Ueda et al.

Asian Pac J Dent 2014; 14: 35-40

Evaluation of occlusal relationship reproducibility withCAD/CAM techniques
Yoji Ueda, DDS,a Daizo Okada, DDS, PhD,a Reiko Ogura, DDS, PhD,a Wataru Komada,DDS, PhD,a Shiho Otake, DDS, PhD,a Masaomi Ikeda, RDT, BSc, PhD,b and Hiroyuki
Miura, DDS, PhDa
aFixed Prosthodontics, Department of Restorative Sciences, Graduate School, Tokyo Medical andbDental University, and Clinical Oral Science, Department of Oral Health Care Sciences, Faculty ofDentistry, Tokyo Medical and Dental University, Tokyo, Japan
Purpose: The objective of this study was to evaluate the reproducibility of determining the area of the occlusal
contact regions by CAD software.
Materials and Methods: Nine subjects were recruited. The maxillary right first molars were the subject teeth.
Optical impressions were taken six times. An optical impression of each antagonist was taken once. For
optical bite registration, optical impressions from the buccal side during clenching were taken six times. The
occlusal contact regions obtained by optical impressions and optical bite registration were represented using
CAD software. The variabilities derived from changes in optical impressions were compared with thosederived from changes in optical bite registration.
Results: The variability of the area of the clearance region depending on changes in optical bite registration wassignificantly higher than that depending on changes in optical impressions.
Conclusion: It was demonstrated that changes in optical bite registration affected the reproducibility of the areaof the clearance region.
(Asian Pac J Dent 2014; 14: 35-40.)
Key Words: CAD/CAM, occlusal contact, optical impression, reproducibilityIntroduction
The technique of computer-aided design/computer-aided manufacturing (CAD/CAM) has evolved by wayof improvements in the measuring system, processing technique, and software.

Long-term prospective studies

of CAD/CAM ceramic restorations have reported survival rates of over 85% after 10 years.1,2More recently,

CAD/CAM systems have been introduced that incorporate a new optical bite registration method to determine
the occlusal relationship between the abutment tooth and its antagonist using CAD software.

With thesesystems, an intraoral camera can be utilized for optical bite registration as well as optical impressions of thedentition.

Optical bite registration is based on optical impressions of the buccal surface of the dentition fromthe buccal side during clenching at the intercuspal position, without any bite registration materials.3,4

These

optical impression data are used to fabricate restorations at the chair-side, and it is possible to replace therestorations on the same day.5
In prosthodontic treatment, the shape and function of the prosthesis must be harmonized with thestomatognathic system to maintain good functional condition for a long time after the treatment.6Many studies

have reported that teeth were moved in function, that is, the amount and direction of tooth displacement and theocclusal relationship between the maxillary and mandibular dentition were changed, depending on the biting
force.6-11

The occlusal relationship between the abutment tooth and its antagonist during clenching at theintercuspal position in vivo differed from the occlusal relationship calculated by CAD software.

Moreover,optical powder must be applied to the occlusal surfaces to make the dentition visible to the intraoral camera.12
Therefore, data from optical impressions cannot duplicate the actual dentition precisely, because of the thicknessof the optical powder covering the occlusal surfaces.

Although previous studies13 have evaluated the accuracyof optical bite registration in the context of resin models, few have evaluated it in the context of actual dentition35

Ueda et al.

in vivo.

Asian Pac J Dent 2014; 14: 35-40

Additionally, it has been reported that the occlusal surface is closely related to masticatory efficiency,

the main occluding area, and tooth displacement in function.7,14-18

Therefore, to fabricate prostheses withfunctional occlusal surfaces using CAD/CAM systems, it is important that CAD software duplicate the occlusal
relationship between the maxillary and mandibular dentition in vivo with high precision.
The objective of this study was to evaluate the reproducibility of determining the area of the occlusal
contact regions of the maxillary and mandibular dentition by CAD software.

Materials and Methods
The surfaces of the subject tooth and adjacent teeth were air-dried, then sprayed with titanium oxide powder(Cerec Optispray, Sirona, Bensheim, Germany) uniformly.

Optical impressions were taken using an intraoral

camera (Cerec Blue-CAM, Sirona) and recorded via CAD software (Cerec AC, Sirona).
were performed six times (P1-P6).
(Q).

