Evaluacion Acuciosidad de Impresion

8/12/2019 Evaluacion Acuciosidad de Impresion

1/838 Volume 25, Number 1, 2010

The accuracy of an impression remains a criticalfactor in achieving passive fit of an implant frame-work.13 Although the implant and bone can usually

tolerate a degree of misfit without adverse biome-

chanical problems,4,5 it is appropriate to ensure accu-

rate reproduction of the interimplant relationship in

the working cast for the fabrication of a passively fit-

ting framework. The accuracy of the master cast is

dependent on the type of impression material, the

implant impression technique, and accuracy of the

die material.1 Most research indicates that the indi-

rect impression technique produces greater mean

distortion than direct techniques.610

Among the direct techniques, both splinting and

nonsplinting have been advocated717 for accurate

impressions. Although splinting with resin or impres-

sion plaster has been recommended for maintaining

a more accurate interimplant relationship, the effi-

cacy of these techniques in yielding accurate casts is

controversial.717The use of bite registration addition

silicone during impression making to hold the

impression copings together rigidly has been

reported in the literature.18The rigidity and dimen-

sional stability of such interocclusal recording materi-

als1924 might make them a good choice for splinting

the impression copings.

Evaluation of Accuracy of Multiple Dental Implant

Impressions Using Various Splinting MaterialsRamasubramanian Hariharan, MDS1/Chitra Shankar, MDS2/Manoj Rajan, MDS, DNB3/

Mirza Rustum Baig, MDS, MRD Pros RCS4/N. S. Azhagarasan, MDS5

Purpose: The aim of the present study was to compare the accuracy of casts obtained from non-

splinted and splinted direct impression techniques employing various splinting materials for multiple

dental implants. Materials and Methods: A reference model with four Nobel Replace Select implant

replicas in the anterior mandible was fabricated with denture base heat-curing acrylic resin. Impres-

sions of the reference model were made using polyether impression material by direct nonsplinted and

splinted techniques. Impressions were divided into four groups: group A: nonsplinted technique; group

B: acrylic resinsplinted technique; group C: bite registration addition siliconesplinted technique; and

group D: bite registration polyethersplinted technique. Four impressions were made for each group

and casts were poured in type IV dental stone. Linear differences in interimplant distances in the x-, y-,

and z-axes and differences in interimplant angulations in the z-axis were measured on the casts using a

coordinate measuring machine. Results: The interimplant distance D1y showed significant variations in

all four test groups (P = .043), while D3x values varied significantly between the acrylic resinsplinted

and silicone-splinted groups. Casts obtained from the polyether-splinted group were the closest to the

reference model in the x- and y-axes. In the z-axis, D2z values varied significantly among the three test

groups (P = .009). Casts from the acrylic resinsplinted group were the closest to the reference model

in the z-axis. Also, one of the three angles measured (angle 2) showed significant differences within

three test groups (P = .009). Casts from the nonsplinted group exhibited the smallest angular differ-

ences. Conclusion: Casts obtained from all four impression techniques exhibited differences from the

reference model. Casts obtained using the bite registration polyethersplinted technique were the most

accurate versus the reference model, followed by those obtained via the acrylic resinsplinted, non-

splinted, and bite registration addition siliconesplinted techniques. INT J ORAL MAXILLOFAC IMPLANTS

2010;25:3844

Key words: accuracy, dental implants, impressions, splinting materials

1Senior Lecturer, Department of Prosthodontics, Ragas Dental

College and Hospital, Chennai, Tamil Nadu, India.2Professor, Department of Prosthodontics, Ragas Dental College

and Hospital, Chennai, Tamil Nadu, India.3Associate Professor, Department of Prosthodontics, Ragas

Dental College and Hospital, Chennai, Tamil Nadu, India.4Assistant Professor, Department of Prosthodontics, Ragas

Dental College and Hospital, Chennai, Tamil Nadu, India.5Professor and Head, Department of Prosthodontics, Ragas

Dental College and Hospital, Chennai, Tamil Nadu, India.

Correspondence to: Dr Ramasubramanian Hariharan, No. 2A,

Sai Ayush Rameshaa, Lakshmi Appadurai Street, Somu Nagar,

Medavakkam, Chennai 600100, Tamilnadu, India.

