Group 2 ITI Consensus Report: Technological developments in implant prosthetics.

OBJECTIVES: Group-2 reviewed the scientific evidence in the field of «Technology¼. Focused research questions were: (1) additive versus subtractive manufacturing of implant restorations; (2) survival, complications, and esthetics comparing prefabricated versus customized abutments; and (3) survival of posterior implant-supported multi-unit fixed dental prostheses. MATERIALS AND METHODS: Literature was systematically screened, and 67 publications could be critically reviewed following PRISMA guidelines, resulting in three systematic reviews. Consensus statements were presented to the plenary where after modification, those were accepted. RESULTS: Additively fabricated implant restorations of zirconia and polymers were investigated for marginal/internal adaptation and mechanical properties without clear results in favor of one technology or material. Titanium base abutments for screw-retained implant single crowns compared to customized abutments did not show significant differences concerning 1-year survival. PFM, veneered and monolithic zirconia implant-supported multi-unit posterior fixed dental prostheses demonstrated similar high 3-year survival rates, whereas veneered restorations exhibited the highest annual ceramic fracture and chipping rates. CONCLUSIONS: For interim tooth-colored implant single crowns both additive and subtractive manufacturing are viable techniques. The clinical performance of additively produced restorations remains to be investigated. Implant single crowns on titanium base abutments show similar clinical performance compared to other type of abutments; however, long-term clinical data from RCTs are needed. The abutment selection should be considered already during the planning phase. Digital planning facilitates 3D visualization of the prosthetic design including abutment selection. In the posterior area, monolithic zirconia is recommended as the material of choice for multi-unit implant restorations to reduce technical complications.

Strain-specific antiviral activity of iminosugars against human influenza A viruses.

OBJECTIVES: Drugs that target host cell processes can be employed to complement drugs that specifically target viruses, and iminosugar compounds that inhibit host α-glucosidases have been reported to show antiviral activity against multiple viruses. Here the effect and mechanism of two iminosugar α-glucosidase inhibitors, N-butyl-deoxynojirimycin (NB-DNJ) and N-nonyl-deoxynojirimycin (NN-DNJ), on human influenza A viruses was examined. METHODS: The viruses examined were a recently circulating seasonal influenza A(H3N2) virus strain A/Brisbane/10/2007, an older H3N2 strain A/Udorn/307/72, and A/Lviv/N6/2009, a strain representative of the currently circulating pandemic influenza A(H1N1)pdm09 virus. RESULTS: The inhibitors had the strongest effect on Brisbane/10 and NN-DNJ was more potent than NB-DNJ. Both compounds showed antiviral activity in cell culture against three human influenza A viruses in a strain-specific manner. Consistent with its action as an α-glucosidase inhibitor, NN-DNJ treatment resulted in an altered glycan processing of influenza haemagglutinin (HA) and neuraminidase (NA), confirmed by MS. NN-DNJ treatment was found to reduce the cell surface expression of the H3 subtype HA. The level of sialidase activity of NA was reduced in infected cells, but the addition of exogenous sialidase to the cells did not complement the NN-DNJ-mediated inhibition of virus replication. Using reassortant viruses, the drug susceptibility profile was determined to correlate with the origin of the HA. CONCLUSIONS: NN-DNJ inhibits influenza A virus replication in a strain-specific manner that is dependent on the HA.

Dental care providers' decision making regarding maintenance of compromised teeth and implant therapy indication: an analysis of gender and enrollment in teaching positions.

