Platform Switching: A Tried And Tested Concept--- A Review

INTRODUCTION

Implants are the most sought after treatment options in modern day dentistry for replacement of missing teeth. A successful implant restoration must include aesthetics and function surrounded by healthy peri-implant tissues. Peri-implant bone level has been used as one of the criteria to assess the success of dental implants.

The peri-implant bone remodelling occurs once the implant is exposed to the oral environment in a second surgical procedure or when the abutment is placed immediately after implant placement. Over the years, attempts have been made to prevent or reduce marginal bone loss through modification of the implant-abutment connection.

ETIOLOGY OF MARGINAL BONE LOSS

Traditionally, a Radiographic marginal bone loss of 1.5 mm during the first year followed by a radiographic marginal bone loss of 0.2 mm during each suceeding year is an important parameter for the assessment of implant success¹. After insertion of the implant into the bone , bone remodelling occurs via coupling mechanisms: bone resorption and depostion.

Crestal bone levels are typically located approximately 1.5-2 mm below the implant-abutment junction (IAJ) at 1 year following implant restoration but are dependent upon the location of the IAJ relative to bony crest². However, the connection between implant fixture and its restorative abutment is termed the implant abutment interface (IAI) or “microgap”. In most cases, it is susceptible to micro movements during clinical function and also permits micro-leakage of fluids³.

Marginal bone loss around implants occur due to various reasons 1) a traumatic surgical technique⁴; 2) excessive loading conditions⁵; 3) the location, shape, and size of the implant abutment microgap and its microbial contamination⁶; 4) the biologic width and soft tissue considerations^6,7; 5)a peri-implant inflammatory infiltrate⁸ ; 6)micro movements of the implant and prosthetic components⁹; 7) repeated screwing and unscrewing^10,11; 8) the implant-neck geometry^6,12; and 9) the infectious process^13,14.

HISTORYOFPLATORM SWITCHING

Historically two-piece dental implant systems have been restored with prosthetic components that locate the interface between implant and attached component element at the outer edge of the implant platform. In 1991, Implant Innovations introduced wide diameter implants with matching wide diameter platforms. When introduced however matching diameter prosthetic components were not available and many of the early 5.0 and 6.0 mm wide implants received standard diameter 4.1 mm prosthetic components. Long term radiographic follow up of these platform switched implant restored wide diameter implants has demonstrated a smaller than expected vertical change in the crestal bone height around these implants than is typically observed around implants restored conventionally with prosthetic components of matching diameters.¹⁵

Several clinical reports^16-18 demonstrated more favorable soft and hard tissue responses using implants placed with platform switching compared to standard platform-matched implants.

BIOMECHANICAL RATIONALE BEHIND PLATFORM SWITCHING

Platform switching helps to prevent crestal bone loss after implant placement and helps obtain satisfactory aesthetic results²³. The biomechanical rationale behind platform switching was investigated by 3D finite element analysis by Maeda et al²⁴ . They reported that the stress level in the cervical bone area at the implant was greatly reduced when the narrow diameter abutment was connected compared with the regular-sized one. Within the limitations of this study, it was suggested that the platform swit ching configuration has the biomechanical advantage of shifting the stress concentration area away from the cervical bone–implant interface. It also has the disadvantage of increasing stress in the abutment or 8 abutment screw. Ericsson et al showed that (i) the bone crest consistently was located about 1-1.5 mm "apical" of the abutment/fixture level, (ii) there was a zone, about 1 mm wide, of a normal noninfiltrated connective tissue that separated the apical portion of the abutment ICT and the bone crest. It is suggested that this infiltrate represents the efforts by the host to close off bacteria present within the implant system and that the establishment of an abutment ICT may explain the 1 mm bone loss observed during the course of the 1st year after bridge installation.

There is a lateral component to bone loss once the biologic width has formed especially in a 2-stage implant. The clinical significance of crestal bone loss is that it results in increase in the distance between base of the contact points between adjacent crowns and crest of bone. Hence to prevent lateral bone loss there should be a minimum inter-implant distance of 3mm or more²⁵.

PLATFROM SWITCHING AND PERI-IMPLANT MICROBIOTA

An implant-abutment interface at the alveolar bone crest is associated with sustained periimplant inflammation. The presence of the peri-implant microbiota was suggested to influence the crestal bone resorption by maintaining the inflammatory cell infiltrate within the IAJ.^11,26 On the contrary, Canullo et al reported that difference in bone crest resorption between implants restored with platform switching compared to traditionally restored implants is not associated with differences in the peri-implant microbiota.²⁷

PLATFROM SWITCHING AND PERI-IMPLANT INFLAMMATORY INFILTRATE

Regardless of the nature of the peri-implant inflammatory infiltrate, the physical repositioning of the IAJ away from the external outer edge of the implant and neighboring bone may limit bone resorption by containing the inflammatory cell infiltrate within the angle formed at the interface away from the adjacent crestal bone¹⁵.

