Precision of maxillo-mandibular registration with intraoral scanners in vitro

Trueness of maxillomandibular relationship in 3D-printed and conventional casts

OBJECTIVES

To compare the trueness of maxillomandibular relationship between articulated 3D-printed and conventional diagnostic casts in maximum intercuspation (MIP).

METHODS

Reference casts were articulated in MIP, and scanned using a Coordinate Measurement Machine (CMM, n = 1). Digital scans were made from the reference casts by using an intraoral scanner (IOS, n = 10) (Trios 4; 3Shape A/S). IOS scans were processed to create 3D-printed casts by using MAX UV385 (Asiga) and NextDent 5100 (3DSystems) 3D-printers. The conventional workflow implemented vinylpolysiloxane (VPS) impressions and Type IV stone. Stone and 3D-printed casts were articulated and digitized with a laboratory scanner (E4; 3Shape A/S). The 3D-printed casts were scanned on two occasions: with and without positioning pins. Inter-arch distances and 3D-contact area were measured and compared. Statistical tests used were Shapiro-Wilk, Levene's, Welch's t-test, and 2-way ANOVA (α=0.05).

RESULTS

IOS group showed similar or better maxillomandibular relationship trueness than stone casts and 3D-printed casts (p < 0.05). 3D-contact area analysis showed similar deviations between 3D-printed and stone casts (p > 0.05). The choice of 3D-printer and presence of positioning pins on the casts significantly influenced maxillomandibular relationship trueness (p < 0.05).

CONCLUSIONS

Articulated 3D-printed and stone casts exhibited similar maxillomandibular relationship trueness.

CLINICAL SIGNIFICANCE

Although 3D-printing methods can introduce a considerable amount of deviations, the maxillomandibular relationship trueness of articulated 3D-printed and stone casts in MIP can be considered similar.

Auxiliary occlusal devices for IO scanning in a complete digital workflow of implant-supported crowns: a randomized controlled trial

OBJECTIVES

To compare the crown accuracy and time efficiency of a complete digital workflow, utilizing an auxiliary occlusal device and IO scanning, with a conventional workflow, for multiple implant-supported single crowns.

MATERIALS AND METHODS

24 patients with two adjacent posterior implants were included. 12 patients were randomly assigned to digital workflow group, involving intra-oral scanning with an auxiliary occlusal device and manufacture of customized abutments and zirconia single crowns (test group). The other 12 were assigned to the conventional workflow (control group), involving conventional impression and CAD-CAM crowns based on stone casts. Crown scanning was done before and after clinical adjustment using an intraoral scanner. Two 3D digital models were overlapped to assess dimension changes. Chair-side and laboratory times for the entire workflow were recorded and a linear mixed model and Independent-sample t tests were used for the statistical analysis.

RESULTS

The maximum occlusal deviation was 279.67 ± 112.17 μm and 479.59 ± 203.63 μm in the test and control group, respectively (p < 0.001). The sizes of the occlusion adjustment areas were 12.12 ± 10.51 mm2 and 25.12 ± 14.14 mm2 in the test and control groups, respectively (p = 0.013). The mean laboratory time was 46.08 ± 5.45 and 105.92 ± 6.10 min in the test and control groups, respectively (p < 0.001).The proximal contact adjustment and mean chair-side time showed no statistically significant difference between two groups.

CONCLUSIONS

A digital workflow for two implants-supported single crowns using an auxiliary device required fewer occlusal crown adjustments, and less laboratory time compared to conventional workflow.

CLINICAL RELEVANCE

The use of auxiliary occlusal devices in IOS enhances the accuracy of virtual maxillomandibular relationship in extended edentulous spans. Consequently, employing a digital workflow for multiple implants-supported crowns using IO scanning and an auxiliary occlusal device proves to be a feasible, accurate and efficient approach.

Reliabilty of recording occlusal contacts by using intraoral scanner and articulating paper - A prospective study

OBJECTIVE

The recording of occlusal contacts is a pivotal step in many dental procedures, yet the lack of a standardized method could introduce clinical errors. The aim of this study was to compare the occlusal contacts recorded using a intraoral scanner to the contacts recorded using articulating paper. As a secondary outcome, the subjective clinical assessment made using the two methods was compared between different observers.

METHODS

Twenty-eight records were analysed for this study. Digital scan and intraoral photos of the coloured marks impressed by articulating paper were taken at the same time point for every patient. Using a standardized occlusal template, two operators recorded the number of occlusal contacts for every tooth provided by the two techniques. Then, 11 clinicians analysed the collected records and answered questions about the quality of the occlusions observed.

RESULTS

The statistical analysis showed significant differences between the number of contacts recorded by digital scan and those recorded by the photographed articulation marks, except in the case of the upper central incisors and first premolars. The Kappa Fleiss showed slight and fair agreement between clinicians when judging the occlusions.

CONCLUSION

The occlusal contacts recorded using the intraoral scanner and those recorded with the articulating paper did not match, and overall the clinicians showed low agreement when rating the recorded data.

CLINICAL SIGNIFICANCE

Despite of the great clinical importance of occlusal contact there is a lack of a precise method for recording and collecting occlusal contacts.

A guide for selecting the intraoral scan extension when fabricating tooth- and implant-supported fixed dental prostheses

OBJECTIVES

To describe a new classification for intraoral scans based on the scan extension and to introduce a decision guideline to choose the scan extension for fabricating tooth- and implant-supported fixed dental prostheses (FDPs).

