An investigation of the reproducibility of face-bow transfers

The accuracy and stability of the maxillary position after orthognathic surgery using a novel computer-aided surgical simulation system

Background

Many reports have been published on orthognathic surgery (OGS) using computer-aided surgical simulation (CASS). The purpose of this study was to evaluate the accuracy of the maxillary repositioning and the stability of the maxilla in patients who underwent OGS using a newly developed CASS program, a customized osteotomy guide, and a customized miniplate.

Methods

Thirteen patients who underwent OGS from 2015 to 2017 were included. All patients underwent a bimaxillary operation. First, a skull-dentition hybrid 3D image was rendered by merging the cone beam computed tomography (CBCT) images with the dentition scan file. After virtual surgery (VS) using the FaceGide® program, patient-customized osteotomy guides and miniplates were then fabricated and used in the actual operation. To compare the VS with the actual surgery and postoperative skeletal changes, each reference point marked on the image was compared before the operation (T0) and three days (T1), four months (T2), and a year (T3) after the operation, and with the VS (Tv). The differences between ΔTv (Tv-T0) and ΔT1 (T1-T0) were statistically compared using tooth-based reference points. The superimposed images of Tv and T1 were also investigated at eight bone-based reference points. The differences between the reference points of the bone surface were examined to evaluate the stability of the miniplate on the maxilla over time.

Results

None of the patients experienced complications. There were no significant differences between the reference points based on the cusp tip between ΔTv and ΔT1 (p > 0.01). Additionally, there were no significant differences between the Tv and T1 values of the bone surface (p > 0.01). The mean difference in the bone surface between Tv and T1 was 1.01 ± 0.3 mm. Regarding the stability of the miniplate, there were no significant differences between the groups. The difference in the bone surface between T1 and T3 was − 0.37 ± 0.29 mm.

Conclusions

VS was performed using the FaceGide® program, and customized materials produced based on the VS were applied in actual OGS. The maxilla was repositioned in almost the same manner as in the VSP plan, and the maxillary position remained stable for a year.

An in vitro evaluation of the maxillary occlusal plane orientation obtained with an electronic application: A preliminary investigation

STATEMENT OF PROBLEM

In the evaluation and fabrication of dental prostheses, maxillary occlusal plane orientation in the sagittal and coronal planes may affect functional and esthetic outcomes. The accuracy of a recently developed electronic application in transferring this orientation to a semiadjustable articulator has not been evaluated.

PURPOSE

The purpose of this in vitro study was to evaluate the coronal and sagittal orientation of the occlusal plane on maxillary casts mounted with an electronic application facebow system onto a corresponding semiadjustable arcon articulator.

MATERIAL AND METHODS

A maxillary typodont was placed into a phantom head (control) oriented with the Frankfort horizontal plane parallel to the horizon. A digital protractor was used to measure the angle between the occlusal plane of the maxillary arch of the phantom head and the Frankfort horizontal plane along the sagittal and coronal planes. The commercial system (test group) was used to make 15 facebow records of the maxillary typodont within the phantom head. The system records were used to mount diagnostic casts of the maxillary typodont onto a semiadjustable arcon articulator. The same measurements were made on the mounted diagnostic casts and were compared with the control. Statistical differences between the occlusal plane of the control and the occlusal plane of the mounted maxillary casts were determined using the 1-sample t test (α=.05).

RESULTS

The coronal orientation of the occlusal plane was significantly different (P<.001) between test group and control. No significant differences (P>.05) were found in the sagittal orientation of the occlusal plane.

CONCLUSIONS

Within the limitations of this study, variations in the coronal plane orientation were observed with the system. Variations in this plane may lead to adverse evaluation and clinical outcomes.

Does a face-bow lead to better occlusion in complete dentures? A randomized controlled trial: part I

OBJECTIVES

In a double-blinded randomized controlled clinical trial, the impact of face-bow registration for remounting complete dentures (CDs) on the occlusal parameters (part I) was evaluated.

MATERIALS AND METHODS

New CDs of 32 patients were duplicated and mounted after intraoral pin registration according to mean settings (group 1) and (group 2) using a face-bow (arbitrary hinge axis). The vertical dimension was reduced to the first occlusal contact point, and a bite record was fabricated in the articulator. The number of contacts and the number of teeth in contact were evaluated by a computer program (laboratory result). After randomization, half of the CDs were adjusted according to protocol of group 1 and group 2 and delivered to the patients. After 3 days (T1) and 84 days (T2), clinical static contact points and teeth in contact were counted. Contact points and teeth in contact of both groups (laboratory results) and at different moments (clinical results) were analyzed statistically with the F test and bootstrapping.

