|Year : 2021 | Volume
| Issue : 2 | Page : 108-117
An in vitro study to assess the positional accuracy in multiple implants using different splinting materials in open-tray impression technique
Nikhil Kumar Chaudhary1, Manisha Gulati1, Salil Pawah1, Bhawana Tiwari2, Chetan Pathak1, Manisha Bhutani1
1 Department of Prosthodontics and Crown and Bridge, Sudha Rustagi College of Dental Sciences and Research, Faridabad, Haryana, India
2 Department of Prosthodontics and Crown and Bridge, ESIC Dental College, Rohini, Delhi, India
|Date of Submission||24-Nov-2020|
|Date of Acceptance||14-Jan-2021|
|Date of Web Publication||22-Mar-2021|
Nikhil Kumar Chaudhary
Department of Prosthodontics and Crown and Bridge, Sudha Rustagi College of Dental Sciences and Research, Faridabad, Haryana
Source of Support: None, Conflict of Interest: None
Context: Numerous implant techniques have been suggested in the literature to obtain an accurate master cast. One of those is to splint the impression copings; however, many controversies exist in type of splinting materials used. Aim: The aim of this study is to evaluate and compare the positional accuracy in multiple implants using different splinting materials in open-tray impression technique. Settings and Design: The study design involves an in vitro study. Materials and Methods: An acrylic resin model of a mandibular edentulous arch was used as a reference model in which four 3.75 mm × 10 mm implant analogs were placed and sequentially numbered as 1, 2, 3, and 4 from left to right. Open tray impression copings were attached to each of them and were then splinted by three different materials and divided into three Groups as Group I, Group II, and Group III splinted with pattern resin, composite resin, and titanium wire, respectively. Five implant level impressions were made from each group and poured in Type IV dental stone. The implant analogs were transferred to the casts and inter-implant distances were compared to the reference model using the Coordinate Measuring Machine. Statistical Analysis Used: One-way ANOVA test was used as a test of significance. Results: The present study revealed that all the three splinting materials can be used for the accurate reproduction of spatial relationship. There was no significant difference between the centroids of implant analogs 1 and 2, 1 and 3, 1 and 4, 2 and 3, 3 and 4, and 2 and 4 of reference model with the master models. Conclusion: Clinically acceptable accuracy in transferring the position of implants to the master cast could be obtained from all the three splinting materials used. However, splinting of impression copings with titanium wire showed greatest accuracy.
Keywords: Accuracy, composite resin, intraoral welder, open tray impression copings, pattern resin, splinting materials, titanium wire
|How to cite this article:|
Chaudhary NK, Gulati M, Pawah S, Tiwari B, Pathak C, Bhutani M. An in vitro study to assess the positional accuracy in multiple implants using different splinting materials in open-tray impression technique. Indian J Dent Sci 2021;13:108-17
|How to cite this URL:|
Chaudhary NK, Gulati M, Pawah S, Tiwari B, Pathak C, Bhutani M. An in vitro study to assess the positional accuracy in multiple implants using different splinting materials in open-tray impression technique. Indian J Dent Sci [serial online] 2021 [cited 2021 Apr 20];13:108-17. Available from: http://www.ijds.in/text.asp?2021/13/2/108/311683
| Introduction|| |
Dental implants have proven to be successful in the rehabilitation of partially or completely edentulous patients with the principle objective of more sure and definitive prosthesis concerning function and longevity.,, The precise transfer of the spatial relationship of implants from the mouth to the master cast with an impression is the first and decisive step to ensure passive fit of prosthesis. Therefore, clinicians should strive to precisely transfer the intraoral position of the implants onto the master cast using impression copings and proper impression technique., Splinting of impression copings together before registration of multiple implants impression is one of the techniques advocated by Branemark et al. Numerous splinting materials have been recommended on the basis of their property to resist dimensional changes such as impression plaster, dual cure acrylic resin, autopolymerizing acrylic resin alone or in combination with dental floss, orthodontic wire, prefabricated acrylic resin bars, and carbon steel pins.,,, However, no consensus is found in the literature about the type of splinting materials used for splinting impression copings., In recent years, titanium wire of various thickness has been used and has gained popularity for their ability to resist the dimensional changes. However, its application as a splinting material has not been studied nor compared to the other commonly used splinting materials. To date, many authors have investigated factors affecting the accuracy of implant impressions, necessity of splinting impression copings, surface treatment of impression copings, direct or indirect impression techniques, and use of different impression materials. However, the results are not always consistent, and there is limited literature available to compare the positional accuracy of multiple implants through different impression techniques as well as different splinting materials., Therefore, in order to have rigid and dimensional stable material to splint the impression copings, an in vitro study was designed to evaluate the dimensional stability of conventionally used splinting materials and newer splinting material on the positional accuracy in multiple implants by open tray implant impression technique.
