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Fit of implant frameworks: an in vitro comparison between two fabricationtechniques

Toshiyuki Takahashi, DDS, PhD,a and Johan Gunne, DDS, PhDb

Tokyo Dental College, Chiba, Japan; Faculty of Medicine and Odontology, Ume University,

Ume, Sweden.Statement of problem. It has been suggested that a precise fit between the implant and the frameworkcylinder is necessary to ensure a satisfactory long-term clinical outcome.

Purpose. The purpose of this study was to compare the precision of fit between implant abutments andframework cylinders in frameworks fabricated by the Procera system and those fabricated from cast gold-alloy.

Material and methods. A total of 19 frameworks, 14 made with the Procera system (type 1) and 5 made ofa cast gold-alloy (type 2), were fabricated. A total of 95 implants, 70 type 1 and 25 type 2 frameworks, were

evaluated. Three replicas of the space between the implant abutments and the framework cylinders of the master

cast were made for each test specimen. The replicas were cut with a scalpel in 2 axial directions: buccal-lingual andright-left. For the purpose of measurement, a microscope with a precision of 0.5 m was used at original

magnification30. The Student ttest was used to determine whether there were significant differences between

the framework designs.

Results. The buccal-lingual measurements for the type 1 and type 2 frameworks showed mean values of 28.1m (SD 9.8) and 42.0 m (SD 1.8) on the buccal side, respectively, and 25.6 m (SD 11.2) and 51.6 m (SD

10.9) on the lingual side, respectively. For the right-left view, the mean measurements were 26.6 m (SD 8.4)

and 49.2 m (SD 11.4) on the right side, respectively, and 27.4 m (SD 8.5) and 44.4 m (SD 6.5) on the left

side, respectively. The total mean value for type 1 frameworks was 26.9 m (SD 9.3); that for type 2 frameworks

was 46.8 m (SD 8.8).

Conclusion. Within the limitations of this experiment, it was demonstrated that the fit of frameworks madewith the Procera system was significantly better than that of the frameworks made with cast gold-alloy (P.01).

(J Prosthet Dent 2003;89:256-60.)

CLINICAL IMPLICATIONS

This study suggests that the fit of implant frameworks fabricated by the Procera system weresignificantly better than that of frameworks made with cast gold-alloy.

It has been suggested that a precise fit between theimplant and the framework cylinder is necessary to en-

sure a satisfactory long-term clinical outcome. Poor fit of

frameworks connected to implants has been shown to

cause a deformation of the surrounding bone1 and an

increase in technical problems.2

Fit of implant-supported prostheses, correlation to

distortion of the surrounding bone, change of marginalbone level around the implants, and technical problems

have recently been addressed in several reports.1-12

However, in most of the reports that deal with the pre-

cise fit, the framework was fabricated from cast gold-alloy. Implant prosthesis frameworks in cast materials,such as gold-alloy, involve a certain risk for built-in ten-sion and stress caused by the wax-up and casting proce-dures.

Recently, frameworks have been milled from puretitanium and, according to the manufacturer, have been

considered to have a high degree of fit. It has beenreported that Procera machined framework (All-in-One) fits better to the implant abutment than the gold-alloy casting framework.11

The purpose of this study was to compare the preci-sion of fit between implant abutments and frameworkcylinders in frameworks fabricated by the Procera systemand those fabricated from cast gold-alloy.

MATERIAL AND METHODS

All superstructures were fabricated in the same labo-ratory but were not fabricated by the same technician.The 19 frameworks had 2 different shapes. Seventeen

Supported by the Department of Odontology/Faculty of Medicineand Odontology, Ume University and Ume Dental Laboratory,Ume, Sweden.

aAssistant Professor, Department of Crown and Bridge Prosthodon-tics, Tokyo Dental College. Guest researcher, Department ofOdontology/Prosthetic Dentistry, Faculty of Medicine and Odon-tology, Ume University.

bProfessor, Department of Odontology/Prosthetic Dentistry, Facultyof Medicine and Odontology, Ume University.

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were completely edentulous (cross arch fixed dentures),and 2 were partially edentulous.

A total of 19 frameworks, 14 made with the Procerasystem (Nobel Biocare, Gothenburg, Sweden) (type 1)and 5 made of a cast gold-alloy (Type 2) were fabricated.A total of 95 implants, 70 type 1 and 25 type 2 frame-

works, were evaluated (Table I). The Procera system is anew CAD-CAM technology developed to fabricate theframework for implant-supported prostheses that origi-nates from a technique to make titanium crowns.13-17

After the fabrication of the frameworks at the labora-tory, 3 replicas of the space between the implant abut-ments and the framework cylinders of the master castwere made for each test specimen. A light-body A-sili-con impression material (Provil Novo green; HeraeusKulzer, Hanau, Germany) was applied, with the help ofa syringe, on and around the implant abutment of themaster cast. The framework was then placed onto theimplant abutments of the master cast and maximal 4-fin-ger pressure (about 8 to 10 kg18) was applied on the

occlusal surfaces of the framework. After the setting ofthe impression material, the framework and the impres-sion material were removed from the master cast, result-

ing in a thin film of light-body material representing thediscrepancy between the framework cylinder and theimplant abutment.

