Georg Watzek

Impact of dental implant length on early failure rates: a meta-analysis of observational studies

AIM To test the null hypothesis of no difference in failure rates of short (minimum length: 7 mm) and longer dental implants (≥ 10 mm), a meta-analysis was performed on prospective observational trials. MATERIALS AND METHODS A systematic electronic and hand search was performed to identify eligible studies. Having additional data supplied by the authors, 54 publications were included (19,083 implants). RESULTS In case of mandibular implants, the null hypothesis of no impact of reduced implant length on failure within the first year of prosthetic loading could not be rejected. A significant impact of implant length could be substantiated for short machined implants in the anterior [odds ratio (OR) 5.4] and posterior maxilla (OR 3.4), while short rough-surfaced implants demonstrated increased failure rates in the anterior maxillary sites. No influence of implant diameter and denture type on the failure rate of short implants could be revealed. CONCLUSION In areas of reduced alveolar bone height the use of short dental implants may reduce the need for invasive bone augmentation procedures.

Mechanical properties of the Schneiderian membrane in vitro

OBJECTIVES Perforation of the Schneiderian membrane (maxillary sinus mucosa) is a common complication of maxillary sinus graft procedures. Membrane perforation increases the chance of postoperative sinusitis and endangers graft as well as implant survival. The aim of the present study was to explore the mechanical properties of the Schneiderian membrane. MATERIAL AND METHODS Three test methods were performed on sinus specimen of 20 fresh human cadavers: one- and two-dimensional membrane elongation as far as perforation, as well as membrane detachment from the adherent bone. RESULTS Perforation of the Schneiderian membrane (mean thickness: 90 mum) occurred at a mean tension of 7.3 N/mm(2). The membrane could be stretched to 132.6% of its original size in one-dimensional elongation, and to 124.7% in two-dimensional elongation. Thicker membranes demonstrated significantly higher load limits (P<0.001). The mean modulus of elasticity accounted 0.058 GPa, the mean adhesion force between sinus membrane and bone surface was 0.05 N/mm. CONCLUSIONS Respecting the mechanical properties of the Schneiderian membrane may help reducing the complication rates and thus patient morbidity in minimally invasive maxillary sinus floor elevation.

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.

Peri‐implantitis and late implant failures in postmenopausal women: a cross‐sectional study

AIM Systemic bone loss is a major cause of fractures in postmenopausal women and may also affect the jawbone; however, its consequences on the success of dental implants remain poorly understood. MATERIALS AND METHODS In this cross-sectional study, the relation between self-reported osteoporosis and the success rate of dental implants in an adult female population was evaluated. The primary outcome parameters were the occurrence of peri-implantitis and late implant failures. Women with unknown bone status were excluded from the study. The potential confounders age, recipient site, smoking, periodontal disease and time of loading were recorded. RESULTS Data from 203 women with a mean age of 63 ± 9 years and 967 dental implants were investigated. The patients were classified according to their medical history into one of three groups: osteoporosis (47 women), osteopenia (16 women) and healthy controls (140 women). Patients with unknown bone status (n=26) were excluded. The multi-level statistical analysis showed no association between peri-implantitis [odds ratio (OR) 2.1; p=0.6] or implant failure [hazards ratio (HR) 2.5; p=0.2] and systemic bone loss. CONCLUSIONS No relation was found between osteoporosis and peri-implantitis in an adult female population.

Is Zoledronate Toxic to Human Periodontal Fibroblasts

Exposed necrotic alveolar bone is a hallmark of bisphosphonate-related osteonecrosis of the jaw. However, it is unknown whether zoledronate causes soft-tissue damage via adverse actions toward periodontal fibroblasts. We therefore examined whether zoledronate causes a cytotoxic response in fibroblasts isolated from the gingiva and the periodontal ligament. We report that micromolar concentrations of zoledronate and serum-free conditions decreased cell activity, as measured by assays for formazan formation, proliferation, and protein synthesis. Under these conditions, periodontal fibroblasts underwent apoptosis and necrosis, as indicated by cleavage of PARP and membrane disruption, respectively. However, these adverse effects of zoledronate were mitigated by the presence of serum. Moreover, zoledronate bound to calcium phosphate failed to reduce cell activity. Analysis of these data suggests that the cytotoxic responses of periodontal fibroblasts require high concentrations of zoledronate and depend on the in vitro experimental conditions. Whether these findings translate into soft-tissue damage will require further investigation.

