Publications by authors named "Ignace Naert"

94 Publications

Oral Implant Restorations By Undergraduate Students: An Up To 5-Years Clinical Outcome.

Int J Prosthodont 2021 Feb 26. Epub 2021 Feb 26.

Purpose: To clinically evaluate oral implant restorations placed by undergraduate students in the dental clinical curriculum at KU Leuven (Belgium) in terms of function and esthetics.

Materials And Methods: A retrospective observational cohort study was designed. The esthetic and functional evaluations of implant-supported restorations placed in the framework of the undergraduate implant dentistry clinical training program using White/Pink Esthetic Score (WES/PES) and visual analog scale (VAS) scoring was performed. Furthermore, complications were registered based retrospectively on the patient's medical file. The following research questions were stipulated: (1) How well do implant-supported restorations placed by undergraduate students perform esthetically? and (2) Which complications occurred and how were these managed?

Results: Between August 2008 and July 2014 (6 academic terms), 251 implants (Brånemark System Mk III, Nobel Biocare) were placed in 113 patients by 155 students (> 40% of all students enrolled in the training program). Of these implants, 228 were restored in 101 patients by 118 students with varying restoration types. Esthetic scoring of the restorations in 83 of these patients revealed a satisfying mean WES of 8.14 ± 2.09 (out of 10) and PES of 9.56 ± 3.14 (out of 14). Complications were registered in 18.9% of the cases.

Discussion: Clinical training in implant dentistry for undergraduates contributes to the development of advanced skills in the dental student's Master education. Overall, patients were satisfied with their implant-supported restorations. Implant and restoration success rates and complication incidence were confirmed by long-term data in the oral implant literature.
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http://dx.doi.org/10.11607/ijp.7215DOI Listing
February 2021

Randomized controlled trial comparing immediate loading with conventional loading using cone-anchored implant-supported screw-retained removable prostheses: A 2-year follow-up clinical trial.

J Prosthet Dent 2019 Feb 7;121(2):258-264. Epub 2018 Aug 7.

Professor-emeritus, Department of Oral Health Sciences, KU Leuven and Dentistry, Prosthetic Dentistry, University Hospitals Leuven, Leuven, Belgium.

Statement Of Problem: Implant-based prosthetic solutions can be time consuming. If implants can be loaded immediately, treatment time can be reduced.

Purpose: The purpose of this prospective randomized controlled trial was to monitor the survival rate of Ankylos implants, comparing conventional with immediate loading by using abutments with the SynCone concept for screw-retained removable prostheses in the edentulous maxilla.

Material And Methods: A total of 90 implants were placed in 15 study participants. The participants were randomly assigned to the immediate or conventional loading treatment group. Radiographic and clinical parameters were recorded at the time of permanent prosthesis installment and at 1- and 2-year follow-up examinations, and participants' satisfaction was measured by using questionnaires before and after prosthesis installation. A linear mixed model was used to measure differences.

Results: One implant in the conventional group was lost during abutment placement; hence, 89 implants could be followed for 2 years. Approximately 90% of these implants showed no bone loss or even bone gain at 1 and 2 years follow-up. Mean values for the immediate group were, respectively, 0.09 ±0.35 mm and 0.13 ±0.38 mm and 0.01 ±0.41 mm and -0.06 ±0.32 mm for the conventional method. No significant differences (P=.053) were found in bone level alterations between the groups. For all participants, the mean number of surfaces (4 per implant) with bleeding on probing (BoP) and plaque were 0.76 ±0.81 and 0.16 ±0.42 at 1 year follow-up and 0.44 ±0.66 and 0.02 ±0.15, respectively, at the second-year follow-up. The mean pocket probing depths were 2.05 ±0.54 mm at 1 year and 2.18 ±0.64 mm at 2 years. For both groups, a significant rise in satisfaction and quality of life was observed (P≤.001) at 1 and 2 years compared with pretreatment.

Conclusions: Ankylos implants placed in the edentulous maxilla, immediately or conventionally loaded by a detachable prosthesis, showed favorable bone-level preservation after 2 years of follow-up. No significant differences could be found between the immediate and conventional groups. A significant increase in quality of life was observed for both loading modes.
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http://dx.doi.org/10.1016/j.prosdent.2018.03.022DOI Listing
February 2019

Effect of high-frequency loading and parathyroid hormone administration on peri-implant bone healing and osseointegration.

Int J Oral Sci 2018 03 13;10(1). Epub 2018 Mar 13.

Division of Advanced Prosthetic Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan.

The objective of this study is to examine the effect of low-magnitude, high-frequency (LMHF) loading, and anti-osteoporosis medications such as parathyroid hormone (PTH) and bisphosphonates on peri-implant bone healing in an osteoporosis model, and to assess their combined effects on these processes. Thirteen-week-old ovariectomized rats (n = 44) were divided into three groups: PTH, alendronate, and saline. After 3 weeks of drug administration, titanium implants were inserted into the tibiae. Each group was subdivided into two groups: with or without LMHF loading via whole-body vibration (50 Hz at 0.5 g, 15 min per day, 5 days per week). Rats were killed 4 weeks following implantation. Removal torque test, micro-CT analyses (relative gray (RG) value, water = 0, and implant = 100), and histomorphometric analyses (bone-to-implant contact (BIC) and peri-implant bone formation (bone volume/tissue volume (BV/TV))) were performed. Removal torque values and BIC were significantly differed by loading and drug administration (ANOVA). Post hoc analysis showed that PTH-treated groups were significantly higher than the other drug-treated groups. BV/TV was significantly enhanced by PTH administration. In cortical bone, RG values were significantly increased by loading. In trabecular bone, however, RG values were significantly increased by PTH administration. These findings suggest that LMHF loading and PTH can act locally and additively on the bone healing process, improving the condition of implant osseointegration.
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http://dx.doi.org/10.1038/s41368-018-0009-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5944597PMC
March 2018

A robust methodology for the quantitative assessment of the rat jawbone microstructure.

Int J Oral Sci 2017 06 16;9(2):87-94. Epub 2017 Jun 16.

Department of Oral Health Sciences &Dental Clinic, Biomaterials-BIOMAT, KU Leuven &University Hospitals Leuven, Leuven, Belgium.

Micro-computed tomography can be applied for the assessment of the micro-architectural characteristics of the cortical and trabecular bones in either physiological or disease conditions. However, reports often lack a detailed description of the methodological steps used to analyse these images, such as the volumes of interest, the algorithms used for image filtration, the approach used for image segmentation, and the bone parameters quantified, thereby making it difficult to compare or reproduce the studies. This study addresses this critical need and aims to provide standardized assessment and consistent parameter reporting related to quantitative jawbone image analysis. Various regions of the rat jawbones were screened for their potential for standardized micro-computed tomography analysis. Furthermore, the volumes of interest that were anticipated to be most susceptible to bone structural changes in response to experimental interventions were defined. In the mandible, two volumes of interest were selected, namely, the condyle and the trabecular bone surrounding the three molars. In the maxilla, the maxillary tuberosity region and the inter-radicular septum of the second molar were considered as volumes of interest. The presented protocol provides a standardized and reproducible methodology for the analysis of relevant jawbone volumes of interest and is intended to ensure global, accurate, and consistent reporting of its morphometry. Furthermore, the proposed methodology has potential, as a variety of rodent animal models would benefit from its implementation.
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http://dx.doi.org/10.1038/ijos.2017.11DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5518971PMC
June 2017

Controlled Clinical Trial on the Outcome of Glass Fiber Composite Cores Versus Wrought Posts and Cast Cores for the Restoration of Endodontically Treated Teeth: A 5-Year Follow-up Study.