These procedures

An optical impression of each antagonist was taken and recorded only once

For optical bite registration, optical impressions from the buccal side during clenching with moderate

biting force at the intercuspal position were taken using the intraoral camera and recorded via CAD software.
These procedures were performed six times (BS1-BS6).

The occlusal contact regions obtained by opticalimpressions and optical bite registration were represented using CAD software.

The occlusal contact regions

were divided into several groups based on the distance between the maxillary and mandibular occlusal surface;specifically, light-blue-colored regions (within 100 µm of the close contact, A), green-colored regions (0-50 µmof the penetrated contact, B), yellow-colored regions (50-100 µm of the penetrated contact, C), and red-coloredregions (over 100 µm of the penetrated contact, D) (Fig. 1).

Fig. 1The occlusal contact regions were divided into several groups based on
the distance between the maxillary and mandibular occlusal surfaces.
dark-blue-colored regions(100-1000 µm of the close contact)
not evaluated in this study
light-blue-colored regions(within 100 µm of the close contact, A)
green-colored regions(0-50 µm of the penetrated contact, B)
yellow-colored regions(50-100 µm of the penetrated contact, C)
red-colored regions(over 100 µm of the penetrated contact, D).

Results
The results derived from each subject are shown (Table 1).

The variability of the area of the clearance

region depending on changes in optical bite registration was significantly higher than that depending on changes
in the optical impressions (p<0.05) (Fig. 2).

Conversely, the variability of the area of the penetration region

depending on changes in optical bite registration did not differ significantly from the variability of the area of thepenetration region depending on changes in the optical impressions.
As shown in a representative example of the results, the location of the occlusal contact regions among thesequence of the results in the same subjects was almost the same, when optical impressions or optical bite
registration were changed (Fig. 3).

However, there were some differences in the areas of each occlusal contact

region.

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Ueda et al.

Asian Pac J Dent 2014; 14: 35-40

Table 1. The variability of the area of the clearance and penetration regions depending on changes in opticalimpression and optical bite registration (mm²)
SubjectA
BC
DEF
GH
I
Mean
Clearance
Penetration

SD

Optical impression

1.17

0.37

0.79

0.46

0.38

1.4

0.04

0.33

0.81

0.64

0.44

Optical bite registration

2.18

0.27

0.39

0.74

0.35

2.88

0.05

0.17

1.77

0.98

1.03

Optical impression

1.01

0.56

0.32

1.43

0.65

0.36

0.99

0.06

0.28

0.63

0.44

Optical bite registration

1.1

1.32

0.27

1.6

0.49

0.58

1.51

0.13

0.49

0.83

0.56

Fig. 2The variability of the area of the clearance (a) and penetration (b) regions depending on changes in optical impression
and optical bite registration

Fig. 3

A representative example of the results in the same subject
P1, Q with BS1 (a), P1, Q with BS2 (b), P1, Q with BS3 (c), P1, Q with BS4 (d), P1, Q with BS5 (e), P1, Q with BS6 (f),P2, Q with BS1 (g), P3, Q with BS1 (h), P4, Q with BS1 (i), P5, Q with BS1 (j), P6, Q with BS1 (k)Discussion
The variability of the area of the clearance region depending on changes in optical bite registration wassignificantly higher than that depending on changes in the optical impressions.
variability was the non-uniform thickness of the optical powder.

37

One of the reasons for thisThe scanning area for the optical impressions

Ueda et al.

Asian Pac J Dent 2014; 14: 35-40

was larger than that for optical bite registration.

In other words, the optical impressions required a larger

powdered area than was required for optical bite registration.

It has previously been reported19 that theprecision of the intraoral camera of this system was only 19 µm in the context of a stone cast, therefore, theprecision of the intraoral camera and the thickness of the optical powder had an insignificant effect on theprecision of this system considering the values of the clearance and penetration regions.

Moreover, given theacceptable range of the occlusal height of crown restorations, threshold level of the periodontal ligament,20 andthe accuracy of crown restorations fabricated with indirect methods, the precision value of 19 µm wasconsidered acceptable.
Based on an in vitro study, Iwaki et al.13 reported that with CAD/CAM systems, the optical bite registration
method provided better dimensional accuracy in the interarch relationship in comparison with the conventional
physical registration.

