Positive effect of early loading on implant stability in the bi-cortical guinea-pig model

Understanding the thrust force evolution and primary stability for dental implantation – An in-vitro experimental investigation

The dental implant is challenging due to the unstable quality of the surrounding bone. This study aimed to explore the feasibility of using thrust force characteristics to identify different bone types and the influencing mechanisms of spindle speed and feed rate on primary stability of dental implants through in-vitro experiments. 13 groups of osteotomy experiments were performed on mandibles and maxillae of pigs with different bone types (I, II, and III) under different spindle speeds (600 and 800 rpm) and feed rates (20 and 60 mm/min). The thrust force evolution under different conditions was extracted and analysed to elaborate the distribution and thickness of the cortical and trabecular bone layers on different bone types. Dental implant placements were performed, and corresponding primary stabilities were obtained. Furthermore, histologic observation was conducted to reveal the bone/implant contact morphology. From the results, the amplitude and trend of thrust force show a regular variation during drilling different bone types. The highly dynamic information of thrust force can be analysed to characterise the distribution and thickness of the cortical and trabecular bone layers, hence effectively detecting different bone types. Since a lower feed rate and resulting bone temperature elevation lead to more thermal damages, primary stability decreases with the decrease of feed rate. Spindle speed has no significant effect. This study establishes a more in-depth understanding into the thrust force evolution and also provide a clinical option for reducing the complexity of bone type and drilling parameters determination in osteotomy.

Development of Digital Twins to Optimize Trauma Surgery and Postoperative Management. A Case Study Focusing on Tibial Plateau Fracture

Background and context: Surgical procedures are evolving toward less invasive and more tailored approaches to consider the specific pathology, morphology, and life habits of a patient. However, these new surgical methods require thorough preoperative planning and an advanced understanding of biomechanical behaviors. In this sense, patient-specific modeling is developing in the form of digital twins to help personalized clinical decision-making.

Purpose: This study presents a patient-specific finite element model approach, focusing on tibial plateau fractures, to enhance biomechanical knowledge to optimize surgical trauma procedures and improve decision-making in postoperative management.

Study design: This is a level 5 study.

Methods: We used a postoperative 3D X-ray image of a patient who suffered from depression and separation of the lateral tibial plateau. The surgeon stabilized the fracture with polymethyl methacrylate cement injection and bi-cortical screw osteosynthesis. A digital twin of the patient’s fracture was created by segmentation. From the digital twin, four stabilization methods were modeled including two screw lengths, whether or not, to inject PMMA cement. The four stabilization methods were associated with three bone healing conditions resulting in twelve scenarios. Mechanical strength, stress distribution, interfragmentary strains, and fragment kinematics were assessed by applying the maximum load during gait. Repeated fracture risks were evaluated regarding to the volume of bone with stress above the local yield strength and regarding to the interfragmentary strains.

Results: Stress distribution analysis highlighted the mechanical contribution of cement injection and the favorable mechanical response of uni-cortical screw compared to bi-cortical screw. Evaluation of repeated fracture risks for this clinical case showed fracture instability for two of the twelve simulated scenarios.

Conclusion: This study presents a patient-specific finite element modeling workflow to assess the biomechanical behaviors associated with different stabilization methods of tibial plateau fractures. Strength and interfragmentary strains were evaluated to quantify the mechanical effects of surgical procedures. We evaluate repeated fracture risks and provide data for postoperative management.

A randomized clinical study to compare implant stability and bone loss using early loading protocol in two implant systems with different design

Aims

The study compared changes in implant stability and bone loss of implants with different designs using early loading at 6 weeks.

Setting and Design

In vivo-comparative study.

Materials and Methods

Forty subjects were selected and divided randomly by sealed envelope method in Group X and Group A for early loading for missing single posterior tooth in mandible. Implants in Group X had flared crest module and buttress thread design, whereas implants in Group A had parallel crest module and V-shaped thread design. All subjects were evaluated by Ostell for implant stability at the interval of baseline, 6 weeks, 3 months, and 6 months. ImageJ software was used for measurement of crestal bone loss in intraoral periapical radiographs at the interval of 6 weeks, 3 months, and 6 months.

Statistical Analysis Used

Unpaired t test, repeated ANOVA, Tukey post hoc test.

