# Spontaneous Bone Regeneration after Enucleation of
## 4 Discussion  
Odontogenic cysts are one of the most frequent pathologies in maxillofacial surgery. The proliferation and/or degeneration of the odontogenic epithelium is believed to result in the development and volume increase of these cysts. The goal of surgical treatment of mandibular cysts is, of course, surgical enucleation, preserving some anatomical structures that may be in intimate contact with the cysts, such as the IAN. Various techniques have been described in order to achieve the final surgical goal of complete enucleation of the cyst. However, although the enucleation of odontogenic cysts has been the standard method of treatment, other commonly used techniques are marsupialization and decompression, which can be considered in the approach to very large cysts. Whichever is the final treatment choice, bone defects after enucleation are always generated, and surgeons must decide whether or not to use filler materials. [PERSON] et al. (2017), in a 2017 paper, confirmed that using bone grafts at the same time as surgical enucleation has a high failure rate, due also to factors that worsen this failure rate, such as the use of non-autogenous and autogenous mixed bone. It has recently been acknowledged that surgical enucleation of the cyst is followed by better healing without the placement of a bone graft or other filling materials. However, in terms of bone regeneration and time length, there is still no consensus. In  
Figure 3: CT scan evaluation of the bone regeneration of a complete case. (**A**): T0 volume; (**B**): T2 volume. fact, many studies conducted over the years have evaluated the quantity of regenerated bone by measuring the maximum diameters of the residual cavities after cyst ablation. [PERSON] et al. (2019) reported that complete bone healing occurred in all patients of their series between 12 and 24 months after surgery. However, some issues with the surgical sample can be assessed: the patients were not treated with the same surgical technique, and the residual cavity evaluation was performed on OPG, with bidimensional issues related to this imaging assessment, although patients are less exposed to radiation. OPG is a two-dimensional analysis method, so it is less accurate in determining the exact volumetric variations, as reported by [PERSON] et al. (2019). For this reason, volumetric studies on bone regeneration of cystic cavities were carried out in recent years, using CT scanning and measuring the three maximum diameters of the cavity. In this way, a geometrical approximated volume can be calculated ([PERSON] et al., 2019). Nonetheless, it is still an approximated volume, not a real volumetric measurement. Moreover, in such papers, it was not reported whether or when the bone restoration was completed. In this scientific context, we developed our study to assess how much bone is restored after cystic ablation and how soon, performing on the CT scan a slice-by-slice measurement, achieving a real volumetric analysis for the first time in the literature to the best of our knowledge. Analyzing the individual cases, the greatest residual volume at both 6 months and 12 months was found for the larger cysts, as expected. However, the results of our measurements, carried out on a homogeneous sample of patients, showed that after 6 months, independent of the initial volume of the cyst, around 90% of the cavity was filled with new generated bone. In addition, in all cases, we reached bone restoration of 99.72% at 12 months after surgery. The bone regeneration of our sample suggested that the healing of the cystic cavity does not follow a linear trend, but proceeds exponentially in the first 6 months, whereas the following 6 months consist of a slower filling of the residual cavity and bone remodeling processes (Figure 4). In all cases, the bone regeneration followed a caudo-cranial and centripetal path, as normally occurs for bone regeneration. For this reason, in cases with no or small alterations of the vestibular or, rarely, lingual cortex, the bone width was fully restored.