Authors
	Shafath Ahmed, M.D.S ( First author) Clinic- in- Charge, Apollo Dental Centre, 47/1, 100 feet road,Vadapalani, Chennai: 600026 E Mail ID: This email address is being protected from spambots. You need JavaScript enabled to view it. . Contact No: 91-9840951231.
	Vamsi Lavu, M.D.S (Second author and Corresponding author) Senior Lecturer in Periodontics, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai- 600116. Consultant Periodontist and Implantologist, Apollo Dental Centre, Vadapalani. E mail ID: This email address is being protected from spambots. You need JavaScript enabled to view it. . Contact No: 91-9841326869

Abstract

Preservation of peri-implant crestal bone is a priority area for long term success of dental implants. The concept of “ Platform switching” introduced by Lazarra and Porter has shown considerable promise in being a predictable method for crestal bone preservation. This review article explains the biologic rationale behind the prosthetic concept of platform switching.

Keywords:

Platform switching, peri-implant bone, abutment –fixture interface, saucerization.

Article

Long term implant success is dependent on the remaining bone levels around the implant thread. It has been observed that around 0.9 to 1.6 mm of bone loss occurs at the crestal aspect of the implant from the time following loading to the end of the first year 1. Several factors have been proposed to be responsible for the bone loss observed in the first year following implant placement. These include: establishment of biologic width around the implant, stress forces generated, implant crest module design, position of the abutment –fixture interface with reference to the bone crest, surgical trauma, microgap, microbial colonization of the peri-implant success 2.

The use of platform switching concept as a method of reducing crestal bone loss is based on the studies of Lazarra RJ & Porter SS in 2006 3 . These authors reported a thirteen year clinical and radiographic follow-up of large diameter (5 to 6 mm implants) restored with small diameter abutments. They observed a reduced loss of crestal bone. This accidental discovery due to the lack of availability of prosthetic components led to the establishment of the concept of “Platform Switching”.

Lazarra and Porter in 20063, based on the studies by Berglundh and Lindhe (1996) 4 and Ericsson et al 19955  , hypothesized that the reduced loss of crestal bone is due the “inward repositioning of the implant- abutment interface”. According to the authors, the inward positioning of the implant- abutment interface, resulted in increased surface area, thereby reducing the amount of bone resorption required to expose a minimum amount of implant surface to which soft tissues can attach. Also, the authors hypothesized that there was an inward movement of the abutment associated inflammatory connective tissue away from bone contributing to reduced bone loss.

Therefore “platform switching” refers to “ the restoration of large diameter implants with smaller diameter abutments”. It achieves the following:

1. Reduces crestal bone loss.
2. Better force transmission from abutment to implant fixture.
3. Superior aesthetics.

1. Reduced crestal bone loss:

Reduction in crestal bone loss has generally been attributed to two reasons:

1. Establishment of biologic width with minimal bone resorption.
2. Movement of the microgap inward from the bone.

Biologic width around implants:

The minimum distance between the abutment –implant interface and bone level has been established as 3 mm (biologic width of the peri-implant mucosa)4. It is believed that location of the implant- fixture interface with respect to the crestal bone determines the amount of bone loss occurring to establish the biologic width around implants. So a movement of the implant fixture – abutment interface in an inward direction results in an increased surface area for the peri-implant mucosa to attach and thereby reduced amount of crestal bone loss to establish biologic width.

Microgap influence on crestal bone loss:

The microgap refers to the minute space between the abutment and fixture in  two stage implants. This area provides a niche for colonization by oral bacteria. In response to the presence of bacteria in the microgap, an inflammatory infiltrate forms in the connective tissue of the peri-implant mucosa around the abutment-implant fixture interface. This was termed the “ abutment associated inflammatory infiltrate’ by Ericsson et al in 1995 5. This inflammatory infiltrate extends at 360 degree around the implant and is believed to contribute to the “saucerization” of bone observed at the end of the first year.
Platform switching results in an inward  repositioning of the abutment associated inflammatory infiltrate inwards and away from the bone thereby reducing the exposure of the bone to the microbial influence from the microgap area. This probably manifests as reduced crestal bone loss around platform switched implants.

2. Force transmission – effect on crestal bone loss.

The generation of shear forces at the crestal area around implants is believed to be one of the major reasons for crestal bone loss. Studies using finite element analysis, around regularly restored implants have reported higher stress concentration at the crestal portion of the implants6, possibly due to the difference in the modulus of elasticity between the implant and bone and generation of shear forces at the implant- bone interface.
Variation of the design of the crest module of the implant fixture ( placement of microthreads) and platform switching has been shown to allow for the better force transmission from the abutment to the fixture reducing the loss of crestal bone (Schrotenboer J et al 2008) 7. Platform switching results in an inward movement of the abutment margin onto the implant platform, thereby converting the forces acting at the abutment – fixture interface from shear to compressive forces8.  Also bone is well adapted to the reception of compressive forces as compared shear forces. In this manner, the placement of a smaller diameter abutment on larger diameter implant platform can reduce the bone loss around crestal area of implants.