Results

The mean bone loss values of Group X at predetermined interval were 1.51 ± 0.20 mm, 2.11 ± 0.21 mm and 2.13 ± 0.21 mm. The mean bone loss values of Group A were 1.79 ± 0.16 mm, 2.92 ± 0.23 mm and 2.95 ± 0.23 mm. The mean bone loss was statistical significant (P < 0.05) at 6 weeks, 3 months and 6 months. It was highly significant in Group A at 6 months (P < 0.001).

Conclusions

It was concluded that Group X implants design showed better implant stability and less bone loss when compared to Group A implants design.

Influence of Nanotopography on Early Bone Healing during Controlled Implant Loading

Nanoscale surface modifications influence peri-implant cell fate decisions and implant loading generates local tissue deformation, both of which will invariably impact bone healing. The objective of this study is to determine how loading affects healing around implants with nanotopography. Implants with a nanoporous surface were placed in over-sized osteotomies in rat tibiae and held stable by a system that permits controlled loading. Three regimens were applied: (a) no loading, (b) one daily loading session with a force of 1.5N, and (c) two such daily sessions. At 7 days post implantation, animals were sacrificed for histomorphometric and DNA microarray analyses. Implants subjected to no loading or only one daily loading session achieved high bone-implant contact (BIC), bone-implant distance (BID) and bone formation area near the implant (BFAt) values, while those subjected to two daily loading sessions showed less BFAt and BIC and more BID. Gene expression profiles differed between all groups mainly in unidentified genes, and no modulation of genes associated with inflammatory pathways was detected. These results indicate that implants with nanotopography can achieve a high level of bone formation even under micromotion and limit the inflammatory response to the implant surface.

Influence of a Novel Surface of Bioactive Implants on Osseointegration: A Comparative and Histomorfometric Correlation and Implant Stability Study in Minipigs

Purpose: The objective of this study was to assess the influence of a novel surface of dental implants (ContacTi^®) on the osseointegration process in a minipig model. The surface was compared with other existing surfaces on the market (SLA^® and SLActive^®) by employing bone implant contact analysis (BIC) and implant stability. Method: Twelve minipigs were used with prior authorisation from an ethics committee. Three types of surfaces were tested: SLA^® (sand-blasted acid-etched titanium), SLActive^® (same but hydrophilic, performed under a nitrogen atmosphere), and ContacTi^® (alumina particle bombardment of titanium, bioactivated when treated thermochemically) in 4.1 mm × 8 mm implants with internal connection and a polished neck. Twelve implants of each surface type (N = 36) were placed, sacrificing 1/3 of the animals at 2 weeks of placement, 1/3 at 4 weeks and the remaining 1/3 at 8 weeks. Numerical variables were compared with Analysis of Variance, and the correlation between ISQ and BIC was established with the Spearman’s rank correlation coefficient. Results: SLActive^® and ContacTi^® surfaces showed elevated osteoconductivity at 4 weeks, maintaining a similar evolution at 8 weeks (large amount of mature lamellar tissue with high maturity and bone quality). The SLA^® surface showed slower maturation. The ISQ values in surgery were elevated (above 65), higher at necropsy and higher at 4 and 8 weeks in the SLA^® group than in the other two (SLActive^® and ContacTi^®). No significant correlation was found between ISQ and BIC for each implant surface and necropsy time. Conclusion: The three surfaces analysed showed high RFA and BIC values, which were more favourable for the SLActive^® and ContacTi^® surfaces. No statistical correlation was found between the RFA and BIC values in any of the three surfaces analysed.

Bone healing response in cyclically loaded implants: Comparing zero, one, and two loading sessions per day

When bone implants are loaded, they are inevitably subjected to displacement relative to bone. Such micro-motion generates stress/strain states at the interface that can cause beneficial or detrimental sequels. The objective of this study is to better understand the mechanobiology of bone healing at the tissue-implant interface during repeated loading. Machined screw shaped Ti implants were placed in rat tibiae in a hole slightly bigger than the implant diameter. Implants were held stable by a specially-designed bone plate that permits controlled loading. Three loading regimens were applied, (a) zero loading, (b) one daily loading session of 60 cycles with an axial force of 1.5 N/cycle for 7 days, and (c) two such daily sessions with the same axial force also for 7 days. Finite element analysis was used to characterize the mechanobiological conditions produced by the loading sessions. After 7 days, the implants with surrounding interfacial tissue were harvested and processed for histological, histomorphometric and DNA microarray analyses. Histomorphometric analyses revealed that the group subjected to repeated loading sessions exhibited a significant decrease in bone-implant contact and increase in bone-implant distance, as compared to unloaded implants and those subjected to only one loading session. Gene expression profiles differed during osseointegration between all groups mainly with respect to inflammatory and unidentified gene categories. The results indicate that increasing the daily cyclic loading of implants induces deleterious changes in the bone healing response, most likely due to the accumulation of tissue damage and associated inflammatory reaction at the bone-implant interface.

