Climate change, society, and pandemic disease in Roman Italy between 200 BCE and 600 CE.

Records of past societies confronted with natural climate change can illuminate social responses to environmental stress and environment-disease connections, especially when locally constrained high-temporal resolution paleoclimate reconstructions are available. We present a temperature and precipitation reconstruction for ~200 BCE to ~600 CE, from a southern Italian marine sedimentary archive-the first high-resolution (~3 years) climate record from the heartland of the Roman Empire, stretching from the so-called Roman Climate Optimum to the Late Antique Little Ice Age. We document phases of instability and cooling from ~100 CE onward but more notably after ~130 CE. Pronounced cold phases between ~160 to 180 CE, ~245 to 275 CE, and after ~530 CE associate with pandemic disease, suggesting that climate stress interacted with social and biological variables. The importance of environment-disease dynamics in past civilizations underscores the need to incorporate health in risk assessments of climate change.

Anammox bacterial populations in deep marine hypersaline gradient systems.

To extend the knowledge of anaerobic ammonium oxidation (anammox) habitats, bacterial communities were examined in two hypersaline sulphidic basins in Eastern Mediterranean Sea. The 2 m thick seawater-brine haloclines of the deep anoxic hypersaline basins Bannock and L'Atalante were sampled in intervals of 10 cm with increasing salinity. (15)N isotope pairing incubation experiments showed the production of (29)N2 and (30)N2 gases in the chemoclines, ranging from 6.0 to 9.2 % salinity of the L'Atalante basin. Potential anammox rates ranged from 2.52 to 49.65 nmol N2 L(-1) day(-1) while denitrification was a major N2 production pathway, accounting for more than 85.5 % of total N2 production. Anammox-related 16S rRNA genes were detected along the L'Atalante and Bannock haloclines up to 24 % salinity, and the amplification of the hydrazine synthase genes (hzsA) further confirmed the presence of anammox bacteria in Bannock. Fluorescence in situ hybridisation and sequence analysis of 16S rRNA genes identified representatives of the marine anammox genus 'Candidatus Scalindua' and putatively new operational taxonomic units closely affiliated to sequences retrieved in marine environments that have documented anammox activity. 'Scalindua brodae' like sequences constituted up to 84.4 % of the sequences retrieved from Bannock. The anammox community in L'Atalante was different than in Bannock and was stratified according to salinity increase. This study putatively extends anammox bacterial habitats to extremely saline sulphidic ecosystems.

Stratified prokaryote network in the oxic-anoxic transition of a deep-sea halocline.

The chemical composition of the Bannock basin has been studied in some detail. We recently showed that unusual microbial populations, including a new division of Archaea (MSBL1), inhabit the NaCl-rich hypersaline brine. High salinities tend to reduce biodiversity, but when brines come into contact with fresher water the natural haloclines formed frequently contain gradients of other chemicals, including permutations of electron donors and acceptors, that may enhance microbial diversity, activity and biogeochemical cycling. Here we report a 2.5-m-thick chemocline with a steep NaCl gradient at 3.3 km within the water column betweeen Bannock anoxic hypersaline brine and overlying sea water. The chemocline supports some of the most biomass-rich and active microbial communities in the deep sea, dominated by Bacteria rather than Archaea, and including four major new divisions of Bacteria. Significantly higher metabolic activities were measured in the chemocline than in the overlying sea water and underlying brine; functional analyses indicate that a range of biological processes is likely to occur in the chemocline. Many prokaryotic taxa, including the phylogenetically new groups, were confined to defined salinities, and collectively formed a diverse, sharply stratified, deep-sea ecosystem with sufficient biomass to potentially contribute to organic geological deposits.

Sulfur cycling and methanogenesis primarily drive microbial colonization of the highly sulfidic Urania deep hypersaline basin.

