Apicoectomy is a surgical procedure performed to remove infected periapical tissue and preserve the affected tooth. Bone graft materials are frequently used to facilitate healing and regenerate lost bone structure¹⁾. While autogenous bone grafts are considered the gold standard for guided bone regeneration (GBR), xenografts offer advantages, particularly in terms of lower resorption rates during remodeling^2,3). Among the various xenografts available, those derived from bovine sources have been widely used. Previous research has suggested that combining mineral trioxide aggregate (MTA) with bovine bone grafts and a collagen membrane in periapical surgery can aid in preserving teeth with poor prognoses and enhance bone healing⁴⁾. This approach has been reported to contribute to the regeneration of bone, periodontal ligament, and cementum following periapical surgery.

In recent years, a moldable bone graft containing type I collagen has been introduced to improve handling properties and has shown promising clinical outcomes^5,6). The incorporation of collagen into xenogenic bone grafts has demonstrated advantages, including enhanced ease of manipulation and improved volume stability⁷⁾. Porcine-derived bone grafts have been explored as an alternative due to their genetic similarities to human tissue. Research has increasingly focused on their potential as bone substitutes, with ongoing studies evaluating their efficacy^8-10). A key advantage of porcine-derived grafts is their ability to mitigate the risks associated with bovine spongiform encephalopathy (BSE), making them a safer option for clinical applications. One of the primary challenges in the clinical use of xenografts is the risk of disease transmission and immune rejection. Xenogenic tissues contain a significant number of α-Gal epitopes, which induce natural circulating antibodies in humans¹¹⁾. A decellularization protocol has been developed to remove most α-Gal epitopes from porcine cancellous bone¹²⁾. In a 2021 animal study, a decellularized and oxidized porcine xenograft was found to be biocompatible and at least equivalent to demineralized bone matrix (DBM) in treating bone defects¹³⁾. Several studies have reported favorable outcomes using porcine-derived bone grafts in various bone augmentation procedures. A recent in vivo study demonstrated that porcine cortical and cancellous bone containing 10-20% collagen yielded promising results in new bone formation¹⁴⁾. However, despite these findings, clinical studies on porcine-derived bone grafts remain limited. This study aimed to retrospectively evaluate the clinical and radiographic outcomes of a demineralized porcine-derived bone graft material combined with high-purity type I collagen in the form of a block-type xenograft. This study focused on its application in maxillary periapical lesions following apicoectomy to assess its effectiveness in bone regeneration.

This study was conducted following the ethical guidelines of the Declaration of Helsinki and was approved by the Institutional Review Board (IRB) of Seoul National University Bundang Hospital (IRB No. B-2409-926-105). A retrospective analysis was performed on patients who underwent apicoectomy with bone grafting using LegoGraft (Deproteinized porcine bone mineral with type I collagen, Purgo Biologics, Seongnam, Republic of Korea) at Seoul National University Bundang Hospital between October 2021 and March 2023. The inclusion criteria consisted of patients aged 18 years or older with a history of root canal treatment and a diagnosis of chronic periapical abscess with a sinus tract. The tooth had undergone apicoectomy with MTA retrograde filling, followed by bone grafting with LegoGraft. Additionally, eligible patients had periapical radiographs taken preoperatively (D0), immediately postoperatively (D1), at three months (D2), and at twelve months (D3). Patients were excluded if their medical records were incomplete or if they had received mixed bone graft materials.

1. Surgical procedure

Surgical procedures were performed by an expert doctor of the department of conservative dentistry under local anesthesia using 2% lidocaine with epinephrine (1:100,000). A semilunar incision was made, followed by the elevation of a full-thickness flap. The apical lesion was accessed using a 2 mm round bur with a low-speed straight handpiece under copious saline irrigation. A minimum 3 mm root-end resection was performed, and any radicular cysts or granulation tissue were carefully removed. The root-end cavity was prepared using ultrasonically powered Chirurgie/Periradicular Retrograde (CPR) Tips (Brasseler USA, Savannah, USA) under 4× magnification with dental loupes (ErgoLoupes, Admetec, Haifa, Israel). Hemostasis was achieved using electrocautery or hemostatic agents when necessary. The prepared root-end cavity was filled with ProRoot MTA® (Dentsply Sirona, York, USA). A 1.2 cc LegoGraft block was hydrated in saline for one minute and shaped appropriately before implantation (Fig. 1). The graft was then covered with Ossix Plus (collagen membrane, Purgo Biologics, Seongnam, Republic of Korea), and primary closure was achieved using 4-0 Vicryl sutures. Patients received antibiotics and analgesics for five days, and sutures were removed one week postoperatively.

