Diagnostics

In this chapter:

■ Esthetic parameters to be evaluated: step-by-step checklist

■ Time points for diagnostics, diagnostic tools

■ Conventional procedures

■ Digital procedures

■ Augmented reality in dentistry

■ Diagnostics for fixed implant-supported restorations, surgical stents

Pretreatment diagnostics is essential for predictable treatment outcomes in prosthodontics. Agreeing on the appearance of the final restoration in this early phase of the treatment is key to obtain satisfactory results in comprehensive restorative dentistry1^–4.

Patients asking for an esthetic improvement of their dental appearance may approach the restorative team with a desired outcome in mind. Yet, the desired appearance can be difficult to achieve due to anatomical or other limitations. It is a challenge for the restorative team (ie, the dentist and dental technician) to determine the desired, yet realistic outcome for the patient before the initiation of restorative treatment.

Diagnostic wax-ups on the study casts and their transfer into the patient’s mouth using silicone indexes and autopolymerizing provisional resin (mock-up out of, eg, Protemp) are useful tools to clinically communicate and test the planned treatment outcome before the treatment.

The simulation of the final outcome helps with identifying the need for preprosthetic interventions, such as orthodontic tooth movement, or surgical procedures like crown lengthening and hard and/or soft tissue grafting. Furthermore, the diagnostic mock-up can serve as a guide for minimally invasive, defect-oriented tooth preparations.

Until recently, the pretreatment diagnostics encompassed the manual fabrication of a wax-up of the desired outcome on the study casts, and its transfer into clinics by means of a manually made resin mock-up. The major disadvantage of the conventional manually made wax-ups/mock-ups is that their fabrication is time-consuming, and in general only one version of the possible treatment outcome can be tested.

Contemporary digital technologies may provide advantageous features to the increase of efficiency of the pretreatment diagnostics. This Chapter reviews the esthetic parameters to be considered in the diagnostics, and the opportunities digital technologies offer in the diagnostic phase illustrating the procedures by means of one representative clinical example.

1.4.2 Esthetic parameters to be evaluated: step-by-step checklist

At the first examination of the patient, several aspects have to be considered as Part of the pretreatment diagnostics. The evaluation starts from the assessment of the general appearance of the patient, increasingly focusing on the details which are crucial for the restorative treatment. The following all-important aspects to be evaluated are listed next, in chronological order.

Facial aspect to be evaluated

■ Shape of the face – square, ovoid, tapered

■ Profile of the patient – flat, convex, concave

■ Midline

■ Interpupillary line

Smile aspect to be evaluated

■ Lip line – gummy smile, high, average, or low lip line

■ Vertical position of the incisal edges in relation to the face and the lip line

■ Horizontal position of the incisal edges in relation to the interpupillary line

■ Position of the dental midline in relation to the facial midline – potential midline shift

■ Angulations of the dental midline in relation to the facial midline and the interpupillary line

■ Outline of the incisal edges – straight, positive curve, negative curve

■ Exposure of posterior teeth

■ Buccal corridor

Tooth-related aspect to be evaluated

■ General shape of the clinical crown – square, ovoid, tapered

■ Size of the clinical crown – height, width, and the relation between height and width

■ Intratooth relation – size of the lateral incisor in relation to the central incisor and size of the canine in relation to the central and lateral incisors

■ Incisal edges steps

■ Tooth color – hue, value, chroma

■ Surface texture – smooth, pronounced

■ Characterization of the crown – translucency, spots, microcracks

Soft-tissue-related aspects to be evaluated

■ Position and curvature of the facial soft tissue

■ Soft tissue color and texture

■ Papillae – intact, reduced papilla height, missing, hyperplastic

After having evaluated these aspects clinically and on standardized extraoral and intraoral photographs (see Photo Documentation Protocol, Appendix 1), the pretreatment diagnostics are performed.

1.4.3 Time points for diagnostics, diagnostic tools

Three time points exist for the assessment of the diagnostic goal.

