'One River, Two Systems': Hong Kong's River Management.

Hong Kong (HK), one of the world's most densely populated metropolises, is home to over 200 rivers and streams extending about 2500 km in length. During the 1970s-1990s, most of these rivers were converted into artificial canals, to which the local society pays little attention. Since the 2010s, the HK government has initiated river revitalization to enhance the social-environmental roles of rivers. This study employed a mixed research method, including literature and policy analysis, expert interviews, field visits, and a public survey, to identify key challenges in HK's Integrated River Basin Management (IRBM). The findings highlighted the lack of IRBM's institutional arrangements in HK, characterized by a fragmented 'one river, two systems' approach without both coordination and collaboration. The Water Supplies Department (WSD) impounds upland streams as reservoirs for securing the local water supply, while the Drainage Service Department (DSD) manages heavily channelized, culverted downstream serving as storm drains with diminished ecological functionality. One significant barrier to the implementation of IRBM in HK was the limited public participation, although our survey revealed a high level of public willingness to participate in river management. Presently, river revitalization efforts have achieved limited success, with ecological measures appearing mostly "cosmetic" and the conservation of freshwater biodiversity neglected. This further underscored the pressing need for the embracement of IRBM in HK to safeguard basin-wide freshwater ecosystems. Our survey also indicated low public awareness of river revitalization initiatives and widespread dissatisfaction with their outcomes. In conclusion, we proposed the development of IRBM in HK by instituting river basin coordination, prioritizing river ecosystem restoration in revitalization projects, and involving the public through tailored strategies.

Evaluation of different debridement strategies for implant-abutment connections: An in vitro study.

STATEMENT OF PROBLEM: Technical complications, including abutment fracture, are a clinical reality. After retrieving failed components, re-establishing a reliable implant-abutment connection is essential, but recommendations on how to clean the interface are lacking. PURPOSE: The purpose of this in vitro study was to evaluate different clinical debridement strategies for removing titanium powder from an implant-abutment interface with regard to their efficacy and associated risk of damaging the interface. MATERIAL AND METHODS: Specimens (n=5) were assembled from previously cut implant halves, which were then contaminated by placing titanium powder inside the implant-abutment connection. Activated rinsing, airflow, and an ultrasound scaler, as well as combinations thereof, were then used to clean the implant-abutment connections. Both parts of each specimen were rated under a light microscope with respect to contamination and damage. In addition, abutments were placed in intact implants (n=10), which had previously been contaminated and cleaned, to record torque curves and abutment stability. Statistical analysis of ratings was based on Kruskal-Wallis tests and the Nemenyi All Pairs test with single-step P value correction, while abutment stability and torque were analyzed using analysis of variance and Tukey HSD tests (α=.05). RESULTS: Erythritol as an abrasive medium led to significantly greater contamination than the scaler (P=.002), activated rinsing (P=.021), and airflow with sodium bicarbonate combined with either conventional (P=.002) or activated rinsing (P=.007). Greater damage was also observed with erythritol because of accumulations of the abrasive media, while scratches were seen after scaler application. Airflow using sodium bicarbonate in combination with activated rinsing showed the lowest level of damage (versus scaler P=.030). Using conventional (P=.010) or activated (P=.029) rinsing, airflow treatment led to a significant reduction in contamination. The scaler led to a significant decrease in abutment stability (P=.048), while activated rinsing and the combination of airflow and activated rinsing did not significantly affect abutment stability. Abutments placed in implants previously contaminated and cleaned required greater torque as compared with original implants (versus activated rinsing, P=.009). CONCLUSIONS: Activated rinsing constituted the best technique for cleaning implant-abutment connections. Cleaning efficiency can be enhanced with airflow using sodium bicarbonate as an abrasive medium.

Adhesive removable partial denture attachments made from zirconia ceramic: A finite element analysis and in vitro study.

