Reconstruction of Former Tooth Position in the Edentulous Maxilla Using the Staub™ Cranial System

Abstract

Objective: The Staub™ Cranial system is based on defined anatomical reference points of edentulous casts that can guide the reconstruction of artificial teeth on the edentulous jaw. The aim of this study was to evaluate the validity of the Staub™ Cranial system in reconstructing the position of natural teeth in edentulous maxillae. Materials and methods: To reconstruct the original position of natural teeth, 20 fully dentate maxillary casts were produced, and 20 duplicates had all teeth eliminated. Subsequently, following the Staub™ Cranial system guidelines, an artificial teeth set-up was completed. The measured distances included the intermolar width #16–26, the intercanine width #13–23, and the incisocervical length #11. Measurements were made using the principle of stripe projection with specially developed software. Original and reproduced casts were then compared. The reproduced casts with measured distances deviating less than 5% from the mean values of control models were considered successful reconstructions. Results: The ability of the system to reconstruct the original position of lost teeth in the edentulous jaw was precise. With a narrow tolerance range of 5%, 80% of the models could be reproduced with zero or a deviation in one dimension only. Conclusions: The results of this study confirmed the efficacy of the Staub™ Cranial system to provide guidance for the customized arrangement of artificial teeth in edentulous jaws.

1. Introduction

For the fabrication of a partial or a complete denture, it is important to re-establish the occlusal plane and the vertical dimension of occlusion of the patient. Arrangement of artificial teeth plays an important role in this process, ensuring not only stable occlusion but also functional performance and esthetic acceptance. For patients needing complete dentures, there are several methods described in the literature to determine the vertical dimension of occlusion, register centric relation, and provide occlusal schemes of acrylic teeth [1,2,3]. However, denture teeth set-up remains an important laboratory stage that is affected by opposing dentition, arch shape, alveolar resorption, facial esthetics, and speech. Wax rims present the standard procedure for setting artificial teeth, while modern technological advances offer the option for digital arrangement [4,5]. Facial characteristics provide a reference for teeth selection and arrangement, resulting in typical prostheses without anatomical customization. In 1981, Staub suggested that it is possible to reconstruct the position of the former (lost) natural teeth of a totally or partially edentulous patient, with their individual occlusal plane and vertical dimension of occlusion based on specific anatomical landmarks. The effective validation of the suggested clinical methodology led to the development of the Staub™ Cranial analysis and fabrication system. Subsequently, the use of this system has been recommended for the fabrication of new fixed and removable dentures, as well as for the analysis of models and existing dentures [6,7,8,9]. The Staub^TM Cranial system is based on defined anatomical reference points of the jaw model. These should be present on every model and typically identifiable in their position (Figure 1).

The combined use of these landmarks should allow a precise indication of the former position of the natural teeth in a partially edentulous or edentulous jaw with mathematical calculations [8,9] (Figure 2). The aim of this study was to examine the effectiveness of the system in reconstructing the former position of lost teeth in the edentulous maxillary jaw.

2. Materials and Methods

In this prospective study, 10 male and 10 female, Caucasian, third-year undergraduate dental students were randomly selected. All the students had complete upper and lower natural dental arches, no fixed dental prostheses of any type, and were orthodontically untreated. Two upper jaw impressions were made as part of their clinical exercise using modified Rim LOCK trays (Orbilock^®, Orbis Dental, Offenbach, Germany) and an alginate impression material (Palgaflex^®, ESPE, Seefeld, Germany). All the impressions were filled with type III dental stone. Two groups of 20 identical duplicate maxillary models were made in this way, with one group of 20 casts serving as control. The remaining 20 casts were prepared by eliminating all teeth with a gypsum-milling cutter. In addition, the alveolar ridge was removed until it had the typical shape of an edentulous jaw. Care was taken to ensure that the two directional points (A and B), the induction points (C, C1), and the conclusion lines (CR and CL) remained on the cast (Figure 3).

The edentulous models were then given to the expert (K.H. Staub). He constructed a set-up according to the principles of the Staub™ Cranial system, without prior knowledge of the initial condition of the casts. Resin teeth (Vitapan^®; Vita tooth factory, Bad Säckingen, Germany) were used for the set-ups (Figure 4).

