What Factors May Influence a Clinician's Choice for an Implant System for Their Patients?

BACKGROUND: Clinicians have to decide which implant system to use for their patients. Factors influencing a clinician's choice of a specific implant are not well-established. PURPOSE: The purpose of this study was to identify factors that may influence clinician's choice of implant. STUDY DESIGN, SETTING, SAMPLE: This cross-sectional study used a survey instrument that was sent to dentists. Inclusion criteria included if the doctor's name was the addressee and if their website indicated they utilize implants. Exclusion criteria included if the email address was directed to individuals other than the clinician or if the respondent does not place implants as indicated by their website. PREDICTOR VARIABLE: The predictor variable was the provider type (oral and maxillofacial surgeon, general dentist, prosthodontist, or periodontist). MAIN OUTCOME VARIABLE: The outcome variables were factors that may influence clinician's choice of implants, measured by their ranked responses. COVARIATES: Age and sex were the covariates. ANALYSES: The survey data were evaluated as group in total and separated for each provider type. Factors affecting clinical choice were ranked. A mean score was determined. Responses were evaluated using analysis of variance with significance at P value < .05 to determine if there were differences among the groups. RESULTS: After applying inclusion and exclusion criteria, the final study sample consisted of 353 clinicians, of whom 230 (65.1%) responded to the survey. Factors scored as extremely or somewhat important were ranked from high to low as follows: clinical trial evidence (92%), ease of use (88%), familiarity with system (73%), restorative dentist's preference (72%), cost (63%), sales representative (59%), key opinion leader (66%), a laboratory's preference (45%), implant company providing continuing education (66%), and implant company can grow practice (65%). There were differences among providers for the factors that influence choice of implant for cost (P value = .02), sales representative (P value = .015), the key opinion leader (P value = .01), laboratory preference (P value = .002), providing continuing education (P value = .02), and implant company can grow my practice (P value = .035). CONCLUSION AND RELEVANCE: Four factors that highly influenced provider's choice of a specific implant were evidence for success, ease of use, cost, and familiarity with the implant.

Transitioning From Teeth to Implants: A Narrative Review.

PURPOSE: Patients may need removal of their teeth with placement of implants for rehabilitation. The clinical problem is the status of the remaining teeth and how this affects the timing for implant placement and the method for provisionalization. The importance of this review is to document the different strategies including sequential tooth removal and grafting and the use of teeth to provide a fixed provisional rather than a removable provisional, to provide surgeons with a reference to maintain patient function during their rehabilitation. METHODS: Pubmed.gov was the information source. Years reviewed included 1990 to 2022. Inclusion criteria included only articles in peer-reviewed journals. Variables evaluated included the success for placing implants immediately into extraction sites, and the methods to transition between steps in their rehabilitation. Data collected were results of systematic reviews and independent clinical series, as well as case reports of prosthetic methods for transitioning. RESULTS: The search used terms which included implants in extraction sites (n = 205) and transitioning teeth to implants (n = 153). Twenty-one articles were reviewed involving extraction sites and 19 articles reviewed concerning transitioning from teeth to implants. The placement of implants immediately into excretion sites did have a relative risk for failure compared to implant placement in healed sites. The use of non-restorable teeth to support a fixed provisional prosthesis was successful; however, variability in reporting prevented a statistical analysis. CONCLUSION: The surgeon needs to utilize teeth to provide support during treatment phases in order to provide the patient with a fixed provisional prosthesis to allow for implant integration and to provide time for graft healing. Specific methods used for transitioning do not have a significant evidence base to recommend one method but routine prosthetic techniques have been used and are reported in case reports.

The Impacted Maxillary Canine in the Adult: A Narrative Review and Implant Treatment Options.

