Impact of vertical loading on the implant-bone interface.

OBJECTIVES: The main aim of this study was to evaluate the impact of vertical loading occurring during removal of cemented restorations on the implant-bone interface. METHODS: Thirty-six titanium implants (Camlog 4.3 × 9 mm) were placed 1 mm supraosseous in the frontal skull of four minipigs. After a 13 week healing period the implants were exposed and the implant stability was measured. Three implants per minipig were vertically loaded using 20 or 100 impulses, respectively with an 18 Ns impulse imitating a crown removal. Three implants were left unloaded as control. The animals were sacrificed after 13 or 18 weeks. The harvested specimens were analyzed using scanning electron microscopy (SEM), light and fluorescence microscopy. RESULTS: No post operative complications or deaths of the minipigs occurred. All implants osseointegrated. The average bone-implant contact area (BIC) was 78 ± 5.1%. No statistically significant difference could be found when comparing the BIC areas of the control and the experimental groups between the sacrificed animals at 13 weeks and 18 weeks (P > 0.05). Therefore, the results of each subgroup were pooled. No significant differences regarding the BIC area could be detected between the control and the experimental groups (P > 0.05). Except one failing implant no cracks due to vertical loading could be evaluated in the SEM. Fluorescence microscopy revealed a significantly higher bone remodeling activity in the vertically loaded groups. CONCLUSIONS: Removal of cemented implant restorations seems not to have an impact on the mechanical implant stability, but seems to increase bone remodeling activity.

Periodontal regeneration employing gingival margin-derived stem/progenitor cells: an animal study.

AIM: This study investigated the periodontal regenerative potential of gingival margin-derived multipotent postnatal stem/progenitor cells. MATERIAL AND METHODS: Periodontal defects were induced at six sites in eight miniature pigs in the premolar/molar area (-4 weeks). Autologous cells isolated from the gingival margin were magnetically sorted using STRO-1 antibodies and characterized flow cytometrically for the expression of CD14, CD31, CD34, CD45, CD117 and STRO-1 surface markers. Colony formation and multilineage differentiation potential were tested. The cells were expanded and loaded on deproteinized bovine cancellous bone (DBCB) and Collagen scaffolds. Within every miniature pig, six periodontal defects were randomly treated with loaded-DBCB (test group 1), unloaded-DBCB (control group 1), loaded-Collagen scaffolds (test group 2), unloaded-Collagen scaffolds (control group 1), scaling and root planing (negative control 1) or left untreated (negative control 2). Differences in clinical attachment level (ΔCAL), probing depth (ΔPD), gingival recession (ΔGR) and radiographic defect volume (ΔRDV) between baseline and 12 weeks, as well as histological attachment level (HAL), junctional epithelium length (JE) and connective tissue adhesion (CTA) after 12 weeks were evaluated. RESULTS: Isolated cells showed stem/progenitor cell characteristics. Cell-loaded scaffolds showed higher ΔCAL, ΔPD, ΔGR, HAL and lower JE and CTA compared with unloaded scaffolds and negative controls. The sort of scaffold had no significant influence on the measured outcomes. CONCLUSION: Gingival margin-derived stem/progenitor cells show significant periodontal regenerative potential.

Impairment of pericardial leaflet structure from balloon-expanded valved stents.

OBJECTIVE: Malpositioning is one of the major problems in transcatheter aortic valve implantation. To evaluate the influence of mechanical balloon inflation on aortic valve stent positioning, the expansion process and the impact on the valve leaflet's structure were investigated. METHODS: Custom-made stents were laser cut from a 22-mm diameter stainless steel tube and mounted with a glutaraldehyde-treated bovine pericardial valve. The valved stents were crimped onto a standard balloon catheter and expanded by inflation of the balloon with 2 bar for 3 seconds. Expansion was studied using a high-speed camera, and the histology of the pericardial tissue was analyzed. RESULTS: The valved stents were fully expanded within 3 seconds. Balloon inflation was observed to be asymmetric starting proximally. At the beginning of expansion, the valved stents were pulled proximally. During further inflation, the stents slipped distally on the balloon and experienced a total displacement of 13.5 mm. Macroscopic examination showed severe imprinting of the stent struts into the pericardial tissue. Histology revealed disrupted tissue layers and collagen fibers. CONCLUSIONS: Analysis of valved stent expansion showed a displacement of the stent on the catheter during balloon inflation. Therefore, precise placement of the valved stent cannot be accomplished. Histologic analysis of the expanded pericardial tissue revealed disruption of collagen fibers. Disruption of pericardial tissue structures due to balloon expansion may result in early functional valve failure.

A pilot study: microbiological conditions of the oral cavity in minipigs for peri-implantitis models.

As peri-implantitis is an emerging problem, the development of validated animal models is mandatory. The aim of this pilot study was to provide a first step in describing the normal oral flora of minipigs. In five minipigs, samples of the oral flora were collected with sterile cotton swabs from the buccal gingiva of the lower jaw. Two swabs per animal were collected, followed by bacterial isolation under both aerobe and anaerobe conditions. Microbiological analyses included biochemical tests, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 16S rDNA gene sequence analysis. A total of 61 taxa were detected, 14-21 different bacterial taxa from each minipig. Among the Gram-positive cocci, mainly staphylococcal and streptococcal species were identified. Different Actinomyces species were the most abundant taxa in the group of Gram-positive rods. Among the anaerobic bacteria, the Gram-negative genera Fusobacterium, Bacteroides and Prevotella were the most often observed taxa. This is the first study which begins to describe the normal oral flora in minipigs in cultures to allow for the detection of a broad spectrum. Several bacterial species identified are different from human ones. No specific species for peri-implantitis could be detected in that healthy sample.

Percutaneous pulmonary polyurethane valved stent implantation.

OBJECTIVES: Transfemoral application of pulmonary heart valves has been studied for the past 10 years. Nevertheless, size restriction of percutaneous heart valved stents is still imminent. METHODS: In this study we implanted percutaneously a novel, low-profile polyurethane valved stent. Percutaneous implantation in pulmonary position was evaluated in 7 sheep. The new valved stent fits into a 14F delivery device. The self-expanding nitinol stent was produced by using a dip-coating technique, and a modified commercially available endovascular stent graft system served as a delivery device. The valved stents were deployed directly over the native pulmonary valve under fluoroscopic control. Transthoracic echocardiography was performed after 4 weeks. At the time of explantation, the animals were reanalyzed and killed. Angiography was performed at implantation and at the end of the study. Explanted constructs were analyzed macroscopically and microscopically. RESULTS: Angiography and echocardiography in all animals demonstrated orthotopic position of the stents at the time of implantation and after 4 weeks. During the deployment procedure, rhythm disturbances occurred in all animals. The peak-to-peak transvalvular gradient was 2.3 +/- 1.2 mm Hg initially and 4.1 +/- 2.4 mm Hg at follow-up. One-month follow-up confirmed competent neovalves without any paravalvular leakage. Gross morphology demonstrated good opening and closure characteristics. No calcification was seen macroscopically, and surrounding tissue was free of calcification. CONCLUSION: In the present study we demonstrated successful merging of 2 novel technologies for percutaneous treatment of pulmonary valve diseases using polyurethane stent valve constructs.