Thermographic Study of AZ31B Magnesium Alloy under Cyclic Loading: Temperature Evolution Analysis and Fatigue Limit Estimation

In this paper, infrared thermography was employed to study the fatigue process of AZ31B magnesium alloy. In order to eliminate the interference caused by the temperature rise of the fixture, a data processing method was proposed, which is based on a special model to describe the temperature change of the specimen. Based on the temperature data after processing, the temperature evolution indicates that AZ31B magnesium alloy has undergone cyclic hardening during fatigue. Three different temperature indicators were selected to evaluate the fatigue limit based on the evolution curve after processing. In addition, the experimental results showed that the temperature data processed by the proposed method can be used to estimate the fatigue limit of AZ31B magnesium alloy. Experiments were performed for both extrusion and transverse directions in consideration of the anisotropy of the AZ31B.

THERMOGRAPHY OF PERIODONTAL TISSUES DURING DIATHERMOCOAGULATION RETRACTION

Gingival retraction at the preparatory stage of orthopedic teeth restoration with fixed dental appliances is a common procedure in daily dental practice, the success of which will depend on the effectiveness of orthopedic treatment in general. Given certain shortcomings of well-known mechanical and mechano-chemical retraction techniques, the consequences of which may lead to unpredictable aesthetic results, the purpose of this work was to study changes in temperature of marginal gums around teeth at different stages of their orthopedic restoration by fixed metal-ceramic structures based on the thermography findings. The study included 54 patients aged 20 to 60 years, with partial or complete destruction of the coronal part, among whom there were 29 people (53.7%) who underwent gum retraction by diathermocoagulation, and 25 people (46.3%) who underwent retraction of the gingival groove with cotton threads "Ultrapak" (“Ultradent", USA). Measurements were performed prior the operation, during it, in 60 minutes after the completion of diathermocoagulation, and in 7 days after fixation of the cermet crown (14 days after retraction). The thermographic study showed that immediately after the procedure of diathermocoagulation retraction, the temperature of the marginal mucosa went up from 27.3° C (St.Err. 0.28) to 60.2° C (St.Err. 0.72) in the group 1, while in group 2 after mechanochemical retraction there was an increase in temperature from 27.3° C (St.Err. 0.30) to 28.9° C (St.Err. 0.3). 60 minutes after the end of the retraction, the average thermographic index in the group 1 was 28° C (St.Err. 0.28), while in group 2 it equalled to 28.1° C (St.Err.0.31). Control thermography on the 14th day after gum retraction showed a slight decrease to 27.1° C (St.Err. 0.29) in the group 1, and 26.72° C (St.Err. 0.29) in the group 2. The use of diathermocoagulation method of preparation (retraction) of abutment teeth in case of partial or complete destruction of their coronal part improves the quality of orthopedic treatment of patients by using metal-ceramic constructions of dentures. Analysis of thermodynamics in dental and periodontal tissues using the latest thermographic devices with subsequent computer processing of information obtained is of great prospects for further in-depth research.