Ignace Naert

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.

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.

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 6h 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.

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.

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). 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). 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. Implant surface treatment with phosphate-containing polymers may positively influence osseointegration.

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 boneimplant contact [bone adaptation area (BAA)] (BFBRA & BFBAA). Boneimplant contact was measured in BRA (BICBRA). 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. BICBRA and BFBRA 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. BFBAA 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 boneimplant interface. Conclusions BMP-2 functionalized implant surfaces failed to stimulate bone regeneration and osseointegration.

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. 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. 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. 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.

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.

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.