Stefan Tangl

In vivo degradation performance of micro-arc-oxidized magnesium implants: A micro-CT study in rats

Biodegradable Mg alloys are of great interest for osteosynthetic applications because they do not require surgical removal after they have served their purpose. In this study, fast-degrading ZX50 Mg-based implants were surface-treated by micro-arc oxidation (MAO), to alter the initial degradation, and implanted along with untreated ZX50 controls in the femoral legs of 20 male Sprague-Dawley rats. Their degradation was monitored by microfocus computed tomography (μCT) over a total observation period of 24weeks, and histological analysis was performed after 4, 12 and 24weeks. While the MAO-treated samples showed almost no corrosion in the first week, they revealed an accelerated degradation rate after the third week, even faster than that of the untreated ZX50 implants. This increase in degradation rate can be explained by an increase in the surface-area-to-volume ratio of MAO-treated implants, which degrade inhomogeneously via localized corrosion attacks. The histological analyses show that the initially improved corrosion resistance of the MAO implants has a positive effect on bone and tissue response: The reduced hydrogen evolution (due to reduced corrosion) makes possible increased osteoblast apposition from the very beginning, thus generating a stable bone-implant interface. As such, MAO treatment appears to be very interesting for osteosynthetic implant applications, as it delays implant degradation immediately after implantation, enhances fracture stabilization, minimizes the burden on the postoperatively irritated surrounding tissue and generates good bone-implant connections, followed by accelerated degradation in the later stage of bone healing.

Effects of Choukroun’s platelet-rich fibrin on bone regeneration in combination with deproteinized bovine bone mineral in maxillary sinus augmentation: A histological and histomorphometric study

PURPOSE The potential effect of Choukrouns platelet-rich fibrin (PRF) in combination with allograft on promoting bone regeneration has been discussed in previous publications. This study aims to evaluate an influence of PRF on bone regeneration in sinus augmentation in combination with a xenograft, deproteinised bovine bone. MATERIALS AND METHODS Eleven sinuses from 10 patients with posterior maxillary bone atrophy were selected for the study. As a test group, six sinus floor elevations were grafted with a Bio-Oss and PRF mixture, and as control group, five sinuses were treated with Bio-Oss alone. Clinical and radiographic examinations were performed pre- and postoperatively. After 6 months of sinus augmentation, bone biopsies were obtained from the grafted posterior maxilla, and un-decalcified ground sections were prepared. Bone characteristics were evaluated using histological observation and histomorphometric analyses. RESULTS No adverse effect was observed in any case within the follow-up period of 6 months after sinus augmentation. Histological observation showed similar morphological characteristics for both the PRF and control groups. The percentage of new bone formation in the PRF group was about 1.4 times of that in control (18.35%±5.62% vs. 12.95%±5.33%), while the percentage of residual bone substitute in the control group was about 1.5 times higher as that in the PRF group (28.54%±12.01% vs. 19.16%±6.89%). The percentage of contact length between newly formed bone and bone substitute in the PRF group was 21.45%±14.57% vs. 18.57%±5.39% in the control. No significant statistical differences between the two groups were found in these observed parameters. CONCLUSIONS Our preliminary result demonstrated neither an advantage nor disadvantage of the application of PRF in combination with deproteinised bovine bone mineral in sinus augmentation after a healing period of 6 months.

The effect of BMP-2 on the osteoconductive properties of β-tricalcium phosphate in rat calvaria defects

Bone formation in critical-sized calvaria defects is strongly dependent on the osteoconductive properties of grafts. It remains a matter of controversy whether biomaterials can replace autografts and whether the supplementation of biomaterials with Bone Morphogenetic Proteins (BMPs) is necessary to enhance bone formation. We examined rat calvaria critical-sized defects (5-mm-diameter) treated with β-tricalcium phosphate (TCP; Cerasorb® M), polylactic and polyglycolic acid gel (PLA/PGA; Fisiograft®) and calcium phosphate cement (CPC; Norian® CRS®), either alone or in the presence of 5 μg of BMP-2 after 45 days. Autografts and untreated defects served as controls. Bone formation was evaluated based on μCT analysis, histomorphometric analysis and fluorescence analysis. We report that TCP supported bone formation more efficiently than did autografts. Bone formation in the presence of TCP alone reached a maximal level, as BMP-2 supplementation failed to enhance bone formation. By contrast, no significant difference in bone formation was observed when PLA/PGA and CPC were compared to autografts. Moreover, the presence of BMP-2 did not substantially change the osteoconductive properties of PLA/PGA or CPC. We conclude that the osteoconductive properties of TCP are superior to those of autografts and that TCP does not require BMP-2 supplementation. Our findings also show that the decreased osteoconductive properties of PLA/PGA and CPC cannot be overcome by BMP-2 supplementation in rat calvaria defects.

