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141

The Effect of Interimplant Distance on

the Height of the Interimplant Bone

Crest When Using Platform-Switched

Implants

Xavier Rodrfguez-Ciurana, MO, PhO*

Xavier Vela-Nebot, MO, 005*

Maribel Segala- Torres, MO, 005*

Jose Luis Calvo-Guirado, ~OS, MS, PhO** .

Jordi Cambra, MO, 005*

Vfctor M~ndez-Blanco, 005***

Dennis P . Tarnow, 005****

A distance of more than 3 mm between two adjacent standard implants has been

shown to preserve the interproximal bone peak, resulting in only 0.45 mm of

resorption. Thepurpose of this study was to determine whether use of the plat-

form-switching technique wou7d change the bone resorption patterns between

adjacent implants placed less than 3mm apart Radiographic studies of bone

resorption around 41 pairs of implants placed less than 3 mm apart in 37 patients

were carried out Mean vertical bone resorption was 0.62 mm, and the mean hori-

zontal component was 0.60 mm. The bone peak that extended coronally beyond

an imaginary line connecting the two implant-abutment interfaces was measured,

and the mean bone height preservation above this interimplant line was 0.24 mm.

(Int J Periodontics Restorative Dent 2009;29: 141-151.)

*Private Practice, Barcelona, Spain.

**Senior Lecturer of General and Implant Dentist ry, University of Murcia, Spain.

***Private Pract ice, Madrid, Spain.

****Professor of Periodontology and Implant Dentistry, New York University College of

Dentistry, New York, New York, USA

Correspondence to: Dr Xavier Rodrfguez-Ciurana, C/ Ganduxer 122 08022, Barcelona

BCN Spain; fax: +34-934181668; email: [email protected].

Multiple researchgroups haveestab-

lished that a biologic width exists

around all dental implants.":" This istrue for all implants of all shapes,

whether on one-stage implantsor after

uncovering in two-stage placement

protocols on two-piece irnplants.l-v'

Peri-implant bone loss around

implants exposed to the oral environ-

ment also has been documented

extensively.':"Suchresorptionappears

to be related primarily to exposure of

the implant to the oralenvironment.v"

It hasbeen demonstrated thatthe gapbetween the implant and the abut-

ment hasa direct effect on bone loss,

reqardless of whether the two parts

are connected at the time of implant

placement or after initial submergence

~nd integration of the implant.' This

phenomenon occurs whether the

implant is loaded or unloaded and

appearsto beunrelated to the implant

surfacetreatment.v? Management of

such bone resorption isan important

factor in achieving good esthetic

results in the anterior maxilla and in

optimizing bone support.10,11

Vertical bone resorption, which

often extends 1 to 2 mm below the

implant-abutment interface,diminishes

Volume 29, Number 2,2009

mailto:[email protected].

mailto:[email protected].



142

the bone-to-implant contact surface

and thus, impairsthe biomechanics of

restorations.3,4 Horizontal bone loss

leadsto resorption of the buccalplate

innarrowalveolarcrests,aswell asloss

of the interproximal bone peak andlossof support for the adjacent inter-

implant papilla.

When two implants are placed

adjacent to one another, the distance

between them has been demon-

strated to affect the extent of lateral

bone lossand interproximalbone peak

resorption. A distance of more than 3

mm between two adjacent implants

appearsto preservethe interproximal

bone peakand result inonly 0.45mmof resorptionon averaqe.l-' Incontrast,

if the space between the implants is

3mmor less,averageresorptionof the

interproximal bone peak increasesto

1.04mm,which compromisessupport

for the interimplant papilla.F

Fig 1 Platform-switching design using the

example of a 4.8-mm implant with a 4.1-

mm abutment.

To reduce the effects of peri-

implant bone resorption, a technique

known as platform switching was

recently developed.13-15 The concept

behind platform switching is that by

shifting ,the implant-abutment inter-facemedially,the deleterious impact of

the implant-abutment microgap on

the peri-implant bone canbe reduced.

