**5. Discussion**

In this review, the number of articles included was limited due to the limited bibliography on the subject; in addition, most of the included studies had a low level of evidence and had small samples. There was a high level of heterogeneity concerning study design, applications of calcium sulfate, and parameters studied. Due to this lack of homogeneity

that complicated the interpretation and summary of the results, it was not possible to compare and analyze the data quantitatively.

Maintaining the volume of the bone crest is important if the placement of implants in the area is subsequently planned, which is why alveolar preservation procedures require graft materials with specific characteristics [5,6].

It is important to take into account the speed and rate of resorption of the graft material, as this influences its osteoconductive capacity. Osteoconduction requires that the bone graft substitute have a rate of resorption similar to the rate of new bone formation. If the rate of resorption is faster than the rate of bone growth, the new bone will not have a scaffold to grow on. Conversely, if the graft material resorbs too slowly, it can remain in the bone defect and block new bone ingrowth [35]. In the case of calcium sulfate, it can be concluded that its resorption rate is favorable for the creation of new bone and for the maintenance of bone volume. The studies included in the review observed a 16% [30,31] residual graft after 4 months. Mahesh et al. [36] quantified its presence between 4.3% and 11.5% after 6 months and other studies [37] stated that, 12 months after the placement of calcium sulfate, it is reabsorbed in 99% and is replaced in 85% by new bone. In this regard, the works carried out by Ricci et al. [38] and, among others, Kadhim et al. [39] are very interesting. They determined that CS acts as a bioactive material when placed in a bone environment. By examining the CS during early periods, with histology, BEI, and XRM, Ricci et al. [38] observed that the CS material did not simply dissolve. As it dissolved and receded, it left behind a consistent latticework of a hydroxyapatite-like calcium phosphate mineral that was stable: in the short term, acted as an osteoconductive trellis for new bone formation, became incorporated in the new bone, and was then remodeled as the bone matured. On the other hand, the main difference between the bioactive glass (BG) and Bond Apatite (biphasic calcium sulfate/hydroxyapatite, BCS/HA) is that the latter (after activation) is injected into the site and can be molded according to the needs of the clinician. It does not require membrane coverage during the augmentation procedure [38].

The alveolar preservation cases that we performed (Case No. 2, Case No. 3, and Case No. 4) using Bond Apatite® as bone regeneration material, obtained good results in terms of maintaining bone volume. It should be noted that, in the cases where the protocol was followed, and closure was not performed by the first intention, alveolitis and partial loss of part of the material were observed after a week (Case No. 2 and Case No. 4); no difficulty was presented for the subsequent insertion of the implants.

Bone grafts continue to be one of the most widely used therapeutic strategies for the correction of periodontal bone defects. Both Trombelli et al. [40] and Reynolds et al. [41] in their systematic reviews summarized that bone substitutes were significantly more effective than open flap debridement in improving attachment levels and reducing probing depth. Both Pandit et al. [28] and Mandlik et al. [29] agree that calcium sulfate is an effective material in the treatment of periodontal defects since it is biocompatible, bioabsorbable, osteoconductive, versatile, and easy to apply. The good results of this material encourage testing its use in peri-implant treatments as it would provide a quick, comfortable, and economical solution for the follow-up of peri-implantitis. Guarnini et al. [42] propose a treatment combining the surface treatment of the implant with powdered abrasives and the use of calcium sulfate as grafting material, obtaining good results.

Laino et al. [33] studied the use of calcium sulfate as a graft in sinus lifts with a lateral window, obtaining good results, including a gain in bone height of more than 8mm, and these results coincide with those of other studies, such as that of Guarnieri et al. [42] who obtained a mean increase in bone height of 8 mm after 6 months and 2 years or that of Kher et al. [43], who reported a slightly greater gain of 10.31 mm. In our series of cases at 4 months, a bone gain of 6 mm and 9 mm was obtained depending on the area in the first case (Case No. 5) and 5.6 mm in the second case (Case No. 6). In the second case, the loss of more than 50% of bone height achieved was surprising when comparing the day of surgery with the follow-up after 4 months.

It is important to consider the size of the defect since it has been established that the width at the base of the defect facilitates space provision and influences bone repair through GBR [44]. Evidently, in tiny faults, the demand for augmentation and consequently the projected gain is slightly smaller than in bigger defects [45]. Large defect augmentation appears to be more difficult and technique-dependent.

Other factors that should be taken into consideration are the location of the defect, since the anterior and posterior mandible and maxilla segments have differing bone properties [46], and the loading timing, since according to the literature, GBR around immediate dental implant placement can improve hard tissue response during the healing period [47].

#### **6. Conclusions**

Calcium sulfate as a graft material in oral surgery has proven to be an effective, predictable, practical, economical, and easy-to-handle material in different areas of implant surgery.

Currently, the available literature on the use of calcium sulfate as a graft material in implant surgery is scarce, and what is available provides low-quality evidence. That is why more research studies on the subject are necessary to allow more comparisons and meaningful conclusions.

After using Bond Apatite® in our case series, we can conclude that it is a useful and easy-to-handle material in implantology practice, but more controlled studies should be carried out in this regard to assess its long-term efficacy, especially in horizontal and/or vertical regeneration.

**Author Contributions:** Conceptualization, J.L.-L. and A.M.-R.; methodology, A.T.-M.; software, B.G.-N.; validation, J.L.-L., A.T.-M. and B.G.-N.; formal analysis, A.A; investigation, A.A.; resources, R.Z.-L.G.; data curation, R.Z.-L.G.; writing—original draft preparation, A.A.; writing—review and editing, A.T.-M.; visualization, J.L.-L.; supervision, J.L.-L.; project administration, A.M.-R.; funding acquisition, R.Z.-L.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** There was no additional funding for this study.

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki, the approval by the Institutional Review Board was not required since the data are properly anonymized and informed consent was obtained at the time of original data collection.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** August Vidal Bel of the Pathological Anatomy Service of the Bellvitge University Hospital (HUB).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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