DR LANKA MAHESH
DR MANESH LAHORI
DR MANMEET GULATI
DR PRERNA KAUSHIK

INTRODUCTION
Gaps between implant and abutment lead to bacterial colonization. Chewing loads cause a relative movement between the components, which in turn causes a pumping effect. This distributes endotoxins, causing an infectious reaction in the tissue at the implant-abutment interface level. Bone is resorbed below the implant-abutment connection until the biological width is established. Only a bacteria-proof connection prevents bone resorption – and stabilizes the soft tissue.

Platform Shifting is the concept of “stepping down” the size of an implant platform to increase the volume of soft tissue around the implant platform during implant treatment.

Platform switching was introduced in literature by Lazzara and Porter and Gardner in 2006.  Lazzara and Porter clearly explained history and importance of microgap and reestablishment of the biological width.

Platform switching is simply using an abutment that is smaller than the implant.
It reduces the microgap, thus the bacterial induced bone loss.

Concept of platform switching is about increasing the width of the epithelial collar around the abutment, hence resulting in thicker and tighter seal around the abutment minimizing the pocketing around the abutment. It focuses on emphasizing and promoting gingival health and beauty, increases the volume of soft tissue, preserving the crestal bone levels by:-

1) medial movement of microgap
Microgap was historically blamed for bone loss to first thread phenomenon
2) more soft tissue
The abutment gets narrow at the implant abutment junction.
This effectively allows a good seal around the transmucosal component of the implant.

HISTORY:-

In 1991, BIOMET 3i introduced 5.0 and 6.0mm wide diameter implants that offered the same external hex interface as their smaller cousins. During this period,some clinicians restored the implants with standard 4.0mm prosthetic components that were smaller than the larger diameter implant platform (Platform Switching).

In 1995, the 1st purchaser of  the frialit (DENTSPLY) system in U.S. made some mistakes with impression posts.
Since, all the hexes were interchangeable on occasion they used impression posts smaller than implants.
 
REVIEW OF LITERATURE:-

LAZZARA AND PORTER 2006

Biologic process resulting in loss of crestal bone height may be altered when the outer edge of the implant abutment interface is horizontally repositioned inwardly and away from the outer edge of the implant platform.
A radiographic follow up demonstrated a smaller than expected vertical change.

VELA-NEBOT 2006

Mean bone loss of 0.7mm at 30 platform switched implants compared to  2.5mm bone loss at 30 control implants, done 6 months post attachment of abutment.

CARDAROPOLI ET AL. 2006

It has been demonstrated that following implant surgery, remodeling takes occurs
and is characterized by a reduction in bone dimension, both horizontally and vertically
The radiographic marginal bone level showed a mean loss of
0.9mm at the time of abutment connection and crown placement and a further
mean loss of 0.7mm at 1 year
MAEDA ET AL. 2007
Examined the biomechanical advantage of platform switching using 3 dimensional finite element models.
Found that the stress concentration at the cervical bone interface would be greatly reduced when narrow diameter abutment was connected.

CANULLO AND RASPERINI 2007

In limited cases implants were placed in the extraction sockets, it was observed that immediate loading with platform switched implants could provide peri-implant hard tissue stability and papilla preservation..

LUONGO ET AL. 2008

Examined histologically by removing a human implant,2 months after placement and speculated that an inward shift of the inflammatory connective tissue zone at the implant-abutment junction could be the reason for bone preservation..

DEGIDI  ET AL. 2008

Reported no resorption of  coronal bone at a human implant 1 month post loading.

HURZELER ET AL. 2008

In a study including 15 patients, they received 14 wide diameter implants with platform switched abutments and 8 implants with regular diameter.
Observation- Lesser mean crestal bone resorption (0.12 vs. 0.29 mm), 0.12 +/- 0.40 mm in platform switched cases compared to 0.29  +/- 0.34mm in control cases, 1 year after final restoration.