| Materials and Methods|| |
Design of the study
This in vitro comparative, experimental study consisted of 15 casts obtained using open tray impression technique where impression copings were splinted with three different splinting materials. The inter-implant distance was measured by the coordinate measuring machine (CMM). Data were collected and were analyzed statistically to obtain the result.
An acrylic resin model (DPI-RR Cold cure) of a mandibular edentulous arch with a metal insert in the posterior region was used as a reference model [Figure 1], to which four 3.75 mm x 10 mm implant analogs (Impact Implant, New Delhi, India) were placed as parallel as possible to each other using a speed controlled micromotor which was attached to a surveyor. These four implant analogs in the acrylic resin model were sequentially numbered as 1, 2, 3, and 4 from left to right [Figure 2].
Open tray impression copings (Impact Implant, New Delhi, India) were then attached and secured with 10 mm flat head guide pins on to the implant analogs using a hex drive (EZ Hi-Tec, Lifecare devices Pvt. Ltd.) by applying a torque of 15 Ncm (Newton Centimeter). A total of 15 specimen master casts were obtained using open tray impression technique where impression copings were splinted with different splinting materials [Table 1] and divided into three groups as follows:-
GROUP I: Casts obtained using open tray impression technique where impression copings were splinted with Pattern resin (GC pattern resin; GC Corp, Tokyo, Japan) [Figure 3].
|Figure 3: Long impression copings attached to analogs and splinted with pattern resin|
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Dental floss was looped tightly around on each of the copings and firmly secured. Pattern resin was mixed and adapted around on the dental floss. It was then sectioned using a diamond disk and sectioned pieces were then reconnected with an incremental application of pattern resin. This technique of sectioning and bonding was used to minimize polymerization shrinkage of the resin. A custom fabricated acrylic impression tray (DPI Cold Cure) on which a window was prepared, coinciding with that of open tray impression copings were coated with vinyl polysiloxane (VPS) adhesive (3M ESPE) and allowed to dry for 15 min. Light bodied polyvinylsiloxane impression material (Flexceed GC) was meticulously syringed around the impression copings to ensure complete coverage of the copings and simultaneously putty consistency polyvinylsiloxane impression material (Flexceed GC) was mixed and loaded onto the tray. They were seated corresponding to the metal bar insert in the posterior region over the resin model with finger pressure. The guide pins were then loosened with a hex driver and the tray was separated from the definitive cast, with the impression copings along with guide pin remaining locked in the impression [Figure 4]. The implant analog was then connected to the hex at the bottom of the impression coping [Figure 5] and the guide pins were tightened with the hex driver. Five impressions were thus made for this group and five casts were poured in Type IV dental stone (Kalrock, Kalabhai Karson Pvt. Ltd) [Figure 6] subsequently.
|Figure 5: Group I impression (implant analogs attached to impression copings)|
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GROUP II: Casts obtained using open tray impression technique where impression copings were splinted with Composite resin (Solare, GC) [Figure 7].
|Figure 7: Long impression copings attached to analogs and splinted with composite resin|
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Dental floss was looped around the impression coping in a similar manner as above, and splinting was done with composite resin. This was then sectioned using a diamond disk and sectioned pieces were then reconnected with an incremental application of composite resin. This technique of sectioning and bonding is to minimize polymerization shrinkage of the resin. The impressions were made [Figure 8], implant analogs were connected to impression copings [Figure 9], and casts were obtained as previously described [Figure 10].
|Figure 9: Group II impression (implant analogs attached to impression copings)|
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GROUP III: Casts obtained using open tray impression technique where impression copings were splinted with titanium wire using intraoral welder (GenWeld MKII, Swiss and Wegman) [Figure 11].
|Figure 11: Using intraoral welder for splinting the copings with titanium wire|
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Splinting was done with titanium wire (1.5 mm) welded onto the impression copings with an intraoral welder [Figure 12]. The impressions were then made [Figure 13], implant analogs were attached [Figure 14] as described previously, and casts were obtained [Figure 15].
|Figure 12: Long impression copings attached to analogs and splinted with titanium wire|
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|Figure 14: Group III impression (implant analogs attached to impression copings)|
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All the casts were stored at the room temperature for a minimum of 24 h before measurements were made. All clinical and laboratory procedures were performed by the same operator. A single examiner, blinded to the nature of the impression technique used, examined the all definitive casts to evaluate the positional accuracy of the implant replicas using a CMM (VMS-OCMM, Sipcon).
