August 1, 2013
by Eli Raviv, DMD., Roy Raviv, DMD, Jan Hanna, DMD, Mili Harel-Raviv, DMD
The design of an implant plays a key role in the success of a final restoration. The two basic designs which are available are the two-piece implant design, (the surgical implant and prosthetic abutment are two separate components) and the one-piece implant design (the surgical implant and prosthetic abutment are one integral piece). This one piece implant design was originally created to eliminate the structural weakness built into the two-piece implant design (the microgap). This review of the literature will outline the advantages and disadvantages of the one piece implant design as well as some of the bio-mechanical parameters which are required for its selection. A case of one piece implant retained fixed partial denture will be presented.
For the past 30 years dental implants have provided a viable alternative treatment to the traditional fixed or removable prosthesis in partial or complete edentulism.1 Most dentists have become familiar with the conventional two piece implant design which is made out of two components: a surgical implant and a prosthetic abutment.
The conventional two piece implant can be placed in two ways:
Two phase technique:
The implant is placed and sealed with a cover screw, then left submerged for a healing period. Three to six months later a minor surgical procedure is undertaken to uncover the implant restorative platform, the cover screw is removed and replaced with a healing abutment. A month later the prosthetic procedure is commenced.
One phase technique:
The implant is placed and sealed with a transmucosal healing abutment. Three to six months later the prosthetic procedure is commenced.
The one piece implant design is unique because it incorporates the prosthetic abutment and surgical implant into one unit (Fig. 1).2,3 This eliminates the fixture abutment interphase (the microgap). As a result, all one piece implant designs fall under the one phase technique (since the prosthetic abutment is always present transmucosally). Furthermore, in many cases they are loaded immediately following the implant placement with a temporary crown.
The purpose of this article is twofold:
1. To review the literature and outline the advantages and disadvantages of the one piece implant design as well as some of the bio-mechanical parameters which are required for its selection.
2. To present a case of one piece implant retained fixed partial denture.
A healthy seventy-year-old Caucasian male presented with:
1) partial edentulism.
2) A failing porcelain fused to metal – fixed partial denture (PFM-FPD) on teeth #17-x-15 due to a root fracture to #17
3) A heavily restored and discolored first upper right bicuspid (#14).
4) Recurrent caries around existing restorations on teeth Nos. 45, 46.
The patient’s chief concern was, “I would like to have teeth again.” The patient requested to restore the missing teeth with a fixed prosthesis.
A panoramic radiograph (Fig. 2) and cone beam CT scan were used to assess the volume and quality of the bone. Sufficient bone quantity and quality for implant placement was found in both arches.
A treatment plan was presented to the patient starting with:
1) Removal of decay on 45, 46 (possible root canal treatment (RCT), post, core and crowns)
2) Removal of the failing FPD 17-x-15, extraction of tooth #17
3) An immediate provisional removable upper partial denture and a provisional fixed partial denture (FPD) for teeth 14, 15, 45, 46.
Subsequently, definitive maxillary and mandibular implant supported FPD as well as single crowns for teeth 14, 15, 45, 46 were to be fabricated.
The patient accepted the plan and the treatment began.
The decay on tooth 45 was into the pulp and necessitated a RCT. The decay on tooth 46 was very close to the pulp and the pt. was advised that a RCT may be necessary.
Two months following fabrication of the maxillary provisional partial denture, six conventional endosseous implants (AB Dental devices) were placed in the maxilla.
In the mandible, two one-piece endosseous implants (I7 AB Dental devices) were placed in sites 37 and 47 (5mm diameter/11.5mm length and 4.2mm diameter/11.5mm length respectively) (Fig. 3). The rational for the use of one piece implants in the mandible was the excellent bone density in sites 37 and 47. Furthermore, the self tapping, sharp threads present on this specific implant design provided the implants with great primary stability. This, combined with the availability of adequate intermaxillary space, allowed the selection of the one piece implant.
Post operative Amoxicillin 500mg, Ibuprofen 400mg and Chlorhexidine 0.12% mouth rinse were prescribed to the patient. One week follow up showed good healing and evidence of good oral hygiene. No side effects were reported.
A month later, the patient presented for an emergency visit with pain in tooth 46. On exam tooth 46, it was found to have a necrotic pulp with an acute apical periodontitis. The patient was informed that the tooth required a RCT. The patient did not like his past RCT experience on tooth 45 and insisted on extracting tooth 46 and placing an implant instead. Tooth 46 was subsequently extracted. Two and a half months later, following healing of the extraction site, another one piece endosseous implant (I7 AB Dental Devices, 5mm width/11.5mm length) was placed in site 46. Amoxicillin 500mg, Ibuprofen 400mg and Chlorhexidine 0.12% mouth rinse were prescribed. A follow up one week later showed normal healing. (Figs. 4 & 5)
Three months later, the prosthetic abutments of implants 37, 46 and 47 were prepared using high speed diamond burs to a deep chamfer finish line (copious irrigation was used to avoid excessive heat transfer to the implant and the bone) (Fig. 6). Upper and lower final impressions were taken. Retraction cords (000 and 0) were used for gingival retraction on abutments 14, 15, 45 and the one piece implants (Ultrapak-Ultradent products Inc. USA). Final impressions were taken utilizing light and heavy body polyvinyl-siloxane (PVS) impression material, in a single phase technique (Affinis precious, Coltene Whaledent- Switzerland) (Fig. 7). Upper and Lower master casts were produced from the final impressions (Figs. 8 & 9). All Zirconium restorations were fabricated both for maxilla and mandible. Maxillary implant restorations were screw retained, mandibular implant restorations were cement retained utilizing temporary cement (Temp-bond-Ne-Kerr, Corporation, USA) (Figs. 10-12). Aesthetics and function were satisfactory.