CAPPIELLO ET AL. 2008

1 year after loading, vertical bone loss in 75 platform switched implants varied between 0.6 and 1.2mm (mean:- 0.95 +/- 0.32mm)
While 56 control implants, bone loss was between 1.3 and 2.1 mm (mean:- 1.67 +/-0.37mm)

PROSPER  ET AL 2009

2 year follow up revealed mean bone loss of 0.04 +/- 0.22 mm on 60 platform switched implants while that for 60 control implants mean was 0.27+/- 0.46 mm.

SCHROTENBOER ET AL 2008

Investigated the effect of microthreads and platform switching on crestal bone stress levels, with finite element analysis. They showed that when the abutment diameter decreased from 5.0 to 4.5 mm and then to 4.0 mm, the microthread model showed a reduction of stress at the crestal bone level from 6.3% to 5.4% after vertical loading.

Crespi R, Capparè P, Gherlone E. 2009

Investigated crestal bone levels in implants that were placed immediately after tooth extraction and were loaded immediately,the first group received 34 implants with an external-hexagon junction with the abutment and the second group received 30 implants with platform-switched abutments.
After 24 months, a cumulative survival rate of 100% was reported for all implants. The platform-switching group showed a mean bone loss of 0.78 +/- 0.49 mm and the external-hexagon group showed a mean bone loss of 0.73 +/- 0.52 mm (no statistically significant difference between groups).

Cappiello M, Luongo R, Di Iorio D, Bugea C, Cocchetto R, Celletti R. 2009
This clinical and radiographic prospective study evaluated bone loss around two-piece implants that were restored according to the platform-switching protocol. All implants were positioned at the crestal level. Clinical and radiographic examinations were performed prior to surgery, at the end of surgery, 8 weeks after implant placement, at the time of provisional prosthesis insertion, at the time of definitive prosthesis insertion, and 12 months after loading. The data collected showed that vertical bone loss for the test cases varied between 0.6 mm and 1.2 mm (mean: 0.95 +/- 0.32 mm), while for the control cases, bone loss was between 1.3 mm and 2.1 mm (mean: 1.67 +/- 0.37 mm).

BONE REMODELLING AROUND AN IMPLANT CAN BE RELATED TO SEVERAL FACTORS:-
1) implant / abutment junction (IAJ) and its size and proximity to the crest of the bone. The larger the microgap the more is bacterial contamination.                                   
2) crown / implant junction is similar to the IAJ, as in case of natural tooth.
3) surface, shape and texture of the implant. A wider polished collar is more likely to permit bone loss than a micro roughened or textured collar region.
4) stability of the interface between the implant and abutment. More micromovement facilitates increased bacterial proliferation and inhibits soft tissue attachment (biologic width).

MICROGAP AND THE CRESTAL BONE LEVELS
Microgap is the term used for the microscopic  space where the bottom of the abutment meets the top of the implant. This tiny area would be a great place for bacteria to grow and impede bone growth , causing bone resorption at the connection.
 
The microgap-crestal bone level relationship was studied radio graphically by Hermann et al , who demonstrated that the microgap between the implant/abutment has a direct effect on crestal bone loss,
independent of surgical approaches. Epithelial proliferation to establish biological width could be responsible for crestal bone loss found about 2mm belowthe microgap.
Bacteria gather around these micro spaces. This dynamic movement pumps the toxins that form in the gaps and creates a ‘zone of toxicity’ at the level of the microgap.
Alveolar bone will then remodel below the zone, resulting in the typical bone loss down to ‘first thread’.
This is one of the reasons for the bone remodeling noted at the crestal area. Any micro-movement compounds the effect of bone loss.
The goal of platform switching is to prevent the (previously) normal bone loss down to the first thread that occurs around most implants, thus enhancing soft tissue aesthetics and stability.

PLATFORM SWITCH TO PRESERVE THE CRESTAL BONE

Lazzara explained that bone loss has vertical and horizontal components within what is considered a normal bone loss- a loss of between approximately 1.5 and 2mm down to the 1st thread during 1st year of loading.

When connecting an abutment of smaller diameter, the stress level and in vertical region is reduced compared with abutment of regular diameter.
Platform switching area where stress is concentrated away from the cervical bone implant interface , while stress increases in the abutment or abutment screw.

