**Preface to "Innovative Prosthetic Device"**

New technologies in the biomedical field are improving the everyday lives of patients. Thanks to the advent of new biomaterials, the higher performance of materials, and the synchronization with new computer technologies, it is possible to create safer and predictable prostheses, which tend to significantly improve a patient's quality of life.

**Marco Cicci `u, Luca Fiorillo, Rosa De Stefano**

*Editors*

## *Communication* **Endo and Exoskeleton: New Technologies on Composite Materials**

**Luca Fiorillo 1,\*, Cesare D'Amico 1, Anna Yurjevna Turkina 2, Fabiana Nicita 1, Giulia Amoroso <sup>1</sup> and Giacomo Risitano <sup>3</sup>**


Received: 10 December 2019; Accepted: 30 December 2019; Published: 2 January 2020

**Abstract:** The developments in the field of rehabilitation are proceeding hand in hand with those of cybernetics, with the result of obtaining increasingly performing prostheses and rehabilitations for patients. The purpose of this work is to make a brief exposition of new technologies regarding composites materials that are used in the prosthetic and rehabilitative fields. Data collection took place on scientific databases, limited to a collection of data for the last five years, in order to present news on the innovative and actual materials. The results show that some of the most commonly used last materials are glass fibers and carbon fibers. Even in the robotics field, materials of this type are beginning to be used, thanks above all to the mechanical performances they offer. Surely these new materials, which offer characteristics similar to those in humans, could favor both the rehabilitation times of our patients, and also a better quality of life.

**Keywords:** biomechanical phenomena; elasticity; bioengineering; fiberglass; carbon fiber; prosthesis; rehabilitation research

#### **1. Introduction**

#### *1.1. Background*

In recent years new technologies in bioengineering and industrial fields have enabled the creation of new materials. These materials suitable for the rehabilitation of patients in the different districts of the body offer excellent integration capabilities and excellent biomechanical characteristics. Some of these materials also show biocompatibility characteristics, which makes them perfect to stay in contact with the body's tissues [1]. Composite materials are the materials on which the study will focus. In material science, a composite material is a heterogeneous material, that is, made up of two or more phases with different physical properties, whose properties are better than those of the phases that constitute it. Usually, the different phases in the composite are made of different materials, as in the case of carbon fiber and epoxy resin composites. However, there are exceptions where the different phases are made of the same material, such as SiC/SiC (SiC–SiC) matrix composite is a particular type of ceramic matrix composite) and self-reinforced polypropylene (SRPP) [2]. Composite materials could be both artificial or natural. Some examples of naturally occurring composite materials are wood, in which cellulose fibers are dispersed in a phase of lignin, and bones, in which collagen is reinforced by mineral apatite.

