying the surface for 2-3 seconds and maintaining the "glistening" appearance. Avoid using compressed air for prolonged periods.

3. Inadequate Adhesive Penetration

Rushing adhesive application prevents complete penetration into dentinal tubules and demineralized collagen⁷.

It is suggested to apply adhesive and agitate actively for a few seconds as much as it allows penetration time per the manufacturer. Then apply a second coat for deeper cavities and light cure for the recommended duration.

4. Moisture Contamination

Even a little bit of saliva or blood contamination can compromise bonding. Saliva proteins can interfere with adhesive polymerisation, and excess moisture may prevent adhesive penetration^8.

Rubber dam isolation is therefore essential for bonding, especially in posterior Class II preparations.

5. Incomplete Polymerization

Under-cured composite creates reduced mechanical properties, increased unreacted monomers and greater polymerization shrinkage over time. 

Contributing factors include inadequate curing time, weak light output, excessive distance from restoration, shadowing in deep proximal boxes, and thick increments.

6. Curing Protocol Errors

Constant-intensity curing generates maximum shrinkage stress immediately. 

Studies comparing soft-start vs. constant curing show reduced postoperative sensitivity with gradual polymerization protocols that allow molecular flow during early polymerization and reduce peak shrinkage stress⁹.

Final Takeaway

Postoperative sensitivity splits into two categories: biomechanical factors you must manage and operator errors you can eliminate.

You may not be able to change cavity depth, C-factor, or polymerization shrinkage, but you can definitely control etching time, drying technique, isolation quality, and curing protocols.

Your next restoration can be sensitivity-free if you prevent the preventable.

References

1. Maghaireh GA, Aslam N, Khalid R, et al. Postoperative sensitivity in posterior restorations restored with self-adhesive and conventional bulk-fill resin composites: A randomized clinical split-mouth trial. Clin Oral Investig. 2023 Oct;27(10):4445-4454
2. Liu XX, Tenenbaum HC, Wilder RS, Quock R, Hewlett ER, Ren YF. Pathogenesis, diagnosis and management of dentin hypersensitivity: an evidence-based overview for dental practitioners. BMC Oral Health. 2020;20(1):220.
3. Demarco FF, Cenci MS, Montagner AF, de Lima VP, Correa MB, Moraes RR, Opdam NJM. Longevity of composite restorations is definitely not only about materials. Dent Mater. 2023 Jan;39(1):1-12.
4. Yu P, Xu YX, Liu YS. Polymerization shrinkage and shrinkage stress of bulk-fill and non-bulk-fill resin-based composites. J Dent Sci. 2022 Jan;17(1):284–292.
5. Eichler E, Vach K, Schlueter N, Jacker-Guhr S, Luehrs AK. Dentin adhesion of bulk-fill composites and universal adhesives in class I cavities with high C-factor. J Dent. 2024 Mar;142:104852. 
6. Perdigão J, Araujo E, Ramos RQ, Gomes G, Pizzolotto L. Adhesive dentistry: current concepts and clinical considerations. J Esthet Restor Dent. 2020 Dec 2.
7. Bourgi R, Kharouf N, Cuevas-Suárez CE, Lukomska-Szymanska M, Haikel Y, Hardan L.A literature review of adhesive systems in dentistry: key components and their clinical applications. Appl Sci. 2024;14(18):8111.
8. Burke FJT, MacKenzie L, Sands P, Shortall ACC. Ten tips for avoiding post-operative sensitivity with posterior composite restorations. Dent Update. 2021;48(10):823-832.
9. Bardocz-Veres Z, Miklós ML, Biró EK, Kántor ÉA, Kántor J, Dudás C, Kerekes-Máthé B. New perspectives in overcoming bulk-fill composite polymerization shrinkage: the impact of curing mode and layering. Dent J (Basel). 2024 Jun 5;12(6):171