Introduction

With implant treatment in the esthetic zone, it is a constant endeavor to maintain and increase the volume of peri-implant tissues. Many recent developments in implant and abutment design have this as the primary goal. Thus we have seen the evolution and creation of “platform switch” abutments, narrowed abutment diameters, and conical implant connections—all in an effort to maximize the volume of the peri-implant bone and soft tissues. The conical connection in particular was developed with the aim of maximizing the integrity of the abutment–implant connection and thus reducing movement, decreasing peri-implant bone stress, and minimizing leakage of the contents inside the abutment into the delicate zone where bone, connective tissue, implant, and abutment all merge (Figure 1).1,2  This concept is sound and it does appear to reduce leakage into the peri-implant tissues,35  but it does not eliminate leakage. This is a problem that worsens over time with repeated loading.6,7  The “platform switch” design has mostly (but not entirely),8  proven to better maintain bone levels than abutments that flare directly from the head of the implant.912  Multiple finite element analyses have shown that the conical connection may serve to significantly reduce the stresses on the peri-implant crestal bone.13  It appears that the mechanical integrity of the conical connection provides a biologic benefit even outside the implant itself.14 

Figure 1

The implant abutment junction leaks with repeated use, which pumps oral flora and nutrients into the internal aspects of the implant and the abutment. Traditionally, cotton has been used to cover the abutment screw and has provided an environment where anaerobic bacteria propagate and are ultimately pumped into the fragile peri-implant tissues.

Figure 1

The implant abutment junction leaks with repeated use, which pumps oral flora and nutrients into the internal aspects of the implant and the abutment. Traditionally, cotton has been used to cover the abutment screw and has provided an environment where anaerobic bacteria propagate and are ultimately pumped into the fragile peri-implant tissues.

The reason for the success seen with platform switch implants appears to be twofold: First, the nonintegrating abutment components are more narrow and thus further away from the bone allowing more space for the necessary biologic width.15  When nonintegrating components encroach upon this space, the bone remodels laterally and apically to create the necessary biologic space. Secondly, the platform switch design moves the implant–abutment junction (IAJ) away from the bone, and thus moves the inflammatory cell infiltrate coming from inside the implant / abutment and exiting at the IAJ further away from the crestal bone.16  Much histological study has been made into the biologic environment adjacent to the IAJ, and it has been well established that bone is maintained at a more coronal position when leakage is minimized by use of conical connections, and when the leakage that does occur is moved further away from the bone by use of platform switch abutments. Recent short-term data suggest that the conical connection and minimizing leakage at the IAJ is the more important factor in limiting bone loss.17  Based on these concepts, it is evident that the contents inside the implant/abutment directly, and negatively, affect the peri-implant bone position. Leakage from the IAJ cannot be eliminated,7,18  but efforts should be made by the clinician to minimize it.

It is clear that the contents of the implant/abutment negatively affect the peri-implant bone, and that they will leak from the IAJ4 . Thus, what is put into the abutment to cover the screw can have a significant effect. According to a 2008 survey,19  59% of prosthodontic residency directors and 77% of restorative department chairpersons in the United States use cotton pellets to cover the screw access opening under the definitive restoration. The use of cotton is an adaptation of the method used to temporarily fill the access for endodontically treated teeth, though it appears to be falling out of vogue for this purpose as well. It should be noted that cotton was never intended for use under a definitive restoration.

The problem with the use of cotton is that the internal aspect of most implants and implant abutments are hollow, whereas the connection at the IAJ between them is prone to leakage. This creates a 35°C,20  mostly oxygen-free, hollow tube filled with saliva, oral flora, and nutrients—an environment ripe for the proliferation of anaerobic bacteria.21  As the patient functions on the implant, the IAJ continues to flex and wear, pumping saliva, nutrients and oral flora into the implant chamber from the peri-implant area (not the screw access hole). As the anaerobic bacteria proliferate and the IAJ continues to flex and leak, the anaerobic byproducts are pumped out of the implant at the IAJ and directly into the peri-implant tissues.3,22,23 