Figure 1. Porcine-derived collagenous block-type xenograft is shaped to fit the defect site, hydrated, and placed into the defect.

2. Radiographic evaluation

Radiographic evaluation was performed using periapical radiographs obtained from INFINITT PACS 3.0 (INFINITT Healthcare Co., Ltd., Seoul, Korea). Radiographic images were captured using Orthoceph OC100 CR (Instrumentarium Imaging, Tuusula, Finland) and Heliodent DS (Sirona, Bensheim, Germany) machines. Bone density was assessed by an oral and maxillofacial surgeon who was not involved in the surgical procedures¹⁵⁾. The region of interest (ROI) was defined as a circular area approximately 10 mm² in size, centered on the radiolucent region. Normal bone density was assessed using an adjacent, unaffected area of alveolar bone as a reference. The mean grayscale value within this ROI was automatically computed using the INFINITT PACS software (Fig. 2). For statistical analysis, paired t-tests were used to compare differences between time points, while independent t-tests were used to assess differences based on gender and anatomical location (anterior vs. posterior teeth). All analyses were conducted using SPSS 25.0 for Windows (SPSS Inc., Chicago, IL, USA).

Figure 2. Radiographic measurement for gray scale value. (A: before the surgery; D0, B: immediately after the surgery; D1, C: three months post-operation; D2, D: 12 months post-operation; D3).

The study included fifteen patients, consisting of nine males and six females, with a mean age of 42.6±12.3 years (Table 1). Bone grafting was performed on eight anterior teeth and seven posterior teeth. During a mean follow-up period of 17.1±8.3 months, no complications such as infection, inflammation, pain, edema, erythema, wound dehiscence, or membrane exposure were observed. Radiographic assessments indicated a significant increase in bone density postoperatively. The mean grayscale values increased from 108.58±45.35 at baseline to 139.37±33.68 immediately after surgery (P<0.001). A slight decrease was observed at four months (137.36±43.58, P=0.025), with stabilization at twelve months (138.20±28.09, P=0.024). When compared to normal bone density, the grayscale values at baseline were 96.15±48.49% lower than the reference bone. Following treatment, bone density at D0 increased to 124.86%±43.75% above normal density. At D1, a slight decrease was observed (122.38%±41.92%), while at D2, the bone density remained stable at 120.56%±24.74% above normal values.

Table 1 . Demographic information and bone density

Male : Female	9 : 6
Anterior : Posterior	8 : 7
	Gray scale value	With comparison of normal density (%)	P-value
Before	108.58±43.35	96.15±48.49
D0	139.37±33.68	124.86±43.75	<0.001*
D1	137.36±43.58	122.38±41.92	0.025*
D2	138.20±28.09	120.56±24.74	0.024*

*Paired t-test compared with Before. D0: immediately after the surgery. D1: three months post-operation. D2: 12 months post-operation.

A gender-based comparison revealed significant differences in bone density at baseline (Table 2). There were no statistically significant differences between genders were observed at D0, D1, or D2 (P>0.05). Similarly, comparisons between anterior and posterior teeth revealed no significant differences in bone density at any time point (P>0.05).

Table 2 . Bone density change with comparison of normal density (%)

	Male (n=9)	Female (n=6)	P-value¶	Anterior (n=8)	Posterior (n=7)	P-value¶
D0	135.97±34.28	108.19±0.98	0.254	130.16±26.35	114.25±10.18	0.476
D1	126.54±21.28	116.13±15.44	0.618	118.73±12.28	129.68±32.28	0.570
D2	116.49±13.70	126.66±28.91	0.426	123.87±22.19	113.94±14.97	0.376

^¶Independent t-test. D0: immediately after the surgery. D1: three months post-operation. D2: 12 months post-operation.

