International Journal of Computerized Dentistry, 04/2021

An increasing number of accuracy studies on 3D digitizing systems, especially intraoral scanning devices, are being published in scientific and educational journals. The methods, measurement values, and statistical parameters of these studies vary. Certain inconsistencies exist, which lead to difficulty in terms of interpretation and sometimes even questionable conclusions being drawn. These issues make it almost impossible to compare the results of such studies. One aspect inherent in this is the mutable use of basic terms describing the quality of measurement outcomes. A clear definition of such terms and clear instructions as to their respective calculation processes is essential for communication among scientists as well as for reporting measurement results to the dental community. Therefore, the aim of the present guideline is to provide a clear definition of the accuracy, trueness, and precision as the basic terms in the context of digital dentistry. The survey for this guideline included the application of ISO Norms and their expansion to special aspects concerning 3D data acquisition and, in particular, surface meshes. Additionally, the literature was screened to collect approaches, which can be seen as useful for dealing with these terms when performing different kinds of studies. Keywords: intraoral scanning, accuracy, precision, trueness, ISO standard, 3D evaluation

Aim: The objective of the present study was to assess the accuracy and reproducibility of permanent dentition and dental arch measurements of three digital scanners compared with the gold standard, a physical plaster cast. Materials and methods: In this cross-sectional study, the following records of 30 patients were used: 1) orthodontic physical plaster study cast (PPSC); 2) digitally scanned physical model (DSPM), 3) direct intraoral model scanned with a Trios color scanner; and 4) direct 3D CBCT digital model. The following 3D measurements were obtained: mesiodistal tooth dimensions; total tooth materials; dental arch perimeters; total arch lengths; and intermolar, interpremolar, and intercanine widths. The measurements on the three digital models were contrasted with those on the PPSC. Differences were tested using a dependent t test for intragroup comparisons. A P value of < 0.05 was considered statistically significant. Intraclass correlation coefficient was used to assess intra- and interexaminer reliability. Results: Except for the mesiodistal dimensions of the mandibular left central incisors (P < 0.001) and the mandibular intercanine width (P = 0.041), no statistically significant differences were found between the measurements made directly on the PPSC and those on the three digital models. The mean discrepancies between the methods ranged from as low as 0.003 mm to as high as 0.67 mm for the total tooth materials, and as low as 0.01 mm to as high as 0.37 mm for the total arch length. For the transverse dimension, the mean discrepancies ranged from as low as 0.3 mm for the maxillary intercanine width to as high as 0.5 mm for the mandibular intercanine width. However, these significant differences were not considered clinically significant. Conclusions: The DSPM, Trios color scanner digital model, and direct 3D CBCT digital model appear to be adequate, reliable, and time-saving alternatives to the PPSC when analyzed using a digital caliper. Keywords: plaster study casts, digital models, dental arch measurements, intraoral scanning, cone beam computed tomography (CBCT)

Aim: The present clinical trial aimed to preliminarily assess whether navigation could help to position impacted supernumerary teeth (STs) and reduce surgical trauma. Materials and methods: Subjects with an impacted supernumerary tooth (ST) in the premaxillary area were enrolled in the study and randomly distributed into a navigation group and a control group. In the navigation group, STs were positioned and extracted under real-time optic navigation. In the control group, STs were extracted depending on the surgeon’s experience. Subjects were followed up for 12 to 24 weeks postsurgery. Operating time, futile bony trauma, and the positioning precision of the STs were the major outcomes assessed. Multivariate correlation analysis was performed. Results: In 24 subjects, 32 STs were removed and no severe complications occurred in either group. The proportion of ST exposure at the planned access point was 100% in the navigation group and 68.75% in the control group (χ² = 5.926, P = 0.015). Futile length, futile width, and the distance between the point where the ST was initially exposed and the bony point planned for accessing it were related to both navigation/control grouping and bone thickness in the access side. For challenging STs with bone thickness of > 0.5 mm in the access side (N = 22), the futile length in the navigation group (0.0 [0.0, 4.0] mm) was significantly smaller than that in the control group (3.0 [0.0, 8.0] mm, P = 0.028). Similarly, the futile width in the navigation group (0.0 [0.0, 2.0] mm) was significantly smaller than that in the control group (2.0 [0.0, 4.0] mm, P = 0.018). Conclusions: Navigation helped to position impacted STs precisely and reduced surgical bony trauma to some extent, especially in challenging cases in which the bone in the access side was thicker than 0.5 mm. Keywords: supernumerary tooth, tooth extraction, image guide, surgical navigation, computer-assisted design, cone beam computed tomography

