## 4 Discussion  
Guided bone regeneration (GBR) is a viable option for treating resorbed edentulous spaces since the 1990s [3; 4; 5; 6]. At the beginning the only material available for GBR was a membrane in PTFE that was later modified by inserting a core of titanium to reinforce it and maintain the space for regeneration underneath [13; 14]. The approach with PTFE and d-PTFE was and still is a viable option; nevertheless, it require excellent surgical skill, case evaluation and a good knowledge on how to handle complications. One of the weaknesses of membranes was the tendency for them to become exposed in the healing period, compromising the desired effects and often requiring more surgeries to fix the complication [16; 17].  
Titanium meshes and grids have surfaced in recent times, and the digital approach has favored the customization of such devices; however, this surgical approach is quite invasive and can only be used by experienced surgeons who can handle properly local anatomy and soft tissue. Even these devices are not error and complication free, and the literature reports rates of early exposure and complications [20; 21]. The complications found with non-resorbable membranes could have been solved with the introduction of resorbable membranes, but if they proved effective when dealing with horizontal bone regeneration, they would be almost unpredictable in cases where vertical augmentation was needed [2; 3]. Ten years ago a new membrane made of collagened porcine bone was introduced in a clinical and histological study representing a breakthrough. This membrane had all the characteristics requested by GBR protocol (stiffness, flexibility, adaptability) and was made of bone, slowly resorbed and giving way to regeneration, and either integrated in the area where applied or resorbed and replaced by native bone [28]. More publications on this biomaterial have followed since then and very few reported complications due to the nature of the membrane that, when exposed to the oral environment, tends to hydrolyze, giving way to the healing of the soft tissue and not severely compromising the final outcome or requiring additional surgery [7; 8; 9; 19; 27]. In 2021 a report of 65 immediate implants placed in 49 patients where the bone lamina was used in the multi-layer technique (MLT) reported 100% success with a follow-up of 5 or more years. In this paper, only four complications were recorded, one patient developed peri-implantitis, one had a little piece of lamina removed after 18 months, one developed a palatal cyst and one broke his temporary crown. Only one patient had a lamina-related complication, which did not hamper the final prognosis of the case [29]. In this publication we have discussed and presented an additional benefit of the bone lamina membrane: in the past, when performing GBR and GTR procedures with membranes, one of the surgical prerequisites was to place the barrier at a distance from the natural teeth. It was understood that if the biofilm penetrated from the gingival margin into the barrier, this would hamper the outcome of the regeneration  
Figure 21: Rx of follow-up completion of restoration (**left**) and at 3 years after load (**right**).  
contaminating the barrier. Nevertheless, with the bone lamina being made of bone, not only is it possible to put it close to the natural teeth, but it also affects them in terms of the gain of attachment and regeneration if they are periodontally compromised. We have called this new evidence the 'GTR effect of GBR' and the cases published are just some of the many observed throughout years of applications of this barrier.