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Depth Perception by Dr. LeRoy Horton, MS, DICOI

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Categories: Implant Dentistry;
Depth Perception 

The science behind the shift toward subcrestal implants

by Dr. LeRoy Horton

You cannot have been an implant provider in the past 10 years and not have had a conversation with a colleague about the nuances of epicrestal versus subcrestal implant placement. Dentists are great at following protocols; however, many practitioners face great difficulty in articulating a sound argument for why they perform a protocol or when it is appropriate. This short article will attempt to provide some language regarding implant depth in light of current concepts.

I should probably begin by explaining that when I refer to implant depth, I’m referring to the placement of the roughened surface of a dental implant that is meant to be osseointegrated. For most cases, this conversation will revolve around bone-level implants; tissue-level implants are designed with a polished transmucosal collar that provides no osseointegrative properties. Bone-level implants, despite some variations in collar designs, are typically meant to have bone contact all the way up the shoulder.

When we consider the classic definition of implant success, peri- and postintegration bone levels have always been important factors. Albrektsson described this as less than 0.2 mm of vertical bone loss annually after the first year of service.1 Understanding this can be daunting. Our responsibility shifts from placing implants in bone to now keeping that bone from resorbing over time. There are many surgical and restorative aspects that have to be properly accommodated to achieve this. As mentioned in the introduction, implant depth will be the focus. If you have placed enough implants, you will have experienced the phenomenon of marginal bone remodeling. In some patients, this is very noticeable, while in others it is indiscernable.

Material-level innovations such as platform switch connections have proven to minimize initial bone loss.2 Biologically, however, there is overwhelming evidence that the thickness of the peri-implant soft tissues plays a major role as well. As part of a series of studies, Linkevicius showed that tissue thickness, or lack thereof, was correlated to statistically significant differences in marginal bone loss when bone-level implants were placed at the level of the crest. One of these studies involving the placement of 80 crestal level implants showed that 85% of the implants placed in thick tissue (> 2mm) showed either no bone loss or nor more than 0.5 mm after one year, where 70% of implants in thin tissue (< 2mm) showed 1 mm of loss or more.3

Traditionally, dentists trained in soft-tissue surgery have addressed thin tissue with augmenting procedures involving autologous connective tissue grafts, gingival grafts, allografts and xenograft products. These wide array of surgeries, which have collectively been termed “periodontal plastic surgery,” have since the 1980s proven very predictable in augmenting patients’ mucogingival complexes.4

Another study by Linkevicius of 102 implants showed that thickening thin tissue (< 2mm) with allogenic membrane compared with no added membrane reduced crestal bone loss after one year from 1.81 mm to 0.44 mm.5

Given that the supracrestal attachment apparatus (formerly known as the biologic width) around implants resemble that of natural teeth, albeit a bit greater in dimensions, thicker tissues translate to greater protection against the oral environment. With a junctional epithelium of 1.4–2.9 mm, and connective that is usually 0.7 to 2.6 mm, full dimensions including the sulcus can range from 3.5 to 6 mm.6

Establishing that a thick or thickened peri-implant gingival complex is beneficial leads us to the question of whether placing an implant deeper in the crest is a viable way to create a thicker complex of vertical tissue without grafting. In other words, if there is only 1.5 mm of tissue width over the crest, can I place an implant 1 mm subcrestal (as long as I’m not violating any vital anatomical structures) and have a result of 2.5 mm of vertical distance to the oral environment? The answer is a resounding yes! (See Figs. 1a–1c.) The data appears to support this phenomenon.7
Depth Perception
Fig. 1a: Illustration of site with adequate thick soft tissue of > 2 mm and an implant placed epicrestal.
Depth Perception
Fig. 1b: Illustration of site with thin soft tissue < 2 mm and the implant placed subcrestal.
Depth Perception
Fig. 1c: Illustration of site with subcrestal implant placed in thin tissue after healing and showing a now-thick tissue over the implant.


