1. IntroductionAlveolar Ridge Preservation (ARP) techniques are used to counteract the physiological bone ridge resorption that occurs after tooth extraction. The literature reports a possible, horizontal alveolar resorption of up to 50%, while vertical resorption also occurs but is less relevant [1,2]. Furthermore, the changes mostly occurred during the first year, especially in the first months of healing. In the past, some authors suggested that immediate implant placement after tooth extraction could prevent the resorption of the alveolar ridge. However, Botticelli et al. proved otherwise [3]. The authors observed that implant insertion failed to avoid alveolar ridge resorption during 4 months of healing. The results were similar to those described by Tan et al. for the spontaneous healing of post-extraction sockets [4].Internal alveolar preservation techniques involve the use of a biomaterial that can be protected in different ways: with collagen membranes, connective tissue harvesting and d-PTFE membranes [5,6,7]. A review of the literature did not reveal which technique was the best to adopt. In addition, all of these ARPs do not guarantee complete volume maintenance but only reduce resorption [8,9,10]. Although there has not been a clear consensus [11], in recent years it has been clear that soft tissues play a key role in the long-term success of dental implants [11,12,13]. Therefore, the clinician’s attention should not only be limited to hard tissues but also include peri-implant soft tissues. Recently, Bambini et al. correlated the apical-coronal position of an implant to the thickness of the soft tissues [14]. This protocol prevented the fixture’s exposure due to the formation of a new biological width during the healing process [15,16].In 2019, Nguyen et al. introduced a new ARP outside the alveolus, modifying the area of interest [17]. Periosteal Inhibition Technique (PI) aimed to inhibit the osteolytic activity on the outer surface of buccal bone. A d-PTFE membrane was placed between the vestibular periosteum and the cortical bone, and no bone grafts were inserted in the sockets. The authors hypothesized that the precursors of osteoclastic cells (9.5 µm in diameter) were unable to come into contact with the outer surface of buccal bone and differentiate due to the porosity of the membrane (0.2–0.3 µm), which acted as a barrier [18,19,20,21]. This prevented the osteoclastic activity of the deep periosteum, consequentially reducing the buccal bone resorption. The preliminary results showed a non-significant average loss of 0.4 ± 0.3 mm of the soft tissue and 0.2 ± 0.4 mm of the bony ridge width after 4 months. However, the main drawback of the PI was the second-stage surgery required for the membrane removal.Modified Periosteal Inhibition (MPI) overcomes the limit of the technique described by Nguyen et al. [17]. The MPI technique aims not only to preserve the vestibular bone by exploiting Periosteal Inhibition but also to increase its thickness by bonding a single or double layer of OsteoBiol® Lamina Soft (Tecnoss®, Giaveno, Italy) 0.5 mm thick. The use of the cortical bone lamina also allows the inclusion of extraction sockets with partial deficiencies in the cortical bone among the indications of the technique. The aim of the study was to describe for the first time the surgical protocol of MPI technique. The primary purpose was to analyze the dimensional changes of the alveolar ridge width over a healing period of 4 months through Cone Beam Computed Tomography (CBCT) comparisons. The secondary purpose was to evaluate the occurrence of early and late biological complications, such as swelling, suppuration, and pain. 3. DiscussionAll ARP techniques involving the filling of the extraction socket with biomaterials have shown results that were not always predictable. The volume shrinkage was often reduced but not completely eliminated [22]. Furthermore, the disadvantages deriving from the insertion of a biomaterial, such as the lengthening of the healing time and formation of vital bone, are much fewer than those resulting from spontaneous healing or from only using collagen [23,24]. As put forward by Hürzeler et al. [25], the only ARP capable of preserving the internal osteo-gingival architecture seems to be the Socket Shield Technique, thanks to the preservation of the vestibular part of the root and periodontal ligament [26,27,28]. Complete preservation at 10 years has been achieved with this procedure. The Modified Socket Shield technique without implant placement with a concomitant extraction socket reconstruction was proposed by Glocker et al. [29]. The disadvantages of the technique include a difficulty to perform it and therefore the dependence on an operator, the fact that it takes a long time to perform, and the fact that the residual root occupies part of the implant space. The PI technique shifted attention to the outside of the extraction socket, working against the osteolytic activity deriving from the deep periosteum [17]. The preliminary results showed an almost total preservation of both hard and soft tissue volumes, without the need to either maintain root fractions inside the socket or resort to a biomaterial. The advantages therefore include extreme ease and speed of execution and a return to normality in 4 months, a relatively short time, not forgetting the most important aspect, which is the formation of only viable bone within the extraction socket.