Time course of peri-implant bone regeneration around loaded and unloaded implants in a rat model

The time-course of cancellous bone regeneration surrounding mechanically loaded implants affects implant fixation, and is relevant to determining optimal rehabilitation protocols following orthopaedic surgeries. We investigated the influence of controlled mechanical loading of titanium-coated polyether-ether ketone (PEEK) implants on osseointegration using time-lapsed, non-invasive, in vivo micro-computed tomography (micro-CT) scans. Implants were inserted into proximal tibial metaphyses of both limbs of eight female Sprague-Dawley rats. External cyclic loading (60 or 100 μm displacement, 1 Hz, 60 s) was applied every other day for 14 days to one implant in each rat, while implants in contralateral limbs served as the unloaded controls. Hind limbs were imaged with high-resolution micro-CT (12.5 μm voxel size) at 2, 5, 9, and 12 days post-surgery. Trabecular changes over time were detected by 3D image registration allowing for measurements of bone-formation rate (BFR) and bone-resorption rate (BRR). At day 9, mean %BV/TV for loaded and unloaded limbs were 35.5 ± 10.0% and 37.2 ± 10.0%, respectively, and demonstrated significant increases in bone volume compared to day 2. BRR increased significantly after day 9. No significant differences between bone volumes, BFR, and BRR were detected due to implant loading. Although not reaching significance (p = 0.16), an average 119% increase in pull-out strength was measured in the loaded implants. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:997-1006, 2017.

Effect of the stiffness of bone substitutes on the biomechanical behaviour of femur for core decompression

Core decompression is the most common procedure for treatment of the early stages of osteonecrosis of the femoral head. The purpose of this study was to compare the biomechanical performance of four different bone graft substitutes combined with core decompression. Subject-specific finite element models generated from computed tomography (CT) scan data were used for a comprehensive analysis. Two different contact conditions were simulated representing states of osseointegration at the interface. Our results showed that the use of a low-stiffness bone substitute did not increase the risk of femoral fracture in the early postoperative phase, but resulted in less micromotion and interfacial stresses than high-stiffness bone substitutes.

Early loading of delayed versus immediately placed implants in the anterior mandible: A pilot comparative clinical study

STATEMENT OF PROBLEM

Numerous studies of the efficacy of immediately placed implants have been published but only a few of the comparative analyses of the early loading of delayed versus immediately placed dental implants.

PURPOSE

The purpose of this pilot prospective clinical study was to evaluate and compare the outcomes of early loaded delayed versus immediately placed implants.

MATERIAL AND METHODS

Eighty-eight participants satisfying predefined inclusion and exclusion criteria were selected for this pilot prospective study of 3 years' duration after obtaining institutional review board approval and informed consent. The immediate and the delayed implant placement group each consisted of 44 participants. The anterior mandible canine region was the implant placement site for all participants, and all implants were of the same size and manufacture. Participants were evaluated for hard (crestal bone loss and stability) and soft (periimplant probing depth) tissue implant success parameters at 6 and 12 months after implant placement. Data were analyzed, and results were computed.

RESULTS

Intergroup comparisons for mean mesial, mean distal, and mean crestal bone loss at 6 and 12 months after immediate and delayed implant placement showed statistically insignificant differences (P≥.05). Intergroup comparisons of mean mesial, mean distal, mean labial, and mean lingual and mean pocket depth at 6 and 12 months also showed statistically insignificant differences (P≥.05). Comparative mean values using the Periotest also demonstrated statistically insignificant differences (P≥.05).

CONCLUSIONS

The short-term outcomes of early loaded delayed and immediately placed implants were comparable. Therefore, early loaded immediately placed implants may be a promising option for the mandibular anterior region.