Glass fibers are used for the production of composite materials or advanced structural materials in which different components are integrated together to produce a material with superior characteristics from a physical, mechanical, chemical, aesthetic point of view. In the science and technology of materials, on the other hand, carbon fiber is a material having a thin, thread-like structure made of carbon, generally used in the production of a great variety of "composite materials", so called because they consist of two or more materials, which in this case are carbon fibers and a so-called matrix, generally of resin (or plastic or metal) whose function is to hold the resistant fibers in place (so as to maintain the correct orientation in absorbing the efforts), to protect the fibers and also to maintain the shape of the composite manufactured article. A separate discussion should be made regarding ceramic composite materials. Moreover, a different topic is all the biomaterials originating from living matter, such as bone substitutes. Thanks to new technologies, these materials, just like those under examination of the communication, could be milled or printed with CAD (Computer Aided Design) CAM (Computer Aided Manufacturing) systems [3–7]. In the technopolymers field, the composite flow molding (CFM) technology allows the production of composite materials strongly reinforced with long fiber without damaging the fibers. The reinforcement content also reaches 62% by volume to ensure maximum strength. With this process various combinations of reinforcements (carbon, glass, and Kevlar fibers) and thermoplastic resins (polyether ether ketone (PEEK), polyetherimide (PEI), polyphenylene sulfide (PPS)) are possible; the products thus obtained allow the industry to meet the growing demand for lightweight materials with excellent mechanical, chemical and thermal properties [8,9]. Form memory polymers, although already present on the market with different types of products, new materials and their development continues today to be able to identify characteristics, shapes and other possible applications. In fact their particular properties, unique in the world of plastics, mean that the still possible uses are infinite, ranging from commonly used products, made with standard industrial techniques, to functional elements of 'intelligent' junction, to pieces with good ergonomics or simply tools to improve the performance or comfort of the product in which they are inserted. In the way of "intelligent materials" there are also some membranes based on shape memory polymers. They exploit the principle of thermal vibration, that is, when the room temperature is below the activation point (dictated by the body temperature), the molecular structure stiffens, lowering the permeability, thus allowing to maintain the body temperature; when the room temperature exceeds the activation point, the molecular structure softens creating free spaces between the molecules, allowing the elimination of water vapor and excess body heat [10,11]. These membranes could be used to make water-proof and wind-resistant fabrics, which are breathable and at the same time permeable to water vapor, thus guaranteeing the anti-condensation characteristic. In the dental field, for the production of removable or fixed, implant prosthetics and orthodontic devices, the use of resins based on methacrylate (poly(methyl methacrylate (PMMA)) and composites (bisphenol A-glycidyl methacrylate (biS-GMA)) is widespread [12]. In this manuscript, different issues related to these two technologies have been evaluated. As far as PMMA is concerned, the limits of these materials are: the imperfect repeatability of the polymerization process, limited processing times, poor biocompatibility, which could lead to the onset of considerable safety problems for the health of operators during the phases of processing of prosthetic devices, as well as of patients during the completion phases in the oral cavity and in the subsequent daily use. As for biS-GMA, the limits concern above all their operating procedures, which are quite complicated and require long transformation times; it could be associated with the high cost of the materials themselves, moreover, there are difficulties in mechanically making surfaces that are perfectly shiny and compact. This causes quite significant plaque engraftment in the oral cavity, affecting the biocompatibility of the finished devices. As for fiberglass, on the other hand, common experience shows that monolithic glass is a fragile material. If it is instead spun at diameters of less than a tenth of a millimeter it loses its characteristic fragility to become a material with high mechanical strength and resilience [12].

#### *1.2. Aim*

The aim of this manuscript is to investigate about modern and innovative prosthetic and rehabilitative materials.

#### **2. Results**

#### *2.1. Search*

The results obtained from a recent (last five years) literature search concerning innovative biomedical materials provide detailed information regarding the physical, chemical and biocompatibility characteristics of these materials; but also, their applications. Used search terms were: ("glass fiber" (All Fields) OR "carbon fiber" (All Fields) OR "composite materials" (All Fields)) AND ("Biomed J Sci Tech Res" (Journal) OR "biomedical" (All Fields)) OR ("prostheses and implants" (MeSH Terms) OR ("prostheses" (All Fields) AND "implants" (All Fields)) OR "prostheses and implants" (All Fields) OR "prosthesis" (All Fields)) OR ("rehabilitation" (MeSH Terms) OR "rehabilitation" (All Fields) OR "rehabilitative" (All Fields)).

#### *2.2. Glass Fiber*

The fragility of the common glass is due to the large number of crystallization defects that act as microfractures and stress concentration zones. On the contrary, glass fiber does not present all these defects, therefore it reaches mechanical strengths close to the theoretical resistance of the covalent bond. Different types of fibers could be distinguished according to their characteristics, which condition their use. Glass fibers are widely used in the production of structural composites in the aerospace, nautical and automotive fields, associated with different matrices, for example polyamide or epoxy, still synthetic resins [13–15]. Glass fiber is largely used in dental field, for single, multi teeth restauration (Figure 1).

**Figure 1.** Glass fiber full arch implant supported dental structure. By emmekappadental.it accessed on 6 July 2019.

They are not usually used in the production of composites with metallic or ceramic matrices for which, beyond the technological problem due to the high temperature in production, it is preferred to use fibers with better performance, for example carbon fibers, in relation to the high production cost.

In the civil engineering field, glass fibers are used in the manufacture of fiber cement products. The production methods for glass fibers are:

• In disused marble, it consisted in passing the spindle through drawing nozzles;


After spinning, the fiber is dressed to improve adhesion with the matrix to be reinforced (Table 1) [10].



