- Once you’ve extracted a tooth, you usually have the option of restoring the space with an implant-supported prosthesis or a conventional prosthesis (e.g. a bridge). In either of these cases, is there a benefit in performing alveolar ridge preservation?
- Understanding the anatomy:
- Alveolar process = the ridge of maxillary or mandibular alveolar bone supporting the roots of erupted teeth and unerupted developing tooth buds. It is composed of alveolar bone proper and supporting bone. Alveolar bone proper is the thin lamella of cortical bone which lines the tooth sockets and embeds periodontal ligament. It is known as the cribriform plate anatomically, bundle bone histologically and lamina dura radiographically. The bundle bone is the thinnest anteriorly and on the buccal aspect of the alveolar process. The bundle bone is associated with the tooth and will therefore be lost when the tooth is extracted.
- Post-extraction ridge dimensional changes are a significant problem. It has been shown that following extraction, there will be moderate changes in the bone height (approx. 1 mm) and a 50% decrease in width of the alveolar ridge. Two-thirds of these changes will occur within the first 3 months (Schropp et al 2003). The average dimensional loss in width (approx. 3.87 mm) is greater than the loss in height (approx. 1.67 mm) (van der Weijden et al 2009).
- Minimising post-extraction dimensional changes:
a) Atraumatic extractions, immediate implant placement
- An atraumatic extraction technique is important – avoid excessive labial luxation, minimal flap/bone removal, dichotomise or trichotomise the tooth to avoid labial luxation, use periotomes, and consider piezoelectric surgery.
- Is immediate implant placement the solution for post extraction ridge dimensional loss? After extraction, bundle bone is lost so we are not able to prohibit (stop) some post-extraction dimensional loss (Araujo et al 2005). Immediate implant placement will also result in some significant bone reduction of the alveolar ridge because the bundle bone resorption is not limited by immediate placement into the fresh extraction socket. The geometry/design of the implant does not influence the results (Botticelli et al 2004, Sane et al 2010, Ferrus et al 2010). However, where the buccal wall is thick (>2 mm) or where the horizontal gap is large (>1 mm) the gap fill may be substantial and the vertical resorption may be less (Ferrus et al 2010). But the later is rare i.e. only 2.6% of cases for the anterior buccal wall and 5% of cases when considering the posterior buccal wall (Ferrus et al 2010).
- Recession of the mid-facial mucosa is also a risk with immediate placement (Chen & Buser 2014).
b) Alveolar ridge preservation
- A number of techniques have been proposed – grafting, guided tissue regeneration, soft tissue ‘”seal”, “sponges/plugs”, systemic medication and growth factors.
- This technique needs to be considered carefully as it is an extra procedure so extra time, money and surgical morbidity for our patients.
- Following tooth/root extraction, the effect of ridge preservation techniques on alveolar ridge dimensions in comparison to unassisted healing has shown less reduction in alveolar ridge width compared to unassisted socket healing (approx. 1.5 mm) and less reduction in alveolar ridge height (x3 better preservation of buccal bone wall in height). Histologically new bone formation is compatible following grafting, however most of the bone formation is in the apical 50% of the socket where different amount of grafting materials are in direct contact with newly formed bone (0-37%)(Horvath et al 2012).
- So ARP is effective in limiting post extraction ridge dimensional loss but 100% ridge preservation is unpredictable and alveolar ridge preservation is unable to prevent resorption (all systematic reviews and consensus papers). Membranes appear to obtain better results (Vignoletti et al 2012, Wang & Lang 2014) but overall there is no evidence to support one technique over the other (Vignoletti et al 2012, Darby et al 2009). There is no evidence regarding local or generic risk factors that might influence the predictability of alveolar ridge preservation.
- When considering which graft material to use there is no clear consensus. A membrane alone might promote new bone formation (Carmagnola et al 2003) but the addition of BioOss may act as a scaffold and serve to preserve the dimensions/profile of the ridge (Araujo & Lindhe 2009). Allografts or alloplasts have been shown to have better bone formation in the earlier healing period.
- Soft tissue seals (e.g. using free gingival graft from palate) have been suggested and some studies suggest this may help preserve the ridge profile (Araujo et al 2014 )/at least the soft tissue contour (Thalmair et al 2013). Alternatives to autogenous soft tissue grafts include: allogenic acellular dermal matrix (Alloderm), xenogeneic porcine collagen matrix (mucograft), xenogenic acellular dermis (mucoderm). Have neen suggested to work well in combination with BioOss (Schneider et al 2014).
- Alveolar ridge preservation for implant treatment or conventional prosthesis:
- When considering implant outcomes the results are similar for alveolar ridge preservation and unassisted socket healing when looking at implant placement feasibility, survival/success rates of the implant and marginal bone loss. However, there is usually a decreased need for GBR during implant placement following alveolar ridge preservation so it may decrease cost/complexity of treatment during implant placement (Mardas et al 2015).
- If alveolar ridge preservation is used, it is advised to wait at least 4-6 months prior to implant placement. Patients should be willing to wait/the treatment plan should allow for this.
- When using conventional prosthesis e.g. a bridge, there is a clear indication for alveolar ridge preservation especially in the aesthetic zone to maintain the external contour of the alveolar ridge and create a better emergence profile for the pontic of the bridge.
- Ridge preservation does not preclude the resorption of “bundle bone”.
- Ridge preservation is to some extent effective in: limiting post extraction ridge dimensional loss, maintaining soft and hard tissue contour of the ridge, supporting bone formation in the extraction socket, permitting implant placement and creating better emergence profiles for pontic sites.
These notes have been adapted from a webinar organised by the BSP. To find out about similar events and to access other resources, please visit – www.bsperio.org.uk.