Progression of bone ingrowth and attachment strength for stability of percutaneous osseointegrated prostheses

BACKGROUND

Percutaneous osseointegrated prosthetic (POP) devices have been used clinically in Europe for decades. Unfortunately, their introduction into the United States has been delayed, in part due to the lack of data documenting the progression of osseointegration and mechanical stability.

QUESTIONS/PURPOSES

We determined the progression of bone ingrowth into porous-coated POP devices and established the interrelationship with mechanical stability.

METHODS

After amputation, 64 skeletally mature sheep received a custom porous-coated POP device and were then randomized into five time groups, with subsequent measurement of percentage of bone ingrowth into the available pore spaces (n = 32) and the mechanical pullout force (n = 32).

RESULTS

Postimplantation, there was an accelerated progression of bone ingrowth (~48% from 0 to 3 months) producing a mean pullout force of 5066 ± 1543 N. Subsequently, there was a slower but continued progression of bone ingrowth (~23% from 3 to 12 months) culminating with a mean pullout force of 13,485 ± 1855 N at 12 months postimplantation. There was a high linear correlation (R = 0.94) between the bone ingrowth and mechanical pullout stability.

CONCLUSIONS

This weightbearing model shows an accelerated progression of bone ingrowth into the porous coating; the amount of ingrowth observed at 3 months after surgery within the porous-coated POP devices was sufficient to generate mechanical stability.

CLINICAL RELEVANCE

The data document progression of bone ingrowth into porous-coated POP devices and establish a strong interrelationship between ingrowth and pullout strength. Further human data are needed to validate these findings.

Clinical study on survival rate of short implants placed in the posterior mandibular region: resonance frequency analysis

OBJECTIVE

Short implants are increasingly used, but there is doubt about their performance being similar to that of regular implants. The aim of this study was to compare the mechanical stability of short implants vs. regular implants placed in the edentulous posterior mandible.

MATERIAL AND METHODS

Twenty-three patients received a total of 48 short implants (5 × 5.5 mm and 5 × 7 mm) and 42 regular implants (4 × 10 mm and 4 × 11.5 mm) in the posterior mandible. Patients who received short implants had <10 mm of bone height measured from the bone crest to the outer wall of the mandibular canal. Resonance frequency analysis (RFA) was performed at time intervals T0 (immediately after implant placement), T1 (after 15 days), T2 (after 30 days), T3 (after 60 days), and T4 (after 90 days).

RESULTS

The survival rate after 90 days was 87.5% for the short implants and 100% for regular implants (P < 0.05). There was no significant difference between the implants in time intervals T1, T2, T3, and T4. In T0, the RFA values of 5 × 5.5 implants were higher than values of 5 × 7 and 4 × 11.5 implants (P < 0.05). A total of six short implants that were placed in four patients were lost (three of 5 × 5.5 mm and three of 5 × 7 mm). Three lost implants started with high ISQ values, which progressively decreased. The other three lost implants started with a slightly lower ISQ value, which rose and then began to fall.

CONCLUSIONS

Survival rate of short implants after 90 days was lower than that of regular implants. However, short implants may be considered a reasonable alternative for rehabilitation of severely resorbed mandibles with reduced height, to avoid performing bone reconstruction before implant placement. Patients need to be aware of the reduced survival rate compared with regular implants before implant placement to avoid disappointments.

Ultrastructural characterization of the implant interface response to loading

Dynamic loading can affect the bone surrounding implants. For ultrastructural exploration of the peri-implant tissue response to dynamic loading, titanium implants were installed in rat tibiae, in which one implant was loaded while the contralateral served as the unloaded control. The loaded implants received stimulation either within 24 hrs after implantation (immediate loading) or after a 28-day healing period (delayed loading) for 4, 7, 14, 21, or 28 days. The samples were processed for histology and gene expression quantification. Compared with the unloaded control, bone-to-implant contact increased significantly by immediate loading for 28 days (p < .05), but not in case of delayed loading. No effect of loading was observed on the bone formation in the implant thread areas, on the blood vessel area, and on endosteal callus formation. Loading during healing (immediate) for 7 days induced, relative to the unloaded control, a 2.3-fold increase of Runx2 in peri-implant cortical bone (p < .01) without a change in the RANKL/Opg ratio. Loading after healing (delayed) for 7 days up-regulated Runx2 (4.3-fold, p < .01) as well as Opg (22.3-fold, p < .05) compared with the unloaded control, resulting in a significantly decreased RANKL/Opg ratio. These results indicate a stimulating effect of dynamic loading on implant osseointegration when applied during the healing phase. In addition, gene expression analyses revealed molecular adaptations favoring bone formation and, at the same time, affecting bone remodeling.

