Johan Caspar Wohlfahrt

Enamel matrix proteins; old molecules for new applications

Emdogain (enamel matrix derivative, EMD) is well recognized in periodontology, where it is used as a local adjunct to periodontal surgery to stimulate regeneration of periodontal tissues lost to periodontal disease. The biological effect of EMD is through stimulation of local growth factor secretion and cytokine expression in the treated tissues, inducing a regenerative process that mimics odontogenesis. The major (>95%) component of EMD is Amelogenins (Amel). No other active components have so far been isolated from EMD, and several studies have shown that purified amelogenins can induce the same effect as the complete EMD. Amelogenins comprise a family of highly conserved extracellular matrix proteins derived from one gene. Amelogenin structure and function is evolutionary well conserved, suggesting a profound role in biomineralization and hard tissue formation. A special feature of amelogenins is that under physiological conditions the proteins self-assembles into nanospheres that constitute an extracellular matrix. In the body, this matrix is slowly digested by specific extracellular proteolytic enzymes (matrix metalloproteinase) in a controlled process, releasing bioactive peptides to the surrounding tissues for weeks after application. Based on clinical and experimental observations in periodontology indicating that amelogenins can have a significant positive influence on wound healing, bone formation and root resorption, several new applications for amelogenins have been suggested. New experiments now confirm that amelogenins have potential for being used also in the fields of endodontics, bone regeneration, implantology, traumatology, and wound care.

In vivo performance of absorbable collagen sponges with rosuvastatin in critical-size cortical bone defects.

Rosuvastatin (RSV) is a synthetic statin with favourable pharmacologic properties, but its local effect in bone has yet to be investigated. The aim of this study was to evaluate the potential of absorbable collagen sponge (ACS) as a carrier for RSV to enhance bone formation in critical-size cortical bone defects adjacent to titanium implants. ACS, treated with different concentrations of RSV (R1 = 8.7 + or - 1.8 microg; R2 = 52.0 + or - 4.4 microg; R3 = 259.1 + or - 8.8 microg) or phosphate-buffered saline alone, were placed into the bone marrow through a defect made in the proximal tibial cortical bone of New Zealand White rabbits. One empty defect (SHAM) served as an internal control in each animal. After a healing time of 4 weeks, a concentration-dependent increase of alkaline phosphatase activity in ACS treated with RSV was detected in the bone fluid after removing the implants. In addition, a significant concentration-dependent increase in BMP-2 mRNA levels was found in the cortical bone tissue adjacent to the RSV-treated ACS. The cortical architecture of bone defects analysed by micro-computed tomography showed a trend towards higher bone volume in the ACS+R1 group compared with SHAM, which was accompanied by an increase in the bone mineral density. Evaluation of histological sections showed new bone formation in ACS treated with RSV but not in untreated ACS. These results indicate that RSV, when administered locally in bone, may have a potential effect in stimulating bone formation.

Porous ceramic titanium dioxide scaffolds promote bone formation in rabbit peri-implant cortical defect model.

Titanium oxide (TiO₂) scaffolds have previously been reported to exhibit very low mechanical strength. However, we have been able to produce a scaffold that features a high interconnectivity, a porosity of 91% and a compressive strength above 1.2 MPa. This study analyzed the in vivo performance of the porous TiO₂ scaffolds in a peri-implant cortical defect model in the rabbit. After 8 weeks of healing, morphological microcomputed tomography analyses of the defects treated with the TiO₂ scaffolds had significantly higher bone volume, bone surface and bone surface-to-volume ratio when compared to sham, both in the cortical and bone marrow compartment. No adverse effects, i.e. tissue necrosis or inflammation as measured by lactate dehydrogenase activity and real-time reverse transcription polymerase chain reaction analysis, were observed. Moreover, the scaffold did not hinder bone growth onto the adjacent cortical titanium implant. Histology clearly demonstrated new bone formation in the cortical sections of the defects and the presence of newly formed bone in close proximity to the scaffold surface and the surface of the adjacent Ti implant. Bone-to-material contact between the newly formed bone and the scaffold was observed in the histological sections. Islets of new bone were also present in the marrow compartment albeit in small amounts. In conclusion, the present investigation demonstrates that TiO₂ scaffolds osseointegrate well and are a suitable scaffold for peri-implant bone healing and growth.

Bone formation in TiO2 bone scaffolds in extraction sockets of minipigs

The osteoconductive capacity of TiO(2) scaffolds was investigated by analysing the bone ingrowth into the scaffold structure following their placement into surgically modified extraction sockets in Gottingen minipigs. Non-critical size defects were used in order to ensure sufficient bone regeneration for the evaluation of bone ingrowth to the porous scaffold structure, and sham sites were used as positive control. Microcomputed tomographic analysis revealed 73.6±11.1% of the available scaffold pore space to be occupied by newly formed bone tissue, and the volumetric bone mineral density of the regenerated bone was comparable to that of the native cortical bone. Furthermore, histological evidence of vascularization and the presence of bone lamellae surrounding some of the blood vessels were also observed within the inner regions of the scaffold, indicating that the highly interconnected pore structure of the TiO(2) scaffolds supports unobstructed formation of viable bone tissue within the entire scaffold structure. In addition, bone tissue was found to be in direct contact with 50.0±21.5% of the TiO(2) struts, demonstrating the good biocompatibility and osteoconductivity of the scaffold material.

