A new method to simplify and increase the precision of maxillary cast mounting procedures in fully adjustable or semiadjustable articulators

This study introduces a new impression procedure that permits mounting the maxillary stone cast in an articulator for any patient treatment and is applicable to any dental arch with any impression material. A transfer tray was designed that makes it possible to transfer the patient's maxillary impression to the articulator in a one-stage procedure without the need for making record bases and occlusion rims or the need to use a face-bow bite fork. (J Prosthet Dent 1997;77:219-24.)     

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.     

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.     

A reevaluation of the axis-orbital plane and the use of orbitale in a facebow transfer record.

A fundamental assumption in prosthetic dentistry is that the axis-orbital plane usually will be parallel to the reference horizontal. Most articulator systems have incorporated this concept into their designs and use orbitale as the anterior reference point for transferring the vertical position of the maxillae to the articulator. The position of the maxillary cast is expected to be in the same vertical position as the maxillae with the subject's head oriented in the esthetic reference position. However, the use of orbitale in conjunction with an articulator whose design assumption places the axis and orbital indicator parallel to the horizontal reference will result in a substantial mounting error. This article examines the cause and correction of the mounting error that results from the use of orbitale as the anterior reference point of a facebow transfer record made to an axis-orbital designed articulator.     

Mounting casts on a mechanical articulator by using digital multisource data: A dental technique

A facebow transfer is typically used for mounting a maxillary gypsum cast in an ideal location in a mechanical articulator. However, the facebow transfer procedure is difficult and may cause the patient discomfort. This proposed technique uses a patient’s cone beam computed tomography (CBCT) data to reproduce the occlusal plane in relation to digital articulator scan data, align the patient’s gypsum cast or intraoral scan data on the reproduced plane, and then transfer the data to a mechanical articulator.     

Face bow and articulator for planning orthognathic surgery: 1 face bow

Orthognathic surgery that involves movement of the maxilla relative to the skull is usually planned using casts mounted on an articulator. Accurate positioning of the maxilla relative to the skull is essential for reliable planning, but current methods of mounting casts on articulators are inaccurate and unreliable. We propose that the casts should be mounted using the relation between the horizontal plane and the resting head position to define the position of the skull. A photographic study of 10 subjects confirmed the reproducibility of the head position and its relation to the horizontal plane. A face bow incorporating a circular spirit level was used to transfer the relation between the horizontal and the maxillary dentition to a semiadjustable articulator. The angle between the horizontal and maxillary occlusal planes was measured from six lateral cephalograms and compared with those of casts mounted on a semiadjustable articulator using a face bow with either an orbital pointer or a spirit level. The face bow with a spirit level produced considerably more accurate results.     

Articulator modification for maxillofacial prosthesis

A modification has been described which will permit the use of a face-bow for maxillofacial prosthesis construction. Any inferior positioning of the maxillary cast can now be compensated for by increasing the condylar inclination to maintain the correct relationship to the occlusal plane. By modifying an existing articulator, versatility has been achieved and the extreme cost of a new instrument has been avoided. While this design does not solve the problems encountered with maxillofacial prostheses, it does serve to make fabrication of prostheses easier for both the dental laboratory technician and the dentist.     

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.     

The relationship of upper facial proportions and the plane of occlusion to anatomic reference planes

A study was made of 28 dentulous Chinese (Singaporean) adults by using lateral skull radiographs. The dimensions of the maxillae and various craniofacial reference lines related to prosthodontic use were analyzed. The craniofacial reference angles that reflect the vertical height and horizontal depth of the maxillae in Chinese adults differed significantly from the norms obtained in a white North American adult population. By comparison, Chinese adults have a vertically high and horizontally receded upper face that could cause planes such as the Frankfort horizontal plane or an arbitrary axis-orbitale plane to assume a steeper anterior inclination, thus modifying the mechanical inclination of the maxillary cast and occlusal plane on the articulator.     

