The need to use an arbitrary face-bow when remounting complete dentures with interocclusal records.

The need for the arbitrary face-bow during finished denture remount is demonstrated and advocated. The face-bow transfer allows a more accurate arc of closure on the articulator when the interocclusal records are removed and the articulator is closed.     

Hinge-axis location and face-bow transfer for edentulous patients.

There are distinct advantages to locating the hinge axis for the edentulous patient by use of the modified Loma Linda hinge-axis locator. These include: (1) alteration of the vertical dimension of occlusion on the articulator may be accomplished since the opening or closing takes place around the patient's terminal hinge axis; (2) valid and verified centric and eccentric relation records may be obtained at an increased vertical dimension of occlusion that is in harmony with the patient's terminal hinge axis; (3) cusp-form posterior teeth can be articulated and verified in the mouth with minimal occlusal correction by use of a terminal hinge axis. Some disadvantages to the procedure may include: (1) the additional procedure of making a modeling compound clutch for hinge-axis location; (2) the initial modification of the edentulous trays to accommodate the recording device; and (3) the technique is used with the Whip-Mix articulator; however, it can be modified for use with other articulators.     

Accuracy of an earpiece face-bow

The validity of the Hanau ear-bow to transfer an arbitrary hinge axis to a Hanau articulator was clinically compared with a Hanau kinematic face-bow. The study was conducted with 18 randomly selected patients. This investigation demonstrated a significant statistical difference between the arbitrary axis located with an ear-bow and the terminal hinge axis. This discrepancy was significant in the anteroposterior direction but not in the superior-inferior direction. Only 50% of the arbitrary hinge axes were within a 5 mm radius of the terminal hinge axis, while 89% were within a 6 mm radius. Furthermore, the ear-bow method was not repeatable statistically. Additional study is needed to determine the practical value of the arbitrary face-bow and to pursue modifications to improve its accuracy.     

Accuracy of face-bow transfer: effect on surgical prediction and postsurgical result.

One of the most common errors in model surgery for orthognathic surgery is in the mounting of the models on the articulator. This study assessed the ability of one type of face-bow to transfer the maxillary model to the articulator. Twenty-five consecutive mountings were evaluated by calculating the angle made between the maxillary occlusal plane on the cephalogram and comparing it with the maxillary occlusal plane angle on the articulator. An accurate face-bow transfer should transfer this angle, making the two similar. It was found that a significant difference between the maxillary occlusal plane angle on the cephalogram and the articulator was found in the average case. The implications of such errors and a technique to avoid them are presented.     

A comparison of 3 methods of face-bow transfer recording: implications for orthognathic surgery.

PURPOSE: The purpose of this study was to compare the occlusal plane inclination of models mounted using 3 different systems for face-bow transfer with the actual occlusal plane inclination as measured on a cephalometric radiograph. PATIENTS AND METHODS: Twenty-two subjects were enrolled in this study. Three alginate impressions of the maxillary dentition were taken, and 3 stone dental models were produced for each subject. Face-bow recordings were obtained on each subject using the SAM Anatomical Face-bow (Great Lakes Orthodontics Products, Ltd, Tonawanda, NY), the Erickson Surgical Face-bow (Great Lakes Orthodontics Products, Ltd) and a new technique developed by one of the authors (J.G.). For each subject, the dental models were mounted on a SAM articulator using each of the 3 face-bow recordings. Finally, a lateral cephalometric radiograph was obtained for each subject. The occlusal plane inclination was measured on the models and on the cephalometric radiographs. Differences among groups were tested using a 1-way analysis of variance. Bonferroni test was used for post hoc comparison between different pairs of groups. RESULTS: The average occlusal plane inclination using the SAM Anatomical Face-bow was 7.8 degrees +/- 4.2 degrees greater than the actual-a difference that was statistically significant. The mean occlusal plane inclination of the models obtained using the Erickson Surgical Face-bow was 4.4 degrees +/- 2.2 degrees greater than the actual-a difference that was also statistically significant. The mean occlusal plane inclination of the models obtained by the new technique was only 0.9 degrees +/- 1.2 degrees greater than the actual; this difference was not statistically significant. CONCLUSIONS: The new mounting technique is more accurate than the conventional SAM Face-bow or the Erickson Face-bow for reproducing the actual occlusal plane inclination.     

Traditional face-bow transfer versus three-dimensional virtual reconstruction in orthognathic surgery

Face-bow transfer is an essential step in articulator-based orthognathic surgery planning. However, it can be a source of inaccuracy. Virtual computer-based planning avoids this error through the use of direct patient-related three-dimensional imaging data. The aim of this prospective observational study was to determine the error of face-bow transfer three-dimensionally and correlate it to the different types of malocclusion. Orthognathic surgery performed on 38 patients (10 male, 28 female; mean (standard deviation) age 24.7 (6.9) years) was planned twice: first articulator-based with plaster models and second computer-based with surgery planning software. Both models were digitized and compared regarding the angle between the Frankfort horizontal plane and the occlusal plane. In most cases, the angle in the sagittal dimension was higher in the articulator-based model than in the computer-based model. The angle in the transverse dimension was as often under- as over-represented. The type of malocclusion, i.e. skeletal class, vertical relationship, and degree of asymmetry, had no significant impact on the amount of error. In conclusion, this study indicates that computer-based planning should be considered as an advantageous alternative in orthognathic surgery planning.     