In most situations, a thin film of impression materialresulted on the inside of the cylinder and the part of thecylinder opposing the abutment. For purposes of stabi-lization a medium-body material (Provil Novo yellow;Heraeus Kulzer) was injected into the cylinder andaround the impression material surface, jointing withthe light-bodyfilm to form one piece (Fig. 1). With thisprocedure it was possible to remove and handle the in-termediate replica of light-body material. The replica

adhering to the medium-body material was cut with ascalpel in 2 axial directions, buccal-lingual side andright-left side (Fig. 2). In this manner the replica wasdivided into 4 pieces.

For purpose of measurement, a microscope (WildLeitz Co, Wetzlar, Germany) with a precision of0.5 m was used at original magnification30. Mea-surements of the thickness of the film were performed at4 points between the abutment and the cylinder, total-ing 4 measurements for each implant abutment. Thethickness of the film was recorded as the shortest dis-tance from the cylinder to the abutment at the fourpoints (Fig. 1). Ninety-five implants, 3 replicas of each

Table I. Number of frameworks and implants (withinparentheses) in type 1 and type 2

Type Maxilla Mandible Total

1 6 (29) 8 (41) 14 (70)

2 3 (13) 2 (12) 5 (25)

Total 9 (42) 10 (53) 19 (95)

Fig. 1. Film thickness was recorded as distance between edge of abutment and edge of cylinder.

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DISCUSSION

The Procera system (CAD-CAM technology), whichoriginated from Andersson,13 was developed14-17 andmodified for fabrication of frameworks for implant-sup-

ported restorations. The All-in-One is a frameworkmilled from a pure titanium block. The reason for thedevelopment of the All-in-One was to create a frame-work with high biocompatibility, low cost, and a fit pre-cision to the abutment through industrial productionwith the latest CAD-CAM technology.

In the clinic, the dentist follows the same routineprocedures as for the fabrication of other types of frame-works. After the final check of design and tooth arrange-ment, the dental technician fabricates a resin pattern ofthe desired framework. The pattern is scanned for com-puterized handling of the implant positions, abutment

replicas, and framework design. The framework is milledfrom the computer data. The accurate position of theimplants and the relation to each other is possible with-out use of welded joints. After the framework has beenmilled, it is carefully measured in a stereomicroscope tocheck the fit against the cast. It has been reported thatthe gap distance between the gold-alloy casting frame-work and the implant abutment was 42 to 74 m,5 andfor Procera-machined and laser-welded frameworks itwas less than 25 m.11

Osseointegrated implants present a significantly dif-ferent mobility compared with the natural teeth sup-

ported with periodontal ligaments.

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Therefore minordistortion of frameworks could invoke a risk of inducingstress from frameworks connected to osseointegratedimplants. Natural teeth have the ability to adjust to themisfit because of the mobility of the periodontal liga-ment. The difference in mobility between implants andnatural teeth means that the precision offit of the frame-work is more important when fixed prostheses are con-nected to implants than to natural teeth.

Several methods for evaluating the implant frame-workfit have been recommended, such as alternate fin-ger pressure, direct vision and tactile sensation, radio-graphs, one-screw test, screw resistance test (half a turn),and disclosing media.12 To quantify the misfit, a com-

puterized coordinate measuring machine,3 a 3-dimen-sional photogrammetric technique,4,5 and laser videog-raphy11 were described. However, most of thesemethods need expensive equipment and an advancedtechnique. In this experiment, a disclosing medium wasused to measure the gap distance between the implantabutments and the framework cylinders (All-in-One andgold-alloy casting) of the master cast. The method ischaracterized by simplicity and low cost.

For all specimens, the type 1 framework differed fromthe type 2 framework (Table I). Because most of theframeworks were fabricated with the Procera system, atthe time of this study it was not possible to find morethan 5 treatments with the type 2 framework. However,the standard deviations were very low for both groups,and data analysis found both a clinically and a statisticallysignificant difference between the 2 groups.

As a result, the total means were 26.9 m (SD 9.3)for type 1 frameworks and 46.8 m (SD 8.8) for type 2frameworks. For type 1 frameworks, this is in agreementwith the data of Riedy et al.11 The mean value of type 2frameworks was lower than reported by Jemt and Lie.5

This increase of the precision offit could be explained byan improved technique at the dental laboratory derivedfrom a long experience with the casting method. It issuggested that the framework with a good precision offit will decrease the stress to the implant componentsand the surrounding bone, thus avoiding deformationof the bone and an increase in technical problems.

CONCLUSION

Within the limitations of this study, it was demon-strated that the fit of implant frameworks fabricated bythe Procera system (All-in-One) were significantly bet-ter than that of frameworks made with cast gold-alloy.For any measurement points (buccal, lingual, right, andleft), the fit of the All-in-One frameworks was statisti-cally better than the framework made with cast gold-alloy. For the All-in-One frameworks, all mean values ofthe thickness of the film at the 4 measurements points(buccal, lingual, right, and left) were less than 30 m.Students unpaired ttest showed a significant difference

Table III. Precision of fit (mean and standard deviation [SD] in micrometers) between implant abutment and cylinder ofsuperstructure for gold-alloy casting frameworks (type 2)

Framework Buccal Lingual Right Left Mean SD No. of implant

1 42.4 42.0 45.4 45.4 43.8 1.9 5

2* 44.2 39.1 40.8 40.6 41.2 2.2 5

3 42.4 64.6 68.9 55.0 57.7 11.8 74* 39.3 53.0 48.3 42.8 45.9 6.0 3

5* 41.6 59.3 42.6 38.1 45.4 9.5 5

Mean 42.0 51.6 49.2 44.4 All-Mean 46.8 Total 25

SD 1.8 10.9 11.4 6.5 All-SD 8.8

*Upper jaw case

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