Andres Stricker

In vivo comparison of hard tissue regeneration with human mesenchymal stem cells processed with either the FICOLL method or the BMAC method.

OBJECTIVE To compare new bone formation in maxillary sinus augmentation procedures using biomaterial associated with mesenchymal stem cells (MSCs) separated by two different isolation methods. BACKGROUND In regenerative medicine open cell concentration systems are only allowed for clinical application under good manufacturing practice conditions. METHODS Mononuclear cells, including MSCs, were concentrated with either the synthetic polysaccharide (FICOLL) method (classic open system--control group, n = 6 sinus) or the bone marrow aspirate concentrate (BMAC) method (closed system--test group, n = 12 sinus) and transplanted in combination with biomaterial. A sample of the cells was characterized by their ability to differentiate. After 4.1 months (SD +/- 1.0) bone biopsies were obtained and analyzed. RESULTS The new bone formation in the BMAC group was 19.9% (90% confidence interval [CI], 10.9-29), and in the FICOLL group was 15.5% (90% CI, 8.6-22.4). The 4.4% difference was not significant (90% CI, -4.6-13.5; p = 0.39). MSCs could be differentiated into osteogenic, chondrogenic, and adipogenic lineages. CONCLUSION MSCs harvested from bone marrow aspirate in combination with bovine bone matrix particles can form lamellar bone and provide a reliable base for dental implants. The closed BMAC system is suited to substitute the open FICOLL system in bone regeneration procedures.

Bone regeneration in sinus lifts: comparing tissue-engineered bone and iliac bone.

Lifting of the sinus floor is a standard procedure for bony augmentation that enables dental implantation. Although cultivated skin and mucosal grafts are often used in plastic and maxillofacial surgery, tissue-engineered bone has not achieved the same success. We present the clinical results of dental implants placed after the insertion of periosteum-derived, tissue-engineered bone grafts in sinus lifts. Periosteal cells were isolated from biopsy specimens of periosteum, resuspended and cultured. The cell suspension was soaked in polymer fleeces. The cell-polymer constructs were transplanted by sinus lift 8 weeks after harvesting. The patients (n=35) had either one or both sides operated on. Seventeen had a one-stage sinus lift with simultaneous implantation (54 implants). In 18 patients the implants were inserted 3 months after augmentation (64 implants). Selected cases were biopsied. A control group (41 patients: one stage=48 implants, two stage=135 implants) had augmentation with autologous bone only. They were followed up clinically and radiologically for at least 24 months. Both implants and augmentation were significantly more successful in the control group. Failure of augmentation of the tissue-engineered bone was more common after large areas had been augmented. Eleven implants were lost in the study group and only one in the control group. Lifting the sinus floor with autologous bone is more reliable than with tissue-engineered transplants. Although lamellar bone can be found in periosteum-derived, tissue-engineered transplants, the range of indications must be limited.

Biodegradable osteosynthesis material for stabilization of midface fractures: experimental investigation in sheep.

The most frequently tested biodegradable osteosynthesis materials have up to now largely consisted of poly-L-lactide (PLLA). The PLLA polymers appear to have sufficient mechanical strength for fracture treatment in the midface, but their degradation does not seem to be uniform enough to allow their clinical use. During the degradation process the disintegration products elicit a foreign body reaction due to non-uniform degradation rates. The foreign body reaction is sometimes combined with a fluctuant swelling at the implantation site. Implants injection-moulded from 90:10 PLLA/PGA (polyglycolic acid) have a more uniform degradation rate and seem to lead to a milder foreign body reaction. We bridged Le Fort I osteotomies in sheep using a system of injection-moulded PLLA/PGA 90:10 plates and screws and compared it with 2 mm AO miniplates and mini-screws made from titanium. Light microscopy evaluation showed that the PLLA/PGA copolymer system experienced its highest mechanical stress at the transition from screw head to screw shaft. Nevertheless, the fragments fixed with the copolymers were on the whole only slightly less stable than those fixed with the titanium system. The foreign body reaction solely due to co-polymer degradation was not severe, considering the fibrous tissue response that was found associated with the titanium components. The study does show that the copolymer investigated is adequate for clinical use as a biodegradable osteosynthesis material, at least in low stress bearing areas.