The follow-up to that question is whether this form of what we can call a passive tissue augmentation bears the same benefits as the aforementioned methods. So far, the literature appears to cautiously support this. Valles et al., in a systemic review and meta-analysis, found that implants placed in a subcrestal position have less marginal bone loss changes when compared with implants placed epicrestal,8 while Cruz et al., also in a systematic review and meta-analysis, found no statistical significance.9 An entire textbook has been written on this protocol,10 as well as many studies that at best afirm the benefits or at worst demonstrate no harm. Hence, there appears to be a very compelling argument … as long as one can understand and articulate it.

Obviously, the location of implant placement considers many factors, including position of the CEJ on neighboring teeth, bone dimensions, restoration angle and size, and aesthetic demands. Also, we can’t forget the caveat of not needing to place an implant deeper if the soft tissue is already thick. Figs. 2a and 2b illustrate one of my cases demonstrating this concept: The soft-tissue outline can be seen above the bone mesial and distal to the implant, and we can appreciate the new vertical soft-tissue dimension over the implant by placing it about 1 mm subcrestal.
Depth Perception
Fig. 2a: Radiograph showing a two-year follow-up of an implant placed subcrestal, with the red arrow indicating the tissue thickness over the bone and the yellow arrow indicating the tissue thickness over the implant.
Depth Perception
Fig. 2b: Intraoral photograph of the same implant.


With every shift in paradigm, an older generation of clinicians will require convincing articulation of the change to, if not accept it, at least respect it. Subcrestal implant placement appears to be one of these current paradigms in our industry.

References
1. Albrektsson T, Zarb G, Worthington P, Eriksson A. The longterm efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillofac Implants 1986; 1(1):11–25.
2. Calvo-Guirado JL, Cambra J, Tarnow DP. The effect of interimplant distance on the height of the interimplant bone crest when using platform-switched implants. Int J Periodontics Restorative Dent 2009; 29:141–51.
3. Linkevicius T, Puisys A, Steigmann M, Vindasiute E, Linkeviciene L. Influence of vertical soft tissue thickness on crestal bone changes around implants with platform switching: a comparative clinical study. Clin Implant Dent Relat Res 2015; 17(6):1228–36.
4. Langer B, Calagna L. The subepithelial connective tissue graft. J Prosthetic Dent 1980; 44(4):363–67.
5. Linkevicius T, Puisys A, Linkeviciene L, Peciuliene V, Schlee M. Crestal bone stability around implants with horizontally matching connection after soft tissue thickening: a prospective clinical trial. Clin Implant Dent Relat Res 2015; 17(3):497–508.
6. Linkevicius T, Apse P. Biologic width around implants. An evidence-based review. Stomatologija 2008; 10(1):27–35.
7. Linkevicius T, Puisys A, Linkevicius R, et al. The influence of submerged healing abutment or subcrestal implant placement on soft tissue thickness and crestal bone stability. A 2 year randomized clinical trial. Clin Implant Dent Relat Res 2020; 22(4):497–506.
8. Valles C, Rodríguez-Ciurana X, Clementini M, et al. Influence of subcrestal implant placement compared with equicrestal position on the peri-implant hard and soft tissues around platform-switched implants: a systematic review and meta-analysis. Clin Oral Investig 2018; 22:555–70.
9. Cruz RS, Lemos CAA, de Luna Gomes JM, et al. Clinical comparison between crestal and subcrestal dental implants: A systematic review and meta-analysis. J Prosthetic Dent 2022; 127(3):408–17.
10. Linkevicius T. Zero Bone Loss Concepts. Quintessence Publishing Berlin, Germany; 2019.

Author Bio
LeRoy Horton Dr. LeRoy Horton, MS, DICOI, a periodontist in the greater Seattle area, is a longtime contributor to Dentaltown magazine and serves on its editorial advisory board. Horton earned his DDS from the University of Washington and a master’s in periodontal science from Oregon Health Sciences University. He is an associate professor and director of the periodontics and implant curriculum at Pacific Northwest Health Sciences University School of Dental Medicine and practices part time.
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