Micromotion-induced strain fields influence early stages of repair at bone-implant interfaces

Implant loading can create micromotion at the bone-implant interface. The interfacial strain associated with implant micromotion could contribute to regulating the tissue healing response. Excessive micromotion can lead to fibrous encapsulation and implant loosening. Our objective was to characterize the influence of interfacial strain on bone regeneration around implants in mouse tibiae. A micromotion system was used to create strain under conditions of (1) no initial contact between implant and bone and (2) direct bone-implant contact. Pin- and screw-shaped implants were subjected to displacements of 150 or 300 μm for 60 cycles per day for 7 days. Pin-shaped implants placed in five animals were subjected to three sessions of 150 μm displacement per day, with 60 cycles per session. Control implants in both types of interfaces were stabilized throughout the healing period. Experimental strain analyses, microtomography, image-based displacement mapping, and finite element simulations were used to characterize interfacial strain fields. Calcified tissue sections were prepared and Goldner trichrome stained to evaluate the tissue reactions in higher and lower strain regions. In stable implants bone formation occurred consistently around the implants. In implants subjected to micromotion bone regeneration was disrupted in areas of high strain concentrations (e.g. >30%), whereas lower strain values were permissive of bone formation. Increasing implant displacement or number of cycles per day also changed the strain distribution and disturbed bone healing. These results indicate that not only implant micromotion but also the associated interfacial strain field contributes to regulating the interfacial mechanobiology at healing bone-implant interfaces.

Effect of decreased implant healing time on bone (re)modeling adjacent to plateaued implants under functional loading in a dog model

OBJECTIVES

The purpose of this study was to evaluate the effect of early functional loading to plateaued implants on bone formation and implant stability in a dog model.

MATERIALS AND METHODS

Early loading (EL), nonloading control, and delayed loading (DL) groups were compared using six beagle dogs under functional loading. The Periotest® values were measured dynamically for 6 weeks. Peri-implant bone architecture was evaluated qualitatively by microcomputed tomography (μCT) and analyzed quantitatively by mineral apposition rates (MAR), bone-to-implant contact (BIC), and bone volumes (BV/TV) after the euthanasia at 3 and 6 weeks after loading.

RESULTS

The EL implants showed poor stability at 1 week, but greater stability at 2 and 4 weeks after loading compared to DL implants. There was no significant difference between MAR of EL and unloaded implants at both time intervals. The EL implants displayed a significantly higher MAR when compared to DL implants at 3-5 weeks. A significantly higher BIC for the DL group was observed when compared to the EL group at 3 weeks following loading, however at 6 weeks; no significant difference between these groups was observed. The EL group gained a higher BIC than the no-treatment control group at 6 weeks.

CONCLUSIONS

For plateaued implant, the decreased healing time (1 week) displays a positive effect on peri-implant bone (re)modeling under functional loading during the early phase.

CLINICAL RELEVANCE

The early application of functional loading on plateaued implants can be used clinically to shorten the course of treatment and improve esthetics.

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

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.

Immediate semi-static loading using compression healing abutments: a stability study in dogs

Loading in implant dentistry to accelerate prosthodontic treatment has been receiving increasing interest. The aim of this study was to investigate the effect of an early controlled lateral loading (after 7 days) on the establishment of osseointegration by means of resonance frequency analysis. Two groups of six beagle dogs each were used. Group I had implants without loading. Group II had implants loaded with a new prototype compression abutment that created controlled semi-static loading. Loaded implants showed slightly better stability after 5 weeks of healing, but the difference was not significant. We concluded that controlled loading is beneficial to maintain, and even improve, stability during the early critical healing period.