OVERVIEW

Multiple operator- and patient-related factors have been identified that can decrease the scanning accuracy of intraoral scanners (IOSs), including scan extension. However, the decision criteria for selecting scan extension for fabricating tooth- and implant-supported restorations is unclear. Based on the extension of the intraoral digital scans, three types of scans can be defined: half-arch (anterior or posterior), extended half-arch, and complete-arch scan. Variables to consider when choosing the scan extension include the number and location of units being restored, as well as the extension and location of edentulous areas. Additionally, the accuracy of the virtual definitive cast and the accuracy of the maxillomandibular relationship captured by using IOSs should be differentiated.

CONCLUSIONS

A decision tree for selecting the scan extension is presented. The decision is based on the number and location of units being restored, and the extension and location of edentulous areas. Intraoral scans with reduced scan extension are indicated when fabricating tooth- and implant-supported crowns or short-span fixed prostheses, when the patient does not have more than one missing tooth in the area of the dental arch included in the scan. For the remaining clinical conditions, complete-arch intraoral scans are recommended.

CLINICAL SIGNIFICANCE

Scan extension is a clinician's decision that should be based on the number and location of units being restored and the extension and location of edentulous areas. Intraoral scans with a reduced scan extension is recommended, when possible.

Virtual occlusal records acquired by using intraoral scanners: A review of factors that influence maxillo-mandibular relationship accuracy

PURPOSE

This review aims to provide a comprehensive summary of how much progress has been made in the field of virtual occlusal records (VOR) obtained with intraoral scanners (IOSs), their accuracy, and what factors influence their accuracy.

MATERIALS AND METHODS

An electronic search was performed in MEDLINE via PubMed and Scopus databases in February 2023. Eligible articles were clinical or in vitro studies evaluating the accuracy of virtual occlusal records with intraoral scanners in completely dentate and partially edentulous arches.

RESULTS

Virtual occlusal records have shown promising results in terms of accuracy, with some studies reporting a high level of agreement with traditional methods. Key factors influencing the accuracy of VOR through intraoral scanners were identified which encompass multiple parameters such as scanner brands, imaging technology, scan quality, best-fit alignment, software algorithms, intermesh penetrations, and the number of sections and dimensions of the virtual occlusal record. In partially edentate areas, the lack of landmarks in the edentulous area compromises the accuracy of VOR, thus limiting the use of IOS in patients with missing teeth.

CONCLUSION

Understanding and recognizing these influencing factors will increase the predictability and reliability of dental treatments completed by using digital workflows.  However, certain challenges need to be addressed which can influence its accuracy and limit its use in daily practice. Future research should focus on improving these factors to enhance the clinical applicability of virtual occlusal records.

Factors that influence the accuracy of maxillomandibular relationship at maximum intercuspation acquired by using intraoral scanners: A systematic review

OBJECTIVE

To review the factors that influence the accuracy of the maxillomandibular relationship at maximum intercuspation (MIP) acquired by using intraoral scanners (IOSs).

MATERIAL AND METHODS

A systematic search was performed using five databases: MEDLINE/PubMed, Cochrane, Embase, World of Science, and Scopus. A manual search was also completed. Studies assessing the factors that influence the MIP acquired by using IOSs were included and organized based on the analyzed factor. Studies were evaluated by applying the Joanna Briggs Institute Critical Appraisal Checklist.

RESULTS

Twenty-nine articles were included. Seven factors have been identified: IOS system, scan extension, edentulous areas, number, location, and extension of occlusal records, occlusal force, tooth mobility, and alignment methods. Nine studies evaluated the influence of IOS system. Four studies assessed the influence of the extension of the arch scan. Three studies evaluated the effect of edentulous spaces. Four studies agreed on the impact of the number, location, and extension of the occlusal records on the MIP accuracy. One study assessed the influence of the occlusal force, showing a smaller average interocclusal space with increased occlusal force. One study evaluated the influence of tooth mobility. Seven studies analyzed the influence of the alignment method on the MIP accuracy.

CONCLUSIONS

Most of the studies reported no difference on the MIP accuracy between half- and complete-arch scans. Areas with 2 or more missing teeth reduce the MIP accuracy. A bilateral and frontal record including 2 teeth or a bilateral posterior occlusal including at least 4-teeth is indicated for maximizing the MIP accuracy.

CLINICAL IMPLICATIONS

When a complete-arch intraoral scans is obtained, a bilateral and frontal record including 2 teeth or a bilateral posterior occlusal record including at least 4-teeth is recommended for maximizing the accuracy of the MIP. When a half-arch intraoral scan is acquired, a posterior occlusal record including at least 4-teeth is indicated for optimizing the accuracy of the MIP.

The effect of generation change on the accuracy of full arch digital impressions

PURPOSE

This study is aimed to evaluate the effect of generation change on accuracy of IOSs on full-arch scans and the inter-operator reliability.

METHODS

In this study, 6 different IOS were tested: 3Shape Trios 3 (20.1.2.), 3Shape Trios 4 (20.1.1.), Medit i500 (2.3.6.), Medit i700 (2.4.6.), Planmeca Emerald (6.0.1.) and Planmeca Emerald S (6.0.1.). Eighteen dental students, inexperienced in scanning, took part in this study as operators. Each operator made 10 digital impressions; altogether, 30 impressions were made by each scanner. The 30 STL files were imported to the Geomagic Control X program, where they were compared to a reference STL file; the surface point's deviation of the full arch and the distance between the second molars' distobuccal cusps were measured, the inter-operator reliability was also investigated.

