Insights into restoring teeth with deep preparation outlines: thinking outside the box

Promotion R. Bresser

This dissertation by Rijkje Bresser investigates the performance of partial adhesive restorations, with a special focus on the challenge of bonding these restorations when the preparation margins are located below the enamel-cement junction (ECJ). Deep Margin Elevation (DME) in combination with a partial indirect restoration is a thoroughly researched component of this dissertation. Through literature review, laboratory experiments, and clinical research, various aspects of partial restorations with and without Deep Margin Elevation are evaluated, including material comparisons and the impact on fracture strength.

A Deep Margin Elevation is only recommended in clinical situations where it is not possible to isolate the operative field. Indirect composite restorations, lithium disilicate, and leucite ceramics seem to achieve similar clinical outcomes in the short term (1 - 6.25 years) based on medium to low quality of evidence. Partial gold restorations exhibit higher survival rates than indirect composite material during a clinical evaluation period of 5-7 years. The dissertation provides a step-by-step overview of the application and indication of Deep Margin Elevation and offers clinical guidelines for approaching deep subgingival cavities.

Furthermore, it investigates the influence of Deep Margin Elevation on the fracture strength of lithium disilicate restorations, finding that Deep Margin Elevation does not affect the fracture strength or reparability of indirectly restored molars with lithium disilicate, regardless of the type of preparation (inlay/onlay). Direct composite restorations with Deep Margin Elevation exhibit comparable average fracture strength to lithium disilicate inlays, both with and without Deep Margin Elevation. These direct composite restorations are a suitable treatment method for restoring three-surface preparations ending below the enamel-cement junction, in terms of fracture strength and reparability.

The dissertation also analyzes the clinical survival of various restorative materials and identifies the risk factors for the failure of such restorations. Partial lithium disilicate restorations, ending above and below the enamel-cement junction, show a survival rate of 97.3% after an average evaluation period of 7.5 years. High caries risk, non-vital elements, and male patients are at higher risk of these restorations failing. Glass-ceramic restorations bonded below the enamel-cement junction show similar survival rates to those with preparation margins in enamel. Deep Margin Elevation combined with partial glass-ceramic or indirect composite restorations shows survival rates of 95.9% over an average evaluation period of nearly 5 years, and thus appears to perform well in the medium to long term.

Finally, the studies demonstrate that indirect restorations with or without Deep Margin Elevation perform well in the medium to long term, but further study is needed due to degradation over time. Findings, limitations, and suggestions for future research are discussed in the final chapter of the dissertation.