Fax: +044-24530009. Email: [email protected]


2/8

Rotation of impression copings in the impression

during fastening of the implant analog is one of the

drawbacks of the direct impression technique. There

is a need for research on the amount of rotational dis-

tortion of impression copings in the z-axis, which can

occur when multiple implant impressions are made

with polyether.The reliability of the measuring system is also vital

to evaluate the accuracy of the impression. Because

distortion of an impression can occur in the x-, y-,

and-z axes, it is of paramount importance to analyze

the distortion in three dimensions. The purpose of

this study was to compare the three-dimensional

accuracy of casts obtained using a nonsplinted

impression technique with those created using a

splinted technique and to evaluate the efficacy of

bite registration addition silicone and bite registra-

tion polyether as splinting materials.

MATERIALS AND METHODS

A reference model with four implant analogs (Nobel

Replace Regular Platform, REF 29500, Nobel Biocare)

in the mandibular symphyseal region was fabricated

in a denture base of heat-curing acrylic resin (DPI

Heat Cure). The reference model resembled a

mandibular implant-supported overdenture situa-

tion. Three stops, one in the anterior and two in the

posterior, were made in the land area of the model for

accurate positioning of custom impression trays. An

indirect impression was made to allow fabrication of

a primary cast. An even spacer of 3 mm was adapted

onto the primary cast and another impression was

made to obtain a spaced primary cast. Sixteen cus-

tom trays (four per group) with windows in the ante-

rior region were made using light-curing acrylic resin

sheets (Plaque Photo, W+P Dental) of 2 mm in thick-

ness. The trays were left undisturbed for 24 hours

prior to impression making to ensure dimensional

stability. The samples were divided into four groups

based on impression technique.

In group A, the impression copings were not

splinted. Manufacturer-recommended polyether

adhesive (3M ESPE) was coated onto the impres-

sion copings (Nobel Replace Regular Platform, REF

33540, Nobel Biocare) and the custom tray. Both

were allowed to dry for 15 minutes. Medium-body

polyether (Impregum Penta, 3M ESPE) wasinjected around the impression copings and

administered into the tray using an electronic

mixer (Pentamix 2, 3M ESPE); then the impression

was made.

In group B, the impression copings were first

splinted with acrylic resin (GC Pattern Resin) (Fig

1). A putty index was made to act as a scaffold for

the splinting material. The splint was allowed to

polymerize for 4 minutes and then sectioned and

reoriented using the same pattern resin in a brush

bead method. The impression was made in a simi-

lar manner after the application of the recom-mended adhesive.

In group C, the impression copings were splinted

with bite registration addition silicone (Imprint

Bite, 3M ESPE) (Fig 2) after the application of the

recommended adhesive. After 5 minutes, the

splint, copings, and tray were coated with poly-

ether adhesive and the impression was made in a

similar manner.

In group D, the impression copings were splinted

with bite registration polyether (Ramitec, 3M ESPE)

(Fig 3) and the impressions were made with poly-

ether in the previously mentioned manner. The

impressions were allowed to set for 6 minutes in

the reference model and after removal were

allowed to polymerize for 30 minutes per the man-

ufacturers recommendation.

Implant replicas were then fastened on to the

impression copings and the impressions were poured

with type IV dental stone (Ultrarock, Kalabhai). All 16

casts were subjected to three-dimensional evaluation

of accuracy using a coordinate measuring machine3,9

(Spectra series 5.6.4, Accurate) (Fig 4). Measurements

The International Journal of Oral & Maxillofacial Implants 39

Hariharan et al

Fig 1 Impression copings splinted with

acrylic resin.

Fig 2 Impression copings splinted with bite

registration addition silicone.

Fig 3 Impression copings splinted with bite

registration polyether.


3/8

were accomplished using a probe with a diameter of

2 mm (Renishaw TP2). The centers of the implant

replicas were first measured by touching four points

on the circumference of the implant replicas and

feeding the data into a computer with processing

software (Accusoft, Accurate). Implant replica 1 waskept as the reference, and all measurements were

made with reference to this implant replica. The dis-

tances between the centers of implant replicas 1 and

2 (D1x/y), 1 and 3 (D2x/y), and 1 and 4 (D3x/y) were

measured in the x- and y-axes (Figs 5 and 6). The

planes formed by the platforms of the implant repli-

cas were then measured. The distances between the

planes formed by implant replicas 1 and 2, 1 and 3,

and 1 and 4 were measured to determine the interim-

plant distances in the z-axis (D1z, D2z, D3z) (Fig 7).