Aim: To evaluate the oral health-related quality of life (OHRQoL) of patients rehabilitated with conventional or 3D-printed implant overdentures. Materials and methods: A randomized clinical trial (RCT) was designed. Twenty-eight completely edentulous participants were randomly allocated into two equal groups. All participants received two implants with ball attachments. Participants in the control group were rehabilitated with conventionally manufactured polymethyl methacrylate (PMMA) maxillary complete dentures (CDs) and mandibular implant overdentures, while those in the intervention group received digital light processing (DLP)-printed photopolymerizable PMMA maxillary CDs (NextDent) and mandibular implant overdentures. Follow-up appointments were scheduled at 3, 6, and 12 months where Oral Health Impact Profile 19 (OHIPEDENT19) data were used to assess the OHRQoL of the participants. Denture retention was measured using a digital force gauge device. Results: The OHRQoL values were significantly higher (less improvement) in the conventional overdenture group at 6 months (P = 0.02) and 12 months (P = 0.04). A statistically significant difference was found between the mean retention values of the conventional and 3D-printed overdenture groups. For all the follow-up periods, the mean retention values were higher for the 3D-printed overdenture group (P = 0.001). Conclusion: 3D-printed overdentures may represent an alternative to conventionally fabricated ones. This study represents a stepping stone and proof of concept that support the potential future use of 3D-printed dentures. Keywords: 3D printing, implant, overdenture, oral health, retention, edentulous

Aim: Innovations in CAD/CAM technology and materials science offer new methodologies for removable prosthodontics. As clinical data are still rare, in vitro performance of both CAD/CAM and comparable conventional materials may help to estimate the clinical outcome. Materials and methods: Specimens (n = 8 per group) from teeth (CediTEC, SR VivodentCAD, Vitapan), base materials (V-Print dentbase, IvoBase CAD, Paladur), adhesives (CediTEC Primer/Adhesive, IvoBase CAD Bond), and a fully printed specimen (Try-In) were created. All specimens underwent thermal cycling and mechanical loading (TCML): 1,200,000 × 50 N; 2x3000 x 5°C/55°C; H2O. Surviving specimens were loaded to fracture. Statistical tests used were the Shapiro-Wilk test and the Kaplan-Meier survival, with the level of significance set to α = 0.05. Results: Mean loading cycles until failure varied between 100 and 621,667 cycles. Up to five specimens per group failed during TCML. With one exception, all specimens of the entirely CAD/CAM-fabricated group survived TCML. The log-rank (Mantel-Cox) test showed significantly different (P = 0.000) loading cycles between the systems (chi-square test: 28,247; degree of freedom: 8). Failure of the dentures during TCML was characterized by failure of the denture base (2x), denture tooth (13x), mixed base/tooth (3x) or adhesive between base and tooth (1x). Conclusion: TCML and fracture testing showed different aspects of denture tooth restoration. The results indicated no correlation between fracture force, fracture pattern, and survival cycles. Denture teeth (milled, heat-pressed), bases (milled, printed, pressed), and primer should be matched up to optimize the performance of dentures. Keywords: CAD/CAM, rapid prototyping, 3D printing, dentures, TCML, FEA, milling

Aim: To investigate retentive forces (RFs) of CAD/CAM-milled and conventionally cast secondary crowns (SCs) after artificial aging in an in vitro study. Materials and methods: Forty artificial premolars were manufactured and provided with 40 primary crowns (PCs) milled from a high noble metal alloy. SCs were fabricated from the same alloy. Ten SCs were produced with the help of a tactile scanning method (group A), 10 with the help of a photo-optical scan (spray; group B), 10 with the help of a photo-optical scan (acrylic dye; group C), and 10 using a conventional casting technique (group D). Cycles of separation were performed and RFs were measured at baseline and after 5,000 and 10,000 cycles. Surfaces were examined under a scanning electron microscope (SEM). Statistical analysis was conducted at a significance level of P ≤ 0.05. Results: Group D showed the highest median RFs with respective interquartile ranges (IQRs) – baseline: 7.0(2.5) N; 5,000 cycles: 5.5(2.0) N; 10,000 cycles: 5.4(1.5) N compared with groups A, B, and C – baseline: 5.2(8.4)/3.4(11.3)/1.3(1.5) N; 5,000 cycles: 1.8(0.8)/2.1(1.7)/1.0(1.3) N; 10,000 cycles: 1.9(1.6)/2.4(2.5)/1.0(1.4) N, respectively. In contrast to groups A, B, and C, group D did not gain RF when RF values were compared after 5,000 and 10,000 cycles. The loss of RF between baseline (7.0 N) and after 10,000 cycles (5.4 N) was significant only for group D (P = 0.007), but not for groups A, B, and C. Conclusion: Both CAD/CAM-milled and conventionally cast SCs from a high noble metal alloy can provide sufficient RF after 10,000 cycles of artificial aging. However, groups A, B, and C showed constantly lower RF values compared with group D. Keywords: CAD/CAM, artificial aging, double crowns, telescopic crowns, retentive force, removable dental prosthesis, high noble metal alloy, gold