OBJECTIVES: The aim of this study was to evaluate Brazilian dentists' decision making regarding periodontally involved teeth and implant therapy indications as well as possible modifying factors such as gender, enrollment in teaching positions, and area of specialization. MATERIAL AND METHODS: This cross-sectional questionnaire-based study was conducted among Brazilian dentists between June and November 2012. The questionnaire comprised 27 questions divided into four different sections: socio-demographic characteristics, questions about their clinical practice toward implant therapy, decision making in four clinical cases, and agreement with different statements regarding endodontic, periodontal, and implant therapy. RESULTS: A total of 155 dentists answered the questionnaire with an average age of 35.5 years. Fifty-one percent were male, and 44.5% were involved in teaching positions. One hundred and thirty-six (87.7%) respondents had already pursued a post-graduation program or were currently involved in one. 33.5% placed dental implants, 42% provided implant maintenance care to their patients, while 30% performed treatment of peri-implant diseases themselves. Dental faculty and dentists who had not followed any further training program, preferred the use of regenerative therapies more frequently. As opposed, dentists not involved in teaching positions, and periodontists were more prone to select resective therapies. CONCLUSION: Results suggest that dentists' decision making did not follow the latest external evidence, which might be related to factors as professional expertise and patients' preferences. Considering the difficulties faced by professionals when handling complex cases, there is an urgent need to establish international protocols and guidelines to help the clinician identify this particular treatment option, which corresponds with their internal evidence and is based on good external evidence.

Impact of adhesive surface and volume of luting resin on fracture resistance of root filled teeth.

AIM: To investigate the correlation between geometric parameters of severely compromised root filled (RCT) pre-molar teeth with irregular root canals and their fracture resistance. The null hypothesis tested was that the fracture resistance of root filled teeth is not influenced by: (i) the adhesive surface of the post-space preparation (A(PS) ), (ii) the coronal tooth surface (A(A) ), (iii) the amount of resin cement (V(C) ) and (iv) the Young's modulus of the specimens. METHODOLOGY: A total of 48 noncarious human pre-molar teeth with irregular root canals were decoronated, root filled and adhesively restored with post-retained direct composite crowns. After thermomechanical loading (1,200,000×, 5-50° C), static load was applied until failure. The geometric parameters of the tooth were evaluated by microcomputed tomography (µCT) using impressions taken after post-space preparation. Linear regression analyses were performed to correlate the geometric parameters of the specimens with their fracture resistance. RESULTS: The amount of resin cement (V(C) ) comprised up to 88% of the entire post-space (mean 67%) and had no impact on the maximal load (P = 0.88). The latter was significantly influenced by post-space preparation (P = 0.003). CONCLUSIONS: Amongst the geometric parameters tested, the surface area in the root canal had the greatest impact on fracture resistance of root filled pre-molars restored with posts and composite crowns, whilst the fit of the post was less important.

[Immediately loaded MonoType implants in the edentulous mandible]. / Sofort belastete MonoType-Implantate im zahnlosen Unterkiefer.

Results of immediately loaded implants are presented. 34 patients with 136 interforaminal MonoType implants (Straumann,Basel, Switzerland) were included in the study. The bar retention was manufactured fter the operation, inserted and covered with a hybrid prosthesis. 28 patients showed up for the follow-up study, the average time range was three years. Five implants were rated as failures, the cumulative six-year success rate being 94%. Interforaminal immediately loaded MonoType implants in edentulous patients showed very good results, comparable to similar studies with different systems.

Disruptive Innovation in Dentistry: What It Is and What Could Be Next.

Dentistry is a technically oriented profession, and the health care sector is significantly influenced by the ubiquitous trend of digitalization. Some of these digital developments have the potential to result in disruptive changes for dental practice, while others may turn out to be just a pipedream. This Discovery! essay focuses on innovations built on artificial intelligence (AI) as the center-technology influencing 1) dental eHealth data management, 2) clinical and technical health care applications, and 3) services and operations. AI systems enable personalized dental medicine workflows by analyzing all eHealth data gathered from an individual patient. Besides dental-specific data, this also includes genomic, proteomic, and metabolomic information and therefore facilitates optimized and personalized treatment strategies and risk management. Based on the power of AI, the triangular frame of "data"/"health care"/"service" is supplemented by technological advancements in the field of social media, Internet of things, augmented and virtual reality, rapid prototyping, and intraoral optical scanning as well as teledentistry. Innovation continues to be critical to tackle dental problems until its routine implementation based on sound scientific evidence. Novel technologies must be viewed critically in relation to the cost-benefit ratio and the ethical implications of a misleading diagnosis or treatment produced by AI algorithms. Highly sensitive eHealth data must be handled responsibly to enable the immense benefits of these technologies to be realized for society. The focus on patient-centered research and the development of personalized dental medicine have the potential to improve individual and public health, as well as clarify the interconnectivity of disease in a more cost-effective way.