To determine the angular relationships between

the replicas, the open tray impression copings were

connected to the implant replicas and tightened to

10 Ncm torque. The plane formed by the flat surfaces

of the impression copings was measured. The angles

formed between implant replicas 1 and 2 (angle 1), 1

and 3 (angle 2), and 1 and 4 (angle 3) were measured

by calculating the angle formed by the flat surfaces

of the respective impression copings (Fig 8). Thus,

nine distances and three angles were measured for

the reference model and for each of the 16 casts. The

values obtained from the casts were compared with

those from the reference model, and the differences

were calculated (Figs 9 to 12). The values were statisti-

cally compared with one-way analysis of variance and

the Tukey post-hoc test at a significance level of .05

(SPSS 11.5 software).

RESULTS

The means and standard deviations of the differences

in interimplant distances measured in the x-, y-, and z-

axes and in the interimplant angulations in the z-axis

(D1/2/3/angle = D1/2/3/angle of the respective

group D1/2/3/angle of the reference group) are

shown in Tables 1 to 4.

X-Axis

The nonsplinted and pattern resinsplinted groups

showed reduced interimplant distances (D1x and

D2x) and showed an increase in the D3x values. The

silicone-splinted and polyether-splinted groups

exhibited an increase in all three interimplant dis-

tances measured. This change in interimplant dis-

tances was largest in the silicone-splinted group

(D3x = 49.4 m) and smallest for the nonsplinted

group (D2x = 1.23 m). The differences in distance

between implant replicas 1 and 4 (D3x) for the sili-

cone-splinted group varied significantly from the val-

ues for the pattern resinsplinted group (P= .02).

40 Volume 25, Number 1, 2010

Hariharan et al

Fig 4 Evaluation of casts using coordinate

measuring machine.

Fig 5 Schematic representation of interim-

plant distances in the x-axis.

Fig 6 Schematic representation of interim-

plant distances in the y-axis.

Fig 7 (Left) Schematic representation of

interimplant distances in the z-axis.

Fig 8 (Right) Schematic representation of

interimplant angulations in the z-axis.

12 3

4

D1x D2x

D3x

D1y D2y D3y

)3

)2

)1

D3zD2zD1z


4/8The International Journal of Oral & Maxillofacial Implants 41

Hariharan et al

Fig 9 Differences in interimplant distances in the x-axis for the

four test groups. *Statistically significant difference between

groups (P< .05).

5040302010

0102030405060

Group AGroup BGroup CGroup D

179.8

19.612.6

1.2

39.8

38.3

13.4

33.0

8.2

49.4

21.2

Differencein

interimplantdistance(m)

D1x D2x D3x

*

Fig 10 Differences in interimplant distances in the y-axis for the

four test groups.

120

100

80

60

4020

0

20D1y D2y D3y


Diffe

rencein

interimplan

tdistance(m)

80.7

103.4112.6

70

51.3 51.2

77.4 77.7

3.2 3.9 4.3

0.6

Fig 11 Differences in interimplant distances in the z-axis for the

four test groups. *Statistically significant difference between

groups (P< .05).

-

40

30

20

10

0

10

20

30D1z D2z D3z

4.37.5

12.3

6.8

28.6

5.4

24.2

15.1 14.6

5.5

20.9

7.6


Differencein


*

*

Fig 12 Differences in interimplant angulations in the z-axis for

the four test groups. *Statistically significant difference between

groups (P< .05).