A computerized visual controlled CMM was used for all measurements [Figure 16] and [Figure 17] which was capable of measuring with an accuracy of ±5 μm. MSU-3DPro software was used for geometric transformation and data processing [Figure 18]. The coordinate system used throughout this study was defined as follows: The centers of the implant analog were first measured by touching four points on the circumference of the implant analog and feeding the data into the computer with processing software (MSU-3DPro, SIPCON Measuring System, Ambala, Haryana, India). The software determines centroids of each platform. The centroids of the implant analog 1 were designated as position 1(D1); similarly, the positions 2 (D2), 3 (D3), and 4 (D4) were determined. The distance from the position 1 and 2, 1 and 3, 1 and 4, 2 and 3, 3 and 4, and 2 and 4 was calculated in mm (millimeters).
|Figure 16: Measurement of reference model under coordinate measuring machine (VMS-OCMM, Sipcon)|
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|Figure 17: Measurement of master model under coordinate measuring machine (VMS-OCMM, Sipcon)|
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To evaluate the accuracy of each splinting technique, the interimplant distance on the reference model was compared with the interimplant distance on the master casts obtained from three different splinting methods. Irrespective of positive or negative values only actual values were taken for the statistical analysis. The values of master cast were then subtracted from the corresponding linear distance of the reference model, to get the deviation in millimeters.
Data thus obtained were analyzed using the analysis of variance (ANOVA) procedure which produces a one-way ANOVA for a quantitative dependent variable by a single factor (independent) variable. ANOVA is used to test the hypothesis that several means are equal.
| Results|| |
Data were normally distributed as tested using the ShaperioWilk W test (P value was more than 0.05). Therefore, analysis was performed using the parametric test ANOVA procedure which produces a one-way ANOVA for a quantitative dependent variable by a single factor (independent) variable. Level of statistical significance was set at P < 0.05.
[Table 2] shows the highest standard deviation was seen in Group II with standard error of 0.2 and the lowest deviation was seen in Group III with a standard error of 0.01.
|Table 2: Descriptives of mean, standard deviations of distance between centroids of the implant analogs 1 and 2 among three groups|
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[Table 3] shows the highest standard deviation was seen in Group I with standard error of 0.1 and the lowest deviation was seen in Group III with a standard error of 0.02.
|Table 3: Descriptives of mean, standard deviations of distance between centroids of the implant analogs 2 and 3 among three groups|
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[Table 4] shows the highest standard deviation was seen in Group II with standard error of 0.005 and the lowest deviation was seen in Group I with a standard error of 0.002.
|Table 4: Descriptives of mean, standard deviations of distance between centroids of the implant analogs 3 and 4 among three groups|
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[Table 5] shows the highest standard deviation was seen in Group II with standard error of 0.12 and the lowest deviation was seen in Group III with a standard error of 0.10.
|Table 5: Descriptives of mean, standard deviations of distance between centroids of the implant analogs 1 and 3 among three groups.|
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[Table 6] shows the highest standard deviation was seen in Group II with standard error of 0.3 and the lowest deviation was seen in Group III with a standard error of 0.06.
|Table 6: Descriptives of mean, standard deviations of distance between centroids of the implant analogs 1 and 4 among three groups|
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[Table 7] shows the highest standard deviation was seen in Group III with standard error of 0.07 and the lowest deviation was seen in Group I with a standard error of 0.01.
|Table 7: Descriptives of mean, standard deviations of distance between centroids of the implant analogs 2 and 4 among three groups|
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[Table 8] shows the comparison of mean of distance between centroids of the implant analogs for D1-D2, D2-D3, D3-D4, D1-D3, D1-D4, and D2-D4 among all groups with master model which was done using one-way ANOVA test. It was not found to be statistically significant having P = 0.891, P = 0.374, P = 0.079, P = 0.424, P = 0.060, and P = 0.274, respectively. The values of coordinates were not found to be significant. Hence, further comparison was not applicable.