The restored dental arch was then compared with that of the control group. This comparison was carried out in collaboration with the Institute for Laser Technologies in Medicine and Metrology at the University of Ulm using the stripe projection technique [10]. The software identifies the precise location of the projected stripes in the captured images. This often involves techniques like edge detection (e.g., using the Sobel filter), Gaussian filtering, or other specialized algorithms. Then, it determines the disparity (shift or offset) of the stripes between the projected pattern and the captured image, which is directly related to the depth of the object. Using the disparity information and camera calibration data, the software reconstructs a 3D point cloud representing the object’s surface [11]. This technique relies on optical triangulation, where a camera captures the distorted stripe pattern, and the geometry of the projection and camera set-up is used to calculate the 3D coordinates of points on the object’s surface. The striped image can be generated using a special software program developed by that institute, which allows the determination of the x/y/z coordinates and measurement of the distances between two selected points [12].

In order to facilitate the subsequent imaging process, the 20 reconstructed casts were first sprayed with a contrast agent (Diffu-Therm^®, H. Klumpf, Herten, Germany). This step was taken to improve the visibility of the denture surfaces for the CCD cameras. Subsequently, the 20 control specimens and the 20 reconstructed specimens were illuminated with a grid pattern and a white light source. The grid was projected onto the surface of the model, causing the striations to deform according to the shape of the model. The amount of the deformation was recorded by three CCD cameras pointed at the illuminated surface at predetermined angles. A personal computer was used to calculate a data set containing information about the three-dimensional arrangement of the teeth, obtained by triangulation algorithms based on the stripe images taken (Figure 5).

The distances between the mesio-buccal cusp tips of teeth #16 and #26, and the distances between the canine tips of teeth #13 and #23, were measured on all the striped photographs (Figure 6).

A second striped picture was used to determine the distance between the incisal edge of tooth #11 and the zenith (highest) point of the gingival margin (Figure 7).

Both visual inspection (Histogram, Q-Q Plot) and the Shapiro–Wilk test suggested that the data was approximately normally distributed, and for this reason, a one-way ANOVA statistical test was used to analyze the independent variables between the two groups. In hypothesis testing, the 5% significance level (α = 0.05) has become a widely accepted benchmark for balancing the risks of type I errors. In this study, Deviations in measured values of more than 5% between the reconstructed and control casts were determined as significant and indicated a discrepancy in the effectiveness of the methodology.

Model #6 was the only cast of the group to display deviations in all three areas of analysis. In the comparison picture (Figure 8), it can be observed that the original model exhibits a crowding of anterior teeth that cannot be predicted and reproduced in the reconstruction model. For this reason, three deviations were calculated.

In the comparison picture of model #9 (Figure 9), both canine teeth are abraded on the original model, to the extent that the cusps of the teeth are no longer discernible. The distance between the tips of teeth #13–23 was measured from the center of the abraded surface. Thus, the measured distance of 1.91 mm exceeds the range of tolerance of 1.7 mm by 0.21 mm and is recorded as a deviation.

The original cast #14 (Figure 10) exhibits considerable interdental spacing between the anterior teeth. Artificial teeth of similar size would not be indicated for the measured dimensions of the jaw. Consequently, larger replacement teeth were selected for prosthetic rehabilitation, resulting in measured deviations for the distances of #13–23 and #16–26 that exceed the tolerance range.

3. Results

The average values of the measured distances are shown in

Table 1. Average values of distances measured on the original casts.

	Distance 13–23	Distance 16–26	Height Tooth 11
Average Values	34.21 mm	51.74 mm	9.48 mm
5% Threshold	1.71 mm	2.58 mm	0.47 mm

. For the reproduced models to be considered acceptable, the tolerance values for the distance between the canine tips of teeth #13–23 must be within 1.7 mm, and for the mesio-buccal cusp tips of teeth #16–26, the tolerance value must be within 2.6 mm. For the distance between the incisal edge of tooth #11 and the highest point of the gingival margin (height), the tolerance value was set at 0.5 mm.

Considering these discrepancies, seven of the twenty models were found to fall within the specified tolerance range, while the rest of the casts presented various levels of differentiation in comparison to the controls (

Table 2. Results of measurement of the differences between the original and reproduced models. NR. = model number; R = reproduced model; O = original model. Distances and height measured in mm; bold numbers = deviation outside of the 5% accuracy tolerance.