Influence of Material and Surface Roughness of Resin Composite Cements on Fibroblast Behavior.

CLINICAL RELEVANCE: A well-polished cement surface increases the viability and spreading of gingival fibroblasts. The tested resin composite cements did not reveal any cytotoxic effects. SUMMARY: Objective: This in vitro study aimed to investigate the effect of cement type and roughness on the viability and cell morphology of human gingival fibroblasts (HGF-1).Methods and Materials: Discs of three adhesive (Panavia V5 [PV5], Multilink Automix [MLA], RelyX Ultimate [RUL] and three self-adhesive (Panavia SA plus [PSA], SpeedCem plus [SCP], RelyX Unicem [RUN]) resin composite cements were prepared with three different roughnesses using silica paper grit P180, P400, or P2500. The cement specimens were characterized by surface roughness and energy-dispersive X-ray spectroscopic mapping. A viability assay was performed after 24 hours of incubation of HGF-1 cells on cement specimens. Cell morphology was examined with scanning electron microscopy.Results: The roughness of the specimens did not differ significantly among the different resin composite cements. Mean Ra values for the three surface treatments were 1.62 ± 0.34 µm for P180, 0.79 ± 0.20 µm for P400, and 0.17 ± 0.08 µm for P2500. HGF-1 viability was significantly influenced by the cement material and the specimens' roughness, with the highest viability for PSA ≥ RUN = MLA ≥ SCP = PV5 > RUL (p<0.05) and for P2500 = P400 > P180 (p<0.001). Cell morphology did not vary among the materials but was affected by the surface roughness.Conclusion: The composition of resin composite cements significantly affects the cell viability of HGF-1. Smooth resin composite cement surfaces with an Ra of 0.2-0.8 µm accelerate flat cell spreading and formation of filopodia.

Precision of maxillo-mandibular registration with intraoral scanners in vitro.

PURPOSE: To compare the precision of maxillo-mandibular registration and resulting full arch occlusion produced by three intraoral scanners in vitro. METHODS: Six dental models (groups A-F) were scanned five times with intraoral scanners (CEREC, TRIOS, PLANMECA), producing both full arch and two buccal maxillo-mandibular scans. Total surface area of contact points (defined as regions within 0.1mm and all mesh penetrations) was measured, and the distances between four pairs of key points were compared, each two in the posterior and anterior. RESULTS: Total surface area of contact points varied significantly among scanners across all groups. CEREC produced the smallest contact surface areas (5.7-25.3mm2), while PLANMECA tended to produce the largest areas in each group (22.2-60.2mm2). Precision of scanners, as measured by the 95% CI range, varied from 0.1-0.9mm for posterior key points. For anterior key points the 95% CI range was smaller, particularly when multiple posterior teeth were still present (0.04-0.42mm). With progressive loss of posterior units (groups D-F), differences in the anterior occlusion among scanners became significant in five out of six groups (D-F left canines and D, F right canines, p<0.05). CONCLUSIONS: Maxillo-mandibular registrations from three intraoral scanners created significantly different surface areas of occlusal contact. Posterior occlusions revealed lower precision for all scanners than anterior. CEREC tended towards incorrect posterior open bites, whilst TRIOS was most consistent in reproducing occluding units.

B-1a cells and plasma cells in periodontitis lesions.