Int J Prosthodont 2017 Jan/Feb;30(1):71-79

Purpose: The aim of this study was to compare the 5-year outcomes of glass fiber composite with cast posts and cores for the restoration of endodontically treated teeth.

Materials And Methods: A total of 143 patients in need of 203 full ceramic restorations on endodontically treated teeth were included. After primary stratification based on the need for post or no post, teeth were randomly allotted to test group 1 (prefabricated glass fiber posts), 2 (custom-made glass fiber posts), or 3 (composite cores without posts). The control group was treated with gold alloy-based wrought posts and cast cores. Success (original present) and survival (present after intervention) probability lifetime curves, corrected for clustering, were drawn over the entire data set.

Results: The mean follow-up time was 5.8 years (range: 0.5 to 7.2 years). At 5 years, the success and survival probabilities were 85.2% and 91.5%, respectively. Lifetime curves did not show any significant differences between the test and control groups for success (P = .85) or survival (P = .57). Moreover, no significant differences for success or survival could be found among the four groups (the three test groups and the control group).

Conclusion: After 5 years of follow-up, cast gold and composite post-and-core systems on teeth with ceramic full restorations provided with a ferrule performed equally well.
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http://dx.doi.org/10.11607/ijp.4861DOI Listing
March 2017

Residual compressive surface stress increases the bending strength of dental zirconia.

Dent Mater 2017 04 8;33(4):e147-e154. Epub 2017 Jan 8.

KU Leuven (University of Leuven), Department of Oral Health Sciences, BIOMAT & University Hospitals Leuven, Dentistry, Kapucijnenvoer 7, blok a bus 7001, B-3000 Leuven, Belgium. Electronic address:

Objective: To assess the influence of surface treatment and thermal annealing on the four-point bending strength of two ground dental zirconia grades.

Methods: Fully-sintered zirconia specimens (4.0×3.0×45.0mm) of Y-TZP zirconia (LAVA Plus, 3M ESPE) and Y-TZP/AlO zirconia (ZirTough, Kuraray Noritake) were subjected to four surface treatments: (1) 'GROUND': all surfaces were ground with a diamond-coated grinding wheel on a grinding machine; (2) 'GROUND+HEAT': (1) followed by annealing at 1100°C for 30min; (3) 'GROUND+AlO SANDBLASTED': (1) followed by sandblasting using AlO; (4) 'GROUND+CoJet SANDBLASTED': (1) followed by tribochemical silica (CoJet) sandblasting. Micro-Raman spectroscopy was used to assess the zirconia-phase composition and potentially induced residual stress. The four-point bending strength was measured using a universal material-testing machine.

Results: Weibull analysis revealed a substantially higher Weibull modulus and slightly higher characteristic strength for ZirTough (Kuraray Noritake) than for LAVA Plus (3M ESPE). For both zirconia grades, the 'GROUND' zirconia had the lowest Weibull modulus in combination with a high characteristic strength. Sandblasting hardly changed the bending strength but substantially increased the Weibull modulus of the ground zirconia, whereas a thermal treatment increased the Weibull modulus of both zirconia grades but resulted in a significantly lower bending strength. Micro-Raman analysis revealed a higher residual compressive surface stress that correlated with an increased bending strength.

Significance: Residual compressive surface stress increased the bending strength of dental zirconia. Thermal annealing substantially reduced the bending strength but increased the consistency (reliability) of 'GROUND' zirconia.
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http://dx.doi.org/10.1016/j.dental.2016.12.007DOI Listing
April 2017

Strength, toughness and aging stability of highly-translucent Y-TZP ceramics for dental restorations.

Dent Mater 2016 12 30;32(12):e327-e337. Epub 2016 Sep 30.

KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, Belgium.

Objective: The aim was to evaluate the optical properties, mechanical properties and aging stability of yttria-stabilized zirconia with different compositions, highlighting the influence of the alumina addition, YO content and LaO doping on the translucency.

Methods: Five different Y-TZP zirconia powders (3 commercially available and 2 experimentally modified) were sintered under the same conditions and characterized by X-ray diffraction with Rietveld analysis and scanning electron microscopy (SEM). Translucency (n=6/group) was measured with a color meter, allowing to calculate the translucency parameter (TP) and the contrast ratio (CR). Mechanical properties were appraised with four-point bending strength (n=10), single edge V-notched beam (SEVNB) fracture toughness (n=8) and Vickers hardness (n=10). The aging stability was evaluated by measuring the tetragonal to monoclinic transformation (n=3) after accelerated hydrothermal aging in steam at 134°C, and the transformation curves were fitted by the Mehl-Avrami-Johnson (MAJ) equation. Data were analyzed by one-way ANOVA, followed by Tukey's HSD test (α=0.05).

Results: Lowering the alumina content below 0.25wt.% avoided the formation of alumina particles and therefore increased the translucency of 3Y-TZP ceramics, but the hydrothermal aging stability was reduced. A higher yttria content (5mol%) introduced about 50% cubic zirconia phase and gave rise to the most translucent and aging-resistant Y-TZP ceramics, but the fracture toughness and strength were considerably sacrificed. 0.2mol% LaO doping of 3Y-TZP tailored the grain boundary chemistry and significantly improved the aging resistance and translucency. Although the translucency improvement by LaO doping was less effective than for introducing a substantial amount of cubic zirconia, this strategy was able to maintain the mechanical properties of typical 3Y-TZP ceramics.

Significance: Three different approaches were compared to improve the translucency of 3Y-TZP ceramics.
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http://dx.doi.org/10.1016/j.dental.2016.09.025DOI Listing
December 2016

Influence of Light Irradiation Through Zirconia on the Degree of Conversion of Composite Cements.

J Adhes Dent 2016 ;18(2):161-71

Purpose: To assess the light irradiance (LI) delivered by two light-curing units and to measure the degree of conversion (DC) of three composite cements and one flowable composite when cured through zirconia or ceramic-veneered zirconia plates with different thicknesses.

Materials And Methods: Three dual-curing composite cements (Clearfil Esthetic Cement, Panavia F2.0, G-CEM LinkAce) and one light-curing flowable composite (G-aenial Universal Flo) were investigated. Nine different kinds of zirconia plates were prepared from three zirconia grades (YSZ: Aadva and KATANA; Ce-TZP/Al2O3: NANOZR) in three different thicknesses (0.5- and 1.5-mm-thick zirconia, and 0.5-mm-thick zirconia veneered with a 1.0-mm-thick veneering ceramic). Portions of the mixed composite cements and the flowable composite were placed on a light spectrometer to measure LI while being light cured through the zirconia plates for 40 s using two light-curing units (n = 5). After light curing, micro-Raman spectra of the composite films were acquired to determine DC at 5 and 10 min, 1 and 24 h, and at 1 week.

