**1. Introduction**

The use of dental implants has become a common treatment modality and an important component of modern dentistry [1]. In many clinical situations, the edentulous areas to be rehabilitated do not offer adequate bone volume for implant placement; this may be due to different causes, such as the presence of anatomical structures that limit it (maxillary sinuses, presence of nerves or vessels, etc.) due to early bone atrophy and the traumatic extraction of a tooth or periodontal disease [2,3]. Tooth extraction is associated with the remodeling of the alveolar process and results in changes, both structural and dimensional, with horizontal losses of up to 29%–63% and vertical losses of 11%–22% at 6 months after tooth extraction [4,5].

For such defects, guided bone regeneration procedures before or in combination with implant placement are necessary [6]. These procedures are based on the use of different types of graft materials and membranes. The bone substitute must be osteoconductive, to act as a scaffold maintaining three-dimensional support during bone healing, and also osteoinductive, stimulating bone formation; the membranes act as a barrier and seal the area to be regenerated to prevent the ingrowth of soft tissue [7,8].

**Citation:** Torrejon-Moya, A.; Apalimova, A.; González-Navarro, B.; Zaera-Le Gal, R.; Marí-Roig, A.; López-López, J. Calcium Sulfate in Implantology (Biphasic Calcium Sul-Fate/Hydroxyapatite, BCS/HA, Bond Apatite®): Review of the Literature and Case Reports. *Coatings* **2022**, *12*, 1350. https://doi.org/ 10.3390/coatings12091350

Academic Editor: Jun-Beom Park

Received: 14 August 2022 Accepted: 12 September 2022 Published: 16 September 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Historically, the most widely used grafting material was autologous bone, both extraoral and intraoral [9,10]; however, obtaining autogenous bone has several negative aspects, such as increased morbidity for the patient, limited supply, and increased duration of the intervention [11,12].

We currently have different types of bone graft materials for dental applications. Depending on the origin, they are classified as autografts, allografts, xenografts, or alloplastic grafts and can be found in the form of granules, putties, gels, and pastes, or blocks [13].

One of these alloplastic grafts is calcium sulfate, which is a common bone substitute and with a history of clinical use spanning more than 100 years, the first report of its use as a bone graft material was by the German physician Dreesman in 1892 when it was used as a treatment to seal bone defects in the long bones of eight patients with tuberculosis, according to Pelteier et al., in their work from 1957 [14]. This material is highly biocompatible and osteoconductive, undergoing practically complete resorption in vivo, and can be used as a vehicle to administer antibiotics, pharmacological agents, and growth factors [14,15].

Therefore, calcium sulfate, which is a bioactive material that produces the release of abundant calcium ions, is used as a synthetic graft material in orthopedics, plastic surgery, oncological surgery, and dentistry, and it has been used in a variety of clinical applications, such as the repair of periodontal defects, the treatment of osteomyelitis, and maxillary sinus augmentation, and as a complement to the placement of dental implants [16–19].

However, despite its many indications, it has some deficiencies that have prevented its daily use in dentistry, highlighting its rapid and complete resorption and hardening difficulties in the presence of saliva and bleeding. In 2010, Dr. Amos Yahav presented Bond Apatite® (Augma Biomaterials Ltd., Caesara Industrial Park, Israel & Microdent, Santa Eulàlia de Ronçana, Barcelona, Spain), a biphasic calcium sulfate that has proven to be more stable and with better properties than classic calcium sulfate [20,21]. It is a bone graft material composed of 2/3 biphasic calcium sulfate and 1/3 synthetic hydroxyapatite of different granulometry. Being the only one available, it is made of calcium sulfate and having the addition of hydroxyapatite. Calcium sulfate is reabsorbed and it is the hydroxyapatite particles that maintain volume during the process of new bone formation [22–24].

According to the study carried out by Yahav et al. [24], the addition of HA prolongs the resorption time and remains within the practical timeframe for dental clinical applications; most of the graft material is converted into young bone within 3 to 6 months, and the remainder is resorbed shortly thereafter.

Recent studies [19,20] have demonstrated successful results in guided bone regeneration with the use of calcium sulfate, and in addition, based on histological analysis, the percentage of graft remaining was relatively low, with no evidence of inflammatory response or graft encapsulation.

In this preparation, there are several considerations of interest. In the first place, thanks to the Biphasic Calcium Sulfate formulation (hemihydrated/dihydrated), the setting process can be reduced from about 20 min to 3, facilitating clinical management. In addition, the synthetic hydroxyapatite particles decrease the rate of graft resorption, maintaining volume; the smaller ones (90 microns) are reabsorbed after 3–4 months and the larger ones (1 mm), which represent 10% of the total hydroxyapatite, are reabsorbed after 8 months. Finally, the high porosity of the product, greater than 46%, favors the infiltration of growth factors, osteoblasts, and angiogenesis [15,25,26].

Whereas with conventional graft materials there is integration with the graft particles resulting in 20%–25% vital bone formation, with Bond Apatite®, there is no integration between the newly formed bone, and the material is completely resorbed. Instead, new vital bone is formed at the end of the regeneration process.

Biphasic calcium sulfate serves as a cement, and its rigid structure after a quick setting prevents epithelial–conjunctive cell infiltration into the material, acting as a barrier membrane. However, connective cells can multiply on the material's surface, encouraging the rapid repair of the overlying soft tissue [24].

Bond Apatite® is presented as a powder in a double barrel syringe and a sodium chloride solution. With the help of a piston, the solution is poured over the powder, obtaining a mixture that can be easily deposited in the bone deficit, since the resulting product is adhesive. Subsequently, pressure must be exerted with a dry sterile gauze for a few seconds, thus eliminating excess liquid and favoring the setting of the product. In addition, the manufacturer recommends closing the flap under tension and it is not necessary to cover the graft with any type of membrane, since when it hardens it acts as a barrier preventing the penetration of epithelial–connective cells [25,26].

This study aims to review the existing literature on calcium sulfate in oral surgery and expose various clinical cases using Bond Apatite® as a bone graft material in different situations. Therefore, the following PICO (Patient, Intervention, Comparison, Outcome) question was: Does the use of calcium sulfate as a material in guided bone regeneration in dentistry have better results compared to other bone graft materials?