STATEMENT OF PROBLEM: Whether adhesive zirconia ceramic removable partial denture attachments are feasible with current technology is unclear. PURPOSE: The purpose of this finite element analysis and in vitro study was to evaluate the effect of the lever arm, tooth preparation, and aging on the loading of the tooth-zirconia attachment interface. MATERIAL AND METHODS: Three different finite element analysis (FEA) models allowing for the loading of an adhesive attachment either directly or through a removable partial denture were used. Two models represented a human tooth with 2 different types of attachments, while the third model also included a removable partial denture. For the evaluation of bond strength, a combination of shear and hydrostatic stress was used. In addition, composite resin teeth were fabricated, and zirconia bars were bonded to them with varying tooth preparations and lever arm lengths. In 1 group the influence of aging was analyzed. Fracture load was determined by using a universal testing machine. Statistical analysis was based on the Shapiro-Wilk normality test, ANOVA, and Games-Howell test (α=.05). RESULTS: The maximum stress of 65 MPa occurring in the bonding area was reduced to 37 MPa by adding a retainer to the attachment. Loading of the denture resulted in a maximum stress of 9 MPa. Mean fracture loads ranged from 33.6 N to 209.1 N. Preparing a flat bonding surface showed a nonsignificant increase (P=.197), whereas aging led to a nonsignificant decrease in fracture load (P=.075). A lever arm extended by 2 mm significantly reduced fracture load (P=.002). The addition of an occlusal-distal (OD) cavity led to a nonsignificant increase (P=.186), which became significant when a mesial-occlusal-distal (MOD) preparation was applied (P=.001). CONCLUSIONS: Adhesive zirconia attachments should use a MOD cavity and have a cross section of at least 2.5×2.5 mm. The attachment should not extend more than 3 mm.

Wedge Shaped vs Round Implants: Bone Strain During the Insertion Process.

A novel implant system resembling the shape of a wedge and employing piezosurgery for implant bed preparation has been introduced with the aim of solving the problem of horizontal bone deficiency. This in vitro study compared emerging bone strain during insertion of a conventionally round implant vs the wedge implant. Adhering to the manufacturers' protocols, implant surgery was performed in polyurethane foam blocks equipped with strain gauges attached to the buccal and occlusal surfaces. Five implants per group were placed while strain development during insertion was recorded. Primary implant stability was determined using resonance frequency analysis. Statistical analysis was based on Welch's 2-sample tests (α = 0.05). In general, greater strain development was found on the buccal aspect of bone compared to the occlusal aspect with an overall range between -724 µm/m and 9132 µm/m. A stepwise increase in strain development was seen in the wedge implants while, in the round implants, a continuous increase in strain development was recorded. Absolute strain development on the buccal aspect of bone was significantly greater in wedge implants (P = .0137) while, on the occlusal aspect, significantly lower strain development was seen for wedge implants (P = .0012). Primary stability of wedge implants was significantly lower compared to round implants (P = .0005). Wedge implants differ from round implants with respect to the insertion process characterized by a stepwise increase in bone deformation. High strain development in buccal bone may constitute a risk factor for bone resorption and should be avoided by reducing the degree of underpreparation of the implant site.

Students at Saarland University dental school-A survey on their background and curriculum perception.

INTRODUCTION: With the aim of optimising dental education without overburdening students, new legislation restructuring the undergraduate dental curriculum in German is under way. The goal of this study was to survey the current situation of dental students at one specific university with respect to their socio-economic background, admission to dental school, curriculum perception and work-life balance. MATERIALS AND METHODS: An online questionnaire was presented to all undergraduate students enrolled at Saarland University who had at least completed the first preclinical practical course in dentistry. RESULTS: A response rate of 85% was reached with two-thirds of the student body being females. The profession of 40% of students' parents either was physicians or dentist. Students reported a slight reduction in time spent for leisure activities during their studies, however, with sports activities hardly being affected. With respect to a proper work-life balance, almost 50% of respondents considered their clinical workload as being too high. Students did not express a clear opinion regarding curriculum structure, whilst the content mostly satisfied their expectations (59%). The majority (71%) of students considered their preclinical training as being demanding whilst less than 3% fully agreed that preclinical training provided an optimal background for patient treatment. The learning modules in the first clinical semester were considered as being adequate by 56% of students. Examinations during courses were seen as properly reflecting the students' knowledge by 79% of students. DISCUSSION: The status quo of German dental students is characterised by a high workload affecting the students' work-life balance and by a transition between preclinical and clinical education which only about half the student body perceives as being adequate. Patient-based examinations obviously are not considered as being problematic.

