## 4 Discussion  
The _Periodest_ device provides a way to measure tooth mobility very quickly, noninvasively and without causing the patient any discomfort or pain. It is easy and simple to use. The tapping on the surface of the teeth is very light and does not jeopardize the periodontal health of teeth nor does it increase mobility in already periodontally compromised dentitions. Where the Miller index fails, the _Periodest_ provides a greater variety of tooth mobility values, allowing the dentist to monitor more closely the changes in compromised dentitions. There are many causes of increased and decreased tooth mobility. Having a reliable device that measures tooth mobility is useful to the clinician as a special test that can be used as required to assist in diagnosis and treatment. The _Periodest_ has been studied by many researchers in an attempt to evaluate its clinical use and verify the reproducibility and accuracy of the results obtained [1; 3; 4; 6; 7; 12; 13; 14]. As mentioned, it has been found to be a noninvasive method that does not cause any discomfort or pain to the patients, and unlike the commonly used Miller index, the results obtained are automated and therefore objective, not relying solely on the practitioner's experience and use of the method. Various factors contribute to the success of the _Periodest_ device as a diagnostic tool to provide correct readings of tooth mobility, most notably, the correct manipulation of the handpiece. Unsteady movements or generally incorrect manipulation of the handpiece must be avoided at all times due to the inaccuracy of the result obtained. Erroneous readings can be identified because they appear in the form of +999 [3; 4], while accurate readings produce a sleeping sound from the main unit during the tapping process. The position of the patient, sitting up or lying down, produces the same measurements without any deviations, but depending on the group of teeth examined, the head must be positioned in the right way. In all cases, and regardless of the position of the head, the handpiece should be parallel to the horizontal plane and at a 90-degree angle from the vertical plane on the buccal surface of the tooth. Another factor that should always be considered and could be responsible for false recordings is mastication. The use of chewing gum or consumption of food prior to the recordings slightly increases the mobility of the posterior teeth. Due to the continuous forces applied on the masticatory surface of the posterior teeth, the elastic fibers of the periodontal ligaments are stretched and the results obtained are incorrect. For this reason, the general dental practitioner should always enquire, as well as always be aware, if the patient has any clenching habits or if he/she is diagnosed with bruxism before using the _Periodest_ device, especially if the recordings are taken early in the morning. Along the same lines, teeth with extensive, old and broken-down restorations, where the forces applied on the masticatory surface are uneven, could also provide inaccurate tooth mobility recordings. This could explain why there was a significant difference in Periotest values and subsequently tooth mobility for #16 in all three groups of patients between appointments, either the baseline visit (visit 1) and the second visit two weeks later or the baseline visit (visit 1) and the third visit four weeks later. A very important parameter in the calculation of tooth mobility is to know the direction of the percussion force: the force used by the device to tap the surface of the tooth in order to identify any existing mobility. All measurements have to be performed with the same percussion force to all teeth otherwise the reaction of each tooth is going to be different, and the results will not be comparable. The direction of the percussive force needs to be centered on the buccal/lingual aspect of the tooth, but sometimes, due to the anatomical limitations in posterior teeth, a mesially eccentric percussion technique is used [3,4].