International Journal of Computerized Dentistry, 04/2019

Aim: To determine the scanning strategy that obtains the most accurate results for two intraoral scanners (IOS) in complete-arch digital impressions. Scan time was evaluated and correlated with scan strategies. Materials and method: A custom model used as the reference standard was fabricated with teeth having dentin- and enamel-identical refractive indices simulating natural dentition. A reference scan of the custom typodont was obtained using an ATOS III Triple Scan 3D optical scanner. Two IOS setups - Omnicam v 5.1.0 and Primescan v 5.0.2 - were used for complete-arch scanning, each using 13 scanning strategies, obtaining 260 digital files (n = 10 per group), recording each scan time, converting all experimental scans to standard tessellation language (STL) format, and using a comprehensive metrology program to compare the reference standard scan with the experimental scans. Statistical analyses utilized Welch's unequal variances t test. Results: Group M exhibited the lowest trueness and precision values (P < 0.05) for Primescan (47.5% of the average among all other groups) and the lowest trueness value (P < 0.05) for Omnicam (53.4% of the average among all other groups), where group B exhibited the lowest precision value (65.6% of the average among all other groups) with P < 0.05. Primescan featured a better trueness index (4.79 µm) than that of Omnicam (19.13 µm), with a statistically significant difference (P < 0.00001). Primescan, group M, also featured a better precision index (4.67 µm) than Omnicam, group B (16.75 µm), with a statistically significant difference (P < 0.00001). Conclusion: For both IOS systems, group M provided the lowest scanning times. For trueness and precision of complete-arch scans, group M was the dominant scanning strategy in Primescan, while there was no dominant strategy in Omnicam. Group M had the best scanning time for both IOS systems. Keywords: CAD/CAM, intraoral scanner, digital impression, accuracy, full-arch dental impression, standard tessellation language

Aim: The production of individual tooth replicas has two applications in dental practice: tooth autotransplantations and dental root analogue implants. These applications require a particularly high degree of precision. The purpose of this study was to establish and evaluate a method for fabricating individual 3D-printed tooth replicas. Materials and methods: 10 patients requiring extraction of a wisdom tooth and a preoperative cone beam computed tomography (CBCT) scan were included; exclusion criteria were intraoperative fragmentation or fracture of the tooth. 3D Slicer 4.6.2 was used for tooth segmentation and model generation based on CBCT data. The tooth replicas were manufactured by selective laser melting (SLM). The extracted teeth and 3D-printed replicas were scanned and tested for surface deviations in CloudCompare 2.8.1. Results: The mean absolute surface deviation between the 3D-printed teeth and the corresponding extracted teeth ranged from 0.13 to 0.25 mm, with standard deviations of 0.10 to 0.21 mm; 95% of the measured surface points deviated less than 0.474 mm; the surface area was reduced by -6.0% and the volume by -3.4%. The root mean square was 0.238 mm and the mean maximum absolute surface deviation was 0.927 mm. The SLM technique showed a high precision with a mean absolute deviation of 0.045 mm and a standard deviation of 0.04 mm. Conclusion: 3D-printed tooth replicas with a very high accuracy could be produced based on CBCT data. The described method is suitable for manufacturing tooth replicas for use in tooth autotransplantations or for fabricating root analogue implants. Keywords: 3D printing, rapid prototyping, selective laser melting, tooth replicas, cone beam computed tomography, autologous tooth transplantation, root analogue implants, implantology