Follow-Up of Implant Survival Comparing Ficoll and Bone Marrow Aspirate Concentrate Methods for Hard Tissue Regeneration with Mesenchymal Stem Cells in Humans

Abstract Objective: Clinical follow-up of implant survival in 11 patients comparing two different methods for mesenchymal stem cell (MSC) isolation (Ficoll and bone marrow aspirate concentrate [BMAC]) applied in maxillary sinus augmentation. Methods: Mononuclear cells, including MSCs, were concentrated with either Ficoll (control group, n=6 sinus) or BMAC (test group, n=12 sinus) and transplanted in combination with bovine bone mineral. A total of 50 implants were placed in a second surgical intervention (17 Ficoll/33 BMAC) and loaded after 4 months. Overall implant survival was assessed with a Kaplan-Meier model using package survival under R. Results: Implant survival of the Ficoll group was 100% compared with the BMAC group, which had 93.4% survival (95% confidence interval, 0.849–1). The difference between the groups was not significant (p=0.381). Conclusion: The BMAC system is an effective and suitable “chair-side” method for clinical application in hard tissue regeneration.

Long-term peri-implant bone level changes of non-vascularized fibula bone grafted edentulous patients

Long-term results of reconstructions and prosthetic rehabilitation of patients presenting severely atrophied edentulous ridges remains a challenge for clinicians. Among the various available augmentation materials there is evidence that avascular fibula bone grafts possess a reliable resistance against resorption and may thus provide a valuable source to reduce the loss of vertical bone height after reconstruction of the severely atrophied mandible and maxilla. The purpose of the present study was to assess long-term crestal bone level stability in avascular fibula bone grafts. 8 edentulous female patients (average age 70.6 years) with Class-VI-atrophy and less than 5 mm residual bone volume received onlay-grafting with avascular fibula bone grafts and were monitored with a mean observation time of 133.7 months (121-186). A total of 39 implants were placed in the maxilla and mandible. Three patients received immediate and five patients delayed implant placement 3 months after grafting. All patients were provided with bar-retained dentures. Postoperative evaluation included clinical implant success (Buser) and radiographic examinations (orthopantomogram) to quantify crestal bone resorption. Grafting was successfully performed in all patients with no regrafting necessary. All implants but one, lost 2 years after abutment connection, remained successfully integrated and fulfilled the Buser criteria, rendering to a success rate of 97%. Mean bone resorption after 10 years was mesial 1.4 mm and distal 1.4 mm at each implant-site. Maximum bone resorption occurred between postoperative and first year, thereafter no significant resorption was measured in re-examinations up to 15 years. Avascular fibula grafts are a reliable bone graft for augmentation procedures in atrophied edentulous ridges. Dental implants that integrated in the autogenous fibular bone grafts showed a stable crestal peri-implant bone level up to 15 years after implant placement.

Rehabilitation of irradiated patients with chemically modified and conventional SLA implants: five-year follow-up

The aim of this study is to evaluate the clinical and radiological parameters of standard SLA surface implants compared to chemically modified hydrophilic SLActive implants in irradiated patients after the initial 12-month loading period up to 5 years. Twenty patients with a mean age of 61·1 years were treated with dental implants after ablative surgery and radio-chemotherapy of oral cancer. All patients were non-smokers. The placement of 102 implants (50 SLA, 52 SLActive) was performed bilaterally according to a split-mouth design. Mean crestal bone changes were evaluated using standardised orthopantomographies and clinical parameters. Data were analysed using a Kaplan-Meier curve, Mann-Whitney U-test and two-factorial non-parametric analysis. The average observation period was 60 months. The amount of bone loss at the implant shoulder of SLA implants was mesial and distal 0·7 mm. The SLActive implants displayed a bone loss of mesial 0·6 mm as well as distal 0·7 mm after 5 years. Two SLA implants were lost before loading. One patient lost five implants due to recurrence of a tumour. The overall cumulative 12-month, 3-year and 5-year survival rate of SLA implants was 92%, 80% and 75·8% and of SLActive implants 94·2%, 78·8% and 74·4%, respectively. Eighteen implants were considered lost because the patients had died. Sandblasted acid-etched implants with or without a chemically modified surface can be used in irradiated patients with a high predictability of success. Lower implant survival rates in patients with irradiated oral cancer may be associated with systemic effects rather than peri-implantitis.

