- Email: [email protected]
The effect of posture and anesthesia on the occlusal relationship in orthognathic surgery
1172
DISCUSSIONS
proximal segment position in orthognatbic surgery. J Oral Maxillofac Surg 49:2, 1991 24. Ellis E: Condylar positioning devices for orthognathic surgery: Are they necessary? J Oral Maxillofac Surg 52:536, 1994 25. Wiffliamson EH, Steinke RhI, Morse PK, et al: Centric relation: A
J Oral Maxiliofac
comparison of muscle determined position and operator guidawe. Am J Orthod 77:133, 1980 26. Jankelson B, Abib F: Effect of variation in manipulative force on the repetitiveness of centric relation registration: A computerbased study. J Am Dent Assoc 113:59, 1986
Surg
57: 1 172-l 174, 1999
Discussions The Effect of Posture and Anesthesia tlie Occlusal Relationship in Orthognathic Surgery Christian
on
S. Stohler, DDS, Dr Med Dent
William R. Mann Professor and Chair, Department of Biologic and Materials Sciences,The University of Michigan School of Dentistry, Ann Arbor, Michigan; e-mail: [email protected]
in this study, the (CO) and centric relation (CR) proved to be statistically different between the upright conscious condition and both the supine conscious and supine anesthetized situations. The authors conclude that their finding “explains the apparent occlusal discrepancies created by rigid fixation of the mandible applied in the supine anesthetized position.” They also suggest to maxillofacial surgeons that “loss of maxillary advancement can be avoided by taking CR records in the supine conscious position” in the planning of complex blmaxillary osteotomies. What has been learned in this research and what are the implications for care? Rather than offering a testable hypothesis, the stated purpose of the investigation was to rationalize a particular aspect of the surgical planning of complex bimaxillary osteotomies. However, in the absence of a hypothesis that can be falsified, it is not clear what result would have changed the authors’ opinion, which was guiding their project in the first place. The authors’ offered conclusion that their results explain the apparent occlusal discrepancy created by fixation of the mandible are somewhat consistent with the intent. However, it is not supported by the data reported in this study. Based on the analysis of the spatial relationship of centric
Rigid fixation was not Occlusal records were
within taken
56 records occlusion
the scope 1) preoperatively
of
this work. with the
patient sitting upright and with the head supported so that the Frankfort horizontal plane was parallel to the floor; 2) in a conscious supine position (presumably in the surgical suite); and 3) in a supine position under general anesthesia before the insertion of the throatpack. Therefore, the first conclusion is unwarranted and unsupported. The second conclusion presented in this article states that maxillofacial surgeons should take CRC records in the supine conscious position to avoid “loss of maxillaty advancement” in cases of bimaxillary osteotomies. Besides the fact that this second conclusion is also beyond the scope of the current
investigation,
it
raises
other
questions,
because
different results were obtained under all 3 recording conditions. What recording is “better” and why? Should the CR bite record be taken in the supine position as opposed to an upright position with the head oriented in a way that the Frankfort horizontal plane is parallel to the floor? Alternatively, the impression is gained that a CR record taken in the supine position is preferred over a CO bite registration. Irrespective of the answer, the reader has to determine whether CR has anything to do with the planning of complex bimaxillaty osteotomies in the first place. The maxillomandibular tooth relationship at the point of initial (premature) tooth contact during mandibular closure on the most retruded and unstrained path represents the centric relation contact position (CR). There is questionable validity and utility of recording this CR position, upright or supine, in the planning of “complex bimaxilIary osteotomies.” There is no question that the primary purpose of this type of surgical intervention is to change the position of the upper and lower dental arches in the skull. If 1) the arc of closure ln the most retruded position changes, or 2) the plane of occlusion is altered with respect to the skull base as a consequence of surgical repositioning, the postoperative CR can never be identical to any kind of preoperative record, upright or supine, unless nothing is surgically done to either maxilla. Unlike centric occlusion, centric relation is dependent on a reference outside the dentition. From this perspective, it remains unclear how “loss of maxillary advancement can be avoided by taking CRC records in the supine
conscious
position.”
There is also insufficient detail given geometric construct and validity of graphics analysis used.” Where is the and how does it relate to a particular fact,
the
illustrations
raise
more
about the underlying the “SD computer origin of the vector patient’s condyle? In
questions
than
provide
answers. Short of offering the reader with the necessary methodologic parameters, statements such as “occasional paradoxical mandibular rotations, for instance where one condyle moved backward and the other forward in the anteroposterior plane” are difficult to accept. Do the paradoxical effects represent geometric artifacts? On a different note, no power estimates are offered to assess the validity of the reported negative results. In sum, although the discussion offers some clinically useful
suggestions,
no
supporting
evidence
has
been
pro-
vided by the results of this work. The authors’ conclusions remain founded on clinical reasoning of matters of convenience and bias.