RESULTS

A significant increase in accuracy was found between Trios 3 and 4 in the case of both parameters and between Medit i500 and i700 in the case of full arch. There was no significant difference between Planmeca generations. In case of the inter-operator reliability no significant difference was detected.

CONCLUSION

Within this current study's limitation, it can be concluded that surface digitalization's accuracy can be modified with generation changes and that digital technology is less technique sensitive than traditional impression taking.

Accuracy of optical interocclusal registration using an intraoral scanner

PURPOSE

This study aimed to clarify the effect of occlusal force on appropriate optical interocclusal registration in clinical practice, considering periodontal ligament and jawbone deformation.

METHODS

Forty participants with natural, healthy dentition were enrolled (19 men and 21 women; mean age, 27.7 ± 2.0 years). A TRIOS3 intraoral scanner was used to scan the right lateral first premolar to the second molar areas of the upper and lower jaws. During scanning for interocclusal registration, participants were instructed to "bite normally," "bite lightly," and "bite strongly" to obtain data for the three occlusal patterns. The standard triangulated language (STL) data for each occlusion condition were superimposed using the appropriate software, following which the tooth displacement was calculated. The conventional method was also used to record the occlusal contact area for a silicone model using a dental contact analyzer.

RESULTS

Tooth displacement was significantly lower for the strong-bite condition than for the weak-bite condition (0.018 mm vs. 0.028 mm, P<0.05). As the occlusal force increased, the occlusal contact area also increased, and significant differences were observed among the different occlusal conditions (P<0.05).

CONCLUSIONS

Occlusal contact area changed depending on the bite force when using the silicone impression or optical intraoral scanning methods. Moreover, using optical impression methods in "strong bite force" may reduce the deviation and allow for stable interocclusal registration.

Trueness of 4 sectional-cast digital methods for transferring the interocclusal relationship in complete mouth rehabilitation

STATEMENT OF PROBLEM

An accurate digital workflow for transferring the interocclusal relationship from complete arch diagnostic interim restorations to complete arch tooth preparations is essential in complete mouth rehabilitation. However, research on the accuracy of digital cross-mounting methods is lacking.

PURPOSE

The purpose of this in vitro study was to compare the trueness of 4 sectional-cast digital cross-mounting methods in transferring the interocclusal relationship for complete mouth rehabilitation.

MATERIAL AND METHODS

Maxillary and mandibular anatomic typodonts were used to build complete arch tooth preparations and diagnostic interim restorations for complete mouth rehabilitation in vitro. Four sectional casts were designed: an anterior cast (AR), a posterior cast (PO), a unilateral cast (UL), and a tripod cast (TR). Both extraoral scanning (EOS) and intraoral scanning (IOS) were used to obtain intermediate digital sectional casts, which were cross-registered with diagnostic interim restorations and definitive casts to transfer the interocclusal relationship. Trueness was determined by assessing tooth distance deviation and mandibular 3-dimensional (3D) deviation. Differences among the 4 sectional-cast methods were analyzed with the Kruskal-Wallis test, and differences between the 2 scanning methods were analyzed with the Mann-Whitney U test (α=.05).

RESULTS

Significant differences in the trueness of interocclusal relationship transfer were observed among the 4 sectional-cast methods (P<.05). Regarding tooth overall distance deviation, TR-EOS found no statistically significant difference compared with PO-EOS (P>.05), but TR-EOS had half the overall distance deviation of PO-EOS. Both TR-EOS and PO-EOS had smaller deviations than the AR-EOS and UL-EOS groups (P<.05). TR-IOS had a smaller distance deviation than the AR-IOS, PO-IOS, and UL-IOS groups (P<.05). The overall distance deviation of EOS was significantly smaller than that of IOS in the TR and PO groups (P<.05). Regarding mandibular 3D deviation, TR-EOS found no statistically significant difference but had half the root mean square (RMS) of 3D deviation compared with the PO-EOS groups (P>.05). Both TR-EOS and PO-EOS groups had a smaller RMS than the AR-EOS and groups (P<.05). The TR-IOS group had a smaller RMS than the AR-IOS, PO-IOS, and UL-IOS groups (P<.05). The 3D deviation of EOS was significantly smaller than that of IOS in the PO group (P<.05).

CONCLUSIONS

Both EOS and IOS with the tripod sectional-cast digital method accurately transferred the interocclusal relationship for complete mouth rehabilitation.

Comparison of occlusal contact errors of 6 chairside CAD/CAM crowns: a self-controlled clinical study

OBJECTIVES

The purpose of this self-controlled clinical study was to evaluate the trueness of occlusal contacts of chairside CAD/CAM crowns fabricated using different ceramic materials.