Results: The zirconia grade and the thickness of the zirconia/veneered zirconia plates significantly decreased LI. Increased LI did not increase DC. Only the Ce-TZP/Al2O3 (NANOZR) zirconia was too opaque to allow sufficient light transmission and resulted in significantly lower DC.

Conclusion: Although zirconia-based restorations attenuate the LI of light-curing units, the composite cements and the flowable composite could be light cured through the YSZ zirconia. LI is too low through Ce-TZP/Al2O3 zirconia, necessitating the use of self-/dual-curing composite cements.
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http://dx.doi.org/10.3290/j.jad.a35842DOI Listing
July 2016

Bonding Effectiveness to Differently Sandblasted Dental Zirconia.

J Adhes Dent 2015 Jun;17(3):235-42

Purpose: To evaluate the effect of different mechanical pre-treatments on the bond durability to dental zirconia.

Materials And Methods: Fully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were randomly assigned to one of 4 groups: (1) kept as-sintered (control), (2) sandblasted with 50-μm Al₂O₃(Danville), or tribochemically silica sandblasted using (3) CoJet (3M ESPE) and (4) SilJet (Danville). The zirconia specimens were additionally pre-treated chemically using a 10-MDP/silane ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake). Two identically pre-treated zirconia blocks were bonded together using resin-composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass shape and stored in distilled water (7 days, 37°C), after which they were randomly tested as is or subjected to additional mechanical aging involving cyclic tensile stress (10 N, 10 Hz, 10,000 cycles). Subsequently, the microtensile bond strength was determined and SEM fractographic analysis performed.

Results: Weibull analysis revealed the highest Weibull scale and shape parameters when zirconia was tribochemically silica sandblasted using either CoJet or SilJet. The Weibull shape parameter of Al₂O₃-sandblasted zirconia was significantly reduced upon mechanical aging, but not when zirconia was tribochemically silica sandblasted.

Conclusion: The mechanical surface pre-treatment of zirconia using tribochemical silica sandblasting (CoJet, SilJet) resulted in the most favorable bond durability of a resin-composite cement (RelyX Ultimate) to dental zirconia before and after aging.
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http://dx.doi.org/10.3290/j.jad.a34401DOI Listing
June 2015

Accuracy and patient-centered outcome variables in guided implant surgery: a RCT comparing immediate with delayed loading.

Clin Oral Implants Res 2016 Apr 28;27(4):427-32. Epub 2015 Mar 28.

Department of Oral Health Sciences, Periodontology, Faculty of Medicine, Catholic University Leuven, University Hospitals Leuven, Leuven, Belgium.

Aim: To assess the accuracy and patient-centered outcome of a novel guided surgery system for placing implants in an edentulous maxilla.

Material And Methods: Fifteen consecutive patients with sufficient bone to place six implants in the maxilla were randomly assigned to the immediate loading (with delivery of the final prosthesis within 24 h) or the delayed loading treatment group. Accuracy was assessed by matching the planning CT with a postoperative CBCT. Patient-centered outcome measures were the Dutch version of the McGill Pain Questionnaire (MPQ-DLV), the health-related quality of life instrument (HRQOL), visual analog scales (VAS), the duration of the procedure, and the analgesic doses taken each day.

Results: A mean deviation was found at the entry point of 0.9 mm (range: 0.1-4.5, median 0.8) and of 1.2 mm (range: 0.2-4.9, median 1.1) at the apex, and an angular deviation of 2.7° (range: 0.0-6.6°, median 2.3) was observed. The mean vertical deviation was 0.5 mm (range: 0.0-3.2, median 0.4), and in a horizontal direction, this was 0.7 mm (range: 0.1-3.1, median 0.6). The mean deviation in mesio-distal direction was 0.5 mm (range: 0.0-2.3, median 0.4) and in bucco-lingual direction 0.5 mm ± 0.4 (range: 0.0-2.2, median 0.3). No statistical differences could be shown between treatment groups on pain response (MPQ-DLV), treatment perception (VAS), number or kind of pain killers, or for the HRQOLI instrument.

Conclusion: The accuracy of a novel CT-based guide is comparable to the accuracy data of other systems. Within the limitations of this study, no difference could be found in patient-centered outcome variables after immediate or delayed loading.
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http://dx.doi.org/10.1111/clr.12583DOI Listing
April 2016

A 5-Year Prospective Study on Cone-Anchored Implants in the Edentulous Maxilla.

Clin Implant Dent Relat Res 2015 Oct 26;17 Suppl 2:e621-32. Epub 2015 Feb 26.

Unit of Prosthetic Dentistry/BIOMAT Research Group, Department of Oral Health Sciences, KU Leuven, Leuven, Belgium.

Purpose: To investigate dentist- as well as patient-centered outcomes of the implant-supported cone-anchored removable prosthesis in the edentulous maxilla over 5 years.

Materials And Methods: Ten patients, edentulous in the maxilla, received six Ti implants after which they were delayed loaded through a cone-anchored removable prosthesis. Clinical parameters such as plaque and bleeding indices, PTV, implant success, marginal bone loss, device and prosthesis complications, and patient satisfaction (visual analogue scale) were collected at follow-up visits scheduled 1, 3, 6, 12, 24, 36, and 60 months postprosthesis delivery.

Results: After at least 5 years of follow-up (mean: 63.7 months), 53/59 implants were rated successful, while two of 59 failed and one implant was kept sleeping. Mean marginal bone loss from prosthesis delivery until 1, 3, and 5 years, respectively, was; 0.15 (SD: 0.87), 0.36 (SD: 1.07), and 0.60 mm (SD: 1.12). The mean Periotest® values at baseline and 5 years did not differ significantly. After 1 year, a significant improvement in patient satisfaction was recorded compared with the old denture, and this remained stable over the 5-year period.

Conclusions: Cone-anchored removable dental prostheses retained by secondary splinted implants offer a safe alternative for patients with an edentulous maxilla in need of more comfort. Dentist- as well as patient-centered outcomes compete with reports using other prosthetic anchoring devices. Larger replica studies are encouraged to further validate this concept.
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http://dx.doi.org/10.1111/cid.12295DOI Listing
October 2015

Digital versus conventional implant impressions for edentulous patients: accuracy outcomes.

Clin Oral Implants Res 2016 Apr 13;27(4):465-72. Epub 2015 Feb 13.

Prosthetics Section, Department of Oral health Sciences, Catholic University of Leuven, Leuven, Belgium.

Purpose: To compare the accuracy of digital and conventional impression techniques for completely edentulous patients and to determine the effect of different variables on the accuracy outcomes.

