MIRA

CLE: A CAD/CAM SYSTEM FOR THE MANUFACTURE OF

DENTAL SURGICAL SPLINTS

Valery Naranjo, Roberto Llor

ens, Mariano Alca

niz, Beatriz Rey, Salvador Albalat

∗

Instituto Interuniversitario de Investigaci

on en Bioingenier

ıa y Tecnolog

ıa Orientada al Ser Humano

Universidad Polit

ecnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain

Juan Fayos, I

nigo Morales

Instituto de Biomec

anica de Valencia (IBV), Universidad Polit

ecnica de Valencia

Keywords:

Computer assisted dental surgery, Surgical splints.

Abstract:

Nowadays, design and manufacturing process of dental prostheses is very handmade, time consuming and

has a raised economic cost. Besides that, there is no objective methodology for the fulﬁllment of its func-

tional design speciﬁcations. This paper presents an overview of MIRACLE project whose objective is the

development and validation of an intelligent system for the design, simulation and ﬂexible manufacture of

implant-supported dental prostheses. The developed system in MIRACLE is a CAD/CAM system which al-

lows to test the functional characteristics of dental prostheses considering mandible-maxilla interaction (called

occlusion) using virtual models, contrary to most commercial solutions where this test is performed using ex-

pensive anatomical replicas tested with mechanical articulators and evaluated with patients. Another objective

of MIRACLE is to develop a parametric ﬁnite elements model (FEM) of the whole prosthesis in order to an-

alyze the failure risk of dental implants and prostheses before its surgical implantation enabling a re-design

process. This paper is focused on the CAD/CAM subsystem developed in order to automatize the process of

manufacturing surgical guides using several 3D models of the patient dental anatomy. A summarized version

of the image processing step will be also presented. The CAD/CAM subsystem has been clinically validated

achieving mean errors less than 5 degrees in the placement of the prosthetic crowns.

1 INTRODUCTION

In an implant-supported prosthesis (PDI), the pros-

thesis is attached to an implant placed directly on the

mandibular or maxillary bone of the patient. The pro-

cess of a PDI implantation has been modiﬁed sub-

stantially in last years. Approximately ﬁve years ago

an implantation was made in two phases of the set

prosthesis-implants. In a ﬁrst step, the implant was

placed and , after 3-6 months, when the osseointegra-

tion between implant and bone took place, the dental

prosthesis was placed. Nowadays the implant load

protocols are being modiﬁed in order to give the im-

plant a fundamentally masticatory function at the mo-

ment of their positioning or in the three following

days (”load or immediate function”).

∗

This

work has been supported by the project MIRA-

CLE (DPI2007-66782-C03-01-AR07) of Spanish Ministe-

rio de Educaci

on y Ciencia.

1.1 State of the Art of

Implant-supported Prosthesis

First antecedents of immediate load were given by

Ledermann (Ledermann, 1979). He placed an over-

denture on 4 implants between the dental foram-

inae in the same day of the surgery. Later on,

Schroeder (Schroeder, 1985), histologically demon-

strated an intimate union between bone and implants

following the same methodology that Ledermann.

Schnitman et al. (Schnitman et al., 1990) obtained a

medium and long-term success rate from 88 to 97%

for implants with immediate function placed in ante-

rior mandible. The load or immediate function on im-

plants can offer great advantages to the patients (Nuz-

zolease, ; Uribe et al., 2004) and the osseointegration

of implants can take place just a short time after the

intervention (Fillies et al., 2005).

The advantages of this type of implants as op-

235

Naranjo V., Lloréns R., Alcañiz M., Rey B., Albalat S., Fayos J. and Morales I. (2010).

MIRACLE: A CAD/CAM SYSTEM FOR THE MANUFACTURE OF DENTAL SURGICAL SPLINTS.

In Proceedings of the Third International Conference on Biomedical Electronics and Devices, pages 235-239

DOI: 10.5220/0002766202350239

 SciTePress

Figure 1: Example of dental implant ﬁxing process.

posed to implants without immediate load are reduc-

tion of treatment time after surgery, stabilization of

height of the bone and improvement of patient’s aes-

thetics. Nevertheless, the greater limitations of this

method are the risk of implants losses due to lack of

retention, the technical difﬁculty for the manufacture

of the prosthesis and the mechanical failure (Esposito

et al., 2006) of ﬁxations.

With this new technique, the success of dental

prostheses depends to a great extent on its functional

beneﬁts and interface adjustment between prosthesis

and implant. This fact forces the laboratories to make

exact and much more customized designs for each pa-

tient. Also, what is more important, we cannot make

multiple tests with the patient, as it happened with the

previous technique, so it is due to make a design that

works perfectly. Figure 1 shows the process of an im-

plant placement.