Porous titanium granules promote bone healing and growth in rabbit tibia peri-implant osseous defects

OBJECTIVES The aim of this study was to investigate the osteoconductive properties and biological performance of porous titanium granules used in osseous defects adjacent to titanium implants. MATERIAL AND METHODS In this animal experimental study, calibrated defects were prepared in the tibias of 24 New Zealand rabbits. The defects were randomized into two tests and one control group. The test defects were grafted with either metallic or oxidized porous titanium granules (PTG or WPTG, respectively), whereas control defects were left empty (sham). The defects were closed with a submerged coin shaped titanium implant. Defects were left for healing for 4 weeks. After healing, the implants were removed and the new bone tissue formed onto the implant surface was analyzed for run x 2, osteocalcin, collagen-I, tartrate-resistant acid phosphatase, H(+)-ATPase, tumor necrosis factor-alpha, interleukin (IL)-6 and IL-10 gene expression using reverse transcriptase polymerase chain reaction. Wound fluid from the healed defects was analyzed for lactate dehydrogenase and alkaline phosphatase activity. Finally osteoconductivity was analyzed by micro-computed tomography and histology. RESULTS Significantly more new bone formed in PTG and WPTG grafted defects compared with sham. The new bone grew both through the porosities of the granules and onto the implant surfaces. The WPTG group showed significantly less expression of key inflammation markers, but with no significant difference in a marker for necrosis. The WPTG also showed a significant increase in collagen-I mRNA expression compared with PTG. CONCLUSION The results suggest that PTG and WPTG are both osteoconductive materials that can be used to promote bone formation in osseous defects adjacent to titanium implants without hampering implant osseointegration.

The effect of permanent grafting materials on the preservation of the buccal bone plate after tooth extraction: an experimental study in the dog

OBJECTIVES The aim of the present study was to evaluate the effects of a novel bone substitute system (Natix(®)), consisting of porous titanium granules (PTG) and a bovine-derived xenograft (Bio-Oss(®)), on hard tissue remodelling following their placement into fresh extraction sockets in dogs. MATERIAL AND METHODS Six modalities were tested; Natix(®) granules with and without a covering double-layered Bio Gide(®) membrane; Bio-Oss(®) with and without a covering double-layered Bio Gide(®) membrane; and a socket left empty with and without a covering double-layered Bio Gide(®) membrane. Linear measurements, indicative of buccal bone height loss, and an area measurement indicative of buccal bulk bone loss were made. The statistical analysis was based on the Latin Square design with two blocking factors (dog and site). Tukeys post hoc test was used to adjust for multiple comparisons. RESULTS Histological observation revealed that while bone formed around both the xenograft and the titanium particles, bone was also noted within titanium granules. Of the five modalities of ridge preservation techniques used in this study, no one technique proved to be superior. CONCLUSION The titanium granules were observed to have promising osseoconductive properties.

Osseointegration of dental implants in extraction sockets preserved with porous titanium granules – an experimental study

OBJECTIVES This study investigated osseointegration of dental implants inserted in healed extraction sockets preserved with porous titanium granules (PTG). MATERIAL AND METHODS Three adult female minipigs (Gøttingen minipig; Ellegaard A/S, Dalmose, Denmark) had the mandibular teeth P2, P3 and P4 extracted. The extraction sockets were preserved with metallic PTG (Tigran PTG; Tigran Technologies AB, Malmö, Sweden) n = 12, heat oxidized white porous titanium granules (WPTG) (Tigran PTG White) n = 12 or left empty (sham) n = 6. All sites were covered with collagen membranes (Bio-Gide; Geistlich Pharma, Wolhausen, Switzerland) and allowed 11 weeks of healing before implants (Straumann Bone Level; Straumann, Basel, Switzerland) were inserted. The temperature was measured during preparation of the osteotomies. Resonance frequency analysis (RFA, Osstell; Osstell AB, Gothenburg, Sweden) was performed at implant insertion and at termination. After 6 weeks of submerged implant healing, the pigs were euthanized and jaw segments were excised for microCT and histological analyses. RESULTS In the temperature and RFA analyses no significant differences were recorded between the test groups. The microCT analysis demonstrated an average bone volume of 61.7% for the PTG group compared to 50.3% for the WPTG group (P = 0.03) and 57.1% for the sham group. Histomorphometry demonstrated an average bone-to-implant contact of 68.2% for the PTG group compared to 36.6% for the WPTG group and 60.9% for the sham group (n.s). Eight out of ten implants demonstrated apical osseous defects in the WPTG group, but similar defects were observed in all groups. CONCLUSIONS PTG preserved extraction sockets demonstrate a similar outcome as the sham control group for all analyses suggesting that this material potentially can be used for extraction socket preservation prior to implant installment. Apical osseous defects were however observed in all groups including the sham group, and a single cause could not be determined.