Platform switching thus involves the

use of abutments with a diameter

smaller than that of the implant plat-

forrn.!" This geometry shifts the

perimeter of the implant-abutment

junction inwardtoward the central axis

of the implant.!" Commonly, for

instance, an implant with a 4.8-mm-diameter platform is connected to a

4.1-mm-diameter abutment, creating

a distance .of 0.35 mm between the

implant-abutment interface and the

peri-implant tissues(Fig 1).

Platform switching has been

shown to result in an average of 0.76

mm of vertical bone resorption, a

reduction of 70%versusconventional

restoration with a matching abut-

rncnt." While a reduction in horizon-tal bone resorption also has been

observed in radiographs of platform-

switched implants, the impact of plat-

form switchingonhorizontal bone loss

hasnot previously been directly stud-

ied and documented.

Thus, the purpose of this study

was to determine whether platform-

switchedadjacent implantsplaced less

than 3mmapartexhibited lessvertical

and/or horizontalbone resorptionthanhas been previously documented

around non-platform-switched

implants.

The International Journal of Periodontics & Restorative Dentistry



143

Fig 2 Measurements obtained around the examined implants.

Fig~2a (left) (nterimplant distance = the

distance between two adjacent implants.

Method and materials

Patientsfrom three private clinicswere

recruitedto participate inthis prospec-

tive study. All participants were

required to be 18 yearsor older and

provide informed consent to undergo

radiography of their implants.

A total of 82 adjacent implants

(41 pairs) placed in 37 patients were

measured(20women and 17men).Of

the 41 pairs of implants, 27 were

placed in the maxilla and 14 in the

mandible. Elevenwere placed in the

anterior zone(incisorsto canines),and

30 were placed in the posterior arch

(premolars and molars). All the

implants were two-piece rough-

surfaced platform-switched designs.

Fig 2b (right) Horizontal bone resorption.

b1 (mesial) =distance from the interimplant

bone peak to the mesial implant; b2 (distal)=distance from the interimplant bone peak

to the distal implant.

Fig 2c (left) Vertical bone resorption. c1(mesial) =mesial distance from the implant-

abutment interface to the most coronal

point of contact between the interproximal

face of the implant and the bone; c2 (distal)

=distal distance from the implant-abutment

interface to the most coronal point of con-tact between the interproximal face of the

implant and the bone.

Fig 2d (right) Bone peak retention. Distance

from the 'bone peak to the imaginary line

connecting the two implant-abutment

interfaces; this is expressed as a positive

(d+) or negative (d-) number in millimeters.

All implants were placed at the lower

bone level of the peri-implant bone

tissue sothat the whole implant plat-

form wascoveredby bone. Thisplace-

ment sometimes meant that the

implant was located at the crest on

one sideand subcrestallyon the other.

All implants had been restoredfor 6 to

,24 month's before being measured

radiographically. This means that the

prosthetic abutment had been dis-

connected and reconnected at least

four times before radiographic mea-

surementswere made.

Thirty pairs had an implant plat-

form diameter of 4.8 mm and anabut-

ment platform of 4.1 mm (Prevail

4/5/4, Biometl3i). Inthese30patients,

the discrepancy between the implant

and abutment platformswas0.35mm.

Three patients had implants with a

diameter of 6.0 mm and abutments

with a 5.0-mm platform (Prevail5/6/5,

Biometl3i). In these 3 cases,the dis-

crepancy between the implant and

abutment platforms was 0.5 mm.

Sevenpatientshad implantsof 5.0mm

diameter and abutments with a 4.1-

mmplatform (XP4/5/4, Biornet/Si),for

adiscrepancyof 0.45mm.One patient

had implants of 4.1 mm diameter and

abutments with a 3.4-mm platform

(Prevail4/3, Biometl3i), for a discrep-

ancy of 0.35 mm. The discrepancies

between the implant and abutment

platforms thus ranged from 0.35 to

0.50 mm.