MATERIALS AND METHODS

Ten volunteers (8 females, 2 males, average aged 20-30) were recruited in this study registered in the Clinical Trials Registry (#NCT05346744). After tooth preparation on tooth 36 or 46, an optical scan unit (CEREC Omnicam, Sirona Dental Systems, Germany) was utilized to perform the intraoral scanning. For each volunteer, 6 crowns were fabricated via the chairside CAD/CAM process (CEREC, Sirona Dental Systems, Germany) using the following materials: InCoris TZI (ZIR), Celtra Duo (CD), e.max CAD (EMA), UP.CAD (UP), Enamic (ENA) and Hyramic (HY). The microhardness of the milled surfaces was measured through a Vickers hardness Tester (HVS-50Z, Trojan, China). Together with the amount of occlusal adjustment, the occlusal contact trueness at both milling and postprocessing stages were quantitatively analyzed by using a high-precision scanner (ATOS, GOM Technologies, USA) and a reverse engineering software (Geomagic Control, 3D Systems, Rock Hill, SC). The times of chairside occlusal adjustment were also recorded. Data were analyzed by one-way analysis of variance (ANOVA) and ANOVA with randomized block design followed by Bonferroni test (p = 0.05).

RESULTS

Significant differences were found in surface microhardness of the materials tested (CD > EMA ~ UP > ENA > HY > ZIR, p < 0.05). Regarding the occlusal contact trueness at milling stage, ZIR showed the lowest (p < 0.05), while no significant difference was found among others (p > 0.05). At postprocessing stage, except for ENA, the occlusal contact trueness of ZIR was significantly lower than that of others (p < 0.05). As for occlusal adjustment amount, ZIR was lower than CD and ENA (p < 0.05). In addition, ENA, HY and ZIR required fewer times of occlusal adjustment than EMA, UP and CD.

CONCLUSIONS

The type of chairside CAD/CAM ceramic materials affected the occlusal contact trueness throughout the process of manufacturing and the amount of clinical occlusal adjustment as well. Zirconia exhibited the worst occlusal contact trueness at both milling and postprocessing stages, while the amount of occlusal adjustment was the least, which recommended the least occlusal compensation.

CLINICAL RELEVANCE

For better trueness, different negative occlusal offsets are suggested to be applied in the design process, so as to suit the material of the restoration.

The Complete Digital Workflow in Fixed Prosthodontics Updated: A Systematic Review

Digital applications have changed therapy in prosthodontics. In 2017, a systematic review reported on complete digital workflows for treatment with tooth-borne or implant-supported fixed dental prostheses (FDPs). Here, we aim to update this work and summarize the recent scientific literature reporting complete digital workflows and to deduce clinical recommendations. A systematic search of PubMed/Embase using PICO criteria was performed. English-language literature consistent with the original review published between 16 September 2016 and 31 October 2022 was considered. Of the 394 titles retrieved by the search, 42 abstracts were identified, and subsequently, 16 studies were included for data extraction. A total of 440 patients with 658 restorations were analyzed. Almost two-thirds of the studies focused on implant therapy. Time efficiency was the most often defined outcome (n = 12/75%), followed by precision (n = 11/69%) and patient satisfaction (n = 5/31%). Though the amount of clinical research on digital workflows has increased within recent years, the absolute number of published trials remains low, particularly for multi-unit restorations. Current clinical evidence supports the use of complete digital workflows in implant therapy with monolithic crowns in posterior sites. Digitally fabricated implant-supported crowns can be considered at least comparable to conventional and hybrid workflows in terms of time efficiency, production costs, precision, and patient satisfaction.

Occlusal adjustment of 3-unit tooth-supported fixed dental prostheses fabricated with complete-digital and -analog workflows: A crossover clinical trial

AIM

This prospective crossover clinical trial aimed to compare the complete-digital and -analog workflows in terms of occlusal adjustment of 3-unit tooth-supported fixed dental prostheses, operator, and patient preferences.

MATERIALS AND METHOD

This study included twelve patients receiving fourteen 3-unit posterior FDPs. 2 FDPs were made for each restoration site: one fabricated in complete-digital workflow comprising intraoral scan with static bite registration (Trios 3) and a monolithic zirconia FDP (test); the other fabricated in complete-analog workflow comprising conventional impression/face-bow transfer and a porcelain-fused-to-metal FDP (control). The FDPs (n=28) were intraorally/provisionally fixed, and quadrant-like intraoral scans were taken for every FDP before & after their occlusal adjustments. Pre- and post-adjustment scans of each FDP were then superimposed using best-fit alignment (GOM Inspect) to measure the volumetric occlusal adjustment amount (mm³) (3Matic) (Mann Whitney U, α=0.05). The patient and operator experience for digital and analog workflows were evaluated using visual analog scales (Wilcoxon test, α=0.05).

RESULTS

Mean occlusal adjustments were 7.63 mm³ [±7.02] and 25.95 mm³ [±39.61] for test and control groups, respectively. The volumetric adjustment difference was clinically noticeable but not significant (P=0.12). The impression and digital workflow adjustment were perceived more favorably by both operator (P=0.003, P=0.046, respectively) and the patients (P=0.003, P=0.002, respectively).

CONCLUSIONS

Within the limitations of this clinical study, the complete digital workflow with digital static bite-registration provided high occlusal accuracy for short-span tooth-supported FDPs. In addition, the patient and operator preferences significantly favored the digital workflow.

CLINICAL SIGNIFICANCE

Complete-digital workflow employing intraoral scanning and model-free fabrication of monolithic-Zr short-span tooth-supported FDPs offers an effective treatment modality with sufficient occlusal accuracy. Therefore complete-digital workflow is a valid alternative for complete-analog workflow comprising conventional impression, face-bow transfer, and use of a semi-adjustable articulator.