#### *2.3. Carbon Fiber*

As far as carbon fibers are concerned, these have properties similar to asbestos, but unlike the latter, their use does not entail health risks. Each weave of carbon filaments constitutes a whole formed by the union of many thousands of filaments. Each single filament has an approximately cylindrical shape with a diameter of 5–8 μm and consists almost exclusively of carbon (at least 92%). The atomic structure of the carbon fiber is similar to that of graphite, consisting of aggregates of planar-structure carbon atoms (graphene sheets) arranged according to regular hexagonal symmetry. The difference lies in the way these sheets are interconnected. Graphite is a crystalline material in which the sheets are arranged parallel to each other forming a regular structure. The chemical bonds that are established between the sheets are relatively weak, giving the graphite its characteristic delicacy and fragility. Carbon fibers have a high chemical inertness towards many aqueous solutions. They will deteriorate if they come into contact with metals and metal oxides at temperatures above 1000 K. The typical density of carbon fiber is 1750 kg/m3. The mechanical strength of the different types of yarn varies between 2–7 GPa (Table 2) [16–20].

**Table 2.** Carbon Fiber commercial classification.


From the point of view of the process from which they are obtained, carbon fibers are further classified into:


#### *Prosthesis* **2020**, *2*


The most commonly used method for obtaining carbon filaments is the oxidation and pyrolysis of polyacrylonitrile (PAN), a polymer obtained from the polymerization of acrylonitrile. The PAN is heated to approximately 300 ◦C in the presence of air, with the result of obtaining the oxidation and rupture of many hydrogen bonds established between the long polymeric chains. The oxidation product is placed in a furnace and heated to about 2000 ◦C in an inert gas atmosphere (for example argon), thus obtaining a radical change in the molecular structure with formation of graphite. By carrying out the heating process at the appropriate conditions, there is the condensation of the polymeric chains with the production of narrow sheets of graphene which merge and generate a single filament. The final result consists in obtaining a material with a carbon content generally ranging between 93%–95% [25].

The mechanical properties of carbon fiber could be further improved by exploiting appropriate heat treatments. Heating in the range of 1500–2000 ◦C results in the so-called carbonization with the formation of a material with a high tensile strength (5650 MPa), while the carbon fiber subjected to graphitization (i.e., to a heating at 2500–3000 ◦C) shows a higher modulus of elasticity (531 GPa). Carbon fiber is mainly used to reinforce composite materials, in particular those with a polymeric matrix. The materials thus obtained have high strength, lightness, low cost, and a certain aesthetic value. For these reasons, carbon fiber materials are widely used in a multiplicity of areas where the weight and mechanical resistance of the object are decisive factors or in consumer products simply for aesthetic purposes [26].

The lightness of these materials is also exploited in the sports field, where the lower weight of the sports equipment allows to increase the resistance of the athletes; in particular, these materials are used in the construction of:


#### *Prosthesis* **2020**, *2*

Another area where the lightness and low cost of carbon fiber materials are exploited is the music industry [10].

Carbon fibers could also be associated with matrices in non-polymeric material. Due to the formation of carbides (for example, water-soluble aluminum carbide) and problems related to corrosion phenomena, the use of carbon in metal matrix composites is underdeveloped. Carbon–carbon (RCC, reinforced carbon–carbon) consists of a reinforcement of carbon fiber in a graphite matrix and is used in applications that require exposure to high temperatures, such as in the case of heat shields for spacecraft or brakes of Formula 1 cars. This material is also used for high temperature gas filtration, as a high surface area corrosion resistant electrode, and as an antistatic component.

