Introduction:Many patients seek for orthodontic treatment either for improving esthetics, mastication, or to correct occlusion problems. Dental problems such as open-bite, deep-bite and cross-bite, affect phonetics, mastication, esthetics and alters speech. One of these problems is cross-bite, a difference in upper and lower arches closure. When involving the premolar region it is called posterior cross-bite. Condylar position and thumb-sucking may be one of the most common causes of posterior cross-bite1, 2.Types:1. Cross-bite that lies buccally accompiend with movement from one side 3.2. Cross-bite that lies buccally from one side without any movement 3.3. Cross-bite lies buccally from both sides 3.4. Cross-bite that lies lingually from one side 3.5. Cross-bite that lies lingually from both sides, known as (scissor cross-bite) 3. Figure 1 1. Quadrant: one or two teeth or whole segment 3.2. Deflection during eruption 3.3. Along with skeletal disharmony 3.4. Due to crowding or primary teeth reservation 3.5. Also along with skeletal disharmony 3. How to manage posterior cross-bite?Unilateral buccal cross-bite:- If displacement of the opposing teeth in opposing directions is required, cross elastics is recommended 3.- If the upper teeth is tilted palatally, then upper removable appliance with midline screw is recommended 3.Bilateral buccal cross-bite:- Young patients: Rapid maxillary expansion (RME) 3.- Adult patients: Surgically assisted RME 3.Lingual cross-bite:- Fixed appliance 3. Recent advances 2016-2017:o A study reported that posterior cross-bite1 is common among children born preterm4.o Tsanidis and colleagues reported that when introducing posterior cross-bite earlier, the muscle of mastication activity return to its normal level5.o Post-treatment retainer with RME is mandatory to wear for 6 months to avoid relapse6. o Non-surgical intervention is possible for adult patients7.DiscussionChildren born preterm have higher chance of having posterior cross-bite4, which violate the mastication activity5. However, there is still possibility of getting it back to its normal activity cycle5.ConclusionNon-surgical treatment accompiend with fixed or removable RME can be done to adult patients and features good results7. References1. Hesse, K.L., et al., Changes in condylar position and occlusion associated with maxillary expansion for correction of functional unilateral posterior crossbite. American Journal of Orthodontics and Dentofacial Orthopedics, 1997. 111(4): p. 410-418.2. Øgaard, B., E. Larsson, and R. Lindsten, The effect of sucking habits, cohort, sex, intercanine arch widths, and breast or bottle feeding on posterior crossbite in Norwegian and Swedish 3-year-old children. American Journal of Orthodontics and Dentofacial Orthopedics, 1994. 106(2): p. 161-166.3. Mitchell, L., An introduction to orthodontics. 2013: Oxford University Press.4. Germa, A., et al., Early risk factors for posterior crossbite and anterior open bite in the primary dentition. The Angle Orthodontist, 2016. 86(5): p. 832-838.5. Tsanidis, N., G. Antonarakis, and S. Kiliaridis, Functional changes after early treatment of unilateral posterior cross?bite associated with mandibular shift: a systematic review. Journal of oral rehabilitation, 2016. 43(1): p. 59-68.6. Costa, J.G., et al., Retention period after treatment of posterior crossbite with maxillary expansion: a systematic review. Dental press journal of orthodontics, 2017. 22(2): p. 35-44.7. Viazis, A., E. Viazis, and T. Pagonis, Non-surgical Orthodontic Adult Molar Crossbite Correction and Sleep Apnea. J Dent Health Oral Disord Ther, 2016. 5(5): p. 00168.