# Force of Intermaximillary Late Elastics from Different Suppliers: A Comparative In Vitro Study
## 4 Discussion  
When choosing suitable elastics for the patient, clinicians need to take into consideration that identically labeled intermaximillary 3/16\" Medium differ among manufacturers in terms of both the reported force values and the diameter of the elastics. In our study, the reported forces of the elastics from five different manufacturers ranged from 113 g to 128 g and diameter varied from 4.6 mm to 4.8 mm. Worldwide, there is no current consensus on the marking of the force on the packaging; it can be given in grams (g), newtons (N), or in ounces (oz), which may result in a lack of awareness and confusion for a clinician using a different measurement system. The resulting force designated on the packaging of elastics can be calculated using the following formula: 1 N = 101.9716212978 gf (gram force) \(\approx\) 102 g; 1 Oz = 28.3495231 g = 28.35 cN (centinewton). From the clinician's perspective, the choice of an intermaximillary elastic depends on the desired movement of teeth to be achieved, the type of appliance used, and the distance between the insertion points of the elastic, which determine the stretching length of the elastic. The manufacturers, as well as most studies in the literature, report that the declared force is achieved when the elastic is stretched to three times its diameter, which is the value also used in our experiment (rule of \"3\") [11]. However, there have been studies reporting a stretch of elastics to only twice their diameter to achieve the declared force [13; 14]. Nonetheless, the validity of proposals on how much stretch is required from an elastic to obtain the declared force has been seriously questioned and, according to some studies, the force may vary with the size and level of force of the elastics [11; 14; 15]. [PERSON] et al. measured the distance of elastic stretch in order to achieve the declared force [5]. They found that, in 3/16\" Medium and Heavy elastics, it was 2.7-fold the diameter. In elastics of other sizes, the stretch ranged from 2.6-fold to 5-fold of the elastic's diameter to achieve the declared force. To avoid the bias created by the differences in diameter, we developed and printed an exact 3D model of a board with spurs in which the spurs for stretching elastics were made at the precise three-fold length of the diameter declared by each manufacturer. The comparison of elastic forces should thus be more accurate than that in studies where all elastics were stretched to the same length [7; 9; 11; 16]. In 1994, [PERSON] et al. [17] reported a possible clinically significant impact when the difference between the measured and the declared force of elastics was more than 10%; however, in the present results, even the initial force differed by more than that from the declared force for most manufacturers. Although the declared initial forces of the 3/16\" Medium did not differ much between the manufacturers, only by 0.147 N, i.e., 15 g, in reality the initial force differed by 0.441 N, i.e., 45 g between the two manufacturers with the lowest and highest force values. For example, the smallest elastics in diameter were the 3M 4.6 mm elastics, which also has the weakest declared initial force, but the measured initial force was the second highest of the five manufacturers. In 2022, [PERSON] et al. [10] also reported differences in the initial forces measured compared with the declared forces for 3/16\" elastics from several manufacturers when stretched to 16.3 mm. Similarly, differences between the measured and declared initial forces were reported in some older studies in smaller samples of elastics [9; 12; 14]. Additionally, the outliers and extreme values of force that we found among some of the samples of the 100 elastics from each brand might influence the clinical outcome of orthodontic treatment by delivering more force than necessary when worn by the patient.