Covering the screw with cotton, in particular, appears to be problematic because it is an open, organic, scaffold-like structure (Figure 2). These properties provide pathogenic oral flora an ideal substrate upon which to flourish and which likely increases the volume and potency of the inflammatory cell infiltrate. Additionally, cotton has been shown to allow the most leakage into the implant, when compared in vitro to gutta-percha,24  silicone plugs, and polyvinyl siloxane (PVS) impression materials.25  The seal created by polytetrafluoroethylene (PTFE) tape has been shown to be effective in sealing endodontically treated teeth26  and in implant abutments when compared with cotton.27  Ultimately, it appears that the quantity and the specific species of bacteria in and around the implant is affected by the filling materials.4,20  The volume and microbial density of this internal leakage will likely prove to have a negative effect on the long-term stability of the peri-implant bone and soft tissue, though further in vivo investigation is needed.

The use of cotton pellets to directly cover implant screws likely continues because it is familiar, easy, and inexpensive. However, viable alternatives exist that meet the requirements of being easily retrievable, pliable, and microbiologically inert: in particular PTFE tape28  and PVS impression materials. Additionally, these materials have the potential to reduce the volume and density of the internal leakage phenomenon. Although some may note that gutta-percha meets the aforementioned requirements, the authors have found it challenging to remove after years in service, which may then require the use of a handpiece and potentially damage the abutment screw. Furthermore, the PVS and PTFE techniques minimize potential leakage by fully occupying the space of the screw access chamber and creating a better long-term seal.

Technique

PTFE technique for screw-retained restorations:

1. Prior to the appointment, individually autoclave 20–40 mm strips of commercial-grade PTFE tape (Figure 3).

2. Torque the abutment to manufacturer's specifications and verify with vertical bitewing radiograph.

3. Clean the screw access with pellets soaked in 2% chlorhexidine (Figure 4).

4. Wipe down the screw access with isopropyl alcohol.

5. Dry the screw access (Figure 5).

6. Roll the PTFE tape into a cylinder shape and deliver into the screw access (Figure 6).

Figures 2–9

Figure 2. Clinical sample of cotton screw cover placed under gutta-percha after 4 years in function. Patient reported foul odor and taste under function. Figure 3. Commercial-grade polytetrafluoroethylene (PTFE) tape is precut and autoclaved prior to use. Figure 4. Two percent chlorhexidine is used to clean the internal aspects of the channel prior to placing the screw cover. Figure 5. The channel is wiped with isopropyl alcohol and dried. Figure 6. The PTFE tape is rolled into a cigar shape, delivered into the screw access channel and condensed. Figure 7. Sufficient PTFE tape is used to fill the screw access to 2 mm from the occlusal surface. Ideally, this will serve to block the graying effect of the metal channel. Figure 8. Light cured composite resin is applied following hydrofluoric acid etching and silanation of the ceramic ring. Figure 9. The completed composite cover is finished and polished.

Figures 2–9

Figure 2. Clinical sample of cotton screw cover placed under gutta-percha after 4 years in function. Patient reported foul odor and taste under function. Figure 3. Commercial-grade polytetrafluoroethylene (PTFE) tape is precut and autoclaved prior to use. Figure 4. Two percent chlorhexidine is used to clean the internal aspects of the channel prior to placing the screw cover. Figure 5. The channel is wiped with isopropyl alcohol and dried. Figure 6. The PTFE tape is rolled into a cigar shape, delivered into the screw access channel and condensed. Figure 7. Sufficient PTFE tape is used to fill the screw access to 2 mm from the occlusal surface. Ideally, this will serve to block the graying effect of the metal channel. Figure 8. Light cured composite resin is applied following hydrofluoric acid etching and silanation of the ceramic ring. Figure 9. The completed composite cover is finished and polished.

7. Condense the PTFE tape into the screw leaving 2–3 mm above (Figure 7).

8. Etch the occlusal ceramic with the appropriate hydrofluoric acid (2%–10%). Alternatively, this can be done prior to placement.