Thirty-six months follow up revealed no bone loss around the implants and no other clinical significant findings (Figs. 13 & 14).
Hermann JS et al,4 Broggini N et al,5 and Archie A. Jones et al6 concluded that the one piece implant system has no micro-gap and therefore does not display bacterial colonization at the FAI (fixture abutment inter-phase) and minimal early bone resorption when compared to the two piece system.
A comprehensive review of the literature regarding the microgap shows the following results: In 1993 and in 1994 M. Quirynen et al7 showed that in implant systems with screw-retained abutments, bacteria can penetrate the internal cavity of the implant as a consequence of leakage at the implant–abutment interface. In 1997, Jansen yr8 showed that the microgap is a hollow space that can act as a trap for bacteria, which might cause an inflammatory reaction in the peri-implant soft tissues. In 2003, Broggini N et al5 stated that the presence of a microgap at the level of the alveolar bone was associated with persistent inflammation and increased alveolar bone loss. In 2005, Callan DP et al9 showed that moderate to high levels of eight d
ifferent putative periodontal pathogens, including A. actinomycetemcomitans and P. gingivalis, were colonizing the FAI (the microgap). Later in 2006, Archie A. Jones et al6 stated that an inflammatory immune reaction is present at the connection of the implant and the abutment. This host response results in bone loss and soft tissue changes including an enlarged biologic width dimension and recession. Then in 2008, C. do Nascimento et al10 claimed that there is a bacterial leakage through the interface but it is in very low percentages.
Steinebrunner L et al11 in 2005 stated that the implant geometry plays a crucial role when it comes to microbial penetration along the internal part of the implants. This was supported in 2009 in the most recent reference, Tesmer M et al12 who showed that the implant design is the deciding factor when it comes to the potential risk for colonization of oral microorganisms into the FAI microgap. They claim that in dental implants with a Morse-taper internal connection a negligible bacterial penetration down to the threaded part of the FAI is observed. To conclude the microgap discussion, based on Tesmer M et al, so long as the implant used is of a morse taper internal connection design, the lack of a microgap on the one piece implant design is not a significant advantage over the two piece implant design (contrary to the thinking a few years ago).
The one piece implant design does, however hold a few genuine advantages over the two piece implant design:
Increased strength due to unified structure of implant and abutment.13 This is especially beneficial when using smaller diameter implants to restore an edentulous space limited by bone volume or inter-dental space.2,3
Less components are used (reduced need for inventory — abutments, impression copings, implant analogs etc…).
No loosening or fracture of the abutment screw (healing abutment or prosthetic abutment).13
The clinician can control the final crown margins, the gingival contours and the angulation of the crown preparation with a bur in a quick and easy manner2 (rather than look for the right abutment and prepare it for the crown).
The one piece design follows the conventional crown and bridge procedure (preparation, temporization, impression, cementation).
The disadvantages associated with the one piece design are:
a) The implant angulation must be ideal as it is not possible to correct more than a 150 error.
b) The implant abutment is not as versatile as a two piece abutment (for ex. An abutment of a two piece design may be changed from a locator attachment to a conventional PFM abutment to accommodate a change from a removable to a fixed prosthesis or vice versa)
When considering a one piece implant design one must assess whether the conventional implant criteria is met (i.e. bone quality and quantity, intra-occlusal and inter-maxillary space, keratinized gingiva etc.) as well as whether the implants can be loaded immediately.
The concept of immediate loading of implants is well documented and is outside the scope of this article, however, a few important points should be mentioned. In 2009 Atieh MA et al14 stated that immediate loading in healed ridges presents lower risk of failure than in extraction sockets (in other words, immediate loading is more predictable on its own than if it was combined with immediate placement). Also in 2009, Esposito M et al15 mentioned in their article which was previously documented by Cannizzaro G et al16 in their 2003 article that to increase the success rates of immediately loaded implants the implants must have high insertion torque and primary stability. (This can be achieved by slightly under-preparing the implant site.) Another key factor mentioned by Roccuzzo M et al in 200917 is the surface roughness of the implant which is essential should the implant be loaded immediately. (15),(22),(23),(24)
The One piece implant design is a viable option to restore an edentulous space. Proper case selection and implant criteria assessment is essential.
The one piece implant design is best suited for cases where the implant and the crown share a similar angulation (long axis) and the bone quantity and quality enables immediate loading.OH
Professor Raviv received his dental degree from the University of Tel-Aviv and his certificate in Prosthodontics from the Hebrew University in Jerusalem, Israel. He is an Associate professor in the Faculty of Dentistry, McGill University- Montreal, Canada. Director of Prosthodontics and Associate Director of the Department of Dentistry, Sir Mortimer B. Davis – Jewish General Hospital, Montreal, Canada.
He is a member of the Editorial Review board of Quintessence International Journal.
Prof. Raviv is the former Editor in Chief of the Dental Tribune Journal – Canada.
For the past 30 years Prof. Raviv is involved in teaching and research of Implant Dentistry. He is published in local and international peer reviewed journals.
Dr. Raviv has a commerical interest in AB Dental Devices.
Oral Health welcomes this original article.
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