Quality Resource Guide

Digital Dental Impressions 2nd Edition

www.metdental.com

for a FPD from #19 to #21 was fabricated.

CAD

software was used to measure margin gap, internal

adaptation, and cervical discrepancies between

the FPDs.

The marginal gap was not significantly

different between conventional and iTero digital

impressions

with

the

internal

and

cervical

discrepancies less for the digital impressions.

Another

in vitro

study evaluated the accuracy of

digital impressions and conventional impressions

using the Lava COS scanner, polyether impressions,

and digital scanning of the models made from the

polyether impressions.

The digital impression made

with the Lava COS scanner had significantly higher

accuracy compared to conventional impressions and

indirect scanning of the models.

Another study compared the clinical fit of crowns

made from digital and conventional impressions.

digital impression using the Lava COS system and

one conventional silicone impression was made of

the same crown preparation in each of 20 patients.

Duplicate zirconia crowns were fabricated from

each impression.

Margin fit for each crown was

measured intraorally at the time of crown delivery

using a replica technique. Crowns fabricated with

the digital impression technique had a significantly

better margin fit (49 microns) than those made from

a conventional impression (71 microns).

One randomized clinical study compared the margin

fit of two types of zirconia crowns made with

conventional impressions and digital impressions.

A conventional polyvinylsiloxane impression and

a digital impression with the Lava COS system

were made for each of fifty crown preparations.

Crowns were made for each preparation using

the two impression techniques.

Each crown was

measured intraorally for margin fit and internal

adaptation using a replica technique.

The crowns

made with the digital impression had a significantly

better margin fit (51.45 + 18.59 microns) than

those made with a conventional impression technique

(78.62 + 25.62 microns).

A more extensive

in vitro

study compared the

accuracy of ceramic crowns from different digital

impression systems and types of conventional

impression techniques.

Conventional impressions

were made of a single crown preparation on a

master model using 2-step and single step, putty-

wash impression techniques.

Digital impressions

were made of the master model crown preparation

using the Lava COS, CEREC AC, and iTero digital

systems.

The mean margin fit of crowns was 48 + 25

microns for Lava COS, 30 + 17 microns for CEREC

AC, 41 + 16 microns for iTero, 33 + 19 microns

for single-step putty wash technique and 60 + 30

microns for the two-step putty wash technique.

The

mean internal fit was 29 + 7 microns for Lava COS,

88 + 20 microns for CEREC AC, 50 + 2 microns

for iTero, 36 + 5 microns for single-step putty wash

technique, and 35 + 7 for two-step putty wash

technique.

There was no significant difference in the

margin fit or internal adaptation of the crowns using

any of the techniques.

Clinical Application

The learning curve for digital impression systems

is significantly less than for chairside CAD/CAM

systems. The digital impression is transferred to

a laboratory where the restoration is fabricated

so there is no software design functions or milling

functions for the clinician to master.

Development of

two primary skills is necessary to become proficient

in making digital impressions.

One is learning to

make the appropriate rotational and translational

movements with the IOS in the mouth to record the

intraoral condition.

The second is management

of the administrative functions of the software

program to identify the case, complete the electronic

prescription, and electronically transmit the case

to sites outside the dental office.

Anyone who is

familiar with on-line shopping websites will easily

recognize the functions of transmitting the case to

the dental laboratory.

Companies marketing a digital

impression system manage the cloud computing

functions of digital file distribution to the locations

requested by the dentist.

The company establishes

the electronic connection through conventional Wi-Fi

equipment when the system is installed in the dental

office.

Recording the occlusal relationships for digital

systems is similar to what is done with mounted

stone models.

Digital impression systems record

the opposing arches as separate virtual models.

third scan, commonly called the buccal bite or buccal

scan, is made of the facial surfaces of teeth in the

maxilla and mandible with the teeth in maximum

intercuspation.

There is generally no opportunity to

record functional movements of the dentition.

The

software uses the buccal bite scan to match the

maxillary and mandibular virtual models with the

surfaces recorded in the buccal bite to virtually align

the models. The software program is able to detect

the areas of contact between the opposing virtual

models similar to articulating paper detecting contact

points between opposing mounted stone models.

The digital mounting also has the advantage of

detecting the intensity of contact or intersection

to help in developing the desired occlusal contact

points and lateral interferences on the restoration

proposal.

Protection of patient privacy is an obvious

concern with the proliferation of digital systems.

Manufacturers of digital systems have developed

HIPPA-compliant safeguards and encryption to

protect the transmission of digital data from the

dental office to the dental laboratory.

However, the

WiFi safeguards in place in the clinical setting also

significantly contribute to the final HIPPA-compliant

safeguards of the data transmission.

This should be

evaluated during discussions with the digital system

manufacturer representative prior to installation in

the clinical setting.

Digital files are not generally

transmitted to the electronic health record and do

not pose a data security risk for the patient record.

The most common application of digital impressions

has been the fabrication of dental restorations.

There are two distinct workflows that may be used.

One option is to transmit the digital file to the

dental laboratory where they process a model

similar to what would be done with a conventional

impression.

Companies generally have selected

specific model processing applications for their

digital impression systems, but the digital files

may also be used to process alternative types of

models such as milled polyurethane, printed resin,

or resin stereolithography (SLA).

Once the model is

fabricated, any standard laboratory procedure may

be used to develop and create the dental restoration.

The second alternative, which is more efficient for

the laboratory, is to input the digital file to a CAD

program to design the desired substructure or full

contour restoration.

Once the design has been

milled, the restoration can be finalized using the