Urania basin in the deep Mediterranean Sea houses a lake that is >100 m deep, devoid of oxygen, 6 times more saline than seawater, and has very high levels of methane and particularly sulfide (up to 16 mM), making it among the most sulfidic water bodies on Earth. Along the depth profile there are 2 chemoclines, a steep one with the overlying oxic seawater, and another between anoxic brines of different density, where gradients of salinity, electron donors and acceptors occur. To identify and differentiate the microbes and processes contributing to the turnover of organic matter and sulfide along the water column, these chemoclines were sampled at a high resolution. Bacterial cell numbers increased up to a hundredfold in the chemoclines as a consequence of elevated nutrient availability, with higher numbers in the upper interface where redox gradient was steeper. Bacterial and archaeal communities, analyzed by DNA fingerprinting, 16S rRNA gene libraries, activity measurements, and cultivation, were highly stratified and metabolically more active along the chemoclines compared with seawater or the uniformly hypersaline brines. Detailed analysis of 16S rRNA gene sequences revealed that in both chemoclines delta- and epsilon-Proteobacteria, predominantly sulfate reducers and sulfur oxidizers, respectively, were the dominant bacteria. In the deepest layers of the basin MSBL1, putatively responsible for methanogenesis, dominated among archaea. The data suggest that the complex microbial community is adapted to the basin's extreme chemistry, and the elevated biomass is driven largely by sulfur cycling and methanogenesis.

Diversity and spatial distribution of prokaryotic communities along a sediment vertical profile of a deep-sea mud volcano.

We investigated the top 30-cm sediment prokaryotic community structure in 5-cm spatial resolution, at an active site of the Amsterdam mud volcano, East Mediterranean Sea, based on the 16S rRNA gene diversity. A total of 339 and 526 sequences were retrieved, corresponding to 25 and 213 unique (≥98% similarity) phylotypes of Archaea and Bacteria, respectively, in all depths. The Shannon-Wiener diversity index H was higher for Bacteria (1.92-4.03) than for Archaea (0.99-1.91) and varied differently between the two groups. Archaea were dominated by anaerobic methanotrophs ANME-1, -2 and -3 groups and were related to phylotypes involved in anaerobic oxidation of methane from similar habitats. The much more complex Bacteria community consisted of 20 phylogenetic groups at the phylum/candidate division level. Proteobacteria, in particular δ-Proteobacteria, was the dominant group. In most sediment layers, the dominant phylotypes of both the Archaea and Bacteria communities were found in neighbouring layers, suggesting some overlap in species richness. The similarity of certain prokaryotic communities was also depicted by using four different similarity indices. The direct comparison of the retrieved phylotypes with those from the Kazan mud volcano of the same field revealed that 40.0% of the Archaea and 16.9% of the Bacteria phylotypes are common between the two systems. The majority of these phylotypes are closely related to phylotypes originating from other mud volcanoes, implying a degree of endemicity in these systems.

Effect of surface topography of screw-shaped titanium implants in humans on clinical and radiographic parameters: a 12-year prospective study.

OBJECTIVES: Although implants with a roughened surface are widely used today, little is known about the long-term effect of a roughened surface compared with the conventional machined surface on clinical and radiographic parameters. The purpose of this study is to investigate the long-term differences between moderately rough (tioblasted) titanium implants and minimally rough machined/turned surfaces with respect to marginal bone resorption and the peri-implant soft tissues in the same patient. MATERIAL AND METHODS: In 20 fully edentulous patients, with severely resorbed mandibles, a total of 80 Astra Tech dental implants were placed in the mandible to support a bar construction with a full overdenture. In each patient two minimally rough-surfaced (turned) and two moderately rough-surfaced (tioblast) implants were placed alternately. Clinical evaluation was carried out at base line (prosthetic installation), 6 months, 1, 2, 3, 4, 5 and 12 years. Radiographic evaluation using standardized individual filmholders was carried out at base line (prosthetic installation), 6 months, 1, 5 and 12 years. RESULTS: In two patients, during the abutment surgery, one turned implant showed insufficient osseointegration and was replaced. One implant showed an abutment fracture after 9 years and was kept as a sleeper. From base line up to 12 years, no implant was lost. No significant differences were found between both implant surfaces concerning the clinical parameters such as plaque, calculus, bleeding and probing pocket depth. The mean (SD) marginal bone changes up to 12 years varied between -0.11 and +0.01 mm for the turned and -0.2 and +0.01 mm for the tioblast implants. No significant difference in marginal bone loss was found between both implant surfaces. CONCLUSION: We conclude that after 12 years of follow-up, no differences could be found between the turned and the tioblasted implants, both for soft and for hard tissue parameters.

Biogeochemistry and community composition of iron- and sulfur-precipitating microbial mats at the Chefren mud volcano (Nile Deep Sea Fan, Eastern Mediterranean).

