Tooth Structure Removed in Primary Molar Prefabricated Crown Preparations of Typodont Teeth.

PURPOSE: Esthetic prefabricated pediatric crowns require more tooth reduction than stainless steel crowns due to their passive fit. The purpose of this study was to determine tooth reduction in primary molar preparations for various pediatric prefabricated crowns. METHODS: Fifty primary maxillary and fifty mandibular typodont molars were scanned with an optical scanner. The teeth were mounted in a typodont, and 10 experienced pediatric clinicians prepared them for five types of pediatric prefabricated crowns: (1) stainless steel (SS); (2) zirconia EZCrowns™ (EZ); (3) NuSmile ® ZR (NS); (4) Zirconia Kinder Krowns ® (KD); and (5) an experimental composite crown (PS). The prepared teeth were rescanned, and the pre- and postpreparation scans were precisely aligned. Mean and maximum reduction depths were calculated for occlusal and mesio- buccal surfaces. Differences in reduction among crown types were compared using one-way analysis of variance followed by the Student-Newman- Keuls post hoc test (α equals 0.05). RESULTS: Reduction depths were not significantly different among the esthetic crowns but were significantly higher than SS crowns. Maximum reduction exceeded two mm in some of the KD and NS crown preparations, with KD consistently showing the highest reduction. CONCLUSIONS: Preparations for esthetic prefabricated molar crowns were more extensive than SS crowns, especially at occlusal and mesiobuccal surfaces. Clinicians should carefully follow manufacturer preparation guidelines to avoid encroaching the mesiobucccal pulp horn.

Justifying the risks of COVID-19 challenge trials: The analogy with organ donation.

In the beginning of the COVID pandemic, researchers and bioethicists called for human challenge trials to hasten the development of a vaccine for COVID. However, the fact that we lacked a specific, highly effective treatment for COVID led many to argue that a COVID challenge trial would be unethical and we ought to pursue traditional phase III testing instead. These ethical objections to challenge trials may have slowed the progress of a COVID vaccine, so it is important to evaluate their merit. One common way of doing so is to make an analogy to other social practices that are relevantly similar and which we currently sanction. We submit that non-directed live organ donation (NDLOD) is a promising analogy. After arguing that the risks to volunteers for each activity appear similar, we explore potential disanalogies that would undermine the comparison. We note that there are differences in both the kind and certainty of benefit secured by NDLOD compared to challenge trials. We conclude these differences are insufficient to make NDLOD permissible and challenge trials impermissible. Ultimately, if we think the risks associated with NDLOD are ethically permissible, then we should think the same of the risks associated with COVID challenge trials.