April 1, 2003
by Suzanne Caudry PhD, DDS, Dip Perio MSc.
Single tooth replacement with an implant is challenging especially in a highly compromised site. If the final outcome of a single tooth implant is to resemble, aesthetically and functionally, a real tooth surrounded by natural looking soft tissues, there are three important factors to consider: i) the original tooth should be in place upon presentation; ii) the original soft and hard tissue profiles should be optimally preserved or reconstructed; and iii) the implant root component must be correctly positioned allowing for its subsequent restoration with an anatomically correct crown. In this paper these principles will be discussed and demonstrated with two sample cases.
CONSIDERATIONS RELATED TO THE IMPORTANCE OF HAVING THE ORIGINAL TOOTH IN PLACE
When the patient presents for an implant consultation with the tooth in question still in situ, aesthetic problems with the final treatment outcome are more likely to be minimal. The major problem associated with tooth extraction is bone resorption with loss of support and disfigurement of the overlying soft tissue architecture resulting in negative aesthetic implications.
When a tooth is extracted without a concurrent “ridge preservation” procedure, the alveolar bone will resorb rapidly both buccolingually and apicocoronally (Tallgren, 1972). In a classic paper by Tallgren (1972), 3-5mm of bone resorption occurred apicocoronally within the first three months following tooth extraction, even where the socket walls had remained intact. Naturally occurring dihescences, fenestrations and buccal alveolar concavities will further accentuate this rapidly occurring and disfiguring resorptive process. Likewise, in situations where a tooth root is cracked or there has been a failed endodontic treatment, the buccal and/or lingual socket wall may be further compromised. A typical clinical outcome in such a scenario is shown in Figure 1.
This unfavourable change in alveolar anatomy could have been easily prevented by doing a ridge preservation procedure at the time of tooth extraction. In this case, in order to achieve a favourable outcome with an implant restoration, or even with a traditional tooth-supported fixed bridge, reconstruction of the collapsed site pre-prosthetically would likely require multiple grafting procedures, additional time, extra expense and inconvenience for the patient.
RECONSTRUCTION OF HARD AND SOFT TISSUES AT THE TIME OF TOOTH REMOVAL
A “ridge preservation” procedure is a grafting procedure done at the time of tooth extraction in order to maintain and further develop hard and soft tissues at the extraction site. The usual approach is to use a graft of bone substitute material and some type of barrier membrane to contain and stabilize the graft particles and prevent epithelial migration into the healing socket (Carlson-Mann et al. 1996, Lekovic et al. 1997, Lekovic et al. 1998, Wang & Carroll 2001). Most membranes, including e-PTFE (expanded Teflon; Gore-Tex Augmentation Material) and resorbable membranes made of cross-linked collagen require primary wound closure to avoid site infection and compromised healing.
Wound closure is generally achieved by using periosteal releasing incisions to mobilize the mucoperiosteal flaps, allowing for coronal repositioning and juxtaposition of the wound edges. The unavoidable outcome in this soft tissue repositioning is a diminution of the vestibule and keratinized tissues (Fig. 2). Bartee (1995) described an alternative technique using a high-density (n-PTFE) Teflon barrier membrane placed over the grafted socket without the traditional primary wound closure. Because n-PTFE, unlike e-PTFE, is non-porous, the risk of wound infection is minimal.
As a result, this material can be intentionally left exposed to the oral cavity and stabilized only by the margins of the mucoperiosteal flaps returned to their original positions with simple suturing. Membranes of n-PTFE are intended to be used only for the time required for initial granulation and epithelialization of the wound by secondary intention healing and are removed at 3 to 4 weeks post-operatively.
Since primary wound closure is not necessary with this technique, soft tissue anatomy (i.e. vestibular depth and dimension of keratinized tissues) is not unfavourably affected. On the contrary, there is an additional thickness and width of keratinized tissue that forms over the extraction socket once the n-PTFE barrier has been removed.
In the present paper a ridge preservation technique, based on Bartee’s (1995), is described using an absorbable collagen socket-base filler (CollaPlug), an osteoconductive bone substitute material (Bio-Oss) and an n-PTFE barrier (Cytoplast).