Sinus augmentation analysis revised: the gradient of graft consolidation

OBJECTIVE Graft consolidation follows a gradient that reflects the properties of bone substitutes at sites of sinus augmentation. Here we present an analytical method to investigate the process of graft consolidation taking the distance from the maxillary host bone into account. MATERIAL AND METHODS We therefore evaluated histological specimens, 6 and 12 weeks after the sinus of minipigs was augmented with Bio-Oss((R)), a deproteinized bovine bone mineral, and Ostim((R)), an aqueous paste of synthetic nanoparticular hydroxyapatite. A curve was drawn that represents the changes in histomorphometric parameters within a given distance from the maxillary host bone. RESULTS Based on this curve, three regions of interest were defined: R1 (0-1 mm) the bridging distance where new bone is laid onto the host bone, R2 (2-3 mm) a region of osteoconduction where new bone exclusively grows on the biomaterial, R3 (4-5 mm) and a region of osteoconduction where bone formation has reached its maximal extension. Qualitative and quantitative analysis of the three regions can reveal differences in graft consolidation, depending on the bone substitutes and the observation period [Bone volume (BV) per tissue volume after 6 weeks: R1: 19+/-8.4% for Bio-Oss((R)) and 42.9+/-13.2% for Ostim((R)) (P=0.03), R2: 3+/-2.4% for Bio-Oss((R)) and 14.7+/-9.5% for Ostim((R)) (P=0.03), R3: 5+/-4.1% for Bio-Oss((R)) and 5.3+/-5.3% for Ostim((R)) (P=0.86). BV per tissue volume after 12 weeks: R1: 38.0+/-13.3% for Bio-Oss((R)) and 53.3+/-6.6 for Ostim((R)) (P=0.04), R2: 14+/-12.2 for Bio-Oss((R)) and 26.4+/-11 for Ostim((R)) (P=0.18), R3: 6.6+/-7 for Bio-Oss((R)) and 10.7+/-5.8 for Ostim((R)) (P=0.32) after 12 weeks]. CONCLUSION Based on the graft consolidation gradient, the impact of bone substitutes to modulate the process of bone formation and the kinetic of degradation within a distinct region of the augmented sinus can be investigated.

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.

New safety margins for chin bone harvesting based on the course of the mandibular incisive canal in CT

OBJECTIVES Altered pulp sensitivity of anterior lower teeth is a frequent finding following chin bone harvesting. Persistent loss of tooth sensitivity has been reported in up to 20% of the patients. The aim of this study was to evaluate current recommendations for the location of the harvest zone with respect to the course of the mandibular incisive canal (MIC), the intrabony continuation of the mandibular canal mesial to the mental foramen. MATERIAL AND METHODS On computed tomographic (CT) scans of 50 dentate mandibles, the MIC was located and its distance to the root apices, to the labial bony surface, and to the inferior margin of the mandible was assessed. The risk of nerve injury and the percentage of patients suitable for chin bone grafting were calculated. RESULTS Respecting current recommendations for chin bone grafting, the content of the MIC was endangered in 57% of the CTs. Therefore, new safety margins are suggested: the chin bone should be harvested at least 8 mm below the tooth apices with a maximum harvest depth of 4 mm. CONCLUSIONS Applying the new safety recommendations and proper patient selection in chin bone harvesting could reduce the risk of altered postoperative tooth sensitivity due to injury of the mandibular incisive nerve.

Prolyl hydroxylase inhibitors increase the production of vascular endothelial growth factor by periodontal fibroblasts.

BACKGROUND AND OBJECTIVE Pharmacological inhibitors of prolyl hydroxylases (PHDs) can induce a proangiogenic response that favors wound healing and bone regeneration. However, the response of periodontal cells to PHD inhibitors is unknown. MATERIAL AND METHODS To determine the effects of PHD inhibitors on periodontal cells, we exposed human fibroblasts from the gingiva and the periodontal ligament to dimethyloxallyl glycine, desferrioxamine, l-mimosine and CoCl(2). Viability, proliferation, and protein synthesis were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), [(3)H]thymidine, and [(3)H]leucine incorporation, respectively. The levels of Ki67, hypoxia-inducible factor 1α (HIF-1α), p27, phosphorylated c-Jun N-terminal kinase (JNK) and phosphorylated p38 were determined by immunohistochemistry and western blotting. Vascular endothelial growth factor (VEGF) mRNA levels were measured by quantitative PCR. Protein levels of VEGF and interleukin (IL)-6 were evaluated by immunoassays. RESULTS We found that PHD inhibitors, while leaving cell viability unchanged, reduced proliferation and protein synthesis. This was paralleled by decreased Ki67 levels and increased p27 levels, suggesting that PHD inhibitors provoke growth arrest. Independently from this response, PHD inhibitors stabilized HIF-1α and increased the production of VEGF. This increase of VEGF was observed in the presence of proinflammatory IL-1 and pharmacological inhibitors of JNK and p38 signaling. Moreover, PHD inhibitors did not modulate expression of IL-6 and the phosphorylation of JNK and p38. CONCLUSION These results suggest that PHD inhibitors enhance the production of VEGF in periodontal fibroblasts, even in the presence of proinflammatory IL-1. The data further suggest that PHD inhibitors do not provoke a significant proinflammatory or anti-inflammatory response in this in vitro setting.

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.