Recent data indicates limited awareness and compliance on infection prevention procedures by dental offices and by dental laboratories. Guidelines for infection prevention in dentistry have been published by Centres for Disease Control and Prevention since 2003; the section “IX-Special consideration” includes a subsection concerning the prevention in dental laboratories, but it has not been modernised in later versions to fit the needs of traditional and computer-aided technology. Traditional techniques required disinfecting items (impression, chewing waxes, and appliances) with well-suited products, which are also chosen for limiting impression changes or appliance deterioration. Effective procedures are available with difficulties. Some of these contain irritant or non-eco-friendly disinfectants. The transport of impression, to dental laboratories, is often delayed with limited precautions for limiting cross-infection. Gypsum casts are frequently contaminated mainly by bacteria and their antibiotic-resistant strains and even stored for long periods during dental implant supported restoration and orthodontic therapy, becoming a hidden source of infection. Nowadays, computer-aided design/computer-aided manufacturing technology seems to be an interesting way to promote both business and safety, being more comfortable for patients and more accurate than traditional technology. A further advantage is easier infection prevention since, for the most part, mainly digital impression and casts are not a source of cross-infection and the transport of contaminated items is reduced and limited to try-in stages. Nevertheless, a peculiar feature is that a digital electronic file is of course unalterable, but may be ruined by a computer virus. Additionally, the reconditioning of scanner tips is determinant for the optical characteristics and long term use of the scanner, but information for its reconditioning from producers is often limited. This study focuses on some critical points including (a) insufficient guidelines, (b) choice of proper procedure for scanner reconditioning, and (c) data protection in relation to patient privacy.
For patient and personnel safety in dentistry, one of the main goals is to break the chain of infection transmission. Nevertheless, infection hazards in prosthodontic and orthodontic practice are rather difficult to control [
The limited compliance with infection prevention is hazardous, taking into account the increasing prevalence of infections by antibiotic-resistant bacteria, killer bugs, or super spreaders [
Nowadays, computer-aided design/computer-aided manufacturing (CAD/CAM), here indicated as CAD/CAM technology (CCT), is widely used since (a) digital impression is more comfortable for patients (mainly vulnerable aging population or younger ones) [
Despite the high interest in dentistry on CCT nowadays, gold standard guidelines for infection prevention did not pay attention to it [
Using CCT, the usually reported advantages for infection prevention are the none requirements of impression disinfection and better occupational safety. To our knowledge, this is the first paper that focuses on infection prevention in detail using CCT compared to traditional technology in dentistry. Here, we report three specific problems related to (a) insufficient guidelines, (b) requirements for scanner reconditioning, and (c) data protection and electronic viruses.
The electronic literature search was conducted via the PubMed and Google Scholar databases (from January 2010 up to and including October 2018) using various combinations of the following key indexing terms: (a) CAD/CAM; (b) cross-infection control; (c) infection prevention; (d) disinfection; (e) reconditioning; (f) semicritical items; (g) critical items; (h) cast; (i) digital model; (j) digital impression scanner; (k) dental impression; (l) guidelines; (m) safety precautions; (n) dental laboratory; (o) occupational health; (p) bacterial adhesion; (q) microbial contamination; and (r) biofilm. In addition, manual searches were carried out in the Hindawi Journal database (from 2010 to 2018) using the following key indexing terms: (a) CAD/CAM (n°=237); (b) CAD/CAM dentistry (n°=118), but very few take into account cross-infection or infection prevention according to our topic [
Currently, there is increasing interest regarding safety of the dental workplace, personnel, and patients and in particular, on the prevention of infectious adverse events and clinical hazards. Adverse events and outbreaks mainly cause an increase in the cost to society (by productivity loss, additional costs for health care, outbreak investigations by molecular diagnostics), and significant legal claims [
On the whole, dental impressions and appliances from all persons must always be treated as if potentially infectious (by microbes present in saliva, occult blood, dental plaque), since persons could be in an asymptomatic stage (early stage of Hepatitis C infection) and could not know their status, or the infection may be diagnosed late, or undeclared to avoid discrimination (HIV infection). Furthermore, the recommendation to isolate prosthesis of high-risk patients from other laboratory work in dental offices and DLs is nowadays without a rational reason and dated.
