Introduction: In the present study, bone density from the new biomaterial composed by calcium phosphate and added silicon is compared with bovine hydroxyapatite by means of Hounsfield units in alveolar ridge preservation. Alveolar ridge preservation is a surgical technique proposed to reduce bone resorption caused by dental extraction, using a bone graft. This technique´s final goal is to facilitate implant insertion and rehabilitation.

Materials and methods: A study was carried out on 6 patients from the Faculty of Dentistry of the Complutense University of Madrid performing the technique of alveolar ridge preservation. Two groups were established, a test group in which the alveolar socket was filled with calcium phosphate and added silicon and a control group where the socket was filled with bovine hydroxyapatite. After 3 months, a cone-beam computed tomography was performed to evaluate the bone density achieved by both biomaterials.

Results: The average bone density achieved in the group treated with calcium phosphate and added silicon was 1100,40 ± 111,19 Hounsfield units whereas in the group treated with bovine hydroxyapatite the average bone density was 1029,46 ± 95,16 Hounsfield units.

Conclusions: Both biomaterials seem to present a similar behaviour in terms of densitometric results obtaining a density greater than 1000 Hounsfield units, having the calcium phosphate and added silicon the highest density.

The loss of alveolar bone can be triggered by different circumstances, such as trauma, an infectious process or as a consequence of periodontal disease. The most frequent cause of bone deficiency in the alveolar ridge is produced by the absence of mechanical function caused by the extraction or loss of a tooth¹ .

Since the alveolar process depends on the presence of teeth, its loss leads to the unleashing of significant structural changes that are manifested in a vertical and horizontal reduction of the bone crest^{2, 3}.

According to Seibert⁴ , alveolar ridge defects can be divided into three categories according to bone deficiency:

• Class 1: when bone deficiency predominates in the horizontal dimension.
• Class 2: when it predominates in the vertical dimension.
• Class 3: when it affects both vertical and horizontal dimensions.

Taking these into account, it has been observed that the horizontal bone component is the most affected after tooth loss, mainly affecting the vestibular cortex. Whereas, the crestal reduction in height is milder, and is also predominant in the vestibular cortex³ . Numerous studies have shown that most of the bone resorption, which occurs after tooth loss, occurs during the first 3 months of healing, and dimensional changes can be observed up to a year later² .

Schropp et al,⁵ revealed that the bone crest loses 50% of its alveolar width during the first 12 months after tooth extraction, which represents a crestal reduction of 5 to 7 mm. Because of this, the ideal implant placement may be compromised^{2, 6}.

Andrés-Veiga et al,⁷ observed that this amount of bone resorption can vary between one individual and another and even in the same individual at different times of life, due to the influence of a series of local and systemic factors. Post-extraction alveolar ridge preservation (PAP) is a surgical technique aimed at reducing the collapse of the alveolar ridge after tooth extraction with a biomaterial, to facilitate subsequent implant rehabilitation^8-10.

Different types of biomaterials have been investigated for bone grafts in recent years, both in preclinical models and in clinical studies. However, none as yet has managed to stop resorption of the alveolar ridge completely after tooth extraction. The different studies carried out show that clinical, radiological and histological results vary according to the type of biomaterial used. Among such materials examined are autologous bone, allografts, xenografts, alloplastics and bone morphogenetic proteins^{10, 11}.

Research lines, aimed at minimising or blocking bone resorption produced after tooth loss, have grown recently, due to the direct impact that this bone reduction has on the reliability of future dental implants^{12, 13}. Adequate bone volume leads to a better chance of obtaining optimal aesthetics, thus reducing the need for additional grafts¹².

A systematic review by Vignoletti et al,² concluded that the PAP technique manages to significantly reduce crestal bone resorption in both width and height. The differences observed between the bone resorption of the groups treated with biomaterial and control groups, which were not treated, was 1.47 mm in height and 1.83 mm in width.

Despite this known reduction in bone resorption, there is still not enough scientific evidence to determine which alveolar filling biomaterial is superior in this technique^{2, 8, 14}.

The aim of this study was to evaluate the bone density, measured in Hounsfield units (HU), achieved by a new biomaterial, composed of calcium phosphate with added silicon (CAPO-Si), and to compare it with bovine hydroxyapatite (HAB) in the PAP technique.