MICROGAP AND MICROTHREADS

The connection between implant fixture and its restorative abutment is termed the implant 3 abutment interface or “microgap”. Bone remodelling around the implant does not occur unless the implant has been exposed to the oral environment and the oral fluids. Exposure invariably leads to bacterial contamination of the gap between the implant and superstructure¹². many studies^12-14 have indicated that bacterial contamination of the micro-gap between the implant and the abutment adversely affects the stability of the peri-implant tissue. If above-average axial forces are exerted on the implant, it may cause a pumping effect, resulting in a flow of bacteria from the micro-gap, thus provoking the formation of inflammatory connective tissue (ICT) in the region of the implant neck²⁸. Ericsson et al.⁷ considered this process to be a biological protective mechanism against the bacteria residing in the micro-gap, and it explains the plaque-independent bone loss of approximately 1 mm during the first year. This bone loss may be a reduction in the marginal bone level in both the vertical and horizontal dimensions.

On the other hand other authors say that crestal bone changes around 2-piece, non-submerged titanium implantsare significantly influenced by possible movements between implants and abutments, but not by the size ofthe microgap (interface). Thus, significant crestal bone loss occurs in 2-piece implant configurations even with the smallest-sized microgaps (10 µ m) in combination with possible movements between implant components²⁹. Because of the peri-implant bone resorption that occurs when a non–platform switched implant is exposed to the oral environment, it has been recommended to maintain 1.5 mm between the tooth and implant to preserve the bone adjacent to the teeth. Vela³⁰ et al confirmed that the use of platform-switched implants reduces bone resorption after two-piece implants have been uncovered and that it is possible to place this type of implant 1 mm from teeth while maintaining the bone level adjacent to them (the bone peak).

Jason Schrotenboer³¹ et al showed that microthreads in implants increased crestal stress upon loading. Reduced abutment diameter (i.e., platform switching) resulted in less stress translated to the crestal bone in the microthread and smooth-neck groups. Also Fickl et al³² showed that platform-switched implants seemto limit crestal bone remodelling.

According to a systematic review by Atieh³³ et al, the degree of marginal bone resorption is inversely related to the extent of the implant-abutment mismatch. However, further long-term, well-conducted, randomized controlled studies are needed to confirm the validity of this concept. Bone resorption is mostly related to biologic (biologic width re-establishment) rather than to biomechanical factors (implant platform diameter). Furthermore long-term studies with a wider sample size are needed to confirm the platform diameter influence on hard tissue response around implants restored according to the platform switching concept³⁴.

PLATFORM SWITCHING AND INTERIMPLANT DISTANCE

Peri-implant bone resorption is reduced with platform switching system and with platform switching there is improvement in peri-implant bone preservation with satisfactory aesthetic results³⁵. Adistance of more than 3 mm between two adjacent standard implants has beenshown to preserve the interproximal bone peak, resulting in only 0.45 mm ofresorption. Radiographic studies of boneresorption around 41 pairs of implants placed less than 3 mm apart in 37 patientswere carried out. Mean vertical bone resorption was 0.62 mm, and the mean horizontalcomponent was 0.60 mm. The bone peak that extended coronally beyondan imaginary line connecting the two implant-abutment interfaces was measured,and the mean bone height preservation above this interimplant line was 0.24 mm³⁴. Standardized periapical radiography can evaluate crestal bone levels around implants clinically accurately(within 0.2 mm) in a high percentage (89%) of cases.³⁶

PLATFORM SWITCHED IMPLANTS VS CONVENTIONAL IMPLANTS

However contrary to these studies, other studies by Linkevicius²³ and Canullo report that crestal bone resorption around conventional and platform switched implants did not report any significant differences. Implants with platform switching did not preserve crestal bone better in comparison with implants with traditional implant abutment connection if, at the time of implant placement, thin mucosal tissues were present²³. Meta-analyses showed less crestal bone loss around immediate implant placement compared with implant placement inhealed bone^29,37. Platform-switched implants showed greater crestal bone preservation than non–platform switched implants³⁸. There was no significant difference in CBL with one- versus two-stage placement or use of immediate versus delayed immediate implant loading. Although immediate implant placement showed favorable outcomesfor crestal bone loss changes, these results should be interpreted with caution because of high heterogeneityamong studies.^{23, 30, 37}

Marginal bone level alterations could be related to the extent of implant/abutment mismatching. Marginal bone levels were better maintained at implants restored according to the platform-switching concept.²⁵ 

Annibali³⁸ et al 2012 systematically reviewed the literature to compare implant survival (IS) and marginal bone loss (MBL) around platform switched (PS) versus conventionally restored platform-matching dental implants. Ten RCTs involving 435 subjects and 993 implants contributed to this review. The cumulative estimated implant success rate revealed no statistically significant difference between the two groups. They concluded that PS technique 38 appeared to be useful in limiting bone resorption. Platform switched implants were followed for a period of 11 years in a prospective study by Wegenberg³⁹ et al. All implants had been placed at the crestal level during surgery. Using the known distance of 0.8mm between the peaks of adjacent threads, a determination was made on the radiographs on the amount of bone lost. 71 of the 94 implants showed no bone loss on the mesial aspect and 67 showed no bone loss on the distal aspect. 84% of the mesial surfaces and 88% of the distal surfaces had 0.8mm or less of bone loss. This study confirms the beneficial effect of platform switching³⁹.

CONCLUSION

Majority of the studies report that platform switching does help in marginal bone preservation and hence ensures long term implant survival as well as aesthetics. However it does have its disadvantages like if normal implants are to be used smaller diameter abutments may compromise the emergence profile in aesthetic areas. At least 3mm of soft tissue should be present to place platform switched implants or else bone resorption is likely to occur. A proper understanding of the platform switching concept is needed in order to utilize it to prevent marginal bone loss.