PURPOSE: The purpose of this article is to provide clinicians with options to restore the adult patient with an impacted maxillary canine using dental implants. Literature was reviewed to provide evidence for the methods suggested. METHODS: The search strategy utilized pubmed.gov to identify articles pertinent to identified treatment options. The search used terms which included dental implants and impacted tooth, tilted implants and fixed partial prostheses, 6 mm dental implants, and 4 mm dental implants. Articles were included if they reported dental implant procedures associated with impacted canines in adults, or if they reported on the use of tilted implants, immediate implant placement at time of canine removal, or the use of short implants. Articles with less than 12 months follow up were excluded. RESULTS: The search identified articles which included dental implants and impacted tooth (n = 142), tilted implants and fixed partial (n = 36), 6 mm dental implants (n = 182), and 4 mm dental implants (n = 162). From this search, 28 articles were collated that satisfied the inclusion criteria. The use of tilted implants had success rates ranging from 93% to 99%. Short implants had success rates ranging from 87 to 90% in the posterior maxilla. Immediate implant placement after removal of the impacted canine lacked long term reports. Two cases are included to demonstrate treatment planning using navigation to guide implant placement in an adult patient with an impacted maxillary canine. CONCLUSIONS: The evidence-based literature concerning implant placement associated with adult maxillary canines is limited. There is evidence to support tilting implants to avoid the impacted canine, or the use of short implants splinted together to avoid the impacted tooth. Other options had insufficient data to offer support.

How to Avoid Errors When Using Navigation to Place Implants - A Narrative Review.

PURPOSE: Surgeons placing implants use navigation for implant placement accuracy. The importance of this review is to document the sources of error that are involved with navigation so surgeons can recognize factors to decrease error. The objective is to provide surgeons with a reference to optimize navigation. METHODS: Pubmed.gov was the information source. Years reviewed included 2010 to 2022. The inclusion criteria included only articles in peer-reviewed journals. In vitro results were included only if they involved testing of variables microgap, cone beam computerized tomography (CBCT) accuracy evaluation, or accuracy of printed models. Variables were searched and evaluated. Data collected included the objectives and outcomes of the study including statistical significance. The conclusions made by the authors were confirmed by evaluating the data analysis, and then these conclusions were listed in each error-related topic. RESULTS: The search used terms which included guided implant surgery complications (n = 4,029), accuracy of CBCT scanners (n = 319), accuracy of implant navigation (n = 983), and the error between drills and static guides (n = 3). From this search, 70 articles were collated that satisfied the inclusion criteria. There are multiple sources of error that are less than 1 mm, including but not limited to errors associated with the scanner and method for scanning, errors associated with merging scanned files with the CBCT scan, errors using different guide stent fabrication methods, errors associated with intraoperative techniques, the learning curve, and planning error. If small errors are not taken into consideration, implant placement errors can exceed 1-2 mm of platform location and angulation errors in excess of 8°. CONCLUSION: The surgeon needs to take into consideration controllable factors that will result in the avoidance of implant malposition and thus be able to effectively utilize navigation for accurate implant placement.

Maxillary Full Arch Restorations - Biological Complications: A Narrative Review Outlining Criteria for Long Term Success.

PURPOSE: Patients receiving full arch implant borne maxillary prostheses require functional, esthetic, and long term success. The importance of this review is to document the difficulty with implant maintenance, the prevalence of peri-implant disease, and the improvement in biologic health when using a prosthesis that can be maintained to minimize plaque. The objective is to provide surgeons with a reference to optimize surgical procedures that can result in improved hygiene and long term maintenance, as well as acceptable functional and esthetic goals. METHODS: Pubmed.gov was the information source. Years reviewed included 1990-2022. Inclusion criteria included only articles in journals referenced in pubmed.gov. The reports excluded were case reports, reports that only included implant survival, and articles without a statistical analysis to generate meaningful conclusions. Biological complications included bone loss, hygiene difficulty, mucositis and recession, the incidence of peri-implantitis, and how complications related to patient co-morbidities. Data collected included outcomes of the study including statistical significance. RESULTS: The search identified articles for review using terms which included full arch maxillary restorations (n = 736), long term success with full arch maxillary prostheses (n = 22), ceramic full arch restorations (n = 102), and complications with full arch restorations (n = 231). From this search, 53 articles were collated that satisfied the inclusion criteria. Factors found to be significant contributors to biological complications included bone loss and peri-implant disease, difficulty with daily hygiene access, plaque and biofilm coverage, and the need for continued maintenance for long term implant health. CONCLUSION: The surgeon needs to place implants to allow a full arch maxillary prosthesis to be fabricated with full access to the implants for maintenance, which should decrease the incidence of biological complications. With excellent maintenance full arch implant restorations can have limited peri-implant disease.

Atom-at-a-time laser resonance ionization spectroscopy of nobelium.

