Saso Ivanovski

Early osseointegration to hydrophilic and hydrophobic implant surfaces in humans

OBJECTIVE To evaluate the rate and degree of osseointegration at chemically modified moderately rough, hydrophilic (SLActive) and moderately rough, hydrophobic (SLA) implant surfaces during early phases of healing in a human model. MATERIAL AND METHODS The devices used for this study of early healing were 4 mm long and 2.8 mm in diameter and had either an SLActive chemically modified or a moderately rough SLA surface configuration. These devices were surgically installed into the retro-molar area of 49 human volunteers and retrieved after 7, 14, 28 and 42 days of submerged healing. A 5.2-mm-long specially designed trephine with a 4.9 mm inside diameter, allowing the circumferential sampling of 1 mm tissue together with the device was applied. Histologic ground sections were prepared and histometric analyses of the tissue components (i.e. old bone, new bone, bone debris and soft tissue) in contact with the device surfaces were performed. RESULTS All device sites healed uneventfully. All device surfaces were partially coated with bone debris. A significant fraction of this bone matrix coating became increasingly covered with newly formed bone. The process of new bone formation started already during the first week in the trabecular regions and increased gradually up to 42 days. The percentage of direct contact between newly formed bone and the device (bone-to-implant contact) after 2 and 4 weeks was more pronounced adjacent to the SLActive than to the SLA surface (14.8% vs. 12.2% and 48.3% vs. 32.4%, respectively), but after 42 days, these differences were no longer evident (61.6% vs. 61.5%). CONCLUSION While healing showed similar characteristics with bone resorptive and appositional events for both SLActive and SLA surfaces between 7 and 42 days, the degree of osseointegration after 2 and 4 weeks was superior for the SLActive compared with the SLA surface.

Systematic review of implant outcomes in treated periodontitis subjects

OBJECTIVES To determine implant outcomes in partially dentate patients who have been treated for periodontitis compared with periodontally healthy patients. MATERIAL AND METHODS All longitudinal studies (until March 2006) of endosseous dental implants of at least 6 months of loading were searched. Studies presented with one or more of the outcome measures (implant survival, success, bone-level change, peri-implantitis) were included. Screening, data abstraction and quality assessment were conducted independently and in duplicate. RESULTS From 4448 citations, 546 full-text papers were screened and nine studies were included. Overall, the non-periodontitis patients demonstrated better outcomes than treated periodontitis patients. However, the strength of evidence showed that the studies included were at a medium to high risk of bias, with lack of appropriate reporting and analysis of outcomes plus lack of accounting for confounders, especially smoking. Furthermore, the studies showed variability in the definitions of treated and non-periodontitis, outcome criteria and quality of supportive periodontal therapy. Meta-analysis could not be performed due to heterogeneity of the chief study characteristics. CONCLUSIONS There is some evidence that patients treated for periodontitis may experience more implant loss and complications around implants than non-periodontitis patients. Evidence is stronger for implant survival than implant success; methodological issues limit the potential to draw robust conclusions.

The influence of surface microroughness and hydrophilicity of titanium on the up-regulation of TGFβ/BMP signalling in osteoblasts.

The topography of titanium implants has been identified as an important factor affecting the osseointegration of surgically placed dental implants. Further modification to produce a hydrophilic microrough titanium implant surface has been shown to increase osseointegration compared with microrough topology alone. This study aimed to determine possible molecular mechanisms to explain this clinical observation by examining differences in the whole genome mRNA expression profile of primary human osteoblasts in response to sand-blasted acid-etched (SLA) and hydrophilic SLA (modSLA) titanium surfaces. A decrease in osteoblast proliferation associated with the titanium surfaces (modSLA > SLA > control) correlated with an increase in expression of the osteogenic differentiation markers BSPII and osteocalcin. Pathway analysis demonstrated that a number of genes associated with the TGFβ‑BMP signalling cascade (BMP2, BMP6, SP1, CREBBP, RBL2, TBS3, ACVR1 and ZFYVE16) were significantly differentially up-regulated with culture on the modSLA surface. BMP2 was shown to have the largest fold change increase in expression which was subsequently confirmed at the protein level by ELISA. Several other genes associated with the functionally important mechanisms relevant to bone healing, such as Wnt signalling (CTNNA1, FBX4, FZD6), angiogenesis (KDR), osteoclastogenesis (HSF2, MCL1) and proteolysis (HEXB, TPP1), were also differentially regulated. These results suggest that chemical (hydrophilic) modification of the SLA surface may result in more successful osseointegration through BMP signalling.