Materials And Methods: A stone cast of an edentulous mandible with five implants was fabricated to serve as master cast (control) for both implant- and abutment-level impressions. Digital impressions (n = 10) were taken with an intraoral optical scanner (TRIOS, 3shape, Denmark) after connecting polymer scan bodies. For the conventional polyether impressions of the master cast, a splinted and a non-splinted technique were used for implant-level and abutment-level impressions (4 cast groups, n = 10 each). Master casts and conventional impression casts were digitized with an extraoral high-resolution scanner (IScan D103i, Imetric, Courgenay, Switzerland) to obtain digital volumes. Standard tessellation language (STL) datasets from the five groups of digital and conventional impressions were superimposed with the STL dataset from the master cast to assess the 3D (global) deviations. To compare the master cast with digital and conventional impressions at the implant level, analysis of variance (ANOVA) and Scheffe's post hoc test was used, while Wilcoxon's rank-sum test was used for testing the difference between abutment-level conventional impressions.

Results: Significant 3D deviations (P < 0.001) were found between Group II (non-splinted, implant level) and control. No significant differences were found between Groups I (splinted, implant level), III (digital, implant level), IV (splinted, abutment level), and V (non-splinted, abutment level) compared with the control. Implant angulation up to 15° did not affect the 3D accuracy of implant impressions (P > 0.001).

Conclusion: Digital implant impressions are as accurate as conventional implant impressions. The splinted, implant-level impression technique is more accurate than the non-splinted one for completely edentulous patients, whereas there was no difference in the accuracy at the abutment level. The implant angulation up to 15° did not affect the accuracy of implant impressions.
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http://dx.doi.org/10.1111/clr.12567DOI Listing
April 2016

Highly-translucent, strong and aging-resistant 3Y-TZP ceramics for dental restoration by grain boundary segregation.

Acta Biomater 2015 Apr 4;16:215-22. Epub 2015 Feb 4.

Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg, 44, B-3001 Heverlee, Belgium.

Latest trends in dental restorative ceramics involve the development of full-contour 3Y-TZP ceramics which can avoid chipping of veneering porcelains. Among the challenges are the low translucency and the hydrothermal stability of 3Y-TZP ceramics. In this work, different trivalent oxides (Al2O3, Sc2O3, Nd2O3 and La2O3) were selected to dope 3Y-TZP ceramics. Results show that dopant segregation was a key factor to design hydrothermally stable and high-translucent 3Y-TZP ceramics and the cation dopant radius could be used as a controlling parameter. A large trivalent dopant, oversized as compared to Zr(4+), exhibiting strong segregation at the ZrO2 grain boundary was preferred. The introduction of 0.2 mol% La2O3 in conventional 0.1-0.25 wt.% Al2O3-doped 3Y-TZP resulted in an excellent combination of high translucency and superior hydrothermal stability, while retaining excellent mechanical properties.
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http://dx.doi.org/10.1016/j.actbio.2015.01.037DOI Listing
April 2015

Aging resistance of surface-treated dental zirconia.

Dent Mater 2015 Feb 5;31(2):182-94. Epub 2015 Jan 5.

Department of Materials Engineering, KU Leuven (University of Leuven), Kasteelpark Arenberg 44, B-3001 Heverlee, Belgium.

Unlabelled: The influence of surface treatment on the low-temperature degradation (LTD) of tetragonal zirconia polycrystalline (TZP) is still unclear.

Objectives: The effect of surface treatments on the LTD behavior of zirconia was investigated.

Methods: Fully-sintered specimens of seven commercial dental zirconia (Aadva, GC; In-CeramYZ, VITA; IPS e.max ZirCAD, Ivoclar Vivadent; LAVA Frame and LAVA Plus, 3M ESPE; NANOZR, Panasonic; ZirTough, Kuraray Noritake) were provided by the manufacturers with specimen dimensions of approximately 10mm×5mm×3mm. For each zirconia grade, samples were kept 'as sintered' (untreated) or were subjected to one of the three surface treatments: rough polished, sandblasted with Al2O3, tribochemical silica sandblasted (n=3/group). The tetragonal to monoclinic transformation was evaluated by X-ray diffraction at several intervals during LTD testing up to 40h in steam in an autoclave (134°C, 2bar).

Results: The five yttria-stabilized TZP (Y-TZP: Aadva, In-CeramYZ, IPS e.max ZirCAD, LAVA Frame, LAVA Plus) zirconia showed a similar trend in LTD behavior. The Al2O3 sandblasted zirconia showed the highest monoclinic volume fraction. The as sintered (untreated) zirconia degraded faster than the surface-treated zirconia. Although the surface-treated ceria-stabilized TZP/alumina (Ce-TZP/Al2O3: NANOZR) zirconia had a higher initial monoclinic volume fraction compared to the Y-TZP zirconia, it showed a stronger aging resistance. The as sintered (untreated) Y-TZP/alumina (Y-TZP/Al2O3: ZirTough) zirconia showed a strong aging resistance, whereas the surface-treated Y-TZP/Al2O3 zirconia degraded slightly.

Significance: Surface treatment improved the aging resistance of Y-TZP zirconia. Surface treatment did not affect the LTD behavior of Ce-TZP/Al2O3 zirconia, while surface treatment decreased the aging resistance of Y-TZP/Al2O3 zirconia.
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http://dx.doi.org/10.1016/j.dental.2014.11.018DOI Listing
February 2015

Stimulation of titanium implant osseointegration through high-frequency vibration loading is enhanced when applied at high acceleration.

Calcif Tissue Int 2014 Nov 11;95(5):467-75. Epub 2014 Sep 11.

BIOMAT KU Leuven, Department of Oral Health Sciences & Dental Clinic, KU Leuven & University Hospitals Leuven, Kapucijnenvoer 7, P.O. Box 7001, 3000, Leuven, Belgium.

Low-magnitude high-frequency loading, applied by means of whole body vibration (WBV), affects the bone. Deconstructing a WBV loading stimulus into its constituent elements and investigating the effects of frequency and acceleration individually on bone tissue kinetics around titanium implants were aimed for in this study. A titanium implant was inserted in the tibia of 120 rats. The rats were divided into 1 control group (no loading) and 5 test groups with low (L), medium (M) or high (H) frequency ranges and accelerations [12-30 Hz at 0.3×g (F(L)A(H)); 70-90 Hz at 0.075×g (F(M)A(M)); 70-90 Hz at 0.3×g (F(M)A(H)); 130-150 Hz at 0.043×g (F(H)A(L)); 130-150 Hz at 0.3×g (F H A H)]. WBV was applied for 1 or 4 weeks. Implant osseointegration was evaluated by quantitative histology (bone-to-implant contact (BIC) and peri-implant bone formation (BV/TV)). A 2-way ANOVA (duration of experimental period; loading mode) with α = 0.05 was performed. BIC significantly increased over time and under load (p < 0.0001). The highest BICs were found for loading regimes at high acceleration with medium or high frequency (F(M)A(H) and F(H)A(H)), and significantly differing from F(L)A(H) and F(M)A(M) (p < 0.02 and p < 0.005 respectively). BV/TV significantly decreased over time (p < 0.0001). Loading led to a site-specific BV/TV increase (p < 0.001). The highest BV/TV responses were found for F(M)A(H) and F(H)A(H), significantly differing from F(M)A(M) (p < 0.005). The findings reveal the potential of high-frequency vibration loading to accelerate and enhance implant osseointegration, in particular when applied at high acceleration. Such mechanical signals hold great, though untapped, potential to be used as non-pharmacologic treatment for improving implant osseointegration in compromised bone.
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http://dx.doi.org/10.1007/s00223-014-9896-xDOI Listing
November 2014

Implant- and patient-centred outcomes of guided surgery, a 1-year follow-up: An RCT comparing guided surgery with conventional implant placement.

