Orientation of craniofacial planes to gravity horizontal plane

1. INTRODUCTION: To proceed clinical and laboratory procedures out of patient’s mouth, it is necessary to precisely register and orientate patients’ casts in the articulator. However, the occlusal plane is evaluated with respect to anatomic relationships, which is then transferred to the articulator (1). Orientation planes for mounting casts in various articulators are thought to be parallel with real horizontal plane (gravity horizontal plane). The face-bow usually aligns the soft-tissue Frankfort horizontal (FHP) plane parallel to the ground with the idea that these two planes are parallel in normal erect posture with a head and shoulders in relaxed natural position (2). However, according to some authors, inclination of the FHP differs significantly from the true horizontal in natural head position (NHP) (3–6). Orientation of craniofacial planes to gravity horizontal plane AIM OF THE STUDY: The aim of the present study was to assess the inclination of occlusal plane and craniofacial planes to the real gravity horizontal plane (GHP). MATERIALS AND METHODS: Fifty six dental students with complete natural dentition and Angle Class I participated. Upper margin of an adhesive tape was placed in the line of the Frankfort plane (left tragus – left orbitale). Left profiles and an-face photographs (Figure 1) with a subject in a natural head position (6,7) and clenching on a Fox plane (FoxP) (Candulor AG, Wangen, Switzerland) were obtained from a distance of 1.5 m. A plumb line was pending from the ceiling to identify gravity vector (true vertical). Perpendicular line to a true vertical line (plumb line) was drawn on digital photographs (true horizontal). Inclinations between Frankfort horizontal plane (FHP) and the true horizontal (GHP), between Camper's line (CP) and true horizontal (GHP), and inclination between the Fox plane (FoxP) and the true horizontal (GHP) were measured on the left profile photographs. Inclination between bipupilar line (BP) and the true horizontal (GHP), as well as inclination between the Fox plane (FoxP) and the true horizontal (GHP) were measured on the an face photographs. ISSA computer program was used for direct angular measurements on digital images (VAMS, Zagreb, Croatia). Statistical analysis (descriptives, t test) was made using SPSS 12 for Windows. Craniofacial planes that were downward-orientated (head flexed) on the left-profile photographs and were counter-clockwise on frontal photographs were defined to have a positive angle to the true (gravity) horizontal plane (GHP). Craniofacial planes that were upward-orientated on the left-profile photographs and were clockwise on the frontal photographs were defined to have a negative angle to GHP. Petričević N, Čelebić A, Krajnović M, Knezović-Zlatarić D, Baučić-Božić M. Department of Prosthodontics, School of Dental Medicine, University of Zagreb, Croatia B) Frontal view A) Lateral view Figure 1. Subject in a natural head position clenching a Fox plane. True vertical is represented by a plumb line. Table 1. Mean angles, standard deviations and the significance of the differences between craniofacial planes and gravity horizontal plane, between Fox plane and gravity horizontal plane RESULTS: No significant differences were found between male and female subjects (p>0.05). Mean angles and standard deviations between planes and GHP are presented in the Table 1, as well as the significance of the differences between the planes and GHP. It was supposed that the planes should be parallel, i.e. that the degree between them should be zero. Therefore, the test value was zero and one-sample t test was used for comparison. In frontal view bipupilar plane was almost parallel to GHP (-0.25 degrees) and no significant difference was observed (t= 0.96; P=0.39, NS). Occlusal plane in frontal view (FoxP) was also almost parallel (-0.53 degrees) to GHP, and no significant difference was observed (t= -1.571; P=0.129, NS). In lateral view, FoxP (cclusal plane) was almost parallel to GHP (1.42 degrees), and the difference was not statistically significant (t= 1.9; P<0.061). FHP was not parallel to GHP (difference was statistically significant (t= -11.62; P<0.001)), neither was CP (difference was statistically significant (t= 5.39; P<0.001)). FHP was upward-orientated (-10.33 degrees) and CP was downward-orientated to GHP (5.384 degrees). † + = downward-orientated to GHP; - = upward-orientated to GHP ‡ + = counter-clockwise to GHP; - = clockwise to GHP NS = Not significant at 95% probability level <0.01** = Significant at 99% probability level DISCUSSION: In frontal view the orientation of the bipupilar plane and the occlusal plane was about horizontal in a natural head position. Parallelism to bipupilar plane is suitable landmark for reconstruction of the occlusal plane. In lateral view, not only that planes of orientation, such as Frankfort horizontal plane and Camper’s line, are not parallel to gravity horizontal plane during natural head position, but are not parallel to the occlusal plane, as well. Absence of parallelism with Camper’s plane makes this landmark unreliable for establishing the occlusal plane, because occlusal plane parallel to Camper’s plane would be too high posteriorly on mandibular dentures, which would cause problems with denture stability and food accumulation in buccal sulci. Results of this study might be compare with other authors (6,7,8-12). The results indicate that with the head in a natural position, the occlusal plane is almost parallel to GHP. It would be impulsively to assume that the position of a head is determined by the position of occlusal plane and further study on this matter should be organized CONCLUSIONS: 1) In frontal view, parallelism with bipupilar plane is a suitable landmark for reconstruction of the occlusal plane. 2) Occlusal plane is almost parallel to gravity horizontal plane in a natural head position. 3) Frankfort horizontal plane and Camper’s plane are not parallel to gravity horizontal plane in a natural head position. 4) Camper’s plane is not a suitable landmark for occlusal plane reconstruction REFERENCES: Academy of Prosthodontics. Glossary of Prosthodontic Terms, Electronic version, 6th Ed. Editorial Council of the J Prosthet Dent 1994. Leitao P, Nanda RS. Relationship of natural head position to craniofacial morphology. Am J Orthod Dentofacial Orthop 2000;117:406. Ferrario VF, Sforza C, Miani A Jr, Tartaglia G. Craniofacial morphometry by photographic evaluations. 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