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From the In vitro evaluation study about the T-Scan III (an interocclusal contact sensor) by Cerna, Ferreira, Zaror, Navarro and Sandaval, Cranio, Journal of Craniomandibular and Sleep Practice, 2015, I have discovered that the validity and reliability of this sensor measures force and timing in “sensels” has been in question.
A sensel is composed of fine integrated conduction lines creating a grid with small (0.1″ per side) square pressure -sensitive areas. The sensor has a thickness of 100μm, which is in the articulating paper range of 8-200μm depending on the articulator brand.
There are two sizes: the larger arch is up to 66 mm wide and 56 mm long, with 1370 sensels. The smaller arch is 58 mm wide and 51 mm long with 122 sensels. Each of the sensels that comprise a T scan sensor encodes in 8 bites, giving 256 possible levels for the force exerted on it. When a sensor is bitten down on, many sensels are excited simultaneously and the combination of their responses produces the final response of the whole sensor. The system ultimately provides an indication of relative force, either the total digital level or the percentage of the total digital level. It has 8 levels of sensitivity adjustments to adapt its use to different patients.
An important requirement for the clinical applicability of any measurement system is that the values provided represents the real values with the greatest accuracy. This is essential for reliability and effective occlusal adjusting treatment.
Results have shown the sensels showed a broad spread in their responses, eg. for a force of 10N, the sensels responded with digital levels between 25 and 55 raw, approximately. Equivalently, a raw value of 50 can be interpreted as a force between 10 and 22 N approximately. Using Lin’s CCC (concordance correlation coefficient) the average values correspondingly show poor levels of agreement (0.698+/- 0.230).
From what I have learned, from previous studies, there were also differences between sensors, suggesting their individual calibration (Throckmorton, Rasmussen, Calos, Calibration of T scan, 2009) and the system contained inaccuracies when measuring force (Lyons, Sharkey, Lamey, Int J. Prosth. 1992). Even Kerstein, et al (A force reproduction analysis of two recordings sensors of a computerized occlusal analysis system, Cranio, 2006) concluded that despite the more consistent values obtained with the HD sensor when compared with the third generation G3 sensor, both designs showed some differences in the force production. When using sensels that are bigger and closer in the HD design, it is best not to reduce the probability during the clinical usage, because some occlusal contacts would fall between sensels and the inactive recording areas on repeated bites.
Under laboratory conditions when studying the behavior of individual sensels the T scan III system does not shows an appropriate degree of validity in estimating absolute force, nor presents an adequate level of reliability (poor agreement mean of 0.099+/-0.185) when measuring relative force; however, it presents a high degree of validity in quantifying times.
The sensels showed significant differences in the individual behavior, which could decrease statistically when an entire sensor is measuring total occlusal forces.
Although HD or forth generation sensors used had increased the active recording area by 33% and had decreased the non-active recording area by 50% compared to the previous third (G3) generation designs.
In the measurement of absolute force, it was found that the representative error of the T scan system reached 9.2% and the maximum error was 22.5%.