Nanoscale surface modifications of medically relevant metals: state-of-the art and perspectives

Evidence that nanoscale surface properties stimulate and guide various molecular and biological processes at the implant/tissue interface is fostering a new trend in designing implantable metals. Cutting-edge expertise and techniques drawn from widely separated fields, such as nanotechnology, materials engineering and biology, have been advantageously exploited to nanoengineer surfaces in ways that control and direct these processes in predictable manners. In this review, we present and discuss the state-of-the-art of nanotechnology-based approaches currently adopted to modify the surface of metals used for orthopedic and dental applications, and also briefly consider their use in the cardiovascular field. The effects of nanoengineered surfaces on various in vitro molecular and cellular events are firstly discussed. This review also provides an overview of in vivo and clinical studies with nanostructured metallic implants, and addresses the potential influence of nanotopography on biomechanical events at interfaces. Ultimately, the objective of this work is to give the readership a comprehensive picture of the current advances, future developments and challenges in the application of the infinitesimally small to biomedical surface science. We believe that an integrated understanding of the in vitro and particularly of the in vivo behavior is mandatory for the proper exploitation of nanostructured implantable metals and, indeed, of all biomaterials.

Impact of implant number, distribution and prosthesis material on loading on implants supporting fixed prostheses

The purpose of this study is to evaluate axial forces and bending moments (BMs) on implants supporting a complete arch fixed implant supported prosthesis with respect to number and distribution of the implants and type of prosthesis material. Seven oral Brånemark implants with a diameter of 3.75 mm and a length of 13 and 7 mm (short distal implant) were placed in an edentulous composite mandible used as the experimental model. One all-acrylic, one fibre-reinforced acrylic, and one milled titanium framework prosthesis were made. A 50 N vertical load was applied on the extension 10 mm distal from the most posterior implant. Axial forces and BMs were measured by calculating signals from three strain gauges attached to each of the abutments. The load was measured using three different models with varying numbers of supporting implants (3, 4 and 5), three models with different implant distribution conditions (small, medium and large) and three models with different prosthesis materials (titanium, acrylic and fibre-reinforced acrylic). Maximum BMs were highest when prostheses were supported by three implants compared to four and five implants (P < 0.001). The BMs were significantly influenced by the implant distribution, in that the smallest distribution induced the highest BMs (P < 0.001). Maximum BMs were lowest with the titanium prosthesis (P < 0.01). The resultant forces on implants were significantly associated with the implant number and distribution and the prosthesis material.

Development and design of a novel loading device for the investigation of bone adaptation around immediately loaded dental implants using the reindeer antler as implant bed

The assessment of the behavior of immediately loaded dental implants using biomechanical methods is of particular importance. The primary goal of this investigation is to optimize the function of the implants to serve for immediate loading. Animal experiments on reindeer antlers as a novel animal model will serve for investigation of the bone remodeling processes in the implant bed. The main interest is directed towards the time and loading-dependant behavior of the antler tissue around the implants. The aim and scope of this work was to design an autonomous loading device that has the ability to load an inserted implant in the antler with predefined occlusal forces for predetermined time protocols. The mechanical part of the device can be attached to the antler and is capable of cyclically loading the implant with forces of up to 100 N. For the calibration and testing of the loading device a biomechanical measuring system has been used. The calibration curve shows a logarithmic relationship between force and motor current and is used to control the force on the implant. A first test on a cast reindeer antler was performed successfully.

Is insertion torque correlated to bone-implant contact percentage in the early healing period? A histological and histomorphometrical evaluation of 17 human-retrieved dental implants

OBJECTIVE

A precise and scientifically established method for the evaluation of the bone quality/primary stability is the measure of the insertion torque (IT). The aim of this study was a comparison between the IT values and the bone-implant contact percentage (BIC) of human implants retrieved after a 4/8-week healing period.

MATERIALS

Seventeen implants, all with a sandblasted and acid-etched surface, were evaluated in the present study.

METHODS

The implants had been retrieved for different causes, after 4/8 weeks, with a 5 mm trephine bur, and immersed in 10% buffered formalin to be processed for histology.

RESULTS

A not statistically significant correlation was found between IT and BIC (P<or=0.892).

CONCLUSIONS

In the present study on human-retrieved implants, no statistically significant correlation was found between the IT values and BIC. These results could be due to a lack of relationship between bone structure and IT, or to the fact that primary stability may not only be influenced by bone volumetrical density and/or bone trabecular connectivity but also by the thickness and density of the cortical layer. Moreover, the present knowledge of the bone microstructure is not enough to explain the relationship of bone quality and primary implant stability.

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.

