Drought-induced lacuna formation in the stem causes hydraulic conductance to decline before xylem embolism in Selaginella.

Lycophytes are the earliest diverging extant lineage of vascular plants, sister to all other vascular plants. Given that most species are adapted to ever-wet environments, it has been hypothesized that lycophytes, and by extension the common ancestor of all vascular plants, have few adaptations to drought. We investigated the responses to drought of key fitness-related traits such as stomatal regulation, shoot hydraulic conductance (Kshoot ) and stem xylem embolism resistance in Selaginella haematodes and S. pulcherrima, both native to tropical understory. During drought stomata in both species were found to close before declines in Kshoot , with a 50% loss of Kshoot occurring at -1.7 and -2.5 MPa in S. haematodes and S. pulcherrima, respectively. Direct observational methods revealed that the xylem of both species was resistant to embolism formation, with 50% of embolized xylem area occurring at -3.0 and -4.6 MPa in S. haematodes and S. pulcherrima, respectively. X-ray microcomputed tomography images of stems revealed that the decline in Kshoot occurred with the formation of an air-filled lacuna, disconnecting the central vascular cylinder from the cortex. We propose that embolism-resistant xylem and large capacitance, provided by collapsing inner cortical cells, is essential for Selaginella survival during water deficit.

A comparison of different sealants preventing demineralization around brackets.

AIM: Aim of the study was to compare how six different sealants resisted thermal, mechanical, and chemical loading in vitro. MATERIALS AND METHODS: In all, 120 extracted human, nondecayed molars were divided into six groups (20 samples each) and embedded in resin blocks. The buccal surfaces of the tooth samples were polished and divided into three areas. Area A contained the product to be analyzed, area B was covered with colorless nail varnish (negative control), and area C remained untreated (positive control). The samples were stored in 0.1% thymol solution. To simulate a 3-month thermomechanical load, the samples were subjected to thermal cycling and a cleaning device. After 7 days incubation in a ten Cate demineralization solution (pH value: 4.6), the samples were dissected using a band saw and the lesion depths and demineralization areas were evaluated and compared microscopically. RESULTS: The tooth surfaces treated with PRO SEAL® showed no demineralization. Mean lesion depths of 108.1, 119.9, 154.9, 149.2, and 184.5 µm were found with Alpha-Glaze®, Seal&Protect®, Tiefenfluorid®, Protecto®, and Fluor Protector, respectively. There was a significant difference between PRO SEAL® and the other products (p > 0.0001). There was no significant difference between the other products. CONCLUSION: PRO SEAL® resisted thermal, mechanical, and chemical loading in vitro, providing protection against white spot lesions.

Influence of piezotomy and osteoperforation of the alveolar process on the rate of orthodontic tooth movement: a systematic review.

OBJECTIVE: The minimally invasive procedures piezosurgical corticocision and osteoperforation have been advocated as methods to accelerate orthodontic tooth movement and to shorten treatment time, but without large-scale trauma of the periosteum and the bone. The aim of this study was to evaluate if there is evidence supporting these claims based on a systematic review of the literature. MATERIALS AND METHODS: A search of PubMed and Google Scholar with the combined search terms "piezo*" and "tooth movement" was performed until May 2016. In addition, the keywords "osteoperforation" and "piezopuncture" were searched in both databases. All scientific articles were considered and examined for suitability by two scientists. Disagreements resolved by consensus. The first inclusion criterion was studies with human species. Second inclusion criterion the surgical procedure had to be performed transmucosally and without the elevation of a mucoperiosteal flap. Case series were also considered. RESULTS: The Google Scholar search delivered 516, the PubMed search 60 references. A total of 36 human trials fulfilling the first inclusion criterion were identified. Among those, in only 13 publications was a transmucosal technique used (12 on piezosurgical corticocision and 1 on osteoperforation). Of the 13 articles, 9 represented case series and only 4 were clinical trials. In all four trials, an acceleration of the orthodontic treatment was reported. However, the extent of the acceleration was inconsistent and in one article it disappeared when assessing the overall orthodontic treatment. CONCLUSION: Evidence for an acceleration of tooth movement in conjunction with the minimally invasive methods piezosurgical corticocision and osteoperforation of the alveolar process in humans is low.