Sandwich technique restoration in posterior teeth – case report

Introduction

Dental caries represents one of the most common diseases in humans, its prevalence being estimated at approximately 90% of the entire population. In Global Oral Health Status Report (2022), World Health Organization (WHO) considers that 2 billion people suffer from caries of permanent teeth and 514 million children suffer from caries of primary teeth⁽¹⁾.

As a result, dental medicine is a field with great responsibilities in human care, and all new technologies and scientific discoveries are immediately introduced and applied. New bioactive and regenerative materials and improved adhesion techniques are being used for dental caries adherent restorations. Adhesive dentistry has changed the old Black’s principles of cavities preparation, and the actual concept is minimal intervention, in respect for sound dental structures⁽²⁾. For molars and premolars, the first restorative criterion is functionality, being the masticatory area, but esthetic restorations are increasingly requested by the patients. The modern approach in restorative medicine implies to focus, at the same time, also at the biological and mechanical properties and the longevity of restorations⁽³⁾. As a result, over time, a large number of technique and working protocols have been developed, in order to counterbalance the limitations of a certain restorative materials or to improve their qualities and benefits.

Resin composites are currently the materials of choice for all types of direct and indirect restorations. To reduce their specific and problematic shrinkage through polymerization, various insertion techniques have been proposed, the layering method being the most widely used. Also, a number of restorative techniques using different dental materials have emerged over time^(4,5).

The sandwich technique

The sandwich restorative dental technique was developed by McLean and Wilson, in 1977, shortly after the introduction of glass ionomer materials, around 1970^(6,7). The idea was to obtain a dental restoration that combines and reproduces both the specific properties of dentin, as well as the enamel. So, the glass ionomer has been proposed as a dentin substitute, and the resin composite plays the role of tooth enamel. A monolithic structure was achieved, with far better results than using just one dental material type^(8,9).

The sandwich technique is a layering restoration method using different dental materials, the first layer being usually represented by glass ionomer cement, and the second by composite resin. There are two variants of this technique:

• Closed sandwich – the glass ionomer is not placed up to the external coronal surface, and it is not in contact with the oral environment, and the base restoration, represented by glass ionomer, is completely covered by the resin composite material.
• Open sandwich – the glass ionomer is placed up to the external coronal surface, in direct contact with the oral environment. It is indicated in case of restorations that extend in the subgingival area, where there is a small amount of enamel or this is completely absent due to the dental caries location and evolution (radicular caries), and the resin composite adhesion cannot be obtained properly. Glass ionomer cement exhibits a chemical bond to all dental tissues through a chelation reaction between the carboxyl groups of the polyacrylic acid and the calcium in the hydroxyapatite crystals.

In the sandwich technique, the glass ionomer material is often replaced with resin modified glass ionomer due to the improved properties of this one⁽¹⁰⁾.

The glass ionomer cements possess very good biocompatibility, chemical adhesion to dental structures, release fluoride ions, have lower setting shrinkage but, unfortunately, not very good esthetics, finishing properties and wear resistance, all these making them very similar to dentin⁽¹¹⁾. On the other hand, resin composites present excellent wear resistance, appearance, fracture resistance and polishability⁽¹²⁾. The sandwich technique is one of the most important methods of reconstruction of hard tooth tissue loss, given the fact that it minimizes the polymerization shrinkage of resin composite by using a reduced amount of resin. The proportion in which the two materials are placed inside the cavity are different: the glass ionomer is used in accordance with the quantity of dentin loss (in medium and deep cavities, an important volume), and resin composite is placed at approximately 2 mm depth, comparable to enamel morphologic thickness.

Case report

In this article, we present the treatment of a posterior dental lesion with direct adhesive materials using the sandwich technique. A male patient (16 years old) presented to the dental practice for restoration of a dental caries located on occlusal surface in tooth 26. The initial aspect suggested a limited hard tissue loss, associated with dental sensitivity triggered by different physical stimuli, like sweet, cold and sour (Figure 1).
 

The treatment steps started with:

• professional brushing for removing the dental plaque from teeth surfaces;
• establishing the proper color shades of resin composite;
• ensuring proper dental isolation with a rubber dam (secondary caries are prevented by avoiding salivary liquid to penetrate and remain inside the prepared cavities, and at the same time, we prevent altering the dental material properties by humidity)⁽¹³⁾.

After these initial stages, we proceeded to completely remove the necrotic tissues inside the tooth 26 dental caries. We obtained two separated occlusal cavities. The specific transverse oblique ridge was maintained, being unaffected (Figure 2).
 

Then, the cavity disinfection was achieved in order to reduce and eliminate, if possible, the microbial remaining load after cavities preparation and, thus, to prevent secondary caries⁽¹⁴⁾. We used the wide-spread 2% chlorhexidine, which is considered the gold standard for this goal, being the most active antimicrobial substance against Streptococcus mutans⁽¹⁵⁾.

The restorative sandwich method we chose for this clinical case used two adhesive materials. The first one was glass ionomer cement Ketac™ Molar Easy Mix (3 M ESPE), generally used as a substrate both for open and closed sandwich technique, and known for releasing fluorides. It presents high compressive strength and bond strength for lasting durability. The second material was the resin composite Filtek™ P60 (3M ESPE), a light-cured micro-hybrid radiopaque composite resin which possesses superior condensation capacity, low polymerization shrinkage, and short polymerization time. It is specifically designed for restorations in the posterior area, given its excellent mechanical resistance and improved resistance to wear. The glass ionomer cement was prepared by hand-mixing and inserted into the profound areas of dental cavities in a continuous layer covering the pulpar walls in 1.5 mm thickness (Figure 3).
 

For resin composite insertion, we first followed the specific dental adhesion steps using total-etch technique, which provide dentin and enamel adhesion and, also, to previously inserted glass ionomer cement (37% orthophosphoric acid Alpha Etch 37™ Etching gel). After removing the acid by washing the cavities, a gentle drying of dental cavities walls was done, and the adhesive system was applied and light cured for 20 seconds (Single Bond Universal, 3M ESPE). The final layer of sandwich restoration consisted of resin composite in A2 shade, which was inserted and completely covered the glass ionomer, restoring occlusal morphology. After light curing, the occlusal adaptation was performed using diamond burs. Then, in the polishing step of treatment, we used rubber cups and polishing discs in order to obtain a smooth surface restoration, which is equally comfortable for the patient and also prophylactic, diminishing the microfilm deposition and the accumulation on dental restoration (Figure 4).
 

Conclusions

The sandwich technique is a common dental restoration procedure, but the working protocol must be rigorously followed for both used materials, for good results. The major advantage is represented by the monolithic structure we obtained by using two different adhesive materials, which reproduce dentin and enamel properties, providing dental pulp protection, high strength and wear resistance, thus a long-life span restoration in oral cavity. 
 

Acknowledgements. For this article, all the authors have equal contributions.

Autori pentru corespondenţă: Sânziana Scarlatescu E-mail: sanzianas@gmail.com

CONFLICT OF INTEREST: none declared.

FINANCIAL SUPPORT: none declared.

This work is permanently accessible online free of charge and published under the CC-BY.