In vivo precision of digital static interocclusal registration for full arch and quadrant arch scans: a randomized controlled clinical trial

BACKGROUND

Clinical studies comparing the accuracy of digital and conventional records for static interocclusal registration are lacking. Therefore, the purpose of this clinical study was to assess the precision of digital interocclusal registration compared to conventional registration for full arch and quadrant arch conditions.

METHODS

Nine individuals with complete natural dentition were enrolled in this study. Each participant received digital scans, conventional impressions, and static interocclusal records according to the following groups: group DF, full arch digital scans and bilateral buccal scans with Medit i700 intraoral scanner (IOS); group DQ, quadrant arch digital scans and unilateral buccal scans with Medit i700 IOS; group CF, full arch polyvinyl siloxane (PVS) impressions and PVS interocclusal records; group CQ, quadrant arch PVS impressions and PVS interocclusal records. For group CF and group CQ, the impressions were poured, mounted with the silicone bites, scanned with a laboratory scanner, and articulated virtually with buccal scans with the laboratory scanner. In each group, each participant received three interocclusal records to repeat the virtual articulation three times and the articulated models were saved as STL files. The STL files were imported into a 3D-processing software to calculate the discrepancies between repeated measures using best-fit-alignment method. The significance between the study groups was calculated with two-tailed paired t-test at P < 0.05.

RESULTS

For full arch, group DF showed significantly better precision with a mean value of 31 ± 19 µm compared to 204 ± 81 µm for group CF (P = 0.0003). Similarly, for quadrant arch, group DQ showed significantly better precision with a mean value of 18 ± 6 µm compared to 255 ± 136 µm for group CQ (P = 0.0009). No significant difference in precision was found between quadrant arch and full arch when the digital or the conventional method was used.

CONCLUSIONS

The digital approach had significantly better precision for static interocclusal registration compared to the conventional method in both full and quadrant arch situations. Trial Registry This clinical trial was registered on 06/07/2022 in the Pan African Clinical Trial Registry database, the number for the registry is PACTR202207648490275.

Accuracy of intraoral scanners for static virtual articulation: A systematic review and meta-analysis of multiple outcomes

STATEMENT OF PROBLEM

Static virtual articulation with intraoral scanners (IOSs) can eliminate the human errors related to conventional articulation methods and enhance accuracy. A systematic review and meta-analysis based on multiple accuracy outcomes can combine the available literature and provide an evidence-based conclusion.

PURPOSE

The purpose of this systematic review and meta-analysis was to investigate whether static virtual articulation with IOSs has acceptable accuracy for completely dentate and partially edentulous patients.

MATERIAL AND METHODS

An electronic search was conducted on the PubMed, Web of Science, and Scopus databases. In addition, a manual search through reference lists of selected articles was performed. Clinical and in vitro studies evaluating the accuracy of static virtual articulation with IOSs based on diagnostic accuracy, trueness, precision, and occlusion of fabricated fixed restorations were included. The pooled results included sensitivity, specificity, positive likelihood ratio (+LR), negative likelihood ratio (-LR), diagnostic odds ratios (DORs), mean values, and 95% confidence intervals (CIs). Results were presented as forest plots. The summary receiver operator characteristic (SROC) was displayed to summarize the diagnostic test performance.

RESULTS

The initial search resulted in a total of 5061 articles, of which 29 articles were included in the analysis. The virtual interocclusal records (VIRs) with IOSs showed acceptable pooled results for diagnostic accuracy (sensitivity: 0.76; specificity: 0.80; DOR: 14.77, area under the SROC (AUC): 0.87; cut off point Q∗: 80; +LR: 3.66; -LR: 0.31). The pooled data for trueness and precision were within the acceptable limits. The pooled mean (95% CI) for trueness based on linear deviations was 243.53 (144.90, 342.17). The pooled mean (95% CI) for precision based on 3D deviation of articulated models was 54.97 (43.49, 66.46). In addition, the included studies reported accurate occlusion for fixed restorations fabricated by using VIRs with IOSs. Moreover, most of the studies on trueness based on virtual occlusal contact area reported acceptable accuracy.

CONCLUSIONS

VIRs with IOSs had acceptable accuracy for static virtual articulation.

The Effect of Scanning Strategy on Intraoral Scanner's Accuracy

The purpose of the present study was to examine the impact of scanning strategy on trueness and precision of the impression acquired from an intraoral scanner. Fifteen complete-arch, mandibular, post-orthodontic treatment casts were scanned with a laboratory scanner (Identica SE 3D, Medit) as the gold standard, and with an intraoral scanner (i500 Medit) following three different paths of the scanning head over the arch (scanning strategies A, B, and C). The hand scans were performed twice by one examiner and repeated by a second examiner, resulting in 180 triangular mesh surfaces (digital casts). The meshes were superimposed on the gold standards using the Viewbox 4 software. The closest distances between the meshes were computed and trueness and precision were evaluated using a General Linear Model. An interaction was found among the examiner and strategy. The accuracy of complete-arch impressions was affected by the scanning strategy; the manufacturer’s recommended strategy (A) was statistically significantly better (p < 0.05) than B and C, which were similar. An average accuracy below 50 μm, which is clinically acceptable in most orthodontic procedures, was achieved with all the examined scanning strategies.

