1. Introduction

Alveolar bone loss is a prevalent global oral health issue, affecting approximately 30% of individuals aged 60 and above worldwide, with higher prevalence rates in developing countries. Various factors including periodontitis, trauma, congenital malformations, and tumor resection can lead to alveolar bone resorption, causing persistent reduction in alveolar ridge width and height. This condition compromises adjacent tooth stability and hinders oral function recovery [1]. Implant restoration has become a common solution for reconstructing dental functionality and aesthetics, where clinical success is closely tied to peri-implant bone quantity. Ideally, intact alveolar ridges provide both initial mechanical stability and long-term osseointegration environments for implants. However, when bone volume is insufficient, implant surgery faces increased initial failure risks and struggles to maintain long-term functional and aesthetic outcomes. Studies indicate that 40%-60% of implant candidates require preoperative bone augmentation procedures to meet minimum requirements [2]. Insufficient bone volume not only reduces implant stability and increases failure rates but also limits osseointegration capacity, ultimately decreasing long-term retention rates.

Bone augmentation techniques constitute the cornerstone of orthodontic implantology for addressing bone deficiency, primarily involving autografts, bone substitutes, and GBR. Autografts utilize the patient's own bone tissue to fill defects, demonstrating excellent biocompatibility and osteogenic potential, and are particularly effective for complex or extensive bone loss. However, this method requires additional bone harvesting procedures, potentially increasing surgical trauma, donor site complications, and patient discomfort. Bone substitutes such as β-TCP, hydroxyapatite, and bioactive glass offer abundant availability and controlled degradation, making them suitable for small-to-medium defect repair. Their osteogenic efficiency and integration degree vary depending on material composition and pore structure, with clinical outcomes and long-term stability requiring further validation [3]. GBR employs absorbable or non-absorbable barrier membranes to create bone-forming spaces within soft tissues, offering simplicity, minimal invasiveness, and broad applicability. Nevertheless, membrane exposure, displacement, or mismatched degradation rates may compromise bone regeneration stability and infection risks. Each strategy has distinct advantages and limitations, necessitating customized selection based on specific defect characteristics, overall health status, and risk profiles [4]. This study investigates the mechanisms and clinical efficacy of three bone augmentation approaches: autografts, bone substitutes, and GBR, providing scientific evidence through meta-analysis to guide personalized bone regeneration protocols.

2. Autologous bone grafting technique

Autologous bone grafts are typically harvested from the ilium, chin, or mandibular ramus. The ilium provides abundant bone material suitable for extensive or multi-segmental defects, though it involves significant trauma and causes considerable patient discomfort. Chin bone harvesting offers less invasiveness with intraoral incisions, limited bone availability, and is ideal for localized horizontal or vertical defects, requiring careful attention to wound healing and nerve protection. The mandibular ramus, being dense and moderately sized, is appropriate for high-mechanical-strength repairs but demands avoidance of the inferior alveolar nerve-vascular complex. Surgeons must meticulously design incisions to minimize soft tissue sacrifice while preserving bone integrity and blood supply – straight incisions are commonly used for iliac bone, whereas intraoral approaches are preferred for chin and mandibular ramus cases to reduce scarring [5]. Bone preparation should maintain structural integrity, with hemostasis achieved through heat coagulation or hemostatic agents. Sutures should utilize tension-free absorbable sutures to promote healing and reduce complications.

Autologous bone grafts rely on three primary mechanisms for osteogenesis. Osteoblasts from the donor directly participate in new bone formation. Endogenous growth factors released by the graft, such as BMP and PDGF, induce the differentiation of host mesenchymal stem cells into the osteogenic lineage. Simultaneously, vascular endothelial cells in the recipient area invade to promote angiogenesis, providing nutrients and oxygen for newly formed bone. In the initial post-transplantation phase, blood vessel reconstruction is primarily mediated by vascular endothelial cells and inflammatory cells. Subsequently, osteoblasts deposit bone matrix and undergo remodeling, while osteoclasts collaborate with osteoblasts to ultimately form bone tissue with physiological structure [6]. Clinically, strategies combining PRF, BMP, or other factors/cell-based approaches can be employed to accelerate angiogenesis and bone formation.