Carbon fiber is increasingly used to manufacture medical equipment due to both its transparency to X-rays and its robustness. Carbon fiber could be found on:


**Figure 2.** Carbon fiber filaments. Public Domain image.

**Figure 3.** "Flex-Foot Cheetah" carbon prosthetic foot. By Anthony Appleyard CC BY SA 3.0.

**Table 3.** Carbon vs. glass fibers mechanical features [10,25].


#### **3. Discussion**

The composite fibers therefore appear to give excellent biomechanical results and their biomechanical characteristics offer performance useful for use also as an endoprosthesis. An important aspect is represented by the fact that these materials, even before they are made with printing or milling systems, could be appropriately designed in such a way that their design respects the necessary biomechanical properties. [27–29]. These simulations could be performed by discretizing a real system and performing a finite element simulation [30–32]. Glass fiber finds its primary application as a reinforcement for long-term temporary crowns, for the temporary Toronto Bridge or the Maryland bridge, and for bridges on inlays. It could be used for bridges or inlays coated with dental composite for aesthetic purposes. Its advantages are: high resistance and elasticity; biocompatibility; adhesion to composites and resins; and optimal translucency. Among the various materials used in the dental field, carbon fiber is certainly one of the most innovative and stand outs from other polymers due to its great capacity to absorb loads, offering maximum patient comfort. It is no coincidence that this material is used in the manufacture of dental prostheses that require exceptional mechanical performance, such as the Toronto Bridge or crowns on implants. In this case the carbon fiber is used as a reinforcement support and generally in most restorative methods. All this was possible also thanks to the development and improvement of adhesive techniques, which allowed an ever increasing use of polymers in the dental field. Other materials already known, such as titanium, are able to be used in contact with tissues and to build prostheses [33,34], but composite materials, as already mentioned, are able to combine the mechanical characteristics of their components [35–41]; thus, obtaining hybrid materials with unique characteristics.

#### **4. Materials and Methods**

The literature search for this Communication was carried out on the most common Scopus, Pubmed, Embase, Clarivate Analytics scientific databases. The aim was to obtain the highest possible number of results on composite materials concerning the prosthetic field. Furthermore, it was to include only innovative materials and technological and prosthetic innovations.

**Author Contributions:** Conceptualization, L.F.; methodology, L.F.; investigation, L.F.; data curation, L.F. and G.A.; writing—review and editing, L.F.; writing—original draft, C.D.; investigation, A.Y.T.; visualization F.N.; supervision and project administration, G.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## *Case Report* **New Tricks in the Preparation Design for Prosthetic Ceramic Laminate Veeners**

**Luca Ortensi 1,\*, Tommaso Vitali 2, Roberto Bonfiglioli <sup>3</sup> and Francesco Grande <sup>4</sup>**


Received: 12 October 2019; Accepted: 27 October 2019; Published: 30 October 2019

**Abstract:** Background: The prosthetic preparation of the teeth for ceramic laminate veneers has to follow the minimally invasive concept brought by the modern Conservative Dentistry and Prosthodontics. However, during the cementation phase under the rubber dam, the loss of the esthetics landmarks could lead to errors in the future positioning of the laminate veneers. Methods: In this article the authors show an accurate operative prosthetic protocol using different fine intraoperative maneuvers and tricks for the realization of ceramic laminates in order to solve the problems of the cementation phase. Results: The treatment of the anterior sector of the upper maxilla with porcelain laminate veneers was realized in a 30 years old woman with aesthetic issues. Conclusion: Different fine intraoperative maneuvers and tricks during teeth preparation, master impression and rubber dam positioning could reduce errors occurring in the cementation phase and increase the predictability of the results.

**Keywords:** ceramic laminate veneers; teeth preparation; dental esthetics; dental porcelain; rubber dam; prosthetic treatment planning; Digital Smile System

#### **1. Introduction**

The advent of adhesive restorative materials has introduced minimal intervention principles in restorative dentistry and prosthodontics [1]. The necessity of making undercuts in the dental tissue has been abandoned due to new adhesive techniques that allow for the reconstruction of the cavities without excessive preparation for macromechanical retention [2]. Also, the correct use of ceramic and composite materials with rigorous adhesive procedures allows a sound tissue preservation because of the minimally or even noninvasive (additive) approach, which is innovative, highly esthetic, and predictable in terms of both result and long-term prognosis [3,4]. The aesthetics have also improved because of the high level of biomimetics of these new adhesive materials, which also allow for a better function within the oral cavity. Because of the hydrophobic characteristics of these materials, the correct use of adhesive techniques requires an effective moisture control in order to promote the bonding of the restorative materials and then to reduce failure rates of dental restorative treatments [5]. Therefore, a performing isolation system that creates a barrier from the rest of the person's mouth is necessary before executing adhesive procedures in order to control the moisture and microbes. Using a rubber dam can isolate the teeth and this allows the teeth to be restored dry and with relatively less exposure to intraoral bacteria [6]. Other advantages of the use of a rubber dam include superior isolation of the tooth to be treated from the saliva in the mouth [7], improved visibility, reduced mirror fogging, enhanced visual contrast, soft tissue retraction [8], protection of the person by preventing