J Clin Periodontol 2014 Dec 11;41(12):1154-60. Epub 2014 Oct 11.

Department of Oral Health Sciences, Periodontology, Faculty of Medicine, KU Leuven, University Hospitals Leuven, Campus Sint-Rafaël, Leuven, Belgium.

Aim: To assess, in a randomized study, the implant (clinical and radiological) and patient outcomes of guided implant placement at 1-year follow-up, compared to conventional implant treatment.

Material And Methods: A total of 314 were placed in 59 patients, randomly assigned to one of the treatment groups. Radiographic and clinical parameters were recorded at the time of implant placement, prosthesis instalment (baseline) and at 1-year follow-up. Patient satisfaction was measured with the oral health-related quality of life instrument (OHIP-49).

Results: No implants were lost. The mean marginal bone loss after the first year of loading was 0.04 mm (SD 0.34) for the guided surgery and 0.01 mm (SD 0.38) for the control groups. In the guided surgery groups, the mean number of surfaces with BOP and plaque at 1-year follow-up was 1.41 (SD 1.25) and 1.10 (SD 1.22), for the control groups this was, respectively, 1.37 (SD 1.25) and 1.77 (SD 1.64). The mean pocket probing depth was 2.81 mm (SD 1.1) for the guided, and 2.50 mm (SD 0.94) for the control groups. For all treatment groups, a significant improvement in quality of life was observed at 1-year follow-up (p ≤ 0.01), no differences between groups were observed.

Conclusion: Within the limitations of this study, no difference could be found at 1-year follow-up between the implant and patient outcome variables of guided or conventional implant treatment.
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http://dx.doi.org/10.1111/jcpe.12305DOI Listing
December 2014

Guided surgery: accuracy and efficacy.

Periodontol 2000 2014 Oct;66(1):228-46

Different computer-assisted implant-placement procedures are currently available. These differ in software, template manufacture, guiding device, stabilization and fixation. The literature seems to indicate that one has to accept a certain inaccuracy of ±2.0 mm, which seems large initially but is clearly smaller than for nonguided surgery. A reduction of accuracy to below 0.5 mm seems extremely difficult. A common shortcoming identified in the studies included in this review is inconsistency in how clinical data and outcome variables are reported. Another limitation is the small number of comparative clinical studies. In order to find the best guiding system or the most important parameters for optimal accuracy, more randomized clinical trials are necessary. Information on cost-effectiveness and patient-centered evaluations (i.e. questionnaires and interviews) must also be included.
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http://dx.doi.org/10.1111/prd.12046DOI Listing
October 2014

Influence of sintering conditions on low-temperature degradation of dental zirconia.

Dent Mater 2014 Jun 1;30(6):669-78. Epub 2014 Apr 1.

Department of Metallurgy and Materials Engineering (MTM), KU Leuven (University of Leuven), Kasteelpark Arenberg 44, B-3001 Heverlee (Leuven), Belgium. Electronic address:

Unlabelled: The effect of sintering conditions and concomitant microstructure of dental zirconia (ZrO2) ceramics on their low-temperature degradation (LTD) behavior remains unclear.

Objectives: Therefore, their effect on LTD of dental ZrO2 ceramics was investigated.

Methods: Three commercial pre-sintered yttria-stabilized dental zirconia materials were sintered at three temperatures (1450°C, 1550°C and 1650°C) applying three dwell times (1, 2 and 4h). Grain size measurements and LTD tests were performed on polished sample surfaces. LTD tests were performed at 134°C in an autoclave. The amount of monoclinic ZrO2 on the exposed surface was measured by X-ray diffraction (XRD).

Results: Higher sintering temperatures and elongated dwell times increased the ZrO2 grain size. Simultaneously, a larger fraction of zirconia grains adopted a cubic crystal structure, resulting in a decreased yttria content in the remaining tetragonal grains. Both the larger grain sizes and the lower average stabilizer content made the tetragonal grains more susceptible to LTD. Overall, independent on the commercial dental zirconia grade tested, the specimens sintered at 1450°C for 1h combined good mechanical properties with the best resistance to LTD.

Significance: In general, increased sintering temperatures and times result in a higher sensitivity to low-temperature degradation of Y-TZP ceramics.
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http://dx.doi.org/10.1016/j.dental.2014.03.005DOI Listing
June 2014

A randomized clinical trial comparing guided implant surgery (bone- or mucosa-supported) with mental navigation or the use of a pilot-drill template.

J Clin Periodontol 2014 Jul 10;41(7):717-23. Epub 2014 Apr 10.

Department of Periodontology, Faculty of Medicine, Catholic University Leuven, Leuven, Belgium.

Aim: To assess the accuracy of guided surgery (mucosa and bone-supported) compared to mental navigation or the use of a surgical template, in fully edentulous jaws, in a randomized controlled study.

Material And Methods: Fifty-nine patients (72 jaws), requiring four to six implants (maxilla or mandible), were consecutively recruited and randomly assigned to one of the following treatment groups; guidance via Materialise Universal(®)/mucosa, Materialise Universal(®)/bone, Facilitate™/mucosa, Facilitate™/bone, or mental navigation or a pilot-drill template. The precision was assessed by matching the planning computed tomography (CT) with a post-operative cone beam CT.

Results: A significant lower mean deviation at the entry point (1.4 mm, range: 0.3-3.7), at the apex (1.6 mm, range: 0.2-3.7) and angular deviation (3.0°, range: 0.2-16°) was observed for the guiding systems when compared to mental navigation (2.7 mm, range: 0.3-8.3; 2.9 mm, range: 0.5-7.4 and 9.9°, range: 1.5-27.8) and to the surgical template group (3.0 mm, range: 0.6-6.6; 3.4 mm, range: 0.3-7.5 and 8.4°, range: 0.6-21.3°). Differences between bone and mucosa support or type of guidance were negligible. Jaw and implant location (posterior-anterior, left-right), however, had a significant influence on the accuracy when guided.

Conclusion: Based on these findings, guided implant placement appears to offer clear accuracy benefits.
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http://dx.doi.org/10.1111/jcpe.12231DOI Listing
July 2014

Modified Titanium Surface-Mediated Effects on Human Bone Marrow Stromal Cell Response.

Materials (Basel) 2013 Nov 28;6(12):5533-5548. Epub 2013 Nov 28.

BIOMAT Research Cluster, Department of Oral Health Sciences and Prosthetic Dentistry, KU Leuven and University Hospitals Leuven, Kapucijnenvoer 7 box 7001, Leuven 3000, Belgium.