Cone-beam CT (CBCT) provides precise three-dimensional evaluation of horizontal and vertical bone gain, confirming improved bone volume and implant stability. Nevertheless, both donor and recipient sites are prone to complications that may compromise outcomes. Donor sites can suffer from infection, nerve injury, and postoperative pain, while recipient sites may experience bone resorption, displacement, or infection caused by hematoma or foreign body reactions. These risks can be mitigated through prophylactic antibiotics, meticulous surgical planning, rigid fixation, careful soft-tissue management, systemic control of underlying conditions, and close radiographic monitoring, with early intervention essential to reduce failure rates [7]. Despite these challenges, autologous bone grafting remains a cornerstone in implant dentistry because of its superior osteogenic potential and reliability in complex defects. However, donor site morbidity, variable resorption, and surgical complexity necessitate careful patient selection and expertise. Emerging alternatives, including synthetic substitutes, GBR, and advanced approaches such as 3D printing and tissue engineering, hold promise for reducing morbidity and improving the predictability of bone augmentation.

3. Bone replacement materials

Bone substitutes are categorized into two main types: inorganic and organic/composite. Inorganic materials include β-tricalcium phosphate (β-TCP), hydroxyapatite, and bioactive glass. β-TCP features controlled degradation, making it ideal for scenarios requiring rapid bone replacement. Hydroxyapatite closely mimics natural bone composition with slow degradation, providing long-term support. Bioactive glass induces bone integration and is typically prepared through high-temperature sintering or chemical synthesis, suitable for small-to-medium bone defects [8]. Organic/composite materials like collagen-based carriers and polymer-ceramic composites offer distinct advantages: collagen mimics bone matrix properties while polymer-ceramic composites combine toughness with strength. These materials are commonly manufactured using freeze-drying or 3D printing techniques, making them ideal for complex bone defect repair.

The porosity and specific surface area of bone substitutes directly influence cell adhesion and proliferation. High porosity enhances cell migration and nutrient exchange, though it may reduce mechanical strength. The degradation rate affects local pH levels: β-TCP degrades rapidly, potentially creating a mildly acidic environment that must align with bone formation rates. In contrast, hydroxyapatite undergoes slow degradation and remains stable over time [9]. Bioactive glass releases calcium and phosphorus ions to stimulate osteoblast activity and promote bone integration. Materials should possess excellent biocompatibility to prevent inflammation or rejection reactions while ensuring effective fusion with host tissues.

The osteogenic capacity of bone substitutes depends on their ability to stimulate bone formation and support bone remodeling. When β-TCP and bioactive glass degrade, the released ions stimulate osteoblast differentiation and promote new bone formation. Hydroxyapatite provides a long-term scaffold that facilitates bone tissue remodeling. After material absorption, bone tissue undergoes remodeling through coordinated interactions between osteoblasts and osteoclasts, gradually replacing with autologous bone [10]. The degradation rate must be synchronized with bone formation: excessive degradation may lead to insufficient bone mass, while slow degradation can impede bone integration. Material selection should be optimized based on defect characteristics.

4. Guided Bone Regeneration (GBR)

4.1. Classification and properties of barrier membranes

GBR technology creates space for bone regeneration by isolating soft tissues through barrier membranes, with the type of membrane directly impacting therapeutic outcomes. Absorbable membranes include collagen membranes and polycaprolactone (PCP) membranes. Collagen membranes derived from animal tissues have a degradation period of 3-6 months, offering flexibility and adaptability for small bone defects but limited strength suitable for low-load areas. PCP membranes, with a longer degradation cycle (6-12 months), provide higher mechanical strength for long-term support cases but may cause mild inflammation during decomposition [11]. Non-absorbable membranes like polytetrafluoroethylene (PTFE) and high-density polyethylene (HDPE) demonstrate excellent stability. PTFE is widely used due to its biocompatibility and anti-infection properties, though requiring secondary surgical removal with precise techniques to avoid tissue damage. HDPE's rigidity makes it ideal for complex bone defects but increases surgical difficulty. Composite membranes enhance osteogenic efficiency and infection resistance through bioactive coatings (e.g., calcium-phosphate compounds) or antibacterial features (e.g., antibiotic-coated layers), particularly for high-risk infections or complex bone defects. However, their higher costs limit clinical adoption. Membrane selection should be determined by comprehensive evaluation of defect type, required degradation duration, and patient status.

