Stability of bioresorbable plates following reduction of mandibular body fracture: Three-dimensional analysis

Biomechanical Evaluation of Hydroxyapatite/poly-l-lactide Fixation in Mandibular Body Reconstruction with Fibula Free Flap: A Finite Element Analysis Incorporating Material Properties and Masticatory Function Evaluation

In reconstructive surgery following partial mandibulectomy, the biomechanical integrity of the fibula free flap applied to the remaining mandibular region directly influences the prognosis of the surgery. The purpose of this study is to evaluate the biomechanical integrity of two fixation materials [titanium (Ti) and hydroxyapatite/poly-L-lactide (HA-PLLA)]. In this study, we simulated the mechanical properties of miniplate and screw fixations in two different systems by finite element analysis. A three-dimensional mandibular model was constructed and a fibula free flap and reconstruction surface were designed. The anterior and posterior end of the free flap was positioned with two miniplates and two additional miniplates were applied to the angled area of the fibula. The masticatory loading was applied considering seven principal muscles. The peak von Mises stress (PVMS) distribution, size of fixation deformation, principal stresses on bones, and gap opening size were measured to evaluate the material properties of the fixation. In the evaluation of properties, superior results were observed with both fixation methods immediately after surgery. However, after the formation of callus between bone segments at 2 months, the performance of Ti fixation decreased over time and the differences between the two fixations became minimal by 6 months after surgery. The result of the study implies the positive clinical potential of the HA-PLLA fixation system applied in fibula free flap reconstruction.

The Use of Lactide Polymers in Bone Tissue Regeneration in Dentistry-A Systematic Review

(1) Background: Different compositions of biodegradable materials are being investigated to successfully replace non-resorbable ones in bone tissue regeneration in dental surgery. The systematic review tried to address the question, "Can biodegradable polymers act as a replacement for conventional materials in dental surgery procedures?" (2) Methods: An electronic search of the PubMed and Scopus databases was conducted in October 2022. The following keywords were used: (lactide polymers) and (hydroxyapatite or fluorapatite) and (dentistry) and (regeneration). Initially, 59 studies were found. Forty-one studies met the inclusion criteria and were included in the review. (3) Results: These usually improved the properties and induced osteogenesis, tissue mineralisation and bone regeneration by inducing osteoblast proliferation. Five studies showed higher induction of osteogenesis in the case of biomaterials, UV-HAp/PLLA, ALBO-OS, bioresorbable raw particulate hydroxyapatite/poly-L-lactide and PLGA/Hap, compared to conventional materials such as titanium. Four studies confirmed improvement in tissue mineralisation with the usage of biomaterials: hydroxyapatite/polylactic acid (HA/PLA) loaded with dog's dental pulp stem cells (DPSCs), Coll/HAp/PLCL, PDLLA/VACNT-O:nHAp, incorporation of hydroxyapatite and simvastatin. Three studies showed an acceleration in proliferation of osteoblasts for the use of biomaterials with additional factors such as collagen and UV light. (4) Conclusions: Lactide polymers present higher osteointegration and cell proliferation rate than the materials compared. They are superior to non-biodegradable materials in terms of the biocompability, bone remodelling and healing time tests. Moreover, because there is no need of reoperation, as the material automatically degrades, the chance of scars and skin sclerosis is lower. However, more studies involving greater numbers of biomaterial types and mixes need to be performed in order to find a perfect biodegradable material.

Titanium or Biodegradable Osteosynthesis in Maxillofacial Surgery? In Vitro and In Vivo Performances

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

A Narrative Review of u-HA/PLLA, a Bioactive Resorbable Reconstruction Material: Applications in Oral and Maxillofacial Surgery

