We congratulate Dr. Gordon Christensen for his provocative June JADA essay, "Is Occlusion Becoming More Confusing? A Plea for Simplicity." With additional references to support his contentions, we agree with Dr. Christensen on several points as follows (italicized words are ours):
The term "centric relation" is highly controversial.1–3
Rehabilitated occlusions restored to retruded centric relation (posterior-superior centric relation) will most likely shift some 1 to 2 millimeters anterior into a physiologic centric occlusion position.4
It is wise to consider restoring the "broken" occlusion back to the "fundamental occlusal characteristics that existed before the rehabilitation" (if the pre-existing occlusion was functional and healthy). Many young patients with "canine rise" will be found later in life to possess "group function" (and/or "balanced occlusion," free of any pathology).2,5
However, we have several points of clarification and disagreement. Much of Dr. Christensen’s terminology related to the subject of occlusion is either outdated or incorrect. Following are examples:
Centric relation is no longer "the most comfortable posterior location of the mandible when it is bilaterally manipulated gently backward and upward into a retrusive position" and has not been since 1987.6–9 There have been a half dozen or so publications of the "Glossary of Prosthodontic Terms" in the Journal of Prosthetic Dentistry, with the most recent publications advocating an anterior superior position of the mandibular condyles in the glenoid fossa—not a retruded posterior superior position, as Dr. Christensen claims.6–9
Dr. Christensen states that "many clinicians describe the situation in which centric relation and centric occlusion are the same position as ‘centric relation occlusion.’ " There are at least two incorrect notions in this statement.
First, centric relation and centric occlusion are not congruent, nor are they comparable terms. Centric relation has always been a position of the condyles in relation to the glenoid fossa, while centric occlusion has always been an interocclusal position of the maxillary to mandiblar teeth. So, centric relation is a condyle position, while centric occlusion is an interocclusal dental position. Even though many publications refer to centric relation–centric occlusion discrepancies, this is like comparing the proverbial apples to oranges.
Second, centric relation occlusion is a term in obsolescence, but it was used in the past by gnathologists to describe the interocclusal position of the teeth (a retruded position) when the condyles are positioned in retruded centric relation (posterior superior centric relation). Synonyms for centric occlusion are "maximum intercuspation" and "intercuspal position." Centric relation occlusion has also been termed the "retruded cuspal position." A past mantra of the gnathologists was centric occlusion (or maximum intercuspation or intercuspal position) coincident with centric relation occlusion (or retruded cuspal position) when the condyles are in retruded centric relation.3
We would argue that Dr. Christensen’s definition of group function is not exactly correct. He defines group function occlusion occurring when "patients have contact between all or most of their teeth, on both sides of their mouths, as the mandible is moved side to side or forward and backward." The functional occlusion type Dr. Christensen is best describing is bilateral balanced occlusion.
The dental literature has described three main functional occlusion types based primarily on laterotrusive movements of the mandible: canine protected occlusion (cuspid rise), group function occlusion and balanced occlusion (unilateral or bilateral). Some publications have used two other terms:
- – mixed canine-protected/ group function occlusion, when the condition presents where one-half of the lateral functioning dentition is "canine-protected" and the other is "group function"; and
- – balanced occlusion, which can be divided into "bilateral balanced" or "unilateral balanced" to denote situations where both sides possess balanced occlusion versus situations where only one-half possesses balanced occlusion and the other side is either canine-protected or group function.
Canine-protected and group function occlusions have the common element of possessing no balancing (nonworking) contacts on the nonworking side during lateral movements of the mandible. Balanced occlusion possesses balancing contacts on the nonworking sides during mandibular movements.3,5
We do not completely agree with Dr. Christensen’s statement that "seldom is nature wrong when used as a guide to determine occlusal characteristics for planned crowns or fixed prostheses." As regards static occlusion, the most common morphologic occlusion type is a malocclusion (Angle’s Class I; some may argue Class II). So, the most prevalent type of static occlusion is not necessarily the most esthetic and desirable. If nature was so perfect, why is malocclusion so pervasive and the normal rather than the exception?
Further, Dr. Christensen seems to imply on page 770 that you can accurately "reproduce the preoperative occlusal characteristics." Does he truly believe that an articulator or any other instrument/technique presently used by gnathologists can accurately capture the fine details of human mandibular movement such as mastication, deglutition, and parafunction? Further, the articulator is based on the faulty notion of a "terminal hinge axis" (i.e., the mandibular condyles rotate and translate "instantaneously").3,10
We ask Dr. Christensen to provide evidence for his statement that "canine rise ... is present in most fully erupted, non-altered occlusions of young adults," when the literature seems to demonstrate that canine rise is not most prevalent among subjects with a normal static occlusion versus subjects with static malocclusions.2,5
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