Maxillary sinus augmentation with porous titanium granules: a microcomputed tomography and histologic evaluation of human biopsy specimens.

PURPOSE The aim of this study was to assess bone ingrowth into porous titanium granules used for maxillary sinus augmentation. MATERIALS AND METHODS Eighteen biopsy specimens from 17 patients participating in a clinical trial on sinus augmentation using porous titanium granules (PTG) were received in the laboratory. The specimens (trephine cores of 4.5 mm) were obtained 6 months after PTG placement. After being embedded in methacrylate, the samples were scanned in a microcomputed tomography (micro-CT) scanner. Specimens were then cut along the long axis and central slices were ground to 70 μm before staining with hematoxylin and eosin. RESULTS The micro-CT analysis demonstrated an average bone fill of 19% (standard deviation [SD] 5.8%), whereas the graft material occupied 22.7% (SD 4.7%). The volume of newly formed bone decreased with the distance from the residual bone of the sinus floor. Two-dimensional histomorphometric analysis demonstrated a mean area of new bone of 16.1% (SD 9.4%). The PTG alone occupied 25.9% of the total mean area (SD 6.1%). The newly formed bone consisted mainly of woven bone growing in close contact with the granules and bridging the intergranular space. The remaining area was occupied predominantly by nonmineralized connective tissue. There were no signs of inflammation in any of the biopsy specimens. CONCLUSIONS After 6 months, new bone had formed at a similar rate and quality as has been reported for other well-recognized bone graft substitutes. The new bone formed in close contact with the PTG, suggesting that the material is osteoconductive.

Porous Titanium Granules in the Treatment of Mandibular Class II Furcation Defects: A Consecutive Case Series

BACKGROUND The osteoconductive potential of titanium is interesting from the perspective of periodontal surgery and reconstitution of osseous defects. The aim of the present consecutive case series is to evaluate a surgical strategy based on the use of porous titanium granules (PTG) in the treatment of Class II buccal furcation defects in mandibular molars in humans. METHODS Surgical intervention with PTG used as a bone graft substitute was performed in 10 patients with 10 mandibular Class II buccal furcation defects. Clinical parameters (probing depth (PD), clinical attachment level (CAL), gingival recession (GR), gingival index (GI), bleeding on probing (BOP), and horizontal and vertical bone sounding) and radiographic measurements of vertical furcation height were compared among baseline (presurgery), 6, and 12 months (post-surgery). The significance level (α) was set at 0.05. RESULTS With respect to vertical and horizontal bone sounding measurements, CAL, and GR, no significant improvements between baseline and the 12-month examination were seen. Both PD and radiographic vertical furcation height were significantly reduced between baseline and 12 months. When comparing the baseline to 12-month data, a significantly lower GI score was seen but the BOP score was unchanged. None of the treated teeth showed radiographic signs of root resorption. CONCLUSION This study suggests that PTG is safe to use in close proximity to root surfaces, but no significant improvements in clinical endpoints of defect resolution were observed.

Microcomputed Tomographic and Histologic Analysis of Animal Experimental Degree II Furcation Defects Treated With Porous Titanium Granules or Deproteinized Bovine Bone

BACKGROUND Titanium is an interesting material for osseous reconstruction given its thrombogenic properties. The aim of this study is to compare the potential of porous titanium granules (PTGs) with sham and deproteinized bovine bone mineral (DBBM) in the reconstructive treatment of surgically created buccal, degree II furcation defects in mini-pigs. METHODS Buccal degree II furcation defects were surgically created in maxillary premolar teeth in adult, female, mini-pigs and filled with PTG or DBBM or were left empty (sham). After 6 weeks of healing, pigs were euthanized. Teeth with defects were excised en bloc and analyzed by microcomputed tomography (microCT) and histology. RESULTS The histologic analysis showed significantly more vertical bone formation in both PTG and sham groups compared to DBBM-treated defects (P <0.01). The microCT analysis showed significantly more bucco-palatal bone formation in furcations treated with PTG compared to the DBBM and sham (P <0.05). Bucco-palatal cylindrical microCT cores demonstrated a median defect fill of 96.8% for PTG-implanted defects, which was significantly greater than sham (72.2%) and DBBM (62.0%) (P <0.001) treatments. Significantly more regenerated periodontal ligament was seen for sham than DBBM-treated defects (P <0.05). Root resorption lacunae were small and infrequent and did not differ among groups. CONCLUSIONS The results of this study in mini-pigs suggest that PTG may integrate well in alveolar bone and supports osseous regrowth in degree II furcation defects. Moreover, PTG seems safe to use in close proximity to root surfaces. Clinical studies will be necessary to further explore these experimental animal findings.