Accuracy of Different Putty-Wash Impression Techniques with Various Spacer Thickness

ABSTRACT One of the most important steps is accurate impression making for fabrication of fixed partial denture. The two different putty-wash techniques that are commonly used are: (1) Putty-wash one-step technique, (2) putty-wash two-step technique. A uniform wash space is needed for an accurate impression. Nissan et al recommended the use of two-step technique for accurate impression making as there is uniform wash space for the light body material to polymerize. The aim of the present study was to compare the accuracy of stone casts obtained from different putty-wash impression techniques using various spacer thickness. The critical factor that influences the accuracy of putty-wash impression techniques is the controlled wash bulk which is absent in one-step putty-wash impression technique and with polyethylene spacer was used. How to cite this article: Chugh A, Arora A, Singh VP. Accuracy of Different Putty-Wash Impression Techniques with Various Spacer Thickness. Int J Clin Pediatr Dent 2012;5(1):33-38.


INTRODUCTION
One of the most important steps is accurate impression making for fabrication of fixed partial denture. The two different putty-wash techniques that are commonly used are: (1) putty-wash one-step technique, (2) putty-wash twostep technique. A uniform wash space is needed for an accurate impression. Nissan et al recommended the use of two-step technique for accurate impression making as there is uniform wash space for the light body material to polymerize.
Putty acts as a tray for wash material. Light body being less viscous has good flow to record the fine details resulting in an accurate impression. An accurate impression produces the stone casts with minimal dimensional change in regard to the vertical and horizontal dimension between the prepared abutments. Clinical success of fixed prosthodontic procedure is dependent upon the dimensional accuracy of elastomeric impression material and impression procedures.

AIMS AND OBJECTIVES
• To compare the accuracy of various impression techniques made with putty-wash impression material.
• To determine the effect of wash space on the accuracy of impressions made with different techniques. • Clinical recommendations based on study and observation.

MATERIALS AND METHODS
In the present study, putty-wash impression techniques with different spacer thickness of 1 and 2 mm and polyethylene spacer has been used. The two putty-wash impression techniques that have been compared for dimensional accuracy are one-step and two-step procedures. Germany) (Fig. 1).

PREPARATION OF MASTER MODEL
A metal master model, containing three complete crown fixed partial denture abutment preparations, was fabricated for making the measurements. The abutments were prepared with occlusal taper of 6° and two perpendicular cross grooves on the occlusal surface as reference points for taking measurements.

Grouping of Impressions
The impressions were categorized into four groups as follows: Group I: One-step technique in which putty and wash impression materials were used simultaneously and the casts obtained from them were categorized as group I casts (Fig. 2).
Group II: Two-step technique in which primary impression with putty was made with 1 mm thick metal copings placed over the abutments. The copings were removed to create a uniform 1 mm wash space. Wash impression material was syringed around the abutments and the primary putty impression was seated to get a complete two-step puttywash impression. The casts obtained from them were categorized as group II casts (Fig. 3).
Group III: Two-step technique in which primary impression with putty was made with 2 mm thick metal copings placed over the abutments. The copings were removed to create a uniform 2 mm wash space. Wash impression material was syringed around the abutments and the primary putty impression was seated to get a complete two-step putty-wash impression. The casts obtained from them were categorized as group III casts (Fig. 3).
Group IV: Two-step technique in which a polyethylene spacer was used with putty impression and later the polyethylene spacer was removed to create a wash space. The wash impression material was syringed around the abutments and the putty impression was seated to get a complete two-step putty-wash impression. The casts obtained from them were categorized as group IV casts (Fig. 4).

Measuring Procedure
The measurements of master model and stone casts (Fig. 5) were done using coordinate measurement machine (three-dimensional measurement machine) ( Fig. 6) with accuracy up to 0.001 mm. It is mechanical system designed to move a measuring probe to locate reference points on the occlusal and horizontal platform. It consists of four components: The machine itself, measuring probe, the control or computing system and measuring software. The probe used can be either mechanical optical or a laser probe.

OBSERVATION AND RESULTS
The difference between the mean of stone model (msm) and mean of master model (mmm) divided by mean of master model multiplied by 100 was expressed as percentage deviation from master model for each impression technique of each measurement location: Percentage of deviation = (msm -mmm)/mmm × 100 All the measurements obtained for all four groups were tabulated and statistically analyzed (Tables 1 to 4 and Fig. 7).

DISCUSSION
• The aim of the present study was to compare the accuracy of stone casts obtained from different putty/wash impression techniques using various spacer thickness (Graphs 1 to 4). • The critical factor that influences the accuracy of puttywash impression techniques is the controlled wash bulk which is absent in one-step putty-wash impression technique and with polyethylene spacer was used. • The above results showed that when stone casts and master model were compared, the vertical distance (intraabutment) of the stone dies decreased, whereas horizontal distance (interabutment) increased. • In the present study, the controlled wash space is essential for accuracy of putty-wash impressions. The controlled wash space was provided by uniform spacer thickness of 1 and 2 mm. The uncontrolled wash bulk was seen in one-step impression technique and two-step impression technique with polyethylene spacer.        • The clinical implication of the present study is that to achieve a controlled wash bulk, temporary crowns can be used to create the desired wash space in the putty impression. • Further investigation is needed to determine the exact amount and technique of achieving wash space that is essential for accuracy in using two-step putty/wash impression techniques in conjunction with polyvinyl siloxane impression materials. Study can also be undertaken for dimensional accuracies in long-span bridges.

1.
A two-step technique with uniform and controlled wash space is recommended for the fabrication of stone dies which will result in precise fitting of the restoration. 2. The two-step putty-wash technique with 1/2 mm spacer thickness produced casts within accepted clinical range. The one-step and two-step with polyethylene spacer produced the most uneven dimensional changes. 3. The clinical implication of this study will be to use temporary crowns to create controlled wash space.