ingestion or aspiration of instruments, materials [9] and preventing oral soft tissues from contact with harmful materials used during operative procedures, such as phosphoric acids [10].

However, some problems related to the use of the rubber dam could be faced during prosthetic treatments, especially when rehabilitation of the anterior regions of the oral cavity has to be done with different indirect aesthetic restorations such as composite or ceramic laminate veneers (lithium disilicate, feldspathic ceramics). Incorrect rubber dam clamps placement may occupy a space that is needed for the restoration, besides possible damages to the marginal gingiva around the teeth. In addition, the use of the rubber dam leads to a loss of esthetics landmarks such as the midsagittal line, with subsequent difficulties [11] for the correct placement of the veneers on the teeth. The small holes made in the sheet could disagree with the position of the teeth that have to be treated. In addition, inaccuracy in the reproduction of the position of the interdental contact points in the gypsum model during indirect restorations could lead to errors in the future positioning of the laminate veneers. The aim of this article is to present a clinical case report demonstrating an accurate operative protocol using different fine intraoperative maneuvers and tricks for the realization of prosthetic ceramic laminates in order to solve the problems mentioned above.

#### **2. Materials and Methods**

A 30 years old woman presented at our attention with aesthetic issues. She expressed the desire to change her smile because her anterior maxillary teeth seemed small and disharmonious because of the discrepancy in the dimension between each other. She refused to undergo orthodontic treatment for her situation of malocclusion (she presented) but she was very motivated for obtaining a more acceptable smile.

Clinical examination showed a right posterior crossbite with a normal overbite and overjet, superior and inferior dental midline misalignment and Altered Passive Eruption (APE) of 2.1 and 2.2. Radiographic evaluation showed an absence of endodontic and periodontal lesions. Esthetic analysis highlighted an important gummy smile, superior and inferior dental midline misalignment, gingival ogives asymmetry. The patient showed good oral hygiene habits. Then, in light of the anamnesis, objective and radiographic examinations, chief complaint, the treatment of the anterior sector of the upper maxilla with porcelain laminate veneers was proposed.

The operative sequence is structured as follows:


#### *2.1. Treatment Planning and Realization*

In the first objective clinical examination of the patient, a correct diagnosis, including medical and dental history, dental and periodontal screening with periodontal probing depths recording, full mouth intraoral X-rays set and initial clinical intraoral and extraoral photos was done (Figures 1 and 2).

**Figure 1.** Extraoral facial photos: (**a**) right lateral view; (**b**) three quarter right view; (**c**) frontal view; (**d**) three quarter left view; (**e**) left lateral view.

**Figure 2.** Extraoral photos of the smile: (**a**) frontal view; (**b**) right lateral view; (**c**) three quarter right view; (**d**) three quarter left view; (**e**) left lateral view.

A preliminary phase with oral professional hygiene and full mouth disinfection was performed to achieve the health oral conditions necessary to do a correct treatment planning.

Oral impressions with alginate material (Hydrogum 5, Zhermack) have been taken and also digital oral impressions were detected for comparison.

Then a treatment proposal with digital prosthodontic previsualization was shown to the patient with the aid of the Digital Smile System. Longer teeth with more harmonic shapes in the cervical and incisal portions were digitally projected and the patients was informed about all the next steps of the treatment (Figure 3).