1.2 State of the Art of Dental

CAD/CAM Systems

The ﬁrst use of CAD/CAM systems in dental ﬁeld

was in early 80s. One of the main application lines

was its intraoperative use to dental restoration using

ceramic pre-manufactured monoblocks (Mrmann,

2004). The use of structural material of high strength

such as structures based on aluminium or zirconium,

which can only be prepared in a CAD/CAM system,

has increased the lifetime of the restoration lead-

ing to a market expansion during last years. The

greatest companies of the dental sector have already

incorporated speciﬁc 3D-design software for dental

prostheses which allows to generate virtual models

improving the accuracy and the automated manufac-

ture of the support structures of the dental prostheses.

On these structures the rest of the prosthesis is

made later. Some of these commercial products

are: CEREC 3D (Sirona Dental Systems) (Mrmann,

2004), Everest (http://www.kavo-everest.com)

and Lava (http://cms.3m.com/cms/US/en/2-

21kzikuFW/view.html).

Basically, all these CAD/CAM systems have three

functional components (J.Strub et al., 2006):

• Data capture or scanning, in order to obtain the

buccal data (dental preparation, adjacent teeth and

dental occlusion geometry).

• CAD for a geometric design of the restoration.

These CAD systems have some simple functional-

ities to geometrically modify the restoration to be

designed. In any case, simulation tools for func-

tional analysis are provided.

• CAM to restoration fabrication. CAM systems

use computer-generated information to shape

physical objects, using subtractive methods (part

of the material of an initial block is removed in or-

der to generate the desired shape) or additive ones.

The additive methods are used in rapid prototyp-

ing which are becoming the most used method

in modern CAD/CAM dental systems (Gebhardt,

2000; Noorani, 2006).

Nevertheless, these systems only cover partially

the prothesis design, excluding simulation of func-

tional and biomechanical behavior. Therefore, MIR-

ACLE project will contribute to develop and to put

into dental sector a methodology of ”digital mockup”

or virtual scale model which is being applied suc-

cessfully in other industrial areas. The results of the

project will allow to do a complete assessment of the

ﬁnal treatment without the need of physical prosthe-

ses.

This paper is only focused on the CAD/CAM sub-

system developed in order to automatize the process

of manufacturing surgical guides using several 3D

models of the patient’s dental anatomy. With this

in mind, in section 2, a brief explanation of MIRA-

CLE is presented and data capture (patient’s anatomy

importation), registration of different 3D models and

dental splint design will be studied in depth. In sec-

tion 3 a clinical validation of the process of splint

design and manufacture, without considering biome-

chanical analysis and virtual articulator information,

will be presented and ﬁnally, some conclusions will

be discussed in section 4.

2 METHOD

MIRACLE system is able to obtain a virtual model

of the prosthesis from the 3D model of the crown,

the patient’s anatomical models obtained from the

CT study and the geometric records of the patient’s

functional characteristics. This virtual model allows

to do the functional and biomechanical validation of

prostheses considering their functional beneﬁts based

on their anatomical characteristics. Advanced CAM

techniques are used for the physical manufacture of

prostheses by means of advanced techniques of fast

manufacturing such as HSM (High Speed Milling and

Rapid Tooling). In order to achieve this goal, high ve-

locity and precise milling machines are used, and also

BIODEVICES 2010 - International Conference on Biomedical Electronics and Devices

236

rapid prototyping/manufacturing equipment based on

SLS (Selective laser Sintering and Stereolitography).

2.1 Patient’s Anatomy Model

Importation and Models

Registration

The ﬁrst step is the capture of the data. The system

imports two 3D models of the patient’s maxillofacial

anatomy: the 3D model obtained from CT scan (CT

model) and a high precision 3D model obtained by

laser-scanning a physical plaster model (laser model).

The information obtained with both models are com-

plementary. On one hand, the CT model provides in-

formation from different anatomical structures (corti-

cal bone, trabecular core, mandibular canal) although

it usually presents metallic artifacts (specially near

the teeth surface) due to the CT scanning process. In

this model, the dentist will plan the surgery. On the

other hand, the scanned model only provides precise

information about the surface of the teeth, without the

presence of these artifacts. Besides the data acqui-

sition using a CT scanner, an image processing step

is required in order to obtain a precise model of the

patient’s anatomy.

The aim of the image processing step can be

divided into two different but related main lines.

Computer-aided dental planning systems must pro-

vide all the available information to the den-

tists/surgeons assuring enough accuracy to take de-

cisions with high reliability. Planning systems usu-

ally represent a 3D view of the jaw, allowing the spe-

cialist to plan the position of the implant. However,

for a precise dental implant planning, an exhaustive

segmentation of the jaw tissues is necessary, focus-

ing on the mandibular channel, which holds the den-

tal nerve, because its injury could cause lip numb-

ness. Consequently, on one hand, the project focuses

on the improvement of image quality reducing metal

artifacts to enhance the 3D reconstruction (Naranjo

et al., 2009) and, on the other hand, the aim is to seg-

ment the tissues present in the human jaw to provide

reliable information to dentists or surgeons. Our seg-

mentation method, presented in (Llor

ens et al., 2009),

has achieved good results in terms of detection and

false alarm probability and merit factors of 96.9993

and 99.7696 for cortical bone and inferior alveolar

nerve, respectively.