RESULTS

Laboratory: No. 2 (face-bow) showed more occlusal contact points than no. 1 (mean setting), p > 0.05. The number of teeth with at least one occlusal contact was significantly higher in no. 2 (p = 0.027). Clinic: The mean number of teeth with at least one clinical contact point was significantly higher in no. 1 (no. 1 = 7.13, no. 2 = 5.31; p = 0.042). Extent of the vertical shift poorly correlated with number of laboratory occlusal contact points (R ² = 0.017).

CONCLUSIONS

Considering the complex multistep study design, a limited number of participants, and referring to one specific arbitrary face-bow, the following conclusion could be drawn: no substantial difference by the use of the arbitrary face-bow compared to a mean setting could be determined, when changing the vertical dimension in the articulator within a remounting procedure of complete dentures.

CLINICAL RELEVANCE

Further research is necessary to determine the effects of different arbitrary face-bows on the fabrication and adaptation of removable dentures.

Influence of a face-bow on oral health-related quality of life after changing the vertical dimension in the articulator: a randomized controlled trial. Part II

OBJECTIVES

In a double-blind randomized controlled clinical trial, the impact of face-bow registration for remounting complete dentures (CDs) on oral health-related quality of life (OHRQoL) was evaluated.

MATERIALS AND METHODS

New CDs of 32 subjects were clinically remounted using intraoral pin registration. CDs were transferred into a semi-adjustable articulator corresponding to group #1: mean settings with Bonwill triangle and Balkwill angle, and group #2: arbitrary hinge axis with a face-bow registration. After occlusal adjustment, subjects were followed up after 3 (T1) and 84 (T2) days. The primary outcome was the change of OHRQoL by OHIP-G49, while as secondary outcome, mucosal alterations were evaluated over time. Mean values of OHIP-G49 total sum scores and OHIP-dimensions were calculated for baseline (T0) and days 3 (T1) and 84 (T2) after intervention. Based on bootstrapping methods (changes of total OHIP sum score) and the Wilcoxon test (changes of sum scores of OHIP dimensions), analyses of between-group differences were performed.

RESULTS

Mean values (MV) of OHIP-G49 sum scores decreased in both groups from T0 (#1 48.56; #2 45.46) to T1 (#1 31.43 (p = 0.012); #2 43.20) and to T2 (#1 29.06; #2 29.40), which represents an improvement in OHRQoL. MV of OHIP-dimension sum scores decreased from T0 to T1 in both groups (#1 seven dimensions; #2 four dimensions); the decrease of sum scores was tested as not statistically significant (p > 0.05).

CONCLUSIONS

From the patient's perspective, mean-value-based remounting methods are of value. The use of a face-bow was not perceived as superior.

CLINICAL RELEVANCE

From the patient's perspective, remounting of CDs will be positively perceived, irrespective of the use of a face-bow.

In vitro comparison of the maxillary occlusal plane orientation obtained with five facebow systems

STATEMENT OF PROBLEM

The sagittal and coronal orientation of the maxillary occlusal plane plays an important role in the esthetic and functional outcome of dental prostheses. The accuracy of contemporary facebow transfer systems in transferring this orientation to semiadjustable articulators has not been quantified.

PURPOSE

The purpose of this in vitro investigation was to analyze the sagittal and coronal orientation of the occlusal plane with 5 different facebow transfer systems.

MATERIAL AND METHODS

A phantom head containing a maxillary typodont (control) was oriented so that the Frankfort horizontal plane was horizontal. The angle between the occlusal plane of the maxillary arch of the phantom head and the Frankfort horizontal plane was measured along the sagittal and coronal planes with a digital protractor. Fifteen facebow records using each of 5 facebow transfer systems (test groups) were made on the phantom head containing the maxillary typodont. Diagnostic casts of the maxillary typodont were mounted on semi-adjustable arcon articulators from the facebow records. The same angles measured on the control were measured on the test groups. These angles were compared with the same angle measured on the maxillary arch of the phantom head (control). All measurements were made by 2 operators.