Comparison of the validity of three dental methods for the estimation of age at death

The aim of the present study was to compare the accuracy, precision, and bias of two macroscopic and one histological age at death estimation methods on human teeth. The sample was comprised of 67 permanent teeth, obtained from 37 individuals aged 20-91 years. Age was predicted according to the methods proposed by Lamendin et al. (LAM), Bang and Ramm (BR), and the quantification of tooth cementum annulations (TCA). TCA was found to be most accurate in all age groups. Its mean absolute error of the estimated age was about half as high as the mean absolute error for both LAM and BR. BR achieved approximately the same mean absolute error as TCA for old adults only. LAM displayed the highest precision in the young and the old age group whereas TCA was more precise in the middle age group. TCA was found to be the most precise method when the precision was calculated for all ages. Considering the bias, all methods displayed a tendency to overestimate age in young and to underestimate it in old specimens. The exception to this rule was TCA, which provided unbiased estimates for young adults. The higher accuracy and precision recommends favouring TCA over LAM and BR, provided that the required know-how and equipment are available.

Simultaneous in vivo comparison of bone substitutes in a guided bone regeneration model

A direct, simultaneous comparison of bone substitutes is hampered by the limited number of samples that can be tested simultaneously. The goal of this study was to establish a preclinical model for guided bone regeneration that offers testing of different bone substitutes in a one-wall defect situation. We show here that up to eight titanium hemispheres can be placed on the calvaria of minipigs. To establish our model, titanium hemispheres were filled with and without Bio-Oss, a deproteinized bovine bone mineral, Ostim, an aqueous paste of synthetic nanoparticular hydroxyapatite, and Osteoinductal, an oily calcium hydroxide suspension, before being positioned on the calvaria. After 6 and 12 weeks, titanium hemispheres were subjected to histological and histomorphometric analysis. We show here that bone filled approximately one-tenth of the area below the hemispheres which were left empty, indicating a critical size model for guided bone regeneration. In accordance with the documented osteoconductive properties of Bio-Oss and Ostim, titanium hemispheres were almost completely filled with bone. Moreover, the expected degradation profile of Bio-Oss and Ostim could be confirmed by histologic and histomorphometric analysis. Under the same conditions, Osteoinductal failed to exert osteoconductive properties, rather a progressive resorption of the host bone was observed. These results demonstrate that the preclinical model presented here is suitable to simultaneously compare bone substitutes with different material properties. Our model based on the titanium hemispheres allows evaluation of graft consolidation under standardized conditions thereby avoiding intra-individual variations.

On the applicability of secondary dentin formation to radiological age estimation in young adults

ABSTRACT: The literature provides linear regression formulas for dental age estimation that is based on radiological two‐dimensional measurements of the pulp size. The aim of the present study was to explore whether the previously presented regression formulas could lead to statistically sound results and to appropriate repeatability when applied to young individuals. Orthopantomograms (OPGs) of 44 Austrian individuals, aged between 13 and 24 years, were selected at random. In accordance with the reported method, six teeth on each OPG were chosen to carry out the measurements. Statistical analysis was performed in order to assess the difference between the estimated and the true chronological age. The regression formulas reported by Kvaal et al. (1995) led to a consistent underestimation; the regression formulas reported by Paewinsky et al. (2005) resulted in a constant overestimation of age. The statistical analysis of intraobserver and interobserver variation revealed a variation width below 2%, respectively.

Atrophy of the residual alveolar ridge following tooth loss in an historical population.

OBJECTIVES To study the natural aetiopathology of jaw atrophy after tooth loss, unaltered by prosthetic procedures, an historical population without modern dental treatment was examined. METHODS Based on the hypothesis that there are predictable changes in shape during jaw-atrophy, frequency and degree of atrophy as well as clinical aspects of bone quality and resorption were determined in the skeletal remains of 263 individuals. The potential association between age and frequency/severity of atrophy was analysed. RESULTS Atrophy in at least one jaw segment was present in 45.2% of the analysed jaw specimens. The residual ridge underwent a series of changes in shape and height following the pattern of resorption described for modern populations. The severity of these alterations was associated with the age of the individual and the region within the jaw. Atrophy was frequently related to structural degradation of the covering cortical layer. CONCLUSIONS These findings prove that atrophy of the jaw evidently does occur, displaying similar patterns of resorption in a population without modern prosthetics, where the negative effect of ill-fitting dentures is excluded. The basic information about alterations of shape and the cortical layer covering the residual crest might help to provide a deeper insight into aetiopathological mechanisms of this common oral disease.

