Constant strain rate and peri-implant bone modeling: an in vivo longitudinal micro-CT analysis.

BACKGROUND: Strain, frequency, loading time, and strain rate, among others, determine mechanical parameters in osteogenic loading. We showed a significant osteogenic effect on bone mass (BM) by daily peri-implant loading at 1.600µÎµ.s(-1) after 4 weeks. PURPOSE: To study the peri-implant osteogenic effect of frequency and strain in the guinea pig tibia by in vivo longitudinal micro-computed tomography (CT) analysis. MATERIAL AND METHODS: One week after implant installation in both hind limb tibiae, one implant was loaded daily for 10' during 4 weeks, while the other served as control. Frequencies (3, 10, and 30Hz) and strains varied alike in the three series to keep the strain rate constant at 1.600µÎµ.s(-1) . In vivo micro-CT scans were taken of both tibiae: 1 week after implantation but before loading (v1) and after 2 (v2) and 4 weeks (v3) of loading as well as postmortem (pm). BM (BM (%) bone-occupied area fraction) was calculated as well as the difference between test and control sides (delta BM) RESULTS: All implants (n=78) were clinically stable at 4 weeks. Significant increase in BM was measured between v1 and v2 (p<.0001) and between v1 and v3 (p<.0001). A significant positive effect of loading on delta BM was observed in the distal peri-implant marrow 500 Region of Interest already 2 weeks after loading (p=.01) and was significantly larger (11%) in series 1 compared with series 2 (p=.006) and 3 (p=.016). CONCLUSIONS: Within the constraints of constant loading time and strain rate, the effect of early implant loading on the peri-implant bone is strongly dependent on strain and frequency. This cortical bone model has shown to be most sensitive for high force loading at low frequency.

In vivo molecular evidence of delayed titanium implant osseointegration in compromised bone.

Optimization of implant osseointegration in patients with reduced bone healing potential is a challenge remaining in implant dentistry. Identification of the genes that are modulated during implant osseointegration in normal versus osteopenic bone is needed to successfully address these pertinent clinical needs. The present study aimed to assess the initial and early molecular events following titanium implant installation in normal and compromised bone in a rat tibia model. Peri-implant tissue from a well-defined tissue regeneration compartment was analyzed at 2 and 7 days post-surgery for the expression of select markers of inflammation, angiogenesis, bone resorption and bone formation. Impaired bone was induced by hindlimb unloading and validated using µCT. The essential step of angiogenesis preceding bone regeneration was evidenced for the peri-implant setting in healthy bone. Compromised bone significantly affected the angiogenesis-osteogenesis coupling in the initial phase (2 days post-surgery), with altered expressions of Vegfa and Epas1 coinciding with downregulated expressions of Col1a1, Bmp2, Bmp4, Alpl and Bglap. At 7 days post-implantation, differences between normal and compromised peri-implant bone were no longer observed. This in vivo molecular evidence of delayed implant osseointegration in compromised bone reassert modern strategies in implant development, such as surface modifications and bioengineered approaches, to improve implant osseointegration in compromised conditions.

Effect of strain at low-frequency loading on peri-implant bone (re)modelling: a guinea-pig experimental study.

OBJECTIVES: To investigate whether controlled early loading enhances peri-implant bone mass and bone-to-implant contact. Low-frequency stimulation (3 Hz) and varying force amplitudes, causing varying strains, were applied in three guinea-pig series. MATERIAL AND METHODS: Three series of guinea-pigs received percutaneous TiO(2)-blasted implants in both tibiae. One week after implant installation, one implant was stimulated with a sinusoidally varying bending moment while the contra-lateral implant served as an unloaded control. Force amplitudes of 0.5, 1 and 2 N were applied on a 20-mm-long cantilever, resulting in strains of 133, 267 and 533 muepsilon, respectively, measured by a strain gauge bonded on the surface of the tibial bone at 1.3 mm from the implant's distal surface. Implant stability was followed by means of resonance frequency analysis. Bone-to-implant contact and bone mass [BM (%) bone occupied area fraction] were analysed histomorphometrically. RESULTS: A significant positive effect on the difference in bone mass at the stimulated vs. at the control side was observed in the distal half peri-implant marrow cavity for early mechanical stimulation at a frequency of 3 Hz (P<0.0001). An optimum was reached for the applied load, which causes a strain of approximately 267 muepsilon 1.3 mm from the implant. Implant stability gradually increased in time; no significant effect of early stimulation could be measured. CONCLUSIONS: The effect of early controlled mechanical stimulation on the peri-implant bone, in this cortical bone model, is strongly dependent on force amplitude/strain at low-frequency stimulation.

In vitro osteogenic potential of bone debris resulting from placement of titanium screw-type implants.

OBJECTIVES: Histological sections of preclinical animal studies have shown that new bone formation around dental implants frequently contains debris derived from the original bone. Whether such debris by itself is osteogenic, i.e., can influence the process of new bone formation after implant placement, is still unknown. We therefore aim to investigate if such debris does have osteogenic potential. MATERIAL AND METHODS: To substantiate our hypothesis, we performed an in vitro study in which titanium screws were placed into animal bone, and immediately removed. Without additional treatment these were placed into a cell culture medium provided with beta-glycerophosphate. We used Von Kossa staining and scanning electron microscopy to examine calcifications on the surface of the implants. Additionally, total DNA analysis, alkaline phosphates activity, and calcium content were assessed on the screw surface. RESULTS: Light and electron microscopy revealed the increasing presence of calcified matter on the implant surface. DNA amounts doubled from days 1 to 6, while alkaline phosphatase activity and calcium content showed a pronounced increase over the entire incubation time. None of these phenomena occurred on the control samples in the same medium. CONCLUSIONS: From these results, we proved that bone debris, which arises from dental implant placement, and which is moved along by the inherent roughness of the implant, by itself has osteogenic potential.