RESULTS

Significant differences in the sagittal and coronal orientation of the occlusal plane were noted. Compared with the control, the Denar system had the least significant difference in the coronal orientation of the occlusal plane, while the Pana-Mount system had the least significant difference in the sagittal orientation of the occlusal plane. An intergroup comparison of the test groups showed significant differences among the groups. The Kois system showed the greatest difference in the coronal plane orientation, while the Denar system showed the greatest difference in the sagittal plane orientation.

CONCLUSIONS

None of the tested facebow systems exactly replicated the sagittal and coronal orientation of the maxillary occlusal plane. Significant differences in the sagittal and coronal orientation of the occlusal plane were observed between the test groups and the control. Intergroup comparisons revealed significant differences in the sagittal and coronal orientation of the occlusal plane.

How accurate is model planning for orthognathic surgery?

The purpose of this study was to evaluate the accuracy of model surgery prediction after orthognathic surgery and to identify possible errors associated with the prediction process. The study included 46 patients who had undergone orthognathic surgical procedures; 22 in Group A who had had a Le Fort I osteotomy; and 24 in Group B who had had a Le Fort I osteotomy and mandibular setback surgery. The immediate postoperative and preoperative lateral cephalograms were analysed to calculate surgical changes; these were compared with those obtained from model surgery prediction and a statistical analysis was undertaken. The maxilla was more under-advanced and over-impacted anteriorly than predicted by model surgery. The amount of mandibular setback was more than that predicted by model surgery. None of the differences between prediction planning and actual surgical changes was statistically significant at p<0.05. Inaccuracy with the face bow recording, the intermediate wafer, and auto-rotation of the mandible in the supine or anaesthetized patient would appear to be the principal reasons for errors. Inaccuracies are associated with the transfer of prediction planning to model surgery planning and prediction, which should be eliminated to improve the accuracy and predictability of orthognathic surgery.

Comparison of three facebow/semi-adjustable articulator systems for planning orthognathic surgery

Our aim was to measure the steepness of the occlusal plane produced by three different semi-adjustable articulators: the Dentatus Type ARL, Denar MkII, and the Whipmix Quickmount 8800, and to assess the influence of possible systematic errors in positioning of study casts on articulators that are used to plan orthognathic surgery. Twenty patients (10 skeletal class II, and 10 skeletal class III) who were having pre-surgical orthodontics at Liverpool University Dental Hospital were studied. The measurement of the steepness of the occlusal plane was taken as the angle between the facebow bite-fork and the horizontal arm of the articulator. This was compared with the angle of the maxillary occlusal plane to the Frankfort plane as measured on lateral cephalometry (the gold standard). The Whipmix was closest to the gold standard as it flattened the occlusal plane by only 2 degrees (P<0.05). The results of the Denar and Dentatus differed significantly from those of the cephalogram as they flattened the occlusal plane by 5 degrees and 6. 5 degrees (P<0.01), respectively. Clinicians are encouraged to verify the steepness of the occlusal plane on mounted study casts before the technician makes the model.

A comparative study of two arbitrary face-bow transfer systems for orthognathic surgery planning

The relative reproducibility of two widely used arbitrary face-bow transfer systems, the Denar Slidematic and the Dentatus type AEB, was assessed for use in orthognathic surgery planning. A novel method was also developed to determine any variation in three-dimensional spatial position and orientation of the maxillary cast. This envelope of movement enabled realistic comparisons to be made for each face-bow system, operator, and skeletal type. The overall face-bow/articulator procedure showed poor reproducibility. However, the Denar Slidematic face-bow was better (P < 0.001) than the Dentatus type AEB standard face-bow, and the errors were higher in the anteroposterior and lateral directions than the vertical direction. There was no significant difference between operators for each system.

Refined intraoperative repositioning of the osteotomized maxilla in relation to the skull and TMJ

In dysgnathic patients, who have to be treated by surgical repositioning of the jaws, the necessary bone movements are predicted preoperatively with the help of sophisticated analysis. A high degree of accuracy, could not however be transferred to the patient, because of lack of an operative procedure as accurate as the preplanning. In this paper a face-bow is described, provided with an interocclusal splint that has been adjusted beforehand on an articulator, in a model operation taking into account the skull and TMJ relationship. Using this face-bow-splint combination the possibility of greater accuracy in transferring the preplanned movements to the patient is facilitated. The computerized preplanning, the model operation and the technical procedure as well as the operation itself are described, step by step.