Moreover, we have to make every effort to reduce the rate of infection transmission to/from dental offices and to/from laboratories and the chance of there being some microbial reservoirs (impression, dental appliances, etc.). Conventional fabrication methods require considerable human intervention and manipulation of impression, wax and cast, materials and try-in-stage items; as a consequence of these two peculiar features, items exhibit microbial contamination caused by the bioburden of the oral cavity, hand skin, environment, and even by some harmful antibiotic-resistant strains. Here, we focus on some underestimated hazards and operative errors and lapses during infection prevention using traditional technology and CCT.
More recent findings indicate insufficient knowledge and very limited awareness by dental healthcare personnel (DHCP) in relation to infection control, taking into account the insufficient use of PPEs, low use of sterilized impression tray (13%), rinsing the impressions with water (37.2%) or brushing away debris (2,6%) before disinfection, blood-contaminated impression (25%), improper disinfection of impression (about 40%) or of metallic impression trays, denture prosthesis, bite registration and wax, face bole and fork, and lack of communication (24,7%) with DL about impression disinfection in dental offices [
In brief, many opportunistic or nonopportunistic species (i.e.,
Some examples of cast microbial contamination (see bluish-black hairy colonies probably from Fungus species) due concurrent factors (improper impression disinfection, prolonged conservation inside the plastic bag, presence of alginate residues after manufacture steps in a traditional DL). The casts represent a hazardous reservoir since DHCP hand-touching.
MRSA is a well-known antibiotic-resistant bacterium with a very low expected infective dose (4 CFU) [
We would like to note some underestimated hazards during traditional prosthetic, prosthodontic, and orthodontic practices as follows: Concerning the procedure using an addition silicone as impression material, the contamination by the hand microbial flora (including MRSA) [ It is a frequent error to touch a cast or contaminated try-in items with gloved contaminated hands [ During partial- or full-denture impressions, it is a frequent error to use the The transport of contaminated impressions, chewing wax, and intermediate tests during prostheses are often carried out without proper precautions against cross-infection, with violation of the national laws, as well as being delayed. Concerning the disinfection of traditional impressions, the instructions for use (IFU) from manufacturers are often insufficient or not usable (i.e., very restrictive use of glutaraldehyde in European Union). The responsibility for ensuring impressions has been cleaned and disinfected before dispatch to the laboratory which lies solely with the dentist. When at the dental chair, the modification of removable orthodontic and prosthetic appliances should be avoided before try-in and after use by all patients, without their preliminary disinfection. We would like to note that removable prosthodontic appliances received from laboratories are often contaminated by
Concerning specific problems on impression disinfection, we add additional operative details in Section
Insufficient data exists on the contamination of dental impression materials supplied by the manufacturers in sealed containers. They are mainly stored in an anhydrous state and are often hydrophobic, which means the microbial contamination is expectedly low. Extra-mouth contaminants represent only 0.06% of total microbial (aerobic mesophilic bacteria) load of alginate, while after mouth contact, alginate microbial load increases significantly (1600 fold); other powders, from impression material containers and irreversible hydrocolloids received from the manufacturers, were contaminated with viable microorganisms to a substantial amount (90-100% in irreversible hydrocolloids) [
Firstly, the use of all PPEs is always required because of the infective risk and the occupational hazard due to splash in the case of immersion, air contamination in the case of spray, or dryout with compressed air. Studies, among DHCP and dental technicians within different Nations (UK, Pakistan, South Arabia, Iran), indicated a wide variety of chemical solutions and concentrations were used to disinfect impression materials [
In general, the impression disinfection, in a dedicated area near the chair side area, is an ideal way to prevent cross-contamination. Many studies report impression surface disinfection with different commercial products, by spay or immersion and with a contact time of about 5-10 min. Disinfection by soaking in chemical materials has been shown to cover all surfaces of impression materials at one time, while spraying is not capable of disinfecting all surfaces effectively and also cannot cover all undercuts.
