24 December 2021

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Ceramic crowns and their finishing line: a systematic review

Edoardo Mancuso

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In ceramic full coverage indirect restoration marginal and internal adaptations have been shown to be a key factor for clinical success. Indeed, poor adaptation of restorations can result in cement dissolution, microleakage, and increased plaque retention, potentially leading to caries and periodontal disease. In addition, the fracture strength of ceramic crowns can be influenced by poor marginal and internal adaptations due to higher stress concentrations at the margins and internal surfaces.

Marginal adaptation is influenced by four main factors: finish-line configuration, value of the cementing space, veneering process, and occurrence of cementation. Whilst the other factors are out of the dentists’ control, the finishing-line configuration is, and although tooth preparation is part of daily routine, dentists often select the cervical finish line based on their experience and personal choice.

In the era of minimally invasive dentistry, more conservative preparation geometries, such as chamfer, should be preferred than the rounded shoulder. However, which finish line offers better marginal and internal adaptations is still not well defined. 

In this regard, an interesting systematic review, written by Professor Hao Yu has been published in the Journal of Prosthetic Dentistry with the aim of evaluating the influences of rounded shoulder and chamfer on the marginal and internal adaptations of ceramic crowns.

Material and methods
For the review, a systematic electronic literature search was conducted in different electronic databases. The articles included met the following inclusion criteria: studies that evaluated the marginal and/or internal adaptations of ceramic crowns; studies that evaluated restorations with rounded shoulder and chamfer finish lines; and studies including well-described marginal and/or internal adaptation measurements.

Results
Among 283 potentially relevant studies, 24 were selected for full-text analysis, and 16 were included in the systematic review and the meta-analysis. All 16 studies were considered in the meta-analysis of marginal adaptation, whereas 4 were considered in the analysis of internal adaptation.
The results showed a significant difference in marginal adaptation between the restorations with rounded shoulder and those with chamfer finish lines, favoring rounded shoulder.
A significant difference in internal adaptation between the crowns with rounded shoulder and those with chamfer finish lines, favoring chamfer.

Discussion
From the analysis conducted in the review a minor but statistically significant difference in marginal adaptation was detected, favoring the rounded shoulder. The authors suggest that this might be due to the complicated production of the tilted surfaces of the chamfer finish line. Moreover, compared with a rounded shoulder finish line, among the studies included in the review, more fractures were observed at the margins of crowns with chamfer finish lines. The authors attribute this trend to the manufacturing procedures. As a matter of fact, during coping design, the marginal adjustment process in the dental laboratory is much more complicated to perform when there is a chamfer finish line.
The analysis showed a significant difference in internal adaptation between the crowns with rounded shoulder and those with chamfer finish lines. The authors correlated the relatively better seating of restorations with chamfer preparation with their poor marginal sealing. They suggest that the design of chamfer allows the cement to escape marginally more readily without filtration, whereas with the rounded shoulder, the margins seal earlier and the emission of the cement could be hindered.

Conclusion

The systematic review concludes drawing the following results:
1. Ceramic crowns with chamfer finish lines showed wider marginal gaps than those with rounded shoulder finish lines (MD=−7.8; 95% CI=−11.6 to −4.1).
2. Ceramic crowns with rounded shoulder finish lines showed wider internal gaps than those with chamfer finish lines (MD=35.0; 95% CI=6.5 to 63.5).
When preparing a tooth for a ceramic crown it seems to be preferable the choice of a chamfer finish line. Restorations with chamfer finish lines have in fact resulted in an inferior reduction of tooth substrates and have exhibited better internal adaptation and comparable marginal adaptation than those with rounded shoulder finish lines.