Fabrication Method for a Mounting Jig and Cast Support for Mounting Complete Dentures

In complete denture fabrication, the definitive maxillary cast is mounted on an articulator using a facebow transfer or mounting jig, and the mandibular cast is mounted using an interocclusal record. The technique presented describes an easy and inexpensive method for fabrication of a mounting jig and rigid cast supports for mounting complete dentures.     

Procedural problems in using the Denar pantograph as a transfer-bow.

A method has been described for using zinc-oxide/eugenol paste as an interclutch support when the Denar pantograph is used as a transfer-bow. Using this technique a stable centric relation position can be maintained during the maxillary cast mounting procedure and the subsequent setting of the articulator to the pantographic recordings.     

Guidelines for the technician in mounting maxillary casts utilizing a modeling-compound face-bow record

A study of five subjects was undertaken to determine the best way to prepare an accurate modeling-compound face-bow record. This enables the laboratory technician to mount the maxillary cast on a semiadjustable articulator. Requirements and recommendations are presented to aid the laboratory technician and dentist in performing this procedure.     

Reproduction accuracy of articulator mounting with an arbitrary face-bow vs. average values—a controlled,randomized, blinded patient simulator study

Objectives

The benefit from positioning the maxillary casts with the aid of face-bows has been questioned in the past. Therefore, the aim of this study was to investigate the reliability and validity of arbitrary face-bow transfers compared to a process solely based on the orientation by means of average values. For optimized validity, the study was conducted using a controlled, randomized, anonymized, and blinded patient simulator study design.

Material and methods

Thirty-eight undergraduate dental students were randomly divided into two groups; both groups were applied to both methods, in opposite sequences. Investigated methods were the transfer of casts using an arbitrary face-bow in comparison to the transfer using average values based on Bonwill’s triangle and the Balkwill angle. The “patient” used in this study was a patient simulator. All casts were transferred to the same individual articulator, and all the transferred casts were made using type IV special hard stone plaster; for the attachment into the articulator, type II plaster was used. A blinded evaluation was performed based on three-dimensional measurements of three reference points.

Results

The results are presented three-dimensionally in scatterplots. Statistical analysis indicated a significantly smaller variance (Student’s t test, p < 0.05) for the transfer using a face-bow, applicable for all three reference points.

Conclusions

The use of an arbitrary face-bow significantly improves the transfer reliability and hence the validity.

Clinical relevance

To simulate the patient situation in an individual articulator correctly, casts should be transferred at least by means of an arbitrary face-bow.

     

Cast articulation accuracy using rigid cast stabilization

PURPOSE: This study evaluated the positional accuracy of casts articulated on a semi-adjustable articulator, with and without rigid cast stabilization using either laboratory plaster or mounting plaster. MATERIALS AND METHODS: A reference articulation of melamine casts in maximum articulation was established and recorded in the horizontal and vertical dimensions using a verification device. The same casts were subsequently remounted 24 times using either laboratory plaster or mounting plaster. Half of the articulations from each group were stabilized using detachable mounting rods and sticky wax, and half were hand-articulated without stabilization, for a total of 6 articulations in each of 4 test groups. The resulting spatial positions established on the articulator were compared to the initial reference position on the verification device grid. Means and standard deviations of the absolute values of the horizontal and vertical displacement for each group were determined separately and compared using a one-way anaylsis of variance. Significant differences (p <0.05) were identified using Tukey's honestly significant difference multiple comparison test. RESULTS: Mean vertical mandibular cast displacement ranged from 0.26 +/-0.21mm for stabilized casts mounted with laboratory plaster to 1.58 +/-0.32 mm for unstabilized casts mounted with mounting plaster. For each mounting material, significantly less vertical displacement (p <0.001) was observed with the mandibular cast stabilized before mounting. The cast mounted with laboratory plaster exhibited horizontal displacement (0.87 +/-0.29 mm) that was significantly greater than the remaining groups (p <0.001), which did not differ from each other. CONCLUSIONS: Rigid stabilization of the mandibular to maxillary cast during mounting with laboratory and mounting plaster improved articulation accuracy.     