Reliability and Time Efficiency of Digital vs. Analog Bite Registration Technique for the Manufacture of Full-Arch Fixed Implant Prostheses

Objective: Information about full-digital protocols for bite registration with intraoral scanners on multiple implants in the edentulous jaw is scarce. The purpose of this comparative in vivo study was to investigate the reliability and time efficiency of a novel full-digital bite registration technique for the manufacture of full-arch maxillary fixed implant prostheses. Material and methods: In ten patients, a full-arch maxillary fixed implant prosthesis was manufactured on multi-unit abutment level through an analog prosthetic workflow. The bite registration was performed with use of a screw-retained polymethyl methacrylate (PMMA) verification jig with detachable wax rim. To articulate the definitive edentulous maxillary implant cast in centric relation at the appropriate occlusal vertical dimension (OVD) to the mandibular antagonist cast, a type II articulator (Artex, Amann Girrbach) was used. Three to six months later, a full-digital bite registration was performed with use of dual-function scan bodies and bilateral connected bite pillars. The bite pillars screwed into the scan bodies were used to adjust and articulate the edentulous maxillary implant arch to the mandibular antagonist arch at the defined OVD. Treatment time for analog and digital bite registration technique was measured in each patient. The reliability of the digital bite registration technique was evaluated by 3D comparison of two sets of stereo lithographic (STL) files obtained from each patient. The three-dimensional deviation was defined along the X-, Y- and Z-axes (Geomagic Control X, 3D Systems Inc., Rock Hill, SC, USA). Results: The treatment time for digital bite registration using dual-function scan bodies and bite pillars was significantly shorter than analog bite registration with verification jig and wax rim (60.30%, SD 5.72%). Minor differences between the two techniques were observed with a linear deviation range of 1115 µm (SD 668 µm) overall, 46.2 µm (SD 731.3 µm) along the X-axis, −200.3 µm (SD 744.3 µm) along the Y-axis and 67.1 µm (SD 752.2 µm) along the Z-axis. Bilateral balanced contacts were registered in all patients during full-digital bite registration. Conclusions: The novel digital bite registration technique with dual-function scan bodies and bite pillars allows for a full-digital workflow for full-arch implant supported restorations. The digital bite workflow was 60% faster, and the overall deviation was around 1 mm, which can be considered clinically acceptable.

Quantitative evaluation of edentulous maxillomandibular relationship record using diagnostic complete dentures fabricated by CAD and 3D printing

PURPOSE

The present study aimed to quantitatively evaluate the accuracy of the edentulous maxillomandibular relationship record for diagnostic complete dentures fabricated using computer-aided design (CAD) and three-dimensional (3D) printing.

METHODS

Six edentulous patients were enrolled. The maxillomandibular relationship obtained from diagnostic complete dentures (DiaCD test group), that obtained from complete dentures with artificial teeth in the intercuspal position (CD control group), and the centric relationship acquired by gothic arch tracing (CR standard group) were recorded, and 3D surface scanning was performed on these records. Using the CR standard group as a reference, the DiaCD test and CD control group displacements were measured in the horizontal antero-posterior, horizontal right-and-left, and vertical directions. The displacements for the DiaCD test group were compared with those for the CD control group using the Wilcoxon matched-pairs signed rank test.

RESULTS

In terms of centric relationship, the 95% confidence interval of displacement in the horizontal antero-posterior direction was (0.54-1.89) mm in the DiaCD test group and (0.32-1.34) mm in the CD control group. The inter-group difference was significant (P = 0.03).

CONCLUSION

It is feasible to record the edentulous maxillomandibular relationship using diagnostic complete dentures fabricated by CAD/3D printing, but the protrusion of edentulous patients should not be neglected.

The use of intraoral scanning and 3D printed casts to facilitate the fabrication and retrofitting of a new metal-ceramic crown supporting an existing removable partial denture

Fabricating a new crown to retrofit with an existing removable partial denture (RPD) is a complex procedure for both clinician and dental laboratory technician. The presented technique facilitates the fabrication and retrofitting of a metal-ceramic crown onto the principal abutment of the existing RPD by using 2-step intraoral scanning (with and without the RPD in place) and 2 different 3-dimensionally printed casts. The technique enables the dental laboratory technician to precisely reproduce the retentive areas, guiding planes, and rest seats on the retrofitted crown.

Clinical study comparing the accuracy of interocclusal records, digitally obtained by three different devices

OBJECTIVE

The aim of the present cross-sectional study was to compare the interocclusal contact records obtained by three different digital methods (intra- and extraoral digital scanners and T-Scan III system) with the conventional method (articulating paper).

MATERIALS AND METHODS

Twenty-five healthy volunteers were selected. As a control group, maximum intercuspation occlusal contacts were registered and photographed from the patients with an 8 µm articulating paper. Then, intraoral conventional elastomer impressions were taken and after obtaining the corresponding plaster models of every patient they were scanned with an extraoral scanner (Zfx Evolution, Zimmer Biomet Dental) (group 1). Moreover, digital impressions were made with an intraoral scanner (Trios Color POD, Phibo, 3Shape) and contacts were also registered (group 2). Finally, T-Scan III records were made and stored for further analysis (group 3). Two previously calibrated examiners independently evaluated the interocclusal contacts from every group. Data was analyzed by using Kappa index test and Pearson's chi-square test. Diagnostic tests and ROC curve were also performed.