Bio-Oss is a bone substitute material widely used in implant dentistry and periodontics (Berglundh & Lindhe, 1997; Valentini & Abesur, 1997; Camelo et al., 1998; Sclar, 1999). It is prepared from deproteinized bovine bone screened and processed using techniques shown to be effective in minimizing risk of transmission of bovine encephalitis (BSE; “mad cow disease”) to patients (Wenz et al., 2001).
The advantages of Bio-Oss are: 1. It is relatively inexpensive; 2. It provides an effective rigid scaffold to support the newly formed blood clot and overlying healing mucoperiosteal soft tissues and 3. It creates an osteoconductive substrate for the migration and differentiation of osteoprogenitor cells. However, it is a very slowly resorbing material, and there is some concern about the practicality of subsequent placement of a dental implant into a site still largely composed of remodeling Bio-Oss, which might not provide for adequate initial dental implant stabilization and osseointegration. For this reason a more rapidly resorbing collagen sponge material (Collaplug) is used as a partial filler particularly for the more apical aspects of the extraction site. Because this material is rapidly resorbed and replaced with new host bone, it is preferable to the more slowly resorbing Bio-Oss; it will ensure a more suitable site for stabilization of the dental implant.
However, the Bio-Oss is preferable to support the mucoperiosteal flap and retain/develop the alveolar ridge anatomy rather than the Collaplug. The amount of Bio-Oss needed is determined by the severity of the socket defect, but a minimum of 30% Bio-Oss at the coronal portion is deemed necessary to ensure soft tissue support. Finally, the n-PTFE barrier material is used, as described by Bartee, to contain and protect the Bio-Oss until it has been covered during the initial secondary intention healing response (three to four weeks).
PLACEMENT OF A DENTAL IMPLANT INTO THE RECONSTRUCTED RIDGE
Extraction sockets managed with this technique are generally left to heal for four to six months before the placement of a dental implant. Even in the case of a single implant, a surgical stent is generally required for optimal aesthetic alignment. To ensure an aesthetically pleasing emergence profile, the preference is to place an implant for a single tooth replacement slightly mesial of centre (i.e. closer to the mesially contiguous tooth), 3 to 4mm apical to the CEJ of the contiguous teeth, and as far buccally as possible without compromising the buccal bony wall (leaving a minimum of 1mm buccal plate thickness, [Fig. 3]).
Generally, an implant with a roughened, highly osteoconductive surface is used. With a threaded dental implant, the longest implant length possible is preferred so that the apical portion of the implant can be tapped into cortical bone, such as that lateral to the anterior nasal spine or the floor of the sinus (Fig. 3).
The choice of whether to place the implant as a one-stage or two-stage procedure will be determined by many factors. Where aesthetics is of ultimate importance, implant placement is usually done as a two-stage procedure. This approach has the advantage, at the re-entry surgery, of allowing the surgeon to further manipulate the peri-implant soft tissues and create an ideal soft tissue profile for the future crown. For example, the additional keratinized tissues formed in
the ridge preservation procedure, described above, can be repositioned buccally to assist with the emulation of the appearance of the original root form without harvesting extra connective tissues from another donor site.
The regeneration of the interdental papillary tissues subsequent to the placement of prosthetic crowns is thought to be determined by the distance between the crest of interdental/ interimplant bone and the contact point of the implant-supported crown with the crown of the adjacent tooth (Tarnow et al., 1992). Tarnow et al. have demonstrated that a papilla will reform predictably if this distance is 5mm or less. If this distance between bone crest and contact point is 6mm, 56% of the papillary dimension can be expected, while at 7mm or more, less than 30% will reform.
As a result, it is not necessary to employ papilla retention techniques, such as the use of temporary ovoid pontics, in achieving optimal aesthetics in the replacement of a single tooth with a dental implant.
CASES REPORTS AND DISCUSSION
The first patient was a twenty-year old Caucasian female with a non-contributory medical history. The case was complicated by a high smile line (Fig. 4A). The maxillary left central incisor (tooth 2.1) had undergone repeated and unsuccessful endodontic procedures (Figs. 4B & 4C). Since the adjacent teeth were virginal, the ideal treatment plan for tooth replacement was a dental implant. The tooth was atraumatically extracted, and the site reconstructed (Fig. 4D) with a Collaplug base (35% volume) and Bio-Oss (65% volume) since both the buccal and palatal socket walls had been largely destroyed by the inflammatory process.
