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P. Jain, M. Gupta (eds.)Digitization in Dentistryhttps://doi.org/10.1007/978-3-030-65169-5_10

10. Digitization in Operative Dentistry

Mahantesh Yeli¹ and Mohan Bhuvaneswaran^{2, 3}

(1)

Department of Operative Dentistry and Endodontics, SDM College of Dental Sciences, Dharwad, India

(2)

Sri Ramachandra University, Chennai, India

(3)

MAHSA University, Petaling Jaya, Malaysia

Keywords

Restorative dentistryCAD/CAMCERECMillingCaries detection

10.1 Introduction

There has been tremendous advancements and innovations in the field of material science, technology and adhesive dentistry which has brought about a sea of change in the way we practice dentistry today. Transformations from the traditional dentistry to digital dentistry are making far-reaching consequences to patient care and also affecting the landscape of digitization of operative dentistry [1]. The CAD/CAM concepts were introduced into dental applications by Dr. Francois Duret in Lyon France in the year 1973. He later developed and patented the CAD/CAM device in the year 1984. Digital impressions were first used in orthodontics, but the use of the first intraoral scanner in restorative dentistry was in the 1980s by a Swiss dentist, Dr. Werner Mormann, and an Italian electrical engineer, Marco Brandestini. They further developed the concept which was introduced in 1987 as CEREC (Sirona dental systems) as the first commercially available CAD/CAM system for dental restorations [2].

The chapter will give a brief introduction about caries detection methods, which have already been introduced to the reader at the beginning of the book, and then guide through the digital processing of a ceramic inlay talking about all the steps from tooth preparation, digital impression taking, data processing and manufacturing/milling to try in and cementation. Subtraction and additive methods of digital manufacturing will also be discussed at the end of the chapter in brief. It is beyond the scope of this book to explain each and every digital technique currently available in detail, but every attempt has been made to introduce the reader to them.

10.2 Digital Caries Diagnosis and Assessment

The carious lesion is a dynamic process, which is affected by numerous factors and varied aetiology. These factors tend to move the equilibrium either towards remineralization or demineralization [3], and as there is greater understanding regarding the advancements and the evidence supporting the carious process, it becomes more imperative to look for preventive measures which preserve the function, aesthetics and structure of the tooth.

The inability to detect early lesions leads to deep enamel caries, resulting in poor outcomes of the remineralization process, so methods have to be devised to quantify early mineral loss and to initiate correct intervention [4]. The traditional caries detection systems facilitated a more qualitative aspect of the disease progress, such as colour and anatomical location [5], and modifying factors like oral hygiene, salivary flow and microorganisms. These assessments gave limited information for early detection of noncavitated lesions; hence, the newer novel diagnostic systems offer true quantification and detection of lesions in the initial stages.

These newer detection systems work on the physical signals that include electronic current, x-rays, lasers, visible light and ultrasound (Table 10.1). These systems should be able to initiate, receive and interpret the signals so that the caries detection systems perform effectively [6].

Table 10.1

Methods of different caries detection based on their underlying principles

Medium of energy source	Clinical applications
X-rays	• Digital subtraction radiography • Digital image enhancement
Visible light	• Fibre optic transillumination. (FOTI) • Diode laser fluorescence (DLF) • Digital imaging fibre optic transillumination (DiFOTI)
Laser light	Laser fluorescence measurement (DIAGNOdent)
Electrical current	Electrical conductance measurement (ECM)
Ultrasound	Ultrasonic caries detector

10.3 Electrical Current Measurement

10.3.1 Electronic Caries Monitor (ECM)

The ECM works on single fixed-frequency alternating current which measures the ‘bulk resistance’ of the tooth tissue. The ECM probe is applied on a particular site or surface level at 5-second measurement cycle (Fig. 10.1). The ECM works on the principle of increased porosity associated with caries which is responsible for the mechanism of action of ECM [7].

../images/482337_1_En_10_Chapter/482337_1_En_10_Fig1_HTML.jpg — Fig. 10.1

The ECM device (Version 4) and its clinical application. (a) The ECM machine, (b) the ECM handpiece, (c) site-specific measurement technique, (d) surface-specific measurement technique. (*Reproduced with permission from Elsevier Publishing*) [6]

10.4 Radiographic Techniques

10.4.1 Digital Radiographs

A digital radiograph is a conventional radiograph which is digitized and comprises a number of pixels, each pixel carries a value of 0–255, with 0 being black and 255 being white [6] (Fig. 10.2) the values in between represent shades of grey. The digital radiographs offer potential of image enhancement by applying range of algorithms, so when these radiographs are assessed, their diagnostic value is as equivalent to that of conventional radiographs [8]. Other additional benefits include decrease in radiographic dose and replication and archiving of images. Detailed information about the digital radiographs is given in Chap. 3.

../images/482337_1_En_10_Chapter/482337_1_En_10_Fig2_HTML.jpg — Fig. 10.2

Radio visiography

10.4.1.1 Subtraction Radiography

Digital radiographs have numerous advantages like image enhancement, processing and manipulation. The most important advancement in radiographic technologies is the development of subtraction radiography in the detection of caries and assessment of bone loss in periodontics. The principle is that two radiographs are compared using their pixel values and any difference in the values might be due to change in the object (Fig. 10.3).

