Biology and innovation. Keys to success in fixed prosthesis
Maintaining the alveolar ridge is of great importance to obtain an aesthetic result for fixed prosthesis on teeth and for implants. Unfortunately, after extracting a tooth there will be significant bone remodeling that can result in an unaesthetic vestibular concavity (Petrovska 1967, Schropp 2003). Most of the dimensional changes in the ridge occur during the first 3 months of healing, but they can continue up to 12 months post-extraction (Schropp 2003).
The sequence of bone healing and biological events following tooth extraction are well documented (Araújo 2005). The loss in the vertical dimension is associated with the thickness of the vestibular table and the amount of remaining bone. Commonly, the apposition of bone at the interior of the alveolus and the reabsorption of the alveolar process do not follow a constant pattern, which can result in irregular or acute defects. To avoid this and other complications, several modalities have been described for the preservation of the alveolar ridge at the time of an exodontia. Whether using a bone graft, or sealing the alveolus through a barrier material, or a combination of both, this treatment is an effective procedure to prevent alveolus collapse and atrophy of the maxillary or mandibular ridge (Avila-Ortiz et al. 2019, De Risi et al. 2013).
The current scientific evidence does not favor an alveolar preservation method (Avila-Ortiz et al. 2019). Filling of the alveolus with a grafting material is indicated in situations were immediate or early implant placement is not possible due to patient- or site-specific reasons and helps to maintain alveolar ridge dimensions and avoid bone augmentation at the time of implant placement. The additional use of a barrier membrane is particularly indicated in case of a thin or deficient socket wall. Closure of the alveolus either with a membrane, an autologous or exogenous soft tissue transplant helps to protect the clot and grafted material against micromovement, air entrapment, compression or inadequate irrigation is indicated. The flap closure may be primary or secondary (Tonetti et al. 2019).
The choice of biomaterial for the selected modality will depend not only on the size of the defect and the need to maintain the space, but also on the rehabilitation protocol, the desired healing time, and the characteristics of the case. For example, if a xenograft material is used for the filling of the alveolus, such as cerabone®, it favors the long-term volume stability of the grafted area thanks to its biomechanical characteristics that are superior to other xenografts, but will need around 6 months before placing an implant. By using an allograft such as maxgraft®, the waiting time can be shortened since this biomaterial is quickly incorporated and continuously replaced by the patient’s own vital bone. Therefore, with maxgraft®, an implant can be placed in about 3-4 months.
The type of barrier will depend on the closure wanted. Although there is no consensus on the technique, a closure by first intention will shift the mucogingival margin which can cause aesthetic and soft tissue problems. By using a non-absorbable PTFE membrane such as permamem®, there is no need to close by first intention. Compared to other PTFE membranes, permamem® not only favors soft tissue stability but it´s remarkably engineered material allows extreme low plaque accumulation, avoiding consecutive tissue inflammation and halitosis. Another option is the use of a collagen sponge such as collafleece®, which favors the vascularization of the coronal area of the alveolus and will be reabsorbed between 2 and 4 weeks. The sponge will protect the graft and there will be re-epithelialization of the coronal opening of the alveolus in approximately 2 weeks. Finally, if it is needed to change the patient´s gingival phenotype and increase the soft tissue volume, favoring the prognosis of implant rehabilitation, mucoderm® can be used. mucoderm® is the acellular dermal matrix alternative to connective tissue that will save time and morbidity in patients.
Recently, a new modality in alveolar ridge preservation favoring the biological bases of bone healing has been described (Pramstraller et al. 2020). To discuss this technique, we talked to Prof. Leonardo Trombelli, director of research in periodontology at the University of Ferrara.
In the last decade, a multitude of techniques and materials for socket preservation have been introduced and published. In your opinion why haven’t we found a consensus about the best technique for ridge preservation?
Although a recent meta-analysis showed a significantly reduction in horizontal ridge dimension when a combination of a graft material (bovine bone particulate) plus socket sealing by a collagen membrane/sponge was used, the available data did not allow ranking the efficacy of different alveolar ridge preservation (ARP) approaches. This may at least in part be due to a wide heterogeneity of proposed techniques and devices used including flap management at suturing, chemical-physical characteristics of graft material, and additional socket sealing.
What are the short comings of the current commonly performed ARP approaches?
Although ARP procedures based on socket grafting can prevent up to a 30% of volume reduction in the coronal third, a limited effect was observed in the remaining middle-apical thirds. Moreover, grafting of the alveolus often results in the persistence of residual graft particles embedded into the newly formed bone with a delay in the rate of bone deposition and mineralization.
Recently you published a case report about a novel ARP modality. What is BARP? And what distinguishes this technique from other established ARP approaches?
Based on the previous considerations, we recently proposed a novel, simplified technique, namely the Biologically oriented Alveolar Ridge Preservation (BARP), that restricts socket grafting to the coronal portion of the socket (Fig. 1). Briefly, BARP is based on three layers of materials placed in the extraction socket: First a deep collagen layer filling the socket up to ≈4 to 5 mm from the most coronal extensions of the buccal and lingual crest to create a support for the coronal graft; Second a graft layer, placed on top of the apical collagen layer to fill the coronal part of the socket and third a superficial collagen layer, used to obtain socket sealing.
Fig. 1 modified from “A Simplified Procedure for Biologically-oriented Alveolar Ridge Preservation: Clinical and Histological Findings from a Case Report”. Pramstraller M, Farina R, Simonelli A, Götz W, Trombelli L., Clinical Advance in Periodontics. 2020.
Which are the main advantages of this technique (BARP)?
The clinical and histological observations derived from the published case and interim results from ongoing studies indicated three major advantages:
First, the deep collagen layer effectively supports the clot during the bone healing process. In the apical and central parts of the socket, abundant trabeculae of mature lamellar bone were evident, with minor signs of bone remodeling and minimal inflammation. Moreover, the deep collagen layer was able to maintain the graft particles confined to the coronal portion of the socket throughout the tissue maturation phase; Second the graft layer in the most coronal part of the socket limited the reduction in vertical and horizontal ridge dimensions. The magnitude of the effect was consistent with other studies where the use of the graft biomaterial was performed on the entire apico-coronal extension of the socket. Third, the superficial layer of collagen sponge used to stabilize clot and graft at socket entrance allowed a successful re-epithelialization of the area left intentionally exposed. This led to an unaltered apico-coronal dimension of the keratinized peri-implant mucosa.
What is the rationale behind the biomaterial choice for this technique?
The rationale of BARP is based on the optimization of the use of biomaterials while limiting the potential drawbacks from their application. In this respect, the selection of collafleece and cerabone has shown to be promising to ensure both stability of alveolar ridge dimensions and ideal conditions for bone healing process. We are currently validating our results in a prospective observational study and a randomized controlled trial.