It is preferable to avoid the use of irritants (aldehydes, hypochlorite solutions), or non-eco-friendly disinfectants (aldehydes, phenols). Hypochlorite solutions, very effective and cheap products with no or minimal certification, may have corrosive or discoloration effect on prosthesis metal parts as far as occupational hazards [
Recently, more ecological approaches have been proposed for dental stone and impression disinfection using microwave and UV radiation [
Before further reconditioning [
Residues of polyether adhesive, alginate, and autopolymerising acrylic resin on impression trays and other items (alginate spatula, laboratory bur, silicone dappen dish) after treatment by washer-disinfectors (a, b) and corrosion of impression trays by an improper or overly long chemical treatment to remove gypsum (c-f). Tips: (i) remove residues before treatment by washer-disinfectors (a, b) [
When traditional technology is used, the work in DLs comes with many physical, chemical, ergonomic, and biological hazards [
Data shows the limited awareness on infection prevention and very poor compliance of infection control procedures by most DLs during the manufacture of dental prostheses and orthodontic appliances; in particular, studies show inadequate adoption of standard precautions in terms of the use of PPEs, disinfection of impression and appliances, and vaccinations [
It is well known that the storage plus transport of impression to DTs takes from 5 to 8 hrs in moist conditions; the influence of humidity on microbial survival is a recently discovered problem; for example, HBV can survive for up to seven days in 42 percent relative humidity. A survey shows that 50% of the responding DTs disinfected all impression partly from uncertainty (no written communication) or inefficiency of disinfection in dental offices [
In addition, other factors could jeopardize infection prevention: the need to rush a case, the absence of disinfection areas within their dental laboratories, and low awareness of legal responsibility towards occupational risks [
Only 6.40% of DTs use all PPEs and just 45.6% stated that they clean and disinfect their work surfaces. Astonishingly, 47,8% of DTs only cleaned the rag wheels, brushes, and acrylic burs with water after use, and only 28.26% of them sterilized by heat or chemicals [
These worrying practices render the rest of the precautions useless because infective agents are able to survive on contact surfaces, air, hand, and work items for several days and then could contaminate already disinfected appliances. Recently, DT behaviour seems to have got worsened as concluded by some authors. Vasquez-Rodriguez’s group concluded: ”
The recent European Union Regulation n° 745/2017 reported only a vague indication to health safety and some notes on cleanliness and sterility of dental appliances, all classified as medical devices (MDs), placed on the market. There is no specific guidance issued to dental custom-made MDs in contrast with the fact that dental appliances should be free of microbial contamination according to CDC guidelines [
Up to now, there are no disinfection protocols which have been accepted as gold standard for disinfecting dental impressions and dental appliances. Chemical disinfection is still the method of choice since sterilization with heat is not an option for dental impressions and occlusal records.
The dental service market is always becoming more competitive. Today, the increased ergonomics of the highly complex “human-technical dental office system” are very important in guaranteeing safer and patient-centred dental care concurrent with earning profit [
Here, we show the main differences in the case of traditional vs. CCT, mainly focusing on dental offices (Table
Main differences for cross-infection prevention in the case of traditional technology vs. CCT in dental office and DL.