Model		Distance (mm)			Difference R to O (mm)
Nr.	R/O	13–23	16–26	Height	13–23	16–26	Height
1.	R	32.02	49.49	8.38	0.49	1.14	0.43
1.	O	32.51	50.63	8.81
2.	R	34.7	50.35	8.8	0.80	3.72	0.46
2.	O	35.5	54.07	9.26
3.	R	33.54	49.48	9.52	0.00	2.14	0.99
3.	O	33.54	51.62	10.51
4.	R	32.76	48.63	9.56	0.16	5.15	0.23
4.	O	32.92	53.78	9.79
5.	R	33.95	51.93	9.56	0.67	0.86	0.62
5.	O	34.62	52.79	10.18
6.	R	32.16	47.4	9.68	2.10	3.04	−0.8
6.	O	34.26	50.44	8.88
7.	R	34.34	49.8	9.42	−1.11	1.71	−0.43
7.	O	33.23	51.51	8.99
8.	R	33.61	51.53	10.47	0.73	0.29	−0.42
8.	O	34.34	51.82	10.05
9.	R	32.78	48.69	8.50	1.91	1.20	0.07
9.	O	34.69	49.89	8.57
10.	R	34.6	49.79	9.16	1.08	−2.20	0.73
10.	O	35.68	47.59	9.89
11.	R	33.9	51.24	10.94	0.16	−1.73	−0.07
11.	O	34.06	49.51	10.87
12.	R	30.82	50.92	9.29	−0.23	−0.32	0.64
12.	O	30.59	50.6	9.93
13.	R	34.97	53.54	9.45	2.13	−0.04	0.47
13.	O	37.1	53.5	9.92
14.	R	33.53	49.56	9.31	3.62	6.06	0.37
14.	O	37.15	55.62	9.68
15.	R	32.19	47.31	9.21	−2.15	−2.13	−1.02
15.	O	30.04	45.18	8.19
16.	R	34.15	53.55	8.77	1.51	−0.51	−0.09
16.	O	35.66	53.04	8.68
17.	R	31.82	47.03	8.17	2.77	4.90	0.37
17.	O	34.59	51.93	8.54
18.	R	34.95	53.24	9.89	0.10	−1.12	−0.41
18.	O	35.05	52.12	9.48
19.	R	34.34	53.24	10.31	1.23	2.64	−0.36
19.	O	35.57	55.88	9.95
20.	R	34.03	52.62	9.93	−0.78	0.69	−0.31
20.	O	33.25	53.31	9.62
Mean (SD)	R	33.46 (1.17)	50.47 (2.11)	9.44 (0.72)	0.76 (1.33)	1.27 (2.35)	0.074 (0.529)
	O	34.22 (1.83)	51.74 (2.55)	9.49 (0.74)

).

Table 3. Number of deviations for the measured distances; 95% CL = 95% confidence limits.

No of Deviations	0	1	2	3
Number	7/20	9/20	3/20	1/20
Rate	35%	45%	15%	5%
95% CL	[15%–59%]	[23%–68%]	[3%–38%]	[0.1%–25%]

shows the estimated probability of reconstructing a tooth position with various levels of deviation. In 80% of the models, the tooth positions could be reproduced with zero or one parameter deviation (95% confidence limit: 56–94%).

4. Discussion

A fundamental aspect of the Staub™ Cranial system is the reconstruction of the original position of missing teeth in the correct occlusal plane, and the results of this study demonstrated that the Staub method is highly effective in reconstructing the position of missing teeth in an edentulous jaw. A narrow tolerance range allowed 80% of the casts to be reproduced with zero or one parameter deviation from the three that were analyzed. Only 5% of the models were reproduced with deviations in all three measured areas. This confirms Staub’s claim that the original position of individual teeth and the individual occlusal plane can be reconstructed by mathematical calculation. Intermolar and intercanine distances are related to the width of the dental arch and size of the teeth, while incisocervical length (height) of the central incisor, along with inter-canthal distance, dictates the size of the maxillary anterior sextant teeth and, depending on the smile line of the patient, affects the pink and white esthetics [14,15]. Our results confirming the ability of the Staub system to correctly select the size of anterior teeth and subsequently the corresponding posterior teeth in accordance with the jaw anatomy were a positive outcome of this study. In our study, all the casts were reconstructed by a single expert (K.H. Staub), who is the developer of the evaluated system. This ensured the standard and precise application of the system guidelines without any inter-operator variations, yet at the same time imposed a concern regarding the effectiveness of the result when less experience or understanding of the system is present. Although this may be considered a limitation of this study, it shows the potential of the Staub system when a certain level of experience is reached. In a similar study where maxillary and mandibular casts were reconstructed with the Staub system guidelines, a high level of duplication was achieved with the former condition when an experienced laboratory technician performed the set-up of acrylic teeth [16]. The time needed to complete the teeth set-up was not a parameter measured in this study, but no differences should be expected for a trained technician since no extra stages or special equipment are required.