The first and ideal time point is before any invasive treatment is performed. A medical and dental anamnesis including a detailed esthetic anamnesis is performed to understand the patient’s needs5, followed by a comprehensive extra- and intraoral examination. The restorative team gathers all the information to evaluate the clinical situation, and elaborates the need for treatment. Considering the complex and subjective nature of esthetics, an objective means for the evaluation of the tentative outcome is helpful for the decision-making process1^,3. The diagnostic wax-up serves as an objective tool for the evaluation of potential treatment outcomes3^,6^,7. It improves the communication between patient, technician, and clinician, illustrating three-dimensionally the tentative treatment outcome1^,3^,8. Commonly, the dental technician models a possible dental configuration in wax using clinical pictures and anatomical landmarks on the diagnostic cast (existing occlusal plane and length and position of the remaining teeth) as references. This process requires an undeniable amount of time and energy since the technician must integrate all the esthetic guidelines and adapt them to each individual case. The wax-up is later tried-in in the patient’s mouth to evaluate its integration into the patient’s smile and face, on what is called a diagnostic try-in. A silicone matrix made from the diagnostic wax-up serves as a negative cast for the fabrication of the diagnostic mock-up, which will be filled with autopolymerizing resin and placed over the unaltered natural teeth until polymerization. This mock-up allows the patient and restorative team to envisage and evaluate the possible restorative outcome1. This procedure, however, is only feasible in certain clinical situations and it will only be effective in situations where additive restorations are foreseen as the mock-up lies over the unprepared teeth. In cases where subtractive procedures are necessary the intraoral transfer of the wax-up will need to be performed at a later treatment stage after the preparation.

The second time point to evaluate the esthetic and functional outcome of the prospective restoration is the provisional phase. Indirect provisional restorations made in the laboratory according to the diagnostics serve as transfer of the desired treatment outcome into the clinical situation and are useful tools to evaluate the diagnostic goal (see also Part I, Chapter 8).

In the present treatment concept, conventional or digital eggshell provisional restorations are the first option. For the conventional eggshell provisionals, the technician duplicates the shapes modeled in wax into a tooth-colored resin, which then is hollowed on the internal side until only a thin outer resin layer remains. Alternatively, the eggshell provisional can be milled out of a resin ingot by means of a computer-assisted design and computer-assisted manufacturing (CAD/CAM) procedure following a virtual wax-up. These eggshell provisional restorations allow the clinician to deliver a high-end laboratory provisional during the first invasive appointment. The tentative final restoration contour is relined intraorally with autopolymerizing resin on the prepared abutments. This method saves time and costs derived from a traditional indirect provisional fabrication (impression on prepared abutments, bite registration, chair-side direct provisional production, and a second appointment to deliver the laboratory provisional), while allowing for a perfect fit of the provisional crown margins. Patients suffering from insufficient restorations or unsatisfactory dental appearances gain significantly from this direct approach, since the esthetic improvement can be perceived immediately after the initial preparation and the insertion of the provisional.

The third and last time point to determine the desired restoration design is after the final impression is performed and before the framework is produced. The patient’s and restorative team’s impression derived from the previous two diagnostic steps (diagnostic mock-up and provisional phase) are thereby taken into consideration, and a new tentative configuration is confectioned over the prepared abutments on the final cast. Using tooth-colored wax, the technician produces a wax try-in that will simulate the color and contour of the final restoration. When the case involves edentulous spans or multiple units, the wax structure can require a metal or resin framework to improve its strength. An advantage of this diagnostic maneuver lies in the plasticity of the wax, which allows for immediate modifications of possible imperfections discussed during the try-in appointment. Once the patient and the restorative team have agreed on the optimal restorative outline, the wax try-in will be used as a reference to determine the shape and thickness of framework and veneering of the final restoration.

1.4.4 Conventional procedures

As previously mentioned, high efforts are devoted to identify and mimic the desired esthetic outcome before the technician begins the final restoration production. Despite the significant amount of energy and time invested to come up with a diagnostic draft, the obtained result may not match the patient’s physiognomy or personality, or it may not represent the desired result the restorative team and the patient expected. In these cases, small changes to modify this initial draft can be attempted. However, the range of modifications is limited and often a new diagnostic version is necessary. The inability to achieve the expected esthetic diagnosis with a try-in leads to patient dissatisfaction and, even worse, professionals’ frustration and increased time and economic expenses since further diagnostic steps are necessary.