However, in the context of actual dentition the precision of the optical impressions isaffected by numerous factors including a lack of space for inserting an intraoral camera, movement of patientsduring taking the optical impressions, saliva, and humidity.21

Therefore, it is important to evaluate theprecision of optical bite registration in vivo.
In this study, the variability of the area of the clearance region depending on changes in optical bite
registration was significantly higher than that depending on changes in the optical impressions.

These results

may have been caused by the difference in the occlusal relationship between the maxillary and mandibularmolars during clenching at the intercuspal position.

The difference was caused by a difference in the directionof tooth displacement, rather than the amount of tooth displacement.

The stress-strain curve (SSC) represented

the relationship between the amount of tooth displacement and the biting force11.

The SSC of the maxillary

molar showed two-phase, with the first phase mainly caused by distortion of the periodontal ligament and thesecond phase representing distortion of the alveolar bone in addition to the periodontal ligament.

In the firstphase, the maxillary molar was substantially displaced in the apical direction with a slight biting force,
approximately 5 N.

Conversely, in the second phase, the molar was displaced only slightly, regardless of theincrease in the biting force.

In this study, optical bite registration was taken during clenching with moderate

biting force at the intercuspal position.

Therefore, in the case of each optical bite registration, the differences in

the amount of tooth displacement of the molars may have been slight.

However, even with moderate biting

force, the tooth was not only translated but also rotated in function, and the occlusal relationship between themaxillary and mandibular molars was easily changed because these molars were moved in the lingual direction
with rotation.

In function, the maxillary first molar is displaced approximately 100 to 150 µm in the palatal

apical direction with rotation, while the mandibular first molar is displaced approximately 50 to 100 µm in thelingual direction with rotation.6-11

Thus, the occlusal relationship between the maxillary and mandibulardentition is easy to change, and in the context of CAD software, the occlusal contact regions were also easy tochange depending on slight differences in the biting force.

Moreover, the buccal side optical bite registration

data were less informative than optical impression data of the occlusal surface because the buccal surface wassmoother than the occlusal surface,22 and so the variability of the area of the clearance region depending onchanges in optical bite registration was higher than that depending on changes in the optical impressions.
Given high variability, it may be difficult to duplicate the occlusal surface of the dentition and the occlusal
relationship between the maxillary and mandibular dentition with high precision using CAD software.
Therefore, it may not be possible to fabricate prostheses with adequate occlusal contact, and there is a possibility

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Asian Pac J Dent 2014; 14: 35-40

that prostheses with excessive high occlusal contact or inadequate occlusal contact may be fabricated.

In thecase of excessive high occlusal contact of prostheses, occlusal trauma or changes in the sensation threshold of
the dental pulp may occur.20,23-26

In the case of inadequate occlusal contact, disuse atrophy of the periodontal

ligament and extrusion of the tooth may occur.
It is very important to fabricate prostheses with adequate close contact (the clearance region defined in thisstudy), as well as adequate actual occlusal contacts on the occlusal surface, to maintain good functional
condition for a long time.

Recently, it was reported7,14-18,27,28 that close occlusal contacts had a strong influenceon masticatory efficiency, the stability of the main occluding area, and the formation of Squeezing Room at thelatest stage of mastication.
It was demonstrated that changes in optical bite registration affected the reproducibility of the area of theclearance region in this study.

To fabricate prostheses with functional occlusal surfaces using CAD/CAM

systems, it is important that optical bite registration is performed with high precision.

Further development ofCAD/CAM systems is expected.
The variability depending on changes in optical bite registration was significantly higher than that
depending on changes in the optical impressions in the clearance region that was closely related to fabricationsof prostheses with functional occlusal surfaces even though there was no significant difference in the penetration
region.
Acknowledgment
This study was partly supported by Grant-in-Aid for Scientific Research from the Japanese Society for the Promotion ofScience (No. 24792061).

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Correspondence to:
Dr. Daizo Okada
Fixed Prosthodontics, Department of Restorative Sciences, Graduate School,
Tokyo Medical and Dental University
1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
Fax: +81-3-5803-0201 E-mail: d.okada.fpro@tmd.ac.jp
Copyright ©2014 by the Asian Pacific Journal of Dentistry.

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Accepted November 18, 2014.
Online ISSN 2185-3487, Print ISSN 2185-3479