- R -
R point (registration point) A cephalometric reference point introduced by Broadbent in his original presentation of the cephalometric technique. It is the midpoint on a perpendicular drawn from the center of sella turcica to the Bolton-nasion line.
radiograph A permanent image, typically on film, produced by ionizing radiation. Sometimes called an x-ray after the most common source of image-producing radiation.
radiographic imaging The process of acquiring representations of structures using ionizing radiation.
ramus Paired vertical posterior parts of the mandible that serve as attachment areas for the muscles of mastication and also contain the condyles that articulate with the temporal bones. Plural-rami.
rapid palatal or rapid maxillary expansion (RPE, RME) An orthopedic procedure using a fixed or removable appliance to separate the two maxillary bones at the mid-palatine suture.
rare earth screens Intensifying screens that are coated with special compounds to reduce x-ray exposure for cephalometric and panoral films.
reciprocal anchorage The use of equal and opposite equilibrium forces from an appliance to produce desired tooth movement on different teeth.
reference frame A set of two or three intersecting axes, ordinarily mutually perpendicular, used as a basis for locations of points and directions of lines, graphically expressing relationships among variables, or undertaking vector analysis, in a plane or in space.
replantation The replacement of a tooth that has been avulsed, usually as the result of an accident.
reproximation (slenderizing) Abrasive reduction of small amounts of enamel from the proximal surfaces of the teeth, in order to reduce combined toothwidth.
resection Surgical removal of part or all of a structure.
root resection Removal of the apical portion of the root of a tooth, usually to eliminate infection.
resilience The amount of energy transferred by mechanical work to take a body from an initial, passive state to its elastic limit; the area under the load-deformation plot up to the elastic limit.
resorption Physiologic or pathologic removal of hard tissue (bone or root) by the activity of osteoclasts. Syn- osteoclasis.
rest position The normal resting position of the mandible, with teeth apart and muscles relaxed.
retainer Any orthodontic appliance, fixed or removable, used to maintain the position of the teeth following corrective treatment.
retention The passive treatment period following active orthodontic correction during which retaining appliances may be used.
retraction Pertaining to desired posteriorly directed, orthodontic or orthopedic displacements of teeth or of bones of the face.
retroinclination Lingual (palatal) angulation (inclination) of anterior teeth.
retrognathic A mandible or maxilla that is retruded in its relationship with other facial structures due to a size discrepancy or positional abnormality.
retrusion Teeth or jaws that are posterior to normal position or movement toward the distal.
reverse-pull or protraction headgear A (primarily) extraoral orthodontic or orthopedic appliance designed to deliver force to the dentition that is principally or totally anteriorly directed.
ribbon arch appliance An appliance developed by E.H. Angle prior to the Edgewise appliance, using a rectangular wire in a vertical slot to gain multidirectional control. Bracket was inverted and used by P.R. Begg for his technique.
rigid fixation Stabilization of two bony segments using metal plates or screws to eliminate movement between the parts.
Risk Retention Group (RRG) Formed under the Risk Retention Act of 1986, Risk Retention Groups are corporations or limited liability associations with the purpose of assuming the liability exposure of their members. RRG?s are chartered and licensed as insurance companies in a specific state known as the domiciliary state. A risk retention group must contain the phrase ?Risk Retention Group? in its official name. See American Association of Orthodontists Insurance Company (a Risk Retention Group).
roentgenogram An image produced on film by roentgenography; radiograph is the preferred term.
roentgenography Production of permanent images through the use of Roentgen rays (x-rays).
root That part of the tooth not covered by enamel, normally lying within the alveolus where it is attached to the bone by the periodontal membrane (ligament).
root movement The transverse tooth movement characterized by little displacement of the crown and the center of rotation located on the long axis and at or near bracket level.
root resorption Resorption of a part of the root of a tooth. May be either internal (pulpal) or external.
RRG See Risk Retention Group. 