1.4.5 Digital procedures

In order to overcome the abovementioned limitations new computerized technology procedures may be helpful. Computer technology is increasingly transforming the way dentistry is being performed. CAD/CAM processes are transforming what were previously manual tasks into easier, faster, cheaper, and more predictable mechanized methods9. Current industrial product development would be impossible without CAD technologies. No engineer would consider designing a prototype layering or carving a structure manually; instead a virtual environment is used, where different versions can be tried-in without increasing significantly the time invested and with no impact on the costs. Carving shapes manually has evolved into designing volumes virtually by means of dedicated software. In restorative dentistry, the wax and modeling are evolving into software and mouse-clicks. The restorative team can profit from virtual libraries from where different tooth morphologies can be selected (Exocad, Darmstadt, Germany; 3Shape A/S; Copenhagen, Denmark; Dental Wings, Montreal, Canada; Sirona Dental, Wals, Austria). These software tools offer a high number of different tooth shapes categorized according to parameters such as size, age, or patient’s phenotype. Moreover, real teeth can be used as a reference to generate tooth morphology proposals10. These standard shapes can later be modified and adapted to individual patient situations. Working time is substantially reduced by eliminating the manual work needed for conventional waxing techniques. This allows the technician to focus solely on shapes and tooth arrangements. Furthermore, certain software enable us to integrate photorealistic 3D restorations of the patients’ face into the virtual design software11. The face is integrated by means of two-dimensional (2D) digital photographs projected onto a three-dimensional (3D) virtual skull or by means of 3D facial scanners. This allows for virtual smile design, taking into consideration important facial reference planes such as midline verticality, smile line, or the true horizontal plane. A further benefit is the possibility to rapidly modify an initial design version in order to effortlessly try-in other tooth arrangements. This grants the technician freedom to generate multiple versions of the future restoration in an efficient manner. Being able to offer different versions at a single appointment streamlines the diagnostic phase and potentially better fulfills the wishes of the most demanding patients and clinicians.

So far, subtractive CAM processes dominate dental manufacturing routines. Restorations are obtained by trimming a solid block of material into the desired 3D object, by means of a computer-controlled milling machine12. However, these procedures present several shortcomings such as waste of considerable amounts of material, impossibility to create geometries that lie below the milling bur diameter, or the impossibility to allow for mass production of components9^,13. These restrictions can be overcome by the introduction of additive processing routes of layered fabrication14. An example of these technologies is 3D printers, which allow the manufacturing of several objects at the same time in a precise and cost-efficient manner. The 3D printers work by jetting to be photopolymerized materials in ultrathin layers. Each layer is cured by ultraviolet light immediately after it is deposited, producing fully cured objects15. The dual jetting printing procedure requires two materials: a hard, fundamental material, and a gel-like support material. The support material is necessary to sustain complex geometries of the fundamental material during fabrication and it is easily removed by water jetting after printing. Micron-accurate shapes can be printed in different combinations of photopolymers, producing materials with specific mechanical and visual properties. Products with different levels of strength, rigidity, color, transparency, heat resistance, or texture can be obtained. This production modality has widened the indication spectrum of restorative computer-assisted dentistry.

In the following, a computer-assisted diagnostic treatment sequence will be described in detail and clinical examples given to illustrate the recent options for virtual diagnostics and CAD/CAM mock-ups (Fig 1-4-1).

The anatomical data acquisition of the patient’s jaws can be obtained either by direct capturing the volumetric information using intraoral optical scanners or by digitalizing a plaster model by a laboratory optical scanner17 (Figs 1-4-2 and 1-4-3).

The .STL data generated is transferred into a software package that allows for virtual dental restoration design. After selecting the abutment teeth to reconstruct, a specific tooth shape set is chosen from the virtual tooth library. The projected tooth forms are manually arranged by the dental technician onto the dental arch (Fig 1-4-3). Variations on the mesiodistal, buccooral, and occlusogingival dimensions, tooth axis, or tooth composition can be easily performed with the design software. Once a first version is completed and saved on the computer, modifications of the first design can be efficiently created with a couple of clicks and saved as new versions. For example, a standard tooth arrangement can easily be individualized by intruding or rotating teeth simply dragging a virtual point.

The chosen blueprints, saved as .STL files, are then exported to a 3D printing machine that will fabricate the restorations (Figs 1-4-4a to c). Nowadays, biocompatible photopolymers are available to produce rigid tooth-colored restorations, approved for a short-term intraoral use as provisional (up to 6 months) (Figs 1-4-4d and e). The ease, speed, and reduced costs derived from this diagnostic workflow in conjunction with the accuracy of the mock-up make the procedure highly efficient and recommendable.