Comparative evaluation of aesthetic outcome of direct polychromatic composite layering and the “index cut-back technique” for restoring class IV defects using a newly patented simulated 3D printed mould: An in vitro study

Abstract

Aim

The Purpose of This In-Vitro Study Was to Comparatively Evaluate the Aesthetic Outcome Of Direct Polychromatic Layering Of Anterior Composites Restoration With The “Index Cut-Back” Technique While Restoring Class IV Defects of Teeth.

Methodology

An extracted tooth specimen of maxillary central incisor crown was 3-D scanned for obtaining its dimensions, these dimensions were transferred to AUTOCAD™ software and a customised 3-D Printed mould was fabricated (Temporary Patent no.336763–001). 50 specimens of Maxillary Central Incisor Crowns were then constructed with the help of Composite restorative material (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) in this mould. Afterwards with the help of a Straight fissure diamond bur a standardized size (4 cm length x 4 cm width) class IV defect was created on all 50 specimens and then they were allocated to 2 groups, Group A & B. 25 specimens for each Group (N = 25). Group A was restored using conventional Direct Polychromatic Layering technique and Group B was restored using the “Index cut-back” Technique. Shade Outcome and Translucency were evaluated using Spectrophotometer and Time taken was evaluated using a stop-watch chair side.

Results

There was a significant difference in the values (P < .05) between Group A (Polychromatic) & Group B (Index cut-back) in terms of both Shade Outcome & Translucency; Group B showed better aesthetic values (closer to baseline) than Group A. In contrast, Time required for restoring the Class IV defects was significantly lower in Group A compared to Group B (P < .05).

Conclusion

The Index Cut-Back Technique showed superior aesthetic outcome restoring Class IV defects, however it requires a planned pre-operative course of action before executing the clinical procedure.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

1. Introduction

Restoration of anterior teeth must meet high aesthetic demands especially the Class IV defects.¹ These defects involve the inciso-proximal edges of maxillary anterior teeth.² Direct Composite restoration is the most sought-after option for restoring these defects followed by indirect restorations like Veneers, Laminates etc.^3,4 However, the invasive nature of these indirect approaches gives an advantage to the direct approach of composite restoration over them.⁵

One of the main difficulties encountered with conventional class IV direct composite restorations is the layering management in terms of three-dimensionality and shape control.⁶ The major concern is the predictability of the aesthetic outcome, which is closely linked to the clinician's skills.⁷ The Index technique is based on stamping composite directly on the tooth surface by means of a transparent index. It allows for an additive treatment without sacrificing healthy tooth tissue. It allows the clinician to shape and restore with composite, directly and separately.⁸

The “Index cut-back technique” is a complementary variant of the Index technique for class IV direct restorations. This technique presents a predictable approach to treat class IV defects as it allows for the shape and thickness of different composite layers (Enamel & Dentin) to be guided through transparent indices that have been carried out previously on a planned wax-up. The final goal is to achieve a good aesthetic outcome in an easy and fast way through a copy and paste approach.⁹

Since there is not a single study reported in the literature comparing this new “Index cut-back technique” with the free-hand Direct polychromatic composites layering, we decided to conduct a comparative in-vitro study.

2. Aims & objectives

The aim of this in-vitro study was to comparatively evaluate the aesthetic outcome; in terms of translucency and shade, of direct polychromatic layering of anterior composite restoration with index cut-back technique while restoring Class IV defects taking the baseline data with the help of a Spectrophotometer and also to compare the time taken to carry out the entire restorative procedure by using both the techniques; direct polychromatic layering technique as well as index cut-back technique.

The null hypothesis stated there will be no difference in the aesthetic outcome of direct polychromatic composite layering technique and index cut-back technique while restoring class IV defects.

3. Materials and methods

After getting the approval from the institutional ethics committee (approval number: SVIEC/ON/Dent/SSR/20003) the study was started.

3.1. Preparation of 3D mould

An extracted tooth specimen of an average Permanent Maxillary Central Incisor Crown was 3D scanned for obtaining its dimensions and measurements which, then, were transferred to AUTOCAD™ software, where the mould was customised and subsequently 3D-printed. The dimensions of this newly designed square shaped mould were: 2 cms length X 2 cms width X 1 cm height, comprising of two equal halves; Labial & Palatal (Fig. 1A, B and 1C). The Labial half consisted of 4 occlusal projections at all four corners of dimensions of 2 mm height and 2 mm width (Fig. 1D). On the other half i.e., the Palatal half had depressions/holes of 2 mm depth and 2 mm radius; corresponding to the occlusal stop son the Labial half, to receive/fit into the respective occlusal stops for the adequate seating of the two halves of the mould when positioned onto each other (Fig. 1E). The mould also had four escape vents of 5 mm length, two on each side adjacent to the mesial and distal margins of the embossed central incisor crown in the mould extending till the outer most border (Fig. 1D and E). An additional and a very important feature of this mould was a uniformly deep marking of 0.5 mm throughout on the inner surface of the walls of both the labial and palatal halves of the mould (Fig. 1F). This feature was incorporated to ensure the precise thickness of the Enamel layer on labial & palatal surface of the crown of the prepared specimens.

