Photoelasticity for Stress Concentration Analysis in Dentistry and Medicine.

Complex stresses are created or applied as part of medical and dental treatments, which are linked to the achievement of treatment goals and favorable prognosis. Photoelasticity is an optical technique that can help observe and understand biomechanics, which is essential for planning, evaluation and treatment in health professions. The objective of this project was to review the existing information on the use of photoelasticity in medicine and dentistry and determine their purpose, the areas or treatments for which it was used, models used as well as to identify areas of opportunity for the application of the technique and the generation of new models. A literature review was carried out to identify publications in dentistry and medicine in which photoelasticity was used as an experimental method. The databases used were: Sciencedirect, PubMed, Scopus, Ovid, Springer, EBSCO, Wiley, Lilacs, Medigraphic Artemisa and SciELO. Duplicate and incomplete articles were eliminated, obtaining 84 articles published between 2000 and 2019 for analysis. In dentistry, ten subdisciplines were found in which photoelasticity was used; those related to implants for fixed prostheses were the most abundant. In medicine, orthopedic research predominates; and its application is not limited to hard tissues. No reports were found on the use of photoelastic models as a teaching aid in either medicine or dentistry. Photoelasticity has been widely used in the context of research where it has limitations due to the characteristics of the results provided by the technique, there is no evidence of use in the health area to exploit its application in learning biomechanics; on the other hand there is little development in models that faithfully represent the anatomy and characteristics of the different tissues of the human body, which opens the opportunity to take up the qualitative results offered by the technique to transpolate it to an application and clinical learning.

Masticatory performance parameters for young adults with "normal" occlusion.

Objective To develop reference data for young men/women on the variability of parameters used for the evaluation of masticatory function with an artificial test food. Methods Subjects included were 200 18-25-year olds with complete dentition and "normal" occlusion. An artificial test food was chewed in two tests (20 cycles and swallowing threshold), during which sequences/cycles were counted and timed. Medium-particle-size (MPS) and broadness of particle distribution were calculated evaluating the chewed material. Reference data was based on order statistics. Sex-specific 95% reference limits with 90% confidence intervals were calculated with RefVal-v2.1-software. Coefficients of variation were also obtained. Results Tables with reference data for young men/women chewing an artificial test food were constructed with the data collected displaying ample variability: MPS after 20 cycles anywhere between 0.7-3.5 mm or 14-84 cycles to deem the test food ready to be swallowed (C.V. 43% males/34% females). Conclusion There is much variability in masticatory parameters for young adults with good oral health.

Digital plaque imaging evaluation of a stabilized stannous fluoride dentifrice compared with a triclosan/copolymer dentifrice.

PURPOSE: To compare the relative plaque control efficacy of a marketed 0.454% stabilized stannous fluoride (SnF2) dentifrice relative to a triclosan/copolymer dentifrice using digital plaque imaging analysis (DPIA). METHODS: This was a randomized, two-treatment, double-blind, parallel group design study that compared SnF2 and triclosan/copolymer dentifrices over a period of 3 weeks. DPIA was used to capture a digital image of the maxillary and mandibular anterior facial surfaces of 12 teeth and to calculate plaque area coverage. Overnight DPIA images were taken at a baseline visit after which subjects were randomly assigned to one of the two treatment groups and were required to brush with their assigned dentifrice according to each manufacturer's instructions. Subjects had DPIA assessments on two separate days at the end of Week 3. RESULTS: 96 subjects were randomized to treatment. Plaque area data for 47 subjects per treatment group were compared at Week 3 using ANCOVA. The SnF2 group demonstrated a statistically significant reduction in overnight plaque at Week 3 compared to baseline (P= 0.002). The reduction for the triclosan group at Week 3 compared to baseline was not statistically significant (P= 0.24). At Week 3, the SnF2 group demonstrated a 17% lower adjusted mean for overnight plaque relative to the triclosan group with a mean difference that was statistically significant (P< 0.05). The Week 3 adjusted mean change from baseline in overnight plaque for the SnF2 group was 3 times greater versus that of the triclosan group (P< 0.05).

Transforming growth factor-beta 3(Tgf-beta3) in a collagen gel delays fusion of the rat posterior interfrontal suture in vivo.

Postnatal expansion of the intramembranous bones of the craniofacial skeleton occurs as bone growth at sutures. Loss of the bone growth site occurs when the suture fails to form, or when the newly formed sutures become ossified, resulting in premature obliteration. Previous experiments demonstrated that removal of dura mater from fetal rat coronal sutures, or neutralizing transforming growth factor-beta 2 (Tgf-beta2) activity using antibodies resulted in premature obliteration of the suture in vitro. Conversely, addition of Tgf-beta3 to coronal sutures in vitro rescued them from osseous obliteration. To examine whether Tgf-beta3 rescues sutures from obliteration in vivo, a collagen gel was used as a vehicle to deliver Tgf-beta3 to the normally fusing rat posterior interfrontal (IF) suture. Surgery was done on postnatal day 9 (P9) rats, in which collagen gels containing 0, 3, or 30 ng Tgf-beta3 were placed above the IF suture, underneath the periosteum for 2 weeks. By P24, 75-100% of animals in control unoperated, sham-operated, and collagen gel-only groups had fused IF sutures. In contrast, 40% of sutures exposed to 3 ng Tgf-beta3 remained open, while sutures exposed to 30 ng Tgf-beta were similar to controls. By immunohistochemistry, sutures rescued from obliteration by Tgf-beta3 had the same Tgf-beta receptor type II (Tbetar-II) distribution as controls. However, Tgf-beta3-treated sutures had altered Tgf-beta2 and Tbetar-I distribution compared to controls.