A biodifferential system of face-bow mechanics.

A review of the literature, both scientific and commercial, did not demonstrate the separation of the inner and outer bows into a biodifferential interchangeable system. The prime design idea, to separate the inner and outer bows, increased versatility and yielded a multiple appliance with a greater range of use and safety. The joint couple systems could be adapted to fulfill the criteria cited in the literature during preliminary treatment (deciduous dentition), partial treatment, full-banded treatment, and retention. The biodifferential design was compatible with most mechanical orthodontic appliances and systems currently used. The three joint designs presented and the three inner bow lock devices fulfilled the parameters expected from the normal use of the present face-bow in necessary strength, stability, and use. Further, the use of a joint couple between the inner and outer bows expanded the versatility of the face-bow into a biodifferential system and allowed for an easily manageable and orderly change of forces, vectors, sizes, and shapes requiring little chair time and minimum instruction to the patient. The inner bow could be used as an intraoral appliance for bumpers, shields, and oral screens. These easily made, preformed, interlocking parts could be marked or color coded as to type and size and keyed, grooved, and designed to prevent inverted interlocking of parts. The inner bow could be tied in, as an aid in patient cooperation, or the inner and outer bows could be pinned or ligated together to prevent separation. One of the most important factors of the biodifferential system is protection of the patient from severe trauma to the eyes, face, and mouth due to misuse or accident, as has occurred in the one-piece face-bow. The biodifferential system fulfills the five criteria of the investigation: (1) a system of interchangeable, interlocking joint parts, (2) safety and dependability, (3) easy changes in force, vectors, and moments, (4) enhanced patient cooperation, and (5) oral hygiene.     

One face-bow adapts to three articulators.

A procedure has been described whereby simple adaptors will allow the convenient Whip-Mix Quick Mount face-bow to be transferred to the commonly used Hanau H-2 and Dentatus ARH semiadjustable articulators.     

Reliability of a facebow transfer procedure.

The three-dimensional orientation of a maxillary cast mounting from a simulated-kinematic facebow transfer was evaluated in multiple trials among three operators on a single subject. The anterior and posterior anatomic facial reference points were marked on the subject. Each operator performed a separate series of trials to reset the anterior facebow component, the two posterior facebow components, and a control series with no resetting of any facebow components relative to the subject. The x, y, and z coordinates of three reference points on the maxillary cast were determined with a machinist microscope relative to a fixed reference after each facebow transfer. A range of differences between mountings of the maxillary cast were found between trials with all three methods used. These mounting errors were due to setting of the instrument and would be expected in routine clinical use of this instrument.     

The importance of face-bow recordings

An acrylic resin developed to be processed by boiling for 20 minutes in water was compared to a conventional heat-processed acrylic resin for porosity when processed according to the manufacturer's directions. No porosity was found in the conventional resin in thicknesses up to 19.5 mm. The boilable resin developed porosity in thicknesses of 6 mm and greater. The porosity increased with increased thickness. The boilable resins should not be used for long-term prostheses or those requiring a thickness of acrylic resin that approaches 6 mm.     

The activated face-bow: simple, safe, extraoral traction.

A simple and safe extraoral traction model is described. This consists of a face-bow with activated outer arms and a neck strap or headgear without any elastic force, such as rubber bands, elastic ribbons, coil springs, etc. The appliance cannot be withdrawn from the mouth by acident; therefore, the patient is protected from possible injuries.     

An investigation of the reproducibility of face-bow transfers

An investigation was conducted to determine the reproducibility of the position of a maxillary cast in two widely-used semi-adjustable articulators when a face-bow transfer was repeated ten times for the same individual. The results obtained with the Dentatus AEB, Whipmix Quickmount and Almore transfer bows were compared. The variations in cast position rarely exceeded ±1.0 mm in any of three planes of space and although the results suggested a ranking in accuracy of the three instruments, all were considered clinically acceptable. On the basis of the results observed, face-bow transfer appears to be a reliable clinical procedure and accuracy in the determination of reference locations is unlikely to be negated by subsequent transfer errors, provided that appropriate care is employed.     

Errors in mounting maxillary casts using face-bow records as a result of an anatomical variation

The relationship of the teeth to the intercondylar axis and horizontal plane is transferred to the articulator by means of a face-bow record. In most semi-adjustable articulators, the horizontal plane to which the maxillary cast is orientated is the Frankfort plane or its near equivalent, the orbital-axis plane. For this purpose the infraorbital notch is used as the anterior reference point Clinical observations of Cantonese patients suggest that in some individuals the Frankfort plane may not be horizontal, with the result that the orientation of the casts in the articulator is incorrect with respect to the horizontal plane, and a preliminary study has been undertaken to investigate this range of variation.

Lateral cephalometric radiographs were taken of 33 Cantonese male adult subjects in natural head posture. The cephalometric landmarks of the Frankfort plane were recorded relative to the true vertical axis and, by the use of a digitizer, fed into a computer for analysis. The results show that there is considerable individual variation in the orientation of the Frankfort plane. Variations ranging between +11° and -2° in relation to the horizontal were recorded. Large anatomical variations may make errors difficult to avoid when the manufacturers' recommended anterior reference point for a particular face-bow is the infraorbital notch. Clearly this is a source of potential error which should be recognized when treating this ethnic group.