The advent of bioresorbable materials to overcome limitations and replace traditional bone-reconstruction titanium-plate systems for bone fixation, thus achieving greater efficiency and safety in medical and dental applications, has ushered in a new era in biomaterial development. Because of its bioactive osteoconductive ability and biocompatibility, the forged composite of uncalcined/unsintered hydroxyapatite and poly L-lactic acid (u-HA/PLLA) has attracted considerable interest from researchers in bone tissue engineering, as well as from clinicians, particularly for applications in maxillofacial reconstructive surgery. Thus, various in vitro studies, in vivo studies, and clinical trials have been conducted to investigate the feasibility and weaknesses of this biomaterial in oral and maxillofacial surgery. Various technical improvements have been proposed to optimize its advantages and limit its disadvantages. This narrative review presents an up-to-date, comprehensive review of u-HA/PLLA, a bioactive osteoconductive and bioresorbable bone-reconstruction and -fixation material, in the context of oral and maxillofacial surgery, notably maxillofacial trauma, orthognathic surgery, and maxillofacial reconstruction. It simultaneously introduces new trends in the development of bioresorbable materials that could used in this field. Various studies have shown the superiority of u-HA/PLLA, a third-generation bioresorbable biomaterial with high mechanical strength, biocompatibility, and bioactive osteoconductivity, compared to other bioresorbable materials. Future developments may focus on controlling its bioactivity and biodegradation rate and enhancing its mechanical strength.

Clinical Evaluation of Unsintered Hydroxyapatite Particles/Poly L-Lactide Composite Device in Craniofacial Surgery

ABSTRACT

A total of 47 patients who underwent the craniofacial implantation of unsintered hydroxyapatite particles and a poly-L-lactide device were evaluated for clinical local findings and computed tomography (CT) images after about 6 months. Long-term follow-up of 3 patients was done from 5 to 11 years. The patients underwent CT imaging pre- and postoperatively, while local clinical examination was done upon follow-up. For the 3 patients who were followed up for more than 5 years, implant changes were evaluated by using CT. Computed tomography revealed 3 patients of dislocation, 2 patients of insufficient bone union, and 3 patients of implant breakage. All patients healed well with no complications requiring a secondary operation. The CT findings of the long-term cases revealed the following: a plate and screw were still present 5 years postsurgery (patient 1), mesh implants were completely resorbed after 9 years and 6 months (patient 2), and plates were almost resorbed after 11 years but some of their shapes remained (patient 3).The unsintered hydroxyapatite/poly-L-lactide device is useful in the maxillofacial region in terms of strength and radiographic contrast. However, since the absorption rate is slow, it is necessary to keep in mind its long-term radiographic detectability and the possibility of late-onset granuloma.

Bioactive Regeneration Potential of the Newly Developed Uncalcined/Unsintered Hydroxyapatite and Poly-l-Lactide-Co-Glycolide Biomaterial in Maxillofacial Reconstructive Surgery: An In Vivo Preliminary Study

Uncalcined/unsintered hydroxyapatite (HA) and poly-l-lactide-co-glycolide (u-HA/PLLA/PGA) are novel bioresorbable bioactive materials with bone regeneration characteristics and have been used to treat mandibular defects in a rat model. However, the bone regenerative interaction with the periosteum, the inflammatory response, and the degradation of this material have not been examined. In this study, we used a rat mandible model to compare the above features in u-HA/PLLA/PGA and uncalcined/unsintered HA and poly-l-lactic acid (u-HA/PLLA). We divided 11 male Sprague–Dawley rats into 3- and 16-week groups. In each group, we assessed the characteristics of a u-HA/PLLA/PGA sheet covering the right mandibular angle and a u-HA/PLLA sheet covering the left mandibular angle in three rats each, and one rat was used as a sham control. The remaining three rats in the 16-week group were used for a degradation assessment and received both sheets of material as in the material assessment subgroup. At 3 and 16 weeks after surgery, the rats were sacrificed, and mandible specimens were subjected to micro-computed tomography, histological analysis, and immunohistochemical staining. The results indicated that the interaction between the periosteum and u-HA/PLLA/PGA material produced significantly more new bone regeneration with a lower inflammatory response and a faster resorption rate compared to u-HA/PLLA alone. These findings may indicate that this new biomaterial has ideal potential in treating maxillofacial defects of the midface and orbital regions.

Bone Coverage around Hydroxyapatite/Poly(L-Lactide) Composite Is Determined According to Depth from Cortical Bone Surface in Rabbits

Composites of unsintered hydroxyapatite (HA) and poly(_L-lactide) (PLLA) reinforced by compression forging are biodegradable, bioactive, and have ultrahigh strength. However, foreign body reactions to PLLA and physical irritation can occur when not covered by bone. We aimed to confirm the relationships between the depth of the implanted HA-PLLA threaded pins and the new bone formation. We inserted HA-PLLA composite threaded pins (diameter: 2.0 or 4.5 mm) into the femoral and tibial bones of 32 mature male Japanese white rabbits (weight 3.0–3.5 kg) with the pin head 1 or 0 mm below or protruding 1 or 2 mm above surrounding cortical bone. Eight euthanized rabbits were radiologically and histologically assessed at various intervals after implantation. Bone bridging was complete over pins of both diameters at ~12 weeks, when inserted 1 mm below the surface, but the coverage of the pins inserted at 0 mm varied. Bone was not formed when the pins protruded >1 mm from the bone surface. No inflammation developed around the pins by 25 weeks. However, foreign body reactions might develop if composites are fixed above the bone surface, and intraosseous fixation would be desirable using double-threaded screws or a countersink to avoid screw head protrusion.