1.5

1.0

0.5

0

0.5

1.0

1.5Angle 1 Angle 2 Angle 3

0.4

0.8

0.30.1 0.04

1.0

0.60.5

0.3

0.1

1.2

0.7


Differencein


**

Table 1 Differences (m) in Interimplant Distances

in the X-Axis

D1x D2x D3x

Group Mean SD Mean SD Mean SD

A 16.95 24.5 1.23 24.2 33.03 20.8

B 9.8 65.4 39.83 54.3 8.25 6.1

C 19.6 8.3 38.3 38.3 49.4 13.4

D 12.55 17.3 13.38 22.4 21.23 20.6


in the Y-Axis

D1y D2y D3y


A 80.7 24.0 51.325 21.9 3.15 7.5

B 103.45 14.1 77.425 17.7 3.925 1.4

C 112.575 21.7 77.725 6.3 0.60 2.6

D 70.0 21.0 51.175 26.9 4.325 10.2


in the Z-Axis

D1z D2z D3z


A 4.3 5.5 28.6 22.2 14.575 61.2

B 7.5 8.4 5.425 2.5 5.5 13.5

C 12.3 11.6 24.225 25.7 20.95 48.9

D 6.825 13.2 15.1 6.3 7.65 13.1

Table 4 Differences (in Degrees) in Interimplant

Angulations in the Z-Axis

Angle 1 Angle 2 Angle 3


A 0.4 0.8 0.04 0.1 0.3 0.8

B 0.8 0.4 1.0 0.6 0.1 0.3

C 0.3 1.0 0.6 0.6 1.2 1.0

D 0.1 0.7 0.5 0.8 0.7 0.8


5/8

Y-Axis

All groups exhibited an increase in the interimplant

distances D1y and D2y and a decrease in interimplant

distance D3y. The silicone-splinted group showed the

greatest increase in interimplant distance (D1y =

112.6 m and D2y = 77.7 m), whereas the poly-

ether-splinted group showed the smallest increase in

interimplant distance (D1y = 70 m and D2y =51.2 m). One-way analysis of variance showed that

the values of D1y varied significantly for all the

groups (P= .043).

Z-Axis

The nonspl inte d and si l ico ne -s plint ed gro ups

showed an increase in D1z and D2z values and a

decrease in D3z values. The pattern resinsplinted

group showed an increase in D1z and a decrease in

D2z and D3z. The polyether-splinted group showed a

decrease in all three measurements in the z-axis. The

largest differences were seen in the nonsplintedgroup (D2z = 28.6 m), whereas the resin-splinted

group showed the smallest differences (D2z = 5.4

m). Statistically significant differences were present

within the nonsplinted and polyether-splinted

groups (P= .018) and between the silicone- and poly-

ether-splinted groups (P= .033) for D2z values.

Interimplant Angulations

All the groups showed a reduction in interimplant

angle 1 (maximum of 0.8 degrees for the resin-

splinted group and minimum of 0.1 degrees for the

polyether-splinted group). Angle 2 decreased in thenonsplinted and resin-splinted groups but increased

in the silicone-splinted and the polyether-splinted

groups. Angle 3 increased in all the groups except for

the acrylic resinsplinted group. Angle 2 for the

pattern resinsplinted group was significantly differ-

ent from that observed for the silicone-splinted group

(P= .011) and the polyether-splinted group (P= .018).

DISCUSSION

Passive fit of an implant prosthesis depends on the

accuracy of the impression made. The impression,

which allows replication, must be accurate so that the

resulting master cast precisely duplicates the clinical

situation.25

Four direct impression techniques were evaluated

in this study: nonsplinted open tray impression cop-

ings, splinting with acrylic resin, splinting with bite

registration addition silicone, and splinting with bite

registration polyether. Only direct impression tech-

niques were evaluated since most research indicates

that direct techniques produce less distortion than

indirect techniques.2,7,9,10,26 Because splinting with

acrylic resin has yielded conflicting results,716,27,28 an

attempt was made to evaluate the reliability of bite

registration silicone and bite registration polyether as

splinting materials. Because polyether has been advo-

cated as an impression material for multiple

implantsupported prostheses for edentulous

patients,1,2,69 medium-body polyether was used asthe impression material. The impression copings were

screwed to the implants at 10 Ncm of torque before

impressions were made.8 The copings were coated

with polyether adhesive to reduce their movement in

the impression.29 When the implant replicas were

tightened to the impression copings in the impres-

sion, the torque wrench was not used; this prevented

rotation of the copings in the impression.8,30The

casts were poured with type IV dental stone accord-

ing to the manufacturers instructions.

Dimensional changes can occur in any direction.

To study the magnitude of error occurring in threedimensions, the interimplant distances and angula-

tions were measured in the x-, y-, and z-axes. All casts

were measured using a coordinate measuring

machine3,9,31 that was accurate to within 5 m. Distor-

tion can be measured as either absolute or relative.1

In absolute distortion analysis, an external reference

point is used, while in relative distortion analysis one

implant/abutment is used as a reference for measur-

ing distortion. Because the prosthesis connects all the

implants together, the amount of strain on the

implants is related to the relative positions of the

implants to one another.1

Therefore, relative distor-tion analysis was done in this study by measuring the

interimplant distances and angulations in reference

to replica no 1.1

The range of difference in the x-axis for group D

(polyether splint) was the least when compared with

other groups, whereas group C (silicone splint)

showed the greatest differences in the x-axis. Irre-

spective of the impression technique, the errors were

more on the positive side, signifying an increase in

the dimension of the master cast. The differences in

the x-axis obtained in this study were within a range

similar to those obtained in previous studies7,9,10,16,25

for all four test groups.

