Mechanics of the tapered interference fit in dental implants

In evaluation of the long-term success of a dental implant, the reliability and the stability of the implant-abutment interface plays a great role. Tapered interference fits provide a reliable connection method between the abutment and the implant. In this work, the mechanics of the tapered interference fits were analyzed using a closed-form formula and the finite element (FE) method. An analytical solution, which is used to predict the contact pressure in a straight interference, was modified to predict the contact pressure in the tapered implant-abutment interface. Elastic-plastic FE analysis was used to simulate the implant and abutment material behavior. The validity and the applicability of the analytical solution were investigated by comparisons with the FE model for a range of problem parameters. It was shown that the analytical solution could be used to determine the pull-out force and loosening-torque with 5-10% error. Detailed analysis of the stress distribution due to tapered interference fit, in a commercially available, abutment-implant system was carried out. This analysis shows that plastic deformation in the implant limits the increase in the pull-out force that would have been otherwise predicted by higher interference values.     

Mechanics of the taper integrated screwed-in (TIS) abutments used in dental implants

The tapered implant-abutment interface is becoming more popular due to the mechanical reliability of retention it provides. Consequently, understanding the mechanical properties of the tapered interface with or without a screw at the bottom has been the subject of a considerable amount of studies involving experiments and finite element (FE) analysis. This paper focuses on the tapered implant-abutment interface with a screw integrated at the bottom of the abutment. The tightening and loosening torques are the main factors in determining the reliability and the stability of the attachment. Analytical formulas are developed to predict tightening and loosening torque values by combining the equations related to the tapered interface with screw mechanics equations. This enables the identification of the effects of the parameters such as friction, geometric properties of the screw, the taper angle, and the elastic properties of the materials on the mechanics of the system. In particular, a relation between the tightening torque and the screw pretension is identified. It was shown that the loosening torque is smaller than the tightening torque for typical values of the parameters. Most of the tightening load is carried by the tapered section of the abutment, and in certain combinations of the parameters the pretension in the screw may become zero. The calculations performed to determine the loosening torque as a percentage of tightening torque resulted in the range 85-137%, depending on the values of taper angle and the friction coefficient.     

Genome analysis and clinical implications of the bacterial communities in early biofilm formation on dental implants restored with titanium or zirconia abutments

This cross-sectional study aimed to identify and quantify up to 42 target species colonizing the early biofilm of dental implants restored with titanium or zirconia abutments. A total of 720 samples from 20 healthy individuals were investigated. Biofilm samples were collected from the peri-implant sulci, inner parts of implants, abutment surfaces and prosthetic crowns over a functioning period of 30 days. Checkerboard DNA–DNA hybridization was used for microbial detection and quantitation. Clinical characteristics (probing depth, bleeding on probing, clinical attachment level and marginal bone loss) were also investigated during the monitoring period. Genome counts were low at the implant loading time point for both the abutment materials, and increased over time. Both the titanium and the zirconia groups presented similar microbial counts and diversity over time, and the microbiota was very similar to that colonizing the remaining teeth. Clinical findings were consistent with a healthy condition with no significant difference regarding marginal bone loss between the two materials.     

Predicting bone remodeling around tissue- and bone-level dental implants used in reduced bone width

The objective of this study was to predict time-dependent bone remodeling around tissue- and bone-level dental implants used in patients with reduced bone width. The remodeling of bone around titanium tissue-level, and titanium and titanium–zirconium alloy bone-level implants was studied under 100 N oblique load for one month by implementing the Stanford theory into three-dimensional finite element models. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x- and y- axes of the implant were evaluated. Maximum and minimum principal stresses around tissue-level implant were higher than bone-level implants and both bone-level implants experienced comparable stresses. Total strain energy density in bone around titanium implants slightly decreased during the first two weeks of loading followed by a recovery, and the titanium–zirconium implant showed minor changes in the axial plane. Total strain energy density changes in the loading and contralateral sides were higher in tissue-level implant than other implants in the cortical bone at the horizontal plane. The displacement values of the implants were almost constant over time. Tissue-level implants were associated with higher stresses than bone-level implants. The time-dependent biomechanical outcome of titanium–zirconium alloy bone-level implant was comparable to the titanium implant.     

