What is the preferred restoration method, partial onlay (partial dental restoration)/overlay or direct restoration, for an endodontically (endo) treated maxillary premolar?

Restoration of Endodontically Treated Maxillary Premolars

For an endodontically treated maxillary premolar, use an indirect ceramic onlay or inlay with palatal cusp coverage rather than direct composite restoration, as these provide superior fracture resistance and restore cuspal stiffness to levels exceeding intact teeth.

Primary Recommendation

• Indirect ceramic onlays demonstrate fracture resistance of 1317-1347N, significantly higher than direct approaches, and restore cuspal stiffness to greater than 100% of sound tooth values 1
• Indirect inlays with palatal cusp coverage achieve fracture resistance of 1062-1073N, which is also superior to direct restorations 1
• Direct composite restorations (MOD inlays without cusp coverage) show the lowest fracture resistance at 893-938N 1

Biomechanical Rationale

Cuspal Stiffness Recovery

• Direct MOD inlays restore only 75% of original cuspal stiffness, leaving teeth vulnerable to flexure under occlusal loads 1
• Ceramic onlays and inlays with palatal cusp coverage restore stiffness to 100% or greater of intact tooth values 1
• The adhesive bonding of indirect restorations reinforces remaining tooth structure more effectively than direct techniques 2

Fracture Pattern Considerations

• Indirect ceramic restorations (particularly leucite-reinforced glass ceramic) produce less severe, more restorable fracture patterns compared to direct composite or amalgam 2
• Direct composite restorations show unpredictable fracture modes with greater variation in failure patterns 2
• Catastrophic fractures are more prevalent with direct restorative approaches 2

Specific Design Parameters

For Indirect Onlays

• Use complete occlusal coverage extending to include palatal cusp 1
• If using endocrown design, limit pulpal extension to 3mm depth rather than 5mm, which reduces stress by 15% 3
• Add axial extension rather than butt margin preparation, which further reduces stress by 15% 3

Material Selection

• Leucite-reinforced glass ceramic or lithium disilicate are preferred materials for indirect restorations 2, 3
• Laboratory-processed composite resin (particularly Ceramage) shows higher fracture resistance than conventional handmade indirect composites 4
• Avoid direct amalgam restorations, which show significantly lower fracture resistance than adhesively bonded indirect restorations 2, 5

Adhesive Protocol

• Bond indirect restorations with resin cement using proper surface preparation 5
• Ensure complete dryness before adhesive application 6
• For metal restorations (if used), sandblasting with 50-μm Al₂O₃ optimizes adhesive retention 6

Clinical Pitfalls to Avoid

• Do not add pulp chamber extensions to ceramic restorations—this is technically challenging and offers no biomechanical advantage 1
• Avoid direct composite for extensive MOD preparations in endodontically treated premolars, as fracture resistance is inadequate 1, 2
• Do not use non-adhesive techniques (zinc phosphate cemented onlays or amalgam), as adhesive bonding significantly improves fracture resistance 2, 5

Evidence Quality Note

The recommendation prioritizes the 2015 study 1 which directly compared multiple restoration designs in endodontically treated maxillary premolars with comprehensive biomechanical testing, supported by consistent findings from multiple studies showing superiority of indirect adhesive restorations 4, 2, 3, 5.