Impact of dietary vitamin D on osseointegration in the ovariectomized rat

AIM Vitamin D deficiency is highly prevalent in the population and associated with impaired peri-implant bone regeneration. Yet, there is a gap in understanding the impact of vitamin D supplementation on the process of osseointegration. In this study, the effect of vitamin D supplementation on peri-implant bone regeneration was investigated. METHODS Fifty ovariectomized Sprague-Dawley rats were divided into three groups. The depletion group was fed a vitamin D-free diet for 8 weeks. The repletion group received vitamin D-free diet for 6 weeks, before animals were switched to standard diet containing 2400 IU/kg vitamin D. The control group was fed the standard diet. Two titanium mini-implants were placed in the tibia. All groups remained on their previous diet until sacrifice. Blood sample testing and histomorphometric analysis were performed. RESULTS Vitamin D depletion caused a significant reduction in 25-hydroxvitamin D in rat serum that returned to control levels in the repletion group. This vitamin deficiency was associated with a decrease in bone-to-implant contact in the cortical area, which was leveled to controls in the repletion group. No significant changes by vitamin D depletion were noticed in the medullar compartment. Moreover, also the peri-implant bone area and the mineral apposition rate remained unchanged upon vitamin D depletion. CONCLUSION These results indicate that vitamin D deficiency has a negative impact on cortical peri-implant bone formation in ovariectomized rats, which can be compensated by vitamin D supplementation. This study provides first insight into the potential beneficial effect of vitamin D supplementation in implant dentistry.

Short-term Teriparatide Delivery and Osseointegration: a Clinical Feasibility Study

Teriparatide is an anabolic osteoporosis therapeutic agent that can improve healing after fractures and periodontal surgeries. Clinical studies investigating the effects of teriparatide on the osseointegration of titanium implants have not been performed. We conducted an open-label randomized controlled feasibility study and included 24 individuals with edentulous lower jaws. The participants received 2 study implants in the mandible during interforaminal dental implant surgery. They were randomly assigned to receive either 20 µg of teriparatide once daily for 28 days or no treatment. Study implants were retrieved from 23 participants after 9 weeks and were subjected to histomorphometric analyses. Endpoints were new bone-volume-per-tissue-volume (NBV/TV) and new bone-to-implant-contact (NBIC). We report here that median values of NBV/TV in the control and the teriparatide groups were 15.4% vs. 17.6% in the periosteal compartment, 11.3% vs. 16.5% in the cortical compartment, and 7.3% vs. 12.0% in the medullary compartment, respectively. NBIC median values in the control and the teriparatide groups were 3.3% vs. 4.1% in the periosteal compartment, 5.0% vs. 4.4% in the cortical compartment, and 0.3% vs. 1.4% in the medullary compartment, respectively. The results provide the first histological data on the osseointegration of titanium study implants in individuals treated with teriparatide. ClinicalTrials.gov number, NCT00089674. Abbreviations: NBV/ TV, new bone-volume per tissue volume; NBIC, new bone-to-implant contact; BV/TV, bone-volume per tissue volume; BIC, bone-to-implant contact; ROI, region of interest.

Are culture‐expanded autogenous bone cells a clinically reliable option for sinus grafting?

OBJECTIVES This prospective clinical study was designed to examine the healing process during the first 12 months after sinus grafting (SG) with autogenous culture-expanded bone cells (ABC) and bovine bone mineral (BBM) histomorphometrically and radiologically. MATERIAL AND METHODS Twenty-two sinuses of 12 patients (mean age 56.2+/-9.3 years) were grafted. Four weeks before, SG bone biopsies were obtained with a trephine burr and the bone cells were isolated and expanded. Every sinus was grafted with BBM and ABC. After 6 months, a biopsy was taken from each sinus and implants (n=82) were placed. These were uncovered after another 6 months and fitted with dentures. The percent newly formed bone (NB) and the NB-to-BBM contact area were determined on undecalcified histologic sections. The sinus graft volume was evaluated by dental CT after SG (CT 1), after implant placement (CT 2) and after implant uncovery (CT 3). RESULTS Postoperative healing was uneventful. The NB was 17.9+/-4.6% and the contact area 26.8+/-13.1%. The graft volume (in mm(3)) was 2218.4+/-660.9 at the time of CT 1, 1694+/-470.4 at the time of CT 2 and 1347.9+/-376.3 at the time of CT 3 (P<.01). Three implants were lost after uncovery. Reimplantation and prosthodontic rehabilitation were successful throughout. CONCLUSIONS These results suggest that SG with ABC and BBM in a clinical setting provides a bony implant site which permits implant placement and will tolerate functional loading.