Aim: Precise tooth preparation is necessary for successful restorative treatments. In the narrow oral space, achieving such precision with traditional manual operation is impeded by visual deviation, human eye blind zones, and hand-orientation errors. To overcome these drawbacks, a mini-robotic system for tooth preparation was developed to manipulate an ultra-short-pulse laser beam for the automatic shaping of a target tooth into a prepared tooth. Automatic tooth preparation is based on three-dimensional (3D) data. The present study was conducted to investigate the basic principles for digitally designing full crown tooth preparations and to quantitatively evaluate the associated design precision. Materials and methods: Cone beam computed tomography (CBCT) and dental model surface scan data were obtained from 20 volunteers. Using these data, a complete and systematic process for the digital design of full crown tooth preparations was conducted. The study included 40 cases with two design types. Software-derived measurements of prepared occlusal thickness, shoulder width, and axial convergence angle were compared with the design preparation data. Results: The design precision for shoulder width exceeded that for occlusal ablation depth, which exceeded that for axial convergence angle. One-way ANOVA analysis results confirmed no significant differences in the design precision of full crown preparations with different tooth morphologies, and the independent samples t test results showed no significant difference among the design standards. The mean errors for occlusal ablation depth, shoulder width, and axial convergence angle were 0.0096 ± 0.0108 mm, 0.0006 ± 0.0004 mm, and 0.1201 ± 0.1288 degrees, respectively. Conclusion: The design route of the full crown computer-aided design (CAD) software reported on in this article is highly feasible and accurate. Keywords: digital model, computer-aided design, accuracy evaluation, restorative treatment, teeth morphologies, tooth preparation

The aim of this study was to assess the influence of a polarizing filter on the accuracy of dental shade matching using digital photography. A comparison was performed using ΔEab parameters between CIE L*a*b* values obtained from digital images taken under two different conditions (with direct light and with polarized light) and the values given by the dental spectrophotometer SpectroShade Micro, which is considered to be the standard. Color differences (ΔEab) calculated between the parameters recorded with the dental spectrophotometer and polarized photography were below or at the level of the 50:50% acceptability threshold of 2.7 in 23% of the cases. Interdevice agreement found between the dental spectrophotometer and polarized photography exceeded 0.82 for all the three parameters recorded. Digital photography with polarizing filters might be a useful tool for dental shade matching. Keywords: spectrophotometer, color, digital photography, shade matching, polarizing filter, computer-based method

The articulation parameters, especially the horizontal condylar inclination angle (HCI), the Bennett angle (BA), and the immediate side shift (ISS) were determined in 259 subjects (100 males; 159 females) of the associated project with reference to the population-representative baseline study (Study of Health in Pomerania, SHIP 0). The evaluations were based on a clinical functional status and electronic motion recording with the ultrasonic measuring system Jaw Motion Analyser (JMA, Zebris, Isny, Germany). The reference plane, to which all measured values were represented and the HCI calculated, was the hinge axis infraorbital plane (HA-IOP). The HCI was determined after an excursive movement with a length of 4 mm to the HA-IOP in the sagittal view and the BA after a mediotrusive excursion movement of 6 mm in the horizontal view to the midsagittal plane. For the standard and limit values, the average value in addition to the standard deviation and the 10th and 90th percentile value (10th percentile value, 90th percentile value) were determined: HCI right 52.1 ± 10.14 degrees (39.4 degrees, 64.0 degrees), HCI left 53.1 ± 9.67 degrees (42.3 degrees, 67.0 degrees), BA right 15.2 ± 7.53 degrees (6.7 degrees, 25.0 degrees), BA left 14.2 ± 7.84 degrees (5.4 degrees, 24.1 degrees). The HCI was approximately 2 to 3 degrees larger in females (males: right 50.5 ± 9.47 degrees, left 51.9 ± 8.99 degrees; females: right 53.1 ± 10.42 degrees, left 53.8 ± 10.03 degrees). Likewise, the BA in the age group ≥ 40 years (males: right 14.4 ± 6.62 degrees, left 13.1 ± 7.14 degrees; females: right 17.0 ± 9.02 degrees, left 16.9 ± 8.72 degrees). The latter proved to be statistically significant in the t test for independent samples, assuming variance equivalence on the right, with P = 0.009, and with rejection of the variant equivalence on the left, with P = 0.002. The right and left HCI and BA joint values showed highly significant linear dependence at P < 0.001, but rather low, however, for the HCI with r2 = 0.175 for the HCI and r2 = 0.228 for the BA. In 46% of cases, the right and left HCI values differed up to 5 degrees only; a further 20.9% were in an interval difference of between 5 and 10 degrees. The following results were shown for the differences in the BA: 56.4% of the cases were between 0 and 5 degrees, and 26.2% were in the interval ranges of 5 to 10 degrees. ISS occurred in 18.1% of cases on the right side of the joint, and in 27.8% of cases on the left side. On both sides of the joint it was significantly more frequent in the age group ≥ 40 years with assumed variance equality than in the age group < 40 years (P = 0.002 right, P = 0.003 left). The groups relating to the Helkimo index (HI) did not differ significantly in all function-specific parameters. If it is assumed that there is no significant influence on the occlusion if the HCI values differ by 7 to 8 degrees from the average value, only approximately one third of all cases (35.1%) were characterized by a purely average value setting in the articulator. In 41.7% of cases, one joint value was situated outside the average value range; in 23.2% of the cases both values were outside the average value range. Without a measurement of the condylar path inclination, however, it is impossible to decide to what extent the HCI deviates from the average value, and which joint side is larger or smaller than the other and to what extent. These results suggest that in extensive and complex cases, the articulator should be adjusted according to individual, function-specific joint values. Keywords: population-based values of condylar adjustment, population-based standard and limit values for the adjustment of joint values, articulator, articulation, sagittal condylar inclination, horizontal condylar inclination angle (HCI), Bennett angle (BA)