144

Results of implant and bone measurements

a=the distance between the two implants in mi ll imeters; b, and b2=distance (b., mesial; b

2, dis-

tal) from the interimplant bone peak to the implant; c, and c2 =vertical bone resorption (c,mesial; c2, distal) determined by measuring from the implant-abutment interface to the mostcoronal point of contact between the interproximal face of the implant and the bone; d= i f thebone peak extended coronally beyond the imaginary l ine connecting the two implant-abutmentinterfaces, it was expressed asa posit ive number in mil limeters. Ifthe bone peak did not reachthe imaginary l ine connecting the two implant-abutment interfaces, it was expressed asa nega-tive number in millimeters.

Periapical radiographs were

obtained with the Kodak RVG 6000

Digital Radiography System (Eastman

Kodak) in high-resolution mode. The

use of periapical radiographs with the

parallel technique in reproducible pro-

jections isa routine diagnostic imagi~g

procedure to evaluate peri-implant

bone."? A mouthpiece was employed

to ensure a parallel technique and

reproducibility between preoperative

and postoperative radiographs. Bone

loss was measured using previously

calibrated Kodak Trophy software.

The following measurements were

then made and recorded (Fig 2):

1. The distance between the two

implants was determined by mea-

suring between the two implants at

the implant shoulder.

2. Horizontal bone resorption was

determined by measuring the dis-

tance from the interimplant bone

peak to the implant (b., mesial; b2,

distal).

3. Vertical bone resorption was deter-

mined by measuring from the

implant-abutment interface to the

most coronal point of contact

between the interproximal face of

the implant and the bone (c.,mesial;

c2, distal).

4. Ifthe bone peak extended coronally

beyond an imaginary line connect-

ing the two implant-abutment inter-

faces, it was expressed asa positive

number in millimeters. If the bone

peak did not reach the imaginary

line connecting the two implant-

abutment interfaces, it was

expressed asa negative number in

millimeters.

Statistical analysis (means, stan-

dard deviations [SDs],frequencies) was

performed with the SPSS12 program

(SPSSInc).




145

Results

Measurements between the implant-

abutment junctions of each pair con-

firmed that each pair had been placed

less than 3 mm apart. The mean dis-

tance between implants (a) was

2.23 mm, with an SD of 0.55 mm.

The mean distance from the

mesial implant shoulder to the inter-

implant bone peak (b.) was 0.60 mm,

with an SD of 0.38 mm. The mean dis-

tance from the distal implant shoulder

to the interimplant bone peak (b2) was

0.59 mm, with an SD of 0.46 mm.

The mean distance from the


most coronal point of contact between

the face of the mesial implant and the

bone (c.) was 0.70 mm, with an SD of

0.57 mm. The mean distance from the


most coronal point of contact between

the face of the distal implant and the

bone (c2) was 0.55 mm, with an SD of

0.52 mm.

The mean distance from the inter-implant bone peak to the imaginary

line connecting the two implant-

abutment interfaces(d)was+0.24 mm,

with an SDof 0.85 mm. In26 ofthe 41

pairs (64%), the peri-implant crestal

bone peak was preserved, while it

was lost in 15 of the 41 cases (36%).

Table 1 summarizes these findings.

Discussion

The results of this study document

less bone resorption in both the ver-

tical and horizontal directions follow-

ing oral exposure of platform-

switched implants, as compared to

non-platform-switched implants (Fig

3). These findings suggest that the

biologic width around platform-

switched implants is located more

coronally than the biologic widt~

around non-platform-switched

implants; these findings are in agree-

ment with the study of Becker et al.18

Some investigators have reported

less bone resorption in platform-

switched implants than in other

non-platform-switched irnplants.l'' 19,20

Infact, the Ankylos implant has shown

vertical bone resorption of less than

0.5 mm up to 2.0 mm after oral expo,:

sure.'?Astra Tech implants have shown

amean vertical bone resorption of 0.09

mm. The absence of radiologic studies

regarding horizontal bone resorption

with platform-switched implant

designs must be noted.2 o

Typically, vertical bone resorption

aroundnon-platform-switched implants

is about 2 mm,3,4whereas the mean

vertical resorption was 0.62 mrn in this

study series,again of 69%. Inan earlier

study,15 the mean vertical bone resorp-tion component around implantswith a

5.0-mm implant collar and a 4.1-mm

abutment platform was 0.76 mm.