RESULTS

Kappa interoperator index was 70.6% (better agreement). In Kappa intraoperator index, the best value was obtained in the intraoral scanner group (moderate agreement) and the worst with T-Scan III group (low agreement). ROC curve showed highest values in the intraoral scanner group (0.817) and lowest values in the T-Scan III group (0.613).

CONCLUSION

Results suggest greater reliability to record occlusal contacts with the intraoral scanner.

CLINICAL RELEVANCE

Intraoral scanners seem to be reliable in registering intermaxillary occlusal contacts when compared with the current gold standard.

Design of wear facets of mandibular first molar crowns by using patient-specific motion with an intraoral scanner: A clinical study

STATEMENT OF PROBLEM

Although computer-aided design has become popular, restorations are typically designed from static occlusion and dynamically by using an average-value virtual articulator. Patient-specific motion recorded by using an intraoral scanner has rarely been used to design restorations, and its design ability has not been analyzed.

PURPOSE

The purpose of this clinical study was to record patient-specific motion by using an intraoral scanner and to analyze its ability to design the morphology of the wear facets on mandibular first molar crowns.

MATERIAL AND METHODS

An intraoral scanner was used to scan complete arch digital casts and to record patient-specific motion of 11 participants. Right and left mandibular first molars were selected as the target teeth. The complete crown preparations of the target teeth were virtually prepared on the digital mandibular casts by using the Geomagic Studio 2013 software program. High points were created by elevating the wear facets of the target teeth by 0.3 mm in the occlusal direction to generate digital wax patterns. The Dental System software program was used to design crowns with the anatomic coping design method. Occlusal adjustment with static occlusion (STA crown), with the average-value virtual articulator (DYN crown), and with patient-specific motion (FUN crown) was carried out. The crowns adjusted with these 3 methods were compared with the original wear facets. The mean value and root mean square (RMS) of 3D deviation were measured. One-way ANOVA was used to analyze the influence of the occlusal surface design methods on the morphology of the wear facets (α=.05).

RESULTS

The STA crowns had the poorest results with the mean ±standard deviation 3D deviation value of 0.15 ±0.05 mm and RMS value of 0.19 ±0.04 mm. The best results occurred in the FUN group, with the mean ±standard deviation 3D deviation value of 0.05 ±0.06 mm and RMS value of 0.13 ±0.03 mm. Significant differences were found among the 3 groups (P<.01). Except for the RMS value between the STA and DYN groups, significant differences were found between groups from the pairwise comparisons.

CONCLUSIONS

The occlusal surface of the crowns designed by using the patient-specific motion recorded with the intraoral scanner had the best coincidence with the morphology of the wear facets on the original teeth.

Time-efficiency and cost-analysis comparing three digital workflows for treatment with monolithic zirconia implant fixed dental prostheses: A double-blinded RCT

OBJECTIVES

This double-blinded randomized controlled trial investigated economic performance indicators (EPI) in terms of time-efficiency and production costs of 3-unit monolithic zirconium-dioxide (ZrO2) implant fixed dental prostheses (iFDP) in three different workflows.

METHODS

Twenty patients with two Straumann Tissue-Level-Implants received three iFDPs; two were fabricated in proprietary complete digital workflows with intraoral optical scanning and model-free fabrication with company-related CAD/CAM lab-software while one iFDP was manufactured on digitized casts from conventional impressions. The sequence of impression-taking for the three workflows (TRIOS 3/3Shape [Test-1]; Virtuo Vivo/Dental Wings [Test-2]; Impregum/3M Espe [Control]) was randomly allocated. Sixty iFDPs bonded to ti-base abutments were analyzed. Clinical and technical worksteps for Test-1/Test-2/Control were recorded and evaluated for time-efficiency including cost-analysis (CHF=Swiss Francs) using ANOVA-Tests (significance level α=0.05).

RESULTS

Mean total work time, as the sum of clinical plus technical steps, was 97.5 min (SD ± 23.6) for Test-1, 193.1 min (SD ± 25.2) for Test-2, and 172.6 min (SD ± 27.4) for Control. Times were significantly different between Test-1/Test-2 (p < 0.00001), Test-1/Control (p < 0.00001), and Test-2/Control (p < 0.03610). Technical costs were 566 CHF (SD ± 49.3) for Test-1, 711 CHF (SD ± 78.8) for Test-2, 812 CHF (SD ± 89.6) for Control, and were also significantly different for all comparisons (p < 0.00001).

CONCLUSIONS

Test-1 demonstrated the best performance for time-efficiency, Test-2 revealed the worst result. This indicates that digital workflows are not the same and not necessarily superior to analog workflows of monolithic ZrO2 iFDPs. Complexity decreases by reducing the number of steps following complete digital workflows, resulting in lower production costs compared to the mixed analog-digital workflow with conventional impressions.

CLINICAL SIGNIFICANCE

Complete digital workflows comprising intraoral optical scanning without physical models for treatment with monolithic ZrO2 iFDPs is an efficient alternative to mixed analog-digital workflows with conventional impressions and labside digitization of dental casts.

