An In Vitro Evaluation of 3D-printed Provisional Restoration Marginal Adaptation on Diverse Finish Lines

INTRODUCTION

The accurate fit of the restoration is the major determinant for its longevity and success. Accuracy in each step of fabrication of the restoration is the primary requisite for an accurate final restoration. Thus, accuracy in impression, interocclusion record, interim restoration, and final prosthesis fabrication process is highly desirable. Focus has always been on the accuracy of impression and the final restoration.¹

For years, there has been gradual upgradation in each step of the prosthodontic procedure. The influence of digitalization is seen from impression-making techniques to final prosthesis fabrication. But the procedure of interim restoration fabrication is still based on conventional technique and has not changed much over the years. Often such prostheses are used to assist in the determination of the therapeutic effectiveness of a specific treatment plan or the form and function of the planned definitive prosthesis. The requirements of an interim restoration are essentially the same as for the definitive restoration, apart from longevity and possibly the sophistication of color.²

The term 3D printing is generally used to describe a manufacturing approach that builds objects one layer at a time, adding multiple layers to form an object. This process is more correctly described as additive manufacturing and is also referred to as rapid prototyping.³

The introduction of computer-aided design/computer-aided manufacture (CAD/CAM) technology in dentistry has allowed the shaping of high-performance material that could not otherwise be easily shaped to form a dental restoration.⁴ Several researchers have criticized the marginal fit of these restorations.^5,6 However, improvements in the CAD/CAM system and software have made the fit more acceptable through precise operating procedures.⁷ This CAD/CAM system can be explored for the fabrication of the interim restoration.

The success of dental restoration is determined by three main factors: esthetic value, resistance to fracture, and marginal adaptation. Inadequate fit leads to plaque accumulation, which increases the risk of carious lesions, and can cause microleakage and endodontic inflammation. Plaque accumulation may also cause periodontal diseases, especially with subgingival margins. Finally, misfit could contribute to cement dissolution.^8,9

The factors that have been documented to influence the marginal adaptation of dental restoration are the preparation design, location, and design of finish line preparation, restorative material, fabrication method, impression material, and technique. The clinical goal of interim prosthesis restoration is to have a minimal marginal gap, protect the tooth, and prevent carries and poor gingival health.

The present study has been designed to evaluate the marginal fit of two different interim restorations fabricated by 3D printing and milling technique on two different finish lines (shoulder and chamfer).

MATERIALS AND METHODS

This study was conducted in the Department of Prosthodontics and Crown and Bridge of Mithila Minority Dental College and Hospital, Darbhanga, Bihar.

RESULTS

The compiled data were analyzed and the following observations in the form of tables and graphs were made. Table 1 and Figure 6 compared the marginal gaps in different surfaces of the restoration fabricated by using different techniques on teeth prepared with a shoulder finish line. In CAD/CAM technique, the maximum mean marginal gap was seen in the palatal cervical margin (77.42 μm), while the lowest was seen in the facial margin (70.25 μm). In 3D printing, the facial margin has the lowest marginal gap (38.50 μm), while the distal surface was having a higher marginal gap (41.08 μm). Overall, there was an increased marginal gap seen in interim restoration fabricated by using CAD/CAM. There was a statistically highly significant difference (p < 0.001) present in the marginal gap between CAD/CAM and 3D printing at various locations in restoration with a shoulder finish line. Table 2 and Figure 7 compared the marginal gaps in different surfaces of the restoration fabricated by using different techniques on teeth prepared with the chamfer finish line. In CAD/CAM technique, the maximum mean marginal gap was seen in the mesial cervical margin (89.00 μm), while the lowest was in the distal margin (85.42 μm). In 3D printing, the facial margin had the lowest marginal gap (44.00 μm), while the distal surface showed the highest (48.25 μm). There was a statistically significant difference in the marginal gap between CAD/CAM and 3D printing at various locations in restoration with chamfer finish line (p < 0.001). Overall, there was a less marginal gap in restorations fabricated by 3D printing.

Comparison of marginal gap (Table 3 and Fig. 8) of interim restorations fabricated on shoulder and chamfer finish line irrespective of the fabrication technique. There was no statistically significant difference (p %3E; 0.05) in the marginal gap in both finish lines. So, both the finish lines were equally effective. Comparison of overall mean marginal gap (Table 4 and Fig. 9) of the restorations. Mean marginal gap in restoration fabricated by CAD/CAM milling on the shoulder (73.61 μm) and chamfer (83.12 μm). While in restoration fabricated by 3D printing on the shoulder (43.44 μm) and chamfer (49.21 μm) marginal gap. A statistically highly significant (p %3C; 0.001) difference was present in the marginal gap between CAD/CAM and 3D printing in both finish lines.

