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The effect of vertical dimension of occlusion (VDO) on maximizing isometric deltoid strength (IDS) was measured in subjects with deep overbite. Sixteen female dental students with deep dental overbite and no history of temporomandibular joint disorder (TMD) were used as their own control and tested for isometric strength of the deltoid muscles, using a hand held strain gauge. Measurements were taken under four mandibular conditions: 1. habitual occlusion; 2. mandibular rest position; 3. biting on a bite elevating appliance set to the functional criterion of peak IDS; and 4. biting on a placebo appliance. Results showed that in deep bite subjects, isometric deltoid strength in habitual occlusion was significantly less than in the mandibular rest position. Isometric deltoid strength with the bite elevating appliance was significantly greater than isometric deltoid strength in habitual occlusion, as well as in the mandibular rest position. Isometric deltoid strength achieved in habitual occlusion and placebo did not differ. Results of this study support previous findings indicating that a change in the VDO will affect isometric strength of the upper extremities.