Bone loss after ridge expansion with or without reflection of the periosteum

OBJECTIVE To evaluate the role of the periosteum in preserving the buccal bone after ridge splitting and expansion with simultaneous implant placement. MATERIAL AND METHODS In 12 miniature pigs, the mandibular premolars and first molars were removed together with the interdental bone septa and the buccal bone. Three months later, ridge splitting and expansion of the buccal plate was performed with simultaneous placement of two titanium implants per quadrant. Access by a mucosal flap (MF) was prepared on test sides, while a mucoperiosteal flap (MPF) with complete denudation of the buccal bone was increased on control sides. After healing periods of six and 12 weeks, the animals were sacrificed for histologic and histometric evaluation. RESULTS In the MF group, all 16 implants were osseointegrated, while in the MPF group, four of 16 implants were lost. Noticeable differences of bone levels on the implant surface and of the bone crest (BC) were found between the MF and the MPF group. Buccally after 6 weeks, the median distance between the implant shoulder (IS) and the coronal-most bone on the implant (cBIC) was for the MF group -1.42 ± 0.42 mm and for the MPF group -4.80 ± 2.72 mm (P = 0.15). The median distance between the IS and the buccal BC was -1.24 ± 0.51 mm and -2.78 ± 1.98 mm (P = 0.12) for the MF and MPF group, respectively. After 12 weeks, median IS-cBIC was -2.12 ± 0.84 mm for MF and -7.19 mm for MPF, while IS-BC was -2.08 ± 0.79 mm for MF and -5.96 mm for MPF. After 6 weeks, the median buccal bone thickness for MF and MPF was 0.01 and 0 mm (P < 0.001) at IS, 1.48 ± 0.97 mm and 0 ± 0.77 mm (P = 0.07) at 2 mm apical to IS, and 2.12 ± 1.19 mm and 1.72 ± 01.50 mm (P = 0.86) at 4 mm apical to IS, respectively. After 12 weeks, buccal bone thickness in the MF group was 0 mm at IS, 0.21 mm at 2 mm apical to IS, and 2.56 mm at 4 mm apical to IS, whereas complete loss of buccal bone was measured from IS to 4 mm apical to IS for the MPF group. CONCLUSIONS In this ridge expansion model in miniature pigs, buccal bone volume was significantly better preserved when the periosteum remained attached to the bone.

Piezosurgery in implant dentistry

Piezosurgery, or the use of piezoelectric devices, is being applied increasingly in oral and maxillofacial surgery. The main advantages of this technique are precise and selective cuttings, the avoidance of thermal damage, and the preservation of soft-tissue structures. Through the application of piezoelectric surgery, implant-site preparation, bone grafting, sinus-floor elevation, edentulous ridge splitting or the lateralization of the inferior alveolar nerve are very technically feasible. This clinical overview gives a short summary of the current literature and outlines the advantages and disadvantages of piezoelectric bone surgery in implant dentistry. Overall, piezoelectric surgery is superior to other methods that utilize mechanical instruments. Handling of delicate or compromised hard- and soft-tissue conditions can be performed with less risk for the patient. With respect to current and future innovative surgical concepts, piezoelectric surgery offers a wide range of new possibilities to perform customized and minimally invasive osteotomies.

Finite Element Analysis and Biomechanical Testing to Analyze Fracture Displacement of Alveolar Ridge Splitting

The alveolar ridge splitting technique enables reconstruction of atrophied alveolar ridges prior implantation. However, in cases of severe atrophy, there is an unpredictable risk of fracturing the buccal lamella during the expansion. Currently, there is no preoperative assessment to predict the maximum distraction of the lamella. The aim of this study was to develop a biomechanical model to mimic the alveolar ridge splitting and a finite element (FE) model to predict the experimental results. The biomechanical testing was conducted on porcine mandibles. To build the FE model high resolution peripheral quantitative computer tomography scans of one specimen was performed after the osteotomy outline, but before the lamella displacement. A servo-electric testing machine was used for the axial tension test to split the lamellae. Results showed, in line with clinical observations, that the lamellae broke primarily at the base of the splits with a median displacement of 1.27 mm. The FE model could predict fracture force and fracture displacement. Fracture force showed a nonlinear correlation with the height of the bone lamella. In conclusion, good correspondence between mechanical testing and virtual FE analysis showed a clinically relevant approach that may help to predict maximum lamella displacement to prevent fractures in the future.