Lazzara et al discovered that during a 13year, radiographic periapical observation period of platform switching improved crestal bone preservation was revealed.
Degidi et al explain that when there is zero microgap and no micro movement shifting platform no resorption this method provides better aesthetic results.

On use of a component narrower than the  implant collar, the prosthetic connection is displaced towards the centre of the implant. Thereby an increased distance seperates the peripheral bone from the base of the abutment.
The ICT(Inflamatory connective tissue infiltrate)  is located at a more coronal level that is at the level of the collar, and no longer migrates apically towards the first thread of the implant.
Thereby resorption is avoided and the crestal bone is stabilized at the level of the implant collar.
With procedure like platform switching a minimum bone loss registered was 0.05- 0.07 mm and maximum of 1.3-1.4 mm.
Implant neck (crest module) :The highest bone stresses have been reported to be concentrated in the cortical bone in the region of the implant neckof loaded implants with or without superstructure.
 For the reduction in the amount of crestal bone resorption it is necessary to expose a minimum amount of implant surface, to which the soft tissue can attach.

BIO MECHANICAL PERSPECTIVE:-

Stress is concentrated around the crestal region where 2 materials with different moduli of elasticity ( bone and implant) interact.
Peak bone stress that appear in marginal bone are believed to cause bone micro fracture.
Peri implant bone loss with saucerisation patterns after prosthetic loading. 
Platform switching helps minimum peak bone stresses at themarginal bone.
By moving the Implant Abutment Junction, in from the implant shoulder, the bone may be shielded from potential irritants.  As a result, the bone may not cup in order for the biologic width to move down and seal it from the source of irritation.
If the bone stays up, there is increased support for the soft tissue.
Radiographic observation suggests that the resulting postrestorative biologic process resulting in the loss of crestal bone height is altered when the outer edge of the implant-abutment interface is horizontally repositioned inwardly and away from the outer edge of the implant platform.

Improved Bone Support for Short Implants
Bone remodeling around a platform switched implant is minimized; therefore, there is potentially a greater bone/implant contact for short implants, thus opening the possibility of treating patients with less extensive therapy. 

SYSTEMS THAT ALLOW SWITCHING PLATFORMS.

1. ANKYLOS FRIADENT DENTSPLY (real platform switch)
2. STRAUMANN BONE LEVEL (just really new)
3. GERMAN IMPLANT “IQ- NECT” (by Heraeus Kulzer)
4. 3i, ASTRA, THE STRAUMANN BONE LEVEL THINGY, NOBEL ACTIVE

are all designed to platform switch.

CONCLUSION:-

To maintain the long term implant stability, it is important to minimize bone loss around implant.Several clinical studies have shown a mean marginal bone around dental implants of 1.5-2mm in the 1st year after prosthetic restoration.
The technique of platform switching which uses prosthetic abutment with reduced width in relation to the implant platform diameter seems to have greatest potential to limit the crestal resorption.

REFERENCES:-

1.Clinical Oral Implants Research
Volume 18 Issue 5, Pages 581 - 584

2. Journal of Oral Implantology
October 2009, Vol. 35, No. 5 : pp. 245-250

3. Journal of Clinical Periodontology
Volume 34 Issue 12, Pages 1089 – 1096

4. Journal of Clinical Periodontology
Schrotenboer et al  2008 Nov;79(11):2166-72

5.Journal of Clinical Periodontology
Hermann J 2001; 72:1372-83

6. Clinical oral implants research
2001;12:559-571

7. International journal of periodontics and restorative dentistry
Volume 26, number 1 ,2006

8. International journal of periodontics and restorative dentistry
Volume 28, number 4, 2008

9.International journal of oral and maxillofacial implants
1997;12:527-540

10. International journal of oral and maxillofacial implants
Volume 24 number1 2009

11. Journal of Oral Maxillofacial Surgery
2007 Jul;65(7 Suppl1):33-9

12.Journal of Clinical and Diagnostic Research.
2009Feb;(3)1348-1352

13. Journal of Prosthodontics.
Hermann et al, 2007

14.Osseonews week in review –January,18th 2007

15.Periodontal expert- platform switching to preserve crestal bone levels, issue 3 , 2006

16.Implant excellance- by Dr Arun K Garg, DMD