After patient approval of the previsualization, the treatment starts by performing a mucogingival surgery with the aid of a mockup used as an oral surgical guide for a highly accurate definition of the emergency profiles and gingival parabolas (Figure 4). A multiple coronal flap technique was used and the gingiva excesses were cut. Little osteotomy and osteoplasty were done in order to reach the accurate vertical dimensions of the teeth established during the treatment planning. In this manner we were able to assess the correct biological width in real-time by placing the mock-up on the teeth. The epithelium of the anatomical papillae was removed and absorbable sutures were applied.

**Figure 3.** Digital planning with DSS (digital smile system): (**a**) photo with cheek retractors and DSS glasses during mouth opening; (**b**) photo with full smile and DSS glasses; (**c**) virtual digital project; (**d**) DSS software screen with design outline and final project; (**e**) DSS software screen with final project; (**f**) comparison between initial clinical photo and final virtual project.

**Figure 4.** Periodontal surgery phases: (**a**) mock-up/periodontal surgical guide; (**b**) biologic width check with surgical guide; (**c**) biologic width check with mock-up; (**d**) follow-up (1–6 weeks postop).

After a healing period of 12 months, as suggested by Pontoriero and Carnevale [12], prosthetic phase with preparation of teeth 1.3, 1.2, 1.1, 2.1, 2.2 and 2.3 for porcelain laminate veneers was done. Then a resin mock-up (C&B, A3.5, NextDent B.V.) was applied on the teeth elected for veneer preparations (Figure 5).

*Prosthesis* **2019**, *1*

**Figure 5.** Resin mock-up on teeth elected for veeners.

After trying the mock-up from the esthetically and mechanically point of view, a minimal iuxta-gingival butt joint preparation was done. A reduction of 0.5 mm of the buccal plate and of 1.5 mm of the incisal portion of the teeth added by the mock-up [13] was performed (Figure 6). Teeth 1.3, 1.2, 1.1, 2.1, 2.2 and 2.3 were prepared.

**Figure 6.** Preparation of the teeth added by the mock-up with proper modifications of the regular technique.

After the buccal plate preparation, a little hole made by a round bur at the center of each tooth was realized in order to ensure the correct positioning of the prosthetic veneers during the cementation phase under rubber dam (Figure 7).

**Figure 7.** Teeth 1.3, 1.2, 1.1, 2.1, 2.2 and 2.3 prepared. Clinical aspects of dental preparations.

A stock tray was chosen to take the master impression, considering that around undercuts, the distance of the tooth to the try wall needs to be at least twice the depth of the undercut [14]. Application of VPS adhesive on the tray and subsequent drying were done. For an accurate reproduction

of the margin preparation, two retraction cords—the first smaller and the second bigger—were positioned around the prepared teeth according to the double cord retraction technique [15].

In order to facilitate the technician in his work, seven small metal sectional matrixes were sprinkled with VPS adhesive and fixed between the anterior teeth and between canines and first premolars before taking the oral impression (Figure 8).

**Figure 8.** Metal sectional matrixes between teeth before vinyl-polysiloxane master impression.

Then, a master impression with a one-step technique using vinyl-polysiloxane impression materials (Acquasil Ultra mono e XLV regular set Dentsply) was taken.

The mockup realized in the first prosthetic phase was used again for making temporary veneers, which were attached on the teeth by using the spot-etching technique (Figure 9).

**Figure 9.** Mock-up for temporary veneers attached by spot-etching technique.

#### *2.2. Cementation Phase*

Six lithium disilicate veneer restorations were manufactured by the technician after seven days from the master impression (Figures 10 and 11).

**Figure 10.** Lithium disilicate veneers.

**Figure 11.** Master model.

The following prosthetic clinical steps for the cementation phase were:


**Figure 12.** N◦9 modified clamp.

*Prosthesis* **2019**, *1*

In order to reach a better control of the interdental contact point, the prosthetic cementation has begun from one central incisor and then continued alternating the tooth for cementation;


**Figure 13.** Matrix application on adjacent teeth positioning during cementation phase.

**Figure 14.** Post cementation check.

**Figure 15.** Extraoral final photos: teeth reharmonization.

#### **3. Discussion**

The rehabilitation of the anterior sector is always a challenging procedure for the prosthodontist. This is especially true when young patients with high aesthetic requests are involved in the prosthetic treatment.

