## 4 Discussion  
Nowadays, an increased prevalence of malocclusions and poor craniocervical posture promptresearchers to assess this relationship and develop new prevention protocols. Recently, [PERSON] et al. [17] concluded that a correlation between posture and maxillomandibular deformity is possible. However, in this paper, the sagittal position of the mandible in association with the head and neck posture was not summarized. Also, no other studies concluding in favour of this relationship were found. Additionally, various reports on the relationship between the lower jaw position and craniocervical posture were found in the literature. Therefore, the aim of this systematic review was to screen the available evidence regarding the relationship between the craniocervical posture and the sagittal position of the mandible. Figure 2: Summary assessment of the risk of bias of the included studies [12; 25; 26; 27; 28; 29; 30] performed using Joanna Briggs Institute Critical Appraisal Checklist for Analytical Cross-Sectional Studies. Two studies [25; 26] of moderate risk of bias demonstrated the association between mandibular ramus angle and upper and lower craniocerical posture angles. Although children were included in one study and adults were included in the other, the results agreed in both studies. The authors noticed that higher values of SN-RL angle are associated with increased OPT-SN and CVT-SN angles, and vice versa. Furthermore, the aforementioned angles were largest in the Class II relationship, followed by the Class I relationship, and were smallest in the Class III relationship [25; 26]. The results of the above authors [25; 26] are in agreement with the results of an earlier study [31], which found a significantly smaller angle between ramus line and cervical tangent in Class III subjects than in Class I and II individuals. The results of five studies of low and moderaterisk of bias [12; 26; 27; 28; 29] that evaluated mandibular pragnathism tend to follow the same pattern. Although SN-RL angle is measured in the sagittal plane, it is related to vertical growth. Increased SN-RL angle shows distal mandible position and rotation of the mandible downwards which is common to FHP. These changes lead to hypertension in cervical muscles, including supra- and infrahyoid muscles as well. It influences and changes mandible growth: prevents forward growth and stimulates vertical growth. In two studies Class II subjects were assessed and compared before and after orthodontic treatment with functional appliances [12; 27]. [PERSON]. [PERSON] et al. [12] noticed no significant changes in craniocerical posture after functional orthodontic treatment in all of the groups. Conversely, [PERSON]. [PERSON] et al. [27] found a significant increase in OPT-SN angle in untreated patients with Class II and a decrease in the exposed group. Although it was not statistically significant, the authors concluded that Twin Block causes craniocerical posture to be more upright and Class II patients have a greater forward inclination of the craniocerical posture [27]. Similar results were found in a prospective clinical study that measured high craniocerical angles by photometry method before treatment with Twin Block appliance [32]. The suggestion that cervical curvature may be linked to mandibular retrognathism has also been previously offered by other authors. It was noted that skeletal Class II children showed a significantly higher extension of the head upon the spinal column compared to Class I and Class III children [32]. Forward head posture predominates among retrognathic teenagers and adults compared to Class III individuals [33]. In addition, [PERSON] et al. [28] measured [PERSON]'s correlation coefficient between the mandibular protrusion and upper craniocerical posture and received results in agreement with the previous studies. The authors found that in all subjects, the OPT-SN angle had a positive correlation with the SNA and ANB angles, and a negative correlation with the SNB angle.