Optical spectroscopy of a primordial isotope has traditionally formed the basis for understanding the atomic structure of an element. Such studies have been conducted for most elements and theoretical modelling can be performed to high precision, taking into account relativistic effects that scale approximately as the square of the atomic number. However, for the transfermium elements (those with atomic numbers greater than 100), the atomic structure is experimentally unknown. These radioactive elements are produced in nuclear fusion reactions at rates of only a few atoms per second at most and must be studied immediately following their production, which has so far precluded their optical spectroscopy. Here we report laser resonance ionization spectroscopy of nobelium (No; atomic number 102) in single-atom-at-a-time quantities, in which we identify the ground-state transition 1S01P1. By combining this result with data from an observed Rydberg series, we obtain an upper limit for the ionization potential of nobelium. These accurate results from direct laser excitations of outer-shell electrons cannot be achieved using state-of-the-art relativistic many-body calculations that include quantum electrodynamic effects, owing to large uncertainties in the modelled transition energies of the complex systems under consideration. Our work opens the door to high-precision measurements of various atomic and nuclear properties of elements heavier than nobelium, and motivates future theoretical work.

Evidence-Based Criteria for an Ideal Abutment Implant Connection-A Narrative Review.

IMPORTANCE: Long-term success with a dental implant restoration relies on a stable connection between the abutment and the implant. The purpose of this article is to review current knowledge of the abutment interface, identify problems that develop due to wear and mismatch of parts, and use a problem list to propose a solution. The objective was to provide a concise overview that clinicians can then use to choose a system that addresses the problems of the abutment implant interface. OBSERVATIONS: Manufacturing methods will result in surface variations across the surface of the abutment and implant. Microgaps change in dimension upon function due to wear. Bacterial leakage can lead secondary to functional wear, and the microgap will get larger. The increase in the microgap with function has been clinically verified. Micromotion will result in larger areas of surface gap in both flat and conical connections, with gaps larger than the size of bacteria. CONCLUSIONS AND RELEVANCE: For an ideal abutment, an implant system must have high tolerances for manufacturing with minimal gap formation along the abutment to implant surface; a connection that is resistant to micromotion; screws that have minimal deformation during loading; and a microgap less than 1 micron which is maintained during implant function.

Algorithmic Approach to Reconstruct Major Implant and Dental Complications.

PURPOSE: Patients with failing implants or teeth may require multiple procedures to correct their problems. The purpose of this article was to describe an algorithmic approach for clinicians to use to simplify the restoration of the patient. METHODS: The topics for this article were used to search for references using PubMed. Topics included the effect of thickening thin gingiva to promote stable soft tissue margins, the use of different bone graft materials for sockets and for ridge augmentation, and methods to use digital technology for efficient planning. Other sources were book chapters, which had an extensive reference section including multiple case series and clinical trial results. Based on the search results, references were chosen that would verify the techniques suggested to be used for these problems. For this narrative, diagnostic information is described using virtual digital methods rather than analog methods to develop the final prosthetic plan, which guides the surgical procedures. The surgical phases are described in detail. RESULTS: The gingiva needs to be healthy and thick to support a hard tissue graft. The timing of procedures begins with assessment of the quality of the soft tissue and the loss of both soft and hard tissues. The operative procedures should be based on the final prosthetic plan, created digitally, to provide information that is required to properly position soft and hard tissue grafts and the implants. CONCLUSIONS: This organized, algorithmic approach can be used for many situations that clinicians are seeing in their daily practice due to complications that can occur.

Prediction of Residual Alveolar Bone Height in the Posterior Maxilla After Dental Extractions.

PURPOSE: After tooth extraction in the posterior maxilla, bone resorption often limits implant placement unless additional grafting procedures are performed. However, it is difficult to predict the amount of bone that will remain after extraction based on current evidence. The purpose of this study was to develop a method for predicting the postextraction alveolar bone height in the posterior maxilla. PATIENTS AND METHODS: The authors conducted a retrospective cohort study that included all patients who were treated for the extraction and replacement of a maxillary first molar with a dental implant from 2008 to 2019. Potential predictor variables included thirteen pre-extraction radiographic measurements obtained via cone-beam computed tomography. The outcome variable was having more than 6 mm of bone height from the alveolar crest to the sinus floor after extraction. Decision tree analyses were used to search for the best predictors of this outcome using random forest analysis with a maximum of 3 randomly chosen covariates in each candidate tree. RESULTS: A total of 63 patients were included in the study; 55.6% were women, and the mean age was 57.6 ± 14.5 years. In this study population, having a bone height from the furcation to the maxillary sinus floor of <6.7 mm had a 7.1% chance of having >6 mm of bone height postoperatively, whereas those patients with ≥6.7 mm at the same position preoperatively had a 61.9% chance of having >6 mm of bone height postoperatively (P < .001). CONCLUSIONS: This study suggests that patients with <6.7 mm of bone from the furcation to the sinus are at increased risk of having insufficient bone to support a dental implant without additional grafting at the maxillary first molar position. When treating these patients, the surgeon should consider performing a procedure at the time of extraction to increase bone height or explain additional bone grafting is expected for ideal implant placement.