Influence of Aviation Emission on the Particle Number Concentration near Zurich Airport.

In addition to the much-publicized environmental impact of CO2 emission by air traffic, aviation particulate emission also deserves attention. The abundant ultrafine particles in the aviation exhaust with diameters less than 100 nm may penetrate deep into the human respiratory system and cause adverse health effects. Here, we quantified the detailed aviation particle number emission from Zurich Airport and evaluated its influences on the annual mean particle number concentrations in the surrounding communities. The actual flight trajectory data were utilized for the first time to develop an emission inventory with high spatial resolution. The estimated total particle number emission was in the magnitude of 1024 particles per year. The annual mean particle mass concentrations in the nearby communities were increased by about 0.1 µg m-3 due to the aviation emission, equivalent to about 1% of the background concentration. However, the particle number concentration could be increased by a factor of 2-10 of the background level (104 cm-3) for nearby communities. Further studies are required to investigate the health effects of the increased particle number concentration and to evaluate whether the regulation based on the mass concentration is still sufficient for the air quality near airports.

High pressure 31P NMR spectroscopy on guanine nucleotides.

The 31P NMR pressure response of guanine nucleotides bound to proteins has been studied in the past for characterizing the pressure perturbation of conformational equilibria. The pressure response of the 31P NMR chemical shifts of the phosphate groups of GMP, GDP, and GTP as well as the commonly used GTP analogs GppNHp, GppCH2p and GTPγS was measured in the absence and presence of Mg2+-ions within a pressure range up to 200 MPa. The pressure dependence of chemical shifts is clearly non-linear. For all nucleotides a negative first order pressure coefficient B 1 was determined indicating an upfield shift of the resonances with pressure. With exception of the α-phosphate group of Mg2+·GMP and Mg2+·GppNHp the second order pressure coefficients are positive. To describe the data of Mg2+·GppCH2p and GTPγS a Taylor expansion of 3rd order is required. For distinguishing pH effects from pressure effects a complete pH titration set is presented for GMP, as well as GDP and GTP in absence and presence of Mg2+ ions using indirect referencing to DSS under identical experimental conditions. By a comparison between high pressure 31P NMR data on free Mg2+-GDP and Mg2+-GDP in complex with the proto-oncogene Ras we demonstrate that pressure induced changes in chemical shift are clearly different between both forms.

In Vitro Handling Characteristics of a Particulate Bone Substitute for Ridge Preservation Procedures.

While particulate bone substitute materials are applied in a variety of augmentation procedures, standardized defects are being used for preclinical testing. This in vitro study evaluated the density and homogeneity of a particulate bone substitute in ridge preservation procedures. Premolars and molars were extracted in ten semimandibles of minipig cadavers. Light body impression material was used for determining the volume of the extraction sites followed by augmentation with particulate material, thereby weighing the graft material needed. Microradiographs and histologic sections were obtained for evaluating the homogeneity and density of the augmentation material. Statistical analyses were based on Shapiro-Wilk tests, Spearman's rho and one sample Wilcoxon test followed by Bonferroni-Holm correction for multiple testing (α = 0.05). Based on 103 single alveoli evaluated, the mean volume determined was 0.120 cm3 requiring a mean amount of graft material of 0.155 g. With only three exceptions, all parameters (volume, mass of augmentation material, density and homogeneity) correlated significantly (p < 0.020). The apical parts of the alveoli showed reduced density as compared to the middle parts (p < 0.001) and the homogeneity of the augmentation material was also lower as compared to the middle (p < 0.001) and cervical parts (p

Using the Multicomponent Aerosol FORmation Model (MAFOR) to Determine Improved VOC Emission Factors in Ship Plumes.

