[VKS]

Если динамически, то попробуй

RegionNorth = new Ext.Toolbar({
            region: "north",
            height: 28,
            items: [
                " ",
            {
                xtype: "button",
                text: "Button",
                menu: {
                    defaults: {
                        iconCls: "no-icon"
                    },
                    items: [{
                        text: "SubButton# 1",
                        ref: '../btn_1'
                    }, {
                        text: "SubButton# 2",
                        ref: '../btn_2',
                    }]
                }
            },
                "->"
            ]
        })



RegionNorth.btn_1.setIconClass('');
RegionNorth.btn_2.setIconClass('');