This study suggests that porcine-derived collagenous block-type xenografts provide stable and predictable bone regeneration after apicoectomy. The findings indicate that LegoGraft effectively maintains bone density over time, showing a remodeling pattern similar to that of surrounding natural bone. No significant differences were observed between gender or tooth location postoperatively. These results highlight the potential of porcine-derived bone grafts as a reliable material for periapical bone regeneration.

The necessity of bone grafting in cystic defects remains a topic of debate. Some studies report that spontaneous bone healing can occur in cystic defects larger than 1∼2 cm^16,17), while others support the need for bone grafting in such cases¹⁸⁾. A 2022 systematic review suggested that bone grafting accelerates the healing process and enhances bone quality; however, variations in assessment methods have prevented a definitive conclusion on the benefits of bone grafting following cyst enucleation¹⁹⁾. Many studies evaluating cystic defects rely on two-dimensional imaging, such as panoramic radiographs. A 2015 randomized clinical trial using CBCT on 18 patients reported that 88.5% of natural bone regeneration occurred six months postoperatively, and healing rates were independent of cyst type²⁰⁾. In a 2022 three-dimensional study by Ku et al., jaw cyst enucleation exhibited similar bone regeneration regardless of preoperative cyst size, patient age, or affected jaw. The bone regeneration rate was only 33.5% in the first year, but the healing rate reached approximately 75% thereafter without complications¹⁹⁾. These findings suggest that bone grafting in cystic defects provides advantages in bone recovery. Additionally, filling the defect with a bone graft material offers the benefit of allowing clearer radiographic monitoring for cyst recurrence.

When considering the addition of collagen to bone substitutes, further research is needed to fully elucidate its specific effects. However, existing evidence suggests that collagen plays a crucial role in enhancing the osteoconductive properties of biomaterials while also facilitating material resorption²¹⁾. During the bone remodeling process, newly recruited osteoprogenitor cells are often located adjacent to osteoclasts that express collagen-integrin receptors, which are involved in collagen internalization and cell migration. This proximity indicates that collagen may contribute to osteogenesis by supporting cellular attachment and differentiation²²⁾. However, an excessive amount of collagen, while improving the handling properties of bone graft materials, may also interfere with the essential process of biomaterial colonization by blood supply, a critical step for successful bone regeneration. Therefore, optimizing the collagen content in bone substitutes is essential to balance its benefits in handling, stability, and regenerative potential¹⁴⁾.

Collagenated bone grafts demonstrate superior volumetric stability compared to conventional particulate grafts, enabling effective bone regeneration even without the need for an additional membrane. A 2023 study compared the effects of deproteinized bovine bone mineral (DBBM) and collagenated xenografts on sinus membrane integrity. After an eight-week healing period, seven cases of sinus membrane perforation occurred in the DBBM group, whereas the collagenated xenograft group exhibited only one minor perforation²³⁾. In a 2025 rabbit study, the addition of 10% collagen to deproteinized bovine bone mineral was shown to prevent membrane thinning and perforation two weeks postoperatively²⁴⁾. In the present study, a collagen membrane was applied in all cases. The biomechanical role of membranes has been proposed to stabilize and protect newly formed blood clots, which are essential for bone regeneration²⁵⁾. However, limited evidence exists supporting the direct biological role of membranes in bone regeneration induced by bone grafting²⁶⁾. One limitation of this study is its retrospective design and the absence of a control group. Future studies should assess the healing of cystic defects treated with membranes alone to establish a clearer understanding of the role of collagenated xenografts in bone regeneration without additional membrane coverage.

This study demonstrates that porcine-derived collagenous block-type xenografts provide stable bone regeneration after apicoectomy, with remodeling patterns similar to natural bone and no significant differences based on gender or tooth location. These findings support their reliability for periapical bone regeneration, though further research is needed to optimize clinical applications.