Porous Bone Increases the Risk of Posterior Mandibular Implant Failure.

PURPOSE: Our recent study indicated that patients with osteoporosis had an increased risk for early and late implant failure perhaps due to a large cancellous space. Therefore, the purpose of the article is to explore the relationship between the amount of cancellous space in an implant site and implant failure. PATIENTS AND METHODS: The authors conducted a retrospective cohort study on patients who received dental implants in the posterior mandible at the senior author's practice from January 1, 2008 to October 1, 2019. The primary outcome variable was time to implant failure. The primary predictor variable was the amount of cancellous bone between the buccal and lingual cortices (cancellous space). Other study variables included demographic variables, medical history variables, and implant site measurements. Statistical analysis was performed using descriptive statistics, chi-squared tests, single variable and multiple Cox proportional hazard analyses. RESULTS: The study cohort (n = 220) was composed of 62.3% women and the average age was 58.2 years. The median follow-up time was 3.5 years (range: 1-12). Five-year survival rates for patients with a cancellous space of <4 mm was 100%, with a cancellous space of 4-6 mm was 95.3%, with a cancellous space of 6-8 mm was 88.2%, and with a cancellous space of >8 mm was 64.1%. In the final multivariate Cox proportional hazard model adjusting for age, gender, smoking status, site and buccal cortex width, cancellous space remained significantly associated with time to implant failure (aHR 1.7 per millimeter change [1.4 - 2.2], P < .0001). CONCLUSIONS: The width of the cancellous space and subsequent gap between implant and cortical bone should be considered when placing implants into the mandibular molar sites. When the patient presents for an implant in the mandibular molar region, if the cancellous space is large, the patient should be informed of the risk.

What Factors Are Associated With Implant Failure?

PURPOSE: Recognition of patient-specific risk factors should reduce implant failure. The purpose of this study was to identify risk factors associated with implant failure and to determine if these factors differ over time after implant placement. METHODS: The investigators implemented a retrospective case-controlled study and enrolled a sample composed of patients who had 1 or more implants removed from December 1, 2007 to February 29, 2020. Risk factors were grouped into demographic, medical history, and treatment-related variables. The primary outcome variable was whether the patient's implant failed, with control patients including those without implant failure. The duration was recorded for follow-up from the time of implant placement to the last visit or implant removal. Backward variable selection was used to predict whether an implant failed within 1 year, 1 to 4 years, or after 4 years in 3 multivariable logistic regressions. RESULTS: Of 224 patients in this cohort, 82 experienced an implant failure. The mean age was 58.6 ± 15.3 years, and 53.1% were females. Patients with osteoporosis had an increased risk of failure in each period. Alcohol use, smoking, depression, and penicillin allergy were all associated with an increased probability of failure within 1 or more of the periods considered. CONCLUSIONS: This study has identified multiple discrete risk factors for implant failure and has demonstrated that these factors are associated with implant failure at different periods after placement.

Does the Use of High-Temperature-Processed Xenografts for Ridge Augmentation Result in Ridge Width Stability Over Time?