Gene expression profile of osseointegration of a hydrophilic compared with a hydrophobic microrough implant surface

OBJECTIVES To compare the gene expression profile of osseointegration associated with a moderately rough and a chemically modified hydrophilic moderately rough surface in a human model. MATERIAL AND METHODS Eighteen solid screw-type cylindrical titanium implants, 4 mm long and 2.8 mm wide, with either a moderately rough (SLA) or a chemically modified moderately rough (SLActive) surface were surgically inserted in the retromolar area of nine human volunteers. The devices were removed using a trephine following 4, 7 and 14 days of healing. The tissue surrounding the implant was harvested, total RNA was extracted and microarray analysis was carried out to identify the differences in the transcriptome between the SLA and SLActive surfaces at days 4, 7 and 14. RESULTS There were no functionally relevant gene ontology categories that were over-represented in the list of genes that were differentially expressed at day 4. However, by day 7, osteogenesis- and angiogenesis-associated gene expression were up-regulated on the SLActive surface. Osteogenesis and angiogenesis appeared to be regulated by BMP and VEGF signalling, respectively. By day 14, VEGF signalling remains up-regulated on the SLActive surface, while BMP signalling was up-regulated on the SLA surface in what appeared to be a delayed compensatory response. Furthermore, neurogenesis was a prominent biological process within the list of differentially expressed genes, and it was influenced by both surfaces. CONCLUSIONS Compared with SLA, SLActive exerts a pro-osteogenic and pro-angiogenic influence on gene expression at day 7 following implant insertion, which may be responsible for the superior osseointegrative properties of this surface.

Mechanisms of bone resorption in periodontitis

Alveolar bone loss is a hallmark of periodontitis progression and its prevention is a key clinical challenge in periodontal disease treatment. Bone destruction is mediated by the host immune and inflammatory response to the microbial challenge. However, the mechanisms by which the local immune response against periodontopathic bacteria disturbs the homeostatic balance of bone formation and resorption in favour of bone loss remain to be established. The osteoclast, the principal bone resorptive cell, differentiates from monocyte/macrophage precursors under the regulation of the critical cytokines macrophage colony-stimulating factor, RANK ligand, and osteoprotegerin. TNF-α, IL-1, and PGE2 also promote osteoclast activity, particularly in states of inflammatory osteolysis such as those found in periodontitis. The pathogenic processes of destructive inflammatory periodontal diseases are instigated by subgingival plaque microflora and factors such as lipopolysaccharides derived from specific pathogens. These are propagated by host inflammatory and immune cell influences, and the activation of T and B cells initiates the adaptive immune response via regulation of the Th1-Th2-Th17 regulatory axis. In summary, Th1-type T lymphocytes, B cell macrophages, and neutrophils promote bone loss through upregulated production of proinflammatory mediators and activation of the RANK-L expression pathways.

The role of bone debris in early healing adjacent to hydrophilic and hydrophobic implant surfaces in man

OBJECTIVE To evaluate morphologically and morphometrically the sequential healing and osseointegration events at moderately rough implant surfaces with and without chemical modification. Particularly the role of bone debris in initiating bone formation was emphasized. MATERIAL AND METHODS Solid, screw-type cylindrical titanium implants (SSI) (n=49), 4 mm long and 2.8 mm wide, with either chemically modified (SLActive(®)) or sandblasted and acid-etched (SLA(®)) surface configurations were surgically installed in the retromolar region of 28 human volunteers. After 7, 14, 28 and 42 days of submerged healing, the devices were retrieved with a trephine. Histologic ground sections were prepared and histomorphometrically analyzed. Linear measurements determined fractions of old bone (OBIC), new bone (NBIC), soft tissue (ST) and bone debris (BD) in contact with the SSI surfaces. RESULTS Healing was uneventful at all installation sites. Sixty-one percent of all devices were suitable for morphometric analyses. All implant surfaces were partially coated with bone debris and new bone formation was observed as early as 7 days after installation. There was a gradual increase in NBIC, whereas OBIC, ST and BD progressively decreased over time. NBIC after 2 and 4 weeks was higher on SLActive(®) than on SLA(®) surfaces, albeit statistically not significant. The BD : ST ratio changed significantly from 7 to 42 days (from 50 : 50 to 10 : 90 for SLActive(®); from 38: 62 to 10 : 90 for SLA(®)) (Fishers exact test, P<0.01). CONCLUSION Both SLActive(®) and SLA(®) devices became progressively osseointegrated, while old bone on the device surface was gradually resorbed. The decrease in BD : ST ratio suggests that bone debris, created during implant installation and adhering to moderately rough surfaces, significantly contributed to the initiation of bone deposition and mediated the connection between the old bone and the new bone on the implant surface.

Multiphasic Scaffolds for Periodontal Tissue Engineering

For a successful clinical outcome, periodontal regeneration requires the coordinated response of multiple soft and hard tissues (periodontal ligament, gingiva, cementum, and bone) during the wound-healing process. Tissue-engineered constructs for regeneration of the periodontium must be of a complex 3-dimensional shape and adequate size and demonstrate biomechanical stability over time. A critical requirement is the ability to promote the formation of functional periodontal attachment between regenerated alveolar bone, and newly formed cementum on the root surface. This review outlines the current advances in multiphasic scaffold fabrication and how these scaffolds can be combined with cell- and growth factor–based approaches to form tissue-engineered constructs capable of recapitulating the complex temporal and spatial wound-healing events that will lead to predictable periodontal regeneration. This can be achieved through a variety of approaches, with promising strategies characterized by the use of scaffolds that can deliver and stabilize cells capable of cementogenesis onto the root surface, provide biomechanical cues that encourage perpendicular alignment of periodontal fibers to the root surface, and provide osteogenic cues and appropriate space to facilitate bone regeneration. Progress on the development of multiphasic constructs for periodontal tissue engineering is in the early stages of development, and these constructs need to be tested in large animal models and, ultimately, human clinical trials.