n° | Need for | Traditional Technology | CCT |
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1 | effective communication and coordination between the dental office and laboratory efforts to asepsis | yes | only in the case of intermediate and completed cases |
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2 | written information regarding the methods (e.g., type of disinfectant and exposure time) used to clean and disinfect the material (e.g., impression, stone model, or appliance) and items (articulators, case pans, or lathes) according to the manufacturer’s instructions. | during all phases | only in the case of intermediate and completed cases |
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3 | heat-tolerant items used in the mouth (e.g., metal impression tray or face bow fork) that should be heat-sterilized before being used on another patient or single-use plastic impression trays | yes | only for scanner tips |
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4 | clean and disinfected pressure pots and water baths between patients since these are particularly susceptible to contamination by microorganisms | yes | No/ only for positioning wax |
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5 | wearing appropriate PPE (including eyewear!) in both the office or laboratory, when handling contaminated items and until disinfection is completed | yes | only in intermediate and completed cases and after the end of the CAD |
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6 | guarantee that the appropriate and effective cleaning and disinfection procedures are performed in the dental office or laboratory | +++ | + |
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7 | use an EPA-registered hospital disinfectant with a tuberculocidal claim, follow IFU and thoroughly rinse item before being handled in the in-office laboratory or sent to an off-site laboratory | yes | no |
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8 | checking IFU and problems regarding the stability of impression and appliance materials during disinfection | yes | no |
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9 | cleaning and disinfection of any items (impressions, prostheses, or appliances) as soon as possible after removal from the patient’s mouth before drying of blood or other bioburden that can occur | yes | only in intermediate and completed cases |
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10 | a separate disinfecting, sending, and receiving area should be established to reduce cross-contamination in the dental office | yes | easier and only in intermediate and completed cases |
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11 | identification and reduction of redundancies of procedures since impression materials could be damaged or distorted because of disinfectant overexposure | yes | no |
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12 | cleaning, disinfecting, and covering of clinical contact surfaces as a function of the rate of use and contamination of the area | +++ | + |
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13 | fabricating stone casts after alginate impression as soon as possible to avoid dimensional changes | yes | no |
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14 | adhesive for impression trays using some impression materials (polyether, polysulfide) | yes | no [ |
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15 | wastage of impression materials due to the remaking at times of conventional dental impression for inadequate detail production | yes | no |
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16 | wastage of time due to the remaking of dental impression for inadequate detail production | +++ | + |
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17 | appliances and prostheses that should be free of contamination delivered to the patient | difficult | easy |
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18 | responsible dental laboratory or dental office staff for the final disinfection process | yes | yes |
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19 | a separate receiving and disinfecting area should be established to reduce contamination in the DL | yes | in intermediate and completed cases |
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20 | waste (gypsum, waxes) management according to national laws | yes | no |
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21 | Appropriated disposal of gypsum and toxic substances (i.e., hydrogen sulphide) when discarded into the environment | yes | no |
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22 | laboratory items (e.g., burs, polishing points, rag wheels, or laboratory knives) which are heat-sterilized, disinfected between patients, or disposable items, or to store items in small quantities (i.e., polishing agents) | yes | low and only to reduce manufacture contamination |
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23 | regulated medical waste and sharp items (e.g., burs, disposable blades, and orthodontic wires) in specific and resistant containers according to national rules | +++ | + |
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24 | paper for dentist prescription to DL | yes | no |
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25 | computer antivirus | no | yes |
Other advantages are related to the following: Better occupational safety for DHCP and DTs by avoiding [ Skin irritation after extensive use of disinfectants for impressions and dental waxes. Silicosis by exposure to airborne particles liberated during the mixing of alginate (dust, lead) in dental offices and melting, grinding, polishing, and finishing procedures in labs. Nonexistent or low biohazard due to waste management. Higher hazard for the younger DHCP, who are concurrently more exposed to cross-infection, mainly when they are students and in the first years of their dental practice [ Progress towards ecofriendly dentistry by reduction of disinfectant use waste material (contaminated gypsum and cast) [ Clinical biosafety because the violation of critical anatomical features is prevented by marginal fit lower than the clinically acceptable value [ the new dental materials (i.e., PMMA, zirconia), usable only by CCT, show reduced adhesion and decreased biofilm accumulation [ DHCP can minimize the risk of osteonecrosis, a rare and unexpected complication during the taking of conventional dental impressions in patients with predisposed anatomic sites, or the risk of
CCT disadvantages are on the prohibition of use on patients with pacemaker and minor occupational hazards (eye safety, extended computer usage, and ultrafine particles and nanosized byproducts) [
The scanner is a very responsive appliance. Several factors have been reported to influence the accuracy of the intraoral scanning including (a) the learning curve, skills, and scanner usage frequencies in clinical practice; (b) the physical resolution of the scanning system and the postprocessing of the data; (c) the movement of the patient and limited intraoral space; and (d) temperature fluctuation; (e) the presence of moisture, water, saliva and sulcular fluid, and reflective surfaces (metal brackets and implant abutments) [
When the powdering procedure is needed to prevent reflections during image capture, there was no way to standardize it for each scan, it is not appreciated by the patient, and the environmental contamination caused by titanium powder nanoparticles is not known.
