|Year : 2011 | Volume
| Issue : 1 | Page : 13-17
Platform switching: An answer to crestal bone loss
Krishna D Prasad, Manoj Shetty, Neha Bansal, Chethan Hegde
Department of Prosthodontics Including Crown and Bridge and Implantology, A. B. Shetty Memorial Institute of Dental Sciences, Mangalore, India
|Date of Web Publication||2-Feb-2011|
Department of Prosthodontics Including Crown and Bridge and Implantology, A. B. Shetty Memorial Institute of Dental Sciences, Mangalore, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: The long-term success of an implant depends on the stability of bone support for the implant. Most crestal bone loss occurs in the first year of implant placement. Platform switching is an approach which can be clinically applied to preserve the crestal bone.
Purpose: The purpose of this review is to discuss the literature dealing with the platform switching concept to preserve the crestal bone, the mechanism by which it contributes to maintenance of marginal bone, its clinical applications, advantages and disadvantages, in order to assess its survival rates.
Materials and Methods: PubMed and Google Scholar were used to find studies involving platform switching concept from 2005 up to October 2009.
Results: Literature search revealed studies involving concepts of platform switching, comparison of platform-switched and non-platform-switched implants, case reports on platform switching and studies with histological and finite element analyses regarding platform switching.
Conclusion: Platform switching helps preserve crestal bone around the implants and this concept should be followed when clinical situations in implant placement permit.
Keywords: Crestal bone loss, crestal bone preservation, immediate implant placement, inflammatory infiltrate, platform switching
|How to cite this article:|
Prasad KD, Shetty M, Bansal N, Hegde C. Platform switching: An answer to crestal bone loss. J Dent Implant 2011;1:13-7
| Introduction|| |
The most important criterion for the success of dental implant is the presence of good amount and quality of bone around the implants, especially the crestal bone. However, early peri-implant bone loss has been commonly observed. Adell et al,  were the first to quantify and report marginal bone loss. Their study indicated greater magnitude and occurrence of bone loss during first year of prosthetic loading.
Once crestal bone loss starts, it can result in increased bacterial accumulation resulting in secondary peri-implantitis which can further result in loss of bone support, which in turn can lead to occlusal overload and crestal bone loss ultimately resulting in implant failure.  Apart from this, resorption of marginal bone will affect the gingival contours and may result in loss of inter-proximal papilla. 
Therefore, crestal bone preservation should be thought of even before the treatment planning for implant placement. Various approaches have been described in the literature to prevent the crestal bone loss. Platform switching is one of them. This paper reviews the literature regarding platform switching, how it preserves the crestal bone and its survival rates.
| Materials and Methods|| |
PubMed and Google scholar were used to find out the studies related to platform switching for crestal bone preservation. Literature search was done from 2005 up to October 2009 issues. Key words used for the search were "crestal bone preservation", "crestal bone loss", "platform switching", "small diameter abutments, "immediate implant placement and platform switching" and "loading in implants".
- The papers which were not published in any of the journals.
- Studies with no results.
- Studies for which the abstracts were only available and the full article was yet to be published.
| Results|| |
Concept of platform switching
The concept of "platform switching" refers to the use of a smaller-diameter abutment on a larger-diameter implant collar. This connection shifts the perimeter of the implant-abutment junction (IAJ) inward toward the central axis (i.e. the middle) of the implant.
In 1991, Implant Innovations, Inc. (3i, Palm Beach Gardens, FL, USA) introduced 5 and 6 mm diameter implants with restorative platforms of the same dimensions. After a 5-year period, the typical pattern of crestal bone resorption was not observed radiographically in cases where platform switching was utilized. Lazzara and Porter  theorized that this occurred because shifting the IAJ inward repositioned the inflammatory cell infiltrate and confined it within a 90° area that was not directly adjacent to the crestal bone. But it was thought that further investigation was needed to prove the real advantages of this technique.
Baumgarten et al,  described the platform switching technique and its use in situations requiring shorter implants, where implants are placed in esthetic zones, and where a larger implant is desirable but prosthetic space is limited. They also stated that a sufficient tissue depth (approximately 3 mm or more) is necessary to accommodate an adequate biologic width. They concluded that platform switching helps in preventing the anticipated bone loss and also preserves crestal bone.
Gardner  discussed the changes that occur when an implant is placed in bone and presented a case study using platform-switched implants. He described that platform switching can limit osseous and esthetic changes around the implants. Though platform switching can effectively control circumferential bone loss around dental implants, he concluded that this concept needed further investigation. Furthermore, he noted several disadvantages like the need for components with similar designs (the screw access hole must be uniform) and the need for enough space to develop a proper emergence profile.
How platform switching reduces crestal bone loss - A critical analysis
The mechanism by which platform switching can contribute to maintain the crestal bone height could be due to four reasons discussed below.
