Factors Modulating Fallow Period of Aerosol-Generating Dental Procedures in a Clinical Setting

The COVID-19 pandemic has resulted in amended regulations and guidelines governing the practice of dentistry and dental hygiene to ensure the protection of both patients and clinicians from transmission of the SARS-CoV-2 virus. These guidelines include changes in personal protective equipment and, under some guidelines, the institution of a fallow period after any aerosol-generating procedure (AGP). This study aimed to investigate the effect of both ventilation and 4-handed dentistry in clinical practice with patients undergoing supportive periodontal therapy (SPT) by air polishing, ultrasonic and hand instrumentation in a closed operatory. We studied 34 patients during SPT using either 2- or 4-handed dentistry in an operatory with either 0 or 20 additional air changes/h (ACH). Under clinical conditions, 20 additional ACH are adequate to eliminate aerosols produced during an SPT and before the cessation of the AGP. The presence of an assistant had no significant effect on the time needed for aerosol particles to return to baseline values following the AGP. This study supports the efficacy of 20 additional ACH during the process of AGP, but does not support the need for an extended fallow period or 4-handed dentistry to provide additional high-volume evacuation throughout the procedure.

Transplantation of articular cartilage following a step-cooling cryopreservation protocol

Using a step-cooling cryopreservation protocol that held the tissue 60 min at -4 degrees C, 30 min at -8 degrees C, and 10 min at -40 degrees C before plunging into liquid nitrogen, we were able to get a substantial improvement in the magnitude and pattern of chondrocyte recovery following cryopreservation, achieving postthaw recoveries of 62 +/- 13%. These results are consistent with the hypothesis that ice growth within articular cartilage is planar, but they provide no direct support for that hypothesis. Transplanting (step-cooled) cryopreserved osteochondral allografts into adult Suffolk/Romanoff crossbred sheep for periods of 3 months and 1 year further tested the efficacy of the cryopreservation protocol. Unfortunately, the cryoinjury sustained by the chondrocytes during cryopreservation, although apparently nonlethal immediately after thawing in many cases, was not innocuous in the long term. The presence of large clusters of chondrocytes at 1 year after transplantation illustrates that cryoinjury not detectable with a membrane integrity assay can still have far-reaching effects on transplanted tissue.

Measurement of cancellous bone strain during mechanical tests using a new extensometer device

A device for measuring mid-substance strain in bone during uniaxial compression was developed with special attention to subsequent FE modelling. It is based on dual instrumented cantilever arms that measure the difference in tip-to-tip deflection. The so-called extensometer device was compared to two standard methods of measuring strain based on platen measurements. The extensometer device output was highly linear with tip deflection (r(2)>0.99), and contact of the devices with the specimen was optimized by using an axial distribution of three devices fixed in a free-floating jig. Deflection of the extensometer arms was accurate to 4.8 microm, and precision was between 2-5 microm. Tests included measuring rubber test specimens and cylindrical cancellous bone cores extracted from canine femoral condyles. A trend of decreasing apparent modulus with decreasing strain rate was evident with the extensometer technique. Correlation between the extensometer method and the other two methods was r(2)=0.55. The measure of mid-substance strain avoids non-linearities in the compression tests caused by early failure at the specimen ends, and the uniaxial testing conditions result in boundary conditions that are well suited for subsequent finite element analysis.

Transplantation of cryopreserved osteochondral Dowel allografts for repair of focal articular defects in an ovine model

The purpose of this study was to test whether successful cryopreservation of osteochondral tissue is possible and whether, with the appropriate surgical procedure, it can be used for the successful repair of focal articular defects within joints. Fresh (nonfrozen) and snap-frozen (plunged in liquid nitrogen and thawed in a water bath at 37 degrees C, repeated three times) autografts were used as positive and negative controls, respectively. Snap-frozen, frozen (fresh tissue placed in a freezer at -80 degrees C), and cryopreserved (immersed in 10% dimethyl sulfoxide for 30 minutes and then frozen at 1 degrees C/min to -80 degrees C) allografts were transplanted into the knees of adult sheep. Outcomes were evaluated 3, 6, and 12 months after transplantation. The morphological, histological, biochemical, and biomechanical behaviors and characteristics of the graft cartilage, the host cartilage adjacent to the grafts, and the opposing tibial cartilage were assessed. Freezing protocols that yielded poor chondrocyte recovery after thawing (frozen and snap-frozen) resulted in poor overall graft outcome. The cryopreservation protocol, however, resulted in intermediate recovery (50%) of chondrocytes and in intermediate overall graft outcome compared with fresh autografts. The membrane integrity of the allograft chondrocytes immediately following cryopreservation was identified as the most reliable predictor of long-term outcome of the graft. Further improvements in cryopreservation technique may lead to an effective method of banking osteochondral tissue for successful transplantation for the repair of focal defects and larger joint reconstructions.