In line with the current minimal requirements for the indication of hazards published [
IFU according to infection prevention from different manufacturers of scanners [
Specific Indications | ||
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Part of the scanner | TRIOS® | iTero® |
System or Base Unit [ | (i) Surface disinfection | (i) Surface disinfection. |
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Monitor [ | (i) Do not spray directly with disinfectant. | (i) Do not spray directly with disinfectant. |
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Handheld scanner [ | (i) Do not submerge the handheld scanner in any liquids. | Not indicated in open source [ |
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Medical-grade peripherals (e.g., keyboards and mice) [ | (i) Easy disinfection. | Not indicated in open source [ |
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Scanner tips with fixed mirror or detachable mirror [ | Not needed. | |
Immediately after clinical use: | ||
(iii) Clean manually and perfectly using soapy water and a soft dish brush. | ||
(a) Wrap the tip using a self-adhesive pouch or heat-sealed pouch. | ||
(b) Sterilization using a steam autoclave class B (EN13060) and cycles at 121/134°C with drying. | ||
(c) Storage in proper condition. | ||
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Disposable plastic sleeve [ | (i) Dispose of scanner sleeves according to standard operating procedures or local regulations for the disposal of contaminated medical waste. | |
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| (i) For optical windows and scanner tips: denatured alcohol (ethyl alcohol or ethanol) – typically 60-70% Alc/Vol. | (i) Many commercial products. |
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| A soft lint-free nonabrasive cloth. | (i) Disinfectant wipes. |
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| (i) Ammonia-based or chloride based solutions or acetone on any surface. | |
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| Normally as other clinical waste. | Normally as other clinical waste. |
Finally, we would like to underline some advice for avoiding (a) lint, stains, and dirt on the optical components, (b) damage on optical component, and (c) fast deterioration of the plastic parts of the unit (Table
Some advices for better scanning.