Proteome analysis of human serum proteins adsorbed onto different titanium surfaces used in dental implants

Titanium dental implants are commonly used due to their biocompatibility and biochemical properties; blasted acid-etched Ti is used more frequently than smooth Ti surfaces. In this study, physico-chemical characterisation revealed important differences in roughness, chemical composition and hydrophilicity, but no differences were found in cellular in vitro studies (proliferation and mineralization). However, the deposition of proteins onto the implant surface might affect in vivo osseointegration. To test that hypothesis, protein layers formed on discs of both surface type after incubation with human serum were analysed. Using mass spectrometry (LC/MS/MS), 218 proteins were identified, 30 of which were associated with bone metabolism. Interestingly, Apo E, antithrombin and protein C adsorbed mostly onto blasted and acid-etched Ti, whereas the proteins of the complement system (C3) were found predominantly on smooth Ti surfaces. These results suggest that physico-chemical characteristics could be responsible for the differences observed in the adsorbed protein layer.     

Efficiency considerations in the analysis of inter-observer agreement

The reliability of binary assessments is often measured by the proportion of agreement above chance, as estimated by the kappa statistic. In this paper, we develop a model to estimate inter-rater and intra-rater reliability when each of the two observers has the opportunity to obtain a pair of replicate measurements on each subject. The model is analogous to the nested beta-binomial model proposed by Rosner (1989, 1992). We show that the gain in precision obtained from increasing the number of measurements per rater from one to two may allow fewer subjects to be included in the study with no net loss in efficiency for estimating the inter-rater reliability.     

Simulated bone remodeling around tilted dental implants in the anterior maxilla

Dental implants have to be placed with the long axis in different angulations due to the change in bone morphology. The objective of this study was to investigate the different bone remodeling response induced by the tilted dental implants and to assess whether it could lead to bone loss and implant failure. In this study, bone remodeling due to palato-labially inclined dental implants placed in the anterior maxillary incisor region was simulated. CT-based finite element models of a maxillary bone with dental implants were created herein. Five dental implants were placed at \(+10^{\circ }\), \(+5^{\circ }\), \(0^{\circ }\), \(-5^{\circ }\) and \(-10^{\circ }\), respectively. The remodeling progression was recorded and compared. Model \(-10^{\circ }\) (palatal side) shows the highest bone density values, but the inclined implant at \(+10^{\circ }\) (labial side) leads to significant bone loss. From a biomechanical perspective, it is speculated that a palatally inclined implant is more likely to enhance the bone density in the maxillary anterior region, but labial inclination of implant could jeopardize its stability.     

Prosthetic rehabilitation of a patient with mandibular resection prosthesis using mini dental implants (MDIs)--case report

Physical disfigurement and functional impairments associated with facial trauma are a challenge to a prosthodontist, because even novel sophisticated surgical reconstructive techniques fail to provide adequate support for dental resection prosthesis. Therefore, different endosseous implants are often used as prosthesis-supporting elements. Manufacturers of dental implants have recently presented mini dental implants (MDIs) with diameter of only 1.8-2.4 mm. These implants allow very suitable prosthetic solutions within the range of their indications due to good osseointegration success rates, simple surgical technique, and immediate loading possibility. In this report, a case was presented for prosthetic rehabilitation including implantation of two Sendax type (IMTEC, Ardmore, Oklahoma, USA) MDIs in mental region, to obtain better retention and stability of the mandibular resection prosthesis and to improve function, phonation and aesthetics. The use of these implants, among aforementioned preferences, is also very cost-effective, so this implantation possibility should be taken into consideration during prosthetic treatment planning.     

A method for in vivo measurements of implants used in the reconstruction of spinal fractures]

Little is known about the forces and moments acting on the spinal column during various movements and activities, and thus about the loading of implants used in the treatment of spinal fractures. A measuring method using an external fixation device was developed to determine the in vivo loading of spinal implants. On the basis of these data the forces acting on the spine can be calculated. The present paper describes this measuring method as applied to the fixation device, and initial experience with this device in a first application is presented.     

