What is it?
Regeneration is defined by the Glossary of Periodontal Terms as:
A reproduction or reconstruction of a lost or injured part in such a way that the architecture and function of the lost or injured tissues are completely restored.
This means that the attachment of the tooth has been regenerated when new cementum with inserting collagen fibers has formed on the detached root surface. This also includes regrowth of the alveolar bone.
Guided tissue regeneration aims to achieve this objective by the principle of selective cell repopulation. In 1976, Melcher (Melcher 1976) in a review paper suggested that the cells which repopulate the root surface after periodontal surgery determine the nature of the attachment that will form. After flap surgery the root surface may be repopulated by four different types of cell: epithelial, gingival connective tissue, bone and periodontal ligament cells. Using a material that allows exclusion of gingival cells will create an environment prone to regeneration of the periodontal tissue. This view was confirmed in a study in monkeys in which both gingival connective tissue and gingival epithelium were prevented from contacting the root surface during healing by the use of a barrier membrane (Gottlow et al 1984).
The key role of periodontal ligament cells in periodontal regeneration was supported by the results of a number of studies in experimental animals evaluating the regenerative capacity of each of the periodontal tissues involved in periodontal wound healing (Karring et al 1980; Nyman et al 1980). These studies indicated that root resorption (instead of new attachment) occurred if a detached root surface was repopulated by cells derived from bone or gingival connective tissue.
Materials used for GTR
In order to achieve selective cell repopulation of the periodontal wound, a barrier is required to isolate the unwanted gingival cells. Two different types of barriers are available in the market: absorbable and non-absorbable.
Absorbable barriers offer the advantage of not requiring removal (re-entry surgery), are easy to manipulate and they are advocated to reduce wound dehiscence due the the collagen content that helps stabilizing the flap. Unfortunately, absorbable barriers are light and insubstantial and can not maintain volume if not supported.
The major advantage offered by non-absorbable barriers is the possibility of reinforcing the barrier itself with titanium. Therefore titanium-reinforced non-absorbable barriers are moldable but strong, and can maintain their shape even when applied to non-supportive type of defects. On the other side, non-absorbable barriers require a second surgical stage for their removal. This increases the risk of morbidity, as well as the cost for the clinician. Moreover, non-absorbable barrier tend to get exposed more frequently and may pose a risk for infection of the surgical site.
Recent systematic reviews (Reynolds 2003, Murphy 2003, Kinaia 2011) showed similar outcome in cases treated with either absorbable or non-absorbable barriers. The only scenario in which non-absorbable barriers provided better results was the treatment of furcation defects (Murphy 2003), however in the most recent systematic review (Kinaia 2011), when a combination therapy consisting in GTR + bone graft is used, the type of barrier does not seem to play a major role in gain of clinical attachment.
When to use GTR
Inspired by the contemporary literature I used this algorithm to decide when to use GTR combined with other regenerative technique. One option that is not contemplated in this decision-tree is the used of GTR in combination with Emdogain. Certain investigators found a significant improvement of clinical attachment gain by the use of GTR+EMD while other did not. At the moment I don’t think there is enough evidence to support the use of GTR+EMD (Venezia 2004).