In this study we determined the composition and biogeochemistry of novel, brightly colored, white and orange microbial mats at the surface of a brine seep at the outer rim of the Chefren mud volcano. These mats were interspersed with one another, but their underlying sediment biogeochemistries differed considerably. Microscopy revealed that the white mats were granules composed of elemental S filaments, similar to those produced by the sulfide-oxidizing epsilonproteobacterium "Candidatus Arcobacter sulfidicus." Fluorescence in situ hybridization indicated that microorganisms targeted by a "Ca. Arcobacter sulfidicus"-specific oligonucleotide probe constituted up to 24% of the total the cells within these mats. Several 16S rRNA gene sequences from organisms closely related to "Ca. Arcobacter sulfidicus" were identified. In contrast, the orange mat consisted mostly of bright orange flakes composed of empty Fe(III) (hydr)oxide-coated microbial sheaths, similar to those produced by the neutrophilic Fe(II)-oxidizing betaproteobacterium Leptothrix ochracea. None of the 16S rRNA gene sequences obtained from these samples were closely related to sequences of known neutrophilic aerobic Fe(II)-oxidizing bacteria. The sediments below both types of mats showed relatively high sulfate reduction rates (300 nmol x cm(-3) x day(-1)) partially fueled by the anaerobic oxidation of methane (10 to 20 nmol x cm(-3) x day(-1)). Free sulfide produced below the white mat was depleted by sulfide oxidation within the mat itself. Below the orange mat free Fe(II) reached the surface layer and was depleted in part by microbial Fe(II) oxidation. Both mats and the sediments underneath them hosted very diverse microbial communities and contained mineral precipitates, most likely due to differences in fluid flow patterns.

High-resolution data from Laser Ablation-ICP-MS and by ICP-OES analyses at the Cretaceous/Paleogene boundary section at Agost (SE Spain).

A high-resolution analysis of the distribution of major and trace elements across the Cretaceous/Paleogene boundary (KPgB) in the distal section of Agost (SE Spain) was performed. The KPgB sediments were drilled to recover a 22 cm-long core; the lower 5 cm corresponding to the uppermost Maastrichtian and the upper 17 cm to the lowermost Danian. The unconsolidated sediments were resin-embedded under O2-free conditions, cut and polished. Laser Ablation-Inductivity Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses were conducted at 10 µm increments and a laser-beam of 80 µm. Discrete samples were taken immediately prior to the resin-embedding and analyzed by Inductivity Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). Results obtained by both analytical methods (LA-ICP-MS and ICP-OES) are presented. (Further interpretations and discussion are included in Sosa-Montes de Oca et al., 2018 [6]).

Life on the edge: active microbial communities in the Kryos MgCl2-brine basin at very low water activity.

The Kryos Basin is a deep-sea hypersaline anoxic basin (DHAB) located in the Eastern Mediterranean Sea (34.98°N 22.04°E). It is filled with brine of re-dissolved Messinian evaporites and is nearly saturated with MgCl2-equivalents, which makes this habitat extremely challenging for life. The strong density difference between the anoxic brine and the overlying oxic Mediterranean seawater impedes mixing, giving rise to a narrow chemocline. Here, we investigate the microbial community structure and activities across the seawater-brine interface using a combined biogeochemical, next-generation sequencing, and lipid biomarker approach. Within the interface, we detected fatty acids that were distinctly 13C-enriched when compared to other fatty acids. These likely originated from sulfide-oxidizing bacteria that fix carbon via the reverse tricarboxylic acid cycle. In the lower part of the interface, we also measured elevated rates of methane oxidation, probably mediated by aerobic methanotrophs under micro-oxic conditions. Sulfate reduction rates increased across the interface and were highest within the brine, providing first evidence that sulfate reducers (likely Desulfovermiculus and Desulfobacula) thrive in the Kryos Basin at a water activity of only ~0.4 Aw. Our results demonstrate that a highly specialized microbial community in the Kryos Basin has adapted to the poly-extreme conditions of a DHAB with nearly saturated MgCl2 brine, extending the known environmental range where microbial life can persist.

Optical performance of an ultra-sensitive horn-coupled transition-edge-sensor bolometer with hemispherical backshort in the far infrared.

The next generation of far infrared space observatories will require extremely sensitive detectors that can be realized only by combining extremely low intrinsic noise with high optical efficiency. We have measured the broad-band optical response of ultra-sensitive transtion edge sensor (TES) bolometers (NEP≈2aW/Hz) in the 30-60-µm band where radiation is coupled to the detectors with a few-moded conical feedhorn and a hemispherical backshort. We show that these detectors have an optical efficiency of 60% (the ratio of the power detected by the TES bolometer to the total power propagating through the feedhorn). We find that the measured optical efficiency can be understood in terms of the modes propagating through the feedhorn with the aid of a spatial mode-filtering technique.