Surface modification of titanium implants is used to enhance osseointegration. The study objective was to evaluate five modified titanium surfaces in terms of cytocompatibility and pro-osteogenic/pro-angiogenic properties for human mesenchymal stromal cells: amorphous microporous silica (AMS), bone morphogenetic protein-2 immobilized on AMS (AMS + BMP), bio-active glass (BAG) and two titanium coatings with different porosity (T1; T2). Four surfaces served as controls: uncoated Ti (Ti), Ti functionalized with BMP-2 (Ti + BMP), Ti surface with a thickened titanium oxide layer (TiO₂) and a tissue culture polystyrene surface (TCPS). The proliferation of eGFP-fLuc (enhanced green fluorescence protein-firefly luciferase) transfected cells was tracked non-invasively by fluorescence microscopy and bio-luminescence imaging. The implant surface-mediated effects on cell differentiation potential was tracked by determination of osteogenic and angiogenic parameters [alkaline phosphatase (ALP); osteocalcin (OC); osteoprotegerin (OPG); vascular endothelial growth factor-A (VEGF-A)]. Unrestrained cell proliferation was observed on (un)functionalized Ti and AMS surfaces, whereas BAG and porous titanium coatings T1 and T2 did not support cell proliferation. An important pro-osteogenic and pro-angiogenic potential of the AMS + BMP surface was observed. In contrast, coating the Ti surface with BMP did not affect the osteogenic differentiation of the progenitor cells. A significantly slower BMP-2 release from AMS compared to Ti supports these findings. In the unfunctionalized state, Ti was found to be superior to AMS in terms of OPG and VEGF-A production. AMS is suggested to be a promising implant coating material for bioactive agents delivery.
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http://dx.doi.org/10.3390/ma6125533DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5452737PMC
November 2013

Dental Implant Macro-Design Features Can Impact the Dynamics of Osseointegration.

Clin Implant Dent Relat Res 2015 Aug 17;17(4):639-45. Epub 2013 Nov 17.

Department of Oral Health Sciences & BIOMAT Research Cluster, KU Leuven & University Hospitals Leuven, Prosthetic Dentistry, Leuven, Belgium.

Purpose: The purpose of this study was to compare the clinical performance of two dental implant types possessing a different macro-design in the in vivo pig model.

Materials And Methods: Titanium Aadva(TM) implants (GC, Tokyo, Japan) were compared with OsseoSpeed(TM) implants (Astra, Mölndal, Sweden), with the Aadva implant displaying significant larger inter-thread dimensions than the OsseoSpeed implant. Implants were installed in the parietal bone of 12 domestic pigs and left for healing for either 1 or 3 months. Implant osseointegration was evaluated by quantitative histology (bone volume relative to the tissue volume [BV/TV]; bone-to-implant contact [BIC]) for distinct implant regions (collar, body, total implant length) with specific implant thread features. The Wilcoxon-Mann-Whitney nonparametric test with α = 0.05 was performed.

Results: An inferior amount of bone enveloping the Aadva implant compared with the OsseoSpeed implant was observed, in particular at the implant body part with its considerable inter-thread gaps (p < .05). Concomitantly, the Aadva macro-design negatively affected the amount of bone in direct contact with the implant for this specific implant part (p < .05), and resulted in an overall impaired implant osseointegration at the initial healing stage (total implant length; 1-month healing; p < .05).

Conclusion: Although the Aadva implant displayed a clinically acceptable level of osseointegration, the findings demonstrate that implant macro-design features can impact the dynamics of implant osseointegration. Consideration of specific implant macro-design features should be made relative to the biological and mechanical microenvironment.
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http://dx.doi.org/10.1111/cid.12178DOI Listing
August 2015

In vitro and in vivo investigation of the potential of amorphous microporous silica as a protein delivery vehicle.

Biomed Res Int 2013 7;2013:306418. Epub 2013 Aug 7.

Department of Prosthetic Dentistry, BIOMAT Research Group, KU Leuven, Kapucijnenvoer 7, 3000 Leuven, Belgium.

Delivering growth factors (GFs) at bone/implant interface needs to be optimized to achieve faster osseointegration. Amorphous microporous silica (AMS) has a potential to be used as a carrier and delivery platform for GFs. In this work, adsorption (loading) and release (delivery) mechanism of a model protein, bovine serum albumin (BSA), from AMS was investigated in vitro as well as in vivo. In general, strong BSA adsorption to AMS was observed. The interaction was stronger at lower pH owing to favorable electrostatic interaction. In vitro evaluation of BSA release revealed a peculiar release profile, involving a burst release followed by a 6 h period without appreciable BSA release and a further slower release later. Experimental data supporting this observation are discussed. Apart from understanding protein/biomaterial (BSA/AMS) interaction, determination of in vivo protein release is an essential aspect of the evaluation of a protein delivery system. In this regard micropositron emission tomography (μ -PET) was used in an exploratory experiment to determine in vivo BSA release profile from AMS. Results suggest stronger in vivo retention of BSA when adsorbed on AMS. This study highlights the possible use of AMS as a controlled protein delivery platform which may facilitate osseointegration.
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http://dx.doi.org/10.1155/2013/306418DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3749544PMC
February 2014

Occlusal overload and bone/implant loss.

Clin Oral Implants Res 2012 Oct;23 Suppl 6:95-107

KU Leuven, Clinical Unit for Prosthetic Dentistry, BIOMAT KU Leuven, Department of Oral Health Sciences & Dental Clinics University Hospitals, KU Leuven (Catholic University of Leuven), Kapucijnenvoer 7 blok a bus 7001, BE, 3000, Leuven, Belgium.

Aim: The aim of this search was to assess the biological consequences that overload might have on already osseointegrated oral implants through a systematic screening of the scientific literature.

Method: Detailed searches through PUBMED, OVID, EMBASE and LILACS databases were made. Articles published up to December 2011 and those reported on the clinical, radiographic and/or histological outcome of oral implants subjected to so-called overload were considered eligible for inclusion. Identified studies were assessed by one non-blinded reviewer according to well-defined inclusion and exclusion criteria. When doubt arose, the co-authors were counselled until final agreement was obtained. The PICO questions formulated was:"what is the effect of overload vs. no overload on bone/implant loss in clinically stable implants?"

Results: The database searches as well as additional hand searching, resulted in 726 potentially relevant titles. Eventually, 16 clinical and 25 animal studies were considered relevant to the topic. After inclusion/exclusion criteria assessment, all clinical studies and all but three animal studies and one systematic review were considered at high risk of bias and excluded. The included animal studies did not reveal an association between overload and peri-implant bone loss in the absence of peri-implant inflammation, whereas in its presence, overload seemed to aggravate the peri-implant tissue breakdown.

Conclusions: The effect of implant overload on bone/implant loss in clinically well-integrated implants is poorly reported and provides little unbiased evidence to support a cause-and-effect relationship. The PICO question remained unanswered. At the animal level, "overload", mimicked by supra-occlusal contacts acting in an uninflamed peri-implant environment, did not negatively affect osseointegration and even was anabolic. In contrast, supra-occlusal contacts in the presence of inflammation significantly increased the plaque-induced bone resorption.
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http://dx.doi.org/10.1111/j.1600-0501.2012.02550.xDOI Listing
October 2012

Bone tissue response to implant surfaces functionalized with phosphate-containing polymers.

Clin Oral Implants Res 2014 Jan 8;25(1):91-100. Epub 2012 Oct 8.

