## 1 Introduction  
Restoring occlusal vertical dimension (OVD), in an optimal maxilla-mandibular relationship, is a main parameter to be establish when complex dental rehabilitation needs to be performed [1]. Loss of the vertical dimension of the lower third of the face in the clinical setting is mainly a result of tooth loss or tooth wear, leading to dramatically changes of the hard and soft tissue of the face and on the jaw complex [2; 3]. If important factors, such as: aesthetics, achieving proper occlusion, space for restorations, are ignored and OVD is altered, there is a risk of instability, with clinical consequences: compromise aesthetic, diminished masticatory function, angular cheilitis, phonetic alteration, alteration of the minimum speech space, pain at the level of the edentulous ridges or temporo-mandibular joint (TMJ) dysfunctions [4]. Determining the OVD is still a challenge in everyday practice, especially in completely edentulous patients, and no generally accepted agreement or scientific consensus for the determination technique was envisaged so far [1]. Therefore, many OVD measurement techniques were described in the scientific literature, based on the vertical dimension of the lower face in the rest position, phonetic methods, swallowing-based methods, pre-extraction recordings, photographs, face measurement, intraoral measurements, cephalometry, telemetry and magnetic methods [5; 6; 7; 8]. Although there are many studies [9; 10; 11; 12] reporting rest mandibular position as a lifelong stable position and using it to determine the OVD, great variability in this parameter was found [13; 14]. Rest mandibular position could vary with head position, body posture or fatigue [15] and was demonstrated that it is not a lifelong constant [16]. Moreover, especially when masticatory muscles or lip tonicity is low, like in the case of edentulous elder patients, or post cancer oral radiotherapy, this method cannot be consider reliable [17]. The most popular method in clinical practice for finding OVD value is by measuring the distance between the septum of the nose (subnasal [Sn]) and the tip of the chin (gnathion [Gn]), Sn-Gn, in the rest mandibular position and subtracting 4 mm [18]. Besides clinically measured Sn-Gn [19] or Sn-Gn measured on the profile photographs [20], various other landmarks have been used for facial measurements, showing a large number of possible statistic correlation to OVD, such as: nose tip to porion [21] or to menton [22], pupil to buccal commissure [23], ear to eye [23], external eye cantus to buccal commissure [24; 25], external eye cantus to anterior point of external ear [19; 24], the distance between the buccal commissures on the inferior lip contour, right external eye cantus to left internal eye cantus, twice the distance between internal eyes cantus [25], the length of the first finger [26], second finger [22; 27] or fifth finger [27; 28], inter-pupillary distance in men [29], nasion-sella distance in men [2], and so on. However, a common method of facial measurement reliability for OVD could not be established, due to a lack of consensus between authors, some of which [22; 26] suggested that the distance nasion-gnathion could be the most suitable for OVD measurement, while others did not recommend the use of this measurement for large oral rehabilitation [30], due the possible errors generated by the resilience of the skin [31] or racial and gender differences [32; 33]. For increasing reliability, cephalometric measurements were suggested to determine the adequate OVD. Following [PERSON]' research [34], [PERSON] proposed the orthodontic norms to be used to define OVD [35] by evaluation of the lower facial height angle (anterior nasal spine-Xi- protuberance menti). This method was also studied by [PERSON] et al. [36], [PERSON] et al. [37], and recently by [PERSON] and co-workers [1].