At the EAO congress 2010 in Glasgow Prof Dr. Daniel Buser, Switzerland, and Dr Michael K McGuire, USA, talked about the treatment of soft and hard tissue defects in the aesthetic region. Based on scientific evidence and their huge experience from daily practice the two experts presented state-of-the-art treatment concepts and new approaches.
Prof. Dr. Daniel Buser, Switzerland: Long-term Stability of Contour Augmentation with GBR in Aesthetic Implant Dentistry
Current dental practice includes the routine application of implants following a rapid global growth rate of 15–20% of this therapy each year, although the recent economic climate has reduced this rate somewhat. Professor Buser’s department treats 500 patients with approximately 800 implants each year, with most referred from colleagues in private practice. Approximately 40% of implants are placed in sites with aesthetic priority.1 In these sites, the primary objective of implant therapy is a successful aesthetic outcome, characterised by a harmonious gingival line, intact papillae, convex buccal contour and a harmonious volume and shape of the crown. Additional objectives for implants are high predictability of success and a low risk of complications.
Most aesthetic failures are related to the expertise of the clinician. There may be misjudgement of implant size and number, malposition of the implant, a too aggressive approach that exceeds tissue healing capacity and insufficient thick facial bone wall to support aesthetic soft tissue. Since 2003 the ITI has recommended the SAC Classification to categorize implant treatment procedures into three levels of difficulty: straightforward, advanced, and complex.2
The benchmarks for successful implantation were defined in two recent studies.1These studies demonstrated a low early failure rate of less than 1% and a high success rate over a 10-year period of greater than 98% for non smokers. An ongoing 10-year study of 350 partially edentulous patients with 500–600 implants treated at the authors institute, will be completed in December 2010.4 Thus far, there are only 4 late implant failures and another 5 patients developed peri-implant infection with bone loss. A total of 15% of patients had a peri-implant mucositis without visible evidence of bone loss. Projecting the data to the end of the study period would yield implant success rates of greater than 95% with a low incidence of peri-implantitis (<3% with bone loss) over a 10-year period. The determining factors for successful outcome in post-extraction implant placement are shown in Table 1.
A facial bone wall of at least 2 mm is desirable to ensure sufficient vascularity of the buccal bone and to support facial soft tissue which negates gingival recession.5 The bundle bone is a tooth related bone structure that delineates the alveolar socket with a thickness of approximately 0.5 mm. Following extraction, this bone structure resorbs irrespective of therapy and is critical for the facial aspect because 2–3 mm of the most coronal bone wall is made of bundle bone.6 Braut et al., demonstrated with cone beam computed tomography that this facial bone wall for teeth in the anterior maxilla was rarely greater than 1 mm, only in approximately 10% of teeth.7 Less bone was present in central incisors (4–8%) and most in the first premolars (greater than 25%).
Pre-surgical evaluation is important for the successful outcome of implant therapy.12 As more than 50% of all implants are placed at sites with horizontal and/or vertical bone deficiencies, a detailed 3D radiographic examination is recommended for the majority of cases.10 Correct 3D positioning of implants is important for a successful outcome. Implants should not be too close to adjacent teeth and not too far facially. In meso-distal direction, the minimal distance to adjacent roots should be greater than 1 mm. For corono-apical positioning the apical to mid facial margin distance should exceed 2 mm for tissue level implants and 3 mm for bone level implants. For oro-facial positioning, implants should be placed 1.0–1.5mm more to the palatal aspect inside the alveolar housing; this allows increased thickness of the facial bone wall for soft tissue support.
Contour augmentation using the GBR technique involves the use of autogenous bone chips to cover exposed implant surfaces that allows more rapid bone formation. A secondary layer of bone substitute material (e.g. Geistlich Bio-Oss®) with a low substitution rate is used over the bone. The area is then covered with a native bioabsorbable membrane (Geistlich Bio-Gide®). Autografts are superior to other methods in accelerating new bone formation, said Professor Buser because they contain non collagenous protein and growth factors in the bone matrix.
There are several basic principles of implant surgery. The implant must be placed in the correct prosthetic position and allowed to achieve primary stability. The implant must be completely imbedded in healthy bone; the facial and oral bone walls should be at least 1 mm in thickness and greater than 2 mm in aesthetic sites, GBR for local bone augmentation is necessary for cases with local bone deficiency. After successful implantation, soft tissue healing is complete at 4–8 weeks and bone healing complete at 6 months or longer.13 Early implant placement is one treatment option for implant therapy following single-tooth extraction in the anterior maxilla. The surgical technique is characterized by tooth extraction without flap elevation, a 4- to 8-week soft tissue healing period, and then implant placement in a correct three-dimensional position. Simultaneous contour augmentation on the facial aspect with guided bone regeneration using a bioabsorbable collagen membrane is combined with autogenous bone chips and a low-substitution bone filler, followed by tension-free primary wound closure.11This technique allows an intact mucosa, an increased width of keratinised mucosa by 3–5 mm and clearance of infection or fistulae. The healing period following contour augmentation mostly depends in the size of the peri-implant defect.
Buser et al. performed a prospective case series study of 20 patients assessing early implant placement with guided bone regeneration following single tooth extraction.14 After a 12-month follow up period, no complications were observed during the healing period and all implants were restored. All of the 20 implants fulfilled strict success criteria and only one case showed bone loss of greater than 0.5 mm and a minor gingival recession of less than 1 mm. These pleasing results were confirmed by the three year follow examinations,15 characterised by high pink aesthetic scores, optimal height of the crown and satisfactory radiographic longitudinal peri-implant bone loss measurements. A similar study of 45 patients followed for 2–4 years showed no evidence of peri-implant infection or obvious gingival recession and the peri-implant bone crest levels were stable.16 A longer follow up study of 5–8 years in 39 patients is in progress and an interim analysis showed healthy implants in all patients and radiographs revealed a slight increase in bone loss.17 Additionally, a radiographic follow up is on-going and results so far demonstrate a mean thickness of facial bone wall at the crest level measuring 2.17 mm and two implants revealed no facial wall in the crestal area.
In summary, we now have a better understanding of ridge alterations following tooth extraction. Resorption of bundle bone is a natural phenomenon that cannot be arrested by surgical means; therefore a local contour augmentation is necessary in the majority of cases. Re-building of facial bone is important for soft tissue support and a pleasing aesthetic outcome. Contour augmentation is performed with the GBR technique using a resorbable, non-crosslinked collagen membrane (Geistlich Bio-Gide®) supported by bone fillers. Additionally a deproteinized bone mineral (Geistlich Bio-Oss®) is used for contour augmentation for long term stability. Timing for post extraction placement is crucial as immediate placement is associated with a significant risk of recession of the facial mucosa. Therefore this approach should only be performed in low risk patients and by experienced clinicians. Early implant placement should occur after 4–8 weeks of soft tissue healing and combined with a contour augmentation using GBR. After 6–8 weeks of healing a re-opening procedure allows the restorative phase with a provisional crown to occur.