A Double-Blind Crossover RCT Analyzing Technical and Clinical Performance of Monolithic ZrO2 Implant Fixed Dental Prostheses (iFDP) in Three Different Digital Workflows

This double-blind randomized controlled trial with a crossover design analyzed the technical and clinical performance of three-unit monolithic ZrO₂ implant-fixed dental prostheses (iFDPs), prepared using two complete digital workflows (Test-1, Test-2) and one mixed analog–digital workflow (Control). Each of the 20 study patients received three iFDPs, resulting in 60 restorations for analysis. The quality of the restorations was assessed by analyzing laboratory cross-mounting and calculating the chairside adjustment time required during fitting. All iFDPs could be produced successfully with all three workflows. The highest cross-mounting success rate was observed for the original pairing iFDP/model of the Control group. Overall, 60% of iFDPs prepared with Test-1 workflow did not require chairside adjustment compared with 50% for Test-2 and 30% for Controls. The mean total chairside adjustment time, as the sum of interproximal, pontic, and occlusal corrections was 2.59 ± 2.51 min (Control), 2.88 ± 2.86 min (Test-1), and 3.87 ± 3.02 min (Test-2). All tested workflows were feasible for treatment with iFDPs in posterior sites on a soft tissue level type implant system. For clinical routine, it has to be considered that chairside adjustments may be necessary, at least in every second patient, independent on the workflow used.

Three-dimensional analysis of the accuracy of conventional and completely digital interocclusal registration methods

STATEMENT OF PROBLEM

Compared with the frequent investigations into the accuracy of digital intraoral scans, studies analyzing digital determinations of jaw relationships based on intraoral scans are scarce.

PURPOSE

The purpose of this in vitro study was to present an optical 3-dimensional method for analyzing deviations in static occlusion and to compare the accuracy of conventional and digital interocclusal registrations.

MATERIAL AND METHODS

A Frasaco jaw model was duplicated, articulated, and scanned with a high-precision industrial scanner, and the data were stored in a virtual standard tessellation language (STL) format, which served as the reference model. Fifteen paired mandibular and maxillary models were scanned with a digital intraoral scanner in the completely digital workflow (IOS group). Forty-five paired gypsum casts were poured from polyvinyl siloxane (PVS) impressions and associated with 2 different PVS registration materials. These casts were digitized with a laboratory scanner and grouped as follows (n=15/group): PVS group, conventional Futar D interocclusal record; sPVS group, conventional Futar Scan interocclusal record; and the AIR group, partially digital antagonist scan of the Futar Scan interocclusal record. The axes (X, Y, Z, and XYZ) of each paired model were aligned to those of the reference model by 3-dimensional superimposition, and deviations were calculated. To determine the ideal zero position, a best-fit over the mandibular teeth between the reference model and the actual model was estimated. Next, a second best-fit was determined between the maxillary models to determine the actual position of the mandibular model. The different registration methods were compared with the Mann-Whitney U test (α=.05).

RESULTS

In the IOS group, the interocclusal registration caused a mandibular deviation of 0.05 ±0.04 mm (mean ±standard deviation). This fit was better than those of conventional registrations with inserted interocclusal registration materials (PVS group and sPVS group), which caused mean z-axis deviations of 0.41 ±0.46 mm and 0.44 ±0.32 mm (P<.001), with the deviations leading to elevation of the mandibular model. The partially digital workflow with a scannable registration material (AIR group) showed significantly larger deviations in the x-axis (0.15 ±0.08 mm; P=.042) compared with the IOS group. No significant difference was observed in the total deviation between the IOS and the AIR groups. Both groups showed significantly smaller deviations than the conventional registration methods (P<.001 for the IOS group and P=.023 for the AIR group).

CONCLUSIONS

In comparison with maxillary and mandibular alignment using conventional interocclusal registration materials, digital interocclusal registrations showed greater accuracy in evaluating complete jaw models and can be recommended for clinical use. Additionally, the partially digital workflow with an antagonist scan of the interocclusal record provided acceptable results.

Influence of Preparation Type and Tooth Geometry on the Accuracy of Different Intraoral Scanners

PURPOSE

To evaluate the influence of preparation design and tooth geometry on the accuracy of scans obtained from three different intraoral scanners (IOS).

MATERIALS AND METHODS

Full coverage crown and inlay preparations with known axial wall tapers (6ᵒ and 12ᵒ) were performed on typodont teeth using a computer numerical control machine. Reference models were scanned with a highly accurate reference scanner (Ineos X5) and saved in standard tessellation language (STL) format then each IOS (Omnicam, Trios, and i500) scanned each model 10 times. The STL files obtained from the intraoral scanners were compared to the reference models (trueness) and within each test group (precision). Data were statistically analyzed using three- way ANOVA and one- way ANOVA.

RESULTS

When comparing trueness values extracoronal preparations (32.30 ± 11.23 µm) was significantly better than intra-coronal preparation (59.61 ± 16.42 µm). As for opposing wall taper, one-way ANOVA revealed that the more the convergence or divergence between opposing walls the better is the trueness. Significant differences were observed between the scanners. 3 Shape Trios (35.70 ± 14.12 µm) and medit i500 (44.31 ± 11.41 µm) showed no statistically significant differences. However, both showed significantly better precision results when compared to Omnicam (57.83 ± 22.14 µm).

CONCLUSION

Extracoronal preparations show better trueness and precision in comparison to intracoronal preparations. Trios and i500 have better trueness and precision than Omnicam. Increasing the taper of the axial wall has a direct effect on trueness of scans obtained from the IOS.