Implant stability during osseointegration in irradiated and non-irradiated minipig alveolar bone: an experimental study

OBJECTIVES

Primary implant stability is related to local bone density. After insertion of an implant, implant stability is subject to changes due to bone remodeling. In patients who have undergone radiotherapy in the head and neck region, implant stability is impaired because irradiation reduces bone vitality. The current study was designed to monitor and test implant stability immediately after implant placement and during osseointegration in irradiated and non-irradiated minipig alveolar bone.

MATERIALS AND METHODS

All maxillary and mandibular premolars and molars of six adult Göttingen minipigs were extracted. The maxilla and mandible of three minipigs received three irradiation exposures at a total dose of 24 Gy. After irradiation, five initial implant holes were drilled in the residual alveolar ridge of each edentulous site. In order to assess bone vascularity, laser Doppler flowmetry recordings were carried out in the initial holes. A total of 120 implants were placed in the six minipigs. Subsequently, and at 8, 16, and 24 weeks after implant placement, implant stability was recorded by resonance frequency analysis (RFA). RFA values were expressed as an implant stability quotient (ISQ).

RESULTS

ISQ values recorded immediately after implant placement showed no differences between irradiated and non-irradiated minipigs. Repeated measurements at the four recording moments showed a decrease of ISQ values in all minipigs, being more pronounced in irradiated bone, when compared with non-irradiated bone. The results at the third and fourth recording moments showed a stabilization or even a slight increase of ISQ values.

CONCLUSIONS

The results document the negative effect of irradiation on bone vascularity and hence on implant stability.

Effect on the Amount of Bone-Implant Contact When Splinting Immediate-Loaded Dental Implants

PURPOSE

Much attention has been focused on the immediate or early loading of implants with or without splinting. The purpose of this study was to evaluate the contact rate between bones and implants, with or without splinting.

MATERIALS AND METHODS

Under general anesthesia, an 8-mm-deep cavity for a dental implant was drilled in the mandibular ridge of dogs where teeth had been extracted 4 months earlier. Rough-surfaced, cylindrical screw implants (International Team for Implantology [ITI] monotype implants 4 mm diameter and 8 mm long, Straumann, Basel, Switzerland) were placed with splinting on the right side and without splinting on the left side using gold abutment. Resin plates for the maxilla were adjusted to attach to the gold abutment in each mandible. At 4, 8, or 12 weeks after the implantation, specimens were stained using toluidine blue and fuchsin. The sections were observed and morphometric analysis was performed to measure the rates of bone-implant contact and new bone-implant contact.

RESULTS

The ratio of bone-implant contact on the lingual side was higher than on the buccal side in both the splinted and the unsplinted groups, and the rates in the splinted group were also higher than in the unsplinted group. The ratio of new bone-implant contact was not significantly different between the splinted and unsplinted groups, except for spongy bone at 4 weeks.

CONCLUSION

Splinting of immediate-loading dental implants can be adequate for osseointegration, particularly in spongy bone.

Histodynamics of bone tissue formation around immediately loaded cylindrical implants in the rabbit

OBJECTIVES

The local mechanical environment influences early peri-implant tissue formation. It is still unclear whether immediate loading limits or promotes peri-implant osteogenesis and which mechanical parameters are important herein. The present study evaluated the influence of well-controlled mechanical stimuli on the tissue response around immediately loaded cylindrical turned titanium implants at two different observation periods.

MATERIAL AND METHODS

A repeated sampling bone chamber, consisting of dual-structure perforated hollow cylinders with a cylindrical implant, was installed in the tibia of 14 rabbits and used to conduct three displacement-controlled immediate loading experiments: (i) 30 microm - 400 cycles/day - 1 Hz frequency - 2 x/week - 6 weeks; (ii) 30 microm - 400 cycles/day - 1 Hz - 2 x/week - 6 weeks, followed by another 6 weeks with a 50 microm - 800 cycles/day - 1 Hz - 2 x/week loading protocol; and (iii) 0 microm implant displacement for 12 weeks. A linear mixed model and logistic mixed model with alpha=5% were conducted on the data set.

RESULTS

The tissue area fraction was significantly the highest after 12 weeks of loading. The bone area fraction was significantly different between all three loading conditions, with the highest values for the 12-week loading experiment. Twelve-week stimulation resulted in a significantly higher mineralized bone fraction than 6 weeks. Loading did have a significantly positive effect on the mineralized bone fraction. The incidence of osteoid-to-implant and bone-to-implant contact increased significantly when loading the implant for 12 weeks.