Localisation of osteogenic and osteoclastic cells in porous beta-tricalcium phosphate particles used for human maxillary sinus floor elevation.

We and others have shown earlier that porous beta-tricalcium phosphate (TCP) (Cerasorb) can be used in patients to augment the maxillary sinus floor prior to placement of oral dental implants. To better understand the transformation of TCP particles into bone tissue, we analyse here the appearance of cells with osteogenic or osteoclastic potential in relation to these particles. In biopsies taken at 6 months after sinus floor augmentation we observed bone growth into the TCP particles but also replacement by soft connective tissue. To identify possible osteoprogenitor cells in this tissue, histological sections were immunostained with an antibody to Runx2/Cbfa1, an essential and early transcription factor for osteoblast differentiation. The osteogenic potential of cells was further confirmed by immunostaining for bone sialoprotein (BSP) and osteopontin (OPN). Other sections were stained for Tartrate Resistant Acid Phosphatase (TRAP) activity to identify cells with osteoclastic capacity. Runx2/Cbfa1 positive connective tissue cells were found in abundance throughout and around the TCP particles, even at a distance of several millimetres from the maxillary bone surface. About 95% of the cells found within TCP particles stained positive for Runx2/Cbfa1. Fewer cells stained positive for BSP and OPN, suggesting more mature osteoblastic properties. Mono- and binucleate TRAP-positive cells, but no multinucleate TRAP-positive osteoclasts, were found in the soft tissue infiltrating the TCP and at the surface of the TCP particles. Both the Runx2/Cbfa1 positive and the TRAP-positive cells decreased apically with increasing vertical distance from the maxillary bone surface. This data suggests that the TCP particles attract osteoprogenitor cells that migrate into the interconnecting micropores of the bone substitute material by 6 months. The lack of large multinucleate TRAP positive cells suggests that resorption of the TCP material by osteoclasts plays only a minor role in its replacement by bone. Chemical dissolution, possibly favoured by a high cell metabolism in the particles, seems the predominant cause of TCP degradation. The abundance of Runx2/Cbfa1 positive cells would indicate that with a greater time of healing there will be further bone deposition into these particles.

Intratympanic gentamicin treatment after endolymphatic sac surgery.

CONCLUSIONS: Interval treatment with up to three intratympanic gentamicin injections once weekly effectively controlled vertigo while preserving hearing in patients with Ménière's disease and recurrent or resistant vertigo after saccotomy. OBJECTIVES: Recurrent or resistant incapacitating vertigo may occur after endolymphatic sac surgery (saccotomy) in patients with Ménière's disease. In these patients, revision saccotomy, vestibular nerve section or labyrinthectomy are the established treatment options. We advocate a once-weekly application of intratympanic gentamicin (12 mg) as an effective alternative in this group of patients. MATERIAL AND METHODS: Five patients (age range 39-65 years) with definite Ménière's disease according to the 1995 American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) criteria and incapacitating vertigo underwent gentamicin treatment after saccotomy. Control of vertigo and hearing preservation were the aims of treatment. The follow-up period ranged from 26 to 59 months. History and pure-tone audiometry were used to assess vertigo control and hearing, respectively. The frequency of vertigo in the 6-month period before gentamicin treatment ranged between 0.5 and four definitive episodes per month. Hearing stage (AAO-HNS criteria) before gentamicin treatment ranged between 2 and 4. Pre- and post-treatment pure-tone hearing thresholds at 0.5, 1, 2 and 3 kHz were compared by means of the Mann-Whitney U-test. RESULTS: Complete vertigo control (class A; AAO-HNS) and hearing preservation at 0.5, 1, 2 and 3 kHz were achieved.

Long-term results after interval therapy with intratympanic gentamicin for Menière's disease.