9. Silanate the occlusal ceramic.

10. Apply an appropriate composite bonding agent to the ceramic, inside the screw access, and over the PTFE plug. PFM crowns may benefit aesthetically by applying an opaquing resin to the walls of the screw channel.

11. Fill the remaining with an opaque composite, shape and polymerize (Figures 8, 9).

As an alternative to steps 10 and 11, Wadhwani et al29  have developed a novel ceramic plug that is more durable and aesthetic than composite (Figures 10, 11).

Figures 10–14

Figure 10. The ceramic plug is pressed concurrently with the crown. It has an opaque apical layer added to prevent show through from the screw access channel as well as an antirotation portion to enable improved seating. Figure 11. The plug is shown seated in the crown. It will be adhesively bonded, after application of ceramic etch and silane; then composite resin is used. Figure 12. A clear polyvinyl siloxane (PVS) material is syringed with a narrow diameter tip into the abutment, directly onto the head of the screw. Figure 13. Excess clear PVS will be wiped away and the plug allowed to polymerize. Figure 14. Should retrieval become necessary, the PVS plug is simple to remove with an explorer.

Figures 10–14

Figure 10. The ceramic plug is pressed concurrently with the crown. It has an opaque apical layer added to prevent show through from the screw access channel as well as an antirotation portion to enable improved seating. Figure 11. The plug is shown seated in the crown. It will be adhesively bonded, after application of ceramic etch and silane; then composite resin is used. Figure 12. A clear polyvinyl siloxane (PVS) material is syringed with a narrow diameter tip into the abutment, directly onto the head of the screw. Figure 13. Excess clear PVS will be wiped away and the plug allowed to polymerize. Figure 14. Should retrieval become necessary, the PVS plug is simple to remove with an explorer.

PVS technique for cement-retained restorations:

  • 1.

    Torque the abutment to manufacture specifications and verify with radiograph.

  • 2.

    Clean the screw access with pellets soaked in 2% chlorhexidine.

  • 3.

    Wipe down the screw access with isopropyl alcohol.

  • 4.

    Dry the screw access.

  • 5.

    Use a narrow diameter syringe tips to inject and backfill the screw access with the PVS material (Figure 12).

  • 6.

    Wipe off excess material prior to polymerization (Figure 13).

  • 7.

    Cement the prosthesis ensuring the abutment margins are no deeper than 1 mm30,31  and that the minimum amount of cement is utilized.32,33 

In the case of necessary retrieval, the PVS plug is simply removed with an explorer (Figure 14).

Summary

The PTFE or PVS screw access cover techniques provide simple alternatives to the traditional use of cotton pellets, and will minimize the colonization and proliferation of oral flora inside the implant system. These materials are likely to minimize the occurrence of patient-reported halitosis and cacogeusia (foul taste) following implant treatment. It is likely that by minimizing the intra-implant bacterial load, inflammation and peri-implant bone loss will be decreased.

Potential disadvantages

Further study (in vitro and in vivo) is needed to quantify the ability of the various materials for preventing leakage, for minimizing the proliferation of the oral flora in the internal aspects of the implant/abutment, and for long-term durability/breakdown tests. Follow-up studies are needed to quantify the effect of the various screw cover materials on the microbial profile inside the implant system and the ultimate effect of this leakage on the long-term stability of the peri-implant tissues.