DISCUSSIONS
proximal segment position in orthognatbic surgery. J Oral Maxillofac Surg 49:2, 1991 24. Ellis E: Condylar positioning devices for orthognathic surgery: Are they necessary? J Oral Maxillofac Surg 52:536, 1994 25. Wiffliamson EH, Steinke RhI, Morse PK, et al: Centric relation: A
J Oral Maxiliofac
comparison of muscle determined position and operator guidawe. Am J Orthod 77:133, 1980 26. Jankelson B, Abib F: Effect of variation in manipulative force on the repetitiveness of centric relation registration: A computerbased study. J Am Dent Assoc 113:59, 1986
Surg
57: 1 172-l 174, 1999
Discussions The Effect of Posture and Anesthesia tlie Occlusal Relationship in Orthognathic Surgery Christian
on
S. Stohler, DDS, Dr Med Dent
William R. Mann Professor and Chair, Department of Biologic and Materials Sciences,The University of Michigan School of Dentistry, Ann Arbor, Michigan; e-mail: [email protected]
in this study, the (CO) and centric relation (CR) proved to be statistically different between the upright conscious condition and both the supine conscious and supine anesthetized situations. The authors conclude that their finding “explains the apparent occlusal discrepancies created by rigid fixation of the mandible applied in the supine anesthetized position.” They also suggest to maxillofacial surgeons that “loss of maxillary advancement can be avoided by taking CR records in the supine conscious position” in the planning of complex blmaxillary osteotomies. What has been learned in this research and what are the implications for care? Rather than offering a testable hypothesis, the stated purpose of the investigation was to rationalize a particular aspect of the surgical planning of complex bimaxillary osteotomies. However, in the absence of a hypothesis that can be falsified, it is not clear what result would have changed the authors’ opinion, which was guiding their project in the first place. The authors’ offered conclusion that their results explain the apparent occlusal discrepancy created by fixation of the mandible are somewhat consistent with the intent. However, it is not supported by the data reported in this study. Based on the analysis of the spatial relationship of centric
Rigid fixation was not Occlusal records were
within taken
56 records occlusion
the scope 1) preoperatively
of
this work. with the
patient sitting upright and with the head supported so that the Frankfort horizontal plane was parallel to the floor; 2) in a conscious supine position (presumably in the surgical suite); and 3) in a supine position under general anesthesia before the insertion of the throatpack. Therefore, the first conclusion is unwarranted and unsupported. The second conclusion presented in this article states that maxillofacial surgeons should take CRC records in the supine conscious position to avoid “loss of maxillaty advancement” in cases of bimaxillary osteotomies. Besides the fact that this second conclusion is also beyond the scope of the current
investigation,
it
raises
other
questions,
because
different results were obtained under all 3 recording conditions. What recording is “better” and why? Should the CR bite record be taken in the supine position as opposed to an upright position with the head oriented in a way that the Frankfort horizontal plane is parallel to the floor? Alternatively, the impression is gained that a CR record taken in the supine position is preferred over a CO bite registration. Irrespective of the answer, the reader has to determine whether CR has anything to do with the planning of complex bimaxillaty osteotomies in the first place. The maxillomandibular tooth relationship at the point of initial (premature) tooth contact during mandibular closure on the most retruded and unstrained path represents the centric relation contact position (CR). There is questionable validity and utility of recording this CR position, upright or supine, in the planning of “complex bimaxilIary osteotomies.” There is no question that the primary purpose of this type of surgical intervention is to change the position of the upper and lower dental arches in the skull. If 1) the arc of closure ln the most retruded position changes, or 2) the plane of occlusion is altered with respect to the skull base as a consequence of surgical repositioning, the postoperative CR can never be identical to any kind of preoperative record, upright or supine, unless nothing is surgically done to either maxilla. Unlike centric occlusion, centric relation is dependent on a reference outside the dentition. From this perspective, it remains unclear how “loss of maxillary advancement can be avoided by taking CRC records in the supine
conscious
position.”
There is also insufficient detail given geometric construct and validity of graphics analysis used.” Where is the and how does it relate to a particular fact,
the
illustrations
raise
more
about the underlying the “SD computer origin of the vector patient’s condyle? In
questions
than
provide
answers. Short of offering the reader with the necessary methodologic parameters, statements such as “occasional paradoxical mandibular rotations, for instance where one condyle moved backward and the other forward in the anteroposterior plane” are difficult to accept. Do the paradoxical effects represent geometric artifacts? On a different note, no power estimates are offered to assess the validity of the reported negative results. In sum, although the discussion offers some clinically useful
suggestions,
no
supporting
evidence
has
been
pro-
vided by the results of this work. The authors’ conclusions remain founded on clinical reasoning of matters of convenience and bias.