Evaluation of local cancellous bone amelioration by poly-L-DL-lactide copolymers to improve primary stability of dental implants: a biomechanical study in sheep.

OBJECTIVES: The aim of this study was to evaluate the clinical performance of local cancellous bone amelioration by a 70:30 poly-(L-lactide-co-D,L-Lacide) copolymer with two different implant designs on primary stability and after 4 and 12 weeks of healing time. MATERIAL AND METHODS: In six sheep, n = 36 implants (TH) with a conditioned, sandblasted, thermal acid-etched micro-rough surface and n = 36 implants (NB) with a highly crystalline and phosphate-enriched anodized titanium oxide surface were placed in the pelvic bone. Using an ultrasound-based process named Constant Amelioration Process (CAP), half of peri-implant trabecular bone structures were locally tested with 70:30 poly-(L-lactide-co-D,L-Lacide) copolymer in both implant groups, TH and NB. The CAP technology employs ultrasonic energy to liquefy 70:30 poly-(L-lactide-co-D,L-Lacide) which enters the inter-trabecular space, leading to local reinforcement of the cancellous bone structure after solidification of the copolymer. The CAP test group was compared with reference implants placed with the conventional site preparation according to the manufacturers' description. Primary stability was assessed by the measurement of torque-in values and implant stability quotient (ISQ; n = 18 per group). Secondary stability was analyzed by biomechanical removal torque testing after 4 and 12 weeks (n = 9 per group). RESULTS: Insertion torque value (23.3 N cm ± 13.6) of reference TH implants demonstrated a statistically significant (P = 0.00) difference in comparison with test TH implants (41.9 N cm ± 19.5). Reference NB implants revealed a statistically significant (P = 0.03) lower insertion torque value (23.7 N cm ± 13.5) than test NB implants (39.7 N cm ± 18.6). ISQ values increased for all implants from initial implant placement until sacrifice at 12 weeks. Reference TH implants tended to result in an increase in torque values from 4 weeks (181.9 N cm ± 22.8) to 12 weeks (225.7 N cm ± 47.4). This trend could be also proven for implants of test sites (4 week: 176.8 N cm ± 24.1; 12 week: 201.5 N cm ± 53.4). For reference, NB implants a non-significant increase in removal torque values from 4 weeks (146. 7 N cm ± 18.0) to 12 weeks (170.2 N cm ± 40.4) was observed. Removal torque values of test NB implants did not increase from 4 weeks (153.3 N cm ± 21.5) to 12 weeks (146.1 N cm ± 37.5). CONCLUSION: Biomechanical data proved significantly enhanced primary stability of dental implants after local amelioration without long-term sequelae and irrespective of implant design. After 4- and 12-week healing time, removal torque of locally test implants was as high as for control implants, and osseointegration was therefore not influenced by the CAP process. No correlation between ISQ values and torque values was found.

Early bone apposition to hydrophilic and hydrophobic titanium implant surfaces: a histologic and histomorphometric study in minipigs.

OBJECTIVE: The first objective of this pilot study was to evaluate the impact of the hydrophilicity on the early phases of osseointegration. The second objective was to compare two hydrophilic implant surfaces with different geometries, surface roughness, and technologies achieving hydrophilicity. MATERIAL AND METHODS: Twelve weeks after extraction, all four quadrants of nine minipigs received three dental implants, alternating between hydrophilic microrough surfaces (INICELL and SLActive) and a conventional hydrophobic microrough surface. After 5, 10, and 15 days of submerged healing, ground sections were prepared and subjected to histologic and histomorphometric analysis. RESULTS: The histologic analysis revealed a similar healing pattern among the hydrophilic and hydrophobic implant surfaces, with extensive bone formation occurring between day 5 and day 10. With BIC values of greater than 50% after 10 days, all examined surfaces indicated favorable osseointegration at this very early point in healing. At day 15, the mean new bone-to-implant contact (newBIC) of one hydrophilic surface (INICELL; 55.8 ± 14.4%) was slightly greater than that of the hydrophobic microrough surface (40.6 ± 20.2%). At day 10 and day 15, an overall of 21% of the implants had to be excluded from analysis due to inflammations primarily caused by surgical complications. CONCLUSION: Substantial bone apposition occurs between day 5 and day 10. The data suggest that the hydrophilic surface can provoke a slight tendency toward increased bone apposition in minipigs after 15 days. A direct comparison of two hydrophilic surfaces with varying geometries is of limited relevance.

Response of human bone marrow stromal cells, MG-63, and SaOS-2 to titanium-based dental implant surfaces with different topography and surface energy.