DISCUSSION

Interim restorations are an essential part of fixed prosthodontic treatment. Interim restoration must be fabricated and applied over the prepared tooth until final or definitive prosthesis placement. Interim restorations are a critical component of fixed prosthodontic treatment, biologically and biomechanically. Interim restoration serves an important diagnostic role as a functional and esthetic try-in and as a blueprint for the design of the definitive prosthesis. Marginal fit of full-coverage crowns is a major requirement for the long-term success of restorations. A perfect marginal seal is one of the most important technical factors for the long-term success of any restoration.²

A considerable marginal opening concedes more plaque accumulation, gingival sulcular fluid flow, and bone loss, recurrent caries, periodontal disease, and a decrease in the longevity of the prosthetics restorations. This kind of problem may be complicated by fixed partial restorations with vital abutments.¹⁰

A restoration, definitive or provisional, is termed successful when it exhibits good marginal and internal fit and is strong enough to withstand the oral environment. This is critical in the case of marginal adaptation of provisional restoration because the poor marginal fit can lead to inflammation of periodontal tissue, a situation that can hamper and postpone the fit of definitive restorations. Provisional restorations are used as an intermediate stage for short- or long-term placement on teeth between the time of tooth preparation until definitive indirect restorations are fabricated and placed.²

The purpose of this study was to evaluate and compare the marginal fit of 3D-printed and CAD/CAM milled interim restorations fabricated on two different finish lines, chamfer and shoulder. Based on the results, the null hypothesis that no difference exists in marginal fit between 3D printing and CAD/CAM milled restorations on different finish lines was rejected. In the literature, several methods are reported to evaluate the marginal fit and adaptation of the different restorations on it. In this study, the optical microscope was used for measuring the marginal gap. This approach offers several advantages of being non-destructive and allows for quantitative measurements in three dimensions. However, one major shortcoming of this method is, all measurements were done without cementation or any pressure application on restoration apically, which of course is not a true representation of the actual clinical situation. Nonetheless, it has been shown that the use of cement may lead to improper seating of the restoration and thus increases the marginal and internal gap.

In this study, the results showed that 3D-printed restorations exhibit significantly lower marginal and internal gap values rather than CAD/CAM milled counterparts. The inferior marginal fit of milled restorations may be attributed to errors resulting from the tolerance of milling burs.

In this study, while the shoulder finish line was used, it was found that there is almost the same marginal discrepancy present on each surface if the restoration fabrication technique was the same. But, the maximum marginal gap in CAD/CAM milled restoration was 77.42 μm while in 3D-printed restoration it was found 41.08 μm. There was a statistically highly significant difference present in the marginal gap between CAD/CAM and 3D printing at various points in restorations fabricated on the shoulder finish line. In the present study, marginal gaps in restoration fabricated on shoulder finish lines were within the clinically acceptable limit. But overall, there was a greater marginal gap in restorations fabricated by CAD/CAM milling.

In the present study in restorations fabricated on the chamfer, finish lines showed slightly increased marginal discrepancy than the shoulder finish line. The maximum marginal gap in CAD/CAM milled restorations was 89.00 μm and in the 3D-printed restoration was 48.25 μm. There was a less marginal gap in restorations fabricated by 3D printing.

Statistical analysis showed that there was no significant difference in the marginal gap in both finish lines. So, both the finish lines were equally effective. Euán et al.¹¹ also found in their study that there is no statistically significant difference in the marginal gap when the restorations were fabricated on different finish lines. Comlekoglu et al.¹² also found in their study that both shoulder and chamfer finish lines exhibit the same type of marginal gap between restoration and prepared tooth. Our result is in concurrence with the findings from the above authors. But in the study conducted by Cho et al.,¹³ it was found that marginal gaps were greater in the chamfer finish line when compared to the shoulder finish line.

In this study, a statistically highly significant difference was present in the marginal gap between CAD/CAM and 3D printing in both finish lines. It means restorations fabricated by 3D printing had a less marginal gap irrespective of the finish line designs. This is in accordance with the results of the study of Alharbi et al.¹⁴ concluded that less marginal discrepancies were present in restorations fabricated by 3D printing.

From the present study, it can be inferred that the restorations fabricated by CAD/CAM milling are having a larger marginal gap than 3D-printed restorations irrespective of finish line designs. Boitelle et al.¹⁵ did a meta-analysis and found that most authors agree that the marginal gap between prepared tooth and restoration below 120 μm are clinically acceptable. In the present study, the maximum marginal gap on shoulder and chamfer finish lines is in a clinically acceptable limit. Hence, it can be concluded that clinically acceptable restorations can be obtained by CAD/CAM milling or 3D printing technique on either of the finish line design.

CONCLUSION

Both the shoulder and chamfer finish lines were equally effective. Restorations fabricated by 3D printing had less marginal gap than CAD/CAM milling but both values were within the clinically acceptable limit.

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