BACKGROUND AND OBJECTIVE: Host response mechanisms in periodontal tissues are complex and involve numerous systems of interactions between cells. The B-cell lineage seems to predominate in chronic periodontitis lesions. The aim of the present investigation was to study the correlation between inflammatory cells and some functional markers in gingival lesions obtained from subjects with severe chronic periodontitis. MATERIAL AND METHODS: Thirty-eight Caucasian subjects volunteered to take part in the study. A gingival biopsy from one randomly selected diseased proximal site (probing pocket depth > 6 mm and bleeding on probing positive) was obtained from each patient. Immunohistochemical preparation was used to identify inflammatory cells and functional markers. Correlations between the different percentages of cell markers were analyzed by pairwise correlation. RESULTS: B cells (B-1a and B-2 cells) occurred in larger proportions than T cells and plasma cells. A statistically significant correlation was found between the percentage of B-1a cells and plasma cells and between all B lymphocytes and plasma cells. About 60% of B lymphocytes exhibited autoreactive features. CONCLUSION: It is suggested that B-1a cells constitute a significant part of the host response in periodontitis lesions and that plasma cells may develop from both B-2 and B-1a cells.

Influence of post fit and post length on fracture resistance.

AIM: To investigate (i) the impact of post fit (form-congruence) and (ii) the influence of post length on the fracture resistance of severely damaged root filled extracted teeth. METHODOLOGY: Ninety-six single-rooted human teeth were root filled and divided into four groups (n = 24 per group). Post spaces were prepared with a depth of 6 mm (group 1, 3) and 3 mm (group 2, 4). Form-congruence with a maximal fit of the post within the root canal space was obtained in groups 1 and 2, whereas there was no form-congruence in groups 3 and 4. In all groups, glass fibre reinforced composite (FRC) posts were adhesively cemented and direct composite crown build-ups were fabricated without a ferrule. After thermo-mechanical loading (1200000x, 5-50 degrees C), static load was applied until failure. Loads-to-failure [in N] were compared amongst the groups. RESULTS: Post fit did not have a significant influence on fracture resistance, irrespective of the post length. Both groups with post insertion depths of 6 mm resulted in significantly higher mean failure loads (group 1, 394 N; group 3, 408 N) than the groups with post space preparation of 3 mm (group 2, 275 N; group 4, 237 N). CONCLUSIONS: Within the limitations of this study, the fracture resistance of teeth restored with FRC posts and direct resin composite crowns without ferrules was not influenced by post fit within the root canal. These results imply that excessive post space preparation aimed at producing an optimal circumferential post fit is not required to improve fracture resistance of roots.

Endodontics or implants? A review of decisive criteria and guidelines for single tooth restorations and full arch reconstructions.

This review describes practical criteria and a systematic process to aid the treatment planning decision of whether to preserve teeth by root canal treatment (RCT) or extract and provide an implant. Recommendations presented are based on best available evidence from the literature and the expert views of specialists in endodontics and restorative dentistry, including dental implantology. A MEDLINE search was conducted using the terms 'root canal therapy', 'dental implants', 'decision making', 'treatment planning', 'outcome' and 'human', and supplemented by hand-searching. When evaluating the outcome of root canal treatment, an observation period of 4-5 years is required for complete healing of periapical lesions. Dental implants, however, present a de novo situation and a functional period of at least 5 years is often required before peri-implant diseases are established and detected. Good long-term success rates and greater flexibility in clinical management indicate that RCT or retreatment should be performed first in most instances unless the tooth is judged to be unrestorable. When deciding if a compromised tooth of questionable prognosis should be maintained or replaced by an implant, both local, site-specific and more general patient-related factors should be considered. Following systematic evaluation and consideration of the best treatment option in a particular case, a treatment recommendation may then be given in favour or against tooth retention. Whilst single risks are possibly accepted for single tooth restorations, teeth with questionable prognosis and multiple pre-treatment requirements are better not included as abutments in fixed dental prostheses to reduce the risk to survival of the entire restoration.

Augmented and virtual reality in dental medicine: A systematic review.

