Fig.1
In today’s post-amalgam era, we often end up coping with cracks more than with caries. In this case, an old amalgam filling presented marginal leakage and a distal ridge fracture. A crack was visible at the distal marginal ridge.

Fig.2
The arrows on the distal marginal ridge show the crack, suggesting that it might have propagated deeper into the tooth.

Fig.3
Upon removing the amalgam and sandblasting with 29 µm aluminum oxide via the Aquacare system, the crack was seen to extend mesially. It was clearly not a natural enamel fissure.

Fig.4
After removing the crack entirely, the cavity was found to be very shallow—barely extending beyond the enamel floor.

Fig.5
Selective enamel etching was done, followed by 30 seconds of rubbing Scotchbond Universal Plus (Solventum) into the cavity.

Fig.6
A thin layer (<0.5 mm) of flowable composite (Filtek Bulk Fill Flowable, Solventum) was used to hybridize the dentin.

Fig.7
With the Condensa Dark Diamond instrument (LM Dental, Finland), paste composite (Filtek Universal, Solventum) was condensed along cuspal slopes of the remainder of the tooth. This step is crucial and will define about 90% of the final shape. Pulling composite over cusps while packing, following their angulation helps with condensation and avoids over- or underfilling, making it easy to remove any excess material.

Fig.8
This is the result after condensing the composite in the cavity and having followed the cusp slopes.

Fig.9
The standard Essential Lines protocol is followed by marking the center of the tooth using the sharp tip of an instrument—in this case, the LM Arte Fissura Dark Diamond (LM Dental, Finland). Since we are working on a lower second molar, the center can be located by drawing lines that connect the cusp tips (as shown by the dotted lines). However, when viewing the occlusal plane from an angled perspective, it’s easy to misplace the center—this would have happened if I had followed the lines as initially drawn. Therefore, it is essential to determine the center from a perpendicular angle to the occlusal plane to ensure that the center is corretcly placed.

Fig.10
From a proper occlusal view, the intersection of the crossed lines accurately reveals the center of the tooth, which serves as the starting point for defining the occlusal anatomy.

Fig.11
From a correct occlusal view, using the crossed lines, the correct center can be located and serves as the starting point for defining occlusal anatomy. From this center, lines should be drawn toward the central buccal, lingual, mesial, and distal grooves. Notice that I intentionally did not draw the lines at a 90° angle—this is the first step toward achieving a natural-looking restoration, as straight lines are rare to non-existent in nature. A certain nonchalance in drawing these lines helps mask the artificial look of a restoration. I’m far from being an artist and don’t carry a mental database of natural occlusal anatomies, so embracing a bit of imprecision is key—as long as the details are guided by the existing anatomy of the tooth.

Fig.12
By further analyzing the tooth, we can identify secondary grooves (indicated by “<”), which help create—or rather emphasize—the cuspal ridges (highlighted in blue). The Essential Lines protocol instructs us to close the initially drawn grooves using instruments of choice by gently pushing on either side of the line. This transforms the wide “canyon” into a narrow, natural-looking fissure, while still separating the distinct composite masses.
It’s important to only push back the composite along the sides of the cuspal ridges, which naturally shapes the secondary grooves or cuspal depressions. This will create high points (ridges) and low valleys (fissures or depressions) that define the occlusal table. Again, although artistry is not a requirement here, the ability to “read” the anatomy of the tooth is essential. Studying reference images and identifying key features—like the ones shown in this picture—can be extremely helpful.

Fig.13
To shape the sides of the cuspal ridges, various instruments can be used. In this case, the LM Arte Fissura Dark Diamond and a standard medium-sized microbrush are shown. I personally prefer to finish the modeling phase using a dry or slightly wetted (with modeling resin) microbrush to even out any imperfections. Using such a big and somewhat unpredicatble instrument will create wobbled, unintentional lines, thinner or thicker fissures and imperfections allowing the clinician to stop overthinking the anatomy and preventing “artistry” from taking over. In fact, I’ve found that the less I try to control the outcome, the more lifelike the restoration appears.
The composite is cured once a satisfactory anatomy has been achieved. There should be no overfilling or underfilling, and the central fissure should remain open—though very narrow.

Fig.14
A stain (OptiGlaze Red Brown, GC, Tokyo, Japan) is applied into the fissure using the Compobrush Posterior.

Fig.15
If the stain were cured at this stage, the result would not look natural—on the contrary, it would appear quite messy. The groove becomes heavily and uniformly stained due to capillarity, which causes the stain to spread throughout the entire fissure. Furthermore, because the stain alone is not filled, it would wear off quickly over time, eventually exposing and opening up the fissure. For this reason, sealing the groove with a flowable composite is mandatory. Remember: flowable is mandatory, stain is optional.

Fig.16
The ultra-fine tip of the Filtek Bulk Fill Flowable (Solventum) is ideal to insert random dots of material into the fissure. Using a dry microbrush, the flowable material is pushed into and mixed with the stain within the fissure. At this point, it’s the depth and shape of the fissure that determines how much stain remains, making the result highly unpredictable—and therefore more natural. No precise planning is involved in this step: the stain is applied throughout the entire fissure, the flowable is added on top, and everything is blended and pressed into place using a large microbrush until all excess is removed.

Fig.17
The result is a naturally stained fissure with some areas showing deep, dark staining and others displaying little to no stain. The key to this outcome is that the staining is guided by the shape of the fissure, not by the artistry of the operator.

Fig.18
The lateral view of the restoration highlights the detail that was shaped by following the natural anatomy of the tooth. Here is the result immediately after curing the flowable in the fissures.

Fig.19
The finishing and polishing steps include the use of a slow-speed diamond bur, followed by beige and pink Sof-Lex spirals (Solventum, Germany). A diamond paste and felt wheel can be used as an alternative to the pink spiral or as an additional step—though it was not used in this case.

Fig.20
A small amount of excess composite was noticed on the mesial marginal ridge when reviewing the pictures.

Fig.21
Using the LM Arte Eccesso Sharp Diamond (LM Dental, Finland), the excess was easily removed.

Fig.22
Final result after finishing and polishing. Any remaining powder in the grooves can be illiminated using light sandblasting with the Aquacare device.

Fig.23
The occlusion check reveals no high points, confirming a fully functional and natural-looking restoration. The Essential Lines protocol has great potential for creating high-quality results with minimal effort, no need for artistic skill, and a touch of nonchalance. Trying to control every step of the restoration and creating perfectly straight lines often leads to restorations that appear awkward and unnaturally man-made.

Conclusions

The Essential Lines technique is a valuable tool for all posterior restorations. However, without experience or artistic ability, achieving a natural appearance can still be challenging. Introducing a bit of controlled chaos into the protocol can quickly lead to an enhanced natural look. I suggest letting go of some control and allowing room for unpredictability.

Bibliography

1. Chiodera G. Essential Lines. 2018, www.styleitaliano.org
2. Akhundov M. Working with LM Arte Posterior Misura. 2017, www.styleitaliano.org
3. Peumans M, Venuti P, Politano G, Van Meerbeek B. Effective Protocol for Daily High-quality Direct Posterior Composite Restorations. The Interdental Anatomy of the Class-2 Composite Restoration. J Adhes Dent. 2021;23(1):21-34.