OBJECTIVES: The new single-shot and interval treatment for Menière's disease with gentamicin was designed to avoid cochlear damage during treatment with gentamicin. METHODS: To date, 90 patients were treated with the single-shot or interval gentamicin therapy. Fifty-seven cases of Menière's disease were followed up prospectively between 2 and 4 years. During one treatment series, a maximum of three intratympanic gentamicin injections within 15 days were applied, each consisting of 0.3 mL (12 mg) of gentamicin (days 1, 8, and 15). Thirty of these 57 patients (53%) needed only one injection to be controlled (single-shot treatment). RESULTS: Vertigo attacks were completely controlled in 95% and partially controlled in 5%, whereas hearing remained unchanged or even improved. Tinnitus as well as aural fullness were controlled in approximately 50% of the cases. CONCLUSION: Our results with this group of patients after interval-treatment or single-shot application of intratympanic gentamicin demonstrate the effectiveness of this treatment modality with very low side effects, and, although our experience is still limited, it allows for expanding the indication on early cases of Menière's disease before permanent hearing loss occurs. Even cases of bilateral Menière's disease can be treated successfully using this method. Cochleotoxic side effects can be prevented by treatment intervals of 7 days.

Fate of the HA coating of loaded implants in the augmented sinus floor: a human case study of retrieved implants.

A histomorphometric study was performed on six retrieved loaded hydroxyapatite (HA)-coated titanium implants. The implants had been clinically functioning in a 50-year-old patient. She originally presented a severely atrophic maxilla that was reconstructed by sinus floor augmentation using autogenous bone from the iliac crest. In spite of good clinical function, because of psychiatric problems, all implants, including some bordering bone, were removed using a trephine bur. Thin ground sections were prepared for histology and used for histomorphometry. The aim of this study was to observe the condition of the calcium phosphate coating after 2.5 years of functional loading, the nature of the bone-to-implant interface, as well as the density of the bone graft around the implants. Intimate and abundant bone-to-implant contact was observed, ranging from 90.4% to 99.8% along the implant surface. Active bone remodeling occurred within all threads, as demonstrated by secondary osteons close to the implant surface. The thickness of the calcium phosphate coating varied from 51 to 88 pm for the loaded retrieved implants, versus 53 to 89 microm for the nonused control implant. All implants showed bone contact including the first thread and up to the smooth titanium neck. Both the nature and thickness of the coating had hardly changed after 2.5 years of loading. The HA-coated implants used achieved excellent osseointegration and must be considered clinically safe and effective in maxillary grafted bone.

A histomorphometric and micro-computed tomography study of bone regeneration in the maxillary sinus comparing biphasic calcium phosphate and deproteinized cancellous bovine bone in a human split-mouth model.

OBJECTIVE: The gain of mineralized bone was compared between deproteinized bovine bone allograft (DBA) and biphasic calcium phosphate (BCP) for dental implant placement. STUDY DESIGN: Five patients with atrophic maxillae underwent bilateral sinus elevation with DBA (Bio-Oss) and BCP (Straumann BoneCeramic). After 3 to 8 months, 32 Camlog implants were placed, and biopsies were retrieved. Bone and graft volume, degree of bone mineralization, and graft degradation gradient were determined using micro-computed tomography, and bone formation and resorption parameters were measured using histomorphometry. Implant functioning and peri-implant mucosa were evaluated up to 4 years. RESULTS: Patients were prosthetically successfully restored. All but one of the implants survived, and peri-implant mucosa showed healthy appearance and stability. Bone volume, graft volume, degree of bone mineralization, and osteoclast and osteocyte numbers were similar, but BCP-grafted biopsies had relatively more osteoid than DBA-grafted biopsies. CONCLUSIONS: The BCP and DBA materials showed similar osteoconductive patterns and mineralized bone, although signs of more active bone formation and remodeling were observed in BCP- than in DBA-grafted biopsies.

The predictors of implant failure after maxillary sinus floor augmentation and reconstruction: a retrospective study of 1045 consecutive implants.

OBJECTIVE: To assess the predictors of implant failure after grafted maxillary sinus (GMS). MATERIAL AND METHODS: A total of 1045 implants were inserted in 224 patients/347 GMS during a period of 14 years. Kaplan-Meyer and multivariate log-regression analysis were used to assess the following variates: patient's age, gender, smoker/nonsmoker, American Society of Anesthesiologists (ASA) class, one/two-stage surgery, merged/submerged healing, membrane, antibiotics, auto/allo/xenogenic bone grafts, implant's lengths/surface/diameter, crestal bone atrophy/quality, implant region, prosthetics, opposing dentition, and implant proximity to evaluate the predictors and relative risk (hazard ratio [HR]) of implant failure. RESULTS: Significant implant failure predictors were the graft material (HR = 4.7), with superior results for autogenic bone, residual crestal bone height (HR = 3.51), ASA class (HR = 2.73), surgical technique (HR = 2.56), implant proximity (HR = 2.07), smoker (HR = 1.98), and age (>60/HR=1.39). All other factors were insignificant. Overall survival rate was 93.3%. CONCLUSIONS: GMS is effective when the predictors are considered. Patient selection, including the ASA status, smoking, residual bone height, and the graft material are the predominant predictors. In highly atrophic situations, autogenic bone grafts showed superiority; however, in less atrophic cases, nonautogenic bone-grafts are equivalent.