|Table 8: Comparison of mean, standard deviations of distance between centroids of the implant analogs among three groups|
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[Table 9] shows for D1-D2, D2-D3, D3-D4, and D2-D4, highest deviation was seen in Group II and lowest was seen in Group III and for D1-D3 and D1-D4, highest deviation was seen in Group I and lowest was seen in Group III [Graphical Representation: [Graph 1]].
|Table 9: Deviation of distance between centroids among groups in relation to reference model|
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| Discussion|| |
Imprecise implant prosthesis may result in mechanical complications such as screw loosening, fracture of the prosthesis and implant components, or accumulation of preload and loading stresses in the restorative complex, thereby causing biological complications such as failure of osseointegration and marginal bone loss.,
Passive fit as described by Branemark et al. is to be ideally within this 10 μm range to enable bone maturation and remodeling in response to occlusal loads. The perineal problem faced during impressions in multiple implant situation is its accuracy, since, the implant may have different angulations and the impressions may undergo deformations while being retrieved. In order to minimize this, the splinting of impression copings is advocated and has been approved to be an acceptable procedure in literature.,,,,,,
Studies conducted by Vigolo et al., Assuncao et al., Del Acqua et al., and Balamurugan et al. have revealed that impressions obtained with the direct technique (open tray) using splinted copings were more accurate than the indirect technique (closed tray).,,,, Hence, in this in vitro study, an open-tray direct impression technique was followed as various studies showed it to be better than the closed-tray impression technique.
Splinting is a common practice of joining the transfer copings with a material in an attempt to stabilize the copings against movement during fixture or abutment analog fastening and control the relationship between implants in a rigid fashion. Studies evaluating the relationship between different types of splinting materials and their accuracy have yielded conflicting results. Some authors have advocated the use of splinting, while others have concluded that splinting does not produce superior results., Choi et al. found no statistically significant difference between splinted and unsplinted impression copings at 8° of angulation. Assuncao et al. reported that the splinted technique was more accurate than the unsplinted technique., Lee and Cho advocated splinted impression techniques in edentulous situations involving four or more implants. A study done by Saini et al. stated that during clinical and laboratory phases, inaccuracy in transferring three dimensional orientation of implants to the cast can be detected due to the movement of impression copings, and hence, the splinting of transfer copings and modifications are emphasized to reduce this movement. The findings of the present study also favor the fact that splinted direct technique is most accurate for multiple implants and the reason for its greater accuracy can be attributed to the fact that splinting provides stabilization of transfer copings.
Different materials and techniques for the same have been suggested by various researchers. Rhyu et al. suggested VPS bite registration material as a splinting material and found that impressions made with square impression coping splinted with VPS bite registration material were more accurate than those splinted with acrylic resins. Assif et al. used impression plaster, autopolymerizing acrylic resin, and dual-cured acrylic resin as a splinting material and concluded that splinting with autopolymerizing polymethylmethacrylate was more accurate. Spector et al. discussed potential problems associated with the splint technique, such as distortion of the splint materials and fracture of the connection between the splint material and the impression copings and reported that the shrinkage of the acrylic resin would create some errors during the transfer procedure. Pattern resin is also one of the most popular splinting materials. Besides pattern resin, impression plaster, dental floss, polyether-based bite registration material, dual-cure acrylic resin, orthodontic wire, prefabricated acrylic resin bars, light-curing composite resin, and carbon steel pins have been used to splint the impression copings. Auto-polymerizing acrylic resin yielded better results, probably because of increased stiffness and greater stability. Temporization material bispenol A-glycidyl methacrylate also showed better results compared to nonsplinted impressions. Splinting material should thus be selected based upon their property to resist any dimensional changes. In recent years, metal splinting and composite-based bis acrylics have gained popularity as a splinting material in lieu of the conventionally used materials. Hence, an attempt has been made through this study to compare and evaluate the accuracy of transfer of the position of multiple implants splinted with different materials.
To minimize the adverse effects of polymerization shrinkage, it is recommended that the resin splint should be separated after polymerization and then reconnected with a small amount of the same material. Martínez-Rus et al. demonstrated that 80% of the resin shrinkage occurs in the first 17 min. In the present study, the separation and reconnection were performed after this time interval to relieve the shrinkage stress. The residual stress on the matrix of chemically activated resin could be released during the impression procedure, causing misfit of the abutment's position on the definite cast. The distortion increases proportionally with the volume of the resin used. To avoid any sort of discrepancy in implant framework or connection, some authors evaluated metal bar for splinting the impression copings. Del Acqua et al. showed the increased splint rigidity of metal bars to withstand the forces of distortion. Metal bars also avoid resin polymerization.
