Why Restorations Fail: Adhesive Fatigue, Bond Degradation

Restorations remain the most frequently performed dental procedure, yet they also have one of the highest long-term failure rates. Understanding why they fail is now just as important as how we place them.

So, we have modern research laid out for you that offers clearer explanations on why restorations truly fail and how clinicians can prevent the breakdown.

Restoration Failure Reasons

Restoration failure isn’t mostly sudden; it is a progressive breakdown of the hybrid layer that may happen due to mechanical stress and hydrolysis.

Here are some common reasons:

1. Adhesive Fatigue Starts Within the First Year

Universal adhesives encounter rapid loss of bond strength in dentin, especially under mechanical and thermal stress¹. 

At the same time, application mode, which can be etch-and-rinse or self-etch, may also influence longevity.
Studies reveal that both hydrolytic and enzymatic degradation lead to early dentin bond loss.​

Latest evidence suggests that universal adhesives perform best when proper technique is followed, but remain vulnerable at dentin margins².​

2. Enamel Bonds Last Longer, but Dentin Bonds Don’t

Enamel’s crystal structure allows stable etch-and-rinse bonding. Whereas, dentin’s moisture and collagen can make it prone to degradation¹. 

Restorations fail faster in high C-factor cavities where stress is concentrated.

A high C-factor cavity is a preparation where most walls are bonded and only a few walls are free.

3. Contamination Reduces Bond Strength by Up to 50%

Saliva, blood, hemostatic agents, glove powder, oil from handpieces, wet dentin, and excess moisture can reduce immediate and long-term bond strength³. 

It is seen that universal adhesives are more sensitive to contamination than manufacturers claim. Effective cleaning protocols post-contamination remain essential.

4. Hybrid Layer Degradation Is MMP-Driven

This slow biochemical breakdown continues for years unless actively inhibited.

Matrix metalloproteinases (MMP-2, MMP-9) activated during bonding can slowly destroy collagen fibrils, causing microleakage and staining, and may lead to sensitivity. Chlorhexidine and MMP inhibitors have been shown to delay degradation⁴.

5. Technique Errors Accelerate Failure

Even with the best adhesives, failures are often operator-induced. Inadequate solvent evaporation, incorrect adhesive mode selection, under-curing, and compromised isolation can all weaken the hybrid layer from day one. 

These technique-sensitive steps can directly influence postoperative stability and, in turn, long-term success.

Beyond technique, the choice of restorative material itself also plays a critical role in long-term success.

Where Restorations Actually Fail?

Understanding failure locations helps predict which restorations need closer monitoring:

Gingival Margins

It is one of the most common failure site and reasons include:

• Difficult moisture control
• Thin enamel margins
• High stress concentration
• Subgingival location complicates bonding

Isthmus Regions

Class II restorations fail at the isthmus due to⁶:

• Maximum polymerization stress concentration
• High C-factor 
• Inadequate bulk in thin areas
• Cyclic loading stress

Proximal Boxes

It may happen due to:⁷

• Limited access for adequate etching
• Moisture contamination from adjacent teeth
• Inadequate light curing 
• High bacterial exposure

Clinical Strategies That Actually Work

Here are a few strategies that can help maintain good restorations- 

1. MMP Inhibition

Chlorhexidine (CHX) application after acid etching can preserve bond strength in the long run.

Protocol: Apply 2% CHX to etched dentin for 60 seconds after phosphoric acid rinse, before you apply the adhesive. Clinical studies demonstrate this prevents bond degradation for extended periods⁴.

Alternative inhibitors:

Zinc oxide nanoparticles in adhesives

Doxycycline-modified adhesives

Cross-linking agents like glutaraldehyde, carbodiimide

2. Optimize Adhesive Strategy

For maximum bond durability you can try⁷:

• Selective enamel etching with self-etch systems
• Avoid over-etching dentin
• Never over-dry after etching 
• Apply adhesive in multiple thin coats
• Extend adhesive application time to allow penetration

3. Stress Management

You can reduce polymerization stress with these steps⁶:

• Incremental layering of max 2mm layers
• Use soft-start or pulse-delay curing protocols
• Consider low-shrinkage materials for large cavities
• Place liner/base in high C-factor situations

4. Margin Location Matters

You can opt these if possible⁸ -

• Locate margins on enamel that provide superior bond strength
• Avoid subgingival margins unless necessary
• Use immediate dentin sealing for indirect restorations
• Consider crown lengthening for deep proximal boxes

Final Takeaway

The success ultimately will depend on meticulous technique, which includes stress reduction, moisture control, and occlusal adjustment. 

Even the best materials cannot compensate for poor clinical execution. Therefore, sticking to evidence-based protocols is crucial for long-lasting, comfortable restorations.

References

1. Hardan L, Bourgi R, Kharouf N, Mancino D, Zarow M, Jakubowicz N, Haikel Y, Cuevas-Suárez CE. Bond strength of universal adhesives to dentin: a systematic review and meta-analysis. Polymers (Basel). 2021 Mar 7;13(5):814.
2. Ñaupari-Villasante R, Matos TP, de Albuquerque EG, Warol F, Tardem C, Signorelli Calazans F, Poubel LA, Reis A, Barceleiro MO, Loguercio AD. Five-year clinical evaluation of universal adhesive applied following different bonding techniques: a randomized multicenter clinical trial. Dent Mater. 2023 Jun;39(6):586-594.
3. Chen AMC, Ekambaram M, Li KC, Cooper PR, Mei ML. A scoping review of the influence of clinical contaminants on bond strength in direct adhesive restorative procedures. J Dent. 2024 Jun;145:104985.
4. Kiuru O, Sinervo J, Vähänikkilä H, Anttonen V, Tjäderhane L. MMP inhibitors and dentin bonding: systematic review and meta-analysis. Int J Dent. 2021 May 29;2021:9949699.
5. Miletić I, Baraba A, Jukić Krmek S, Perić T, Marković D, Basso M, Atalayin Ozkaya C, Kemaloğlu H, Turkun LS. Clinical performance of a glass-hybrid system in comparison with a resin composite in two-surface class II restorations: a 5-year randomised multi-centre study. Clin Oral Investig. 2024 Jan;28(1):104.
6. 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.
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 (Basel). 2024;14(18):8111.
8. Cardoso JA, Almeida PJ, Negrão R, Oliveira JV, Venuti P, Taveira T, Sezinando A. Clinical guidelines for posterior restorations based on Coverage, Adhesion, Resistance, Esthetics, and Subgingival management (CARES concept): Part I – partial adhesive restorations. Int J Esthet Dent. 2023 Jul 18;18(3):244–265.