**Clinical paper** 
Naturally aesthetic restorations and minimally invasive dentistry.

ABSTRACT

The risks of iatrogenic actions when we apply therapies to the tooth itself, or to collateral teeth, are potentially high when combined with low sensitivity and specificity of our diagnosis tools. There are therapeutic tools, both for the occlusal and proximal surfaces, in the form of infiltration products, specific inserts for cavity preparation, a fluorescent camera for magnification and early detection, and others; however, preservation of the natural tooth aesthetics also requires early detection of the carious lesion, associated with comprehensive patient care so that our therapies are perpetuated.  The purpose of this article is to discuss the advantages and drawbacks of minimally invasive dental techniques, distinguishing those that preserve or reinforce the enamel and enamel-dentine structures (MIT1) from those that require minimum preparation of the dental tissues (MIT2).  The discussion is rounded off by an illustration of how the natural tooth aesthetics are preserved in two clinical cases. 

CLINICAL SIGNIFICANCE

A minimalist therapeutic approach aiming to preserve the natural tooth aesthetics.
 
Key words: sono-abrasion, Icon, minimally invasive techniques, natural aesthetics


Natural esthetic restorations and minimally invasive dentistry.

INTRODUCTION
Approaches in dentistry unfortunately all too often employ damaging prosthetic techniques, rather than a real philosophy of preserving the dental tissues. The major problem is the ability to inhibit the progression of the carious lesion as early as possible, thereby achieving maximum preservation of the natural tooth aesthetics and structure. This involves gaining a better knowledge of the carious process so as to intercept it better, and determining the therapeutic tools enabling us to treat the carious lesion as early as possible and with minimum invasion. Dental caries is a complex and multi-factorial disease resulting in lesions that affect enamel, dentine, pulp, and even cementum if the root portion of the tooth is involved. Caries are accompanied by tissue changes in the affected primary dentine and an inflammatory reaction in the pulp [1]. The development of a carious lesion is an intermittent cause of demineralization interspersed with remineralization. Under unfavorable conditions, the lesion process is referred to as active, with dull, white enamel and soft, yellowish dentine [2,3] . However, under favorable conditions including sensible diet, accurate excavation of the infected tissue, cariostatic sealed restorations, or even with incomplete removal of the carious dentine and good oral hygiene, the process may be reversed, and is referred to as arrested, even in the deep part of the lesion [2,3,4]. Whatever the type of lesion, depending on the size and pulp proximity of the lesion, various types of caries extension have been described [5,6] which can dramatically interfere with the esthetic goals during the restorative steps. In fact the first main goal and difficulty is to intercept the carious process quickly and to remove all the infected dentine accurately in a complex shaped cavity [7] without injuring sound dentine and pulp, whilst preserving occlusal or proximal dental tissue and the marginal ridge, and providing favorable aesthetic and biological conditions. The caries process can be reversed as long as the surface layer remains intact, and in the case of proximal surfaces, perfect diagnosis of the structural integrity of the enamel layer remains very difficult. Specifically, traditional Class 2 restoration usually leads to reduced tooth stiffness of around 30%  [8], and dramatically increases the difficulties of the restorative procedure in terms of  acceptable contact areas and natural aesthetics (choice of composite type, shade and shape of restoration) [9]. There are a host of dramatic risks inherent in iatrogenic actions: damaging collateral teeth faces during preparation, excessively mutilating preparation, poor control of dentine excavation, secondary infection due to absence of a dental dam, etc.

A variety of strategies have also been employed to minimize or eliminate microleakage in Class 2 restorations: 
• Light-focus-tip polymerization devices concentrating the light to the ends of optical fibers [10].  
• Incremental filling methods using self-cure or flow composite, etc. [11].
• Decoupling techniques [12].
• Several soft or pulse delay polymerization devices [13].