Aim: Modern microsurgical techniques have increased the success rate of apicoectomy relative to that of traditional approaches. This case report introduces a novel workaround for guided apicoectomy using a patient-specific computer-aided design/computer-aided manufacturing (CAD/CAM) three-dimensional (3D)-printed template. Materials and methods: Apicoectomy was performed on the mesial root of tooth 36 using template-guided trephine drilling, followed by retrograde filling with mineral trioxide aggregate (MTA). Initially, a cone beam computed tomography (CBCT) scan and an intraoral surface scan were imported into the planning software. After superimposition, virtual planning was performed to determine the exact localization for root resection. Subsequently, a tooth-supported drilling template was designed and 3D printed. Endodontic microsurgical approaches, including root-end cavity preparation and root-end filling, completed the surgical treatment. Result: The apical resection was easily feasible. There were no postoperative complications. Radiological assessment after a 6-month period showed signs of reossification. Conclusion: Guided apicoectomy allowed precise root resection, suggesting that this technique may be advantageous in complex anatomical situations. Keywords: guided apicoectomy, guided surgery, digital planning, 3D printing, CAD/CAM, tooth-supported template, drilling template, CBCT imaging

Aim: The objective of this case study is to present the manufacturing process and delivery of a removable partial denture (RPD) using computer-aided design/computer-aided manufacturing (CAD/CAM) technology. Materials and methods: A 46-year-old female patient presented at the Federal University of Rio Grande do Norte complaining of the lack of retention in her mandibular RPD. After the design and preparation of the abutment teeth, further appointments were made. In the first appointment, intraoral scanning (IOS) with a Trios scanner was performed, followed by virtual planning of the framework. The RPD was then printed, invested, cast by induction, and polished. In the second appointment, the RPD was delivered. Conclusion: The technique proved to be efficient in terms of clinical time and sufficient for patient comfort and satisfaction. Keywords: 3D printing, removable partial denture, precision, CAD/CAM, accuracy, trueness

The present application report describes a cast-free and chairside workflow that enables the manufacturing of monolithic restorations on custom-made abutments without damaging the periimplant soft tissue for impression taking. An easily achievable checklist for the individualization of standard abutments is presented so that the shape of the abutment is compatible with especially developed software after optical impressions. The principle of the method contains an extraoral impression of the finish line of the abutment and an intraoral impression that indicates the abutment position in relation to the adjacent teeth. The software needed for the semi-automated registration of the intra- and extraoral impression operates with .stl data and can be provided by the corresponding author on request. Keywords: customized abutments, chairside, cast-free, registration, intraoral, scanner, software, finish line