The PI technique’s limits include having to remove the d-PTFE membrane later and not being able to increase alveolar volumes but only preserve them. The MPI technique aims to overcome these limitations. Thanks to the use of soft cortical lamina and human fibrin glue, nothing is removed during implant placement. Comparing the preoperative and postoperative ridge width of the present study, the radiographic measurement showed an increase equal to 0.41 ± 0.21 mm (primary purpose), suggesting a good Periosteal Inhibition effect by the bone lamina. No biological complications occurred during the follow-up, and healing was uneventful (secondary purpose). The MPI technique could therefore be the first ARP technique to provide an extraction socket with an increased volume in only 4 months.

OsteoBiol® Lamina Soft (Tecnoss®, Giaveno, Italy) is a membrane made of collagenated porcine cortical bone [30]. Several studies have shown its osteoconductive properties for both horizontal and vertical bone augmentation procedures [31,32,33]. Fischer et al. [34] demonstrated that the cortical membrane, positioned on the outer surface of the buccal bone, was able to maintain the ridge volume of the socket. The histological analyses at 4 months showed the formation of new bone below the membrane and the absence of resorption of the buccal bone. In cases of injury or inflammation, a portion of monocytes can differentiate into preosteoclast. Through the vessels of the periosteum, these precursors migrate to the affected bone cortex. Mononuclear precursors only fuse to form osteoclasts after attaching to the bone surface [18,19,20,21]. Not only does the cortical lamina prevent this destructive process from affecting the bone cortex, but at the same time it allows the latter to increase or be recreated if partially damaged. Since the bone lamina is more resistant than the d-PTFE membrane, we can extend the indications for the technique to extraction sockets with partial deficits of the buccal bone, greatly increasing the range of cases that can be treated. Festa et al. [35] described the use of the cortical membrane in combination with a porcine-derived xenograft (OsteoBiol GenOs®, Tecnoss®, Giaveno, Italy) for ARP. After 6 months of healing, the authors observed a reduction of the ridge width from 9.8 ± 1.2 mm to 8.0 ± 1.1 mm in test sites (treated with the ARP technique). On the contrary, the control group (spontaneous healing) showed a horizontal reduction of the alveolar ridge from 9.9 ± 1.0 mm to 6.2 ± 1.3 mm. In both cases, the reductions were statistically significant (p35] positioned the membrane so as to have it cover the socket, while in MPI the membrane was placed between the buccal periosteum and the outer surface of the alveolar ridge. Furthermore, unlike Festa et al. [35], in MPI no bone substitutes were inserted in the sockets, leaving the blood clot to form the matrix for new bone formation.In the MPI surgical protocol, the extraction sockets were filled with resorbable collagen sponges. It could be assumed that the material could affect the healing process and, consequentially, the results. Collagen sponges act as a provisional extracellular matrix that promotes the early stages of socket healing [36]. However, they have not been effective in preventing alveolar ridge shrinkage after dental extraction [37]. Recently, Crespi et al. [38] compared the dimensional changes of alveolar sockets filled with collagen sponges and porcine cortico-cancellous bone (MP3, OsteoBiol®, Tecnoss, Coazze, Italy) in the molar and premolar areas. After 3 months, the width of the alveolar ridge decreased by 2.9 (0.9) mm and 3.9 (1.4) mm, respectively. The difference was statistically significant between the two groups (p39]. Most importantly, the use of a porcine xenograft alone within the socket did not prevent the horizontal contraction of the alveolar ridge during the healing period. The results of this study were in line with those reported by Barone et al. [39].The major limitation of this study is the absence of a control group. However, analyzing the recent data in the literature [2], it is possible to observe in the molar area an average horizontal resorption of the crest equals 3.61 mm (95% CI: 3.24–3.98) after dental extraction. These data are essentially in line with the systematic review of Tan et al. [4], according to which the horizontal resorption of the ridge was 3.79 ± 0.23 mm after 6 months of healing. Considering the data of the present study, MPI has shown promising results. Further clinical trials will be needed in the future to compare the effectiveness of MPI with both spontaneous socket healing and other ARP procedures.