CONCLUSION

Immediate loading had a positive effect on the tissue differentiation and bone formation around cylindrical turned titanium implants. Controlled implant micro-motion up to 50 microm had a positive effect on the bone formation at its interface.

Micro-morphologic changes around biophysically-stimulated titanium implants in ovariectomized rats

Background

Osteoporosis may present a risk factor in achievement of osseointegration because of its impact on bone remodeling properties of skeletal phsiology. The purpose of this study was to evaluate micro-morphological changes in bone around titanium implants exposed to mechanical and electrical-energy in osteoporotic rats.

Methods

Fifteen 12-week old sprague-dowley rats were ovariectomized to develop osteoporosis. After 8 weeks of healing period, two titanium implants were bilaterally placed in the proximal metaphyses of tibia. The animals were randomly divided into a control group and biophysically-stimulated two test groups with five animals in each group. In the first test group, a pulsed electromagnetic field (PEMF) stimulation was administrated at a 0.2 mT 4 h/day, whereas the second group received low-magnitude high-frequency mechanical vibration (MECHVIB) at 50 Hz 14 min/day. Following completion of two week treatment period, all animals were sacrificed. Bone sites including implants were sectioned, removed en bloc and analyzed using a microCT unit. Relative bone volume and bone micro-structural parameters were evaluated for 144 μm wide peri-implant volume of interest (VOI).

Results

Mean relative bone volume in the peri-implant VOI around implants PEMF and MECHVIB was significantly higher than of those in control (P < .05). Differences in trabecular-thickness and -separation around implants in all groups were similar (P > .05) while the difference in trabecular-number among test and control groups was significant in all VOIs (P < .05).

Conclusion

Biophysical stimulation remarkably enhances bone volume around titanium implants placed in osteoporotic rats. Low-magnitude high-frequency MECHVIB is more effective than PEMF on bone healing in terms of relative bone volume.

Osseointegration Timing for Baha System Loading

OBJECTIVES

The process of osseointegration for creating a biological bond between titanium oxide and bone is time dependent. However, different surgeons have used very varied time frames before loading the implant. The waiting time in dental implant loading ranged from immediate to 6 months. The Baha system (Cochlear Limited, Englewood, CO) traditional waiting period consisted of 3 months for adults and 4 to 6 months for children. The purpose of the study was to evaluate the safety of reducing the waiting time to 6 weeks in adults.

STUDY DESIGN

Retrospective study of patients who underwent Baha implantation and exteriorization between March, 2004 and July 2005.

METHODS

Twenty-six adult patients underwent Baha titanium implantation and exteriorization in a single stage. They were loaded with the external processor after an average of 6.5 weeks. The etiology of their hearing loss (HL) included conductive HL, mixed HL, and unilateral sensorineural HL. Follow-up period ranged between 6 and 20 months.

RESULTS

All patients were successfully implanted with the titanium implants, loaded at the 6 week interval, and have safely retained their prosthesis. The only reported complication was dermatitis, which occurred in three patients. Patients were pleased to receive the external processor earlier.

CONCLUSION

The reduction of the waiting period from 3 months to 6 weeks did not result in any failure of osseointegration of the titanium implants. The earlier activation resulted in enhanced patient satisfaction. A larger series would be needed to definitively recommend shortening of the interval between Baha implantation and device loading.

Resonance frequency analysis of implants in the guinea pig model: Influence of boundary conditions and orientation of the transducer

The goal of this study was to identify the parameters that must be controlled during in vivo resonance frequency measurements with a custom Osstell transducer for custom implants in the guinea pig animal model. A numerical study and in vitro measurements were performed to determine the influence of the boundary conditions as well as the transducer orientation on the resonance frequency measured by the custom Osstell transducer. In the reported guinea pig model, the type of boundary condition, the orientation of the transducer (parallel or perpendicular to the long axis of the bone) and the length of the modelled bone have a large influence on the resonance frequency values. This implies that a follow-up in time of the stability of an implant requires the boundary conditions applied to the bone in which the implant is installed as well as the orientation of the transducer to be highly repeatable. Applying controlled boundary conditions during in vivo measurements had a highly positive influence on the repeatability of the Osstell measurements. This improves the possibility of the technique to measure changes in the implant-bone interface during healing of the implant.