4.2. Surgical procedure and soft tissue management

The GBR repair procedure requires precise design to ensure bone regeneration efficacy. Flap techniques are categorized as full-thickness or half-thickness. Full-thickness flaps provide adequate exposure of bone surfaces, facilitating surgical manipulation but causing greater soft tissue trauma that may prolong healing time. Half-thickness flaps involve less trauma and are suitable for patients with thinner soft tissues or those requiring reduced tissue removal, though meticulous tension control is essential to prevent soft tissue tears or compromised blood supply. Soft tissue tension management is critical – excessive tension may cause suture splitting, affecting the stability and coverage of the membrane. Barrier membrane fixation methods include titanium nails and absorbable sutures [12]. Titanium nails provide strong fixation suitable for extensive bone defects but may irritate soft tissues or induce local inflammation. Absorbable sutures combined with minimally invasive positioning techniques reduce trauma for small defects, though offering slightly weaker fixation strength. Bone graft selection directly impacts osteogenic outcomes: autografts demonstrate superior osseogenic capacity for complex defects but require additional bone harvesting. Bone substitutes like β-tricalcium phosphate or hydroxyapatite are readily available and easy to use for small-to-medium defects. Hybrid grafts combining autograft bioactivity with substitute convenience should be selected based on defect size and osteogenic requirements. During surgery, ensure tight adhesion between grafts and membranes to avoid voids that hinder bone regeneration.

4.3. Evaluation of bone augmentation outcomes

The effectiveness of GBR is assessed through pre-and post-operative CBCT evaluations, which measure three-dimensional bone mass and density changes while precisely quantifying horizontal and vertical bone increments to ensure compliance with implant bone requirements. CBCT imaging demonstrates the uniformity of bone defect repair and bone integration extent, providing critical evidence for subsequent restorations. Postoperative soft tissue thickness and coverage integrity are vital for healing outcomes, as insufficient coverage may lead to membrane exposure or infection. The quality of coverage must be confirmed through clinical examination and radiographic assessment [13]. The functional load time window serves as a key indicator for GBR evaluation, typically allowing implant loading 4-6 months after bone density stabilization, with specific timing determined by bone defect severity, filler type, and patient's healing capacity. Regular follow-up combined with imaging monitoring helps maintain long-term stability of bone increments, ensuring successful implant restoration.

4.4. Clinical complications

Common complications of GBR include membrane exposure, infection, and soft tissue retraction. Membrane exposure often results from excessive soft tissue tension, inadequate flap design, or postoperative mechanical stress. Early detection through local debridement and re-epithelialization can reduce failure risks. Severe cases may require secondary repair or membrane replacement [14]. Infection management should combine local irrigation (e.g., chlorhexidine) with systemic antibiotic therapy, as severe infections may lead to bone regeneration failure requiring prompt intervention. Soft tissue retraction affects both aesthetics and bone integration. Mucosal thickening can be addressed by autologous soft tissue grafts or collagen-based materials to increase thickness, while improved suturing techniques like horizontal mattress sutures may reduce retraction risk [15]. Postoperative close monitoring and patient compliance management (e.g., avoiding smoking and maintaining oral hygiene) are crucial for preventing complications.

5. Conclusion

The application of bone augmentation techniques in dental restoration has greatly improved treatment outcomes for patients with bone deficiency, offering reliable support for the restoration of oral function and aesthetics. Autologous bone grafts possess superior osteogenic potential and are suitable for complex or extensive defects, though they are associated with donor site morbidity and greater surgical trauma. Bone substitutes provide abundant sources and less invasive procedures that reduce patient burden, yet their osteogenic efficiency and long-term stability remain dependent on material properties. GBR involves relatively minor trauma and broad clinical applicability, but the risks of membrane exposure and infection persist. Emerging strategies such as novel biomaterials, 3D printing, and tissue engineering technologies have expanded the possibilities of bone regeneration, demonstrating advantages in precision and bioactivity, although high cost and limited accessibility constrain their widespread adoption. Future research should emphasize improving biocompatibility, reducing costs, and promoting clinical translation to achieve safer and more predictable dental restoration.