app.config(['$mdDialogProvider', function($mdDialogProvider){
    console.log($mdDialogProvider);
    // ^ $get/addMethod/addPreset/setDefaults

    var defaults = {
        options: function(){
            return {
                hasBackdrop: false
            }
        }
    }
    $mdDialogProvider.setDefaults(defaults);
}]);

$provide.decorator(name, decorator);

.config(function ($provide) {
  // Decorate the $mdDialog service using $provide.decorator
  $provide.decorator("$mdDialog", function ($delegate) {
    // Get a handle of the show method
    var methodHandle = $delegate.show;

    function decorateDialogShow () {
      var args = angular.extend({}, arguments[0], { hasBackdrop: false })
      return methodHandle(args);
    }

    $delegate.show = decorateDialogShow;
    return $delegate;
  });
});

var dialogFactory = function($mdDialog) {
      var options = {};
  return {

    create: function(conf) {
      var preset = $mdDialog.alert()._options; //get defaults
      var newOptions = angular.extend(preset, conf, options);//extend with yours
      $mdDialog.show(newOptions);
    },
    //toggle various props
    setProp: function(prop, val) {
      options[prop] = val;
    }
  };

};

$scope.toggleBackdrop = function() {
        $scope.backdrop = !$scope.backdrop;
        //here we change the state of the service internal var
        dialogService.setProp('hasBackdrop', $scope.backdrop);
      };
      $scope.showDialogViaService = function(ev) {
        //here we fill in the needed params of the modal and pass to the service
        var obj = {
          'title': 'title',
          'content': 'content',
          'ok':'Ok!'
        };
        dialogService.create(obj);
      }