Stability of bioabsorbable fixation systems according to different locations of mandibular fracture: A three-dimensional analysis

This study aimed to elucidate whether the stability of an unsintered hydroxyapatite particles/poly-_l-lactide (uHA/PLLA) system is comparable with that of titanium, according to different load-bearing areas of the mandible. The study included patients who underwent open reduction and internal fixation of the mandibular body, angle, or subcondylar fracture. The stability of uHA/PLLA systems was compared between the immediate and 6-month postoperative time points using three-dimensional cone-beam CT image analysis. The positional changes of each landmark were measured in three-dimensional (3D) coordinate systems using simulation software. Among 36 patients, there were more displacements of the landmarks between the immediate and 6-month postoperative time points after subcondylar fracture reduction than after body or angle fracture reductions. Strong upward displacements of the landmarks after subcondylar fracture reduction were found in the lateral pole [mean (SD) = 1.75 (3.16), p-value = 0.003] and medial pole [mean (SD) = 1.64 (2.50), p-value = 0.024], but not in the center. Subgroup analyses revealed similar unstable results in males on the condylar landmarks after subcondylar fracture reduction. There were tendencies for lateral displacement of the coronoid process in the body fracture group [mean (SD) = 0.8 (0.83)] and angle fracture group [mean (SD) = 0.75 (0.58)] postoperatively (p-value = 0.01). This study concluded that bioresorbable osteosynthesis can be recommended for body or angle fractures, while the indication for subcondylar fractures is less clear.

Change of body composition, physical strength, and nutritional status of patients with mandibular fractures

The aim was to determine changes in various parameters indicating physical conditions and nutritional status of patients during surgical and conservative treatment of mandibular fractures. A round by a nutrition support team was done once postoperatively for the surgical treatment group. For the conservative treatment group, three rounds were performed during the period of intermaxillary fixation. Data obtained from the rounds were compared between the groups. There were 29 patients surgically and 30 patients conservatively treated. A significant weight loss was observed in both groups postoperatively. The mean weight loss of the surgical treatment group measured at the postoperative round was 1.73 kg (SD ± 1.78) (P < 0.001) and that of the conservative treatment group at the third round was 2.74 kg (SD ± 2.35) (P < 0.001). During the entire treatment period, weight loss, body fat percentage, skeletal muscle percentage, grip strength and parameters indicating body composition and nutritional status of the conservative treatment group did not substantially differ from those of the surgical group. The influence of the conservative procedure on the nutritional condition of the patients seems to be limited and reversible at the end of the treatment. The weight loss observed here suggests that systematic nutrition support is necessary during both surgical and conservative treatment.

Biomechanical evaluation of unilateral subcondylar fracture of the mandible on the varying materials: A finite element analysis

Fixation materials used in the surgical treatment of subcondylar fractures contribute to successful clinical outcomes. In this study, we simulated the mechanical properties of four fixation materials [titanium (Ti), magnesium alloy (Mg alloy), poly-L-lactic acid (PLLA), and hydroxyapatite/poly-L-lactide (HA-PLLA)] in a finite-element analysis model of subcondylar fracture. Two four-hole plates were fixed on the anterior and posterior surfaces of the subcondyle of the mandible. In the simulation model of a subcondylar fracture, we evaluated the stress distribution and mechanical deformation of fixation materials. The stress distribution conspicuously appeared on the condylar neck of the non-fractured side and the center of the anterior plate for all materials. More stress distribution to the biologic component appeared with HA-PLLA than with Ti or Mg alloy, but its effects were less prominent than that of PLLA. The largest deformation was observed with PLLA, followed by HA-PLLA, Mg alloy, and Ti. The results of the present study imply the clinical potential of the HA-PLLA fixation material for open reduction of subcondylar fractures.