Leuven BIOMAT Research Cluster, School of Dentistry, Oral Pathology and Maxillofacial Surgery, Catholic University of Leuven, Leuven, Belgium.

Objectives: Inorganic polyphosphates are said to stimulate the activity of osteoblast-like cells in vitro. The purpose of this study was to evaluate in vivo bone regeneration around implants treated with polyphosphoric acid (PPA) and phosphorylated pullulan (PPL).

Material And Methods: Two types of implants with different surface roughness (R1: Sa ≈ 0.23 μm; R2: Sa ≈ 1.35 μm) were treated with three solutions (distilled water, 10%wt PPA, or 10%wt PPL) prior to implantation in both tibia of twelve female white rabbits. Each animal received six implants randomly positioned according to their surface roughness and treatment: R1 + water; R1 + PPA; R1 + PPL; R2 + water; R2 + PPA; R2 + PPL. Animals were sacrificed after 1 or 4 weeks, and samples were prepared for histological and histomorphometrical analysis. Bone regeneration areas were evaluated for bone-to-implant contact (BIC) and bone fraction (BF) in areas 100 and 500 μm remote from the implant surface. Data were statistically analyzed by means of Friedman and Wilcoxon matched-pair tests (P < 0.05).

Results: After 1 week, bone tissue was rarely formed in the regeneration areas. After 4 weeks, implants treated with PPA presented higher ratios of BIC (R1 = 52.3 ± 13.1; R2 = 54.6 ± 11.0) than the ones treated with water (R1 = 24.1 ± 15.1; R2 = 32.4 ± 13.0). On the other hand, around the implant surface (100 μm), PPL-treated implants induced higher BF (R1 = 78.3 ± 34.1; R2 = 71.2 ± 21.8) as compared with the water-treated ones (R1 = 46.1 ± 22.0; R2 = 49.6 ± 21.0). At 500 μm, however, no statistically significant differences in BF were found among the groups evaluated (P > 0.05). Surface roughness influenced neither BIC nor BF.

Conclusions: Implant surface treatment with phosphate-containing polymers may positively influence osseointegration.
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http://dx.doi.org/10.1111/clr.12053DOI Listing
January 2014

Bone tissue response to BMP-2 adsorbed on amorphous microporous silica implants.

J Clin Periodontol 2012 Dec 8;39(12):1206-13. Epub 2012 Oct 8.

Department of Prosthetic Dentistry, BIOMAT Research Group, KU Leuven, Leuven, Belgium.

Aim: To evaluate bone regeneration potential of bone morphogenetic protein-2 (BMP-2) adsorbed on amorphous microporous silica (AMS).

Materials & Methods: Four implants [titanium as control (CTR); AMS-coated titanium (AMS), BMP-2 adsorbed on titanium (CTR+BMP) and AMS (AMS+BMP)] were implanted randomly in the tibiae of 20 New Zealand white rabbits. Bone specimens with implants were retrieved 2/4 weeks post implantation and analysed histologically and histomorphometrically. Bone fraction was measured in initial bone-free area (bone regeneration area, BRA) and in the area with initial bone-implant contact [bone adaptation area (BAA)] (BF(BRA) & BF(BAA) ). Bone-implant contact was measured in BRA (BIC(BRA) ). In vitro BMP-2 release profiles were determined to evaluate the impact of the carrier surface. Mixed models were used for statistical analysis.

Results: BMP-2 release profiles were different for CTR+BMP and AMS+BMP. BIC(BRA) and BF(BRA) were significantly increased after 4 weeks compared to 2 weeks for AMS, CTR+BMP and AMS+BMP. However, no differences between the implant types were observed within both healing periods. BF(BAA) for CTR+BMP was smaller than that for CTR and AMS+BMP after 4 weeks. Despite slower BMP-2 release, AMS+BMP did not stimulate bone regeneration. CTR+BMP caused bone resorption at the bone-implant interface.

Conclusions: BMP-2 functionalized implant surfaces failed to stimulate bone regeneration and osseointegration.
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http://dx.doi.org/10.1111/jcpe.12005DOI Listing
December 2012

Enhancement of implant osseointegration by high-frequency low-magnitude loading.

PLoS One 2012 10;7(7):e40488. Epub 2012 Jul 10.

Department of Prosthetic Dentistry, BIOMAT Research Cluster, University of Leuven, Leuven, Belgium.

Background: Mechanical loading is known to play an important role in bone remodelling. This study aimed to evaluate the effect of high- and low-frequency axial loading, applied directly to the implant, on peri-implant bone healing and implant osseointegration.

Methodology: Titanium implants were bilaterally installed in rat tibiae. For every animal, one implant was loaded (test) while the other one was not (control). The test implants were randomly divided into 8 groups according to 4 loading regimes and 2 experimental periods (1 and 4 weeks). The loaded implants were subject to an axial displacement. Within the high- (HF, 40 Hz) or low-frequency (LF, 8 Hz) loading category, the displacements varied 2-fold and were ranked as low- or high-magnitude (LM, HM), respectively. The strain rate amplitudes were kept constant between the two frequency groups. This resulted in the following 4 loading regimes: 1) HF-LM, 40 Hz-8 µm; 2) HF-HM, 40 Hz-16 µm; 3) LF-LM, 8 Hz-41 µm; 4) LF-HM, 8 Hz-82 µm. The tissue samples were processed for resin embedding and subjected to histological and histomorphometrical analyses. Data were analyzed statistically with the significance set at p<0.05.

Principal Findings: After loading for 4 weeks, HF-LM loading (40 Hz-8 µm) induced more bone-to-implant contact (BIC) at the level of the cortex compared to its unloaded control. No significant effect of the four loading regimes on the peri-implant bone fraction (BF) was found in the 2 experimental periods.

Conclusions: The stimulatory effect of immediate implant loading on bone-to-implant contact was only observed in case of high-frequency (40 Hz) low-magnitude (8 µm) loading. The applied load regimes failed to influence the peri-implant bone mass.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0040488PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3393711PMC
March 2013

Impaired osteoblastogenesis potential of progenitor cells in skeletal unloading is associated with alterations in angiogenic and energy metabolism profile.

Biomed Mater Eng 2012 ;22(4):219-26

Laboratory of Bioengineering and Biomechanics for Bone Articulation, Faculty of Medicine, University Paris Diderot, France.