Once the system has imported the necessary data,

and the surgeon has planned the location of the pros-

thesis in the CT model, the next step is to register the

laser model and the CT model including the implants

planned by the clinic. All this information must be

referred to the same coordinate system in order to de-

sign the surgical splint. Hence the need of the regis-

tration.

The registration process consists of two steps:

1. A pre-registration stage where the specialist se-

lects manually a set of points in one of the mod-

els and its correspondences in the other. After

that, the models are coarsely registered using the

method proposed by Arun (K.Arun et al., 1987),

which uses the Singular Value Decomposition to

obtain the registration matrix. Figure 2-a shows

the result of this step. On the left, the ﬁgure shows

the CT model, the locations of the planned im-

plants marked with numbers, and the points se-

lected by the user for the pre-registration.

2. Registration reﬁnement. To improve the preci-

sion of the registration the Iterative Closest Point

(ICP) algorithm (P.Besl and Mckay, 1992) is used.

This algorithm tries to minimize the difference be-

tween two clouds of points. In our case, only

those areas selected by the specialist, which are

present in both models will be taken into account

in the ICP algorithm. Figure 2-b shows the ﬁnal

result of the registration process. On the left, the

area selected by the user in order to be taken into

account in the ICP algorithm is highlighted in red.

On the right, the superimposition of both models

is shown.

2.2 Surgical Splint Design and

Manufacture

The last step in the process of design using the

CAD/CAM system will be the design of the surgi-

cal splint. The splint is designed using the result of

the registration stage and considering the information

provided by the laser model (surface of the teeth) and

the implant locations, necessary to determine where

the holes in the guide will be needed. Figure 3 shows

different views of the virtual designed splint.

The system performed the simulation of the pros-

thetic abutments, crowns and suprastructures, and the

relationships with the antagonist arch before surgery.

The planning provided information to make surgi-

cal splints by means of stereolitographic techniques.

Stereolithography is a new technology able to provide

physical models solidifying selectively an ultraviolet-

sensitive liquid resin, by means of a laser beam, repro-

ducing the true maxillary and mandibular anatomic

dimensions. With these models, it is possible to make

surgical guides that can place the implants in vivo in

the same places and same directions as those in the

planned computer simulation.

MIRACLE: A CAD/CAM SYSTEM FOR THE MANUFACTURE OF DENTAL SURGICAL SPLINTS

237

Figure 2: Registration results. a)Pre-registration result.

b)ICP algorithm result.

3 VALIDATION AND RESULTS

In this section the validation of the process of splint

design and manufacture, without biomechanics anal-

ysis and articulation data, is presented.

A test set of 23 patients, with mean age of 35

years, has been considered for this study. All the pa-

tients needed rehabilitation treatments from a single

dental piece up to the whole jaw (edentulous patients)

and all they presented common clinical and psycho-

logical parameters. No signiﬁcant diseases were de-

tected. Particularly, the test set consists of 18 partially

edentulous patients and 5 edentulous ones. The pa-

tient data required for this study consists of medical

history, cast of lower and upper jaw, study of bite reg-

istration in an adjustable articulator and radiographic

diagnosis CT-scan study with Cone Beam technology.

CT data is obtained by means of GE MEDICAL SYS-

TEMS HiSpeed QXi and Philips Medical Systems -

Philips CT Aura.

In order to validate the results obtained by the

planning system CT data was processed and the

placement of the implants was estimated according

some criteria. On one hand, according to anatomi-

Figure 3: Virtual model of the designed splint.

cal criterion, the placement was inferred depending

on the osseous suitability. The implant must be sur-

rounded with the largest available bone extension,

looking for the largest osseointegration surface. On

the other hand, according to prosthetic criterion, start-

ing from the estimated placement as explained above,

the placement was adapted to the antagonist teeth. Di-

ameter and length of the implant were reﬁned.

The implant surgery was done using a standard

protocol. The patient was anesthetized with lido-

caine 2% with 1:100 000 epinephrine. The osteotomy

and subsequent implant-drilling procedures were per-

formed using the personalized surgical-guidance tem-

plate which ﬁtted snugly onto the patient’s teeth dur-

ing the implant procedure. The surgical-guidance

template had 2.2-, 2.8-, and 3.5-sleeve apertures, cor-

responding to each successive drill. Once the ﬁnal

drill was used, standard implant was placed. Forty

implants were evaluated (in 23 patients). The mean

estimated error was 5.0 degrees. 23 implants (57.5%)

were estimated with errors under 5 degrees. Figure 4

shows the results of the different process steps for a

BIODEVICES 2010 - International Conference on Biomedical Electronics and Devices

238

patient: surgical planning, splint design, splint manu-

facture and clinical surgery.