Abbreviations

    Abbreviations
     
  • IAJ

    implant-abutment junction

  •  
  • PTFE

    polytetrafluoroethylene

  •  
  • PVS

    polyvinyl siloxane

References

References
1
Hansson
S.
A conical implant–abutment interface at the level of the marginal bone improves the distribution of stresses in the supporting bone
.
Clin Oral Implants Res
.
14
:
286
293
.
2
Merz
BR,
Hunenbart
S,
Belser
UC.
Mechanics of the implant-abutment connection: an 8-degree taper compared to a butt joint connection
.
Int J Oral Maxillofac Implants
.
2000
;
15
(
4
):
519
526
.
3
Assenza
B,
Tripodi
D,
Scarano
A,
et al.
Bacterial leakage in implants with different implant-abutment connections: an in vitro study
.
J Periodontol
.
2012
;
83
:
491
497
.
4
Canullo
L,
Penarrocha-Oltra
D,
Soldini
C,
Mazzocco
F,
Penarrocha
M,
Covani
U.
Microbiological assessment of the implant-abutment interface in different connections: cross-sectional study after 5 years of functional loading
.
Clin Oral Implants Res
.
2015
;
26
:
426
434
.
5
Schmitt
CM,
Nogueira-Filho
G,
Tenenbaum
HC,
et al.
Performance of conical abutment
(
Morse
Taper
)
connection implants: a systematic review
.
J Biomed Mater Res Part A
.
2014
;
102
:
552
574
.
6
Harder
S,
Dimaczek
B,
Açil
Y,
Terheyden
H,
Freitag-Wolf
S,
Kern
M.
Molecular leakage at implant-abutment connection—in vitro investigation of tightness of internal conical implant-abutment connections against endotoxin penetration
.
Clin Oral Invest
.
2010
;
14
:
427
432
.
7
Aloise
JP,
Curcio
R,
Laporta
MZ,
Rossi
L,
Da Silva
AM,
Rapoport
A.
Microbial leakage through the implant–abutment interface of Morse taper implants in vitro
.
Clin Oral Implants Res
.
2010
;
21
:
328
335
.
8
Gamborena
I,
Lee
J,
Fiorini
T,
et al.
Effect of platform shift/switch and concave abutments on crestal bone levels and mucosal profile following flap and flapless implant surgery
.
Clin Implant Dent Relat Res
.
2015
;
17
:
908
916
.
9
Lazzara
RJ,
Porter
SS.
Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels
.
Int J Periodontics Restorative Dent
.
2006
;
26
:
9
17
.
10
Degidi
M,
Iezzi
G,
Scarano
A,
Piattelli
A.
Immediately loaded titanium implant with a tissue-stabilizing/maintaining design (‘beyond platform switch') retrieved from man after 4 weeks: a histological and histomorphometrical evaluation. A case report
.
Clin Oral Implant Res
.
2008
;
19
:
276
282
.
11
Hürzeler
M,
Fickl
S,
Zuhr
O,
Wachtel
HC.
Peri-implant bone level around implants with platform-switched abutments: preliminary data from a prospective study
.
J Oral Maxillofac Surg
.
2007
;
65
:
33
39
.
12
Atieh
MA,
Ibrahim
HM,
Atieh
AH.
Platform switching for marginal bone preservation around dental implants: a systematic review and meta-analysis
.
J Periodontol
.
2010
;
81
:
1350
1366
.
13
Hansson
S.
A conical implant–abutment interface at the level of the marginal bone improves the distribution of stresses in the supporting bone
.
Clin Oral Implant Res
.
2003
;
14
:
286
293
.
14
Quaresma
SE,
Cury
PR,
Sendyk
WR,
Sendyk
C.
A finite element analysis of two different dental implants: stress distribution in the prosthesis, abutment, implant, and supporting bone
.
J Oral Implantol
.
2008
;
34
:
1
6
.
15
Canullo
L,
Fedele
GR,
Iannello
G,
Jepsen
S.
Platform switching and marginal bone-level alterations: the results of a randomized-controlled trial
.
Clin Oral Implant Res
.
2010
;
21
:
115
121
.
16
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
.
17
Wang
YC,
Kan
JY,
Rungcharassaeng
K,
Roe
P,
Lozada
JL.