Skeletal unloading provokes bone loss. These bone alterations have been shown to be associated with impairment of osteoblastic activity. In the present study, we evaluated the effect of skeletal unloading on bone marrow progenitor cells, for exploration of the underlying mechanism. Wistar rats were randomized to be either hindlimb unloaded for 9 days or to act as controls. Micro-CT was used to detect tibial trabecular architecture changes in response to skeletal unloading. Microgravity conditions for 9 days resulted in a decreased number and an increased spacing of the bone trabeculae in the proximal tibia. The proliferative capacity of the femoral bone marrow samples was assessed (fibroblast-colony-forming assay). By using qPCR, the expression of selected markers of vascularization (Vegfa; Hif1a; Angpt1), energy metabolism (Prkaa2; Mtor), bone formation (Runx2; Alp; Bglap; Bmp2; Bmp4; Bmp7) and bone resorption (Acp5; Tnfsf11; Tnfrsf11b) in these bone marrow suspensions was measured. We demonstrated a striking decrease in the number of fibroblastic progenitors in response to hindlimb unloading. This deficit in proliferation was shown to be accompanied by altered hindlimb perfusion and cellular energy homeostasis. Ex vivo culture assays of the bone marrow-derived progenitor cells screened for osteogenic (Runx2; Alp; Bglap) and adipogenic (Pparg; Fabp4) differentiation alterations in response to microgravity. Induced progenitor cells from unloaded rats showed a delay in osteogenic differentiation and impaired adipogenic differentiation compared to control. The data of this multi-level approach demonstrate that skeletal unloading significantly affects the bone tissue and its metabolism at the progenitor stage. The molecular expressions of the bone marrow population support a role of cellular metabolic stresses in skeletal alterations induced by inactivity.
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http://dx.doi.org/10.3233/BME-2012-0711DOI Listing
November 2012

In vivo assessment of the effect of controlled high- and low-frequency mechanical loading on peri-implant bone healing.

J R Soc Interface 2012 Jul 25;9(72):1697-704. Epub 2012 Jan 25.

Department of Prosthetic Dentistry, BIOMAT Research Cluster, Biomechanics Section, KU Leuven, Leuven, Belgium.

The aim of this study was to investigate the effect of controlled high- (HF) and low-frequency (LF) mechanical loading on peri-implant bone healing. Custom-made titanium implants were inserted in both tibiae of 69 adult Wistar rats. For every animal, one implant was loaded by compression through the axis of tibia (test), whereas the other one was unloaded (control). The test implants were randomly distributed among four groups receiving different loading regimes, which were determined by ex vivo calibration. Within the HF (40 Hz) or LF (2 Hz) loading category, the magnitudes were chosen as low- (LM) and high-magnitude (HM), respectively, leading to constant strain rate amplitudes for the two frequency groups. This resulted in the four loading regimes: (i) HF-LM (40 Hz-0.5 N); (ii) HF-HM (40 Hz-1 N); (iii) LF-LM (2 Hz-10 N); and (iv) LF-HM (2 Hz-20 N) loading. Loading was performed five times per week and lasted for one or four weeks. Tissue samples were processed for histology and histomorphometry (bone-to-implant contact, BIC; and peri-implant bone fraction, BF) at the cortical and medullar level. Data were analysed statistically with ANOVA and paired t-tests with the significance level set at 0.05. For the one-week experiments, an increased BF adjacent to the implant surface at the cortical level was exclusively induced by the LF-HM loading regime (2 Hz-20 N). Four weeks of loading resulted in a significant effect on BIC (and not on BF) in case of HF-LM loading (40 Hz-0.5 N) and LF-HM loading (2 Hz-20 N): BIC at the cortical level significantly increased under both loading regimes, whereas BIC at the medullar level was positively influenced only in case of HF-LM loading. Mechanical loading at both HF and LF affects osseointegration and peri-implant BF. Higher loading magnitudes (and accompanying elevated tissue strains) are required under LF loading to provoke a positive peri-implant bone response, compared with HF loading. A sustained period of loading at HF is needed to result in an overall enhanced osseointegration.
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http://dx.doi.org/10.1098/rsif.2011.0820DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3367822PMC
July 2012

Randomized controlled trial to compare two bone substitutes in the treatment of bony dehiscences.

Clin Implant Dent Relat Res 2013 Aug 11;15(4):558-68. Epub 2012 Jan 11.

Department of Periodontology, Faculty of Medicine, Catholic University Leuven, Leuven, Belgium.

Aim: This in vivo split-mouth randomized controlled trial compared a synthetic bone substitute with a bovine bone mineral to cover bone dehiscences after implant insertion.

Materials And Methods: Fourteen patients received four to six implants to support an overdenture. Two comparable dehiscences within the same patient were first covered with a layer of autogenous bone, followed by a layer of either Bio-Oss® (group 1; Geistlich Pharma AG, Wolhusen, Switzerland) or Straumann BoneCeramic® (group 2; Institut Straumann AG, Basel, Switzerland) and sealed by a resorbable membrane. The change in vertical dimension of the defect was measured at implant placement and at abutment connection (6.5 months). Clinical and radiological parameters were evaluated up to 1 year of loading.

Results: The vertical size of the defect at surgery was 6.4 ± 1.6 mm for group 1 and 6.4 ± 2.2 mm for group 2 sites, measured from the implant shoulder. After 6.5 months, the depth of the defect was reduced to 1.5 ± 1.2 mm and 1.9 ± 1.2 mm for group 1 and group 2 sites, respectively (p > 0.05). No implants failed during follow-up. Mean marginal bone loss over the SLActive surface was 0.94 mm (group 1), 0.81 mm (group 2), and 0.93 mm (group 3, no dehiscence) after 1 year of loading.

Conclusion: Both bone substitutes behaved equally effectively.
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http://dx.doi.org/10.1111/j.1708-8208.2011.00408.xDOI Listing
August 2013

Bone tissue response to porous and functionalized titanium and silica based coatings.

PLoS One 2011 15;6(9):e24186. Epub 2011 Sep 15.

Department of Prosthetic Dentistry, BIOMAT Research Group, K. U. Leuven, Leuven, Belgium.

Background: Topography and presence of bio-mimetic coatings are known to improve osseointegration. The objective of this study was to evaluate the bone regeneration potential of porous and osteogenic coatings.

Methodology: Six-implants [Control (CTR); porous titanium coatings (T1, T2); thickened titanium (Ti) dioxide layer (TiO(2)); Amorphous Microporous Silica (AMS) and Bio-active Glass (BAG)] were implanted randomly in tibiae of 20-New Zealand white rabbits. The animals were sacrificed after 2 or 4 weeks. The samples were analyzed histologically and histomorphometrically. In the initial bone-free areas (bone regeneration areas (BRAs)), the bone area fraction (BAF) was evaluated in the whole cavity (500 µm, BAF-500), in the implant vicinity (100 µm, BAF-100) and further away (100-500 µm, BAF-400) from the implant. Bone-to-implant contact (BIC-BAA) was measured in the areas where the implants were installed in contact to the host bone (bone adaptation areas (BAAs)) to understand and compare the bone adaptation. Mixed models were used for statistical analysis.

Principal Findings: After 2 weeks, the differences in BAF-500 for different surfaces were not significant (p>0.05). After 4 weeks, a higher BAF-500 was observed for BAG than CTR. BAF-100 for AMS was higher than BAG and BAF-400 for BAG was higher than CTR and AMS. For T1 and AMS, the bone regeneration was faster in the 100-µm compared to the 400-µm zone. BIC-BAA for AMS and BAG was lower after 4 than 2 weeks. After 4 weeks, BIC-BAA for BAG was lower than AMS and CTR.

Conclusions: BAG is highly osteogenic at a distance from the implant. The porous titanium coatings didn't stimulate bone regeneration but allowed bone growth into the pores. Although AMS didn't stimulate higher bone response, it has a potential of faster bone growth in the vicinity compared to further away from the surface. BIC-BAA data were inconclusive to understand the bone adaptation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0024186PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3174147PMC
April 2012