../images/482337_1_En_10_Chapter/482337_1_En_10_Fig3_HTML.jpg — Fig. 10.3

(a) Radiograph showing proximal lesion on the mesial surface of the first molar, (b) follow-up radiograph taken 12 months later, (c) the areas of difference between the two films are shown as black, i.e. in this case, the proximal lesion has become more radiolucent and hence has progressed. *(Reproduced with permission from Elsevier Publishing)* [6]

10.4.1.2 DiFOTI

A new reliable method for detecting dental caries, where images of teeth are captured through visible-light is the fibre optic transillumination with CCD camera which are relayed to the computer for analysis with predetermined algorithms. The algorithms are developed to facilitate the location and diagnosis of carious lesions in real time which provides quantitative characterization for monitoring of lesions [9] (Fig. 10.4).

../images/482337_1_En_10_Chapter/482337_1_En_10_Fig4_HTML.jpg — Fig. 10.4

DIFOTI working principle

10.5 Fluorescent Techniques

10.5.1 QLF (Quantitative Laser Fluorescence)

QLF is an optical diagnostic technique for the detection of early carious lesions in enamel. In 1998, Ferreira Zandona et al. used QLF technology for the very first time to assess caries on occlusal surfaces. Characteristic features of the technique are the detection, quantification and analysis of the lesion.

10.5.1.1 Working Principle

QLF uses the natural fluorescence of teeth to differentiate between sound enamel and carious lesion. In a white-spot lesion, there is the disintegration of the crystalline structure resulting in more internal reflection sites. This results in the increased scattering of incident light which implies that the mean ‘free path of photon transport’ inside a lesion is shorter than in sound enamel. A lesion observed with QLF appears dark compared to highly luminescent sound enamel. Table 10.2 gives its benefits and drawbacks.

Table 10.2

Advantages and disadvantages of QLF

Advantages	Disadvantages
• Noninvasive diagnostic tool • User-friendly • Reproducible and reliable method of quantifying mineral loss in enamel • Exhibits high sensitivity and specificity	• Not a confirmatory diagnostic tool • Not suitable for use on proximal lesions • Plaque, calculus, and extrinsic stains obstruct detection of lesion • Fluorosis and developmental defects give a similar appearance as a white-spot lesion

Advantages

Disadvantages

• Noninvasive diagnostic tool

• User-friendly

• Reproducible and reliable method of quantifying mineral loss in enamel

• Exhibits high sensitivity and specificity

• Not a confirmatory diagnostic tool

• Not suitable for use on proximal lesions

• Plaque, calculus, and extrinsic stains obstruct detection of lesion

• Fluorosis and developmental defects give a similar appearance as a white-spot lesion

10.5.1.2 Uses

Detection of early carious lesions in enamel in conjugation with ICDAS.
Detection and differentiation of noncavitated root caries on root surfaces.
Detection of early secondary caries adjacent to existing restorations.
Detection of white-spot lesions after de-bracketing in orthodontic patients.
Localization of enamel cracks and quantification of their severity.
Assessment of severity of tooth wear and monitoring its changes in clinical situations.
Measure the efficacy of treatment in patients, e.g. remineralization of a white-spot lesion.

10.5.1.3 DIAGNOdent

The DIAGNOdent is a device which utilizes fluorescence to detect caries. A red light is produced with the excitation of the laser at a wavelength of 655 nm which is designed to be delivered to pits and fissures and the smooth surfaces by one of the two intraoral tips. The tips emit the light and record the resultant fluorescence. The DIAGNOdent (Fig. 10.5) doesn’t produce an image unlike the QLF, but displays a numerical value. Spitzer and Bosch (1975) suggested that when subjected to certain wavelengths, carious lesions emit more intense fluorescence than sound tissue due to organic compounds and proteinic chromophores in the affected tooth tissue. The DIAGNOdent produces a single-digit reading (0–99) and relies on the principle of validation that has high sensitivity for detecting early carious lesions [10].

../images/482337_1_En_10_Chapter/482337_1_En_10_Fig5_HTML.jpg — Fig. 10.5

DIAGNOdent

10.6 Digital Restoration Workflow- the CAD/CAM Technique

This section will talk about the steps required for the fabrication of a CAD/CAM restoration, namely, the digital restoration workflow, beginning with the tooth preparation to digital impressions taking to data processing and manufacturing to finally try in and cementation.

There are mainly three phases in the digital workflow:

1.

The first phase is to record the geometry of the patient’s intraoral status to a computer system using an intraoral camera. This is called as digital impression.
2.

The second phase uses a software program to design and construct the volume proposal of the restoration.
3.

The third phase involves the production of the restoration using a machining device [11].