Fig. 1.

Preparation of 3D printed mould and restoration of group 1 specimen using free hand direct polychromatic restoration technique.

3.2. Specimen Preparation

50 samples of maxillary central incisor's crown were then prepared in this custom-made 3D mould.

3.2.1. Procedure

Firstly, the Enamel shade increment of a 0.5 mm thickness placed as a uniform layer (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) on the buccal half of the mould (with the help of the marking (Fig. 1F) provided for the uniform Enamel thickness inside the mould) followed by its curing (Woodpecker curing light). Again, the aforementioned procedure is repeated on the palatal half of the mould. This is how both the Enamel layers (Labial & Palatal) were fabricated. Now the Dentin shade composite increment (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) was placed between the buccal and palatal halves of the mould, on the cured Enamel composite intact inside, then approximating the two halves followed by its curing. Before curing, the excess composite was allowed to escape through the vents provided in the mould. Once the curing is over the prepared specimen were retrieved from the mould carefully.

Before creating the artificial GV Black's Class IV defects, one of the prepared specimens was evaluated to obtain the baseline values of Translucency & Shade outcome with a Spectrophotometer (VITA Easyshade). These values were considered as the positive control values (Fig. 1G).

3.2.2. Simulated GV Black’s class IV defect preparation

Identical Simulated G V Black's Class IV defects were created on each specimen of equal length and width (4 cm × 4 cm) in the inciso-proximal region of the prepared tooth specimen with the help of a straight fissure diamond bur (Fig. 1H) followed by creating of a short bevel of 1 mm width on prepared labial and palatal surfaces and long bevel of 2 mm width on the labial surface only (Fig. 1I and J).

3.3. Randomization

50 prepared tooth specimens were randomly allocated using computer randomization to 2 groups (n = 25 each).

3.4. Restoration of the class IV defects

GROUP A: Direct Polychromatic Composite Layering Technique.

GROUP B: ‘Index Cut-Back’ Technique.

GROUP A: In this group, the specimens with the Class IV defects were restored using the conventional direct polychromatic layering technique. Firstly, the Palatal index was fabricated using putty impression material (Fig. 1K) upon which the palatal shelf was created using Enamel shade composite (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) (Fig 1L and M). Now upon this Enamel layer, the Dentin body shade composite layer of appropriate thickness was applied and cured (Fig. 1N and O). After this the Labial Enamel layer (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) was applied by the freehand sculpturing and cured correctly (Fig 1P). Final finishing of the restoration was carried out initially with a low-grain bur to reproduce the macro-anatomy followed by a high-grain bur reproducing the micro-anatomy which was followed by final polishing using Shofu Discs (Shofu Super Snap Finishing kit) (Fig. 1Q and R).

GROUP B: The specimens in group B were restored using the new Index cut-back technique. Here firstly a wax build-up of the Class IV defects was done with mock up wax. A transparent silicone key (Exaclear, GC, India) of the full wax-up was built achieving the full ‘Enamel’ index (Fig. 2a and b). Now through a cutback step, wax thickness of 0.2 mm in the cervical third, 0.5 mm in the middle third, and 0.8 mm in the incisal third was removed from the wax build up with the help of a lacron's carver and it was confirmed with a periodontal probe. A second transparent silicone key (Exaclear, GC, India) was then built on this cut-back wax-up (the remaining wax up after removal) to achieve the cut-back ‘Dentin’ index (Fig. 2C and D). The full Enamel index was cut with a blade along the incisal edge to achieve palatal and labial Enamel indices, which were then used as guides for the palatal and labial walls of the composite Enamel build up. The Dentin shade (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) was applied on the cut-back Dentin index, and then pressed onto the specimen tooth to be restored and cured (Fig. 2F, G and 2H). Afterwards, the palatal wall was restored with Enamel composite layer (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) by means of the full Enamel palatal index. The last layering step was performed with Enamel composite layer through the full Enamel labial index; the enamel composite shade (Palfique Estelite LX5, Tokuyama Dental Corporation, Japan) was placed in the full enamel index, placed in the correct position and cured for 20 s (Fig. 2I, J and 2K). Finishing and polishing was then carried out using Shofu Discs (Shofu Super Snap Finishing kit) (Fig. 2L).

Fig. 2.

Restoration of group 2 specimen using 'Index Cut-back' technique.

4. Data evaluation & statistical analysis

Both the groups were assessed for the following parameters:

• 1.Translucency parameter (TP)

The translucency for each colour combination was determined using the following formula for the translucency parameter (TP):

TP = [(L∗ W − LB∗)2 + (a∗ W − a∗ W) 2 + (b∗ W − b∗ W) 2] ½

• 2.Shade Outcome

Translucency parameter (TP) & Shade Outcome were calculated using a SPECTROPHOTOMETER.

• 3.Time taken

Total time taken (in seconds) was calculated chairside using a stop watch.

For statistical analysis, the data was analysed using IBM SPSS 20 for windows statistical software. Statistical analysis will be done using a sample t-test. For all statistical analyses, probability levels of P < .05 were considered statistically significant.