Background: A combination of facial and intraoral scans produces a fully digitalized virtual patient. This concept allows for a 3D smile design and individualized virtual articulator application, which makes the rehabilitation outcome more predictable in terms of esthetics and function. Case presentation: In the present clinical case, the patient was ‘digitalized’ with the use of facial and intraoral scans. The full-mouth rehabilitation by means of implant- and tooth-supported single ceramic restorations was performed through both digital and analog workflows. The 3D printing of the restoration patterns was achieved through the rapid prototyping (RP) approach, and the ceramic milling through the rapid manufacturing approach. The clinical and technical performance of both additive and subtractive manufacturing methods were assessed for this type of rehabilitation. Conclusion: Both additive and subtractive manufacturing of ceramic restorations yielded a clinically acceptable marginal fit, which was inspected on the conventionally fabricated stone cast. As the milling of small ceramic restorations has met with failure in the past, the 3D printing of restoration patterns in the context of an RP approach may be regarded as a viable technical option. Keywords: additive manufacturing, 3D printing, 3D smile design, augmented reality, intraoral scan, face scan

The treatment of teeth with severely calcified canals is a difficult procedure for clinicians. Procedural accidents such as drill path deviation or perforation of the root canal often occur. 3D-printed directional guides made using CBCT and CAD/CAM can help the clinician to accurately drill in the original root canal direction. Furthermore, chairside operating times and excessive loss of tooth structure are reduced, and the risk of perforation is avoided. The present case report describes two cases of calcified root canals with path deviations that were retreated utilizing a guided endodontic technique. Keywords: guided endodontics, calcified root canal, CAD/CAM, root canal retreatment

The significantly faster fabrication technique of chairside restorations with the aid of the Cerec Primemill milling unit makes it possible to restore an entire quadrant in a reasonable amount of time. Furthermore, the procedure described in this article made it possible to use a new type of medium-strength ceramic that achieved a very good esthetic result overall. Keywords: Cerec CAD/CAM Chairside, inlays, crowns, CAD/CAM chairside materials

The majority of complete dentures are not initially made for the rehabilitation of an edentulous jaw; in most cases, they replace an existing complete denture. Since the ability to adapt to a new complete denture decreases with age, the replica denture procedure represents a smart opportunity. The aim is to copy the clinically successful parts of the old prosthesis and to change the destroyed parts. There are many advantages of this technique, including increased patient acceptance, especially among older people who may not be able to adapt easily to a new prosthesis. The advantages of digital technology are very apparent in the creation of a replica prosthesis. Various cases are presented in the present article to illustrate the procedure and the advantages of this technique using the example of computer-aided fabrication with the Baltic Denture System. Keywords: CAD/CAM, complete dentures, milled prosthesis, replica denture

Purpose: The purpose of this article is to propose a new protocol for the accurate transfer of the peri-implant soft tissue emergence profile (EP) using a customized healing abutment or a provisional restoration whose shape is integrated into prosthetic design software. Report: The EP of the future restoration is created extraorally with an ideally shaped customized healing abutment or a provisional crown. Before insertion, the latter is screwed into a repositionable analog placed on a specially designed device and scanned with an intraoral scanner (IOS). This repositionable analog (Straumann RB Repositionable Implant Analog, Art. no. 065.0023), whose original purpose is to keep the correct orientation of the implant platform when placed in a printed model, is already available on the market. It is an exact replica of the implant with a corresponding external index. When scanned, it allows the digital transfer of the exact implant position and index. After healing, a full-mouth impression is made with an IOS without removing the customized healing abutment or provisional restoration. The STL files issued from both impressions are merged to produce a digital model used to design the final restoration, which can be inserted at the next appointment. Conclusion: The technique described is simple, predictable, and precise. It does not require a traditional implant level impression or the use of a digital accessory such as a scanbody to transfer the 3D implant position and the peri-implant gingival contour. Keywords: dental implants, esthetic zone, immediate placement