Influence of Implant Angulation and Implant Number on the Accuracy of Definitive Casts.

BACKGROUND: The present study determined the effect of implant angulation and implant number on the dimensional precision of implant definitive casts.
MATERIALS AND METHODS: Three definitive casts with implant analogs placed in a triangular pattern were made from dental stone. Group I was control group, Group II in which implant numbers 1 and 3 were at 5° convergence to the implant number 2. Group III in which implant numbers 1 and 3 are at 5° divergence to the implant number 2. Group IV in which implant numbers 1 and 3 are at 10° convergence to the implant number 2. Implant analogs were secured in all the definitive casts with cyanoacrylate. Three open tray impressions of the definitive cast were obtained and poured in Type IV dental stone. Coordinates in the three planes were measured at implant analog top surface and base of the cast using a fine tip measuring stylus. The data were aligned and angular differences between implant analog vectors from definitive and duplicate casts were measured.
RESULTS: There was a significant correlation between dental implant number and dental implant angulation (P < 0.05). There was a significant result when comparing the effect of the parallel group from 5° divergence and 10° convergence groups. A significant results while comparing the parallel group with 5° divergence and 10° convergence was obtained whereas while comparing 5° divergence, 5° divergence, and 10° convergence a nonsignificant difference was obtained (P > 0.05).
CONCLUSION: Close proximity of implant angulation toward right-angled direction results in higher precision of implant. Copyright:

INTRODUCTION

Dental implants are one of the superior inventions in the field of dentistry. For ensuring successful dental implant treatment, accurate impression procedures are necessary for passively fitting prosthesis. Impression covering all aspects of dental implants is the foremost point in order to achieve better results.[1] Inaccurate superstructure fit may result into mechanical and biologic complications affecting the functioning of dental implants. Among various complications, implant loosening, bending, and fracture of the prosthetic or implant components are important and commonly seen. Biologic complications comprised of fracture of the interface between the dental implant and the alveolar bone due to overloading physiologic tolerance levels.[2]

It is found that integrated implants are immobile, hence it is imperative to make certain an accurate relationship on the definitive cast.[3] It is evident that impression technique, type of tray, dental stone manipulation technique, and compatibility of the cast with impression materials are few factors that affect the accuracy of the master cast. There are various methods employed for the transfer of the implant positions from the intraoral position to a working cast. The open tray technique and the closed tray technique are commonly used methods.[4]

The technique of open tray encompasses implant fastening to an impression handling with a screw and through impression tray's opening cut. In the closed tray technique, there is no detachment of the tray after the removal of impression. The objective of a multi-implant impression is that a precise and accurate transfer of the impression can be achieved between implant abutments or implants.[5] The present study determined the effect of implant angulation and implant number on the dimensional precision of implant definitive casts.

MATERIALS AND METHODS

This in vitro study was conducted in the department of prosthodontics. This study was approved by the institutional ethics committee. It comprised four definitive casts that were made by manipulating Type IV gypsum following the manufacturer's instructions and pouring into a 4.0 cm × 2 cm hemispherical preformed mold. The casts were then retrieved.

A plane was created on definitive casts with three implants placed in a triangular pattern with the distance of 1.1 cm between implants 1 and 2, implants 2 and 3, and 1.5 cm between implants 1 and 3. Three points were punched on the base of the cast each at a distance of 0.2 cm from the outer surface of the cast. The holes were plunged cut in the casts using vertical milling machine which matched the diameter and depth of implant analogs and degrees convergence or divergence of implant numbers 1 and 3 from the center implant. The holes for these implants were milled at 5°, 10°, and 15° of divergence or convergence. Four groups were made. Group I was control group in which all three implants were kept perpendicular to the plane of the cast. Group II in which implant numbers 1 and 3 were at 5° convergence to the implant number 2. Group III in which implant numbers 1 and 3 are at 5° divergence to the implant number 2. Group IV in which implant numbers 1 and 3 are at 10° convergence to the implant number 2. Implant analogs were secured in all the definitive casts with cyanoacrylate.

Three open tray impressions of the definitive cast were obtained and poured in Type IV dental stone. Coordinates in the three planes were measured at implant analog top surface and base of the cast using a fine tip measuring stylus. The data were aligned and angular differences between implant analog vectors from definitive and duplicate casts were measured. Results were subjected for statistical analysis where P < 0.05 was considered statistically significant.