1. Peri-implant aesthetics.

A major area of concern especially in the anterior region is the creation of the inter-dental/ inter- implant papilla. The lack of inter-dental papilla leads to unaesthetic black triangles, which if closed with prostheses contribute to an artificial appearance and affects the patients smile.
Interdental bone preservation is one of the most important factors for preservation of the inter-dental papillary height. Platform switching by virtue of preserving the bone at the crest of the implant fixture will contribute to preservation of papillary height between implants and between implant and teeth 9.

Microbiota around Platform switched implants:

Implants surface at the time of insertion are devoid of micro-organisms. Following insertion and during second stage surgery, the possibility of microbial contamination of the exposed platform of the crest module is high. The composition of microbiota around the normally restored implants has been found to be influenced by the composition of microbiota at the remaining tooth sites10.  In addition an increased proportion of spirochetes and motile organisms has been observed in sites with increased peri-implant probing depth 11.

A study by Luigi Canullo et al 2010 12, performed a comparative study of the composition of the microbiota around platform switched and implants restored with standard internal connection protocol. The authors examined the levels of 40 sub-gingival species checker board DNA-DNA hybridization and reported a trend for lower level of colonization of early colonizers (purple and yellow complexes) and also red complex pathogens ( T. forsythia & P.gingivalis) among platform switched implants.

However the composition of the microbiota (quality remained the same between platform switched implants and teeth. The authors concluded that the difference in the bone crest resorption between platform switched implants and traditionally restored implants was not due to the difference in peri-implant microbiota.

Summary:

A recent systematic review and meta analysis of randomized controlled trials on the influence of platform switching for implants by Altech MA et al 2010 13, concluded that platform switching preserves both inter-implant bone height and soft tissue levels and further hypothesizes that the degree of marginal bone resorption may be inversely related to the extent of the implant- abutment mismatch.

Conclusion:

Platform switching represents a prosthetic concept, which has significant positive periodontal impact in terms of preservation of bone and papillary height (esthetics) around implants.

REFERENCES:

1. Adell R, Lekholm U, Rockler B, Branemark PI. A 15 year study of osseointegrated implants in the treatment of the edentulous jaw. Int J oral Surg 1981; 10: 387-416.
2. Cox JF, Zarb GA. The longitudinal clinical efficacy of osseointegrated dental implants: A 3 year report. Int J Oral Maxillofac Implants 1987; 2: 91-100.
3. Lazarra RJ, Porter SS. Platform switching: A new concept in implant dentistry for controlling post restorative crestal bone levels. Int J Periodontics Restorative Dent 2006; 26: 9-17.
4. Berglundh T, Lindhe J. dimension of the peri-implant mucosa. Biologic width revisited. J Clin Periodontol 1996; 23: 971-973.
5. Ericsson I, Persson LG, Berglundh T, Marinello CP, Lindhe J, Klinge B. Different types of inflammatory reactions in peri-implant soft tissues. J clin Periodontol 1995; 22: 255-261.
6. Ko CC, Kohn DH, Hollester SJ. Micromechanics of implant/ tissue interface. J Oral Implantol 1992; 18 (3): 220-230.
7. Schrotenboer J, Tsao YP, Kinariwala V, Wang HL. Effect of microthreads and platform switching on crestal bone levels: a finite element analysis. J Periodontol 2008 Nov; 79 (11): 2166-2172.
8. Maeda Y, Muira J, Taki I, Sogo M. Biomechanical analysis on platform switching: is there any biomechanical rationale?. Clin Oral Implants Res 2007 Oct; 18 (5): 581-584.
9. Canullo L, Rasperini G. Preservation of peri-implant soft and hard tissues using platform switching of implants placed in immediate extraction sockets: a proof of concept study with 12 to 36 month follow up. Int J Oral Maxillofac Implants 2007 Nov-Dec; 22(6): 995-1000.
10. Quirynen M, Listgarten MA. Distribution of bacterial morphotypes around natural teeth and titanium implants ad modum Branemark. Clin Oral Implants Res 1990; 1: 8-12.
11. Papaioannou W, Quirynen M, Nys M, van Steenberghe D. The effect of periodontal parameters on the subgingival microbiota around implants. Clin Oral Implants Res 1995; 6: 197-204.
12. Canulla L, Quaranta A, Teles PR. The microbiota associated with implants restored with platform switching: A preliminary report. J Periodontol 2010; 81: 403-411.
13. Atieh MA, Ibrahim HM, Atieh Ah. Platform Switching for marginal bone preservation around dental implants: a systematic review and meta analysis. J Periodontol 2010 Oct; 81 (10):1350-1366.