According to Magne and Belser [19], ceramic laminate veneers represent a well-documented, effective, and predictable treatment option when teeth bleaching was ineffective and when major morphologic modifications and extensive restorations in adult patients are required.

The prosthetic preparation of the teeth for ceramic laminate veneers has to follow the minimally invasive concept brought by the modern Prosthodontic and Conservative Dentistry in order to provide esthetic and functional rehabilitation. Three different preparation designs have been suggested regarding the incisal edge preparation: the feathered incisal edge, the butt joint and the overlapped incisal edge with palatal chamfer. Some authors have found that the butt joint is the preparation that least affects the strength of the tooth and that the chamfer preparation type is more susceptible to ceramic fractures [20].

For labial surface preparation, which is the most esthetic portion of ceramic laminate veneers, an accurate preparation depth can be achieved via several methods: freehand, use of depth cuts/grooves and use of a silicon putty index obtained after the wax up or the provisional have all shown good predictable results in reducing the buccal plate for the thickness previously planned [21].

For interproximal extension, no conclusive evidence demonstrates what is the best technique to prepare. Then, the clinician has to choose for each case if it is better to not prepare or to prepare until the interproximal contact point or to slightly open the interproximal contact.

However, in some cases no teeth preparation is required to restore the teeth ("no prep technique") [22].

All these preparation techniques are based on the need to give optimal biomechanics and aesthetic characteristics—at the same time respecting the highly conservative concepts. However, in order to achieve those final goals, it is also mandatory that the prosthetic cementation phase is free of mistakes. These techniques do not consider the difficulty in maintaining the correct spatial orientation during the cementation phase, and the subsequent possibility to design a preparation for laminates in order to position in a correct way the veneers on the teeth. In this direction, we perform some different fine intraoperative maneuvers and tricks that help the clinician in the preparation of the teeth and in the subsequent placement of the laminates on the teeth prepared under the rubber dam.

The modification of the labial preparation by performing a little hole with a round bur at the center of buccal plate of the tooth is important to achieve the correct placement of the veneers under the rubber dam when extraoral and intraoral landmarks disappear. Moreover, during the prosthetic cementation phase, the attention of the clinician is mainly referred to factors such as the cement excesses and the pressure applied on the veneers during its positioning, as these factors could lead to cement the veneers in an incorrect position [23].

Another little trick that could prevent possible errors during the luting phase is the modification of number 9 hook. The objective is to avoid small shifts during veneer positioning because of the interference between the hook and the most coronal part (zenith) of the veneer itself. This adaptation consists in the elimination of the flattened part of the labial clamp beak in order to put the hook in an apical position that cannot interfere with the zenith of the veneer.

The correct positioning of the prosthetic veneers on teeth is also dependent on how accurate the technician works and how precise the fitting of the veneers is. Then, in order to facilitate the technician, during the master impression phase seven small metal sectional matrixes were sprinkled with vinyl-polysiloxane adhesive and fixed between the anterior teeth and between canines and first premolars before taking the oral impression. The goal is to highlight the interdental contact points in the model, aiding the technician to separate the teeth from each other with the bur, without any risk to remove the contact points because of the additional space obtained during the manufacturing of the cast with the removable abutments.

#### **4. Conclusions**

Adhesive and minimally invasive dentistry is nowadays a consolidated reality in Prosthetic Dentistry. New materials and techniques must guarantee a good predictability of the final goal from the beginning to the end of treatment and not only an optimal aesthetics, which could also improve.

However, other studies with more patients and longer follow-ups are required to prove the reliability of this new tricks and techniques improving the technical procedures of the treatment.

**Author Contributions:** Conceptualization, L.O., T.V. and F.G.; methodology, L.O., T.V and T.V.; software, L.O., T.V. and T.V.; resources, T.V.; data curation, F.G.; writing—original draft preparation, F.G.; writing—review and editing, L.O., T.V. and F.G.; visualization, L.O., T.V. and F.G.; supervision, T.V. R.B. fabricated the laminate veneers.

**Funding:** This research received no external funding

**Acknowledgments:** The authors thank Gianni Ortensi, CDT and Marco Ortensi, CDT, who fabricated the mock-up and supported laboratory digital processes.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

*Article*