PURPOSE: Alveolar ridge augmentation is often required before implant placement. The purpose of the present study was to determine whether maxillary and mandibular ridge augmentation with a high-temperature xenograft remains stable over time. MATERIALS AND METHODS: A retrospective case series was performed of subjects who had undergone maxillary anterior or posterior ridge augmentation with a high-temperature xenograft (HTX). The primary predictor variable was the HTX. The primary outcome variable was the ridge width, measured T0 (before augmentation), T1 (immediately after augmentation), T2 (4 to 6 months after augmentation), and T3 (>4 years after augmentation). The secondary outcome variable was implant success. Analysis of variance and linear regression analysis were used to determine significance. A P value < .05 was considered statistically significant. RESULTS: A total of 31 patients (age, 52.4 ± 18 years; 61.3% women) were identified who had undergone ridge width augmentation performed using HTX. Of these, 23 had cone-beam computed tomography scans available 4 to 10 years after augmentation had been performed. At the anterior maxilla, the initial ridge augmentation (T1) was 4.7 ± 1.3 mm, which had decreased to 3.7 ± 1.0 mm within 6 months of augmentation (T2) and to 3.3 ± 1.1 mm after an average of 7 years (T3) of follow-up (P < .05). At the posterior mandible, the initial ridge augmentation was 5.4 ± 0.9 mm, which had decreased to 4.1 ± 0.7 mm within 6 months of augmentation and to 3.5 ± 1.0 mm at an average of 7 years of follow-up. A total of 61 implants had been placed in these 23 patients, 3 (4.9%) of which had failed to integrate. CONCLUSIONS: The use of HTX does result in long-term stability for ridge augmentation.

Use of Tisseel, a Fibrin Sealant, for Particulate Graft Stabilization.

One clinical problem when augmenting a narrow or vertically deficient ridge is maintenance of the graft position during the immediate healing phase and preservation of the augmentation over time. The use of Tisseel (Baxter, Deerfield, IL), a fibrin sealant product, to stabilize particulate grafts, has been reported, and we have reviewed its use. Fibrinogen is converted to fibrin and forms a fibular network that binds the particulate graft. A protease inhibitor is included, which prevents lysis of the coagulum for at least 2 weeks and allows for fibrous ingrowth and graft stabilization. We have reviewed the reported data and included 2 case reports to demonstrate the use of Tisseel.

Hypochlorous Acid: A Review.

The surgeon needs to have an inexpensive, available, nontoxic, and practical disinfectant that is effective in sanitizing against the COVID-19 (Coronavirus Disease 2019) virus. The purpose of this article was to review the evidence for using hypochlorous acid in the office setting on a daily basis. The method used to assemble recommendations was a review of the literature including evidence for this solution when used in different locations and industries other than the oral-maxillofacial clinic facility. The results indicate that this material can be used with a high predictability for disinfecting against the COVID-19 (Coronavirus Disease 2019) virus.

Emergent airway management outside of the operating room - a retrospective review of patient characteristics, complications and ICU stay.

BACKGROUND: Emergent airway management outside of the operating room is a high-risk procedure. Limited data exists about the indication and physiologic state of the patient at the time of intubation, the location in which it occurs, or patient outcomes afterward. METHODS: We retrospectively collected data on all emergent airway management interventions performed outside of the operating room over a 6-month period. Documentation included intubation performance, and intubation related complications and mortality. Additional information including demographics, ASA-classification, comorbidities, hospital-stay, ICU-stay, and 30-day in-hospital mortality was obtained. RESULTS: 336 intubations were performed in 275 patients during the six-month period. The majority of intubations (n = 196, 58%) occurred in an ICU setting, and the rest 140 (42%) occurred on a normal floor or in a remote location. The mean admission ASA status was 3.6 ± 0.5, age 60 ± 16 years, and BMI 30 ± 9 kg/m2. Chest X-rays performed immediately after intubation showed main stem intubation in 3.3% (n = 9). Two immediate (within 20 min after intubation) intubation related cardiac arrest/mortality events were identified. The 30-day in-hospital mortality was 31.6% (n = 87), the overall in-hospital mortality was 37.1% (n = 102), the mean hospital stay was 22 ± 20 days, and the mean ICU-stay was 14 days (13.9 ± 0.9, CI 12.1-15.8) with a 7.3% ICU-readmission rate. CONCLUSION: Patients requiring emergent airway management are a high-risk patient population with multiple comorbidities and high ASA scores on admission. Only a small number of intubation-related complications were reported but ICU length of stay was high.

Bone Levels Are Preserved After Simultaneous Sinus Elevation at Time of Implant Placement.