RESULTS

Table 1 shows that there was a significant correlation between dental implant number and dental implant angulation (P < 0.05).

Table 1

Assessment of effect of implant number and angulation on impression accuracy

Effect	Degree of freedom	Mean square	P
Main effect of implant angulation	5	0.231	0.071
Main effect of implant number	3	1.251	0.02
Interaction between implant number and angulation	10	0.365	0.03

Table 2 shows that there were significant results when comparing the effect of the parallel group from 5° divergence and 10° convergence groups.

Table 2

Assessment of comparison of three implant numbers for implant angulation

Implant angulation	Degree of freedom	Mean square	P
Parallel	2	0.41	0.512
5° convergence	2	1.241	0.001
5° divergence	2	0.942	0.001
10° convergence	2	0.065	0.436

Table 3 shows significant results while comparing parallel group with 5° divergence and 10° convergence, whereas while comparing 5° divergence, 5° divergence, and 10° convergence, a nonsignificant difference was obtained (P > 0.05).

Table 3

Post hoc analysis

Group	Mean difference	Significance
Parallel
5° convergence	0.1215	0.07
5° divergence	0.1361	0.01
10° convergence	0.2163	0.02
5° convergence
5° divergence	0.064	0.41
10° convergence	0.0215	0.71
5° divergence
10° convergence	−0.0419	0.91
10° convergence
10° divergence	−0.0712	0.45

DISCUSSION

Proper working casts are vital to manufacture passively fitting implant prostheses. A good and precise implant impression plays a major role and serves as an initial point in the process of creating good working casts.[6] Hence, the comparative accuracy of the impression techniques becomes a significant issue in consideration of passive fit.[7] The present study determined the effect of implant angulation and implant number on the dimensional precision of implant definitive casts.

In the present study, we found that there was a significant correlation between dental implant number and dental implant angulation (P < 0.05). Conrad et al.[8] evaluated the effect the combined interaction of impression technique, implant angulation, and implant number on the accuracy of implant definitive casts. It was found that there was nonsignificant difference for the closed and open tray impression techniques (P > 0.05). Implant angulations and implant numbers differed in average angle errors but not in any easily interpreted pattern. The combined interaction of impression technique, implant angulation, and implant number had no effect on the accuracy of the duplicate casts compared to the definitive casts (P = 0.19).

We found that there was a significant result when comparing the effect of the parallel group from 5° divergence and 10° convergence groups. Assuncao et al.[9] determined the accuracy of the transfer process in respect to implant analog angulations 90°, 80°, 75°, and 65° and different impression materials. It was concluded that the more perpendicular the implant analog angulation was in relation to the horizontal surface, the more accurate the impression was.

We observed significant results while comparing parallel group with 5° divergence and 10° convergence, whereas while comparing 5° divergence, 5° divergence, and 10° convergence, a nonsignificant difference was obtained (P > 0.05).

The open tray and closed tray impression techniques are routinely used for transferring implant positions before the fabrication of prosthesis. The type of impression material, the implant impression technique, die material accuracy, and the implant master cast technique determine the accuracy of the implant cast. Vigolo et al.[10] compared direct splinted technique with acrylic splinting with indirect technique or the nonsplinted direct techniques. Results found a direct splinted technique better than indirect technique.

Martínez-Rus et al.[11] assessed the effect of different implant-level impression techniques on the accuracy of definitive casts. Six tapered screw-vent implants were placed in a reference model with 0°, 15°, and 30° angulation and at 0, 1, and 3 mm subgingival positions. Twenty medium-consistency polyether impressions of this model were made with indirect technique, unsplinted direct technique, acrylic resin-splinted direct technique, and metal-splinted direct technique. Results showed that four impression procedures showed significant differences. Only Group 4 casts showed no significant differences in comparison with the reference model (P = 0.666).

In the present study, Type IV die stone was used to pour the casts. Custom impression trays using light cure hybrid composite resin material were fabricated providing double thickness of modeling wax as spacer. Master casts poured in addition silicone and polyether with Type IV die stone give better results.[5]

The shortcoming of the study is small sample size.

CONCLUSION

Authors found that close proximity of implant angulation toward right-angled direction results in higher precision of implant.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.