Figure 4: Shaping of splints by means of stereolitogra-

phy. Planning view, virtual surgical splint and real surgical

guide.

4 DISCUSSION

This paper presents MIRACLE project, whose objec-

tive is the development and validation of an intelligent

system for the design, simulation and ﬂexible manu-

facture of implant-supported dental prostheses. The

system, which is still being developed, is described

in this paper. Its efforts are focused on data captur-

ing, surgical planning and surgical guide design and

fabrication.

In order to validate the modules of data capturing,

image processing, planning system and surgical guide

design, an experimental study has been done. Forty

implants were evaluated in 23 patients with mean age

of 35 years. All implants were placed by two step

surgery in the mandible. A surgical template based

on the CT images and on the abutment replica of

the working models was used for the evaluation of

the accuracy of implant placements. The difference

between the proposed and real directions was mea-

sured by the clinical protocol. After surgery the sur-

geons tried to ﬁx the prosthetics crowns designed be-

fore surgery. Errors under 5 degrees were taken as

valid in terms of accuracy. The mean estimated error

was 5.0 degrees. 23 implants (57.5%) were estimated

with errors under 5 degrees. Consequently, this study

proves the accuracy achieved by the system developed

in MIRACLE project.

REFERENCES

Esposito, M., Koukoulopoulou, A., Coulthard, P., and Wor-

thington, H. (2006). Interventions for replacing miss-

ing teeth: dental implants in fresh extraction sock-

ets (immediate, immediate-delayed and delayed im-

plants). Cochrane Database System Review, 4.

Fillies, T., Wiesmann, P., Sommer, D., Joos, U., and

Meyer, U. (2005). Osteoblast reaction on sla and

microgrooved implant surfaces. Mund Kiefer und

Gesichtschirurgie, 9(1):24–28.

Gebhardt, A. (2000). Rapid prototyping. Munich: Hauser.

J.Strub, E.Rekow, and S.Witokowski (2006). Computer-

aided design and fabrication of dental restorations.

JADA, 137(9):1289–1296.

K.Arun, T.Huang, and S.Blostein (1987). Least square ﬁt-

ting of two 3-d point sets. IEEE Transactions on

Pattern Analysis and Machine Intelligence, 9(5):698–

700.

Ledermann, P. (1979). Stegprothetische versorgung

des zahnlosen unterkiefers mit hilfe von plas-

mabeschichteten titan-schaubenimplantaten. Dtsch

Zahnarztl Z, 34:907–911.

Llor

ens, R., Naranjo, V., Clemente, M., niz, M. A., and Al-

balat, S. (2009). Validation of fuzzy connectedness

segmentation for jaw tissues. In Bioinspired Appli-

cations in Artiﬁcial and Natural Computation, pages

41–47. Springer Berlin / Heidelberg.

Mrmann, W. (2004). The origin of the cerec method: a per-

sonal review of the ﬁrst 5 years. Int. Journal Comput

Dent, 7(1):11–24.

Naranjo, V., Llor

ens, R., Paniagua, P., niz, M. A., and Al-

balat, S. (2009). A new approach in metal artifact re-

duction for ct 3d reconstruction. In Bioinspired Appli-

cations in Artiﬁcial and Natural Computation, pages

11–19. Springer Berlin / Heidelberg.

Noorani, R. (2006). Rapid prototyping: Principles and ap-

plications. Hoboken, N.J.: Wiley.

Nuzzolease, E. Immediate loading of two single tooth im-

plants in the maxilla: Preliminary results after one

year. Journal of Contemporary Dental Practice, 6.

P.Besl and Mckay, H. (1992). A method for registration of

3-d shapes. IEEE Transactions on Pattern Analysis

and Machine Intelligence, 14(2).

Schnitman, P., Wohrle, P., and Rubenstein, J. (1990). In-

mediate ﬁxed interim prostheses supported by two-

stage threaded implants: methodology and results.

Journal of Oral Implantology, 19:96–105.

Schroeder, A. (1985). The iti hollow-cylinder implant. in-

ternationales team fur orale implantologie. Schweiz

Monatsschr Zahnmed, 85:876–878.

Uribe, R., Pearrocha, M., and Sanchis, J. (2004). Marginal

peri-implantitis due to occlusal overload: A case re-

port. Medicina Oral, Patologa Oral y Ciruga Bucal,

MIRACLE: A CAD/CAM SYSTEM FOR THE MANUFACTURE OF DENTAL SURGICAL SPLINTS

239