5. RESULTS

Independent-t test was used to evaluate and compare firstly the Delta E values (change in colour) and secondly time taken for both the groups. Delta E values were obtained by a mathematical formula which incorporated the L,a,b values obtained from each specimen. The resultant Delta E Values showed significant difference between GROUP A and GROUP B for translucency and shade outcome (First Parameter) indicating that Group B showed statistically better shade outcome and translucency while Group A proved to be statistically less time consuming.

5.1. Results of individual parameters

• (1)The Translucency and Shade outcome: Results from Table-1 showed that there was a significant difference (P < .05) in the values of both Shade Outcome &Translucency between both Group A and Group B. As the Delta E values of Group B (Index Cut Back Technique) were closest to the baseline readings obtained pre-operatively when compared to Group A (Direct Polychromatic Layering), hence Group B showed aesthetically superior outcome.
• (2)Total Time Taken: Results from Table-2 showed that there was a significant difference (P < .05) for the parameter of time taken between Group A and Group B. Group A showed significantly less time taken to complete the restorative technique when compared to Group B.

Table 1.

Independent T-Test analysis for Comparison of mean L, A & B parameters (Shade outcome and Translucency) between both the groups.

Group	N	Mean Delta E	Std. Deviation	Std. Error Mean
Group-A	25	6.107	2.144	0.678
Group-B	25	2.084	0.982	0.311

Mean Difference	t-value	df	P-value	95% Confidence Interval of the Difference
				Lower	Upper
4.023	5.394	18	<0.001	2.456	5.589

Table 2.

Independent T-Test analysis for Comparison of mean Time Taken between both the groups.

Group	N		Mean Time (in min)	Std. Deviation	Std. Error Mean
Group-A	25	4.917		0.544	0.172
Group-B	25	6.565		0.494	0.156

Mean Difference	t-value	df	P-value	95% Confidence Interval of the Difference
				Lower	Upper
−1.648	−7.088	18	<0.001	−2.136	−1.159

6. Discussion

One of the main difficulties in approaching a class IV direct composite restoration is the management of composite layers three-dimensionally because two different composite materials need to be handled: (1) the dentin, which is the inner body mass (2) the enamel, which is placed to create palatal, buccal, and interproximal surfaces. The lack of guided layering management can lead to colour matching failure. For example, under-application of dentin layer results in a thicker enamel layer, which may cause a final greyish effect. This does happen with many enamel composite masses when the thickness of the layer increases.^{10, 11, 12, 13, 14}

The index cut-back technique, which is a complementary approach to the index technique for class IV direct restorations, is a procedure that allows the clinician to previsualize – through a double wax-up (full as well as cut-back) – the dentin composite and the enamel composite thicknesses, besides the shape, for a class IV restoration. From the full and the cut-back wax-up, two different transparent indices are obtained. This procedure allows for the control of the correct amount of dentin and enamel, as planned preoperatively by the clinician according to the diagnostic data, as well as the material employed. Along with the predetermination of the different composite material thicknesses that have to be managed, another interesting aspect associated with this approach is that the shape can also be predetermined and can easily be achievable. Basically, there are two aspects to a restoration, firstly shade matching and secondly thickness of the layers. In our technique, the layering aspect plays a predominant role over the shade matching because of the following reasons:

• •As enamel composite layer is translucent, when placed in thin layers it reflects the colour of the underneath dentin layer.
• •However, on increasing the bulk of the enamel layer, the increased thickness hinders with the reflection of the underneath layer and reduces the translucency.

The driving force behind this index cut-back technique is an easier management of the restoration, which is made possible by the transparent guiding indices. This leads to a more predictable final result, independent of the clinician's skills. This technique, despite having more steps, ensures an exact and repeatable reproduction of dentin and coronal anatomy. Above all, it once again demonstrates the versatility of modern composite systems when applied to innovative clinical protocols. Interestingly, with the advent of ‘Single shade’ composite materials,^15,16 where the shade matching step is eliminated, this ‘index cut-back technique’ becomes more relevant now because now the control on the thickness of the restorative material plays an important role in final aesthetic outcome.

Talking about the total time taken to carry out both the techniques, the index cut-back technique proved to be more time consuming than the polychromatic restorative technique. The obvious reason for that is that the index cut-back technique involves a greater number of steps. This parameter is of clinical significance because it increases the chairside time for this technique in clinical scenario, but it is expected that, as the clinician masters this technique over a period of time, the time taken can be reduced.

7. Limitations of this studys

As it is an In-vitro study, its correlation with clinical trials could vary. An In-Vivo prospectus of the same technique needs to be explored with the requirement of a portable spectrophotometer.

8. Conclusion

Under the limitations of the present study, it could be concluded that:

• 1.The Index Cut Back technique displays a more controlled way of managing the layering of direct composite restorations when to conventional polychromatic restorations.
• 2.However, the time to bring the direct composite restoration to life with index cut back technique as compared to its polychromatic counterpart is a drawback that needs to be tackled.

9. Future perspectives

Further clinical trials are required to validate this technique and explore its future applications in aesthetic and restorative dentistry.