- Shifting the inflammatory cell infiltrate inward and away from the adjacent crestal bone.
- Maintenance of biological width and increased distance of IAJ from the crestal bone level.
- The possible influence of micro-gap on the crestal bone is diminished.
Decreased stress levels in the peri-implant bone.
Lazzara and Porter  first theorized that shifting the IAJ inward repositioned the inflammatory cell infiltrate and confined it within a 90° area, thereby reducing marginal bone loss.
Luongo et al,  studied biopsy specimen to find out the biologic process occurring around the platform-switched implant. They found that an inflammatory connective tissue infiltrate was localized over the entire surface of the implant platform and approximately 0.35 mm coronal to the IAJ but did not reach the crestal bone, which may be the reason for crestal bone preservation by platform switching.
Maeda et al,  in a three-dimensional finite element analysis, found the biomechanical advantages of platform switching. They noted that this procedure shifts the stress concentration away from the bone-implant interface and increases the forces in the abutment or the abutment screw.
Jason Schrotenboer et al,  fabricated a two-dimensional model to analyze the bone-implant interactions under masticatory forces. Two abutment diameters, 4.5 mm representing platform switching and 5 mm representing a standard platform, were used in conjunction with a 5-mm diameter fixture. A 100 N force was applied vertically and obliquely to the abutments. Results showed that reduction of abutment diameter resulted in measurable but minimal effect on Von Mises stresses in the crestal region of cortical bone. However, it was concluded that further clinical trials are warranted before any firm conclusion could be drawn.
Canay et al,  designed eight different implant-abutment connections. Implant-abutment micro-gap at bone level was hypothetically set-off inward toward the central axis of implant to create "diameter shifting" or "platform switching" concept. They concluded in their study that stresses are confined to the cortical bone region around the implant neck. For the designs with greater horizontal offset, intensity of stresses are higher at the abutment part resting above the bone level. Thus, platform switching may risk the mechanical properties of abutments if horizontal set-off is increased. Though decrease in abutment diameter decreases the stresses generated around the implant, the differences are very slight. They remarked that platform switching may not be related to changes in load transfer.
Hsu et al,  concluded in their study that bone strains were reduced by <10% when platform switching was used compared to no platform switching. However, increasing implant diameter significantly decreased the bone strains. They also concluded that neither a wide implant nor platform switching reduced micro-motion at the bone-implant interface for enhancing implant stability.
Comparison of platform and non-platform-switched implants
Markus Hurzeler et al,  compared crestal bone loss around platform-switched and non-platform-switched implants. They found the mean crestal bone loss was 0.22 mm in platform-switched implants and 2.02 mm in non-platform-switched implants. They also concluded that reduction of the abutment of 0.45 mm on each side is sufficient to avoid peri-implant bone loss. Another study by Cappiello et al, found that vertical bone loss for the platform-switched cases varied between 0.6 and 1.2 mm (mean: 0.95 ± 0.32 mm), while for the cases without platform switching, the bone loss was between 1.3 and 2.1 mm (mean: 1.67 ± 0.37 mm).
An average of 1-2 mm of bone loss occurs in non-platform-switched implants, while minimal bone loss occurs in platform-switched implants [Figure 1].
|Figure 1 :Comparison of crestal bone loss in platform-switched and non-platform-switched implants|
Click here to view
Thus, all preliminary evidences in literature suggest that the anticipated bone loss that occurs around two-stage hexed implants may be reduced or eliminated when implants are restored with smaller-diameter abutments, a practice termed as "platform switching".
Platform switching and Morse taper connection
The use of Morse taper connection implants represents a successful procedure for the rehabilitation of partially and completely edentulous arches. Mangano et al,  evaluated 1920 Morse tapered connection implants clinically and radiographically at 12, 24, 36 and 48 months after implant insertion. They noted an overall cumulative implant survival rate of 97.56% (96.12% in maxilla and 98.91% in the mandible). The absence of an implant-abutment interface (micro-gap) is associated with minimal crestal bone loss.
Rodriguez Ciurana et al,  completed a finite element analysis to compare the biomechanical response of three types of implant-abutment configurations both before and after establishment of a new biologic width. The three functional units studied were: a 5-mm implant platform connected with an external hexagon to a 5-mm-diameter abutment (type 1), a 5-mm implant platform connected with an external hexagon to a 4.1-mm-diameter abutment (type 2), and a 4.8-mm implant platform connected with an internal hexagon to a 4.1-mm-diameter abutment (type 3). The type 3 design, which combined platform switching with an internal connection, exhibited the smallest distortions in stress distribution after bone modeling. Also, the design with smaller-diameter abutment with larger-diameter implant showed better results.
Degidi et al,  evaluated the histology and histomorphology of three Morse cone connection implants with immediate loading in a case report and they explained that platform switching in the absence of micro-gap and micro-movement showed no resorption.