The n-PTFE barrier was used for the first 3 weeks of site healing and then removed non-surgically without local anaesthetic. This barrier is easily removed because it is non-porous and does not become attached to the overlying soft connective tissues.
After 6 months of healing, a 15mm x 3.75mm 3i Osseotite (Implant Innovations Inc., Palm Beach Gdns. FL 33410) implant was chosen to ensure that the apical aspect of the implant would be in contact with host bone that had formed following resorption of the CollaPlug. The implant was placed as a two-stage procedure because the aesthetic outcome was paramount (Fig. 4E).
Temporization was achieved with a removable, acrylic partial denture with no ovate pontic in the treated site, as this would have impinged on the healing tissues and had a negative impact on the desired tissue development. During second stage surgery, the additional keratinized tissues formed over the extraction socket by means of the ridge preservation procedure were repositioned buccally to emulate natural root form (Fig. 4F). Both papillae regenerated fully because the distance between the interproximal bone crest and the contact point of the implant-supported crown with the adjacent tooth, both mesially and distally, was 5mm. The entire procedure required a twelve-month time period.
The second patient was a fifty-five year old Caucasian woman with a previous history of moderate to advanced periodontitis. There was a deep, localized angular bony defect mesial of tooth 1.4 that involved the furcation and extended towards the mesially adjacent tooth 1.3 (Fig. 5A). Teeth 1.3 and 1.5 had 30-40% horizontal bone loss and tooth 1.5 had a mobility of M1.5.
A dental implant was chosen to replace tooth 1.4 because tooth 1.5 would have been a poor abutment for a tooth-supported fixed bridge, and tooth 1.3 was virginal. Tooth 1.4 was extracted and the ridge reconstructed with Collaplug (40% volume) and Bio-Oss (60% volume), and the site covered with an n-PTFE barrier membrane for 3 weeks. After 6 months of site healing, it was determined that there were approximately 9mm of bone height remaining below the sinus floor, and therefore an Endopore implant (4.1mm x 9mm, Innova Co. Toronto) was placed as a two-stage procedure.
Re-entry was undertaken after 6 months of healing, and the implant was restored with a crown fabricated to have a contact point with tooth 1.3 at a distance of 5mm from the interdental bone crest, to ensure the reformation of an aesthetically pleasing papilla. On the other hand, the contact point with tooth 1.5 was placed 7mm from the bone crest so that a full papilla would not form (Figs. 5B & C). In this latter site, aesthetics was of less importance and the space was created to ensure optimal opportunity for interproximal cleaning by the patient.
In this paper a technique is described for alveolar ridge preservation at the time of extraction of compromised teeth using a combined bone graft and barrier membrane. The benefits of this technique are:
1. Creation of an anatomically correct edentulous space in preparation for the subsequent placement of a dental implant or an aesthetically pleasing pontic;
2. Customization of socket healing through the use of Collaplug (to promote new host bone formation at the apical portion of the socket later to maximize dental implant stability and osseointegration) and Bio-Oss (to provide a suitable template coronally to support overlying mucoperiosteal tissues and alveolar anatomy);
3. Formation of significant amounts of new keratinized tissue over the grafted extraction socket once the n-PTFE barrier has been removed;
4. Minimization of the number of surgical procedures while achieving an optimal aesthetic result with prosthetic restorations;
5. Simplification of overall treatment for the single tooth implant in a highly compromised site.
Dr. Suzanne Caudry recieved her Ph.D. from the Dept. of Microbiology of La Trobe University in Melbourne, Australia, a D.D.S. from McGill University and a combined Dip. Perio./ MSc from the U. of T. Dr Caudry teaches at the Faculty of Dentistry, U. of T. and is in private practice specializing in Implant Dentistry.
Oral Health welcomes this original article.
Sincere thanks is extended to Dr. Douglas Deporter, Rodney Walker, Karen Thompson and Tracy Bright.
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