OBJECTIVES: Osseointegration is dependent on different parameters of the implant surface like surface roughness and physicochemical properties. In vitro studies using a wide variety of surface parameters and cell lines make it difficult to address the influence of a single parameter. With this study the influence of surface topography and energy on different osteoblast derived cell lines, namely MG-63 and SaOS-2 and of human mesenchymal stromal cells (hMSC) were investigated. MATERIAL AND METHODS: Cells were cultured on polished (POL) and sandblasted/hot acid etched (SBA) titanium surfaces which were partly alkaline treated (SBA NaOH). Cell morphology, metabolic activity, tissue non-specific alkaline phosphatase (TNAP) activity and prostaglandin E(2) (PGE(2) ) formation were determined. RESULTS: Impaired spreading was found on both SBA surfaces. Proliferation after 4 and 7 days increased on POL compared to both SBA surfaces. TNAP activity of hMSC and MG-63 was increased on POL compared to both SBA surfaces whereas SaOS-2 did not discriminate between the three surfaces. PGE(2) formation of hMSC and MG-63 was on both SBA surfaces after 2 days significantly higher than on POL. CONCLUSIONS: The results of this study show that surface roughness has a distinct influence on proliferation and differentiation of osteoblasts. However, variations in physicochemical properties seem to have little influence under the used experimental conditions. It is suggested that more sever and long-lasting modifications of surface chemistry would have an influence on osteoblastic cells.

Influence of the fiber diameter and surface roughness of electrospun vascular grafts on blood activation.

Electrospun grafts have been widely investigated for vascular graft replacement due to their ease and compatibility with many natural and synthetic polymers. Here, the effect of the processing parameters on the scaffold's architecture and subsequent reactions of partially heparinized blood triggered by contacting these topographies were studied. Degrapol® (DP) and poly(lactic-co-glycolic acid) (PLGA) electrospun fibrous scaffolds were characterized with regard to fiber diameter, pore area and scaffold roughness. The study showed that electrospinning parameters greatly affect fiber diameter together with pore dimension and overall scaffold roughness. Coagulation cascade activation, early platelet adhesion and activation were analyzed after 2h of exposure of blood to the biomaterials. While no differences were found between DP and PLGA with similar topographies, the blood reactions were observed to be dependent on the fiber diameter and scaffold roughness. Scaffolds composed of thin fibers (diameter <1µm) triggered very low coagulation and almost no platelets adhered. On the other hand, scaffolds with a bigger fiber diameter (2-3µm) triggered higher thrombin formation and more platelets adhered. The highest platelet adhesion and activations rates as well as coagulation cascade activation were found in blood incubated in contact with the scaffolds produced with the biggest fiber diameter (5µm). These findings indicate that electrospun grafts with small fiber diameter (<1µm) could perform better with reduced early thrombogenicity due to lower platelet adhesion and lower activation of platelets and coagulation cascade.

Response of osteoclasts to titanium surfaces with increasing surface roughness: an in vitro study.

Osteoclasts are responsible for bone resorption and implant surface roughness promotes osseointegration. However, little is known about the effect of roughness on osteoclast activity. This study aims at the characterization of osteoclastic response to surface roughness. The number of osteoclasts, the tartrate-resistant acid phosphatase and matrix metalloproteinase (MMP) activities, the cell morphology and the actin-ring formation were examined on smooth (TS), acid-etched (TA) and sandblasted acid-etched (TLA) titanium and on native bone. Cell morphology was comparable on TA, TLA and bone, actin rings being similar in size on TLA and bone, but smaller on TA and virtually absent on TS. Gelatin zymography revealed increased proMMP-9 expression on TA, TLA, and bone compared to TS. In general, osteoclasts show similar characteristics on rough titanium surfaces and on bone, but reduced activity on smooth titanium surfaces. These results offer some insight into the involvement of osteoclasts in remodeling processes around implant surfaces.

A comparison of osteoclast resorption pits on bone with titanium and zirconia surfaces.

Osteoclasts resorb bone at surfaces, leaving behind pits and trails where both mineral and organic phases of bone have been dissolved. Rough surface structures are deliberately imparted to synthetic implants, in order to improve osseointegration. The aim of this study is to characterize osteoclastic resorption pits on native bone surfaces and to compare these with state-of-the-art titanium and zirconia implant surfaces. The size (i.e. length, width and depth) of resorption pits was compared to the size of surface features of sandblasted and etched titanium and zirconia surfaces. It was found that resorption pits from native bone and surface features of the sandblasted and etched titanium and zirconia surfaces were quite similar in their dimensions. Most structures showed a length between 5 and 40 mum, a width between 2 and 20 mum and a depth between 1 and 8 mum. Additionally, the wavelength-dependent surface roughness was measured, revealing an S(a) value of 60 nm in the resorption pits, 86 nm on zirconia and between 127 and 140 nm on titanium surfaces. The results of this study may provide some insight into structural requirements for the bone-remodeling cycle and help to improve the design of new implant surfaces for osseointegration applications.