International shipping's particulate matter primary emissions have a share in global anthropogenic emissions of between 3% and 4%. Ship emissions of volatile organic compounds (VOCs) can play an important role in the formation of fine particulate matter. Using an aerosol box model for the near-plume scale, this study investigated how the changing VOC emission factor (EF) for ship engines impacts the formation of secondary PM2.5 in ship exhaust plumes that were detected during a measurement campaign. The agreement between measured and modeled particle number size distribution was improved by adjusting VOC emissions, in particular of intermediate-, low-, and extremely low-volatility compounds. The scaling of the VOC emission factor showed that the initial emission factor, based on literature data, had to be multiplied by 3.6 for all VOCs. Information obtained from the box model was integrated into a regional-scale chemistry transport model (CTM) to study the influence of changed VOC ship emissions over the Mediterranean Sea. The regional-scale CTM run with adjusted ship emissions indicated a change in PM2.5 of up to 5% at the main shipping routes and harbor cities in summer. Nevertheless, overall changes due to a change in the VOC EF were rather small, indicating that the size of grid cells in CTMs leads to a fast dilution.

Genomic BCR-ABL1 breakpoints in pediatric chronic myeloid leukemia.

Chronic myeloid leukemia (CML) is a rare disease in children and adolescents and various aspects-from molecular genesis to therapy regimen-have been taken over from studies on the more prevalent adult CML. However, differences have been observed between malignancies with identical underlying chromosomal translocations, but occurring at different age groups, suggesting some diversity in the mechanisms of formation and leukemogenesis. A multiplex long-range PCR-based assay was developed to allow fast and reliable amplification of patient-specific BCR-ABL1 fusion sequences from genomic DNA. The localization of breakpoints was analyzed with respect to distribution within the breakpoint cluster regions, sequence features, and association to repetitive elements or motifs associated with DNA recombination. The genomic fusion sites of 59 pediatric CML patients showed a bimodal breakpoint distribution in BCR that was different from the distribution in adult CML cases, but with similarities to BCR-ABL1-positive, acute lymphoblastic leukemia in adults. BCR breakpoints were found more frequently positioned within, or close to, Alu repeats than would be expected based on their overall sequence proportion. Technical aspects of the highly sensitive DNA-based quantification of residual CML cells by specific fusion sequence during tyrosine kinase inhibitor therapy are exemplified in a subcohort of pediatric CML patients.

Effect of model parameters on finite element analysis of micromotions in implant dentistry.

Micromotion between dental implant and bony socket may occur in immediate-loading scenarios. Excessive micromotion surpassing an estimated threshold of approximately 150 µm may result in fibrous encapsulation instead of osseointegration of the implant. As finite element analysis (FEA) has been applied in this field, it was the aim of this study to evaluate the effect of implant-related variables and modeling parameters on simulating micromotion phenomena. Three-dimensional FEA models representing a dental implant within a bony socket were constructed and used for evaluating micromotion (global displacement) and stress transfer (von Mises equivalent stress) at the implant-bone interface when static loads were applied. A parametric study was conducted altering implant geometry (cylinder, screw), direction of loading (axial, horizontal), healing status (immediate implant, osseointegrated implant), and contact type between implant and bone (friction free, friction, rigid). Adding threads to a cylindrically shaped implant as well as changing the contact type between implant and bone from friction free to rigid led to a reduction of implant displacement. On the other hand, reducing the elastic modulus of bone for simulating an immediate implant caused a substantial increase in displacement of the implant. Altering the direction of loading from axial to horizontal caused a change in loading patterns from uniform loading surrounding the whole implant to localized loading in the cervical area. Implant-related and bone-related factors determine the degree of micromotion of a dental implant during the healing phase, which should be considered when choosing a loading protocol.

Effect of rotating osteotomes on primary implant stability-an in vitro investigation.