The effect of hydrophilic titanium surface modification on macrophage inflammatory cytokine gene expression

OBJECTIVES Chemical modification of microrough titanium dental implants to produce a hydrophilic surface with increased wettability and improved surface energy has been demonstrated clinically to achieve superior bone wound healing and osseointegration compared to that achieved with a microrough titanium surface alone. As the recruitment of the necessary osseoinductive precursors involved in bone wound healing and osseointegration to the wound site is facilitated by the action of cytokines, this study sought to determine the in vitro effect of hydrophilic surface modification on the expression of pro-inflammatory cytokines from adherent macrophages. MATERIAL AND METHODS The surface topography and composition of the titanium surfaces was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Macrophage attachment and proliferation was assessed using an MTT assay. The expression of 84 pro-inflammatory cytokines and chemokines by adherent RAW 264.7 cells, a murine leukaemic monocyte cell line, was assessed by PCR array after 24 h culture on either smooth polished, sand-blasted acid-etched (SLA) or hydrophilic-modified SLA (SLActive) titanium surfaces. RESULTS Following 24 h culture on titanium, surface microroughness activated pro-inflammatory cytokine gene transcription in RAW 264.7 cells. Although there was no significant difference in the degree of cellular attachment or proliferation of RAW 264.7 cells to the different titanium surfaces, by 24 h the hydrophilic surface elicited a gene expression profile with significant down-regulation of the key pro-inflammatory cytokines Tnfα, IL-1α, IL-1β and the chemokine Ccl-2. CONCLUSIONS Down-regulation of the expression of pro-inflammatory cytokine genes may thus modulate the inflammatory response and may facilitate the enhanced bone wound healing and osseointegration observed clinically using implants with a microrough hydrophilic surface.

Transcriptional profiling of osseointegration in humans

OBJECTIVE To determine the temporal gene expression profile associated with the early healing events during osseointegration in a human model. MATERIAL AND METHODS Nine solid screw-type cylindrical titanium implants, 4 mm long and 2.8 mm wide, with a chemically modified surface (SLActive) were surgically inserted in the retromolar area of nine human volunteers. The devices were removed using a trephine following 4, 7 and 14 days of healing. The tissue surrounding the implant was harvested, total RNA was extracted and microarray analysis was carried out to identify the differences in the transcriptome between days 4, 7 and 14. RESULTS Gene ontology (GO) analysis of the temporal transcriptional changes was characteristic of a maturing, osteogenic process over the course of the study (4-14 days). At day 4, a gene expression profile associated with proliferation and immuno-inflammatory processes was predominant. However, by day 14, by far the most predominant mechanisms were associated with skeletogenesis, with the GO categories of skeletal system development, bone development and ossification being predominant, with the majority of changes occurring between days 7 and 14. Furthermore, the biological processes of angiogenesis and neurogenesis were also predominant by day 14. In terms of signal transduction, I-κB kinase/NF-κB cascade was predominant at day 4, whereas TGF-β/BMP, Wnt and Notch signalling were all associated with the osteogenic process over the duration of the study. Furthermore, Ras and Rho protein signal transduction was regulated throughout the osseointegration process. CONCLUSION The temporal transcriptional changes during osseointegration involve the expression of proliferation and immuno-inflammatory response associated genes during the early stages of osseointegration, which are ultimately replaced by genes associated with the biological processes of skeletogenesis, angiogenesis and neurogenesis. The early immuno-inflammatory changes appear to be regulated via the I-κB kinase/NF-κB cascade, whereas the later osteogenesis-related mechanisms are regulated by TGF-β/BMP, Notch and Wnt signaling.

Three-Dimensional Bioprinting for Regenerative Dentistry and Craniofacial Tissue Engineering

Craniofacial tissues are organized with complex 3-dimensional (3D) architectures. Mimicking such 3D complexity and the multicellular interactions naturally occurring in craniofacial structures represents one of the greatest challenges in regenerative dentistry. Three-dimensional bioprinting of tissues and biological structures has been proposed as a promising alternative to address some of these key challenges. It enables precise manufacture of various biomaterials with complex 3D architectures, while being compatible with multiple cell sources and being customizable to patient-specific needs. This review describes different 3D bioprinting methods and summarizes how different classes of biomaterials (polymer hydrogels, ceramics, composites, and cell aggregates) may be used for 3D biomanufacturing of scaffolds, as well as craniofacial tissue analogs. While the fabrication of scaffolds upon which cells attach, migrate, and proliferate is already in use, printing of all the components that form a tissue (living cells and matrix materials together) to produce tissue constructs is still in its early stages. In summary, this review seeks to highlight some of the key advantages of 3D bioprinting technology for the regeneration of craniofacial structures. Additionally, it stimulates progress on the development of strategies that will promote the translation of craniofacial tissue engineering from the laboratory bench to the chair side.