BACKGROUND: The aim of this systematic review was to provide an update on the contemporary knowledge and scientific development of augmented reality (AR) and virtual reality (VR) in dental medicine, and to identify future research needs to accomplish its clinical translation. METHOD: A modified PICO-strategy was performed using an electronic (MEDLINE, EMBASE, CENTRAL) plus manual search up to 12/2018 exploring AR/VR in dentistry in the last 5 years. Inclusion criteria were limited to human studies focusing on the clinical application of AR/VR and associated field of interest in dental medicine. RESULTS: The systematic search identified 315 titles, whereas 87 abstracts and successively 32 full-texts were selected for review, resulting in 16 studies for final inclusion. AR/VR-technologies were predominantly used for educational motor skill training (n = 9 studies), clinical testing of maxillofacial surgical protocols (n = 5), investigation of human anatomy (n = 1), and the treatment of patients with dental phobia (n = 1). Due to the heterogeneity of the included studies, meta-analyses could not be performed. CONCLUSIONS: The overall number of includable studies was low; and scientifically proven recommendations for clinical protocols could not be given at this time. However, AR/VR-applications are of increasing interest and importance in dental under- and postgraduate education offering interactive learning concepts with 24/7-access and objective evaluation. In maxillofacial surgery, AR/VR-technology is a promising tool for complex procedures and can help to deliver predictable and safe therapy outcomes. Future research should focus on establishing technological standards with high data quality and developing approved applications for dental AR/VR-devices for clinical routine.

Patient assessment and diagnosis in implant treatment.

As in any dental treatment procedure, a thorough patient assessment is a prerequisite for adequate treatment planning including dental implants. The literature was searched for references to patient assessment in implant treatment up to September 2007 in Medline via PubMed and an additional handsearch was performed. Patient assessment included the following aspects: (1) evaluation of patient's history, his/her complaints, desires and preferences; (2) extra-and intra-oral examination with periodontal and restorative status of the remaining dentition; (3) obligatory prerequisites were a panoramic radiograph and periapical radiographs (at least from the adjacent teeth) for diagnosis and treatment planning. Additional tomographs are required depending on the anatomic situation and the complexity of the planned restoration; (4) study casts are needed especially in more complex situations also requiring a diagnostic set-up, which can be tried-in and transferred into a provisional restoration as well as into a radiographic and surgical template. The current review clearly revealed the necessity for a thorough, structured patient assessment. Following an evaluation, a recommendation is given for implant therapy or, if not indicated, conventional treatment alternatives can be presented.

Performance of Monolithic and Veneered Zirconia Crowns After Endodontic Treatment and Different Repair Strategies.

OBJECTIVES: To investigate failure loads of monolithic and veneered all-ceramic crowns after root canal treatment and to analyze marginal integrity of repair fillings. METHODS AND MATERIALS: Seventy-two human molars were restored with monolithic (Zr-All) or veneered (Zr-Ven) zirconia crowns. Molars were assigned to six groups (n=12 per group) depending on restoration material, access type (no access cavity [control] or endodontic treatment [test]), and type of filling (one-step [1-st] or two-step [2-st]). For type of filling, molars were treated using a self-etch universal adhesive and cavities were either filled with layered composite (1-st) or filled until the crown material was reached, which was additionally conditioned and then filled (2-st). Scanning electron microscopic analysis of the restoration margins was performed before and after thermomechanical loading (TML), and the percentage of continuous margins was assessed. Crowns were then loaded to failure. RESULTS: Preparation of the access cavity required more time in monolithic (445 s) than in veneered crowns (342 s). Loads to failure were higher in control groups (Zr-All: 5814 N; Zr-Ven: 2133 N) and higher in monolithic test (2985 N) than in veneered test crowns (889 N). In monolithic crowns, 1-st had lower fracture loads than 2-st fillings (2149 N vs 3821 N). Continuous margins of 66% to 71% were achieved, which deteriorated after TML by 39% to 40% in Zr-All, by 34% in Zr-Ven-1-st, and by 24% in Zr-Ven-2-st. CONCLUSIONS: Endodontic access and adhesive restorations resulted in reduced fracture load in monolithic and veneered zirconia crowns. Two-step fillings provided higher fracture loads in Zr-All and better marginal quality in Zr-Ven crowns.