The enigma of prokaryotic life in deep hypersaline anoxic basins.

Deep hypersaline anoxic basins in the Mediterranean Sea are a legacy of dissolution of ancient subterranean salt deposits from the Miocene period. Our study revealed that these hypersaline basins are not biogeochemical dead ends, but support in situ sulfate reduction, methanogenesis, and heterotrophic activity. A wide diversity of prokaryotes was observed, including a new, abundant, deeply branching order within the Euryarchaeota. Furthermore, we demonstrated the presence of a unique, metabolically active microbial community in the Discovery basin, which is one of the most extreme terrestrial saline environments known, as it is almost saturated with MgCl2 (5 M).

High concentrations of bioactive glass material (BioGran) vs. autogenous bone for sinus floor elevation.

In this study, high concentrations of bioactive glass (BG) particles were compared with autogenous bone in their capacity to augment maxillary bone when grafted in the human sinus floor using a split mouth design. Three female patients with severe maxillary atrophy underwent bilateral sinus floor elevation and bone grafting using 80-100% BG particles (300-355 microm in size) mixed with 20% to 0% iliac crest bone particles at one (experimental) side, and 100% iliac crest derived bone particles at the other (control) side. A total of 22 bone biopsies was taken at the time of fixture installation; that is, at 4, 6 and 15 months after grafting, and processed for histology and histomorphometry. At the control (autogenous bone) sides, trabecular bone amounted to 39% of the biopsy volume in the graft (site) at 4 months, almost 41% at 6 months, and 42% at 15 months. This bone contained viable osteocytes and was mostly of mature, lamellar type. At the experimental (BG particles) sides, the graft consisted of 27% of mostly woven (and some lamellar) bone at 4 months, 36% (woven and lamellar) bone at 6 months, and 39% (mainly lamellar) bone at 15 months. The grafted BG particles started to excavate at 4 months and their centers gradually filled with bone tissue. As a consequence, the volume of BG particles in the biopsy decreased from 29% at 4 months to 15% at 6 months and 8% at 15 months. The BG particles appeared to resorb within 1-2 years by dissolution rather than by osteoclastic activity. Parameters for bone turnover (% osteoid surface, % resorption surface) indicated that bone remodeling was very active at both experimental and control sides, during more than 6 months. These results suggest that mixtures of mainly (80-90%) BG particles and some (10-20%) autogenous bone are effective for bone regeneration in the augmented sinus offer 6 months healing time, while about 12 months healing time is needed for 100% BG particles.

Fate of monocortical bone blocks grafted in the human maxilla: a histological and histomorphometric study.

Local bone defects in the anterior maxilla are commonly grafted with monocortical blocks of autologous bone in order to restore the defect site prior to the placement of dental implants. Increasing evidence suggests that osteocytes are involved in the control of bone remodelling and thus may be important for optimalisation of bone structure around implants, and thus for implant osseointegration. However, it is not well known whether osteocytes will survive when bone blocks are grafted into defects. We grafted 19 patients with monocortical bone blocks derived from the symphysis, to the defect site in the maxillary alveolar process. The bone grafts were left to heal for times varying from 2.5 to 7 months. During implant installation, bone biopsies were removed using a trephine burr, and processed for hard tissue histology. Bone histology and histomorphometry were then carried out in order to gain insight into the density, viability and remodelling of the graft. Clinically, all the bone grafts were successful, with no implant failures, and little resorption was seen. Histologically, bone volume expressed as percentage of tissue volume at the implant site varied from 27% to 57% with an overall average of 41%. Bone fields with empty osteocyte lacunae were observed and measured. The amount of this so-called nonvital bone (NVB) varied between 1% and 34% of the total tissue volume. The amount of NVB decreased significantly with the time of healing. The data suggest that the majority of the osteocytes of the monocortical bone do not survive grafting. The results indicate that the NVB is progressively remodelled into new vital bone 7 months after grafting.