10.6.1 Tooth Preparation for Digital Restorations/CAD/CAM Inlay or Onlay

The aesthetic inlay or onlay procedures using ceramic and composites began to be used in 1980s to counter the drawbacks of amalgam and direct composite restorations. The recent advances in adhesive dentistry coupled with material advancements in stacked, feldspathic porcelain were vital in addressing the deficiencies associated with direct composite like high wear, high shrinkage, low strength and technique sensitivity. The lab-fabricated ceramic and processed indirect composites had better physical properties, contacts and contours, and ideal proximal contacts and potential for better and efficient occlusal contacts; restorations and guidelines are based on the type of restorative material used for the particular type of restoration [12]. Tables 10.3 and 10.4 gives the indications, contraindications, advantages and drawbacks of using the technique. According to the author, there is not much demarcation between the digital CAD-CAM and conventional method of tooth preparation.

Table 10.3

Indications and Contraindications of CAD/CAM restorations

Indications	Contraindications
• Indirect tooth-coloured restorations are indicated in class 1 and class 2 (inlays and onlays) which are located in aesthetic areas as desired by the patient • Extensive carious lesions or large defects, (class 1 and class 2) with wide facio-lingual or mesiodistal caries and teeth which require cuspal coverage	• High occlusal forces, ceramic restorations which are subject to excessive occlusal stress for, e.g. bruxism or clenching habits • Isolation • Deep subgingival preparations, where margins are difficult to record in digital impressions and are difficult to evaluate and also for finishing and polishing

Indications

Contraindications

• Indirect tooth-coloured restorations are indicated in class 1 and class 2 (inlays and onlays) which are located in aesthetic areas as desired by the patient

• Extensive carious lesions or large defects, (class 1 and class 2) with wide facio-lingual or mesiodistal caries and teeth which require cuspal coverage

• High occlusal forces, ceramic restorations which are subject to excessive occlusal stress for, e.g. bruxism or clenching habits

• Isolation

• Deep subgingival preparations, where margins are difficult to record in digital impressions and are difficult to evaluate and also for finishing and polishing

Table 10.4

Advantages and disadvantages of CAD/CAM restorations

Advantages	Disadvantages
• Improved physical properties • Varieties of materials and techniques • Wear resistance • Reduced polymerization shrinkage • Support of remaining tooth structure • More precise control of contact and contours • Biocompatibility and good tissue response	• Increased cost and time • Technique sensitivity • Difficult try in and delivery • Brittleness of ceramics • Wear of opposing dentition • Low potential for repair

Advantages

Disadvantages

• Improved physical properties

• Varieties of materials and techniques

• Wear resistance

• Reduced polymerization shrinkage

• Support of remaining tooth structure

• More precise control of contact and contours

• Biocompatibility and good tissue response

• Increased cost and time

• Technique sensitivity

• Difficult try in and delivery

• Brittleness of ceramics

• Wear of opposing dentition

• Low potential for repair

10.6.2 Principle of Inlay and Onlay

10.6.2.1 Outline Form

The outline form is generally governed by the extension of caries and existing restorations and is quite similar to the conventional metal inlay/onlay preparations, as the cavity preparation is dictated by the principles of adhesive dentistry employed; undercuts are avoided or blocked by resin-modified GIC and by preserving most of the enamel for adhesion.

Most of the undermined enamel or weakened enamel should be eliminated; the central groove reduction of 1.8 mm (occlusal surface) should follow the anatomy of the unprepared tooth surface. The outline should avoid occlusal contacts and have a clearance of 1.5 mm in all excursions to prevent ceramic fracture.

The box should be extended to allow for a minimum of 0.6 mm of proximal clearance for ease of impression making, margins are preferably kept supragingival for better recording and accuracy of a digital impression and also luting and finishing procedures. The width of the gingival seat should be approximately 1 mm. To prevent stress concentration all the internal line angles and point angles should be rounded and also to prevent voids during the cementation procedure.

10.6.2.2 Margin Design

Ceramic inlay margins are given a 90-degree butt joint; bevels are contraindicated as the margins need bulk of ceramic to prevent fracture. A heavy chamfer is recommended for ceramic onlay margins.

10.6.2.3 Occlusal Clearance

A clearance of approximately 1.5 mm is needed to prevent fracture in all excursions. This can be evaluated by using a dial caliper [13]. The principles of cavity preparation for aesthetic inlays differs from the gold restorations. In aesthetic inlay/onlay restorations, bevels and retention forms are not required, and resistance form is necessary for only large onlay restorations. An estimation of 5–15 degrees of flare is given on the cavity walls, and butt joint is given on the gingival seat/floor. All the internal line angles are rounded and a minimum of 2 mm isthmus width is given and depth of 1.5 mm (Fig. 10.6).

../images/482337_1_En_10_Chapter/482337_1_En_10_Fig6_HTML.jpg — Fig. 10.6

Inlay preparation

The functional and the nonfunctional cusps are given at least 1.5–2 mm of clearance so as to achieve bulk of material in these areas; if the margins of the onlay are visible on the buccal/facial side, then there can be further reduction of 1–2 mm with a minimum of 1 mm chamfer (Fig. 10.7).

../images/482337_1_En_10_Chapter/482337_1_En_10_Fig7_HTML.jpg

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10. Digitization in Operative Dentistry

10.1 Introduction

10.2 Digital Caries Diagnosis and Assessment