A cost-effectiveness analysis of implant overdentures.

Placement of dental implants may improve the retention and stability of complete dentures in edentulous patients. Treatment costs, however, substantially increase with implant treatment. We therefore performed a stochastic cost-effectiveness analysis, comparing implant-supported over-denture prostheses (4 implants), implant-retained overdentures (2 implants), and complete dentures, from the patient's perspective in Switzerland, to assess whether implant treatment in the mandible represents value for money spent. Twenty patients were included in each treatment group and were followed up for three years. Health outcomes were expressed in Quality-adjusted Prosthesis Years, and dental health care costs and time costs were recorded in year 2000 Swiss Francs (CHF 100 = US dollars 61). The cost per Quality-adjusted Prosthesis Year gained for implant treatment was CHF 9100 (2 implants) and CHF 19,800 (4 implants) over 3 years. Over a ten-year period, these threshold ratios were reduced to CHF 3800 (2 implants) and CHF 7100 (4 implants) per Quality-adjusted Prosthesis Year gained.

Structural characterisation of two forms of procyclic acidic repetitive protein expressed by procyclic forms of Trypanosoma brucei.

A procyclic acidic repetitive protein (PARP) fraction was purified from long-term cultures of Trypanosoma brucei procyclic forms by a solvent-extraction and reverse phase chromatography procedure. The PARP fraction yielded small quantities of a single N-linked oligosaccharide with the structure Man alpha1-6(Man alpha1-3)Man alpha1-6(Man alpha1-3)Manbeta1-4GlcNAcbeta1-4GlcNAc (Man5GlcNAc2). Fractionation of PARP on Con A-Sepharose revealed that the majority (80 to 90%) of the PARP fraction did not bind to Con A and was composed of the parpA alpha gene product that contains repeats of -Glu-Pro-Pro-Thr- (GPEET-PARP) and that lacks an N-glycosylation site. This form of PARP has not been previously identified at the protein-level. The minor Con-A-binding fraction was shown to be rich in the previously described form of PARP, encoded by the parpAbeta and/or parpB alpha genes, that contains a -Glu-Pro- repeat domain (EP-PARP) and an N-glycosylation site. Analysis of longer and shorter-term cultures suggested that procyclic cells initially express predominantly EP-PARP that is gradually replaced by GPEET-PARP. Both forms of PARP were shown to contain indistinguishable glycosylphosphatidylinositol (GPI) membrane anchors, where the conserved GPI core structure is substituted by heterogeneous sialylated branched polylactosamine-like structures that are predicted to form a dense surface glycocalyx above which the polyanionic -Glu-Pro-Pro-Thr- and -Glu-Pro- repeat domains are displayed. The phosphatidylinositol (PI) component of the GPI anchor was shown to be a mixture of 2-O-acyl-myo-inositol-1-HPO4-(sn-1-stearoyl-2-lyso-glycerol) and 2-O-acyl-myo-inositol-1-HPO4-(sn-1-octadecyl-2-lyso-glycerol), where the acyl chain substituting the inositol ring showed considerable heterogeneity. Mass spectrometric and light scattering experiments both suggested an average mass of approximately 15 kDa for GPEET-PARP, with individual glycoforms ranging from about 12 kDa to 20 kDa, that is consistent with its amino acid and carbohydrate composition. A measured translational diffusion coefficient of 3.9 x 10(7) cm2 s(-1) indicates that this molecule has a highly elongated shape. The possible functions of these unusual glycoproteins are discussed.

Alpha-glucosidase inhibitors as potential broad based anti-viral agents.