PURPOSE: The purpose of this study was to confirm that after simultaneous implant placement and vertical bone augmentation in the posterior maxilla, the immediate postoperative bone height is maintained after 2 to 3 years of follow-up. PATIENTS AND METHODS: Consecutive patients treated with implant placement in the posterior maxilla were evaluated. Cone-beam scans were taken preoperatively; immediately after implant placement; and for the sinus-grafted cases, 2 to 3 years after surgery. Crestal bone heights were measured. Patients were grouped according to the use of sinus augmentation or no sinus augmentation at the time of implant placement. RESULTS: The increase in bone height was significant in the graft group when we compared immediate and 3-year follow-up measurements (P < .00001). In the graft group, there were no significant differences in bone height when we compared the immediate and 3-year follow-up periods (P = .31). CONCLUSIONS: Simultaneous sinus floor elevation with grafting at implant placement results in stable bone levels after 2 to 3 years' follow-up.

The Processing of Xenografts Will Result in Different Clinical Responses.

PURPOSE: Clinicians might decide to use a xenograft to reconstruct an osseous defect. Xenografts are processed differently depending on the manufacturer. The purpose of this article is to review the processing methods and clinical ramifications of these processing methods on the behavior of xenografts. MATERIALS AND METHODS: Differences in surface morphology of xenografts based on processing, xenografts used for sinus augmentation, onlay grafting using particulate xenografts, and available clinical trials are reviewed. RESULTS: When used for grafting the extraction socket or preserving or reconstructing the ridge contour, xenografts can result in different resorption rates over time. CONCLUSION: Based on the available information gleaned from the literature, clinical recommendations are included for specific clinical applications.

Accurate Assessment of Blood Loss during Cesarean Delivery Improves Estimation of Postoperative Hemoglobin.

OBJECTIVE: To determine if accurate blood loss determination during cesarean delivery can improve the prediction of postoperative hemoglobin levels. STUDY DESIGN: This is a retrospective cohort study using visually estimated blood loss (traditional, n = 2,025) versus estimates using a mobile application that photographs sponges and canisters and calculates their hemoglobin content (device, n = 756). RESULTS: The correlation between the actual and predicted postoperative day 1 hemoglobin value (PPO1 Hgb) was better in the device group (R 2 = 0.519, correlation = 0.720) than in the traditional group (R 2 = 0.429, correlation = 0.655) (p = 0.005). For patients in the device group where the estimated blood loss was >1,000 mL (n = 53), the PPO1 Hgb was also better correlated with the actual value (R 2 = 0.319, correlation = 0.565) than the predictions using visually estimated blood loss for those patients in the device group whose visual estimation was >1,000 mL (n = 32) (R 2 = 0.035, correlation = 0.187) (p = 0.027). CONCLUSION: Implementation of a device that accurately measures blood loss allows for a better prediction of postoperative day 1 hemoglobin concentration than is possible using visual blood loss estimation. This improvement was seen in the entire patient group and was particularly prominent in patients with blood losses of > 1,000 mL.

Human neutrophil kinetics: modeling of stable isotope labeling data supports short blood neutrophil half-lives.

Human neutrophils have traditionally been thought to have a short half-life in blood; estimates vary from 4 to 18 hours. This dogma was recently challenged by stable isotope labeling studies with heavy water, which yielded estimates in excess of 3 days. To investigate this disparity, we generated new stable isotope labeling data in healthy adult subjects using both heavy water (n = 4) and deuterium-labeled glucose (n = 9), a compound with more rapid labeling kinetics. To interpret results, we developed a novel mechanistic model and applied it to previously published (n = 5) and newly generated data. We initially constrained the ratio of the blood neutrophil pool to the marrow precursor pool (ratio = 0.26; from published values). Analysis of heavy water data sets yielded turnover rates consistent with a short blood half-life, but parameters, particularly marrow transit time, were poorly defined. Analysis of glucose-labeling data yielded more precise estimates of half-life (0.79 ± 0.25 days; 19 hours) and marrow transit time (5.80 ± 0.42 days). Substitution of this marrow transit time in the heavy water analysis gave a better-defined blood half-life of 0.77 ± 0.14 days (18.5 hours), close to glucose-derived values. Allowing the ratio of blood neutrophils to mitotic neutrophil precursors (R) to vary yielded a best-fit value of 0.19. Reanalysis of the previously published model and data also revealed the origin of their long estimates for neutrophil half-life: an implicit assumption that R is very large, which is physiologically untenable. We conclude that stable isotope labeling in healthy humans is consistent with a blood neutrophil half-life of less than 1 day.