Some implant systems (e.g. Ankylos) have incorporated the principle of platform switching in their implant design. They use one size diameter abutment, a 90° step external implant-abutment connection and a Morse taper internal connection. The combination of these features decreases the crestal bone resorption, assures a bacteria-proof seal and minimizes peri-implant inflammation.
Platform switching and immediate implant placement
A study by Canullo et al,  evaluated the soft- and hard-tissue response to immediately placed implants. Implants with a 6-mm platform diameter were placed immediately into the fresh extraction sockets. A provisional 4-mm-diameter transmucosal abutment was subsequently connected, and a provisional crown was adapted and adjusted for non-functional immediate positioning. Three months after implant placement, definitive prosthetic rehabilitation was performed. Software analysis of radiographic films showed bone resorption of 0.78 ± 0.36 mm. Rather than recession, there was a mean gain in the buccal margin of 0.2 mm and a mean gain in papilla height of 0.25 mm.
Calvo et al,  evaluated the survival rates at 12 months of platform-switched implant placed in maxillary anterior and premolar fresh extraction areas. They concluded that the implants remained stable over the course of 12 months and had an overall survival rate of 96.7%. Minimal crestal bone loss was recorded around the surviving implants.
| Discussion|| |
Having reviewed the available literature, it has been confirmed that platform switching is a major contributing factor in limiting crestal bone resorption. Certain biological width is necessary to maintain the soft tissues and hard tissue. In platform switching, the IAJ is shifted inward [Figure 2] and [Figure 3]. This will not only shift the inflammatory infiltrate inward away from the crestal bone but also provides an additional horizontal biological width, hence preserving the crestal bone. At the same time, the micro-gap is shifted away from the crestal bone, decreasing the probability of resorption.
|Figure 3 :Inward shifting of connective tissue maintaining biological width|
Click here to view
Another reason suggested for maintenance of marginal bone by platform switching is the decreased stresses around the implant neck, but the differences are very slight. So, decreased stresses may not be the only reason for the positive results shown by platform switching. Moreover, by decreasing the abutment diameter, more stresses are concentrated near the abutment, increasing the likelihood of abutment fracture. However, further studies in this area are warranted before definite conclusions are made.
All studies comparing the platform-switched and non-platform-switched implants suggested that platform-switched implants result in lesser marginal bone resorption.
Implant-abutment interface is a very important criterion for implant success. Platform switching increases the distance between IAJ and the crestal bone, thereby increasing micro-gap to crestal bone distance, hence preserving the crestal bone, but it does not affect the width of the micro-gap. Precision fit of implant-abutment connection in Morse taper or internal hex implants offer an additional advantage of reduced micro-gap. So, the introduction of combination of Morse taper connection and platform switching can be a boon to implant dentistry.
Immediate implant placement in compromised bone after extraction of the natural tooth can help preserve denser bone and prevent bone atrophy, resulting in lesser loading of the marginal bone. More than 90% success rate for immediate implants has been documented histologically and radiographically. Combining platform switching with immediate implant placement may give great results with minimal amount of crestal bone loss and excellent esthetics.
Benefits of platform switching
- Increased implant longevity.
- Improved esthetics as crestal bone preservation helps preserve papilla.
- The effect of inter-implant distance is minimized. A minimum of 3 mm inter-implant distance is needed to preserve marginal bone. Arthur et al,  found that distances of 1, 2 and 3 mm between implants do not result in statistically significant differences in crestal bone loss around submerged or non-submerged implants with a Morse cone connection and platform switching.
The only requirement of platform-switched implant is that the implant should be placed crestally if sufficient soft tissue height and inter-occlusal space are present, or sub-crestally if insufficient soft tissue height and inter-occlusal space are present.  So, soft tissue depth of approximately 3 mm should be present to place platform-switched implants or else bone resorption is likely to occur, irrespective of implant geometry. Also, sufficient bone width should be present to accommodate the larger-diameter implant.
Limitations of platform switching
- If normal size abutments are to be used, larger size implants need to be placed. This is not possible every time clinically, especially if bone width is less.
- If normal sized implants are placed, smaller-diameter abutments are necessary, which may compromise the emergence profile, especially in anterior cases. 
| Conclusion|| |
The success of dental implants is highly dependent on integration between implant and intraoral hard and soft tissues. Hence, an understanding of the etiology of crestal bone loss is very important. Crestal bone preservation is a very important key to success in implant dentistry. The use of prosthetic abutments with a reduced diameter in relation to the implant diameter (platform switching) limits crestal resorption usually seen after loading. It maintains the biological width and helps improve esthetics by preserving the inter-proximal papilla. Thus, platform switching may be clinically applied in implant placement every time the clinical situation permits.
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[Figure 1], [Figure 2], [Figure 3]