Achieving sufficient primary implant stability in poor-quality bone is difficult. Other than for conventional osteotomes, little is known about the effectiveness of screw-shaped spreaders in condensing bone and increasing primary stability. Therefore, implant stability quotient (ISQ) measurements of implants placed in bone surrogate models were conducted. Whereas bony microarchitecture had no effect on implant stability, initial bone density, presence of a cortical layer, and the use of screw-shaped spreaders significantly increased ISQ levels.

Implant-Supported Overdentures: Current Status and Preclinical Testing of a Novel Attachment System.

Numerous attachment systems exist for implant-supported overdentures, with each having specific limitations in terms of retention, cost, wear, maintenance and cleanability. A retrospective analysis of patients restored with implant-supported overdentures using bars, telescopic crowns and Locator-type attachments was performed and the patients were interviewed. An in vitro strain gauge study compared telescopic crowns, Locator-type attachments and a novel flexible attachment system employing a shape memory alloy (NiTi) with respect to peri-implant strain development during insertion, loading and removal of an overdenture. A significantly lower number of attachment-related complications was observed in bars as compared to telescopic crowns (p = 0.00007) and Locator-type attachments (p = 0.00000), respectively. Greater overall patient satisfaction was noted in bar-retained restorations while Locator-type attachments led to lower levels of satisfaction regarding prosthesis retention. In vitro, telescopic crowns caused maximum strain development during prosthesis insertion and loading, while during removal this was observed in Locators with white retentive inserts. NiTi attachments caused significantly lower strain development during insertion as compared to telescopic crowns (p = 0.027). During loading, NiTi attachments caused significantly lower strain development than Locators with blue retentive inserts (p = 0.039). During removal, NiTi attachments caused significantly less strain development as compared to Locators with white retentive inserts (p = 0.027). Positional discrepancies between male and female attachment parts affected the retention and reaction force between both components, which may be minimized by using the novel NiTi attachment system. This may be beneficial in terms of component wear and implant loading.

Measurement and Modeling of Ship-Related Ultrafine Particles and Secondary Organic Aerosols in a Mediterranean Port City.

Maritime transport emerges as a major source of ultrafine particle (UFP) pollution in coastal regions with consequences for the health of people living in port cities. Inhalation of UFPs can cause inflammation and oxidative stress, which are starting points for further diseases. In addition to primary particles, secondary organic aerosol (SOA) may form through the photo-oxidation of volatile organic compounds emitted in ship exhaust. The characterization of size-segregated and chemical properties of particles is essential for assessing the health implications related to shipping. We applied a coupled regional-local chemistry transport modeling system to study the effects of ship emissions on atmospheric concentrations of UFP and SOA in the Mediterranean port city Marseille (France), which is characterized by the combination of high port activity, industrialized emissions, and active photochemistry in summer. Our results show that the average potential impact from local shipping in the port area was 6-9% for SOA and 27-51% for total particle number concentration in July 2020. The estimated oxidative potential of daily mean particulate organic matter related to shipping was lower than the oxidative potential reported for heavy fuel oil (HFO). The lower oxidative potential in this study is very likely due to the low share of ships using HFO during stopover.

Passivity of fit of CAD/CAM and copy-milled frameworks, veneered frameworks, and anatomically contoured, zirconia ceramic, implant-supported fixed prostheses.