Biodegradable dental implants of ciprofloxacin beta-cyclodextrin inclusion complex in the treatment of periodontitis

Dental implants of ciprofloxacin beta-cyclodextrin inclusion complex were formulated using poly (epsilon-caprolactone), a biodegradable polymer and evaluated. Clinical evaluation was carried out in ten patients with acute peridontitis. Various clinical parameters, viz. gingival index, plaque score, attachment gain, reduction in pocket depth were evaluated at 10, 20, 30, 40 days of treatment and compared with placebo as control. A significant (P < 0.0001) improvement in the healing of periodontal pockets treated with ciprofloxacin beta-cyclodextrin implant was observed in most of the clinical parameters. Estimation of gingival crevicular fluids (GCF) for the drug content revealed that drug levels above the minimum inhibitory concentration (10.2 micrograms/mg) for many of the periodontal pathogens were maintained throughout the period of study (40 days). This confirms the clinical efficacy of the dose and the duration of the study. It was found that biodegradable carrier was better accepted than the non-biodegradable carriers reported earlier.     

Assessment of the genetic risks of a metallic alloy used in medical implants

The use of artificial implants provides a palliative or permanent solution for individuals who have lost some bodily function through disease, an accident or natural wear. This functional loss can be compensated for by the use of medical devices produced from special biomaterials. Titanium alloy (Ti-6Al-4V) is a well-established primary metallic biomaterial for orthopedic implants, but the toxicity of the chemical components of this alloy has become an issue of concern. In this work, we used the MTT assay and micronucleus assay to examine the cytotoxicity and genotoxicity, respectively, of an extract obtained from this alloy. The MTT assay indicated that the mitochondrial activity and cell viability of CHO-K1 cells were unaffected by exposure to the extract. However, the micronucleus assay revealed DNA damage and an increase in micronucleus frequency at all of the concentrations tested. These results show that ions released from Ti-6Al-4V alloy can cause DNA and nuclear damage and reinforce the importance of assessing the safety of metallic medical devices constructed from biomaterials.     

Perinatal dental development in the chimpanzee (Pan troglodytes)

The synthesis of both ontogenetic and phylogenetic data should provide the ideal explanation of morphologic variation, but for the primate dentition, this has not yet occurred. Information concerning growth and development of primate teeth is lacking, in part because of the paucity of specimens. We have therefore examined the deciduous second molars (dm2) and tooth buds of the permanent first molar (M1) of 12 chimpanzees (Pan troglodytes), aged 6.5 months of gestation to 4 postnatal months. The ordering of cusp calcification was identical to that of other primates. By regression analysis, correlations of mesial and distal widths with buccal, lingual, and mesiodistal lengths were low, most probably because of decreased rates of change (slopes) and the relatively small sample size. Correlations were, however, greater for mandibular than for maxillary dentition and higher for age than for body weight; for both the dm2 and M1, distal moieties increased faster and were more highly correlated with other dental variables and age than were mesial ones. Comparison with data from humans revealed both differences and similarities in the absolute size and growth rate of dental moieties during the perinatal period. As the reasons for ontogenetic variation become understood for individuals, species, and higher taxa, the phylogenetic implications of differential growth should become clearer as well.     

Guidelines and ethical considerations for housing and management of psittacine birds used in research

The Psittaciformes are a large order of landbirds comprising over 350 species in about 83 genera. In 2009, 141 published studies implicated parrots as research subjects; in 31 of these studies, 483 individuals from 45 different species could be considered laboratory animals. Amazons and budgerigars were by far the most represented psittacine species. The laboratory research topics were categorized as either veterinary medicine and diagnostics (bacteriology, hematology, morphology, and reproduction; 45%) or behavioral and sensory studies (behavior, acoustics, and vision; 17%). Confinement of psittacine species for research purposes is a matter of concern as scientifically based species-specific housing guidelines are scarce. The aim of this article is to provide scientific information relevant to the laboratory confinement of Psittaciformes to promote the refinement of acquisition, housing, and maintenance practices of these birds as laboratory animals. We briefly discuss systematics, geographical distribution, legislation, and conservation status as background information on laboratory parrot confinement. The following section presents welfare concerns related to captive containment (including domestication status) and psittacine cognition. We then discuss considerations in the acquisition of laboratory parrots and review important management issues such as nutrition, zoonoses, housing, and environmental enrichment. The final section reviews indications of distress and compromised welfare.     