Th e di ff er en ce s obse rve d in th e y- ax is we re

greater in magnitude when compared to other axes

in all the four groups. Greater differences were seen

in D1y and D2y values for all four groups with respect

to the reference model. They were similar to the dif-

ferences reported in earlier studies.7,9,10The reason

for such increased dimensional changes in the y-axis

needs to be explored.


Hariharan et al


6/8

In the z-axis, the acrylic resinsplinted copings

showed the smallest error, followed by bite registra-

tion polyether, whereas nonsplinted copings and bite

registration silicone splinting showed greater devia-

tions. These differences could be attributed to the

rigidity of the splinting material that was used to pre-

vent the movement of copings in the vertical direc-

tion during connection of the implant replica to theimpression coping. The differences in this study were

similar to the findings of earlier studies.6,9 A variability

of 20 m caused by repeated screw fastening has

been reported.2 Also, a vertical gap of 50 to 100 m

has been published as acceptable, as it can be com-

pensated by an extra half turn of the screw that con-

nects the different implant components.32

With regard to rotational distortion in the z-axis,

maximum differences were seen in the silicone-

splinted group (1.2 degrees), followed by the acrylic

resinsplinted and polyether-splinted groups; the

smallest differences were seen in the nonsplintedgroup. The angular differences could be a result of

finger tightening of the implant replica to the impres-

sion coping.2,8The lower values for rotational error in

the nonsplinted group could be attributed to the fact

that polyether adhesive was coated over the impres-

sion copings.29 The negative values seen in the pat-

tern resinsplinted group reflected the rigidity of the

resin in preventing rotation of the impression copings.

Reports of tolerance between implant and abut-

ment31,33 and the existence of rotational freedom of

about 5.5 degrees between implant and abutment33

suggest that tolerance between the machined com-ponents might compensate for the errors to a certain

extent. The minimal rotational discrepancies (mini-

mum of 0.09 degrees to a maximum of 1.2 degrees

among all test groups) obtained in this study also

reinforce the need for a rigid impression material,

such as polyether, to prevent rotational distortions.

From these data, it appears probable that the applica-

tion of polyether adhesive, rigidity of polyether

impression material, rigidity of the splinting material,

tolerances between the implant components, and

torque employed during fastening of the implant

replica could determine, either individually or collec-

tively, the extent of distortion.1,8,29,31,33

Although splinting might rigidly hold the impres-

sion copings together, the time consumed for impres-

sion making is considerably greater when compared

to the nonsplinted technique. The reason that sili-

cone splinting showed the largest differences could

be a result of the relatively lower rigidity of the mate-

rial when compared to bite registration polyether

and acrylic resin.

Measurements made in all three axes in the pre-

sent study showed that certain techniques resulted in

accurate reproduction of interimplant relationships

in one or more axes, but not in all three axes.

Although significant differences might not be pre-

sent in individual axis measurements, the collective

error occurring because of dimensional changes in all

the axes might play a role in the fit (or misfit) of theprosthesis. The lack of any reference value for defin-

ing misfit makes it difficult to recommend any partic-

ular impression technique. The encouraging results

obtained from the nonsplinted technique after the

application of adhesive kindles the authors interest

in further research on the effect of polyether adhe-

sive on impression copings. Also, research on the

dimensions of the splint and the dimensions of the

section of resin splint, along with in vivo studies on

the efficacy of bite registration polyether as a splint-

ing material, could shed light on the importance of

splinting impression copings.

CONCLUSION

Within the limitations of this study, the following con-

clusions were drawn:

1. When impressions made with nonsplinted and

splinted impression copings were compared, the

casts obtained from copings splinted with bite

registration polyether were the closest to the ref-

erence model, followed by those made via acrylicresin splinting, nonsplinting, and addition silicone

splinting.

2. The differences between the test groups were sta-

tistically similar to each other and within the range

observed in previous studies.

3. Selection of impression technique can be based

on the clinical situation and the individual clini-

cians preference.

ACKNOWLEDGEMENTS

We thank Nobel Biocare, Sweden, and 3M ESPE, India, for their

generous support.

The International Journal of Oral & Maxillofacial Implants 43

Hariharan et al


7/8

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Evaluacion Acuciosidad de Impresion

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