STATEMENT OF PROBLEM: There is less information on the quality of fit of zirconia frameworks with or without ceramic veneer than on anatomically contoured milled zirconia restorations. PURPOSE: The purpose of this in vitro study was to evaluate the strain development of CAD/CAM fabricated zirconia ceramic frameworks with and without ceramic veneering, copy-milled zirconia ceramic frameworks, and copy-milled zirconia ceramic anatomic contour restorations. MATERIAL AND METHODS: Four groups of 3-unit implant-supported cement-retained restorations were fabricated (n=10) to fit an in vitro model with 2 implants. Strain gauges which recorded the strain development of all restorations during cementation were attached to the model mesially and distally adjacent to the implants. Mean absolute strain values were recorded for statistical analysis (MANOVA with Pillai's trace; α=.05). RESULTS: Mean absolute strain development at the different strain gauge locations ranged from 83.23 µm/m for copy-milled zirconia ceramic anatomic contour restorations to 301.20 µm/m for veneered CAD/CAM fabricated zirconia ceramic restorations. Significant effects (P<.001) of the fixed factors restoration type and veneering status, as well as of their interaction term (P=.001) were found. Ceramic veneering of CAD/CAM frameworks resulted in higher strain development, whereas the greater volume in copy-milled anatomic contour restorations did not affect accuracy. CONCLUSIONS: With the systems used in this study, zirconia ceramic-based anatomic contour restorations show greater passivity of fit than ceramic veneered CAD/CAM fabricated zirconia ceramic frameworks.

Rationale for a novel attachment system for implant-supported overdentures.

PURPOSE: To quantify the effect of support stiffness on the retention forces of telescopic crowns and to evaluate a prototype attachment system incorporating a nickel-titanium element. MATERIALS AND METHODS: In the first part of the study, telescopic crowns were fabricated employing standard laboratory procedures. For six combinations of telescopic crowns, the separation force was determined while varying the stiffness of their supporting implants. In the second study part, an in vitro mandibular model with three interforaminal implants was equipped with strain gauges and extensometers. Two prostheses either employing cylindrical telescopic crowns or prototype attachments were fabricated and statically loaded on the model using either the midline or the left canine or both canine implants for support while strain in the peri-implant area and prosthesis displacement were recorded. Statistical analysis of both study parts was based on pairwise comparisons with the level of significance set at α = .05. RESULTS: With one exception (P = .161), for each assembly of two telescopic crowns, the separating force was always dependent on the stiffness of the supporting implants. With 3 exceptions out of a total of 14 comparisons for peri-implant strain and prosthesis displacement, the use of the prototype attachments always led to significantly lower mean values compared to the use of cylindrical telescopes (P < .00). CONCLUSION: The individual retention force of telescopic crowns on implants should be set at a lower level compared to telescopic crowns on natural abutments. Incorporating a nickel-titanium element into attachment systems for implant-supported removable prostheses reduces peri-implant strain and may facilitate the use of telescopic crowns.

Pilot study on the applicability of boron-doped diamond electrodes for tooth whitening.

OBJECTIVES: While various approaches are available for tooth whitening, the basic concept employs the use of peroxides in the form of gels, which are applied to tooth surfaces. Previous studies have shown that reactive oxygen species acting as potent disinfectants can be produced using boron-doped diamond (BDD) electrodes for the electrolysis of water. With these electrodes being applicable, for example, for endodontic treatment, it was the goal of this pilot study to use such electrodes for tooth whitening. MATERIAL AND METHODS: Two groups (n = 10) of intact clinical crowns were obtained by horizontally cutting off roots of extracted human teeth. The crowns were either bleached by applying a commercially available agent based on 40% hydrogen peroxide or were immersed in saline undergoing electrolysis with BDD electrodes. Whitening of specimens was judged on standardized photographs by examiners with three different levels of experience. Statistical analysis was based on Gwet's AC2 coefficient with quadratic weights, Shapiro-Wilk tests, and two-way analysis of variance of aligned rank transformed data (level of significance set at α = .05). RESULTS: Levels of reliability ranging from fair to substantial were recorded for single persons while the level of reliability ranged between fair and moderate for groups of raters. The level of experience had no significant effect on the ratings (p = .2500). The bleaching method had a significant effect on ratings (p = .0005) with BDD electrodes showing less effect. CONCLUSIONS: Bleaching by applying BDD electrodes was possible, but was not as effective as the use of commercially available in-office whitening gel. A potential explanation may be seen in different concentrations of reactive oxygen species.

Preclinical Testing of Boron-Doped Diamond Electrodes for Root Canal Disinfection-A Series of Preliminary Studies.