Virtual facebow technique using standardized background images

The procedure described provides a novel and accessible virtual facebow transfer based on standardized photographs loaded in the virtual articulator module of a computer-assisted design and computer-assisted manufacturing (CAD-CAM) software program for dental applications. The practical application of the technique in a digital workflow is the correct alignment of the digital maxillary cast to the virtual articulator with respect to the patient’s planes and the skin markings of the condylar axis.     

Three-dimensional analysis of dental casts based on a newly defined palatal reference plane

The purpose of this study was to establish a new method for orthodontic diagnosis that integrates the three-dimensional (3-D) shape of a dental cast and the craniofacial morphology using a newly defined palatal reference plane. We also measured the accuracy of this new palatal reference plane as a reference for measurement and its spatial relationship to the framework of the craniofacial skeleton using lateral and frontal cephalometric radiography and maxillary dental casts, which were transferred using an anatomical face-bow. Eighteen female subjects were included in this study. The new reference plane in dental cast analysis corresponded to the A-PNS plane in the lateral view and to the J-J' plane in the frontal view, which have been shown to be sufficiently accurate as a reference for measurement. These results indicate that the application of this palatal reference plane, as a reference structure, should provide accurate and abundant 3-D data concerning malocclusion.     

Practical considerations for using the face-bow for complete denture prosthodontics

Until an instrument that can adjust to all the anatomic hinge axis asymmetries becomes available, it is more appropriate to use a method other than the face-bow record for orienting the maxillary cast in an articulator for complete denture prosthetics. The objective of the alternate method should be to achieve a cast-articulator assembly that reflects the patient's vertical cranial posture.     

A new articulator emphasizing centric occlusion and the anterior determinants.

A new articulator is described which has the advantages of the rigidity of a simple articulator in the upper member and the flexibility of an adjustable articulator in the lower member. A link between the members and the frame along with the posterior controls establishes a full range of functional chewing movements and defines the extreme lateral or border paths. The articulator has condylar element controls which permit releasing and remounting the mandibular cast in a manner that serves the same function as the split-cast technique, but this method is faster and shows the amount of discrepancy. The condylar element control is an improvement over existing devices for comparing interocclusal records in that it not only indicates differences in position but it also provides quick remounting of the casts in a working articulator. Other features of the articulator are: (1) a condylar lock mechanism which is activated by only a half turn, (2) adjustable spring tension, (3) precise long centric and wide centric controls, (4) an incisal pain which can be removed and replaced on the articulator without changing its setting, (5) a Bennett movement carefully selected to avoid the complication of a pantograph type of face-bow, and (6) a new sponge wall type of mounting plate which supports both casts for simultaneous mounting.     

Reliability of an ear-bow arbitrary face-bow transfer instrument.

STATEMENT OF PROBLEM: Accuracy of techniques for recording the orientation of the maxillary arch to the articulation of the temporomandibular joints has been reported. The variability contributed by the dentist and the equipment within a technique may also contribute to technical error. PURPOSE: This study investigated the variability of a group of dentists who used an arbitrary ear-face-bow instrument to mount a maxillary cast. MATERIAL AND METHODS: The same maxillary cast on a single experimental subject was mounted on an articulator with a common arbitrary ear-face-bow instrument. This cast was equipped with 4 reference points for the measurement of changes of spatial orientation of the cast, which were determined through coordinate measurements with a machinist's microscope. A repeated measures analysis of variance was used to determine statistically significant changes in spatial orientation with a Wilks' Lambda test to compare mean values. RESULTS: A confidence interval of 95% demonstrated that any dentist might expect a range of +/-1.2 mm error in using this instrument/articulator combination. The 3 dentists did not demonstrate any significant differences in the spatial orientation of their mountings in the vertical or horizontal directions. However, there were significant differences in their mountings in linear distance changes of the patient's posterior right side. CONCLUSION: A range of inherent error attributable to the operator using this instrument was recorded.