Immediate functional loading of single-tooth TIO2 grit-blasted implant restorations: a controlled prospective study in a porcine model. Part I: Clinical outcome.

BACKGROUND: Although favorable integration occurs with immediately loaded implants, the relationship between implant outcome, levels of occlusion, and diet requires optimization. PURPOSE: Pertubating load on single implant restorations immediately after placement by a hard food diet will increase the strains at the bone-implant interface, increasing the risk for failure. MATERIALS AND METHODS: Forty-eight implants replaced the first and third mandibular premolars in 12 pigs, allocated into two groups based on soft- and hard-diet feeding. Cylindrical and tapered implants replaced the first and third premolars, respectively. Each animal received at random four different masticatory loading conditions (group 1 control]: implant with either a cover screw or a healing abutment, and group 2 test]: implant with a crown either with or without occlusal contacts). RESULTS: Thirteen implants out of 44 failed in 11 animals (one with a cover screw, one with a healing abutment, three with nonocclusal, and eight with occlusal restorations). The failure rate of restored implants (either in occlusion or not) was significantly higher in the third premolar sites (p=.007), although diet had no significant effect (p=.421). CONCLUSIONS: While diet had no effect on the failure pattern of immediately loaded single implants, the position and type of load under the masticatory mode were significant. Immediately loaded implants both in and out of occlusion were less successful than the controls, and this is probably attributed to detrimental strain induced on the bone-implant interface.

Immediate functional loading of single-tooth TiO2 grit-blasted implant restoration. A controlled prospective study in a porcine model. Part II: Histology and histomorphometry.

BACKGROUND: Evidently, there is a fast-moving shift from delayed to immediate implant loading. The hypothesis to be tested was that bone reactions adjacent to single TiO2-microthreaded implants exposed to immediate masticatory loading for 10 weeks after placement would modulate osseointegration. MATERIALS AND METHODS: Cylindrical- and tapered-designed implants (Astra Tech AB, Mölndal, Sweden) replaced first and third mandibular premolars respectively in 12 pigs. The animals were allocated into two groups based on soft and hard diet feeding. Each animal received, at random positions, four different masticatory loading conditions: implant with either (1) a cover screw only, (2) a healing abutment, (3) an implant with a crown without occlusal contact, or (4) an implant with a crown in contact with the antagonistic teeth. RESULTS: Histomorphometry showed that there were no statistically significant differences in bone-implant contact (BIC), bone mass inside/outside of the threads and soft tissue ingrowth ratio for all the implants at 10 weeks after placement irrespective of masticatory loading condition. Bone loss showed a trend of progressive increase for implants with a healing abutment toward implants with occlusal contact. CONCLUSIONS: The results of this study rejected the hypothesis and could be explained by the fact that grit-blasted acid-etched implants were already placed in dense bone.

Effect of controlled early implant loading on bone healing and bone mass in guinea pigs, as assessed by micro-CT and histology.

Without controlled loading, the failure of early loaded oral implants is higher than in delayed loading, unless loading regimens can be identified that stimulate bone formation. The purpose of this study was to investigate whether controlled early loading optimizes osseointegration. Six series of guinea pigs received percutaneous implants in both tibiae. One implant was stimulated, the contra-lateral served as the control. The strain rate amplitude varied from 1,620 to 12,000 microstrain s(-1). In vivo microfocus computed tomography (micro-CT) was used to study the peri-implant bone at three time points: 1 wk after implantation, but before starting stimulation (V1); 2 wk after stimulation (V2); and 4 wk after stimulation, after the guinea pigs were killed (PM). Bone implant contact and bone mass [BM (%) bone occupied area fraction] were analyzed. The implant failure was 5.9% (six control/one test). Although bone implant contact did not significantly differ, bone mass in the distal half peri-implant marrow cavity was significantly higher around test implants. Strain rate amplitude and the difference in bone mass between test and control implants were inversely correlated. A strain rate amplitude of 1,620 microstrain s(-1) in the cortical bone at a distance of 1.3 mm from the implant showed the highest effect. Based on these results, early loading did not negatively affect the implant outcome. On the contrary, an improved bone reaction in the marrow cavity around early loaded implants was achieved.

Validation of microfocus computed tomography in the evaluation of bone implant specimens.

BACKGROUND: Microfocus computed tomography (muCT) is an emerging technique owing to its speed, full three-dimensional information, and nondestructive properties. PURPOSE: The aim of this study was to explore the efficacy of a muCT system (Philips HOMX 161, Philips Medical Systems GmbH, Hamburg, Germany) for visualization of the bone structure around screw-type titanium implants by comparing muCT images with their histologic homologues. MATERIALS AND METHODS: Eight screw-type titanium implants were placed in the femoral condyles of two goats. After the excised implant-bone specimens were embedded in resin, three-dimensional muCT of the excised implant and bone specimens was performed. Histologic sections were subsequently made. A total of 150 histologic sections were matched with muCT images. RESULTS: Bone trabeculae were clearly visible on the muCT scans. However, bone close to the implant or present in the apical surface features of the implant could not be detected. The overall matching between muCT scans (slices) and the histologic sections was 89%. CONCLUSION: Investigation of trabecular bone around titanium implants by muCT can be considered highly reliable for determining trabecular bone parameters, with the exception of measuring direct bone-to-implant contact.