While numerous approaches have meanwhile been described, sufficient disinfection of root canals is still challenging, mostly due to limited access and the porous structure of dentin. Instead of using different rinsing solutions and activated irrigation, the electrolysis of saline using boron-doped diamond (BDD) electrodes thereby producing reactive oxygen species may be an alternative approach. In a first step, experiments using extracted human teeth incubated with multispecies bacterial biofilm were conducted. The charge quantities required for electrochemical disinfection of root canals were determined, which were subsequently applied in an animal trial using an intraoral canine model. It could be shown that also under realistic clinical conditions, predictable disinfection of root canals could be achieved using BDD electrodes. The parameters required are in the range of 5.5 to 7.0 V and 9 to 38 mA, applied for 2.5 to 6.0 min with approximately 5 to 8 mL of saline. The direct generation of disinfective agents inside the root canal seems to be advantageous especially in situations with compromised access and limited canal sizes. The biologic effect with respect to the host reaction on BDD-mediated disinfection is yet to be examined.

Surface characteristics of zirconia-based posterior restorations: clinical and scanning electron microscopic analysis.

AIM: The aim of this prospective clinical trial was to evaluate the performance of zirconia-based all-ceramic posterior fixed partial dentures (FPDs) after 4 years of clinical use. MATERIALS AND METHODS: Fifteen patients who needed 3- or 4-unit posterior FPDs were enrolled in the study. One manufacturer fabricated all restorations, following established clinical protocols and using computer-aided design/computer-aided manufacturing technology and one veneering material. Survival and success were evaluated clinically. Impressions were taken immediately after definitive cementation and after 48 months. Gold-coated epoxy replicas of the restorations were analyzed with scanning electron microscopy (SEM). Surface alterations were also evaluated clinically. RESULTS: After 48 months, the survival rate for the FPDs was 100%. Three restorations exhibited minor chipping, for a fracture rate of 20% after 4 years. Thirty (59%) of the 51 individual restoration units revealed clinically rough occlusal surfaces, a finding that was confirmed by SEM. CONCLUSION: The placement of 3- and 4-unit zirconia-based posterior FPDs can be considered a reliable treatment modality for medium-term clinical use. However, surface alterations of the veneering ceramics were observed after 4 years and are of notable clinical concern.

Observational study on primary and secondary stability of two current bone level implant designs.

Objective: Achieving high levels of primary implant stability is considered to be desirable, despite some studies warning of the risk of bone damage. It was the goal of this observational clinical study to compare two current bone level implant systems with respect to primary and secondary stability. Method and materials: Data on bone quality, insertion torque, implant stability at insertion and after healing, as well as number of implants lost during healing were obtained from two centers either placing BLT (Bone Level Tapered, Straumann) or Nobel Parallel CC (Nobel Biocare) implants. Statistical analysis was based on Spearman rank correlation tests, analysis of variance, and t tests with the level of significance set at α = .05. Results: A total of 312 BLT and 92 Nobel Parallel CC implants were placed. Ten BLT and two Nobel Parallel CC implants failed resulting in survival rates of 96.79% and 97.83%, respectively. Mean insertion torque recorded in the different bone classes showed large standard deviations, and only torque values for BLT implants recorded in type 3 bone differed significantly from type 2 bone and type 1 bone (P = .024). For BLT implants, bone quality and insertion torque correlated (Spearman rho = -.3326; P = .0023) as did ISQ at insertion (Spearman rho = -.2241; P = .0429). Implant diameter significantly affected primary (P = .0013) and secondary (P = .0050) stability of Nobel Parallel CC implants while for BLT implants a significant effect was only seen for secondary stability (P = .0000). Bone quality had a significant effect on implant insertion torque for BLT implants (P = .0059). Bone quality had no general effect on ISQ changes during healing but 3.3-mm BLT implants showed significantly (P = .0005) lower stability after healing. Conclusion: Huge variation with respect to primary and secondary stability seems to exist among similar looking implant systems clinically used for identical indications.