Pujari et al. evaluated of the accuracy of casts of multiple internal connection implant prosthesis obtained from different impression materials and techniques revealed casts obtained from polyether impression material were more accurate than the casts obtained from VPS impression material. The choice of an impression material should be based on the consideration of several variables, like the material accuracy, the amount of intraoral undercuts, the length of time before the impression is poured, and the experience of the clinician. In the present study, one standard impression material and technique was used as followed by various researchers who had conducted similar studies.
Taking all these factors into consideration, this study evaluated the accuracy of three different splinting materials to transfer the position of multiple implants using open tray impression technique. The study also attempted to evaluate the feasibility of titanium wire as a splinting material as an alternative to the commonly used splinting materials.
For the study, CMM was preferred because of the higher degree of accuracy it provides in its readings. The CMM manufacturer (Sipcon, India) specifies a measurement accuracy and repeatability of up to 0.0001 mm which is very significant. Most measuring devices such as calipers, strain gauges, measuring microscopes, and profile projector are less accurate as compared to CMM.
The result of the present study revealed that all splinting materials used in the study can be used for accurate reproduction of spatial relationship. One-way ANOVA was done to analyze the significant difference between the four implant analogs of each group with the master model. There was no significant difference between the centroids of implant analog 1 and 2, 1 and 3, 1 and 4, 2 and 3, 3 and 4, and 2 and 4 of master models with the experimental model. The values were taken to consideration in measuring the accuracy of splinting and showed that splinting with titanium wire (Group III) was highly accurate as compared to other materials, followed by Group I pattern resin and Group II composite resin, in which the resins were sectioned and rejoined.
The titanium wire splinted to the impression copings using intraoral welder may be considered as an excellent splinting material to prevent the linear displacement of transfer copings and obtain accurate master cast. This, in turn, improves the passivity of the framework and longevity of the treatment in multiple implant cases.
Joseph et al. in their study concluded that composite and bite registration material can also be recommended as splinting material of choice for multiple implant cases, as these exhibited similar results which is acceptable and accurate with other groups (pattern resin and acrylic resin) which are conventionally used. The present study similarly has shown no significant difference in the values of composite resin splinting compared to the pattern resin splinting, so it can be stated that the positional accuracy of implants when splinting with composite resin is at par with conventionally used pattern resin.
The limitation of this study is that the rotational movement discrepancy as well as discrepancies in X, Y, and Z axis of each implant was not analyzed. The results of this study are limited to four implants and might not apply to impressions with different number of implants and at different angulations. Furthermore, it might be assumed that tissue undercuts and different implant angulations may cause greater inaccuracy in the impression procedures that were not addressed in the present study.
Although the present investigation did not simulate clinical conditions, the techniques evaluated are expected to produce similar results in the oral environment. A more comprehensive research with various readily available materials of clinical use, using multiple parameters and more sample size is required for full understanding of the subject. Future studies, particularly long-term prospective clinical trials, are needed to determine the amount of distortion tolerable biologically and mechanically. It will also help to analyze the clinical failures and complications in implant-supported prosthesis.
| Conclusion|| |
In vitro study conclusively showed that the splinting of impression copings with titanium wire showed greatest accuracy in transferring the position of implants to master cast, followed by the compensating technique where pattern resin and composite resin were sectioned and rejoined.
Within the realm and purview of this study, the following conclusions were drawn:
- Splinting of open-tray impression copings with titanium wire showed the best accuracy followed by pattern resin and composite resin
- Titanium wire can be recommended as a splinting material of choice for multiple implants, as it exhibited acceptable and accurate results, with minimal inter implant discrepancy
- No statistically significant difference was found in splinting with pattern resin and composite resin. Hence, it can be concluded that the positional accuracy of implants when splinting with conventionally used pattern resin is at par with composite resin
- This study concluded that clinically acceptable accuracy in transferring the position of implants to the master cast could be obtained from all the three splinting materials used.
Future studies, particularly long-term prospective clinical trials, are needed to determine the amount of distortion tolerable biologically and mechanically.
In vitro study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9]