N-Linked oligosaccharides play many roles in the fate and functions of glycoproteins. One function is to assist in the folding of proteins by mediating interactions of the lectin-like chaperone proteins calnexin and calreticulin with nascent glycoproteins. These interactions can be prevented by inhibitors of the alpha-glucosidases and this causes some proteins to be misfolded and retained within the endoplasmic reticulum. In human immunodeficiency virus (HIV) and hepatitis B virus (HBV) the misfolding of key viral envelope glycoproteins interferes with the viral life cycle. It has been demonstrated in an animal model of chronic HBV that glucosidase inhibitors can alter glycosylation and have anti-viral activity. As the mechanism of action of alpha-glucosidase inhibitors is the induction of misfolded or otherwise defective viral glycoproteins, such inhibitors may be useful therapeutics for many viruses, especially those which bud from the endoplasmic reticulum (where protein folding takes place). For example bovine viral diarrhea virus, a pestivirus akin to hepatitis C virus, is also extremely sensitive to glucosidase inhibition.

The glycosylation of the variant surface glycoproteins and procyclic acidic repetitive proteins of Trypanosoma brucei.

Trypanosoma brucei, in common with the other African trypanosomes, exhibits unusual cell-surface molecular architecture. The bloodstream form of the parasite is coated with a continuous layer of approximately five million variant surface glycoprotein (VSG) dimers that provide the parasite with a macromolecular diffusion barrier to guard against lysis by the alternative complement pathway. The procyclic form of the parasite has a more diffuse cell-surface coat made up of approximately 2.5 million copies of procyclic acidic repetitive protein (PARP). Within the VSG and PARP coats exist lower-abundance surface glycoproteins such as receptors and nutrient transporters. Both the VSG molecules and the PARP molecules are attached to the membrane via glycosylphosphatidylinositol (GPI) membrane anchors and the VSGs and one form of PARP are N-glycosylated. In this article, the structures of the N-glycans and the GPI anchors of T. brucei VSGs and PARPs are reviewed and simple models of the surfaces of bloodstream and procyclic trypomastigotes are presented.

RNA replication kinetics, genetic polymorphism and selection in the case of the hepatitis C virus.

We show in a simple theoretical quasispecies model that the replication dynamics of hepatitis C virus and a related model-system, the bovine viral diarrhoea virus, result in an effective reduction of RNA templates in infected cells. Viral fitness does not translate directly into RNA sequence replication efficiency, and hence the abundance of the viral master sequences diminishes over time. Our results suggest that genes not involved in RNA replication accumulate mutations over time because they do not undergo selection during this phase. The selection of viral RNA occurs not only during replication but also during the ensuing stages of the viral life cycle: (i) envelopment of viral RNA and (ii) successful infection of other cells, which also requires functionality of non-replicative genes. In particular, viral fitness requires the ability of the genome to encode structural proteins which do not encounter selective pressure during RNA replication. We conclude by discussing the potential value of antiviral drugs which inhibit selection on parts of the viral genome.

Resorbable versus nonresorbable membranes in combination with Bio-Oss for guided bone regeneration.

The purpose of this clinical investigation was to compare the new resorbable collagen membrane, Bio-Gide, to the conventional expanded polytetrafluoroethylene material (Gore-Tex) for guided bone regeneration in situations involving exposed implant surfaces. Over a 2-year period, 25 split-mouth patients were treated randomly: one defect site was treated with Bio-Gide and the other defect site with Gore-Tex; all 84 defects were filled with Bio-Oss and covered with the respective membrane. The defect types, their dimensions, and their morphology were measured in detail initially and at re-entry to allow for calculation of the exposed implant surface. Changes in defect surface for both types of membranes were statistically significant (P < .0001); however, no statistical significance (P > .94) could be detected between the two membranes. The mean average percentage of bone fill was 92% for Bio-Gide and 78% for Gore-Tex sites. In the latter group, 44% wound dehiscences and/or premature membrane removal occurred. The resorbable membrane, Bio-Gide, in combination with a bone graft, can be a useful alternative to the well-established expanded polytetrafluoroethylene membranes.