All of the above have been identified as strategies which increase the marginal seal and the degree of conversion of various composite resin restorative materials, but none have gained universal acceptance [14,15]. 
There are many new products now available with the aim of remineralization and reversing the caries dynamic. Their systematic use should be promoted, since they have the advantage of maintaining and improving aesthetics, being less damaging, and above all, most of their actions are reversible [16,17,18].

The general philosophy of the patient centred approach is also of crucial importance. Indeed, all the techniques described below can only be applied within a medical approach of determining the patient’s caries risk via a Cariogram [19], CAMBRA (Caries management by risk assessment) [20,21] or MITP (Minimally Invasive Treatment Plan, GC Europe) [22]. The threshold of intervention seems to be whether there is a cavitated lesion; and we must also have the tools enabling correct detection and diagnosis. The choice between the preventive care advised (PCA) and the preventive and operative care advised (P&OCA) will depend on this decision [6,23,24,25]. Therefore we can divide our preventive and minimalist therapies into 2 groups: the first (Minimally Invasive Treatment 1 or MIT1) for treating enamel and enamel-dentine lesions without any preparation, provided that there is no surface cavitation (radiographic lesion depth classification according to bitewing X-rays from E1 to D1 included). The second group (Minimally Invasive Treatment 2 or MIT2) is for treating early enamel-dentine lesions with surface cavitation (from D1 with cavitation to D2). From D3 onwards, a more conventional therapeutic approach is advisable.

The challenge is to intervene early and on a minimal basis, to achieve maximum preservation of the natural tooth aesthetics.

Regarding the second group, changes in restorative techniques such as the use of micro-burs (e.g. minimally invasive set, Intensive, Grancia, Switzerland; Komet, minimally invasive bur set, Lemgo, Germany), laser technique, air abrasion device, sonic and ultrasonic preparations, could also partly prevent these problems, and facilitate the use of ultraconservative restorations for all carious lesions reaching the first third or the middle third of dentine (Hume and Mount, 1997) with cavitation. If we focus on sonic techniques, both ultrasonic and sonic are useful in minimally invasive procedures. These devices are similar and could be used in combination with other techniques (e.g., air-abrasion, ozone treatment, photoablation, antibacterial therapy, etc.) [27,27,28].

Another main point is the usefulness of visual aids or other diagnosis tools [29]: indeed, preservation of aesthetics is directly correlated with how early the lesion is detected, especially in the proximal zones, as well as through a minimalist approach in all the restorative phases.  
Processes aiming to detect carious lesions in the initial stage with optimum sensitivity and specificity employ a variety of technologies, such as loupes, laser fluorescence and autofluorescence, electric current/impedance, tomographic imaging, and image processing [30]. Despite the availability of these technologies, their high cost, physical size, excessively variable sensitivity and specificity have prohibited their use on a daily basis unlike conventional diagnosis tools, such as film or digital radiography [30]. These different means of analysis are also dependent on the clinicians’ experience and proficiency in viewing magnified images using a magnifying glass or microscope. Conventional strategies for caries detection, such as visual observation or probing with a dental instrument, are unfortunately based on subjective criteria [31]. In the present cases, clinical decisions were based on the LIFEDT (Light Induced Fluorescence Evaluator for Diagnosis and Treatment) concept (Table 1) (Soprolife camera, Sopro, La Ciotat, France) which combined magnification, fluorescence and visual signal amplification to assist clinicians with the assessment of tooth structure [32,33]. These principles call for a comprehensive patient approach in terms of caries risk assessment, diagnosis, and appropriate therapies that are consistent with the concepts of minimally invasive dentistry (MID), or Minimal Intervention (MI), terms accepted by the World Dental Federation in 2000 [34].
The present review was undertaken to evaluate the clinical advantages and disadvantages of minimally invasive techniques (MIT) (Table 2) in such a way as to promote natural dental aesthetics whilst preserving dental tissue, and to describe an intermediate operating interval postponing conventional operative and prosthetic dentistry.