What are the most common reasons for failure of direct and indirect restorations and endodontic treatments?

Most Common Reasons for Restoration and Endodontic Treatment Failure

Direct and Indirect Restorations

Secondary caries is the single most common cause of failure for both direct and indirect posterior restorations, followed by material fracture and marginal deficiencies. 1, 2

Primary Failure Mechanisms

• Secondary caries accounts for the majority of restoration failures across all material types, representing a breakdown at the tooth-restoration interface 1, 3
• Material fracture and loss is the second most common failure mode, particularly affecting composite restorations where it accounts for approximately 35 cases per 100 restorations over 4 years 4
• Marginal deficiencies including marginal discoloration, gap formation, and marginal fracture represent the third major failure category 1, 2

Material-Specific Failure Rates

The annual failure rates vary significantly by material type:

• Glass ionomer restorations show the highest failure rates at 7.2% annually for regular formulations and 6.0% for ART (atraumatic restorative treatment) applications 2
• Direct composite restorations fail at 2.2% annually, with loss of material being more common than secondary caries 2, 4
• Amalgam restorations demonstrate a 3.0% annual failure rate 2
• Indirect restorations perform better overall: cast gold inlays/onlays (1.4% annual failure), CAD/CAM ceramics (1.7%), and ceramic restorations (1.9%) 2, 3

Secondary Failure Mechanisms

Beyond the primary triad of secondary caries, fracture, and marginal deficiencies:

• Wear contributes to long-term restoration failure, particularly in stress-bearing posterior areas 2, 3
• Postoperative sensitivity can necessitate restoration replacement 3
• Pulpal involvement accounts for approximately 16% of Type 2 failures (process-related failures) 4

Critical Distinction: Early vs. Late Failures

Early failures (within 2-4 years) are predominantly caused by material loss and technique-related factors, while late failures (after several years) are primarily due to secondary caries and wear. 2, 3

Endodontic Treatment Failure

Endodontic treatment failures are remarkably uncommon when proper protocols are followed, with the most common causes being vertical root fracture and extensive recurrent caries leading to restorative failure rather than endodontic failure per se. 5

Endodontic-Specific Outcomes

• Vertical root fracture represents the most common true endodontic failure, accounting for 50% of failures in one case series (3 of 6 failed cases) 5
• Horizontal root fracture and extensive recurrent caries causing restorative failure each account for additional cases 5
• Healing rates for properly performed nonsurgical endodontic treatment through retained full coverage restorations reach 95.3% at 2-4 year follow-up 5

Important Clinical Context

The distinction between endodontic failure and restorative failure is critical:

• Pure endodontic failures (periapical pathology, inadequate obturation) are rare with modern techniques 5
• Most "endodontic failures" are actually restorative failures where recurrent caries or crown fracture leads to reinfection of an otherwise successfully treated root canal system 5
• Root fractures (vertical or horizontal) represent structural failures rather than treatment technique failures 5

Common Pitfalls and Clinical Implications

For Restorations

• Inadequate cavity seal remains the fundamental problem underlying secondary caries, despite improvements in adhesive technology 1
• Operator technique significantly influences outcomes—the "center effect" in multicenter trials shows substantial variation in failure rates based on the treating dentist 4
• Material selection should account for the specific clinical situation: glass ionomers show 3-4 times higher failure rates than other materials and should be reserved for specific indications 2

For Endodontic Treatment

• Maintaining restoration integrity is as important as the endodontic treatment itself for long-term success 5
• Access through existing crowns can be successful when following standardized protocols, with 95.3% success rates 5
• Patient selection matters—elderly patients with complex restorations face higher risks of catastrophic failure when problems arise, particularly with inadequate oral hygiene 6