Marginal bone response of implants with platform switching and non-platform switching abutments in posterior healed sites: a 1-year prospective study
.
Clin Oral Implant Res
.
2015
;
26
:
220
227
.
18
Scarano
A,
Assenza
B,
Piattelli
M,
et al.
A 16-year study of the microgap between 272 human titanium implants and their abutments
.
J Oral Implantol
.
2005
;
31
:
269
275
.
19
Tarica
DY,
Alvarado
VM,
Truong
ST.
Survey of United States dental schools on cementation protocols for implant crown restorations
.
J Prosthet Dent
.
2010
;
103
:
68
79
.
20
Choi
JE,
Loke
C,
Waddell
JN,
Lyons
KM,
Kieser
JA,
Farella
M.
Continuous measurement of intra-oral pH and temperature: development, validation of an appliance and a pilot study
.
J Oral Rehab
.
2015
;
42
:
563
570
.
21
Canullo
L,
Radovanović
S,
Delibasic
B,
Blaya
JA,
Penarrocha
D,
Rakic
M.
The predictive value of microbiological findings on teeth, internal and external implant portions in clinical decision making
.
Clin Oral Implant Res
.
In press
.
22
Koutouzis
T,
Gadalla
H,
Lundgren
T.
Bacterial colonization of the implant-abutment interface (iai) of dental implants with a sloped marginal design: an in-vitro study
.
Clin Implant Dent Relat Res
.
2016
;
18
:
161
167
.
23
D'Ercole
S,
Tripodi
D,
Marzo
G,
et al.
Microleakage of bacteria in different implant-abutment assemblies: an in vitro study
.
J Appl Biomater Funct Mater
.
2015
;
13
:
e174
e180
.
24
Cavalcanti
AG,
Fonseca
FT,
Zago
CD,
Brito
Junior
RB,
França
FM.
Efficacy of gutta-percha and polytetrafluoroethylene tape to microbiologically seal the screw access channel of different prosthetic implant abutments
.
Clin Implant Dent Relat Res
.
2016
;
18
:
778
787
.
25
Park
SD,
Lee
Y,
Kim
YL,
Yu
SH,
Bae
JM,
Cho
HW.
Microleakage of different sealing materials in access holes of internal connection implant systems
.
J Prosthet Dent
.
2012
;
108
:
173
180
.
26
Paranjpe
A,
Jain
S,
Alibhai
KZ,
Wadhwani
CP,
Darveau
RP,
Johnson
JD.
In vitro microbiologic evaluation of PTFE and cotton as spacer materials
.
Quintessence Int
.
2012
;
43
:
703
707
.
27
Nascimento
C,
Pita
MS,
Calefi
PL,
et al.
Different sealing materials preventing the microbial leakage into the screw-retained implant restorations: an in vitro analysis by DNA checkerboard hybridization
.
Clin Oral Implants Res
.
In press
.
28
Moráguez
OD,
Belser
UC.
The use of polytetrafluoroethylene tape for the management of screw access channels in implant-supported prostheses
.
J Prosthet Dent
.
2010
;
103
:
189
191
.
29
Wadhwani
C,
Pineyro
A,
Avots
J.
An esthetic solution to the screw-retained implant restoration: introduction to the implant crown adhesive plug: clinical report
.
J Esthet Restor Dent
.
2011
;
23
:
138
143
.
30
Linkevicius
T,
Vindasiute
E,
Puisys
A,
Peciuliene
V.
The influence of margin location on the amount of undetected cement excess after delivery of cement-retained implant restorations
.
Clin Oral Implants Res
.
2011
;
22
:
1379
1384
.
31
Linkevicius
T,
Puisys
A,
Vindasiute
E,
Linkeviciene
L,
Apse
P.
Does residual cement around implant-supported restorations cause peri-implant disease? A retrospective case analysis
.
Clin Oral Implants Res
.
2013
;
24
:
1179
1184
.
32
Wadhwani
C,
Piñeyro
A.
Technique for controlling the cement for an implant crown
.
J Prosthet Dent
.
2009
;
102
:
57
58
.
33
Wadhwani
C,
Hess
T,
Piñeyro
A,
Opler
R,
Chung
KH.
Cement application techniques in luting implant-supported crowns: a quantitative and qualitative survey
.
Int J Oral Maxillofac Implants
.
2012
Aug
1
;
27
:
859
864
.