It should be noted that the Staub™ Cranial system does not reconstruct former gaps or individual special conditions of the tooth arch. Instead, the appropriate tooth size is calculated in accordance with the dimensions of the jaw. This selection process is different from the widely used method of facial landmarks that act as references for anterior teeth selection, canine position, and midline. Accordingly, discrepancies may arise between the original condition and the reproduction. The discrepancies observed in the respective pairs of models in the present study were confirmed on the basis of comparison photographs. The Staub™ Cranial system helps identify the guiding landmarks for the customized arrangement of artificial teeth on the edentulous jaw while respecting the basic principles of denture fabrication. Pre-existing individualized differentiations cannot be duplicated without prior references from pictures or casts. However, modifications involving tooth rotation or inclination can be applied in order to achieve a more natural result. Depending on the degree of alveolar bone resorption, anatomy of the edentulous jaw may be modified to a level that Staub system landmarks could be difficult to identify [17]. The Staub system is an additional alternative tool facilitating the spatial orientation of artificial teeth on the edentulous jaw and can be applied in conjunction with any other method depending on the experience and the level of confidence that is needed during the prosthesis fabrication. Contemporary CAD-CAM techniques allowing the digital design and fabrication of the prosthesis are the current trend. Staub system guidelines could be applied in the digital environment by marking the suggested anatomical landmarks on the scanned casts and either initiating the design process or controlling and evaluating the automated software options [18,19]. Differentiations may exist between the maxillary and mandibular edentulous jaw, arising from different patterns of resorption and ease of identifying the guiding landmarks [20]. Maxillary teeth set-up is affected and thus controlled not only by jaw anatomy but also by esthetics, occlusal plane orientation, and speech, allowing a more detailed and defined framework of action [21,22]. For this reason it is suggested to consider the Staub guidelines as the starting point for teeth set-up that should be assessed intraorally before final arrangement and further processing. Lower teeth set-up follows in centric relation and exhibits less freedom in arrangement. This study evaluated the efficacy of the Staub system in the maxillary jaw as a starting point in the rehabilitation of the edentulous mouth, without underestimating either the importance of lower jaw anatomy or the effective application of Staub guidelines. Limited application of the Staub methodology in daily practice is attributed to the fact that it is not widely included in teaching curricula and may initially appear more detailed and thus complicated. Further studies are needed to clinically evaluate its efficiency and possible advantageous performance in real dental prosthesis fabrication and use by patients. The small number of participating subjects with favorable dentitions may have imposed a bias in the research design. A larger sample size and evaluation of both upper and lower arch, regardless of their restorative status, with various patterns of bone resorption, could be the goal of future studies.

The study was evaluated with the stripe projection principle. The collection of determined values in three dimensions allows for the computation of multiple characteristics. Knussmann [23] refers to the principle of electronic digitization as a means of collecting skeletal material. The stripe projection method, also known as fringe projection or structured light projection, is a 3D metrology technique used to capture and measure the shape of an object’s surface and provides a precise means of capturing three-dimensional structures. The precision of the stripe projection method in 3D shape measurement is affected by several factors, including stripe pattern design, image processing techniques, and the characteristics of the measured surface. Highly reflective or low-reflective surfaces can cause issues with stripe detection and measurement. Smooth, featureless surfaces can be challenging for stripe projection, while surfaces with complex textures can help with pattern recognition. In the present study, casts were sprayed with an anti-reflective powder, and the teeth provided definitive morphology for the capturing and measuring process [24,25]. The margin of error is minimal, as the distances between two points on the stripe image are calculated twice behind the decimal point by the computer and the appropriate software program and displayed digitally. It can therefore be hypothesized that such measuring systems may also prove to be of interest in the context of dental questions. The results obtained in the present study were remarkably accurate due to the rigorous evaluation process. It can be reasonably stated that the results would be less explicit if the evaluation had been conducted with the use of conventional means as opposed to the stripe pictures, particularly for the reason that no ruler could read two decimal point values, and the stripe picture method is contact-free. Technological advances and contemporary metrology methods could provide additional measuring options that could be compared in terms of efficiency and precision [26,27].

5. Conclusions/Clinical Relevance

The Staub™ Cranial system uses a series of simple mathematical equations to establish the occlusal plane and the position of the patient’s former teeth.

Future studies would be beneficial to determine whether the Staub method can perform the following:

• Can be used to assess the three-dimensional relationship of the alveolar ridges and, if so, to produce surgical templates for guided implant placement.
• Can be used in the fabrication of obturators/prostheses in patients with partially resected maxillae.
• Can be used as a diagnostic tool for occlusal and functional disorders.
• Is capable of producing a digital set-up that can be used and integrated with CAD software, such as DentalCAD Exocad^® (Darmstadt, Germany).