Target | Actions |
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To avoid lint, stains, and dirt on the optical components: | Select disinfectants that do not produce faded stains and are nontoxic [ |
Do not allow any solution to dry. | |
Sterilization in wrapped pouches to protect the optical parts and to guarantee the use of sterile tip. | |
Put outside the pouch a type 5 chemical integrators (UNI EN ISO 11140), to avoid the possible interference of their released products. | |
Attention before and during steam sterilization: in particular, it is important: | |
Check water quality, the cleanliness of the steam autoclave camera and trays, autoclave loading, and perfect drying of the wrapped pouches. | |
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To protect optical component from damage: | Put the pouch far from other devices. |
Use absorbent TNT gauze for protection. | |
It is not known if it is better: (a) to put the mirror tip towards the paper or the plastic side of the barriers, (b) up or down in the autoclave camera. | |
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To prevent fast deterioration of the plastic parts of the unit: | Use single-use wipes soaked with disinfectant, which also act quickly against antibiotic-resistant strains and have good compatibility with optical and plastic parts [ |
It is well known that gingival retraction procedures are part of impression procedures; generally, this step is considered “safe” and effective, but also time-consuming, uncomfortable for dental patients, and may delay periodontal tissue repair [
Data protection is at the core of the recent EU General Data protection Regulation [
All dentists and DTs must pay attention to the health data of their patients, in terms of purpose limitation, data minimization, accuracy, storage limitation, integrity, and confidentiality. Data retention and reuse time must be explicit, while the need to retain the files for defensive dentistry (i.e., medical-legal and insurance reasons) or for future appliance repair is a matter of discussion. Orthodontists can easily backup the digital data and keep them for at least 10 years; meanwhile, gypsum casts could be lost or broken or need space in dental office, in addition to being a hidden source of contamination [
The main advantage of CCT depends on the capability of forwarding some images, static or dynamic, coming from different sources (digital camera, CBCT, video, etc.), to a milling centre that will integrate them using Digital Smile Design software. After elaboration and dentist approval, the files will be used by computer-aided design (CAM) software to guide robotic devices which create objects and eventually assemble their parts in a virtual environment. Concerning the safety of the digital workflow, it is highly important to stay protected by installing a robust antivirus program, to protect key functions, applications, and emails and mainly to prevent the copy/deletion/stealing or encryption of the patient’s personal and sensitive data. It is obvious that digital dental casts can be controlled more easily by computer cryptographic and pseudonymisation tools, than by paper documents and analogue casts; this feature is expected to prevent clerical errors, involved in the majority of patient safety incidents [
In every day practice, CCT is one of the most important innovations that support infection prevention compared to traditional technology since it breaks or reduces cross-infection during impression and manufacturing steps. These advantages are expected to balance the higher cost of investments in hardware (scanner in the dental office and CAM in the milling service and dental labs) and software for “digital smiles”.
As life expectancy increases, the prevalence of Alzheimer’s disease will increase even further. Dentistry seems to be in the first line of prevention and should begin to equip itself with skills, updated knowledge for taking care of the different needs, and demands and aspirations of typically aged and Alzheimer’s patients, including innovation through digital dentistry [
Unfortunately, guidelines for infection prevention using CCT have not been updated. DHCP needs better IFU and transparency from manufactures. Additionally, the presence of an infection prevention coordinator is necessary to follow IFU, as well as a plan for coordinated infection prevention between dental office, DT, and milling centre.
It is necessary to respect patients’ rights in terms of privacy and large data protection.
American Dental Association
Dental Healthcare Personnel
Dental Implant Supported Restoration
Dental Laboratory
Dental Technician
Computer-Aided Design/Computer-Aided Manufacturing
CAD/CAM Technology
Centres for Disease Control and Prevention
Hepatitis B Virus
Food and Drug Administration
Human Immunodeficiency Virus
Medical Device
Poly(methyl methacrylate)
Material Safety Data Sheet
Personal Protective Equipment.
Livia Barenghi had a service agreement with KerrHawe and was a consultant for Dental Trey Il Blog (
The project started from the Cadeo’s thesis entitled “Digital scanning delle arcate dentarie: una innovazione nella formulazione diagnostica e programmazione terapeutica in ortodonzia e gnatologia” discussed at Parma University, in July, 2018 for “Master di II livello in Ortodonzia intercettiva”. Livia Barenghi conceived the project, conducted electronic literature search, selected the references, directed the work and wrote the manuscript. Livia Barenghi prepared photos related to cross-infection. Livia Barenghi, Alberto Barenghi, Alberto Di Blasio e Carlo Cadeo, discussed the data. Alberto Barenghi, Alberto di Blasio revised the manuscript.
This research was supported by Integrated Orthodontic Services S.r.l. (Lecco, Italy). The authors would like to thank LaStruttura (Varese, Italy;