Mechanical anchorage and peri-implant bone formation of surface-modified zirconia in minipigs.

AIM: To test the hypothesis that peri-implant bone formation and mechanical stability of surface-modified zirconia and titanium implants are equivalent. MATERIALS AND METHODS: Twelve minipigs received three types of implants on either side of the mandible 8 weeks after removal of all pre-molar teeth: (i) a zirconia implant with a sandblasted surface; (ii) a zirconia implants with a sandblasted and etched surface; and (iii) a titanium implant with a sandblasted and acid-etched surface that served as a control. Removal torque and peri-implant bone regeneration were evaluated in six animals each after 4 and 13 weeks. RESULTS: The titanium surface was significantly rougher than both tested zirconia surfaces. Mean bone to implant contact (BIC) did not differ significantly between the three implant types after 4 weeks but was significantly higher for titanium compared with both zirconia implants after 13 weeks (p<0.05). Bone volume density (BVD) did not differ significantly at any interval. Removal torque was significantly higher for titanium compared with both zirconia surfaces after 4 and 13 weeks (p<0.001). The sandblasted and etched zirconia surface showed a significantly higher removal torque after 4 weeks compared with sandblasted zirconia (p<0.05); this difference levelled out after 13 weeks. CONCLUSIONS: It is concluded that all implants achieved osseointegration with similar degrees of BIC and BVD; however, titanium implants showed a higher resistance to removal torque, probably due to higher surface roughness.

Response of osteoblast-like SAOS-2 cells to zirconia ceramics with different surface topographies.

OBJECTIVES: Zirconia is a suitable biomaterial for use in medicine (stomatology, orthopaedics) due to its good biocompatibility and outstanding mechanical properties. This study compares the effect of (i) zirconia to the widely used titanium and (ii) zirconia with two different surface topographies (sandblasted and sandblasted/etched) on the adhesion, proliferation and differentiation of SAOS-2 osteoblasts. METHODS: SAOS-2 cells were cultured on either sandblasted or sandblasted/etched zirconia and compared with sandblasted/etched titanium. 2 and 24 h after plating, cell morphology was investigated by scanning electron microscope (SEM) and fluorescence imaging. At 24 and 48 h, cell number-relevant parameters were determined. Alkaline phosphatase (ALP) activity and mineral accumulation were measured at days 8, 11, 15 and day 22 of culture, respectively. RESULTS: SEM and fluorescence images revealed a faster spreading as well as higher number of adherent cells after 24 h incubation on zirconia compared with titanium. Also, the cellular metabolic activity after 24 h and the proliferation rate after 48 h is higher with zirconia compared with titanium. Zirconia had a more pronounced effect compared with titanium on the differentiation of SAOS-2 cells: ALP activity, an early differentiation marker increased earlier and mineralization, a late differentiation marker was increased. Only minor differences were found between zirconia with two different surface topographies; etched zirconia promoted slightly greater the differentiation of SAOS-2 cells. CONCLUSIONS: These data indicate that zirconia mediates a pronounced stronger effect on the adhesion, proliferation and differentiation compared with titanium; and that topographical differences of zirconia have minor effects on osteoblast biology.

Surface-conditioned dental implants: an animal study on bone formation.

AIM: The aim of this study was to determine whether bone formation around surface-conditioned implants is enhanced compared with non-surface-conditioned sandblasted acid-etched titanium implants. MATERIALS AND METHODS: One hundred and forty-four implants were placed in the mandible of 18 minipigs. Before placement, implants were either surface conditioned in a solution containing hydroxide ions (conSF) or assigned to controls. Animals were euthanized after 2, 4 and 8 weeks of submerged healing, the 8-week group receiving polyfluorochrome labelling at week 2, 4, 6 and 8. One jaw quadrant per animal was selected for histological and histomorphometrical evaluation of mineralized bone-implant contact (mBIC), osteoid-implant contact (OIC) and bone volume (BV) analysis. RESULTS: Polyfluorochrome labelling showed no general differences in bone dynamics. mBIC showed the most pronounced differences after 2 weeks, reaching 65.5% for conSF compared with 48.1% for controls, p=0.270. Differences levelled out after 4 weeks (67.4% control, 65.7% conSF) and 8 weeks (64.0% control, 70.2% conSF). OIC levels were initially comparable, showing a slower decline for conSF after 4 weeks. BV was higher for conSF at all times. No significant differences could be found. CONCLUSION: A tendency towards increased mBIC was shown for surface-conditioned implants after short-term healing.