Unintentional or repeated inten-

tional disconnection ofthe abutments

on two-piece implants hasbeen shown

to disrupt soft tissue integration. This

induces increased marginal bone

remodeling and buccal recession and

has important clinical irnplications."

The handling protocol of our studyincluded at least 4 abutment manipu-

lations before seating of the definitive

prosthesis. This means that the

observed bone resorption would be

that typically seen with the standard

loading protocol.




146

Fig 3 Radiographs of seven patients in whom two adjacent implants were placed less than 3 mm apart in dif ferent locat ions.

Fig 3a Patient 1. Implants placed in the

maxilla (central incisors). (left) Before load-

ing. (right) After 12 months of loading.

Fig 3b Patient 2. Implants placed in the

maxilla (left premolar area). (left) Before

loading. (right) After 12 months of loading.

Fig 3c Patient 3. Implants placed in the

maxilla (central incisors). (left) Before load-


The Internat ional Journal of Periodont ics & Restorat ive Dent istry



147

Fig 3d Patient 4. Implants placed in the

mandible (right first and second molars).

(left) Before loading. (right) After 12 months

of loading.

Fig 3e Patient 5. Implants placed in the

maxilla (right premolars). ~eft) Before load-


Fig 3f Patient 6. Implants placed in the

mandible (right firs t and second molars).

(left) Before loading. (right) After 12 months

of loading.




148

Fig 3g Patient 7. Implants placed in the

mandible (left first and second molars). (left)

Before loading. (right) After 12 months of

loading.

Fig 4 Radiographs of two patients with adjacent implants placed less than 2 mm apart. Note the preservation of the interimplant bone peak.

Fig 4a Patient 8. Implants placed in the

maxillary right premolar area. (left) Before

loading. (right) After 12 months of loading.

Fig 4b Patient 9. Implants placed in the

maxillary central incisor positions. (left )

Before loading. (right) After 12 months of

loading.

The International Journal of Periodont ics & Restorative Dentistry



149

Fig S Esthetic results after prosthetic restoration.

Fig Sa Patient 8. Screw-retained porcelain-

fused-to-metal prosthesis. Implants were

placed in the maxillary right premolar

positions, as seen in Fig 4a.

Fig Sb Patient 9. Screw-retained porcelain-

fused-to-metal prosthesis for the four

incisors, with the lateral incisors as can-

tilevers. Implants were placed inthe central

incisorpositions, as seen in Fig 4b.

The mean horizontal bone resorp-

tion inthe present study was 0.60 mm,

a 57% improvement over that seen in

an earlier study of non-platform-switched implants of (1.4 mm).12With

a platform-switching design, the bone

resorption is significantly less. This

bone preservation may also provide

better support for the soft tissues.

It must be noted that in seven

cases, the implants were placed less

than 2 mm apart, and the distance

from the crestal bone peak to the

imaginary line connecting the two

implant-abutment interfaces was pos-itive (Fig 4).The esthetic and functional

advantages of a more coronal biologic

width location are obvious. Inedentu-

lous sectors when the implants must

be placed less than 3 mm apart

(between 1.5 and 3 rnrn), it is possible

to retain a bone peak. This aids in the

formation of the interimplant papilla.

By reducing the vertical and horizontal

components of bone loss,the buccalbone margin is preserved, protecting

the implant and improving esthetic

results (Fig 5).

The use of an immediately loaded

abutment that issmallerthan the diam-

eter of the implant body can help to

protect the peri-implant mineralized

tissues.F Thisfact could be very impor-

tant in the rehabilitation of atrophic

arches.




150

Conclusions

The platform-switching technique can

help to preserve peri-implant bone

and retain the interproximal bone peak

better than conventional implant

restorations. This bone preservation

leads to better support for the soft

tissues and improves the crown-to-

implant ratio. In narrow edentulous

sectors where implants must be placed

lessthan 3 mm apart (between 1.5 and

3 mrn), it is possible to retain a bone

peak with platform-switched implants.

Because this implant design results in

more coronal bone-to-implant con-

tact, it may be more suitable for the use

of short implants and in atrophic areas.

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