There is an abundance of factors that the dental professional must consider when recording impressions for indirect restorative care. Ensuring occlusal contacts are properly recorded so that a new solution works with the existing dentition is fundamental, and accurately covering the surrounding structures so that an aesthetic and harmonious restoration can be designed is also important.
In a matter that concerns both aesthetics and oral health, clinicians must make the decision to either implement a supragingival or subgingival margin. It’s important to recognise when either solution may be necessary, and ensure accuracy of the impression for a precise restoration.
Sub and supra suitability
When providing an indirect restoration, a subgingival margin placement is often required when covering old restorations or decay, increasing the length of the tooth structure, or enhancing the aesthetics in the anterior dentition.[i] It can be as much of a functional decision as one to improve the aesthetic result. When working this way, however, there are risks that can compromise the viability of a solution. Without proper access to the subgingival margin and sufficient drainage of fluid at the treatment site, the impression-taking process and restoration will be impaired.[ii]
Poor margin adaption is of high concern when placing a subgingival restoration. Patients risk an increase in accumulation of bacteria at the treatment site, which, if not cleaned thoroughly, can prompt gingival inflammation and an increased risk of secondary caries development.ii
This is one reason why a supragingival finish is preferred where at all possible.i When margins are kept supragingival, the environment is optimised for an ideal patient tissue response,[iii] which could lead to more predictable treatment recovery. Such an approach to indirect restorations has also come under the umbrella of minimally invasive dentistry when used in tandem with adhesive solutions, with some professionals going as far as to suggest it should replace traditional mechanically retained restorative dentistry.[iv]
As expected, the supragingival margins present different difficulties. Primarily, there is a possible aesthetic misalignment between natural and restored tooth structure, and in these circumstances, it is recommended to limit the use of supragingival restorations to the proximal and lingual areas of the dentition.[v] With the demand for aesthetic dental treatments growing,[vi] a compromise may have to be made.
The necessary impression
Dental professionals need an accurate representation of the dentition to prepare an indirect restoration, whether it is placed subgingivally or supragingivally. The latter approach provides the advantage of easier impression acquisition within the necessary anatomical interactions.[vii] This is understandable; the restoration will only interact with the opposite arch, requiring adequate occlusal contacts that work with the surrounding dentition, and the relationship with the teeth laterally within the same arch must also be considered for aesthetics, function, and future interdental cleaning. Where the gingival margin is unaffected, the creation of the restoration will not need an accurate impression of the sulcus at the treatment site for an effective result.
However, when an indirect restoration needs to be placed with an aspect in the subgingival margin, high-quality accuracy at this point is non-negotiable. The detection of a finish line in the subgingival margin requires a clean, healthy gingival sulcus, with proper soft tissue displacement, and clear visibility of the prepared tooth anatomy.[viii] This is the case when using both conventional and digital impression taking methods.
The literature has shown that intraoral scanners struggle to accurately capture the margin where it finishes deeper into the sulcus.viii A 2021 study goes as far as stating that when placing a crown’s margins deep (1.5-2mm) into the sulcus, it is ill-advised to use digital impressions.viii
Return to convention
To adequately record the subgingival margin when creating an indirect restoration with a conventional approach, it’s essential to retract and displace the adjacent soft tissue. This allows the chosen impression material to capture the features of the preparation and finish line, as well as some unprepared tooth structure apically.[ix] The margin width should be a minimum of 0.2mm in order to give the impression material enough space to develop, and not tear or distort upon removal.ix
Moisture control at the site is another controllable variable that may affect the outcome, but optimising the impression is also possible by choosing the best-suited material for the task. The KemKat impression compound from Kemdent is ideal for adding to an impression tray, and its high viscosity allows for impressive recording of the full sulcal depth. Clinicians can break off only what is needed for partials or additions, but be sure to develop optimal detail for the restoration.
Both subgingival and supragingival restorations have their merits. No matter the clinical need, and the preference of the patient, its essential to be able to deliver a high-quality result. This begins with an accurate impression, and ends with a restored smile.
For more information about the leading solutions available from Kemdent, please visit www.kemdent.co.uk or call 01793 770 256
[i] Suwanwalaikorn, P., Ekworapoj, P., & Aimjirakul, N. (2021). Penetration ability of various elastomeric impression materials using a gingival sulcus model. Journal of Current Science and Technology, 11(3), 424-431.
[ii] Tennert, C., Maliakal, C., Machado, L. S., Jaeggi, T., Meyer-Lueckel, H., & Richard, J. W. (2024). Longevity of posterior direct versus indirect composite restorations: A systematic review and meta-analysis. Dental Materials.
[iii] Sisler, Z. S., (2018). No-Preperation Veneers: A Minimally Invasive Approach for a Naturally Esthetic Smile. Compendium of Continuing Education in Dentistry, Nov/Dec 2018, Volume 39, Issue 10. (Online) Available at: https://www.aegisdentalnetwork.com/cced/2018/11/no-preparation-veneers-a-minimally-invasive-approach-for-a-naturally-esthetic-smile [Accessed November 2024]
[iv] Ruiz, J-L., (2015). Avoiding Subgingival Margins For Healthier Dentistry: Using a Supragingival Preparation Protocol. Dentistry Today. (Online) Available at: https://www.dentistrytoday.com/avoiding-subgingival-margins-for-healthier-dentistry-using-a-supragingival-preparation-protocol/ [Accessed November 2024]
[v] Yu, H., Zhao, Y., Li, J., Luo, T., Gao, J., Liu, H., … & Zhou, X. (2019). Minimal invasive microscopic tooth preparation in esthetic restoration: a specialist consensus. International journal of oral science, 11(3), 31.
[vi] Abbasi, M. S., Lal, A., Das, G., Salman, F., Akram, A., Ahmed, A. R., … & Ahmed, N. (2022, October). Impact of social media on aesthetic dentistry: General practitioners’ perspectives. In Healthcare (Vol. 10, No. 10, p. 2055). MDPI.
[vii] Fleming, M., (2012). The Ins and Outs of Gingival Margins. Spear. (Online) Available at: https://www.speareducation.com/spear-review/2012/09/the-ins-and-outs-of-gingival-margins [Accessed November 2024]
[viii] Ferrari Cagidiaco, E., Zarone, F., Discepoli, N., Joda, T., & Ferrari, M. (2021). Analysis of the reproducibility of subgingival vertical margins using intraoral optical scanning (IOS): a randomized controlled pilot trial. Journal of Clinical Medicine, 10(5), 941.
[ix] Adnan, S., & Agwan, M. A. S. (2018). Gingival retraction techniques: a review. Dental update, 45(4), 284-297.