Sampling considerations for garden symphylans (Order: Cephalostigmata) in western Oregon

Sampling recommendations were developed for a potato bait sampling method used to estimate garden symphylan (Scutigerella immaculata Newport) densities in western Oregon. Sample size requirements were developed using Taylor's power law to describe the relationship between sample means and variances. Developed sampling recommendations performed well at sample sizes of 30 and greater, when validated by resampling a cohort of 40 independent data sets. Sample size requirements for the bait sampling method were 1.5 times greater than the requirements for the soil sampling method over densities from 1 to 20 S. immaculata per sample unit. As S. immaculata densities increased from April to May, sample size requirements decreased by 36% for fixed precision levels. For sampling in April, decreasing the damage threshold from 20, to 10 and five S. immaculata per sample unit, required a 1.6 and 2.5 times greater sample size requirement, respectively, for a fixed precision level (c) appropriate for pest management (c = 0.25). The bait sampling method provides an efficient reliable alternative to the standard soil sampling method used to monitor garden symphylan populations.     

Studies on RTD and continuous culture (SCP) in cylindrical and tapered reactors

The performance of a tapered reactor for the continuous cultivation of bakers' yeast (SCP) from cane molasses has been compared with that of a conventional cylindrical reactor. It is found that the tapered reactor has less non-idealities (bypass and deadspace).Using the experimentally evaluated bypass and deadspace values, a model for predicting conversions of substrate (cane molasses), based on the RTD model proposed by Cholette and Cloutier has been developed. The experimental substrate conversions are found to match the model satisfactorily.List of Symbols D h^–1 dilution rate - E() exit age distribution function - K _s kg/m³ Monod's saturation constant - -r _sa kg/(m³ · h) rate of substrate utilization - S kg/m³ substrate concentration expressed as dextrose equivalent (DE) - S _a kg/m³ substrate concentration in active zone - S ₀ kg/m³ initial substrate concentration - S/S ₀ dimensionless substrate concentration - v _a dm³/h volumetric flow through active zone - v _b dm³/h volumetric flow through bypass stream - u _l dm³/h substrate feed rate - v _g dm³/min air-flow rate - V dm³ total working volume of the reactor - V _a dm³ volume of active zone in reactor - V _d dm³ volume of dead zone in reactor - X kg/m³ biomass concentration Greek Letters fraction of bypass of feed, v _b /v _l - fraction of deadspace, V _d /V - dimensionless residence time - _m h^–1 maximum specific growth rate - h mean residence time, V/v _l      

Substrate-induced conformational fit and headpiece closure in the Ca2+ATPase (SERCA)

Protection of the Ca2+ATPase (SERCA) from proteinase K digestion has been observed following the addition of Ca2+, Mg2+, and nucleotide and interpreted as a substrate-dependent conformational change (1). The protected digestion site is located on the loop connecting the A domain and the M3 transmembrane helix. We studied by mutational analysis the protective effect of AMP-PCP, an ATP analog that is not utilized for enzyme phosphorylation. We found that the nucleotide protective effect is interfered with by single mutations of Arg-560 and Glu-439 in the N domain and Lys-352, Lys-684, Thr-353, Asp-703, and Asp-707 in the P domain. This is consistent with a transition from the open to the compact configuration of the ATPase headpiece and approximation of the N and P domains by interactions with the nucleotide adenosine and phosphate moieties, respectively. The A domain-M3 loop is consequently involved. Protection by nucleotide substrate increased following the mutations of Asp-351 (the residue undergoing phosphorylation by ATP) and neighboring Asn-706 to Ala, underlying the importance of side chain specificity in positioning the nucleotide terminal phosphate and limiting the stability of the substrate-enzyme complex. Protection is not observed when AMP-PCP is added in the absence of Ca2+ or following mutations (E771Q or N796A) that interfere with Ca2+ binding. Therefore, nucleotide binds to the Ca2+-activated enzyme in the open headpiece conformation and the consequent approximation of the N and P domains occurs while the transmembrane domain is still in the Ca2+-bound conformation. Mg2+ is not required for the protective effect of nucleotide, even though it is specifically required for the subsequent catalytic reactions.